MODELING OF STRUCTURED BED REACTOR

Abstract

The last decade a clear trend has been set in chemical industry towards sate, clean and energy efficient production methods, ultimately aiming at zero emission processes. Routes to accomplish this include at chemical side the development of new, highly selective catalysts, opening alternative production routes, and at the engineering side the integrated approach to improved or new processes. Process intensification is currently the fashionable phrase and includes multifunctional and structured reactors. These approaches meet where catalysts are applied in a structured way in a reactor. A monolithic reactor is an example of the structured reactor or catalyst. This monolithic reactor is well known world wide from automotive application as exhaust gas converter and probably the most popular catalytic reactor. The structured catalysts and reactors are the one or the important innovation Ior the chemical industries as well pollution abatement. The structured catalysis is cable in the process intensification and opening the new area for the react mu engineering and catalysis innovation. Solid acid catalysis is attractive replaccnien for processes using conventional homogeneous catalysts. Reactor modeling demonstrates the advantages of this reactor concept, which include the low-pressure drop, high active surface area and easy catalyst handling and catalyst regeneration. In the present study the modeling of monolithic reactor for the esterification reaction has been carried out.. The esterification reaction is one of the important reactions in the chemical industries. 'J:Ke system chosen for pe modeling the esterification of hexanoic acid with I -octanol on BEA zeolite and Nfion (cation exchange resin) anW~steri(tcation of acetic acid with amyl alcohol on cation exchange resin Tulsian-42. A one-dimensional model has been developed for the isothermal operation ul' reactor. The effect of different parameters, like temperature, pressure and superficial velocity, catalyst loading has been discussed. The models developed have been solved using numerical technique based on the Runge-Kutta Method and Finite difference approximation with application of the Newton-Raphson Method. For this study Ilse kinetic rate equations available in the literature have been used. In the esterification of an alcohol and carboxylic acid, the side product water strongly inhibits the forward reaction and deactivates the solid acid catalyst. Since an esterification is equilibrium limited reaction, full conversion is not possible uii1ess 6e of the products is not' removed from the reaction system. In a solid acid catalyst coated monolithic reactor water can be removed from the liquid mixture by means of reactive stripping and complete conversion can be achieved. The results obtained from this study are: The initial rate of reaction increases with increase in the initial concentration of hexanoic acid and decreases with initial concentration of 1-octanol and water concentration. 2. The initial rate of reaction for nation catalyst is slower than the zeolite catalyst. 3. The concentration of the hexanoic acid decreases exponentially along the height of reactor and the conversion increases in similar fashion. 4. Surface concentration of hexanoic acid decreases in similar lashiun as that of liquid phase concentration. Conversion without water removal reaches to a value of 72% while 100% conversion can be achieved with complete water removal. iv 5. The conversion profile and concentration profile for the haxanoic acid for nafion and zeolite catalysts varyin similar manner, i owever the equilibrium conversion for the nafion catalyst V.x-m obtained at higher reactor height. Similarly the equilibrium concentration achieved at higher reactor length for nation catalyst. 6. The equilibrium conversion tained at lower axial distance liar higher catalyst loading. 7. The conversion obtained for the esterification of acetic acid with amyl alcohol is 52% without water removal. Conversion can be reached to 100% with complete water removal. The concentration profile following Vie nearly same trend and decreases with axial distance. 8. Higher conversion has obtained at higher temperature I'or the IN estcri(ication of acetic acid. The bt,phyd resul / from (lie simulation on esterification of hexan()ic acid with 1-octanol on zeolite and Nafion catalysts, have not been validated experimentally, since no experimental data were available on this study, k1wever the results of simulation are reasonably close to the actual experimental data observed for the esterification of acetic acid with ethyl alcohol, in a laboratory scale structured bed reactor recently installed at Indian Institute of Petroleum, Dehradun.