An alcohol conversion process

Abstract

The present invention relates to an alcohol conversion process wherein a homogenous transition metal catalyst is used. The catalyst is kept in solution throughout the whole process, including the reaction in liquid phase, passing several distillation steps and an aqueous extraction step. The catalyst neither precipitates as a solid nor is solved in the wash water due to the use of a solvent or solvent mixture having a high boiling point and a specific miscibility gap regarding the wash water.

Description

[0001] An alcohol conversion process

[0002] The present invention relates to an alcohol conversion process.

[0003] A commonly used industrial production of alcohols is mainly based on an oxo process. Said process comprises the reaction of an alkene with oxo gas, which is a mixture of hydrogen and carbon monoxide in a 1 :1 molar ratio. The reaction is followed by hydrogenation of the aldehyde into the desired alcohol.

[0004] An alternative process for the synthesis of alcohols is based on the Guerbet reaction, which is known for many decades (M. Guerbet, C. R. Hebd. Seances Acad. Sc / . 1899, 128, p. 511-513). It is generally accepted that the mechanism leading to Guerbet alcohols comprises the following three steps: (i) dehydrogenation of a primary alcohol to the respective aldehyde; (ii) aldol condensation of two aldehyde molecules to an a,p-unsaturated aldehyde with elimination of water; and (iii) hydrogenation of the unsaturated aldehyde to the dimer alcohol. An alkaline catalyst, e.g. sodium or potassium hydroxide or sodium or potassium alkoxides, is required for the Guerbet reaction. Often homogeneous or hetereogeneous metal catalysts are added to accelerate the dehydrogenation and hydrogenation steps. However, the Guerbet reaction generally suffers from harsh conditions, poor selectivity, separation issues and low yield.

[0005] In the chemical industry, butanol is an important intermediate product and solvent for a broad variety of products, including paints and various plastics. Up to now, butanol is produced from a petro-based feedstock, leading to a significant product carbon footprint for butanol and the resulting products. Therefore, it is important for the chemical industry to find and open an economical and sustainable process route to butanol with a lower product carbon footprint.

[0006] Ethanol may be a sustainable feedstock to produce chemicals. Using ethanol in the Guerbet reaction may be a profitable and sustainable approach to produce butanol. Whereas the Guerbet reaction is used up to date to produce higher alcohols from higher boiling alcohol feedstocks than ethanol, there is so far no industrial usage for the Guerbet reaction for ethanol as the feedstock to produce butanol. While the Guerbet reaction itself may seem a simple chemical reaction, employing ethanol as the feedstock causes inherent problems particularly concerning selectivity. Because the product, n-butanol, can itself also undergo dehydrogenation, higher alcohols often result as side products in the process, making the reaction so far not profitable on an industrial scale.

[0007] Y.Xie et aL, “Highly efficient Process for Production of Biofuel from ethanol Catalyzed by Ruthenium Pincer Complexes”, Journal of the American Society, vol. 138, no. 29, 2016-07-18, pages 9077 to 9080, relates to a ruthenium pincer-catalyzed Guerbet-type process for the production of biofuel from ethanol.

[0008] WO 2012 / 119928 A1 discloses a method for producing alkanol amines, which comprise a primary amino group and a hydroxyl group, by alcohol amination of diols comprising two hydroxyl groups, using ammonia, and elimination of water. The reaction is homogeneously catalyzed in the presence of at least one complex catalyst, which contains at least one element selected from groups 8, 9 and 10 of the periodic table and at least one donor ligand.

[0009] WO 2013 / 156399 A1 relates to a method for producing branched alcohols using at least one alcohol of formula R1-CH2-CH2-OH, the groups R1being different or the same and being selected from C2-C3 alkyl, linear or branched, in a homogeneous phase in the presence of at least one base, characterized in that at least one complex compound containing Ru(ll) is used, in which the Ru(ll) has at least one ligand L1, which is at least bidentate, at least one coordination site of L1being a nitrogen atom.

[0010] Therefore, it was an object of the present invention to provide an alcohol conversion process allowing a profitable and sustainable approach to produce alcohols such as butanol in a way such that the employed catalyst is recycled in the chemical process.

[0011] The present invention thus relates to an alcohol conversion process based on the Guerbet reaction, wherein a homogenous transition metal catalyst is used. Due to economical as well as sustainability reasons, this catalyst must be recycled in the chemical process. Advantageously, in the provided alcohol conversion process, the catalyst is kept in solution throughout the whole process, including the reaction in liquid phase, passing several distillation steps and an aqueous extraction step. The catalyst neither precipitates as solid nor is solved in the wash water due to the use of a solvent or solvent mixture having a high boiling point and a specific miscibility gap regarding the wash water.

[0012] The present invention in particular relates to an alcohol conversion process, comprising

[0013] (i) providing at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor;

[0014] (ii) preparing a liquid mixture ME comprising at least one alcohol R-CH2-CH2-OH, a base, a solvent, and the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor provided according to (i), R being selected from the group consisting of H and Ci-C4-alkyl;

[0015] (iii) subjecting the liquid mixture ME prepared according to (ii) to alcohol conversion conditions in a reaction space SG and obtaining in said reaction space a reaction mixture MG comprising at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH, x being an integer in the range of from 1 to 4, wherein the alcohol conversion conditions comprise a temperature of the reaction mixture MG in the range of from 100 to 250 °C and a pressure in the reaction space SG in the range of from 1 x 105Pa to 4 x 106Pa;

[0016] (iv) separating the at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH from the reaction mixture MG obtained according to (iii), obtaining the at least one alcohol R-CH2-CH2- (CHR-CH2)X-OH and a mixture Mos comprising the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and the solvent; (v) recycling one or more of at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and at least a part of the solvent comprised in the mixture Mcs obtained according to (iv) to (ii) or (iii); wherein the base is selected from the group consisting of ammonium hydroxide, alkali hydroxides, alkaline earth hydroxides, ammonium carbonate, ammonium hydrogen carbonate, alkali carbonates, alkali hydrogen carbonates, alkaline earth carbonates, alkaline hydrogen carbonates, alkali alkoxides, alkaline earth alkoxides, alkali metal amides, alkaline earth metal amides, secondary amino acids, and a mixture of two or more thereof; the solvent has a boiling point of at least 110 °C at atmospheric pressure, wherein the solvent has a solubility in water at 25 °C of from 0 to 1 weight.-%; the catalyst comprises a compound of formula (A) wherein

[0017] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0018] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0019] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0020] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;

[0021] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted C1-C10 alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and C1-C10 alkyl; Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0022] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH; the precursor of the catalyst comprising a compound of formula (A) comprises a mixture comprising a compound comprising a metal M and at least one component selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, organic carbonyl compounds, Ci-Cio-alkyl, Ci-Ci2-cycloalkyl, C2-Ci2-alkenyl, Cs-Cis-cycloalkenyl, C5-C20- aryl, CN, CO, OH, OC(=O)CF3, OSO2CF3, hydrides, pyridines, halogenides, hydroxides, and thiophenes; and a compound of formula (H) wherein M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru; L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0023] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst comprising a compound of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;

[0024] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-C -alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and C C -alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-O -heterocycle comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S.

[0025] The process in accordance with the present invention is preferably a continuous process. Alternatively, the process is preferably a semi-batch process or a batch process.

[0026] Preferably, from 90 to 100 weight-%, more preferably from 95 to 100 weight-%, more preferably from 98 to 100 weight-%, more preferably from 99 to 100 weight-% of the liquid mixture ME prepared according to (ii) consist of the at least one alcohol R-CH2-CH2-OH, the base, the solvent and the at least one of a catalyst, a precursor thereof, or a reduced form of the catalyst or the precursor.

[0027] The alcohol conversion conditions according to (iii) preferably comprise the presence of at least one inert gas in the reaction space SG, wherein the at least one inert gas is preferably selected from the group consisting of nitrogen, argon, and a mixture thereof. It is also preferred that the alcohol conversion conditions according to (iii) comprise a pressure in the reaction space SG in the range of from 1 x 105to 3.5 x 106Pa, preferably in the range of from 1 x 105to 3.1 x 106Pa, more preferably in the range in the range of from 1 x 105to 2 x 106Pa, more preferably in the range in the range from 1 x 105to 1 .5 x 106Pa, .

[0028] Preferably, the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 200 °C, preferably in the range of from 120 to 180 °C, more preferably in the range of from 130 to 160 °C. The alcohol conversion conditions according to (iii) preferably comprise an amount of the base in the reaction mixture MG in the range of from 0.1 to 10 weight-%, preferably in the range of from 0.5 to 8 weight-%, more preferably in the range of from 1 to 5 weight-%, based on the total weight of the reaction mixture MG.

[0029] Furthermore, the alcohol conversion conditions according to (iii) preferably comprise an amount of the solvent in the reaction mixture MG in the range of from 5 to 50 weight-%, preferably in the range of from 5 to 30 weight-%, more preferably in the range of from 5 to 10 weight-%, based on the total weight of the reaction mixture MG.

[0030] In another preferred embodiment, the alcohol conversion conditions according to (iii) comprise an amount of the catalyst in the reaction mixture MG in the range of from 0.001 to 2 weight-%, preferably in the range of from 0.001 to 1 weight-%, more preferably in the range of from 0.001 to 0.5 weight-%, based on the total weight of the reaction mixture MG.

[0031] Also preferred is the reaction space in step (iii) comprising a the reaction mixture MG and a gas phase, wherein the gas phase comprises H2, and wherein the alcohol conversion conditions according to (iii) comprise maintaining the H2 partial pressure of the gas phase in the range of from 2 x 104to 3.1 x 106Pa, preferably in the range of from 2 x 104to 1.1 x 106Pa, more preferably in the range of from 2 x 104to 6 x 105Pa, even more preferably in the range of from 5 x 104to 6 x 105Pa, even more preferably in the range of from 7 x 104to 6 x 105Pa.

[0032] The H2 partial pressure of the gas phase is preferably maintained by introducing H2 into the gas phase. The H2 partial pressure of the gas phase is also preferably maintained by relaxation of the gas phase.

[0033] “Maintaining” the H2 partial pressure of the gas phase in the sense of the present invention includes ensuring that the H2 partial pressure is within the desired range during the reaction. In case the H2 partial pressure is within the desired range, no active steps have to be carried out mandatorily, but the pressure may still be adjusted to a different part of the range if desired. However, in order to ensure that the H2 partial pressure is neither too high nor too low, the H2 partial pressure may preferably be adjusted, or must be adjusted in case of ensuring that the H2 partial pressure is maintained within the desired range, for example by relaxation of the gas phase, in which case the H2 partial pressure may be reduced, or, alternatively, by introducing H2 into the gas phase, in which case the H2 partial pressure may be increased. Depending upon the H2 partial pressure during the reaction, one or even both of said alternatives may be carried out if desired to adjust the H2 partial pressure and to maintain the H2 partial pressure within the desired pressure range at all times during the reaction.

[0034] In a further preferred embodiment, preparing a liquid mixture ME in step (ii) comprises at least one alcohol R-CH2-CH2-OH, a base, a solvent, and the at least one of a catalyst, or precursor thereof provided according to (i). Preferably, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound comprising a metal M selected from the group consisting of lrCI3x H2O, [lr(COD)CI]2, [lr(COE)2CI]2, [lr(C2H4)2CI]2, [lr(COD)OH]2, [lr(COD)MeO]2, [lrCp*CI2], [IrCp Cl2], lr4(CO)i2, [lr(PPh3)2(CO)CI], [lr(acetylacetonate)3], and [lr(acetylacetonate)(COD)], wherein Cp is cylclopentadienyl, Cp* is pentamethylcyclopentadi- enyl, COD is 1 ,5-cyclooctadienyl, COE is cyclooctenyl, and methylallyl is 2-methylallyL Alternatively, preferably, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound comprising a metal M selected from the group consisting of [Ru(p-cymene)CI2]2, [Ru(benzene)CI2]y, [Ru(CO)2CI2]y, where y is in each case in the range from 1 to 1000, [Ru(CO)3CI2]2, [Ru(COD)(allyl)], RuCI3x H2O, [Ru(acety- lacetonate)3], [Ru(DMSO)4CI2], [Ru(cyclopentadienyl)(CO)2CI], [Ru(cyclopentadienyl)(CO)2H], [Ru(cyclopentadienyl)(CO)2]2, [Ru(Cp)(CO)2CI], [Ru(Cp*)(CO)2H], [Ru(Cp*)(CO)2]2, [Ru(in- denyl)(CO)2CI], [Ru(indenyl)(CO)2H], [Ru(indenyl)(CO)2]2, ruthenocene, [Ru(COD)CI2]2, [Ru(Cp*)(COD)CI], [RU3(CO)I2], [Ru(PPh3)4(H)2], [Ru(PPh3)3(CI)2], [Ru(PPh3)3(CO)(CI)2], [Ru(PPh3)3(CO)(CI)(H)], [Ru(PPh3)3(CO)(H)2], and [Ru(cyclooctadienyl)(methylallyl)2], wherein Cp is cylclopentadienyl, Cp* is pentamethylcyclopentadienyl, COD is 1 ,5-cyclooctadienyl, and methylallyl is 2-methylallyL

[0035] Preferably, the reduced form of the precursor comprises a compound of formula (P-l) or (P-ll): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroquinoline unit, a decahydroquinoline unit, a tetrahydroacridine unit, or a tetradecahydroacridine unit; and wherein L1and L2are, independently of each other, as defined above; wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above.

[0036] More preferred is that the reduced form of the precursor comprises a compound of formula (P-l): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroacridine unit, or a tetradecahydroacridine unit.

[0037] In another more preferred embodiment, the reduced form of the precursor comprises a compound of formula (P-ll): wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above.

[0038] Preferably, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (B) wherein

[0039] M is selected from the group consisting of Ir, Ru, and Mn;

[0040] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0041] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0042] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-C -alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-C -alkyl; unsubstituted or substituted Ci-C -cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-Cio-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0043] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH. In another preferred embodiment, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (C) wherein

[0044] M is selected from the group consisting of Ir, Ru, and Mn;

[0045] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0046] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0047] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-C -alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-C -alkyl; unsubstituted or substituted Ci-C -cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-Cw-heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0048] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH.

[0049] Preferably, M is selected from the group consisting of Ir and Ru, wherein M is more preferably Ru. In a more preferred embodiment, M is Ru, and wherein the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 170 °C, preferably in the range of from 120 to 170 °C, more preferably in the range of from 120 to 160 °C, more preferably in the range of from 130 to 150 °C.

[0050] Preferably, L3is CO.

[0051] It is also preferred that L1and L2are each (PRaRb), and wherein Raand Rbare Ci-Cw-alkyl, preferably wherein Raand Rbare each isopropyl or tert-butyl. Alternatively, wherein L1and L2are each (PRaRb), and wherein Raand Rbare Ci-Cio-cycloalkyl, preferably wherein Raand Rbare each cyclohexyl. Also preferred is that L1and L2are each (PRaRb), and wherein Raand Rbare Cs-C -aryl.

[0052] Preferably, Y is selected from the group consisting of F, Cl, Br, and I, preferably wherein Y is selected from the group consisting of Cl or Br, more preferably wherein Y is Cl. Also preferred is

[0053] Y being CO.

[0054] Preferably, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (D) wherein Cy is cyclohexyl.

[0055] Also preferred is that the reduced form of the catalyst comprises a compound of formula (D’) wherein Cy is cyclohexyl.

[0056] In a further preferred embodiment, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (E) wherein iPr is isopropyl.

[0057] Also preferred is that the reduced form of the catalyst comprises a compound of formula (E’) wherein iPr is isopropyl.

[0058] In a further preferred embodiment, the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (F) wherein tBu is tert-butyl.

[0059] It is also preferred that the reduced form of the catalyst comprises a compound of formula (F’) wherein tBu is tert-butyl.

[0060] Preferably, integer x is 1 or 2, more preferably wherein integer x is 1 .

[0061] Preferably, R is selected from the group consisting of H, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl, preferably from the group consisting of H, methyl, ethyl, propyl, and isopropyl, more preferably selected from the group consisting of H, ethyl, and propyl, wherein more preferably R is H.

[0062] In a further preferred embodiment, the liquid mixture ME prepared according to (ii) further comprises a compound of formula ( wherein R1, R2, R3and R4, L1, L2, and n are identical to R1, R2, R3and R4, L1, L2, and n of the catalyst of formula (A).

[0063] More preferred is that in the liquid mixture ME prepared according to (ii) and subjected to alcohol version conditions according to (iii), the molar ratio of the compound of formula (G) relative to the compound of formula (A) is in a range of from 0.01 :1 to 10:1 , preferably in the range of from 0.05:1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.3:1 to 10:1 , more preferably in the range of from 0.5:1 to 10:1 , more preferably in the range of from 0.7:1 to 10:1 , more preferably in the range of from 0.8:1 to 10:1 , more preferably in the range of from 1 :1 to 10:1 more preferably in the range of from 1.01 :1 to 10:1 , more preferably in the range of from 1.02:1 to 8:1 , more preferably in the range from 1 .03:1 to 7:1 , more preferably in the range from 1 .04:1 to 6:1 , and more preferably in the range from 1 .05:1 to 5:1. Also preferred is that the compound of formula (G) is selected from the group consisting of dicyclohexyl-[[5-(dicyclohexylphosphanylmethyl)ac- ridin-4-yl]methyl]phosphane, diisopropyl-[[5-(diisopropylphosphanylmethyl)acridin-4-yl]me- thyl]phosphane, dicyclohexyl-[[5-(dicyclohexylphosphanylmethyl)pyridin-4-yl]methyl]phosphane and diisopropyl-[[5-(diisopropylphosphanylmethyl)pyridin-4-yl]methyl]phosphane, preferably wherein the compound of formula (G) is cyclohexyl-[[5-(dicyclohexylphosphanylmethyl)acridin-4- yl]methyl]phosphane or diisopropyl-[[5-(diisopropylphosphanylmethyl)acridin-4-yl]methyl]phos- phane.

[0064] Preferably, the base is selected from the group consisting of alkali hydroxides, alkali alkoxides, and a mixture thereof. More preferably, the alkali hydroxide is selected from the group consisting of NaOH, KOH, and a mixture thereof, preferably wherein the alkali hydroxide is KOH. It is also preferred that the alkali alkoxide is selected from the group consisting of sodium alkoxides, potassium alkoxides, and a mixture thereof, preferably from the group consisting of sodium ethoxide, potassium ethoxide, and a mixture thereof.

[0065] Preferably, step (v) includes recycling at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprised in the mixture Mcs obtained according to (iv) to (ii) or (iii). Also preferred is that step (v) includes recycling at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and at least a part of the solvent comprised in the mixture Mcs obtained according to (iv) to (ii) or (iii).

[0066] In a further preferred embodiment, the at least one alcohol R-CH2-CH2-OH is a bio-based alcohol, preferably obtainable or obtained from sugar-containing crops, preferably from one or more of sugar cane and corn.

[0067] In the process in accordance with the present invention, a solvent is employed. Preferably, the solvent has a boiling point of 140 °C or more, preferably a boiling point of 160 °C or more, more preferably a boiling point of 180 °C or more, more preferably a boiling point of 190 °C or more. The solvent preferably has a solubility in water at 25 °C of from 0 to 0.5 weight-%, preferably a solubility in water at 25 °C of from 0 to 0.1 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.05 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.01 weight-%, based on 100 weight-% water. Also preferred is that a distribution coefficient of the catalyst in a system of the solvent and water is from 0 to 0.01 , preferably from 0 to 0.005, more preferably from 0 to 0.005, based on 1 kg catalyst.

[0068] Preferably, the solvent is a mixture of at least two solvents with a boiling point of 140 °C or more, more preferably 160°C or more, more preferably 180 °C or more. More preferably, the mixture of at least two solvents includes at least one aromatic solvent. Also preferred is the solvent being a mixture of at least two aromatic solvents. More preferably, the solvent is a mixture of at least two aromatic solvents with a boiling point of 140 °C or more, more preferably the solvent is a mixture of at least two aromatic solvents with a boiling point of 160 °C or more, more preferably the solvent is a mixture of at least two aromatic solvents with a boiling point of 180 °C or more, more preferably the solvent is a mixture of at least two aromatic solvents with a boiling point of 190 °C or more.

[0069] In a preferred embodiment, the solvent does not include any one of benzene, toluene, xylene or mesitylene.

[0070] Preferably, the solvent does not form an azeotrope with water. An azeotrope or a constant heating point mixture is a mixture of two or more components in fluidic states whose proportions cannot be altered or changed by simple distillation. This happens because when an azeotrope is boiled, the vapour has the same proportions of constituents as the unboiled mixture. Each azeotrope has a characteristic boiling point. It is not possible to separate the components by fractional distillation.

[0071] Preferably, the solvent is selected from the group consisting of biphenyl, diphenyl ether, 1-tert- butyl-3,5-dimethyl-benzene, ethylbenzene, cyclododecane, cyclononane, cyclooctane, cycloheptane, decaline, n-butylbutyrate, n-hexylhexyrate, n-octyloctyrate, texanole, di-n-butylether, di-iso-butylether, di-sec-butylether, and a mixture of two or more thereof, preferably from the group consisting of biphenyl, diphenyl ether, and a mixture thereof, wherein more preferably, the solvent is a mixture of biphenyl and diphenyl ether. Also preferred is that the solvent is a mixture of biphenyl and diphenyl ether, preferably wherein the solvent is a mixture of biphenyl and diphenyl ether at a molar ratio of biphenyl relative to diphenyl ether in the range of from 1 :2 to 1 :6, preferably in the range of from 1 :2.5 to 1 :4.

[0072] Preferably, the liquid reaction mixture MG obtained according to (iii) further comprises at least one unreacted alcohol R-CH2-CH2-OH, the process further comprising separating at least a part of said unreacted alcohol R-CH2-CH2-OH from the liquid reaction mixture MG. More preferably, separating at least a part of the unreacted alcohol R-CH2-CH2-OH from MG is carried out by distillation, extraction, flashing, or by employing a membrane. Also preferred is that at least a part of the at least one unreacted alcohol R-CH2-CH2-OH separated from MG is recycled to (ii) or (iii).

[0073] Preferably, the reaction space SG is comprised in a reactor vessel, wherein the reactor vessel is preferably a complete-mixing reactor vessel.

[0074] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1 , 2, 3 and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention. An alcohol conversion process, comprising

[0075] (i) providing at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor;

[0076] (ii) preparing a liquid mixture ME comprising at least one alcohol R-CH2-CH2-OH, a base, a solvent, and the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor provided according to (i), R being selected from the group consisting of H and Ci-C4-alkyl;

[0077] (iii) subjecting the liquid mixture ME prepared according to (ii) to alcohol conversion conditions in a reaction space SG and obtaining in said reaction space a reaction mixture MG comprising at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH, x being an integer in the range of from 1 to 4, wherein the alcohol conversion conditions comprise a temperature of the reaction mixture MG in the range of from 100 to 250 °C and a pressure in the reaction space SG in the range of from 1 x 105Pa to 4 x 106Pa;

[0078] (iv) separating the at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH from the reaction mixture MG obtained according to (iii), obtaining the at least one alcohol R-CH2-CH2- (CHR-CH2)X-OH and a mixture Mos comprising the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and the solvent;

[0079] (v) recycling one or more of at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and at least a part of the solvent comprised in the mixture Mos obtained according to (iv) to (ii) or (iii); wherein the base is selected from the group consisting of ammonium hydroxide, alkali hydroxides, alkaline earth hydroxides, ammonium carbonate, ammonium hydrogen carbonate, alkali carbonates, alkali hydrogen carbonates, alkaline earth carbonates, alkaline hydrogen carbonates, alkali alkoxides, alkaline earth alkoxides, alkali metal amides, alkaline earth metal amides, secondary amino acids, and a mixture of two or more thereof; the solvent has a boiling point of at least 110 °C at atmospheric pressure, wherein the solvent has a solubility in water at 25 °C of from 0 to 1 weight.-%; the catalyst comprises a compound of formula (A) (A), wherein

[0080] M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0081] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0082] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0083] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;

[0084] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted C1-C10 alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and C1-C10 alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-Cw-aryl; and Cs-Cw-heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0085] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH; the precursor of the catalyst comprising a compound of formula (A) comprises a mixture comprising a compound comprising a metal M and at least one component selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, organic carbonyl compounds, Ci-Cw-alkyl, Ci-Ci2-cycloalkyl, C2-Ci2-alkenyl, Cs-Cw-cycloalkenyl, C5-C20- aryl, CN, CO, OH, OC(=O)CF3, OSO2CF3, hydrides, pyridines, halogenides, hydroxides, and thiophenes; and a compound of formula (H) wherein M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;

[0086] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Rda;

[0087] R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst comprising a compound of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;

[0088] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cw-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-C -cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; Cs-Cw-heterocycle comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-Cw-heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S.

[0089] 2. The process of embodiment 1 , wherein the process is a continuous process. 3. The process of embodiment 1 , wherein the process is a semi-batch process or a batch process.

[0090] 4. The process of any one of embodiments 1 to 3, wherein from 90 to 100 weight-%, preferably from 95 to 100 weight-%, more preferably from 98 to 100 weight-%, more preferably from 99 to 100 weight-% of the liquid mixture ME prepared according to (ii) consist of the at least one alcohol R-CH2-CH2-OH, the base, the solvent and the at least one of a catalyst, a precursor thereof, or a reduced form of the catalyst or the precursor.

[0091] 5. The process of any one of embodiments 1 to 4, wherein the alcohol conversion conditions according to (iii) comprise the presence of at least one inert gas in the reaction space SG, wherein the at least one inert gas is preferably selected from the group consisting of nitrogen, argon, and a mixture thereof.

[0092] 6. The process of any one of embodiments 1 to 5, wherein the alcohol conversion conditions according to (iii) comprise a pressure in the reaction space SG in the range of from 1 x 105to 3.5 x 106Pa, preferably in the range of from 1 x 105to 3.1 x 106Pa, more preferably in the range in the range of from 1 x 105to 2 x 106Pa, more preferably in the range in the range from 1 x 105to 1 .5 x 106Pa.

[0093] 7. The process of any one of embodiments 1 to 6, wherein the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 200 °C, preferably in the range of from 120 to 180 °C, more preferably in the range of from 130 to 160 °C.

[0094] 8. The process of any one of embodiments 1 to 7, wherein the alcohol conversion conditions according to (iii) comprise an amount of the base in the reaction mixture MG in the range of from 0.1 to 10 weight-%, preferably in the range of from 0.5 to 8 weight-%, more preferably in the range of from 1 to 5 weight-%, based on the total weight of the reaction mixture MG.

[0095] 9. The process of any one of embodiments 1 to 8, wherein the alcohol conversion conditions according to (iii) comprise an amount of the solvent in the reaction mixture MG in the range of from 5 to 50 weight-%, preferably in the range of from 5 to 30 weight-%, more preferably in the range of from 5 to 10 weight-%, based on the total weight of the reaction mixture MG.

[0096] 10. The process of any one of embodiments 1 to 9, wherein the alcohol conversion conditions according to (iii) comprise an amount of the catalyst in the reaction mixture MG in the range of from 0.001 to 2 weight-%, preferably in the range of from 0.001 to 1 weight-%, more preferably in the range of from 0.001 to 0.5 weight-%, based on the total weight of the reaction mixture MG. 11 . The process of any one of embodiments 1 to 10, wherein the reaction space in step (iii) comprises a the reaction mixture MG and a gas phase, wherein the gas phase comprises H2, and wherein the alcohol conversion conditions according to (iii) comprise maintaining the H2 partial pressure of the gas phase in the range of from 2 x 104to 3.1 x 106Pa, preferably in the range of from 2 x 104to 1 .1 x 106Pa, more preferably in the range of from 2 x 104to 6 x 105Pa, even more preferably in the range of from 5 x 104to 6 x 105Pa, even more preferably in the range of from 7 x 104to 6 x 105Pa.

[0097] 12. The process of embodiment 11 , wherein the H2 partial pressure of the gas phase is maintained by introducing H2 into the gas phase.

[0098] 13. The process of embodiment 11 , wherein the H2 partial pressure of the gas phase is maintained by relaxation of the gas phase.

[0099] 14. The process of any one of embodiments 1 to 13, wherein preparing a liquid mixture ME in step (ii) comprises at least one alcohol R-CH2-CH2-OH, a base, a solvent, and the at least one of a catalyst, or precursor thereof provided according to (i).

[0100] 15. The process of any one of embodiments 1 to 14, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound comprising a metal M selected from the group consisting of I rCh x H2O, [lr(COD)CI]2, [lr(COE)2CI]2, [lr(C2H4)2CI]2, [lr(COD)OH]2, [lr(COD)MeO]2, [lrCp*CI2], [IrCp CI2], lr4(CO)i2, [lr(PPh3)2(CO)CI], [lr(acetylacetonate)3], and [lr(acety- lacetonate)(COD)], Cp is cylclopentadienyl, wherein Cp* is pentamethylcyclopentadienyl, COD is 1 ,5-cyclooctadienyl, COE is cyclooctenyl, and methylallyl is 2-methylallyl.

[0101] 16. The process of any one of embodiments 1 to 14, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound comprising a metal M selected from the group consisting of [Ru(p-cy- mene)Cl2]2, [Ru(benzene)Cl2]y, [Ru(CO)2Cl2]y, where y is in each case in the range from 1 to 1000, [Ru(CO)3Ch]2, [Ru(COD)(allyl)], RuCh x H2O, [Ru(acetylacetonate)3], [Ru(DMSO)4Ch], [Ru(cyclopentadienyl)(CO)2CI], [Ru(cyclopentadienyl)(CO)2H], [Ru(cyclo- pentadienyl)(CO)2]2, [Ru(Cp)(CO)2CI], [Ru(Cp*)(CO)2H], [Ru(Cp*)(CO)2]2, [Ru(in- denyl)(CO)2CI], [Ru(indenyl)(CO)2H], [Ru(indenyl)(CO)2]2, ruthenocene, [Ru(COD)Ch]2, [Ru(Cp*)(COD)CI], [RU3(CO)I2], [Ru(PPh3)4(H)2], [Ru(PPh3)3(CI)2], [Ru(PPh3)3(CO)(CI)2], [Ru(PPh3)3(CO)(CI)(H)], [Ru(PPh3)3(CO)(H)2], and [Ru(cyclooctadienyl)(methylallyl)2], wherein Cp is cylclopentadienyl, Cp* is pentamethylcyclopentadienyl, COD is 1 ,5-cyclooc- tadienyl, and methylallyl is 2-methylallyl.

[0102] 17. The process of any one of embodiments 1 to 16, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (B) wherein

[0103] M is selected from the group consisting of Ir, Ru, and Mn;

[0104] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0105] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0106] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cw-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-Cw-aryl; and Cs-Cw-heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;

[0107] Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH. The process of any one of embodiments 1 to 16, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (C) wherein

[0108] M is selected from the group consisting of Ir, Ru, and Mn;

[0109] L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;

[0110] L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;

[0111] Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-Cw-alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; unsubstituted or substituted Ci-C -cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cw-alkyl; Cs-Cw-heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-Cw-heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S; Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH.

[0112] 19. The process of any one of embodiments 1 to 18, wherein M is selected from the group consisting of Ir and Ru, wherein M is preferably Ru.

[0113] 20. The process of any one of embodiments 1 to 18, wherein M is Ru, and wherein the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 150 °C, preferably in the range of from 120 to 150 °C, more preferably in the range of from 130 to 150 °C.

[0114] 21 . The process of any one of embodiments 1 to 20, wherein L3is CO.

[0115] 22. The process of any one of embodiments 1 to 21 , wherein L1and L2are each (PRaRb), and wherein Raand Rbare Ci-Cio-alkyl, preferably wherein Raand Rbare each isopropyl or tert-butyl.

[0116] 23. The process of any one of embodiments 1 to 21 , wherein L1and L2are each (PRaRb), and wherein Raand Rbare Ci-Cio-cycloalkyl, preferably wherein Raand Rbare each cyclohexyl.

[0117] 24. The process of any one of embodiments 1 to 21 , wherein L1and L2are each (PRaRb), and wherein Raand Rbare Cs-C -aryl.

[0118] 25. The process of any one of embodiments 1 to 24, wherein Y is selected from the group consisting of F, Cl, Br, and I, preferably wherein Y is selected from the group consisting of Cl or Br, more preferably wherein Y is Cl.

[0119] 26. The process of any one of embodiments 1 to 24, wherein Y is CO.

[0120] 27. The process of any one of embodiments 1 to 16, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (D) wherein Cy is cyclohexyl.

[0121] 28. The process of any one of embodiments 1 to 16, wherein the reduced form of the catalyst comprises a compound of formula (D’) wherein Cy is cyclohexyl.

[0122] 29. The process of any one of embodiments 1 to 16, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (E) wherein iPr is isopropyl.

[0123] 30. The process of any one of embodiments 1 to 16, wherein the reduced form of the catalyst comprises a compound of formula (E’) wherein iPr is isopropyl.

[0124] 31. The process of any one of embodiments 1 to 16, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula wherein tBu is tert-butyl.

[0125] 32. The process of any one of embodiments 1 to 16, wherein the reduced form of the catalyst comprises a compound of formula (F’) wherein tBu is tert-butyl.

[0126] 33. The process of any one of embodiments 1 to 32, wherein integer x is 1 or 2, preferably wherein integer x is 1 .

[0127] 34. The process of any one of embodiments 1 to 33, wherein R is selected from the group consisting of H, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl, preferably from the group consisting of H, methyl, ethyl, propyl, and isopropyl, more preferably selected from the group consisting of H, ethyl, and propyl, wherein more preferably R is H.

[0128] 35. The process of any one of embodiments 1 to 34, wherein the liquid mixture ME prepared according to (ii) further comprises a compound of formula (G) wherein R1, R2, R3and R4, L1, L2, and n are identical to R1, R2, R3and R4, L1, L2, and n of the catalyst of formula (A).

[0129] 36. The process of embodiment 35, wherein in the liquid mixture ME prepared according to (ii) and subjected to alcohol version conditions according to (iii), the molar ratio of the compound of formula (G) relative to the compound of formula (A) is in a range of from 0.01 :1 to 10:1 , preferably in the range of from 0.05:1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.1 :1 to 10:1 , more preferably in the range of from 0.3:1 to 10:1 , more preferably in the range of from 0.5:1 to 10:1 , more preferably in the range of from 0.7:1 to 10:1 , more preferably in the range of from 0.8:1 to 10:1 , more preferably in the range of from 1 :1 to 10:1 more preferably in the range of from 1.01 :1 to 10:1 , more preferably in the range of from 1.02:1 to 8:1 , more preferably in the range from 1 .03:1 to 7:1 , more preferably in the range from 1 .04:1 to 6:1 , and more preferably in the range from 1 .05: 1 to 5: 1 .

[0130] 37. The process of embodiment 35 or 36, wherein the compound of formula (G) is selected from the group consisting of dicyclohexyl-[[5-(dicyclohexylphosphanylmethyl)acridin-4- yl]methyl]phosphane, diisopropyl-[[5-(diisopropylphosphanylmethyl)acridin-4-yl]me- thyl]phosphane, dicyclohexyl-[[5-(dicyclohexylphosphanylmethyl)pyridin-4-yl]methyl]phos- phane and diisopropyl-[[5-(diisopropylphosphanylmethyl)pyridin-4-yl]methyl]phosphane, preferably wherein the compound of formula (G) is cyclohexyl-[[5-(dicyclohex- ylphosphanylmethyl)acridin-4-yl]methyl]phosphane or diisopropyl-[[5-(diiso- propylphosphanylmethyl)acridin-4-yl]methyl]phosphane.

[0131] 38. The process of any one of embodiments 1 to 37, wherein the reduced form of the precursor comprises a compound of formula (P-l) or (P-ll): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroquinoline unit, a decahydroquinoline unit, a tetrahydroacridine unit, or a tetradecahydroacridine unit; and wherein L1and L2are, independently of each other, as defined above; wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above.

[0132] 39. The process of any one of embodiments 1 to 38, wherein the reduced form of the precursor comprises a compound of formula (P-l): wherein R1, R2, R3and R4either are hydrogen, or form together with the N-containing ring a tetrahydroacridine unit, or a tetradecahydroacridine unit.

[0133] 40. The process of any one of embodiments 1 to 38, wherein the reduced form of the precursor comprises a compound of formula (P-ll): wherein R1, R2, R3and R4are hydrogen; and wherein L1and L2are, independently of each other, as defined above.

[0134] 41 . The process of any one of embodiments 1 to 40, wherein the base is selected from the group consisting of alkali hydroxides, alkali alkoxides, and a mixture thereof.

[0135] 42. The process of embodiment 41 , wherein the alkali hydroxide is selected from the group consisting of NaOH, KOH, and a mixture thereof, preferably wherein the alkali hydroxide is KOH.

[0136] 43. The process of embodiment 41 , wherein the alkali alkoxide is selected from the group consisting of sodium alkoxides, potassium alkoxides, and a mixture thereof, preferably from the group consisting of sodium ethoxide, potassium ethoxide, and a mixture thereof.

[0137] 44. The process of any one of embodiments 1 to 43, wherein step (v) includes recycling at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprised in the mixture Mcs obtained according to (iv) to (ii) or (iii).

[0138] 45. The process of any one of embodiments 1 to 44, wherein step (v) includes recycling at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and at least a part of the solvent comprised in the mixture Mcs obtained according to (iv) to (ii) or (iii).

[0139] 46. The process of any one of embodiments 1 to 45, wherein the at least one alcohol R-CH2- CH2-OH is a bio-based alcohol, preferably obtainable or obtained from sugar-containing crops, preferably from one or more of sugar cane and corn.

[0140] 47. The process of any one of embodiments 1 to 46, wherein the solvent has a boiling point of 140 °C or more, preferably a boiling point of 160 °C or more, more preferably a boiling point of 180 °C or more, more preferably a boiling point of 190 °C or more.

[0141] 48. The process of any one of embodiments 1 to 47, wherein the solvent has a solubility in water at 25 °C of from 0 to 0.5 weight-%, preferably a solubility in water at 25 °C of from 0 to 0.1 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.05 weight-%, more preferably a solubility in water at 25 °C of from 0 to 0.01 weight-%, based on 100 weight-% water. 49. The process of any one of embodiments 1 to 48, wherein a distribution coefficient of the catalyst in a system of the solvent and water is from 0 to 0.01 , preferably from 0 to 0.005, more preferably from 0 to 0.005, based on 1 kg catalyst.

[0142] 50. The process of any one of embodiments 1 to 48, wherein the solvent is a mixture of at least two solvents with a boiling point of 180 °C or more, preferably wherein the solvent is a mixture of at least two solvents with a boiling point of 190 °C or more.

[0143] 51 . The process of any one of embodiments 1 to 50, wherein the solvent is a mixture of at least two solvents including at least one aromatic solvent.

[0144] 52. The process of any one of embodiments 1 to 51 , wherein the solvent is a mixture of at least two solvents including at least two aromatic solvents.

[0145] 53. The process of any one of embodiments 1 to 52, wherein the solvent does not form an azeotrope with water.

[0146] 54. The process of any one of embodiments 1 to 53, wherein the solvent does not include any one of benzene, toluene, xylene or mesitylene.

[0147] 55. The process of any one of embodiments 1 to 51 , wherein the solvent is selected from the group consisting of biphenyl, diphenyl ether, 1-tert-butyl-3,5-dimethyl-benzene, ethylbenzene, cyclododecane, cyclononane, cyclooctane, cycloheptane, decaline, n-butylbutyrate, n-hexylhexyrate, n-octyloctyrate, texanole, di-n-butylether, di-iso-butylether, di-sec-butyl- ether, and a mixture of two or more thereof, preferably from the group consisting of biphenyl, diphenyl ether, and a mixture thereof, wherein more preferably, the solvent is a mixture of biphenyl and diphenyl ether.

[0148] 56. The process of any one of embodiments 1 to 55, wherein the solvent is a mixture of biphenyl and diphenyl ether, preferably wherein the solvent is a mixture of biphenyl and diphenyl ether at a molar ratio of biphenyl relative to diphenyl ether in the range of from 1 :2 to 1 :6, preferably in the range of from 1 :2.5 to 1 :4.

[0149] 57. The process of any one of embodiments 1 to 56, wherein the liquid reaction mixture MG obtained according to (iii) further comprises at least one unreacted alcohol R-CH2-CH2- OH, the process further comprising separating at least a part of said unreacted alcohol R- CH2-CH2-OH from the liquid reaction mixture MG.

[0150] 58. The process of embodiment 57, wherein separating at least a part of the unreacted alcohol R-CH2-CH2-OH from MG is carried out by distillation, extraction, flashing, or by employing a membrane.

[0151] 59. The process of embodiment 57 or 58, wherein at least a part of the at least one unreacted alcohol R-CH2-CH2-OH separated from MG is recycled to (ii) or (iii). 60. The process of any one of embodiments 1 to 59, wherein the reaction space SG is comprised in a reactor vessel, wherein the reactor vessel is preferably a complete-mixing reactor vessel.

[0152] The present invention is further illustrated by the following examples, which are set forth to illustrate certain aspects of the present invention and are not to be construed as limiting thereof.

[0153] Examples

[0154] The determination of the distribution coefficient of the solvent in water comprises the following steps:

[0155] 1 . combining the two components, e.g. feed and solvent, in a predefined solvent ratio;

[0156] 2. turbulent mixing of the combined components over a longer period of time (> 10 min) at a defined extraction temperature;

[0157] 3. allowing for phase separation;

[0158] 4. taking samples of each phase at the extraction temperature;

[0159] 5. centrifuging the samples and withdrawing clear samples at the extraction temperature;

[0160] 6. analyzing the samples; and

[0161] 7. comparing the results of extract- and raffinate - calculation of the partition equilibrium / parti- tion coefficient at the selected temperature.

[0162] Example 1

[0163] In a glovebox, an autoclave was filled with 48.13 g ethanol, 41.6 mg Ru(acac)s (ruthenium(lll) acetylacetonate), 41.3 mg 2,6-bis(di- / er / -butylphosphaneyl)methylpyridine , 20.63 g diphenyl and diphenyl ether in a molar ratio of 1 :3 as a solvent, and 3.52 g potassium ethoxide. The stirrer was set at 700 rpm and the reaction mixture was heated to 150 °C. The reaction mixture was kept under autogenous pressure for 2 h and then cooled to room temperature. The autoclave was carefully depressurized. The yellow-orange solution with little brownish solid (70.24 g) was concentrated, leaving 25.3 g of a yellow-orange suspension. 7.9 g butanol and 32.4 g water were added to the suspension and stirred for 1 .5 h at room temperature. The phases were separated overnight. The yellow aqueous phase (35.9 g) was removed and the orange organic phase (29.0 g) was reconcentrated, leaving 20.5 g behind.

[0164] This mixture was transferred to an autoclave and 48.3 g ethanol and 3.52 g potassium ethanolate were mixed. The stirrer was set to 700 rpm and the reaction mixture was heated to 150 °C. The reaction mixture was kept under autogenous pressure for 2 h and then cooled to room temperature. The autoclave was carefully depressurized. The yellow-orange solution with little beige solid (69.7 g) was concentrated, leaving 25.3 g of a yellow-orange suspension. 7.9 g butanol and 34 g water were added to the suspension and stirred for 1 .5 h at room temperature. The phases were separated overnight. The yellow aqueous phase (37.8 g) was removed and the orange organic phase was reconcentrated with little dark mulm (28.8 g), leaving 19.7 g behind. This mixture was transferred to an autoclave and 48.2 g ethanol and 3.52 g potassium ethanolate were mixed. The stirrer was set to 700 rpm and the reactant mixture was heated to 150 °C. The reaction mixture was kept under autogenous pressure for 2 h and then cooled to room temperature.

[0165] The layers were separated to afford a brown-orange organic layer (27.2 g, small amounts of a brown third layer) and an orange-yellow aqueous layer (35.7 g). Both these layers, and a sample of the crude reaction mixture after cooling to room temperature, were analyzed via quantitative 1 H NMR spectroscopy (acetate content) and atom spectroscopy (Ru / P content).

[0166] Ru in the organic phase with the solvent:

[0167] Ru: 320 ppm

[0168] P: 220 ppm

[0169] As may be seen from the Table, using diphenyl and diphenyl ether at a molar ratio of 1 :3 as a solvent, a complete recycle was observed, including aqueous work-up. Product formation was still observed after the recycle. The lower conversions were to be expected since the catalysts are very sensitive to air.

[0170] Cited literature:

[0171] M. Guerbet, C. R. Hebd. Seances Acad. Sci. 1899, 128, p. 511-513

[0172] - Y.Xie et aL, “Highly efficient Process for Production of Biofuel from ethanol Catalyzed by Ruthenium Pincer Complexes”, Journal of the American Society, vol. 138, no. 29, 2016- 07-18, pages 9077 to 9080

[0173] - WO 2012 / 119928 A1

[0174] - WO 2013 / 156399 A1

Claims

Claims1 . An alcohol conversion process, comprising(i) providing at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor;(ii) preparing a liquid mixture ME comprising at least one alcohol R-CH2-CH2-OH, a base, a solvent, and the at least one of a catalyst, precursor thereof, reduced form of the catalyst or reduced form of the precursor provided according to (i), R being selected from the group consisting of H and Ci-C4-alkyl;(iii) subjecting the liquid mixture ME prepared according to (ii) to alcohol conversion conditions in a reaction space SG and obtaining in said reaction space a reaction mixture MG comprising at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH, x being an integer in the range of from 1 to 4, wherein the alcohol conversion conditions comprise a temperature of the reaction mixture MG in the range of from 100 to 250 °C and a pressure in the reaction space SG in the range of from 1 x 105Pa to 4 x 106Pa;(iv) separating the at least one alcohol R-CH2-CH2-(CHR-CH2)x-OH from the reaction mixture MG obtained according to (iii), obtaining the at least one alcohol R-CH2-CH2- (CHR-CH2)X-OH and a mixture Mos comprising the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and the solvent;(v) recycling one or more of at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and at least a part of the solvent comprised in the mixture Mos obtained according to (iv) to (ii) or (iii); wherein the base is selected from the group consisting of ammonium hydroxide, alkali hydroxides, alkaline earth hydroxides, ammonium carbonate, ammonium hydrogen carbonate, alkali carbonates, alkali hydrogen carbonates, alkaline earth carbonates, alkaline hydrogen carbonates, alkali alkoxides, alkaline earth alkoxides, alkali metal amides, alkaline earth metal amides, secondary amino acids, and a mixture of two or more thereof; the solvent has a boiling point of at least 110 °C at atmospheric pressure, wherein the solvent has a solubility in water at 25 °C of from 0 to 1 weight.-%; the catalyst comprises a compound of formula (A)whereinM is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;L3is selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, pyridine, and thiophene;R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted C1-C10 alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and C1-C10 alkyl; Cs-C -heterocyclyl comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S;Y is selected from the group consisting of H, F, Cl, Br, I, OC(=O)CF3, OSO2CF3, CN, CO, and OH; the precursor of the catalyst comprising a compound of formula (A) comprises a mixture comprising a compound comprising a metal M and at least one component selected from the group consisting of CO, PRaRbRc, SRaRb, RaCN, RaNC, N2, PF3, organic carbonyl compounds, Ci-Cio-alkyl, Ci-Ci2-cycloalkyl, C2-Ci2-alkenyl, Cs-Cis-cycloalkenyl, C5-C20- aryl, CN, CO, OH, OC(=O)CF3, OSO2CF3, hydrides, pyridines, halogenides, hydroxides, and thiophenes; and a compound of formula (H)wherein M is selected from the group consisting of Ir, Mn, Os, Pd, Pt, Rh, and Ru;L1and L2are, independently of each other, PRaRb, NRaRb, SRa, SH, and S(=O)Ra;R1, R2, R3and R4either are hydrogen, or form together with the pyridyl unit of the catalyst comprising a compound of formula (A) an acridinyl unit; n is 0 or 1 , and if R1, R2, R3and R4are hydrogen, n is 0;Ra, Rb, Rcand Rdare, independently of each other, selected from the group consisting of H, unsubstituted or substituted Ci-C -alkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and C C -alkyl; unsubstituted or substituted Ci-Cio-cycloalkyl wherein the substituents are selected from the group consisting of F, Cl, Br, OH, CN, NH2, and Ci-Cio-alkyl; Cs-C -heterocycle comprising at least one heteroatom selected from the group consisting of N, O, and S; Cs-C -aryl; and Cs-C -heteroaryl comprising at least one heteroatom selected from the group consisting of N, O, and S.

2. The process of claim 1 , wherein M is selected from the group consisting of Ir and Ru.

3. The process of claim 1 or 2, wherein M is Ru, and wherein the alcohol conversion conditions according to (iii) comprise a temperature of the reaction mixture MG in the range of from 100 to 150 °C.

4. The process of any one of claims 1 to 3, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (D)wherein Cy is cyclohexyl.

5. The process of any one of claims 1 to 3, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (E)wherein iPr is isopropyl.

6. The process of any one of claims 1 to 3, wherein the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprises a compound of formula (F)wherein tBu is tert-butyl.

7. The process of any one of claims 1 to 6, wherein integer x is 1 .

8. The process of any one of claims 1 to 7, wherein R is selected from the group consisting of H, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, and tert-butyl.

9. The process of any one of claims 1 to 8, wherein the liquid mixture ME prepared according to (ii) further comprises a compound of formula (G)wherein R1, R2, R3and R4’ L1, L2and n are identical to R1, R2, R3and R4’ L1, L2and n of the catalyst of formula (A).

10. The process of any one of claims 1 to 9, wherein the solvent has a boiling point of 140 °C or more.11 . The process of any one of claims 1 to 10, wherein the solvent has a solubility in water at 25 °C of from 0 to 0.01 weight-%, based on 100 weight-% water, and / or wherein a distribution coefficient of the catalyst in a system of the solvent and water is from 0 to 0.01 , based on 1 kg catalyst, and / or wherein the solvent does not form an azeotrope with water.

12. The process of any one of claims 1 to 11 , wherein step (v) includes recycling at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor comprised in the mixture Mcs obtained according to (iv) to (ii) or (iii), preferably wherein step (v) includes recycling at least a part of the at least one of a catalyst, a precursor thereof, a reduced form of the catalyst, or a reduced form of the precursor and at least a part of the solvent comprised in the mixture Mcs obtained according to (iv) to (ii) or (iii).

13. The process of any one of claims 1 to 12, wherein the solvent is a mixture of at least two solvents with a boiling point of 180 °C or more, and the mixture of at least two solvents includes at least one aromatic solvent.

14. The process of any one of claims 1 to 13, wherein the solvent is a mixture of biphenyl and diphenyl ether.

15. The process of any one of claims 1 to 14, wherein the liquid reaction mixture MG obtained according to (iii) further comprises at least one unreacted alcohol R-CH2-CH2-OH, the process further comprising separating at least a part of said unreacted alcohol R-CH2-CH2- OH from the liquid reaction mixture MG, and wherein at least a part of the at least one unreacted alcohol R-CH2-CH2-OH separated from MG is recycled to (ii) or (iii).

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