Process for purifying hydrocarbon streams including heterogeneously and homogeneously catalysed reactions

Abstract

The present invention relates to a process for purifying a hydrocarbon stream comprising at least Cx alkanes, Cx olefins, low boilers such as Cx-1 hydrocarbons and high boilers such as Cx+1 hydrocarbons, with x = 3 to 5. According to the invention, first low boilers are removed and then the stream is separated into two substreams, each of which is subjected to a chemical reaction. After the products have been separated off, the streams are combined again and subjected to a high boiler removal step.

Description

[0001] Processes for the purification of hydrocarbon streams including heterogeneous and homogeneously catalyzed reactions

[0002] The invention relates to a process for purifying a hydrocarbon stream containing at least Cx-alkanes, Cx-olefins, low boilers such as Cx-i hydrocarbons, and high boilers such as Cx+i hydrocarbons, where x = 3 to 5. In the process according to the invention, low boilers are first removed, followed by a separation into two substreams, each of which is subjected to a chemical reaction. After separation of the products, the streams are recombined and subjected to a high boiler removal.

[0003] The production of C3 to C5 alkane streams that can be used, for example, as propellants has been known for a long time. To be used as propellants, the resulting C3 to C5 alkane streams must meet certain product specifications, meaning they may contain only small amounts of undesirable and / or odor-causing substances. In this context, the term "odor-causing substance" refers to any substance or compound that is different from the substance constituting the propellant. If the propellants are to be used in the cosmetic or medical sector, any contamination with reactive components such as olefins, as well as any odorous contamination with other substances or compounds, should be avoided, since these usually involve applications close to the body.

[0004] The general objective is to improve existing processes to obtain streams with lower contamination from off-odor substances. It is also important to provide a process that is as efficient and cost-effective as possible.

[0005] It has surprisingly been shown that the separation of a stream obtained from a low-boiling separation and the passage through different reaction steps leads to a lower load with foreign odor-forming substances.

[0006] 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, where x is an integer from 3 to 5, the process comprising the following steps: a) separating at least a portion of the low boilers from the hydrocarbon stream in a first separation unit to obtain a hydrocarbon stream at least partially freed from low boilers and separating the hydrocarbon stream at least partially freed from low boilers into two substreams A1 and A2; b) carrying out a heterogeneously catalyzed reaction with the substream A1 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 from step b) have been at least partially removed; d) carrying out a homogeneously catalyzed reaction with the partial stream A2 to obtain a reaction mixture A2; e) separating the resulting reaction product from the reaction mixture A2 to obtain a hydrocarbon stream A2 from which the reaction products from 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 a hydrogenation to obtain a hydrogenation product; g) separating at least some of the high boilers from the hydrogenation product from step f) in a second separation unit to obtain a purified hydrocarbon stream which contains more than 98% by weight of Cx-alkanes.

[0007] The process according to the invention has the advantage that it can produce a high-purity alkane stream. Both a homogeneously catalyzed and a heterogeneously catalyzed reaction are operated simultaneously, allowing the olefins contained in the hydrocarbon stream to be converted into more valuable products. The separation task in the high-boiler removal in the final stage is thus easier to accomplish. Furthermore, it is possible to respond flexibly to market needs. If there is greater demand for products from the heterogeneously catalyzed reaction, the subset A1 of the hydrocarbon stream freed of low-boiling components, which is fed to the heterogeneously catalyzed reaction, can be increased to produce more of these products. The same applies conversely if the demand for the product of the homogeneously catalyzed reaction is higher, in which case the subset A2 must be increased.A further advantage of this process is that it can be integrated into existing petrochemical production plants.

[0008] The hydrocarbon stream to be purified is a Cx-hydrocarbon stream with x = 3 to 5, i.e. x = 3, 4 or 5. Such streams contain both Cx-alkanes and Cx-olefins, but also low boilers such as Cx-i-hydrocarbons and high boilers such as Cx+i-hydrocarbons. Such streams are available on an industrial scale from cracking processes and are used in a wide variety of petrochemical processes. The streams used here do not contain any alkyl tert-butyl ethers (ATBE) such as MTBE (methyl tert-butyl ether) or ETBE (ethyl tert-butyl ether), since these would enter the reaction steps described below as high boilers and can lead to serious disruptions there. The aim of the present invention is to obtain streams containing more than 98 wt. % Cx-alkanes, since there is a demand for such streams. For this purpose, the streams are purified according to the invention.

[0009] The hydrocarbon stream to be purified is accordingly a C3 hydrocarbon stream, a C4 hydrocarbon stream, or a C5 hydrocarbon stream. C3 hydrocarbon streams according to the invention comprise at least propene, propane, C2 hydrocarbons (e.g. ethene, ethane), and C4 hydrocarbons (e.g. butane, butene). Such a C3 hydrocarbon stream is also referred to in the context of the present invention as a propene stream (to be purified). C4 hydrocarbon streams according to the invention comprise at least butene (e.g. 1-butene, 2-butene, optionally isobutene), butane, C3 hydrocarbons (e.g. propene, propane), and C5 hydrocarbons (e.g. pentene, pentane). Such a C4 hydrocarbon stream is also referred to in the context of the present invention as a butene stream or isobutene stream (to be purified). C5 hydrocarbon streams according to the invention contain at least pentene (e.g. 1-pentene, cis- or trans-2-pentenes), pentane, C4 hydrocarbons (e.g.Butenes, butane) and C6 hydrocarbons (e.g., hexenes, hexane). Such a C5 hydrocarbon stream is also referred to in the present invention as a pentene stream (to be purified). In a preferred embodiment, a butene stream is used as the hydrocarbon stream to be purified.

[0010] The composition of the preferably used butene stream is fundamentally not limited to a specific composition. The only requirement is that the individual components according to claim 1 are present. Preferred butene streams contain butane, isobutane, and butenes (1-butene and 2-butene and optionally isobutene). According to the invention, however, the butene stream can contain from 0.0001 to 3 wt. % C3 hydrocarbons, from 0.01 to 90 wt. % butenes, and from 0.0001 to 20 wt. % C5 hydrocarbons. Furthermore, the butene stream can additionally contain, among other things, small amounts of dimethyl ether, water, methanethiol, ethanethiol, dimethyl sulfide, dimethyl disulfide, and / or hydrogen sulfide (each up to 100 wt. ppm). The butene stream can contain traces of other substances or compounds that cannot be listed individually. Some of these substances may have a perceptible odor. Their presence is undesirable and is minimized by the procedure described here.

[0011] In the first step a) of the process according to the invention, the hydrocarbon stream to be purified, in particular the propene stream, the butene stream, or the pentene stream, is fed to a low boiler removal unit in a first removal unit, where at least a portion of the low boilers is removed. Suitable processes are generally familiar to those skilled in the art. The removal 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. It is understood that the low boilers present are obtained at the top and are at least partially removed there. The hydrocarbon stream at least partially freed of low boilers by the low boiler removal in step a) can then be removed, in particular, as a bottom stream.

[0012] The distillation column preferably used for the separation of at least a portion of the low boilers in step a) can in principle be designed as desired and have any internals such as separation stages, as long as the function, i.e. the separation of at least a portion of the low boilers, is ensured.

[0013] In a further preferred embodiment of the present invention, the removal of at least a portion of the low boilers in step a) is carried out at a pressure of 1 to 25 barg, particularly preferably 2 to 20 barg. The temperature during the removal in step a) is preferably in the range of 30 to 150°C, particularly preferably in the range of 35 to 100°C. In the context of the present invention, the unit "barg" means bar gauge pressure, i.e., an overpressure above the respective ambient pressure.

[0014] After separating at least a portion of the low boilers from the hydrocarbon stream used, the resulting hydrocarbon stream, at least partially freed from low boilers, is separated into two substreams A1 and A2. This separation also falls within step a) within the scope of the present invention. Such a separation can be carried out, for example, simply via a T-piece in the line together with one or more valves.

[0015] Substream A1 is then subjected to a heterogeneously catalyzed reaction in step b). A nickel-containing catalyst is used. The heterogeneously catalyzed reaction at least partially converts the olefins present in substream A1. This results in a reaction mixture A1 that contains at least the reaction products formed during the reaction, unreacted olefins, and the Cx-alkanes. The heterogeneously catalyzed reaction preferred within the scope of the present invention, which can be carried out as step b) of the process according to the invention, is an oligomerization of the olefins present, i.e., propenes, butenes, or pentenes.

[0016] In a preferred embodiment of the present invention, the heterogeneously catalyzed

[0017] The reaction in step b) is an oligomerization. The olefins present in substream A1, i.e., propenes, butenes, or pentenes, are converted into the corresponding oligomers. Since the use of a butene stream in step a) is particularly preferred in the context of the present invention, this would result in an oligomerization of butenes in step b).

[0018] The heterogeneous nickel-containing catalyst used in the oligomerization can be selected from the known nickel catalysts suitable for use in oligomerization. Numerous catalyst systems are known to the person skilled in the art. By way of example, reference is made here to the catalysts whose preparation has been described in EP 21213152.8, EP 3 546 065 A1, and EP 3 549 669 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.% Al2O3, 55 to 80 wt.% SiO2, and up to 2.5 wt.%, preferably 0.01 to 2 wt.% of an alkali metal oxide, preferably sodium oxide. The data in each case relate to a total composition of 100 wt.%.

[0019] According to the invention, the nickel-containing catalyst used in step b) for the oligomerization can have a specific surface area (calculated according to BET) of 150 to 400 m2 / g, preferably 190 to 350 m 2 / g, particularly preferably from 220 to 330 m 2 / g. The BET surface area is measured using nitrogen physisorption according to DIN-ISO 9277 (as of January 2014).

[0020] In a further preferred embodiment, the nickel-containing catalyst for oligomerization used in step b) has mesopores and macropores, i.e. has a bimodal pore size distribution. The mesopores of the nickel-containing catalyst for oligomerization used in step b) have an average pore diameter of 5 to 15 nm, preferably 7 to 14 nm, particularly preferably 9 to 13 nm. The macropores of the nickel-containing catalyst for oligomerization used in step b), in contrast, preferably have an average pore diameter of 1 to 100 pm, particularly preferably 2 to 50 pm. The average pore volume of the nickel-containing catalyst for oligomerization used in step b), i.e. both of the mesopores and the macropores, can be 0.5 to 1.5 cm3 / g, preferably 0.7 to 1.3 cm3 / g.The mean pore diameter and the mean pore volume can be determined by mercury porosimetry according to DIN 66133 (as of 1993-06).

[0021] Furthermore, the nickel-containing catalyst used in step b) for the oligomerization can have an average particle diameter (d50) of 0.1 mm to 7 mm, preferably 0.5 to 6 mm, particularly preferably 1 mm to 5 mm. The average particle diameter can be determined using imaging methods, in particular those specified in the standards ISO 13322-1 (as of December 1, 2004) and ISO 13322-2 (as of November 1, 2006). A suitable device for analyzing the particle diameter is, for example, the Camsizer 2006 (Retsch Technology). If oligomerization is carried out in step b), this can be carried out under conditions known to those skilled in the art. In the context of the present invention, the oligomerization in step b) is preferably carried out at a temperature in the range from 50 to 200 °C, further preferably 60 to 180 °C, particularly preferably in the range from 60 to 130 °C.The pressure during the oligomerization in step b) can be in the range from 10 to 70 bar, preferably in the range from 20 to 55 bar. If the oligomerization is to take place in the liquid phase, the pressure and temperature parameters must be selected such that the reactant stream (the olefins or olefin mixtures used) is in the liquid phase. The weight-based space velocities (reactant mass per catalyst mass per time; weight hourly space velocity (WHSV)) are in the range between 1 g of reactant per g of catalyst and per h (= 1 h). 1 ) and 190 h 1 , preferably between 2 tr 1 and 35 tr 1 , particularly preferably between 3 tr 1 and 25 h- 1 .

[0022] The reaction mixture A1 obtained from the heterogeneously catalyzed reaction in step b) is subsequently worked up in step c) by at least partially removing the reaction products from step b). This yields a hydrocarbon stream A1 which is depleted in the reaction products from step b). The reaction products are preferably separated in step c) by distillation. The distillation conditions, for example temperature and pressure, are usually determined by the structure (column height, number of trays, type of trays or packing, spacing, etc.). During operation, the separation properties of the distillation can be further controlled via the temperature distribution and / or the heat input in the column and the reflux in the distillate. Likewise, the separation properties can be adjusted within certain limits by changing the pressure.The exact settings cannot therefore be defined at a higher level and independently of the structure of the distillation column, which is, however, known to the person skilled in the art.

[0023] The hydrocarbon stream A1 obtained from step c), from which the reaction products from step b) have been at least partially removed, is subjected to hydrogenation in step f). This has the advantage that even small residual olefins are hydrogenated, thus allowing the purest possible hydrocarbon stream to be obtained after separation in step g). Hydrogenation is the final reaction step of the process according to the invention, after which the hydrogenated stream is subjected only to high boiler removal.

[0024] The hydrogenation is preferably a liquid-phase hydrogenation. The process conditions, such as the pressure, must be selected such that liquid-phase hydrogenation is possible. Corresponding conditions are familiar to the person skilled in the art. In the hydrogenation in step f), olefins still present in the hydrocarbon stream A1 from step c) are hydrogenated as completely as possible to the corresponding alkanes. The hydrogenation in step f) is preferably carried out in a hydrogenation unit consisting of one or more reactors. The reactors can be operated in a recycle or in a straight pass. In a preferred embodiment of the present invention, the hydrogenation is carried out in at least two reactors, the first reactor being operated in a recycle and the second and possible further reactors being operated in a straight pass.During hydrogenation, hydrogen is preferably used in a slight stoichiometric excess, particularly preferably in a stoichiometric excess of 5 to 30%.

[0025] In the hydrogenation in step f), known supported catalysts can be used which contain at least one transition metal from the group consisting of palladium, platinum, rhodium, ruthenium, nickel, or mixtures thereof, and a support material from the group consisting of aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide, or mixtures thereof. In principle, however, carbon-based supports can also be used, for example, activated carbon, graphitic supports, carbon nanotubes, or the like. In a preferred embodiment of the present invention, a supported catalyst containing palladium or platinum as the transition metal and aluminum oxide as the support material is used in the hydrogenation in the optional step.

[0026] The hydrogenation in step f) is preferably carried out at a temperature of 25 to 80°C, particularly preferably at a temperature of 35 to 60°C. The pressure during the hydrogenation in step f) is preferably 5 to 25 barg, particularly preferably 8 to 15 barg. These conditions apply in particular when a butene stream is used in the process according to the invention. After the hydrogenation f), a phase separation known to the person skilled in the art takes place in order to separate the gas phase, which comprises unreacted hydrogen and optionally also small amounts of hydrocarbons, from the liquid phase, which is then fed to the separation in step g).

[0027] With the exception of the hydrogenation in step f), this sequence of the previously described process steps applies exclusively to the substream A1 obtained from step a). Instead, the substream A2 from step a) is subjected to a homogeneously catalyzed reaction in step d). The homogeneously catalyzed reaction can be a hydroformylation, an alkoxycarbonylation, or an epoxidation.

[0028] The epoxidation can be carried out using methods familiar to those skilled in the art. All substances containing active oxygen are conceivable as epoxidizing agents, for example, hydrogen peroxide, peracetic acid, or other peracids, or even oxygen. The epoxidation can be carried out either in the gas phase with heterogeneous catalysts or in the liquid phase with heterogeneous or homogeneous catalysts. Suitable epoxidation processes are described in the prior art, for example, in WO 2011 / 107199 A2 or WO 2017 / 089075 A1. If the homogeneously catalyzed reaction in step d) is a hydroformylation, the following process conditions are preferred:

[0029] The olefins used in the process are hydroformylated with synthesis gas in the presence of a homogeneously dissolved catalyst system. The molar ratio between synthesis gas and the feed mixture should be between 6:1 and 1:1, preferably between 3:1 and 1:1, particularly preferably between 2:1 and 1:1. The hydroformylation can optionally be carried out in the presence of a solvent known to those skilled in the art.

[0030] The homogeneous catalyst system usable in the hydroformylation can comprise Co or Rh, preferably Rh, and preferably a phosphorus-containing ligand. Corresponding catalyst systems are familiar to those skilled in the art. Co-based hydroformylations can, in principle, also be carried out without ligands. In a particularly preferred embodiment, the homogeneous catalyst system comprises or consists of Rh and a phosphorus-containing ligand.

[0031] Suitable ligands for the catalyst systems according to the invention are known to the person skilled in the art (see, for example, the textbooks “Rhodium Catalyzed Hydroformylation” (from 2002) by PWN M van Leeuwen or “Hydroformylation - Fundamentals, Processes and Applications in Organic Synthesis” (from 2016) by A. Börner and R. Franke).

[0032] The phosphorus-containing ligand for the catalyst system according to the invention, when Rh is used, is preferably a phosphine (e.g., TPP (triphenylphosphine)), a monophosphite (e.g., Alkanox 240 (tris(2,4-di-tert-butylphenyl)phosphite)) or a bisphosphite (e.g., Biphephos). Mixtures of ligands can also be used.

[0033] The temperature in the homogeneously catalyzed hydroformylation is preferably in the range from 80 to 250 °C, further preferably in the range from 90 to 225 °C and particularly preferably in the range from 100 to 210 °C. The pressure in the homogeneously catalyzed hydroformylation is preferably in the range from 20 to 350 bar, further preferably in the range from 30 to 325 bar and particularly preferably in the range from 45 to 300 bar.

[0034] The pressure during hydroformylation typically corresponds to the total gas pressure. In the context of the present invention, the total gas pressure refers to 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 sum of the partial pressures of CO and H2, i.e., the total gas pressure is then the synthesis gas pressure.

[0035] Homogeneous-catalyzed hydroformylations can be operated as liquid recycle or gas recycle processes. Both process variants are known to those skilled in the art and are described in many textbooks. A specific selection of such a process is not necessary within the scope of the present invention because the process can, in principle, be carried out in both ways.

[0036] If the homogeneously catalyzed reaction in step d) is an alkoxycarbonylation, the following process conditions are preferred:

[0037] The homogeneous catalyst system used for the alkoxycarbonylation preferably comprises at least one metal from group 8 to 10 of the Periodic Table of Elements (PSE) or a compound thereof, a phosphorus-containing ligand and an acid as co-catalyst.

[0038] The metal from group 8 to 10 of the PSE is preferably palladium. The palladium is preferably used in the form of a precursor compound, which is coordinated by the phosphorus-containing ligand. Examples of palladium compounds that can be used as precursors are palladium chloride [PdCl], palladium(II) acetylacetonate [Pd(acac)2], palladium(II) acetate [Pd(OAc)2], dichloro-(1,5-cyclooctadiene)palladium(II) [Pd(cod)2Cl2], bis(dibenzylideneacetone)palladium(0) [Pd(dba)2], tris(dibenzylideneacetone)dipalladium(0) [Pd2(dba)s], bis(acetonitrile)dichloropalladium(II) [Pd(CH3CN)2Cl2], and palladium(cinnamyl)dichloride [Pd(cinnamyl)Cl2]. The compounds [Pd(acac)2] or [Pd(OAc)2] are preferably used.The metal concentration of palladium in the alkoxycarbonylation is preferably between 0.01 and 0.6 mol%, preferably between 0.03 and 0.3 mol%, particularly preferably between 0.04 and 0.2 mol%, based on the amount of hydrocarbon used.

[0039] Suitable phosphorus-containing ligands for the catalyst system according to the invention preferably have a bidentate structure. Preferred phosphorus-containing ligands for the catalyst system according to the invention are benzene-based diphosphine compounds, as disclosed, for example, in EP 3 121 184 A2. The ligands can be combined with the palladium in a preliminary reaction, so that the palladium-ligand complex is fed to the reaction zone, or they can be added to the reaction in situ and combined with the palladium there. The molar ratio of ligand to metal in the alkoxycarbonylation can be from 1:1 to 10:1, preferably from 2:1 to 6:1, particularly preferably from 3:1 to 5:1.

[0040] In the alkoxycarbonylation, the homogeneous catalyst system further comprises an acid, which can in particular be a Brønsted acid or a Lewis acid. Suitable Lewis acids include, in particular, aluminum triflate, aluminum chloride, aluminum hydride, trimethylaluminum, tris(pentafluorophenyl)borane, boron trifluoride, boron trichloride, or mixtures thereof. Of the Lewis acids mentioned, aluminum triflate is preferably used. The Lewis acid is preferably added in a Lewis acid:ligand molar ratio of 1:1 to 20:1, preferably 2:1 to 15:1, particularly preferably 5:1 to 10:1. Suitable Brönsted acids preferably have an acid strength of pKs < 5, particularly preferably an acid strength of pKs < 3. The stated acid strength pKs refers to the pKs value determined under standard conditions (25°C, 1.01325 bar).For a polybasic acid, the acid strength pKa in the context of this invention refers to the pKa value of the first protolysis step. The Brønsted acid is preferably added in a Brønsted acid:ligand molar ratio of 1:1 to 15:1, preferably 2:1 to 10:1, particularly preferably 3:1 to 5:1.

[0041] Perchloric acid, sulfuric acid, phosphoric acid, methylphosphonic acid, or sulfonic acids can be used as Brønsted acids. Suitable sulfonic acids include, 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 at all suitable.

[0042] The homogeneously catalyzed alkoxycarbonylation is preferably carried out at a temperature of 25 to 140 °C, more preferably at a temperature of 80 to 120 °C, and particularly preferably at a temperature of 90 to 110 °C. The pressure can be between 5 and 60 bar, preferably between 10 and 40 bar, particularly preferably between 15 and 30 bar.

[0043] The homogeneously catalyzed alkoxycarbonylation yields a product mixture comprising at least the ester formed by the reaction, the homogeneous catalyst system, low boilers, for example low-boiling by-products such as ethers, high boilers, unreacted alcohols, and possibly unreacted hydrocarbons. The product mixture can therefore be subjected to subsequent catalyst separation. This can be achieved, for example, using a membrane separation, whereby the homogeneous catalyst system and unreacted hydrocarbon and / or unreacted alcohol are enriched in the retentate, while the formed ester is enriched in the permeate. The retentate, which comprises the enriched homogeneous catalyst system, can be recycled to the reaction zone.

[0044] The reaction mixture A2 obtained from step d), which generally contains at least the reaction products formed during the reaction, unreacted olefins, and the Cx-alkanes, is subsequently worked up in step e) by at least partially removing the reaction products from step d). This yields a hydrocarbon stream A2 which is depleted in the reaction products from step d). The reaction products from step d) are preferably separated by distillation. In homogeneously catalyzed reactions, the catalyst system is also present in the reaction effluent and should be separated before product separation. This can be achieved, for example, by evaporation and / or membrane separation. Corresponding processes and conditions are familiar to those skilled in the art.

[0045] The hydrocarbon stream A2 obtained from step e), from which the reaction products from step d) have been at least partially removed, is then passed together with the hydrocarbon stream A1 from step c) for hydrogenation in step f). The process conditions have already been described above. The hydrogenation product obtained is then fed to the separation stage in step g).

[0046] During the separation in step g), any remaining high boilers are to be removed to obtain a purified hydrocarbon stream containing more than 98 wt.% Cx-alkanes. The resulting purified hydrocarbon stream, which contains more than 98 wt.% 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 from steps c) and / or e), which may not have been completely removed in the subsequent separations.

[0047] The separation in step g) is preferably carried out by distillation in one or more distillation columns, preferably a single distillation column. The high boilers are obtained in the bottom of the distillation column and the purified hydrocarbon stream at the top of the distillation column. The process conditions can vary depending on the composition and type of hydrocarbon stream. However, the selection of suitable conditions does not pose any major problems for the person skilled in the art. The separation of at least some of the high boilers in step g) can preferably be carried out at a pressure of 1 to 25 barg, particularly preferably 2 to 20 barg. The temperature during the separation in step g) is preferably in the range from 30 to 150°C, particularly preferably in the range from 35 to 100°C. This applies in particular when a butene stream is used in the process according to the invention.

Claims

Patent claims 1. A process for purifying a hydrocarbon stream containing at least Cx alkanes, Cx olefins, light boilers such as Cx-1 hydrocarbons and heavy boilers such as Cx+1 hydrocarbons, but no alkyl tert-butyl ethers (ATBE), where x is an integer from 3 to 5, the process comprising the following steps: a) separating at least some of the light boilers from the hydrocarbon stream in a first separation unit to obtain a hydrocarbon stream at least partially free of light boilers, and separating the hydrocarbon stream at least partially free of light boilers into two partial streams A1 and A2; b) carrying out a heterogeneously catalyzed oligomerization with the partial stream A1 using a nickel-containing catalyst to obtain a reaction mixture A1;c) Separation of the reaction product obtained from the reaction mixture A1 to obtain a hydrocarbon stream A1 from which the reaction products from step b) have been at least partially removed; d) Carrying out a homogeneously catalyzed reaction with the partial stream A2 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) Separation of the reaction product obtained from the reaction mixture A2 to obtain a hydrocarbon stream A2 from which the reaction products from 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 a hydrogenation to obtain a hydrogenation product;g) Separation of at least some of the heavy-boiling elements from the hydrogenation product from step f) in a second separation unit to obtain a purified hydrocarbon stream containing more than 98 wt% Cx alkanes.; 2. The method according to claim 1, wherein the hydrocarbon stream used and to be purified is a C4 hydrocarbon stream.

3. Method according to claim 1 or 2, wherein the separation in step a) takes place at a pressure of 2 to 10 bar.

4. Method according to one of the preceding claims, wherein the separation in step a) takes place at a temperature in the range of 30 to 90 °C.

5. Method according to one of the preceding claims, wherein a heterogeneous nickel-containing catalyst is used in the oligomerization in step b).

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

7. A method according to any of the preceding claims, wherein the homogeneous catalyst system for the hydroformylation comprises Co or Rh, preferably Rh, and preferably a phosphorus-containing ligand.

8. A method according to any of the preceding claims, wherein the homogeneous catalyst system in the alkoxycarbonylation comprises a metal from group 8 to 10 of the periodic table of elements (PSE) or a compound thereof, preferably Pd, a phosphorus-containing ligand and an acid as a co-catalyst.

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

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

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

12. Method according to one of the preceding claims, wherein the separation in step g) takes place at a pressure of 1 to 25 bar g. Method according to one of the preceding claims, wherein the purified hydrocarbon stream obtained in step f), which contains more than 98 wt.% Cx alkanes, is removed from the process.