PRODUCTION OF TRIALKOXYPROPANE

Abstract: This invention relates to a process for the production of 1,1,3-trialkoxypropanes by reacting acrolein with an aliphatic alcohol in the presence of an acidic catalyst and removing from the reaction mixture water that is present in the reactants and/or formed in situ. Water is removed by bringing at least a portion of the reaction mixture into contact with an adsorbent material capable of selectively adsorbing water. An example of such material is a molecular sieve. The removal of water reduces the formation of unwanted by-products which reduce selectivity to the desired dialkoxy propane formed by the hydrogenation of the trialkoxypropane.

Description: PRODUCTION OF TRIALKOXYPROPANE The present invention relates to an improvement in the process for the production of trialkoxypropanes in general and triethoxypropane (hereafter "TREP") in particular by the reaction of acroiein with an aliphatic alcohol. The reason for producing trialkoxypropanes is for the conversion thereof by hydrogenation into desirable and useful commercial solvents such as the corresponding dialkoxy propanes. It is well known to prepare 1,1,3- trialkoxyalkanes in general by reacting α,β-unsaturated aldehydes with alcohols in the presence of an acid catalyst. The method entails allowing the mixture of the aldehyde and alcohol to react in the presence of the catalyst over a period of time at ambient or slightly above ambient temperatures and then working up the reaction mixture. However in this reaction, not all of the unsaturated aldehyde undergoes the addition reaction with the alcohol; in the products, a small but significant amount of the unreacted aldehyde is present together with some of the corresponding unsaturated acetal. Moreover, the process also yields from 5-15% of the less desirable 3-ethoxypropanal. It was realised that the presence of water either in the reactants or formed in situ during the addition reaction may be responsible for the low yield of the desired product. If water is not removed from this reaction mixture, the reaction equilibrium also favours the formation of the unwanted by-product 3-ethoxypropanal. The hydrogenation of a reaction mixture containing significant quantities of 3-ethoxypropanal yields a product which contains undesirable by-products and relatively low amounts of the desirable 1,3- diethoxypropane. This is wasteful of the acroiein and ethanol reactants. Furthermore, the presence of any significant quantities of acroiein in the reaction product is hazardous and has toxicity and safety implications. To improve the yield of the desired trialkoxyalkanes, GB-A-713833 suggested the removal of water formed during the process by continuously entraining away the water from the reaction mixture as an azeotrope. The continuous removal of water as an azeotrope using a suitable entrainer has the following disadvantages: a. the azeotrope suitably has a boiling point lower than that of the 5 reactant aldehyde; b. means for distillation of the resultant azeotrope are required; c. the water-containing azeotrope has to be separated into aqueous and organic phases; and d. the organic phase has to be treated in order to recover therefrom the i o entrainer and any unreacted aldehydes for the purposes of recycling. Ideally, this entraining method works best when the azeotrope with water is removed as the lowest boiling fraction in the reaction mixture in order to avoid undesirable entrainment of the other reactants in the reaction mixture. This process is thus cumbersome and expensive not only because of the i 5 limited choice of azeotroping entrainers but also because of the relatively complex procedure for recovery and recycle of both the entrainer and the unreacted aldehydes. Moreover, this process becomes even more complicated and limited in the case of TREP where the azeotrope has to have a lower boiling point than acroiein (the reactant aldehyde) which has a boiling point of 52.5-53°C, has a 0 40% w/w solubility in water and is totally miscible with ethanol. Thus, in this case, if water has to be removed as an azeotrope, one has to resort to the use of an entrainer such as eg pentane, diethylether or dichloromethane. The water- azeotropes formed using these entrainers contain only low amounts ( 1 -2% w/w) of water which would therefore necessitate using either large amounts of the 5 entrainer or very high recycle rates. In addition, an entrainer such as dichloromethane would be considered environmentally less friendly due to the presence of halogen atoms therein. Several other methods have been suggested in the prior art for the removal of water from reaction mixtures. One such prior art is GB-A- 1407945 which 0 relates to a process for the production of di-unsaturated aldehydes by the pyrolysis of a di-alkenyloxy alkyl butene. The latter in turn is formed by the reaction between an unsaturated C5-alcohol and an alkyl substituted butenal in the presence of a dehydrating agent which is preferably a molecular sieve, sodium sulphate, magnesium sulphate or calcium chloride. This document states that the 5 molecular sieves contain metal oxides which are acid anhydrides and, when used, act both as dehydrating agents and condensing agents for this reaction. However, the complications of close-boiling by-products formed during the production of 1, 1,3-trialkoxy propane from acroiein and a saturated aliphatic alcohol - these reactants and products being different from those described in this prior art - and s the effect of water on these by-products are neither implied nor explained in this art. Moreover, the undesirable effects of the unwanted by-products during subsequent hydrogenation of the 1, 1 ,3-trialkoxy propane to form 1,3-dialkoxy propane is different from the production of di-unsaturated aldehyde desired in this art. •i o It has now been found that the above problems associated with the production of tri-alkoxy propanes can be mitigated by using a method of water- removal which not only avoids the use of an entrainer and is very effective but is highly economic and easy to separate from the reactants and products. Accordingly, the present invention is a process for the production of 1, 1,3 - i s trialkoxypropanes said process comprising reacting acroiein with an aliphatic alcohol in the presence of an acidic catalyst and removing from the reaction mixture water that is present in the reactants and/or formed in situ, characterised in that water is removed by bringing at least a portion of the reaction mixture into contact with an adsorbent material capable of selectively adsorbing water. 20 The aliphatic alcohols that may be reacted with acroiein are suitably primary or secondary alcohols having 1 - 10 carbon atoms, preferably from 1 -8 carbon atoms. Examples of alcohols that may be used include ter alia methanol, ethanol, propanol, isopropanol, n-butanols, isobutanol and ethyl hexanol. Ethyl alcohol is preferred. - - The relative mole ratios of aliphatic alcohol to acroiein in the reaction mixture is suitably in the range from 1 : 1 to 20: 1, and preferably in the range from 3: 1 to 10: 1. The reaction is suitably carried out in the presence of any conventional acidic catalyst such as eg sulphuric acid, hydrochloric acid or phosphoric acid, J O organic sulphonic acids, acid clays, acidic zeolites or an acidic ion-exchange resin such as eg Amberiyst® 15. The amount of acidic catalyst used would suitably be in the range from about 0.1 to about 10% w/w, preferably from about 1 to about 5% w/w of the reactant mixture. The adsorbent material capable of selectively adsorbing water is suitably 35 pre-dried before use. The adsorbent material is suitably a molecular sieve such as eg zeolites are agglomerates of crystalline metal aluminosuicates of a Group IA or Group IIA metal (according to the Periodic Table due to Mendeleef) such as sodium, potassium, calcium and/or magnesium and which aluminosuicates have been heated to remove their water of hydration. Their pore size can be controlled accurately to the desired narrow range of molecular dimensions. They generally enable separation by (i) adsorption due to a strong preference for one of the components in a mixture - in this case water - or (ii) size of the molecules by retaining molecules which fit into the pore openings of the sieve. It is preferable to use eg molecular sieves which have a pore opening size only large enough to adsorb water but which would not allow bigger molecules to pass through. In the context of the present invention, molecular sieves having sizes in the range from 3 A to lOA can be suitably used for maximum efficiency of water removal. Specific examples of molecular sieves that may be used include inter alia sieves having sizes in the range from 3 A to 5 A. In particular, the zeolites that can be used as adsorbent material include the dehydrated forms of zeolites having A, X, Y or mordenite type structures. Aluminium-rich zeolites are good adsorbent materials for this purpose. The zeolites could have their cations exchanged for more suitable ones such as eg potassium, barium or calcium for sodium. Particularly preferred is zeolite A. These adsorbent materials are capable of adsorbing upto 30% w/w of water when compared with about 1% w/w entrainment of water by the azeoptroping entrainers specified above. Water is removed from the reaction mixture by bringing at least a portion of the reaction mixture into contact with the adsorbent material. By a "portion of the reaction mixture" as used herein and throughout the specification is meant some or all of the reaction mixture including inter alia the light distillates from the reaction mixture as described below The water-adsorbent material may be used either by simply adding said material to the reaction mixture or it can be used as a bed through which aliquots of the vapours of the reaction mixture or condensates of overhead light distillates from the reaction mixture are passed continuously prior to recycle to the reaction mixture. The latter method is preferred where such overhead light distillates, especially those distilled when the reaction is carried out under reduced pressure, usually comprise the reactant alcohol, acroiein and water. This latter method has the advantage of not allowing the adsorbent material to come into contact with the relatively heavier fractions in the reaction mixture, especially any oligomers present therein thereby adversely affecting the life time and recyclability of the adsorbent material. The reaction is suitably carried out at a temperature in the range from 30- 80°C, preferably from 40-60°C. It is essential to avoid very high temperatures since such temperatures may lead to the resinification of either the reactant 5 aldehyde or the unsaturated by-products such as the propanals formed during the reaction. When operating the process in a mode in which either aliquots of the vapours of the reaction mixture or the condensates of the overhead light distillates are passed through a sieve bed, it is preferable to carry out the reaction under reduced pressure eg by carrying out the reaction under a low vacuum. ι o By carrying out the process using a water-adsorbent material the reaction product comprises substantially only the unreacted alcohol and trialkoxypropane. This mixture can be fed directly without further purification to the hydrogenation stage in order to produce the desired dialkoxy propane since one of the by¬ products of the hydrogenation reaction is the corresponding alcohol. Thus, this 15 method of water removal further simplifies the process considerably and saves on capital cost and complexity of the process. In certain cases where the reaction mixture cannot be directly fed to the hydrogenation stage due to the presence of some unwanted by-products which may adversely affect the hydrogenation reaction or catalyst, it would be possible to insert an intermediate separation stage 0 in order to remove or recycle such offending by-products to improve the economics of the process. The process of the present invention is relatively simple, has low capital costs and hence significantly improves the economics of the process. The present invention is further illustrated with reference to the following 5 Examples and Comparative Tests. In all the Examples and Comparative Test below the analyses were carried out as follows: a) Organic material was analysed by gas liquid chromatography using a Chrompack Gas Chromatograph with autosampler, 50M X 0.32MM i d. CP-SI 5 column and Flame Ionisation Detector. 0 b) Water content of the product was determined using a Mettler Karl Fischer titrator. Example 1 A 500 ml 3 -neck round bottomed flask was fitted with a double- walled reflux condenser with nitrogen top cover, a thermowell and a dropping funnel. 49.85g 5 4A molecular sieves (dried overnight at 200°C), 4.19g ethanol-washed Amberlyst®15 ion-exchange resin (water content 5% w/w), 39.18g dry ethanol (water content < 0.05% w/w) were charged to the reaction flask. The reaction mixture was stirred and heated to 50°C and 91.7g of a 2.45: 1 molar ethanol:acrolein mixture added dropwise, via the dropping funnel, over a period s of 15 minutes. Once addition of the ethanol: acroiein mixture was complete the reaction was stirred for a further 360 minutes at 50°C and then allowed to cool. The final product contained (% w/w), ethanol (31.81), acroiein (0.29), 3- ethoxypropanal (2.64), 3,3-diethoxypropene (0.25), 1,1,3- triethoxypropane (57.31) and water (0.82). o Example 2 To a 500 ml three-port jacketed flask was fitted a drying rig/decanter and on top of this a double walled reflux condenser connected to a vacuum system. The remaining two reaction flask ports were fitted with a thermowell and a sampling tap/dropping funnel arrangement. The drying rig/decanter was designed to condense and recirculate light boiling material through a separate bed of molecular sieves, and return dried material to the reaction flask. A calibrated side arm with 3-way tap was fitted to allow approximate measurement of rate of cycle through sieve bed. 49.5 lg 4A molecular sieves (dried overnight at 200°C) were charged to the drying rig/decanter. 4.19g ethanol-washed Amberiyst® 15 ion-exchange resin (water content 5% w/w) and 38.69g dry ethanol (water content < 0.05% w/w) were charged to the reaction flask. The reaction mixture was stirred and heated to 50°C. When stable at 50°C 90.6g of a 2.45: 1 molar ethanol:acrolein mixture was added dropwise, via the dropping funnel, over a period of 15 minutes. Once addition of the ethanol: acroiein mixture was complete the reaction was held at 50°C for 120 minutes. At this point the reaction pressure was slowly decreased to 148 mmHg to achieve a good reflux with material recirculating through the drying rig/condenser at -3.6-5.4 ml min. The reaction was allowed to continue for a further 240 minutes at 50°C and then cooled. When cool, any material remaining in the drying rig/decanter was drained back into the reaction flask and a sample of product was removed for analysis. The final product contained (% w/w), ethanol (25.37), acroiein (0.03), 3- ethoxypropanal (1.16), 3,3-diethoxypropene (0.23), 1,1, 3 -triethoxypropane (63.19) and water (0.37). Comparative Test 1 (not according to the invention): To a 500 ml flanged flask was fitted an overhead stirrer, a double walled reflux condenser, dropping funnel and thermowell. 4.25g Ethanol-washed .Amberiyst® 15 ion-exchange resin (water content 5% w/w), 99.55g dry ethanol (water content < 0.05% w/w) were then charged to the reaction flask. The reaction mixture was stirred and heated to 50°C. When stable at 50°C, 30.2g of dry acroiein was added dropwise, via the dropping funnel, over a period of 15 minutes. Once addition of the acroiein was complete the reaction was held at 50°C for a further 330 minutes and then cooled. The final product contained (% w/w), ethanol (36.48), acroiein (0.60), 3- ethoxypropanal (9.37), 3,3-diethoxypropene (0.20), 1,1, 3 -triethoxypropane (39.64) and water (3.8).

Claims: Claims: 1. A process for the production of 1, 1,3-trialkoxypropanes said process comprising reacting acroiein with an aliphatic alcohol in the presence of an acidic catalyst and removing from the reaction mixture water that is present in the reactants and/or formed in situ, characterised in that water is removed by bringing at least a portion of the reaction mixture into contact with an adsorbent material capable of selectively adsorbing water. 2. A process according to Claim 1 wherein the aliphatic alcohols that may be reacted with acroiein are primary or secondary alcohols having 1-10 carbon atoms. 3. A process according to Claim 1 or 2 wherein the aliphatic alcohols have from 1-8 carbon atoms. 4. A process according to any one of the preceding Claims wherein the aliphatic alcohol is selected from the group consisting of methanol, ethanol, propanol, isopropanol, n-butanols, isobutanol and ethyl hexanol. 5. A process according to any one of the preceding Claims wherein the relative mole ratios of aliphatic alcohol to acroiein in the reaction mixture is in the range from 1 : 1 to 20: 1. 6. A process according to any one of the preceding Claims wherein the relative mole ratios of aliphatic alcohol to acroiein in the reaction mixture is in the range from 3: 1 to 10: 1. 7. A process according to any one of the preceding Claims wherein the reaction is carried out in the presence of an acidic catalyst selected from the group consisting of sulphuric acid, hydrochloric acid, phosphoric acid, organic sulphonic acids, acid clays, acidic zeolites and acidic ion-exchange resins. 8. A process according to any one of the preceding Claims wherein the acidic catalyst is Amberiyst® 15. 9. A process according to any one of the preceding Claims wherein the acidic catalyst is used in an amount ranging from about 0.1 to about 10% w/w of the reactant mixture. 5 10. A process according to any one of the preceding Claims wherein the adsorbent material capable of selectively adsorbing water is a molecular sieve. 11. A process according to Claim 10 wherein the molecular sieve is an agglomerates of crystalline metal aluminosuicates of a Group IA or Group IIA metal (according to the Periodic Table due to Mendeleef) which have been heated ι o to remove their water of hydration. 12. A process according to Claim 10 or 1 1 wherein the molecular sieve has a pore opening size in the range from 3 A to 10 A. 13. A process according to any one of the preceding Claims 10-12 wherein the molecular sieve is the dehydrated form of a zeolite having A, X, Y or mordenite 15 type structure. 14. A process according to any one of the preceding Claims wherein water is removed from the reaction mixture by bringing at least a portion of the reaction mixture into contact with the adsorbent material either by simply adding said material to the reaction mixture or by passing aliquots of the vapours of the 0 reaction mixture or condensates of overhead light distillates continuously through a bed of said material prior to recycle to the reaction mixture. 15. A process according to Claim 14 wherein the process when operated in a mode in which either aliquots of the vapours of the reaction mixture or the condensates of the overhead light distillates are passed through a bed of the 5 molecular sieve, the reaction is carried out under reduced pressure. 16. A process according to any one of the preceding Claims wherein the reaction between acroiein and the aliphatic alcohol is carried out at a temperature in the range from 30-80°C. 0 5

Inventors: BREW STEPHEN ALEXANDER, FROOM SIMON FREDERICK THOMAS, HODGE STEPHEN ROBERT, BREW, STEPHEN, ALEXANDER, FROOM, SIMON, FREDERICK, THOMAS, HODGE, STEPHEN, ROBERT
Applicants: BP CHEM INT LTD, BREW STEPHEN ALEXANDER, FROOM SIMON FREDERICK THOMAS, HODGE STEPHEN ROBERT, BP CHEMICALS LIMITED, BREW, STEPHEN, ALEXANDER, FROOM, SIMON, FREDERICK, THOMAS, HODGE, STEPHEN, ROBERT
Application year: 1996
Main classification: C07C41
IPC codes: B01J31, C07B61, C07C41, C07C43