GB742553A - Improvements in or relating to process for producing polyhydric alcohols - Google Patents

Abstract

A sorbitol-mannitol mixture is produced by hydrolysing sucrose in aqueous solution, interrupting the hydrolysis when the specific rotation of the solution first reaches the value corresponding to a selected degree of hydrolysis within the range of 95-99 per cent, preferably 97-98 per cent, complete, adjusting the pH to between 6 and 8, catalytically hydrogenating in a continuous system at a temperature of 140 DEG to 170 DEG C. and a pressure of 1000 to 2000 p.s.i. until the reducing sugar content is less than 0.2 per cent based on dissolved solids, and separating the hydrogenation catalyst from the resulting solution. The initial sucrose content may be 25 to 75 per cent, preferably 40 to 60 per cent by weight. The hydrolysis is preferably effected by heating with a dilute acid, e.g. sulphuric, hydrochloric, phosphoric, acetic, tartaric or oxalic acids or with potassium bisulphate, at a pH below 3, preferably between 1 and 2, and a temperature in the range of 45 DEG to 70 DEG C., although any temperature from room temperature to 90 DEG C. is suitable. The inversion is checked by adding alkali. The hydrogenation may be effected by passing a slurry of supported, reduced catalyst, containing 0.5 to 5 per cent of nickel, in the neutralized, hydrolysed sugar solution, and hydrogen under pressure upward through a vertical reactor or a plurality of reactors in series. Preferably a large excess of hydrogen is used with a linear velocity many times that of the slurry. Detailed examples are given and the results are compared with those obtained when the extent of hydrolysis lies outside the specified range.