Process for producing a jet fuel composition

Abstract

The present invention relates to a process for producing a jet fuel composition (12), the process comprising: a) Processing an oxygenate stream (1) in an Oxygenate-to-Olefin (OtO) unit (2) to produce an olefin stream (3); b) Providing an oligomerization feed (8) comprising at least a portion of the olefin stream (3) and at least a portion of an external C4+-olefin stream (30) comprising C4+-olefins; c) Processing the oligomerization feed (8) in an oligomerization unit (9) to produce an oligomerized olefin stream (10); d) Hydrogenating at least a portion of the oligomerized olefin stream (10).

Description

[0001] Process for producing a jet fuel composition

[0002] The present invention relates to a process for producing a jet fuel composition.

[0003] The quest for sustainable alternatives to fossil fuels has intensified in recent years due to the escalating concerns over climate change and the depletion of non-renewable resources. In this context, fuels derived from methanol and other oxygenates have gained more and more attention.

[0004] Methanol and other oxygenates have emerged as pivotal intermediate products in the chemical industry, playing a crucial role in diverse processes to serve as alternative paths with the potential to substitute conventional fossil production routes. Their versatility as feedstocks for various chemicals, plastics, and fuels has heightened their significance, driving an increasing demand globally. Methanol is often produced from natural gas or coal but can also be produced from renewable resources such as biogenic feedstocks or carbon dioxide and water. Its eco- friendly attributes as a potential green energy carrier further amplify its importance, aligning with the industry's growing emphasis on sustainability and environmental responsibility.

[0005] Oxygenates may be converted into olefins in so-called oxygenate to olefins (OtO) processes. In such processes, oxygenates such as alcohols and / or ethers are typically processed in a flu- idized-bed or fixed-bed reactor using a catalyst at elevated temperatures and pressures to yield olefins. Olefins derived from such OtO processes can be further processed into fuels such as gasoline, diesel, or jet fuel.

[0006] Oxygenate to fuel processes known in the art typically comprise the steps of converting oxygenates to olefins in an OtO process, oligomerizing the resulting olefins to form longer chain olefins, and hydrogenating the resulting olefins. The resulting hydrocarbon mixtures or fractions thereof can be used as sustainable gasoline, diesel, or jet fuel. Such processes are disclosed, e.g., in US 4,482,772 A, which describes the so- called Mobil Olefins to Gasoline / Distillate ("MOGD") process. A similar process is described in US 4,506,106 A. Recently, the production of j et fuel from renewable methanol and other renewable oxygenates has gathered great interest , since the fuel-based propulsion systems of aircraft cannot easily be replaced by electrical motors . Thus , there have been various ef forts in the prior art to improve oxygenate to fuel processes , especially to produce j et fuel .

[0007] WO 2023 / 196394 Al discloses a process for converting oxygenates to distillate fuel , wherein oligomeri zation may comprise a first stage ethylene and / or propylene oligomeri zation step followed by a second stage oligomeri zation step of the first stage oligomeri zed olefin stream to higher olefins . The oligomeri zed olefin stream can be separated into j et and diesel fuel streams .

[0008] US 2022 / 0396741 Al discloses a process comprising oligomeri zing an ethylene stream to a C4+-olefin stream in a first olefin oligomeri zation unit and oligomeri zing said C4+-olefin stream and a propylene / C4+-olef in stream in a second oligomerization unit to produce an isoolefinic stream . This isoolefinic stream can be further processed into a blended j et boiling range composition .

[0009] WO 2016 / 067033 Al discloses a further two-stage oligomeri zation process , wherein ethylene is oligomeri zed to form a first oligomeri zation product containing a maj ority concentration of mixed olefins with a carbon number between C4 to C8 ; and wherein the mixed olefins are further oligomeri zed to form a second oligomeri zation product containing mixed linear olefins and branched olefins with a carbon number between C8 and C23 suitable for production of selected hydrocarbon fuels and fuel blend stocks .

[0010] WO 2023 / 138876 Al discloses a process for co-producing a C3- olefin product stream and a hydrocarbon stream comprising hydrocarbons boiling in the j et fuel range , wherein the C3-olefin product stream is separated from an olefin product stream obtained from an OtO process before said olefin product stream is passed through an oligomeri zation step .

[0011] However, despite concerted ef forts within the industry, current processes for producing j et fuel from oxygenates still suffer from various limitations . These processes are frequently characteri zed by low overall ef ficiencies , high degrees of complexity and costs, or both. Existing processes typically require high quantities of oxygenate starting material and energy to produce a given amount of jet fuel. Specifically, the efficiency with which oxygenates are converted into jet fuel is often low, meaning that a high proportion of the carbon contained in the oxygenate starting material does not end up as hydrocarbons boiling in the jet fuel range. Although this deficiency can be partly offset by producing side products, e.g., by fractionating hydrocarbon streams suitable as diesel fuel or gasoline fuel from the hydrogenated hydrocarbon stream, it would be desirable to maximize the yield of jet fuel as the primary product .

[0012] It is an object of the present invention to address this need by providing new and improved processes for producing jet fuel from oxygenates. In particular, it is an object to provide simple processes with a high efficiency of converting oxygenates into jet fuel.

[0013] Therefore, the present invention provides a process for producing a jet fuel composition, the process comprising: a) Processing an oxygenate stream in an Oxygenate-to-Olef in (OtO) unit to produce an olefin stream; b) Providing an oligomerization feed comprising at least a portion of the olefin stream and at least a portion of an external C4+-olefin stream comprising C4+-olefins; c) Processing the oligomerization feed in an oligomerization unit to produce an oligomerized olefin stream; d) Hydrogenating at least a portion of the oligomerized olefin stream.

[0014] The inventive process enhances the efficiency of traditional methods for producing jet fuel from oxygenates. Specifically, the process enables the production of large amounts of jet-range hydrocarbons from a given amount of oxygenate starting material in a simple and highly efficient manner. This is particularly crucial when utilizing renewable methanol or other renewable oxygenates as starting materials. For the production of renewable fuels to be economically viable, it must be ensured that a high proportion of the renewable carbon ends up in high-value products such as j et fuel rather than being converted to lower- value commodity byproducts .

[0015] OtO processes typically yield mixtures of olefins whose composition is not optimal to achieve a maximum yield of hydrocarbons boiling in the j et fuel range in the oligomeri zation step . This is in part due to the high yields of the light olefins ethylene and propylene , since these light olefins are less favorable for oligomeri zation to j et-range hydrocarbons . The inventive process provides a solution to this problem and makes it possible to signi ficantly enhance the yield of j et-range hydrocarbons compared to conventional processes . More speci fically, the present invention allows to increase the amount of j et-range hydrocarbons that can be obtained from a given amount of oxygenate starting material , leading to a more ef ficient and economical overall process .

[0016] In the context of the present invention this can advantageously be achieved speci fically by including at least a portion of an external C4+-olefin stream comprising C4+-olefins in the oligomeri zation feed .

[0017] The external C4+-olefin stream may be obtained from any suitable refinery unit , preferably a hydrocarbon cracking unit , such as a steam cracker, FCC reactor, or delayed coker . In another alternative , which is also preferred, the C4+-olefin stream may be obtained from dehydrating an alcohol stream . Preferably, the alcohol stream comprises renewable alcohols . More preferably, the alcohol stream essentially consists of renewable alcohols . The renewable alcohol s may preferably be produced from feedstocks eligible for the production of advanced biofuels according to Renewable Energy Directive (RED) I I I ( Directive (EU) 2023 / 2413 ) , Annex IX . Preferably, the alcohol stream is a C2-C4- alcohol stream, preferably wherein said alcohol stream is obtained from syngas fermentation or catalytic conversion to mixed alcohols , synthesis of iso-propanol butanol ethanol ( IBE ) via fermentation, conversion of glycerol to propanol , or conversion of biomass or syngas to ethanol via fermentation . As used herein, " syngas" preferably refers to a mixture containing hydrogen as well as carbon monoxide and / or carbon dioxide . Preferably, said refinery unit is at least partially, more preferably completely, fed with renewable feedstock, so that the C4+-olefin stream contains renewable carbon . This is particularly preferred when the oxygenate stream contains renewable oxygenates since in this case the overall process can advantageously be used to produce renewable j et fuel .

[0018] Including an external C4+-olefin stream in the oligomeri zation feed allows reducing the proportion of lighter olefins such as ethylene and propylene in the oligomeri zation feed without necessarily having to remove such lighter olefins from the OtO product that is sent to the oligomeri zation unit . Thus , the concentration of j et-range hydrocarbons in the oligomeri zed olefin stream can be increased without reducing the proportion of the OtO product sent to the oligomeri zation unit , thus resulting in a higher proportion of carbon from the oxygenate starting material that is converted into j et-range hydrocarbons .

[0019] Moreover, including an external C4+-olefin stream as described above allows to advantageously tune the composition of the oligomeri zation feed depending on the current circumstances . For instance , at times when larger amounts of the external C4+- olefin stream are available , more or even all of the light olefins contained in the olefin stream obtained from the OtO unit can be sent to the oligomeri zation unit , whereas at times when lower amounts of the external C4+-olefin stream are available , higher proportions of ethylene and / or propylene may be removed from the process prior to oligomeri zation .

[0020] For the purposes of the present invention, any suitable OtO process known in the art can be used .

[0021] The oxygenate stream preferably comprises methanol , ethanol , propanol , butanol , or any ether derived from these alcohols , or combinations thereof . Methanol , dimethyl ether, and ethanol are particularly preferred, especially methanol . In a preferred embodiment , the oxygenate stream may therefore also be referred to as a methanol stream and the OtO unit may also be referred to as a Methanol to Olefins (MtO) unit . Preferably the oxygenate stream comprises at least 30 wt% , more preferred at least 50 wt% , more preferred at least 70 wt% methanol . Preferably, at least 50 wt% , more preferred at least 70 wt% , more preferred at least 90 wt% of oxygenates contained in the oxygenate stream are methanol . In this context , "oxygenates" preferably refers to the group consisting of alcohols and ethers . Methanol may advantageously be derived by synthesis from carbon dioxide and hydrogen . Alternatively, methanol may also be derived from biogenic feedstocks .

[0022] The skilled person is familiar with suitable reaction conditions and catalysts for operating an OtO unit . Such suitable reaction conditions and catalysts are disclosed, e . g . , in WO 2023 / 196394 Al and WO 2023 / 138876 Al .

[0023] A typical OtO process comprises the dehydration of alcohol s to olefins . For instance , the process may comprise a first step of dehydrating methanol to form dimethyl ether ( DME ) . This step involves removing a water molecule from two methanol molecules , resulting in the formation of DME . In a second process step, DME may be cracked to olefins .

[0024] In the context of the invention, any suitable catalyst can be used in the OtO unit to convert the oxygenate stream into the olefin stream . Preferably, the catalyst comprises a solid acid catalyst , especially a zeolite such as ZSM-5 , ZSM-22 , ZSM-23 or ZSM-48 , or a silicoaluminophosphate ( SAPO) such as SAPO- 18 or SAPO-34 .

[0025] It is preferred i f the OtO unit is operated at a temperature between 250 ° C and 500 ° C, preferably 350 ° C and 450 ° C, and a pressure from 1 to 25 bar, preferably from 1 to 13 bar, more preferred 1 to 3 bar .

[0026] In a preferred embodiment , diolefins and / or acetylenes contained in the ef fluent obtained from the OtO unit are hydrogenated to monoolefins . This hydrogenation can be done prior to the processing in the oligomeri zation unit since diolefins and / or acetylenes may cause unwanted side reactions or fouling in the oligomeri zation unit . The skilled person is familiar with selective hydrogenation techniques to convert diolefins and acetylenes to monoolefins .

[0027] The olefin stream obtained from the OtO unit preferably comprises at least C2-olefins , C3-olefins and C4+-olefins . However, as laid out above , the composition of the olefin stream obtained directly from the OtO unit is typically not optimal to achieve a maximum yield of hydrocarbons boiling in the j et fuel range in the oligomeri zation step . In a preferred embodiment, the inventive process further comprises the step of separating the olefin stream in a fractionation unit into at least a C2-olef in-rich stream and a C4 + - olefin-rich stream. In this embodiment, the oligomerization feed comprises at least a portion of the C4+-olef in-rich stream. It is particularly preferred if the olefin stream is separated in the fractionation unit into at least a C2-olef in-rich stream, a C3-olef in-rich stream and a C4+-olef in-rich stream, wherein the oligomerization feed comprises at least a portion of the C4+- olefin-rich stream. In addition, the oligomerization feed may further comprise at least a portion of the C3-olef in-rich stream, as laid out in more detail below.

[0028] In this way, different components of the olefin stream can be treated independently from each other, which advantageously allows optimizing the composition of the oligomerization feed. It is particularly advantageous that the ethylene contained in the C2-olef in-rich stream and the propylene contained in the C3- olefin-rich stream can be processed differently from each other as well as differently from C4+-olefins contained in the olefin stream.

[0029] Separating the olefin stream as laid out above can be achieved using any suitable type of fractionation unit known in the art, e.g., comprising distillation columns, flash drums and the like. For instance, the fractionation unit may consist of a single distillation column. Alternatively, the fractionation unit may comprise multiple separation stages, e.g., a flash drum followed by one or more distillation columns.

[0030] The C2-olef in-rich stream preferably comprises more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the ethylene contained in the olefin stream. Preferably more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the olefins contained in the C2-olef in-rich stream is ethylene.

[0031] On the other hand, it was found that in some instances it can be advantageous not to aim for overly high separation ef ficiencies . It was found that even when signi ficant amounts of ethylene contained in the olefin stream do not end up in the C2 - olefin-rich stream, the process can nevertheless yield excellent results . Aiming for lower separation ef ficiencies allows using simpler equipment , saving costs and energy . Thus , it is preferred that the C2-olef in-rich stream comprises between 50 wt% and 99 wt% , more preferred between 60 wt% and 98 wt% , more preferred between 70 wt% and 97 wt% , more preferred between 80 wt% and 96 wt% , more preferred between 90 wt% and 95 wt% of the ethylene contained in the olefin stream . Similarly, it is preferred that between 50 wt% and 99 wt% , more preferred between 60 wt% and 98 wt% , more preferred between 70 wt% and 97 wt% , more preferred between 80 wt% and 96 wt% , more preferred between 90 wt% and 95 wt% of the olefins contained in the C2-olef in-rich stream is ethylene .

[0032] The C3-olef in-rich stream preferably comprises more than 50 wt% , more preferred more than 60 wt% , more preferred more than 70 wt% , more preferred more than 80 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred substantially all of the propylene contained in the olefin stream . Preferably more than 50 wt% , more preferred more than 60 wt% , more preferred more than 70 wt% , more preferred more than 80 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred substantially all of the olefins contained in the C3-olef in-rich stream is propylene . It is further preferred that the C3-olef in-rich stream comprises less than 30 wt% , more preferred less than 25 wt% , more preferred less than 20 wt% , more preferred less than 15 wt% , more preferred less than 10 wt% , more preferred less than 5 wt% , more preferred less than 1 wt% , more preferred substantially no ethylene .

[0033] On the other hand, for the same reasons as laid out above for the C2-olef in-rich stream, it was found that in some instances it can be advantageous not to aim for overly high separation ef ficiencies , allowing the use of simpler equipment , saving costs and energy . Thus , it is preferred that the C3-olefin- rich stream comprises between 50 wt% and 99 wt% , more preferred between 60 wt% and 98 wt% , more preferred between 70 wt% and 97 wt%, more preferred between 80 wt% and 96 wt%, more preferred between 90 wt% and 95 wt% of the propylene contained in the olefin stream. Similarly, it is preferred that between 50 wt% and 99 wt%, more preferred between 60 wt% and 98 wt%, more preferred between 70 wt% and 97 wt%, more preferred between 80 wt% and 96 wt%, more preferred between 90 wt% and 95 wt% of the olefins contained in the C3-olef in-rich stream is propylene. Additionally, it is preferred that the C3-olef in-rich stream comprises between 0.5 wt% and 20 wt%, more preferred between 1 wt% and 15 wt%, more preferred between 2 wt% and 10 wt%, more preferred between 3 wt% and 5 wt% ethylene.

[0034] The C4+-olef in-rich stream preferably comprises more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the C4+-olefins contained in the olefin stream. Preferably more than 20 wt%, more preferred more than 30 wt%, more preferred more than 40 wt%, more preferred more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the olefins contained in the C4+-olef in-rich stream are C4+-olefins. It is further preferred that the C4+-olef in-rich stream comprises less than 30 wt%, more preferred less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 1 wt%, more preferred substantially no ethylene. It is further preferred that the C4+-olef in-rich stream comprises less than 30 wt%, more preferred less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 1 wt%, more preferred substantially no propylene.

[0035] On the other hand, for the same reasons as laid out above for the C2-olef in-rich stream and the C3-olef in-rich stream, it was found that in some instances it can be advantageous not to aim for overly high separation efficiencies, allowing the use of simpler equipment, saving costs and energy. Thus, it is preferred that the C4+-olef in-rich stream comprises between 50 wt% and 99 wt%, more preferred between 60 wt% and 98 wt%, more preferred between 70 wt% and 97 wt%, more preferred between 80 wt% and 96 wt%, more preferred between 90 wt% and 95 wt% of the C4 + - olefins contained in the olefin stream. Similarly, it is preferred that between 50 wt% and 99 wt%, more preferred between 60 wt% and 98 wt%, more preferred between 70 wt% and 97 wt%, more preferred between 80 wt% and 96 wt%, more preferred between 90 wt% and 95 wt% of the olefins contained in the C4+-olefin- rich stream are C4+-olefins. Additionally, it is preferred that the C4+-olef in-rich stream comprises between 0.5 wt% and 20 wt%, more preferred between 1 wt% and 15 wt%, more preferred between 2 wt% and 10 wt%, more preferred between 3 wt% and 5 wt% C2-C3- olef ins .

[0036] The C4+-olef in-rich stream comprises C4-olefins, preferably wherein at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt% of the olefins contained in the C4+-olef in-rich stream are C4-olefins. In addition, it is preferred if the C4+-olef in-rich stream further comprises C5+-olefins, preferably wherein at least 5 wt%, more preferred at least 10 wt%, more preferred at least 15 wt%, more preferred at least 20 wt%, more preferred at least 25 wt%, more preferred at least 30 wt% of the olefins contained in the

[0037] C4+-olef in-rich stream are C5+-olefins, especially C5-C6 olefins, in particular C5-olefins.

[0038] As laid out above, the present invention allows optimizing the composition of the oligomerization feed that is processed in the oligomerization unit to increase the yield of jet-range hydrocarbons in the oligomerized olefin stream. For this purpose, it is preferred if the oligomerization feed contains a low amount of ethylene. This has been found to improve the efficiency of the oligomerization and to increase the yield of jetrange hydrocarbons obtained from the process. On the other hand, it has been found to be advantageous when the oligomerization feed comprises a high amount of C4+-olefins.

[0039] Therefore, preferably less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred none of the C2-olefin- rich stream is included in the oligomerization feed. In addition, it is preferred that less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 2 wt%, more preferred less than 1 wt%, more preferred substantially none of the ethylene contained in the olefin stream obtained from the OtO unit is included in the oligomerization feed.

[0040] On the other hand, as explained above, it can be advantageous not to aim for overly high separation efficiencies, allowing the use of simpler equipment, saving costs and energy. In addition, a certain proportion of ethylene may also be converted to higher olefins in the oligomerization unit, making it possible to increase the total amount of jet-range hydrocarbons obtained from a given amount of oxygenate starting material. Therefore, in a preferred embodiment, between 0.5 wt% and 20 wt%, more preferred between 1 wt% and 15 wt%, more preferred between 2 wt% and 10 wt%, more preferred between 3 wt% and 5 wt% of the ethylene contained in the olefin stream obtained from the OtO unit is included in the oligomerization feed.

[0041] In order to provide a high amount of C4+-olefins in the oligomerization feed, it is preferred that at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C4+-olef in-rich stream is included in the oligomerization feed. Thus, preferably, the oligomerization feed comprises the C4+-olef in-rich stream. In addition, it is preferred that at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C4+-olefins, especially C4-olefins, contained in the olefin stream obtained from the OtO unit is included in the oligomerization feed.

[0042] In the context of the inventive process, it is preferred that at least a portion of the propylene obtained from the OtO unit is included in the oligomerization feed. Thus, preferably, at least 1 wt%, more preferred at least 5 wt%, more preferred at least 10 wt%, more preferred at least 20 wt%, more preferred at least 30 wt% , more preferred at least 40 wt% , more preferred at least 50 wt% , more preferred at least 60 wt% , more preferred at least 70 wt% , more preferred at least 80 wt% , more preferred at least 90 wt% of the propylene contained in the olefin stream are included in the oligomeri zation feed . On the other hand, it is also preferred that not all of the propylene obtained from the OtO unit is included in the oligomeri zation feed . Preferably between 1 wt% and 99 wt% , more preferred between 5 wt% and 98 wt% , more preferred between 10 wt% and 97 wt% , more preferred between 20 wt% and 95 wt% , more preferred between 30 wt% and 90 wt% , more preferred between 40 wt% and 85 wt% , more preferred between 50 wt% and 80 wt% of the propylene obtained from the OtO unit is included in the oligomeri zation feed .

[0043] It was found that this allows striking a balance between maximi zing the proportion of the olefin stream obtained from the OtO unit that is further processed in the oligomeri zation unit , and optimi zing the conditions in the oligomeri zation step, where a higher proportion of C4+-olefins is preferred to increase the yield of j et-range hydrocarbons . When only a low proportion of the C3-olef in-rich stream is included in the oligomeri zation feed, a higher proportion of the OtO product is removed from the process and thus a higher proportion of carbon contained in the oxygenate starting material does not end up as hydrocarbons boiling in the j et fuel range . On the other hand, when the proportion of propylene in the oligomeri zation feed becomes very high, the proportion of j et-range hydrocarbons in the oligomeri zed olefin stream may be reduced, depending on the circumstances . Thus , the amount of j et-range hydrocarbons obtained from a given amount of oxygenate starting material can be maximi zed by balancing these two extremes depending on the current circumstances , and by including at least a certain amount of the propylene contained in the olefin stream in the oligomeri zation feed .

[0044] The features of the inventive process , as described herein, make it possible to include a particularly high amount or even substantially all of the propylene in the oligomeri zation feed, while nevertheless keeping the yield of j et-range hydrocarbons in the oligomeri zation step high . This ensures that a higher proportion of the olefin stream obtained from the OtO unit is further processed in the oligomeri zation unit and thus that a higher amount of carbon contained in the oxygenate starting material remains in the process for producing a j et fuel composition . This allows ultimately obtaining a higher total amount of j et-range hydrocarbons from a given amount of oxygenates .

[0045] Moreover, the C3-olef in-rich stream can advantageously be used to tune the amount of propylene included in the oligomerization feed, thereby making it possible to flexibly adapt the composition of the oligomeri zation feed depending on the current need . This is particularly advantageous when some or multiple further components are included in the oligomeri zation feed, such as portions of the C2-olef in-rich stream that have undergone dimeri zation, portions of external C4+-olefin streams and recycle streams , as described in more detail below .

[0046] The part of the C3-olef in-rich stream that is not included in the oligomeri zation feed can be used as a source for propylene that can be sold as a separate product or used in other refinery processes .

[0047] Therefore , in a preferred embodiment , the C3-olef in-rich stream is separated in a further fractionation unit to obtain a propylene product stream . Preferably, the C3-olef in-rich stream is separated into the propylene product stream and one or more further streams containing compounds other than propylene , such as ethylene , C4+-olefins , or paraf fins . Preferably, the one or more further streams contain propane .

[0048] The propylene product stream is preferably a high-purity propylene stream . Preferably, it comprises at least 90 wt% , more preferred at least 92 wt% , more preferred at least 99 wt% propylene , more preferred at least 99 . 5 wt% propylene . In a particularly preferred embodiment , the propylene product stream substantially consists of propylene .

[0049] The amount of propylene included in the oligomeri zation feed can advantageously be tuned by regulating how much of the C3- olefin-rich stream is included in the oligomeri zation feed . Therefore , preferably at least 1 wt% , more preferred at least 5 wt% , more preferred at least 10 wt% , more preferred at least 20 wt% , more preferred at least 30 wt% , more preferred at least 40 wt% , more preferred at least 50 wt% , more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C3-olef in-rich stream is included in the oligomerization feed. Preferably, between 1 wt% and 100 wt%, more preferred between 5 wt% and 99 wt%, more preferred between 10 wt% and 98 wt%, more preferred between 20 wt% and 97 wt%, more preferred between 30 wt% and 95 wt%, more preferred between 40 wt% and 90 wt%, more preferred between 50 wt% and 85 wt%, more preferred between 60 wt% and 80 wt% of the C3-olef in-rich stream is included in the oligomerization feed.

[0050] In a preferred embodiment, the weight ratio between the C4+- olefin-rich stream and the C2-olefin rich stream included in the oligomerization feed is at least 2, more preferred at least 3, more preferred at least 4, more preferred at least 5, more preferred at least 7, more preferred at least 10. This ensures that the oligomerization feed comprises a higher proportion of C4+- olefins relative to C2-olefins.

[0051] In a further preferred embodiment, the weight ratio between the C4+-olef in-rich stream and the C3-olef in-rich stream included in the oligomerization feed is at least 0.5, more preferred at least 1, more preferred at least 2. Preferably, the weight ratio between the C4+-olef in-rich stream and the C3-ole- fin-rich stream included in the oligomerization feed is between 0.5 and 8, more preferred between 0.75 and 6, more preferred between 1 and 5, more preferred between 1.5 and 4.

[0052] As outlined above, it has been found in the course of the present invention that the efficiency of the process can be increased and the yield of jet-range hydrocarbons can be improved by optimizing the composition of the oligomerization feed. A particularly advantageous oligomerization feed has been found to contain low amounts of oxygenates, relatively low amounts of aromatic compounds, low amounts of ethylene, and higher amounts of C4+-olefins, as laid out in more detail below.

[0053] The term "oligomerization feed" as used herein preferably refers to the total material processed in the oligomerization unit. As laid out herein in more detail, the oligomerization feed may comprise multiple separate and distinct oligomerization feed streams. When the composition of the oligomerization feed is specified herein, this refers to the combined total of all feed streams processed in the oligomerization unit over a given time period. For instance, when a first oligomerization feed stream and a second oligomerization feed stream are separately sent to the oligomerization unit, the composition of the "oligomerization feed" can be determined by summing the compositions of the first and second oligomerization feed streams that arrive at the oligomerization unit per unit of time.

[0054] It is preferred in the context of the invention that the oligomerization feed comprises less than 5 wt%, more preferred less than 2 wt%, more preferred less than 1 wt% oxygenates. This has been found to improve the efficiency of the oligomerization step .

[0055] Advantageously the oligomerization feed comprises low amounts of aromatic compounds. Preferably, the oligomerization feed comprises less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 3 wt%, more preferred less than 1 wt% aromatic compounds.

[0056] Advantageously the oligomerization feed comprises low amounts of ethylene. Ethylene typically exhibits low conversion rates to jet-range hydrocarbons under typical oligomerization conditions. Higher amounts of ethylene in the oligomerization feed can therefore result in lower yields of jet-range hydrocarbons in the oligomerized olefin stream. Thus, preferably, the oligomerization feed comprises less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 3 wt% ethylene. It is further preferred that less than 35 wt%, more preferred less than 30 wt%, more preferred less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% of the olefins contained in the oligomerization feed are ethylene.

[0057] In connection with the invention, it was found to be particularly advantageous, when the ratio of C4+-olefins to ethylene in the oligomerization feed is high. Therefore, the weight ratio of C4+-olefins to ethylene in the oligomerization feed is preferably more than 1, more preferred more than 2, more preferred more than 3, more preferred more than 4, more preferred more than 5, more preferred more than 6, more preferred more than 7, more preferred more than 8. Preferably, the weight ratio of C4- olefins to ethylene in the oligomerization feed is more than 0.5, more preferred more than 1, more preferred more than 2, more preferred more than 3, more preferred more than 4.

[0058] It is further preferred that the concentration of propylene in the oligomerization feed is not too high. Preferably, the oligomerization feed comprises less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt% propylene. It is further preferred that less than 70 wt%, more preferred less than 60 wt%, more preferred less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt% of the olefins contained in the oligomerization feed are propylene.

[0059] Preferably, the weight ratio of C4+-olefins to propylene in the oligomerization feed is more than 0.25, more preferred more than 0.5, more preferred more than 0.75, more preferred more than 1, more preferred more than 1.5, more preferred more than 2. It has been found to particularly advantageous when the weight ratio of C4+-olefins to propylene in the oligomerization feed is between 0.25 and 25, more preferred between 0.5 and 20, more preferred between 0.75 and 15, more preferred between 1 and 10, more preferred between 1.5 and 6.

[0060] Preferably, the weight ratio of C4-olefins to propylene in the oligomerization feed is more than 0.15, more preferred more than 0.25, more preferred more than 0.5, more preferred more than 0.75, more preferred more than 1, more preferred more than 1.5. It has been found to particularly advantageous when the weight ratio of C4-olefins to propylene in the oligomerization feed is between 0.15 and 20, more preferred between 0.25 and 15, more preferred between 0.5 and 10, more preferred between 0.75 and 7.5, more preferred between 1 and 4.

[0061] As outlined above, it has been found to be advantageous, when the concentration of C4+-olefins in the oligomerization feed is high. Preferably, the oligomerization feed comprises at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt% C4+-olefins. It is further preferred that at least 30 wt%, more preferred at least

[0062] 40 wt%, more preferred at least 50 wt%, more preferred at least

[0063] 60 wt%, more preferred at least 70 wt%, more preferred at least

[0064] 80 wt%, more preferred at least 90 wt% of olefins contained in the oligomerization feed are C4+-olefins.

[0065] It has further been found to be advantageous, when the weight ratio of C4-olefins to C5+-olefins in the oligomerization feed is in a certain range. Preferably, said ratio is between 0.25 and 30, more preferred between 0.5 and 15, more preferred between 0.75 and 10, more preferred between 1 and 8.

[0066] Preferably, the concentration of olefins in the oligomerization feed is at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%.

[0067] It has been found to be advantageous, when the amount of iso-olefins in the oligomerization feed is high compared to the amount of n-olefins. Thus, preferably, the weight ratio of isoolefins to n-olefins in the oligomerization feed is at least 1, preferably at least 1.5, more preferred at least 2, more preferred at least 3.

[0068] It has further been found that it can be advantageous to include a certain amount of paraffins in the oligomerization feed. Paraffins can advantageously act as a diluent to decrease the operating temperature and to limit temperature increase from the exothermal reaction in the oligomerization unit. Therefore, preferably the weight ratio of olefins to paraffins is at least 0.2, preferably at least 0.4, more preferred at least 0.5.

[0069] As outlined above, the inventive process makes it possible to convert a high proportion of carbon from the oxygenate starting material into hydrocarbons boiling in the jet fuel range. Therefore, it is preferred that a large proportion of olefins, especially C3+-olefins, contained in the olefin stream obtained from the OtO unit are included in the oligomerization feed. Preferably, at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 85 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred at least 98 wt%, more preferred at least 99 wt%, more preferred substantially all of the C3+-olefins contained in the olefin stream are included in the oligomerization feed.

[0070] Moreover, it is preferred that also a portion of C2-olefins contained in the olefin stream are included in the oligomerization feed. Preferably, a large proportion of all olefins are included in the oligomerization feed. Preferably, at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 85 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred at least 98 wt%, more preferred at least 99 wt%, more preferred substantially all of the olefins contained in the olefin stream are included in the oligomerization feed. As described in more detail herein, this may for instance advantageously be achieved by also including olefins contained in the olefin stream in the oligomerization feed through indirect means, e.g., by dimerizing ethylene contained in a C2-olefin- rich stream separated from the olefin stream and by including the resulting dimerization product in the oligomerization feed.

[0071] Preferably, at least 70 wt%, more preferred at least 75 wt%, more preferred at least 80 wt%, more preferred at least 85 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred at least 98 wt%, more preferred at least 99 wt%, more preferred substantially all of the carbon contained in the oxygenate feed is included in the oligomerization feed.

[0072] In the inventive process, the oligomerization feed is processed in the oligomerization unit to produce an oligomerized olefin stream. The skilled person is familiar with suitable catalysts and suitable reaction conditions for operating an oligomerization unit. Such suitable reaction conditions and catalysts are disclosed, e.g., in WO 2023 / 196394 Al, US 2022 / 0396741 Al and WO 2023 / 138876 Al.

[0073] The oligomerization unit can be operated at reaction conditions that are typically used for such units in the art. However, since the present invention allows optimizing the composition of the oligomerization feed as described above, it is possible to operate the oligomerization unit at relatively mild conditions compared to conventional processes without optimized oligomerization feeds, e.g., relatively low temperature and relatively low pressure. In this way, energy consumption of the oligomerization step can be reduced, and the catalyst cycle length and overall lifetime of the oligomerization catalyst can be increased, both factors leading to reduced OpEx . Furthermore, process risk is minimized when performing the oligomerization step at less severe operating conditions. Additionally, the requirements for the process equipment such as reactors or heat exchangers are lower, leading to a reduction in CapEx.

[0074] Preferably, the oligomerization unit is operated at a temperature between 140 °C and 260 °C, preferably between 160 °C and 240 °C, more preferred between 170 °C and 220 °C. Preferably, the oligomerization unit is operated at a pressure from 20 bar to 50 bar, more preferred between 25 bar and 40 bar.

[0075] In a preferred embodiment of the inventive process, the step of processing the oligomerization feed in the oligomerization unit comprises processing an oligomerization feed comprising a first oligomerization feed stream containing at least a portion of the C3-olef in-rich stream and a second oligomerization feed stream containing at least a portion of the C4+-olef in-rich stream in the oligomerization unit to produce the oligomerized olefin stream; wherein the oligomerization unit comprises at least a first reaction zone, and a second reaction zone downstream of the first reaction zone; wherein the first oligomerization feed stream is introduced into the oligomerization unit at a position upstream of the first reaction zone, and the second oligomerization feed stream is introduced into the oligomerization unit at a position downstream of the first reaction zone and upstream of the second reaction zone. This embodiment offers several unique advantages, as will be explained in the following .

[0076] In this embodiment, prior to the step of processing the oligomerization feed in the oligomerization unit, the process comprises the step of separating the olefin stream in a fractionation unit into at least a C2-olef in-rich stream, a C3-olefin- rich stream and a C4+-olef in-rich stream. In this way, ethylene contained in the C2-olef in-rich stream and propylene contained in the C3-olef in-rich stream can be processed differently from each other and di f ferently from C4+-olefins contained in the olefin stream .

[0077] The first oligomeri zation feed stream, which may contain high amounts of C3-olefins , is introduced into the oligomeri zation unit at a position upstream of the first reaction zone . Thus , this stream passes through the first reaction zone followed by the second reaction zone , and optionally further reaction zones , before the stream exits the oligomeri zation unit as part of the oligomeri zed olefin stream . On the other hand, the second oligomeri zation feed stream, which may contain high amounts of C4+-olefins , is introduced into the oligomeri zation unit at a position between the first reaction zone and the second reaction zone . Said stream therefore skips the first reaction zone and only passes through the second zone , and optionally further reaction zones , before it exits the oligomeri zation unit as part of the oligomeri zed olefin stream . In this way, high amounts of C3-olefins contained the first oligomeri zation feed stream, which are typically less favorable for oligomeri zation and exhibit low per-pass conversion rates under typical oligomeri zation conditions , pass through an additional reaction zone of the oligomeri zation unit , making it possible to enhance conversion and increase the overall yield of j et-range hydrocarbons in the ef fluent of the oligomeri zation unit .

[0078] Moreover, passing only the first but not the second oligomeri zation feed stream through the first reaction zone makes it possible to tune the conditions of the individual reaction zones to the needs of each stream . For instance , as will described in further detail below, the reaction zones may be operated at di f ferent temperatures , pressures , weight hourly space velocities (WHSV) and / or using di f ferent catalysts . It is particularly advantageous when the first reaction zone is operated at harsher reaction conditions , especially at a higher temperature , than the second reaction zone . Such harsher reaction conditions are advantageous in relation to high amounts of propylene contained in the first oligomeri zation feed stream, since harsher conditions can increase the conversion rate of propylene to higher olefins . On the other hand, such harsher conditions may be less favorable for C4+-olefins , since C4+-olefins may be broken down at harsh conditions , defeating the purpose of the oligomerization unit, or be converted into undesired byproducts such as aromatic compounds outside the jet fuel range or coke deposits on the catalyst, thereby lowering the jet fuel yield and conversion efficiency of the process. Thus, for C4+-olefins, milder conditions in the second reaction zone are more favorable. For this reason, it is highly advantageous that the second oligomerization feed stream containing high amounts of C4+-ole- fins skips is allowed to skip the first reaction zone and directly passes through the second reaction zone.

[0079] By operating the first reaction zone at harsher reaction conditions and the second reaction zone at milder reaction conditions, and by allowing only the first but not the second oligomerization feed stream to pass through the first reaction zone, it is possible to tailor the oligomerization reaction conditions to each oligomerization feed stream. High amounts of propylene contained in the first oligomerization feed stream may be converted under harsher reaction conditions to C4+-olefins in the first reaction zone, which then pass to the second reaction zone, where they find milder conditions that are better suited for converting C4+-olefins to jet-range olefins. The second oligomerization feed stream, which may already contain high amounts of C4+-olefins, is instead allowed to skip the harsher conditions of the first reaction zone, in which there would be an increased risk of higher olefins being broken down.

[0080] The first oligomerization feed stream comprises at least a portion of the C3-olef in-rich stream. Preferably, the first oligomerization feed stream comprises at least 10 wt%, more preferred at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C3-olef in-rich stream.

[0081] By treating the first oligomerization stream differently than the second oligomerization stream, in particular in a further reaction zone and preferably under harsher conditions, it is possible to process a high amount of propylene in the oligomerization unit while still ensuring a high yield of jet-range hydrocarbons. Thus, preferably, at least 1 wt%, more preferred at least 5 wt%, more preferred at least 10 wt%, more preferred at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt% of the propylene contained in the olefin stream are included in the first oligomerization feed stream. On the other hand, it is also preferred that not all of the propylene obtained from the OtO unit is included in the first oligomerization feed stream. Preferably between 1 wt% and 99 wt%, more preferred between 5 wt% and 98 wt%, more preferred between 10 wt% and 97 wt%, more preferred between 20 wt% and 95 wt%, more preferred between 30 wt% and 90 wt%, more preferred between 40 wt% and 85 wt%, more preferred between 50 wt% and 80 wt% of the propylene obtained from the OtO unit is included in the first oligomerization feed stream.

[0082] Preferably more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the olefins contained in the first oligomerization feed stream is propylene.

[0083] It is further preferred that less than 30 wt%, more preferred less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% of the olefins contained in the first oligomerization feed stream are C4+-olefins. This is advantageous, in particular, when the first reaction zone is operated under harsh reaction conditions, which may partially break down C4+-olefins.

[0084] Moreover, it is preferred that the first oligomerization feed stream comprises low amounts of ethylene. Preferably, less than 30 wt%, more preferred less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt% of the olefins contained in the first oligomerization feed stream is ethylene. On the other hand, it has been found that a certain proportion of ethylene can also be converted in the oligomerization unit, especially when the first reaction zone is operated under harsh reaction conditions. Thus, preferably between 1 wt% and 30 wt%, more preferred between 2 wt% and 25 wt%, more preferred between 3 wt% and 20 wt%, more preferred between 4 wt% and 15 wt%, more preferred between 5 wt% and 10 wt% of the olefins contained in the first oligomerization feed stream is ethylene.

[0085] It has further been found that it can be advantageous to include a certain amount of paraffins in the first oligomerization feed stream. Paraffins can advantageously act as a diluent to decrease the operating temperature and to limit temperature increase from the exothermal reaction in the oligomerization unit. This has been found to be particularly advantageous, when the first reaction zone is operated under harsher reaction conditions. Therefore, preferably the first oligomerization stream comprises at least 10 wt%, preferably at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt% paraffins, especially C3-C8 paraffins.

[0086] The second oligomerization feed stream comprises at least a portion of the C4+-olef in-rich stream. Preferably, the second oligomerization feed stream comprises at least 10 wt%, more preferred at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C4+-olef in-rich stream.

[0087] Preferably, at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of C4+-olefins contained in the olefin stream are included in the second oligomerization feed stream.

[0088] Preferably more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the olefins contained in the second oligomerization feed stream are C4+-ole- f ins .

[0089] It is further preferred that less than 30 wt%, more preferred less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% of the olefins contained in the second oligomerization feed stream are C2-C3-olef ins .

[0090] Similarly as for the first oligomerization stream, it has further been found that it can be advantageous to include a certain amount of paraffins in the second oligomerization feed stream. Preferably, the second oligomerization stream comprises at least 10 wt%, preferably at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt% paraffins, especially C3-C8 paraffins.

[0091] As outlined above, the oligomerization unit used for the inventive process may comprise at least a first reaction zone and a second reaction zone. The second reaction zone is located downstream of the first reaction zone, meaning that a stream entering the oligomerization unit upstream of the first reaction zone can pass through the first reaction zone followed by the second reaction zone, before it exits the oligomerization unit as part of the oligomerized olefin stream. In a preferred embodiment, in which the oligomerization unit comprises a third reaction zone, said third reaction zone is located downstream of the second reaction zone, so that a stream entering the oligomerization unit upstream of the first reaction zone may pass through the first, second and third reaction zones in this order.

[0092] As used herein, a "reaction zone" preferably refers to a catalyst bed contained in the oligomerization unit. Thus, the "first reaction zone" can also be referred to as the "first catalyst bed" and the "second reaction zone" can be referred to as the "second catalyst bed", etc. Preferably, the first reaction and the second reaction zone, and optionally the further reaction zones (or the first, second and further catalyst beds) may be contained in separate reactor vessels or in a single reactor vessel. It is particularly preferred if they are contained in a single reactor vessel, as this can simplify the overall process and reduce costs.

[0093] The skilled person is familiar with operating conditions for typical oligomerization units. In the context of the inventive process, the first reaction zone and the second reaction zone, and optionally further reaction zones, may be operated at different conditions. More specifically, the conditions of the first reaction zone may be more optimized towards the oligomerization of propylene, whereas the second reaction zone and optionally the further reaction zones may be optimized towards the oligomerization of C4+-olefins. Thus, it is particularly preferred that the first reaction zone is operated under harsher operating conditions than the second reaction zone.

[0094] In a preferred embodiment, the first reaction zone is operated at a higher temperature than the second reaction zone. Preferably, the temperature in the first reaction zone is at least 5 °C higher than the temperature in the second reaction zone, more preferred at least 10 °C, more preferred at least 20 °C, more preferred at least 30 °C, more preferred at least 40 °C. For the reasons laid out above, a higher temperature in the first reaction zone is more favorable for the oligomerization of propylene and a lower temperature in the second reaction zone is more favorable for the oligomerization of C4+-olefins.

[0095] Preferably, the first reaction zone is operated at a temperature between 180 °C and 320 °C, more preferred between 200 °C and 300 °C, more preferred between 220 °C and 280 °C. It was found that these temperature ranges are particularly well suited for the oligomerization of propylene.

[0096] On the other hand, it is preferred that the second reaction zone is operated at a temperature between 140 °C and 260 °C, preferably between 160 °C and 240 °C, more preferred between 170 °C and 220 °C. It was found that these temperature ranges are particularly well suited for the oligomerization of C4+- olef ins .

[0097] In a preferred embodiment, the second oligomerization feed stream is introduced into the oligomerization unit at a temperature that is lower than the temperature of the second reaction zone. It has been found that this allows using the second oligomerization feed stream as a coolant to achieve a decrease in operating temperature going from the first reaction zone to the second reaction zone. In this context, the phrase "introduced into the oligomerization unit at a temperature" preferably specifies the temperature of the second oligomerization feed stream at the point immediately prior to entering the oligomerization unit. Preferably, the second oligomeri zation feed stream is introduced into the oligomeri zation unit at a temperature that is at least 10 ° C, more preferred at least 20 ° C, more preferred at least 40 ° C lower than the temperature of the second reaction zone .

[0098] In a preferred embodiment , the first reaction zone is operated at a higher pressure than the second reaction zone . Preferably, the pressure in the first reaction zone is at least 5 % higher than in the second reaction zone , preferably at least 10 % , more preferred at least 20% . However, in another embodiment , which is also preferred, the first reaction zone and the second reaction zone are operated at the same pressure .

[0099] Preferably, the first reaction zone is operated at a pressure between 20 bar and 50 bar, more preferred between 25 bar and 45 bar, more preferred between 30 and 40 bar . Preferably, the second reaction zone is operated at a pressure between 20 bar and 45 bar, more preferred between 25 bar and 40 bar .

[0100] In a preferred embodiment , the first reaction zone is operated at a higher weight hourly space velocity (WHSV) than the second reaction zone . Thus , preferably, the residence time of the feed in the first reaction zone is shorter than in the second reaction zone . This is particularly advantageous when the first reaction zone is operated under harsher reaction conditions , since the shorter residence time allows balancing out unwanted side-product formation .

[0101] Preferably, the WHSV in the first reaction zone is at least 5 % higher than in the second reaction zone , preferably at least 10 % , more preferred at least 20% , more preferred at least 30 % .

[0102] Any suitable catalyst known in the art can be used in the oligomeri zation unit to convert the olefin stream into the oligomeri zed olefin stream . Preferably, the catalyst comprises a solid acid catalyst , especially a zeolite such as ZSM-5 , ZSM-23 , ZSM-48 or UZM- 8 , or amorphous silica-alumina (ASA) .

[0103] It is particularly preferred when the first reaction zone comprises a non-metal-doped catalyst . Preferably, the term "nonmetal-doped catalyst" refers to a catalyst that is not doped with metals , especially not doped with transition metals . Preferably, said term refers to a catalyst that does not contain transition metals , especially a catalyst that does not contain a metal selected from Ni , Ti , Zr, Pt and Pd . In the prior art , metal-doped catalysts are typically used to convert less reactive components . In the context of the invention, it was found that even though propylene is more di f ficult to convert in an oligomeri zation reaction than higher olefins , such a conversion can nevertheless be achieved to a high degree by using a nonmetal-doped catalyst and by tuning the conditions , in particular the temperature , as laid out above . This has the advantage that non-metal-doped catalysts are typically lower in costs and typically also less sensitive than metal-containing catalysts , such as Pt-based or Ni-based catalysts . Thus , preferably, the catalyst used for operating the first reaction zone is a non-metal- doped catalyst .

[0104] Similarly, it is also preferred for the second reaction zone and the further reaction zones that non-metal-doped catalysts are used . Thus , preferably the second reaction zone and / or the further reaction zones comprise non-metal-doped catalysts .

[0105] In the context of the invention, it was found to be advantageous when the first reaction zone and the second reaction zone comprise the same catalyst . This results in a simpli fication of the process , further reducing complexity and costs . Moreover, it was found that when the first reaction zone and the second reaction zone comprise the same catalyst , the reaction conditions can be tuned in a simple and predictable manner by modi fying the temperature at which the reaction zone is operated .

[0106] Preferably, the catalyst used in the first reaction zone and / or the second reaction zone comprises a solid acid catalyst , especially a zeolite such as ZSM-5 , ZSM-23 , ZSM-48 or UZM- 8 , or amorphous silica-alumina (ASA) .

[0107] In a preferred embodiment of the inventive process , the oligomeri zation unit comprises at least a third reaction zone located downstream of the second rection zone . Including a third reaction zone downstream of the second reaction zone can further increase the yield of j et-range hydrocarbons obtained from the oligomeri zation unit . For the third reaction zone the same temperature and pressure ranges are preferred as for the second reaction zone. Preferably, the third reaction zone is operated at the same temperature and at the same pressure as the second reaction zone.

[0108] Preferably, the third reaction zone comprises a catalyst that comprises a solid acid catalyst, especially a zeolite such as ZSM-5, ZSM-23, ZSM-48 or UZM-8, or amorphous silica-alumina (ASA) . However, it has turned out to be advantageous when the third reaction zone contains a different catalyst than the second reaction zone, and preferably also than the first reaction zone. This allows to further tune the composition of the oligomerized olefin stream obtained from the oligomerization unit so as to further increase the yield of jet-range hydrocarbons .

[0109] The oligomerized olefin stream preferably comprises at least a fraction of hydrocarbons boiling in the jet fuel range. Preferably, the oligomerized olefin stream comprises a large proportion of C8-C16 olefins.

[0110] Preferably more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 75 wt%, more preferred more than 80 wt%, more preferred more than 85 wt%, more preferred more than 90 wt%, more preferred more than 95 wt% of olefins contained in the oligomerized olefin stream are C8-C16 olefins.

[0111] It is further preferred that the proportion of lighter olefins in the oligomerized olefin stream is low. Preferably, less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% of the olefins contained in the oligomerized olefin stream are C2-C7- olef ins .

[0112] It is also preferred that the proportion of heavier olefins in the oligomerized olefin stream is low. Preferably, less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt% of olefins contained in the oligomerized olefin stream are C17+ olefins.

[0113] It is further preferred that the oligomerized olefin stream contains low amounts of aromatic compounds. Preferably, the oligomeri zed olefin stream comprises less than 25 wt% , more preferred less than 20 wt% , more preferred less than 15 wt% , more preferred less than 10 wt% , more preferred less than 5 wt% , more preferred less than 3 wt% , more preferred less than 1 wt% aromatic compounds .

[0114] In the inventive process , at least a portion of the oligomeri zed olefin stream is hydrogenated . The skilled person is familiar with suitable methods for hydrogenating olefin streams . Typically, during hydrogenation, hydrogen gas is added in the presence of a hydrogenation catalyst to saturate olefins leading to the formation of single bonds between carbon atoms .

[0115] In a preferred embodiment , the j et fuel composition is obtained from the oligomeri zed olefin stream by hydrogenating olefins contained in the oligomeri zed olefin stream and by separating a stream rich in j et-range hydrocarbons in a further fractionation unit . The sequence of hydrogenation and separation can be performed in either order, providing flexibility in the processing steps according to speci fic operational requirements or desired outcomes . Thus , in one embodiment , the oligomeri zed olefin stream is hydrogenated to obtain a hydrogenated stream, and the hydrogenated stream is processed in the further fractionation unit to obtain a stream rich in C8 -C16-hydrocarbons . However, it was found to be advantageous , when the recycle stream is withdrawn from the oligomeri zed olefin stream before hydrogenation, as this reduces the amount of material that needs to be processed in the hydrogenation step . Therefore , in a preferred embodiment , the oligomeri zed olefin stream is processed in the further fractionation unit to obtain a stream rich in C8- C16 olefins and said stream rich in C8 -C16 olefins is hydrogenated to obtain the j et fuel composition . Also a combination of these embodiments is preferred, wherein the oligomeri zed olefin stream is processed in a further fractionation unit to obtain a stream rich in C8-C16 olefins , said stream rich in C8-C16 olefins is hydrogenated, and the resulting hydrogenated stream is processed in yet a further fractionation unit to obtain the j et fuel composition .

[0116] The j et fuel composition preferably comprises at least 50 wt% , more preferred at least 60 wt% , more preferred at least 70 wt% , more preferred at least 80 wt% , more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred at least 98 wt%, more preferred at least 99 wt% C8-C16-hydrocarbons .

[0117] Preferably the jet fuel composition has a boiling range with an initial boiling point of at least 80 °C, more preferred at least 90 °C, more preferred at least 100 °C, more preferred at least 110 °C, more preferred at least 115 °C, more preferred at least 120 °C. Preferably, the jet fuel composition has a boiling range with a final boiling point of at most 350 °C, more preferred at most 340 °C, more preferred at most 330 °C, more preferred at most 320 °C, more preferred at most 310 °C, more preferred at most 300 °C. Preferably the jet fuel composition has a boiling range between 80 °C and 350 °C, more preferred between 90 °C and 340 °C, more preferred between 100 °C and 330 °C, more preferred between 110 °C and 320 °C, more preferred between 115 °C and 310 °C, more preferred between 120 °C and 300 °C,

[0118] In a particularly preferred embodiment, the jet fuel composition is sustainable aviation fuel (SAP) , preferably SAF according to any approved ASTM standard for SAF, preferably the standard ASTM D7566-22.

[0119] In a preferred embodiment of the present invention, a C4-C7- olefin-rich fraction is separated from the oligomerized olefin stream. Preferably, at least a portion of said C4-C7-olef in-rich fraction is recycled and included in the oligomerization feed. Preferably the C4-C7-olef in-rich fraction is separated from the oligomerized olefin stream using a further fractionation unit. It has been found that by recycling a C4-C7-olef in-rich fraction in this way, the yield of jet-range hydrocarbons obtained from the inventive process can be further increased. In particular, C4-C7-olef ins withdrawn as part of the C4-C7-olef in-rich fraction can be converted into heavier olefins by processing them in the oligomerization unit again. In addition, by including a fraction containing high amounts of C4-C7-olef ins, the conditions for oligomerization can be further optimized.

[0120] Preferably, the C4-C7-olef in-rich fraction contains at least

[0121] 50 wt%, more preferred at least 60 wt%, more preferred at least

[0122] 70 wt%, more preferred at least 80 wt%, more preferred at least

[0123] 90 wt%, more preferred at least 95 wt%, more preferred at least

[0124] 98 wt%, more preferred at least 99 wt%, more preferred substantially all of the C4-C7 -olef ins contained in the oligomeri zed olefin stream . Preferably more than 50 wt% , more preferred more than 60 wt% , more preferred more than 70 wt% , more preferred more than 75 wt% , more preferred more than 80 wt% , more preferred more than 85 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred more than 98 wt% , more preferred more than 99 wt% , more preferred substantially all of the olefins contained in the C4 -C7-olef inrich fraction are C4-C7-olef ins .

[0125] In the embodiment in which the oligomeri zation feed comprises at least a first and a second oligomeri zation feed stream, preferably, at least a portion of the C4-C7-olef in-rich fraction is recycled and added to the second oligomeri zation feed stream . Thus , preferably, the at least a portion of the C4- C7-olef in-rich fraction is introduced into the oligomeri zation unit at a position downstream of the first reaction zone and upstream of the second reaction zone . As detailed above , the second reaction zone may be optimi zed towards the conversion of C4+-olefins , whereas the first reaction zone may be less favorable for higher olefins , in particular i f the first reaction zone is operated under harsher conditions . Thus , it is advantageous when the C4-C7-olef in-rich fraction is allowed to skip the first reaction zone and directly passes to the second reaction zone .

[0126] In a further preferred embodiment of the inventive process , a C3-olef in-rich fraction is separated from the oligomeri zed olefin stream . Preferably, at least a portion of the C3-olefin- rich fraction is recycled and included in the oligomeri zation feed . Similarly as described above for the C4 -C7-olef in-rich fraction, this allows further increasing the yield of j et-range hydrocarbons obtained from the inventive process . Preferably the C3-olef in-rich fraction is separated from the oligomeri zed olefin stream using a further fractionation unit .

[0127] Preferably, the C3-olef in-rich fraction contains at least 50 wt% , more preferred at least 60 wt% , more preferred at least

[0128] 70 wt% , more preferred at least 80 wt% , more preferred at least

[0129] 90 wt% , more preferred at least 95 wt% , more preferred at least

[0130] 98 wt% , more preferred at least 99 wt% , more preferred substantially all of the C3-olefins contained in the oligomeri zed olefin stream . Preferably more than 50 wt% , more preferred more than 60 wt% , more preferred more than 70 wt% , more preferred more than 75 wt% , more preferred more than 80 wt% , more preferred more than 85 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred more than 98 wt% , more preferred more than 99 wt% , more preferred substantially all of the olefins contained in the C3-olef in-rich fraction are C3-olef ins .

[0131] In the embodiment in which the oligomeri zation feed comprises at least a first and a second oligomeri zation feed stream, preferably, at least a portion of the C3-olef in-rich fraction is recycled and added to the first oligomeri zation feed stream . Thus , preferably, the at least a portion of the C3-ole- fin-rich fraction is introduced into the oligomeri zation unit at a position upstream of the first reaction zone . As detailed above , this allows the C3-olefins contained in the C3-olefin- rich fraction to pass through both the first reaction zone and the second reaction zone , which can enhance the conversion ef ficiency and thus ultimately further increase the yield of j etrange hydrocarbons .

[0132] In a preferred embodiment of the present invention, the oligomeri zed olefin stream is separated in the further fractionation unit into at least the C3-olef in-rich fraction, the C4-C7- olefin-rich fraction and a C8-C16-olef in-rich fraction . The C3- olefin-rich fraction and the C4 -C7-olef in-rich fraction are preferably recycled to the oligomeri zation unit as described above . The C8-C16-olef in-rich fraction is preferably hydrogenated in a hydrogenation unit . Thus , in this embodiment , the step of "hydrogenating at least a portion of the oligomeri zed olefin stream" entails hydrogenating at least the C8 -C16-olef in-rich fraction obtained from the oligomeri zed olefin stream .

[0133] In a further preferred embodiment , a C3-C7-paraf fin-rich fraction is separated from the hydrogenated oligomeri zed olefin stream . Preferably, at least a portion of said C3-C7-paraf fin- rich fraction is recycled and included in the oligomeri zation feed . In this way, the C3-C7-paraf fin-rich fraction can advantageously act as a diluent . In the embodiment in which the oligomeri zation feed comprises at least a first and a second oligomeri zation feed stream, it is particularly preferred that at least a portion of said C3-C7-paraf fin-rich fraction is recycled and added to the first oligomeri zation feed stream and / or the second oligomeri zation feed stream . It has been found that the C3-C7-paraf fin-rich fraction can advantageously act as a diluent to decrease the operating temperature and to limit temperature increase from the exothermal reaction in the oligomeri zation unit . It has turned out to be particularly advantageous , when the C3-C7-paraf fin-rich fraction is added to the first oligomeri zation feed stream, since in this case it passes through both the first reaction zone and the second reaction zone and therefore exert its beneficial ef fects in both zones . In an alternative embodiment , which is also preferred, the 03- C7-paraf fin-rich fraction is added to the second oligomeri zation feed stream . It has been found that this is also particularly advantageous , since it allows maintaining a higher concentration of propylene in the first reaction zone . In addition, it is also possible to withdraw a portion of the C3-C7-paraf fin-rich fraction from the process and util i ze it further in a suitable refinery unit .

[0134] In a preferred embodiment of the present invention, the inventive process further comprises the step of dimeri zing at least a portion of ethylene contained in the C2 -olef in-rich stream to C4-olefins in a dimeri zation unit , thereby producing a dimeri zed product stream; wherein at least a portion of the dimeri zed product stream is included in the oligomeri zation feed .

[0135] Dimeri zing the C2-olef in-rich stream prior to the oligomerization step allows to increase the proportion of C4+-olefins in the oligomeri zation feed, which can result in a higher yield of j et-range hydrocarbons , as described above . Thus , ethylene contained in the olefin stream indirectly ends up in the oligomerization feed, without negatively af fecting the oligomeri zation step, resulting in a larger amount of oxygenate starting material carbon ending up as j et-range hydrocarbons .

[0136] The skilled person is familiar with suitable catalysts and suitable conditions for operating a dimeri zation unit . For instance , similar catalysts and conditions can be employed as described for oligomeri zation reactions in WO 2023 / 196394 Al , US 2022 / 0396741 Al and WO 2016 / 067033 Al .

[0137] Any suitable catalyst can be used in the dimeri zation unit to dimerize ethylene contained in the C2-olef in-rich stream. Preferably, the catalyst comprises a solid acid catalyst such as ZSM-5, ZSM-23, ZSM-48, or amorphous silica-alumina (ASA) , which preferably contains metals of the subgroup IV, such as Ti or Zr, or metals from the subgroup X, such as Ni .

[0138] The dimerization unit can be operated at reaction conditions that are typically used for such units in the art. Preferably, the dimerization unit is operated at a temperature between 50°C and 200 °C, more preferred between 120 °C and 180 °C. Preferably, the dimerization unit is operated at a pressure from 20 bar to 80 bar, more preferred between 30 bar and 60 bar.

[0139] Preferably the majority of ethylene contained in the C2-ole- fin-rich stream is converted into C4+-olefins in the dimerization unit. Preferably, more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the ethylene contained in the C2-olef in-rich stream is converted into C4+-olefins in the dimerization unit.

[0140] It is further preferred that the dimerized product stream comprises a high proportion of C4+-olefins. This allows to increase the proportion of C4+-olefins in the oligomerization feed, which is advantageous for the reasons outlined above. Thus, preferably, more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of olefins contained in the dimerized product stream are C4+-olefins. It is further preferred that the dimerized product stream comprises less than 30 wt%, more preferred less than 25 wt%, more preferred less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 1 wt%, more preferred substantially no ethylene .

[0141] It is particularly preferred that the dimerized product stream comprises high amounts of iso-olefins, especially iso-bu- tene. It was found that increasing the proportion of such isoolefins, especially iso-butene, in the oligomerization feed can further enhance the efficiency of the oligomerization step, further increasing the yield of jet-range hydrocarbons. Thus, preferably, more than 10 wt%, more preferred more than 20 wt%, more preferred more than 30 wt%, more preferred more than 40 wt% of olefins contained in the dimerized product stream are iso-bu- tene. It is particularly preferred that more than 20 wt%, preferably more than 30 wt%, more preferred more than 40 wt%, more preferred more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt% of C4-olefins contained in the dimerized product stream are iso-butene. Preferably, the dimerized product stream comprises at least 5 wt%, more preferred at least 10 wt%, more preferred at least 20 wt%, more preferred at least 30 wt% iso-butene.

[0142] Preferably, the at least a portion of the dimerized product stream that is included in the oligomerization feed is included in the second oligomerization feed stream. Thus, preferably, the dimerized product stream is introduced into the oligomerization unit at a position downstream of the first reaction zone and upstream of the second reaction zone. As detailed above, the second reaction zone may be optimized towards the conversion of C4+-olefins, whereas the first reaction zone may be less favorable for higher olefins, in particular if the first reaction zone is operated under harsher conditions. Thus, it is advantageous when the dimerized product stream is allowed to skip the first reaction zone and directly passes to the second reaction zone.

[0143] As outlined above, in the inventive process the oligomerization feed further comprises at least a portion of an external C4+-olefin stream comprising C4+-olefins.

[0144] In a preferred embodiment, at least a portion of the external C4+-olefin stream is introduced into the oligomerization unit at a position downstream of the first reaction zone and upstream of the second reaction zone. Thus, preferably, the at least a portion of the external C4+-olefin stream is included in the second oligomerization feed stream. This is particularly advantageous when the second oligomerization zone is operated at a lower temperature than the first oligomerization zone. In this case, the external C4+-olefin stream can serve as a coolant, to help cool the effluent of the first oligomerization zone to the lower temperature of the second oligomerization zone. Preferably, the external C4+-olefin stream contains a high amount of C4+-olefins. This allows to advantageously tune the composition of the oligomerization feed as described above. Thus, preferably, the external C4+-olefin stream comprises at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt% C4+-olefins. It is particularly preferred that more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of olefins contained in the external C4+-olefin stream are C4+-olefins. It is further preferred that the external C4+-olefin stream comprises less than 50 wt%, more preferred less than 40 wt%, more preferred less than 30 wt%, more preferred less than 20 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 1 wt%, more preferred substantially no ethylene.

[0145] It is preferred, that the external C4+-olefin stream contains a high amount of C4-olefins. It was found in the context of the present invention that increasing the amount of Ci-ole- fins in the oligomerization feed is particularly beneficial for increasing conversion and the yield of jet-range hydrocarbons. Therefore, preferably, the external C4+-olefin stream comprises at least 20 wt%, more preferred at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt% C4-olefins. It is particularly preferred that more than 30 wt%, more preferred more than 40 wt%, more preferred more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of olefins contained in the external C4+-olefin stream are C4-olefins. Thus, in a preferred embodiment, the "external C4+-olefin stream" can also be referred to as an "external C4-olefin stream".

[0146] It is particularly preferred, that the external C4+-olefin stream contains a high amount of isobutene. Increasing the amount of isobutene in the oligomerization feed was found to be particularly advantageous for increasing conversion and the yield of j et-range hydrocarbons . Therefore , in particularly preferred embodiments , the external C4+-olefin stream comprises at least 15 wt% , more preferred at least 20 wt% , more preferred at least 30 wt% , more preferred at least 40 wt% , more preferred at least 50 wt% , more preferred at least 60 wt% , more preferred at least 70 wt% , more preferred at least 80 wt% isobutene . It is particularly preferred that more than 20 wt% , more preferred more than 30 wt% , more preferred more than 40 wt% , more preferred more than 50 wt% , more preferred more than 60 wt% , more preferred more than 70 wt% , more preferred more than 80 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred substantially all of olefins contained in the external C4+-olefin stream are isobutene . Thus , in a particularly preferred embodiment , the "external C4+-olefin stream" can also be referred to as an "external isobutene stream" .

[0147] In a preferred embodiment , the external C4+-olefin stream is an ef fluent of a hydrocarbon cracking unit or a dehydrated alcohol stream . Preferably, the external C4+-olefin stream is derived from a hydrocarbon cracking unit , preferably selected from a steamcracking unit , a fluid catalytic cracking ( FCC ) unit , a delayed coker unit , a thermal cracking unit or a visbreaking unit . In connection with the invention, it has proven to be particularly advantageous when the external C4+-olefin stream is derived from a steamcracking unit .

[0148] In the embodiment where the external C4+-olefin stream is derived from a hydrocarbon cracking unit , the external C4+-ole- fin stream may also be referred to as "C4+-olef inic cracking product" . "C4+-olef inic cracking product" refers to a stream that has been derived from a hydrocarbon cracking unit as specified above , wherein said stream contains C4+-olefins .

[0149] When the external C4+-olefin stream is derived from a hydrocarbon cracking unit as described above , the portion included in the oligomeri zation feed may be obtained as the direct product of the hydrocarbon cracking process , or it may be derived as the product of downstream processes . Such downstream processes may include , for example , fractionation via distillation, or other refinery processes . In a preferred embodiment , the oligomeri zation feed comprises at least a distillation fraction of the external C4+-ole- fin stream, especially of the C4+-olefinic cracking product . Preferably, the distillation fraction is a C4+-olef in-rich distillation fraction . Thus , preferably, a C4+-olef in-rich distillation fraction is separated from the external C4+-olefin stream, especially the C4+-olefinic cracking product , and said C4+-olef in-rich distillation fraction is included in the oligomeri zation feed . The C4+-olef in-rich distillation fraction may be obtained directly from a distillation unit , or it may have undergone further processing steps after distillation, such as selective hydrogenation or isomeri zation . For the reasons laid out above , it is particularly preferred i f said C4+-olef in-rich distillation fraction is added to the second oligomeri zation feed stream . In this way, said fraction is allowed to skip the first reaction zone when it enters the oligomeri zation unit , and directly passes through the second reaction zone . Thus , it is particularly preferred that the oligomeri zation feed, in particular the second oligomeri zation feed stream, comprises a C4+- olefin-rich distillation fraction of an external C4+-olefin stream obtained as an ef fluent of a hydrocarbon cracking unit or as a dehydrated alcohol stream, preferably as defined above .

[0150] Preferably the distillation fraction comprises a high proportion of C4+-olefins . This allows to increase the proportion of C4+-olefins in the oligomeri zation feed, which is advantageous for the reasons outlined above . Thus , preferably, the distillation fraction comprises at least 30 wt% , more preferred at least 40 wt% , more preferred at least 50 wt% , more preferred at least 60 wt% , more preferred at least 70 wt% , more preferred at least 80 wt% , more preferred at least 90 wt% C4+-olefins , in particular C4-olefins , especially isobutene . It is particularly preferred that more than 50 wt% , more preferred more than 60 wt% , more preferred more than 70 wt% , more preferred more than 80 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred substantially all of olefins contained in the distillation fraction are C4+-olefins , in particular C4-olefins , especially isobutene . It is further preferred that the distillation fraction comprises less than 30 wt% , more preferred less than 25 wt% , more preferred less than 20 wt% , more preferred less than 15 wt% , more preferred less than 10 wt% , more preferred less than 5 wt% , more preferred less than 1 wt% , more preferred substantially no ethylene .

[0151] In a further preferred embodiment , a C3-olef in-rich distillation fraction of the external C4+-olefin stream is added to the first oligomeri zation feed stream and a C4+-olef in-rich distillation fraction of the external C4+-olefin stream is added to the second oligomeri zation feed stream . This is particularly preferred, when the external C4+-olefin stream also contains substantial amounts of C3-olefins . This can advantageously be achieved by passing the external C4+-olefin stream through the same fractionation unit that is used for separating the olefin stream . Thus , preferably, the external C4+-olefin stream is also separated in the fractionation unit so that the C3-olef in-rich stream comprises at least a part , preferably the maj ority, of C3-olefins contained in the external C4+-olef in-stream and the C4+-olef in-rich stream comprises at least a part , preferably the maj ority, of C4-olefins contained in the external C4+-olefin stream .

[0152] In the embodiment , in which the inventive process further comprises the step of dimeri zing at least a portion of ethylene contained in the C2-olef in-rich stream to C4 -olefins in a dimeri zation unit , it is preferred that a C2-olef in-rich distillation fraction of the external C4+-olefin stream is also conveyed to the dimeri zation unit , wherein at least a portion of the ethylene contained in said C2-olef in-rich distillation fraction is dimeri zed to C4-olefins , which are included in the dimeri zed product stream . As explained above for the C3-olef in-rich distillation fraction, this can advantageously be achieved by passing the external C4+-olefin stream through the same fractionation unit that is used for separating the olefin stream . Thus , preferably, the external C4+-olefin stream is also separated in the fractionation unit so that the C2 -olef in-rich stream comprises at least a part , preferably the maj ority, of ethylene contained in the external C4+-olef in-stream .

[0153] In a preferred embodiment of the present invention, a fraction of the oligomeri zed olefin stream is withdrawn as a recycle stream and passed to a steamcracking unit to produce a steamcracking product stream, wherein at least a portion of the steamcracking product stream is included in the oligomeri zation feed .

[0154] Recycling a fraction of the oligomeri zed olefin stream in this way via a steamcracking unit allows to increase the ef ficiency of the overall process in a particularly advantageous manner . Speci fically, it was found that this allows to substantially increase the proportion of oxygenate starting material carbon that can ultimately be converted into j et-range hydrocarbons . Additionally, the steamcracking product stream can be used to tune the composition of the oligomeri zation feed, thereby optimi zing the oligomeri zation process . Thus , the oligomeri zation process can be optimi zed to yield a larger proportion of j etrange hydrocarbons by tuning the oligomeri zation feed and, at the same time , the proportion of oxygenate carbon that ends up in the j et-range product can be further increased by recycling non j et-range fractions to the oligomeri zation step via steamcracking .

[0155] It is particularly advantageous when the portion of the steamcracking product stream included in the oligomeri zation feed comprises a high amount of C4+-olefins . In this way, the proportion of lighter olefins such as ethylene and propylene in the oligomeri zation feed can be reduced without necessarily having to remove such lighter olefins from the OtO product that is sent to the oligomeri zation unit . Thus , the concentration of j et-range hydrocarbons in the oligomeri zed olefin stream can be increased without reducing the proportion of the OtO product sent to the oligomeri zation unit , thus resulting in a higher proportion of carbon from the oxygenate starting material that is converted into j et-range hydrocarbons .

[0156] Moreover, in the context of the invention it was found that the steamcracking unit can advantageously be used to flexibly obtain hydrocarbons such as e . g . ethylene , propylene , isobutene , benzene and / or xylene as co-products of the inventive process . Thus , in a preferred embodiment , the process further comprises isolating at least one co-product from the steamcracking product stream, preferably wherein said at least one co-product is selected from ethylene , propylene , isobutene , benzene and / or xylene . Advantageously, this allows tuning the distribution of products obtained from the inventive process and to flexibly react to changing demands .

[0157] The recycle stream may be withdrawn from the oligomerized olefin stream before or after hydrogenation. However, it is particularly preferred when the fraction of the oligomerized olefin stream is withdrawn as the recycle stream before the at least a portion of the oligomerized olefin stream is hydrogenated. This allows reducing the amount of material that needs to be treated in the hydrogenation step. In particular, the hydrogenation of hydrocarbons boiling outside of the jet-range, which would otherwise be separated at a later stage, can be avoided. This can significantly reduce capital investment and operating costs associated with the hydrogenation step, increasing the economic viability of the overall process.

[0158] Moreover, it was found that non-hydrogenated recycle streams containing high amounts of olefins can efficiently be processed in the steamcracking unit and the resulting steamcracking products can advantageously be included again in the oligomerization feed. Thus, preferably the weight ratio of olefins to paraffins in the recycle stream is at least 0.1, preferably at least 0.25, more preferred at least 0.5, more preferred at least 0.75, more preferred at least 1.

[0159] In this context, it is particularly preferred if an external steamcracker feed is also processed in the steamcracking unit. Preferably, the external steamcracker feed has a lower ratio of olefins to paraffins than the (preferably non-hydrogenated) recycle stream. In this case, the olefin to paraffin ratio of a combined steamcracker feed consisting of the external steamcracker feed and the recycle stream is lower than the olefin to paraffin ratio of the recycle stream. This can improve the quality of the product obtained from the steamcracking unit, by decreasing the formation of undesired side products from the steamcracking reaction.

[0160] Preferably the recycle stream is withdrawn from the oligomerized olefin stream using a further fractionation unit, preferably the further fractionation unit specified above.

[0161] Thus, in a particularly preferred embodiment, the oligomerized olefin stream is separated in the further fractionation unit into at least the C3-olef in-rich fraction, the C4-C7- olefin-rich fraction, the C8-C16-olef in-rich fraction, and the recycle stream . The C3-olef in-rich fraction and the C4-C7-ole- fin-rich fraction are preferably recycled to the oligomeri zation unit as described above , preferably wherein the C3-olef in-rich fraction is added to the first oligomeri zation feed stream and the C4-C7-olef in-rich fraction is added to the second oligomerization feed stream . The C8-C16-olef in-rich fraction is preferably hydrogenated in a hydrogenation unit , and the recycle stream is passed to the steamcracking unit .

[0162] It has been found to be particularly advantageous , when the recycling stream comprises a high amount of heavier hydrocarbons that are outside of the j et fuel boiling range . In this case , such heavier hydrocarbons can be broken down to lighter hydrocarbons in the steamcracking unit and the resulting lighter hydrocarbons can again be included in the oligomeri zation feed to produce further j et-range hydrocarbons . Thus , preferably, the recycle stream has a boiling range with an initial boiling point of more than 260 ° C, more preferred more than 270 ° C, more preferred more than 280 ° C, more preferred more than 290 ° C, more preferred more than 300 ° C, more preferred more than 310 ° C, more preferred more than 320 ° C .

[0163] Preferably, the recycle stream is a Cl 8+-hydrocarbon-rich stream . Speci fically, it is preferred that the recycle stream contains at least 50 wt% , more preferred at least 60 wt% , more preferred at least 70 wt% , more preferred at least 80 wt% , more preferred at least 90 wt% , more preferred at least 95 wt% , more preferred at least 98 wt% , more preferred at least 99 wt% , more preferred substantially all of the Cl 8+-hydrocarbons contained in the oligomeri zed olefin stream .

[0164] Even more preferably, the recycle stream is a C17+-hydrocar- bon-rich stream . Speci fically, it is preferred that the recycle stream contains at least 50 wt% , more preferred at least 60 wt% , more preferred at least 70 wt% , more preferred at least 80 wt% , more preferred at least 90 wt% , more preferred at least 95 wt% , more preferred at least 98 wt% , more preferred at least 99 wt% , more preferred substantially all of the C17+-hydrocarbons contained in the oligomeri zed olefin stream .

[0165] Preferably more than 50 wt% , more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 75 wt%, more preferred more than 80 wt%, more preferred more than 85 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred more than 98 wt%, more preferred more than 99 wt%, more preferred substantially all of the hydrocarbons contained in the recycle stream are C17+-hydro- carbons .

[0166] In an alternative embodiment, which is also preferred, the recycling stream comprises a high amount of lighter hydrocarbons that are outside of the jet fuel boiling range. In this case, such lighter hydrocarbons can be processed in the steamcracking unit and be included in the oligomerization feed to produce further jet-range hydrocarbons. In this case, preferably, the recycle stream has a boiling range with a final boiling point of less than 150 °C, preferably less than 140 °C, more preferred less than 120 °C, more preferred less than 110 °C, more preferred less than 100 °C.

[0167] Preferably, the recycle stream is a C2-C7-hydrocarbon-rich stream. Specifically, it is preferred that the recycle stream contains at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C2-C7-hydrocarbons contained in the oligomerized olefin stream. Preferably more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 75 wt%, more preferred more than 80 wt%, more preferred more than 85 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred more than 98 wt%, more preferred more than 99 wt%, more preferred substantially all of the hydrocarbons contained in the recycle stream are C2-C7-hydrocarbons .

[0168] In a further preferred embodiment, the recycle stream is a C4-C7-hydrocarbon-rich stream. Specifically, it is preferred that the recycle stream contains at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C4-C7- hydrocarbons contained in the oligomerized olefin stream. Preferably more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 75 wt%, more preferred more than 80 wt%, more preferred more than 85 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred more than 98 wt%, more preferred more than 99 wt%, more preferred substantially all of the hydrocarbons contained in the recycle stream are C4-C7-hydrocarbons .

[0169] In yet a further preferred embodiment, the recycle stream is a C2-C3-hydrocarbon-rich stream. Specifically, it is preferred that the recycle stream contains at least 30 wt%, more preferred at least 40 wt%, more preferred at least 50 wt%, more preferred at least 60 wt%, more preferred at least 70 wt%, more preferred at least 80 wt%, more preferred at least 90 wt%, more preferred at least 95 wt%, more preferred substantially all of the C2-C3- hydrocarbons contained in the oligomerized olefin stream. Preferably more than 50 wt%, more preferred more than 60 wt%, more preferred more than 70 wt%, more preferred more than 75 wt%, more preferred more than 80 wt%, more preferred more than 85 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred more than 98 wt%, more preferred more than 99 wt%, more preferred substantially all of the hydrocarbons contained in the recycle stream are C2-C3-hydrocarbons .

[0170] Preferably, the recycle stream contains a low amount of jetrange hydrocarbons. This is advantageous, since a large part of jet-range hydrocarbons should be obtained as the product of the inventive process rather than being recycled and broken down again in the steamcracking unit. Thus, it is preferred that the recycle stream contains less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 2 wt%, more preferred less than 1 wt%, more preferred substantially no C8-C16-hydro- carbons . Preferably, less than 20 wt%, more preferred less than 15 wt%, more preferred less than 10 wt%, more preferred less than 5 wt%, more preferred less than 2 wt%, more preferred less than 1 wt%, more preferred substantially none of the hydrocarbons contained in the recycle stream are C8-C16-hydrocarbons .

[0171] The recycle stream is processed in the steamcracking unit to produce a steamcracking product stream. The steamcracking product stream may be directly included in the oligomeri zation feed . However, it is particularly preferred i f a C4+-olef in-rich fraction of the steamcracking product stream is included in the oligomeri zation feed, as this allows to optimi ze the conditions for the oligomeri zation reaction, as outlined above .

[0172] Thus , in a preferred embodiment , the oligomeri zation feed comprises at least a distillation fraction of the steamcracking product stream . Preferably, the distillation fraction is a C4 + - olefin-rich distillation fraction . Thus , preferably, a C4+-ole- fin-rich distillation fraction is separated from the steamcracking product stream and said C4+-olef in-rich distillation fraction is included in the oligomeri zation feed . The C4+-olefin- rich distillation fraction may be obtained directly from a distillation unit , or it may have undergone further processing steps after distillation, such as selective hydrogenation or isomeri zation . For the reasons laid out above , it is particularly preferred i f said C4+-olef in-rich distillation fraction is added to the second oligomeri zation feed stream . In this way, said fraction is allowed to skip the first reaction zone when it enters the oligomeri zation unit , and directly passes through the second reaction zone .

[0173] Preferably the distillation fraction comprises a high proportion of C4+-olefins . This allows to increase the proportion of C4+-olefins in the oligomeri zation feed, which is advantageous for the reasons outlined above .

[0174] Thus , preferably, the distillation fraction comprises at least 30 wt% , more preferred at least 40 wt% , more preferred at least 50 wt% , more preferred at least 60 wt% , more preferred at least 70 wt% , more preferred at least 80 wt% , more preferred at least 90 wt% C4+-olefins . It is particularly preferred that more than 50 wt% , more preferred more than 60 wt% , more preferred more than 70 wt% , more preferred more than 80 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred substantially all of olefins contained in the distillation fraction are C4+-olefins . It is further preferred that the distillation fraction comprises less than 30 wt% , more preferred less than 25 wt% , more preferred less than 20 wt% , more preferred less than 15 wt% , more preferred less than 10 wt% , more preferred less than 5 wt% , more preferred less than 1 wt% , more preferred substantially no ethylene .

[0175] In a further preferred embodiment , a C3-olef in-rich distillation fraction of the steamcracking product stream is added to the first oligomeri zation feed stream and a C4+-olef in-rich distillation fraction of the steamcracking product stream is added to the second oligomeri zation feed stream . This can advantageously be achieved by passing the steamcracking product stream through the same fractionation unit that is used for separating the olefin stream . Thus , preferably, the steamcracking product stream is also separated in the fractionation unit so that the C3-olef in-rich stream comprises at least a part , preferably the maj ority, of C3-olefins contained in the steamcracking product stream and the C4+-olef in-rich stream comprises at least a part , preferably the maj ority, of C4 -olefins contained in the steamcracking product stream .

[0176] In the embodiment , in which the inventive process further comprises the step of dimeri zing at least a portion of ethylene contained in the C2-olef in-rich stream to C4 -olefins in a dimeri zation unit , it is preferred that a C2-olef in-rich distillation fraction of the steamcracking product stream is conveyed to the dimeri zation unit , wherein at least a portion of the ethylene contained in said C2-olef in-rich distillation fraction is dimeri zed to C4-olefins , which are included in the dimeri zed product stream . As explained above for the C3-olef in-rich distillation fraction, this can advantageously be achieved by passing the steamcracking product stream through the same fractionation unit that is used for separating the olefin stream . Thus , preferably, the steamcracking product stream is also separated in the fractionation unit so that the C2-olef in-rich stream comprises at least a part , preferably the maj ority, of ethylene contained in the steamcracking product stream .

[0177] As also laid out above , in a particularly preferred embodiment , an external steamcracker feed is also processed in the steamcracking unit . Preferably, the external steamcracker feed comprises renewable hydrocarbons . More preferably, the external steamcracker feed essentially consists of renewable hydrocarbons . Thus , preferably, the steamcracking product stream is derived in part from the recycle stream and in part from an external steamcracker feed . By processing an external steamcracker feed in the steamcracker unit in addition to the recycle stream, the overall process can be more flexibly tuned . For instance , at times when the demand for external C4+-olefins obtained from steamcracking the external steamcracker feed in other processes is low but the demand for other products , e . g . ethylene and propylene , obtained from steamcracking the external steamcracker feed is still high, a larger amount of C4+-olefins from the steamcracking product stream can be included in the oligomeri zation feed . As a result , more or even all of the light olefins contained in the olefin stream obtained from the OtO unit can be sent to the oligomeri zation unit . At other times , higher proportions of ethylene and / or propylene may be removed from the process prior to oligomeri zation .

[0178] As described in more detail above , when a portion of an external C4+-olefin stream such as a C4+-olefinic cracking product is included in the oligomeri zation feed, it is preferred i f said portion comprises at least a distillation fraction of the external C4+-olefin stream, especially a C4+-olef in-rich fraction and preferably also a C3-olef in-rich fraction . Similarly, when a portion of the steamcracking product stream derived from the recycle stream is included in the oligomeri zation feed, it is preferred i f said portion comprises at least a distillation fraction of the steamcracking product stream, especially a C4+-ole- fin-rich fraction and preferably also a C3-olef in-rich fraction . As also detailed above , it is preferred that the C4+-olef in-rich fraction is included in the second oligomeri zation feed stream, whereas the C3-olef in-rich fraction is included in the first oligomeri zation feed stream . In both cases , it is particularly preferred i f the same fractionation unit is used for obtaining said distillation fractions as for fractionating the olefin stream obtained from the OtO unit . Thus , in a particularly preferred embodiment , the at least a portion of the external C4+- olefin stream, especially of the C4+-olefinic cracking product , is mixed with the olefin stream and the resulting mixture is passed to the fractionation unit for separation into at least the C2-olef in-rich stream, the C3-olef in-rich stream and the C4+-olef in-rich stream . Alternatively, or in addition thereto , preferably, the at least a portion of the steamcracking product stream is mixed with the olefin stream and the resulting mixture is passed to the fractionation unit for separation into at least the C2-olef in-rich stream, the C3-olef in-rich stream and the C4+-olef in-rich stream .

[0179] It has been found that synergistic benefits can be obtained by such an integration of fractionation units downstream of a hydrocarbon cracking unit , especially a steamcracking unit , and downstream of the OtO unit . This allows achieving both lower CapEx and lower OpEx costs , resulting in a more ef ficient and more economical overall process .

[0180] In alternative embodiments , which are also preferred, the external C4+-olefin stream, preferably the C4+-olefinic cracking product , is separated in a further fractionation unit into at least a further C2-olef in-rich stream, a further C4+-olef in-rich stream, and preferably a further C3-olef in-rich stream . Similarly, it is preferred that the steamcracking product stream is separated in a further fractionation unit into at least a further C2-olef in-rich stream, a further C4+-olef in-rich stream, and preferably a further C3-olef in-rich stream . In these embodiments , it is preferred that at least a portion of the further C4+-olef in-rich stream is included in the oligomeri zation feed, especially in the second oligomeri zation feed stream . In addition, it is preferred that at least a portion of the further C3- olefin-rich stream is included in the oligomeri zation feed, especially in the first oligomeri zation feed stream . Moreover, in the embodiment , in which the inventive process further comprises the step of dimeri zing at least a portion of ethylene contained in the C2-olef in-rich stream to C4 -olefins in a dimeri zation unit , it is preferred that at least a portion of the further C2 - olefin-rich stream is conveyed to the dimeri zation unit , wherein at least a portion of the ethylene contained in said further C2- olefin-rich stream is dimeri zed to C4 -olefins , which are included in the dimeri zed product stream .

[0181] In a preferred embodiment , the at least a portion of the further C4+-olefin rich stream is added to the second oligomerization feed stream . As detailed above , the second reaction zone may be optimi zed towards the conversion of C4+-olefins , whereas the first reaction zone may be less favorable for higher olefins , in particular i f the first reaction zone is operated under harsher conditions . Thus , it is advantageous when the further C4+-olefin rich stream is allowed to skip the first reaction zone and directly passes to the second reaction zone .

[0182] In addition, it is preferred i f at least a portion of the further C3-olef in-rich stream is included in the first oligomeri zation feed stream . As detailed above , this allows the C3-ole- fins contained in the C3-olef in-rich fraction to pass through both the first reaction zone and the second reaction zone , which can enhance the conversion ef ficiency and thus ultimately further increase the yield of j et-range hydrocarbons .

[0183] Preferably less than 50 wt% , more preferred less than 40 wt% , more preferred less than 30 wt% , more preferred less than 20 wt% , more preferred less than 10 wt% , more preferred less than 5 wt% , more preferred none of the further C2 -olefin- rich stream is included in the oligomeri zation feed . On the other hand, in the embodiment in which the inventive process further comprises the step of dimeri zing at least a portion of ethylene contained in the C2-olef in-rich stream to C4-olefins in a dimeri zation unit , it is preferred that at least a portion of the further C2-olef in-rich stream is also conveyed to the dimeri zation unit . Preferably, at least a portion of the ethylene contained in said further C2-olef in-rich stream is dimeri zed to C4-olefins , which are included in the dimeri zed product stream .

[0184] On the other hand, to provide a high amount of C4+-olefins in the oligomeri zation feed, it is preferred that at least 5 wt% , preferably at least 10 wt% , more preferred at least 20 wt% , more preferred at least 30 wt% , more preferred at least 40 wt% , more preferred at least 50 wt% of the further C4+-olef in-rich stream is included in the oligomeri zation feed, especially in the second oligomeri zation feed stream . Moreover, it is preferred that at least 1 wt% , preferably at least 5 wt% , more preferred at least 10 wt% , more preferred at least 20 wt% of the further C3-olef in-rich stream is included in the oligomeri zation feed, especially in the first oligomeri zation feed stream .

[0185] All embodiments speci fied herein for the C2 -olef in-rich stream, the C3-olef in-rich stream and the C4+-olef in-rich stream are also preferred for the further C2 -olef in-rich stream, the further C3-olef in-rich stream and the further C4+-olef in-rich stream . This includes the composition of the further Cx-olefin- rich streams as well as the proportions of the further Cx-ole- fin-rich streams that are included in the oligomerization feed.

[0186] Unless specified otherwise, all parameters as used herein correspond to parameters at IUPAC SATP-conditions ("Standard Ambient Temperature and Pressure") , in particular a temperature of 25 °C and a pressure of 101.300 Pa.

[0187] Percentages (indicated as "%", "wt%" and the like) as used herein correspond to weight per weight (w / w) unless specified otherwise. Similarly, ratios used herein correspond to weight ratios (w / w) unless specified otherwise. Unless otherwise specified, references to percentages of a given component in any stream refer to the weight percent relative to the total weight of the respective stream. Thus, when it is specified that a certain stream comprises X wt% compound A, this means that compound A constitutes X wt% of said stream, i.e., that said stream contains X wt% compound A based on the total weight of said stream. For instance, if it is stated that "the oligomerization feed comprises at least 20 wt% C4+-olef ins", this means that C4+-ole- fins constitute at least 20 wt% of the oligomerization feed.

[0188] Pressures given in "bar" indicate absolute pressures ("bara") , unless specified otherwise.

[0189] Boiling ranges mentioned herein are preferably determined according to ISO 3405:2019 or ASTM D86-23ae, preferably ASTM D86-23ae .

[0190] Concentrations of individual compounds in hydrocarbon streams can be determined using standard analytical methods known in the art, preferably using gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS) methods. The skilled person is familiar with such standard methods. For instance, concentrations of individual compounds may be determined according to ASTM D6729-20, UOP990-11, ASTM D8396-22, ASTM D8267-24, ASTM D6839-21a, EN ISO 22854:2021, ASTM D6729-20, ASTM D8369-21, ASTM D2425-21, or ASTM UOP990-11. Preferably, concentrations are determined using ASTM D6729-20. For components that cannot be determined using ASTM D6729-20, determination according to ASTM UOP990-11 is preferred.

[0191] As used herein, the term "renewable" in the context of phrases such as "renewable carbon", "renewable oxygenates", "renewable hydrocarbons" , "renewable alcohols" and the like preferably refer to carbon derived from non-petroleum sources such as biogenic feedstocks , synthesis from carbon dioxide and hydrogen, or streams eligible for the production of renewable fuels of non-biological origin ( RFNBO) . Particularly preferred sources include vegetable oils , pyrolysis oils , crude tall oil , used cooking oils , animal fats , other feedstocks listed in Annex IX of Renewable Energy Directive (RED) I I I ( Directive (EU) 2023 / 2413 ) , or other feedstocks eligible for the production of SAF according to Regulation (EU) 2023 / 2405 (ReFuel EU Aviation) .

[0192] As used herein, the phrase "at least a portion of" or similar phrases refers to any subset of a speci fied material , component , or stream, which may include part or all of the speci fied entity . This definition is intended to encompass not only partial quantities but also the entirety of the material , component , or stream in question . Consequently, whenever "at least a portion of" a stream or other entity is mentioned, it is also preferred to use the entire stream or entity . For instance , when it is mentioned that the oligomeri zation feed comprises at least a portion of the C4+-olef in-rich stream, it is also preferred that the oligomeri zation feed comprises the C4+-olef in-rich stream . Similarly, when step of hydrogenating at least a portion of the oligomeri zed olefin stream is mentioned, it is also preferred to hydrogenate the oligomeri zed olefin stream ( as a whole ) .

[0193] As used herein, the term "Cx-hydrocarbons" refers to hydrocarbon molecules having the number of carbon atoms represented by the number "x" . "Cx+-hydrocarbons" refers to hydrocarbon molecules having x or more carbon atoms per molecule . "Cx-Cy-hydro- carbons" refers to hydrocarbon molecules having from x to y carbon atoms per molecule . Thus , for instance , "C4 -hydrocarbons" refers to hydrocarbons having 4 carbon atoms , such as butane , isobutane , butene , isobutene , etc . "C4+-hydrocarbons" refers to hydrocarbons having 4 or more carbon atoms , such as butane , pentane , butene , pentene , etc . "C8 -C16-hydrocarbons" refers to hydrocarbon molecules having from 8 to 16 carbon molecules per molecule .

[0194] Similarly, the term "Cx-olefins" refers to olefins having x carbon atoms per molecule and "Cx+-olef ins" refers to olefins having x or more carbon atoms per molecule . "Cx-Cy-olef ins" refers to olefins having from x to y carbon atoms per molecule . Thus , for instance , the term "C4 -olefins" encompasses 1-butene , 2-butene and isobutene . The term "C4+-olef ins" additionally encompasses pentene and its isomers . The terms "C2-olefin" and "ethylene" , as well as "C3-olefin" and "propylene" can be used interchangeably .

[0195] As used herein, the term "Cx-olef inic" means "containing Cx- olefins" . Thus , for instance , when a stream is referred to as being a "Cx-olefinic stream" it means that said stream comprises Cx-olef ins . Similarly, a "Cx+-olef inic stream" should be understood as a stream comprising Cx+-olefins . For instance , a "C4+- olefinic stream" is a stream that contains a least one of C4- olefins , C5-olefins or heavier olefins .

[0196] As used herein, the terms "Cx-olef in-rich" or "rich in Cx- olef ins" as in "Cx-olef in-rich stream" , "Cx-olef in-rich fraction" , or " stream / f raction rich in Cx-olefins" preferably means that said stream or fraction comprises the maj ority of Cx-olefins contained in the composition from which said stream or fraction was derived . For instance , when an olefin stream is separated into a C2-olef in-rich stream, a C3-olef in-rich stream and a C4+-olef in-rich stream, the C2 -olef in-rich stream preferably comprises the maj ority of C2 -olefins contained in the olefin stream, the C3-olef in-rich stream preferably comprises the maj ority of C3-olefins contained in the olefin stream, and the C4+-olef in-rich stream preferably comprises the maj ority of C4+- olefins contained in the olefin stream . In preferred embodiments , any "Cx-olef in-rich" stream or fraction and any stream or fraction "rich in Cx-olefins" comprises more than 50 wt% , preferably more than 60 wt% , more preferred more than 70 wt% , more preferred more than 80 wt% , more preferred more than 90 wt% , more preferred more than 95 wt% , more preferred substantially all of the Cx-olefins contained in the stream from which said "Cx-olef in-rich" stream or fraction, or stream or fraction "rich in Cx-olefins" was derived .

[0197] Similarly, the terms "Cx-hydrocarbon-rich" or "rich in Cx- hydrocarbons" as in "Cx-hydrocarbon-rich stream" , "Cx-hydrocar- bon-rich fraction" , or " stream / f raction rich in Cx-hydrocarbon" preferably means that said stream or fraction comprises the majority of Cx-hydrocarbons contained the composition from which said stream or fraction was derived. For instance, when a stream rich in C8-C16-hydrocarbons is separated from a hydrocarbon stream, the stream rich in C8-C16-hydrocarbons preferably comprises the majority of C8-C16-hydrocarbons that were contained in the hydrocarbon stream. In preferred embodiments, any "Cx-hy- drocarbon-rich" stream or fraction and any stream or fraction "rich in Cx-hydrocarbons" comprises more than 50 wt%, preferably more than 60 wt%, more preferred more than 70 wt%, more preferred more than 80 wt%, more preferred more than 90 wt%, more preferred more than 95 wt%, more preferred substantially all of the Cx-hydrocarbons contained in the stream from which said "Cx- hydrocarbon-rich" stream or fraction, or stream or fraction "rich in Cx-hydrocarbons" was derived.

[0198] The terms "olefins", as used herein, preferably refers to monoolefins. Thus, preferably, in all instances herein where olefins are not explicitly specified as "diolefins" or otherwise, the term "olefins" may also be replaced by "monoolefins".

[0199] As used herein, "jet fuel boiling range" preferably refers to a boiling range from 120 °C to 300 °C. Expressions such as "jet fuel", "jet-range hydrocarbons", "hydrocarbons boiling in the jet fuel range", etc. therefore preferably refer to hydrocarbons or hydrocarbon mixtures having a boiling range between 120 °C and 300 °C. Preferably, "jet-range hydrocarbons", "hydrocarbons boiling in the jet fuel range" and similar expression refer to hydrocarbons with a carbon number between C8 and Cl 6. The term "jet fuel composition" preferably refers to a composition comprising jet-range hydrocarbons.

[0200] The present invention is further illustrated by the following figures, without being limited thereto.

[0201] Figure 1 shows a schematic process flow diagram of a first embodiment of a process for producing a jet fuel composition.

[0202] Figure 2 shows a schematic process flow diagram of a further embodiment of a process for producing a jet fuel composition.

[0203] Figure 3 shows a schematic process flow diagram of a further embodiment of a process for producing a jet fuel composition.

[0204] In the embodiment shown in Figure 1, an oxygenate stream 1 comprising oxygenates such as methanol is conveyed to an OtO unit 2. In the OtO unit 2, oxygenates contained in the oxygenate stream 1 are transformed into olefins, thereby producing an olefin stream 3. The olefin stream 3 comprises a mixture of olefins, including C2-olefins, C3-olefins, and C4+-olefins. The composition of the olefin stream 3 obtained from the OtO unit 2 is typically not optimal for use in an oligomerization step; therefore, in the embodiment shown in Figure 1, the effluent from the OtO unit 2 is further processed. More specifically, the olefin stream 3 is conveyed to a fractionation unit 4, which preferably comprises a distillation column for separating C2-, 03- and C4+-olefins. Using this fractionation unit 4, the olefin stream 3 is separated into a C2-olef in-rich stream 5, a C3-ole- f in-rich stream 6 and a C4+-olef in-rich stream 7. The C2-olef inrich stream 5 contains the majority of ethylene that was contained in the olefin stream 3, the C3-olef in-rich stream 6 contains the majority of propylene of the olefin stream 3, and the C4+-olef in-rich stream 7 contains the majority of C4+-olefins. By fractionating the olefin stream 3 in this way, ethylene, propylene and C4+-olefins contained in the olefin stream 3 can all be processed different from each other, making it possible to advantageously tune the composition of an oligomerization feed 8 that is processed in an oligomerization unit 9. Specifically, in the embodiment shown in Figure 1, an oligomerization feed 8 is provided that comprises a portion of the C3-olef in-rich stream 6 together with the entire C4-olef in-rich stream 7, ensuring that the composition treated in the oligomerization unit 9 contains a high amount of C4+-olefins, which enhances the efficiency of the oligomerization process and increases the yield of hydrocarbons boiling in the jet fuel range. Thus, the oligomerized olefin stream 10 obtained from the oligomerization unit 9 contains a high amount of C8-C16-olef ins . The oligomerized olefin stream 10 is then processed in a hydrogenation unit 11 to obtain a jet fuel composition 12 comprising C8-C16-paraf f ins .

[0205] In the process shown in Figure 1, an external C4+-olefin stream 30 is introduced into the process and included in the oligomerization feed 8. The external C4+-olefin stream may for instance be derived from a hydrocarbon cracking unit or from dehydration of an alcohol stream. This external C4+-olefin stream 30 contains a high amount of C4+-olefins and can therefore improve the composition of the oligomeri zation feed 8 for the oligomerization reaction . Speci fically, it allows increasing the proportion of C4+-olefins relative to lighter olefins such as ethylene and propylene without necessarily having to remove such lighter olefins obtained from the OtO unit 2 from the process . Moreover, including an external C4+-olefin stream 30 allows to flexibly tune the composition of the oligomeri zation feed 8 depending on the current circumstances . For instance , at times when larger amounts of the external C4+-olefin stream 30 are available , a higher proportion of light olefins contained in the olefin stream 3 obtained from the OtO unit 2 can be sent to the oligomeri zation unit 9 , whereas at times when lower amounts of external C4+-olefin streams 30 are available , lower amounts of lighter olefins may be included in the oligomeri zation feed 8 .

[0206] The process shown in Figure 2 contains all the features of the process shown in Figure 1 . In addition, Figure 2 shows a preferred embodiment , in which the oligomeri zation unit 9 comprises several distinct reaction zones 9a, 9b, 9c . In this embodiment , the oligomeri zation feed that is sent to the oligomeri zation unit 9 comprises a first oligomeri zation feed stream 8a and a second oligomeri zation feed stream 8b . The first oligomeri zation feed stream 8a comprises a portion of the C3-olef in-rich stream 6 . The second oligomeri zation feed stream 8b comprises the C4+-olef in-rich stream 7 . The oligomeri zation unit 9 comprises a first reaction zone 9a, a second reaction zone 9b, and a third reaction zone 9c, each comprising a catalyst bed . The first oligomeri zation feed stream 8a enters the oligomeri zation unit 9 at a position upstream of the first reaction zone 9a and subsequently passes through the first reaction zone 9a, the second reaction zone 9b and the third reaction zone 9c , in that order . The second oligomeri zation feed stream 8b , on the other hand, enters the oligomeri zation unit 9 at a position between the first reaction zone 9a and the second reaction zone 9b and therefore skips the first reaction zone 9a . Thus , it only passes through the second reaction zone 9b followed by the third reaction zone 9c before it exits the oligomeri zation unit 9 as part of the oligomeri zed olefin stream 10 . Advantageously, the first reaction zone 9a is operated at harsher conditions , especially at a higher temperature , than the second reaction zone 9b and the third reaction zone 9c . This allows selectively subj ecting the first oligomeri zation feed stream 8a, which contains high amounts of propylene , to harsher oligomeri zation reaction conditions . This is beneficial , as harsher conditions can increase the conversion ef ficiency of propylene . However, milder conditions are more favorable for C4+-olefins , since such higher olefins may be broken down or converted to undesirable side products under harsh conditions . Thus , providing two separate oligomeri zation feed streams 8a, 8b allows to selectively treat propylene and C4+-olefins obtained from the OtO unit 2 in an optimi zed fashion, which enhances the ef ficiency of the oligomerization process and increases the yield of hydrocarbons boiling in the j et fuel range .

[0207] In the embodiment shown in Figure 2 , a C4+-olef in-rich distillation fraction 31 containing a large proportion of C4+-ole- fins is derived from the external C4+-olefin stream 30 and added to the second oligomeri zation feed stream 8b . In this way, it is allowed to skip the first reaction zone 9a when it enters the oligomeri zation unit 9 , and directly passes through the second reaction zone 9b, which may be optimi zed towards the conversion of C4+-olefins rather than C3-olefins . In addition, a portion of the external C4+-olefin stream 32 is mixed with the olefin stream 3 and the resulting mixture is passed to the fractionation unit 4 for separation into the C2 -olef in-rich stream 5 , the C3-olef in-rich stream 6 and the C4+-olef in-rich stream 7 . Thus , in this embodiment the fractionation unit 4 is used for separating both hydrocarbons contained in the olefin stream 3 obtained from the OtO unit 2 and hydrocarbons contained in the external C4+-olefin stream 30 . In this way, at least a portion of C3-ole- fins contained in the external C4+-olefin stream 30 are included in the first oligomeri zation feed stream 8a and at least a portion of C4+-olefins contained in the external C4+-olefin stream 30 are included in the second oligomeri zation feed stream 8b .

[0208] The process shown in Figure 3 contains all the features of the processes shown in Figure 1 and 2 . In addition, it contains a number of further features that allow achieving an even higher ef ficiency of the process and increasing the amount of j et-range hydrocarbons that can be obtained from a given amount of oxygenate starting material .

[0209] More speci fically, the embodiment shown in Figure 3 includes several recycle streams . First , the oligomeri zed olefin stream 10 is passed to a further fractionation unit 13 , in which a C4- C7-olef in-rich fraction 14 is separated from the oligomeri zed olefin stream 10 and recycled to the oligomeri zation unit 9 . The C4-C7-olef in-rich fraction 14 is included in the oligomeri zation feed by being added to the second oligomeri zation feed stream 8b . In this way, it is allowed to skip the first reaction zone 9a when it enters the oligomeri zation unit 9 . This is particularly advantageous since the second reaction zone 9b may be optimi zed towards the conversion of C4+-olefins , whereas the first reaction zone 9a may be less favorable for higher olefins , in particular when the first reaction zone is operated under harsher conditions .

[0210] In addition, the further fractionation unit 13 is used to separate a C3-olef in-rich fraction 15 from the oligomeri zed olefin stream 10 . The C3-olef in-rich fraction 15 is also recycled to the oligomeri zation unit 9 to be included in the oligomeri zation feed . However, in contrast to the C4 -C7-olef inrich fraction 14 , the C3-olef in-rich fraction 15 is added to the first oligomeri zation feed stream 8a . This allows C3-olefins contained in the C3-olef in-rich fraction 15 to pass through the first reaction zone 9a in addition to the second reaction zone 9b and the third reaction zone 9c, which can enhance the conversion ef ficiency and thus ultimately further increase the yield of j et-range hydrocarbons .

[0211] Moreover, in the process shown in Figure 3 , the hydrogenated oligomeri zed olefin stream 16 obtained from the hydrogenation unit 11 is sent to a further fractionation unit 17 , to withdraw a C3-C7-paraf fin-rich fraction 18 from the hydrogenated oligomeri zed olefin stream 16 . The C3-C7-paraf fin-rich fraction 18 is also recycled to the oligomeri zation unit 9 , wherein a first portion of the C3-C7-paraf fin-rich fraction 18a is added to the first oligomeri zation feed stream 8a and a second portion of the C3-C7-paraf fin-rich fraction 18b is added to the second oligomeri zation feed stream 8b . The C3-C7-paraf fin-rich fraction 18 advantageously acts as a diluent to decrease the operating temperature within the oligomeri zation unit 9 and to limit temperature increase from the exothermal oligomeri zation reactions .

[0212] In addition, in the embodiment shown in Figure 3 , a fraction of the C2-olef in-rich stream 5 is sent to a dimeri zation unit 20 . In this dimeri zation unit 20 , at least a portion of ethylene contained in the C2-olef in-rich stream 5 is dimeri zed to Ci -ole- fins , producing a dimeri zed product stream 21 , which is included in the oligomeri zation feed . More speci fically, the dimeri zed product stream 21 is added to the second oligomeri zation feed stream 8b, so that it is allowed to skip the first reaction zone 9a when it enters the oligomeri zation unit 9 , and directly passes through the second reaction zone 9b, which may be optimi zed towards the conversion of C4+-olefins rather than C3-ole- fins . Dimeri zing the C2-olef in-rich stream 5 prior to the oligomeri zation step allows to advantageously increase the proportion of C4+-olefins in the oligomeri zation feed . At the same time , more ethylene remains in the process and is ultimately converted into j et-range hydrocarbons .

[0213] Moreover, in the embodiment shown in Figure 3 , a fraction of the oligomeri zed olefin stream 10 is withdrawn as a recycle stream 40a, 40b and passed to a steamcracking unit 41 to produce a steamcracking product stream 42 . More speci fically, in the depicted process , a first recycle stream 40a is withdrawn from the oligomeri zed olefin stream 10 before it is hydrogenated in the hydrogenation unit 11 . Optionally, a further recycle stream 40b is withdrawn from the oligomeri zed stream 10 after it has passed through the hydrogenation unit 11 . However, it is advantageous i f a recycle stream 40a is primarily withdrawn prior to hydrogenation, as this reduces the amount of material that needs to be processed in the hydrogenation unit . Both recycle streams 40a, 40b are sent to the steamcracking unit 41 . The recycle streams 40a, 40b contain high amounts of hydrocarbons that do not boil in the j et fuel range . By conveying these streams to the steamcracking unit 41 and by including at least a portion of the resulting steamcracking product stream 42 in the oligomerization feed, these hydrocarbons can undergo oligomeri zation again, making it possible to obtain higher overall yields of j et-range hydrocarbons . In addition, by including a portion of the steamcracking product stream 42 that is rich in C4+-olefins in the oligomeri zation feed, the composition of the oligomeri zation feed can be further enhanced, resulting in an increased proportion of j et-range hydrocarbons in the oligomeri zed olefin stream 10 . More speci fically, in the depicted process , the steamcracking product stream 42 is processed in a further fractionation unit 43 to obtain a further C2 -olef in-rich stream 44 , a further C3-olef in-rich stream 45 , and a further C4+-olefin- rich stream 46 . The further C4+-olef in-rich stream 46 is included in the oligomeri zation feed, thereby increasing the amount of j et fuel that can be obtained from the process . More speci fically, the further C4+-olef in-rich stream 46 is added to the second oligomeri zation feed stream 8b, so that it is allowed to skip the first reaction zone 9a when it enters the oligomerization unit 9 , and directly passes through the second reaction zone 9b, which may be optimi zed towards the conversion of C4+- olefins rather than C3-olefins . A portion of the further C2-ole- fin-rich stream 44 is conveyed to the dimeri zation unit 20 , in which at least a portion of ethylene contained in the C2 -olefin- rich stream 44 is dimeri zed to C4 -olefins , which are included in the dimeri zed product stream 21 . Another portion of the further C2-olef in-rich stream 44 is removed from the process and can be used as a source for ethylene to be sold or used in other refinery processes . The further C3-olef in-rich stream 45 is preferably partially included in the oligomeri zation feed, thereby balancing the proportion of hydrocarbons that remains in the process for the production of j et-range hydrocarbons and the optimi zation of the composition of the oligomeri zation feed for the oligomeri zation step . More speci fically, in the depicted process , a portion of the further C3-olef in-rich stream 45 is added to the first oligomeri zation feed stream 8a, which allows C3- olefins contained in the further C3-olef in-rich stream 45 to pass through the first reaction zone 9a in addition to the second reaction zone 9b and the third reaction zone 9c, enhancing the conversion ef ficiency . Additionally, in the depicted embodiment , an external steamcracker feed 47 is also processed in the steamcracking unit 41 . This allows to tune the overall process even more flexibly, since the amount of steamcracking product stream 42 introduced into the process can be tuned according to the current availability and need . In the embodiment shown in Figure 3 , a portion of the steamcracking product stream 42 derived from the recycle streams 40a, 40b is mixed with the olefin stream 3 and the resulting mixture is passed to the fractionation unit 4 for separation into the C2-olef in-rich stream 5 , the C3-olef in-rich stream 6 and the C4+-olef in-rich stream 7 . Thus , in this embodiment the fractionation unit 4 is used for separating both hydrocarbons contained in the olefin stream 3 obtained from the OtO unit 2 and hydrocarbons contained in the steamcracking product stream 42 . In this way, at least a portion of C3-olefins contained in the steamcracking product stream 42 is included in the first oligomeri zation feed stream 8a and at least a portion of C4+-ole- fins contained in the steamcracking product stream 42 is included in the second oligomeri zation feed stream 8b , leading to synergistic benefits and a particularly ef ficient and economical overall process .

[0214] Example 1 : Impact of oligomerization feed composition on olefin conversion and hydrocarbon yield .

[0215] Experimental runs were conducted in an oligomeri zation pilot plant to determine the impact of varying oligomeri zation feed compositions on olefin conversion and yields of desired products .

[0216] To tune the composition of the oligomeri zation feed, separate C2- , C3- , C4- , and C5-olefin feeds were provided, whose flow rate could be individually regulated, so that the oligomeri zation feed composition could be flexibly tuned . Oligomeri zation was carried out under typical oligomeri zation conditions . 50 g of a commercially available oligomeri zation catalyst was used, and oligomeri zation was carried out at 40 bar, with average catalyst bed temperatures of approximately 170 ° C . The feed rates of the fresh olefins were adj usted so that the Weight Hourly Space Velocity (WHSV) was maintained at 1 g of fresh olefin per gram of catalyst per hour in all experiments . In addition, 40 vol . % nitrogen (N2) was co- fed as an inert diluent .

[0217] Four oligomeri zation runs with di f ferently composed feed compositions were carried out . The feed rates of the individual olefins along with the resulting weight ratios between olefins in the feed are shown in Table 1 . The sum of all feed streams was equal to 50 g / h, so that only the composition but not the total amount of feed was varied .

[0218] Table 1 . Tested oligomeri zation feed compositions . "Cx' ' " denotes Cx-olefins .

[0219] The compositions of the ef fluents obtained from the oligomeri zation unit were analyzed to determine the percentage conversion of individual olefins ( Table 2 ) as well as the obtained yields in various hydrocarbons fractions ( Table 3 ) .

[0220] Table 2 . Conversion of individual olefins . The total conversion corresponds to the average of individual conversions weighted by their weight fraction in the oligomeri zation feed .

[0221] Table 3 . Obtained yields of individual hydrocarbon fractions .

[0222] "C1-C3" denotes Cl-C3-hydrocarbons , "C4 -C7" denotes C4-C7-hydro- carbons , "C8-C16" denotes the desired j et-range fraction of C8- C16-hydrocarbons , "C17+" denotes heavier C17+-hydrocarbons .

[0223] Incorporating an external C4+-olefin stream allows increasing the amount of C4+-olefins, especially C4-olefins, in the oligomerization feed.

[0224] The impact of including additional C4-olefins in the oligomerization feed is demonstrated by comparing experiments #2 and #4. In experiment #2 an olefin feed stream comprising a high amount of propylene and lower amounts of C4-olefins and C5-ole- fins was oligomerized. In experiment #4, which was carried out under the same oligomerization conditions, significantly less propylene and more C4-olefins were included in the oligomerization feed. Thus, the weight ratio of C4-olefins to propylene in the oligomerization feed was significantly higher in experiment #4 (1.64) than in experiment #2 (0.37) . In experiment #4, the overall conversion (86.8 % vs. 75.1 %) , propylene conversion (79.0 % vs. 68.8 %) , C4-olefin conversion (93.9 % vs. 90.5 %) , and the C8-C16-hydrocarbon yield (71.9 wt% vs. 60.3 wt%) were all increased in comparison to experiment #2, demonstrating the benefits of including additional C4-olefins in the oligomerization feed.

[0225] Moreover, the results of experiments #2 and #4 demonstrate that C4-olefins exhibit even higher conversion than C5-olefins, demonstrating the beneficial effects of increasing the amount of C4-olefins specifically.

[0226] In addition, comparing the results of experiments #1, #2, #3, and #4 demonstrates the benefits of including some, but not all, of the C3-olef in-rich stream in the oligomerization feed. Even knowing that propylene has a lower reactivity than Ci-ole- fins under typical oligomerization conditions, one might expect that including more propylene would still be beneficial when trying to maximize C8-C16-hydrocarbon output. However, the results of these experiments show not only that propylene exhibits lower conversion percentages than C4-olefins, but also that the conversion percentages of both propylene and C4-olefins, each individually, are increased when the C4-olefin content is increased relative to the propylene content. The lowest propylene conversion (53.7 wt%) was observed in experiment #1, which used a feed consisting only of propylene. In experiment #2, with a 62 wt% propylene content and a C4-olef in / C3-olef in weight ratio of 0.37 (w / w) , propylene and C4-olefin conversions were 68.8% and 90.5%, respectively. Finally, in experiment #4, with a 33 wt% propylene content and a C4-olef in / C3-olef in weight ratio of 1.64 (w / w) , conversions increased to 79.0% and 93.9%, respectively. This demonstrates that including some, but not all, of the C3-olef in-rich stream in the oligomerization feed is particularly advantageous. At the same time, these results demonstrate that by increasing the amount of C4-olefins in the feed, also more of the C3-olef in-rich stream can be included, without decreasing the C4-olef in / C3-olef in ratio and thus negatively affecting conversion percentages.

[0227] Experiment #3 demonstrates that ethylene conversion is minimal under the oligomerization conditions used. This underscores that including high ethylene concentrations in the oligomerization feed is not beneficial.

[0228] Example 2: Generation of oligomerization feed components by steamcracking .

[0229] Steamcracking trial runs were conducted to test the generation of steamcracking product streams suitable for inclusion in the oligomerization feed.

[0230] The steamcracking unit was operated at typical coil outlet temperatures (COT) between 800 °C and 840 °C and a typical steam to hydrocarbon ratio of 0.5, in a once-through mode of operation. A naphtha stream was used as feed stream. The results are shown in Table 4 below.

[0231] Table 4. Yields obtained from steamcracking at different coil outlet temperatures (COT) .

[0232] These results demonstrate that under typical steam cracking conditions, a significant amount of C4+ olefins, in particular C4 olefins, can be produced, which can advantageously be included in the oligomerization feed. As demonstrated by the results in Example 1, including such olefins in the oligomerization feed, and thus increasing the C4-olef in / C3-olef in ratio, can increase the overall conversion and the yield of the desired C8-C16 -hydro carbons .

[0233] Example 3: Two-stage oligomerization utilizing sequential reaction zones for C3-olefins and C4+-olefins.

[0234] Experiments were conducted in a pilot plant to investigate the effects of using an oligomerization unit comprising multiple distinct reaction zones, wherein a C3-olef in-rich stream is sent to a first reaction zone, and a C4+-olef in-rich stream is only added to the effluent of the first reaction zone prior to a second reaction zone, bypassing the first reaction zone.

[0235] For these experiments, an oligomerization feed composition comprising 62 wt% C3-olefins, 23 wt% C4-olefins and 15 wt% C5- olefins was used. In a first set of experiments, this feed composition was processed as a whole in a single stage (experiments "M-low" and "M-high", corresponding to lower and higher temperatures) . In a second experiment, a two-stage oligomerization process was used, wherein the C3-olefins and the C4+-olefins of the oligomerization feed composition were processed separately. For the first stage (corresponding to the first reaction zone) , oligomerization was conducted using a pure C3-olefin stream (stage 1, "SI") . For the second stage (corresponding to the second reaction zone) , a composition corresponding to the effluent from the first oligomerization experiment (SI) was combined with additional C4-olefins and C5-olefins in the same amounts relative to the C3-olefin stream as in the single-stage experiment (stage 2, "S2") .

[0236] The first oligomerization stage was conducted at harsher conditions (temperature set at 220 °C) than the first oligomerization stage (temperature set at 210 °C) . The single-stage experiment was conducted once at the harsher conditions corresponding to the first stage (temperature set at 220 °C; "M- high") , and once at the milder conditions corresponding to the second stage (temperature set at 210 °C; "M-low") . For all experiments, 50 g of a commercially available oligomerization catalyst was used. The feed rates of the fresh olefins were adjusted so that the Weight Hourly Space Velocity (WHSV) for the single-stage experiments M-high and M-low matched the overall WHSV of the two-stage configuration (SI + S2) . In both cases, the WHSV was maintained at 1 g of fresh olefin per gram of catalyst per hour. 40 vol.% nitrogen (N2) was co-fed as an inert diluent in all experiments.

[0237] The feed compositions and oligomerization conditions are summarized in Table 5.

[0238] Table 5. Feed composition and oligomerization conditions used. "M-low" and "M-high" represent the single-stage oligomerization experiments conducted at lower and higher temperatures, respectively. "SI" represents the first oligomerization stage, "S2" represents the second oligomerization stage, and "S1+S2" represents the calculated sum of both stages. Under feed composition, "Cx' ’ " denotes Cx-olefins, and "SI" denotes the composition of the oligomerization product obtained from the first stage. Under oligomerization conditions, "p" represents the pressure; "T" refers to the temperature set for the coolant, which flowed through an annulus encompassing the reactor.

[0239] The compositions of the effluents obtained from the oligomerization unit were analyzed to determine the percentage conversion of individual olefins as well as the obtained amounts in various hydrocarbons fractions. The results are shown in Table 6.

[0240] Table 6. Conversion of individual olefins and obtained yields of individual hydrocarbon fractions. "C1-C3" denotes Cl-C3-hydro- carbons, "C4-C7" denotes C4-C7-hydrocarbons, "C8-C16" denotes the desired jet-range fraction of C8-C16-hydrocarbons, "C17+" denotes heavier C17+-hydrocarbons . The total conversion corresponds to the average of individual conversions weighted by their weight fraction in the oligomerization feed.

[0241] As can be seen from Table 6, a very high conversion of C3- olefins could be achieved using the two-stage oligomerization setup. 79.4 wt% of the C3-olefins in the oligomerization feed were already converted in the first stage, and another 70.2 wt% of the propylene that was not converted in the first stage was converted in the second stage, leading to a total C3-olefin conversion of 94 wt%. Thus, the conversion of propylene was significantly higher in the two-stage oligomerization setup compared to the single-stage setup, in which values of 86.2 wt% and 91.9 wt% were achieved for the milder conditions (corresponding to those used in S2) and the harsher conditions (corresponding to those used in SI) , respectively. In addition, also the overall yield of desired C8-C16-hydrocarbons was increased in the two-stage setup (69.9 wt%) compared to the single-stage setup (69.4 wt% for the milder conditions, and 68.5 wt% for the harsher conditions) .

Claims

Claims :

1. A process for producing a jet fuel composition (12) , the process comprising: a) Processing an oxygenate stream (1) in an Oxygenate-to-Olef in (OtO) unit (2) to produce an olefin stream (3) ; b) Providing an oligomerization feed (8) comprising at least a portion of the olefin stream (3) and at least a portion of an external C4+-olefin stream (30) comprising C4+-olefins; c) Processing the oligomerization feed (8) in an oligomerization unit (9) to produce an oligomerized olefin stream (10) ; d) Hydrogenating at least a portion of the oligomerized olefin stream (10) .

2. The process according to claim 1, wherein more than 30 wt% of olefins contained in the external C4+-olefin stream (30) are C4-olef ins .

3. The process according to any one of claims 1 or 2, wherein more than 20 wt% of olefins contained in the external C4+-olefin stream (30) are isobutene.

4. The process according to any one of claims 1 to 3, wherein the external C4+-olefin stream (30) comprises at least 20 wt% C4-olef ins .

5. The process according to any one of claims 1 to 4, wherein the external C4+-olefin stream (30) comprises at least 15 wt% isobutene .

6. The process according to any one of claims 1 to 5, wherein the external C4+-olefin stream (30) is derived from a hydrocarbon cracking unit, preferably selected from a steamcrackingunit, a fluid catalytic cracking (FCC) unit, a delayed coker unit, a thermal cracking unit or a visbreaking unit.

7. The process according to any one of claims 1 to 6, wherein the oligomerization feed (8) comprises a C4+-olef in-rich distillation fraction of the external C4+-olefin stream (30) , preferably wherein the external C4+-olefin stream (30) is obtained as an effluent of a hydrocarbon cracking unit or as a dehydrated alcohol stream.

8. The process according to any one of claims 1 to 7, wherein the process further comprises the step of separating the olefin stream (3) in a fractionation unit (4) into at least a C2-ole- fin-rich stream (5) and a C4+-olef in-rich stream (7) , wherein the oligomerization feed (8) comprises at least a portion of the C4+-olef in-rich stream (7) .

9. The process according to any one of claims 1 to 8, wherein the process further comprises the step of separating the olefin stream (3) in a fractionation unit (4) into at least a C2-ole- fin-rich stream (5) , a C3-olef in-rich stream (6) and a C4+-ole- fin-rich stream (7) , wherein the oligomerization feed (8) comprises at least a portion of the C4+-olef in-rich stream (7) .

10. The process according to claim 9, wherein the external C4 + - olefin stream (30) is mixed with the olefin stream (3) and the resulting mixture is passed to the fractionation unit (4) for separation into at least the C2-olef in-rich stream (5) , the C3- olefin-rich stream (6) and the C4+-olef in-rich stream (7) .

11. The process according to any one of claims 9 or 10, wherein step c) comprises processing an oligomerization feed (8) comprising a first oligomerization feed stream (8a) containing at least a portion of the C3-olef in-rich stream (6) and a second oligomerization feed stream (8b) containing at least a portion of the C4+-olef in-rich stream (7) in an oligomerization unit (9)to produce an oligomerized olefin stream (10) ; wherein the oligomerization unit (9) comprises at least a first reaction zone (9a) , and a second reaction zone (9b) downstream of the first reaction zone (9a) ; wherein the first oligomerization feed stream (8a) is introduced into the oligomerization unit (9) at a position upstream of the first reaction zone (9a) , and the second oligomerization feed stream (8b) is introduced into the oligomerization unit (9) at a position downstream of the first reaction zone (9a) and upstream of the second reaction zone (9b) .

12. The process according to claim 11, wherein the first reaction zone (9a) is operated at a higher temperature than the second reaction zone (9b) .

13. The process according to any one of claims 11 or 12, wherein the oligomerization unit (9) comprises at least a third reaction zone (9c) located downstream of the second rection zone (9b) .

14. The process according to any one of claims 1 to 13, wherein a C4-C7-olef in-rich fraction (14) is separated from the oligomerized olefin stream (10) , wherein at least a portion of the C4-C7-olef in-rich fraction (14) is recycled and included in the oligomerization feed (8) .

15. The process according to any one of claims 11 to 14, wherein a C3-olef in-rich fraction (15) is separated from the oligomerized olefin stream (10) , wherein at least a portion of the C3-olef in-rich fraction (15) is recycled and added to the first oligomerization feed stream (9a) .

16. The process according to any one of claims 1 to 15, wherein a C3-C7-paraf fin-rich fraction (18) is separated from the hydrogenated oligomerized olefin stream (16) , wherein at least a portion of the C3-C7-paraf fin-rich fraction (18) is recycled and included in the oligomerization feed (8) .

17. The process according to any one of claims 9 to 16, wherein the process further comprises the step of dimerizing at least a portion of ethylene contained in the C2-olef in-rich stream (5) to C4-olefins in a dimerization unit (20) , thereby producing a dimerized product stream (21) ; wherein at least a portion of the dimerized product stream (21) is included in the oligomerization feed (8) , preferably in the second oligomerization feed stream (8b) .

18. The process according to any one of claims 1 to 17, wherein a fraction of the oligomerized olefin stream (10) is withdrawn as a recycle stream (40a, 40b) and passed to a steamcracking unit (41) to produce a steamcracking product stream (42) , wherein at least a portion of the steamcracking product stream (42) is included in the oligomerization feed.

19. The process according to claim 18, wherein the recycle stream (40a, 40b) contains at least 50 wt% of the C17+-hydrocar- bons contained in the oligomerized olefin stream (10) .

20. The process according to any one of claim 18 or 19, wherein the at least a portion of the steamcracking product stream (42) is mixed with the olefin stream (3) and the resulting mixture is passed to the fractionation unit (4) for separation into at least the C2-olef in-rich stream (5) , the C3-olef in-rich stream (6) and the C4+-olef in-rich stream (7) .

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