山杨和速生杨硫酸盐浆多相水解动力学的研究

STUDY ON KINETICS OF CELLULOSES IN HYDROLYTIC DEGRADATION OF POPULUS DAVIDIANA AND 72-POPLAR PULPS

研究了木质素含量为０．２３％的山杨漂白浆和１．０５％的速生杨未漂浆稀酸低温多相水解降解反应动力学特性。结果表明，该过程与棉浆、桦木和针叶材浆具有相类似的特点，即纤维素多相水解降解过程分为两个明显阶段（快速降解和缓慢降解），而最终降至极限聚合度（山杨漂白浆为１８０；速生杨未漂浆为２０６）。两个阶段的纤维素水解降解动力学以其不同反应速度为特征，根据试验数据计算出反应速度常数：山杨漂白浆为Ｋ＝２．５×１０￣（－４）／ｍｉｎ；速生杨未漂浆为Ｋ＝１．６×１０￣（－４）／ｍｉｎ，前者明显地高于后者。随着水解时间的增加，水解残渣得率下降，最终结果达到８３％～８４％。测定了各水解试样的木质素含量，结果表明，水解前期（１０～４０ｍｉｎ）木质素变化较大，山杨漂白浆下降４８％，速生杨未漂浆下降３８％；水解后期，木质素含量变化不大。木质素的存在对于多相（固－液）水解降解反应起着阻碍作用并降低其反应速度常数。木质素含量越高水解液渗透至纤维素大分子链之β－Ｄ－葡糖键的速度越慢。

Kinetics of hydrolytic degradation of bleached Populus davidiana and unbleached 72-poplarpulps with lignin contents of 0.23%and l.05%respectively was investigated.It was shown that the characteristics of this process is similar to that observed previously for celluloses of cotton,birch and conif-erous species,i.e. the existence of two stages of hydrolysis(a rapld and slow stage) and the attainment of“limiting”DP_L(DP_L=180 for cellulose of aspen;DP_L=206 for cellulose of popular).The kinetics of the hy-drolytic degradation of celluloses are expressed by two stages characterized by different rates. The calcula-tion of reaction rate constants was based on the experimental data :that bleached Populus davidiana cellu-lose are hydrolyzed at a higher rate(K=2.5 × 10￣(-4)/min) than that of 72-poplar cellulose(K=1.6×10￣(-4)/min).The yield of the residue after hydrolysis decreases with increasing hydrolysis time and theterminal product yield was 83%～84%of initial materials. The lignin contents of samples were determined. Results showed that lignin contents varid greatlyonly in the early stages of hydrolysis (10～40 min).The lignin contents of unbleached and bleached pulpsdecreased 38%and 48%,respecaively. However,in the late stages (40～120 min),there were little differ-ences in the lignin contents. The presence of lignin plays a blocking role in the heterogeneous hydrolysisand decreases the rate constant.The greater amount of lignin present,the slower the penetration of hy-drolyzing agents into β-D-glucoside bond of the cellulose chain.