优化温度相关力场预测正构烷烃热力学性质

为了实现不同温度下正构烷烃及其混合物热力学性质的准确预测,以正构烷烃（n-C₄~C₁₀）为训练集,通过对全原子OPLS-AA力场中非键相互作用参数（ε）的模拟优化,得到了ε与对比温度（T_r）以及正构烷烃碳原子个数（N_C）的经验关系式。利用该关系式计算出不同温度不同种类的正构烷烃的ε值,预测了正构烷烃纯物质及其混合物的黏度、密度、扩散系数等物性,并将新力场模拟计算值与理论估算值以及实验值进行比较。结果表明,采用优化温度相关力场预测烷烃及其混合物的物性与实验值最为吻合。密度、黏度和扩散系数的预测值与实验值的相对偏差分别小于2%、5%和10%,显著优于目前的理论方法和原OPLS-AA力场模拟计算的预测值。上述温度相关力场参数的确立,对于利用分子动力学模拟方法准确地预测正构烷烃及其混合物的热力学性质具有重要的实际应用价值。     

聚丙烯酸十八酯降凝剂对合成蜡油结蜡特性影响的研究

采用自主研发的Couette结蜡装置研究了聚丙烯酸十八酯（POA）降凝剂对合成蜡油体系结蜡特性的影响。通过对结蜡层表面样（远离结蜡筒）和底部样（靠近结蜡筒）的宏观观察、DSC放热、气相色谱及蜡晶微观结构的分析发现：POA的加入降低了蜡油体系的结蜡速率,加快了蜡油体系的老化速率,且在一定浓度范围内（50～200 μg·g^-1）导致了径向不均质蜡沉积结构的形成,从结蜡层表面到底部含蜡量逐渐升高,但在较高加剂浓度（400 μg·g^-1）时径向不均质蜡沉积结构消失;POA的加入使得结蜡层表面样和底部样的临界碳数（CCN）都由C₂₄升高到C₂₅,但结蜡层底部样与表面样相比低碳数正构烷烃（≤ C₂₅）有所减少,高碳数正构烷烃（≥ C₂₆）有所增加;随着油样中POA浓度的增大,结蜡层表面样与底部样的蜡晶形貌由针状蜡晶逐渐转变为片状蜡晶,且蜡晶尺寸逐渐变大,结构更为致密。     

正构烷烃在Pt/SAPO-11催化剂上加氢异构反应性能

采用SAPO-11分子筛制备Pt/SAPO-11双功能加氢异构催化剂,以n-C₈、n-C₁₂和n-C₁₆为模型化合物考察正构烷烃的加氢异构反应性能。结果表明,所制备的催化剂具有较好的异构化活性和选择性,其中单甲基支链异构产物收率和总异构产物收率分别可达60%和75%以上,是低凝柴油和高档润滑油基础油的理想组分。不同链长正构烷烃的异构化产物分布基本一致,但链长较长的正构烷烃更容易发生异构化反应和裂解反应,在保证相同转化率条件下长链烷烃裂解产物收率偏高且异构选择性降低。     

长链正构烷烃（n-C16~C20）脱氢制直链单烯烃反应热力学分析

对长链正构烷烃（n-C₁₆~C₂₀）一次脱氢制直链单烯烃反应进行了详细的热力学分析,考察反应温度、反应压力、氢烃物质的量比和原料碳数对热力学平衡的影响。结果表明,n-C₁₆~C₂₀脱氢反应的平衡常数及平衡转化率随烷烃碳数的增大而增加;提高温度和降低压力均可显著提高平衡转化率,降低氢烃物质的量比在一定程度上提高平衡转化率。适宜的工艺条件为：反应温度>430 ℃,反应压力(0.10~0.20) MPa,氢烃物质的量比为6~8。     

CO2和O2在聚乳酸/聚偏二氟乙烯共混物中扩散行为的分子动力学模拟研究

采用分子动力学模拟方法研究了CO₂和O₂分子在聚乳酸/聚偏二氟乙烯（PLA/PVDF）共混物中的扩散行为;通过菲克第一定律和Einstein关系式计算了共混物体系模型的自由体积分数以及CO₂和O₂分子在体系中的扩散系数,研究探讨了自由体积分数与探头半径的关系及自由体积分数与扩散系数的关系。结果表明,当PLA/PVDF共混物中PLA和PVDF的质量比为9∶1时,CO₂和O₂气体分子的扩散系数均为最小,共混物阻隔性能最好;共混体系中小分子的动力学半径越小,扩散系数越大;自由体积分数随硬球探头模型中探头半径的增大而减小;不同共混物体系中,自由体积分数的变化趋势与扩散系数一致,与Fox和Flory的自由体积理论相符。     

临邑-濮阳原油管道结蜡层的组成与流变性研究

以临邑-濮阳管道所输原油与临邑-赵寨子(结蜡层1)和赵寨子-莘县(结蜡层2)管段处的结蜡层为研究对象,通过SARA分析、DSC热分析、流变测量、气相色谱分析和宏观、微观形貌观察的方法,研究了管输原油与结蜡层的组成与流变特性。实验结果表明,与管输原油相比,结蜡层的凝点、析蜡点、含蜡量、饱和分含量和沥青质含量均有大幅升高,而芳香组分和胶质含量减少;黏度和屈服值显著增大;低碳数正构烷烃显著减少,高碳数正构烷烃显著增加;蜡晶结构由细小的针状和片状蜡晶变为类球状蜡晶和大针状和片状蜡晶。两种结蜡层相比,结蜡层1的析蜡点更高,蜡含量更少,沥青质含量更多;黏度和屈服值更大;高碳数正构烷烃含量更多;宏观和微观形态上来看,结蜡层1的片状针状蜡晶更多、尺寸更大、结构更为致密。因此,在临邑-濮阳管道的临邑站-赵寨子站管段,清管球卡死的现象更容易发生。     

反渗透、纳滤过程的物理化学研究（Ⅱ） 多孔荷电膜的溶质分离规律

在多孔膜溶质的脱除率方程和溶液渗透通量方程的基础上由溶液电中性条件导出了荷电膜的单价电解质、中性分子混合溶液体系离子的脱除率方程,中性分子的脱除率方程,溶液渗透体积通量方程和离子、中性分子的浓缩比表达式。由方程的函数性质讨论了荷电膜的单价电解质、中性分子混合溶液的溶质组分脱除率和溶液渗透体积通量随离子浓度、pH值的变化规律。预测了盐和中性分子的脱除率和溶液渗透体积通量随浓度变化曲线出现极大和极小值的现象,由此得出了下列结果：随pH值的增加,单价电解质溶液的阳离子、阴离子和氢离子的脱除率变化顺序为由 R _M⁺ > R _X^- > R _H⁺变化到R _M⁺ =R _X^-> R _H⁺再变化到R _X^->R _M⁺> R _H⁺,离子脱除率变化曲线将出现极大和极小值;有机酸的总脱除率表达式阐明了文献中的可电离有机分子与pH值的关系式中参数的物理意义,解释了该关系式的对氨基苯甲酸水溶液的脱除率随pH值变化的拟合曲线高于脱除率实验值的原因,解释了对氨基苯甲酸的甲醇溶液的溶质脱除规律;离子的浓缩比依赖于料液中离子组成和离子所对应盐的浓缩比。     

聚丙烯酸十八酯降凝剂对合成蜡油结蜡特性影响的研究

采用自主研发的Couette结蜡装置研究了聚丙烯酸十八酯(POA)降凝剂对合成蜡油体系结蜡特性的影响。通过对结蜡层表面样(远离结蜡筒)和底部样(靠近结蜡筒)的宏观观察、DSC放热、气相色谱及蜡晶微观结构的分析发现:POA的加入降低了蜡油体系的结蜡速率,加快了蜡油体系的老化速率,且在一定浓度范围内(50~200μg·g~(-1))导致了径向不均质蜡沉积结构的形成,从结蜡层表面到底部含蜡量逐渐升高,但在较高加剂浓度(400μg·g~(-1))时径向不均质蜡沉积结构消失;POA的加入使得结蜡层表面样和底部样的临界碳数(CCN)都由C_(24)升高到C_(25),但结蜡层底部样与表面样相比低碳数正构烷烃(≤C_(25))有所减少,高碳数正构烷烃(≥C_(26))有所增加;随着油样中POA浓度的增大,结蜡层表面样与底部样的蜡晶形貌由针状蜡晶逐渐转变为片状蜡晶,且蜡晶尺寸逐渐变大,结构更为致密。     

尿素络合法生产液蜡的影响因素考察

尿素络合法是生产液蜡的一种重要工艺,主要是依靠尿素易与正构烷烃络合,而较难与非正构烷烃络合的原理实现正构烷烃的提取。在整个过程中,存在很多因素影响反应效果。以直馏柴油为原料,对尿素络合过程中的各因素开展趋势试验,总结各因素对产品纯度的影响规律并分析产生这些规律背后的原因。通过试验发现:液蜡制备过程中的各因素对液蜡性质的作用机制是通过影响尿素与不同碳数正构烷烃的反应程度以及影响尿素与正构/非正构烷烃的反应程度来影响液蜡产品纯度;溶剂洗涤过程的温度和强度也会对液蜡的纯度和收率产生影响。     

优化温度相关力场预测正构烷烃热力学性质

为了实现不同温度下正构烷烃及其混合物热力学性质的准确预测,以正构烷烃(n-C4~C10)为训练集,通过对全原子OPLS-AA力场中非键相互作用参数(ε)的模拟优化,得到了ε与对比温度(Tr)以及正构烷烃碳原子个数(NC)的经验关系式。利用该关系式计算出不同温度不同种类的正构烷烃的ε值,预测了正构烷烃纯物质及其混合物的黏度、密度、扩散系数等物性,并将新力场模拟计算值与理论估算值以及实验值进行比较。结果表明,采用优化温度相关力场预测烷烃及其混合物的物性与实验值最为吻合。密度、黏度和扩散系数的预测值与实验值的相对偏差分别小于2%、5%和10%,显著优于目前的理论方法和原OPLS-AA力场模拟计算的预测值。上述温度相关力场参数的确立,对于利用分子动力学模拟方法准确地预测正构烷烃及其混合物的热力学性质具有重要的实际应用价值。     

Swelling and electrical properties of rubber vulcanizates loaded with paraffin wax

The influence of the concentration of paraffin wax on the penetration rate, P, and the average diffusion coefficient, D, of kerosene in an SBR–NR composite and also on the coefficient of viscosity were investigated. All decreased with the addition of wax. Also, the effect of the concentration of paraffin wax on both the current–voltage characteristics and the temperature dependence of the dc electrical conductivity were studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3169–3177, 2001     

Diffusion in polyacrylamide gels

Using a novel sorption technique, the diffusion of some series of solutes in polyacrylamide gels has been investigated with regard to: (a) molecular size of solute; (b) concentration of solute and gel polymer; and (c) temperature. The approach used also yields the partition coefficient pertaining to sorption equilibrium. The ratio, $\text{D}\text{D}{}_{\mathrm{o}}$, where D_o refers to diffusion in the pure solvent, is found to reflect in part the characteristic interactions between solute and gel polymer. The temperature results indicate that the apparent activation energy for solute diffusion is approximately independent of the polymeric component for dilute gels.     

Solute diffusion through swollen polymer membranes

Experiments were designed to study the role of the solvent in the transport of a solute through a solvent-swollen polymer membrane. A single solute (an organic dye), a single polymer (cross-linked natural rubber), and 24 different organic solvents were used for this purpose. The solute diffusion coefficient D was calculated from the measured permeability P and distribution coefficient K, and was compared to the diffusion coefficient of the solute in the pure solvent. The main parameters of the solvent were shown to be its viscosity and the degree it swells the polymer. At high swelling, the results are in agreement with a model that pictures the resistance to solute diffusion as hydrodynamic interaction with the solvent while the polymer acts as an obstruction that increases the tortuosity of the diffusion path. At very low swelling, the diffusion coefficient approaches an asymptotic limit which is independent of solvent viscosity. However, even with as low as 10% solvent, some effects of viscosity are still seen. These results are discussed in terms of a quantitative theory for the obstruction effect proposed by Meares and compared to other literature data.     

Estimation of the compositional gradient in a PVC/PMMA graded blend prepared by the dissolution-diffusion method

We reported a new preparation method in the previous paper, by which an excellent graded polymer blend was simply prepared. In this report, we propose a new model for the dissolution-diffusion process. The model was derived by obeying Fick's second law for diffusion and by assuming that the evaporation of the solvent in PMMA solution during the diffusion could be neglected. We then proved that this model was applicable to the graded structure of a PVC/PMMA graded blend. Further, it was confirmed that the dissolution rate of PVC into PMMA solution remained constant during preparation. Thus, our model was found to be reliable. However, while the apparent diffusion coefficients (D_ABs) of PVC in 0.183 and 0.274 ml/cm² of the initial solution volumes were equal to each other, they were larger than the D_AB in 0.091 ml/cm² of the initial solution volume. Thus, the effects of PVC concentration dependency of D_AB and changing of PMMA concentration in the solution on D_AB were discussed, because all of the D_ABs should be equal to each other. Then, our model was modified as follows. We considered that PVC finished diffusing below a PMMA concentration of 0.18 g/ml, because the diffusion coefficient of PVC immediately increased at a higher PMMA concentration. Then, the solution layer was shrunk to about 1/6, in order to form a blend film. Thus, it was found that the D_AB in each of the initial solution volumes was 4.2 ± 0.25 × 10⁻⁸ cm²/s. Further, the D_ABs estimated by diffusion thickness method, were from 1.5 to 3.5 times larger than those estimated by our model. Therefore, it was proved that our modified model was applicable to the experimental data.     

Peak parking-moment analysis: A strategy for the measurement of molecular diffusivity in liquid phase

The peak-parking (PP) method permits the measurement of molecular diffusivities (D_m) in solutions. D_m is first measured for benzene in pure methanol and acetonitrile (ACN), using an empty open tube. This yields an effective axial diffusion coefficient (D_ax,m) equal to D_m because there is no tortuosity nor constriction in the flow channel. The same measurements made for the same combinations of solute and solvents, using a column packed with non-porous silica particles provides the obstructive factor (Y_m), defined as the ratio D_ax,m/D_m, which accounts for the influence of tortuosity and constriction of the interparticulate space in packed columns on axial molecular dispersion. The value obtained for Y_m, 0.74–0.75, is constant, irrespective of the solvent. Then, PP experiments were made with the same apparatus and column to measure D_m for benzene, toluene, and ethylbenzene in aqueous solutions of methanol and ACN. The values of D_m obtained by correcting the experimental D_ax,m values with Y_m were compared with values previously reported and those estimated by several literature correlations. They were in good agreement with each other. The average relative error is estimated at 4.5–10%, demonstrating that the PP method is practically effective for experimental measurements of D_m.     

Theoretical and Experimental Estimation of Binary Gas Diffusivities in a Nonisothermal Stefan Diffusion Column

Binary gas diffusivities D_AB are essential to analyze chemical engineering transport processes. One of Josef Stefan's memorable moving-front problems involved a column with liquid A at the bottom and a gas mixture of A and B on top. This system has been used by several groups to determine D_AB's under assumed isothermal conditions. A device for such purposes is Armfield's CERa apparatus; however, its operation is not isothermal. This study's hypothesis is that the nonisothermality of the gas relative to the liquid affects the D_AB estimates. A mass and energy transport model was developed to describe events in the gas once the evaporation-diffusion of A begins. The model included D_AB as a key parameter and different phase temperatures (liquid hotter than gas). A numerical algorithm solved for the instantaneous mole fraction of A, temperature, and interfacial position. The model predicted the transient and spatial transport phenomena of four gas pairs (A = common solvent; B = bone-dry air). The simulations gave lower D_AB's in nonisothermal versus isothermal columns, the errors being proportional to the temperature difference between the phases. Six binary gas experiments were carried out in a nonisothermal CERa at two room temperatures. The experimental D_AB's underestimated the isothermal diffusivities with errors of 23–52%, while the parallel simulations followed this trend but with smaller errors (4.1–6.3%). D_AB underestimation due to column nonisothermality is novel in the gas diffusivity literature. Improvements to the theoretical and experimental techniques presented should result in better D_AB estimates.     

Diffusion coefficients of l-menthone and l-carvone in mixtures of carbon dioxide and ethanol

The molecular diffusion coefficients of l-menthone and l-carvone in supercritical carbon dioxide (SCCO₂) and carbon dioxide containing 5 and 10 mol% ethanol as a modifier were measured by the Taylor-Aris chromatographic peak broadening (CPB) method over the ranges of temperature from 308.15 to 338.15 K and pressure from 15 to 30 MPa. It was found that the correlation relationships between diffusion coefficients and the temperature, pressure, viscosity, and density, such as the linear correlation between the D₁₂ and ρ, and between the D₁₂ and T/η, which were valid in binary systems, were also suitable for ternary systems of carbon dioxide containing modifier. The diffusion coefficients in modified SCCO₂ decreased with increasing the ethanol mole fraction due to the chemical association between the two solutes and ethanol. Of several models used to predict experimental data in pure carbon dioxide, the two models of Funazukuri-Ishiwata-Wakao and He-Yu-1998 were the best with the AAD less than 3.2%. Furthermore, the models of modified Wilke-Chang, Scheibel, Reddy-Doraiswamy, Lusis-Ratcliff, Hayduck-Minhas, Tyn-Calus, and Lai-Tan overestimated the diffusion coefficient in ethanol modified SCCO₂ with the AAD values increaseing with the percentage of ethanol, which were probably due to the increase of the volume of solvaton sphere as a true diffusion unit with the percentage of ethanol. Moreover, the free volume model of Dymond is good for predicting the experimental data in pure carbon dioxide and ethanol modified SCCO₂ with the AAD values range from 3.21 to 1.90%.     

管道蜡沉积模型中扩散系数的研究

分子扩散是管道蜡沉积的主要驱动力,蜡分子的径向扩散质量流(J=D?(dC/dr))决定了蜡沉积层增长速率,其中关键参数为蜡分子在原油中的扩散系数D。原油为多组分复杂混合物,扩散过程复杂,不利于定量研究。从简单的二元烷烃体系入手,研发了Taylor分散法测试装置,并总结了国内外学者的理论和实验研究,针对n-C18+n-C7体系进行比较分析,为深入研究多元蜡分子扩散现象提供了基础。     

Experimental study of diffusivity of hexane in bitumen-saturated porous media under high temperature/pressure conditions

Solvent mass transfer plays a key role in a thermal gravity drainage process involving solvent. The diffusion coefficients of solvent in such a process are not well studied. This article presents the effective diffusion coefficients of solvent in bitumen-saturated sands under high temperature/pressure conditions measured using a CT scanning technique. Experimental results show that the effective diffusion coefficient of n-hexane in bitumen-saturated sands varied with the solvent concentration or with the viscosity of solvent–bitumen mixture (i.e., D_e ∝ c^0.4 or D_e ∝ μ_m^−0.46). The solvent concentration weighted diffusion coefficient of n-hexane in the bitumen under the condition 160–170°C/1,900 kPa had an order of magnitude of about 10⁻⁵ cm²/s for solvent volume concentration less than 0.2. The penetration distance of n-hexane in bitumen-saturated sands depended on the nonlinearity of diffusion and had a value of −2 cm after 1-day diffusion. The stronger the nonlinearity of diffusion, the shorter the penetration distance.     

Gas transport properties of polycarbonate–polyurethane membrance

Polyurethanes (PU) were prepared using polymeric diols, containing polar groups, as ? O? C(O)? O? (carbonate) groups, carbonate and ether (? O? ) groups, or carbonate and ester groups [? C(O)? O? ]. PUs were prepared by the prepolymer two-step technique using ethyl acetate (EA) as the solvent; the diol was reacted at about +80°C with TDI (ratio 1:2) to give the prepolymer terminated with NCO, which was then cross-linked with triisopropanolamine (TIPA). The membranes were prepared using a Gardner knife and were characterized by differential thermal analysis (DSC). Most of the polymers prepared from low and medium molecular weight diols were amorphous and elastomeric at the temperature of gas transport measurement (35°C). The permeabilities (P) and the diffusion coefficients (D) of different gases (O₂, N₂, CO₂, CH₄, CO) were measured by a modified Lyssy apparatus, the solubility coefficient (S) was also calculated. The water-vapor transport properties D and S were measured according to ASTM. Diffusivity data follow the Fujita model and the solubility coefficients the regular solution theory, as developed by Prausnitz and Shair. © 1993 John Wiley & Sons, Inc.