【摘要】 <正> 早在四十年代,中性亚硫酸钠（NS）制浆技术就已经应用于生产。由于它的一些特殊性质和优点,及其对于草类原料制浆的较好的适应性,使其在当今造纸原料紧张、价格上涨的情况下,日益受到国内外的重视。数十年来,许多人做了中性亚硫酸盐蒸煮机理的研究。众所周知,温度影响水以及碱溶液的电离平衡,因而,温度升高,碱性亚硫酸钠溶液PH下降。在100～150^C下,NS蒸煮液PH10.5（25℃）将降为8—9。根据Whitney的研究,PH8—9的亚硫酸盐溶液离子组成绝大部分以SO₃^-形式存在（93％）,SO₃^-水解产生的HSO₃^-离子只占很少一部分（7％）。木素的磺化反应为亲核取代反应,SO₃^-的亲核性大于HSO₃^-,SO₃^-与木素的反应能力应更多还原

【Abstract】 Neutral sodium sulfite （NS） cooking process is particularly suitable for the production of straw pulps. The authors carried out studies on the kinetics and mechanism of the delignification of wheat straw in neutral sodium sulfite cooking on a laboratory scale. A search through current literature revealed that SO₃⁼ ion is a comparatively strong sulfonating agent, and the sulfonation of lignin and dissolution of both lignin and lignosulfonate could be carried out simultaneously. It was claimed that the hydrolyzing rate of lignosulfonates affects significantly the delignification rate. All of these views were rather different from traditional concepts. Accordingly, the sulfonation and dissolution of lignin seemingly are the controlling factors of the rate of delignification in NS cooking, previous studies by others on the kinetics of delignification revealed that Na₂SO₃ charge and its concentration of the NS cooking liquor may have a possible strong effect on the delignification. So we should check the factors of the rate of delignification in NS wheat straw cooking. The studies on the kinetics and mechanism of delignification in neutral sodium sulfite cooking of wheat straw were carried out. UV spectrophotometric determination of lignin contents and IR spectra investigation for both wheat straw and its resulted pulps were carried out. Data for the activation energies, E, of delignification during the course of cooking （with high liquor-to-straw ratio） were collected. Variations in lignin contents of pulps, pulping yield, and Na₂SO₃ concentration and PH of the cooking liquor during NS cooking were also observed. Crystallinity and degree of polymerization （DP） of pulps, strength properties of pulp from NS cooks were determined and compared with those available in literature. Data on E were used to explain the mechanism of the NS digestion.whereas IR spectra analysis gave information on the chemical composition and chemical structure of the resulted pulps during different stages of the NS cook. Variations in the crystallinity of pulps, on the other hand,did to a certain extent reflect what happened to the strength properties of the pulps. Cooking temperature,Na₂SO₃ concentration, cooking time, and residual lignin etc. helped to give a more clear pictu- re about the NS process. It was hoped that experimental data obtained through this study may serve as a guide for improvements in commercial cooks. Results and conclusions arrived at were as follows: 1. Experimental results revealed that around 2/3 of total lignin was rapidly removed during the early stages of NS wheat straw cooking. The residual lignin was found to be very hard to handle. At maximum temperatures of 160—170℃ and with other conditions much similar to those in commercial practice, a good cook was obtained within a relatively short period.Curves expressing delignification rate and pulp yields of such a cook were characterized by the existences of inflection points, at which pulps of better crystallinity, lighter colour, and better strength properties were obtained.Any attempt to further remove the residual lignin by prolonging the at-temperature period turned out to be a failure. Consequently, the authors suggested that such an inflection point should be taken as the end point of a NS wheat straw cooking. 2. Neutral sodium sulfite cooking process （with high Charge of Na₂SO₃ and high liquor-to-straw ratio） may be subdivided into three different delignification stages, in accordance with their rates of delignification.The E. values for the first two stages were 31.56KJ/mole and 60.96 KJ/mole, which were considered to be comparatively low. In the third stage, with lignin contents below 7—4% （UV lignin contents） , the E value was much higher. 3. Na₂SO₃ was consumed rather rapidly in the NS process, accompanied by a similar fast sulfonation of the wheat straw lignin. pissolution of lignin seemed to have come to an end when Na₂SO₃ concentration in the cooking liquor was very small. Apparently,termination of the cook was related to Na₂SO₃ concentration.更多还原