Spontaneous change in porosity of a reacting pressed material and non-one-dimensional regimes of diffusion combustion

Essentially non-one-dimensional regimes of synthesis-wave propagation are considered within the framework of a model describing two-dimensional diffusion combustion and taking into account a change in porosity of a reacting composition attributed to a change in its physical and chemical properties. The surface and layer-by-layer burning of a pressed specimen in gas is described qualitatively as well as the interaction front propagation wherein unreacted material remains in skin layers of the specimen. The conditions of development of a gastight layer on the specimen surface and incomplete material conversion because of pore volume exhaustion have been determined. Dynamics of a number of unstable regimes of front propagation is studied. The role of diffusion supply of a gaseous reagent is analyzed under the conditions of changing porous space in the reacting material. The surface and layer-by-layer burning of pressed specimens, with the reagents interacting in an unstable regime, is considered.Institute of Structured Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 47–58. March–April, 1995.     

Efficient integration of optimal solvent and process design using molecular clustering

We present a molecular clustering approach for the efficient incorporation of solvent design information into process synthesis in the integrated design of solvent/process systems. The approach is to be used in conjunction with an integrated solvent/process design approach where the solvent design stage utilises multi-objective optimisation in order to identify Pareto optimal solvent candidates that are subsequently evaluated in a process synthesis stage. We propose to introduce the solvent design information into the process synthesis stage through the use of molecular clusters. The partitioning of the original Pareto optimal set of solvents leads to smaller compact groups of similar solvent molecules from which representative molecules are introduced into the process synthesis model as discrete options to determine the optimal process performance associated with the optimal solvent. We investigate two clustering strategies, serial and parallel clustering, that allow to effectively exploit the solvent-process design interactions to minimise the computational demands of the process synthesis stage. We further propose a clustering heuristic probability that can aid decision making in clustering and can significantly accelerate the search for the best integrated solvent-process systems. The presented method is illustrated with case studies in the design of solvents for liquid-liquid extraction, gas-absorption and extractive distillation systems.     

阻燃高抗冲聚苯乙烯的溶剂法再生工艺研究

采用天然无毒柠檬烯作为高抗冲聚苯乙烯的溶剂、以低毒正丙醇作为沉淀剂,考察了影响高抗冲聚苯乙烯树脂沉淀颗粒形态的各种因素,探讨了高抗冲聚苯乙烯溶液的浓度、沉淀温度、搅拌速度等因素对沉淀过程的影响规律。实验结果表明,当聚苯乙烯质量分数为15%、沉淀剂用量为3倍HIPS溶液的体积,在40℃及2 000 r/min的搅拌作用下,能获得沉淀颗粒大小合适的再生聚苯乙烯产品,聚苯乙烯的回收率达到97%(质量分数),原料中近90%多溴联苯醚可同时被去除。     

涂料干燥过程中溶剂扩散系数的预测与测试方法

基于改进的自由体积模型,计算了不同温度下和溶剂质量分数的聚甲基丙烯酸甲酯(PMMA)?丙酮体系中溶剂的扩散系数,并通过称重法和热重分析法进行验证.结果表明,溶剂扩散系数的预测值与称重法的测试值吻合程度较高,证明改进的自由体积模型可以较好地预测涂料中溶剂的扩散系数.     

Thickness of a modified surface layer formed in a silsesquioxane-based low-k material during etching in a fluorocarbon plasma

This paper explains the origin of our previous observation that, when a silsesquioxane-based low-k film is etched in fluorocarbon plasmas, the thickness of a surface modified layer, in which cage-like Si-O bonds are dissociated to extents greater than a specified level, changes linearly with log[F]²/[CF₂], where [F] and [CF₂] denote concentrations of F and CF₂ radicals in the bulk plasma. During the etching process, the substrate consists of three distinct layers: a fluorocarbon layer, a modified surface layer, and an unmodified layer. F density at the interface between the fluorocarbon and the modified surface layers, denoted as F₀ in this study, is determined in proportional to [F]²/[CF₂], and the density decreases exponentially with the film depth. As a result, the thickness of the modified surface layer changes in proportion to a parameter, log[F]²/[CF₂].     

The impact of solvent characteristics on performance and process stability of printed carbon resistive materials

Carbon conductive pastes deposited by screen printing are used in many commercial applications including sensors, PCB, batteries, and PV, and as such represent an important value-added coating. An experimental investigation was carried out into the role of the solvent on the drying characteristics, conductivity, and process consistency in screen printed carbon pastes. Four materials with solvent boiling points between 166 and 219°C were deposited at film thickness between 6 and 16 μm, and the sheet resistance and film thickness were measured after successive passes through an industrial dryer operating with an air temperature of 155°C. Sheet resistances of 14 Ω/sq. were obtained with the thicker films while thinner films produced a sheet resistance of 46 Ω/sq. Thinner films achieved a stable resistivity within a 2.5-min residence time, while the thicker films required a residence time in excess of 12.5 min to achieve a stable resistivity. As well as prolonging drying times, the higher boiling point increased the resistivity of the cured film. It is postulated that the lower resistance of the faster drying materials is a result of film stressing increasing inter particle contact. Process models indicate that multiple thin layers are a more efficient means of manufacture for the process parameters examined.     

Residual solvent and its diffusion in acrylic fibers

A survey showed that some commercial acrylic fiber products contain small quantities of residual solvent (dimethylacetamide). No diffusion of solvent from these products could be detected on laundering, dry cleaning, or exposure to synthetic perspiration. Acrylic carpets containing residual solvent were enclosed in sealed boxes to simulate a closed room. Air in the boxes was monitored for solvent content over a 14-day period at 24°C (75°F) and 38°C (100°F) at both low and high humidity conditions. In all cases the solvent content of the air was below the detection limit of the best analytical procedure available (below 0.1 ppm). Diffusion rates of sol vent from 15-denier carpel fiber into nitrogen were measured over the temperature range of 25–100°C. There was no detectable diffusion below 60°C measured over a 24-h period. Mass diffusivities ranged from 2.5 × 10^?19 cm²/s at 60°C to 6.4 × 10^?14 cm²/s at 100°C. Under the conditions of expected use, the rate of diffusion of residual solvent from acrylic fibers is very low. Based on the low concentrations of residual solvent and its very low diffusion rate, there is an extremely low probability of any exposure to solvent from the residual solvent present in commercial acrylic fiber products.     

Analysis of nonvolatile material in solvent hexane

The amount and composition of the nonvolatile residue in solvent hexane are important quality criteria. These residue characteristics are particularly significant in the hexane extraction of foods because of the possibility of contaminating edible products. A laboratory evaluation of the residue from a typical hexane was made to find if there was any trace of multi-ring aromatics which might be potential carcinogens. Samples of hexane directly from a refinery and after storage and transportation to two solvent extraction plants were analyzed. All residues were separated by paper chromatography and analyzed by ultraviolet spectrophotometry. In no case, were they found to contain polynuclear aromatic carcinogenic materials. The test method is sensitive to less than 0.01 ppm. In order to verify the accuracy of the test, an analysis was made for the quantitative recovery of a known carcinogen. For this purpose, 0.01 ppm of 3,4 benzpyrene was added to the hexane as an internal standard and the analysis conducted as before. In these tests, the benzpyrene was recovered quantitatively.     

Short Communication: application of a surrogate material in assessing the impact of porosity on re‐ignition of wood‐based materials

Re‐ignition behaviour of charred solid fuels after extinction by water is studied. In this communication the effect of material porosity on re‐ignition is investigated. A surrogate ceramic material is used so as to separate the pyrolysis and combustion processes from those associated with heat transfer. Experimental data are reported for different sample thickness and porosity, and varying heat flux and water application time. Copyright © 2002 John Wiley & Sons, Ltd.     

Dynamics of solvent diffusion in an aromatic polyimide

Diffusion behaviors of two polyimides (PIs) synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-oxydianiline (ODA), and 4,4′-diaminodiphenylsulfone (DDS) were investigated by the gravimetric method. The weight uptake of penetrants (solvents) was nearly proportional to the exposure time in solvent. This phenomenon was considered as the Case II diffusion (non-Fickian) mechanism. Two PI films had an affinity to N-methyl-2-pyrrolidinone (NMP) rather than to dimethylsulfoxide (DMSO). The solubility parameter differences between two polyimides and NMP are less than 5, whereas that between polyimides and DMSO are greater than 5, as calculated by Hoy's group contribution method. The solvent uptake of anisotropic films contributed to an increase in the thickness. The swollen amount of anisotropic films increased with the swelling temperature but tended to decrease with the imide content and the thickness of the anisotropic films. Isotropic films of two PIs did not swell in both NMP and DMSO. © 1994 John Wiley & Sons, Inc.     

Prediction of continuous porosity gradients in ceramics using ZnO as a model material

Materials with gradient microstructures have a wide range of applications such as cutting tools, armor, and electronic devices. However, it is difficult to predict and control the gradient microstructure during processing. In the present work, a continuous porosity gradient was successfully achieved in ZnO material via spark plasma sintering with a large induced thermal gradient. The porosity is overestimated if isothermal prediction is applied. The current work proposed a more accurate prediction of the porosity by considering the stress-shielding effect caused by the thermal gradient. The shielding effect results from different stress states in the sample due to differential sintering: the hotter side of the specimen experiences a higher strain rate and more shrinkage while the colder side experiences a lower strain rate and less shrinkage simultaneously. Therefore, the axial strains are varied throughout the sample thickness. Using the constituent equations in advanced sintering analysis, the shield stress was calculated to be approximately 13 MPa for the viscoelastic assumption of sintering. To improve the accuracy of predicting porosity gradient, it is necessary to add a load to overcome the shield stress when the materials are sintered with a thermal gradient.     

Solvent and temperature effects on diffusion in polymer–solvent systems

The temperature dependence of the mutual diffusion coefficient at zero solvent concentration for a number of polystyrene–solvent systems is satisfactorily represented by an equation derived from a new version of the free-volume theory of molecular transport. The free-volume parameter which governs the temperature dependence of the diffusion rate is linearly related to the size of the solvent as estimated by its molar volume at OK. Data taken on various polystyrene–solvent systems are used to deduce information on the mechanism of solvent transfer in polymeric systems.     

纤维状纤维素高吸附材料制备工艺的研究

本文研究对水和生理液有很好吸附和保持能力的纤维状高吸附材料的制备工艺。该材料是将纤维素纤维（棉短绒、外科用纱布）经由一种处理液进行醚化、交联等反应得到，使纤维的表面形成一层交联聚电解质，而芯层保持原有的天然结构。文中讨论了影响水吸附保持值（WRV）和生理盐水吸附保持值（SRV）的工艺因素，检测了聚电解质层中纳和铜可迁移金属平衡离子对血浆吸附性能的影响。结果表明，采用本工艺使改性棉短绒的WRV和SRV分别为未变性时的12倍和6倍，变性纱布则分别为未改性时的6倍和4．7倍。     

Establishment of a solvent map for formation of crystalline and amorphous paclitaxel by solvent evaporation process

This study intended to establish a solvent map for formation of crystalline and amorphous paclitaxel by a solvent evaporation process. Crystalline paclitaxel was produced by evaporation with polar solvents (acetone, acetonitrile, ethanol, isobutyl alcohol, methanol, methyl ethyl ketone, and n-butyl alcohol) having a polarity index above 4.00. On the other hand, amorphous paclitaxel was produced by evaporation with non-polar solvents (methylene chloride, n-butyl chloride, and toluene) having a polarity index of about 4.00 or lower. The formation of paclitaxel was very closely associated with the polarity index of the organic solvent used in the solvent evaporation process. In the case of crystalline paclitaxel, the higher the polarity index and the lower the viscosity of the organic solvent (n-butyl alcohol, methyl ethyl ketone, and acetonitrile), the higher the degree of crystallinity. In the case of amorphous paclitaxel, the shape and size of particles varied according to the solvent (methylene chloride, n-butyl chloride, and toluene) used in the solvent evaporation process.     

溶剂脱沥青工艺优化研究进展

介绍了溶剂脱沥青的原理、工艺流程及发展情况。就目前国内外对溶剂脱沥青工艺优化的研究进展情况,从超临界溶剂回收技术、高效传质设备的使用和组合工艺的开发等几个方面进行综述,对未来我国溶剂脱沥青工艺的优化方向进行了分析与展望。     

A/O-MFC处理垃圾渗滤液与产电性能研究

构建了序批式A/O-MFC运行装置,以垃圾填埋场渗滤液为底物,考察A/O-MFC在不同浓度渗滤液作为阴极液的产电性能和污染物去除效果。结果表明,MFC两极的COD、氨氮的去除率均随阴极渗滤液浓度的增加而增大,且阴极室去除效果明显好于阳极室。MFC输出电压随阴极渗滤液浓度的增加而增大,高效脉冲波动幅度随渗滤液浓度增加而减缓。最大功率密度分别0.030,0.096,0.129 W/M²。第3阶段功率密度分别是前两个阶段4.30,1.34倍。可见,微生物燃料电池产电能力随阴极渗滤液浓度的增加而增大,处理高浓度垃圾渗滤液的A/O-MFC的除污-产电性能最好。因此,以垃圾填埋场的渗滤液作为底物运行A/O-MFC具有可行性。     

Effect of ultrasound irradiation on solvent extraction process

The temperature and pressure profiles of four solvents were simulated at various ultrasonic power levels to suggest models for predicting the energy density. The acoustics mode and heat transfer mode of COMSOL Multiphysics? were used to predict the temperature and pressure profiles, respectively. For water, the maximum and minimum pressure at 300 W and 450 W of ultrasonic power level were 8.838 × 10⁶ Pa and ?9.533 × 10⁶ Pa, and 1.028 × 10⁷ Pa and ?1.1167 × 10⁷ Pa, respectively. The pressure gap was in the order of water, hexane, methanol and ethanol. For ethanol, the maximum and minimum temperature of 450 W in 1200 s was 337.15 K and 298.25 K, respectively. The energy density of ethanol was the highest among solvents while that of water showed the lowest value. The pressure, temperature and energy density increased with increasing ultrasonic power and irradiation time. The energy density was inversely proportional to temperature, but the cavitation density was in proportion to temperature. The solubility increased with increasing temperature. In overall, the temperature-dependent effect was considered in ultrasound-induced extraction process.     

Experimental studies on the influence of porosity on membrane absorption process

Eight kinds of flat membranes with different micro-structures were chosen to carry out the membrane absorption experiments with CO₂ and de-ionized water or 0.1 mol·L⁻¹ NaOH solution as the experimental system. According to experimental results, the membrane pores shape (stretched pore and cylinder pore) and membrane thickness do not affect the membrane absorption process, and the membrane porosity has only little influence on membrane absorption process for slow mass transfer system. However, the influence of porosity on the membrane absorption process became visible for fast mass transfer system. Moreover, the mass transfer behavior near the membrane surface on liquid side was studied. The results show that the influence of membrane porosity on mass transfer relates to flow condition, absorption system and distance between micro-pores, etc. __________ Translated from Journal of Chemical Engineering of Chinese Universities, 2007, 21(1): 14–19 [译自: 高校化学工程学报]