【作者】 刘闰昌；

【导师】 樊永明；

【作者基本信息】 北京林业大学 ， 林产化学加工工程， 2009， 硕士

【摘要】 木片浸渍过程中,化学药液以液体流、离子及其它可溶性物质的形式进入木片。木片浸渍主要研究一定条件下液体进入木片的途径、方式以及液体的量,常用的方法有定量法和定性法。本研究以CTMP预浸渍工艺条件为背景,通过溶液电导率法间接地测定了药液在木片中的扩散系数,探讨了药液在木片中的渗透规律,并研究了浸渍过程中木材抽出物的溶出动力学。电导率测定扩散系数表明,药液在木材中扩散分为三个阶段:开始“未扩散”阶段、扩散+化学反应阶段、快速纯扩散阶段。扩散系数与碱液浓度、木片性质有关。碱液浓度越高,扩散系数越大。浓度越高,木片含水率越高,渗透速率越快;碱液在木片轴向的扩散速率较弦向快,而碱液在木片心、边材中的扩散速率差异不明显。在本研究中,对应实验条件下的扩散系数在5.01*10^-4～1.59*10^-3cm²min^-1范围内。渗透实验表明,渗透过的木块试样可分三个区域,完全渗透区、渗透及未渗透混合区以及未渗透区。从浸渍表面开始,沿浸渍方向往前,渗透区木块切片中碱含量较高,每个切片中碱含量没有明显差别;混合区在浸渍方向上碱含量变化梯度大,碱含量下降迅速,直至为零;未渗透区即是碱液未达到区域,切片中碱含量为零。此外,碱浓、浸渍温度是影响渗透的两个重要因素。高温下碱液能以较大速率渗透至木片内部,同时化学反应更易发生。浸渍时间是木片浸渍程度最终指标,时间越长,浸渍越完全,但工业上应考虑经济等因素。药液在木块径向的渗透快于弦向。抽出物动力学研究表明,浸渍时抽出物的溶出分为三个阶段,快速溶出阶段、缓慢溶出及后期稳定阶段。在稳定阶段,抽出物基本不溶出。温度较高时,抽出溶出速率较快,达到平衡时所需时间较短,且残余在木粉中的抽出量较少。在本实验条件下,抽出物在前10min内大量迅速溶出,从10min至25min缓慢溶出,25min时抽出物基本完全溶出,进入稳定阶段。抽出物溶出的反应可视为一级反应,反应级数为1.04,随着温度的升高,反应速率常数增大,反应的活化能E_a=21884.44 J/mol,指前因子A=314.19min^-1。更多还原

【Abstract】 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.更多还原