Date of Award

Fall 1997

Document Type

Thesis

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Kamalesh K. Sirkar

Second Advisor

Basil Baltzis

Third Advisor

Henry Shaw

Abstract

The coupling of a pervaporation membrane unit with a reactor has been investigated as a means of improving the overall process efficiency. As model system, the esterification of salicylic acid with methanol in the presence of a homogeneous catalyst was studied in a unit consisting of a batch reactor externally coupled with a pervaporation module containing a composite poly(vinyl alcohol) membrane. The reaction was carried out at temperatures between 336 and 345 K. The catalyst was sulfuric acid at concentrations varying from 0.5 to 2.0 molar. Various initial molar ratios (ΘB) of methanol and salicylic acid, ranging from 8 to 50, were used. The by-product, water, was selectively and continuously removed from the reaction mixture by pervaporation. Consequently, the reaction processing time was reduced by about 60% compared to that in a conventional batch reactor. At 345 K, almost complete conversion was attained for an initial molar ratio of 8 within 10 h in the integrated system. Experiments performed at 341 K and ΘB = 8 with different membrane areas showed that the processing time needed for 95% conversion of the salicylic acid drops from 30 h in the absence of the pervaporation membrane to 13 h with a membrane having a specific surface area of 66 m-1.

A mathematical model, written in terms of operating variables and design parameters of the system, was developed to provide a fundamental understanding of the behavior of the pervaporation-integrated reactor. The mathematical model takes into consideration details of the reaction kinetics. To validate the model, independent batch kinetic experiments were performed with different molar ratios (ΘB) and catalyst concentrations at different temperatures. The rate constant of the forward reaction was found to have a linear dependence on the catalyst concentration. The model was used successfully in describing the performance of the integrated (pervaporation-assisted) system. The validated model can now be used in simulation studies for parameter sensitivity and optimization purposes.

The coupling of the pervaporation unit with the chemical reactor was shown to be an efficient technique for enhancing performance of organic esterification processes. Moreover, it is easy to scale up and it contributes to pollution prevention by increasing conversion, and reducing the consumption of solvents and energy.

Share

COinS