A comprehensive mathematical model for the Fischer-Tropsch synthesis in well-mixed slurry reactors

A new product distribution quasi-steady-state model was proposed for the Fischer-Tropsch (FT) synthesis in slurry reactors, being applicable to their transient simulation. It may consider two chain propagation mechanisms or sites and the possibility of 1-olefin readsorption with secondary reactions, recovering the Anderson-Schulz-Flory (ASF) model, the two superimposed ASF model and the 1-olefin readsorption model as particular cases. The hydrocarbon compounds were lumped according to the number of carbon atoms in their molecules for the paraffin and 1-olefin families. The phases were assumed to be well mixed in the reactor and transient mass balances were performed for each component, allowing simulation of operation in constant liquid level and no liquid withdrawal conditions. A rigorous calculation of the vapor-liquid equilibrium (VLE) through cubic equations of state was used to describe the phase behavior. Rate expressions for the FT and the water gas shift reactions are taken from the literature and expressed in terms of fugacities. Simulation results showed that the inclusion of both the olefin readsorption and the two chain propagation mechanisms may explain the anomalies present in experimental hydrocarbon product distribution. Moreover, the effect of phase-equilibrium modeling on product distribution simulation was shown to be slightly important in the conditions analyzed. Compositional lumping schemes for the hydrocarbons were investigated to speed up the simulations. Results showed that lumping can speed up computations up to 250 times with negligible loss of accuracy.     

PEG整理涤纶织物吸湿性的研究

研究了低分子量 PEG,乙二醛等对涤纶织物涂层整理、结果表明这种整理工艺可有效改变涤纶织物的亲水性、吸湿性 ,改善涤纶织物的服用性能。适宜的工艺配方和条件为 PEG80 0 5 4.2 %、乙二醛 (4 0 % )9.8%、浓硫酸 1 .6 3% ,1 2 0℃焙烘 3min     

A comprehensive fractal char combustion model☆

The char combustion mechanisms were analyzed and a comprehensive fractal char combustion model was developed to give a better understanding and better predictions of the char combustion characteristics. Most of the complex factors affecting the char combustion were included, such as the coupling effects between the pore diffusion and the chemical reactions, the evolution of the char pore structures and the variation of the apparent reaction order during combustion, the CO/CO2 ratio in the combustion products and the correction for oxy-char combustion. Eleven different chars were then combusted in two drop tube furnaces with the conversions of the partly burned char samples measured by thermogravimetric analysis. The combustion processes of these chars were simulated with the predicted char conversions matching very well with the measured data which shows that this char combustion model has good accuracy. The apparent reaction order of the char combustion decreases, stabilizes and then increases during the combustion process. The combustion rates in the oxy-mode are general y slower than in the air-mode and the effect of the char-CO2 gasification reac-tion becomes obvious only when the temperature is relatively high and the O2 concentration is relatively low.     

Dissolution/reprecipitation: A model process for PET bottle recycling

A dissolution/reprecipitation route was followed for the recycling of poly(ethylene terephthalate) (PET). Model experiments on virgin material, either in the form of pellets or blow‐molded bottles, are presented. The process proposed comprises dissolution of the plastic in an appropriate solvent, reprecipitation by using a nonsolvent, thorough washing of the material obtained, and drying. The solvent mixtures involved are separated by fractional distillation for further reuse. N‐Methyl‐2‐pyrrolidone (NMP)/n‐octane + n‐hexane proved to be a particularly effective solvent/nonsolvent system. Further investigation was focused on the effect of the sample history through successive recycling cycles. The recycled material was evaluated in terms of molecular weight, crystallinity, and grain‐size analysis, resulting in an excellent quality, competing with the virgin grade. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 91–95, 2001     

Chemical recycling of post-consumer PET: Alkyd resins synthesis

The recycling of post-consumer poly(ethylene terephtalate) (PET) is a worldwide concern due to its environmental impact and the large and increasing volume of these materials produced by society. We use post-consumer PET in alkyd resin synthesis for coatings, replacing a fraction of phthalic anhydride (PA) and ethylene glycol (EG) of conventional synthesis for post-consumer PET.     

五釜工艺聚酯工业装置的稳态模拟

针对大型连续PTA直接酯化法PET工艺过程装置,以Aspen Plus和Polymers Plus为模型开发工具,建立了以反应和传质过程机理为基础的稳态模型。结果表明:该模型中包括了酯化反应、缩聚反应、二甘醇生成反应、链降解反应和乙醛生成等主副反应,且考虑了端羧基对酯化反应的自催化效应;更重要的是模型考虑了酯化阶段PTA在酯化反应器中的溶解过程和终缩聚阶段小分子的脱挥,并建立了小分子脱挥的传质系数与缩聚反应器内聚合度、黏度、温度和搅拌器转速等的关联;在此模型基础上模拟研究了第一酯化反应操作温度对各反应器出口指标的影响,指出酯化段的酯化率有一个适宜的控制范围。     

抗静电PET树脂的合成及性能研究

采用聚乙二醇、间苯二甲酸双羟二乙酯磺酸钠、无机盐与对苯二甲酸双羟二乙酯共聚合的方法合成了一种新型抗静电聚对苯二甲酸乙二酯(PET)树脂。该树脂的体积电阻率达到10~8Ω·cm数量级,静电半衰期达到0.02s,且不受长时间水洗的影响,其抗静电性能明显优于用共混等其他方法获得的抗静电PET树脂。     

A comprehensive heat transfer model for rotary desorbers

A model that describes the heat transfer processes within a rotary desorber is presented. This model has several advantages over previous models. The method for calculating the wall-to-bed heat transfer rate includes the effects of moisture in the feed solids and allows for evaporation from the bed before the bulk bed temperature reaches the saturation temperature of the moisture. The method for calculating radiative heat transfer in the desorber accounts for the real nature of the participating gas and the amounts of CO₂ and H₂O in the gas phase from both combustion and evaporation. Results from experiments performed using a pilot-scale desorber are discussed, and the model is validated by comparing the predicted bed temperature profiles and evaporation rates to those found experimentally. A preliminary attempt to account for the effects of a non-uniform bed on the evaporation rate from the bed is also presented along with several parametric studies.     

The film formation of acrylic latexes: A comprehensive model of film coalescence

A comprehensive model of film formation that was proposed in an earlier article by the present authors was evaluated for latexes having a wide range of physical properties. In this model, capillary force and interfacial forces act in tandem to promote film coalescence. The emulsion polymers studied were all based on poly(methyl methacrylate-co-butyl acrylate). The viscoelastic nature of the copolymer was varied by the addition of molecular weight modifiers (CBr₄ chain-transfer agent and ethylene glycol dimethacrylate cross-linking monomer) during synthesis. In contrast to the simplifications of the previous analysis, the experimental system was well characterized. The effect of water plasticization was investigated. The surface energetics of the system were studied. Also, drying kinetics were considered. Results showed that the degree of coalescence ranged from complete fusion to superficial fusion. The minimum film temperature was found to increase with increasing polymer rigidity, as is expected. Comparison of the model predictions and experimental observations validated the model. © 1994 John Wiley & Sons, Inc.     

A model for diazacyclopropane synthesis

The formation of 3-methyl-3-ethyl diazacyclopropane, an intermediate in the manufacture of hydrazine and its derivatives, was studied by reacting chloramine, ammonia and methyl ethyl ketone in a semi-batch reactor provided with a stirrer. The conversion (based on chlorine) was found to increase with ammonia to chlorine ratio (8–20), agitator speed (1000–3000 rev/min), temperature (5–65°C), and lower ketones. The reaction was mass transfer controlled and first order with respect to chloramine with an activation energy and frequency factor of 5.67 kcal/gmol and 4.61 s^?1 respectively. The stirred cell model due to Gal-Or and Resnick represented the experimental data with an average absolute deviation of 5.3%.     

A comprehensive model of nitrogen-free ordered carbon quantum dots

We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen contents in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp²-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp²-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp²-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.     

A comprehensive thermodynamic model for high salinity produced waters

Reuse of produced waters in oil and gas production is a major concern due to high treatment cost and regulations on disposal in the environment. To support development of separation techniques and process innovations, we report a comprehensive thermodynamic model for the aqueous hexary system of Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, and SO₄²⁻, the major ionic species present in high salinity produced waters. Based on the electrolyte NRTL theory, the model accurately calculates thermodynamic and phase equilibrium properties with two binary interaction parameters per water-electrolyte pair and electrolyte-electrolyte pair sharing a common ion. This article presents the methodology to identify the binary interaction parameters from literature data and the model results for wide varieties of thermodynamic and phase equilibrium properties including salt solubility for selected binary, ternary, quaternary, and quinary subsystems. The model is validated with the electrolyte concentrations up to salt saturation and temperatures from 273 to 473 K.     

A comprehensive CFD model of anode-supported solid oxide fuel cells

The two-dimensional comprehensive CFD model of anode-supported SOFCs operating at intermediate temperature has been presented. This model provides transport phenomena of gas species with electrochemical characteristics and micro-structural properties, and predicts SOFC performance. The mathematical model solves conservation of electrons and ions, continuity equation, conservation of momentum, conservation of mass, and conservation of energy. A continuum micro-scale model based on statistical properties together with a mole-based conservation model was employed. CFD technique was used to solve the set of governing equations. The cell performance was decomposed with contributions of each overpotential and was presented at several operating temperatures with analysis of effective diffusivity. It was found that the contribution of potential gain due to temperature rising was considerably high. However it became non-significant at high operating temperature due to decreasing of effective diffusivity in AFL. These results showed that the performance and the distributions of current density, overpotentials, and mole fractions of gas species have a strong dependence upon temperature. From these results, it was concluded that the conservation of energy should be accommodated in comprehensive SOFC model. Also the useful information for the effect of parameters on cell performance and transport phenomena was provided.     

PET synthesis in the presence of lanthanide catalysts

Syntheses of poly(ethylene terephthalate), PET, by transesterification of dimethyl terephthalate with ethylene glycol in the presence of well-known catalysts and various lanthanide compounds were performed. Lanthanide catalysts appeared to be much more efficient in the first stage of the process (transesterification in the presence of an excess of ethylene glycol), and less active in polycondensation. PET produced with lanthanides was found to possess enhanced thermal and hydrolytic stability as compared to PET synthesized with well-known catalysts and commercial PET. © 1995 John Wiley & Sons, Inc.     

A comprehensive phenomenological model for erosion of materials in jet flow

A phenomenological erosion model, which captures the effects of impingement velocity, angle, particle size, properties of target, has been developed. The model incorporates removal of material due to both deformation damage and cutting. For the cutting removal, the volume loss has a power-law relation with particle's impingement velocity, angle, mass and size and the exponents depend on the particle's shape (cutting ways). Two critical cases, line cutting and area cutting, indicate that the range of the exponent of impingement velocity is 2∼2.75 which is consistent with the experimental findings. For deformation damage removal, the model indicates that the exponent of the particle's mass is independent on the target material, while the exponents of particle's impingement angle, velocity and density depend on the properties of target material. To validate the model, the simplified version of the model was applied to predict erosion rates, impingement angle where the maximum weight loss occurs and particle size effect. The predictions are in good agreement with the experiments conducted by Finnie. Such models could be used locally together with CFD models to predict erosion and wear patterns under varying flow scenarios.     

Microwave energy application to combustion synthesis: A comprehensive review of recent advancements and most promising perspectives

Microwave heating fundamentally differs from other heating techniques as the consequence of its unique characteristic of being based on the electromagnetic energy transfer from the microwaves source to the interacting material, which according to its electric, dielectric, and magnetic properties can convert the absorbed energy into heat. This peculiar heating mechanism is at the basis of plenty of unquestionable advantages that were reported during the last three decades in most of the different branches of chemistry as well as materials science, thus including also combustion synthesis. After a brief overview of the microwave heating fundamentals as well as of the different components constituting the scientific microwave applicators, all the most significant and recent advancements in the use of microwaves as energy source in both solid-state as well as solution combustion synthesis processes will be comprehensively reviewed, highlighting the unique opportunities arising from the coupling of these two energy efficient techniques. Moreover the possible employment of less conventional frequencies as well as the use of new-generation solid state generators will be critically discussed also in the framework of scaling-up and microwave reactor design considerations.     

PET固相缩聚反应器动态模型

PET固相缩聚过程涉及反应固体颗粒和反应器床层两个空间尺度的传质,是一个复杂的多维多相对象。以反应过程控制为目标,在已有的反应动力学模型基础上,同时考虑可逆化学反应和小分子产物内外扩散两个控制因素,并借用固定床拟均相模型的建模思想,将小分子产物在颗粒内外扩散形成的浓度梯度用一个有效系数来表示,从而建立了简化的PET固相缩聚反应器一维动态模型。在相关文献的实验条件下求解分布参数模型的数值解,并进行启动过程仿真和过程动态分析,计算反应器出口质量指标,与文献曲线和数据对照,验证了模型的正确性。     

新型两釜PET装置

介绍了惠通新型的两釜PET技术,对新型酯化/预缩聚反应器的工艺及设备结构做重点说明。对新型两釜装置的特点进行了总结。