WO2022079057A1

WO2022079057A1 - Recovery of aliphatic hydrocarbons

Info

Publication number: WO2022079057A1
Application number: PCT/EP2021/078225
Authority: WO
Inventors: Jean-Paul Andre Marie Joseph Ghislain LANGE; Guus VAN ROSSUM; Willem Derks; Kai Jürgen FISCHER; Timothé Johannes OLTHOF; Johannes Pieter Haan
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2020-10-16
Filing date: 2021-10-12
Publication date: 2022-04-21

Abstract

The invention relates to a process for the recovery of aliphatic hydrocarbons from a liquid stream comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons, involving a) liquid-liquid extraction of said liquid stream with an extraction solvent; b) mixing the extract stream, comprising extraction solvent, heteroatom containing organic compounds and optionally aromatic hydrocarbons, with a demixing solvent to remove heteroatom containing organic compounds and optional aromatic hydrocarbons; and c) membrane separation of the remaining stream into a demixing solvent containing permeate stream and an extraction solvent containing retentate stream. Further, the invention relates to a process for the recovery of aliphatic hydrocarbons from plastics comprising the above-mentioned process; and to a process for steam cracking a hydrocarbon feed comprising aliphatic hydrocarbons as recovered in one of the above-mentioned processes.

Description

RECOVERY OF ALIPHATIC HYDROCARBONS Field of the invention The present invention relates to a process for the recovery of aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons; to a process for the recovery of aliphatic hydrocarbons from plastics comprising the above- mentioned process; and to a process for steam cracking a hydrocarbon feed comprising aliphatic hydrocarbons as recovered in one of the above-mentioned processes. Background of the invention Waste plastics can be converted via cracking of the plastics, for example by pyrolysis, to high-value chemicals, including olefins and aromatic hydrocarbons. Pyrolysis of plastics can yield product streams containing hydrocarbons in a wide boiling range. Hydrocarbons from such pyrolysis product streams can be further cracked in a steam cracker to produce high-value chemicals, including ethylene and propylene which are monomers that can be used in making new plastics. WO2018069794 discloses a process for producing olefins and aromatic hydrocarbons from plastics wherein a liquid pyrolysis product stream is separated into a first fraction having a boiling point <300 °C and a second fraction having a boiling point ≥300 °C. Only said first fraction is fed to a liquid steam cracker, whereas said second fraction is recycled to the pyrolysis unit. In the process shown in Figure 1 of WO2018069794, said separation is performed in a hydrocarbon liquid distillation unit. Having to separate the liquid pyrolysis product stream into two fractions is cumbersome (e.g. energy intensive). A further disadvantage is that the heavier portion of the liquid pyrolysis product stream has to be sent back to the pyrolysis unit for a deeper pyrolysis. This results in yield loss through the formation of gas and an increasing amount of solid side-product (coke) which is eventually not sent to the steam cracker. In one embodiment of the process of above-mentioned WO2018069794 (see Figure 2), the first fraction having a boiling point <300 °C is first conveyed together with hydrogen to a hydroprocessing unit to produce a treated hydrocarbon liquid stream which is then fed to the liquid steam cracker. Such hydroprocessing is also cumbersome, as it is capital intensive and requires the use of expensive hydrogen (H₂). Further, US20180355256 discloses a method for deriving fuel from plastics, the method comprising subjecting a quantity of plastics to a pyrolytic process, thereby to convert at least part of the plastics to a crude fuel; and extracting the fuel in a directly usable form by way of: 1) a first extraction step comprising counterflow liquid-liquid extraction using one or more extraction solvents to extract one or more impurities from the crude fuel; and 2) a second extraction step comprising counterflow extraction of resultant contaminated extraction solvent(s) from the first extraction step. In the process as shown in Figure 2 of US20180355256, a crude fuel (i.e. a crude diesel) that is made by pyrolysis of plastics, is first subjected to extraction with N-methyl-2-pyrrolidone (NMP) to extract one or more impurities, including sulfur compounds and aromatics, from the crude fuel. The contaminated NMP from the first extraction step is then subjected to a second extraction step using water, to increase the polarity of the contaminated extraction solvent, thereby separating off said impurities. In a final step, the water-contaminated NMP from the second extraction step is distilled using a standard distillation column, which gives rise to recycle water and recycle NMP. Such distillation is cumbersome, because it is energy intensive, requiring a significant heating duty to evaporate water and a temperature of greater than 110 °C when performed at atmospheric pressure. In addition, the feed to the distillation column as disclosed in above-mentioned US20180355256 (Figure 2) may still comprise a certain amount of heteroatom containing organic contaminants and aromatic contaminants. Said distillation may result in that part of said contaminants is separated off together with the recycle water because water and such contaminants may form an azeotrope, thereby reducing the quality of the water recycle stream. In case that recycle water is recycled to the column used in the second extraction step, the concentration of these contaminants in the recycle water will increase in what is denominated “build-up”, in addition to a build-up of these contaminants in the recycle NMP to be used in the first extraction step. This can result in a lower efficiency of the first and second extraction steps. US20180355256 concerns a method for deriving fuel from plastics. Such build-up of these contaminants (in said recycle NMP) may result in that the cleaned oil still comprises a relatively high amount of these contaminants, which is of particular concern when such cleaned oil would be fed to a steam cracker, instead of being used as a fuel, because of the negative impact of these contaminants on the yield, selectivity and reliability of steam crackers. There is an ongoing need to develop improved processes for the recovery of aliphatic hydrocarbons from liquid streams comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons which may originate from cracking waste plastics, in specific mixed waste plastics, especially before feeding such recovered aliphatic hydrocarbons to a steam cracker. It is an object of the present invention to provide such process for the recovery of aliphatic hydrocarbons from such liquid streams, which process is technically advantageous, efficient and affordable, in particular a process which does not have one or more of the above- mentioned disadvantages, as discussed above in connection with WO2018069794 and US20180355256. Such technically advantageous process would preferably result in a relatively low energy demand and/or relatively low capital expenditure. Summary of the invention Surprisingly it was found by the present inventors that such process can be provided by a) liquid-liquid extraction of a liquid stream which comprises aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons, with an extraction solvent a) which contains one or more heteroatoms; b) mixing a stream resulting from step a) which comprises extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons, with a demixing solvent b) to remove heteroatom containing organic compounds and optional aromatic hydrocarbons, wherein demixing solvent b) contains one or more heteroatoms and has a miscibility in heptane which is lower than the miscibility of extraction solvent a) in heptane; and c) membrane separation of a stream resulting from step b) which comprises extraction solvent a) and demixing solvent b), and recovering a permeate stream comprising demixing solvent b) and a retentate stream comprising extraction solvent a). Accordingly, the present invention relates to a process for the recovery of aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons, said process comprising the steps of: a) contacting at least part of the liquid hydrocarbon feedstock stream with an extraction solvent a) which contains one or more heteroatoms and subjecting the liquid hydrocarbon feedstock stream to liquid-liquid extraction with the extraction solvent a), resulting in a first stream comprising aliphatic hydrocarbons and a second stream comprising extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons; b) mixing at least part of the second stream resulting from step a) with a demixing solvent b) which contains one or more heteroatoms and has a miscibility in heptane which is lower than the miscibility of extraction solvent a) in heptane, and separating the resulting mixture into a first stream comprising heteroatom containing organic compounds and optionally aromatic hydrocarbons and a second stream comprising extraction solvent a) and demixing solvent b); c) contacting at least part of the second stream resulting from step b) with a membrane and recovering a permeate stream comprising demixing solvent b) and a retentate stream comprising extraction solvent a); d) recycling at least part of the extraction solvent a) from the retentate stream resulting from step c) to step a); and e) optionally recycling at least part of the demixing solvent b) from the permeate stream resulting from step c) to step b). Advantageously, in the present invention, there is no need for hydrotreating (treatment with H₂) because of said liquid-liquid extraction in step a). Furthermore, advantageously, a liquid hydrocarbon stream having a wide boiling range, such as plastics pyrolysis oil, may be treated in the present process with a relatively low yield loss and feed degradation. This implies that the costs of a hydrocarbon feed to a steam cracker may be reduced considerably by applying the present invention. Further, advantageously, because of the membrane separation in step c) of the present process, significant energy savings can be made as compared to a process wherein the separation method applied to the stream resulting from step b) and comprising extraction solvent a), such as N- methyl-2-pyrrolidone (NMP), and demixing solvent b), such as water, would consist of distillation only, as disclosed in above-mentioned US20180355256. Still further, heteroatom containing organic compounds and any aromatic hydrocarbons may eventually partition into the stream comprising extraction solvent a) and demixing solvent b) resulting from step b) of the present process. Said heteroatom containing organic compounds and aromatic compounds may comprise the components with the highest polarity of all the heteroatom containing organic compounds and aromatic compounds as extracted in step a) of the present process. In such case, advantageously, the membrane separation in step c) can then still deliver a relatively pure demixing solvent b) containing permeate stream that is substantially free of heteroatom containing organic compounds and aromatic hydrocarbons. In turn, such pure demixing solvent b) stream can then advantageously be recycled and used to extract extraction solvent a), either in step a) itself or in another additional step, thereby preventing extraction solvent a) from entering the final hydrocarbon raffinate stream, without contaminating such raffinate stream with heteroatom containing organic compounds and aromatic hydrocarbons. This latter benefit would not materialise if distillation is applied as the only separation method to separate demixing solvent b) from extraction solvent a), as disclosed in above-mentioned US20180355256, in which distillation water will entrain any heteroatom containing organic compounds and aromatic compounds that form an azeotrope with water. Thus, in the present invention, using a demixing solvent b)-permeating membrane in step c) will advantageously concentrate any heteroatom containing organic compounds and optional aromatic hydrocarbons not removed in step b), into the extraction solvent a)-rich retentate. These heteroatom containing organic compounds and optional aromatic hydrocarbons can be recycled together with the extraction solvent a) to extraction step a) and eventually equilibrate (steady state), that is to say removed in following step b). Further, the present invention relates to a process for the recovery of aliphatic hydrocarbons from plastics, wherein at least part of the plastics comprises heteroatom containing organic compounds, said process comprising the steps of: (I) cracking the plastics and recovering a hydrocarbon product comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons; and (II) subjecting a liquid hydrocarbon feedstock stream, which comprises at least part of the hydrocarbon product obtained in step (I), to the above-mentioned process for the recovery of aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream. Still further, the present invention relates to a process for steam cracking a hydrocarbon feed, wherein the hydrocarbon feed comprises aliphatic hydrocarbons as recovered in one of the above-mentioned processes for the recovery of aliphatic hydrocarbons. Brief description of the drawings Figure 1 shows one embodiment of the process for the recovery of aliphatic hydrocarbons in accordance with the present invention. Figures 2 and 3 show two other embodiments of the above- mentioned process. Detailed description of the invention Each of the processes of the present invention comprises multiple steps. In addition, said process may comprise one or more intermediate steps between consecutive steps. Further, said process may comprise one or more additional steps preceding the first step and/or following the last step. For example, in a case where said process comprises steps a), b) and c), said process may comprise one or more intermediate steps between steps a) and b) and between steps b) and c). Further, said process may comprise one or more additional steps preceding step a) and/or following step c). Within the present specification, a phrase like “step y) comprises subjecting at least part of the stream resulting from step x) to” means “step y) comprises subjecting part or all of the stream resulting from step x) to” or, similarly, “step y) comprises partially or completely subjecting the stream resulting from step x) to”. For example, the stream resulting from step x) may be split into one or more parts wherein at least one of these parts may be subjected to step y). Further, for example, the stream resulting from step x) may be subjected to an intermediate step between steps x) and y) resulting in a further stream at least part of which may be subjected to step y). While the process(es) of the present invention and the stream(s) and composition(s) used in said process(es) are described in terms of “comprising”, “containing” or “including” one or more various described steps and components, respectively, they can also “consist essentially of” or “consist of” said one or more various described steps and components, respectively.”. In the context of the present invention, in a case where a stream comprises two or more components, these components are to be selected in an overall amount not to exceed 100%. Further, where upper and lower limits are quoted for a property then a range of values defined by a combination of any of the upper limits with any of the lower limits is also implied. Within the present specification, by “substantially no” in relation to the amount of a specific component in a stream, it is meant an amount which is at most 1,000, preferably at most 500, more preferably at most 100, more preferably at most 50, more preferably at most 30, more preferably at most 20, and most preferably at most 10 ppmw (parts per million by weight) of the component in question, based on the amount (i.e. weight) of said stream. Within the present specification, by “top stream” or “bottom stream” from a column reference is made to a stream which exits the column at a position, which is between 0% and 30%, more suitably between 0% and 20%, even more suitably between 0% and 10%, based on the total column length, from the top of the column or the bottom of the column, respectively. Unless indicated otherwise, where in the present specification reference is made to a boiling point this means the boiling point at 760 mm Hg pressure (101.3 kPa). Liquid hydrocarbon feedstock stream In the present invention, the liquid hydrocarbon feedstock stream comprises aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons. Preferably, the liquid hydrocarbon feedstock stream comprises both aliphatic hydrocarbons having a boiling point of from 30 to 300 °C and aliphatic hydrocarbons having a boiling point of from greater than 300 to 600 °C in a weight ratio of from 99:1 to 1:99. The amount of aliphatic hydrocarbons having a boiling point of from 30 to 300 °C, based on the total amount of aliphatic hydrocarbons having a boiling point of from 30 to 600 °C, may be at most 99 wt.% or at most 80 wt.% or at most 60 wt.% or at most 40 wt.% or at most 30 wt.% or at most 20 wt.% or at most 10 wt.%. Further, the amount of aliphatic hydrocarbons having a boiling point of from 30 to 300 °C, based on the total amount of aliphatic hydrocarbons having a boiling point of from 30 to 600 °C, may be at least 1 wt.% or at least 5 wt.% or at least 10 wt.% or at least 20 wt.% or at least 30 wt.%. Thus, advantageously, the liquid hydrocarbon feedstock stream may comprise varying amounts of aliphatic hydrocarbons within a wide boiling point range of from 30 to 600 °C. Accordingly, as with the boiling point, the carbon number of the aliphatic hydrocarbons in the liquid hydrocarbon feedstock stream may also vary within a wide range, for example of from 5 to 50 carbon atoms. The carbon number of the aliphatic hydrocarbons in the liquid hydrocarbon feedstock stream may be at least 4 or at least 5 or at least 6 and may be at most 50 or at most 40 or at most 30 or at most 20. The amount of aliphatic hydrocarbons in the liquid hydrocarbon feedstock stream, based on the total weight of the liquid hydrocarbon feedstock stream, may be at least 30 wt.% or at least 50 wt.% or at least 80 wt.% or at least 90 wt.% or at least 95 wt.% or at least 99 wt.% and may be smaller than 100 wt.% or at most 99 wt.% or at most 90 wt.% or at most 80 wt.% or at most 70 wt.%. The aliphatic hydrocarbons may be cyclic, linear and branched. The aliphatic hydrocarbons in the liquid hydrocarbon feedstock stream may comprise non-olefinic (paraffinic) and olefinic aliphatic compounds. The amount of paraffinic aliphatic compounds in the liquid hydrocarbon feedstock stream, based on the total weight of the liquid hydrocarbon feedstock stream, may be at least 20 wt.% or at least 40 wt.% or at least 60 wt.% or at least 80 wt.% and may be smaller than 100 wt.% or at most 99 wt.% or at most 80 wt.% or at most 60 wt.%. Further, the amount of olefinic aliphatic compounds in the liquid hydrocarbon feedstock stream, based on the total weight of the liquid hydrocarbon feedstock stream, may be smaller than 100 wt.% or at least 20 wt.% or at least 40 wt.% or at least 60 wt.% or at least 80 wt.% and may be at most 99 wt.% or at most 80 wt.% or at most 60 wt.%. Further, the olefinic compounds may comprise aliphatic compounds having one carbon-carbon double bond (mono-olefins) and/or aliphatic compounds having two or more carbon-carbon double bonds which latter compounds may be conjugated or non- conjugated. That is to say, the two or more carbon-carbon double bonds may be conjugated or not conjugated. The aliphatic compounds having two or more carbon-carbon double bonds may include compounds having double bonds at alpha and omega positions. The amount of mono-olefins in the liquid hydrocarbon feedstock stream, based on the total weight of the liquid hydrocarbon feedstock stream, may be at least 20 wt.% or at least 40 wt.% or at least 60 wt.% or at least 80 wt.% and may be smaller than 100 wt.% or at most 99 wt.% or at most 80 wt.% or at most 60 wt.%. Further, the amount of conjugated aliphatic compounds having two or more carbon- carbon double bonds in the liquid hydrocarbon feedstock stream, based on the total weight of the liquid hydrocarbon feedstock stream, may be greater than 0 wt.% or at least 10 wt.% or at least 20 wt.% or at least 40 wt.% or at least 60 wt.% and may be at most 80 wt.% or at most 60 wt.% or at most 40 wt.%. Within the present specification, an aliphatic hydrocarbon which contains one or more heteroatoms is a “heteroatom containing organic compound” as further described below. Unless indicated otherwise, either explicitly or by context, within the present specification, the term “aliphatic hydrocarbons” does not include heteroatom containing aliphatic hydrocarbons. Further, unless indicated otherwise, either explicitly or by context, within the present specification, the term “aliphatic hydrocarbons” does not include conjugated aliphatic compounds having two or more carbon-carbon double bonds. In addition to the above-described aliphatic hydrocarbons, the liquid hydrocarbon feedstock stream comprises heteroatom containing organic compounds and optionally aromatic hydrocarbons. The amount of aromatic hydrocarbons in the liquid hydrocarbon feedstock stream, based on the total weight of the liquid hydrocarbon feedstock stream, may be 0 wt.% or greater than 0 wt.% or at least 5 wt.% or at least 10 wt.% or at least 15 wt.% or at least 20 wt.% or at least 25 wt.% or at least 30 wt.% and may be at most 50 wt.% or at most 40 wt.% or at most 30 wt.% or at most 20 wt.%. The aromatic hydrocarbons may comprise monocyclic and/or polycyclic aromatic hydrocarbons. An example of a monocyclic aromatic hydrocarbon is styrene. The polycyclic aromatic hydrocarbons may comprise non-fused and/or fused polycyclic aromatic hydrocarbons. An example of a non-fused polycyclic aromatic hydrocarbon is oligostyrene. Styrene and oligostyrene may originate from polystyrene. Examples of fused polycyclic aromatic hydrocarbons are naphthalene and anthracene, as well as alkyl naphthalene and alkyl anthracene. The aromatic ring or rings in the aromatic hydrocarbons may be substituted by one or more hydrocarbyl groups, including alkyl groups (saturated) and alkylene groups (unsaturated). Within the present specification, an aromatic hydrocarbon which contains one or more heteroatoms is a “heteroatom containing organic compound” as further described below. Unless indicated otherwise, either explicitly or by context, within the present specification, the term “aromatic hydrocarbons” does not include heteroatom containing aromatic hydrocarbons. Further, the amount of heteroatom containing organic compounds in the liquid hydrocarbon feedstock stream, based on the total weight of the liquid hydrocarbon feedstock stream, is greater than 0 wt.% and may be at least 0.5 wt.% or at least 1 wt.% or at least 3 wt.% or at least 5 wt.% or at least 10 wt.% or at least 15 wt.% or at least 20 wt.% and may be at most 30 wt.% or at most 20 wt.% or at most 10 wt.% or at most 5 wt.%. The heteroatom containing organic compounds in the liquid hydrocarbon feedstock stream contain one or more heteroatoms, which may be oxygen, nitrogen, sulfur and/or a halogen, such as chlorine, suitably oxygen, nitrogen and/or a halogen. The heteroatom containing organic compounds may comprise one or more of the following moieties: amine, imine, nitrile, alcohol, ether, ketone, aldehyde, ester, acid, amide, carbamate (occasionally named urethane) and urea. Further, the above-mentioned heteroatom containing organic compounds may be aliphatic or aromatic. An example of an aliphatic, heteroatom containing organic compound is oligomeric polyvinyl chloride (PVC). Oligomeric PVC may originate from polyvinyl chloride. Aromatic, heteroatom containing organic compounds may comprise monocyclic and/or polycyclic aromatic, heteroatom containing organic compounds. Examples of monocyclic aromatic, heteroatom containing organic compounds are terephthalic acid and benzoic acid. An example of a polycyclic aromatic, heteroatom containing organic compound is oligomeric polyethylene terephthalate (PET). Terephthalic acid, benzoic acid and oligomeric PET may originate from polyethylene terephthalate. Examples of nitrogen containing organic compounds are compounds originating from polyurethane and polyamides including nylon. Unless indicated otherwise, either explicitly or by context, within the present specification, the term “heteroatom containing organic compounds” means heteroatom containing organic compounds in or originating from the liquid hydrocarbon feedstock stream. Further, unless indicated otherwise, either explicitly or by context, within the present specification, the term “heteroatom containing organic compounds” does not include the extraction solvent, demixing solvent and/or washing solvent as defined in the present specification. Additionally, the liquid hydrocarbon feedstock stream may comprise salts. Said salts may comprise organic and/or inorganic salts. The salts may comprise ammonium, an alkali metal, an alkaline earth metal or a transition metal as the cation and a carboxylate, sulphate, phosphate or a halide as the anion. Preferably, at least part of the components in the liquid hydrocarbon feedstock stream, which comprises aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons, are synthetic compounds, and not natural compounds as present in for example fossil oil. For example, such synthetic compounds include compounds originating from the pyrolysis of plastics synthesized from biomass, for example polyethylene synthesized from bio- ethanol through dehydration of the ethanol and subsequent polymerization of the ethylene thus formed. Further, since in the present process heteroatom containing organic compounds are easily removed, the feed to the present process can advantageously tolerate a relatively high amount of such heteroatom containing organic compounds. Thus, waste plastic that may be pyrolyzed to produce a feed to the present process may comprise heteroatom-containing plastics, such as polyvinyl chloride (PVC), polyethylene terephthalate (PET) and polyurethane (PU). In specific, mixed waste plastic may be pyrolyzed that in addition to heteroatom-free plastics, such as polyethylene (PE) and polypropylene (PP), contains a relatively high amount of such heteroatom-containing plastics. Step a) – Extraction with extraction solvent a) In step a) of the present process, at least part of the liquid hydrocarbon feedstock stream, comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons, is contacted with an extraction solvent a) which contains one or more heteroatoms, and the liquid hydrocarbon feedstock stream is subjected to liquid-liquid extraction with the extraction solvent a), resulting in a first stream comprising aliphatic hydrocarbons and a second stream comprising extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons. In step a) of the present process, the liquid hydrocarbon feedstock stream may be fed to a first column (first extraction column). Further, a first solvent stream which comprises the extraction solvent a) may be fed to the first column at a position which is higher than the position at which the liquid hydrocarbon feedstock stream is fed, thereby enabling a counterflow liquid-liquid extraction and resulting in a top stream from the first column (above “first stream”) comprising aliphatic hydrocarbons and a bottom stream from the first column (above “second stream”) comprising extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons. In step a), the weight ratio of the extraction solvent a) to the liquid hydrocarbon feedstock stream may be at least 0.05:1 or at least 0.2:1 or at least 0.5:1 or at least 1:1 or at least 2:1 or at least 3:1 and may be at most 5:1 or at most 3:1 or at most 2:1 or at most 1:1. Further, the temperature in step a) may be at least 0 °C or at least 20 °C or at least 30 °C or at least 40 °C or at least 50 °C and may be at most 200 °C or at most 150 °C or at most 100 °C or at most 70 °C or at most 60 °C or at most 50 °C or at most 40 °C. The pressure in step a) may be at least 100 mbara or at least 500 mbara or at least 1 bara or at least 1.5 bara or at least 2 bara and may be at most 50 bara or at most 30 bara or at most 20 bara or at most 15 bara or at most 10 bara or at most 5 bara or at most 3 bara or at most 2 bara or at most 1.5 bara. The temperature and pressure in step a) are preferably such that both the hydrocarbons from the feedstock stream and the extraction solvent a) are in the liquid state. In step a), aliphatic hydrocarbons are recovered by liquid-liquid extraction of heteroatom containing organic compounds and optionally aromatic hydrocarbons with extraction solvent a). Further, preferably, the recovered aliphatic hydrocarbons comprise aliphatic hydrocarbons having a boiling point of from 30 to 300 °C and aliphatic hydrocarbons having a boiling point of from greater than 300 to 600 °C in a weight ratio of from 99:1 to 1:99. The above description of the weight ratio of aliphatic hydrocarbons having a boiling point of from 30 to 300 °C to aliphatic hydrocarbons having a boiling point of from greater than 300 to 600 °C in relation to aliphatic hydrocarbons in the liquid hydrocarbon feedstock stream also applies to the recovered aliphatic hydrocarbons. In step a), said liquid-liquid extraction results in a first stream comprising aliphatic hydrocarbons and a second stream comprising extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons. Within the present specification, the former stream (first stream) comprising recovered aliphatic hydrocarbons may also be referred to as a “raffinate stream” and the latter stream (second stream) may also be referred to as an “extract stream”. Such raffinate stream has a reduced content of aromatic hydrocarbons, conjugated aliphatic compounds having two or more carbon-carbon double bonds, and heteroatom containing organic compounds. Such raffinate stream comprises no or at most 10 wt.% or at most 5 wt.% or at most 1 wt.% or substantially no aromatic hydrocarbons. Further, such raffinate stream comprises no or at most 15 wt.% or at most 10 wt.% or at most 5 wt.% or at most 1 wt.% or substantially no conjugated aliphatic compounds having two or more carbon-carbon double bonds. Further, such raffinate stream comprises no or at most 1 wt.% or substantially no heteroatom containing organic compounds. The extraction solvent a) used in step a) of the present process, which may be fed as a first solvent stream to a first column in step a), preferably has a density which is at least 3% or at least 5% or at least 8% or at least 10% or at least 15% or at least 20% higher than the density of the liquid hydrocarbon feedstock stream. Further, said density may be at most 50% or at most 40% or at most 35% or at most 30% higher than the density of the liquid hydrocarbon feedstock stream. Further, the extraction solvent a) used in step a) contains one or more heteroatoms, which may be oxygen, nitrogen and/or sulfur. Still further, it is preferred that said extraction solvent a) is thermally stable at a temperature of 200 °C. Still further, said extraction solvent a) may have a boiling point which is at least 50 °C or at least 80 °C or at least 100 °C or at least 120 °C and at most 300 °C or at most 200 °C or at most 150 °C. Still further, it is preferred that said extraction solvent a) has no or a relatively low miscibility in heptane. Preferably, extraction solvent a) has such miscibility in heptane that at most 30 wt.% or at most 20 wt.% or at most 10 wt.% or at most 3 wt.% or at most 1 wt.% of extraction solvent a), based on weight of heptane, is miscible in heptane. The miscibility of a certain compound in another compound, such as heptane, may be determined by any general method known to a skilled person in the art, including ASTM method D1476. Where in the present specification reference is made to the miscibility of a compound in another compound, this means miscibility at 25 °C. Further, the extraction solvent a) in step a) may have a Hansen solubility parameter distance R_a,heptane with respect to heptane as determined at 25 °C of at least 3 MPa^1/2, preferably at least 5 MPa^1/2, more preferably at least 10 MPa^1/2, more preferably at least 15 MPa^1/2. Further, said R_a,heptane for extraction solvent a) may be lower than 45 MPa^1/2 or at most 40 MPa^1/2, preferably at most 35 MPa^1/2, more preferably at most 30 MPa^1/2, more preferably at most 25 MPa^1/2. For example, said R_a,heptane for N-methylpyrrolidone (NMP) is 15 MPa^1/2. Still further, said extraction solvent a) may have a difference in Hansen solubility parameter distance R_a,heptane with respect to heptane compared to Hansen solubility parameter distance R_a,toluene with respect to toluene (i.e. R_a,heptane - R_a,toluene) as determined at 25 °C of at least 1.5 MPa^1/2, preferably at least 2 MPa^1/2. Further, said difference in R_a,heptane compared to R_a,toluene for extraction solvent a) may be at most 4.5 MPa^1/2, preferably at most 4 MPa^1/2. Hansen solubility parameters (HSP) can be used as a means for predicting the likeliness of one component compared to another component. More specifically, each component is characterized by three Hansen parameters, each generally expressed in MPa^0.5: δ_d, denoting the energy from dispersion forces between molecules; δ_p, denoting the energy from dipolar intermolecular forces between molecules; and δ_h, denoting the energy from hydrogen bonds between molecules. The affinity between compounds can be described using a multidimensional vector that quantifies these solvent atomic and molecular interactions, as a Hansen solubility parameter (HSP) distance R_a which is defined in Equation (1): (R_a)² = 4(δ_d2 – δ_d1)² + (δ_p2 – δ_p1)² + (δ_h2 – δ_h1)² (1) wherein R_a = distance in HSP space between compound 1 and compound 2 (MPa^0.5) δ_d1, δ_p1¸ δ_h1 = Hansen (or equivalent) parameter for compound 1 (in MPa^0.5) δ_d2, δ_p2¸ δ_h2 = Hansen (or equivalent) parameter for compound 2 (in MPa^0.5) Thus, the smaller the value for R_a for a given solvent calculated with respect to the compound to be recovered (i.e., the compound to be recovered being compound 1 and the solvent being compound 2, or vice versa), the higher the affinity of this solvent for the compound to be recovered will be. Hansen solubility parameters for numerous solvents can be found in, among others, CRC Handbook of Solubility Parameters and Other Cohesion Parameters, Second Edition by Allan F.M. Barton, CRC press 1991; Hansen Solubility Parameters: A User's Handbook by Charles M. Hansen, CRC press 2007. In specific, the extraction solvent a) used in step a) of the present process may comprise ammonia or, preferably, one or more organic solvents selected from the group consisting of diols and triols, including monoethylene glycol (MEG), monopropylene glycol (MPG), any isomer of butanediol and glycerol; glycol ethers, including oligoethylene glycols, including diethylene glycol, triethylene glycol and tetraethylene glycol, and monoalkyl ethers thereof, including diethylene glycol ethyl ether; amides, including N- alkylpyrrolidone, wherein the alkyl group may contain 1 to 8 or 1 to 3 carbon atoms, including N-methylpyrrolidone (NMP), formamide and di- and monoalkyl formamides and acetamides, wherein the alkyl group may contain 1 to 8 or 1 to 3 carbon atoms, including dimethyl formamide (DMF), methyl formamide and dimethyl acetamide; dialkylsulfoxide, wherein the alkyl group may contain 1 to 8 or 1 to 3 carbon atoms, including dimethylsulfoxide (DMSO); sulfones, including sulfolane; N- formyl morpholine (NFM); furan ring containing components and derivatives thereof, including furfural, 2-methyl-furan, furfuryl alcohol and tetrahydrofurfuryl alcohol; hydroxy esters, including lactates, including methyl and ethyl lactate; trialkyl phosphates, including triethyl phosphate; phenolic compounds, including phenol and guaiacol; benzyl alcoholic compounds, including benzyl alcohol; aminic compounds, including ethylenediamine, monoethanolamine, diethanolamine and triethanolamine; nitrile compounds, including acetonitrile and propionitrile; trioxane compounds, including 1,3,5-trioxane; carbonate compounds, including propylene carbonate and glycerol carbonate; and cycloalkanone compounds, including dihydrolevoglucosenone. More preferably, said extraction solvent a) comprises one or more of above-mentioned dialkylsulfoxide, in specific DMSO; sulfones, in specific sulfolane; above-mentioned N- alkylpyrrolidone, in specific NMP; and a furan ring containing component, in specific furfural. Even more preferably, said extraction solvent a) comprises one or more of above-mentioned N-alkylpyrrolidone, in specific NMP, and a furan ring containing component, in specific furfural. Most preferably, extraction solvent a) comprises NMP. An aqueous solution of a quaternary ammonium salt, in specific trioctyl methyl ammonium chloride or methyl tributyl ammonium chloride, may also be used as the extraction solvent a) in step a). In addition to extraction solvent a), a washing solvent, such as water, may also be added to step a). This washing solvent is herein referred to as washing solvent c) and is further described below. In such case, step a) preferably results in a first stream comprising aliphatic hydrocarbons and a second stream comprising washing solvent c), extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons. Thus, advantageously, said washing solvent c) as added in step a), functions as an extraction solvent extracting extraction solvent a) and thereby making it possible that no or substantially no extraction solvent a) ends up in the first stream resulting from step a) and comprising recovered aliphatic hydrocarbons. In case washing solvent c) is also added to step a), the weight ratio of extraction solvent a) to washing solvent c) in step a) may be at least 0.5:1 or at least 1:1 or at least 2:1 or at least 3:1 and may be at most 30:1 or at most 25:1 or at most 20:1 or at most 15:1 or at most 10:1 or at most 5:1 or at most 3:1 or at most 2:1. In case washing solvent c) is also added to step a), a second solvent stream which comprises washing solvent c) may be fed to the above-mentioned first column (first extraction column) at a position which is higher than the position at which the above-mentioned first solvent stream which comprises the extraction solvent a) is fed, thereby enabling a counterflow liquid-liquid extraction and resulting in a top stream from the first column (above “first stream”) comprising aliphatic hydrocarbons and a bottom stream from the first column (above “second stream”) comprising washing solvent c), extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons. In the above case, the first solvent stream in extraction step a) may comprise demixing solvent b), such as water, and/or above-mentioned optional washing solvent c) in addition to extraction solvent a). Demixing solvent b) is also further described below. Said demixing solvent b) and washing solvent c) may originate from one or more recycle streams after step c) of the present process. In case washing solvent c) is also added to step a), it is preferred that the stream comprising washing solvent c) to be added comprises no or substantially no heteroatom containing organic compounds originating from the liquid hydrocarbon feedstock stream. This preference applies especially in a case where said stream is fed to the first extraction column at a relatively high position, as described above, where these heteroatom containing organic compounds could re-contaminate the raffinate (top) stream resulting from step a). Advantageously, in the present invention, at least part of the demixing solvent b) containing permeate stream resulting from step c), which may contain no or substantially no heteroatom containing organic compounds, may be used as such washing solvent c) stream for feeding (recycling) to step a), especially in case demixing solvent b) is identical to washing solvent c), especially water. As mentioned above, the second stream resulting from step a), which stream for the above-mentioned first (extraction) column corresponds with the bottom stream from such column, comprises extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons. Said stream may additionally comprise salts and/or conjugated aliphatic compounds having two or more carbon-carbon double bonds in a case wherein such salts and/or compounds are present in the liquid hydrocarbon feedstock stream. In the present invention, extraction solvent a) is recovered from the second stream resulting from step a) and then advantageously recycled to step a), through steps b), c) and d) of the present process. Step b) – Demixing with demixing solvent b) In step b) of the present process, at least part of the second stream resulting from step a), comprising extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons, is mixed with a demixing solvent b) which contains one or more heteroatoms and has a miscibility in heptane which is lower than the miscibility of extraction solvent a) in heptane, and the resulting mixture is separated into a first stream comprising heteroatom containing organic compounds and optionally aromatic hydrocarbons and a second stream comprising extraction solvent a), demixing solvent b), optionally heteroatom containing organic compounds and optionally aromatic hydrocarbons. Depending on the partition coefficient, a certain amount of heteroatom containing organic compounds and any aromatic hydrocarbons may also end up in said second stream, wherein the first stream is more hydrophobic than the second stream. Thus, said second stream may additionally comprise heteroatom containing organic compounds and optionally aromatic hydrocarbons. The demixing solvent b) used in step b) contains one or more heteroatoms, which may be oxygen, nitrogen and/or sulfur. Still further, it is preferred that just like extraction solvent a), said demixing solvent b) has no or a relatively low miscibility in heptane. Preferably, demixing solvent b) has such miscibility in heptane that at most 10 wt.% or at most 3 wt.% or at most 1 wt.% or at most 0.5 wt.% or at most 0.1 wt.% of demixing solvent b), based on weight of heptane, is miscible in heptane. In the present invention, the miscibility of demixing solvent b) in heptane is lower than the miscibility of extraction solvent a) in heptane. The miscibility of said solvents a) and b) in heptane may be determined by any general method known to a skilled person in the art, including above-mentioned ASTM method D1476. Further, suitably, demixing solvent b) is miscible in extraction solvent a). This implies that up to 50 wt.% of demixing solvent b), based on total amount of demixing solvent b) and extraction solvent a), can be mixed in extraction solvent a). Further, the demixing solvent b) in step b) may have a Hansen solubility parameter distance R_a,heptane with respect to heptane as determined at 25 °C of at least 10 MPa^1/2, preferably at least 20 MPa^1/2, more preferably at least 30 MPa^1/2, more preferably at least 40 MPa^1/2. Further, said R_a,heptane for demixing solvent b) may be at most 55 MPa^1/2, more preferably at most 50 MPa^1/2, more preferably at most 45 MPa^1/2. For example, said R_a,heptane for water is 45 MPa^1/2. As mentioned above, the miscibilities, in heptane, of extraction solvent a) and demixing solvent b) are different. Hence, said solvents a) and b) are not identical. In specific, demixing solvent b) may have a Hansen solubility parameter distance R_a,heptane with respect to heptane as determined at 25 °C which is greater than such R_a,heptane for extraction solvent a). Preferably, said difference in R_a,heptane for solvents a) and b) is at least 1 MPa^1/2, more preferably at least 5 MPa^1/2, more preferably at least 10 MPa^1/2, more preferably at least 15 MPa^1/2, more preferably at least 20 MPa^1/2, more preferably at least 25 MPa^1/2. Further, preferably, said difference in R_a,heptane for solvents a) and b) is at most 55 MPa^1/2, more preferably at most 50 MPa^1/2, more preferably at most 45 MPa^1/2, more preferably at most 40 MPa^1/2, more preferably at most 35 MPa^1/2, more preferably at most 30 MPa^1/2. In specific, the demixing solvent b) used in step b) of the present process may comprise one or more solvents selected from the group consisting of water and the solvents from the group of solvents as defined hereinabove for extraction solvent a). Preferably, said demixing solvent b) comprises one or more of water and above-mentioned diols and triols, in specific monoethylene glycol (MEG) and glycerol. More preferably, demixing solvent b) comprises water, most preferably consists of water. Other preferences and embodiments as described above with reference to the extraction solvent a) used in step a) also apply to demixing solvent b), with the exception that demixing solvent b) is not identical to extraction solvent a), as it has a lower miscibility in heptane, and that demixing solvent b) may comprise and preferably comprises water. Further, the second stream resulting from step b) may additionally comprise salts. Any conjugated aliphatic compounds having two or more carbon-carbon double bonds may end up in the first or second stream resulting from step b), together with heteroatom containing organic compounds and optionally aromatic hydrocarbons. Generally, in the present invention, said conjugated aliphatic compounds may behave similarly as aromatic compounds so that these may end up in the same stream or streams as the optional aromatic hydrocarbons. In step b), demixing solvent b) is added, separately from the second stream resulting from step a), and in addition to any demixing solvent b) that may be present in the latter stream, and mixed with the latter stream. In step b), at least part of a second stream comprising washing solvent c), such as water, and extraction solvent a), resulting from the below-described optional, additional extraction step wherein at least part of the first stream resulting from step a), wherein said first stream comprises recovered aliphatic hydrocarbons and extraction solvent a), is subjected to liquid-liquid extraction with a washing solvent c), may be added to provide for said demixing solvent b) that needs to be added in step b). The mixing in step b) may be performed in any way known to a skilled person. For example, a mixer may be used upstream of a phase separation apparatus as described below. Further, for example, in-line (or static) mixing may be performed upstream of such phase separation apparatus. Still further, mixing may be effected in a column as described below. Through such addition of demixing solvent b) and mixing in step b), different phases are formed including a more hydrophobic, first phase and a less hydrophobic, second phase comprising extraction solvent a), demixing solvent b), optionally heteroatom containing organic compounds and optionally aromatic hydrocarbons, which phases are separated in step b) into said first stream and second stream, respectively. Thus, advantageously, said demixing solvent b) as added in step b) separately from the second stream resulting from step a), functions as a so-called “demixer” (or “antisolvent”), thereby removing the more hydrophobic compounds from the extraction solvent a) to be recovered and recycled. The phase separation in step b) may be performed by any apparatus capable of separating two phases, including a decanter, a flotation device, a coalescer and a centrifuge, suitably a decanter. It is preferred that the phase separation in step b) is carried out in a single stage, for example in a decanter, a flotation device, a coalescer or a centrifuge. For example, when using a decanter in step b), a first, upper phase comprising more hydrophobic compounds and a second, lower phase comprising extraction solvent a), demixing solvent b) and less hydrophobic compounds (i.e. less hydrophobic than compounds in said first phase) may be separated into said first stream and second stream, respectively. Further, step b) may be carried out in a column comprising multiple separation stages. In the latter case, step b) comprises mixing at least part of the second stream resulting from step a), respectively, with demixing solvent b) in the column and separating the resulting mixture into the above-mentioned first stream and second stream, suitably resulting in a top stream from the column (above “first stream”) and a bottom stream from the column (above “second stream”). Preferably, said demixing solvent b) and the other, extraction solvent a) rich stream are fed co-currently to the column, at the bottom thereof. Internals in the above-mentioned column contribute to the mixing of the extraction solvent a) rich stream and the demixing solvent b). Such column internals are known in the art. The column internals may comprise a packing such as Raschig rings, Pall rings, Lessing rings, Bialecki rings, Dixon rings; sieving plates; or a random structured packing, among others, as described in Perry’s Chemical Engineer’s Handbook. Furthermore, the column may be provided with stirring means. For example, a shaft may run along the column and may be provided with rotors and stators fixed to the column. Further, the above description of temperature and pressure in extraction step a) also applies to step b). Still further, in step b), the weight ratio of the demixing solvent b) to the extraction solvent a), based on the amount of extraction solvent a) in the second stream resulting from step a), may be at least 0.005:1 or at least 0.01:1 or at least 0.5:1 or at least 1:1 or at least 2:1 and may be at most 10:1 or at most 7:1 or at most 5:1 or at most 4:1 or at most 2:1. Suitably, the amount of demixing solvent b) added in step b), based on total amount of (i) said amount of demixing solvent b) and (ii) the amount of extraction solvent a) in the second stream resulting from step a), may be of from 0.1 to 45 wt.%, more suitably of from 1 to 40 wt.%, more suitably of from 5 to 35 wt.%, more suitably of from 10 to 30 wt.%. Thus, advantageously, in step b) at least part of the heteroatom containing organic compounds and optional aromatic hydrocarbons are removed from the extraction solvent a) to be recycled, so that there is no need to separate the extraction solvent a) from such removed compounds in a later step, for example by means of distillation which is cumbersome and energy consuming. Further, advantageously, any aromatic hydrocarbons and conjugated aliphatic compounds having two or more carbon-carbon double bonds removed in step b) may be blended with pygas and processed into fuel or used in the production of aromatic compounds. Likewise, the heteroatom containing organic compounds removed in step b) may also be converted into fuel, optionally after a hydrotreatment to remove the heteroatoms. Further, said compounds removed in step b) may be further separated into various fractions which may be used as solvents. Step c) – Membrane separation of extraction solvent a) and demixing solvent b) In step c) of the present process, at least part of the second stream resulting from step b), comprising extraction solvent a) and demixing solvent b), is contacted with a membrane, and a permeate stream comprising demixing solvent b) and a retentate stream comprising extraction solvent a) are recovered. In case the below-described optional washing solvent c) is used in the present invention, which washing solvent c) may be identical to or different from, preferably identical to, demixing solvent b), such washing solvent c) may end up in said second stream resulting from step b) and subsequently in said permeate stream resulting from step c). Thus, a feed stream to step c) comprises at least part of the second stream resulting from step b). In a case wherein the feed stream to step c) additionally comprises heteroatom containing organic compounds and optionally aromatic hydrocarbons and/or salts, said retentate stream may additionally comprise such compounds and/or salts. If the feed stream to step c) or the retentate stream resulting from step c) contains any solid salts, they may be removed therefrom by any method, including filtering. Preferably, the membrane used in step c) is a membrane through which demixing solvent b) preferentially permeates and through which no or substantially no extraction solvent a), heteroatom containing organic compounds and aromatic hydrocarbons can permeate, thereby increasing the quality of the demixing solvent b) containing permeate stream obtained in step c), at least part of which stream may then advantageously be recycled in the present process. In the present invention, the membrane used in step c) may be a non-porous reverse osmosis membrane (no pores) or a nanofiltration membrane which can be non-porous (no pores) or porous (nanopores having an average size of at most 30 nm). If a solvent other than water is used as a demixing solvent b) in step b), a nanofiltration membrane may be preferred in step c). Reverse osmosis and nanofiltration membranes as such are known in the art. In principle, any non-porous or nanoporous membrane capable of retaining at least 80 wt.%, preferably at least 90 wt.%, more preferably at least 95 wt.%, and most preferably at least 99 wt.% of the extraction solvent a), optional heteroatom containing organic compounds and optional aromatic hydrocarbons contained in the second stream resulting from step b), can be used in the present invention. Further, preferably, in the present invention, any non-porous or nanoporous membrane capable of permeating at least 20 wt.%, more preferably at least 40 wt.%, more preferably at least 60 wt.%, more preferably at least 80 wt.%, more preferably at least 90 wt.%, more preferably at least 95 wt.%, and most preferably at least 99 wt.% of the demixing solvent b) contained in the second stream resulting from step b), can be used in the present invention. Suitable membranes for step c) of this invention have a molecular weight cut off (MWCO) below 2000 Daltons (Da), preferably below 500 Da, more preferably below 250 Da. Preferably, in step c) of the present invention, a membrane having an average pore size of from 0 to 30 nm (reverse osmosis or nanofiltration membrane) is used. Where nanofiltration membranes are used which are porous, they have an average membrane pore size which is at most 30 nm (nanoporous membranes). Where such nanofiltration or nanoporous membrane is used in step c), the average membrane pore size is suitably less than 30 nm, preferably at most 25 nm, more preferably at most 20 nm, more preferably at most 15 nm, more preferably at most 10 nm, more preferably at most 5 nm, more preferably less than 5 nm, more preferably at most 3 nm, more preferably at most 2 nm, more preferably at most 1 nm, more preferably at most 0.7 nm, more preferably at most 0.5 nm, more preferably at most 0.3 nm, most preferably at most 0.1 nm. The material of the membrane used in step c) must be compatible with the extraction solvent a) used in step a), demixing solvent b) used in step b) and those components from the liquid hydrocarbon feedstock stream which are fed to step c). Preferably, the membrane used in step c) is a reverse osmosis or nanofiltration membrane which is a polymeric membrane. Such polymeric membrane is preferably cross-linked to provide the necessary network for avoiding dissolution of the membrane once being in contact with the extraction solvent a) used in step a), demixing solvent b) used in step b) and optional heteroatom containing organic compounds and optional aromatic hydrocarbons originating from the liquid hydrocarbon feedstock stream. Examples of suitable cross-linked polymeric membranes are membranes comprising per-fluoropolymers derived from perfluoro cycloalkene (PFCA), ethylene, vinyl fluoride (VF1), vinylidene fluoride (VDF), trifluoro ethylene (TrFE), tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTEF), propylene, hexafluoropropylene (HFP), perfluoropropylvinylether (PPVE), perfluoromethylvinylether (PMVE) or a combination thereof which further may contain at least one chlorinated monomer such as chlorofluoroethylene (CFE), chlorotrifluoroethylene (CTFE), 2-chloro-3,3,3- trifluoropropene, 1-chloro-3,3,3-trifluoropropene. The copolymer may further contain at least one other unit derived from a fluorinated monomer, which may be chosen from: tetrafluoroethylene (TFE), hexafluoropropylene (HFP), 2- (trifluoromethyl)acrylic acid, trifluoro-propene, tetrafluoropropene, hexafluoroisobutylene, (perfluorobutyl)ethylene, pentafluoropropene, perfluoro-alkyl ethers such as PMVE, PEVE, and PPVE and mixtures thereof. Preferably, the membrane used in step c) is a per- fluoropolymer copolymerized with tetrafluoroethylene. Further, other polymers that are not soluble in the extraction solvent a) used in step a) and that could be used in the preparation of suitable membrane modules are polyethylene (PE), polypropylene (PP), polyethylene/vinyl acetate, polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyethylene terephthalate (PET), and polyether-block- amide. Depending on the type of solvent used in step a) and the other compounds in the feed stream, other materials could be used. Further, preferably, the membrane used in step c) is a nanofiltration membrane which is part of a composite membrane which comprises a zeolite membrane supported on an organic or inorganic porous sintered body (the support) or which is a composite membrane comprising an organic compound and zeolite-based components. As an example of a composite membrane, a zeolite membrane comprises a membranous material composed of a zeolite and it is preferably a membrane obtained by crystallizing a zeolite on an inorganic porous support. Specifically, the zeolite membrane is a zeolite membrane containing a Chabazite (CHA)- type zeolite as main component, which may partially contain a zeolite of another structure such as Mordenite (MOR)-type or a ZSM-5 MFI-type or contain an amorphous component or the like. Still further, preferably, the membrane used in step c) is a nanofiltration membrane which is part of a polymer- zeolite composite wherein the zeolite is embedded in the membrane and enhances its transport properties. An example of such composite membrane results from a combination of polyether-block-amide and Linde type 4A zeolite (LTA4A). Other zeolites that could be used in the separation of demixing solvent b), such as water, from the extraction solvent a) are 13X (called NaX), Zeolite A or a variant such as NaA, KA or CaA, and Zeolite T. Any hydrophilic zeolite, which may be part of a composite, which can separate demixing solvent b) from the extraction solvent a) may be used. As known by those skilled in the art, a pressure differential, or trans-membrane pressure (TMP), of the feed over a membrane is the driving force that enhances transport through the membrane, such as a reverse osmosis or nanofiltration membrane. In step c) of the present invention, a reverse osmosis membrane may be used. The operation of such membrane is based on osmotic pressure. The operating pressure of the feed stream must be higher than its osmotic pressure. Differential pressure drives the permeating molecules through the membrane. The pressure of the feed stream to the membrane may be increased to a pressure in the range of from 5 to 100 bar, preferably of from 20 to 40 bar. The permeate stream may have a pressure in the range of from 1 bar to 10 bar. The retentate stream may have a pressure in the range of from 1 bar to 40 bar. The preferred operating temperature range in step c) of this invention, when using a reverse osmosis membrane, is of from 4 to 90 °C but is more preferably of from 30 to 60 °C. Alternatively, pervaporation may be used in step c) of the present invention. Pervaporation is based on solubility and diffusion in addition to differential pressure. The second stream resulting from step b) which is directed to the membrane would remain at its process pressure and does not need to be increased in pressure as it is the case for a reverse osmosis membrane. However, the permeate side of a pervaporation type membrane will operate under vacuum with a pressure which may be in the range of from 0.01 bara to 1 bara. Furthermore, when separating through a pervaporation type membrane the temperature of the feed stream may be increased to a temperature in the range of from 70 to 120 °C. In the present invention, the amount of demixing solvent b) in the feed stream to step c) may be at least 10 wt.% or at least 20 wt.% and may be at most 70 wt.% or at most 50 wt.% or at most 40 wt.%. The retentate stream resulting from step c) may still comprise demixing solvent b), for example in an amount of at most 50 wt.% or at most 40 wt.% or at most 30 wt.% or at most 20 wt.% or at most 10 wt.% or at most 5 wt.% or at most 3 wt.%. Advantageously, in case the amount of demixing solvent b) in said retentate stream is relatively low, for example up to 5 wt.%, such demixing solvent b) does not need to be removed before extraction solvent a) from said same stream is recycled to step a) of the present process. However, in case the amount of demixing solvent b) in said retentate stream is still relatively high, for example of from 5 wt.% up to 50 wt.%, it is preferred to first remove such demixing solvent b) from said retentate stream by evaporation, for example through distillation, as further described below. Further, in the present invention, part of the second stream resulting from step b), comprising extraction solvent a) and demixing solvent b), may be subjected to step c) of the present process, whereas another part may by-pass said step c) and demixing solvent b) may be removed from said other part, optionally in combination with at least part of the retentate stream resulting from step c) in case the retentate stream comprises extraction solvent a) and demixing solvent b), by evaporation, for example through distillation, as further described below. Separation of demixing solvent b) from retentate stream Further, the present process may comprise an additional step comprising separating at least part of the retentate stream resulting from step c), wherein the retentate stream comprises extraction solvent a) and demixing solvent b), by distillation into a top stream comprising demixing solvent b) and a bottom stream comprising extraction solvent a). The latter separation may be performed in a distillation column. Thus, a feed stream to said optional, additional distillation step comprises at least part of the retentate stream resulting from step c). The latter feed stream comprises demixing solvent b) and extraction solvent a) and may comprise of from 5 to 50 wt.% of demixing solvent b), for example at least 5 wt.% or at least 10 wt.% and at most 40 wt.% or at most 30 wt.% or at most 20 wt.% of demixing solvent b). In a case wherein the feed stream to the above-mentioned optional, additional distillation step comprises heteroatom containing organic compounds and optionally aromatic hydrocarbons in addition to extraction solvent a) and demixing solvent b), the top stream resulting from the distillation step comprises demixing solvent b), heteroatom containing organic compounds and optionally aromatic hydrocarbons. For, advantageously, in distillation, at least part of said heteroatom containing organic compounds and aromatic hydrocarbons is removed azeotropically with the demixing solvent b), especially water. In the latter case, said top stream may be separated into two phases, one phase comprising demixing solvent b) and another phase comprising heteroatom containing organic compounds and optionally aromatic hydrocarbons. Such phase separation may be performed by any apparatus capable of separating two phases, including a decanter, a flotation device, a coalescer and a centrifuge, suitably a decanter. Advantageously, demixing solvent b) from such separated phase comprising demixing solvent b) may be recycled as further described below, whereas the other phase may be bled from the process thereby reducing the risk of any build-up of heteroatom containing organic compounds and aromatic hydrocarbons in the present process. In the above-described case wherein at least part of the retentate stream resulting from step c) is subjected to distillation, the present invention may still be advantageous in terms of process efficiency (e.g. energy savings) because a relatively large amount of demixing solvent b) is already removed in preceding membrane separation step c). Further, in said case, at least part of any heteroatom containing organic compounds and any aromatic hydrocarbons is removed azeotropically with the demixing solvent b), especially water, from the extraction solvent a) to be recovered and recycled. Advantageously, in such case, because less demixing solvent b) is present in the retentate stream resulting from step c) than in the feed stream to step c), said heteroatom containing organic compounds and aromatic hydrocarbons upon separation from the extraction solvent a) will be concentrated in a relatively low amount of demixing solvent b) through this additional distillation step, whereby they more readily form a separate phase upon condensation, leading to (i) a relatively smaller demixing solvent b) stream that may still be contaminated to some extent and (ii) a relatively larger enriched stream comprising said heteroatom containing organic compounds and aromatic hydrocarbons. Recycle steps In step d) of the present process, at least part of the extraction solvent a) from the retentate stream resulting from step c) is recycled to step a). As described above, before such recycle, at least part of the retentate stream resulting from step c) may first be subjected to distillation, after which at least part of the extraction solvent a) from the resulting bottom stream may be recycled to step a). Further, as also described above, part of the second stream resulting from step b) may by-pass step c) and be subjected to distillation instead, after which at least part of the extraction solvent a) from the resulting bottom stream may be recycled to step a). The retentate stream resulting from step c) may additionally comprise aromatic hydrocarbons and/or heteroatom containing organic compounds. In a case where a stream comprising extraction solvent a) to be recycled to step a) comprises a relatively high amount of such compounds, additional demixing solvent b) may be added to step b) so as to prevent any build-up of these contaminants in such recycle stream to step a). Further, these contaminants may be removed before recycling extraction solvent a) to step a), by bleeding part of the stream comprising extraction solvent a) to be recycled to step a) wherein either such bleed stream may be discarded or extraction solvent a) may be recovered from such bleed stream, for example by distillation thereof. Further, in optional step e) of the present process, at least part of the demixing solvent b) from the permeate stream resulting from step c) is recycled to step b). The latter recycle to step b), in step e), is suitable in a case wherein said permeate stream resulting from step c) still comprises a relatively high amount of heteroatom containing organic compounds and/or aromatic hydrocarbons originating from the liquid hydrocarbon feedstock stream. However, in a case wherein such stream comprises no or substantially no or a relatively low amount of heteroatom containing organic compounds and/or aromatic hydrocarbons, which is advantageously enabled by membrane separation step c) in the present process, it is preferred to recycle at least part of the demixing solvent b) from such stream to step a) in case a washing solvent c), such as water, is added to step a) as described above, or to the below-described optional, additional extraction step wherein such washing solvent c) is added. Further, as described above, before recycling at least part of the extraction solvent a) from the retentate stream resulting from step c), that retentate stream may first be subjected to distillation, after which at least part of the demixing solvent b) from the resulting top stream may be recycled to step b). Further, as also described above, part of the second stream resulting from step b) may by-pass step c) and be subjected to distillation instead, after which at least part of the demixing solvent b) from the resulting top stream may be recycled to step b). The latter recycles to step b) are preferred in a case where said top streams additionally comprise a relatively high amount of heteroatom containing organic compounds and/or aromatic hydrocarbons. Separation of extraction solvent a) from raffinate stream In a case wherein the stream comprising recovered aliphatic hydrocarbons resulting from the liquid-liquid extraction by the extraction solvent a) in step a) (raffinate stream) additionally comprises extraction solvent a), it is preferred that extraction solvent a) is separated from that stream which is the first stream resulting from step a), and is optionally recycled to step a). In this way, the recovered aliphatic hydrocarbons are advantageously separated from any extraction solvent a) in the above-mentioned raffinate stream, and the separated extraction solvent a) may advantageously be recycled to step a). Extraction solvent a) may be separated from the above- mentioned first stream resulting from step a), wherein said stream comprises aliphatic hydrocarbons and extraction solvent a), in any way, including distillation, extraction, absorption and membrane separation. In specific, in the above-mentioned case wherein the first stream resulting from step a) comprises aliphatic hydrocarbons and extraction solvent a), in an additional step, at least part of said first stream is contacted with a washing solvent c) and is subjected to liquid-liquid extraction with the washing solvent c), resulting in a first stream comprising aliphatic hydrocarbons and a second stream comprising washing solvent c) and extraction solvent a). In the present invention, the optional washing solvent c) that may be used in the above-mentioned additional extraction step or that may be separately added to step a) or that may be added together with extraction solvent a) in a stream to step a), may be identical to or different from, preferably identical to, demixing solvent b). The preferences and embodiments as described above with reference to demixing solvent b) also apply to optional washing solvent c). Preferably, washing solvent c) comprises water, more preferably consists of water. Further, preferably, both demixing solvent b) and washing solvent c) comprise water, more preferably consist of water. In the above-mentioned additional step, the first stream resulting from step a) and comprising aliphatic hydrocarbons and extraction solvent a) may be fed to a second column (second extraction column). Further, a second solvent stream which comprises washing solvent c) may be fed to the second column at a position which is higher than the position at which said first stream resulting from step a) is fed, thereby enabling a counterflow liquid-liquid extraction and resulting in a top stream from the second column (above “first stream”) comprising aliphatic hydrocarbons and a bottom stream from the second column (above “second stream”) comprising washing solvent c) and extraction solvent a). Thus, advantageously, said washing solvent c) as added in the above-mentioned additional step, functions as an extraction solvent extracting extraction solvent a) thereby making it possible that advantageously no or substantially no extraction solvent a) ends up in the recovered aliphatic hydrocarbons. In the above-mentioned additional step, the weight ratio of extraction solvent a) to washing solvent c) may be at least 0.5:1 or at least 1:1 or at least 2:1 or at least 3:1 and may be at most 30:1 or at most 25:1 or at most 20:1 or at most 15:1 or at most 10:1 or at most 5:1 or at most 3:1 or at most 2:1. Further, the above description of temperature and pressure in extraction step a) also applies to the above-mentioned additional (extraction) step. In case the present process comprises the above-mentioned additional step, the first solvent stream in extraction step a) may comprise demixing solvent b) in addition to extraction solvent a) in which case the bottom stream from the first extraction column additionally comprises demixing solvent b). In the above-mentioned additional step wherein washing solvent c) is added, it is preferred that the stream comprising washing solvent c) to be added comprises no or substantially no heteroatom containing organic compounds originating from the liquid hydrocarbon feedstock stream. This preference applies especially in a case where said stream is fed to the second extraction column at a relatively high position, as described above, where these heteroatom containing organic compounds could re-contaminate the raffinate (top) stream. Advantageously, in the present invention, at least part of the permeate stream resulting from step c) and comprising demixing solvent b) and optionally washing solvent c), which streams may contain no or substantially no heteroatom containing organic compounds originating from the liquid hydrocarbon feedstock stream, may be used as such washing solvent c) stream for feeding (recycling) to said additional step, especially in case demixing solvent b) is identical to washing solvent c), especially water. Further, at least part of the second stream comprising washing solvent c) and extraction solvent a) resulting from the above-mentioned additional (extraction) step may be fed to step b) to provide for at least part of the demixing solvent b) that needs to be added in step b), especially in case demixing solvent b) is identical to washing solvent c). Thus, advantageously, such washing solvent c) may function both as an extraction solvent extracting residual extraction solvent a) in said additional step and as a so-called “demixer” (or “antisolvent”) in step b), i.e. as demixing solvent b), as further discussed above. In case a washing solvent other than water is fed to an extraction column for extracting extraction solvent a) used in step a), either in the above-mentioned additional step or in step a) itself as described above, it may be preferred that in addition to such other solvent, water is fed to the extraction column at a position which is higher than the position at which that other solvent is fed. In this way, advantageously, the water fed at the higher position may extract any washing solvent other than water away thereby preventing such other washing solvent from entering the (final) raffinate stream. Alternatively, the latter raffinate stream may be washed with water in a separate step. Upstream and downstream integration In the present invention, the liquid hydrocarbon feedstock stream may comprise at least part of a hydrocarbon product formed in a process comprising cracking of plastics, preferably waste plastics, more preferably mixed waste plastics, wherein at least part of the plastics comprises heteroatom containing organic compounds. Accordingly, the present invention also relates to a process for the recovery of aliphatic hydrocarbons from plastics, wherein at least part of the plastics comprises heteroatom containing organic compounds, said process comprising the steps of: (I) cracking the plastics and recovering a hydrocarbon product comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons; and (II) subjecting a liquid hydrocarbon feedstock stream, which comprises at least part of the hydrocarbon product obtained in step (I), to the above-described process for the recovery of aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream. The preferences and embodiments as described above with reference to the present aliphatic hydrocarbons recovery process as such also apply to step (II) of the present process for the recovery of aliphatic hydrocarbons from plastics. In above-mentioned step (I), the resulting hydrocarbon product may be either a liquid or a solid or wax. In the latter case, the solid or wax is first heated to make it liquid, before subjecting it to the aliphatic hydrocarbons recovery process in step (II). In the above-mentioned process, at least part of the plastics as fed to step (I) comprises heteroatom containing organic compounds, which plastics are preferably waste plastics, more preferably mixed waste plastics. In said step (I), the cracking of the plastics may involve a thermal cracking process and/or a catalytic cracking process. The cracking temperature in step (I) may be of from 300 to 800 °C, suitably of from 400 to 800 °C, more suitably of from 400 to 700 °C, more suitably of from 500 to 600 °C. Further, any pressure may be applied, which pressure may be sub- atmospheric, atmospheric or super-atmospheric. Heat treatment in step (I) causes melting of the plastics and cracking of its molecules into smaller molecules. The cracking in step (I) may be carried out as pyrolysis or as liquefaction. Both in pyrolysis and in liquefaction a continuous liquid phase is formed. In addition, in pyrolysis a discontinuous gas phase is formed that escapes the liquid phase and segregates into a continuous gas phase. In liquefaction, there is no significant gas phase by applying a relatively high pressure. Further, in step (I), subsequent condensation of a gas phase and/or cooling of a liquid phase provides a hydrocarbon product, which may be either a liquid or a solid or wax, comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons, at least part of which is subjected to the above-described aliphatic hydrocarbons recovery process in step (II). Above-described step (I) may be carried out in any known way, for example in a way as disclosed in above-mentioned WO2018069794 and in WO2017168165, the disclosures of which are herein incorporated by reference. Advantageously, aliphatic hydrocarbons as recovered in one of the above-described processes for the recovery of aliphatic hydrocarbons, which may comprise varying amounts of aliphatic hydrocarbons within a wide boiling point range, may be fed to a steam cracker without a further pre-treatment, such as treatment with hydrogen (hydrotreating or hydroprocessing) as disclosed in above-mentioned WO2018069794. In addition to being used as a feed to a steam cracker, said recovered aliphatic hydrocarbons may also advantageously be fed to other refining processes including hydrocracking, isomerization, hydrotreating, thermal catalytic cracking and fluid catalytic cracking. Further, in addition to being used as a feed to a steam cracker, said recovered aliphatic hydrocarbons may also advantageously be separated into different fractions which each may find a different application, such as diesel, marine fuel, solvent, etc. Accordingly, the present invention also relates to a process for steam cracking a hydrocarbon feed, wherein the hydrocarbon feed comprises aliphatic hydrocarbons as recovered in one of the above-described processes for the recovery of aliphatic hydrocarbons. Further, accordingly, the present invention also relates to a process for steam cracking a hydrocarbon feed, comprising the steps of: recovering aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream in one of the above-described processes for the recovery of aliphatic hydrocarbons; and steam cracking a hydrocarbon feed which comprises aliphatic hydrocarbons as recovered in the preceding step. In the present specification, said phrase “steam cracking a hydrocarbon feed which comprises aliphatic hydrocarbons as recovered in the preceding step” may mean “steam cracking a hydrocarbon feed which comprises at least part of the recovered aliphatic hydrocarbons”. The hydrocarbon feed to the steam cracking process may also comprise hydrocarbons from another source, other than the present processes for the recovery of aliphatic hydrocarbons. Such other source may be naphtha, hydrowax or a combination thereof. Advantageously, in a case wherein the liquid hydrocarbon feedstock stream comprises aromatic hydrocarbons, especially polycyclic aromatics, heteroatom containing organic compounds, conjugated aliphatic compounds having two or more carbon-carbon double bonds, or a combination thereof, these have already been removed by the present aliphatic hydrocarbons recovery process as described above before feeding recovered hydrocarbons to a steam cracking process. This is particularly advantageous in that said removed compounds, especially polycyclic aromatics, can no longer cause fouling in the preheat, convection and radiant sections of a steam cracker and in the downstream heat exchange and/or separation equipment for a steam cracker, for example in transfer line exchangers (TLEs) which are used to rapidly cool the effluent from a steam cracker. When hydrocarbons condense, they may thermally decompose into a coke layer which may cause fouling. Such fouling is a major factor determining the run length of the cracker. Reducing the amount of fouling results in longer run times without maintenance shutdowns, and improved heat transfer in the exchangers. The steam cracking may be performed in any known way. The hydrocarbon feed is typically preheated. The feed can be heated using heat exchangers, a furnace or any other combination of heat transfer and/or heating devices. The feed is steam cracked in a cracking zone under cracking conditions to produce at least olefins (including ethylene) and hydrogen. The cracking zone may comprise any cracking system known in the art that is suitable for cracking the feed. The cracking zone may comprise one or more furnaces, each dedicated for a specific feed or fraction of the feed. The cracking is performed at elevated temperatures, preferably in the range of from 650 to 1000 °C, more preferably of from 700 to 900 °C, most preferably of from 750 to 850 °C. Steam is usually added to the cracking zone, acting as a diluent to reduce the hydrocarbon partial pressure and thereby enhance the olefin yield. Steam also reduces the formation and deposition of carbonaceous material or coke in the cracking zone. The cracking occurs in the absence of oxygen. The residence time at the cracking conditions is very short, typically in the order of milliseconds. From the cracker, a cracker effluent is obtained that may comprise aromatics (as produced in the steam cracking process), olefins, hydrogen, water, carbon dioxide and other hydrocarbon compounds. The specific products obtained depend on the composition of the feed, the hydrocarbon-to-steam ratio, and the cracking temperature and furnace residence time. The cracked products from the steam cracker are then passed through one or more heat exchangers, often referred to as TLEs (“transfer line exchangers”), to rapidly reduce the temperature of the cracked products. The TLEs preferably cool the cracked products to a temperature in the range of from 400 to 550 °C. Figures The present process for the recovery of aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream is further illustrated by Figures 1, 2 and 3. In the process of Figure 1, a liquid hydrocarbon feedstock stream 1, which comprises aliphatic hydrocarbons (including conjugated aliphatic compounds having two or more carbon-carbon double bonds, which are hereinafter referred to as “dienes”), aromatic hydrocarbons and heteroatom containing organic compounds; a first solvent stream 2 which comprises an organic solvent (for example N-methylpyrrolidone) which is an extraction solvent a) in accordance with the present invention; and a second solvent stream 3 which comprises water which is an optional washing solvent c) in accordance with the present invention, are fed to an extraction column 4. In column 4, liquid hydrocarbon feedstock stream 1 is contacted with first solvent stream 2 (organic solvent), thereby recovering aliphatic hydrocarbons by liquid-liquid extraction of dienes, aromatic hydrocarbons and heteroatom containing organic compounds with the organic solvent. Further, the water in second solvent stream 3 removes organic solvent from the upper part of column 4 by liquid-liquid extraction of organic solvent with water. A stream 5 comprising recovered aliphatic hydrocarbons exits column 4 at the top. Further, a stream 6 comprising organic solvent, water, dienes, aromatic hydrocarbons and heteroatom containing organic compounds exits column 4 at the bottom. Stream 6 and a stream 14 comprising additional water, which is a demixing solvent b) in accordance with the present invention, are combined, and the combined stream is fed to a decanter 13. In decanter 13, the combined stream is separated into a stream 15 comprising dienes, aromatic hydrocarbons and heteroatom containing organic compounds and a stream 16 comprising organic solvent and water. Stream 16 is fed to a membrane unit 7. Permeate stream 8 from membrane unit 7 comprises water. Water from permeate stream 8 may be recycled via water stream 14 and/or water stream 3. Retentate stream 9 from membrane unit 7 comprises organic solvent. Organic solvent from retentate stream 9 is recycled via organic solvent stream 2. In the process of Figure 2, a liquid hydrocarbon feedstock stream 1, which comprises aliphatic hydrocarbons (including conjugated aliphatic compounds having two or more carbon-carbon double bonds, which are hereinafter referred to as “dienes”), aromatic hydrocarbons and heteroatom containing organic compounds; and a first solvent stream 2 which comprises an organic solvent (for example N- methylpyrrolidone) which is an extraction solvent a) in accordance with the present invention, are fed to a first extraction column 4a. In column 4a, liquid hydrocarbon feedstock stream 1 is contacted with first solvent stream 2 (organic solvent), thereby recovering aliphatic hydrocarbons by liquid-liquid extraction of dienes, aromatic hydrocarbons and heteroatom containing organic compounds with the organic solvent, resulting in a top stream 5a comprising recovered aliphatic hydrocarbons and organic solvent and a bottom stream 6 comprising organic solvent, dienes, aromatic hydrocarbons and heteroatom containing organic compounds. Stream 5a and a second solvent stream 3 which comprises water, which is an optional washing solvent c) in accordance with the present invention, are fed to a second extraction column 4b. In column 4b, stream 5a is contacted with second solvent stream 3 (water), thereby removing organic solvent by liquid-liquid extraction of organic solvent with water. A stream 5b comprising recovered aliphatic hydrocarbons exits column 4b at the top. Further, a stream 14 comprising organic solvent and water, which water is a demixing solvent b) in accordance with the present invention, exits column 4b at the bottom. Streams 6 and 14 are combined, and the combined stream is fed to a decanter 13. In respect of the treatment in decanter 13 and further, downstream treatments in the process of Figure 2 reference is made to the above description of the corresponding treatments in the process of Figure 1. The process of Figure 3 is similar to the process of Figure 2, except that in the process of Figure 3 stream 16 also comprises dienes, aromatic hydrocarbons and heteroatom containing organic compounds in addition to organic solvent and water. Water from permeate stream 8 may be recycled via water stream 3. Retentate stream 9 comprises organic solvent, water, dienes, aromatic hydrocarbons and heteroatom containing organic compounds, and is fed to a distillation column 10, where it is separated into a top stream 12 comprising water, dienes, aromatic hydrocarbons and heteroatom containing organic compounds and a bottom stream 11 comprising organic solvent. Organic solvent from bottom stream 11 is recycled via organic solvent stream 2. Stream 12 is fed to an overhead decanter 17, wherein it is separated into a stream 18 comprising dienes, aromatic hydrocarbons and heteroatom containing organic compounds and a stream comprising water, which may additionally comprise a relatively low amount of dienes, aromatic hydrocarbons and heteroatom containing organic compounds, part of which water stream (stream 19a) is sent back to distillation column 10 as a reflux stream whereas the other part (stream 19b) may be recycled via water stream 14.

Claims

C L A I M S 1. A process for the recovery of aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons, said process comprising the steps of: a) contacting at least part of the liquid hydrocarbon feedstock stream with an extraction solvent a) which contains one or more heteroatoms and subjecting the liquid hydrocarbon feedstock stream to liquid-liquid extraction with the extraction solvent a), resulting in a first stream comprising aliphatic hydrocarbons and a second stream comprising extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons; b) mixing at least part of the second stream resulting from step a) with a demixing solvent b) which contains one or more heteroatoms and has a miscibility in heptane which is lower than the miscibility of extraction solvent a) in heptane, and separating the resulting mixture into a first stream comprising heteroatom containing organic compounds and optionally aromatic hydrocarbons and a second stream comprising extraction solvent a) and demixing solvent b); c) contacting at least part of the second stream resulting from step b) with a membrane and recovering a permeate stream comprising demixing solvent b) and a retentate stream comprising extraction solvent a); d) recycling at least part of the extraction solvent a) from the retentate stream resulting from step c) to step a); and e) optionally recycling at least part of the demixing solvent b) from the permeate stream resulting from step c) to step b).

2. The process according to claim 1, wherein the membrane in step c) is a non-porous membrane or a nanofiltration membrane comprising nanopores having an average size of at most 30 nm.

3. The process according to claim 1 or 2, further comprising the step of: separating at least part of the retentate stream resulting from step c), wherein the retentate stream comprises extraction solvent a) and demixing solvent b), by distillation into a top stream comprising demixing solvent b) and a bottom stream comprising extraction solvent a).

4. The process according to any one of claims 1 to 3, wherein: the extraction solvent a) has a R_a,heptane of at least 5 MPa^1/2, preferably at least 10 MPa^1/2, and the demixing solvent b) has a R_a,heptane of at least 20 MPa^1/2, preferably at least 30 MPa^1/2, wherein R_a,heptane refers to the Hansen solubility parameter distance with respect to heptane as determined at 25 °C; and the R_a,heptane for the demixing solvent b) is greater than the R_a,heptane for extraction solvent a), wherein said difference in R_a,heptane for solvents a) and b) is at least 1 MPa^1/2, preferably at least 5 MPa^1/2, more preferably at least 10 MPa^1/2, more preferably at least 15 MPa^1/2. 5. The process according to any one of claims 1 to 4, wherein the extraction solvent a) comprises ammonia or, preferably, one or more organic solvents selected from the group consisting of diols and triols, including monoethylene glycol (MEG), monopropylene glycol (MPG), any isomer of butanediol and glycerol; glycol ethers, including oligoethylene glycols, including diethylene glycol, triethylene glycol and tetraethylene glycol, and monoalkyl ethers thereof, including diethylene glycol ethyl ether; amides, including N-alkylpyrrolidone, wherein the alkyl group may contain 1 to 8 or 1 to 3 carbon atoms, including N- methylpyrrolidone (NMP), formamide and di- and monoalkyl formamides and acetamides, wherein the alkyl group may contain 1 to 8 or 1 to 3 carbon atoms, including dimethyl formamide (DMF), methyl formamide and dimethyl acetamide; dialkylsulfoxide, wherein the alkyl group may contain 1 to 8 or 1 to 3 carbon atoms, including dimethylsulfoxide (DMSO); sulfones, including sulfolane; N-formyl morpholine (NFM); furan ring containing components and derivatives thereof, including furfural, 2-methyl-furan, furfuryl alcohol and tetrahydrofurfuryl alcohol; hydroxy esters, including lactates, including methyl and ethyl lactate; trialkyl phosphates, including triethyl phosphate; phenolic compounds, including phenol and guaiacol; benzyl alcoholic compounds, including benzyl alcohol; aminic compounds, including ethylenediamine, monoethanolamine, diethanolamine and triethanolamine; nitrile compounds, including acetonitrile and propionitrile; trioxane compounds, including 1,3,

5- trioxane; carbonate compounds, including propylene carbonate and glycerol carbonate; and cycloalkanone compounds, including dihydrolevoglucosenone.

6. The process according to any one of claims 1 to 5, wherein the demixing solvent b) comprises one or more solvents selected from the group consisting of water and the solvents from the group of solvents as defined for extraction solvent a) in claim 5, and wherein the demixing solvent b) preferably comprises water.

7. The process according to any one of claims 1 to 6, wherein: a washing solvent c) is added to step a) resulting in a first stream comprising aliphatic hydrocarbons and a second stream comprising washing solvent c), extraction solvent a), heteroatom containing organic compounds and optionally aromatic hydrocarbons; or the first stream resulting from step a) comprises aliphatic hydrocarbons and extraction solvent a), at least part of which first stream is contacted with a washing solvent c) and is subjected to liquid-liquid extraction with the washing solvent c), resulting in a first stream comprising aliphatic hydrocarbons and a second stream comprising washing solvent c) and extraction solvent a).

8. The process according to claim 7, wherein the washing solvent c) is identical to or different from, preferably identical to, demixing solvent b), and preferably comprises water.

9. A process for the recovery of aliphatic hydrocarbons from plastics, wherein at least part of the plastics comprises heteroatom containing organic compounds, said process comprising the steps of: (I) cracking the plastics and recovering a hydrocarbon product comprising aliphatic hydrocarbons, heteroatom containing organic compounds and optionally aromatic hydrocarbons; and (II) subjecting a liquid hydrocarbon feedstock stream, which comprises at least part of the hydrocarbon product obtained in step (I), to the process of any one of claims 1- 8.

10. Process for steam cracking a hydrocarbon feed, wherein the hydrocarbon feed comprises aliphatic hydrocarbons as recovered in a process according to any one of claims 1-9.

11. Process for steam cracking a hydrocarbon feed, comprising the steps of: recovering aliphatic hydrocarbons from a liquid hydrocarbon feedstock stream in a process according to any one of claims 1-9; and steam cracking a hydrocarbon feed which comprises aliphatic hydrocarbons as recovered in the preceding step.