Modeling mass transfer in volatile organic compounds separation by pervaporation (PV) and application of PV in blueberry aroma recovery.

摘要

Concentration polarization is a detrimental phenomenon in pervaporation (PV) operation that decreases mass transfer in upside stream near the membrane surface thus significantly reducing achievable separation efficiency. A numerical model was developed to describe pervaporative mass transfer in a slit membrane module used for removal of volatile organic compound. Computational Fluid Dynamics (CFD) program was employed to solve hydrodynamics and mass transfer equations. In order to validate the results from CFD analysis, grid independence of final predicted value was established in both local and universal scale. The modeling approach was further validated by re-examining a classical diffusion problem for which there was a known solution. Numerical modeling predicted mass transfer coefficient of 0.76–1.85 × 10−5 m/s for laminar flow with Re between about 450–1800. This prediction was higher than that predicted by semi-empirical correlation, which could be explained by the module geometry used in modeling and follow-up experiments. After modeling normal PV module, efforts were taken in modeling the effect of baffle in enhancing mass transfer. Different types of baffle structure, including single baffle of three different heights and two baffles with changing distance between each other, were chosen for modeling.; Experiments were conducted using polydimethylsiloxane (PDMS) membrane installed on a bench-scale PV unit. Experimental result using 1,1,1-trichloroethane as solute showed very good agreement with modeling result in the low end of laminar flow while an increasing discrepancy was observed at the high end of laminar flow. As an example of applying PV in extracting aroma compounds during aroma stripping or from processing side streams, model solution containing aroma compound such as ethyl acetate, trans-2-hexenal, 1-hexanol, 1-heptanol, limonene, linalool, representing typical aroma compounds in blueberry was used for feed solution. The results confirmed technical capability of PV in aroma separation.; The established model provides better understanding of the concentration polarization existing in PV operation. The modeling result related to the effect of baffle(s) can be used for optimization of module design to enhance separation of target organic compound. This approach in analyzing concentration polarization in flat module can be extended to tubular and spiral wound module.