CS196886B1 - Method of preparing alcoholic sugars by hydrogenation ofmonosaccharides - Google Patents

Description

The invention describes the preparation of alcoholic sugars by catalytic hydrogenation of monosaccharides with hydrogen under pressure, at adjusted pH of hydrogenated solutions, followed by ion exchange treatment of the hydrogenation product.

Alcoholic sugars, in particular sorbitol and xylitol, are used as a sweetener in the diabetic diet, but are also widely used in cosmetics and as a substitute for glycerin in the food industry. Alcoholic sugars are prepared by oxyethylation of surfactants. They can generally be used in chemical synthesis wherever polyols are used as one component.

The preparation of alcoholic sugars has long been known by the classical method of reducing aldoses and ketoses with sodium amalgam.

They can also be prepared by catalytic hydrogenation under atmospheric hydrogen pressure, but the reaction is carried out only very slowly. With Raney nickel catalyst, it is possible to hydrogenate dxylose as a 70% solution in ethanol. It is preferred to clarify the solutions before hydrogenation e.g. activated carbon. Far more efficient is the catalytic hydrogenation of monosaccharides to sugar alcohols under elevated hydrogen pressure of 5 to 20 MPa. As catalysts, nickel for silica, Raney nickel, chromium-prized nickel, mixed nickel-cobal-chromium catalyst and medium-based catalysts are used.

A disadvantage of the catalysed hydrogenation of aqueous monosaccharide solutions is the increase in their cysticity by the formation of the oxykyselfn Cannizar reaction. Acids can also be formed from aldoses via pyranoses, their dehydrogenation and subsequent hydration. The acids deactivate the hydrogenation catalysts, as a result of which the rate of hydrogenation is reduced and the conversion of monosaccharides to alcohol sugars is lowered.

Improvement of the preparation of alcoholic sugars is achieved by the process according to the invention, which achieves high yields of pure end products.

The process for preparing alcoholic sugars by hydrogenating monosaccharides according to the invention is carried out at a hydrogen or hydrogen pressure of 2 to 25 MPa in the presence of hydrogenation catalysts, most preferably nickel, batch or continuous process, such that in a hydrogenated solution containing 5 to 50% monosaccharides preferably by hydrolysis of the timber, provides for the addition of alkaline reactants to pH 7-10 and the product of the hydrogenation is adjusted to the cationic and anionic ion-exchange at a space velocity of 0.5 to 5 h ^_1 1 1 1 ion exchange cartridge.

196 886

196 886

The following examples show the process according to the invention.

Example 1

In a 0.5 L stainless steel rotary autoclave, 100 g of a 20% aqueous xylose aqueous solution was hydrogenated with 1.6 g of nlkel catalyst on silica gel containing 49.1% nickel. The pH of the hydrogenated solution was adjusted to 8.4 by addition of solid calcium oxide.

Hydrogenation was carried out in two stages. In the 1st stage at 80 ° C and in the 2nd stage at 110 ° C. The hydrogen pressure in the autoclave was maintained at 12.5 MPa. After a reaction time of 90 minutes, a 98.3% conversion of xylose was achieved.

The product of hydrogenation was demineralized by passing through a cation exchanger column of Wofatit KPS200, Wofatit SBW at volumetric rate

2,5 1 h ^_1 per 1 liter ion exchange filler. A clear product was obtained, from which xylitol with a melting point of 92.5 ° C was obtained by crystallization in a yield of 75.1%.

Example 2

Continuous hydrogenation of the beech sawdust hydrolyzate was carried out in a stainless steel reactor, 4000 mm long, containing 2.8 L of hydrogen and 1.129 kg.h ^{-1 of} hydrolyzate were fed countercurrently into the reactor. The catalyst used was a piece of Raney nlkel, grain size 6 to 8 mm, containing 41.83% Ni in the non-activated alloy. The hydrolyzate contained 49.4 wt. dry matter of this composition: xylose 75.58% by weight, arabinose 8.9% by weight, glucose 4.24% by weight and galactose 6.82 wt%, the remainder of the mineral and unidentified substance. The pH of the hydrogenated solution was adjusted to 8.7 by the addition of 10% aqueous sodium hydroxide. continuous

Claims (1)

SUBJECT A process for preparing alcoholic sugars by hydrogenating monosaccharides under a hydrogen or hydrogen pressure of 2 to 25 MPa in the presence of hydrogenation catalysts, most preferably nickel, batch or continuous, characterized in that the hydrogenated solution containing 5-50% of mohydrogenation was carried out in two stages at 14.5 MPa, at the top of the reactor at 89 ° C and at the bottom at 121 ° C. Upon hydrogenation, the conversion of the reducing sugars was 95.7%. The hydrogenation product was treated on Ostion KS and Ostion AT ion exchangers at a volumetric rate of 4.9 l / ^l to 1 liter. ion exchanger. After concentration, xylitol with a melting point of 92.5 to 93 ° C is obtained in the yield by crystallization. 93.2% calculated on hydrogenated xylose. By adjusting the ion-exchange Amberlite space velocity of 1.45 h ^_1 1 to 1 lit. of the ion exchanger, the xylitol yield was 96.1% calculated on the treated xylose. In the mother liquors after crystallization there were arabitol, galactitol and sorbitol as well as an unreduced proportion of monosaccharides. In the same way, the beech chip prehydrolysates prepared in cellulose production were hydrogenated. Xylitol was isolated from the hydrogenate in 71.5% yield, calculated on the amount of xylose in the prehydrolysate. Example 3 In a 5L stainless steel rotary autoclave, a solution of 355 g of arabinose in 1419 g of distilled water was hydrogenated. The pH of the solution was adjusted to 8.6 by the addition of pulverulent calcium oxide. 53.4 g of Raney nickel powder were used as catalyst. Hydrogenation was carried out at a hydrogen pressure of 12 MPa, in the first stage for 90 mm at 80 ° C and in the second stage also for 90 min. at 125 ° C. The hydrogenation product was adjusted to 1 liter on Ostion KS and Ostion AT ion exchangers at a volumetric rate of 0.7 lh ^-1 . ion exchangers. After concentration, pure arbitol of melting point was obtained by crystallization 102.5 ° C, 87.2% yield, calculated for hydrogenated arabinose. INVENTION It nosacharldov, preferably prepared by hydrolysis of the timber, provides for the addition of alkaline reactants to pH 7-10 and the product of the hydrogenation is adjusted to the cationic and anionic ion exchangers, at a space velocity of 0.5 to 5 h ^_1 1 1 1 inonomeničovej charge.