Chemical Engineering Journal (v.125, #3)
Kinetic study of the liquid-phase hydrogenation of 1-butyne over a commercial palladium/alumina catalyst
by J.A. Alves; S.P. Bressa; O.M. Martínez; G.F. Barreto (pp. 131-138).
Hydrorefining of C4 cuts of unsaturated hydrocarbons involves the selective removal of 1-butyne by catalytic hydrogenation. Due to its technological relevance, we investigated the hydrogenation of 1-butyne over a commercial palladium-based catalyst of the eggshell type. The experimental conditions were selected to reproduce those of industrial hydrorefining reactors: liquid-phase reaction, seven levels of temperature between 27 and 62°C, initial concentrations of 1-butyne up to 0.6mol/l and hydrogen partial pressure ranging from 0.8 to 8atm. Under these conditions, the overall effectiveness factor of 1-butyne hydrogenation was less than 0.15. Provided that hydrogen was the limiting reactant inside the active shell, 1-butene was the only product yielded by 1-butyne hydrogenation. The regression analysis of experimental data corresponding to the hydrogenation of 1-butyne to 1-butene was restricted to experimental compositions in which 1-butyne concentration was higher than 0.07mol/l. An intrinsic kinetic expression with reaction orders 1 and −1 for hydrogen and 1-butyne, respectively, predicts experimental data with an average deviation of 2.1%. Estimates of the activation energy and kinetic coefficient at 44°C are (1.55±0.06) 104cal/mol and (4.6±0.1) mol/(kgs).
Keywords: Liquid-phase hydrogenation; 1-Butyne; Pd eggshell catalyst
Kinetic modeling of steam reforming of ethanol for the production of hydrogen over Co/Al2O3 catalyst
by D.R. Sahoo; Shilpi Vajpai; Sanjay Patel; K.K. Pant (pp. 139-147).
The kinetics study of steam reforming of ethanol was done using Co/Al2O3 catalysts to investigate the effect of reaction temperature, contact-time and steam to ethanol molar ratio on hydrogen production. Co/Al2O3 catalysts, prepared by wet impregnation method, were characterized for their surface area, pore volume, pore size and X-ray diffraction pattern. All the experiments were carried out in a fixed-bed tubular reactor. Surface reaction mechanism has been proposed based on the literature and product distribution obtained in the present study. The mechanistic kinetic model using Langmuir–Hinshelwood (L–H) approach was developed considering surface reaction mechanisms of steam reforming of ethanol, water gas shift and ethanol decomposition reactions. The kinetic parameters of the multi-response non-linear mechanistic kinetic model were estimated using a non-linear least-square regression by fitting the expression to the experimental data. A reasonably good fit of the data indicates that the formation of acetaldehyde from ethoxy is the rate-determining step (RDS) for reforming reaction. The kinetic model is able to describe the steam reforming of ethanol process adequately for a wide range of experimental data.
Keywords: Ethanol steam reforming; Hydrogen; Kinetics; Co/Al; 2; O; 3; catalyst
Design of a gas distributor: Three-dimensional CFD simulation of a coupled system consisting of a gas chamber and a bubble column
by M.T. Dhotre; J.B. Joshi (pp. 149-163).
CFD simulation for bubble column and a large number of chamber configurations have been carried out. The numerical simulations were based on a two-fluid k– ɛ model. An attempt has been made to simulate the flow pattern on the upstream and downstream of the distributor and its effect on performance of the bubble column. A procedure has been proposed for connecting the gas chamber to bubble column reactor. The extreme cases of uniform and mal-distribution were considered and the effect of mal-distribution was investigated on the flow pattern in the bubble column. The effects of opening area and hole diameter were investigated in the range of 0.64–4% and 2–4mm, respectively. The effect of inlet nozzle size and its location with respect to the distributor were found to be very important. The flow pattern within the gas chamber has been comprehensively analyzed and the velocities through all the holes have been estimated for assessing the uniformity of the gas distribution. It was found that, the chamber configuration has an effect on the uniformity of gas distribution particularly in the sparger region of bubble column reactors. The uniformity of gas distribution was found to increase with an increase in the distributor pressure drop and a decrease in the inlet kinetic head of the gas. Recommendations have been made for the inlet nozzle size and its location, opening area and hole diameter. Further, the development of hold-up profile and its significance on design parameters have been explored. From the quantitative information reported in this paper, it may be possible to select the design parameters of distributor and gas chamber depending upon the desired level of uniformity of distribution and for a given bubble column in terms of diameter ( D), height of dispersion ( HD), superficial gas ( VG) and liquid velocity ( VL).
Keywords: Bubble column; Gas chamber; CFD; Distributor design
Study on a novel POM-based magnetic photocatalyst: Photocatalytic degradation and magnetic separation
by Wei Qiu; Ying Zheng; Katy A. Haralampides (pp. 165-176).
The photocatalytic performance of a novel polyoxometalate (POM)-based magnetic photocatalyst was studied by photocatalytic degradation of a model compound (formic acid) in an annular fluidized bed photoreactor. Degradation rate, apparent quantum efficiency, and energy efficiency were evaluated and compared with suspended TiO2 fine particles (Degussa P25) and quartz sand supported TiO2 photocatalysts. All degradation experiments were conducted under fully irradiated photoreaction (FIP) conditions. Results showed that this novel POM-based magnetic photocatalyst exhibited 2.7–4.2 times higher initial degradation rate and 2.7–3.8 times higher apparent quantum efficiency than the quartz sand supported TiO2 photocatalyst, depending on the pH of the solution. Though it had lower degradation efficiency and apparent quantum efficiency than suspended P25, it was proved that this POM-based magnetic photocatalyst could be efficiently separated from treated water by high-gradient magnetic separation (HGMS), while the separation for P25 fine particles is quite difficult. The magnetic field/gradient in a lab-constructed HGMS was modeled and simulated by finite element analysis (FEA) to examine the particle capture feasibility. Experimental results proved that separation efficiency higher than 90.1% could be achieved under investigated conditions, i.e., flow velocity lower than 1.375mms−1 under the studied magnetic photocatalyst concentration.
Keywords: Magnetic photocatalyst; Photocatalytic degradation; Finite element analysis; Magnetic separation
Adsorption characteristics of inorganic salts and detergents on sand beds
by G. Thirupathi; C.P. Krishnamoorthy; S. Pushpavanam (pp. 177-186).
Experiments were carried out to study the adsorption of two inorganic salts and a commercial detergent on sand. Adsorption isotherms were obtained from batch experiments by measuring the bulk concentration of the feed and that of the liquid after the equilibration period. Langmuir isotherm was found to predict the experimental observations accurately. Column experiments were performed to obtain the breakthrough curves for these inorganic salts and detergents. Two different modes of operation are discussed: (1) straight through mode and (2) recycle mode. The latter can be used for studying features of expensive chemicals in a cost effective manner. The experimental setup was designed so that by switching the valves, the same column can be utilized to study both modes. A convective-dispersion equation is used to describe the continuous operation and the effective dispersivity, D is estimated from the experimental breakthrough curves using an optimization technique. The optimized dispersivity, D is calculated so that the theoretical predictions match the experimental breakthrough curves. In our studies, we find that the behavior of the recycle mode is sensitive to the parameter, D. Hence, the dispersion coefficient is obtained using the recycle mode data. The results of the adsorption study described here can be used in scale up to the field level.
Keywords: Adsorption; Isotherms; Non-linear optimization; Dispersivity; Porous media
Study on a new structure of the separator plate assembly for molten carbonate fuel cell (MCFC) stacks
by Li Zhou; Huaxin Lin; Baolian Yi; Huamin Zhang (pp. 187-192).
A new structure of separator plate assembly (SPA), which consisted of a separator plate, flow field plates, perforated plates, frame plates and seal gaskets, was developed for a molten carbonate fuel cell (MCFC) in this study. In this structure, the separator plate, flow field plates and perforated plates were hard-contacted (directly contacted each other); meanwhile the frame plates and the separator plates were bound with the inorganic seal gaskets. SPA and electrodes could be combined together to form a unit of electrode-SPA. The new structure SPA promoted the smooth volatilizing and complete burning of the organic compounds in the matrix. It was effective and reliable to press the stack with a suitable stacking pressure. It was facile and simple to assemble a stack by using electrode-SPA. With the electrode-SPAs, two MCFC stacks were assembled in co-flow and counter-flow, respectively. The performance of Stack B in counter-flow was higher than that of Stack A in co-flow at the same current density. The more uniform temperature distribution and current density distribution in Stack B were responsible for its higher performance.
Keywords: Molten carbonate fuel cell (MCFC); Separator plate assembly (SPA); Stack; Structure