CO_2在苯乙烯-丙烯腈聚合物中的溶解和扩散

采用重力分析法研究了超临界二氧化碳在苯乙烯-丙烯腈聚合物中的溶解与扩散行为,计算出不同工艺条件下CO_2在SAN中的扩散系数。结果表明:吸附过程中,随着饱和温度升高,SAN对CO_2的最大吸附量会减小;随饱和压力增大,SAN对CO_2的最大吸附量会增大;CO_2在SAN中的吸附速率比在PS中的大;解吸附过程中,当CO_2含量低于10.0%时,CO_2在SAN中的解吸附扩散系数随其含量提高而略有增加;当其含量高于10.0%时,由于CO_2的塑化作用,造成其解吸附扩散系数有显著增加;相同条件下,CO_2在SAN树脂中的溶解度比CO_2在PS树脂中的溶解度大,但解吸附过程中,CO_2在SAN中的扩散系数要比在PS中的扩散系数小。     

Z-藁本内酯在超临界CO_2中无限稀释扩散系数的测定与计算

在温度305.15~323.15 K、压力10~18 MPa范围内,采用Taylor峰扩展法测定了Z-藁本内酯在超临界CO2中的无限稀释扩散系数。结果表明,扩散系数范围在(2.75~5.55)×10-8m2/s之间,并随温度升高而增大,随压力和超临界CO2密度增大而减小,当温度和压力一定时,改性剂乙醇含量的增加能促进扩散系数缓慢增大。分别采用修正的Wilke-Chang、Scheibel、Lusis-Ratcliff、Reddy-Doraiswamy、He-Yu-Su模型预测了Z-藁本内酯的扩散系数,与实验测定值对比表明,平均绝对偏差分别为9.352%、9.356%、9.354%、9.360%和10.444%,均能很好的预测Z-藁本内酯在超临界CO2中的无限稀释扩散系数。     

芍药苷及芍药内酯苷在超临界CO_2中无限稀释扩散系数的测定与计算

在温度308.15~328.15 K,压力10~18 MPa,运用Taylor峰扩展法测定了芍药苷及芍药内酯苷在超临界CO_2中无限稀释扩散系数,两组分的扩散系数均随温度升高而增大,随压力升高而减小,随改性剂乙醇含量的增加而减小,并建立了芍药苷与芍药内酯苷的扩散系数与超临界CO_2的密度关联方程。分别采用修正的Wilke-Chang、Lusis-Ratcliff、Hayduck-Minhas模型和Dymond-Hildbrand-Batschinski(DHB)模型预测了芍药苷及芍药内酯苷在夹带乙醇的超临界CO_2中的三元扩散系数,与实验测定值对比表明,DHB模型的预测效果最好,对芍药苷及芍药内酯苷的平均绝对偏差分别为3.11%和4.96%。     

苦荞活性组分在SC-CO_2/CH_3OH中无限稀释扩散系数的测定及计算

为了测定苦荞活性组分(芦丁与山奈酚-3-O-芸香糖苷)在超临界二氧化碳-甲醇(SC-CO_2/CH_3OH)体系中的无限稀释三元扩散系数,采用色谱峰扩展法在温度为308.15～323.15K,压力为8～14MPa进行实验,考察了压力、温度、密度及夹带剂等因素对扩散系数的影响规律,结果表明三元扩散系数随压力、密度及夹带剂质量分数的升高而减小,随温度的升高而增大。分别采用了修正的Wilke-Chang、He-1997及Dymond-Hildebrand-Batschinski模型对相关溶质分子在SC-CO_2/CH_3OH中的三元扩散系数进行理论关联及预测,计算结果与实验数据比较发现,Dymond-Hildebrand-Batschinski模型的预测效果最佳,芦丁与山奈酚-3-O-芸香糖苷组分的平均绝对偏差分别为2.48%和3.71%。     

超临界CO2在聚苯乙烯熔体中的扩散系数

微孔发泡材料的质量与超临界CO₂在聚合物熔体中的溶解量和溶解速率紧密相关,采用有限元模拟的方法得出不同条件下的等效扩散系数来表征溶解速率。首先,通过基于体积法的实验装置测出不同条件下超临界CO₂在聚合物熔体中的溶解量;其次,通过COMSOL软件计算得出不同的扩散系数下溶解量的变化,最后通过实验值与模拟计算值之间的对比,得出不同条件下,超临界CO₂在聚合物中的等效扩散系数,并分析了误差来源。结果表明,超临界CO₂在聚苯乙烯（PS）熔体中的溶解量随着压力的增加而增加,相反,随着温度的升高呈下降的趋势;模拟计算所得等效扩散系数与实验保持一致,温度与压力的增大都会提高扩散系数的数值;模拟的溶解平衡时间与实验的溶解平衡时间之间的误差不超过20 %。实验结果与模拟计算的结果吻合较好。因此,计算溶解量及等效扩散系数具有重要意义,可为微孔发泡工艺提供理论指导。     

利用孔径均一催化剂测定加氢脱硫条件下重油分子的有效扩散系数

采用反应-动力学法测定了加氢条件下风城减压渣油超临界萃取窄馏分在四种孔径均一催化剂(WDUPS)中的有效扩散系数。结果表明:在400℃,6.0 MPa下,重油分子在催化剂孔道中的扩散系数的数量级在10-9~10-8 cm2·s-1。随着馏分变重,各馏分的有效扩散系数均逐渐降低;随着催化剂孔径增加各馏分的有效扩散系数逐渐增加,但当孔径大于48 nm后,有效扩散系数基本不受孔径影响。受限扩散因子的计算结果表明,相比轻馏分,重馏分在催化剂孔道中的扩散更容易受到催化剂孔径的限制。     

煤的超临界气体抽提

煤的超临界气体抽提是英国国家煤炭局开发的一项煤液化过程。它是基于超临界气体对煤有机质有显著的溶解能力,同时超临界气体扩散系数大,粘度小,因而对煤的抽提较好。由于超临界气体抽提液-固自行分离,避开了传统液化过程中液-固分离难题,同时超临界气     

常用夹带剂在超临界CO2中无限稀释扩散系数的MD计算

缺乏物性数据是制约超临界流体(SCF)技术在化工领域广泛应用的瓶颈问题之一.基于Einstein理论,使用分子动力学(MD)技术计算了三种常用夹带剂丙酮、乙酸乙酯和环己烷在超临界CO2中的无限稀释扩散系数,并针对Einstein法测定扩散系数的误差因素提出了一种数据处理的新方法.最后采用Taylor分散法和超临界色谱技术对夹带剂丙酮和乙酸乙酯在超临界CO2中的扩散系数进行了实验验证,结果表明使用新的数据处理法方法得到的扩散系数和实验测定结果吻合良好.     

MgCl_2水溶液分子动力学模拟

采用分子动力学的方法 ,对无限稀释 Mg Cl2 水溶液进行了模拟。计算了包括 3个超临界点在内的 7个状态下无限稀释 Mg Cl2 水溶液中 Mg2 + - O,Mg2 + - H ,Cl- - O与 Cl- - H的径向分布函数 ,Mg2 + -水 (质心 )和 Cl- -水 (质心 )的配位数。采用均方位移与速度自相关函数两种方法计算了 Mg2 + 、Cl- 的扩散系数。计算结果表明 ,Mg2 + 有较强的第二层水化。超临界状态下 ,Mg2 + 与 Cl- 间有着较强的缔合作用。模拟得到的扩散系数与仅有的常温下实验数据相一致     

超临界流体特性及在有机溶剂中相行为研究

超临界流体具有许多独特的性质,如粘度、密度、扩散系数、溶剂化能力等性质随温度和压力变化十分敏感:粘度和扩散系数接近气体,而密度和溶剂化能力接近液体。本文通过实验首先进行了超临界二氧化碳与氟原子作用考察氟原子的引入对膨胀效果的影响、超临界二氧化碳与羰基作用,考察羰基对膨胀效果的影响、从而确定出最佳的共溶剂[1]。随后,使之与肉桂醛做一系列比例的膨胀对比实验。     

气体在水中的分子动力学模拟

采用分子动力学（ＭＤ）模拟的方法在常温及工业应用背景条件下对ＣＨ４、ＮＨ３、ＣＯ２、Ｏ２这些气体在水中的结构及扩散情形进行了研究。ＭＤ模拟可以为这些涉及到气体在水中的工业应用情形的机理提供分子水平的解释,同时ＭＤ模拟还可为一些不易实验测定扩散性质的体系提供工程初步设计和过程开发所需的数据。     

苯在超临界水中的分子动力学研究

Microscopic structure and diffusion properties of benzene in ambient water (298 K, 0.1 MPa) and supercritical water (673--773 K, 25---35 MPa) are investigated by molecular dynamics simulation with site-site models.It is found that at the ambient condition, the water molecules surrounding a benzene molecule form a hydrogen bond network. The hydrogen bond interaction between supercritical water molecules decreases dramatically under supercritical conditions. The diffusion coefficients of both the solute molecule and solvent molecule at supercritical conditions increase by 30---180 times than those at the ambient condition. With the temperature approaching the critical temperature, the change of diffusion coefficient with pressure becomes pronounced.     

Study on the Diffusion Coefficient of Sodium Chloride at Infinite Dilution in Supercritical Water

The molecular dynamics (MD) was employed to simulate the diffusion coefficient of sodium chloride at infinite dilution in supercritical water from 703.2 K to 763.2 K and from 30 MPa to 45 MPa. Based on the simulated data and the Patel-Teja(PT) equation of state and the Liu-Ruckenstein equation, an equation for calculating the diffusion coefficient of NaCl at infinite dilution in supercritical water is proposed. Both the agreement between the simulated and correlated data, and that between the simulated and predicted data of diffusion coefficients for NaCl in supercritical water ranging from 703.2K to 803.2 K and from 25 MPa to 50 MPa show that this equation is applicable for the calculation of diffusion coefficients.     

超临界二氧化碳自扩散系数的模拟研究

运用分子动力学模拟方法研究超临界二氧化碳的自扩散系数。总的来说,二氧化碳自扩散系数的模拟值与文献实验值吻合得很好。而450 K和50 MPa、424 K和100 MPa、450 K和200 MPa这三个条件下,模拟值与实验值相对误差异常大,通过作图探讨其原因。     

加压和超临界条件下乙醇分子的缔合

引言 在化学和化工领域,分子扩散系数是过程设计和装置优化所需的基本数据之一[1].乙醇作为一种高效绿色溶剂,具有良好的溶剂性能和比较温和的临界温度、临界压力(Tc=514.3 K,pc=6.38MPa),在食品、医药和化工等领域有巨大的应用空间[2].     

分子模拟二氧化碳在狭缝炭微孔中的吸附

Both the grand canonical Monte Carlo and molecular dynamics simulation methods are used to investigate the adsorption and diffusion of carbon dioxide confined in a 1.86 nm slit carbon pore at 4 temperatures from subcritical (120 K) to supercritical (313 K) conditions. Layering transition, capillary condensation and adsorption hysteresis are found at 120 K. The microstructure of carbon dioxide fluid in the slit carbon pore is analyzed. The diffusion coefficients of carbon dioxide parallel to the slit wall are significantly larger than those normal to the slit wall.     

Equilibrium and Transport Properties of Gases in E-Glass Melts

The solubility and diffusion coefficients of oxygen, sulfur dioxide, and water were determined (and those for nitrogen, carbon dioxide, and argon were estimated) in commercial E-glass melts as a function of melt temperature and atmosphere. Knowledge of these fundamental constants of gases in glass melts is required for the development of models for bubble growth and elimination within the melt. The effectiveness of fining agents can be traced to the production of those gases in the melt which possess the greatest variation in solubility and diffusion as a function of the temperature and atmosphere. Accordingly, oxygen through multivalent elements and sulfur are the best fining agents for glass production.     

描述CO2的柔性模型

A fully flexible potential model for carbon dioxide has been developed to predict the vapor-liquid coexistence properties using the NVT-Gibbs ensemble Monte Carlo technique (GEMC). The average absolute deviation between our simulation and the literature experimental data for saturated liquid and vapor densities is 0.3% and 2.0%, respectively. Compared with the experimental data, our calculated results of critical properties (7.39 MPa, 304.04 K, and 0.4679 gcm－3) are acceptable and are better than those from the rescaling the potential parameters of elementary physical model (EPM2). The agreement of our simulated densities of supercritical carbon dioxide with the experimental data is acceptable in a wide range of pressure and temperature. The radial distribution function es-timated at the supercritical conditions suggests that the carbon dioxide is a nonlinear molecule with the C O bond length of 0.117 nm and the O C O bond angle of 176.4°, which are consistent with Car-Parrinello molecular- dynamics (CPMD), whereas the EPM2 model shows large deviation at supercritical state. The predicted self-diffusion coefficients are in agreement with the experiments.     

Molecular probe technique for the assessment of the carbon molecular sieve structure

Nitrogen adsorption at 77 K is the most common technique for defining the surface area and pore volume of a porous material. However it is not adequate to assess the microporosity of carbon molecular sieves (CMS), because of activated diffusion effects. In this paper, a molecular probe technique was used to defining the pore size of CMS materials. Adsorption of gases (vapors) with different molecular sizes, were measured by a gravimetric method using a spring balance. The amount adsorbed at room temperature was recorded over a 24-h period. The following molecular probes were chosen: CO₂ (0.33 nm), C₂H₆ (0.4 nm), n-C₄H₁₀ (0.43 nm), i-C₅H₁₁₂ (0.5 nm), and CCl₄ (0.6 nm). The micropore volumes were estimated by the Dubinin-Raduhkevich (DR) equation. Assuming that the diameters of the micropores are larger than those of the adsorbed molecules, the micropore volume distribution of each sample was estimated. The results demonstrated that the main pore size of the studied CMSs are less than 0.5 nm. One of the samples had a narrow pore size distribution in the range of 0.33–0.43 nm, which is the critical pore size for kinetic separation of oxygen from nitrogen. It is concluded that the molecular probe technique is an effective mean to assess the CMS adsorbents structure, which is not currently possible using conventional approaches with a single adsorbate, such as nitrogen or argon.