Method for the regeneration of a solvent used in the extractive distillation of c4 unsaturated hydrocarbon mixtures

Abstract

The subject of the invention is a method for the regeneration of a solvent used in the extractive distillation of C4 unsaturated hydrocarbon mixtures, preferably a polar solvent from the group consisting of DMF, ACN, NMP, DMSO, wherein the mixture contains unsaturated acetylenic and diene hydrocarbons, in particular methylacetylene, ethylacetylene, vinylacetylene, 1,2-butadiene, propadiene, optionally 1,3-butadiene, butene isomers, dimers and other heavy C5+ hydrocarbons, wherein the method is based on hydrogenating the solvent before its regeneration by distillation.

Description

[0001] Method for the regeneration of a solvent used in the extractive distillation of C4 unsaturated hydrocarbon mixtures

[0002] The subject of the invention is a method for the regeneration of the solvent used in the extractive distillation of C4 unsaturated hydrocarbons mixtures.

[0003] Pyrolysis is used in industry to obtain light unsaturated hydrocarbons from various gaseous or liquid petroleum streams.

[0004] The preparation of butadiene is based mainly on extractive distillation processes of the C4 fraction produced in pyrolysis of paraffin hydrocarbons, which is usually oriented to the production of ethylene and propylene. The C4 fraction containing butadiene can also be obtained from renewable raw materials, e.g. ethanol. The term C4 fraction refers to mixtures of hydrocarbons containing mainly 4 carbon atoms per molecule. Separating the C4 fraction into its components is a complicated problem due to small differences in the relative volatility of its components during common distillation. For this reason, the separation into individual components is carried out by extractive distillation, i.e. distillation with the addition of a selective solvent (extractant). Polar solvents such as acetonitrile (ACN), dimethylformamide (DMF), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP) and others are used for the extractive distillation of the C4 fraction. Extractive distillation processes use differences in the solubility of individual C4 hydrocarbons and butadiene in a given solvent, and especially differences in their volatility. It is assumed that the higher unsaturation degree of the hydrocarbon, the better its solubility in these solvents [W. Oleksy, I. Wiecowska, J. Wojtania, Przemysl Chemiczny, 2005, 84 / 9, 658 - 661] or [W.C White, Chemico-Biological Interactions, 166 (2007) 10-14],

[0005] In the first step of separating the C4 hydrocarbon fraction, a solution of butadiene and other components that are well soluble in the solvent is obtained, from witch less soluble components, such as n-butane, isobutane, butene isomers, i.e. 1- butene, cis-2-butene and trans-2-butene, are separated by distillation, as the so- called raffinate.

[0006] By changing the pressure and temperature conditions in the next step, most of the butadiene is removed from the extraction solvent solution and subjected to further stages of distillation purification.

[0007] On the other hand, in the prior art solutions the solvent containing mainly very soluble hydrocarbons (better soluble than 1 ,3-butadiene), such as unsaturated acetylenic and diene hydrocarbons, heavy hydrocarbons, the so-called dimers and residual butadiene, is then regenerated in the distillation process. The acetylenic hydrocarbons dissolved in the extraction solvent are mainly ethylacetylene and vinylacetylene, and the diene hydrocarbons are 1 ,2-butadiene, propadiene and possibly residual 1 ,3-butadiene. Due to the good solubility of the components remaining in the extraction solvent, it is necessary to conduct distillative regeneration of the solvent under relatively hard conditions of high temperature. Typically, the regeneration system consists of two distillation columns. In the first column, light components are stripped, such as C4 acetylene and diene hydrocarbon residues. In the second column heavy components such as dimers and heavy hydrocarbons, the so-called tar are removed from the solvent. The disadvantage of this solvent regeneration process is the need to use a high distillation temperature, which favors the formation of heavy tar products and may even lead to clogging the column with sediments.

[0008] Many methods of separating C4 fraction by extractive distillation using selective solvents have been described in the literature. In all these methods, the gaseous C4 fraction, which is separated into individual components, is contacted countercurrently with a liquid selective solvent under appropriate thermodynamic conditions. Subsequent steps of C4 fraction separation are then carried out as described above and illustrated in the documents cited below.

[0009] Patent descriptions PL 163803, PL 201117 and EP 2914568 provide methods for conducting extractive distillation of the C4 hydrocarbon fraction, wherein the separation of the fraction into individual components was the result of maintaining appropriate distillation conditions. For example, EP 2914568 describes a method for separating 1 ,3-butadiene from the C4 fraction using a liquid ring compressor.

[0010] In the presence of a selective solvent, the volatility of components, such as n- butane, trans-2-butene, cis-2-butene, 1 -butene, isobutylene, increases significantly in comparison to 1 ,3-butadiene, while the volatility of C4 acetylenes decreases. In this way, it is possible to separate all components of the C4 pyrolysis fraction from 1 ,3-butadiene.

[0011] Typically, before separating the C4 hydrocarbon fraction by extractive distillation, it is hydrogenated to remove acetylenic hydrocarbons, 1 ,2-butadiene, propadiene and others. As a result of selective hydrogenation, vinylacetylene and ethylacetylene are reacted to butadiene or butene, increasing the efficiency of the entire process. Research is being carried out to achieve the greatest possible selectivity in these processes in order to limit the simultaneously occurring hydrogenation of 1 ,3- butadiene.

[0012] An example of combining the processes of the C4 fraction hydrogenation and extractive distillation is the hydrogenation process developed by UOP (KLPTM) integrated with the extractive distillation process of BASF [W. Oleksy, I. \A / i$cowska, J. Wojtania, Chemical Industry, 2005, 84 / 9, 658 - 661].

[0013] Patent description US 3898298 presents a method for selective hydrogenation of a butadiene stream containing vinyl acetylene, using aluminum oxide AI2O3 supported palladium catalyst, at a temperature of 35°C and under pressure of 7 bar. Such conditions provides for the presence of C4 hydrocarbons in liquid and gas phases in the reaction system. The reaction conducted in this way resulted in selective hydrogenation of vinylacetylene to butadiene, and its content in the butadiene stream decreased from 0.84% to 0.5%. The content of vinyl acetylene in the product has been significantly reduced, but it has not been completely removed.

[0014] US Patent No 4230897 discloses a method for the selective hydrogenation of acetylenic hydrocarbons, such as vinylacetylene, wherein the efficiency of the hydrogenation process of vinylacetylene and other impurities in a stream of unsaturated hydrocarbons, such as the C4 fraction, is improved, using a palladium catalyst of suitable crystallinity.

[0015] US Patent No 6437206 also claims the use of a hydrogenation catalyst with suitable crystallinity. An example is the selective hydrogenation of the C4 fraction in the presence of a palladium catalyst with the suitable diffraction spectrum. This fraction contained over 40% of 1 ,3-butadiene, ethylacetylene and vinylacetylene, in addition to the desired butenes (1 -butene, cis- and trans-2-butene, isobutene) and smaller amounts of n-butane and isobutane. As a result of selective hydrogenation, the content of 1 ,3-butadiene, ethylacetylene and vinylacetylene decreased to about 1 %. US Patent No 6127310 describes a method for selective hydrogenation of alkynes or diolefins to less unsaturated hydrocarbons, such as alkenes, in the presence of a palladium catalyst supported on aluminum oxide with an admixture of silver and other metals. The process gives an example of hydrogenation of the C5 hydrocarbon fraction.

[0016] European Patent EP 0087980 describes a method of selective hydrogenation of hydrocarbons having 4 or more carbon atoms in the molecule and having double and triple bonds, in the presence of solid hydrogenation catalysts (e.g. palladium), which consists in dividing the catalyst bed into sections and adding a stream of fresh hydrogen to each section. As a result of this process, 1 ,3-butadiene, propadiene, 1 ,2-butadiene and vinylacetylene were hydrogenated, but butene isomers were not hydrogenated.

[0017] Another European Patent EP2545019 describes steps of the process for the selective hydrogenation of acetylene and the isolation of pure 1,3-butadiene from the C4 fraction by extractive distillation using a selective solvent.

[0018] In turn, International Patent Application WO 98 / 12160 describes a method for selective hydrogenation of a C4 hydrocarbon stream in order to remove vinylacetylene, ethylacetylene and 1 ,2-butadiene using catalytic distillation. In addition to hydrogenation of hydrocarbons, the process also involves distillation to separate the C4 hydrocarbon fraction from heavier hydrocarbons. In this process, mainly unwanted hydrocarbons, such as vinylacetylene or ethylacetylene, are hydrogenated, while the level of 1 ,3-butadiene conversion is small.

[0019] US Patent No 6734328 describes a method for isolating and purifying 1 ,3-butadiene by selective two-step hydrogenation of ethylacetylene, vinylacetylene and other acetylenic compounds contained in the 1 ,3-butadiene stream. In the first step, the hydrogenation reaction is carried out in a flow reactor with a fixed bed of catalyst, while in the second step, catalytic distillation is carried out, which in addition to hydrogenation provides for the concentration of the 1 ,3-butadiene stream. Both reactors use AI2O3 supported palladium-copper catalysts. The possibility of using C4-C10 paraffinic or aromatic hydrocarbons and ethers as a solvent is also claimed. The process of separating pure 1 ,3-butadiene from the C4 hydrocarbon stream is known from US Patent No 9062262, in which acetylenic compounds such as vinylacetylene contained in the C4 fraction are hydrogenated in a three-stage reactor, and then the hydrogenizate is separated using various types of extractive distillation with the isolation of pure 1 ,3-butadiene.

[0020] In all these processes, the C4 hydrocarbon fraction is hydrogenated to remove unwanted components with many unsaturated and acetylenic bonds, and then it is subjected to extractive distillation to separate into individual fractions and isolate pure 1 ,3-butadiene.

[0021] In selective hydrogenation of the C4 fraction, it is difficult to sufficiently remove unwanted components without hydrogenating desirable components, such as 1 ,3- butadiene. On the other hand, separation of the unhydrogenated C4 fraction only by extractive distillation may lead to butadiene of inappropriate quality or large losses of butadiene and other hydrocarbons.

[0022] A significant problem of the processes used is the regeneration of the extraction solvent, which is returned to the process after distillative removal of components dissolved therein. In addition to the residual 1 ,3-butadiene and butene isomers, the extraction solvent before regeneration contains unsaturated acetylene and diene hydrocarbons, such as e.g. ethylacetylene, vinylacetylene, methylacetylene, 1 ,2- butadiene, propadiene, as well as dimers and other heavy C5+ hydrocarbons. Due to the good solubility of these components, the distillative regeneration process of the solvent requires the use of relatively high temperatures. This causes these ingredients to undergo side reactions, forming unwanted tar products and deposits. There are also losses of the solvent itself, e.g. as a result of irreversible reactions with these substances and high temperature conditions during distillation.

[0023] Vinylacetylene present in C4 fractions during the regeneration of the extraction solvent may be particularly hazardous, as its presence in process streams at a concentration above 30 mol% may lead to spontaneous explosion. In processes used to date for separating 1 ,3-butadiene from the C4 fraction using extractive distillation, vinylacetylene and other acetylenic compounds are removed from the extraction solvent by distillation, using additional dilution of gas streams, e.g. with raffinate fractions, other hydrocarbon fractions or inert gas, to maintain the concentration of acetylenic compounds in all pumped streams at an appropriately low level. Such streams are usually further burned, because other ways of their management are not economically justified.

[0024] Surprisingly, it has been found that gas hydrocarbon fractions absorbed in a polar solvent used in extractive distillation can be hydrogenated before regeneration of the extraction solvent - without separating them from the solvent - using typical hydrogenation catalysts and under typical conditions for hydrogenation of olefinic hydrocarbons, while the extraction solvent is not hydrogenated. According to the invention, the fraction of the extraction solvent containing unsaturated hydrocarbons is hydrogenated and then regenerated by distillation. This makes solvent regeneration by distillation more effective, easier and safer to implement. In the method according to the invention, a mixture of unsaturated hydrocarbons is hydrogenated in a polar extraction solvent used in a given extractive distillation process, preferably selected from the group of DMF, ACN, NMP, DMSO. The advantage of the method according to the invention is the selectivity of hydrogenation of unsaturated hydrocarbons contained in the mixture. In the case of hydrogenation of mixtures of unsaturated hydrocarbons with one or more double bonds, hydrocarbons with multiple double bonds are selectively hydrogenated at first as compared to hydrocarbons with lower bonds number, i.e. with one double bond. Similarly, in the case of hydrogenation of mixtures of unsaturated hydrocarbons with double and / or triple bonds, the hydrocarbons with triple bond are selectively hydrogenated at first, followed by the hydrocarbons with double bond. Similarly, when a mixture of C4 hydrocarbons contains 1,3-butadiene and butene isomers, butadiene is first hydrogenated to butenes, and n-butane, i.e. the product of butene hydrogenation, is usually not observed in the product. If an acetylenic compound is present in a mixture of unsaturated hydrocarbons, it will be first hydrogenated, followed by the olefinic compound with double bonds.

[0025] The method according to the invention allows for the hydrogenation of all unsaturated bonds in hydrocarbons, leading to the production of paraffinic hydrocarbons. The degree of hydrogenation depends on the process conditions, including temperature, pressure, catalyst contact time, and especially an excess of hydrogen.

[0026] An important advantage of the method according to the invention is that in the case of hydrogenation of a solution of unsaturated C4 hydrocarbons containing methylacetylene, ethylacetylene and other acetylenic impurities, in particular those containing vinylacetylene, the safety of handling streams containing vinylacetylene is improved. During the process, vinylacetylene absorbed in the extraction solvent is hydrogenated to butadiene or butene and it can be fully hydrogenated, therefore, further processing of this stream does not lead to the accumulation of vinylacetylene above explosive concentration. It is not necessary to dilute the hydrogenizate streams, and after separation from the extraction solvent, the hydrocarbon stream can be returned to the extractive distillation process or used for other purposes, e.g. as a gas fuel.

[0027] An additional advantage of the method according to the invention is that due to differences in the solubility of individual hydrocarbons in the selective extraction solvent, hydrocarbons with a higher hydrogenation level (more saturated) are more easily separated from the solvent, facilitating its purification.

[0028] In the C4 hydrocarbon mixture containing vinylacetylene, ethylacetylene, butadiene and butenes, vinylacetylene and ethylacetylene have the highest solubility in extraction solvents such as DMF, ACN and NMP, followed by butadiene. The ratio of the content of individual components in the mixture undergoing hydrogenation can be changed during extractive distillation as required by changing the parameters of the absorption of C4 hydrocarbons in the solvent or their desorption from the extraction solvent. Hydrocarbons with triple bonds and / or multiple double bonds are concentrated in the extraction solvent before hydrogenation, while hydrocarbons with lower number or without triple bonds remain mostly outside the solution undergoing hydrogenation. This promotes selectivity of the entire solvent regeneration process and the production of the desired C4 hydrocarbons. The parameters influencing the absorption or desorption of individual components of the hydrocarbon mixture in the polar extraction solvent are, for example, temperature, pressure, and contact time of the hydrocarbon mixture with the solvent.

[0029] The method for regenerating a solvent used in the extractive distillation of mixtures of unsaturated C4 hydrocarbons, preferably a polar solvent from the group consisting of DMF, ACN, NMP, DMSO, containing absorbed unsaturated acetylenic and diene hydrocarbons, in particular methylacetylene, ethylacetylene, vinylacetylene, 1 ,2-butadiene, propadiene, optionally 1 ,3-butadiene, butene isomers, dimers and other heavy C5+ hydrocarbons according to the invention, is distinguished by hydrogenation of the solvent before its regeneration by distillation. Hydrogenation can be carried out by any suitable method, and it can be carried out in a fixed bed reactor, as well as using other known methods for conducting the hydrogenation process, for example using a fluidized bed reactor, catalytic distillation, or hydrogenation with a homogeneous catalyst.

[0030] Hydrogenation is preferably carried out in a flow reactor with a fixed bed of catalyst. In preferred embodiment hydrogenation is carried out in a flow reactor in the presence of a solid metal catalyst supported on a solid oxide support.

[0031] The hydrogenation reaction is carried out in the presence of catalysts commonly used for the hydrogenation of hydrocarbons with unsaturated bonds, such as olefins, dienes or acetylenes.

[0032] Preferably, Pd, Pt, Ni, Ru, Rh, Cr, Cu, Ag, Au Ir, or their mixtures are used as the metal catalyst, and AI2O3, SiC>2, TiOz, ZrO2 are preferably used as the solid oxide support. However, this does not limit the use of other catalysts used in hydrogenation processes.

[0033] If necessary, the catalyst should be activated before the hydrogenation reaction, in accordance with the procedure provided for a given catalyst. In the process according to the invention, the hydrogenation reaction is carried out at a temperature that provides the activity of a given catalyst, but this temperature should be optimized for a given mixture of unsaturated hydrocarbons dissolved in a polar solvent, so as to maximize the desired reactions (e.g. hydrogenation of acetylenic bonds) and limit the unwanted ones (e.g. .hydrogenation of single bonds). Preferably, the hydrogenation temperature should be in the range of 10°C to 250°C. The pressure at which the hydrogenation reaction is carried out should provide good solubility of the olefinic hydrocarbons intended for hydrogenation in a liquid polar solvent at a given temperature, so as to limit their release into the gas phase.

[0034] Preferably, the reaction pressure should be in the range from atmospheric pressure to 50 bar and higher, however using too high pressure, i.e. above 50 bar, is not economically justified.

[0035] In the method according to the invention, the process is carried out in such a way that a stream containing unsaturated hydrocarbons dissolved in a polar solvent is contacted with hydrogen gas, and then the mixture is fed to the reactor. The amount of hydrogen added is not limited, but it is preferably close to or slightly higher than the amount of hydrogen needed to hydrogenate the unsaturated bonds in the unwanted components of the hydrocarbon mixture. For example, in the case of removing vinylacetylene from the C4 fraction, the amount of dosed hydrogen should be close to the stoichiometric amount and adjusted to the vinylacetylene content in the liquid stream, determined e.g. by gas chromatography, so as to hydrogenate only triple bonds, and limit the hydrogenation of e.g. butadiene. In turn, a large excess of hydrogen in relation to the number of unsaturated bonds present in the hydrogenated hydrocarbon fraction means that all unsaturated bonds may be hydrogenated and the product will contain only paraffinic hydrocarbons.

[0036] The catalyst load, i.e. the amount of unsaturated hydrocarbons solution fed to the hydrogenation reactor in relation to the amount of catalyst, depends on the content of these hydrocarbons in the solution and should be selected so as to obtain a sufficiently long contact time of the reactants with the catalyst, allowing for high conversion of unsaturated components, which hydrogenation is expected and limiting the conversion of target hydrocarbons. Too long residence time of unsaturated hydrocarbons in the reactor causes hydrogenation of butadiene or other desired components and the formation of by-products, e.g. olefin dimers and oligomers. On the other hand, if the contact time is too short, the hydrogenation level of acetylenic or other unwanted hydrocarbons is insufficient. Hydrogenation is preferably carried out at catalyst hourly volume load with liquid solution of the extraction solvent containing C4 hydrocarbons, LHSV, ranging from 0.1 h-1 to 100 h-1.

[0037] The hydrogenation reaction leads to hydrocarbons with reduced number of unsaturated bonds, which are less soluble in the extraction solvent, and therefore they can desorb from the solution while leaving the reactor, to give a separate gas phase. This facilitates the separation of the hydrogenated hydrocarbon fraction from the extraction solvent in the next regeneration step, i.e. the step of purification by distillation. In addition, the solvent contains hydrogenated hydrocarbons, which are less reactive at elevated temperatures, and as a result side reactions occurring during distillation, which cause solvent losses and increase the amount of byproducts (tars) are limited. This makes it possible to reduce the temperature of the extraction solvent regeneration by distillation.

[0038] The following examples illustrate the method of the invention involving hydrogenation of unsaturated hydrocarbons, without limiting the scope of the protection claimed.

[0039] Example I

[0040] The residue from the extractive distillation of butadiene with DMF, containing dissolved residues of the C4 fraction with the composition given in Table 1 , was used as the liquid raw material for hydrogenation.

[0041] The hydrogenation reaction was carried out in a flow reactor with a fixed bed of Pd / ALOs hydrogenation catalyst (0.5% Pd), previously activated in a stream of hydrogen. A stream of hydrogen was passed through the reactor at a pressure of 5 bar and a rate of GHSV = 500 h'1, and the temperature in the reactor was raised to the reaction temperature of 50°C. After achieving this temperature, feeding of the liquid raw material began at a rate providing the catalyst load LHSV = 1 h’1. The hydrogen flow provided the volume ratio of hydrogen to liquid raw material H2 / L = 500. The gaseous phase and liquid phase were analyzed and the results are presented in Table 1 together with the raw material composition. The analysis includes only hydrocarbons, and not unreacted hydrogen.

[0042] Table 1

[0043] Table 1 shows that most of the C4 hydrocarbons and dimers were in the gaseous phase at 50°C. However, the purity of DMF in the liquid phase increased and the content of heavy hydrocarbons decreased. The conversion of 1,3-butadiene was about 75% and as a result of hydrogenation, mainly butene isomers were formed. No n-butane or isobutane was detected in liquid and gaseous products. The hydrogenation reaction was also accompanied by an isomerization reaction, which resulted in the formation of cis-2-butene and trans-2-butene from 1 -butene.

[0044] Example II

[0045] The example illustrates the possibility of hydrogenation according to the method of the invention using a hydrogenation catalyst other than palladium. The residue from the extractive distillation of butadiene with DMF was used as the hydrogenation raw material, with the composition given in Table 2. The hydrogenation reaction was carried out as in Example I, with the difference that instead of the palladium catalyst, a nickel catalyst Ni / Al2O3 (20% Ni) was used and the catalyst load with liquid raw material was LHSV = 3 h'1instead of 1 h'1.

[0046] Tabela 2.

[0047] Table 2 shows that all acetylenic compounds were fully hydrogenated. 1 ,3- Butadiene was also converted (about 86%), therefore 1 -butene appeared in the C4 fraction and the content of 2-butene isomers increased. As a result of hydrogenation, the degree of bond saturation in the C4 fraction and in heavy products increased, therefore most of them evaporated into the gas phase at the reaction temperature. The purity of DMF in the liquid phase increased from 98.7% to 99.8%. No n-butane or isobutane was detected in the products.

[0048] Example III

[0049] The example illustrates the possibility of hydrogenation according to the method of the invention using a different extraction solvent. Instead of a solution of C4 hydrocarbons in DMF, a solution of C4 hydrocarbons in acetonitrile (ACN) was prepared. For this purpose, the C4 fraction was absorbed in ACN by passing a gaseous stream of hydrocarbons through the liquid. The raw material contained C5+ hydrocarbons, in addition to ACN and C4 hydrocarbons. The composition of the raw material subjected to hydrogenation and liquid and gaseous products is given in Table 3. The hydrogenation reaction was carried out as in Example II, with the difference that the catalyst load was LHSV = 2 h'1instead of 3 h'1.

[0050] Tabel 3.

[0051] Table 3 shows that most of the C4 hydrocarbons and most of the heavy hydrocarbons were in the gaseous phase. A large amount of ACN was also found in the gaseous phase, which was related to the lower boiling point of ACN than DMF. The conversion of 1 ,3-butadiene was about 79%. Hydrogenation resulted mainly in formation of butenes. No n-butane or isobutane was detected in the products. The hydrogenation reaction was also accompanied by the isomerization of butenes, which resulted in the formation of cis-2-butene and trans-2-butene from 1 -butene.

[0052] SUBSTITUTE SHEET (RULE 26)

Claims

Claims1 . A method for the regeneration of a solvent used in the extractive distillation of unsaturated C4 hydrocarbon mixtures, preferably a polar solvent from the group consisting of dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethylsulfoxide, wherein the mixture comprises unsaturated acetylenic and diene hydrocarbons, in particular methylacetylene, ethyl acetylene, vinylacetylene, 1,2-butadiene, propadiene, optionally 1 ,3-butadiene, butene isomers, dimers and other heavy C5+ hydrocarbons, wherein the solvent is hydrogenated before its regeneration by distillation.

2. The method according to claim 1 , wherein the hydrogenation is carried out in a flow reactor with a fixed-bed of catalyst.

3. The method according to claim 1 , wherein the hydrogenation is carried out in a flow reactor in the presence of a metal catalyst supported on solid oxide.

4. The method according to claim 1 or 3, wherein the used metal catalyst is Pd, Pt, Ni, Ru, Rh, Cr, Cu, Ag, Au Ir, or their mixtures, and the solid oxide support is AI2O3, SiO2, TiO2, ZrO2.

5. The method according to claim 1 , wherein the hydrogenation temperature is from 10°C to 250°C.

6. The method according to claim 1 , wherein the reaction pressure ranges from atmospheric pressure to 50 bar.

7. The method according to claim 1 , wherein the hydrogenation is carried out at the hourly catalyst volume load, LHSV, ranging from 0.1 h-1to 100 h-1.SUBSTITUTE SHEET (RULE 26)

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