Study On Kinetics Of De - Delignification By Eucalyptus Low Temperature Sulfate Process

As the strains on the shortage of wood resources for the papermaking industry increase seriously, the research of the kinetics of delignification and reaction mechanism of lignocellulosic materials not only can help us to know delignification reaction, also can be used for controlling the cooking quality, and further enabling efficient utilization of wood resources. In this thesis, the fast-growing Eucalyptus provided by Yunjing Forestry-paper Co., Ltd., was subjected to Kraft pulping at the low temperature for investigation of its delignification reaction mechanism and kenetics, and the change of the structure to the dissolving lignin and dissolution component of carbohydrate was revealed by using infrared spectrum (IR),1H-NMR, 1C-NMR and gas chromatogram technology analyzed.It was showed that the kinetics of delignification of eucalyptus with Kraft low-temperature pulping well fit the first order reaction, displayed three stages in delignification the initial phase, the bulk phase and the residual phase. Under the same cooking conditions (alkali charge, sodium sulfide charge, time at Tmax),the difference of the reaction rate between 130℃ and 140℃ of Tmax was not obvious, but from 140℃ to 160℃, the reaction rate increased about three times along with Tmax rising 10℃, so the temperature is the main factor affecting the pulping. On the premise of the liquid penetration uniformity and the indeclinable selectivity delignification, the appropriate increase of temperature within low-temperature zone and extending of the time at Tmax can realize the perfect effect of low temperature Kraft pulping. Through the viscosity variationunder different Tmax levels, carbohydrate degradation was serious at a higher temperature level (160℃ and 150℃), the final viscosities were 1395 mL/g and 1598 mL/g, respectively, while the values were up to around 1700 mL/g and 1580 mL/g at lower temperature levels (140℃ and 130℃). Taking into account with alkaline charge, preservation temperature at 140℃ showed that the degradation of the carbohydrates could be restrained to a least extent, and Kraft low-temperature pulping should be introduced in industry.Infrared spectrogram analysis of dissolved lignins from the pulp with residual lignin of 19%,16%,10%,6%　and 3%under four Tmax level showed that they mainly contained S and G lignin units. At the initial cooking, the fractures with S units was fast dissolved, and this dissolving slow downalong the reduction of the preservation temperature　1H-NMR and 13C-NMR spectra of these lignins indicated that the structure with non-conjugated double bond mainly occurred at the initial cooking. At the bulk phase, the dissolving lignin displayed obvious polycondensation structure, there existing more condensation structure content of Hp, Ha and Hγ in β-O-4 units. Along with cooking reaction, alcohol hydroxyl groups of the dissolution lignin decreased whereas phenolic hydroxyl increased. Through gas chromatographic analysis of dissolved carbohydrates, it showed that the dissolution rate of arabinose and galactose was significantly higher than other sugar composition. Dissolved xylan was resorpted on fibers under the higher temperature and appropriate alkali charge.