The Mechanism Of Wood Impregnation And Dissolving Kinetic Of Extractives In The Pulping Process Of Populus Tomentosa CTMP

It is widely recognized today that chemicals transport into the chip voids in terms of liquor flows, ions and other soluble matters during the process of impregnation.Quantitative and qualitative methods are commonly used to investigate the access,ways and quantity of liquid penetration into wood under certain condition.Under the background of pre-impregnation conditions of CTMP,this research has indirectly examined the diffusion coefficient of liquor penetration into wood through the variation of solution electric conductivity,has discussed the mechanisms of liquor penetration into wood and evaluated the dissolving kinetic of wood extractives in the process of impregnation.The results of the determination of diffusion coefficient show that there are three steps in liquor penetration into wood:the beginning "undiffusion" step,combination of diffusion and chemical reaction step and fast pure diffusion step,which compose the complete diffusion process.It also can be found in this experiment that alkali diffusion coefficient is related to the consistency of alkali and the properties of wood chips.The diffusion coefficient and rate of diffusion are positively related to alkali consistency and water retention rate of wood.The liquor diffusion into wood in axis direction is easier than that in tangential direction,while there is no apparent difference between the results obtained from the heartwood and sapwood samples.Under the conditions used in this research,the determined diffusion coefficients vary from 5.01*10^-4 to 1.59*10^-3cm²min^-1.The results of the penetration experiment reveals that the impregnated wood sample can be divided into three zones,completely penetrated zone,unpenetrated zone and the mingled-zone between the above two,according to alkali content of the slices peeled from each zone.This alkali content is high,and to some extent is constant in the completely penetrated zone,while this content can not be determined in the unpenetrated zone,which indicates that the chemicals in the alkaline solution have not proceeded at this area.The phenomenon showed in the mingle-zone is a little more complicated,the alkali content of each slices descends dramatically along the penetration direction.Additionally,alkali consistency and temperature are both important factors influencing the penetration process.The alkaline liquor transports into wood voids at a higher speed under higher alkali consistency and temperature,in the meantime,the chemical reaction between the alkali and wood constituents is more intense.The duration of impregnation is the ultimate factor used to evaluate the extent of wood impregnation.Wood chips will be impregnated more completely when treated much more time,but economical factors should be taken into consideration when it comes to industrial application.What is more,the properties of wood also influence the impregnation process. Alkaline liquor transports into wood faster at the radial direction than tangential direction.The kinetic of extractive dissolving indicates that extractive removal during impregnation can be divided into three phases:the rapid extractive removal phase,moderate removal phase and the stable phase.According the results obtained in this research,there is nearly no extractive dissolving at the stable phase,and it also find that extractives dissolve rapidly under high temperature,and needs less time to get to the stable phase.What is more,the residual extractive content is much lower at high temperature.Under the conditions used in this study,extractives remove rapidly and significantly during the initial 10min,and slowly and moderately from 10min to 25min,and eventually stable phase is coming,before which extractives have almost been removed clearly.Removal of the extractive follows as a first order reaction.As the result of this study,the reaction order is 1.04.The reaction rate constant is positively related to the temperature,the active energy of the reaction E_a=21884.44 J/mol,and the factor of pre-index A=314.19min^-1.