Improved process and plant for converting olefins to distillate fuels

Abstract

Process and plant for converting olefins to a distillate fuel, the distillate fuel being at least one of jet fuel and diesel, the process comprising: i) supplying an olefin feed to an oli- gomerization section comprising at least one oligomerization reactor and withdrawing 5 from the oligomerization section an oligomerized product; ii) directly or indirectly supply- ing at least a portion of the oligomerized product to a distillate fuel fractionation section and withdrawing therefrom at least: ii-a) a first light fraction comprising hydrocarbons boiling in the jet fuel range; ii-b) a second light fraction of hydrocarbons, which is heavier than the first light fraction of hydrocarbons; ii-c) a third balancing heavy fraction compris-10 ing: hydrocarbons boiling in the diesel fuel range and hydrocarbons boiling in the jet fuel range; the third balancing fraction being heavier than the second light fraction of hydro- carbons; iii) supplying at least a portion of the second light fraction of hydrocarbons to the oligomerization section.

Description

[0001]

[0002] The present invention relates to an improved process and plant scheme for converting an olefin feed, such as ethylene (C2=) feed, to distillate fuels, the distillate fuels being any of jet fuel and diesel.

[0003] BACKGROUND

[0004] It is known to oligomerize olefins to higher product olefins in one or more steps, e.g., via catalyzed reactions taking place in the liquid phase in the presence of a diluent. Oligomerization reactors comprise reactors catalytically converting olefins by oligomerization reactions, being of either of the ethylene oligomerization type, involving essentially progressive ethylene additions to ethylene itself (dimerization) or to olefin components produced in the reactor as intermediates (OLI-1); or of the oligomer oligomerization type, not involving ethylene additions, but essentially oligomerization reactions between any of the C3-C30 olefin components present in the reactor feed or produced in the reactor as intermediates (OLI-2). Depending on composition of the olefin feed a combination of OLI-1 and OLI-2 reactors are needed to efficiently convert the olefin to desired fuel product. As product there is obtained an oligomerized product stream comprising the diluent components, unconverted olefins, the olefinic products from oligomerization and cracking reactions, and saturated side product, i.e., alkane components, produced in the oligomerization reactions. The olefinic products may comprise product olefins of sufficiently as well as insufficiently higher molecular weight or carbon number (deficient olefins) in regard to the desire to eventually obtain distillate fuel boiling in the jet and / or diesel range as product, by hydrogenation.

[0005] The diluent needed for oligomerization in e.g. the liquid phase, typically a range of alkanes, is conventionally obtained as a stream of hydrocarbons boiling in the jet range, or higher, recovered as a split fraction in the backend of the process, where the olefins are saturated to their associated alkanes and fractionated. The proportion of the diluent stream to the reactant and product olefins in the oligomerization section is in the range

[0006] 03093-WO 1 :1 to 20:1 on a weight basis, this in order to limit the temperature increase in the exothermic oligomerization reactors. The proportion of diluent needed will be depending on the reactor configuration, the composition of olefin make-up and recycle; and the synthesis pressure prevailing so as to keep the olefins in the liquid / dissolved phase.

[0007] The hydrocarbons (olefins and alkanes) produced in the oligomerization comprise different isomers, i.e., components of the same carbon number that boil at different temperature. Furthermore, conventionally, the definition of a jet fuel and / or distillate fuel varies, in view of different standards, and must fulfill criteria such as boiling range. Thus, the range of components achievable as jet fuel product from a given oligomerized product stream, i.e., distillate, and the distribution of the different carbon numbers in the refined jet fuel product, depends on the actual product isomers and their distribution in the oligomerized product. The total number of isomers comprised in the naphtha, jet fuel and diesel ranges may amount to several hundred thousand, and boiling ranges for different carbon numbered isomers may in principle overlap. However, roughly speaking, naphtha components range from C5-C9 such as C5-C8, jet fuel components primarily range from C9 to C19, and diesel components range from C8-C25 hydrocarbons or C9-C30 hydrocarbons, such as C9-C24 hydrocarbons. As an example, on the fuel boiling range crite- rium a C5 olefin or alkane will be under-spec jet fuel or diesel component, whereas, depending on the remainder distillate fuel composition, a certain fraction of the highest boiling C8 alkanes may be acceptable. Due to catalyst deactivation and changed product selectivity in the oligomerization reactors, the distribution of carbon numbers of alkane isomers in the fuel ranges may change over time. In addition, the distillate fuel products, either jet fuel or diesel, should live up to the other distillate fuel standards required.

[0008] Conventionally, stream fractions may be obtained via simple division, i.e., splitting, of a process stream, for example controlled by mass flow controllers, by which each of the stream fractions downstream of the split point maintain the same composition. Stream fractions may also be obtained from a process stream via more advanced processes, e.g., by distillation, whereby the product fractions obtained from the separation step are of different composition; advanced separation also includes phase separation, membrane separation or other methods known in the art, where the composition of the product streams differ. Herein, the “split fractions” are defined as streams of the same

[0009] 03093-WO composition, whereas “fractionated streams” are obtained by advanced separation (distillation, phase or membrane separation etc.) and are of different compositions.

[0010] Conventionally, an oligomerized product stream obtained from the oligomerization(s) of fed olefins is fractionated by distillation in one or more steps, obtaining thereby a fractionated oligomerized product stream to be undergoing hydrogenation downstream, and one or more fractionated balance streams of deficient olefins and lower alkanes. The oligomerized product stream comprises sufficiently oligomerized olefins, useful as jet fuel and diesel product precursors, higher alkanes, hereunder diluent components, at least some of which are useful as jet fuel and diesel product, and to some extent insufficiently oligomerized olefins, and under-spec alkanes. The stream(s) of deficient olefins and lower alkanes may be recycled to the oligomerization reactors, in order for the deficient olefins to be converted over the OLI-1 and OLI-2 oligomerization reactor(s) and progressively build up to sufficiently oligomerized olefins through one or more / recycle passages over the oligomerization reactor(s). A purge of the unreactive lower alkanes from the olefin recycle must be foreseen.

[0011] Under-spec hydrocarbons, in particular under-spec higher alkanes, are herein defined as the portion of hydrocarbons, in particular higher alkanes, primarily octanes, that constitute a loss of jet fuel and diesel product yield, which need to be fractionated from the remainder oligomerized product because they are boiling in a boiling range below the required. Insufficiently oligomerized olefins, or deficient olefins, are defined herein as the portion of olefins typically with a carbon number of 8 or less, that when present in the oligomerized product, results in a corresponding portion of under-spec alkanes when hydrogenated downstream of the oligomerization, and thus loss of product yield in the final distillate fuel product. Deficient olefins may constitute a significant weight fraction of the total of olefins produced per pass in the oligomerization section, whereby the fractionation and recycle of these becomes beneficial.

[0012] The fractionated oligomerized product stream obtained from the oligomerization(s) and olefin fractionation is then hydrogenated, and the hydrogenated product is fractionated to ensure that the jet fuel and diesel products meet certain distillate fuel standards, such as oxidation requirements and other applicable requirements. In the hydrogenation section, the olefins react with hydrogen in a catalyzed process, whereby they form their

[0013] 03093-WO associated alkanes, that tend to boil at a higher temperature than their olefinic origin; the sufficiently oligomerized olefins will be converted to alkanes that meet the distillate fuel standards, whereas the insufficiently oligomerized olefins will be converted into under- spec alkanes. As said, the under-spec alkanes produced during hydrogenation will be removed as off-gas by fractionation from the hydrocarbon products that meet the distillate fuel standards. Some of the alkanes contained in the fractionated oligomerized product stream, being inert in the hydrogenation process, are also under-spec and will be removed, too. The off-gas stripped off typically comprises low-boiling highly branched alkane oligomers of chain length up to C8. The stripped hydrogenated oligomerization product may further be fractionated into streams of jet, diesel, or mixtures typically conducted by distillation in the distillate fuel fractionation section.

[0014] Conventionally, in order to increase the yield of a desired distillate, typically jet fuel or diesel, obtained in a process based on olefin oligomerization, one would aim to recover insufficiently converted olefins in the oligomerization section to the highest degree possible and recycle these to the oligomerization reactor(s) rather than fractionating these together with sufficiently oligomerized olefins into the oligomerized product stream, as then they will be hydrogenated in the hydrogenation section processing the oligomerized product and lost as under-spec alkanes in the downstream fractionation. The recovery of deficient olefins relies on the conditions in the olefin fractionation section.

[0015] Conventionally also, the distillate fuel product boiling in the jet and diesel range may be fractionated into fractionated jet fuel streams, a fractionated diesel stream and / or a fractionated mixed jet fuel and diesel stream, from which an alkane recycle stream is obtained as a split fraction of the fractionated streams among the latter two mentioned and recycled to the oligomerization section as diluent. In one embodiment known in the art, a product stream of alkanes boiling in the jet fuel range, is fractionated from the distillate fuel, leaving a fractionated diesel stream from which a split fraction is obtained and recycled as diluent to the oligomerization section. Optionally, depending on the olefin product distribution obtained in the oligomerization, the fraction of alkanes boiling in the diesel range is of a small or insignificant proportion as compared to the jet fuel fraction. In another embodiment known in the art, a mixed product stream of alkanes boiling in the jet fuel and diesel range is obtained by stripping off the off-gas, from which a split fraction is obtained and recycled as diluent to the oligomerization section; the balancing mixed

[0016] 03093-WO jet fuel and diesel stream may be further fractionated into jet fuel and diesel product streams downstream in the distillate fuel fractionation section.

[0017] WO 2023192376 discloses an olefin oligomerization process comprising OLI-1 and OLI- 2 reactors, in which a first oligomerization reactor (OLI-1) feed suitably contains more than 20 wt% ethylene. The deficient olefins are separated in an olefin fractionation section, and the deficient olefins are recycled to the ethylene oligomerization reactors (OLI- 1) as well as to the oligomer oligomerization reactors (OLI-2). The diluent needed for the direct cooling in OLI-1 is recovered as a split fraction of the mixed jet fuel and diesel stream from the distillate fuel fractionation section and recycled.

[0018] US 2024 / 0025821 discloses an olefin oligomerization process comprising OLI-1 and OLI-2 reactors with stagewise addition of ethylene and intercooling in the OLI-1 section, in which the OLI-1 reactor feed streams contain preferably no more than 6 wt% olefins. The deficient olefins are separated in an olefin fractionation section and recycled to the OLI-2 reactor(s). Unconverted ethylene will be lost. The diluent needed for the internal cooling in OLI-1 is recovered as a split fraction of the diesel product stream from the distillate fuel fractionation section and recycled.

[0019] US 2024 / 0067586 discloses a process layout similar to the above, but in which the deficient olefins are recovered and recycled to the OLI-1 reactor(s). This way unconverted ethylene may be oligomerized and its carbon recovered as distillate.

[0020] The prior art consistently and repeatedly teaches that diluent needed to absorb the exotherm in OLI-1 and OLI-2 reactors which is recycled to the front-end of an olefin-to-jet fuel plant, i.e., to the oligomerization section, is taken as a simple split stream from a fractionated diesel fuel product stream or from a fractionated mixed jet fuel and diesel product stream in the product fuel i.e. distillate fuel fractionation section.

[0021] The prior art is thus at least silent on any benefits associated with the provision of a dedicated distillate fuel fractionation specifically directed to the production of a stream of mid-range jet fuel hydrocarbons, selected from a broad range of lower boiling, i.e., lighter jet fuel stream and a broad range of higher boiling, i.e., heavier diesel and / or jet fuel

[0022] 03093-WO stream, as well as the improved use of such mid-range jet fuel hydrocarbons as a diluent in the oligomerization reactors of the upstream oligomerization section.

[0023] SUMMARY

[0024] During the olefin fractionation, a portion of the deficient olefins, typically olefin isomers with carbon number up to 8, i.e., C8- =, may undesirably be carried on in the fractionated, thus enriched in C9+= oligomerization product from the oligomerization section, only to end up as a loss of product yield when the oligomerized product is fractionated downstream in a distillate fuel fractionation section, conventionally after hydrogenation.

[0025] It would therefore be desirable to be able to provide an improved oligomerization process and plant a higher yield of jet fuel and diesel.

[0026] It would also be desirable to be able to provide an improved oligomerization process and plant for producing jet fuel and diesel with a lower energy consumption and / or simpler fractionation section for treatment of oligomerized product or hydrogenated oligomerized product.

[0027] Accordingly, in a first aspect of the invention, there is provided a process for converting olefins to a distillate fuel, the distillate fuel being at least one of jet fuel and diesel, the process comprising: i) supplying an olefin feed comprising at least 50wt% ethylene (C2=) to an oligomerization section comprising at least one oligomerization reactor and withdrawing from the oligomerization section an oligomerized product; ii) directly or indirectly supplying at least a portion of the oligomerized product to a distillate fuel fractionation section and withdrawing therefrom at least: ii-a) a first light fraction comprising hydrocarbons boiling in the jet fuel range; ii-b) a second light fraction of hydrocarbons, which is heavier than the first light fraction of hydrocarbons; ii-c) a third balancing heavy fraction comprising: hydrocarbons boiling in the diesel fuel range and hydrocarbons boiling in the jet fuel range; the third balancing heavy fraction being heavier than the second light fraction of hydrocarbons;

[0028] 03093-WO iii) supplying at least a portion of the second light fraction of hydrocarbons to the oligomerization section.

[0029] It has now been found that by fractionating the oligomerized product, suitably a hydrogenated oligomerized product, into more fractions of hydrocarbons, suitably alkanes, boiling in the jet fuel and optionally in the diesel fuel range, withdrawing at least the first light fraction of hydrocarbons, a second light fraction of hydrocarbons and a third balancing heavy fraction of hydrocarbons, and further specifically utilizing at least a portion of the second light fraction of hydrocarbons as a diluent recycle to the oligomerization section, there is an increase in the recovery of the deficient olefins recycled inside the oligomerization section.

[0030] This surprising effect of supplying this now specific diluent to the oligomerization section, thus recycling a range of the second light fraction of hydrocarbons i.e. the second lowest boiling hydrocarbons, suitably alkanes, may be rationalized, as the fractionation of the deficient olefins from the sufficiently oligomerized olefins and the second light fraction of hydrocarbons acting as a diluent in the olefin section is apparently eased, and the overall utilization of the olefins feed is therefore increased, reflected in a higher carbon efficiency, thus higher carbon yield or simply yield of the process / plant. Hence, more carbons in the olefin feed end up as distillate fuel: the easing of the fractionation of deficient olefins is for example capitalized into a higher distillate fuel product yield in the process, a lower energy consumption and / or the distillate fuel fractionation unit requiring fewer ideal trays (gas-liquid equilibrium stages). Another advantage of the invention is that the fraction of under-spec C8- hydrocarbons, suitably C8- alkanes, distilled off in the distillate fuel fractionation section, is strongly reduced, thereby reducing the distillate fuel fractionation column overhead system. For example, in an olefin fractionation section suitably being provided in the oligomerization section, C8- olefins and associated alkanes are maintained and processed therein, while sufficiently oligomerized C8+ olefins being carried in the second light fraction of diluent hydrocarbon compounds, are suitably withdrawn as the oligomerized product. It is understood that a fraction of the C8= isomers are to be regarded as sufficiently oligomerized because their associated alkanes will in combination with the remainder jet components boil in the jet range. The diluent compounds are, in an embodiment, C10+ hydrocarbons, preferably C10-C15 hydrocarbons.

[0031] 03093-WO It is understood that for the purposes of the present application, the term “at least a portion of the second light fraction of hydrocarbons” and the term “diluent” may be used interchangeably.

[0032] The invention provides an improved carbon efficiency, defined as the amount of carbon in the distillate fuel product relative to the carbon fed to the process / plant in the olefin feed. Improved carbon efficiency means improved yield, hence higher yield, which is of paramount importance when producing distillate fuels, as even small yield improvements provide a significant benefit. Furthermore, a lower energy consumption than normal is required for processing the oligomerized feed into the final distillate fuel.

[0033] It is understood that, without diverging from the concept of the invention, several side draw streams in the distillate fuel fractionation section may make up the first light fraction comprising hydrocarbons boiling in the jet fuel range, i.e., lowest boiling hydrocarbons such as alkanes. Likewise, several side draw streams in the distillate fuel fractionation section may make up the second light fraction of hydrocarbons without diverging from the concept of the invention. Likewise, several side draw streams in the distillate fuel fractionation section may make up the third or higher numbered balancing heavy fractions comprising hydrocarbons boiling in the diesel range and also in the jet fuel range. The first light fraction starts boiling at a lower temperature (the lower cut-point temperature, TL) than the second light fraction, which in turn has a lower TL value than the third balancing heavy fraction, etc, the order of light fractions characterized by a difference in the lower cut-point temperature value, as it will become apparent from one or more below embodiments. It is understood that in principle a fourth, fifth etc light fraction of jet may be fractionated from the third balancing heavy stream, comprising diesel and jet fuel components without diverging from the concept of the invention.

[0034] In an embodiment, the olefin fractionation section, or an olefin fractionation unit, or the distillate fuel fractionation section and associated step(s), i.e., fractionation(s), is any of a distillation column, membranes or other conventional unit operations in the art creating fractionated streams.

[0035] For the purposes of the present application:

[0036] 03093-WO The term “first aspect of the invention” means the process of the invention. The term “second aspect of the invention” means a plant (system), i.e., process plant.

[0037] The term “comprising” includes “comprising only”, i.e., “consisting of”.

[0038] The term “suitably” is used interchangeably with the term “optional”, i.e., an optional embodiment.

[0039] The term “process / plant” means process and / or plant.

[0040] The term “and / or” means in connection with a given embodiment any of the three options. The term “and / or” may be used interchangeably with the term “at least one of”.

[0041] The term “present invention” or simply “invention” are used interchangeably with the term “present application” or simply “application”.

[0042] The term “distillate fuel” means any of jet fuel and diesel. The term “distillate boiling range hydrocarbon product” means C5-C30 hydrocarbons and comprises hydrocarbons boiling in the naphtha boiling range, hydrocarbons boiling in the jet fuel boiling range, hydrocarbons boiling in the diesel boiling range; optionally, a heavy hydrocarbon fraction, i.e., maritime fuel. It is understood that the term “distillate fuels” is a subset of “distillate boiling range hydrocarbon product”.

[0043] The term “hydrocarbons boiling in the jet fuel range” may be used interchangeably with the term “jet fuel hydrocarbons” or “jet fuel range hydrocarbons”, or respectively, “jet fuel” or “jet fuel range”. The term means a mixture of isomers of C8-C19 hydrocarbons, such as C8-C17, C9-C18 or C8-C16 hydrocarbons, but is more specifically restricted by the fulfillment of the desired boiling range 130-300°C of the mixture and other fuel standards. For instance, the jet fuel is sustainable aviation fuel (SAF) in compliance with ASTM D7566 and ASTM D4054. For instance, the jet fuel is in compliance with ASTM D7566. Likewise, the term “hydrocarbons boiling in the diesel fuel range” may be used interchangeably with the term “diesel” or “diesel product” and means C)8-C25 hydrocarbons boiling in the range 120-360°C, for instance 160-360°C.

[0044] The term “hydrocarbons boiling in the naphtha boiling range may be used interchangeably with the term “naphtha” and means C5-C9 hydrocarbons boiling in the range 30- 160°C, such as C5-C8 hydrocarbons, e.g., C5-C8 olefins. The term “naphtha” is sometimes used interchangeably with the term “naphtha stream”.

[0045] For completeness, the term “hydrocarbons boiling in the gasoline boiling range” is normally used interchangeably with the term “gasoline” and means C5-C12 hydrocarbons boiling in the range 30-210°C.

[0046] 03093-WO The term boiling in a given range, shall be understood as a hydrocarbon mixture of which at least 80 wt% boils in the stated range.

[0047] Unless otherwise stated, when percentages are provided for a given stream it is meant wt% which is normally used for liquid streams.

[0048] The term “at least a portion” of a stream means a portion of the stream or the entire stream. More generally, the term “at least a portion” of an item means a portion of the item or the entire item. The item is for instance a process stream or a conduit.

[0049] The term “conduit” means a process line, such as a pipe, carrying a given process stream.

[0050] The use of the article “a” or “an” means at least one.

[0051] The term “CX-=” is used interchangeably with “CX- olefins” where X is the number of carbon atoms and means olefins having X carbons or lower. For instance, C8-= means C8- olefins and means olefins having 8 carbons, or less.

[0052] The term “CX=” is used interchangeably with “CX olefins” where X is the number of carbon atoms. For instance, C2= means C2 olefin, i.e. , ethylene.

[0053] The term “deficient olefins” means insufficiently oligomerized olefins in the oligomerization section and is defined herein as the portion of olefins with a carbon number of 8 or less, i.e., C8-=, which when hydrogenated form associated under-spec alkanes.

[0054] The use of a given stream comprising a given compound or compounds is understood as comprising at least 50 wt% of said compound(s). For instance, the term “a first light fraction comprising hydrocarbons boiling in the jet fuel range” means at least 50 wt% hydrocarbons boiling in the jet fuel range. For instance, the term “the second light fraction of hydrocarbons comprises C10-C15 hydrocarbons” means at least 50 wt% C10-C15 hydrocarbons, e.g., at least: 60, 70, 80, 90 wt% C10-C15 hydrocarbons (e.g., at least 60 wt%, or at least 70 wt%, or at least 80 wt%, or at least 90 wt% C10-C15 hydrocarbons). For instance, the term “a third balancing heavy fraction comprising hydrocarbons boiling in the diesel fuel range and hydrocarbons boiling in the jet fuel range”, means at least 50 wt% hydrocarbons boiling in the diesel fuel range, further comprising less than 50 wt% hydrocarbons boiling in the jet fuel range; or vice versa. For instance, an olefin feed comprising ethylene (C2=) means at least 50 wt% C2=, e.g., at least 60, 70, 80, 90 wt% C2=. For instance, a C8- = stream means a hydrocarbon stream comprising at least 50 wt% C8-=, e.g., at least: 60, 70, 80, 90 wt% C8=. For instance, a stream of C2= - C3= and associated alkanes means at least 50 wt% of C2= (ethylene) to C3= (propylene or

[0055] 03093-WO interchangeably propene) and associated alkanes, e.g., at least: 60, 70, 80, 90 wt% C2=

[0056] - C3= ; the associated alkanes being C2 to C3 alkanes, i.e. , ethane and propane.

[0057] The term “directly supplying” means that there is no intermediate unit or step changing the composition of a process stream. The units are arranged in “direct fluid communication”. Conversely, “indirectly” means that there are intermediate units and associated process steps between the corresponding units changing the composition of the associated process stream. The units are arranged in “indirect fluid communication”. More generally, the term “directly supplying” means that there is no intermediate unit or step changing the composition of a process stream.

[0058] The term “olefin make-up” is the composition fed to the oligomerization section, thus the olefin feed. The olefin feed is supplied to one or more feeding points. The term “reactor feed” is the composition that is fed to a reactor, herein an oligomerization reactor, and which may be directly supplied from a recycle stream, an upstream reactor effluent, or result from mixing of a recycle stream or an upstream reactor effluent with a split stream of the make-up in any proportion, e.g., the olefin make-up.

[0059] Oher definitions are provided in connection with one or more of above or below embodiments.

[0060] In an embodiment,

[0061] - the first light fraction comprises at least 50 wt% of hydrocarbons boiling in the jet fuel range;

[0062] - the third balancing heavy fraction comprises: at least 1 wt% of hydrocarbons boiling in the diesel range; and less than 99 wt% hydrocarbons boiling in the jet fuel range.

[0063] In an embodiment,

[0064] - the third balancing heavy fraction comprises: at least 50 wt% of hydrocarbons boiling in the diesel range; and less than 50 wt% hydrocarbons boiling in the jet fuel range.

[0065] In an embodiment,

[0066] - the second light fraction of hydrocarbons comprises C10-C15 hydrocarbons, such as C10-C14 hydrocarbons or C11-C14 hydrocarbons.

[0067] This specific second light fraction thus comprises mid-range jet fuel hydrocarbons and may be regarded as a “long recycle”, as at least a portion thereof is supplied to the upstream oligomerization section, as a diluent, i.e., a diluent co-feed, to one or more

[0068] 03093-WO oligomerization reactors of the oligomerization section. The C10-C15 hydrocarbons, such as C10-C14 hydrocarbons or C11-C14 hydrocarbons, suitably as diluting alkanes, are thus the diluent components, i.e. , the diluent compounds.

[0069] In an embodiment, the second light fraction comprises at least 50 wt% of C10-C15 hydrocarbons, such as at least 50 wt% of C10-C14 hydrocarbons or at least 50 wt% of C11-C14 hydrocarbons.

[0070] For instance, the second light fraction comprises at least: 60, 70, 80, 90 wt% of C10-C15 hydrocarbons.

[0071] In an embodiment, in step i) the oligomerization section comprises a first oligomerization reactor and a second oligomerization reactor, and in step iii) the at least a portion of the second light fraction of hydrocarbons to the oligomerization section is supplied as a diluent to any of the first and second oligomerization reactors.

[0072] It is understood that the oligomerization section comprises one or more oligomerization reactors. The oligomerization reactors may be arranged in parallel or in series and be of any kind known in the art. For instance, different types of oligomerization reactors, ethylene oligomerization (OLI-1) or oligomer oligomerization (OLI-2) reactors may be arranged in the oligomerization section, in addition to at least one OLI-1 or OLI-2 oligomerization reactor, as shown in the appended figures. A third, fourth or fifth etc. oligomerization reactor may be arranged in advantageous constellations of cooling / heating and stagewise feeding of olefin make-up, olefin recycle and diluent, depending on the features of the oligomerization catalyst, the olefin make-up, the stream compositions and proportions fed to the oligomerization section without diverging from the concept of the invention.

[0073] In conducting the invention, the first light fraction comprising hydrocarbons boiling in the jet fuel range, this comprising the lowest boiling fraction of jet fuel, is withdrawn from the distillate fuel fractionation section, e.g. from a distillate fuel fractionation unit such as a fractionation column, having a lower cut-point temperature TL than the second light fraction of hydrocarbons, this comprising the second lowest boiling fraction, and from which at least a portion is supplied to the oligomerization section as diluent. This enables, in

[0074] 03093-WO turn, an improved recovery of deficient olefins in the olefin recycle of the oligomerization section. Thereby, a higher fraction of deficient C8- olefins and associated alkanes, including lighter alkanes, are maintained within the oligomerization section. The effect of the improved product yield immediately increases, as a continuum function, with the magnitude of the lightest boiling hydrocarbon fraction, e.g., lightest boiling alkane fraction, withdrawn as jet fuel from the distillate fuel fractionation section, e.g., fractionation unit.

[0075] Oligomerization of ethylene may take place over a nickel containing oligomerization catalyst contained in a first type oligomerization reactor at a temperature from 30 to 300°C and a pressure of at least 10 bar, forming an ethylene oligomerization raw product comprising higher olefins, primarily of even numbered carbon numbers. This type of oligomerization reactor, herein referred to as OLI-1 , is utilized to convert the ethylene contents of the olefin feeds, if present. Olefins in the size range C4 to more than C22, preferably up to C14, most preferably up to C10, may be obtained in such a first ethylene oligomerization reactor. A small fraction of the olefins fed or produced as intermediates will be cracked catalytically into smaller olefins in OLI-1.

[0076] A supplemental or alternative oligomer oligomerization conversion step of an olefinic feed comprising higher olefins, oligomers, having three carbon atoms or more, e.g., including the higher olefins produced from the ethylene oligomerization, may also be conducted. This step is conducted in a second oligomerization reactor, herein referred to as OLI-2, which operates as an oligomer oligomerization reactor. The oligomer oligomerization reactor is conducted over an oligomer oligomerization catalyst, such as ASA (Amorphous Silica Alumina) type, yielding higher olefin products, including branched olefins. Suitably, Ni-ASA i.e. Ni supported on ASA is provided in OLI-1 and ASA in OLI-2. Byproducts of the size C3 to more than C25 alkanes produced by saturation (or H2 transfer) and olefins produced by cracking may be produced in parallel with the oligomerization products.

[0077] For the purposes of the present application, an oligomerization reactor such as a first oligomerization reactor and second oligomerization reactor, may operate with a heterogeneous catalyst or with a homogeneous catalyst. The oligomerization may take place in the gas phase or in the liquid phase.

[0078] 03093-WO For the purposes of the present application, a product withdrawn from an oligomerization reactor prior to an olefin fractionation is denoted as “raw oligomerization raw product”.

[0079] In an embodiment, in step iii) the at least a portion of the second light fraction of hydrocarbons being supplied to the oligomerization section is the entire portion of the second light fraction of hydrocarbons.

[0080] The term “entire portion” means at least 90 wt% of the stream, such as at least 95 wt% of the stream, preferably 100 wt% of the stream.

[0081] Conventionally, one would prefer few fractions being withdrawn from a fractionation unit of the distillate fuel fractionation section downstream the oligomerization section, e.g., from a distillation column, as in this way the design and operation is simpler. As a starting point, therefore, in order to obtain the diluent stream as the “long recycle”, the simple splitting of the top draw of jet fuel, i.e. , the first light fraction of jet, or the simple splitting of the third balancing heavy fraction draw of mixed jet fuel and diesel, or diesel, the latter two options as known in the prior art, is preferred to a diluent specific fractionation. In other words, alkane / paraffinic streams are normally diverted from the heavy diesel containing balancing fraction, which corresponds to the third balancing heavy fraction of the present application, and then supplied as the “long recycle” to oligomerization reactors upstream. Now, we have found that prior art solutions for provision of diluent, which are probably resulting from conventional teaching, are sub-optimal, but that dedicated fractionation of a second lightest fraction, to obtain a specific diluent composition, provides for an overall improved process.

[0082] Furthermore, a high solubility in the “long recycle” of the olefins contained in the olefin feed, i.e., diluent co-fed to the e.g. liquid phase oligomerization reactor(s), is desired. In this light, in choosing between a higher, rather than a lower boiling diluent fraction as diluent, the prior art also teaches away from selecting the higher boiling fraction, corresponding to the second light fraction of hydrocarbons of the present application, since lower boiling hydrocarbons, suitably C9-C10 alkanes, and corresponding to the first light fraction of the present application, are said to provide higher olefins solubility on a mass basis. Thus, even in the case where one considers separating the diluent from the

[0083] 03093-WO oligomerized and optionally hydrogenated product by fractionation, the natural choice would be fractionating the lowest boiling hydrocarbons, thus corresponding to the first light fraction of the present application.

[0084] Again, it has surprisingly been found that, when at least a portion of a higher boiling fraction, i.e. , the second light fraction of hydrocarbons, rather than the lower boiling fraction i.e., the first light fraction, for instance as defined and measured by the lower cut point TL, is being recycled as diluent to an oligomerization reactor of the oligomerization section, a higher jet fuel and diesel yield is obtained.

[0085] Accordingly, in an embodiment, the first light fraction comprising hydrocarbons boiling in the jet fuel range has a lower cut point value (TL1) than the lower cut point value (TL2) of the second light fraction of hydrocarbons. In other words, TL1 < TL2.

[0086] For the purposes of the present application, the lower cut point value (TL) means the temperature at which a specific fraction or component starts to vaporize and separate from the rest of the mixture during the fractionation. It represents the lower limit of the temperature range at which the desired fraction can be collected.

[0087] In an embodiment, the difference between TL2 and TL1 is defined as delta-T, i.e. delta- T = TL2 - TL1 , and delta-T is greater than 5°C; for instance, delta-T is at least: 10°C, 15°C, 20°C, 25°C, 30°C.

[0088] For instance, delta-T is: 6°C, 7°C, 8°C, 9°C. For instance, delta-T is: 11 °C, 12°C, 13°C, 14°C.

[0089] In an embodiment, the difference between TL2 and TL1 is defined as delta-T, and delta- TL is in the range 6-120°C, preferably in the range 10-60°C.

[0090] For the purposes of the present application, a given range includes the individual values of the ranges. Individual values of a given range may be combined with individual values of a different range.

[0091] 03093-WO For instance, in connection with the above embodiment, delta-T may be greater than 5°C and up to 30°C. For instance, delta-T may be 10-30°C.

[0092] For instance, delta-TL is greater than 5°C and up to 120°C, such as 6-120°C, more preferably in the range 10-60°C.

[0093] For instance, the first light fraction comprising hydrocarbons in the jet fuel range (C8- C19 hydrocarbons) may have a TL1 of 130°C, while the second light fraction of hydrocarbons, these preferably being C10-C15 hydrocarbons, may have a TL2 of >135°C, such as at least 140°C. For instance, the first light fraction comprising hydrocarbons in the jet fuel range (C8-C19 hydrocarbons) may have a TL1 of 150°C, while the second light fraction of hydrocarbons, these preferably being C10-C15 hydrocarbons, may have TL2 of >155°C, such as at least 160°C.

[0094] The oligomerization section also comprises an olefin fractionation section. In order to enable a pronounced effect of improved deficient olefin recovery in the olefin fractionation of the oligomerization section, the first light fraction comprising hydrocarbons boiling in the jet fuel range, thus fractionated downstream the oligomerization section as jet fuel, is characterized by a significantly lower TL1 , for example delta-TL > 5°C, compared to the TL2 of the second light fraction of hydrocarbons. On the other hand, the maximum value of the delta-TL of the second light fraction draw should be limited by the counterbalances of recycling and storing very high boiling fractions of diluent, having a high melting point, or exerting low solubility of the olefin feed to an oligomerization reactor of the oligomerization section such that this may not be held in e.g. the liquid phase at conventional oligomerization synthesis pressures.

[0095] Preferably, as recited above, the delta-TL is in the range 6-120°C, more preferably in the range 10-60°C.

[0096] In an embodiment, the olefin feed comprises at least 50 wt% C2=, for instance at least: 60, 70, 80, 90 wt% C2=.

[0097] It is understood that the olefin feed refers to a fresh olefin feed stream, i.e., prior to being combined with a recycle stream. The recycle stream is for instance an internal recycle

[0098] 03093-WO stream from an olefin fractionation unit of the oligomerization section, herein also referred to as “internal recycle of the oligomerization section”. The recycle stream is for instance the at least a portion of the second light fraction of hydrocarbons from the downstream distillate fuel fractionation section, i.e. , the diluent stream.

[0099] Ethylene is a suitable and available olefin feed as it is a common product or byproduct of upstream oxygenate conversion. For instance, ethylene may be a byproduct of a oxygenate to jet fuel conversion process, the oxygenate being any of methanol (MeOH) and / or dimethyl ether (DME). For instance, ethylene is a product of oxygenate dehydration, where the oxygenate is ethanol (EtOH). The present invention thus enables the use of ethylene as a valuable source or precursor for producing valuable distillate fuels.

[0100] In an embodiment, in step ii) the at least a portion of the oligomerized product is indirectly supplied to the distillate fuel fractionation section via a hydrogenation section, optionally the hydrogenation section further comprising a hydrogen recovery section, and withdrawing from the hydrogenation section: a hydrogenated oligomerized product, preferably as alkanes, as said oligomerized product.

[0101] The olefins of the oligomerized product, further comprising the diluent components, are hydrogenated, preferably catalytically hydrogenated, to obtain a corresponding range of alkanes useful as distillate fuel components, thus boiling in the jet fuel range and optionally further in the diesel range. Downstream of the hydrogenation the under-spec gases and other light off-gases, primarily octanes (part of the naphtha range hydrocarbons), are fractionated from the range of the desired alkane products, and from which the second light fraction of hydrocarbons i.e., the diluent, now as alkanes, is withdrawn and recycled to the oligomerization section. The jet fuel and diesel fuel streams, including the first light fraction and a third balancing heavy fraction, are withdrawn and suitably further processed into a final distillate fuel product, i.e., a final jet fuel product and / or a final diesel product.

[0102] If deficient olefins are lost in the oligomerized product together with the sufficient in molecular weight higher olefin and alkanes, the hydrogenation of these will unavoidably end up as a distillate fuel production loss. Furthermore, the hydrogen requirement in the hydrogenation section is increased.

[0103] 03093-WO In an embodiment, in the oligomerization section the process comprises: i-1) supplying the olefin feed and the at least a portion of the second light fraction of hydrocarbons to the first oligomerization reactor and withdrawing therefrom a first raw oligomerized product; i-2) directly or indirectly supplying the first raw oligomerized product to the second oligomerization reactor and withdrawing therefrom a second raw oligomerized product; i-3) supplying the first or second raw oligomerized product to an olefin fractionation section and withdrawing therefrom the oligomerized product; and wherein:

[0104] - the olefin fractionation section comprises: a heavy end (HE) fractionation unit in direct fluid communication with the second oligomerization reactor; and supplying the second raw oligomerized product to the HE fractionation unit and withdrawing therefrom: a HE fractionation unit bottom stream as the oligomerized product and a HE fractionation unit overhead stream.

[0105] In an embodiment, in the oligomerization section the process comprises: i-1) supplying the olefin feed and the at least a portion of the second light fraction of hydrocarbons to the first ethylene oligomerization reactor (OLI-1) and withdrawing therefrom a first raw oligomerized product; i-2) directly or indirectly supplying the first raw oligomerized product to the second oligomer oligomerization reactor (OLI-2) and withdrawing therefrom a second raw oligomerized product; i-3) supplying the first or second raw oligomerized product to an olefin fractionation section and withdrawing therefrom the oligomerized product; and wherein:

[0106] - the olefin fractionation section comprises a heavy end (HE) fractionation unit in direct fluid communication with the second oligomerization reactor (OLI-2) and a light end (LE) fractionation unit in direct fluid communication with the HE fractionation unit; and step i-3) further comprises: supplying the second raw oligomerized product to the HE fractionation unit and withdrawing therefrom: a HE fractionation unit bottom stream as the oligomerized product and a HE fractionation unit overhead stream; supplying the HE fractionation unit overhead stream to the LE fractionation unit and withdrawing therefrom: a LE fractionation unit bottom stream as an oligomerization section first recycle stream, preferably comprising C3= to C8= along with the associated

[0107] 03093-WO alkanes; and a LE fractionation unit overhead stream as an oligomerization section second recycle stream, preferably comprising C2= to C3= along with the associated alkanes; supplying the oligomerization section a first recycle stream to the second oligomerization reactor, preferably by combining the oligomerization section first recycle stream with the first raw oligomerized product and / or by combining with another portion of the second light fraction of hydrocarbons; supplying the oligomerization section second recycle stream to the first oligomerization reactor, preferably by combining with the olefin feed.

[0108] Any of the oligomerization section first and second recycle may be referred to as a “short recycle” or interchangeably as an “internal recycle of the oligomerization section”, as any of these streams are supplied to the upstream oligomerization reactor(s) within the oligomerization section.

[0109] It is understood that by e.g. combining the oligomerization section first recycle stream with the first raw oligomerized product, the first raw oligomerized product is indirectly supplied to the second oligomerization reactor, as the composition of the first raw oligomerized product is changed.

[0110] In order to obtain olefins of sufficient size to comply with distillate fuel specifications, herein also referred to as “product spec.”, an adequate degree of oligomerization must take place in the olefin to distillate fuel process / plant. Insufficiently oligomerized olefins, i.e. , deficient olefins, and byproducts boiling below a limiting boiling point as well as unconverted olefin feed, e.g., unconverted ethylene, which do not fulfill the desired oligomerized product characteristics when converting these in a downstream hydrogenation process, may be recycled to an oligomerization reactor of the oligomerization section. Optionally, and independently of the order of the fractionations or the number of fractionators in the oligomerization section, a further fractionation of the deficient olefins into two fractions may take place, one being richer in ethylene than the other.

[0111] By the invention, most of the lower olefins not converted in the oligomerization section are recycled and fed to any of the oligomerization reactors. As an example, as shown in appended Fig. 1 and 2, the deficient olefins may be recovered in the olefin fractionation section, which may consist of a single heavy end column, HE, wherein the oligomerized

[0112] 03093-WO product is withdrawn as a bottom stream, or one may in addition arrange for a separation of the lightest of the deficient olefins from the heavier of the deficient olefins in a light end column, LE, in order to recycle these to preferred additions points in the oligomerization section, such as to the first raw oligomerized product, thus in between the first and second oligomerization reactor.

[0113] The prior art fails at least to describe the criticality of effectively separating in the oligomerization section a relatively large bottom flow of combined diluent and jet fuel hydrocarbons, which is withdrawn as the oligomerized product, from the recycle flow of unconverted olefin and alkanes, as illustrated by the vertical double arrow inside the HE column of appended Fig. 1. Yet again, not-recycled deficient C8-= represents a loss of yield potential as downstream of the HE column, the bottom product, i.e., the oligomerized product, will optionally be hydrogenated to octane, especially in the OLI-2 step, an alkane which is unable to react further, i.e. it represents a dead-end product. The off-gas withdrawn from the downstream distillate fuel fractionation section will then carry the octane originating from deficient octene, the lightest fraction (lowest boiling) of octene that is converted to a fraction of octanes that cannot be included in the jet fuel, while another fraction of higher boiling octanes may. Furthermore, unnecessary recycle in the oligomerization section of jet fuel precursors, C9+=, leads to risk of undesired cracking and the loss of desirable C9+ alkanes in necessary recycle bleeds. By the invention, the desired jet fuel precursors, such as said C9+=, are withdrawn with the bottom product of the HE column, i.e., the oligomerized product.

[0114] The oligomerization reactors OLI-1 and OLI-2 may preferably be arranged in several steps, in series or parallel reactors, optionally preheated / intercooled and / or stagewise fed, as is known conventionally and exemplified below. In yet another embodiment, the above process only comprises one type of oligomerization reactor.

[0115] The oligomerizations may for instance take place in the liquid phase for which purpose a diluent stream is advantageously provided, here the second light fraction of hydrocarbons from the distillate fuel fractionation section, and mixed with the olefin feed upstream any of the oligomerization reactors, for example, but not limited to, the stagewise additions of both olefin make-up streams, internal recycle streams of insufficiently oligomerized olefins and diluent streams or the stagewise additions of one into the other feed

[0116] 03093-WO stream. Depending on the desired product distribution, OLI-1 is followed by OLI-2, which is in turn followed by a polishing OLI-1 , removing most of remaining unconverted ethylene, whereby the need for a light end column (LE) is alleviated.

[0117] Also, by process simulation we find that shifting the single component diluent nonane (C9H20) for undecane (C11H24) strongly reduces the loss of deficient C8-= to the bottom product of fractionation units of the oligomerization section, such as the bottom product of the heavy end (HE) column, the bottom product being withdrawn as the oligomerized product or a portion thereof.

[0118] Furthermore, depending on the kinetics of OLI-1 and OLI-2 conversions, fractionations may be provided in one or the other positions between the two oligomerization reactors, as exemplified in appended Fig. 3.

[0119] Accordingly, in an embodiment, in the oligomerization section the process further comprises: i-1) supplying the olefin feed and at least a portion of the second light fraction of hydrocarbons to the first oligomerization reactor and withdrawing therefrom a first raw oligomerized product; i-2) indirectly supplying the first raw oligomerized product via a first olefin fractionation unit to the second oligomerization reactor and withdrawing from the second oligomerization reactor a second raw oligomerized product; supplying the first raw oligomerized product to the first olefin fractionation unit and withdrawing therefrom: a first olefin fractionation unit bottom stream as a portion of the oligomerized product and a first olefin fractionation unit overhead stream; supplying the first olefin fractionation unit overhead stream to the second oligomerization reactor and withdrawing therefrom: the second raw oligomerized product; supplying the second raw oligomerized product to a second olefin fractionation unit and withdrawing therefrom: a second olefin fractionation unit bottom stream as a portion of the oligomerized product and a second olefin fractionation unit overhead stream; i-3) supplying the second olefin fractionation unit overhead stream to the first oligomerization reactor, preferably by combining the second olefin fractionation unit overhead stream with the olefin feed.

[0120] 03093-WO Hence, the second olefin fractionation unit overhead stream, comprising deficient olefins and alkanes, is recycled to the first oligomerization reactor.

[0121] This feature of the process to recover deficient olefin into the olefin recycle stream and recycling it back for further build-up, further contributes to ensure a high carbon efficiency of the overall olefin conversion to distillate fuel, in terms of carbon yield.

[0122] In an embodiment, the third balancing heavy (higher boiling) fraction comprising hydrocarbons boiling in the diesel fuel range and in the jet fuel range, and the first light (lower boiling) fraction comprising hydrocarbons boiling in the jet fuel range, are combined into one jet product stream.

[0123] In an embodiment, the process further comprises:

[0124] - supplying the third balancing heavy fraction comprising hydrocarbons boiling in the diesel fuel range and hydrocarbons boiling in the jet range, to a further fractionation in the same fractionation unit of the fractionation section from which said third balancing heavy fraction is withdrawn, or to a separate fractionation section; and withdrawing from any of the same fractionation unit or the separate fractionation section: a first enriched jet fuel fraction and an enriched diesel fraction;

[0125] - supplying the enriched diesel fraction to a cracking step in a cracking reactor, such as a hydrocracking reactor; and withdrawing therefrom: a second enriched jet fuel fraction and a diesel fuel product stream.

[0126] In an embodiment, the process further comprises:

[0127] - optionally, withdrawing a split fraction of the second light fraction of hydrocarbons;

[0128] - combining any of: the first light fraction comprising hydrocarbons boiling in the jet fuel range, said optional split fraction of the second light fraction of hydrocarbons, the first enriched jet fuel fraction, and the second enriched jet fuel fraction, into a jet fuel product stream.

[0129] Hence, the third balancing heavy fraction is separated by further distillation, providing: a first enriched jet fuel fraction as the lighter fraction, and an enriched diesel fraction as the heavier fraction. The enriched diesel fraction is then treated by a cracking step, such

[0130] 03093-WO as a hydrocracking step, providing a second enriched jet fuel fraction, thereby increasing the overall jet fuel yield, along with a diesel fuel product stream. A jet fuel product stream is suitably provided by combining any of: the first light fraction comprising hydrocarbons boiling in the jet fuel range, the split fraction of the second light fraction of hydrocarbons, suitably a minor portion thereof, i.e. , less than 50 wt%, such as less than: 40, 30, 20, 10 wt%, the first enriched jet fuel fraction, and the second enriched jet fuel fraction.

[0131] In a second aspect of the invention, there is provided a plant for carrying out the process according to any of the preceding embodiments according to the first aspect (process) of the invention; the plant comprising:

[0132] - an oligomerization section comprising at least one oligomerization reactor, the oligomerization section arranged to receive an olefin feed and provide an oligomerized product;

[0133] - a distillate fuel fractionation section arranged in direct or indirect fluid communication with the oligomerization section, the fractionation section arranged to receive the oligomerized product and provide at least: a first light fraction comprising hydrocarbons boiling in the jet fuel range; a second light fraction of hydrocarbons, which is heavier than the first light fraction of hydrocarbons; a third balancing heavy fraction comprising hydrocarbons boiling in the diesel fuel range and in the jet fuel range, the third balancing fraction being heavier than the second light fraction of hydrocarbons;

[0134] - a conduit arranged to supply at least a portion of the second light fraction of hydrocarbons to the oligomerization section.

[0135] In another second aspect of the invention, there is provided a plant for converting olefins to distillate fuel, the distillate fuel being at least one of jet fuel and diesel, the plant comprising:

[0136] - an oligomerization section comprising at least one oligomerization reactor, the oligomerization section arranged to receive an olefin feed and provide an oligomerized product;

[0137] - a distillate fuel fractionation section arranged in direct or indirect fluid communication with the oligomerization section, the fractionation section arranged to receive the oligomerized product and provide at least:

[0138] 03093-WO a first light fraction comprising hydrocarbons boiling in the jet fuel range; a second light fraction of hydrocarbons, which is heavier than the first light fraction of hydrocarbons; a third balancing heavy fraction comprising hydrocarbons boiling in the diesel fuel range and in in the jet fuel range, the third balancing fraction being heavier than the second light fraction of hydrocarbons;

[0139] - a conduit arranged to supply at least a portion of the second light fraction of hydrocarbons to the oligomerization section.

[0140] It is understood that any of the embodiments according to the first aspect of the invention and associated benefits may be used in connection with the second aspect of the invention, or vice versa.

[0141] BRIEF DESCRIPTION OF THE FIGURES

[0142] Fig. 1 shows a layout of an olefin to distillate fuel process / plant according to an embodiment of the invention.

[0143] Fig. 2 shows the oligomerization section of the olefin to distillate process / plant according to another embodiment of the invention.

[0144] Fig. 3 shows the oligomerization section of the olefin to distillate process / plant according to yet another embodiment of the invention.

[0145] Fig. 4 shows simulation results of the HE fractionation according to the example.

[0146] DETAILED DESCRIPTION

[0147] Fig. 1 shows one embodiment of the improved process / plant layout 100 for converting an olefin feed 101 to distillate fuels 129, 133 according to an embodiment of the invention. The layout comprises an oligomerization section 100’, where the olefin feed 101 , suitably an olefin feed comprising ethylene, is oligomerized in one or more oligomerization reactors, OLI-1 110, OLI-2 120, of the oligomerization section 100’ to sufficiently and insufficiently oligomerized (deficient) olefins. According to this embodiment, in the

[0148] 03093-WO oligomerization section 100’ deficient olefins being synthesized are recovered in recycle stream 103, herein referred to as oligomerization section second recycle stream, suitably as a recycle stream of C2= - C3= and associated alkanes, from the olefin fractionation section. The olefin fractionation section comprises a heavy end (HE) fractionation unit 130, e.g. column (HE column) and a light end (LE) fractionation unit 140 e.g. column (LE column), which fractionates the deficient and unconverted olefins into a lighter and lightest fraction to be fed back to the oligomerization reactors, OLI-1 110 and OLI-2 120. The olefin feed 101 is supplied, together with at least a portion 107’ of second light fraction of hydrocarbons 107 from downstream distillate fuel fractionation section 100’”, to the first oligomerization reactor OLI-1 110, from which a first raw oligomerized product 109 is withdrawn. The first raw oligomerized product 109 is optionally mixed with oligomerization section first recycle 111 obtained as a bottom stream from the LE (140), then supplied as stream 113 to the second oligomerization reactor OLI-2 120 from which a second raw oligomerized product 115 is withdrawn. The second raw oligomerized product 115 is supplied to the olefin fractionation section comprising the HE column 130 and LE column 140. The (HE) fractionation unit 130 is here in direct fluid communication with the upstream second oligomerization reactor OLI-2 120 and the downstream low end (LE) fractionation unit 40 is in direct fluid communication with the HE fractionation unit 130. From the HE fractionation unit 130 the following streams are withdrawn: a HE fractionation unit bottom stream 117 as oligomerized product 117 and a HE fractionation unit overhead stream 119. The latter is supplied to the LE fractionation unit 140, from which the following streams are withdrawn: a LE fractionation unit bottom stream 111 as the oligomerization section first recycle stream, which comprises deficient olefins such as C3= to C8-= along with the associated alkanes; and the above mentioned LE fractionation unit overhead stream 103 as the oligomerization section second recycle stream, comprising deficient olefins such as C2= to C3= along with the associated alkanes. The oligomerization section first recycle stream 111 is supplied to the second oligomerization reactor OLI-2 120, preferably by combining it with the first raw oligomerized product 109, as already described. The oligomerization section second recycle stream 103 is supplied to the first oligomerization reactor OLI-1 110, preferably by combining it with the olefin feed 101 into feed stream 105, as also depicted in the figure. A purge gas 123 and a liquid bleed 125 may also be withdrawn from the LE fractionation unit 140.

[0149] 03093-WO The oligomerized product 117 withdrawn from the HE fractionation unit 130 comprises the sufficiently oligomerized olefins, the associated alkanes, i.e., co-produced alkanes, and the diluent components, i.e., diluent compounds. The desired C9+ hydrocarbons are carried in the oligomerized product 117, while C8-= and lighter compounds are kept within the oligomerization section 100’ and recycled via the oligomerization section first and / or second recycle stream 111 ,103.

[0150] Downstream of the oligomerization section 100’ a hydrogenation section 100” is provided to which a feed stream of hydrogen 126 is fed. Optionally, this hydrogenation section 100” further comprises a hydrogen recovery section. From the hydrogenation section 100” a hydrogenated oligomerized product 127 is withdrawn, as alkanes.

[0151] Downstream the hydrogenation section 100”, the fractions of alkanes obtained are fractionated in distillate fuel fractionation section 100’” into under-spec off-gases 135, for instance comprising octane originating from deficient octene, the lightest fraction (lowest boiling) of octene that is converted to a fraction of octanes that cannot be included in the jet fuel. From the distillate fractionation section 100’” at least two fractions of alkanes are withdrawn: a) a first light fraction 129 comprising hydrocarbons boiling in the jet fuel range, i.e. the lowest boiling fraction(s) of alkanes is recovered as a first product stream; b) a second light fraction of hydrocarbons 107 which is heavier than the first light fraction 129 of hydrocarbons, i.e. the second lowest boiling fraction(s) of alkanes. Further c) a third balancing heavy fraction 133 comprising hydrocarbons boiling in the diesel fuel range and in the jet fuel range, is withdrawn, the third balancing fraction being heavier than the second light fraction of hydrocarbons. The third balancing heavy fraction 133 is herein also referred to as the highest boiling fraction.

[0152] From the second light fraction of hydrocarbons 107 which comprises at least a major portion of the diluent compounds, at least a portion, i.e., at least a fraction 107’ is recovered and recycled to the up-stream oligomerization section 100’ and used as diluent stream. The lowest boiling 129 and the highest boiling jet fraction 133 are optionally combined into a product stream or optionally processed further, together, or individually. For example, the highest boiling fraction 133 is advantageously subjected to further distillation and cracking to increase the jet fuel yield in the process, where jet fuel is the more desirable product.

[0153] 03093-WO Fig. 2 shows another embodiment of the oligomerization section 100’ of Fig. 1. The same ref. numbers of the process streams and units as in Fig. 1 apply. Now, the second light fraction of hydrocarbons 107 which comprises diluent compounds is supplied as stream 107’ to the first oligomerization reactor OLI-1 110 and as stream 107” to the second oligomerization reactor OLI-2 120 of the oligomerization section 100’.

[0154] Fig. 3 shows another way of arranging the oligomerization units and associated process steps in now an oligomerization section 200’. Olefin feed 201 is supplied to the first oligomerization reactor OLI-1 210 along with: second light fraction of hydrocarbons 207 acting as a diluent which is withdrawn from downstream distillate fuel fractionation section (not shown); second olefin fractionation unit overhead stream 203, which comprises deficient olefins and alkanes. A first raw oligomerized product 209 is withdrawn and supplied to first olefin fractionation unit 230. From this unit 230, a first olefin fractionation unit bottom stream 217’ as a portion of the oligomerized product 217 and a first olefin fractionation unit overhead stream 219, are withdrawn. The overhead stream 219 is supplied to second oligomerization reactor OLI-2 220 from which second raw oligomerized product 221 is withdrawn. The first and second oligomerization reactors OLI-1 210 and OLI- 2 220 are thus in indirect fluid communication via the first olefin fractionation unit 230. The second raw oligomerized product 221 is supplied to the second olefin fractionation unit 240, from which a second olefin fractionation unit bottom stream 217” as a portion of the oligomerized product 217 is withdrawn. In addition, the above mentioned second olefin fractionation unit overhead stream 203 is withdrawn and recycled to the first oligomerization reactor OLI-1 210. Streams 217’ and 217” are suitably combined into oligomerized product and supplied to downstream distillate fuel fractionation, as shown in Fig. 1.

[0155] EXAMPLE

[0156] Reference is made to Fig. 1 and 2. In a generalized process layout for converting olefins to distillate fuel by oligomerization in first and second oligomerization reactors OLI- 1+OLI-2 110+120 of oligomerization section 100’. The oligomerization reactor OLI-1 is fed with ethylene 101 and recycled diluent (a portion 107’ of the second light fraction of hydrocarbons 107), the product of which is withdrawn as second raw oligomerized

[0157] 03093-WO product 115, which is then fractionated in HE fractionation column 130, thereby producing a C8- recycle top stream (HE fractionation unit overhead stream 119) and a C8+ raw product bottom stream (HE fractionation unit bottom stream 117 as oligomerized product), optionally followed by LE fractionation column, 140. The HE fractionation unit bottom stream as oligomerized product 117 is processed in a downstream hydrogenation section 100”, thus hydrogenating the C8+ of the oligomerized product 117 to alkanes, and then to distillate fuel fractionation section 100”’, thereby fractionating off an off-gas stream 135, a first light fraction comprising hydrocarbons boiling in the jet fuel range i.e. lighter jet stream 129, and the second light fraction of hydrocarbons i.e. diluent jet 107 from the a third balancing heavy fraction 133 comprising hydrocarbons boiling in the diesel fuel range and in the jet fuel range, in this example for simplicity referred to as jet product 133. The diluent jet stream 107 or a portion 107’ thereof is being recycled to the oligomerization section comprising OLI-1 and OLI-2. This layout represents one nonlimiting embodiment of the present invention. A high recovery of C8(-) components e.g. C8-= and light hydrocarbons in the HE fractionation unit overhead stream 119 is achieved, which is relevant, as contents of sub-jet C8 components in the HE fractionation unit bottom stream as oligomerized product 117 eventually end up in off-gas stream 135 which in turn represents an overall distillate yield loss.

[0158] For the sake of simplicity, the sensitivity of the choice of diluent on C8 recovery in the HE fractionation unit overhead stream 119 has been demonstrated through simulation of the HE fractionation unit by keeping the composition and weight fraction of the OLI1+OLI2 unconverted reactants and products of the downstream distillate fuel fractionation unit feed constant while varying only the type of diluent. The variation of the diluent boiling range has been represented by using simple alkanes of increasing carbon numbers herein, i.e. n-nonane, n-decane, n-undecane etc.

[0159] Simulation method

[0160] A distillation software and thermodynamic parameters were set up in a simulation tool to simulate the HE fractionation with specified constant bottom and overhead mass rates. Hereby, the recoveries of the C8 obtained in the HE fractionation unit overhead stream is made comparable across the number of different diluents.

[0161] 03093-WO The composition of the resulting oligomerized feed stream (second raw oligomerized product 115) sent to the HE fractionation unit 130 was kept constant except for the balance of the alkane diluent which was changed systematically to illustrate the impact of the diluent boiling range on the C8 recovery.

[0162] The total number of C8 isomers produced in the oligomerization section 100’ is high. For the sake of clarity, a few representatives of C8 components that reflect the relevant C8 components boiling ranges have been selected. Accordingly, five (5) C8 isomer components were included in the simulation within the boiling range, i.e. volatility, from that of octane to that of 2,3-methyl-2-heptene. This way the most prominent C8 components in the oligomerization section 100’ are represented in the C8 boiling range defined.

[0163] Similarly, the number of different jet compositions that may be withdrawn as diluent downstream in the backend distillate fuel fractionation section 100” is unsurmountable. Therefore, for the sake of simplicity and clarity five (5) different pure component alkanes have been used in the modelling. The variation of these limited-in-number pure component diluents may anyhow very efficiently demonstrate the impact of increasing the diluent boiling point on the C8 recovery in the HE fractionation unit 130 of the oligomerization section 100’, without limiting the validity of the simulation results to the pure component diluents alone.

[0164] Accordingly, the composition of alkanes, alkenes, naphthenes, arenes etc., grouped as per carbon number, in wt% of the feed to the HE fractionation unit was as follows: 0.24 C2, 0.10 C3, 19.4 C4, 0.050 C5, 3.08 C6, <0.02 C7, 12.74 C8, 2.39 C9 (excl. dil), 6.44 C10+ (excl. dil), balanced by the constant weight fraction of 55.5 wt% diluent.

[0165] Nonane diluent represents in this context the ‘closest boiling fractionation fraction’ (rendering 129 very small) recovered in the distillate fuel fractionation section 100”’down- stream of the hydrogenation 100”, whereas decane, undecane, dodecane and tridecane represent streams of increasingly higher lower cut temperatures in the distillate fuel fractionation section 100’”, leaving an increasingly higher flow rate of stream 129.

[0166] 03093-WO Simulation results

[0167] The recovery of C7- components in the HE fractionation unit overhead stream 119 was literally 100%.

[0168] The recovery of C8 components in the HE fractionation unit overhead stream 119 determines how much of the insufficiently oligomerized C8 may be subjected to further oligomerization into the jet range (foremostly C9+).

[0169] Appended Fig. 4 shows the simulation results of the HE fractionation unit. The graphs in Fig. 4 show that the optimal recovery of C8 is not obtained with the closest boiling component or diluent, here represented by nonane (carbon number = 9), but rather a diluent composition of a little higher average carbon number or having a little higher boiling range, e.g. decane (carbon number=10) or undecane (carbon number = 11). The C8 recovery enhancing effect occurs universally across a selection of C8 components prevailing in the oligomerization process converting olefins to distillate fuel. It is also shown that for diluents of higher carbon number than the optimum, the recovery of C8 declines. The optimum carbon number of diluent in this concrete example is 11 , but this example only serves to illustrate that an optimum diluent boiling range does exist. Therefore, as discussed above, the incremental C8 recovery obtained as compared to the closest boiling diluent above C8 (here nonane), rather concerns a continuum of diluent compositions with boiling points lying in the range up to the optimum.

[0170] In conclusion, the action of increasing the diluent carbon number of the present example above its minimum, or in effect the diluent boiling temperature range, corresponds to fractionating in distillate fuel fractionation section 100”’, apart from the off gas stream 135, a) a first light fraction 129 comprising hydrocarbons boiling in the jet fuel range, i.e. the lowest boiling fraction(s) of alkanes as a first jet product stream, b) a second light fraction of hydrocarbons 107, which is heavier than the first light fraction 129 of hydrocarbons, and c) a bottom product stream of jet product 133, and using, the second lowest boiling fraction(s) of alkanes as a diluent for recycling; obtaining hereby the improved C8 recovery in the HE fractionation unit 130.

[0171] 03093-WO By means of the above example it is principally shown that the preferred diluent is not the immediate jet fractionation cut, adjacent to the product cut (i.e. the sum of 129+107) in the distillate fuel fractionator downstream of the hydrogenation unit, but a jet fraction cut with a higher value of the lower cut temperature, i.e. stream 107 or a portion 107’ thereof. The jet fraction cut with the lower value of the lower cut temperature may be exported as jet and does not represent a loss. Hereby, it is thus surprisingly demonstrated how the recovery of C8- components in the HE fractionation unit overhead 119 and hereby the overall jet yield, is improved with the boiling point of diluent (lower cut temperature of stream 107, up to an optimum diluent boiling point, whereafter the C8- recovery declines).

[0172] Depending on the resulting jet product composition, more or less C8 is acceptable as part of the jet fuel, i.e. the HE fractionation unit bottom stream 117 (oligomerized product) may contain more or less of the C8 components. Meanwhile, the principle of recycling a diluent 107 with a higher boiling point, thus withdrawing from the downstream distillate fuel fractionation section 100”’ a lighter jet stream 129 in order to obtain a higher recovery of insufficiently oligomerized C8- olefins in the HE fractionation unit overhead 119, remains.

[0173] The benefits of using an optimum diluent fraction may be capitalized in other manners as discussed above, e.g. for a fixed C8 recovery the number of theoretical trays in the HE fractionation unit, e.g. a HE column, may be reduced in the HE column, and the increased recovery of C8- in the HE column vice versa implies that the fraction of under- spec C8- hydrocarbons, suitably C8- alkanes, distilled off in the distillate fuel fractionation section, is correspondingly reduced, as may be deduced by those skilled in the art.

[0174] 03093-WO

Claims

32CLAIMS1 . Process for converting olefins to a distillate fuel, the distillate fuel being at least one of jet fuel and diesel, the process comprising: i) supplying an olefin feed comprising at least 50wt% ethylene (C2=) to an oligomerization section comprising at least one oligomerization reactor and withdrawing from the oligomerization section an oligomerized product; ii) directly or indirectly supplying at least a portion of the oligomerized product to a distillate fuel fractionation section and withdrawing therefrom at least: ii-a) a first light fraction comprising hydrocarbons boiling in the jet fuel range; ii-b) a second light fraction of hydrocarbons, which is heavier than the first light fraction of hydrocarbons; ii-c) a third balancing heavy fraction comprising: hydrocarbons boiling in the diesel fuel range and hydrocarbons boiling in the jet fuel range; the third balancing fraction being heavier than the second light fraction of hydrocarbons; iii) supplying at least a portion of the second light fraction of hydrocarbons to the oligomerization section.

2. Process according to claim 1 , wherein:- the first light fraction comprises at least 50 wt% of hydrocarbons boiling in the jet fuel range;- the third balancing heavy fraction comprises: at least 1 wt% of hydrocarbons boiling in the diesel range; and less than 99 wt% hydrocarbons boiling in the jet fuel range.

3. Process according to any of claims 1-2, wherein the third balancing heavy fraction comprises: at least 50 wt% of hydrocarbons boiling in the diesel range; and less than 50 wt% hydrocarbons boiling in the jet fuel range.

4. Process according to any of claims 1-3, wherein the second light fraction of hydrocarbons comprises C10-C15 hydrocarbons, such as C10-C14 hydrocarbons or C11-C14 hydrocarbons.03093-WO335. Process according to claim 4, wherein the second light fraction comprises at least 50 wt% of C10-C15 hydrocarbons, such as at least 50 wt% of C10-C14 hydrocarbons or at least 50 wt% of C11-C14 hydrocarbons.

6. Process according to any of claims 1-5, wherein in step i) the oligomerization section comprises a first oligomerization reactor and a second oligomerization reactor, and in step iii) the at least a portion of the second light fraction of hydrocarbons to the oligomerization section is supplied as a diluent to any of the first and second oligomerization reactors.

7. Process according to any of claims 1-6, wherein in step iii) the at least a portion of the second light fraction of hydrocarbons being supplied to the oligomerization section is the entire portion of the second light fraction of hydrocarbons.

8. Process according to any of claims 1-7, wherein the first light fraction comprising hydrocarbons boiling in the jet fuel range has a lower cut point value (TL1) than the lower cut point value (TL2) of the second light fraction of hydrocarbons.

9. Process according to claim 8, wherein the difference between TL2 and TL1 is defined as delta-T, and delta-T is greater than 5°C; for instance, delta-T is at least: 10°C, 15°C, 20°C, 25°C, 30°C.

10. Process according to claim 8, wherein the difference between TL2 and TL1 is defined as delta-T, and delta-TL is in the range 6-120°C, preferably in the range 10- 60°C.

11. Process according to any of claims 1-10, wherein the olefin feed comprises at least: 60, 70, 80, 90 wt% C2=.

12. Process according to any of claims 1-11 , wherein in step ii) the at least a portion of the oligomerized product is indirectly supplied to the distillate fuel fractionation section via a hydrogenation section, optionally the hydrogenation section further comprising a hydrogen recovery section, and withdrawing from the hydrogenation section: a hydrogenated oligomerized product, preferably as alkanes, as said oligomerized product.

13. Process according to any of claims 6-12, wherein in the oligomerization section the process comprises:03093-WOi-1) supplying the olefin feed and the at least a portion of the second light fraction of hydrocarbons to the first oligomerization reactor and withdrawing therefrom a first raw oligomerized product; i-2) directly or indirectly supplying the first raw oligomerized product to the second oligomerization reactor and withdrawing therefrom a second raw oligomerized product; i-3) supplying the first or second raw oligomerized product to an olefin fractionation section and withdrawing therefrom the oligomerized product; and wherein:- the olefin fractionation section comprises: a heavy end (HE) fractionation unit in direct fluid communication with the second oligomerization reactor; and- supplying the second raw oligomerized product to the HE fractionation unit and withdrawing therefrom: a HE fractionation unit bottom stream as the oligomerized product and a HE fractionation unit overhead stream.

14. Process according to any of claims 6-12, wherein in the oligomerization section the process comprises: i-1) supplying the olefin feed and the at least a portion of the second light fraction of hydrocarbons to the first oligomerization reactor and withdrawing therefrom a first raw oligomerized product; i-2) directly or indirectly supplying the first raw oligomerized product to the second oligomerization reactor and withdrawing therefrom a second raw oligomerized product; i-3) supplying the first or second raw oligomerized product to an olefin fractionation section and withdrawing therefrom the oligomerized product; and wherein:- the olefin fractionation section comprises: a heavy end (HE) fractionation unit in direct fluid communication with the second oligomerization reactor; and a light end (LE) fractionation unit in direct fluid communication with the HE fractionation unit; and step i-3) further comprises: supplying the second raw oligomerized product to the HE fractionation unit and withdrawing therefrom: a HE fractionation unit bottom stream as the oligomerized product and a HE fractionation unit overhead stream; supplying the HE fractionation unit overhead stream to the LE fractionation unit and withdrawing therefrom: a LE fractionation unit bottom stream as an oligomerization 03093-WOsection first recycle stream, preferably comprising C3= to C8= along with the associated alkanes; and a LE fractionation unit overhead stream as an oligomerization section second recycle stream, preferably comprising C2= to C3= along with the associated alkanes; supplying the oligomerization section first recycle stream to the second oligomerization reactor, preferably by combining the oligomerization section first recycle stream with the first raw oligomerized product and / or by combining with another portion of the second light fraction of hydrocarbons; supplying the oligomerization section second recycle stream to the first oligomerization reactor, preferably by combining with the olefin feed.

15. Process according to any of claims 6-12, wherein in the oligomerization section the process further comprises: i-1) supplying the olefin feed and the at least a portion of the second light fraction of hydrocarbons to the first oligomerization reactor and withdrawing therefrom a first raw oligomerized product; i-2) indirectly supplying the first raw oligomerized product via a first olefin fractionation unit to the second oligomerization reactor and withdrawing from the second oligomerization reactor a second raw oligomerized product; supplying the first raw oligomerized product to the first olefin fractionation unit and withdrawing therefrom: a first olefin fractionation unit bottom stream as a portion of the oligomerized product and a first olefin fractionation unit overhead stream; supplying the first olefin fractionation unit overhead stream to the second oligomerization reactor and withdrawing therefrom: the second raw oligomerized product; supplying the second raw oligomerized product to a second olefin fractionation unit and withdrawing therefrom: a second olefin fractionation unit bottom stream as a portion of the oligomerized product and a second olefin fractionation unit overhead stream; i-3) supplying the second olefin fractionation unit overhead stream to the first oligomerization reactor, preferably by combining the second olefin fractionation unit overhead stream with the olefin feed.

16. Process according to any of claims 1-15, wherein the process further comprises:03093-WO36- supplying the third balancing heavy fraction comprising hydrocarbons boiling in the diesel fuel range and hydrocarbons boiling in the jet range, to a further fractionation in same fractionation unit of the fractionation section from which said third balancing heavy fraction is withdrawn, or to a separate fractionation section; and withdrawing from any of the same fractionation unit or the separate fractionation section: a first enriched jet fuel fraction and an enriched diesel fraction;- supplying the enriched diesel fraction to a cracking step in a cracking reactor, such as a hydrocracking reactor; and withdrawing therefrom: a second enriched jet fuel fraction and a diesel fuel product stream.

17. Process according to claim 16, further comprising:- optionally, withdrawing a split fraction of the second light fraction of hydrocarbons;- combining any of: the first light fraction comprising hydrocarbons boiling in the jet fuel range, said optional split fraction of the second light fraction of hydrocarbons, the first enriched jet fuel fraction, and the second enriched jet fuel fraction, into a jet fuel product stream.

18. Plant for carrying out the process according to any of the preceding claims; the plant comprising:.- an oligomerization section comprising at least one oligomerization reactor, the oligomerization section arranged to receive an olefin feed and provide an oligomerized product;- a distillate fuel fractionation section arranged in direct or indirect fluid communication with the oligomerization section, the fractionation section arranged to receive the oligomerized product and provide at least: a first light fraction comprising hydrocarbons boiling in the jet fuel range; a second light fraction of hydrocarbons, which is heavier than the first light fraction of hydrocarbons;03093-WOa third balancing heavy fraction comprising hydrocarbons boiling in the diesel fuel range and in in the jet fuel range, the third balancing fraction being heavier than the second light fraction of hydrocarbons;- a conduit arranged to supply at least a portion of the second light fraction of hydrocarbons to the oligomerization section.03093-WO

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