搅拌床中甲基氯化铝法甲基三氯硅烷转化反应

针对“直接法”合成二甲基二氯硅烷过程中产生的副产物甲基三氯硅烷（M₁）,在搅拌床反应器中,对甲基氯化铝法甲基三氯硅烷气固相转化反应进行了系统研究.结果表明,该反应经历了约100 min的诱导期后,产物组成趋于稳定.机械搅拌促进了铝粉表面氧化膜的去除和表面更新,使得转化反应无须外加催化剂.提高搅拌速度和反应温度有利于转化反应程度的提高,但存在一个最佳值.原料组成MeCl/M₁摩尔比（m）对转化反应的进行程度和产物组成影响较大,当m＜2.0时,M₁转化率较低,转化产物主要为二甲基二氯硅烷（M₂）和三甲基氯硅烷（M₃）;当m＝2.0时,产物主要为M₃;当m＞2.0时,M₁转化率较高,主要产物为四甲基硅烷（M₄）.采用SEM对反应前后Al粉粒子表面形态进行了表征,探讨了该气固相转化反应的机理和历程.     

一种基于Zn/ZnO的新型煤气化系统理论能效分析及其环境性能评估

本文以基于Zn/ZnO的两步式热化学循环为基础构建了一种新型的煤气化系统。该系统流程主要由两步构成：首先煤与ZnO在高温下发生吸热反应,气化生成CO气体和锌蒸汽。锌蒸气经冷凝后自动从混合气体产物中分离出来被送入下一步反应中与水发生放热反应,生成氢气和ZnO固体。ZnO又可被回收进行第一步反应。本文在设计第一步反应供热系统时分别考虑了煤部分氧化自热和太阳能加热两种方式,并对基于这两种加热方式的新型煤气化系统分别进行了理论能效评估和环境性能评估。评估结果显示：自热式煤气化系统的理想热效率和火用效率分别达到了89％和80％;而按现有太阳能加热系统的热效率计算,太阳能加热式煤气化系统的整体理想热效率和火用效率最高分别可以达到67％和66％。从环境性能上来看,太阳能加热式煤气化系统远远优于自热式系统,前者的CHR（产CO与产H2比）不到后者的1/6。     

Fabrication of Dense Lithium Fluoride for Neutron Shielding

Polycrystalline LiF suitable for use as a thermal neutron shielding material was fabricated by both hot-pressing and pressureless sintering to greater than 99.5% theoretical density. To achieve this, the poorly sinterable as-received LiF powder had to be (a) ball-milled to reduce particle size, (b) calcined to substantially remove porosity from the cubic particles, and (c) ball-milled again to break up agglomerates formed during calcination.     

Computational fluid dynamic modeling of a chemical vapor synthesis process for aluminum nanopowder as a hydrogen storage precursor

A chemical vapor synthesis (CVS) process for synthesizing nano-sized aluminum powder as a precursor for various hydrogen storage materials was simulated by the use of computational fluid dynamic modeling. The fluid flow, heat transfer and chemical reaction phenomena taking place inside the reactor were analyzed together with particle formation and growth in the CVS process. The temperature, velocity and particle size distribution fields inside the reactor were computed. Chemical reaction rate and population balance model were used to calculate the particle formation and growth. The particle size computed by the program was compared with the experimental data, and the calculated average size of the final product particles was consistent with those obtained in the experimental work.     

气固错流移动床高温煤气脱硫过程模拟

在合理假设的基础上，考虑过程的传质和传热，建立了气固错流移动床反应器的数学模型，并采用数值模拟计算方法分析了过程的操作特点．结果表明，由于气固错流接触的特点，气固反应区沿颗粒移动方向逐渐向气体出口侧偏移，在竖直截面上气体浓度存在较大的差异，固体颗粒出口处脱硫剂转化率呈一定的分布．能量衡算表明，反应区温度变化不大，即使考虑到脱硫剂颗粒温度变化，也不会对反应造成太大的影响．在保证高脱硫率的基础上，减小出口脱硫剂转化率分布，提高脱硫剂利用率是反应器优化的关键．     

Comparison of the performance of a direct-contact bubble reactor and an indirectly heated tubular reactor for solar-aided methane dry reforming employing molten salt

A theoretical approach is presented for the comparison of two different atmospheric pressure reactors—a direct-contact bubble reactor (DCBR) and an indirectly heated tubular reactor (IHTR)—to evaluate the reactor performance in terms of heat transfer and available catalytic active surface area. The model considers the catalytic endothermic reactions of methane dry reforming that proceeds in both reactors by employing molten salts at elevated temperatures (700–900 °C) in the absence of catalyst deactivation effects. The methane conversion process is simulated for a single reactor using both a reaction kinetics model and a heat transfer model. A well-tested reaction kinetics model, which showed an acceptable agreement with the empirical observations, was implemented to describe the methane dry reforming. In DCBR, the heat is internally transferred by direct contact with the three phases of the system: the reactant gas bubbles, the heat carrier molten salts and the solid catalyst (Ni-Al₂O₃). In contrast, the supplied heat in the conventional shell-and-tube heat exchanger of the IHTR is transferred across an intervening wall. The results suggest a combination system of DCBR and IHTR would be a suitable configuration for process intensification associated with higher thermal efficiency and cost reduction.     

Pressureless Sintering and Reaction Mechanisms of Ti3SiC2 Ceramics

Easy sinterable Ti₃SiC₂ powder was synthesized from a powder mixture with a molar ratio of 1.0 Ti, 0.3 Al, 1.2 Si, and 2.0 TiC by heating at 1200°C in the flowing Ar. Here, the Al powder acts as a deoxidation agent and provides a liquid phase for the reaction. The powder compacts subjected to pressureless sintering at 1300°C in Ar had a relative density up to 99%. The results of chemical analysis and the measured lattice constant suggest that the Al–Si liquid phase was formed at approximately 1200°C and that liquid‐phase sintering was promoted by the 0.1 molar ratio of Al and the 0.2 molar ratio of Si remaining in excess. The three‐point bending strength, fracture toughness, and electrical resistivity of the sintered samples were 380 MPa, 4.1 MPa m^1/2, and 0.34μΩm, respectively.     

Self-Propagating High-Temperature Synthesis of Aluminum Nitride under Lower Nitrogen Pressures

The synthesis of aluminum nitride (AlN) via self-propagating high-temperature synthesis (SHS) was attempted, using aluminum powder that was mixed with AlN powder as a diluent. The AlN content in the reactant was varied over a range of 30%–70%, and the nitrogen pressure was varied over a range of 0.1–1.0 MPa. The SHS reaction that was performed using a reactant that contained 50% AlN diluent, under a nitrogen-gas pressure of 0.8 MPa, yielded the highest conversion ratio of aluminum powder to AlN powder. A mechanism for the reaction of aluminum with nitrogen gas during the SHS process was discussed, based on observations of the microstructures of the reaction zone and products.     

Feedback-Controlled Firing of Reaction-Bonded Aluminum Oxide

The reaction-bonded aluminum oxide (RBAO) process utilizes the oxidation of intensely milled aluminum/alumina powder compacts that are heat treated in air to make alumina-based ceramics. RBAO samples are typically oxidized in a furnace which is heated at 1^°C/min to 1100^°C. Heat-treating samples with a characteristic dimension >1 mm, without adjusting the furnace temperature program, usually results in a cracked ceramic. Cracking is caused by the excessive thermal and chemical stresses that result from steep temperature gradients (>30^°C/mm) and compositional gradients (>5000 mol·(m³·mm)⁻¹), which develop under the deleterious ignition and shrinking core reaction regimes. While adjustments to the furnace temperature program based on continuum models have had some success, the use of feedback-controlled firing is investigated as a means to avoid the furnace temperature program design step and to decrease the firing time. Feedback-controlled firing is shown to improve yields and significantly reduce the time required to completely oxidize the aluminum. For example, a 16 g sample with a characteristic dimension of 7.56 mm, which previously took >100 h to oxidize completely, was successfully oxidized crack free in 18.3 h using feedback control. Using the typical heat-treatment cycle, a 1 mm sample was fired in 18 h. With feedback-controlled firing, the same sized sample was fired in only 5 h.     

碳热还原法合成AIN粉末的径向反应器设计

本文将传质原理与化学反应动力学相结合,导出了氮气流量与碳热还原法合成AIN反应速率之间的关系。基于动量守恒定律分析了径向反应器内部气体压力及其分布的规律,提出了气体在反应器内均匀分布的条件和反应器选型准则。根据这些条件和准则设计了合成AIN粉末的径向反应器。实验结果显示AIN的转化率及颗粒度在径向反应器内均匀分布,且产率高于平底状反应器。这一结果证明反应器设计合理,径向反应器比平底状反应器有更好的传质效果。     

操作参数对余热回收甲醇水蒸气重整制氢过程的影响

以模拟汽车尾气供热的甲醇水蒸气重整（MSR）制氢反应为研究对象,设计了集余热加热与MSR制氢反应于一体的肋式微反应器,考察了反应器进口热风速度、温度,反应物进口速度、温度、水醇比及顺逆流情况对MSR制氢过程的影响。计算结果表明,逆流、水醇比1.3、热风进口速度1.1 m/s、温度773 K、反应物进口速度0.1 m/s、温度493 K为该反应过程的最佳工况参数,此时甲醇转化率为99.4%,模拟汽车尾气余热的热效率为28%,反应器出口氢气的体积分数为69.6%。研究结果对开展余热综合利用及发动机尾气重整制氢掺氢燃烧的研究有借鉴意义。     

板翅式反应器中甲醇水蒸气重整制氢

研制了一种高效板翅式反应器,其特点是体积相对较小,便于放置,便于扩大规模;集预热、气化、重整、催化燃烧于一体;板翅式反应器内部热量利用合理,放热反应与吸热反应、气化与冷却之间实现了较好的热量耦合;可实现完全自供热.在反应器中进行了一系列甲醇水蒸气重整的实验,考察了不同条件对甲醇重整制氢过程的影响、对反应器床层温度分布的影响,及反应器的稳定性.另外,由于板翅式结构的良好传热性,甲醇水蒸气重整在获得较高转化率的同时重整气中CO浓度较低,且反应器的稳定性良好.     

A case study for reactor network synthesis: the vinyl chloride process

A key objective of the integrated reactor network synthesis approach is the development of waste minimizing process flowsheets (Lakshmanan & Biegler, 1995). With increasing environmental concerns in process design, there is a particularly strong need to maximize conversion to product and avoid generation of wasteful byproducts within the reactor network. This also avoids expensive treatment and separation costs downstream in the process. In this study, we present an application of the mixed integer nonlinear programming (MINLP)-based reactor network synthesis strategy developed by Lakshmanan and Biegler (1996a). Here we focus on applying these reactor network synthesis concepts to the vinyl chloride monomer production process. Vinyl chloride is currently produced by a balanced production process from ethylene, chlorine and oxygen with three separate reaction sections: oxychlorination of ethylene; direct chlorination of ethylene; and pyrolysis of ethylene dichloride. The hydrogen chloride produced in the pyrolysis reactor is used completely in the oxychlorination reactor. Byproducts such as chlorinated hydrocarbons and carbon oxides are generated by these reaction sections. These are studied using reaction kinetic models for the three reaction sections. The case study results in optimal reactor networks that improve the conversion of ethylene to vinyl chloride and minimize the formation of byproducts. These results are used to generate an improved flowsheet for the production of vinyl chloride monomer. Moreover, an overall profit maximization, that includes the effect of heat integration, is presented and a set of recommendations that improve the selectivity of vinyl chloride production are outlined. Finally, the optimal reactor structures, overall conversion and annual profit are shown to be only mildly sensitive with respect to small changes in the kinetic parameters.     

Kinetic model‐aided reactor design for peroxidase‐catalyzed removal of phenol in the presence of polyethylene glycol

A batch‐mixed reactor and a plug‐flow reactor were shown to have identical reaction kinetics for peroxidase‐catalyzed removal of phenol. Semi‐batch operation and step‐addition operation of the plug‐flow reactor with respect to hydrogen peroxide produced similar output. In the presence of polyethylene glycol, a continuous stirred tank reactor needed a long time to complete the reaction at the minimum enzyme dose. It was not necessary to stir the reaction mixture continuously during the reaction, hence polymerization and settling of products happened simultaneously. Recycling of the precipitates was not beneficial either for the removal efficiency or for the operation of a settling tank. A model previously developed to simulate the reaction in a batch reactor was used to predict the process in different types of reactor system. A plug‐flow reactor system is recommended for the reaction in the presence of polyethylene glycol; the system consisting of a small mixing tank followed by a tank in which reaction and settling occur simultaneously. © 1999 Society of Chemical Industry     

Calorimetric determination of polymerisation conversion in a large laboratory reactor

A calorimetric measuring system for continuous recording of rate of reaction and conversion in a 14 1 polymerisation reactor has been developed. The reactor was jacketed and thermostated with circulating water. The measuring signals to the calculating unit represented the temperature difference between inlet and outlet water, the water flow and the heat losse from reactor to the environment. The measuring system was constructed to calculate correctly the conversion even if the heat losses to the environment changes during the reaction. The applicability of the reactor system was demonstrated by its use in suspension polymerisation of vinyl chloride.     

三氯化磷生产工艺的优化

对三氯化磷生产工艺进行了改进：在不停车的情况下,依据黄磷与氯气反应和黄磷与五氯化磷反应时温度与压力的不同变化判断氯化釜内的底磷量;液氯汽化设备由用热水加热的汽化罐改为用蒸汽加热的套管式汽化器;精馏塔中的列管式换热器改为布液器,夹套式冷却器改为喷淋式冷凝器;压磷泵投磷改为水压式投磷等。进行这些工艺优化后,三氯化磷的生产能力由250t／月提高到350t／月以上,产品质量等级由合格品提升到优等品,设备的使用寿命延长,液氯汽化速度加快,换热效率提高,消除了三氯化氮富集爆炸的隐患,提高了生产系统的安全系数,改善了生产环境,节约了动力电和维修费。     

Sialon／SiC复相材料研究进展

根据相图，合成Ｓｉａｌｏｎ相的技术途径包括采用Ｓｉ３Ｎ４粉末和其它反应添加物以无压或热压工艺高温合成，或以Ｓｉ粉与其它金属及其氧化物为原料无压反应烧成而成，ｉａｌｏｎ粉末也可通过粘土类矿物的碳热还原反应来合成，但前两种技术作乱在原料及合成工艺上的高成本使其难于在耐火材料领域大规模开发应用，后一种工艺目前仅见到合成Ｓｉａｌｏｎ粉末的试验报道，本研究在对粘土类矿物合成Ｓｉｌａｏｎ粉末的研究基础上，由廉     

Controlling Thermophoresis in the Exothermic Nitridation of an Aluminum Aerosol

Thermophoretic deposition in an exothermic aluminum (AI) nitridation aerosol process was redirected from the reactor wall to a flowing inert powder when the inert powder was admixed with the feed atomized AI. The inert powder can be a compatible (aluminum nitride) or removable (carbon) powder, which provides for a lower-temperature surface to be in close proximity to the exothermic reaction sites. Aluminum nitride manufactured by this process was pressurelessly sintered with 3 wt% Y₂O₃ to fabricate dense AIN parts exhibiting high thermal conductivity (141 W/m – K).     

Novel SiC synthesis method applicable to SiC solid phase sintering

Most of the present production processes of SiC sintered bodies require some powder mixing using a mechanical milling process (ball milling, and so on). In this case, relatively long hours are required, and there is the problem of contamination during the preparation process. To avoid these problems, we developed a new process for obtaining a self-sinterable, stoichiometric SiC powder, whose precursor material is water-soluble; the precursor material was synthesized from aqueous silica and citric acid containing a small amount of aluminum compound. In order to obtain the stoichiometric SiC composition, the above aqueous precursor material was adequately cured in air (200°C-400°C); subsequently carbonization reaction (~800°C) in nitrogen atmosphere, carbothermal reduction (~1600°C) in argon atmosphere, and pressureless sintering (~1900°C) were performed. Among these processes, the curing process (cross-linking process) is very important for obtaining the equivalent composition (silica and carbon) for the subsequent carbothermal reduction. In this study, the adequate curing temperature and suitable preparation condition for the carbothermal reduction were investigated for the production of stoichiometric self-sinterable SiC powder. The pressureless sintered body achieved using the obtained SiC powder demonstrated a desirable trans-crystalline fracture behavior.     

Kinetics and Mechanisms for Nitridation of Floating Aluminum Powder

Aluminum powder entrained by ammonia-containing nitrogen gas was reacted at various temperatures and time to form aluminum nitride powder. The kinetics of nitride formation were determined by a quantitative X-ray analysis and compared with those determined by a nitrogen analysis of the product. The conversion to aluminum nitride increased with the reaction time following a sigmoidal rate law. The reaction time for full conversion decreased as the temperature increased in the range 1050°–1300°C. The reaction rate constant at a given temperature was evaluated using the Avrami equation. The activation energy for the reaction was 1054 ± 91 kJ/mol in the temperature range of 1050°–1200°C, and decreased to 322 ± 70 kJ/mol above 1200°C. Comparative analysis of powders formed below and above 1200°C suggested strongly that the rate-controlling step changed from chemical reaction to mass transport above 1200°C.