Study on reaction magnitude of solid reactive spray tray

用强酸型阳离子交换树脂作催化剂,以乙醇和乙酸催化反应生成乙酸乙酯为研究对象,对立体催化精馏塔板的反应量进行了系统的实验研究。考察了催化剂高度、醇酸摩尔比、流速对反应量的影响,并关联得到了反应量的经验式。基于反应量的经验公式与质量守恒定律,建立了塔板上液相中乙酸乙酯质量分数的模型,并通过对工业试验塔板上反应量的测量对模型进行了验证。     

质子交换膜燃料电池阴极催化剂的位置效应

考虑局部几何效应,通过二维稳态数学模型研究了质子交换膜燃料电池阴极催化剂的位置与其表面传质和反应能力的关系。模型方程涉及氧气在催化层气孔的传输,氧气在气相和电解质相界面的分配以及氧气和质子在电解质中的传递和电化学反应过程。计算结果表明,催化剂表面的氧气扩散能力对催化剂的位置变化非常敏感,随催化剂深入电解质内部,其表面的氧气扩散能力经短暂上升后迅速下降。催化剂位置对质子传递阻力的影响与氧气扩散类似,但位置效应要弱些。性能比较确定最优的催化剂位置是恰好处于刚被电解质膜完全覆盖的位置。     

Biphasic synthesis of α-Tetralone using nickel complex catalysts

Organic-water interfacial autoxidation of tetralin was investigated using surface-active ligand complexes of transition metals (Cr, Ni, Mn, and Co) as catalysts, tetralin as the substrate and organic phase, and dodecyl sodium sulfate as an emulsifier. The major products formed under the experimental conditions of 60°C and 1 atm were α-tetralone and α-tetralol, and the highest selectivity of 71 % to the desired product a-tetralone was achieved with nickel-tetraethylenepentamine complex. The optimum ligand to catalyst ratio was established to be 2:1 for the improved reaction rate and phase separation. The organic-water phase volume ratio around which the maximum reaction rate was attained was 2:1. The reaction order with respect to oxygen shifted from first to zero as its partial pressure increased, and the reaction order with respect to nickel catalyst concentration varied from 1.7 to 1, and subsequently to with further increases in the metal concentration.     

Electrochemical reaction engineering of polymer electrolyte fuel cell

Although fuel cells can be considered as a type of reactor, methods of kinetic analysis and reactor modeling from the viewpoint of chemical reaction engineering have not yet been established. The rate of an electrochemical reaction is a function of concentration, temperature, and interfacial potential difference (or electromotive force). This study examined the cathode reaction in a polymer electrolyte fuel cell, in which oxygen and protons react over platinum in the catalyst layer (CL). The effects of the oxygen partial pressure and the cathode electromotive force on the reaction rate were assessed. Resistance to proton transport increases the electromotive force and reducing the reaction rate. It was established that the effectiveness factor of the cathode CL is determined by competition between the reaction and mass transport of oxygen and protons. Two dimensionless moduli that govern the cathode behavior are proposed as a means of depicting the processes in the cell. © 2016 American Institute of Chemical Engineers AIChE J, 63: 249–256, 2017     

Catalytic Liquid Phase Oxidation of Toluene to Benzoic Acid

The production of benzoic acid from toluene in the liquid phase with pure oxygen was studied. Investigations have been carried out with a view to determining the most suitable reaction conditions with respect to operating variables including oxygen flow rate, reaction temperature, batch time and catalyst loading. In a series of batch experiments carried out at 4 atm, the optimum values of mole ratio of oxygen to toluene, temperature, reaction time, and catalyst loading were found to be 2, 157 °C, 2 h and 0.57 g/L, respectively. In addition, a kinetic study was carried out by taking into consideration the optimum reaction conditions. The model dependent on the formation of benzyl radical was found to be feasible for describing the catalytic oxidation of toluene to benzoic acid in the liquid phase. The activation energy was determined as 40 kJ/mol.     

Modeling the photocatalytic degradation of formic acid in a reactor with immobilized catalyst

A kinetic model for the photocatalytic degradation of formic acid in an immobilized system is presented, including the dependency of the reaction rate on the concentration of formic acid and oxygen, the catalyst layer thickness and the light flux. In the system some external mass transfer limitation occurs which is included in the modeling with experimentally determined values for the mass transfer coefficient of both formic acid and oxygen. The model describes the measurements well. The degradation rate appears to depend linearly on the light intensity. The adsorption of formic acid and oxygen on the catalyst layer appears to play an important role in the degradation rate.     

瞬变应答法研究苯催化氧化的反应机理

采用瞬变应答法研究了苯在钒催化剂上催化氧化的反应机理。通过对应答曲线的分析,证明氧首先被催化剂表面吸附,然后以较慢的速率转化为晶格氧,这一步是苯催化氧反应速率的控制步骤。吸附氧是生成 CO 和 CO_2的氧源;晶格氧是生成顺酐的氧源。气相苯不直接参与反应,但以较快的速率可逆吸附于催化剂上,吸附的苯与晶格氧反应生成中间物 IN,IN 进一步氧化生成顺酐。顺酐可逆吸附于催化剂上,其介吸速率较慢。中间物和吸附的顺酐对反应起阻滞作用。     

在改性HZSM-5和氧气气氛下氧化二苯并噻吩

以氧气为氧化剂,使用14种金属离子改性的HZSM-5为催化剂,对含二苯并噻吩(DBT)的模型硫化物进行氧化脱硫实验,筛选最佳催化剂,并考察了最佳催化剂的金属负载量、催化剂用量、反应温度、氧气流速、反应时间对二苯并噻吩转化率的影响。实验结果表明,经钨原子改性的HZSM-5活性最好。最佳反应条件为:以WO3/HZSM-5(W原子质量分数为8%)为催化剂,反应温度90℃,氧气流速100 mL/min,反应时间5 h时,DBT转化率可达100%。催化剂经离心分离、干燥、煅烧后循环使用5次,活性没有明显下降。     

Kinetics of thermal oxidation of polyolefins—A review

The kinetics of uncatalyzed autoxidations for polyolefin films, such as atactic and isotactic polypropylene and poly-(butene-1) are reviewed in light of recent work. Reaction temperatures generally varied from 100 to 150°C and oxygen concentrations from 5 to 100% by volume. A general reaction scheme is suggested and kinetic expressions subsequently derived therefrom have been satisfactorily applied to account for experimental results. Linear relationships between a maximum rate and concentration of oxygen for both low and high concentrations were obtained. In the case of the catalyzed autoxidations [Co(III) acetylacetonate] the general reaction scheme was modified to take into account the presence of the catalyst. From this modified scheme, various kinetic expressions relating maximum rate and concentrations of oxygen, polymer and the catalyst were derived. First-order reaction with respect to the concentration of the catalyst was found at low concentrations of the catalyst, and near zero-order at relatively high catalyst concentrations. A correlation between catalytic activities of metal acetylacetonates [Co(III), Mn(III), Cr(III), Fe(III) and Cu(II)] and the oxidation-reduction potentials has been established. Experimental dependencies of maximum carbonyl formation rates as a function of polymer concentration were found to agree well with the theoretical both for catalyzed and uncatalyzed oxidations.     

磷钨酸烷基甜菜碱催化氧化燃料油脱硫的性能

以磷钨酸烷基甜菜碱为相转移催化剂,双氧水为氧化剂,在乳液体系下,催化氧化脱除燃料油中的硫化物,研究了磷钨酸十四烷基二甲基甜菜碱、磷钨酸十六烷基二甲基甜菜碱以及磷钨酸十八烷基二甲基甜菜碱的催化性能,考察了催化剂用量、制乳时间、制乳转速以及氧硫比对脱硫效果的影响。结果表明,烷基甜菜碱的烷基链越长,催化效果越好;在催化剂的用量为0.003（剂油比）、制乳时间8min、制乳转速2500r/min、氧硫比为11的条件下,脱硫率可达到91.23%。     

Electrochemical promotion of catalysis controlled by chemical potential difference across a mixed ionic-electronic conducting ceramic membrane – an example of wireless NEMCA

A La_0.6Sr_0.4Co_0.2F_0.8O₃ mixed ionic electronic conducting (MIEC) membrane was used in a dual chamber reactor for the promotion of the catalytic activity of a platinum catalyst for ethylene oxidation. By controlling the oxygen chemical potential difference across the membrane, a driving force for oxygen ions to migrate across the membrane and backspillover onto the catalyst surface is established. The reaction is then promoted by the formation of a double layer of oxide anions on the catalyst surface. The electronic conductivity of the membrane material eliminates the need for an external circuit to pump the promoting oxide ion species through the membrane and onto the catalyst surface. This renders this “wireless” system simpler and more amenable for large-scale practical application. Preliminary experiments show that the reaction rate of ethylene oxidation can indeed be promoted by almost one order of magnitude upon exposure to an oxygen atmosphere on the sweep side of the membrane reactor, and thus inducing an oxygen chemical potential difference across the membrane, as compared to the rate under an inert sweep gas. Moreover, the rate does not return to its initial unpromoted value upon cessation of the oxygen flow on the sweep side, but remains permanently promoted. A number of comparisons are drawn between the classical electrochemical promotion that utilises an external circuit and the “wireless” system that utilises chemical potential differences. In addition a ‚surface oxygen capture’ model is proposed to explain the permanent promotion of the catalyst activity.     

Modelling the mode of operation of PEMFC electrodes at the particle level: influence of ohmic drop within the active layer on electrode performance

Numerical modelling of charge transfer using the finite element method within the whole active layer of proton exchange membrane fuel cell (PEMFC) electrodes is proposed in order to study the electrocatalyst utilization as characterized by the effectiveness factor. In this way, two modified approaches based on the thin film and agglomerate models are developed for studying ionic ohmic drop effects in the active layer at both the electrolyte layer and electrocatalyst particles scales. The catalyst phase is considered to be a network of spherical nanoparticles instead of the classical representation as a uniform distribution over a surface (thin film model) or in a volume (agglomerate model). Simulations point out unexpected effects at the local level due to the discrete distribution of the catalyst phase as nanoparticles. Finally, the results are applied to the practical case of oxygen reduction and hydrogen oxidation.     

乙醇在Pt/ZSM-5上催化氧化动力学

在内径为4 mm的石英管燃烧器中进行了富氧条件下乙醇在Pt/ZSM-5上的催化深度氧化动力学实验,反应温度控制在428 K以下,建立了Power-rate law模型和Langmuir-Hinshelwood模型来表征乙醇的低温深度氧化反应,Power-rate law模型和Langmuir-Hinshelwood模型的活化能分别为95.96和103.72 kJ·mol^-1,乙醇和氧气的反应级数分别为0.38和1.38。Langmuir-Hinshelwood模型中,乙醇的吸附常数比氧气的吸附常数大,说明乙醇在催化剂表面的吸附能力比氧气强,提高氧气的浓度比提高乙醇的浓度更有利于提高反应速率,这一点同样反映在氧气的反应级数比乙醇的反应级数大。     

Modeling nanostructured catalyst layer in PEMFC and catalyst utilization

A lattice model of the nanoscaled catalyst layer structure in proton exchange membrane fuel cells (PEMFC) was established by Monte Carlo method. The model takes into account all the four components in a typical PEMFC catalyst layer: platinum (Pt), carbon, ionomer and pore. The elemental voxels in the lattice were set fine enough so that each average sized Pt particulate in Pt/C catalyst can be represented. Catalyst utilization in the modeled catalyst layer was calculated by counting up the number of facets of Pt voxels where “three phase contact” are met. The effects of some factors, including porosity, ionomer content, Pt/C particle size and Pt weight percentage in the Pt/C catalyst, on catalyst utilization were investigated and discussed.     

无外界氧补偿条件下乳状液中多不饱和脂肪酸氧化模型

建立了在无外界氧补偿条件下乳状液中多不饱和脂肪酸(PUFA)氧化的数学模型。该模型综合考虑了乳化剂形成的液膜边界层阻力、PUFA自催化氧化反应以及油水相比表面积等因素的影响。实验验证了该模型能较好地拟合无外界氧补偿条件下乳状液中氧的扩散和亚油酸的氧化过程,并模拟计算了乳化剂膜传质系数和油水相比表面积等因素对扩散-氧化的影响程度。结果表明,乳化剂膜传质系数和油水相比表面积是影响乳状液中PUFA的氧化的主要因素。     

Synthesis of bis(2-butoxyethyl) sebacate catalyzed by HZSM-5

以癸二酸和乙二醇单丁醚为原料,用HZSM-5分子筛催化合成环保耐寒性增塑剂癸二酸二丁氧基乙酯。考察了催化剂的硅铝比、催化剂用量、带水剂用量、原料配比、反应时间对酯化率的影响。最佳工艺条件为：醇酸摩尔比为2.5∶1,催化剂用量为酸质量的5%,带水剂用量为酸质量的15%,反应时间为3.5 h,反应温度为170～200 ℃,该工艺条件下酯化率可达91.91%。经过5次使用后,酯化率仍在90%以上。同时建立了该酯化合成的表观动力学模型,得到反应速率方程为： 。     

Process intensification and waste minimization in liquid–liquid–liquid phase transfer catalyzed selective synthesis of mandelic acid

Conversion of biphasic reactions into triphasic reactions can lead to process intensification, waste minimization and selectivity enhancement. Unlike liquid–liquid (L–L) PTC, the Liquid–Liquid–Liquid phase transfer catalysis (L–L–L PTC) offers high order of intensification of rates of reaction and catalyst reuse. The rate of reaction is remarkably enhanced by the catalyst-rich middle phase, which is the main reaction phase. Separation of catalyst can be done easily and the separated catalyst can be reused several times by using L–L–L PTC. This leads to waste minimization and other benefits of Green Chemistry. Mandelic acid and its derivatives are used for their dual activities as antibacterial and anti-aging agents. In this work, mandelic acid was produced by L–L–L PTC reaction of dichlorocarbene with benzaldehyde. Dichlorocarbene was generated in situ by the reaction of chloroform and sodium hydroxide in the presence of poly ethylene glycol (PEG) 4000 as the catalyst. The selectivity to mandelic acid was 98%. The reaction mechanism and kinetics model were established to validate the experimental data.     

Dissolved oxygen removal by combination with hydrogen using wetproofed catalysts

Dissolved oxygen in water at parts per million levels could be reduced to a few parts per billion by reaction with hydrogen using Pt catalysts supported on carbon and stainless steel in random and structured bed configurations. The carbon supported catalyst was Teflon coated to wetproof it. Both gas phase and liquid phase reactions occurred simultaneously under trickle bed operation, resulting in higher oxygen removal efficiency for this mode of operation than for the liquid-filled condition. The structured catalyst bed yielded greater hydraulic capacity than the random bed, and with wetproofed catalyst it gave the best oxygen removal efficiency. Since the gas phase reaction rate could be increased by reducing the wetted fraction of the catalyst through wetproofing, wetproofed catalysts offer a unique advantage over conventional hydrophilic catalysts.     

Spatiotemporal patterns in a porous catalyst during light-off and quenching of carbon monoxide oxidation

A detailed numerical model was used to simulate the behavior of carbon monoxide oxidation within a porous platinum/alumina catalyst during temperature ramps. The model was validated in previous work by fitting step-response experiments which were performed over a range of temperatures and in which concentration gradients over the catalyst layer were directly measured. As a result of the low CO and O₂ concentrations used, the catalyst layer could be considered isothermal. The numerical experiments performed with the model in this work reveal complex spatial patterns of species and local reaction rate which change with time and temperature.As temperature is increased, CO desorbs and reaction rapidly increases, reacting adsorbed CO off the Pt surface and producing a peak in CO₂ production during catalyst light-off. Over a nonporous surface of the same material, the reaction rate would be an order-of-magnitude lower and no CO₂ peak would be produced. At steady state after reaction light-off has been obtained, reaction occurs in a narrow zone below the external face of the layer which is exposed to the constant feed gas composition. As temperature is then decreased, the CO₂ production rate decreases gradually as the front of the region covered with adsorbed CO penetrates further and pushes the reaction zone deeper into the catalyst layer. When the adsorbed CO front reaches the internal face, the CO₂ production rate drops abruptly as the reaction “quenches”.Catalyst layer thickness was changed over the range 0.06-1.0 mm at constant total Pt content. As the layer thickness was decreased, the steady-state CO₂ production rate after light-off increased, however the range of temperatures in which the catalyst was active decreased. Three qualitatively different sets of spatiotemporal patterns were obtained as the layer thickness was changed from relatively thin, to medium, to thick. Analysis of the patterns provides understanding of the temperature-dependent behavior of the catalyst and how this behavior varies with catalyst layer thickness.