GB740560A - Improvements in hydrogenation of monosaccharides - Google Patents

Abstract

<PICT:0740560/IV(a)/1> Non-gelling, non-crystallizing high-viscosity polyol compositions are made by introducing a monosaccharide and an alkali metal or an alkaline earth metal hydroxide into water to form a mixture containing from 40 to 70 per cent by weight of monosaccharide and from 0.15 to 0.4 hydroxyl equivalents of hydroxide per litre; heating the resulting mixture to 40-80 DEG , preferably 50-65 DEG C.; maintaining the mixture at the said temperature for a time corresponding to a time-temperature point within the polygon ABCDE; adjusting the pH of the resulting solution to a value of from 7 to 5.0, preferably 7-6; and hydrogenating the resulting solution in the presence of a hydrogenation catalyst, at a temperature of 120-170 DEG C., preferably 140-160 DEG C., and a hydrogen pressure above 500, preferably 1500-2000, pounds per square inch. Glucose, invert sugar, fructose, mannose and xylose are specified saccharides, glucose and invert sugar being preferred. Readily crystallizable products such as mannitol may be removed and the composition mainly comprising sorbitol is obtained non-gelling and non-crystallizing by limitation of the quantity of sorbitol in the syrup (determined by means of a pyridine-sorbitol complex) so that its pyridine number is not substantially above 60, such limitation being effected by working within the conditions of the polygon. Neutralization before hydrogenation may be effected by means of acids or by ion-exchange materials. Reduced supported nickel hydrogenation catalysts are preferred. Hydrogenation may be effected as in Specification 721,260. Calcium hydroxide is the preferred hydroxide and preferably not over 0.3 hydroxyl equivalents are used per litre. With invert sugar limits imposed by ABCGF are preferred and with glucose those set by AHCDE. Particularly preferred for invert sugar are temperatures of 60-65 DEG C. for about 6 hours and for glucose 50-55 DEG C. for about 16 hours. Examples illustrate the conversion of glucose and invert sugar into humectant polyol syrups, alkali treatment being with sodium, barium or calcium hydroxides, any mannitol obtained in the processes being removed after crystallization.