Reaction kinetics between carbon dioxide and glycidyl methacrylate using trihexylamine immobilized ionic liquid on MCM41 catalyst

An ionic liquid (THA-CP-MS41), trihexylamine-immobilized on chloropropyl-functionalized MCM41, was synthesized by a grafting technique through a co-condensation method and used as a catalyst in the reaction of carbon dioxide with glycidyl methacrylate (GMA). CO₂ was absorbed into the heterogeneous system of the GMA solution and dispersed with solid particles of the catalyst in a batch stirred tank with a plane gas–liquid interface at 101.3 kPa. The absorption of CO₂ was analyzed using the mass transfer mechanism accompanied by chemical reactions based on the film theory. The proposed model fits the measured data of the enhancement factor to obtain the reaction rate constants.Solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidinone, and dimethyl sulfoxide influenced reaction rate constants.     

3-甲基-2-丁烯-1-醇的制备新工艺

研究了以溴代异戊烯水解工艺和精馏分离工艺为基础来制备3-甲基-2-丁烯-1-醇的新工艺。通过优化溶剂种类得到当水解溶剂为偶极类溶剂乙腈时,得到产物的选择性最高。并通过进一步优化实验操作条件,得到当溶剂加入量为v(乙腈):v(溴代异戊烯)=1:1,水解温度为70℃,碱用量为n(NaOH):n(溴代异戊烯)=1.2:1和反应时间为25min时,水解部分3-甲基-2-丁烯-1-醇的转化率最高可达63.35%。水解后的料液通过间歇精馏得到纯的3-甲基-2-丁烯-1-醇,最终的3-甲基-2-丁烯-1-醇总收率达到57.4%。     

Absorption of carbon dioxide into glycidyl methacrylate solution containing the triethylamine immobilized ionic liquid on MCM-41 catalyst

An ionic liquid (TEA-MS41), triethylamine-immobilized on chloropropyl-functionalized MCM-41, was synthesized by a grafting technique through a co-condensation method and used as a catalyst in the reaction of carbon dioxide with glycidyl methacrylate (GMA). CO₂ was absorbed into the heterogeneous system of the GMA solution and dispersed with solid particles of the catalyst in a batch stirred tank with a plane gas-liquid interface at 101.3 kPa. The absorption of CO₂ was analyzed by using mass transfer accompanied by chemical reactions based on film theory. The proposed model fits the measured data of the enhancement factor to obtain the reaction rate constants. Solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidinone, and dimethyl sulfoxide influenced the reaction rate constants.     

Mass transfer characteristics of wire-mesh honeycomb reactors

The mass transfer characteristics in honeycombs made of catalyst-deposited metal wire meshes (wire-mesh honeycomb; WMH) were studied to test the prediction that WMH has better flow distribution and a higher rate of interphase mass transfer than the conventional ceramic type of honeycomb module. The WMH module was constructed from alternating layers of flat and corrugated wire-mesh sheets packed within a frame. Wire-mesh sheets were coated with aluminum particles using electrophoretic method. Thermal sintering at 800°C and then calcinations at 500°C yielded a porous layer of Al/Al₂O₃ composite particles that were firmly attached on the wire surface. The alumina-protected wire meshes were further deposited with Pt/TiO₂ catalyst powder by washcoating method. The oxidation of ethyl acetate was monitored as model reaction. A one-dimensional model was established and the parameters of intrinsic first-order kinetics were regressed from the reaction results obtained in the region controlled by chemical reaction, after which interphase mass transfer coefficients were regressed in other region. Three expressions for the Sherwood number that are typically used for honeycomb, wire-mesh gauze and packed bed reactors were examined to determine the optimal expression for WMHs. The mass transfer coefficient in the WMH was found to be quite different from that in the conventional ceramic honeycomb reactor and much higher than that in the wire-mesh gauze reactor. The best-fit results were obtained with packed-bed expression, Sh=1.06Re^0.50Sc^1/3, indicating the mechanism of reaction in the WMH is most similar to that in a packed bed. The optimal Sh expression was then used to predict the behavior of systems with a larger channel size or longer bed; the model predictions showed good agreement with experimental results from real WMH reactors.     

Liquid-solid mass transfer in a trickle-bed reactor measured by means of a catalytic reaction

Global rates of reaction (the hydrogenation of cyclohexene to cyclohexane on Pd/Al₂O₃) were measured in a trickle-bed reactor at various gas and liquid flow rates. The liquid superficial velocity was higher than 1.2 × 10⁻² m/s so as to achieve complete wetting of the catalyst particles. Liquid-solid mass transfer coefficients were calculated from the rate data. In the low interaction regime, the coefficients depend on both the gas and liquid rates, in contrast with most of the previous studies. At the transition to the high interaction regime, a significant change in the values of the coefficients was observed. The experimental liquid-solid mass transfer coefficients are in good agreement with values predicted by correlations published in the literature.     

On the use of internal mass transfer coefficients in modeling of diffusion and reaction in catalytic monoliths

We utilize the recently developed concept of internal or intraphase mass transfer coefficient to simplify the problem of diffusion and reaction in more than one spatial dimension for a washcoated monolith of arbitrary shape. We determine the dependence of the dimensionless internal mass transfer coefficient (Sh_i) on washcoat and channel geometric shapes, reaction kinetics, catalyst loading and activity profile. It is also reasoned that the concept of intraphase transfer coefficient is more useful and fundamental than the classical effectiveness factor concept. The intraphase transfer coefficient can be combined with the traditional external mass transfer coefficient (Sh_e) to obtain an overall mass transfer coefficient (Sh_app) which is an experimentally measurable quantity depending on various geometric and transport properties as well as kinetics. We present examples demonstrating the use of Sh_app in obtaining accurate macro-scale low-dimensional models of catalytic reactors by solving the full 3-D convection-diffusion-reaction problem for a washcoated monolith and comparing the solution with that of the simplified model using the internal mass transfer coefficient concept.     

Trickle bed reactor diluted with fine particles and coiled tubular flow-type reactor for kinetic measurements without external effects

Gas and liquid velocities in laboratory scale trickle bed reactors are one or two orders of magnitude lower than those in commercial reactors. Then, the kinetic data may include the external effects. This shortcoming of laboratory scale trickle bed reactor can be resolved by diluting the catalyst bed with fine inert particles. The catalyst bed dilution increases dynamic liquid holdup, pressure drop, gas–liquid mass transfer coefficient. Hydrogenation of 2-phenylpropene on Pd/Al₂O₃ was performed with the trickle bed reactor diluted with fine inert particles and the coiled tubular flow-type reactor to compare the kinetics with that of the basket type batch reactor. The trickle bed reactor diluted with fine inert particles is suitable to obtain the reaction rate without external effects even if the liquid velocity is low. The coiled tubular flow-type reactor should be used at high gas velocities.     

Rapid Hydrogen Peroxide Decomposition Using a Microreactor

The rapid decomposition of hydrogen peroxide (H₂O₂) is often desired in the cleanup of excess H₂O₂ when it is used as an oxidant. Although the decomposition process has been studied in batch reactors, it has never been performed before in a fixed‐bed microreactor with residence time on the scale of seconds. With enhanced mass and heat transfer in microreactors, higher H₂O₂ decomposition efficiency compared to batch reactors was obtained. A variety of parameters including length of microchannels, flow rate, solvent composition, and gas pressure were examined carefully and a first‐order kinetic model was established. Within a few seconds, more than 70 % of the H₂O₂ was decomposed successfully. The challenge of catalyst passivation was discussed as well.     

The Hydrogenation of 2-butyne-1,4-diol over a Carbon-supported Palladium Catalyst

The hydrogenation of 2-butyne-1,4-diol in propan-2-ol over a carbon-supported palladium catalyst has been investigated in a batch reactor. At low conversions complete selectivity to cis-but-2-ene-1,4-diol is observed. However, further hydrogenation leads to a wide variety of products, most notably 2-isopropoxy-tetrahydrofuran and butane, neither of which have previously been associated with this reaction system. The former is thought to occur as a result of a surface-mediated process, involving the insertion of dissociatively adsorbed solvent molecules. Butane formation is attributed to the double condensation and hydrogenation of a chemisorbed cis-but-2-ene-1,4-diol intermediate. The alkane preferentially partitions in the gaseous phase, which results in an marked mass imbalance for the liquid phase. A reaction scheme is presented to rationalise these observations.     

Lateral mixing in trickle bed reactors

Knowledge of lateral mixing is essential to understand heat and momentum transfer parameters in both single-phase liquid and two-phase gas-liquid co-current down flow through packed bed columns. The reactors through which gas and liquid concurrently flow downwards through a bed of catalytic packing are called trickle bed reactors. Experimental data on lateral mixing coefficients from both the heat transfer and radial liquid distribution studies are obtained over a wide range of flow rates of gas and liquid using glass spheres (4.05 and 6.75 mm), ceramic spheres (2.59 mm), and ceramic raschig rings (4 and 6.75 mm) as packing materials covering trickle flow, pulse flow, and dispersed bubble flow regimes. In the present work, an expression for estimation of lateral mixing coefficient (αβ)_L is derived using the data on radial liquid distribution studies. The agreement between the values of (αβ)_L obtained from heat transfer studies and from radial liquid distribution studies using the experimental data shows that there exists an analogy between the heat transfer and radial liquid distribution in packed beds. Since (αβ)_L is an important variable for estimation of various heat and mass transfer parameters, a correlation for (αβ)_L based on present heat transfer study is proposed. The agreement between the (αβ)_L values estimated from the proposed correlation and experimental values is satisfactory with a standard deviation (s.d.) of 0.119.     

Hydrodynamik und Stofftransport in einem Perlschnurreaktor für Gas/Flüssig/Fest‐Reaktionen

In this work, a pellet string reactor was characterized with respect to hydrodynamics and mass transfer. The catalyst packing consists of a cylindrical channel with a diameter of 1.41 mm, which was filled with spherical catalyst particles, having an outer diameter of 0.8 mm. Under reaction conditions (liquid phase hydrogenation of α‐methylstyrene) overall (gas‐liquid‐solid) volumetric mass transfer coefficients for hydrogen between 0.8 and 5.5 s^–1 were computed. Due to high mass transfer rates and simple reactor geometry, pellet string reactors can be applied in industry as highly efficient reaction units.     

Mass transfer in trickle-bed reactors at low reynolds number

Mass transfer rates were determined in a 3.4 cm i.d. trickle-bed reactor in the absence of reaction by absorption measurements and in presence of reaction. Gas flow rates were varied from 0-100 l/h and liquid flow rates from 0-1.5 l/h. The catalyst particles were crushed to an average diameter of 0.054 and 0.09 cm. Mass transfer coefficients remained unaffected by change in gas flow rate but increased with liquid rate. The data from absorption measurements were evaluated with predictions based upon plug-flow and axial dispersion model. Mass transfer coefficients were found greater in case of axial dispersion model than that of plug-flow model specially at low Reynolds number (Re₁ < 1).Hydrogenation of α-methylstyrene to cumene using a Pd/Al₂O₃ catalyst was taken as a model reaction. Intrinsic kinetic studies were made in a laboratory-stirred-autoclave. Mass transfer coefficients were determined using these intrinsic kinetic data from the process kinetic measurements in trickle-bed reactor. Mass transfer coefficients under reaction conditions were found to be considerably higher than those obtained by absorption measurements.Correlations were suggested for predicting mass transfer coefficients at low Reynolds number.The gas to liquid mass transfer coefficients for lower gas and liquid flow rates were determined in a laboratory trickle-bed reactor. The effect of axial dispersion on mass transfer was considered in order to evaluate the experimental data. Three correlations were formulated to calculate the mass transfer coefficients, which included the effect of liquid loading, particle size and the properties of the reacting substances. The gas flow rate influences the gas to liquid mass transfer only in the region of low gas velocities. In the additional investigations of gas to liquid mass transfer without reaction in trickle-bed reactor, the mass transfer coefficients were determined under reaction conditions and the intrinsic kinetics was studied in a laboratory scale stirred autoclave with suspended catalyst. A few correlations are formulated for the mass transfer coefficients. A comparison with the gas-liquid mass transfer coefficient obtained by absorption measurements showed considerable deviations, which were illustrated phenomenologically.     

Chemical absorption of carbon dioxide into phenyl glycidyl ether solution containing THA-CP-MS41 catalyst

Carbon dioxide was absorbed into the phenyl glycidyl ether (PGE) solution within a range of 0–2.0 kmol/m³ in a stirred batch tank with a planar gas-liquid interface at 333–363 K and 101.3 kPa. Trihexylamine-immobilized on chloropropyl-functionalized MCM-41 (THA-CP-MS41) was used as a mesoporous catalyst, dispersed in organic liquid for the reaction between carbon dioxide and PGE. The measured absorption rates were analyzed to obtain the reaction kinetics of the consecutive chemical reactions which consisted of two steps using the mass transfer mechanism based on film theory. The overall reaction kinetics, analyzed with the pseudo-first-order reaction constant in the consecutive reaction model, was equivalent to the consecutive reaction kinetics. Effects of polar solvent, such as N, N-dimethylacetamide, N-methyl-2-pyrrolidinone, and dimethyl sulfoxide, on the reaction rate constants were observed using the solubility parameter of the solvent.     

Asymmetric transfer hydrogenation of prochiral ketone catalyzed over Fe-CS/SBA-15 catalyst

A heterogeneous chiral catalyst Fe(III)-CS (chitosan) complex/mesoporous molecular sieve SBA-15 (Santa Barbara Amorphous) was prepared. The asymmetric transfer hydrogenations of prochiral acetophenone and 4-methyl-2-pentanone to corresponding chiral alcohols were carried out on Fe-CS/SBA-15 at atmosphere pressure using 2-propanol as hydrogen donor. Effects of Fe content in catalyst, reaction temperature, reaction time and promoter KOH concentration on the conversion of substrates and enantio-selectivity were investigated. Fe-CS/SBA-15 with 2.2% mass fraction Fe exhibits considerable enantioselectivity and catalytic activity for the asymmetric transfer hydrogenations of aromatic ketone and aliphatic ketone. Under optimal reaction conditions: KOH concentration 0.03 mol/L, reaction temperature 70°C and reaction time 4 h, enantiomer excess (ee) of (R)-1-phenylethanol and conversion of acetophenone can reach 87.4% and 27.7%, respectively. Under the above KOH concentration and reaction temperature and reaction time of 8 h, the ee of (R)-4-methyl-2-pentanol and conversion 4-methyl-2-pentanone amounted to 50.2% and 25.5%, respectively. Translated from Petrochemical Technology, 2006, 35(9): 858–862 [译自: 石油化工]     

Cyclone flow cell for the investigation of gas-diffusion electrodes

Electrochemical gas–liquid reactions can be efficiently carried out at porous gas diffusion electrodes (GDE). These electrodes are simultaneously in contact with a gas phase and a liquid phase. For the design and scale-up of electrochemical reactors based on these GDE their macrokinetic behaviour (i.e., the interaction of reaction and internal mass transport phenomena) must be investigated under well defined external mass transfer conditions and controlled wetting conditions. To meet these requirements, a novel cyclone cell has been designed in which two vortex flow fields are realised on either side of a horizontally positioned GDE. The external mass transfer coefficients in this cell are determined from limiting current measurements for the oxidation of Fe(CN₆)^4–.     

Modeling of annular reactors with surface reaction using computational fluid dynamics (CFD)

A CFD-based model for predicting the performance of annular reactors with surface reaction was developed. The capability of several hydrodynamic models to predict successfully the kinetic behavior of the reactor under diffusion limiting conditions was assessed against experimental data. The evaluation included five models: laminar, standard k–ε, realizable k–ε, Reynolds stress (RSM), and Abe–Kondoh–Nagano (AKN). The catalytic decomposition of hydrogen peroxide over a Mn/Al oxide catalyst coated on the reactor surface was used as a model reaction. The reactor was tested within a range of flow rates corresponding to 530<Re<11,000 and intrinsic reaction rate constants of 5×10^?5 to 1 m/s. The results demonstrated that the performance of the hydrodynamic models is associated with their capability to predict external mass transfer and ultimately, the level of mass transfer limitation present in the reacting system. For laminar flow conditions, the laminar model is capable of predicting the experimental behavior of the system. For transient and turbulent flow regimes, all the analyzed turbulence models provided good predictions of the system when the process was controlled by surface reaction. When the system presented some degree of mass transfer limitation, AKN and RSM exhibited better performance.     

CFD modelling of liquid–liquid multiphase microstructured reactor: Slug flow generation

Microreactor technology, an important method of process intensification, offers numerous potential benefits for the process industries. Fluid–fluid reactions with mass transfer limitations have already been advantageously carried out in small-scale geometries. In liquid–liquid microstructured reactors (MSR), alternating uniform slugs of the two-phase reaction mixture exhibit well-defined interfacial mass transfer areas and flow patterns. The improved control of highly exothermic and hazardous reactions is also of technical relevance for large-scale production reactors. Two basic mass transfer mechanisms arise: convection within the individual liquid slugs and diffusion between adjacent slugs. The slug size in liquid–liquid MSR defines the interfacial area available for mass transfer and thus the performance of the reactor. There are two possibilities in a slug flow MSR depending on the interaction of the liquids with the solid wall material: a dispersed phase flow in the form of an enclosed slug in the continuous phase (with film—complete wetting of the continuous phase) and an alternate flow of two liquids (without film—partial wetting of the continuous phase). In the present work, a computational fluid dynamics (CFD) methodology is developed to simulate the slug flow in the MSR for both types of flow systems. The results were validated with the experimental results of Tice et al. (J.D. Tice, A.D. Lyon and R.F. Ismagilov, Effects of viscosity on droplet formation and mixing in microfluidic channels, Analytica Chimica Acta507 (1) (2004), pp. 73–77.).     

Synthesis of tertiary amyl methyl ether (TAME): Influence of internal and external mass transfer resistance

An experimental set-up is presented for the measurement of reaction rates in the liquid phase synthesis of tertiary amyl methyl ether (TAME) from methanol and a mixture of 2-methyl-1-butene and 2-methyl-2-butene using an acidic ion exchange resin (Lewatit SPC 118) as catalyst. The reaction was performed in a continuous-flow recycle reactor at a temperature of 333.15 K and a pressure of 1.6 MPa. Determination of the age distribution (Fcurve) of the reactor showed that mixed flow is approached at a recycle ratio of R = 10. Experiments were performed to reveal the limits of operating conditions where the various resistances do not affect the rate. In agreement with estimation of Reynolds numbers, hindrance by external mass transfer can be excluded at a volumetric flow rate of 10 ml/min and a recycle ratio of R = 10. The maximum temperature increase of the whole particle resulting from limitation of external heat transfer was estimated to be about 3 K. Variation of the size of resin particles revealed the existence of a critical methanol concentration, above which reaction rates can be determined without influence of internal mass transport phenomena. The maximum temperature increase in the particle was estimated to be 0.3 K.