Facile and Rapid Synthesis of Neopentyl Glycol in a Continuous-Flow Microreactor

Neopentyl glycol (NPG) synthesis by condensation disproportionation of formaldehyde and isobutyraldehyde (IBD) with sodium hydroxide as catalyst was studied in a continuous-flow microreactor under various experimental conditions, such as reaction temperature, residence time, and the molar ratio of reactants. All the conditions were determined by Box-Behnken experimental design and the response surface method based on the preferred range selected by single-factor experiments. For comparison, NPG was synthesized by condensation disproportionation of the same reactants in a batch reactor. The results showed that higher NPG yield and shorter residence time were achieved in a continuous-flow microreactor than in a batch reactor when the other experimental conditions were similar.     

Co-Ni/y-Al2O3催化剂上乙醇催化氨化合成乙腈反应的本征动力学

引言乙腈是一种重要的溶剂和化工原料,广泛用于有机合成、农药、医药、石油化工、表面活性剂以及高分子材料等领域。此外,由于高纯乙腈对紫外线的吸收为零,并且具有独特的物理化学性质,因此,乙腈在高压液相色谱、电化学以及分光光度法分析中作为溶剂广泛使用[1]。目前,工业上主要通     

Hydrodynamics,mass transfer,and photocatalytic phenol selective oxidation reaction kinetics in a fixed TiO2 microreactor

Photocatalytic phenol dissociation was studied in a microreactor, with a TiO₂ layer immobilized on the reactor inner walls. Experiments were conducted for various residence times, initial concentrations, pH values, and UV light irradiation intensities. The intermediates and products (catechol, hydroquinone, and resorcinol) were quantitatively investigated to determine the predominant reaction pathways for the investigated anatase catalyst. A three‐dimensional mathematical model was used to simulate the heterogeneous photocatalysis reaction conditions with Langmuir–Hinshelwood mechanism, considering the adsorption/desorption thermodynamic equilibria, and for kinetic parameter estimation via regression analysis. The effectiveness factor, Thiele modulus, and the correction function were calculated to determine the pore diffusion effects. The value of pH had the dramatic effect of lowering the reaction rate due to the competitive adsorption of hydroxide ions and protons on the catalyst surface. A phenol conversion of 79.5% was achieved at the residence time of 7.22 min, but without total mineralization. © 2014 American Institute of Chemical Engineers AIChE J, 61: 572–581, 2015     

Electrochemical synthesis and corrosion performance of poly(pyrrole-co-o-anisidine)

The electrochemical synthesis of poly(o-anisidine) homopolymer and its copolymerization with pyrrole have been investigated on mild steel. The copolymer films have been synthesized from aqueous oxalic acid solutions containing different ratios of monomer concentrations: pyrrole:o-anisidine, 9:1, 8:2, 6:4, 1:1. The characterization of polymer films were achieved with FT-IR, UV–visible spectroscopy and cyclic voltammetry techniques. The electrochemical synthesis of homogeneous-stable poly(o-anisidine) film with desired thickness was very difficult on steel surface. Therefore its copolymer with pyrrole has been studied to obtain a polymer film, which could be synthesized easily and posses the good physical–chemical properties of anisidine. The kinetics and rate of copolymer film growth were strongly related to monomer feed ratio. The introduction of pyrrole unit into synthesis solution increased the rate of polymerization and the substrate surface became covered with polymer film soon, while this process required longer periods in single o-anisidine containing solution. The protective behavior of coatings has been investigated against steel corrosion in 3.5% NaCl solution. For this aim electrochemical impedance spectroscopy (EIS) and anodic polarization curves were utilized. The synthesized poly(o-anisidine) coating exhibited significant protection efficiency against mild steel corrosion. It was shown that 6:4 ratio of pyrrole and anisidine solution gave the most stable and corrosion protective copolymer coating.     

Experimental, kinetic and 2-D reactor modeling for simulation of the production of hydrogen by the catalytic reforming of concentrated crude ethanol (CRCCE) over a Ni-based commercial catalyst in a packed-bed tubular reactor

Mechanistic kinetic models were formulated based on Langmuir-Hinshelwood-Hougen-Watson and Eley-Rideal approaches to describe the kinetics of hydrogen production by the catalytic reforming of concentrated crude ethanol over a Ni-based commercial catalyst at atmospheric pressure, temperature range of 673-863 K, ratio of weight of catalyst to the molar rate of crude ethanol 3472-34722 kg cat s/kmol crude in a stainless steel packed bed tubular microreactor. One of the models yielded an excellent degree of correlation, and was selected for the simulation of the reforming process which used a pseudo-homogeneous numerical model consisting of coupled material and energy balance equations with reaction. The model was solved using finite elements method without neglecting the axial dispersion term. The crude ethanol conversion predicted by the model was in good agreement with the experimental data (AAD%=4.28). Also, the predicted concentration and temperature profiles for the process in the radial direction indicate that the assumption of plug flow isothermal behavior is justified within certain reactor configurations. However, the axial dispersion term still contributed to the results, and thus, cannot be neglected.     

Kinetic Investigation of the Heterogeneous Synthesis of Flavanone over MgO

The synthesis of flavanone was studied over a magnesium oxide solid catalyst in a batch reactor. The reaction scheme consists of the Claisen–Schmidt condensation of 2'-hydroxyacetophenone with benzaldehyde towards the formation of a 2'-hydroxychalcone intermediate and the subsequent isomerization of this intermediate to flavanone. An initial parametric study yielded a range of values for key experimental parameters (i.e., catalyst particle size and weight percentage and stirring rate) for which the batch reactor system operates in the kinetic regime. The kinetic investigation that followed indicates that over the MgO catalyst studied the Claisen–Schmidt condensation reaction follows first-order kinetics in 2-hydroxyacetophenone and half-order kinetics in benzaldehyde, while the 2'-hydroxychalcone isomerization follows first-order kinetics; activation energies of 40 and 48 kJ/mol were obtained for the two reactions, respectively.     

MeOH to DME in bubbling fluidized bed: Experimental and modelling

Methanol dehydration over a ZSM‐5 containing catalyst was studied in a fluidized bed reactor. At temperatures ranging from 250 to 325°C, methanol conversion varied from 30% at a contact times of 0.14 s and approached 100% of the equilibrium conversion at a contact time starting from 10 s. Sequential and parallel reactions were negligible at low temperatures while hydrocarbon formation became appreciable at 325°C. Online gas analysis by mass spectrometry provided real‐time measurements at a frequency of 4.4 Hz that allowed for fast determination of steady‐state conditions. Gas phase residence time distribution (RTD) measurements indicated that axial dispersion was essentially negligible at short contact times with a shallow bed of catalyst. With longer residence times, the flow pattern could be approximated by six continuously stirred‐tank reactors (CSTR) in series. Both the simple 1D hydrodynamic model and a detailed multi‐zone fluidized model were used to interpret the experimental data to derive a kinetic expression for the dehydration of methanol to di‐methyl ether (DME). The expression includes the reverse reaction that is most often neglected in the literature. The reaction data were best fit with the kinetics based on the 1D model. The fluidized bed is a viable reactor type for kinetic measurements of highly exothermic reactions where hotspots and radial and axial temperature gradients are problematic in fixed beds.     

Heterogeneous Photocatalysis in Microreactors for Efficient Reduction of Nitrobenzene to Aniline: Mechanisms and Energy Efficiency

Aniline was synthesized from nitrobenzene through photo‐induced reduction in microreactors under UV irradiation. Nitrobenzene solution and the nanofluid prepared by a TiO₂ nanocatalyst, PEG‐400, and deionized water were mixed in a capillary microreactor. The effects of catalyst composition, residence time, and substrate concentration on the reaction performance were systematically investigated. The conversion of nitrobenzene and the yield of aniline reached high values under optimized conditions. The excellent reusability of the photocatalyst was realized for four runs. A mechanism was proposed for this photocatalytic reduction process based on reaction kinetics. Both photo‐induced electrons and ^?CO₂^? could reduce nitrobenzene to aniline. The photonic efficiency in the microreactor was still much higher than that obtained in batch reactors, which was mainly attributed to the much larger effective radiation area of the microreactor.     

A kinetic approach to catalytic pyrolysis of tars

A kinetic model to describe the catalytic pyrolysis of tars is proposed and validated through the experimental pyrolysis of three tars of different characteristics and origin; calcined limestone (11 m²/g) was used as catalyst. Experiments were carried out in a catalytic fixed bed reactor. The model assumes that tars are composed of two pseudo-components, described as heavy and light tars, which can be experimentally determined by a split temperature. Tar pyrolysis is described by two simultaneous chemical reactions; catalyst deactivation due to carbon deposition is also considered. Expressions for product concentrations as functions of residence time, selectivity and deactivation were obtained and the kinetic parameters evaluated.     

Kinetic study of hydrogen peroxide decomposition at high temperatures and concentrations in two capillary microreactors

On the background of the direct adipic acid synthesis from cyclohexene and H₂O₂, a kinetic model was derived for the H₂O₂ decomposition catalyzed by sodium tungstate at high H₂O₂ concentrations and high temperatures. A perfluoroalkoxy (PFA) and a stainless steel micro‐flow capillary match commonly used microreactor materials. In the PFA capillary, the decomposition of hydrogen peroxide increased with residence time, reaction temperature and catalyst loading. The reaction order with respect to hydrogen peroxide and sodium tungstate was zero and one, respectively. Simulated data fit well with experimental data in the PFA capillary. While showing a similar trend as that in the PFA capillary, the stainless steel capillary exhibited much higher reaction rates. The steel surface participated in the decomposition process as a heterogeneous catalyst. Key influencing factors of the H₂O₂ decomposition provided some clues on the reaction mechanism of the adipic acid synthesis and its process optimization. © 2016 American Institute of Chemical Engineers AIChE J, 63: 689–697, 2017     

Catalytic reduction of NOx over Cu/ZSM-5 catalyst

Catalytic decomposition of NO on Cu/ZSM-5 catalyst was carried out in tubular fixed-bed reactor at atmospheric pressure. The influence of temperature and flow rate on the reaction rate was investigated. The kinetic model of reaction was proposed and compared with the literature results. The formation of NO₂ during the catalytic decomposition of NO was also monitored. Therefore, additional experiments were performed aimed at examining the kinetics of NO oxidation under the same reaction conditions. Both kinetic models were used to develop the reactor model and to describe quantitatively the behavior of the overall reaction system. Satisfactory degree of correlation between experimental data and values predicted by reactor model has been achieved.     

Kinetic modeling of oxidative coupling of methane over Mn/Na2WO4/SiO2 catalyst

A comprehensive kinetic model for oxidative coupling of methane (OCM) on Mn/Na₂WO₄/SiO₂ catalyst was developed based on a microcatalytic reactor data. The methane conversion and ethylene, ethane, carbon monoxide and carbon dioxide selectivities were obtained in a wide range of operating conditions including 750 < T < 875 °C, 4 < CH₄/O₂ < 7.5 and space time between 30 and 160 kg · s/m³ at P = 657 mmHg. The reaction networks of five kinetic models with appropriate rate equation type were compared together. The kinetics rates parameters of each reaction network were estimated using genetic algorithm optimization method. After comparing the reaction networks, the reaction network presented by Stansch et al. was found to best represent the OCM reaction network and was further used in this work. This kinetic network considers both catalytic and gas-phase as well as primary and consecutive reaction steps to predict the performance of the OCM. Comparing the experimental and predicted data showed that presented model has a reasonable fit between the experimental data and the predicted values with average absolute relative deviation of ± 9.1%.     

芳烃催化加氢交叉流反应器模型

提出了一种抗硫中毒的芳烃加氢催化反应器模型,称之为交叉流反应器模型,把反应物料分为两股,其中含有噻吩的乙苯物料采用轴向连续流动方式由反应器进口进入催化剂床层,而氢气由铅直导管直接进入催化剂床层中,然后与乙苯物料混合。在氢气导管出口处形成含硫乙苯浓度低而氢气浓度高的特殊区域,因而硫对催化剂的中毒效应大幅度降低,整体上提高了乙苯加氢饱和反应效率。与传统轴向混合流反应器进行比较,在相同条件下交叉流反应器具有更好的整体加氢反应性能。分别建立了交叉流反应器与传统轴向混合流反应器模型,提出了两种反应器的催化反应转化率方程;利用此转化率方程,对实验数据进行处理,得到动力学参数,模型的计算结果与实验数据相吻合,也验证了在交叉流反应器中,硫的中毒效应明显减弱。     

Overall kinetics of hydrogen peroxide formation by direct combination of H2 and O2 in a microreactor

Direct combination (DC) of hydrogen and oxygen over a heterogeneous catalyst in a microreactor is a novel method of producing hydrogen peroxide with significant economic advantages over the currently dominant anthraquinone autoxidation method. A kinetic rate expression for this reaction is required for design and modeling of a microreactor for the DC process. Since the formation of H₂O₂ by the DC process involves four simultaneous reactions (synthesis of H₂O₂, synthesis of water, reduction of H₂O₂ by H₂ and decomposition of H₂O₂), the overall rate expression must take into account each of these reactions. In this work, we describe a reactor model that involves the four component reactions as well as mass transfer effects. The model is verified by comparing the predicted reactor performance with experimental data. In addition to providing a tool for reactor design, the model also confirms important assumptions regarding the mechanism of DC reaction.     

Combined differential and integral kinetic modeling in an infrared cell-recycle reactor

The dehydration of 2-propanol over γ-alumina was studied at 246 °C by combined in situ ir measurements of adsorbed species and steady-state reaction kinetics. The resulting kinetic model accounted for catalyst deactivation, product inhibition, and autoinhibition by 2-propanol. The model also predicted the integral kinetic behavior during transient (batch) operation of the reactor.     

微反应器内甲苯气固催化氧化反应动力学

微通道反应器具有优良的传热、传质性能，能有效避免催化剂床层内热点的形成，为研究强放热反应动力学提供有利条件。开展了微反应器内的V2O5/TiO2催化剂上的甲苯气相选择氧化动力学研究，在简化反应网络的基础上建立了动力学模型，并给出动力学参数。该模型能较好地反映和预测较宽的反应条件范围内的甲苯气固相催化氧化反应转化率及产物分布，为优化操作条件提供依据。     

Kinetics of transesterification of methyl acetate and n-octanol catalyzed by cation exchange resins

The transesterification kinetics of methyl acetate with n-octanol to octyl acetate and methanol were studied using Amberlyst 15 as catalyst in a batch stirred reactor. The influence of the agitation speed, particle size, temperature, catalyst loading, and initial reactants molar ratio was investigated in detail. A pseudo-homogeneous (PH) kinetic model was applied to correlate the experimental data in the temperature range of 313.15 K to 328.15 K. The estimated kinetic parameters made the calculated results in good agreement with the experimental data. A kinetic model describing the transesterification reaction catalyzed by cation exchange resins was developed.     

Intrinsic kinetics for the synthesis of acetonitrile from ethanol and ammonia over Co–Ni/γ–Al2O3 catalyst

The intrinsic kinetics was studied for the synthesis of acetonitrile from amination–dehydrogenation of ethanol over the Co–Ni/γ–Al₂O₃ catalyst in the fixed-bed reactor. Experiments were carried out at reaction temperatures in the range 613–643 K, reactor pressure of 0.1 MPa, the ratios of volume feed velocity to catalyst volume (V₀/V_R) more than 12.99 min⁻¹ and large excesses of ammonia concentration over that of ethanol. The power-law model was used to fit the experimental data, and the model parameters were estimated using the Matlab software. Finally, a reaction kinetic model was proposed to describe the reaction, the calculated activation energy was 51.18 kJ mol⁻¹ and the reaction order to ethanol was 1.183.     

Methanation of carbon dioxide by hydrogen reduction using the Sabatier process in microchannel reactors

This paper describes the development of a microchannel-based Sabatier reactor for applications such as propellant production on Mars or space habitat air revitalization. Microchannel designs offer advantages for a compact reactor with excellent thermal control. This paper discusses the development of a Ru-TiO₂-based catalyst using powdered form and its application and testing in a microchannel reactor. The resultant catalyst and microchannel reactor demonstrates good conversion, selectivity, and longevity in a compact device. A chemically reacting flow model is used to assist experimental interpretation and to suggest microchannel design approaches. A kinetic rate expression for the global Sabatier reaction is developed and validated using computational models to interpret packed-bed experiments with catalysts in powder form. The resulting global reaction is then incorporated into a reactive plug-flow model that represents a microchannel reactor.     

Characterization of coal—liquid fractions. Molar enthalpies of quinoline interaction with coal-derived asphaltenes and heavy oils

The toluene-insoluble (Tl), asphaltene (A), and heavy oil (HO) fractions were isolated from three centrifuged SYNTHOIL liquid product (CLP) samples, prepared under different process conditions at 450 °C, 27.6 MPa hydrogen pressure from the same feed coal, Kentucky hvAb, from Homestead Mine. Run FB 53 was made with CoMo catalyst, 11-min preheater residence time, and 3-min reactor residence time. The much higher viscosity of FB 53–59 compared to FB 53-1 correlates with the larger contents of its toluene-insolubles and asphaltene, larger oxygen and sulphur contents of its asphaltene and toluene-insolubles, larger molecular weight and smaller aromaticity of its asphaltene, and the larger enthalpy of interaction (ΔH^o) of its asphaltene with quinoline in benzene. The average molecular weight and percentage of heteroatoms of the heavy oil from FB 53–59 are also greater than that from FB 53-1, and the value of ΔH^o of the heavy oil with quinoline, follows the same order. Run FB 57 was made with glass pellets, 17-min preheater residence time and 6-min reactor residence-time. Since in FB 53–59 the CoMo catalyst has lost part of its activity, a comparison of FB 53–59 with FB 57 yields information on the effect of residence times on the properties. The toluene-insoluble and asphaltene contents, as well as the viscosity, of FB 53–59 is larger, while the heavy oil content of FB 53–59 is smaller than that of FB 57. This comparison indicates that a larger-residence-time preheater and reactor may, to some extent, favour conversion as well as decrease the viscosity of the product oil. The values of ΔH^o for the interaction of quinoline with the heavy oil and asphaltene fractions obtained from the three CLP samples are in the order: FB 53–59 > FB 57-42 > FB 53-1, and they are attributed to the varying degree of hydrogen-bonding effects involving largely aromatic phenols which serve as hydrogen donors to quinoline.