NL2010393C2

NL2010393C2 - Process for preparing bã¨ta-alkylated alcohols.

Info

Publication number: NL2010393C2
Application number: NL2010393A
Authority: NL
Inventors: Jaap Willem Hal; Rudie Johan Hendrik Grisel
Original assignee: Stichting Energie
Priority date: 2013-03-05
Filing date: 2013-03-05
Publication date: 2014-09-08
Also published as: WO2014137212A3; WO2014137212A2

Abstract

The invention relates to a new catalyst for the gas phase Guerbet reaction, in particular for the Guerbet reaction of ethanol, wherein the catalyst comprises at least 20 atom% copper, based on total metal content, and wherein the catalyst preferably exhibits acidic character. This catalyst for the Guerbet reaction is unprecedented in the art, in view of its acidic character, and is surprisingly effective in catalysing all steps of the Guerbet reaction, without the need for additional catalysts, such as bases, and with reduced degradation by-products such as CO and CO2.

Description

Process for preparing β-alkylated alcohols

[0001] The present invention relates to an advanced process for the preparation of β-alkylated alcohols from lower alcohols.

Background

[0002] In a Guerbet reaction, non-tertiary aliphatic alcohols (alkanols) are converted to the corresponding β-alkylated non-tertiary alcohols. The reaction is accompanied by release of water. The resulting β-alkylated alcohols are referred to as Guerbet alcohols. At least one alcohol having two or three β-hydrogens is required for the Guerbet reaction. Typically, the Guerbet reaction is performed in the presence of a strong base, e.g. alkali metal hydroxides or alkoxides, a hydrogenation catalyst, e.g. Raney Nickel, at elevated temperatures, e.g. above 250 °C. In a first step, the alcohol is dehydrogenated to the corresponding aldehyde (or ketone). Subsequently, two aldehydes (or two ketones, or one aldehyde and one ketone) dimerise via an aldol condensation and subsequent release of water to the corresponding vinyl aldehyde. The vinyl aldehyde is then catalytically reduced to the β-alkylated alcohol. The non-tertiary alkanol can be a single alcohol, e.g. ethanol, or it can be a mixture, e.g. ethanol plus methanol.

[0003] Especially interesting is the Guerbet reaction of ethanol. Ethanol is conveniently used, as it is cheap and available in huge quantities. Ethanol is converted to acetaldehyde, which condenses to crotonaldehyde and then hydrogenates to 1-butanol. Thus 1-butanol is the primary Guerbet product from ethanol as a single starting alcohol. 1-Butanol can subsequently undergo Guerbet reactions with itself, forming 2-ethyl-1-hexanol, or with ethanol, forming 2-ethyl-1-butanol or 1-hexanol. As such, the higher alcohols may react further, either with themselves or with ethanol, giving mixtures of alcohols. Multiple subsequent Guerbet reactions, yielding long chain alcohols, are only possible as long as ethanol is present as a reaction partner.

[0004] When using mixed alcohols as a starting material, at least one should have at least two hydrogen atoms in β-position. A second alcohol may also be an alcohol lacking β-hydrogens, such as methanol, or only have one, such as isobutanol. All alcohols must have at least one α-hydrogen, i.e. not be tertiary. Primary alcohols, i.e. having two α-hydrogens, are preferred. The primary reaction product of a mixture of methanol and ethanol is 1-propanol.

[0005] Various catalysts for Guerbet reactions have been suggested in the art, including zeolites and other carriers, with or without added transition metals, such as copper, nickel, palladium etc. WO2012/035772 describes a Guerbet reaction in the gas phase using a calcium hydroxyapatite, hydrotalcite or similar catalyst. US 8,071,823 describes a Guerbet reaction using the decomposition product of hydrotalcite and copper carbonate as a catalyst. Also metal oxides, with or without added (transition) metals, have been studied in the Guerbet reaction, such as MgO (see e.g. A.S. Ndou, et al. Applied Catalysis A-General, 251 (2003) 337-345)) and several rare earth oxides (see e.g. US 7,807,857).

[0006] All known Guerbet catalysts have the common feature that they exhibit basic surface character. Such basic character is commonly determined by carbon dioxide desorption experiments, wherein the catalyst is first saturated with carbon dioxide gas, and the release of carbon dioxide is measured as a function of temperature. Surface acidity may be determined by ammonia desorption experiments. Such measurements may be referred to in the art as thermal desorption spectroscopy (TDS) or temperature programmed desorption (TPD). In the prior art, the basic character of Guerbet catalysts is considered essential for the condensation step, wherein the carbon-carbon bond is formed.

[0007] The conversion of ethanol to higher alcohols, i.e. alcohol compounds having more than two or three carbon atoms, is of great current interest, especially for biorefinery purposes. Higher alcohols contain an increased caloric value compared to short chain alcohols such as ethanol. Thus, ethanol, which is readily obtained from biomass, may be converted to biofuels comprising higher alcohols using the Guerbet reaction. In addition, Guerbet alcohols, especially branched alcohols, such as 2-ethyl-hexanol, are promising candidates as lubricants, as the hydroxyl moiety imparts a high boiling point, while their branched hydrocarbon chain imparts a low melting point. As such, Guerbet alcohols are generally liquid over a broad temperature range, which property facilitates lubrication.

[0008] Guerbet alcohols, in particular the Guerbet alcohols having a linear alkyl chain of four to twelve carbons, are suitable as detergents, in view of their hydrophilic hydroxyl moiety and hydrophobic hydrocarbon chain. The hydrophilicity of the hydroxyl moiety may be even further enhanced by deprotonation by e.g. NaOH. Branched Guerbet alcohols, on the other hand, are particularly suitable as (precursors for) plasticizers. Exemplary is the phthalate ester of 2-ethylhexanol (also known as dioctyl phthalate or DOP), which is used extensively as a plasticizer for PVC. Of course, the applicability of the products or product mixtures of the Guerbet reaction is closely associated with the purity of those products or product mixtures. The presence of by-products may hamper the applicability greatly (e g. by inhibiting the Guerbet reaction, polluting the system, creating large amounts of waste such as polluted water), or may require extensive purification steps.

[0009] Commonly used catalysts in the Guerbet reaction have several drawbacks. First of all, the Guerbet reaction is often accompanied by dehydration of the primary aliphatic alcohol, e g. from 1-propanol to propene or from ethanol to ethylene. This undesired side-reaction is especially apparent for ethanol as starting material, as significant amounts of ethylene are obtained. Other commonly encountered side products include the carboxylic acid derivative of the employed primary alcohol, such as acetic acid, and degradation products such as CO and CO2.

[0010] Thus, a need exists in the art for improved catalysts for the Guerbet reaction, resulting in higher conversion rates and efficiencies and/or in product mixtures with improved purity, especially for ethanol as starting material.

Summary of the invention

[0011] The invention relates to a new catalyst for the Guerbet reaction, in particular for the Guerbet reaction of ethanol, wherein the catalyst comprises at least copper, preferably in the form of copper oxide. Preferably, the catalyst exhibits acidic character. This catalyst for the Guerbet reaction is unprecedented in the art, partly in view of its acidic character, and is surprisingly effective in catalysing the Guerbet reaction. Unexpectedly, this catalyst is capable of catalysing all steps of the Guerbet reaction, without the need for additional catalysts, such as bases, and with reduced degradation by-products such as CO and CO2.

Detailed description

[0012] The invention thus relates to a process for gas phase coupling of a non-tertiary alkanol containing at least two β-hydrogen atoms, comprising contacting the alkanol with a solid catalyst which comprises at least 20 atom% copper, and at least 20 atom% of one or more metals selected from magnesium, aluminium, silicon and zinc, based on total metal atoms. The catalyst preferably comprises a metal oxide composition carried on or mixed with a catalyst carrier, wherein the metal oxide composition comprises at least copper oxide, and the catalyst preferably exhibits acidic character.

Catalyst

[0013] Suitable catalysts to be used in the present invention are catalysts and catalyst precursors comprising at least a copper oxide (cuprous oxide (Cu[I]20), cupric oxide (Cu[II]0), or a mixture thereof, preferably at least cupric oxide). The catalyst may be described as comprising a metal oxide composition carried on or mixed with a catalyst carrier, wherein the metal oxide composition comprises at least a copper oxide as described above, and the catalyst preferably exhibits acidic character. Preferably, the carrier is mixed with the metal oxide composition and the catalyst has a homogeneous distribution of all elements. The catalyst may be in any physical form known in the art, e g. as a powder, as pellets, incorporated in or adsorbed on a catalyst bed. As used herein, the term “catalyst” encompasses both the final active form and the preceding form prior to activation, also referred to as catalyst precursor. Both forms may differ in the actual oxidation state of the various metals, and in the amount of non-metals, including oxygen and hydrogen, but not in the atomic ratio of the metals.

[0014] Preferably, the catalyst or catalyst precursor is described in terms of its atomic composition of the complete catalyst, i.e. including the carrier. Here below, the atomic composition is given in atom% (atom percentage), which designates the number of atoms of a particular element present in the catalyst, based on the total number of metal atoms present in a particular part of the catalyst, i.e. irrespective of the oxidation state and molecular state (elemental, oxide, or other) and the site of the metals. In the context of the present invention, metal atoms include all alkali metal atoms, alkaline earth metal atoms, transition metal atoms, post-transition metal atoms (Al, Ga, In, Sn, Tl, Pb, Bi, Po), lanthanide atoms, actinide atoms and metalloid atoms (B, Si, Ge, As, Sb, Te, At). Suitable catalysts comprise at least copper, preferably in the form of copper oxide, and the catalysts preferably exhibit acidic character. The catalyst preferably comprises between 20 atom% and 80 atom% copper, more preferably between 30 atom% and 60 atom% copper, most preferably between 32 atom% and 52 atom% copper and especially between 40 and 48 atom%, based on total metal atoms. In the final active catalyst, the copper may be in the form of metallic copper.

[0015] The catalyst may comprise further metals and/or metalloids, e.g. Be, Mg, Ca, Sr, Ba, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, Sn, La, W, Al, Si and B. Here below, the metalloids are also referred to as metals. Preferably, the catalyst comprises further metals selected from the group consisting of magnesium, aluminium, silicon, zinc, calcium, strontium, barium, titanium, chromium, iron and nickel, more preferably from the group consisting of magnesium, aluminium, silicon and zinc. It is preferred that the elements copper, magnesium, aluminium, silicon and zinc together make up for at least 80 atom%, more preferably at least 90 atom%, most preferably 95 to 100 atom% and in particular 96 to 99 atom%, based on total metal atoms. Preferably, the metals other than copper, zinc, magnesium, aluminium and silicon are each present in an amount of at most 2.5 atom% (i.e. 0 to 2.5 atom%), preferably at most 1 atom%, and their total at most 10 atom%, preferably at most 5 atom%, based on total metal atoms. In an embodiment, the total amount of the metals Ca, Sr, Ba, Ti, Cr and Ni may be between 0.5 and 5 atom%. These metals present in minor amounts may act as promoter in the catalysis of the Guerbet reaction, as such enhancing the catalytic activity of the catalyst.

[0016] Preferably, the catalyst according to the invention also comprises zinc, preferably between 0.2 atom% and 60 atom%, more preferably between 0.5 atom% and 45 atom%, In a particular embodiment, the catalyst comprises between 1 and 5 atom%, based on total metal atoms. In an alternative embodiment, the catalyst may comprise between 5 atom% and 60 atom% zinc, in particular between 25 and 50 atom% zinc, based on total metal atoms. In case both copper and zinc are present, the atomic ratio copper to zinc is preferably between 50:1 and 1:2, more preferably between 30:1 and 1:1. In an especially preferred embodiment, the atomic ratio copper to zinc is between 30:1 and 20:1.

[0017] Preferably, the catalyst according to the invention also comprises aluminium, preferably between 0.1 atom% and 40 atom%, more preferably between 0.2 atom% and 30 atom%, most preferably between 0.2 and 5 atom%, based on total metal atoms. In case both copper and aluminium are present, the atomic ratio copper to aluminium is preferably between 200:1 and 1:1, more preferably between 150:1 and 2:1. In an especially preferred embodiment, the atomic ratio copper to aluminium is between 150:1 and 20:1.

[0018] Preferably, the catalyst according to the invention also comprises silicon, preferably at most 50 atom%, more preferably between 5 atom% and 45 atom%, most preferably between 20 and 40 atom%, based on total metal atoms. In case both copper and silicon are present, the atomic ratio copper to silicon is preferably between 10:1 and 1:10, more preferably between 5:1 and 1:2. In an especially preferred embodiment, the atomic ratio copper to silicon is between 2:1 and 1:1.

[0019] Preferably, the catalyst according to the invention also comprises magnesium, preferably at most 50 atom%, more preferably between 5 atom% and 40 atom%, most preferably between 15 and 30 atom%, based on total metal atoms. In case both copper and magnesium are present, the atomic ratio copper to magnesium is preferably between 10:1 and 1:2, more preferably between 5:1 and 1:1. The combined content of zinc, aluminium, silicon and magnesium is preferably between 20 atom% and 80 atom%, more preferably between 40 atom% and 70 atom%, most preferably between 50 atom% and 60 atom%, based on total metal atoms. In a preferred embodiment, the combined content of magnesium and silicon is between 40 % and 70 atom%, most preferably between 50 atom% and 60 atom%, based on total metal atoms.

[0020] All metals mentioned above may be present in any form known in the art, e.g. as metal salt or as elemental metal. As the active catalyst (i.e. after activation) comprises elemental metals, it does not matter whether those originate from metal oxides, other metal salts or the elemental metal itself. As metal oxides are generally stable to air, the incorporation of metal oxides is preferred. Other metal salts, such as metal hydroxides, metal carbonates, metal bicarbonates, metal nitrates and metal chlorides, or elemental metals may also be suitable. The metals, preferably the metal oxides, may originate from or be present in any form known in the art, such as acidic aluminates (preferably zinc-aluminates, gamma-alumina and boehmite), acidic silicates (preferably magnesium silicates and zinc silicates), hydrotalcite, acidic zeolites (e g. ZSM-5), and mixtures thereof. For example, zinc may be present as zinc aluminate and/or zinc silicate. In particular, zinc may be present as ZnsAbOg. Magnesium is preferably present as magnesium silicate. As the metals are conveniently present as metal oxide, it is especially preferred that the catalyst comprises oxygen atoms next to the metal atoms described above, preferably the oxygen atom content is between 10 atom% and 75 atom%, more preferably between 25 atom% and 60 atom%, most preferably between 45 and 55 atom%, based on total atoms. In case both copper and oxygen are present, the atomic ratio copper to oxygen is preferably between 1:2 and 1:5, more preferably between 1:1 and 1:2.5. In an especially preferred embodiment, the atomic ratio copper to oxygen is between 1:2 and 1:2.5. Preferably, the catalyst consists of metals, metalloids and oxygen atoms, in the preferred amounts and ratios as discussed above.

[0021] In a preferred embodiment, the catalyst comprises copper, zinc, aluminium and oxygen, in the preferred amounts and ratios as discussed above. Most preferably, the catalysts comprises copper, zinc, aluminium, silicon and oxygen, in the preferred amounts and ratios as discussed above. In an especially preferred embodiment, the catalyst exhibits acidic character. In the context of the present invention, acidic character is the ability to adsorb bases to the surface of the catalyst. Preferably, the catalyst shows a maximum in its ammonia-TPD profile above 200 °C, more preferably between 250 °C and 500 °C. A maximum above 200 °C in the ammonia-TPD profile is indicative of an acidic character.

[0022] Alternatively, the catalyst is described as having a metal oxide composition and a carrier. The weight ratio of the metal oxide composition to carrier is preferably between 9:1 and 1:9, more preferably between 2:1 and 1:2. Preferably, the metal oxide composition comprises at least 20 wt% copper oxide, more preferably between 25 wt% and 75 wt% copper oxide, even more preferably between 30 and 60, most preferably between 35 wt% and 55 wt% copper oxide, calculated as CuO, and based on total weight of the catalyst. In the final active catalyst, the copper may be in the form of metallic copper. The catalyst may comprise further metals, and/or metalloids, e.g. Be, Mg, Ca, Sr, Ba, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, Sn, La, W, Al, Si and B. Herein, the metalloids are also referred to as metals. Preferably, the metal oxide composition comprises further metal oxides and/or metalloid oxides selected from the group consisting of magnesium oxide (magnesia, MgO), aluminium oxide (alumina, AI2O3), silicon oxide (silica, S1O2), zinc oxide (ZnO), calcium oxide (CaO), oxides of strontium, barium, titanium, chromium, iron and nickel. Apart from those oxides, metal hydroxides and mixed metal oxides-hydroxides may be present. It is preferred that the oxides of copper, magnesium, aluminium, silicon and zinc together make up for at least 75 wt.% of the catalyst, more preferably 80 wt.% to 99 wt.%, most preferably 85 wt.% to 95 wt.% on total catalyst weight.

[0023] Preferably, the metal oxides other than copper, zinc, magnesium, aluminium and silicon oxides are each present in an amount of at most 2.5 wt%, and their total at most 5 wt%, based on total weight of the catalyst, and calculated as SrO, BaO, T1O2, Cr2C>3, FeO, NiO etc. These metal oxides present in minor amounts may act as promoter in the catalysis of the Guerbet reaction, as such enhancing the catalytic activity of the catalyst. In a preferred embodiment, the metal oxide composition comprises at least copper oxide and zinc oxide. Zinc oxide is preferably present in an amount of between 1 and 60 wt%, based on total weight of the catalyst. Zinc oxide may be present as such, or e.g. as a zinc aluminate or a zinc silicate. In particular, the zinc oxide may be present as In a preferred embodiment, the combined level of zinc oxide and/or aluminium (calculated as ZnO and AI2O3) is between 20 and 75 wt.%, more preferably between 35 and 65 wt.% In case the metal oxide composition comprises CuO and ZnO, the weight ratio CuO to ZnO preferably is between 50:1 and 1:2, more preferably between 30:1 and 1:1.5. In an especially preferred embodiment, the weight ratio CuO to ZnO is between 30:1 and 20:1. In another, particularly preferred embodiment of the invention, the catalyst to be used comprises between 20 and 65 wt.% of the combination of magnesium and silicon oxide (calculated as MgO and S1O2), more preferably between 40 and 50 wt.% of MgO and S1O2 taken together. In particular, at least a part of these oxides is present as magnesium silicate, especially between 10 and 40 wt%, more especially between 15 and 30 wt% (calculated as Mg2Si04).

[0024] In case the catalyst is described as having a metal oxide composition and a carrier, suitable carriers exhibit an acidic character and include, but are not limited to, acidic aluminates (preferably gamma-alumina or boehmite), acidic silicates, magnesium silicates, zinc-aluminates, hydrotalcite, acidic zeolites (e.g. ZSM-5), and mixtures thereof. Preferably, the carrier is selected from magnesium silicate and zinc-alumina, most preferably the carrier is magnesium-silicate. In an especially preferred embodiment, the catalyst exhibits acidic character. In the context of the present invention, acidic character is the ability to adsorb bases to the surface of the catalyst, preferably, the catalyst shows a maximum in its ammonia-TPD profile above 200 °C, more preferably between 250 °C and 500 °C. A maximum above 200 °C in the ammonia-TPD profile is indicative of an acidic character.

[0025] Prior to being contacted with the reactants for the Guerbet reaction, the catalyst is activated. Activation typically occurs at elevated temperature (e.g. >150 °C) under a reducing atmosphere (e.g. an atmosphere comprising hydrogen gas, ethylene, CO and/or hydrazine), but alternative activating procedures may also be used (e.g. activation in the reaction mixture, heating in an inert gas). Activation is typically performed according to the protocol provided by the manufacturer of the catalyst, and may vary for different catalysts. After activation, at least the copper oxide in the metal oxide composition is reduced to metallic copper or elemental copper (e.g. CuO is reduced to metallic copper). Depending on the exact procedure of activation, other metals may also be reduced to their elemental form. As the active catalyst comprises elemental copper and possibly other elemental metals, it does not matter whether those originate from metal oxides, other metal salts or the elemental metal itself. As metal oxides are generally stable to air, the incorporation of metal oxides is preferred. Other metal salts, such as metal hydroxides, metal carbonates, metal bicarbonates, metal nitrates, metal chlorides, or elemental metals may also be suitable.

[0026] In case the catalyst is described as having a carrier and a metal oxide composition, the values for wt% and weight ratios for the different metal components is to be recalculated to the values for wt% and weight ratios for the metal oxides, as discussed. Whether a particular salt or the elemental metal is suitable to be used in the catalyst or in the metal oxide composition, depends on the specific metal in suit. The skilled artisan appreciates which salts or elements are suitable to incorporate the metals in the catalyst as discussed above, or to replace the metal oxides as discussed above, and how to recalculate the content of the different metal components to the values given for the metal oxides.

[0027] Catalyst compositions are readily determined using analysis techniques known in the art. Those include but are not limited to X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), Elemental Analysis (EA), and combinations thereof.

[0028] The catalysts according to the invention are highly active in the conversion of non-tertiary alkanols, preferably ethanol, into the corresponding β-alkylated non-tertiary alkanols and/or related condensed products, as is discussed below and shown in the examples.

Process

[0029] The process according to the invention involves contacting at least one non-tertiary alkanol containing a non-tertiary hydroxyl moiety having at least two β-hydrogen atoms with the catalyst according to the invention. The non-tertiary alkanol may be represented as R*-CH2-CH(OH)-R2, wherein each of R1 and R2 are individually selected from hydrogen and alkyl, preferably C1-C20 alkyl, more preferably C|-C6 alkyl, most preferably C1-C2 alkyl. In the context of the present invention, the term “alkyl” includes linear alkyl chains and branched and cyclic alkyl chains, such as alkyl chains comprising a cycloalkyl moiety. Suitable linear or branched alkyl groups may bear a substituent other then hydrogen, such as a second alcohol moiety, an aldehyde moiety, a ketone moiety. It is especially preferred that the non-tertiary alkanol is gaseous at the processing conditions. The skilled person will understand how to determine which alkanol is gaseous at the processing conditions, which may be influenced by the concentration of the alkanol, the boiling point of the alkanol, the pressure and temperature at which the process is performed. Typically, the alkanol has a boiling point below the temperature at which the Guerbet reaction is performed, such as a boiling point below 500 °C, below 450 °C, or below 400 °C.

[0030] Preferably, R1 is selected from hydrogen and alkyl and R2 is a hydrogen atom (i.e. the non-tertiary alkanol is a primary alkanol), most preferably both R1 and R2 are hydrogen atoms (i.e. the non-tertiary alkanol is ethanol). The term “non-tertiary alkanols” encompasses a single non-tertiary alkanol or a mixture of different non-tertiary alkanols, of which at least one is a non-tertiary alkanols containing a non-tertiary hydroxyl moiety having at least two β-hydrogen atoms. Further non-tertiary alkanols in the mixture of different alkanols may contain a non-tertiary hydroxyl moiety having no, one, two or three β-hydrogen atoms. Suitable non-tertiary alkanols comprise at least one hydroxyl moiety which is either a primary or a secondary hydroxyl moiety and an alkyl moiety, which may be linear, branched or cyclic and saturated or unsaturated. The non-tertiary alkanols may comprise further hydroxyl moieties, each of which may either be primary, secondary or tertiary. Preferably, the non-tertiary alkanols comprise 1 to 20 carbon atoms, more preferably 1 to 6 carbon atoms, even more preferably 1 to 4 carbon atoms. Suitable non-tertiary alkanols include, but are not limited to ethanol, propanol (1-, 2-), butanol (1-, 2-, iso-), pentanol (e.g. 1-, 2-, 3-, iso-, neo-, cyclo-), hexanol (e.g. 1-, 2-, 3-, iso-, cyclo-), or mixtures thereof. Preferably, the non-tertiary alkanols include at least ethanol and/or 1-butanol. In an especially preferred embodiment, the non-tertiary alkanols comprise ethanol, more preferably the non-tertiary alkanols consist of ethanol. Further non-tertiary alkanols which may optionally be present in the mixture of different alkanols include, but are not limited to, ethanol, propanol (1-, 2-), butanol (1-, 2-), pentanols, hexanols, or mixtures thereof.

[0031] Guerbet reactions on an industrial scale are typically performed in the gas phase, wherein a flow comprising the alcohol starting material(s), e.g. a stream of nitrogen containing 25% ethanol (w/w), is fed over or through a catalyst bed at elevated temperatures. The catalytic reaction itself typically takes place at a temperature between 200 and 500 °C with contact times up to several seconds. The process may be performed at ambient pressure, but other pressures may also be suitable. In a preferred embodiment, the process according to the reaction is performed above ambient pressure, e.g. between 2 bar and 10 bar, more preferably between 2.5 bar and 5 bar. At elevated pressures, the occurrence of side-reactions may be reduced. Thus far, research has mainly focused on liquid phase Guerbet reaction.

[0032] The process according to the invention typically occurs with the at least one non-tertiary alkanol containing a non-tertiary hydroxyl moiety having at least two β-hydrogen atoms in the gas phase, preferably at a temperature between 200 °C and 500 °C, more preferably between 250 °C and 450 °C, most preferably between 250 °C and 400 °C. The catalysts is preferably present in the solid phase, preferably in a catalyst bed, through or over which a stream comprising the reactant(s), i.e. the non-tertiary alkanols as described above, is led. Preferably, the contact time between the reactant(s) (at least one non-tertiary alkanol) and the catalyst is between 0.1 sec and 30 sec, preferably between 0.5 sec and 10 sec. Contact times are determined at ambient temperature and pressure with respect to the volume of active catalyst in the catalytic bed. Contact times t may be calculated by: t (s) = 3600/GHSV, wherein GHSV is the Gas Hourly Space Velocity in h"1, i.e. the flow of reactant (i.e. non-tertiary alkanol) in e g. mL/min divided by the volume of active catalyst in e.g. mL. The velocity at which the stream comprising the reactants is led through or over the catalyst may be used to manipulate the GHSV and thus the contact time between the reactant(s) and the catalyst.

[0033] Suitably, the alkanol is fed into the catalytic bed in a stream of nitrogen, argon or other inert carrier which is gaseous at the process temperature. Alternatively, the non-tertiary alkanol may be fed to the catalytic bed as a stream of pure gaseous non-tertiary alkanol. The stream that is fed through or over the catalyst typically comprises 5 wt% to 100 wt% of the non-tertiary alkanols, preferably 25 wt% to 100 wt%. The stream may also contain hydrogen gas. In a preferred embodiment, the stream does not comprise hydrogen gas.

[0034] In one embodiment of the process according to the invention, the catalyst is activated prior to contacting it with the non-tertiary alkanols, preferably by exposing it to a reductive environment at elevated temperature. Activation typically occurs at elevated temperature (e.g. above 150 °C) under a reducing atmosphere (e.g. an atmosphere comprising hydrogen gas, ethylene, CO and/or hydrazine, preferably an atmosphere comprising hydrogen gas). Alternatively, activation may occur ex situ or even at a different location, e.g. the catalysts may be purchased in activated form.

[0035] The process for coupling of non-tertiary alkanols according to the invention affords the corresponding β-alkylated non-tertiary alkanols and/or related condensed products efficiently and in a single step. The productivity of the catalysts may be determined as the amount of condensed product per liter active catalyst in the catalytic bed per hour. Condensed products are those in which a carbon-carbon single bond has been formed during the reaction. In the context of the present invention, the formation of carbon-oxygen bonds (e.g. in the Tishchenko reaction) is not considered to be a form of condensation. Thus, in case ethanol is the reactant for the process according to the invention, condensed products include the C4-compounds butyraldehyde, croton-aldehyde and butanol. The process according to the invention gives condensed products in a productivity above 300 g/L h and a selectivity for condensed products as high as 50%.

Preferred embodiments

[0036] The following embodiments are preferred according to the invention: 1. A process for gas phase coupling of a non-tertiary alkanol containing at least two alpha-hydrogen atoms comprising contacting the alkanol with a solid catalyst, wherein the catalyst comprises between 20 and 80 atom% copper, and between 20 and 80 atom% of one or more elements selected from magnesium, aluminium, silicon, and zinc, based on total metal atoms.

2. A process according to embodiment 1, wherein the catalyst exhibits an acidic character as determined by temperature-controlled ammonia desorption.

3. A process according to embodiment 1 or 2, wherein the catalyst comprises between 30 and 60 atom%, preferably between 32 and 52 atom% copper, based on total metal atoms.

4. A process according to any one of embodiments 1-3, wherein the catalyst comprises between 0.1 and 50 atom% zinc, based on total metal atoms.

5. A process according to any one of embodiments 1-4, wherein the catalyst comprises between 10 and 60 atom% magnesium and/or silicon, based on total metal atoms.

6. A process according to embodiment 5, wherein at least part of the magnesium and the silicon is present as magnesium silicate.

7. A process according to any one of embodiments 1-6, wherein the catalyst comprises between 1 and 45 atom% zinc, based on total metal atoms.

8. A process according to any one of the preceding embodiments, wherein the copper is present as copper oxide which is reduced to metallic copper prior to contacting the alkanol with the catalyst.

9. A process according to any one of the preceding embodiments, wherein the reaction temperature is between 250 and 450 °C.

10. A process according to any one of the preceding embodiments, wherein the alkanol is contacted with the catalyst for a period of between 0.1 and 30 sec.

11. A process according to any one of the preceding embodiments, wherein the alkanol is contacted with the catalyst for a period of between 0.5 and 10 sec.

12. A process according to any one of the preceding embodiments, wherein the alkanol comprises ethanol.

Figures

[0037] The figure depicts the ammonia-TPD profiles of catalyst A and B and ZSM-5 (control).

Examples

[0038] The following examples, two catalysts have been tested for their activity in the Guerbet reaction. Catalyst A (R3-11G purchased from Research Catalysts Inc.) comprises a metal oxide composition containing 50 wt% CuO, 2 wt% ZnO and traces of CaO, BaO, CrOx and AI2O3, and 22.8 wt% magnesium silicate (Mg2Si04), all based on total dry weight of the catalyst. Catalyst B (R3-15 purchased from Research Catalysts Inc.) comprises a metal oxide composition containing 50 wt% CuO, and 50 wt% of Zn6Al209 and Boehmite, all based on total dry weight of the catalyst. The approximate atomic compositions of the catalysts before activation are determined by SEM-EDX and are given in table 1.

Table 1: Atomic composition of the catalysts

i) in atom% based on total atoms; ii) in atom% based on total metal atoms.

Example 1: Acidity of the catalysts

[0039] The acidity of catalyst A and catalyst B have been tested using temperature programmed ammonia desorption (ammonia-TPD), using ZSM-5 as control. 300 mg of each of catalyst A and catalyst B (particle diameter = 106 - 300 micrometer) was loaded in the reactor (Autosorb iQ-C equipped with a TDP detector). The samples were treated according to table 2. ZSM-5 (purchased from Penta Zeolithe GmbH) was calcined at 550°C ex situ in stagnant air and 350 mg was loaded in the reactor. The sample was treated according to table 3. Differences in treatment are because of different protocols provided by the manufacturers.

[0040] Table 2: Ammonia-TPD of catalyst A and catalyst B

[0041] Table 3: Ammonia-TPD ofZSM-5

[0042] The TPD profiles are given in figure 1. The surface of ZSM-5 is known to contain two sites of distinct acidity, one of which releases ammonia at a temperature of approximately 250 °C, and one of which releases ammonia at a temperature of approximately 500 °C. Both catalyst A and catalyst B show extensive ammonia desorption at temperatures above the main desorption signal ofZSM-5, which appeared around 250 °C. Catalyst A shows extensive desorption between 200 °C and 500 °C, with a maximum at 300 °C, and catalyst B shows extensive desorption between 250 °C and 550 °C, with a maximum at 500 °C. As ammonia remains adsorbed to the catalyst until higher temperatures are reached, the catalyst surface is exhibits stronger acidic character, compared to ZSM-5.

Example 2: Ethanol conversion

[0043] Catalysts A and B (particle diameter = 106 - 300 micrometer; catalytic bed volume V = 1.4 mL, corresponding to 1020 mg catalyst A and 1450 mg catalyst B) are activated in situ according to the protocol provided by the manufacturer (table 4). After purge with N2, the reactor is brought to the lowest reaction temperature (T = 275 °C), and the reaction gas (composition: 67.5% N2 + 7.5% CH4 + 25% EtOH (v/v/v); inert methane is present as internal standard) is led over the catalyst (flow = 84 mL/min, which gives a contact time t of 4 seconds). The product mixture is continuously analysed by on-line gas chromatography (ZB-Wax plus column). After 24 h of reaction, the temperature is increased to 300 °C, and the product mixture is continuously analysed. After another 24 h of reaction, the temperature is increased to 325 °C, and the product mixture is continuously analysed. The pressure during the experiment was 1 bar. For catalyst A, the experiment is repeated with a catalytic bed volume of 3.0 mL, at T = 250 °C and 350 °C, t = 8 s and pressure = 3 bar. Analysis of the product mixtures is given in table 5.

[0044] Table 4 : Activation of catalyst A and catalyst B

[0045] Table 5: Product mixtures of the Guerbet reaction with catalyst A or B at various temperatures.

[1] Ethanol conversion (percentage EtOH reacted).

[2] Selectivity for C2-products (mole product produced / mole EtOH converted); Aal = acetaldehyde; Ac = acetone; EA = ethyl acetate; AA = acetic acid.

[3] Selectivity for Coproducts (mole product produced / (mole EtOH converted χ 0.5) (0.5 mole product per mole EtOH converted)); Bol = 1-butanol; BA = butyraldehyde; CA = crotonaldehyde.

[4] Productivity of Coproducts in gram product per liter active catalyst in the catalytic bed per hour.

[5] Performed at a pressure of 3 bar.

[0046] The product mixtures contained a C2 and a C4 fraction, as shown in table 5. The C2 fraction contains significant amounts of acetaldehyde, which is the product of the first step in Guerbet alcohol condensation. Minor amounts of the acetaldehyde is converted into ethyl acetate (Tishchenko reaction) and acetic acid (Cannizzaro reaction), and also some decarboxylation of those compounds towards acetone is observed. In the context of the present invention, ethyl acetate is considered a C2-product, as no condensation (i.e. C-C bond formation) has occurred in the formation thereof. Large part of the ethanol is converted into C4-compounds, by conversion of acetaldehyde into the Guerbet products crotonaldehyde, butyraldehyde and 1-butanol, all of which are readily converted into 1-butanol upon hydrogenation.

Claims

A process for coupling in the gas phase a non-tertiary alkanol containing at least two beta hydrogen atoms, which comprises contacting the alkanol with a solid catalyst, wherein the catalyst is between 20 and 80 atomic% copper and between 20 and 80 atomic% of one or more elements selected from magnesium, aluminum, silicon and zinc, based on the total of metal atoms.

The method of claim 1, wherein the catalyst has an acidic character as determined by temperature-controlled ammonia desorption.

The process according to claim 1 or 2, wherein the catalyst comprises between 30 and 60 atomic%, preferably between 32 and 52 atomic% copper, based on the total of metal atoms.

The process according to any of claims 1-3, wherein the catalyst comprises between 0.1 and 50 atomic% zinc, based on the total of metal atoms.

Process according to any one of claims 1-4, wherein the catalyst comprises between 10 and 60 atomic% magnesium and / or silicon, based on the total of metal atoms.

The method of claim 5, wherein at least a portion of the magnesium and the silicon are present as magnesium silicate.

The process according to any of claims 1-6, wherein the catalyst comprises between 1 and 45 atomic% zinc, based on the total of metal atoms.

A method according to any one of the preceding claims, wherein the copper is present as copper oxide which has been reduced to metallic copper prior to contacting the alkanol with the catalyst.

The method according to any of the preceding claims, wherein the reaction temperature is between 250 and 450 ° C.

The process according to any of the preceding claims, wherein the alkanol is contacted with the catalyst for 0.1 to 30 seconds.

The process according to any of the preceding claims, wherein the alkanol is contacted with the catalyst for 0.5 to 10 seconds.

The method of any one of the preceding claims, wherein the alkanol comprises ethanol.