International Journal of Chemical Reactor Engineering

Clean Synthesis of 2-Methylglycidol over a Novel Titanosilica Catalyst – Ti-MWW under Autogenic Pressure

Anna Fajdek et al. — Fri, 03 Feb 2012 18:46:51 PST

In this work the epoxidation of methallyl alcohol (MAA) with 30 wt% H₂O₂ over the Ti-MWW catalyst has been studied. The significant parameters for the MAA epoxidation were established as temperature (20-120°C), the molar ratio of MAA/H₂O₂ (1:1-5:1), methanol (solvent) concentration (5-90 wt%), Ti-MWW catalyst concentration (0-5.0 wt%), reaction time (5-300 min) and intensity of stirring (0-500 rpm). The process of MAA epoxidation was carried out the most effective at temperature of 100°C, the molar ratio of MAA/H₂O₂=1:1, methanol concentration of 40 wt%, the catalyst concentration of 2 wt%, the reaction time of 15 min and with the stirring intensity over 350 rpm. These the best technological parameters (mild and relatively safe) allow to obtain the selectivity of transformation to 2MG 37 mol%, the MAA conversion 52 mol%, and the selectivity of transformation to organic compounds in relation to H₂O₂ consumed 48 mol%.

Multiobjective Optimization of an Industrial Styrene Reactor Using the Dual Population Evolutionary Algorithm (DPEA)

Salim Fettaka et al. — Fri, 03 Feb 2012 18:46:48 PST

In the last few years, multiobjective evolutionary algorithms (MOEAs) have gained significant interest as a reliable option to optimize problems with conflicting objectives in science and engineering. These algorithms generate an optimal set of trade-off solutions referred to as the Pareto domain. In this investigation, a MOEA was used to optimize simultaneously conflicting design variables of an industrial styrene reactor. The dual population evolutionary algorithm (DPEA) was implemented to optimize the productivity, yield, and selectivity of styrene. To evaluate the robustness and versatility of the algorithm, two and three objective optimization case studies were conducted for three different configurations of the reactor: adiabatic, steam-injected, and isothermal.

Results indicated that DPEA is a robust optimization strategy to generate a well-defined Pareto domain with a wide range of solutions. In addition, the Pareto-optimal solutions of the steam-injected configuration were superior to the adiabatic reactor and to a portion of the isothermal configuration. The optimal operating conditions corresponding to the Pareto domains were also slightly better in terms of profit when compared with previously published studies. The Pareto domains were then ranked using the Net Flow Method (NFM), a ranking algorithm that incorporates the knowledge and preferences of an expert into the optimization routine.

MHD Flow of an Oldroyd-B Fluid Through a Porous Channel

Tasawar Hayat et al. — Fri, 03 Feb 2012 18:46:41 PST

This paper discusses the hydromagnetic boundary layer flow of an Oldroyd-B fluid in a porous channel. Both suction and injection (blowing) cases are considered. Appropriate similarity transformations are invoked to convert the partial differential equations into ordinary ones. Homotopy analysis method (HAM) is used for the presentation of analytic solution of the nonlinear differential system. Graphical results provide the salient features of the embedded flow parameters which include the Reynolds number, the Deborah numbers, and the Hartman number. Comparison between the existing numerical solution in a Maxwell fluid and present deduced series solution in a limiting sense is excellent.

Adsorption of Thiophenic Compounds in the Gasoline Boiling Range over FCC Catalysts under Process Conditions

Daniel Del Rio et al. — Wed, 18 Jan 2012 19:50:44 PST

Experiments on commercial FCC equilibrium catalysts with different hydrogen transfer properties and content of Ni and V contaminant metals were performed in a CREC Riser Simulator reactor to study the behavior of thiophenic compounds in the gasoline boiling range. Thiophene and alkylthiophenes were used as test reactants dissolved in aromatic and paraffinic solvents in usual concentrations of the process, from about 150 to 400 ppm of each compound. The experiments were performed under conditions similar to those of the industrial operation (510 º C, contact time 5 to 20 s). The reaction effluents were analyzed by on-line gas chromatography using two detectors simultaneously: FID (hydrocarbons) and PFPD (sulfur). The results showed that a higher hydrogen transfer capacity in a catalyst favors the decrease of the concentration of sulfur compounds in gasoline by adsorption and / or coke formation. These results were more pronounced as the molecular weight of the alkylthiophene increased. Reductions in total sulfur concentration in the gas phase as high as 65 % were observed. Among contaminant metals, Ni seemed to have an important contribution to this effect.

Fischer Tropsch Synthesis: The Promoter Effects, Operating Conditions, and Reactor Synthesis

Majid Sarkari et al. — Wed, 18 Jan 2012 19:50:43 PST

The effects of K, Ce, Zn, Cs, and Rb promoters on the structure and catalytic behavior of precipitated 50%Fe/50%Mn catalyst in Fischer–Tropsch synthesis (FTS) were investigated in a fixed-bed reactor. The effects of promoter on Fischer-Tropsch iron catalysts caused an increased growth probability of hydrocarbon chains from 0.67 to 0.75 for K to Rb promoter, and the olefin/paraffin ratios increased from 0.99 to 1.36 for Rb to K-promoted catalyst. The effect on the olefin selectivity was certainly due to increased adsorption strength of CO causing an enhanced displacement of olefin. The catalysts were assessed in terms of their FTS activity and product selectivity using Anderson–Schulz–Flory (ASF) models. The effects of various reaction conditions such as flow rates, temperatures, and H2/CO feed ratios were studied and process synthesis concepts were used to investigate interactions between the optimum regions for reactor operation and the experimental results.

The Investigation of the Selected Parameters of Catalysis on the Effectiveness Factor of MTBE Synthesis in the Case of a Pellet Catalyst

Carles Fite et al. — Wed, 18 Jan 2012 19:50:41 PST

The influence of selected parameters on the effectiveness factor of catalyst particles for the synthesis reaction of methyl tert-butyl ether (MTBE) from methanol and isobutene is analyzed. The catalyst is the sulfonated ion-exchange resin Bayer K2631. To this aim, the mass and heat balance equations that are presented as a system of differential equations, has been solved by means of the commercial mathematical software MathCad, for which a tailor - made program has been created. Four chosen parameters (tortuosity, particle radius, methanol to isobutene molar ratio and temperature) have been considered to carry out the calculations. The obtained results have been analyzed and presented in a graphical form. They show that the effectiveness factor can be equal, lower or higher than unity depending on the value of the considered parameters. The effectiveness factor is mainly dependent on mass and heat diffusional limitations at certain reaction conditions.

Reaction Engineering Studies of Homogeneous Rhodium-Catalyzed Methanol Carbonylation in a Laboratory Semi-Batch Reactor

Reza Golhosseini et al. — Wed, 18 Jan 2012 19:50:39 PST

Thermodynamic restrictions and simultaneous effects of operational conditions on the homogeneous rhodium-catalyzed carbonylation of methanol are studied in this line of research. It is shown that the general NRTL-Virial model can be appropriated to study thermodynamics of the carbonylation. It is obtained that the reaction is kinetically and thermodynamically reasonable at temperatures above 420K and below 520K, respectively. Moreover, at carbon monoxide partial pressures above 10 bar, the reaction rate is independent of the partial pressure. These results are in full accord with those reported in the literature. In addition, P_CO > 2 bar is necessary for initializing the reaction. The parameters involved in the rate expression, equilibrium constants, CO solubility, and rate constant, are determined. The equilibrium constants are calculated with B3LYP/SDD ab initio method, and the value of Henry’s coefficient for CO (H_CO) is determined as a function of temperature and methyl acetate conversion. The results predicted by this function agree well with those proposed by the general NRTL-Virial model with the errors below 11%. The Variation of CO solubility with acetic acid and methyl acetate concentrations is in good agreement with that obtained by others. It is found that the determined parameters give satisfactory predictions in modeling and simulation of the reaction.

A Comprehensive Review of Just Suspended Speed in Liquid-Solid and Gas-Liquid-Solid Stirred Tank Reactors

Rouzbeh Jafari et al. — Wed, 18 Jan 2012 19:50:35 PST

For successful design and operation of Liquid-Solid (LS) and Gas-Liquid-Solid (GLS) stirred tank reactors engineers and scientists must define geometrical and operating conditions for a specific medium (specified physical properties) in such a way that provides the optimum level of solid suspension. Failure to design the stirred tank reactor to achieve optimum conditions and maintain the system at these conditions during operation may be detrimental to product quality (selectivity and yield) and cost. Successful design and operation require comprehensive knowledge about how the state of solid suspension may be affected by changing physical, operational, and geometrical parameters. Also, accurate correlations are necessary to fulfill that objective. This article intends to provide that background for scientists and engineers. It critically surveys the published work in this field and makes specific recommendations for the appropriate conditions that provide the successful operation of agitated vessels.

Modeling a New Rotational Reciprocating Plate Impeller Using Computational Fluid Dynamics

Yun Lin et al. — Thu, 12 Jan 2012 19:13:07 PST

A new impeller, the rotational reciprocating plate impeller (RRPI), designed to handle highly viscous fermentation broth, was modeled using computational fluid dynamics (CFD) to gain more insight into its performance. A standard Rushton turbine was first simulated using CFD software Fluent(r) for validation purposes. Under experimental conditions, the prediction of the power number obtained from CFD simulation agrees qualitatively with the experimental data. Multiphase simulation was used to better represent the gas-liquid interactions using Eulerian multiphase model. The rotational reciprocating movement of the RRPI was approximated using small time steps, each of which has a different rotation speed. Water and carboxymethyl cellulose (CMC) solutions were used as model fluids to represent the different stages of a typical fermentation with a rheologically-evolving broth. By comparing the simulation results to experimental data, the efficiency of the toothed belt used to drive the Rushton turbine impeller was confirmed to be high as expected, while the efficiency of the three-arm linkage system used to achieve the rotational reciprocation of the RRPI was estimated to be around 80%. The uniformity of mixing with the 3-Rushton impeller and the RRPI was compared to each other by investigating the distribution of liquid velocity, shear rate, and broth viscosity. The simulation results proved that the RRPI eliminated the dead zones that usually form when the Rushton turbines are used in viscous medium.

Competitive Sorption of Pb, Cd, and Ni on Chicken Feathers from Binary Aqueous Solutions

Hilda Elizabeth Reynel-Avila et al. — Thu, 12 Jan 2012 19:13:02 PST

In this paper, we report the competitive removal of Pb, Cd, and Ni ions from binary metal solutions using chicken feathers. These heavy metals are very toxic for human being and are present in wastewaters of several industrial activities. Therefore, multi-component sorption studies are required to identify the capabilities and limitations of chicken feathers as low-cost sorbent for the simultaneous removal of these metal ions from wastewaters. To the best of our knowledge, sorption equilibrium studies involving chicken feathers and Pb, Cd, and Ni in binary aqueous solutions have not been reported. Therefore, the binary sorption data for systems Pb - Cd, Pb – Ni, and Cd - Ni at different pH conditions are reported in this paper. Our experimental data are modeled using multi-component isotherm equations and desorption studies were also performed. In summary, this study provides new experimental data to identify the competitive effects of these metal ions onto the multi-component sorption performance of chicken feathers.

Optimization of Fluidized Bed Reactor of Oxidative Coupling of Methane

Mohammad-Hosein Eghbal-Ahmadi et al. — Sun, 08 Jan 2012 21:41:43 PST

Optimization of process variables in the oxidative coupling of methane (OCM) over Mn/Na₂WO₄/SiO₂ catalyst in a fluidized bed reactor was carried out. Effects of operating temperature, distribution pattern of oxygen injected to the reactor and the number of injections on the reactor performance on C₂ (ethane + ethylene) yield were investigated. Process variables for one, two and three secondary oxygen injections were investigated to obtain the maximum C₂ yield by genetic algorithm optimization method. The maximum C₂ selectivity and yield of 47.1% and 22.87%, respectively, were achieved for three secondary oxygen injections at operating temperature of 746.05°C. The C₂ yield achieved in this study is approximately 4% better than previous works reported in literature while the optimum temperature is lower.

Glucose Mass Transfer Under Substrate Inhibition Conditions in a Stationary Basket Bioreactor with Immobilized Yeast Cells

Anca Irina Galaction et al. — Tue, 03 Jan 2012 22:46:51 PST

The work is dedicated to the study on the external and internal mass transfers of glucose for alcoholic fermentation under glucose inhibition limitation using a bioreactor with stationary basket beds of immobilized Saccharomyces cerevisiae cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the kinetic model adapted for the inhibitory effect of glucose, specific mathematical models have been developed for describing the profiles of the substrate concentration in the outer and inner regions of biocatalysts and, implicitly, for estimating its mass flows in the liquid boundary layer surrounding the particle and inside the particle. The values of the mass flows are significantly influenced by the internal diffusion velocity of substrate and rate of the biochemical reaction of substrate consumption, but also by the position inside the basket bed. These influences cumulated led to the appearance of biological inactive region near the particle centre, its magnitude varying from 0.34 to 31% from the overall volume of particles.

The presented results are the first unitary approach of the aspects of substrate mass transfer in a basket bed of immobilized biocatalysts, the proposed models being original and complex.

Unsteady Rotating Flows of Oldroyd-B Fluids with Fractional Derivatives

Muhammad Jamil et al. — Sat, 17 Dec 2011 12:02:43 PST

Exact solutions corresponding to the unsteady flows of an Oldroyd-B fluid with fractional derivatives, between two infinite coaxial circular cylinders are obtained by means of Laplace and finite Hankel transforms. The motion of the fluid is produced by the inner cylinder that, at time t=0⁺, is applied a time dependent rotational shear stress to the fluid. The expressions of the velocity field and the shear stress are presented in series form in term of generalized G_{a,b,c}(•,t) and R_{a,b}(•,t) functions. The solutions that have been obtained satisfy all imposed initial and boundary conditions. The corresponding solutions for ordinary Oldroyd-B, fractional Maxwell, ordinary Maxwell, fractional second grade, ordinary second grade and Newtonian fluids performing the same motion are obtained as limiting cases of general solutions. Moreover, as a check of our calculi, our present solutions for ordinary second grade and Oldroyd-B fluids are compared with known solutions form the literature. Finally, the influence of the pertinent parameters on the fluid motion as well as a comparison between the models is underlined by graphical illustrations.

Quantification of Mixing in RIM Using a Non-Diffusive Two-Phase Flow Numerical Model

Cláudio P. Fonte et al. — Thu, 01 Dec 2011 20:59:01 PST

Mixing in RIM is made mainly by advective mechanisms, rather than diffusion. In this paper, the advective mechanisms that enable reducing the mixing scales down to the values required for the complete chemical reaction of the two monomers inside the RIM mixing chamber are identified and studied. From Computational Fluid Dynamics (CFD) simulations of non-diffusive two-phase flow using the Volume-of-Fluid (VOF) model, a linear scale of segregation is determined as a measure of the degree of mixing and the effect of the Reynolds number is studied.

Melting Effect on Unsteady Hydromagnetic Flow of a Nanofluid Past a Stretching Sheet

Ali J. Chamkha et al. — Thu, 01 Dec 2011 20:58:56 PST

This paper considers unsteady, laminar, boundary-layer flow with heat and mass transfer of a nanofluid along a horizontal stretching plate in the presence of a transverse magnetic field, melting and heat generation or absorption effects. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing partial differential equations are transformed into a set of non-similar equations and solved numerically by an efficient implicit, iterative, finite-difference method. A parametric study illustrating the influence of various physical parameters is performed. Numerical results for the steady-state velocity, temperature and nanoparticles volume fraction profiles as well as the time histories of the skin-friction coefficient, Nusselt number and the Sherwood number are presented graphically and discussed.

Kinetics Study of Esterification Reaction of 2-Methyl-4-Chlorophenoxyacetic Acid (MCPA Acid)

Pei San Kong et al. — Thu, 01 Dec 2011 20:58:51 PST

MCPA ester is a postemergence and selective herbicide widely used in controlling weed growth. This is due to the low solubility of MCPA ester in water which differs from majority of the other herbicides. With low solubility, the chance of water pollution is lesser comparatively. MCPA ester can degrade in soil by biological and biotic mechanism which reduces the soil pollution. Despite the wide application of this ester, the kinetic data on synthesis of MCPA ester is still considered as a proprietary data and it is not available in the open literature. Therefore kinetic studies are conducted in this work. MCPA ester was synthesized by reacting MCPA acid and 2-ethylhexanol in the presence of sulfuric acid as a catalyst. The parameters studied were reaction temperature, catalyst concentration and alcohol to acid molar ratio. The reaction was conducted in a jacketed batch reactor and samples were taken at an appropriate time intervals. The concentration MCPA ester was determined by gas chromatography mass spectrometry (GC-MSD) analysis. The experimental data were fitted with proposed homogeneous integrated second order kinetic model and the fitting accuracy at 373K, 383K and 393K were 0.99, 0.95 and 0.99 respectively. The activation energy and frequency factor were estimated to be 71.559 kJmol^-1 and 1.221 x 107 Lmol^-1 min^-1 respectively. Kinetic constant values were 0.844 x 103 to 6.331 x 103 Lmol^-1 min^-1 within the range of the temperature and concentration studied. As predicted, the activation energy decreases with increases in catalyst concentration and the values at 0.01M, 0.1M and 0.5M catalyst concentration were 73.6, 71.7 and 69.4 kJmol^-1 respectively.

Performance Analysis of Immobilized Enzyme Semifluidised Bed Bioreactors

C.M. Narayanan et al. — Thu, 01 Dec 2011 20:58:46 PST

In spite of the many-sided advantages of semifluidised bed bioreactors, no attempt has been made to simulate their performance mathematically. Only scattered experimental data are available in literature. In the present study, therefore, attempts have been made to simulate immobilized enzyme semifluidised bed bioreactors’ performance as equivalent to CSTR – PFR combinations, but with due allowances for the heterogeneity of the system. Bioconversions that follow Michaelis – Menten kinetics (with and without substrate inhibition) and reversible Michaelis – Menten kinetics have been considered. Substrate transfer into the particle (that accommodates the immobilized enzyme) is governed by the magnitude of effectiveness factor which is evaluated based on the generalized integral for the estimation of Thiele – type modulus and the corresponding correlation for effectiveness factor (as a hyperbolic tangent function) and also based on the analytical expression proposed by Gottifredi and Gonzo. Parameters such as operating semifluidisation velocity, porosity of fluidized section, height ratio of packed section to fluidized section are estimated from experimental correlations that are selected through elaborate trial and error procedure. Though the simulation model involves simplifications and empirical estimation of a few parameters, model results are found to exhibit reasonably good agreement with data collected through extensive experimental investigations, the maximum deviation being ±12.5 %. This confirms the acceptability of the software package developed. The developed software could be, therefore, recommended for the design and installation of industrial semifluidised bed bioreactors and also for the performance analysis of existing industrial bioreactors.

The Effect of Gas Flow Rate on the Thin Film Deposition Rate on Carbon Steel Using Thermal CVD

Mohammad A. Chowdhury et al. — Thu, 01 Dec 2011 20:58:39 PST

Solid thin films have been deposited on carbon steel substrates in a chemical vapor deposition (CVD) reactor where natural gas, mostly methane (CH₄), was used as a precursor gas. The effect of gas flow rate on the thin film deposition rate has been investigated experimentally. The effect of gap between activation heater and substrate on the deposition rate has also been observed. To do so, a hot filament thermal chemical vapor deposition unit is used. The flow rate of natural gas varies from 0.5 to 2 l/min at normal temperature and pressure (NTP) and the gap between activation heater and substrate varies from 4 to 6.5 mm. Results show that the deposition rate on carbon steel increases with the increase of gas flow rate. It is also seen that deposition rate increases with the decrease of gap between activation heater and substrate within the observed range. These results are analyzed by dimensional analysis to correlate the deposition rate with gas flow rate, surface roughness and film thickness. In addition, friction coefficient and wear rate of carbon steel sliding against SS 304 under different normal loads are also investigated before and after deposition. The obtained results reveal that in general, the values of friction coefficient and wear rate are lower after deposition than that of before deposition.

Frictional Pressure Drop of Gas-Newtonian and Gas-Non Newtonian Slug Flow in Vertical Pipe

Subrata Kumar Majumder et al. — Tue, 29 Nov 2011 22:55:15 PST

Experimental study on two-phase pressure drop in a vertical pipe with air-Newtonian and non-Newtonian liquid in slug flow regime has been carried out within a range of gas and liquid flowrate of 0.5×10^-4 to 1.92×10^-4 m^-3/s and 1.6×10^-4 to 6.7×10^-4 m³/s respectively. In the present study air and four types of liquids such as water, amyl alcohol, glycerin (two different concentrations), and CMC (Sodium Carboxymethyl Cellulose) are used. The present data were analyzed by two-phase friction method. To predict the two-phase pressure drop, correlations have been developed with Newtonian and non-Newtonian liquid. A general correlation was also developed to predict the two-phase pressure drop in a vertical column of diameter 0.01905 m and 3.4 m height combining both the Newtonian and non-Newtonian liquid systems.

A Novel Biodiesel and Glycerol Carbonate Production Plant

Nghi T. Nguyen et al. — Wed, 16 Nov 2011 21:38:28 PST

Crude glycerol is the byproduct of biodiesel production plant and the economic value of glycerol may affect the profitability of the biodiesel production plant. As the production rate of bioglycerol increases, its market values drop considerably. Therefore, conversion of bioglycerol into value-added products can reduce the overall cost, hence, leading to a more economical biodiesel production plant. In a direct carboxylation reaction, CO₂ reacts with glycerol to produce glycerol carbonate and water. This study presents a direct comparison of the economic analysis of the conventional biodiesel production plant and the possible next generation biodiesel-glycerol carbonate production plant. At the end of 15-year project, the net present value of the biodiesel-glycerol carbonate production plant is $13.21 million higher than the conventional biodiesel plant. The stochastic model has predicted that the biodiesel-glycerol carbonate and conventional biodiesel production plants has about 30% and 63% chance of getting negative net present value, respectively. Heterogeneous catalyst, Ca₃La₁, is used for transesterification reaction to reduce separation steps in the biodiesel production process.