Study On The Process Of1,4-butanediol Solvent Pulping For Cotton Stalks

Using cotton stalks as raw material and1,4-butanediol as solvent this paper is aimed at developing a novel and low polluting pulping process (high boiling-point solvent pulping process) to realize the complete utilization of agricultural wastes which possesses significance both in material utilization and environmental protection. Research included:comparison of pulping effect of different high boiling-point solvents used for pulping cotton stalks, process conditions analysis and optimization of1,4-butanediol pulping, the effect of acid catalysts on1,4-butanediol pulping, cooking reaction course, the kinetic of delignification, the spectral analysis and antioxidant capacity of HBS lignin obtained from our research. The main results were as follows:Dimethyl formamide, tetrahydrofurfuryl alcohol, ethyleneglycol, and1,4-butanediol were applied to pulping for cotton stalks and the results showed that the pulping effect of1,4-butanediol was the best. The process variables of1,4-butanediol pulping for cotton stalks were analyzed respectively. Using response surface to analyze the influence of the independent cooking variables on the characteristics pulp the optimal conditions of cooking applied1,4-butanediol solvent concentration of78%, cooking temperature of192℃, time at cooking temperature of100min, the liquor to material ratio of8:1(kg/L), and time to cooking temperature of70min, which showed the following optimum values of the dependent variables:49.6%(pulp yield),52(kappa number),0.92(pulping selectivity). The real experimental results under the optimal conditions was52.7% (pulp yield),56(kappa number),0.94(pulping selectivity). The effect of acid catalysts on1,4-butanediol pulping showed that it was able to accelerate the removal of lignin, reduce cooking temperature and cooking time during pulping, whereas, acid catalyst didn’t have the capacity to reduce1,4-butanediol concentration. The results of researching cooking course of1,4-butanediol pulping for cotton stalks showed the division of the pulping into two phases:the bulk delignification phase, which was from the beginning to60min of192℃, and the delignification rate was87.3%; the residual delignification phase, which was from60min of192℃until210min of1928℃, and the delignification rate was8.5%. The activation energy in two phases was35.85kJ/mol and40.89kJ/mol, respectively. The results of structural characterization by FTIR and UV spectroscopy showed that cotton stalks HBS lignin had more guaiacyl phenylpropanoid units than syringyl, and had conjugated structure and obvious bands of different chemical structure. The HBS lignin from our research was more effective free radical scavengers whose1,1-di-phenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity (IC50) was lower than that from NH4OH-KOH method.