Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Patent
1992-05-12
1994-04-26
Jones, W. Gary
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
162 78, 162 90, D21C 304
Patent
active
053063929
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for the preparation of chemical pulp in a large quantity and in a continuous manner from cellulose raw materials without spoiling the environment or natural resources.
BACKGROUND ART
Heretofore, a number of processes have been developed with the object of chemically producing pulp from cellulose raw materials. Many processes have been weeded out so far; the processes which are currently available for the preparation of chemical pulp are the AP method (alkali method), SP method (sulfite method), KP method (kraft method) and variants thereof.
The AP method employs a sodium hydroxide aqueous solution (consisting of two components) as a cooking liquor. This method offers the advantages that no malodorous substances are produced, unlike the KP method, and that the chemicals can be recovered from the pulp waste liquor with relative ease. However, it suffers from the disadvantages that the removal of lignin does not readily occur in the process of pulping so that the resulting pulp is poor in strength and the kappa value (an indicator of the content of lignin in pulp having the relationship: lignin (%)=kappa value.times.0.15) is so remarkably high that a large quantity of chemical is required for bleaching. Hence, this method is not usually applied to the pulping of wood and it is utilized, in part, only for pulping cellulose raw materials derived from non-wooden materials.
The SP method employs an acidic, neutral or alkaline solution of a sulfite as a cooking liquor, and the acidic SP method is particularly superior in its ability to elute lignin so that the unbleached SP pulp is low in kappa value and refining and bleaching are readily carried out; however, the strength and the yield of the pulp are poor. Hence, this method is practically applied for the preparation of dissolution pulp from needle-leaved trees and some broad-leaved trees; however, the demand for such pulp is extremely low. Further, the SP method is not suited for pulping general broad-leaved trees or those needle-leaved trees which are difficult to digest, and the treatment of pulp waste liquor and recovery of the chemical substances used are not easy, so that this method is currently applied only in an extremely small sector of the industry.
The KP method uses an aqueous solution of sodium sulfide and sodium hydroxide (consisting of three components) as a cooking liquor and can pulp various kinds of needle-leaved trees and broad-leaved trees. The resulting pulp is tough and the kappa value is relatively low; however, its bleaching is not so easy. Generally, five- to seven-step bleaching gives a bleached pulp having a high degree of whiteness. Further, this method offers the advantages that sodium sulfide and sodium hydroxide can be recovered for reuse in the cooking liquors by concentrating pulp wastes, burning them in a reducing atmosphere and subjecting them to causticization. In addition, the energy used in burning can also be recovered. For the foregoing reasons, the KP method is today generally used to a remarkably wide extent, and more than 70% of total production of pulp and more than 95% of production of chemical pulp in Japan is by the KP method.
It is to be noted, however, that recent and more severe requirements for protection of the environment and conservation of earth resources, are difficult to meet with the KP method, thus creating an increasing demand to develop a new method for the preparation of pulp, which can serve as a substitute for the KP method currently prevailing in this industry. In other words, while the KP method is superior to the other conventional methods in terms of utilization of resources of cellulose, because the KP method can pulp a wider variety of needle-leaved and broad-leaved trees, the KP method is not suited for pulping so far unavailable trees including many kinds of tropical trees, ceders, deciduous trees and the like and for bleaching pulp therefrom. Further, this method can utilize only a limited number of raw materials, i.e. it is in
REFERENCES:
patent: 4466861 (1984-08-01), Hultman et al.
patent: 4507172 (1985-03-01), Steltenkamp
patent: 4826567 (1989-05-01), Gratzl
patent: 4851082 (1989-07-01), Mita et al.
Jones W. Gary
Nguyen Dean T.
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