Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Patent
1996-10-11
2000-07-11
Bell, Mark L.
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
127 30, 127 42, 127 58, 127 60, 127 61, C13K 102, C13F 300, C13F 100, C13F 102
Patent
active
060866810
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the recovery of xylose by crystallization from solutions having a comparatively low xylose purity. In particular, the invention relates to a method for recovering xylose in the form of a crystalline product from biomass-derived solutions. By employing the method of the invention, purification treatments on the solutions, such as decolouring, ion exchange and chromatographic separations that have been required in the prior art methods before the recovery of xylose, can be considerably diminished or entirely avoided. The need for auxiliary solvents can also be eliminated.
In the context of the present description and claims, xylose purity means the proportion of xylose in the dry solids contained in the solution or mixture and, if not otherwise stated, the purity is indicated as per cent by weight.
Xylose is a valuable raw material in the sweets and spices industries and particularly as a starting material in the production of xylitol. Xylose is formed in the hydrolysis of xylan-containing hemicellulose, for example in the direct acid hydrolysis of biomass, in enzymatic or acid hydrolysis of prehydrolysate obtained from biomass by prehydrolysis (with steam or acetic acid, for instance), and in sulphite cooking processes of the pulp industry. Vegetable materials rich in xylan include the wood material from wood species, particularly hardwood, such as birch, aspen and beech, various parts of grain (such as straw and husks, particularly corn and barley husks and corn cobs), bagasse, coconut shells, cottonseed skins, etc.
In conventional methods, it has only been possible to crystallize xylose if the xylose purity of the solution has been at least about 70% by weight on dry solids. In such cases, it has been necessary to initially purify the xylose-containing solution obtained as a result of the hydrolysis of vegetable-derived material to the required degree of purity by various ultrafiltration, ion exchange, decolouring, ion exclusion or chromatographic separation methods or combinations of such methods. Furthermore, auxiliary solvents reducing the solubility of xylose have been employed to crystallize xylose.
An alternative to the above methods for producing a xylose solution having sufficient purity required for xylose to crystallize is purification of xylan prior to its hydrolysation into xylose. In that case, it is expedient to pre-purify the material to be treated (removal of starch, pectin, proteins, lignin, etc.), followed by extraction with a KOH or NaOH solution and separation of hemicellulose from the solution by precipitation. This method has many steps and is cumbersome, as is apparent from Browning, B. L., Methods of wood chemistry, II, Interscience Publishers, New York, 1967, and Fry, S. C., The Growing Plant Cell Wall: Chemical and Metabolic Analysis, Longman Scientific & Technical Publishers, England, 1988.
Xylose is produced in large amounts for example in the sulphite cooking of a hardwood raw material in the pulp industry. Separation of xylose from such cooking liquors is described in U.S. Pat. No. 4,631,129 (Heikkila, H.; Suomen Sokeri Oy), for instance. The method disclosed in this patent comprises two chromatographic separations, after which xylose can be recovered subsequent to the evaporation of the product fraction (xylose purity about 70% or more) by crystallization.
Acid hydrolysis of a xylan-containing material to produce xylose is disclosed for example in U.S. Pat. No. 4,075,406 (Melaja, A. J. & Hamalainen, L.; Suomen Sokeri Oy) and U.S. Pat. No. 5,084,104 (Heikkila, H. & Hyoky, G.; Cultor Ltd) and in the publications incorporated therein by reference. The hydrolysis is based on purification of hydrolysate by ion exclusion, decolouring, and chromatographic separation methods, and subsequent to the purification treatments xylose can be recovered from the product fraction after its evaporation by crystallization.
U.S. Pat. No. 4,168,988 (Riehm, T. & Hofenk, G; Institut voor Bewaring en Verwerking van Landbouwprodukten) describes xylose pro
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Eroma Olli-Pekka
Heikkila Heikki
Lindroos Mirja
Nurmi Juha
Bell Mark L.
Hailey Patricia L.
Xyrofin Oy
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