Absence Of Mass Transfer Resistance Research Articles

Wadsworth–Emmons Reaction by Using the Fluorapatite Catalyst: Kinetic Studies

Wadsworth–Emmons reaction was successfully carried out by using the fluorapatite (FAP) catalyst. The reaction of 2-methoxybenzaldehyde and triethylphosphonoacetate using FAP afforded α,β-unsaturated ester with 100% conversion and 80% selectivity. A kinetic model was validated at different temperatures by Langmuir–Hinshelwood–Hougen–Watson (LHHW), and the absence of mass transfer resistance was verified by the Weisz Prater criterion. The effect of different catalysts, temperature, catalyst loading, solvent, mole ratio, and speed of stirring was studied. The FAP catalyst was characterized by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller method, nitrogen adsorption–desorption, transmission electron microscopy, energy-dispersive X-ray spectroscopy, temperature programmed desorption (TPD-NH3), X-ray diffraction, and X-ray photoelectron spectroscopy. The FAP catalyst was found to be stable up to three recycles with no loss in activity.

Imine Oxidation Catalyzed by Zinc Hydroxyapatite: Kinetic Studies

AbstractThe synthesis of N,N‐diphenylformamide from N‐benzylideneaniline and urea hydrogen peroxide is investigated using a zinc hydroxyapatite (ZnHAP) catalyst. It was found that the catalyst resulted in the highest activity of 91 % conversion and 40 % selectivity at 130 °C in 2 h. A kinetic model was validated by Langmuir‐Hinshelwood‐Hougen‐Watson (LHHW) at different temperatures and the absence of mass transfer resistance was proved by the Weisz Prater criterion. Effect of different catalysts, catalyst loading, temperature, mole‐ratio, and speed of stirring was studied. The as‐synthesized catalyst is characterized by FTIR, BET nitrogen adsorption‐desorption, TEM, EDX, TPD‐NH3, XPS, ICP‐MS and XRD. ZnHAP catalyst was found to be stable up to three recycles with no loss in activity.

Nanocatalysts for biodiesel production

Biofuels are a class of clean fuels and promising for energy demand. Biodiesel is relatively costly, which limits the commercialization of the product. The waste edible oil and animal fats are raw materials for biodiesel production. This paper focuses on the catalytic production of biofuels and reviews the application of different catalysts to produce biodiesel from waste oils by using esterification and transesterification reactions. The reaction in the presence of nanocatalysts is carried out under mild operating conditions. Nowadays, magnetic nanocatalysts are preferred to bulk catalysts due to the absence of mass transfer resistance and fast deactivation as well as high recovery rate during the separation. Functionalized magnetic nanocatalysts are more attractive for biodiesel production. Further studies should do to develop highly active and selective nanocatalysts for industrial scale.

Kinetics of Henry reaction catalyzed by fluorapatite

Kinetics of Henry reaction was performed to investigate the performance of fluorapatite. (FAP) catalyst. It was found that the catalyst showed the highest conversion and selectivity of 65% and 80%, respectively at 323 K. Kinetic model was validated, and the absence of mass-transfer resistance was proved by the Weisz Prater criterion. The as-synthesized catalyst is characterized using BET nitrogen adsorption-desorption, FTIR, FE-SEM, TPD-CO2, XPS, and XRD. Effect of catalyst loading, temperature, mole-ratio, speed of stirring, and solvents were studied. FAP catalyst showed good reusability up to four cycles.

Photoenzymatic decarboxylation to produce renewable hydrocarbon fuels: A comparison between whole-cell and broken-cell biocatalysts

The recently discovered fatty acid photodecarboxylase from Chlorella variabilis NC64A (CvFAP) is a potential photoenzyme to produce sustainable aviation fuels from lipid-rich wastewater. Herein, we compared the catalytic performance in photoenzymatic decarboxylation reactions between recombinant Escherichia coli cells containing CvFAP (CvFAP@E. coli) and broken cells (CvFAP BCs) prepared by supersonic treatment of CvFAP@E. coli under various catalytic conditions for the first time. The conversion of palmitic acid as a model substrate by CvFAP BCs was 1.87 times higher than that by CvFAP@E. coli at a rotation speed of 100 rpm due to the absence of mass transfer resistance from the cytomembrane for CvFAP BCs. However, no significant difference in the conversion of palmitic acid between CvFAP@E. coli (88.4%) and CvFAP BCs (95.4%) was obtained under the optimal reaction conditions: a cell dry weight of 35.2 mg·mL−1, a rotation speed of 200 rpm, a pH of 8.0, and a light intensity of 200 μmol·m−2·s−1 for 3 h. Good stabilities for CvFAP BCs (92.4%) and CvFAP@E. coli (87.7%) were retained at 30 °C for 3 days. CvFAP BCs was capable of decarboxylating palmitic acid at a high concentration of 54 mM with the highest conversion rate of 17.2 mM/h as previously reported. This work demonstrates the continuous potential of CvFAP in producing hydrocarbon fuels.

Silicon microfabricated reactor for operando XAS/DRIFTS studies of heterogeneous catalytic reactions

A novel microreactor for operando XAS and DRIFTS studies of catalytic reactions is reported, exhibiting plug-flow, isothermal behaviour and absence of mass transfer resistances and dead volume, enabling time- and spatially-resolved experiments.

Kinetics study and process simulation of transesterification of ethylene glycol with methyl acetate for ethylene glycol diacetate

The kinetics of transesterification of methyl acetate with ethylene glycol catalyzed by acidic ion‐exchange resin NKC‐9 is investigated in detail. The effects of reaction temperature, catalyst loading, and initial reactants molar ratio on the reaction rate are studied in the absence of mass transfer resistance. The kinetic equation is obtained by utilizing the PH model to correlate the experimental data. Then a distillation process is designed to produce high‐purity ethylene glycol diacetate, which includes a reactive distillation column, an extractive distillation column, and a solvent recovery column. The extractive distillation column and solvent recovery column are used to recycle excess methyl acetate and entrainer. Operational and structural parameters are optimized by minimizing the total annual costs (TAC) while meeting the product specifications.

Monolithic Stirrer Reactor: Performance in the Partial Hydrogenation of Sunflower Oil

In the present paper, the performance of monolithic catalysts obtained from a catalytic converter was analyzed in the partial hydrogenation of sunflower oil. The monoliths were reimpregnated with palladium and installed as a blade in a monolithic stirrer reactor. The use of this type of reactor was explored in the reaction at 373 K and 413 kPa, analyzing the effect variables such as stirrer speed, hydrogen supply, and stirrer design on the catalyst activity and selectivity to trans-isomers and saturated product. The volumetric gas–liquid and liquid–solid mass transfer coefficients were calculated, and the influence of the stirrer speed was examined. Estimations of the Carberry numbers and Weisz–Prater modulus were used for establishing the presence or absence of mass transfer resistances. The performance of the catalyst was studied in consecutive tests, and different procedures for catalyst regeneration were applied.

Investigating the Activity of Zirconia as a Catalyst and a Support for Noble Metals, in Green Oxidation of Cyclohexane

Abstract Green oxidation of cyclohexane by molecular oxygen was carried out over ZrO2 and noble metals (Pd and Pt) supported on zirconia in solvent free conditions. Studies have been carried out in a typical three-necked batch reactor. Reaction products were identified by GC and UV spectrophotometer. Reaction rates were determined as a function of temperature, partial pressure of oxygen, amount of catalyst, volume of reactants, agitation and reaction duration. The agitation effect and activation energy revealed the absence of mass transfer resistance. Experimental results unveiled the effect of morphology of ZrO2 on catalysis. 1.0 wt.% noble metal/ZrO2(m) was found more selective for cyclohexanol production at low temperature, agitation 900rpm and partial pressure of 101.325 KPa while at high temperature cyclohexanol was further oxidized to cyclohexanone. Comparison of Pt/ZrO2 and Pd/ZrO2 catalysts was made on the basis of reactivity and selectivity. Catalysts were characterized by using BET surface area and pore size analyzer, XRD and SEM. To conclude shortly, for the oxidation of cyclohexane, platinum or palladium supported on zirconia are selective, recyclable and could behave as truly heterogeneous catalysts.

Catalytic Hydrolysis of Ethyl Acetate using Cation Exchange Resin (Amberlyst - 15) : A Kinetic Study

The kinetic behavior of the heterogeneous hydrolysis of aqueous ethyl acetate over an acidic cation exchange resin, Amberlyst 15, was investigated. The experiments were carried out in a fixed bed reactor at temperatures from 313.15 to 343.15 K and feed molar ratios ,θBo (water to ethyl acetate) from 62.4 to 265.88. The conversion of ethyl acetate was found to increase with increasing reaction temperature. Gas bubble formation was observed at reaction temperature ≥ 343.15K. Absence of mass transfer resistance was verified by conducting the experiments at different catalyst loadings (20 g, 40 g, 64 g) under varied feed flow rates (1 to 25 cm3/min ). The kinetic data was correlated with pseudo first order model and model parameters were determined using Nelder-Mead algorithm for minimizing the objective function. © 2009 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Catalytic Hydrolysis of Ethyl Acetate using Cation Exchange Resin (Amberlyst - 15) : A Kinetic Study

The kinetic behavior of the heterogeneous hydrolysis of aqueous ethyl acetate over an acidic cation exchange resin, Amberlyst 15, was investigated. The experiments were carried out in a fixed bed reactor at temperatures from 313.15 to 343.15 K and feed molar ratios ,θBo (water to ethyl acetate) from 62.4 to 265.88. The conversion of ethyl acetate was found to increase with increasing reaction temperature. Gas bubble formation was observed at reaction temperature ≥ 343.15K. Absence of mass transfer resistance was verified by conducting the experiments at different catalyst loadings (20 g, 40 g, 64 g) under varied feed flow rates (1 to 25 cm3/min ). The kinetic data was correlated with pseudo first order model and model parameters were determined using Nelder-Mead algorithm for minimizing the objective function. Copyright (c) 2009 by BCREC . All Rights reserved. [Received: 19 July 2009, Revised: 20 August 2009, Accepted: 22 August 2009] [How to Cite : K.R. Ayyappan, A.P. Toor , R. Gupta, A. Bansal, R.K. Wanchoo (2009). Catalytic Hydrolysis of Ethyl Acetate using Cation Exchange Resin (Amberlyst - 15) : A Kinetic Study. Bulletin of Chemical Reaction Engineering and Catalysis , 4(1): 16-22. doi:10.9767/bcrec.4.1.7114.16-22 ] [ How to Link/ DOI : http://dx.doi.org/10.9767/bcrec.4.1.7114.16-22 || or local: http://ejournal.undip.ac.id/index.php/bcrec/article/view/7114 ]

Kinetics of Tricyclopentadiene Hydrogenation over Pd-B/γ-Al2O3 Amorphous Catalyst

The kinetics of tricyclopentadiene hydrogenation to tetrahydrotricyclopentadiene over Pd-B/γ-Al2O3 amorphous catalyst has been studied in a stirred semibatch reactor over a range of temperatures (353−413 K), hydrogen pressures (1.0−3.5 MPa), initial feed concentrations (0.2−0.4 mol/L), and catalyst concentrations (0.60−5.33 g/L). The reaction is found to be a consecutive reaction with 14,15-dihydrotricyclopentadiene as the intermediate product. Analysis verifies that the kinetic experiments are conducted in the absence of mass transfer resistance. An Eley−Rideal kinetic model is formulated with the assumption that single-site adsorbed organic species are saturated by hydrogen dissolved in the liquid phase and the surface reaction is rate-determining. This model can accurately fit the experimental data in the ranges studied and correctly explain the observed tendencies. The kinetic parameters are obtained by minimizing the error between the model predications and the experimental results. The activation energies for the first and second step reactions are 11.11 kJ/mol and 34.71 kJ/mol, respectively. The kinetic model provides a useful tool for the reactor design and performance estimation of amorphous Pd catalysts.

Measurements of Kinetic Parameters in a Microfluidic Reactor

Continuous flow microfluidic reactors that use immobilized components of enzymatic reactions present special challenges in interpretation of kinetic data. This study evaluates the difference between mass-transfer effects and reduced efficiencies of an enzyme reaction. The kinetic properties of immobilized alkaline phosphatase (AP) were measured by the dephosphorylation of 6,8-difluoro-4-methylumbelliferyl/phosphate to a fluorescent 6,8-difluoro-4-methylumbelliferone. A glass microfluidic chip with an in-channel weir was created for the capture of solid silica microbeads functionalized with enzyme. The input substrate concentrations and flow rates across the bed were varied to probe the flow-dependent transport and kinetic properties of the reaction in the microreactor bed. Unlike previous reactors, substrate was titrated directly over the fixed enzyme bed by controlling the air pressure over the chip reservoirs. The reactor explored substrate conversions from near zero to 100%. The average bed porosity, residence time, and bed resistance were measured with dye pulses. A simple criterion was derived to evaluate the importance of flow-dependent mass-transfer resistances when using microreactors for calculating kinetic rate constants. In the absence of mass-transfer resistances, the Michaelis-Menten kinetic parameters are shown to be flow independent and are appropriately predicted using low substrate conversion data. A comparison of the kinetic parameters with those obtained using solution-phase enzymatic reactions shows a significant decrease in enzyme activity in the immobilized conformation. The immobilized Km of AP is approximately 6 times greater while the kcat is reduced by approximately 28 times. Contradictions found in literature on the evaluation of Michaelis-Menten kinetic parameters for immobilized enzymes in microfluidic reactors are addressed. When product molecules occupy a significant number of enzymatic sites or modify the enzyme activity, the assumed Michaelis-Menten mechanism can no longer be valid. Under these conditions, the calculations of "apparent" kinetic rate constants, based on Michaelis-Menten kinetics, can superficially show a dependence on flow rate conditions even in the absence of mass-transfer resistances. High substrate conversions are shown to depend on flow rate. A kinetic model based on known mechanisms of the alkaline phosphatase enzyme reaction is tested to predict the measurements for high substrate conversion. The study provides a basis for appropriate use of mass-transfer and reaction arguments in successful application of enzymatic microreactors.

Kinetics of heterogeneous oxidation of benzyl alcohol with hydrogen peroxide

Abstract A clean catalytic process for the synthesis of benzaldehyde (BzH), with high selectivity, from benzyl alcohol (BzOH) by oxidation with hydrogen peroxide (H 2 O 2 ), without any organic solvent in a batch reactor is studied. Oxidation of BzOH to BzH was carried out at different speeds of agitation (800–1500 rpm), temperatures (343–363 K), catalyst loadings ((3.4–5.9) × 10 −3 mol/L) and mole ratios of BzOH:H 2 O 2 (1:1–1:2). Effect of various catalysts, e.g. tungstic acid, ammonium molybdate, and sodium tungstate and sodium molybdate on the oxidation of BzOH to BzH was studied. Ammonium molybdate was found to be the best catalyst for the oxidation of BzOH as compared to other catalysts. Increasing the speed of agitation beyond 1000 rpm has no significant effect on the rate of the oxidation of BzOH, indicating the absence of mass transfer resistance. Kinetics of the reaction have been established and values of activation energy have been reported.

THE EFFECT OF SURFACTANTS ON THE GROWTH OF UNDERPRESSURIZED, ANNULAR LIQUID JETS

The effects of surfactants on the growth of isothermal, underpressurized, inviscid, annular liquid jets are studied under both steady state and transient conditions by means of an interfacial mass transfer law which depends on the equilibrium interfacial concentration and a mass resistance parameter. Equilibrium interfacial concentrations governed by both Henry's and Sievert's solubility laws are considered. It is shown that, for mass Biot numbers larger than unity, the underpressurized jet grows until the pressure of the gases enclosed by the annular liquid jet is equal to that of those surrounding the jet, while, for mass Biot numbers less than or equal to one, the pressure coefficient increases very little. It is also shown that, in some cases and contrary to the results observed in the absence of mass transfer resistance, the time required by the annular jet to reach a steady equilibrium configuration may be shorter when the equilibrium interfacial concentration is governed by Sievert's law than when it is governed by Hennry's solubility law, particularly at low Peclet numbers and for high mass transfer resistances.

High Performance Liquid Chromatography of Small and Large Molecules with Nonporous Silica-Based Stationary Phases

Nonporous monodispersed, microspherical silica particles, having mean particle diameters of 0.8 and 1.1 μm, were surfacel-modified with octadecyl or triphenyl functions as well as with lectin proteins for high performance liquid chromatography of small and large molecules. “Monomeric” or “polymeric” octadecyl-silica (C18-silica) bonded phases were formed, depending on the silane compounds used. Monomeric C18-silica stationary phases yielded high resolution in the separation of 2-pyridylamino derivatives of xyloglucan oligosaccharides and proteins. The effect of particle size of the support on resolution was also examined. For comparative study, the chromatographic behavior of large molecular weight proteins on a triphenyl-silica stationary phase was also conducted. Polymeric C18-silica stationary phases yielded higher phase ratios and better support surface coverage which proved useful in the separation of small hydrophilic species such as derivatized chitooligosaccharides of lower degree of polymerization (d.p.). The slopes of the linear dependence of logarithmic retention factor on volume percent of organic modifier were determined for the monomelic and polymeric C18-silica stationary phases with low molecular weight aromatic compounds. Lectin affinity stationary phases with lens culinaris agglutinin and wheat germ agglutinin covalently bound to nonporous silica support were examined for the applications of nonporous stationary phases in lectin affinity chromatography of glycoproteins. In all cases, rapid separations in the time scales of seconds and minutes could be obtained because of the absence of mass transfer resistance in the nonporous stationary phase matrices.

Pressure swing adsorption processes: intraparticle diffusion/convection models

The dynamic behavior of a three-step one-column isothermal PSA process is assessed by simulation; three models are used: equilibrium, intraparticle diffusion, and intraparticle diffusion/convection. Two process performance parameters, product enrichment and recovery of the light component, are used to measure the separation performance. The effects of several operating variables on the process performance are addressed. Higher pressure ratios (P[sub h]/P[sub l]) and higher adsorption capacities increase the process performance. The process performance is practically independent of the step rates, although it can decrease if high feed rates are used together with large feed duration times. The limiting performance of the system is found in the absence of mass-transfer resistances. Intraparticle convection, enhancing mass transfer inside particles, increases the process performance relative to intraparticle diffusion alone; the improvement is limited by the equilibrium situation.