DE1567336B2 - METHOD FOR PREPARING XYLOSE SOLUTIONS - Google Patents

Description

The technical representation of xylose solutions has recently gained considerable importance, since the The hydrogenation product of xylose, xylitol, has proven to be an excellent sweetener that is far superior to sorbitol proven for diabetics shark.

A number of processes for preparing xylose solutions are known which are rich in pentosan Natural substances such as hardwoods, straw, oat fur, corn on the cob, cottonseed pods, flax kebabs or apricot kernels, go out.

Thus, according to British patent specification 922685, wood is treated with 10 to 40% hydrochloric acid at a temperature of 40 to a maximum of 90 ° C. The yield, based on the pentosan present, is in the examples a maximum of 73%, the xylose crystallizing out very poorly.

Used according to UK Patent 934904 the acid content of the wood for digestion. Here too, a maximum of 70% xylose is obtained, based on the product on existing pentosans. Also from "apricot kernels one has already won xylose" whereby yields of 12 to 13%, based on the starting material, were obtained.

All of these processes have the disadvantage of inadequate yields.

It has also long been known that coconut shells contain pentosans and that xylose can be obtained from them can produce (cf. A. ToIle ns, Annalen der Chemie, Volume 286 [1895], page 306); This method is made using a pretreatment of the material with dilute hydrochloric acid, dilute ammonia and extraction performed with alcohol. The hydrolysis takes place with the 10fold amount 4% sulfuric acid, the xylose yield is only about 7%. This method therefore has none Obtained technical importance.

The invention is based on the knowledge that a pretreatment is required for the hydrolysis of coconut shells is not necessary and that one in the hydrolysis with a much lower! Liquid meter. can work than it was previously used.

The subject of the invention is the method mentioned in the claim.

The method according to the invention has several advantages.

Pre-treatment is not required. Furthermore, the amount of liquid to be processed in the hydrolysis stage is small. You also need less acid than with the known methods.

The xylose solution obtained after the solids have been separated off is treated with activated charcoal immediately discolored, which is hardly the case with the known processes. The decolorized xylose solution is convenient free of crystallization-inhibiting substances and after neutralization of the acid, e.g. B. by ion exchangers, be hydrogenated directly to xylitol in a known manner. If the xylose solution is concentrated is to be, for example, for the crystallization of xylose, so has the method according to the invention The solution obtained has the advantage that its volume is considerably less than that of the known solutions Procedure. The separation of the solids from the xylose solution after the hydrolysis is very easy because the solids retain practically no reaction solution. The separated residue can therefore just as well as the coconut shells used in the plastics industry. So it falls practically no unusable residue in the process according to the invention. The yields are 85 to 90%, based on the pentosans present, and up to over 20%, based on the starting material.

Sulfuric acid is preferred as the acid. The preferred amount of aqueous acid used per part by weight Coconut shells is 2.5 to 3.0 weight parts.

If the work is carried out at atmospheric pressure, preference is given to using 2 to 3 percent strength by weight aqueous Hydrochloric acid, 3 to 4 weight percent aqueous sulfuric acid or 1.5 to 3 weight percent aqueous Hydrogen bromide.

If, on the other hand, you work at excess pressure, the acid concentration is preferably 0.5 to 1.0 percent by weight. The preferred pressure range when working under excess pressure is 2 to 4 atmospheres and the preferred temperature range 110 to 135 ° C, especially 125 to 130 ° C. With excess pressure it is preferably heated for 95 to 125 minutes.

The removal of the acid from the xylose solution after hydrolysis and the separation of the residue, in general up to a pH of 3 can be done in the usual way by ion exchangers, in the case of sulfuric acid as hydrolyzing acid, also with barium carbonate or calcium carbonate make.

example 1

2.5 liters of approximately 4% strength sulfuric acid are preheated to 100 ° C. in an oil bath, and 1000 g of coconut shell flour are added added and heated under reflux for 2 hours. Then one sucks off the insoluble residue and washes it with a little water. The filtrate is neutralized with calcium carbonate up to a pH value Of 3.

The coconut shell flour residue after drying is about 735 g and can if not to be further developed, can be used directly in the plastics industry.

The neutralized, aqueous solution is decolorized with activated charcoal.

If this solution is boiled in under reduced pressure at 40 to 45 ° C to form a light syrup, the same volume of methanol is added, the solid which has separated out is filtered off with suction and in vacuo evaporates, the remaining syrup soon solidifies in crystalline form; it has a weight of about 240 g and contains about 85% xylose. A simple recrystallization gives initially 140 g of pure xylose, from which Mother liquor can easily be isolated even further components.

If you work as described above, but with 2% sulfuric acid, a residue is obtained of about 760 g and about 200 g of raw sugar (xylose content 72%). By recrystallization about 140 g of pure xylose are obtained.

If you work as described above, but with a 6% strength aqueous sulfuric acid, then a residue of approximately 705 g, a sugar crude product of approximately 265 g (75% xylose) from which about 155 g of pure xylose are obtained.

Example 2 1000 g of coconut shell flour are mixed with 2.5 1 of a hydrolysis liquid that is 1.2 percent by weight Contains hydrogen chloride and 0.3 percent by weight hydrogen bromide, heated vigorously under reflux for 2 hours. After suctioning off and washing with water, a residue of 670 g remains. The sour Solution is deionized with ion exchangers and decolorized with activated carbon.

After evaporation in a vacuum at a temperature of up to 45 ° C, a syrup remains, which quickly crystallizes through and has a weight of approximately 295 g. About 160 g of pure xylose can be obtained from it by a single recrystallization.
Example 3

1000 g of coconut shell flour are in the autoclave at about 2.5 atmospheres with 3 1 of 0.5% sulfuric acid hydrolyzed at 125 to 130 ° C for about 100 minutes. The work-up is carried out in the manner described in Example 1 described way.

18% pure xylose, based on the coconut shell flour used, can be obtained from the syrup obtained, to win.

Claims (1)

Claim: Process for the preparation of xylose solutions, which are practically free of crystallization-inhibiting Accompanying substances are caused by the hydrolysis of crushed coconut shells with dilute mineral acid at elevated temperature, characterized in that 1 part by weight is comminuted, chemically non-pretreated coconut shells either at atmospheric pressure and Boiling point with 2.5 to 4 parts by weight of an aqueous, a total of 1.5 to ogewicbtsprozentigen Hydrochloric, hydrobromic and / or sulfuric acid or at excess pressure and temperatures from 110 ° to 135 ° C with 2.5 to 4 parts by weight of an aqueous, a total of 0.3 to 1, 5 percent by weight hydrogen chloride, Treated hydrobromic and / or sulfuric acid and the undissolved in a known manner The reaction residue separates from the liquid, which is decolorized and neutralized.