Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Patent
1986-11-17
1988-12-27
Alvo, Steve
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
162 78, D21C 304, D21C 916
Patent
active
047938986
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for preparing bleached pulp out of lignocellulosic raw material. According to the present process, the raw-material is first treated with a pulping liquor containing oxidizing components, whereupon the pulp is bleached.
The preparation of fully bleached pulp is nowadays carried out by means of methods which call for the use of sulphur- and chlorine-containing chemicals. These materials have a detrimental influence on the environment, the minimization of which forms an important cost factor in industry. The environmental requirements of ever increasing stringency are obviously going to increase said costs even further in the future. It is easily conceivable that the efforts to provide less contaminating pulping processes during the last few years have been the objects of constant interest.
Non-polluting pulping has been aimed at by using closed processes. Furthermore, there have been efforts to find chemicals, the use of which is accompanied by a diminished adverse environmental influence, when compared with conventional pulping chemicals, and which would allow the process to be closed even better.
The closing of the process in the first stage of conventional pulping, i.e. during cooking has, to a rather large degree already been achieved for the present pulping processes. This is true especially for the chemical circulation of the main process, i.e. the kraft process. In this context, the formation of malodorous sulphur-containing volatile compounds which exhibit an adverse environmental influence is, however, still a problem.
The closing of the process of the second stage of pulping, i.e. bleaching, is difficult. The present bleaching processes are mainly based on the use of chlorine and compounds thereof, but 100% recirculation of bleaching waste-liqours containing chlorine compounds in the process has proved to be very difficult mainly due to corrosion problems. The various detrimental chlorine compounds formed during bleaching are therefore, to rather a large extent, emitted to the environment.
In pulping, the chemicals which cause a minimum of pollution and which are preferable when it comes to the closing of the process, have met with ever increasing interest, as the possibilities of the present pulping processes for meeting the stricter environmental requirements have been shown to be limited. Industrial applications have not yet been reached, although the matter is being largely investigated around the world today. The new methods are expensive and this has frequently been mentioned as the reason for their not being widely used.
Pulping which causes a minimum of environmental pollution is best reached when the chemicals used therein contain only carbon, hydrogen, and oxygen. Many of the new methods tested do not, however, fulfil this requirement; they may contain e.g. nitrogen which is an unpredictable element when considering its environmental influence. It may even prove to be very troublesome.
The first stage of pulping, i.e. cooking, using chemicals containing carbon, hydrogen, and oxygen only, has mainly been investigated in the connection with so-called organosolv pulping methods. Said methods are based on the use of organic solvents. These usually contain some compound which is called a catalyst, which enhances the degradation of lignin and the conversion thereof into a dissolving form. The drawback of the organosolv-methods lies in their relatively low delignification capacity and the difficulty of pulping softwood. Furthermore, the catalysts often times contains undesired elements, such as chlorine or sulphur, which make the non-polluting character of the method questionable wheh larger amounts of catalysts are employed.
However, it has been discovered that the dissolving of lignin in certain organosolv-solvents, e.g., carboxylic acids, may be significantly increased when a lignin-oxidizing chemical, e.g. hydrogen peroxide, is used instead of a catalyst. If hydrogen peroxide is added to a liquid carboxylic acid, such as acetic or formic acid, lign
REFERENCES:
patent: 3193445 (1965-07-01), Parker
patent: 3867246 (1975-02-01), Hebbel
patent: 4400237 (1983-08-01), Kruger
patent: 4462864 (1984-07-01), Carles
Rydholm, "Pulping Processes", Interscience Publishers, New York, 1967, pp. 916-917.
Kutney, "Hyrogen Peroxide: Stabilization of Bleaching Liquors"; Pulp & Paper Canada; 12-1985, presented Montreal 2-3-1984.
Kauliomaki Seppo V.
Laamanen Lauri A.
Poppius Kristiina J.
Sundquist Jorma J.
Wartiovaara Ilkka Y. P.
Alvo Steve
Oy Keskuslaboratorio - Centrallaboratorium Ab
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