ABSTRACT

Results from two recent investigations, one dealing with pervaporation-aided esterification and the other with biological reactors, are discussed in this presentation. Reactors coupled with membrane separation, such as pervaporation, can help enhance the conversion of reactants for thermodynamically or kinetically limited reactions via selective removal of one or more product species from the reaction mixture. An example of these reactions is esterification of carboxylic acids and alcohols. Esterification of lactic acid (C3H6O3) and ethanol (C2H5OH) is investigated in well-mixed reactors with/without a solid catalyst (Amberlyst XN-1010) in this study. Rate expressions for homogeneous and heterogeneous esterification are obtained from the experimental data using differential and integral methods. Experiments with a closed-loop system of a “batch” catalytic reactor and a pervaporation unit reveal that fractional conversions of the two reactants and yield of ethyl lactate exceeding the corresponding maximum values in a reaction-only operation are obtained by stripping of water, a product. The efficacy of pervaporation-aided esterification is illustrated by the substantial gains in fractional conversion of each reactant. A protocol for recovery of ethyl lactate from pervaporation retentate is proposed. Simulations based on empirical correlations for kinetics of esterification and pervaporation reveal the trends observed in experiments.

Biological wastewater reactors are traditionally divided into two groups based on modes of cell growth –suspension and attached (biofilm) growth. The reactors in practice always contain void space and solid surfaces and both forms of microbial growth must occur in principle. Kinetic descriptions of suspension cultures are based on neglecting cell growth on surfaces, while kinetic descriptions of surface-attached growth usually confine cell growth to biofilms. A dual-growth model is developed here to fully account for cell growth and substrate utilization in both modes, suspension and attached. Model simulations enable a comparison of the two forms of biomass (attached and suspended) in terms of biomass accumulation, substrate degradation and effectiveness of substrate utilization and illustrate the complex interactions that arise between the two forms of biomass. The concept of suspended-attached duality provides a unified way to analyze and design biological wastewater processes.