邻二甲苯在醋酸中扩散系数的测定

利用金属膜池并用氯化钾水溶液标定了膜池常数。用已有可靠文献值的乙酸水溶液验证了装置的可靠性。测定了298．15～323．15K不同温度下邻二甲苯在醋酸中的积分扩散系数,还分别给出了微分扩散系数与邻二甲苯浓度的关联式。结果表明在相同温度下邻二甲苯在醋酸中的扩散系数随着邻二甲苯浓度的增加而减小,在同一浓度下随着温度的升高而增加。     

对二甲苯在醋酸中扩散系数的测定

为了提供精对苯二甲酸（PTA）生产过程中相关体系的扩散系数,利用金属膜池并用氯化钾水溶液标定了膜池常数。用已有文献值的乙酸水溶液验证了装置的可靠性。测定了298.15-323.15K不同温度下对二甲苯在醋酸中的积分扩散系数,还分别给出了微分扩散系数与对二甲苯浓度的关联式。结果表明在相同温度下对二甲苯在醋酸中的扩散系数随着对二甲苯浓度的增加而减小,在同一浓度下随着温度的升高而增加。     

凝胶网络中溶剂性质的分子动力学模拟

本文利用分子动力学(MD)方法模拟了三种不同结构的凝胶网络系统,对系统的压力、溶剂的自扩散系数以及溶剂在凝胶不同区域的密度分布等进行了考察。模拟结果表明,被吸收进入凝胶网络的溶剂的性质与纯溶剂的性质有很大的差别,但凝胶结构的不均匀性对凝胶网络中溶剂的性质几乎没有什么影响。     

非离子型凝胶球在水中的溶胀行为

以过硫酸铵和N,N,N',N',-四甲基乙二胺氧化-还原体系引发丙烯酰胺聚合,制备球状非离子型水凝胶.利用带刻度的显微镜记录了凝胶球在水中的溶胀扩散过程,采用Tanaka-Fillmore凝胶溶胀动力学模型进行数学处理,得到凝胶网络扩散系数.在此基础上,进一步考察了交联剂、引发剂、单体浓度对凝胶网络扩散系数的影响,结果表明:随着交联剂用量的提高,扩散系数先变小后增大;增加引发剂﹑单体浓度,扩散系数均增大.对凝胶网络扩散系数-温度理论模型进行修正,更加符合实验结果,可用于凝胶网络扩散系数的预测.     

动态光散射法测定凝胶中大分子有效扩散系数

引　言凝胶广泛应用于生化分离和医学材料等领域 ,其中溶质分子在凝胶中的扩散特性尤为关键[1] 凝胶中溶质分子有效扩散系数的测定方法主要有扩散法[2 ]、荧光恢复法[3]、强制瑞利散射法[4 ]、全息衰减法[5 ]和动态光散射法 (ＤＬＳ) [6～ 8],后者一般用于较软且透明的凝胶 前人在用ＤＬＳ法测定凝胶中溶质分子的扩散系数时均忽略凝胶结构的非均匀性 ,具有较大的局限 本文在处理含大分子凝胶体系的ＤＬＳ数据时 ,在考虑凝胶结构的非均匀性基础上提出了遍历介质非均匀校正法 ,并以溶菌酶在聚丙烯酰胺 (ＰＡＡ)凝胶中的扩散为例 ,验证了该方…     

青霉素钾在水溶液中扩散系数的测定

用金属膜池法测定了２９８Ｋ条件下青霉素钾在水溶液中的积分扩散系数,给出了微分扩散系数与浓度的关联式。     

氨基酸在水溶液中扩散系数的预测

以F ick定律和不可逆过程热力学为基础,结合文献中对扩散系数预测模型的分析,提出了一个氨基酸在水溶液中扩散系数预测的半经验模型。用实验测定的7种氨基酸在水溶液中的扩散系数和一些文献中的扩散系数数据对模型参数进行了拟和。利用该模型对多种氨基酸及尿素在水溶液中的扩散系数进行了计算,计算值与实验值的平均相对误差均小于0.6%。     

蛋白质分子在聚丙烯酰胺凝胶中扩散和分配特性的研究

利用凝胶内溶质分子向缓冲溶液中扩散的方法,测定了溶菌酶、β－乳球蛋白、卵清蛋白、牛血清白蛋白和γ－球蛋白５种蛋白在聚丙烯酰胺凝胶中的有效扩散系数和分配系数,研究了单体质量浓度、交联度和蛋白分子粒径等因素的影响,讨论了聚丙烯酰胺凝胶中蛋白分子的扩散和分配机制,发现不能用Ｏｇｓｔｏｎ理论解释聚丙烯酰胺凝胶中蛋白分子的扩散和分配特性     

L-抗坏血酸在水溶液中扩散系数的测定

用金属膜池法测定了２９８．１５Ｋ的抗坏血酸在水溶液中可溶解范围内积分扩散系数,该金属膜池法用已知扩散系数的乙酸＋水物系进行校验,证明了本方法及装置的可靠性。此外,还分别给出了它们的微分扩散系数与浓度的关联式,关联式误差较小     

氨基酸扩散系数的分子动力学模拟

采用分子动力学模拟的方法模拟了298. 15 K正则系综下甘氨酸、丙氨酸等12种氨基酸在水中的扩散过程，扩散系数的计算采用微分-区限变分法。计算结果表明：相同浓度下按不同分子数样本计算得到的扩散系数有较大差别，且分子数越多则模拟结果越接近于实验值。5种氨基酸在水中的扩散系数与文献值相对比，误差小于7%。还用同样的方法模拟了氧气在水中的扩散过程，模拟结果与实验结果吻合也较好。实验表明采用分子模拟手段可以获得具有工业应用价值的扩散系数，从而有助于计算传质学的发展。     

Estimation of surface diffusion coefficient in liquid phase adsorption

An estimation procedure of surface diffusion coefficient, D_s, in liquid phase adsorption was proposed. The procedure is based on a restricted diffusion model, in which D_s is correlated with molecular diffusivity by considering a restriction energy due to an adsorptive interaction between adsorbates and adsorbents. In some adsorption systems, D_s of different adsorbates could be calculated with an error less than about 50% from only one datum of each adsorption equilibrium constant. Irrespective of temperature, the procedure, can be applied for the estimation of D_s even in a wide range of D_s of about 4 orders of magnitude.     

纸张干燥中湿分扩散系数的估算

纸张干燥过程涉及到多孔介质的热质传递,如何确定质量扩散系数是所建立的多孔物料湿分扩散模型能否进行数值计算的关键。按Liukov公式将湿分扩散系数视为含湿质量分数的非线性函数,在恒温下进行纸张干燥实验,通过比较湿分蒸发质量的测量值与理论计算值,采用多变量寻优的方法对多孔介质一维情况下的湿分扩散系数进行估算,得到了实验条件下的纸张湿分扩散系数的计算公式。并进一步确定了纸张中的湿分扩散系数与含湿质量分数和温度之间的函数关系式。     

Estimation of an effective water diffusion coefficient during infrared-convective drying of a polymer solution

This article deals with the drying of an aqueous solution of polyvinyl alcohol mixed with a plasticizer. A heating combining forced convection and short-infrared radiation was investigated. A one-dimensional model taking into account the shrinkage of the product was developed to get the temperature and moisture content evolutions during the drying. The water diffusion coefficient was estimated by an inverse method. A sensitivity analysis and numerical tests showed the relevance of using an objective function taking both mass and temperature measurements into account for the estimation procedure. This estimation was performed on several convective and infrared-convective experimental drying kinetics. The model predictions fit well mass and temperature experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Effective diffusion coefficient of chloride in porous concrete

A simplified diffusion model is given in the present paper to represent the chloride diffusion in porous concrete. The model with appropriate effective diffusion coefficient is shown to represent equally well as the more complex diffusion/reaction model proposed by Pereira and Hegedus.⁴ However the present model has the main advantages of being amenable to an analytic solution and ease of model parameter estimation.     

Concentration-dependent molecular diffusion coefficient of gaseous ethane in liquid toluene

We report new experimental data on concentration-dependent molecular diffusion coefficient of ethane in toluene at temperatures ranging from 21 to 125°C and pressures up to 4.14 MPa. An analytical model has also been developed for estimation of the diffusion coefficient utilizing the experimental data of the interface velocity as a result of swelling and the rate of gas dissolution in the liquid phase. It is shown that the diffusion coefficient of ethane in toluene is dependent on the initial mass fraction of the gaseous component in the liquid. In addition, the effect of concentration dependency of the molecular diffusion coefficient on diffusive mass flux is quantified. The results reveal that the assumption of a constant diffusion coefficient introduces ~10–60% error in calculation of diffusional mass transfer flux. The developed methodology finds application in estimation of the concentration-dependent molecular diffusion coefficient of gases in liquids.     

镀层中基体金属扩散系数的测定

铜在防渗铜镀层中的扩散系统是评价镀层防渗铜能力的重要参数。采用电子显微探针法,“俣野”数值方法推导出扩散系数。并分析了铜在柱状和块状镍镀层中的扩散系数。     

NMR measurements of self diffusion in polymer gel electrolytes

The pulsed field gradient NMR spin-echo technique has been used to measure the self diffusion coefficients of solvent molecules, Li⁺ cations and CF₃SO₃⁻¹ anions in polyvinylidene fluoride (PVDF) gel electrolytes incorporating liquid electrolytes based on either N,N-dimethylformamide (DMF) or tetraglyme (TG) and lithium triflate (LiT). Using the Nernst–Einstein equation with the NMR diffusivities, calculated values for the ionic conductivity were obtained and compared with those determined by ac conductivity measurements to provide estimates of ionic association. These results for the gel electrolytes are compared with those for the corresponding liquid electrolytes, over a range of salt concentrations and temperatures. In general terms, the comparisons support the simple conclusion that regions of liquid electrolyte exist within the gel electrolytes, consistent with limited measurements of the transverse relaxation time T₂ on these systems, which are also reported. There are, however, some small but significant differences between the behaviours of the gel electrolytes and the liquid electrolytes and these are discussed.     

Partial separation of polyunsaturated fatty acid esters from FAMEs mixtures by adsorption on silver nitrate-impregnated silica gel

Mixtures of FAMEs derived from soybean and canola oils were fractionated by contacting their hexane solutions with AgNO₃/SiO₂ adsorbents. Methyl linolenate (18∶3) adsorbed most strongly, followed by methyl linoleate (18∶2), on the AgNO₃/SiO₂. Conditions of the extractions (AgNO₃ loading, amount of adsorbent, methyl soyate/hexane solution concentration, use of successive extractions, and methods of adsorbent regeneration) were varied. Under optimal conditions, the 7.0% of 18∶3 in methyl soyate could be reduced to 0.1%. The described process is a simple method for separating a FAMEs mixture into a fraction that is depleted in polyunsaturated FAMEs and one that is enriched.