| Wheat straw is an important non-wood fiber resource. Soda pulping is the most common pulping process for the wheat straw. Due to high silica content, recovery of the black liquor from the soda pulping process has never been economically practiced. The black liquor has traditionally been simply discharged into the nearest receiving water therefore causing a severe environmental impact. With strict environmental control regulations, this old disposal practice can not continue. Converting lignin into lignosulfonates is a viable disposal approach for the black liquor, since lignosulfonates have numerous applications, especially in the agricultural area. It could sustain the utilization of wheat straw as a major non-wood fiber resource in the paper industry.; In this study, a continuous laboratory reactor is designed and built for postsulfonation of the wheat straw soda lignin. With a L9(4 3) orthogonal experimental design, an optimal bisulfite postsulfonation condition is obtained. The optimal continuous bisulfite postsulfonation condition can achieve 64% sulfonation of acid insoluble lignin in black liquor from the soda cooking of wheat straw and reduce the amount of acid insoluble material from 22% to 10% of the black liquor total solids content. It was found that high temperature alkaline pretreatment can completely degrade hemicelluloses into useful carboxylic acids. Additional further work is needed to test the effectiveness of these lignosulfonates in agricultural applications. |
