Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Continuous chemical treatment or continuous charging or...
Reexamination Certificate
2002-01-14
2004-06-22
Fortuna, José A. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Continuous chemical treatment or continuous charging or...
C162S076000, C162S090000
Reexamination Certificate
active
06752902
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the preparation of chemical pulp and xylose, and particularly to recovering xylose from pulp, such as sulphate pulp, prepared by alkaline or neutral cooking, and simultaneously achieving the desired characteristics for the pulp. The method of the invention utilizes a direct acid hydrolysis of the pulp, resulting in a good xylose yield. At the same time, the obtained pulp is usable as paper pulp or dissolving pulp.
In a plurality of plants, the main portion of hemicellulose is xylan, which can be hydrolyzed to xylose. The foremost starting material for xylan is hemicellulose from hardwood, particularly birch, mainly composed of xylan.
For example birch sulphate pulp typically contains about 15 to 25% xylan, which is usable as a raw material of xylose. When xylose is prepared from pulp, the problem involved has been to achieve sufficient xylose yields and to simultaneously achieve acceptable characteristics for the pulp.
Finnish Patent 55516 (Kemi Oy) discloses a method of preparing pure xylan, suitable for the raw material of xylose and xylitol, in particular. The method uses bleached or unbleached hardwood cellulose as the raw material. The cellulose is treated with an alkali solution, whereby the hemicelluloses are dissolved. The alkali solution containing hemicellulose is pressed and filtered from pulp. The dissolved hemicellulose is precipitated by the addition of carbon dioxide to the solution, whereby the xylan precipitates. In the method, most of the xylan in the pulp, the xylan being in principle usable as the raw material of xylose, is, however, not utilized. Moreover, the method uses much alkali.
Several methods are also known in which enzymatic hydrolysis is used to separate hemicellulose components from the pulp. For example Paice, M. G. & Jurasek, L.,
Removing Hemicellulose from Pulps by Specific Enzymic Hydrolysis
, J. Wood Chem. and Tech., 4 (2), 187 to 198, 1984, describes a method of separating hemicellulose from aspen pulp by xylanase treatment. The most important hemicellulose products thus obtained were xylan and xylobiose. However, the enzyme dose is uneconomically large.
WO 98/56958 (Xyrofin Oy) discloses a method of preparing xylose by first extracting xylan from a cellulose pulp or its alkali solution with an aqueous solution of a xylanase enzyme and by then using acid to hydrolyze the xylan in the solution to xylose. However, the acid hydrolysis is not performed directly on the chemical pulp, and therefore all the xylan in the pulp cannot be utilized.
Acid hydrolysis is also applied as pre-hydrolysis in the separation of xylose from wood material. In this case, the acid hydrolysis is performed directly on wood chips before the pulp is prepared. One such method is disclosed in Guangyu, Yao et al.,
Production of Pulp and Recovery of Xylose from Hardwood. II. The Optimal Process Conditions for Prehydrolysis of Eucalyptu Citriodora Chips with Dilute Sulphuric Acid and Sulfate Pulping
, Journal of Nanking Technological College of Forest Products, No. 4 (1988), p. 32. The publication relates to a method of preparing sulphate pulp with simultaneous recovery of xylose. As raw material is used Eucalyptu Citriodora chips, on which prehydrolysis is carried out with dilute sulphuric acid. A xylose-containing solution and prehydrolyzed wood chips are obtained. Sulphate pulp is then prepared from the prehydrolyzed wood chips. The pulp is said to be suitable for the preparation of viscose, for example.
U.S. Pat. No. 4,008,285 (Melaja, A. J. & Hämäläinen, L.) discloses a method of recovering xylitol from a xylan-containing raw material, which may be for example wood material, such as birch chips. The birch chips are first hydrolyzed with for example acid, the hydrolysate is purified and the purified hydrolysate is subjected to chromatographic fractionation to provide a solution containing a high level of xylose. However, the pulp is not recovered in this method.
BRIEF DESCRIPTION OF THE INVENTION
It is therefore an object of the invention to provide a method of recovering xylose from pulp prepared by alkaline or neutral cooking with a sufficient xylose yield, and, simultaneously, preparing paper pulp or dissolving pulp so as to obtain acceptable characteristics for the pulp. The objects of the invention are achieved by a method, which is characterized in what is disclosed in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.
In accordance with the present invention, it has now been surprisingly found that high-quality paper pulp and dissolving pulp can be prepared by first subjecting the pulp to alkaline or neutral cooking and then, as post hydrolysis, to acid hydrolysis in order to recover the xylose. In the method of the invention, simultaneous extraction and hydrolysis of xylan are achieved, and extensive use of alkali in the extraction of xylan can be totally avoided.
In the context of the present invention, the expression ‘sufficient xylose yield’ refers to a xylose yield of at least 5% (50 g xylose/1,000 g pulp), preferably at least 10% (100 g xylose/1,000 g pulp), calculated on the dry substance of the pulp.
In the context of the present invention, the expression ‘acceptable pulp characteristics’ means that the viscosity of the acid-treated pulp remains sufficient for paper pulp or dissolving pulp. Typically, the viscosity of paper pulp or dissolving pulp should be at least 300 ml/g, preferably at least 450 ml/g, and most preferably at least 600 ml/g. The acceptable viscosity values depend on the final purpose of use of the pulp. If the pulp is used for the preparation of paper whose strength characteristics have to be good, a higher viscosity is required for the pulp, typically at least 600 ml/g. Pulp having a lower viscosity is feasible particularly when acid-treated pulp obtained by the method of the invention is used in a mixture with non-acid-treated pulp in the production of paper, for example.
The expression ‘post hydrolysis is performed directly on the pulp’ means that the acid treatment for hydrolyzing xylan to xylose is performed on the pulp itself, not for example on a xylan solution extracted from the pulp (such as in the method of WO 98/56958, for example). In this case, xylan is hydrolyzed into xylose in connection with the acid treatment of the pulp.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a method of preparing paper pulp or dissolving pulp and a xylose solution by the use of alkaline or neutral cooking and post hydrolysis of the pulp. The method is characterized in that the post hydrolysis is performed directly on the pulp by the use of an acid.
In the method of the invention, the pulp is typically post-hydrolyzed with an acid until the xylose yield is at least 5%, preferably at least 10%, while the viscosity of the pulp remains at a value of at least 300 ml/g, preferably 450 ml/g.
When the hydrolysis of xylan is performed directly on the pulp in connection with the acid treatment of the pulp without pre-treatment steps, the xylan contained by the pulp can be utilized as completely as possible. In this case the xylan can be hydrolyzed as efficiently as possible into xylose, and the xylose yields can be optimized.
In the present invention, alkali cooking refers to a sulphate process, soda process, soda/anthraquinone process and alkali sulphite process, and neutral cooking to a neutral sulphite process. Post hydrolysis is thus typically performed on pulp prepared by alkaline or neutral cooking, typically the sulphate process, the soda process, the soda/anthraquinone process, the alkali sulphite process or the neutral sulphite process. Sulphate pulp is the most preferably used.
In the cooking, hardwood or herbaceous plants can be used as the raw material. Examples of usable hardwood include birch, aspen, alder, oak, poplar, beech, gum tree and acacia tree. Especially important are birch and beech, for example. Examples of herbaceous plants include reed, reed canary grass, bagasse, bamboo and straw, such as cor
Heikkilä Heikki
Kauliomäki Seppo
Lindroos Mirja
Rasimus Raimo
Sundquist Jorma
Danisco Sweeteners Oy
Fortuna Jos'e A.
Scully Scott Murphy & Presser
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