Methods for carbonate pretreatment and pulping of cellulosic material

Abstract

A method of pretreating comminuted fibrous material with sodium carbonate and then cooking the pretreated material in the presence of anthraquinone (AQ) is provided. The resulting pulp produced has a higher yield, enhanced strength, and better bleachability compared to pulp produced by prior art methods. AQ may also be introduced to the carbonate pretreatment stage. The method may further include an acid pretreatment providing further enhanced properties to the pulp produced.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from co-pending provisional application Ser. No. 60 / 747,717, filed May 19, 2006, and co-pending provisional application Ser. No. 60 / 824,995, filed Sep. 8, 2006. The disclosures of these provisional applications are incorporated by reference herein.REFERENCE TO GOVERNMENT CONTRACTS [0002] This invention was made with government support under grant number CHE 0553323 entitled “An Investigation of Depolymerization and Condensation Reactions of Lignin Under Alkaline Conditions” awarded by the National Science Foundation. Accordingly, the United States government has certain rights in the invention.FIELD OF THE INVENTION [0003] The present invention relates to a process for treating comminuted cellulosic fibrous material, for example, wood chips, with a carbonate pre-treatment prior to cooking the cellulosic material with a cooking chemical in the presence of an anthraquinone (AQ). BACKGROUND OF THE INVENTION...

AI Technical Summary

Benefits of technology

[0019] One aspect of the invention may further include an oxygen delignification treatment as well as at least one bleaching stage, where the method produces a cellulosic pulp having a brightness greater than 88% elrepho. When an oxygen delignification treatment is provided, the method may produce a pulp having a lower kappa number after the oxygen delignification treatment at a predetermined screened y

Problems solved by technology

One disadvantage of soda cooking includes a lower pulp yield (for both softwoods and hardwoods) than realized by kraft cooking, that is, cooking using sodium hydroxide (NaOH) and sodium sulfide (Na2S) as the pulping chemicals.

Even with AQ addition, however, pulp from soda cooking processes exhibits weaker pulp strength and poorer bleaching compared to kraft cooking.

However, disadvantages also exist with soda anthraquinone (SAQ) cooking as compared to kraft cooking.

For instance, SAQ cooking requires higher amounts of NaOH and it is more difficult to bleach pulp produced from a SAQ pulping process.

These low MW organics are difficult to recover from the pulping effluent, referred to in the art as “black liquor,” and they do not have high calorific values.

Additionally, the pulp produced from hardwood material processed using the Lo-Solids® Cooking method with soda-AQ as a cooking chemical can obtain a better terminal brightness than conventional Soda-AQ, but not as bright as pulp produced from kraft cooking.

Though pretreatment with sodium carbonate at about 165 degrees C. is disclosed in the above-referenced patent, the high temperature treatment disclosed in the '241 patent (published in 1932), for various reasons, has not been accepted in the pulping industry, and is typically not practiced today.

Images