Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Patent
1985-11-27
1987-07-21
Griffin, Ronald W.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
127 34, 127 37, 536 57, 162 29, 162 41, 162 42, 162 43, 162 44, C08B 3714, D21C 302
Patent
active
046819355
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a procedure for recovering soluble carbohydrates contained in wood, wherein the carbohydrates contained in wood that is to be digested to cellulose and which shall be recovered are brought into a solution from which they are separated, and wherein the processing of the wood continues thereafter as an alkaline cellulose digesting process.
The object of the invention is to teach a procedure by which it is possible in connection with manufacturing chemical or chemical-mechanical cellulose pulp to separate a remarkable part of those polysaccharides which are dissolved in the digesting liquor and which in conventional sulphate digesting largely undergo cleaving into saccharic acids and other decomposition products during the digesting process, to end up with the waste liquor in combustion in the digesting chemicals recovery process. The carbohydrates which are solved from the wood or other raw material containing lignocellulose are then recovered in such form that they can be used e.g. in manufacturing monosaccharides or sugar derivatives, as cattle fodder, or for manufacturing alcohol and proteins.
It is previously known that soluble carbohydrates can be manufactured from wood or other lignocellulosic raw materials by hydrolyzing them with a mineral acid, such as dilute or concentrated sulphuric acid or hydrochloric acid. However, these processes have proved uneconomical compared with the producing of cellulose from the raw materials mentioned.
It is also alternatively possible in connection with the manufacturing of cellulose pulp by hydrolyzing wood chips with the aid of steam and mineral acids, in a particular prehydrolysis step prior to the cellulose digesting proper, to produce soluble carbohydrates originating in the hemicelluloses. Depending on hydrolysis conditions, these carbohydrates are more or less completely hydrolyzed, that is, they are in monosaccharide or polysaccharide form. If softwood has been used for wood material, the carbohydrates will contain, among others, glucose, mannose, galactose, xylose and arabinose. If the wood material that has been used is hardwood, the carbohydrates contain mainly xylose.
Hydrolysates of this kind may be used for instance in manufacturing sugar alcohols, such as xylitol or sorbitol, as a raw material in biotechnical processes, for cattle fodder, etc. However, the prehydrolysis procedure is encumbered by the drawback that the yield and quality of cellulose pulp suffer from the hydrolysis and the range of application of this type of pulps is narrow, being primarily restricted to viscose manufacturing.
It is possible to isolate polysaccharides in connection with the mercerizing process included in the manufacturing of viscose fibres. In the mercerizing process, dissolving pulp is treated with NaOH solution, the aim being to dissolve the hemicellulose components from the cellulose. From the solution thus obtained, the solved polysaccharides can be recovered with the aid of ultrafiltration, as these compounds cannot pass through the ultrafiltration membranes and are therefore enriched in the ultrafiltration concentrate. We refer in this context to the U.S. Pat. No. 4,270,914 and to Hurlen, S. Olsen, A.: Removal of Hemicellulose from Steeping Lye by Ultrafiltration. TAPPI/OEZEPA 5th Int. Dissolving Pulps Conf. (Vienna) Papers: 54-58 (Oct. 8-10 1980). The greater part of the polysaccharides originating in the wood have however been dissolved in connection with the cellulose manufacturing process, in the waste liquor, and the polysaccharide quantities obtained in connection with the mercerizing process are therefore minor. It should moreover be kept in mind that the demand of dissolving pulp is limited.
It is known that when cellulose pulp is being manufactured by digesting wood chips or other lignocellulose-containing raw materials by alkaline digesting methods, e.g. by the sulphate process, by soda digesting or by the alkaline sulphite process, part of the polysaccharides present in the raw material (the cellulose and hemicellulose) g
REFERENCES:
patent: 3935022 (1976-01-01), Sihtola
patent: 4270914 (1981-06-01), Dahl
patent: 4277626 (1981-07-01), Forss et al.
patent: 4450106 (1984-05-01), Forss
Forss Kaj
Jokela Veikko
Peltonen Juhani
Sten Matti
Enso-Gutzeit Oy
Griffin Ronald W.
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