US1818618A - Method for the purification of carbohydrates obtained by hydrolysis of cellulose by means of hydrochloric acid - Google Patents

Description

Patented Aug. 11,- 1931 UNITED STATES PATENT OFFICE ERIK HAGGLUND, OF ABO, FINLAND, ASSIGNOR TO THE FIRM HOLZHYDROLYSE AKTIENGESELLSCHAFT, OF HEIDELBERG, GERMANY METHOD FOR THE PURIFICATION OF CARBOHYDRATES OE B'IAINED BY HYDROLYSIS OF CELLULOSE BY MEANS OF HYDROGHLOBIG ACID 7 No Drawing. Application filed December 10, 1928, Serial No. 825,129., and in Germany December 14, 1927.

It is known that by hydrolysis of cellulose containing material such as wood, preferably in the form of saw dust, by means of hydrochloric acid a carbohydrate product can be obtained. However this carbohydrate product or sugar is, even after having been subjected to an evaporation process with a view to removing the hydrochloric acid therefrom, not very well adapted for 10 use as food material owing to certain residues of acid in it which cannot be removed by evaporation, and which deteriorate the taste of the product and its salubrity. Attempts have already been made to overcome this difiiculty by subjecting the product of the hydrolysis to a purifying process consisting in transforming the carbohydrate into saccharate and subjecting the saccharate to a washing process and thereafter recoveringthe sugar by decomposition of the saccharateby carbonation. However the effect of this purification is not entirely satisfactory. Moreover a considerable loss in saccharate is caused by the washing process. Now this invention has for its object to avoid thedeficiency of the above mentioned known purification process by the application of a special method for the transformation of the carbohydrate into saccharate.

' This special method according to the invention consists in that the carbohydrate or sugar suitably after a preliminary partial removal of acid by evaporation is subjected to wet grinding together with an added oxide or hydroxide of an alkaline earth-metal preferably slaked lime. The, grinding is advantageously effected in a so-called ball-mill, the grinding bodies of which consist of porcelain.

The effect of the grinding process consists in that the'carbohydrate is very completely converted into saccharate and that the acidresidue remaining, as above mentioned, in the carbohydrate even after evaporation is bound to the alkaline earth metal. The ground material is thereafter subjected'to a draining operation, preferably by subjecting it to centrifugation in a centrifuge having a bowl with pervious wall. If so treated, together with the liquid, also a considerable part of the chlorides dissolved therein are removed. Inorder to remove also the last traces of chlorides it is advisable to subject the material, which has been freed from liquid by centrifugation, to a washing process which may be effected in.

the same centrifuge. This washing process requires only small quantities of water and does not cause a remarkable loss in saccharate. 1

In this way a saccharate is obtained which 7 is free from chlorides and which in known manner by saturation, that is treatment with carbonic acid, preferably under pressure can be converted into pure carbohydrate.

The liquid which is separated off by the centrifugation process contains besides chlorides and other soluble substances also sugar material which does not form insoluble saccharates. I

The product which. is obtained after saturation is a pure tasteless carbohydrate, that is a carbohydrate which is neither sweet nor has any other characteristic taste. It is possible to convert it into a sweet sugar by a so-called inversion process, for instance by heating it in the presence ofsulfuric acid.

Example 100 parts by weight of a carbohydrate or sugar material, obtained by hydrolyz'ing saw dust with hydrochloric acid and concentration of the product of hydrolysis by evaporation, are dissolved by 400 parts by weight of water and the solution introduced into a ball-mill with porcelain balls. 100 parts by weight of fresh slaked lime are added and stirred into the solution. The mixture is subjected to a grinding operation for a period of 1 hours. The ground product consists of a thin impalpable pulp which is introduced ,into a centrifuge with pervious wall and subjected to centrifugation so as to remove the water contained therein. The 'solid constituents of the pulp form] a dense layer adhering to the wall of the bowl. As soon as the water of thepulp has been removed ice-water is added, and

from the precipitated gypsum.

centrifu ation continued till no chlorine can be foun in the washing water. The saccharate is retransformed into a pulp, this being advantageously done by re eated grinding with addition of water. guch saccharate pulp is introduced into pressure proof receptacles and subjected to saturation by treating it with carbonic acid at elevated pressure, for instance at a pressure of two atmospheres. The carbohydrate is separated from the saturation sludge and in usual manner converted into invert sugar by heating with 2% sulfuric acid. The invert sugar solution is freed from sulfuric acid asusual by addition of chalk and se aration e solution is treated with active carbon and thereafter concentrated by evaporation. The yield in pure sugar is about 65% by weight of the raw carbohydrate material or, if the raw carbohydrate had been obtained by hydrolysis of saw dust, about 45% by weight of the hydrolyzed wood..

Considering the fact that about by weight of the wood can .be recovered as carbohydrate by hydrolysis a portion of raw carbohydrate equal to about 25% by weight of the wood remains in the solution separated oif by centrifugation from the product of grinding the mixture of raw carbohydrate and slaked lime. If desired, this solution can be subjected to fermentation or be used in the manufacture of yeast.

The essentially novel steps of my. above described method are recited in the annexed claims in connection with which it is to be understood that the term oxide of an alkaline earth-metal is intended to cover not only the oxide but also the hydroxide.

What I claim is A method of treating carbohydrates which have been obtained by hydrolysis of cellulose with the aid of hydrochlorlc acid which comprises subjecting the carbohydrates in solution in admixture with an oxide of an alkaline earth metal to grinding, removing chloride containing liquid from the solid material, washing the separated solid material with fresh water, subjectin the washed solid material to reaction wit carbonic acid under elevated pressure so as to decompose the saccharate and to liberate the carbohydrates, separating the sludge from the carbohydrate solution, and inverting the carbohydrate contained in the separated solution.

In testimony whereof I afiix my signature.

ERIK HKGGLUND.