Process for the manufacture of a cracker feedstock

Abstract

A process for the manufacture of a cracker feedstock comprises the steps of: a) providing Jatropha oil; b) pretreating the Jatropha oil to reduce the amounts of potassium and iron contained therein; and c) catalytically hydrodeoxygenating the pretreated Jatropha oil to obtain the cracker feedstock. The process ensures that the quality of the Jatropha oil is adequate in terms of its impurity profile for use in a hydrodeoxygenation process.

Description

[0001] The present invention relates to a process for the manufacture of a cracker feedstock, and to a process for the operation of a cracker.

[0002] Chemical production processes such as cracking require huge amounts of raw materials ("feedstock"). The feedstock commonly originates from non-renewable, i.e. fossil, resources and typically contains natural gas, naphtha, liquefied petroleum gas (LPG), ethane, propane, butane etc. Apart from the finite availability of such fossil resources, it is desirable, at least for environmental reasons, to provide at least a part of the feedstock from sustainable, i.e. renewable, sources. Thus, it is of great importance to broaden the sustainable / renewable raw material basis for feedstocks for use in chemical production processes such as cracking.

[0003] Jatropha curcas is a species of flowering plant in the spurge family, Euphorbiaceae. Jatropha curcas trees provide seeds containing up to 50 wt.-% of oil which are inedible for humans. The seeds may be converted to a bio-oil ("Jatropha oil"). Such a bio-oil from a plant is a sustainable / renewable source of energy. Therefore, Jatropha oil may be envisaged as a renewable feedstock for various chemical processes, e.g. for cracking to produce olefins such as ethylene or propylene. However, the oil obtained from seeds of Jatropha curcas contain high contents of oxygenates. The presence of oxygenates in a cracking feedstock is disadvantageous as oxygenates often result in the formation of unwanted by-products such as water and carbon dioxide during cracking. Thus, Jatropha oil cannot be used directly as a feedstock for cracking.

[0004] In order to make Jatropha oil accessible for cracking, oxygenates should advantageously be removed prior to cracking, e.g. by subjecting the Jatropha oil to a hydrodeoxygenation step. During hydrodeoxygenation, oxygen heteroatoms present in the Jatropha oil are removed and the triglycerides are transformed into linear or substantially linear paraffins. Typically, in catalytic hydrodeoxygenation, nickel-molybdenum catalysts are used.

[0005] Inorganic materials may be naturally present in biomass material such as Jatropha oil. The minerals could interfere with subsequent conversion processes and may poison catalysts used in downstream processes. They may cause decreased service life of the catalyst, and make frequent regeneration of the catalysts necessary, reducing the cost effectiveness of the catalyst.

[0006] Jatropha curcas has the ability to phytoextract high amounts of heavy metals from the soil, and, thus, can be regarded as a hyperaccumulator plant.

[0007] P. Arora et al., Catalysis Today 2021, 367, 28-42 relates to hydrodeoxygenation activity of nickel-molybdenum catalysts in the presence of catalyst poisons, especially iron, potassium, sodium and phospholipids containing phosphorus, in bio-based feedstocks. The document is silent on treating Jatropha oil.

[0008] R. Kumar et al., Green Chem. 2010, 12, 2232-2239 relates to hydroprocessing of Jatropha oil with gas oil. The document describes that iron is present in Jatropha oil, but is silent in terms of catalyst deactivation (hereinafter synonymously referred to as "catalyst poisoning").

[0009] US 9,969,940 B2 relates to a method for avoiding catalyst plugging comprising: purifying a biological feedstock from at least one iron-comprising renewable source, e.g. Jatropha oil; hydrotreating the purified biological feedstock with a catalyst to form hydrocarbons during a catalytic reaction in a trickle bed reactor; and avoiding plugging of the catalyst used in hydrotreating that causes an increase in the pressure drop of the hydrotreatment reactor. The document relates to catalyst plugging and is silent in terms of catalyst poisoning.

[0010] Indian Patent Application No: 750 / KOL / 2010 relates to a process for the demetallation of vegetable oils and animal fats to reduce the metal content below 1 ppm to make them suitable for hydroprocessing feedstocks.

[0011] One major objective for the production process is to maximize the performance and service times of the hydrodeoxygenating catalyst. Accordingly, there is a need to identify potential poisonous substances to deal with this objective. Moreover, the concentration of poisonous substances in Jatropha oil may vary depending on the origin and the process of refining of the raw materials.

[0012] The object has been solved by the inventive process for the manufacture of a cracker feedstock, the process comprising the steps of: a) providing Jatropha oil; b) pretreating the Jatropha oil to reduce the amounts of potassium and iron contained therein; and c) catalytically hydrodeoxygenating the pretreated Jatropha oil to obtain the cracker feedstock.

[0013] Iron and potassium have been found, individually and cooperatively, to be major catalyst poisons for hydrodeoxygenating catalysts. Advantageously, the process of the invention ensures that the quality of the Jatropha oil is adequate in terms of its impurity profile, especially regarding iron and potassium, for use in a hydrodeoxygenation process. In other words, the process of the invention allows for providing pretreated Jatropha oil which avoids or minimizes poisoning of a hydrodeoxygenation catalyst when the Jatropha oil being subjected to a hydrodeoxygenation process. This results in enhanced hydrodeoxygenation in the inventive process for the manufacture of a cracker feedstock. Hence, the availability and usability of Jatropha oil as a raw material for steam cracker feedstocks is improved.Step a)

[0014] Step a) of the method of the invention relates to providing Jatropha oil. Methods for producing Jatropha oil are known in the art and, e.g., described in A. Lang et al., "Jatropha oil production for biodiesel and other products - a study of issues involved in production at large scale" (2013), SD-ARC-WBA-G09-002 / 2013, or in S. Yahaya et al., Int. J. ChemTech Res. 2016, 9, 758-770.

[0015] Generally, different methods can be used to obtain Jatropha oil from Jatropha seeds. Common methods used for the extraction of Jatropha oil include mechanical pressing, chemical extraction ("solvent extraction"), supercritical extraction, and enzyme-based extraction. Mechanical pressing, chemical extraction are preferred.

[0016] In the mechanical pressing method, Jatropha seeds are subjected to mechanical pressing. Any suitable device for removing oil from seeds by pressing may be used, e.g. a hydraulic press. Generally, pressing of the seeds is carried out in a pressing chamber at high pressures in the range of from 20 to 70 MPa. For improving oil recovery, the pressing chamber may be heated to a temperature in the range of from 60 to 120 °C, e.g. using an electrical-resistance heating ring attached around the pressing chamber. Suitable pressing times are in the range of from 1 to 30 min. For improving oil recovery, a twin screw press with an operating pressure in the range of from 5 to 25 MPa may be used. The mechanical pressing method is the most widely used method and is advantageous due to its low initial and operational cost, and because it can be easily operated, even by semi-skilled personnel.

[0017] For carrying out the solvent extraction method, the Jatropha seeds are typically de-shelled, and the de-shelled seeds may be subjected to milling to obtain milled Jatropha seeds having a particle size in the range of from 0.5 to 0.8 mm. The milled Jatropha seeds are then extracted using a solvent such as n-hexane. Extraction may suitably be carried out at a solvent-to-solid ratio in the range of from 50:1 to 1:1, preferably about 6:1. Suitable extraction times are in the range of from 30 min to 24 h, preferably about 7 h. Suitable extraction temperatures are in the range of from 40 to 70 °C. Said method has several advantages in comparison to mechanical pressing, especially in obtaining higher yields of oil being less turbid.

[0018] Prior to step a), it may be suitable to subject the Jatropha seeds to a drying step. Drying may be carried out by exposing Jatropha seeds to sunlight, e.g. for 1 h to 10 d.Step b)

[0019] Jatropha curcas has the ability to phytoextract high amounts of heavy metals such as arsenic, iron, potassium, calcium, magnesium etc. from the soil, and, thus, can be regarded as a hyperaccumulator plant. Jatropha oil prepared from Jatropha seeds has thus been found to contain relevant amounts of iron (see, e.g., R. Kumar et al., Green Chem. 2010, 12, 2232-2239; D. Singh et al., Fuel 2021, 285, 119110), and potassium (see, e.g., S.-Y. Chen et al., Eur. J. Lipid Sci. Technol. 2015, 117, 1079-1087).

[0020] It has been found that it may be desirable to reduce the amounts of iron and potassium in Jatropha oil prior to subjecting the Jatropha oil to a hydrodeoxygenating step. Therefore, step b) of the method of the invention relates to pretreating the Jatropha oil obtained in step a) to reduce the amounts of potassium and iron contained therein.

[0021] For the pretreating step to reduce the amounts of potassium and iron contained in Jatropha oil, any measure for removing metal(s) from plant oils may be used.

[0022] In an embodiment, step b) comprises at least one of b-1) a degumming step, and b-2) a bleaching step.

[0023] Degumming is used to remove phospholipids, waxes, trace metals, mucilaginous materials and other impurities from oils such as plant oils and / or fats. During degumming, phosphatides are converted to hydrated gums which are insoluble in oils / fats and may readily be separated as a sludge by settling, filtering or centrifugal action. The lipid handbook, edited by Frank D. Gunstone et al., chapter 3.4 describes degumming processes in further detail. Typically, the degumming step b-1) involves treating the Jatropha oil with a degumming agent, and heating.

[0024] Preferably, the degumming agent is selected from water, aqueous salt solutions, enzymes, caustic soda, and aqueous acids. Acid degumming using acid as degumming agent and enzymatic degumming using enzymes as degumming agent are preferred processes for step b-1).

[0025] Acid degumming involves treating Jatropha oil obtained in step a) with an aqueous acid, preferably with a diluted aqueous acid. The acid may be selected from phosphoric acid, citric acid and maleic acid. Phosphoric acid and citric acid are especially preferred. This is as they are sufficiently strong and bind divalent metal ions. Suitably, phosphoric acid is used in a concentration in the range of from 0.05 to 1.2 wt.-%. Suitably, citric acid is used in a concentration in the range of from 5 to 10 wt.-%.

[0026] Acid degumming as step b-1) involves mixing the aqueous acid with the Jatropha oil, stirring the mixture, and heating the mixture to a temperature in the range of from 70 to 90 °C. Suitable reaction times are in the range of from 15 to 45 min. Residual acid is suitably neutralized by adding a base such as aqueous NaOH, followed by removing gums by centrifugation and washing with water. Further impurities such as trace metals are removed together with the gums during acid degumming. The process equipment used for acid degumming and neutralization includes any suitable device, e.g., a Continuous Stirrer Tank Reactor (CSTR), a high shear mixer, and a disk stack centrifuge.

[0027] Enzymatic degumming involves adding an enzyme such as phospholipase A1 to Jatropha oil. Degumming enzymes convert phospholipids into lysophospholipids and free fatty acids. Further impurities such as trace metals are removed together with the phospholipids during enzymatic degumming.

[0028] Enzymatic degumming as step b-1) involves adjusting the pH value of the Jatropha oil using a buffer, the pH value being in the range of from 4.8 to 6.5, adding the degumming enzyme to the Jatropha oil, and separating of sludge. The process equipment used for enzymatic degumming includes high shear mixers and disk stack centrifuges.

[0029] Generally, bleaching allows for reducing color bodies such as chlorophyll, residual soap and gums, trace metals and oxidation products from oils subjected to bleaching. Typically, the bleaching step b-2) involves contacting the Jatropha oil with a bleaching clay, and heating. Jatropha oil obtained in step a) or step b-1) may be subjected the bleaching step b-2).

[0030] Bleaching clays (also referred to as "bleaching earths" or "Fuller's earth") are typically composed of one or more of the following types of clay minerals: calcium montmorillonite, attapulgite, and sepiolite. Any suitable natural or activated bleaching clay may be used in step b-2), including neutral and acid activated clays (e.g. bentonite).

[0031] In step b-2), for example, 0.5 to 5 wt.-% of bleaching clay, optionally together with up to 1 wt.-% of activated carbon, may be contacted with Jatropha oil, based on the weight of the Jatropha oil.

[0032] Jatropha oil is suitably contacted with the bleaching clay for 15 to 45 min, preferably 20 to 40 min, before the bleaching clay is separated, typically by filtration.

[0033] The oil is typically contacted with the bleaching clay at a temperature in the range of from 80 to 125 °C, preferably 90 to 110 °C.

[0034] Following an initial period of contacting ("wet bleaching") conducted under atmospheric pressure, a second stage of the bleaching process may be conducted under reduced pressure ("dry bleaching"), for example at 2 to 3 kPa (20 to 30 mbar).

[0035] As described above, it has been found that it may be desirable to reduce the amounts of iron and potassium in Jatropha oil prior to subjecting the Jatropha oil to a hydrodeoxygenating step. Step b) allows for reducing the amounts of iron and potassium contained in the Jatropha oil. It may furthermore be desirable to determine the contents of metal impurities in the Jatropha oil to be subjected to step c). Therefore, in an embodiment, the process additionally comprises determining the amounts of potassium and iron prior and / or after step b). This means that specific measures are taken to determine the amounts of potassium and iron. It may be desirable to repeat the determination of the amounts of potassium and iron, e.g. in a case where the amounts of potassium and iron in the Jatropha oil exceed a certain threshold above which the hydrodeoxygenation catalyst might be at risk to be deactivated. In other words, determining the amounts of potassium and iron prior and / or after step b) allows for reducing the risk of hydrodeoxygenation catalyst deactivation.

[0036] Determining the amounts of iron may be carried out by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), e.g. using a PS-3000UV device, available from Leeman Labs Inc., USA (see R. Kumar et al., Green Chem. 2010, 12, 2232-2239).

[0037] Determining the amounts of potassium may be carried out according to prEN 14538 by inductively coupled plasma-optic emission spectrometry (ICP-OES), e.g. using a OptimaTM 8000 ICP-OES device, available from PerkinElmer, Inc. (see S.-Y. Chen et al., Eur. J. Lipid Sci. Technol. 2015, 117, 1079-1087; and references 5 to 7 cited therein).

[0038] In an embodiment, the pretreated Jatropha oil comprises concentrations of potassium and iron being below tolerable nonzero concentrations of potassium and iron. The tolerable concentration may be determined by means of a test. The tolerable concentration is the highest concentration of catalyst poison at which an adequate service time of the hydrodeoxygenation catalyst is still achieved. At some point, further reduction of concentrations of potassium and iron will reach a point of diminishing returns, when the effort and resources that are expended to further remove potassium and iron are no longer producing significant improvements in catalyst service live.

[0039] In an embodiment, the pretreated Jatropha oil comprises less than 1 ppm of potassium and iron. Such low amounts of less than 1 ppm of potassium and iron are tolerable as they do not result in excessive catalyst deactivation, e.g. of hydrodeoxygenation catalysts.

[0040] Besides potassium and iron, also calcium and magnesium as metal impurities have also been found to affect catalyst activity, e.g. of hydrodeoxygenation catalysts. Thus, in an embodiment, step b) additionally comprises reducing the amounts of calcium and magnesium contained in the Jatropha oil.

[0041] As outlined above, it may be desirable to determine the contents metal impurities in the Jatropha oil to be subjected to step c). Therefore, in an embodiment, the process additionally comprises determining the amounts of calcium and magnesium prior and / or after step b). This means that specific measures are taken to determine the amounts of calcium and magnesium. It may be desirable to repeat the determination of the amounts of calcium and magnesium, e.g. in a case where the amounts of calcium and magnesium in the Jatropha oil exceed a certain threshold above which the hydrodeoxygenation catalyst might be at risk to be deactivated. In other words, determining the amounts of calcium and magnesium prior and / or after step b) allows for reducing the risk of hydrodeoxygenation catalyst deactivation.

[0042] Determining the amounts of calcium and magnesium may be carried out according to prEN 14538 by inductively coupled plasma-optic emission spectrometry (ICP-OES), e.g. using a OptimaTM 8000 ICP-OES device, available from PerkinElmer, Inc. (see S.-Y. Chen et al., Eur. J. Lipid Sci. Technol. 2015, 117, 1079-1087; and references 5 to 7 cited therein).

[0043] In an embodiment, the pretreated Jatropha oil comprises less than 1 ppm of calcium and magnesium. Such low amounts of less than 1 ppm of calcium and magnesium are tolerable as they do not result in excessive catalyst deactivation, e.g. of hydrodeoxygenation catalysts.Step c)

[0044] Step c) of the method of the invention relates to catalytically hydrodeoxygenating the pretreated Jatropha oil to obtain the cracker feedstock. "Catalytic hydrodeoxygenation (HDO)" of the pretreated Jatropha oil, i.e. of a feedstock comprising triglycerides, fatty acids and fatty acid derivatives, refers to the removal of carboxyl oxygen atoms as water by means of molecular hydrogen under the influence of a catalyst. The hydrodeoxygenation may be accompanied by hydrodesulfurisation, hydrodenitrification, and / or hydrodechlorination reactions. Hydrodeoxygenation of bio-oils is known in the art, see, e.g., Brännström et al., Bioenerg. Res. 2018, 11, 592-613. Several process conditions for hydrodeoxygenation are known.

[0045] In an embodiment, step c) comprises contacting the pretreated Jatropha oil with a hydrodeoxygenating catalyst. Suitable hydrodeoxygenation catalysts for hydrodeoxygenating the pretreated Jatropha oil are selected from sulfided metal catalyst and metal sulfide catalysts. The metal may comprise one or more Group VI metals, such as Mo or W, or one or more Group VIII non-noble metals such as Co or Ni. The catalyst may be supported on any convenient support, such as alumina, silica, zirconia, titania, amorphous carbon, zeolite, molecular sieves or combinations thereof. Usually, the metal is impregnated or deposited on the support as metal oxides and then typically converted into their sulfides.

[0046] Examples of typical hydrodeoxygenation catalysts are molybdenum containing catalysts, NiMo, CoMo, or NiW catalysts, supported on alumina or silica, but many other hydrodeoxygenation catalysts are known in the art, and have been described together with or compared to NiMo and / or CoMo catalysts, in particular noble metal-based catalysts, such as Rh / C, Rh / ZrO 2 , Ru / C, Pt / SiO 2 , Pd / C, and Pd / Al 2 O 3 . Preferred hydrodeoxygenation catalysts are selected from sulfided NiMo or sulfided CoMo or NiW catalysts. In an especially preferred embodiment, the hydrodeoxygenating catalyst is selected from a nickel-molybdenum catalyst, a cobalt-molybdenum catalyst, a ruthenium catalyst, and a palladium catalyst.

[0047] Hydrodeoxygenation is carried out in the presence of hydrogen. Hydrodeoxygenation may be performed under a hydrogen pressure from 10 to 200 barg (bar gauge). Hydrodeoxygenation may be performed at temperatures in the range of from 200 to 400 °C. Hydrodeoxygenation may be performed at liquid hourly space velocities in the range of from 0.2 to 10 h -1< .

[0048] Effective conditions for hydrodeoxygenation may reduce the oxygen content (as determined via ASTM D 5622-24) of the pretreated Jatropha oil to less than 1.0 wt.-%, such as less than 0.7 wt.-%, preferably less than 0.5 wt.-%. Thus, in an embodiment, the cracker feedstock comprises less than 500 ppm, preferably less than 300 ppm, more preferably less than 100 ppm, of oxygen-containing compounds (i.e., oxygenates as determined via ASTM D 4815).

[0049] The oxygen-containing compounds may be selected from mono-, di-, and triglycerides of fatty acids, glyercol, and fatty acids, and mixtures thereof, mainly they are triglycerides of fatty acids. In the case of the oxygen-containing compounds being triglycerides of fatty acids, hydrodeoxygenation primarily yields C 14 to C 18 paraffins.

[0050] The hydrodeoxygenation may be accompanied by hydrodesulfurisation, hydrodearomatization, hydrodenitrification, and / or hydrodechlorination reactions.

[0051] Preferably, the cracker feedstock obtained in step c) contains less than 1 ppm of iron, more preferably less than 10 ppb, most preferably less than 1 ppb.

[0052] The present invention further relates to a process for the operation of a cracker, the process comprising the steps of: a) providing Jatropha oil; b) pretreating the Jatropha oil to reduce the amounts of potassium and iron contained therein; c) catalytically hydrodeoxygenating the pretreated Jatropha oil to obtain the cracker feedstock; and d) subjecting the cracker feedstock to a cracking process which produces a cracked gas.

[0053] Steps a) to c) of this process may be carried out as described above.Step d)

[0054] Step d) of the method of the invention relates to a cracking process. More specifically, step d) relates to subjecting the cracker feedstock obtained according to steps a) to c) to a cracking process which produces a cracked gas. Cracking is a petrochemical process wherein saturated hydrocarbons having long molecular structures are broken down, i.e. cracked, into smaller saturated or unsaturated molecules. Generally, crackers aim at producing light alkenes as valuable products, especially ethylene and propylene. Cracking processes include fluid catalytic cracking (FCC) and steam cracking. In a preferred embodiment, the cracking process is a steam cracking process.Steam cracking

[0055] Steam cracking is known in the art and, e.g., described in detail in H. Zimmermann et al., Ullmann's Encyclopedia of Industrial Chemistry, Vol. 13.

[0056] Conventional steam cracking utilizes a pyrolysis furnace which has two main sections: a convection section and a radiant section. The cracker feedstock obtained in steps a) to c) typically enters the convection section of the furnace as a liquid, wherein it is typically heated and, if necessary, vaporized by indirect contact with hot off-gas from the radiant section and by direct contact with steam. The vaporized feedstock and steam mixture is then introduced into the radiant section where the cracking takes place.

[0057] The resulting stream having a temperature typically in the range of from 500 to 650 °C enters a fired tubular reactor and is heated to a temperature typically in the range of from 700 to 900 °C for 0.1 to 0.5 s, wherein the residence time, temperature profile and partial pressure is controlled. During this short reaction time, hydrocarbons in the cracker feedstock are cracked into smaller molecules yielding light olefins such as ethylene, propylene, butylenes, other small olefins, and diolefins as major products besides methane. These reaction products suitably typically leave the radiant tube at a temperature in the range of 800 to 850 °C and are preferably cooled to a temperature typically in the range of from 550 to 650 °C within 0.02 to 0.1 s in order to prevent degradation of the highly reactive compounds by secondary reactions. Then, the resulting reaction products leave the furnace for further downstream processing.Fluid catalytic cracking

[0058] In fluid catalytic cracking (FCC), a particulate catalyst, often having a particle size in the range of from 20 to 100 µm, circulates between a cracking reactor and a catalyst regenerator. In the reactor, a hydrocarbon feed such as the cracker feedstock obtained in steps a) to c), contacts the hot, regenerated catalyst. The hot catalyst vaporizes and cracks the cracker feedstock, typically at 425 to 600 °C. The cracking reaction deposits carbonaceous hydrocarbons, which eventually turn to coke on the catalyst, thereby deactivating it. The cracked products are separated from the coked catalyst, usually with the aid of a catalyst stripper, and the stripped catalyst is then regenerated within the regenerator. A catalyst regenerator burns coke from the catalyst with oxygen containing gas, usually air. Regeneration of the catalyst by oxidation restores catalyst activity and simultaneously typically heats the catalyst to 500 to 900 °C. The heated catalyst is recycled to the cracking reactor to crack more fresh cracker feedstock. Catalytic cracking is an endothermic reaction. Suitably, the heat for cracking and vaporization of the cracker feedstock is supplied by the hot regenerated catalyst from the regenerator.Processing of the cracked gas

[0059] Herein, the designator "C x " refers to a hydrocarbon including x carbon atoms, "C x+ " refers to a hydrocarbon or mixture of hydrocarbons including x or greater carbon atoms, and "C xminus " refers to a hydrocarbon of mixture of hydrocarbons including x or fewer carbon atoms.

[0060] Usually, the resulting reaction mixture comprising light olefins such as ethylene, propylene, butylenes, other small olefins, and diolefins besides methane is separated by using a sequence of separation and chemical-treatment steps. The process typically also generates light side products such as hydrogen, carbon oxides, light saturated hydrocarbons, and water. Suitably, the resulting product-of-interest streams (hereinafter referred to as "product streams"), especially ethylene and propylene, are either used directly in downstream processes or stored in storage vessels for subsequent use or long-term storage.

[0061] As the products of interest from the cracked gas are separated, i.e., condensed or distilled out, one or more hydrocarbon-containing by-product streams, such as off-gas streams, having little commercial value remain. These streams are collectively referred to as hydrocarbon-containing by-product-streams herein. These by-product-streams contain at least one hydrocarbon which may be selected from methane, saturated hydrocarbons, in particular saturated C 2 to C 3 hydrocarbons, or C 5-9 hydrocarbons. The by-product-streams may contain hydrogen in addition to these hydrocarbons. In an embodiment, the by-product-stream includes methane as a main hydrocarbon constituent, e.g., at least 75 wt.-% of methane, preferably at least 85 wt.-% of methane, relative to the hydrocarbons comprised in the by-product-stream. These by-product-streams have conventionally been burnt as fuel gas or else recycled as feedstock to the cracker unit.

[0062] The hot cracked gas leaving the cracker is cooled down quickly in order to prevent unwanted follow-up reactions. This is usually done in several steps. In a first step, the cracked gas is cooled down to about 450 °C by heat exchangers. A further cooling step occurs via direct contact between the cracked gas and a high boiling liquid, usually referred to as quench oil. The quench results in a partial condensation of the cracked gas. In this step, a heavy stream rich in C 10+ hydrocarbons is separated from the cracked gas. A further cooling step of the cracked gas takes place in a water quench column for primary fractionation, cooling down the gas to around 30 °C. In this step, a C 5-9 fraction, commonly referred to as pyrolysis gasoline, is separated from C 4minus components.

[0063] The pyrolysis gasoline may be hydrogenated to remove olefinic unsaturation and sent to benzene extraction. Extractive benzene separation may be performed in an extractive distillation column. For this purpose, the pyrolysis gasoline or, more preferably, the hydrogenated pyrolysis gasoline, is introduced into the extractive distillation column and benzene is absorbed by means of a suitable absorbent such as N-methylpyrrolidone (NMP). In the extractive distillation column, a bottom product obtained from NMP with dissolved benzene is discharged to a benzene stripper. The overhead vapor from the extractive distillation flows to the raffinate column in order to recover NMP. The NMP with some dissolved hydrocarbons is discharged back to the extractive distillation column. The top product from the raffinate column mainly contains saturated hydrocarbons.

[0064] Hence, in a preferred embodiment, the method involves a quench of hot cracked gas with a high-boiling liquid, wherein a heavy stream comprising C 10+ hydrocarbons is separated from the cracked gas, and a water quench, wherein pyrolysis gasoline is separated from the cracked gas, optionally subjecting the pyrolysis gasoline to hydrogenation, optionally subjecting the hydrogenated pyrolysis gasoline to extractive separation of benzene.

[0065] The recovery of the various olefin products from cracked gas is usually carried out by fractional distillation using a series of distillation steps or columns to separate out the various components. The unit which separates hydrocarbons with one carbon atom (C 1 ) and lighter fraction is referred to as "demethanizer". The unit which separates hydrocarbons with two carbon atoms (C 2 ) from the heavier components is referred to as "deethanizer". The unit which separates the hydrocarbon fraction with three carbon atoms (C 3 ) from the heavier components is referred to as "depropanizer". The unit which separates the hydrocarbon fraction with four carbon atoms (C 4 ) from the heavier components is referred to as "debutanizer."

[0066] The residual heavier components having a higher carbon number fraction (C 5 +) may be used as gasoline or recycled back to the cracker.

[0067] The various fractionation units may be arranged in a variety of sequences in order to provide desired results based upon various feedstocks. To that end, a sequence which uses the demethanizer first is commonly referred to as the "front-end demethanizer" sequence. Similarly, when the deethanizer is used first, it is commonly referred to as the "front-end deethanizer" sequence. And, when the depropanizer is used first, it is commonly referred to as "front-end depropanizer" sequence.

[0068] In the conventional front-end demethanizer sequence, the cracked gas containing hydrocarbons having one to five or more carbon atoms per molecule (C 1 to C 5+ ) first enters a demethanizer, where methane and lighter fractions (hydrogen) are separated as an over-head stream. The demethanizer operates at relatively low temperatures, typically ranging from about -100 °C to about 25 °C.

[0069] The heavy ends exiting the demethanizer consist mainly of C 2 to C 5 , molecules. These heavy ends then are routed to a deethanizer where the C 2 hydrocarbons are taken over the top and the C 3 to C 5+ compounds leave as bottoms. The C 2 components leaving the top of the deethanizer may be fed to an acetylene converter or acetylene removal unit. As some methane remains dissolved in the heavy ends exiting the demethanizer and ends up in the C 2 components leaving the deethanizer, the C 2 components stream may be subsequently sent to a demethanizer for removal of the remaining methane.

[0070] The over-head stream from the demethanizer comprises methane and hydrogen as the main components. The ratio of methane and hydrogen in the over-head stream may vary depending on the cracking operation, respectively the cracking feedstock (see for example Ullmann's Encyclopedia of Industrial Chemistry, Ethylene 5.1.3 Commercial Cracking Yields, DOI: 10.1002 / 14356007.a10_045.pub3 for different cracking yields depending on different cracker feedstocks) but the methane content is generally in the range of from 40 to 95 wt.-%, preferably 90 to 95 wt.-% of methane, with the remainder being mainly hydrogen.

[0071] In an embodiment, the over-head stream is separated into a hydrogen rich stream and a methane rich stream. Preferably, the methane rich stream has a methane content of at least 96 wt.-%, more preferably at least 98 wt.-%, most preferably at least 99 -wt.%, in particular at least 99.9 wt.-%. Preferably, the hydrogen rich stream has a hydrogen content of at least 90 wt.-%, more preferably at least 95 wt.-%. The hydrogen rich stream may be subjected to combustion to provide thermal energy to the cracking process.

[0072] Separation of hydrogen and methane can be achieved by pressure swing adsorption.

[0073] The C 2 components from which methane has been removed are then sent to a C 2 splitter which produces ethylene as the light product and ethane as the heavy product. The C 3 to C 5+ stream leaving the bottom of the deethanizer is routed to a depropanizer, which sends the C 3 components overhead and the C 4 to C 5+ components below.

[0074] The C 3 product may be hydrotreated to remove C 3 acetylene and dienes before being fed to a C 3 splitter, where it is separated into propylene at the top and propane at the bottom.

[0075] Hence, in a preferred embodiment, the method comprises recovery of the product streams from the cracked gas by a series of distillation steps including a separation of saturated and unsaturated C 2 hydrocarbons in a C 2 splitter and / or separation of saturated and unsaturated C 3 hydrocarbons in a C 3 splitter.

[0076] The C 4 to C 5+ stream is fed to a debutanizer, which produces C 4 components at the top with the balance of C 5+ components leaving as bottoms. Both the C 4 and the C 5+ streams may be separately hydrotreated to remove undesirable acetylenes and dienes.

[0077] In conventional front-end deethanizer sequences, the cracked gas containing C 1 to C 5+ components first enters a deethanizer. The light ends exiting the deethanizer consist of C 2 and C 1 components along with any hydrogen (C 2minus fraction). These light ends are fed to a demethanizer (C 2minus demethanizer) where the hydrogen and C 1 are removed as light ends and the C 2 components are removed as heavy ends. The C 2 stream leaving the bottom of the demethanizer may be fed to an acetylene converter and then to a C 2 splitter which produces ethylene as the light product and ethane as the heavy product. The heavy ends exiting the deethanizer which consist of C 3 to C 5+ components are routed to a depropanizer which sends the C 3 components over-head and the C 4 to C 5+ components below. The C 3 product is fed to a C 3 splitter where it is separated into propylene at the top and propane at the bottom, while the C 4 to C 5+ stream is fed to a debutanizer which produces C 4 compounds at the top with the balance leaving as bottoms to be used for gasoline or to be recirculated as feed into the cracking process. As with the front-end demethanizer sequence, the C 3 , C 4 , and C 5+ streams may be separately hydrotreated to remove undesirable acetylenes and dienes.

[0078] In conventional front-end depropanizer sequences, the quenched and acid-free gases containing hydrocarbons having from one to five or more carbon atoms per molecule (C 1 to C 5+ ) first enter a depropanizer. The heavy ends exiting the depropanizer consist of C 4 to C 5+ components. These are routed to a debutanizer where the C 4 components and lighter species are taken over the top with the rest of the feed leaving as bottoms which can be used for gasoline or other chemical recovery. These streams may be separately hydrotreated to remove undesired acetylenes and dienes. The tops of the depropanizer, containing C 1 to C 3 components, may be fed to an acetylene converter and then to a demethanizer system, where the C 1 components and any remaining hydrogen are removed as an over-head. The heavy ends exiting the demethanizer system, which contains C 2 and C 3 components, are introduced into a deethanizer wherein C 2 components are taken off the top and C 3 compounds are taken from the bottom. The C 2 components are, in turn, fed to a C 2 splitter which produces ethylene as the light product and ethane as the heavy product. The C 3 stream is fed to a C 3 splitter which separates the C 3 species, sending propylene to the top and propane to the bottom.

[0079] The saturated C 2 hydrocarbons and / or the saturated C 3 hydrocarbons or a partial stream thereof may be recycled as feed into the cracking process.Cracker feedstock

[0080] As described above, step d) involves subjecting the cracker feedstock obtained in steps a) to c) to a cracking process. Besides the cracker feedstock obtained in steps a) to c), at least one further hydrocarbon-containing feed stream may be introduced into the cracker. The at least one further hydrocarbon-containing feed stream may originate from upstream refinery processes such as an atmospheric distillation tower, hydrocracker, coker etc. The at least one further hydrocarbon-containing feed stream typically contains naphtha, liquefied petroleum gas (LPG), ethane, propane and / or butane. Alternatively or additionally, it may contain natural gas, recyclate, bio-based gas, bio-naphtha, and / or bio-liquefied petroleum gas (bio-LPG).

[0081] The term "natural gas" encompasses a naturally occurring mixture of gaseous hydrocarbons which primarily consists of methane in addition to small amounts of other higher alkanes such as ethane, propane etc.

[0082] The term "recyclate" encompasses pyrolysis oils obtained by pyrolysis of recycled plastic waste materials.

[0083] The term "bio-based gas" encompasses is a mixture of gases, primarily consisting of methane besides carbon dioxide and hydrogen sulfide which is produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, food waste etc.

[0084] The term "naphtha" encompasses liquid hydrocarbon mixtures produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat.

[0085] The term "bio-naphtha" encompasses naphtha produced from complex mixtures of naturally occurring fats and oils.

[0086] The term "liquefied petroleum gas (LPG)" encompasses a fuel gas containing a flammable mixture of hydrocarbon gases, in particular propane and butane. Liquefied petroleum gas is prepared by refining petroleum or "wet" natural gas.

[0087] The term "bio-liquefied petroleum gas (bio-LPG)" encompasses liquefied petroleum gas produced from complex mixtures of naturally occurring fats and oils.

Claims

1. Process for the manufacture of a cracker feedstock, the process comprising the steps of: a) providing Jatropha oil; b) pretreating the Jatropha oil to reduce the amounts of potassium and iron contained therein; and c) catalytically hydrodeoxygenating the pretreated Jatropha oil to obtain the cracker feedstock.

2. The process according to claim 1, additionally comprising determining the amounts of potassium and iron prior and / or after step b).

3. The process according to claim 1 or 2, wherein the pretreated Jatropha oil comprises less than 1 ppm of potassium and less than 1 ppm of iron.

4. The process according to any one of the preceding claims, wherein step b) additionally comprises reducing the amounts of calcium and magnesium contained in the Jatropha oil.

5. The process according to claim 4, additionally comprising determining the amounts of calcium and magnesium prior and / or after step b).

6. The process according to claim 4 or 5, wherein the pretreated Jatropha oil comprises less than 1 ppm of calcium and less than 1 ppm of magnesium.

7. The process according to any one of the preceding claims, wherein step b) comprises at least one of b-1) a degumming step, and b-2) a bleaching step.

8. The process according to claim 7, wherein the degumming step b-1) involves treating the Jatropha oil with a degumming agent, and heating, the degumming agent preferably being selected from water, aqueous salt solutions, enzymes, caustic soda, and diluted acids.

9. The process according to claim 7 or 8, wherein the bleaching step b-2) involves contacting Jatropha oil with a bleaching clay, and heating.

10. The process according to any one of the preceding claims, wherein the cracker feedstock comprises less than 500 ppm of oxygen-containing compounds.

11. The process according to claim 10, wherein the oxygen-containing compounds are selected from mono-, di-, and triglycerides of fatty acids, glyercol, and fatty acids, and mixtures thereof.

12. The process according to any one of the preceding claims, wherein step c) comprises contacting the pretreated Jatropha oil with a hydrodeoxygenating catalyst.

13. The process according to claim 12, wherein the hydrodeoxygenating catalyst is selected from a nickel-molybdenum catalyst, a cobalt-molybdenum catalyst, a ruthenium catalyst, and a palladium catalyst.

14. Process for the operation of a cracker, the process comprising the steps of: a) providing Jatropha oil; b) pretreating the Jatropha oil to reduce the amounts of potassium and iron contained therein; c) catalytically hydrodeoxygenating the pretreated Jatropha oil to obtain the cracker feedstock; and d) subjecting the cracker feedstock to a cracking process which produces a cracked gas.

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