MXPA98010399A - Procedure for preparing alcohol - Google Patents

Abstract

The present process for preparing alcohols comprises the hydrogenation of aldehydes in the presence of a hydrogenation catalyst in the gas phase, in this process, nitrogen-containing bases are added to the aldehyde to be hydrogenated, whereby the by-product formation is suppressed to a large extent, and it is possible to isolate the desired alcohols in high selectivity and yield correspondingly to the

Description

PROCEDURE FOR PREPARING ALCOHOLS DESCRIPTIVE MEMORY The present invention relates to a process for preparing alcohols by hydrogenation of aldehydes in the gas phase. It is known that alcohols can be prepared by catalytic hydrogenation of the corresponding saturated and unsaturated aldehydes at elevated temperature and at atmospheric or superatmospheric pressure. The reaction can be carried out intermittently or continuously in a homogeneous or heterogeneous phase. Correspondingly, the hydrogenation catalyst is used in dissolved form or in finely divided form as a suspension, or in pellet or pellet form as a fixed bed catalyst. The compounds that will be hydrogenated can be supplied to the catalyst in a gaseous or liquid state. Particularly, the hydrogenation of saturated aldehydes obtained by hydroformylation of alkenes, and the hydrogenation of 6, β-unsaturated aldehydes formed by aldolization of aldehydes are of great importance. Among these, the hydrogenations of n- and isobutyraldehyde, n- and iso-valeraldehyde, hydroxipivalaldehyde, ne iso-hexanal, 2-ethylhexenal, mixtures of isomeric and / or nonanal isomeric noanals, and also mixtures of isomeric and / or decadal isomeric decanales , are of particular industrial relevance. A broad discussion of the preparation of alcohols by catalytic hydrogenation of carbonyl compounds, in particular ketones, aldehydes and their derivatives, can be found in Houben-Weyl, Methoden der organischen, Chemie, Georg Thieme Verlag, Stuttgart-New York 1984, volume Vi / Ib, pgs. 9 to 111. In hydrogenations in the liquid phase, reactor pressures of 20 to 300 bar are usual to achieve satisfactory hydrogenation. In addition, hydrogenation often has to be carried out in a plurality of stages (DE-B-12 31 227). Since the reaction is strongly exothermic, the recirculation of a considerable part of the hydrogenated product or dilution with a solvent for capacitive heat removal is necessary in industrial reactors. This allows only comparatively low aldehyde space velocities through the reactors, as a result of which the disadvantageous downstream product formation of the reactive aldehydes is promoted due to the consequently high residence time. These difficulties can be avoided by hydrogenation in the gas phase. The hydrogenation of rapidly vaporisable aldehydes is therefore preferably carried out in the gas phase at elevated temperatures and pressures in the presence of several catalysts containing predominantly nickel and / or copper. Thus, EP-A-0 421 196 describes a process for preparing alcohols, in which organic carbonyl compounds are reacted with hydrogen in the gas phase at a temperature of 60 to 150 ° C and at atmospheric or superatmospheric pressure in the presence of a supported catalyst comprising nickel, aluminum oxide and zirconium dioxide. However, in the same way, the hydrogenation of aldehydes in the gas phase on said nickel and / or copper-containing catalysts results in the formation of by-products that reduce the yield of the desired alcohols, although to a lesser degree, than when working in the liquid phase. Therefore, numerous efforts in this field have been directed to improve the selectivity of the hydrogenation reaction and thus the yield of the desired products by further development of the catalysts to be used. Thus, Belgian patent 690 249 describes a process for preparing saturated aliphatic alcohols by catalytic hydrogenation of aldehydes in the gas phase, in which a copper / nickel catalyst is used on a silica gel support in the first stage, and use a catalyst containing nickel and / or palladium in the second stage. This procedure allows the preparation of saturated alcohols with sensible yields under moderate conditions. Nevertheless, a disadvantage is the high sensitivity of the supported catalysts comprising silica gel, for example, to unforeseen malfunctions such as temperature increases, or to impurities that can easily lead to permanent catalyst damage. In particular, these catalysts are not suitable for regeneration by combustion of the impurities at high temperatures, since the formation of by-products such as hydrocarbons and ethers is in general considerably increased when the catalysts that have been regenerated by said high-temperature treatment are reused. in a hydrogenation reaction. The importance of the pH of the surface of the hydrogenation catalysts for the formation of inconvenient by-products was recognized for a long time. Thus, the citation Journal of Catalysis 128, 337-351 (1991) describes the formation of ether by-products in aldehyde hydrogenation in the presence of acid centers on the surface of catalysts of NÍ / SÍO2 • To reduce the formation of ether, the DE-C 16 43 856 describes the hydrogenation on supported catalysts containing copper and / or nickel comprising silica gel, in which the pH of the surface of the silica gel is adjusted from 6 to 10. However, in the case of a high space velocity on the catalyst, the formation of saturated and unsaturated hydrocarbons also occurs to an increasing degree for these catalysts, thus reducing the selectivity of the hydrogenation and also the yield of the desired product. The unsaturated hydrocarbons are formed by decarbonylation, that is, by removal of the carbonyl group from the aldehydes used, and thus have a carbon atom less than the aldehyde used. The subsequent hydrogenation then leads to the formation of the saturated hydrocarbons and methane from carbon monoxide. The hydrogenation of carbon monoxide to methane is strongly exothermic, which leads to an increased temperature in the catalyst bed and, as a result, back to the increased formation of inconvenient by-products. EP-A 0 470 344 discloses a two stage aldehyde hydrogenation process, in which a specific copper catalyst that has been made alkaline in the first stage is used, and a specific nickel catalyst is used in the second stage. stage, and more than 85% of the hydrogenation reaction is carried out in the first stage. Here again, the formation of hydrocarbons having a carbon atom less than the desired alcohol, and of ethers and esters having twice the number of carbon atoms than the aldehyde used is observed. These esters are formed from the aldehyde used by a Tishtshenko reaction.

US-A-4,626,604 discloses a process of at least three steps using different catalysts to hydrogenate unsaturated compounds to prevent the formation of the aforementioned by-products. A disadvantage of this method is the extraordinary complexity that results from the use of different conditions for the respective catalysts and their different operating time. The formation of hydrocarbons, ethers, steres and acetals as byproducts of the hydrogenation reaction not only reduces the yield, but also incurs non-inconsiderable costs in the isolation of pure alcohols where, in particular, the removal of the ethers presents difficulties particular due to its boiling point since it can only be achieved at a high cost. To avoid the formation of the aforementioned byproducts, not only improved catalysts have been produced and multi-step reaction methods have been proposed in the past, but a number of additional measures have also been developed. Thus, for example, the dilution of the steam stream entering the hydrogenation, which comprises an excess of hydrogen in addition to the aldehydes to be hydrogenated, has an advantageous effect. This makes it possible to reduce the formation of by-products by a large excess of hydrogen or a low concentration of the aldehydes in the vapor stream. A disadvantage of this measure is the specific low yield of the aldehyde that will be hydrogenated, or the need for a large excess of hydrogen that has to be circulated for economic reasons. In addition, it is known that the addition of water can lead to a decrease in the formation of by-products. The procedure here is that water vapor at a concentration of a low percent by volume is added to the stream entering the hydrogenation. However, this water has to be completely removed again after the condensation of the alcohols as a product, which makes the process complicated. Therefore, an object of the present invention is to provide a process by means of which the formation of by-products in the hydrogenation of aldehydes on hydrogenation catalysts in the gas phase, and the isolation of the desired alcohols in high form is largely suppressed. selectivity and correspondingly high performance is thus made possible in a simple and economical way. This object is achieved by a process for preparing alcohols by hydrogenation of aldehydes in the presence of a hydrogenation catalyst in the gas phase, where nitrogen-containing bases are added to the aldehyde to be hydrogenated. The bases containing nitrogen are usually primary, secondary or tertiary amines of the formula I, or diamines of the formula II NR3 I R2N- (CH2)? -NR2 II wherein the radicals R may be identical or different, and may be hydrogen, branched or unbranched C2-C10 alkyl radicals, branched or unbranched 5-C10 cycloalkyl radicals, branched or unbranched C2-C10 hydroxyalkyl radicals, and x is an integer from 2 to 6. Preferred branched or unbranched C2-C alkyl radicals are ethyl, propyl, n- or i-butyl, n- or i-pentyl, hexyl, heptyl and octyl radicals. As branched or unbranched C2-C] _Q hydroxyalkyl radicals, preference is given to 2-hydroxyethyl, 2-hydroxypropyl and 3-hydroxypropyl radicals. As diamines of formula II above, particular preference is given to using ethylenediamine, propylene diamine or 1,4-diaminobutane, in which x is thus 2, 3 or 4, and all radicals R are hydrogen. However, other bases containing nitrogen can also be used, in principle, in the process of the invention as long as they have a sufficiently high vapor pressure to be able to be added in the form of steam to the aldehyde in amounts of 1 to 50 ppm, preferably 1. at 25 ppm, calculated in ppm of nitrogen based on the aldehyde used, under the selected hydrogenation conditions. In the hydrogenation of 2-ethylhexenal to 2-ethylhexanol, for example, it has been found that the addition of tri-i-octylamine in an amount of 1 to 20 ppm of nitrogen, based on the aldehyde used (corresponding to 25.2-504) ppm of tri-i-octylamine), it is useful to significantly reduce the formation of hydrocarbons, ethers and esters. The aldehydes that can be used are saturated or unsaturated aldehydes having from 2 to 10 carbon atoms, or mixtures thereof. The aldehydes can be used in relatively pure form or also as crude reaction products such as those obtained in the preparation by means of hydroformylation, aldol condensation, or substitution or addition, possibly in diluted solutions. Examples of saturated aldehydes are acetaldehyde, propanal, n- and i-butyraldehyde, n- and i-pentanal, n- and i-hexanal, n- and i-heptanal, n- and i-octanal, in particular 2-ethylhexanal, n- and i-nonanal, and n- and i-decanal. Examples of unsaturated aldehydes that can be used are acrolein, crotonaldehyde, n-and i-pentenal, n- and i-hexenal, hexadienal, n- and i-heptenal, n- and i-octenal, in particular 2-ethylhexenal, n - e i-nonenal, and also n- and i-decenal. However, it is also possible to use other aldehyde derivatives which can be prepared by a series of usual syntheses such as aldolization, aldol condensation, substitution or addition reactions, for example the addition of water over unsaturated aldehydes, and can be converted successfully. in the corresponding alcohols by the process of the invention. These aldehyde derivatives can be, for example, relatively high molecular weight aldehydes, ring-containing aldehydes, bifunctional aldehydes or aldehydes containing other functional groups such as hydroxyl groups. In particular, the process of the invention is applied to the hydrogenation of n- and i-butyraldehyde, n- and i-valeraldehyde and 2-ethylhexenal. The hydrogenation of the aldehydes can be carried out in the presence of conventional hydrogenation catalysts. It has been found that catalysts containing nickel and / or copper, and also noble metal catalysts based on platinum, palladium, rhodium or ruthenium, are particularly useful. For the complete hydrogenation of unsaturated aldehydes such as 2-ethylhexenal, it is possible to use the known nickel and / or palladium-containing catalysts from GB 1,276,618. The catalysts can be applied to support materials such as SIO2 and / or AI2O3 of various types. Copper catalysts supported on zinc oxide and known from US-A-2, 549,416 can also be used for the hydrogenation of aldehydes in the gas phase. In addition, catalysts known for the hydrogenation of sulfur-containing starting materials from naphthalene disintegrants can also be used in the process of the invention. Suitable catalysts of this type are known, for example, from documents US-A-2, 709, 714, US-A-2, 760, 994, SU 179,757 and SU 638,585. As activators and promoters, the catalysts used may further comprise oxides of various monovalent to pentavalent metals. These are, for example, the oxides of Zn, Mg, Mn, Cr, Zr, Fe or rare earth metals. Phosphates, tungstates, chromates, dichromates, molybdates, pyroacids and polyacids of sulfur, phosphorus, boron, molybdenum, titanium and tungsten or their salts, may also be present. It is also possible to add silver, palladium or ruthenium to catalysts containing copper and / or nickel. Other catalysts that are suitable for the process of the invention are described, for example, in Hydrocarbon Processing 1993, 67. A specific catalyst that can be used successfully is that described in EP-A-0 421 196, and which comprises from 20 to 90% by weight of nickel, based on the catalyst composition, and from 1 to 30, preferably from 3 to 15, and in particular from 4 to 10, parts by weight of aluminum oxide, and from 0.5 to 20, preferably from 1 to 10, and in particular from 1.5 to 5, parts by weight of zirconium dioxide, in each case with base in 100 parts by weight of nickel, as co-precipitated on a support material. The suitable support materials are activated carbon, aluminum oxides, pumice stone-Al203, Si02, silica gel, diatomite and siliceous earths. It has been found that Si02, silica gel, diatomite and siliceous earth are particularly useful. The use is usually made from 6 to 80, preferably from 15 to 65, and in particular from 35 to 50, parts by weight of the support material per 100 parts by weight of nickel. The preparation of these catalysts is described in EP-A-0 421 196, which is expressly incorporated herein by reference. Also suitable are the copper oxide / zinc oxide / aluminum oxide catalysts claimed in EP-A-0 604 792 and comprising, per 100 parts by weight of copper oxide, from 40 to 130 parts by weight of zinc oxide, from 2 to 50 parts by weight of aluminum oxide and from 1 to 4 parts by weight of sodium oxide, having a total BET surface area of 50 to 100 m2 / g, and in which 75 to 95% of the total surface area is formed by pores having radii from 9 to 1000 nm, and from 5 to 25% of the total surface area is formed by pores having radii of less than 9 nm. The description of these catalysts in EP-A-0 604 792 is expressly incorporated herein by reference. It is also possible to use the catalysts claimed in EP-A-0 618 006 in the process of the present invention. These are hydrogenation catalysts comprising from 25 to 50% by weight of metallic nickel, from 10 to 35% by weight of nickel oxide, from 4 to 12% by weight of magnesium oxide, from 1 to 5% by weight of sodium oxide, and the balance of support material, where the sum of nickel and nickel oxide is from 40 to 70% by weight, the total BET surface area is from 80 to 200 m2 / g and the pore volume total determined by mercury porosimetry is from 0.35 to 0.6 ml / g, where from 30 to 60% of the total pore volume is formed by pores having a radius% 40 Á, from 4 to 10% of the total pore volume is formed by pores having a radius greater than 40 to 300 A, and from 30 to 60% of the total pore volume is formed by pores having a radius greater than 300 to 5000 A. The description of these catalysts in the EP- A-0 618 006 is expressly incorporated herein by reference. Also suitable is the hydrogenation catalyst described in EP-A-0 528 305, which comprises, per 100 parts by weight of copper oxide, from 40 to 130 parts by weight of zinc oxide, from 2 to 50 parts. by weight of aluminum oxide and, if desired, from 0.5 to 8 parts by weight of manganese oxide, molybdenum oxide, vanadium oxide, zirconium oxide and / or alkaline earth metal oxide, and has a surface area of Total BET of 80 to 175 m / g of catalyst in an unreduced state, wherein from 75 to 95% of the total BET surface area is formed by pores having a radius rp 3A 15 nm. The description of these catalysts in EP-A-0 528 305 is expressly incorporated herein by reference. To carry out the hydrogenation, the aldehyde and the nitrogen-containing base are vaporized together and passed in admixture with hydrogen on the granulated / pelletized catalyst arranged as a fixed bed in a reaction flask. Use is made here of at least 2 moles, preferably from 2 to 100 moles, and in particular from 3 to 30 moles, of hydrogen per equivalent of the aldehyde to be hydrogenated. Unreacted hydrogen can be recirculated to the reaction. The vapors emanating from the reaction flask are condensed and the condensate is, if necessary, prepared by distillation under atmospheric or reduced pressure. The hydrogenation temperature is generally 50 to 250 ° C, preferably 80 to 160 ° C. The choice of hydrogenation temperature is determined by the boiling point of the aldehyde, the pressure and the amount of hydrogen used. The pressure is 0.01 to 2.5 MPa, and can be freely selected within this scale, taking into account the boiling point and the amount of hydrogen used in order to satisfy the requirement that the starting materials will be hydrogenated, and that the corresponding hydrogenated products will remain in gaseous form. The process of the invention can be carried out continuously or intermittently. When the procedure is carried out continuously, the space velocity, expressed as volume of liquid starting material / volume of catalyst x hour (V / Vh), it is from 0.2 to 1.5, preferably from 0.3 to 1.2, and in particular from 0.5 to 1.0. Surprisingly, even very low concentrations of the nitrogen-containing bases and a few ppm, calculated as ppm of nitrogen based on the aldehyde used, are sufficiently effective to substantially reduce the formation of the different by-products in the hydrogenation reaction. Another considerable advantage is that the presence of bases containing nitrogen at low concentration in the aldehydes used for hydrogenation does not lead to known side reactions such as the Cannizzaro reaction or the Claisen-Tishtshenko reaction. Thus, the total selectivity of the hydrogenation of aldehydes is increased.

EXAMPLES The following general experimental description applies to all examples: An electrically heated jacket reactor (length: 1500 mm, internal diameter: 200 mm) is charged with 150 ml (140 g) of a commercial nickel catalyst (60% by weight of Ni, 27% by weight of diatomite, 3% by weight of l? 3 and 2% by weight of Zr0). After activating the catalyst, 90 g / h of n-butanal (purity of 98.7%) is pumped into a jacketed reactor at a temperature of 105 ° C and at a pressure of 0.35 MPa (abs.). The n-butanal is vaporized in a vaporizer installed upstream of the reactor, and is passed over the catalyst in the form of vapor. Along with the n-butanal, hydrogen (99% by volume of H2, 1% by volume of N2) is fed into the vaporizer in an amount such that the gas flow leaving the vaporizer is 200 standard liters / h. The reaction products are cooled to 18 ° C under the reaction pressure, and separated in a separator in a liquid and a gaseous product stream. The amounts of both product streams are measured, and the currents are analyzed by gas chromatography. For the calculation of product loss by dissociation, it is assumed that 1 mole of methane is formed per mole of dissociated n-butanal.

COMPARATIVE EXAMPLE 1 To decrease the initial activity of the catalyst, the reaction is carried out under constant conditions for a period of 180 hours. After this time, the following data are determined (liquid product,% by weight): n-butanal 0.04 n-butanol 84.91 di-n-butyl ether 14.61 n-butyl n-butyrate 0.14 hydrocarbons 0.30 Losses (dissociation, by-products): 15.2% by weight, based on the n-butanal used).

COMPARATIVE EXAMPLE 2 To reduce the formation of by-products, 9 g / h of water (10% by weight, based on n-butanal) are fed into the vaporizer in addition to the n-butanal (90 g / h), and are passed along with the n-butanal and hydrogen vaporized on the catalyst. After a period of 266 hours of operation under these conditions, the following data are determined (liquid product,% by weight): n-butanal 0.10 n-butanol 97.31 di-n-butyl ether 2.31 n-butyl n-butyrate 0.14 hydrocarbons 0.15 Losses (dissociation, by-products): 2.85% by weight, based on the n-butanal used).

The addition of water reduces the losses, but the selectivity of the hydrogenation remains unsatisfactory.

EXAMPLE 1 90 g / h of n-butanal are fed into the reactor. The n-butanal tri-isooctylamine is added in an amount of 250 ppm (0.025% by weight based on the n-butanal, corresponding to 9.9 ppm of nitrogen with base 'in the n-butanal used). After an operation time of 158 hours, the following data are determined (liquid product,% by weight): n-butanal 0.13 n-butanol 99.31 di-n-butyl ether 0.011 n-butyl n-butyrate 0.02 hydrocarbons 0.53 Losses (dissociation, by-products): 0.61% by weight, based on the n-butanal used).

Claims (10)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for preparing alcohols by hydrogenation of aldehydes in the presence of a hydrogenation catalyst in the gas phase, characterized in that bases containing nitrogen are added to the aldehyde to be hydrogenated.

2. The process according to claim 1, further characterized in that the nitrogen-containing bases are primary, secondary or tertiary amines of the formula I, or diamines of the formula II NR3 I R2N- (CH2)? - NR2 II wherein the radicals R may be identical or different, and may be hydrogen, branched or unbranched C2-C alkyl radicals, C5-C10 branched or unbranched cycloalkyl radicals, branched or branched C2-C hydroxyalkyl radicals or unbranched, and x is an integer from 2 to 6.

3. The process according to claim 2, further characterized in that the branched or unbranched 2-C-alkyl radicals R are ethyl, propyl, n-radicals. or i-butyl, n- or i-pentyl, hexyl, heptyl or octyl, the branched or unbranched C2-C hydroxyalkyl radicals are 2-hydroxyethyl, 2-hydroxypropyl or 3-hydroxypropyl radicals, and in diamines of formula II x is 2, 3 • or 4, and all radicals R are hydrogen.

4. The process according to one or more of claims 1 to 3, further characterized in that the nitrogen-containing base is added in vapor form to the aldehyde in amounts of 1 to 50 ppm, preferably 1 to 25 ppm, calculated in ppm of nitrogen based on the aldehyde used. 5. The process according to one or more of claims 1 to 4, further characterized in that the aldehydes used are saturated or unsaturated aldehydes having from 2 to 10 carbon atoms, or mixtures thereof. 6. The process according to claim 5, further characterized in that the saturated aldehydes used are acetaldehyde, propanal, n- and i-butyraldehyde, n- and i-pentanal, n- and i-hexanal, n- and i -heptanal, n- and i-octanal, in particular 2-ethylhexanal, n- and i-nonanal, and n- and i-decanal, and the unsaturated aldehydes used are acrolein, crotonaldehyde, n- and i-pentenal, n- and i-hexenal, hexadienal, n- and i-heptenal, n- and i-octenal, in particular 2-ethylhexenal, n- and i-nonenal or n- and i-decenal. 7. The process according to one or more of claims 1 to 6, further characterized in that the hydrogenation of the aldehydes is carried out in the presence of a catalyst containing nickel and / or copper or a noble metal based catalyst. of platinum, palladium, rhodium or ruthenium, whose catalyst is applied to a support material. 8. The process according to claim 7, further characterized in that the catalyst comprises from 20 to 90% by weight of nickel, based on the catalyst composition, and also from 1 to 30, preferably from 3 to 15, and in particular from 4 to 10, parts by weight of aluminum oxide, and from 0.5 to 20, preferably from 1 to 10, and in particular from 1.5 to 5, parts by weight of zirconium dioxide, in each case based on 100 parts by weight of nickel, as co-precipitated on a support material. 9. The process according to one or more of claims 8, further characterized in that the aldehyde and the nitrogen-containing base are vaporized together and then passed in admixture with hydrogen on the granulated / pelletized catalyst arranged as a bed fixed in a reaction flask, wherein at least 2 moles, preferably 2 to 100 moles, and in particular 3 to 30 moles, of hydrogen are used per equivalent of the aldehyde to be hydrogenated, the hydrogenation temperature is 50 to 250 ° C, preferably 80 to 160 ° C, and the pressure is 0.1 to 2.

5 MPa. 10. The process according to one or more of claims 1 to 9 carried out continuously at a space velocity, expressed as volume of liquid starting material / volume of catalyst per hour (V / Vh), of

0. 2 to 1.5, preferably from 0.3 to 1.2, and in particular from 0.5 to 1.0.