Rengaswamy Jaganathan

Hydrogenation of nitrobenzene to p-aminophenol in a four-phase reactor : reaction kinetics and mass transfer effects

The kinetics of catalytic hydrogenation of nitrobenzene in acid medium to p-aminophenol was investigated in a batch slurry reactor in a temperature range of 323-353 K. Aniline was formed as a byproduct (upto 20%). The initial rate data were analyzed to assess the mass transfer effects and it was found that gas-liquid mass transfer resistance was important under certain reaction conditions. A Langmuir-Hinshelwood type rate model has been proposed based on the initial rate data in the kinetic regime and considering the reaction taking place in both organic as well as aqueous phase. Since this was a four-phase system, the rate equation was suitably modified to include gas-liquid and liquid-liquid mass transfer steps. The kinetic parameters evaluated from a semibatch reactor model were found to represent the observed experimental data very well indicating the applicability of the proposed rate model.

A trickle-bed reactor model for hydrogenation of 2,4 dinitrotoluene: experimental verification

Abstract A trickle-bed reactor model has been developed for hydrogenation of 2,4 dinitrotoluene (DNT). This model incorporates the contributions of partial wetting and stagnant liquid hold-up effects in addition to external and intraparticle mass transfer resistances for a complex consecutive/parallel reaction scheme under consideration represented by L-H-type kinetics. As the reaction is highly exothermic, the heat effects have also been incorporated in the model. The reactor performance for complete wetting, partial wetting of catalyst particles and in the presence of stagnant liquid pockets has been compared and the significance of different parameters discussed. Experimental data were obtained for different particles sizes, different gas and liquid velocities in a temperature range 318–328 K. The model predictions were compared with experimental data and were found to agree very well for a wide range of operating conditions. The model proposed here also allowed prediction of maximum temperature rise in the catalyst bed and which was also found to agree well with the steady-state experimental data. Under certain conditions, hysteresis behaviour of the reactor performance has been observed.

Kinetic modelling of a complex consecutive reaction in a slurry reactor: hydrogenation of phenyl acetylene

Abstract Kinetics of hydrogenation of phenyl acetylene to styrene to ethyl benzene using Pd/C catalyst has been reported. The experiments were carried out in a mechanically agitated autoclave over a temperature range of 15–45°C. Effect of catalyst loading, H 2 pressure, concentrations of reactants and products on the rate of hydrogenation as well as the concentration profile in a batch reactor was investigated. The analysis of initial rates showed that the data were in kinetic regime for 0.1% Pd/C catalyst. For interpretation of the kinetics, the observed concentration time data were directly used and the rate parameters evaluated using a simulation model for the batch reactor. It was found that the rate of hydrogenation was strongly inhibited in the presence of phenyl acetylene, while styrene and ethyl benzene showed negligible effects. The activation energies observed for the two consecutive steps were 51.5 and 53.6 kJ/mol, respectively.

Kinetics of hydrogenation of maleic acid in a batch slurry reactor using a bimetallic Ru–Re/C catalyst

Abstract The hydrogenation of maleic acid was investigated using a bimetallic Ru–Re/C catalyst powder in a semi-batch stirred slurry reactor with the main objective of developing a kinetic model that would provide reliable predictions of the observed reactant and product distributions and selectivities. The combined effects of hydrogen pressure, catalyst loading and initial maleic acid (MAC) concentration on the concentration vs. time profiles were studied over the temperature range of 523– 543 K . The direct hydrogenation of aqueous MAC solutions with the Ru–Re/C catalyst powder showed that succinic acid (SAC), γ -butyrolactone (GBL) and tetrahydrofuran (THF) were the major products while n-butanol (BuOH), methane and propane were the principal side products. The selectivities of GBL and THF were found to be strongly dependent on the initial MAC concentration, H 2 pressure, catalyst powder loading and reaction temperature. Kinetic rate equations for the key steps in the reaction sequence were developed using the observed concentration vs. time profiles as the starting basis and the kinetic parameters were estimated using non-linear parameter estimation. The predictions of the semi batch slurry reactor model were found to agree reasonably well with the experimental data. The kinetic data showed a strong substrate inhibition effect for the consecutive reactions sequence with the extent of inhibition decreasing in the order of MAC>SAC>GBL. This observation suggests that a high space-time yield to THF can be obtained in a slurry reactor with significant liquid phase backmixing by the use of elevated temperature and pressure and long slurry residence time. Implications for commercial implementation are also suggested.

Platinum catalyzed hydrogenation of 2-butyne-1,4-diol

Hydrogenation of 2-butyne-1,4-diol (B3D) using 1% Pt/CaCO3 catalyst was carried out to give 2-butene-1,4-diol (B2D) or butane-1,4-diol (B1D) selectively or a mixture of two diols eliminating the formation of acetal, aldehyde, and alcohols as side products. In presence of ammonia, nearly complete selectivity to B2D was obtained in a batch reactor while, in a fixed bed reactor total selectivity to B1D was obtained. Effect of concentration of ammonia, metal loading and catalyst pre-treatment on catalyst activity and selectivity has been investigated in a batch reactor. The formation of B1D and B2D is explained on the basis of associative or dissociative adsorption of B3D via carbene and carbyne type intermediates which react with adsorbed hydrogen to give the corresponding products. A kinetic model based on Langmuir–Hinshelwood (L–H) type mechanism has been proposed which shows a good agreement with experimental data.

Hydrogenation of crotonaldehyde to n-butyraldehyde: reaction kinetics in a slurry reactor

Hydrogenation of crotonaldehyde was studied in liquid phase using Pd/C catalyst. The only product formed was n-butyraldehyde under the reaction conditions of the present work. The concentration-time profiles were obtained under various operating conditions. The rate constants were evaluated by simulating the concentration-time plots. The model predictions and the experimental data were found to be in good agreement.

Analysis of mass transfer effects in ethyl cellulose manufacture

A theoretical analysis of mass transfer effects in ethyl cellulose manufacture has been reported. This is the first model to describe a complex fluid–solid reaction in the presence of two immiscible liquids. The model derived here can be used to evaluate the dependency of the overall rate on different parameters incorporating the multiphase mass transfer effects.