Process for purifying hydrocarbon stream comprising heterogeneous and homogeneous catalytic reactions

Abstract

The invention relates to a method for purifying a hydrocarbon stream containing at least Cx alkanes, Cx olefins, low boilers such as Cx-1 hydrocarbons and high boilers such as Cx + 1 hydrocarbons, where x = 3 to 5. In the method according to the invention, first the low boilers are separated out and then divided into two partial streams, each of which undergoes a chemical reaction. After separation of the product, the streams are combined again and high boilers are separated.

Description

[0001] The subject of the invention is a method for purifying a hydrocarbon stream which contains at least Cx alkanes, Cx olefins, low boilers such as Cx-1 hydrocarbons and high boilers such as Cx+1 hydrocarbons, where x=3 to 5. In the method according to the invention, the low boilers are first separated off and then divided into two substreams which are each subjected to a chemical reaction. After the products have been separated off, the streams are recombined and the high boilers are separated off.

[0002] It is already known to provide C3 to C5 alkane streams which can be used, for example, as propellant gases. In order to be able to be used as propellant gases, the C3 to C5 alkane streams obtained need to have a specific product specification, i.e. they can contain only small amounts of undesirable and / or odor-forming substances. In this context, the term "odor-forming substances" refers to various substances or compounds which do not correspond to the substances constituting the propellant gas. If the propellant gas is to be used in the cosmetic or medical field, even any contamination with reactive components such as olefins, as well as any odor contamination with other substances or compounds should be avoided, since applications close to the body are generally involved.

[0003] The general object is to improve the known processes in order to obtain a less contaminated stream with substances forming foreign odors. Here, it is also important to provide a process that is as efficient and cost-effective as possible.

[0004] Surprisingly, it has been found that the division of the stream obtained from the separation of the low boilers and the passage through different reaction steps leads to less contamination with foreign odor-forming substances.

[0005] The process according to the invention is accordingly a process for purifying a hydrocarbon stream which contains at least Cx alkanes, Cx olefins, low boilers such as Cx-1 hydrocarbons and high boilers such as Cx+1 hydrocarbons, wherein x is an integer from 3 to 5, wherein the process comprises the following steps:

[0006] a) separating at least a portion of low boilers from a hydrocarbon stream in a first separation unit to obtain a hydrocarbon stream at least partially freed of low boilers, and dividing the hydrocarbon stream at least partially freed of low boilers into two substreams A1 and A2;

[0007] b) subjecting the substream A1 to a heterogeneous catalytic reaction using a nickel-containing catalyst to obtain a reaction mixture A1;

[0008] c) separating the resulting reaction product from the reaction mixture A1 to obtain a hydrocarbon stream A1 from which the reaction products of step b) have been at least partially removed;

[0009] d) subjecting the substream A2 to a homogeneous catalytic reaction to obtain a reaction mixture A2;

[0010] e) separating the resulting reaction product from the reaction mixture A2 to obtain a hydrocarbon stream A2 from which the reaction products of step d) have been at least partially removed;

[0011] f) feeding the hydrocarbon stream A1 from step c) and the hydrocarbon stream A2 from step e) to hydrogenation to obtain a hydrogenated product;

[0012] g) separating at least a portion of the high boilers from the hydrogenation product of step f) in a second separation unit to obtain a purified hydrocarbon stream containing more than 98% by weight of Cx alkanes.

[0013] The method of the present invention has the advantage that a high-purity alkane stream can be obtained thereby. Homogeneous catalysis and heterogeneous catalysis reactions are carried out simultaneously, so the olefins contained in the hydrocarbon stream used can be converted into more valuable products. This makes it easier to complete the separation task of separating out high boilers in the final stage. In addition, market demand can also be flexibly responded to. If there is a greater demand for the products of heterogeneous catalytic reactions, the component A1 of the hydrocarbon stream from which low boilers have been removed and directed to the heterogeneous catalyst reaction can be increased to produce more of these products. The same applies to the opposite situation, if the demand for the products of homogeneous catalytic reactions is greater, then the component A2 is increased. Another advantage of this method is that it can be integrated into existing petrochemical production equipment.

[0014] The hydrocarbon stream to be purified is a Cx hydrocarbon stream, wherein x=3 to 5, i.e. x=3, 4 or 5. Such a stream contains both Cx alkanes and Cx olefins, as well as low boilers such as Cx-1 hydrocarbons and high boilers such as Cx+1 hydrocarbons. Such a stream can be obtained on an industrial scale by a cracking process and is used in various petrochemical processes. The stream used here does not contain alkyl tert-butyl ethers (ATBE), such as MTBE (methyl tert-butyl ether) or ETBE (ethyl tert-butyl ether), because these substances will enter the reaction steps described below as high boilers and may cause serious interference there. The object of the present invention is to obtain a stream containing more than 98% by weight of Cx alkanes, because such a stream is needed. For this reason, the stream is purified according to the present invention.

[0015] Thus, the hydrocarbon stream to be purified is a C3 hydrocarbon stream, a C4 hydrocarbon stream or a C5 hydrocarbon stream. The C3 hydrocarbon stream according to the present invention comprises at least propylene, propane, C2 hydrocarbons (e.g. ethylene, ethane) and C4 hydrocarbons (e.g. butane, butene). In the context of the present invention, such a C3 hydrocarbon stream is also referred to as a propylene stream (to be purified). The C4 hydrocarbon stream according to the present invention comprises at least butenes (e.g. 1-butene, 2-butene, optionally isobutylene), butanes, C3 hydrocarbons (e.g. propylene, propane) and C5 hydrocarbons (e.g. pentene, pentane). In the context of the present invention, such a C4 hydrocarbon stream is also referred to as a butene stream (to be purified) or an isobutylene stream. The C5 hydrocarbon stream according to the present invention comprises at least pentenes (e.g. 1-pentene, cis or trans-2-pentene), pentanes, C4 hydrocarbons (e.g. butylene, butane) and C6 hydrocarbons (e.g. hexene, hexane). In the context of the present invention, such a C5 hydrocarbon stream is also referred to as a pentene stream (to be purified). In a preferred embodiment, a butene stream is used as hydrocarbon stream to be purified.

[0016] The composition of the butene stream that is preferably used is not limited to a specific composition in principle. The only prerequisite is the presence of each component according to claim 1. The preferred butene stream contains butane, isobutane, butene (1-butene and 2-butene and optional isobutene). However, according to the present invention, the butene stream can contain 0.0001% by weight to 3% by weight of C3 hydrocarbons, 0.01% by weight to 90% by weight of butenes and 0.0001% by weight to 20% by weight of C5 hydrocarbons. In addition, the butene stream can additionally contain especially small amounts of dimethyl ether, water, methyl mercaptan, ethyl mercaptan, dimethyl sulfide, dimethyl disulfide and / or hydrogen sulfide (up to 100 ppm by weight in each case). The butene stream can contain traces of other substances or compounds that cannot be enumerated one by one. Some of these substances may have a noticeable odor. Its presence is undesirable and is minimized by the method described here.

[0017] In the first step a) of the method according to the invention, the hydrocarbon stream to be purified, in particular a propylene stream, a butene stream or a pentene stream, is fed to a first separation unit to separate low boilers, wherein at least a portion of the low boilers is separated. Suitable methods are basically familiar to those skilled in the art. The separation of at least a portion of the low boilers is preferably carried out in one or more distillation columns, particularly preferably in a single distillation column. Obviously, the low boilers present are obtained at the top and are at least partially removed there. Then, the hydrocarbon stream from which the low boilers are at least partially removed by separating the low boilers in step a) can be removed in particular as a bottom stream.

[0018] In principle, the distillation column preferably used for separating off at least part of the low boilers in step a) can be of any configuration and have any accessories, such as separating trays, as long as the function, ie separation of at least part of the low boilers, is ensured.

[0019] In a further preferred embodiment of the present invention, the separation of at least part of the low boilers in step a) is carried out at a pressure of 1 to 25 bar gauge, particularly preferably 2 to 20 bar gauge. The temperature during the separation in step a) is preferably 30° C. to 150° C., particularly preferably 35° C. to 100° C. In the context of the present invention, the unit bar gauge pressure refers to the bar overpressure, i.e. the overpressure above the respective ambient pressure.

[0020] After separating at least a portion of the low boilers from the hydrocarbon stream used, the resulting hydrocarbon stream, which has been at least partially freed of low boilers, is divided into two substreams A1 and A2. In the context of the present invention, this separation also falls under step a). Such a separation can be achieved, for example, simply using a T-piece in the pipeline together with one or more valves.

[0021] Then in step b), sub-stream A1 is subjected to heterogeneous catalytic reaction. This uses a nickel-containing catalyst. Through heterogeneous catalytic reaction, the olefins contained in the sub-stream A1 are at least partially reacted. Thus, reaction mixture A1 is obtained, which at least comprises the reaction product, unreacted olefins and Cx alkanes formed in the reaction. In the context of the present invention, the heterogeneous catalytic reaction that is preferably and can be used as the step b of the inventive method) is the oligomerization of contained olefins, i.e. propylene, butene or pentene.

[0022] In a preferred embodiment of the present invention, the heterogeneous catalytic reaction in step b) is an oligomerization reaction. Here, the olefins contained in the substream A1, i.e. propylene, butene or pentene, are converted into the corresponding oligomers. Since it is particularly preferred in the context of the present invention to use a butene stream in step a), this leads to an oligomerization reaction of butenes in step b).

[0023] The heterogeneous nickel-containing catalyst for oligomerization can be selected from known nickel catalysts suitable for oligomerization. Many catalyst systems are known to those skilled in the art. For example, reference is made here to the catalysts prepared in EP21213152.8, EP 3546065 A1 and EP 3549669 A1. In general, the catalyst systems disclosed therein have a composition of 15 to 40 wt %, preferably 15 to 30 wt % NiO, 5 to 30 wt % Al 2 O 3 , 55 wt % to 80 wt % SiO 2%, and up to 2.5% by weight, preferably 0.01% to 2% by weight, of an alkali metal oxide, preferably sodium oxide. These data are each based on 100% by weight of the total composition.

[0024] According to the present invention, the nickel-containing catalyst used for the oligomerization reaction in step b) may have a carbon content of 150 to 400 m 2 / g, preferably 190 to 350m 2 / g, particularly preferably 220 to 330m 2 The specific surface area of ​​200 m / g (calculated according to BET) is measured by nitrogen physical adsorption according to DIN ISO 9277 (version: 2014-01).

[0025] In another preferred embodiment, the nickel-containing catalyst used for the oligomerization reaction in step b) contains mesopores and macropores, i.e. has a bimodal pore size distribution. The mesopores of the nickel-containing catalyst used for the oligomerization reaction in step b) have an average pore size of 5 to 15 nm, preferably 7 to 14 nm, particularly preferably 9 to 13 nm. In contrast, the macropores of the nickel-containing catalyst used for the oligomerization reaction in step b) preferably have an average pore size of 1 to 100 μm, particularly preferably 2 to 50 μm. The average pore volume of the nickel-containing catalyst used for the oligomerization reaction in step b), i.e. both mesopores and macropores, can be 0.5 to 1.5 cm 3 / g, preferably 0.7 to 1.3 cm 3 The average pore diameter and the average pore volume can be determined by mercury porosimetry according to DIN 66133 (Edition: 1993-06).

[0026] In addition, the nickel-containing catalyst used for the oligomerization reaction in step b) can have an average particle size (d50) of 0.1 mm to 7 mm, preferably 0.5 to 6 mm, particularly preferably 1 mm to 5 mm. The average particle size can be determined by imaging methods, in particular by those methods in standards ISO 13322-1 (version: 2004-12-01) and ISO 13322-2 (version: 2006-11-01). A suitable instrument for analyzing the particle size is, for example, Camsizer 2006 (Retsch Technology).

[0027] If an oligomerization reaction is carried out in step b), it can be carried out under conditions known to those skilled in the art. In the context of the present invention, the oligomerization reaction of step b) is preferably carried out at a temperature of 50°C to 200°C, further preferably 60°C to 180°C, particularly preferably 60°C to 130°C. In the oligomerization reaction of step b), the pressure can be 10 to 70 bar, preferably 20 to 55 bar. If the oligomerization reaction is to be carried out in the liquid phase, the pressure and temperature parameters must be selected for this purpose so that the reactant stream (olefin or olefin mixture used) is in the liquid phase. The weight-based space velocity (mass of reactant per unit mass of catalyst per unit time; weight hourly space velocity (WHSV)) is 1 gram of reactant per gram of catalyst per hour (=1h -1 ) to 190h -1 , preferably 2h -1 Up to 35h -1 , especially preferably 3h -1 Until 25h -1 .

[0028] Then, in step c), the reaction mixture A1 obtained by the heterogeneous catalytic reaction of step b) is post-treated by at least partially removing the reaction product of step b). A hydrocarbon stream A1 is obtained here, which has been depleted of the reaction product of step b). Separation of the reaction product in step c) is preferably carried out by distillation. The conditions of distillation, such as temperature and pressure, are usually determined by the structure (tower height, number of plates, type of plates or packing, spacing, etc.). The separation performance of the distillation can also be controlled during operation by temperature distribution and / or heat supply to the tower and reflux in the distillate. By changing the pressure, the separation performance can also be adjusted within a certain range. Therefore, the precise adjustment cannot be defined above and independently of the structure of the distillation column, but this is known to those skilled in the art.

[0029] The hydrocarbon stream A1 obtained in step c) from which the reaction products of step b) have been at least partially removed is fed to the hydrogenation in step f). This has the advantage that even small amounts of olefin residues are hydrogenated and that a hydrocarbon stream which is as pure as possible can therefore be obtained after separation in step g). The hydrogenation is the last reaction step of the process according to the invention, after which the hydrogenated stream is only subjected to separation of high boilers.

[0030] The hydrogenation is preferably liquid phase hydrogenation. Here, process conditions such as pressure should be selected so that liquid phase hydrogenation becomes possible. The corresponding conditions are familiar to those skilled in the art. In the hydrogenation of step f), the olefins still contained in the hydrocarbon stream A1 from step c) are hydrogenated as completely as possible to form the corresponding alkanes. The hydrogenation of step f) is preferably carried out in a hydrogenation unit consisting of one or more reactors. The reactor can be operated in a circulation or straight-through mode. In a preferred embodiment of the present invention, the hydrogenation is carried out in at least two reactors, wherein the first reactor is operated in a circulation mode, and the second and possible other reactors are operated in a straight-through mode. In the hydrogenation, hydrogen is preferably used in a slight stoichiometric excess, particularly preferably in a stoichiometric excess of 5% to 30%.

[0031] In the hydrogenation of step f), known supported catalysts can be used, which contain at least one transition metal selected from palladium, platinum, rhodium, ruthenium, nickel or mixtures thereof and a support material selected from aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide or mixtures thereof. In principle, carbon-based supports such as activated carbon, graphite supports, carbon nanotubes, etc. can also be used. In a preferred embodiment of the present invention, a supported catalyst containing palladium or platinum as transition metal and aluminum oxide as support material is used in an optional step in the hydrogenation.

[0032] The hydrogenation of step f) is preferably carried out at a temperature of 25° C. to 80° C., particularly preferably at a temperature of 35° C. to 60° C. In the hydrogenation of step f), the pressure is preferably a pressure of 5 to 25 bar gauge, particularly preferably a pressure of 8 to 15 bar gauge. These conditions apply in particular if a butene stream is used in the process of the invention. The hydrogenation f) is followed by a phase separation known to those skilled in the art to separate the gas phase comprising unconverted hydrogen and optionally also small amounts of hydrocarbons from the liquid phase, which is then fed to the separation of step g).

[0033] With the exception of the hydrogenation in step f), the sequence of process steps described above relates only to the substream A1 obtained from step a). In contrast, the substream A2 of step a) is subjected to a homogeneously catalyzed reaction in step d). The homogeneously catalyzed reaction may be a hydroformylation, an alkoxycarbonylation or an epoxidation.

[0034] Epoxidation can be carried out by methods familiar to those skilled in the art. Conceivable epoxidants are all active oxygen-containing substances, such as hydrogen peroxide, peracetic acid or other peracids or oxygen. Epoxidation can be carried out in the gas phase with a heterogeneous catalyst, or in the liquid phase with a heterogeneous or homogeneous catalyst. Suitable methods for epoxidation are described in the prior art, for example, in WO 2011 / 107199A2 or WO 2017 / 089075 A1.

[0035] If the homogeneously catalyzed reaction in step d) is a hydroformylation, the following process conditions are preferred:

[0036] The olefins used in the process are hydroformylated by means of synthesis gas in the presence of a homogeneously dissolved catalyst system. The molar ratio between synthesis gas and feed mixture should be from 6:1 to 1:1, preferably from 3:1 to 1:1, particularly preferably from 2:1 to 1:1. The hydroformylation can optionally be carried out in the presence of solvents known to those skilled in the art.

[0037] Homogeneous catalyst systems that can be used for hydroformylation can comprise Co or Rh, preferably Rh, and preferably phosphorus-containing ligands. Suitable catalyst systems are familiar to those skilled in the art. In principle, hydroformylation reactions based on Co can also be carried out without ligands. In a particularly preferred embodiment, the homogeneous catalyst system comprises Rh and phosphorus-containing ligands or consists of Rh and phosphorus-containing ligands. Suitable ligands for the catalyst system according to the present invention are known to those skilled in the art (for example, see the textbook "Rhodium Catalyzed Hydroformylation (Rhodium Catalyzed Hydroformylation)" (2002) of PWNM van Leeuwen or A. and the textbook “Hydroformylation–Fundamentals, Processes and Applications in Organic Synthesis” by R. Franke (2016).

[0038] If Rh is used, the phosphorus-containing ligands used in the catalyst system according to the invention are preferably phosphines, such as TPP (triphenylphosphine), monophosphates, such as Alkanox 240 (tris(2,4-di-tert-butylphenyl) phosphite), or bisphosphites, such as BiPhePhos. It is also possible to use mixtures of ligands.

[0039] The temperature of the homogeneous catalytic hydroformylation is preferably 80° C. to 250° C., more preferably 90° C. to 225° C., particularly preferably 100° C. to 210° C. The pressure of the homogeneous catalytic hydroformylation is preferably 20 to 350 bar, more preferably 30 to 325 bar, particularly preferably 45 to 300 bar.

[0040] The pressure in the hydroformylation generally corresponds to the total gas pressure. In the context of the present invention, the total gas pressure is the sum of the pressures of all gaseous substances present, i.e. the pressure of the (entire) gas phase. In the present process, this corresponds in particular to the pressure of CO and H 2 The sum of the partial pressures of the gases, that is, the total gas pressure, is the synthesis gas pressure.

[0041] Homogeneously catalyzed hydroformylation can be operated as a liquid discharge process ("liquid cycle") or as a gas discharge process ("gas cycle"). Both process variants are known to the person skilled in the art and are described in many textbooks. In the context of the present invention, there is no need to specifically select such a process, since the process can be carried out in essentially two ways.

[0042] If the homogeneously catalyzed reaction in step d) is an alkoxycarbonylation, the following process conditions are preferred:

[0043] The homogeneous catalyst system used for the alkoxycarbonylation preferably comprises at least one metal from Groups 8 to 10 of the Periodic Table of the Elements (PTE) or a compound thereof, a phosphorus-containing ligand and an acid as a promoter.

[0044] The metal of PTE Group 8 to 10 is preferably palladium. Palladium is preferably used in the form of a precursor compound as a palladium compound coordinated by a phosphorus-containing ligand. An example of a palladium compound that can be used as a precursor compound is palladium chloride [PdCl 2 ]、Acetylacetonate palladium(II)[Pd(acac) 2 ]、palladium(II) acetate[Pd(OAc) 2 ]、Dichloro(1,5-cyclooctadiene)palladium[Pd(cod) 2 Cl 2 ]、Bis(dibenzylideneacetone)palladium(0)[Pd(dba) 2 ], tris(dibenzylideneacetone)dipalladium(0)[Pd 2 (dba) 3 ], bis(acetonitrile)dichloropalladium(II)[Pd(CH 3 CN) 2 Cl 2 ]、Pd(cinnamyl)palladium dichloride[Pd(cinnamyl)Cl 2 ]. Preferably, the compound [Pd(acac) 2 ] or [Pd(OAc) 2 The concentration of the palladium metal in the alkoxycarbonylation is preferably from 0.01 to 0.6 mol %, preferably from 0.03 to 0.3 mol %, particularly preferably from 0.04 to 0.2 mol %, based on the molar amount of the hydrocarbon used.

[0045] Suitable phosphorus-containing ligands of the catalyst system according to the present invention preferably have a bidentate structure. Preferred phosphorus-containing ligands of the catalyst system according to the present invention are benzene-based diphosphine compounds, such as disclosed in EP 3121184A2. The ligand can be combined with palladium in a preliminary reaction, thereby feeding the palladium-ligand complex to the reaction zone, or added in situ to the reaction and combined with palladium there. In the alkoxycarbonylation, the molar ratio of ligand to metal can be 1:1 to 10:1, preferably 2:1 to 6:1, and particularly preferably 3:1 to 5:1.

[0046] In the alkoxycarbonylation, the homogeneous catalyst system further comprises an acid, which can be in particular a Bronsted acid or a Lewis acid. The Lewis acid used can in particular be aluminum trifluoromethanesulfonate, aluminum chloride, aluminum hydride, trimethylaluminum, tri(pentafluorophenyl)borane, boron trifluoride, boron trichloride or a mixture thereof. Among the Lewis acids mentioned, aluminum trifluoromethanesulfonate is preferably used. The Lewis acid is preferably added in a molar ratio of Lewis acid to ligand of 1:1 to 20:1, preferably 2:1 to 15:1, particularly preferably 5:1 to 10:1.

[0047] Suitable Bronsted acids preferably have an acid strength of pKa ≤ 5, particularly preferably an acid strength of pKa ≤ 3. The acid strength pKa relates to the pKa value determined under standard conditions (25° C., 1.01325 bar). For polyprotic acids, in the context of the present invention, the acid strength pKa relates to the pKa value of the first protonation step. The Bronsted acid is preferably added in a molar ratio of Bronsted acid to ligand of 1:1 to 15:1, preferably 2:1 to 10:1, particularly preferably 3:1 to 5:1.

[0048] The Bronsted acids used may in particular be perchloric acid, sulfuric acid, phosphoric acid, methylphosphonic acid or sulfonic acid. Suitable sulfonic acids are, for example, methanesulfonic acid, trifluoromethanesulfonic acid, tert-butanesulfonic acid, p-toluenesulfonic acid (PTSA), 2-hydroxypropane-2-sulfonic acid, 2,4,6-trimethylbenzenesulfonic acid and dodecylsulfonic acid. Particularly preferred acids are sulfuric acid, methanesulfonic acid, trifluoromethanesulfonic acid and p-toluenesulfonic acid. The acid is preferably sulfuric acid. Carboxylic acids, on the other hand, are less suitable or not suitable at all.

[0049] The homogeneously catalyzed alkoxycarbonylation is preferably carried out at a temperature of 25 to 140° C., further preferably at a temperature of 80 to 120° C., particularly preferably at a temperature of 90 to 110° C. The pressure can be 5 to 60 bar, preferably 10 to 40 bar, particularly preferably 15 to 30 bar.

[0050] The product mixture obtained by the homogeneous catalytic alkoxycarbonylation comprises at least the ester formed by the reaction, the homogeneous catalyst system, low boilers, for example low boiling point by-products, such as ethers, high boilers, unreacted alcohol and optional unreacted hydrocarbons. Therefore, the product mixture can be subsequently separated out of the catalyst. This can be achieved, for example, by membrane separation, whereby the homogeneous catalyst system and unreacted hydrocarbons and / or unreacted alcohol are enriched in the retentate, and the formed ester is enriched in the permeate. The retentate comprising the enriched homogeneous catalyst system can then be recycled to the reaction zone.

[0051] The reaction mixture A2 obtained by step d) which usually comprises at least the reaction product formed in the reaction, unconverted olefins and Cx alkanes is then post-treated in step e), which is carried out by at least partially removing the reaction product of step d). The hydrocarbon stream A2 obtained here has been depleted of the reaction product of step d). It is preferably carried out by distillation to separate the reaction product in step d). In the case of homogeneous catalytic reaction, the catalyst system is also present in the reaction discharge and should be separated before separating the product. This can be achieved, for example, by evaporation and / or membrane separation. Suitable methods and conditions are familiar to those skilled in the art.

[0052] The hydrocarbon stream A2 obtained in step e) from which the reaction products of step d) have been at least partially removed is then fed together with the hydrocarbon stream A1 from step c) to the hydrogenation in step f). The process conditions have already been described above. The hydrogenation product obtained here is then fed to the separation in step g).

[0053] The separation in step g) should remove the high boilers still present to obtain a purified hydrocarbon stream containing more than 98% by weight of Cx alkanes. The purified hydrocarbon stream obtained containing more than 98% by weight of Cx alkanes is then discharged from the process. The discharged hydrocarbon stream can then be sold and used, for example, as a propellant gas. Possible high boilers that can be removed here are the reaction products of steps c) and / or e), which are sometimes not completely removed in the subsequent separation there.

[0054] The separation in step g) is preferably carried out by distillation in one or more distillation columns, preferably in a single distillation column. The high boilers are obtained at the bottom of the distillation column and the purified hydrocarbon stream is obtained at the top of the distillation column. The process conditions may vary depending on the composition and type of the hydrocarbon stream. However, the selection of suitable conditions will not cause major problems for those skilled in the art. Separating at least a portion of the high boilers in step g) may preferably be carried out at a pressure of 1 to 25 bar gauge, particularly preferably 2 to 20 bar gauge. The temperature during separation in step g) is preferably 30°C to 150°C, particularly preferably 35°C to 100°C. This is particularly applicable to the case where a butene stream is used in the process of the present invention.

Claims

1. A method for purifying a hydrocarbon stream, the hydrocarbon stream containing at least Cx alkanes, Cx olefins, low boilers such as Cx-1 hydrocarbons and high boilers such as Cx+1 hydrocarbons, but no alkyl tert-butyl ether (ATBE), wherein x is an integer from 3 to 5, wherein the method comprises the following steps: a) separating at least a portion of low boilers from a hydrocarbon stream in a first separation unit to obtain a hydrocarbon stream at least partially freed of low boilers, and dividing the hydrocarbon stream at least partially freed of low boilers into two substreams A1 and A2; b) subjecting the substream A1 to a heterogeneously catalyzed oligomerization reaction using a nickel-containing catalyst to obtain a reaction mixture A1; c) separating the resulting reaction product from the reaction mixture A1 to obtain a hydrocarbon stream A1 from which the reaction products of step b) have been at least partially removed; d) subjecting the substream A2 to a homogeneously catalyzed reaction to obtain a reaction mixture A2, wherein the homogeneously catalyzed reaction is a hydroformylation, an alkoxycarbonylation or an epoxidation, preferably a hydroformylation or an alkoxycarbonylation; e) separating the resulting reaction product from the reaction mixture A2 to obtain a hydrocarbon stream A2 from which the reaction products of step d) have been at least partially removed; f) feeding the hydrocarbon stream A1 from step c) and the hydrocarbon stream A2 from step e) to hydrogenation to obtain a hydrogenated product; g) separating at least a portion of the high boilers from the hydrogenation product from step f) in a second separation unit to obtain a purified hydrocarbon stream containing more than 98% by weight of Cx alkanes.

2. The process according to claim 1, wherein the hydrocarbon stream to be purified is a C4 hydrocarbon stream.

3. The process according to claim 1 or 2, wherein the separation in step a) is carried out at a pressure of 2 to 10 bar gauge.

4. The process according to any one of the preceding claims, wherein the separation of step a) is carried out at a temperature of 30°C to 90°C.

5. The process according to any of the preceding claims, wherein a heterogeneous nickel-containing catalyst is used in the oligomerization reaction in step b).

6. The process according to any one of the preceding claims, wherein the separation in step c) is a distillation.

7. The process according to any one of the preceding claims, wherein the homogeneous catalyst system in the hydroformylation comprises Co or Rh, preferably Rh, and preferably a phosphorus-containing ligand.

8. The process according to any one of the preceding claims, wherein the homogeneous catalyst system in the alkoxycarbonylation comprises a metal from Groups 8 to 10 of the Periodic Table of Elements (PTE) or a compound thereof, preferably Pd, a phosphorus-containing ligand and an acid as a promoter.

9. The process according to any one of the preceding claims, wherein the separation in step e) is a distillation.

10. The process according to any one of the preceding claims, wherein the hydrogenation in step f) is a liquid phase hydrogenation.

11. The process according to claim 10, wherein a supported catalyst is used in the hydrogenation, the supported catalyst comprising at least one transition metal selected from palladium, platinum, rhodium, ruthenium, nickel or mixtures thereof and a support material selected from aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide or mixtures thereof.

12. The process according to any one of the preceding claims, wherein the separation in step g) is carried out at a pressure of from 1 to 25 barg.

13. The process according to any one of the preceding claims, wherein a purified hydrocarbon stream obtained in step f) containing more than 98% by weight of Cx alkanes is discharged from the process.