IE44306B1 - Production of alcohols by catalytic hydrogenation of carboxyhlic acids,lactones or anhydrides - Google Patents

Abstract

1534232 Hydrogenation catalysts VEBACHEMIE AG 3 Feb 1977 [10 Feb 1976] 4497/77 Heading BIE [Also in Division C2] A hydrogenation catalyst comprises palladium and rhenium in a weight ratio of 0.01:1 to 5:1, and an acid-resistant carrier, e.g. silicic acid, alumina or activated charcoal.

Description

The invention relates to a method for producing alcohols by the catalytic hydrogenation of carboxylic acids,-lactones or anhydrides.

It is known to produce alcohols from the corresponding carboxylic acids by catalytic hydrogenation after previous esterification of the acid with low alcohols, general methanol: This esterification entails an additional step in the process which gives rise to expense, while the recovery of the alcohol results in losses.

It has therefore always been endeavoured to develop a method which permits the hydrogenation of carboxylic acids themselves to give the corresponding alcohol. Thus, some catalysts are known which enable the reaction of a carboxylic acid with hydrogen to form the corresponding alGohol. According to German Auslegeschrift Nc. 1,240,061 dicarboxylic acids are hydrogenated in the presence of a large excess of the corresponding diol using a copper chromite contact material.

In German Patent No. 1,235,879 a cobalt catalyst is used for direct acid hydrogenation, this catalyst also containing copper, manganese, and/or chromium.

The known catalysts are not adequately resistant under the reaction conditions used;-after, a few weeks a decline of activity is observed. The life of a catalyst is a major factor in the cost of an industrial process, since the catalysts frequently consist of valuable substances or combinations of substances whose regeneration or recovery entails heavy expense.

' The present invention aims to provide a catalyst for the hydrogenation of carboxylix acids which catalyst.will under the reaction conditions used remains -Z44306 resistant to the carboxylic acids which are to be hydrogenated, even in the presence of the water produced by the reaction, over a long period of operation.

According to the present invention there is provided a process for the production of an alcohol by catalytic hydrogenation of a carboxylic acid at elevated temperature and elevated pressure, in the presence of water and/or other solvents, the hydrogenation being performed in the presence of 3 catalyst comprising palladium and rhenium in a weight ratio of from 0.01:1 to 5:1 and an acid-resistant carrier.

The catalyst used in the process of the present invention is distinguished by high activity and a long life. While the throughput is good, the carboxylic acid reactant is converted practically completely.

It is surprising that the combinations of palladium and rhenium as catalysts for direct acid hydrogenation should result in a long catalyst life together with high activity and selectivity, because use of each component alone results in only inadequate hydrogenation of the carboxylic acid. The use of rhenium by itself as a hydrogenation catalyst is described in a number of publications by various authors, who however do not refer to any special stability of the catalyst. Reference is made for example to: W.H. Davenport, Ind. Eng. Chem. 60 11-19 (1968), U.S. Broadbent et al., J. org. Chem. 24 1847 (1959) and A.B. Balandin et al., Translation of Doklady Akademii Nauk SSSR, Vol 139 No. , 1101 (1961).

It has however been possible to show that a reference catalyst which contained only rhenium as the catalytic substance showed differences from the catalyst of the invention both in respect of activity and in respect of selectivity.

Other metal combinations with rhenium which are described in patent literature for hydrogenation of carboxylic acids likewise showed less favourable hydrogenation results. In addition to more rapid decline of activity, increased formation of by-products resulting from the destruction of the carbon skeleton of the carboxylic acids was observed.

In contrast thereto the catalyst used in the process of the present invention -34 4 3 0® is found to be completely acid-resistant. After an operating period of several months it retains its full activity in relation to acids such as the aliphatic and cycloaliphatic carboxylic acids and polycarboxylic acids which are to be reduced, and which may optionally be substituted by hydroxyl groups. There may also be in the carboxylic acid-containing molecule other functional groups, which are then simultaneously subject to a hydrogenation reaction, such as for example a carbonyl group or an olefinic double bond. Lactones and anhydrides of the carboxylic acids mentioned above are also included in the compounds which can be converted into the corresponding hydroxyl compounds by direct hydrogenation.

Suitable starting compounds for the hydrogenation process of the-invention are for example acetic acid, propionic acid, butyric acid, higher fatty acids, dimeric fatty acids, pyruvic acid, malonic acid, succinic acid, glutaric acid, adipic acid, decandicarboxylic acid, maleic acid, fumaric acid, butyrolactone, caprolactone, or maleic anhydride.; The catalyst is usually prepared by applying a mixture of perrhenate solution and a palladium salt solution in the desired ratio to a suitable carrier by spraying or impregnation, followed by activation in an atmosphere of hydrogen while the temperature is slowly raised to 280°C.

The weight ratio of palladium to rhenium on the carrier may vary within a wide range and is from 0.01:1 to 5:1. The total amount of metal depends on the carboxylic acid to be hydrogenated, and is usually from 0.1 to 20 by weight, based on the weight of the carrier.

Any acid-resistant material may be used as carrier substance, such as acidresistant silicic acid or aluminium oxides, and also in particular carriers based on activated charcoal.

The process of the present invention is preferably carried out at a temperature of from 150 to 320°C, preferably from 180 to 280°C, and generally at a pressure of from 50 to 1000 atmospheres.

The presence of water is advantageous in order to make it difficult for 30 esters to be formed from unreacted carboxylic acid and the resultant alcohol, which is possible under the conditions of the reaction. -4+4-3 Ο e If the material used is not sufficiently soluble in water, it is advisable also to use another solvent, such as for example tetrahydrofuran, dioxan, low alcohols, or the actual hydrogenation product formed.

Generally, the carboxylic acid is dissolved in water, optionally with heating, and reacted in a suitable pressure vessel with hydrogen at an elevated temperature in the presence of the catalyst. It is possible to work either discontinuously in autoclaves or continuously in suitable reactors.

When the preferred continuous method of working is adopted, the hydrogenation of the invention may be either in the form of a trickling process or of a liquidphase process.

The reaction product is usually recovered by distillation.

The following Examples illustrate the method of the present invention. Preparation of catalyst A A 2-litre round flask was filled with 1 litre (410 g) of activated charcoal extrudates (commercial product known as Degussa Katepan F 40h-Degussa is a Trade Mark) and evacuated by slow rotation on a rotary evaporator (about 30 torr). 800 g (780) ml) of an impregnating solution containing 20 g of Re in the form of rhenium-VII oxide and 2 g of Pd in the form of palladium nitrate were then drawn in. while the mixture was slowly agitated. With a bath temperature of about 80°C, water was then distilled off, with continuous rotation, until the material in the evaporator rolled and was externally dry. The material was then dried for three hours to a constant weight in an air circulating drying cabinet at 110°c, the material being frequently turned carefully.

The dry material was activated by placing it in a reactor, in which it was treated at 280°C for six hours in a pressureless current of hydrogen to generate an active catalyst.

Preparation of catalyst B One litre of granulated silicic acid, grain size 3-8 mm (commercial product No. 341, Degussa) was sprayed at 120°C with continuous rotation in a pressure tube oven with 400 ml of a solution containing 20 g of palladium (in the form of palladium nitrate) and 10 g of rhenium (in the form of rhenium-VII oxide). The resultant material was activated for si» hours at 280°C in a pressureless current -54 4 3 Ο 6 of hydrogen to give an active catalyst.

Preparation of reference catalyst C The reference catalyst C was produced in the same way as catalyst A, but the impregnating solution contained no palladium nitrate.

Preparation of reference catalyst 0 _ 495 g of nickel nitrate-hexahydrate (100 g Ni) were dissolved in 340 ml of water and mixed with 80 mg of rhenic acid (25% Re of 20 g of Re). 1000 ml of activated charcoal extrudates (see catalyst A) were treated with this solution in the manner described for the preparation of catalysts A.

The dry material was also activated similarly to catalyst A, the tempes’Sture being increased to 400°C.

Example 1 1,6-hexanediol from adipic acid 500 g of 20% aqueous adipic acid were heated together with 50 g of catalyst A in a T-litre autoclave in an atmosphere of hydrogen at 100 atmospheres. When the absorption of hydrogen commenced at 218°C the pressure was increased to 300 atmospheres. The temperature increased gradually to 242°C, and after three hours the absorption of hydrogen had ended.

The7 colourless reaction product had anacid number of 0.7 mg KOH/g. Gas chromatographical analysis gave the following results: 0.2% n-propanol 0.42% n-pentanol 0.06% unknown substance 1.80% n-hexanol 0.35% unknown substance 97.0% 1,6-hexanediol Example 2 Diol mixture from acid mixture.

Similarly to Example 1, 500 g of a 20% solution of a mixture of succinic acid, glutaric acid, and adipic acid (acid number 174 mg KOH/g) was hydrogenated at 225°C and at 300 atmospheres.

The reaction product separated from the catalyst v/as colourless and clear λ -644306 and had an acid number of 1.1 mg KOH/g.

Gas chromatographical analysis of the organic components of this solution gave the following: 4.2% first runnings 11.3% 1,4-butanediol 62.4% 1,5-pentanediol 20.2% 1,6-hexanediol Example 3 Continuous production of 1,6-hexanediol from adipic acid. a) liquid-phase process 500 ml of 20% aqueous adipic acid preheated to 70°C were pumped per hour into a reactor tube containing 500 ml of catalyst A, at a temperature of 210°C (measured in the contact zone) and in an atmosphere of hydrogen at 300 atmospheres. Hydrogen was also introduced from below at a rate controlled by adjusting the outgoing gas to 200 litres per hr (pressureless).

The reaction product was drawn off continuously by way of a separator. The colourless-clear product had an acid number smaller than 1.

Gas chromatographical analysis gave: 0.22% n-propanol 0.23% n-pentanol 2.22% n-hexanol 0.22% unknown 0.17% caprolactone 97.05% 1,6-hexanediol The distillation residue (2-3%) was reused for hydrogenation after hydrolytic splitting. b) Trickling process In this arrangement 600 ml per hour of the starting material (see(a) above) were introduced at the top of the reactor and passed over catalyst A in parallel flow with the hydrogen (300 atmospheres). The reaction temperature was 210-220°C. The product continuously removed from the separator had an acid number of 2.4 mg -7443°6 KOH/g. Gas chromatograph!cal analysis showed the following composition: 0.22% propanol 0.50% pentanol 3.10% hexanol 5 94.7% 1,6-hexanediol Experiment 3a also showed no variation in the proportion of hydrogenated products after a trial period of over 100 days. The activity also showed no decline.

Example 4 2.2.4 - (2.4,4) - trimethyl hexanediol - (1,6) from 2.2.4 - (2.4.4) - trimetliyl10 adipic acid.

In a similar experimental arrangement to Example 3a (catalyst A) 20% trimethyl adipic acid (techinical, highly discoloured) was used. The reaction temperature was 230°C, and the amount used was 350 ml/h. The reaction product vzas formed in two phases, colourless. This solution of the separated top phase gave the following gas chromatographic analysis: 19.8% first runnings 74.7% dial mixture .5% distillation residue.

The aqueous bottom phase containing about 4% of dissolved reaction product was fed into the reactor together with the residue and fresh trimethyladipic acid.

Example 5 1,10-decanediol from sebacic acid 100 g of sebacic acid mixed with 200 g of water and 200 g of tetrahydrofuran were heated together with 50 g of catalyst B in a 1-litre autoclave in an atmosphere of hydrogen at 100 atmospheres. On commencement of absorption of hydrogen at 215°C the pressure was increased to 300 atmospheres. With a reaction temperature of 228°C the hydrogenation ended after about three hours.

The catalyst was filtered off and reused for hydrogenation. The acid number of the colourless reaction product was 1.4 mg KOH/g.

After separation by distillation of the solvent the reaction product was 30 fractionated in vacuo. -810 4 3 0 G Yield: 76 g {88.2% of theory) of 1,10- decanediol BP2q 190-192°C The distillation residue (6 g) was resubjected to direct hydrogenation in the following batch in the presence of fresh sebacic acid. The yield was thereby increased to 94.9% of theory.

Comparative Example 1 ι Similarly to Example 3a, the continuous preparation of 1,6-hexanediol was effected by direct hydrogenation of adipic acid with the aid of catalyst C.

The reaction temperature was 235°C and the pressure 300 atmospheres. 300 ml per hour of a 20% aqueous adipic acid were pumped into the reactor.

A colourless product was obtained which had the following composition: 2.45% n-propanol 0.30% n-pentanol 0.17% unknown 16.55% n-hexanol .63% unknown 73.90% 1,6-hexanediol 0.99% unknown After operating for 10 days the activity of the catalyst had fallen to two-thirds of the original activity.

Comparative Example 2 1,6-hexanediol from adipic acid.

In the experimental arrangement according to Example 3a, 400 ml per hr of a 20% aqueous adipic acid were hydrogenated at 210°C and at 300 atmospheres using reference catalyst D.

The reaction product comprised two phases. It had an acid number of 3.5 mg kOH/g and contained clear traces of nickel.

Gas chromatographical analysis gave: 0.76% n-propanol 0.06% unknown 4.29% n-pentanol 11.80% n-hexanol 0.66% unknown 82.43% 1,6-hexanediol

Claims (7)

1. A process for the production of an alcohol by the catalytic hydrogenation of a carboxylic acid or of a lactone or anhydride derived therefrom at elevated temperature and elevated pressure in the presence of water and/or other solvents, the hydrogenation being performed in the presence of a catalyst 5 comprising palladium and rhenium in a weight ratio of from 0.01:1 to 5:1 and an acid-resistant carrier.

2. A process according to Claim 1, wherein the temperature is from 150 to 320°C.

3. A process according to claim 1 or Claim 2, wherein the pressure is from 50 10 to 1000 atmospheres.

4. A process according to Claim 1,2, or 3, wherein the carboxylic acid, lactone or anhydride is chosen from acetic acid, propionic acid, butyric acid, higher fatty acids, dimeric fatty acids, pyruvic acid, malonic acid, succinic acid, glutaric acid, adipic acid, decandicarboxylic acid, maleic acid, fumaric acid, 15 butyrolactone, caprolactone, and maleic anhydride.

5. A process according to any one of the preceding claims, wherein the carrier is an acid-resistant silicic acid, an acid-resistant aluminium oxide or a carrier based on activated charcoal.

6. A process according to Claim 1 substantially as described in any one of 20 Examples 1 to 5.

7. An alcohol prepared by a process as claimed in any one of the preceding claims.