Thesis (M.Eng.)--Chulalongkorn University, 2013

The objective of this work is to investigate the pervaporative transport behavior of orange juice model solution consisting of four key flavor compounds, namely, ethyl butyrate, trans-2-hexenal, 1-hexanol and D-limonene through the tubular polydimethylsiloxane (PDMS) membrane. The effect of variables on the separation performance were investigated such as feed concentration (original orange juice concentration, at 75-fold and at 150-fold of the original orange juice concentration), feed temperature (30, 40 and 45 °C) and permeate pressure (5, 10 and 15 mmHg). The results show that, increase in feed concentration resulted in increase in the partial flux of flavor compounds but decreased selectivity and recovery percentages. The increase in feed temperature leads to higher permeation flux and recovery percentages of each flavor compound but lower selectivity. In addition, increase in permeate pressure slightly reduced the permeation flux, selectivity and recovery percentages. However, the behavior of some flavor compounds did not follow this trend at some experimental conditions such as that of D-limonene and trans-2-hexenal. The selectivity of D-limonene increased as feed concentration increased. But the selectivity of trans-2-hexenal on the other hand increased slightly with the same increase in permeate pressure. As permeation flux of flavor compounds is inversely proportional to the compound selectivity, the pervaporation separation index (PSI) was more often used in membrane separation processes as a criterion for the selection of appropriate conditions. Base on the PSI, it has been found that increase in feed concentration and decrease in feed temperature led to the decrease in the PSI values of ethyl butyrate, trans-2-hexenal and 1-hexanol, and the increase in PSI value of D-limonene. Whereas, increase in permeate pressure decreased the PSI values of all flavor compounds except for trans-2-hexenal. It should be noted that the PSI for D-limonene was negative at low feed concentration, and to increase the PSI value of the key flavor compound like D-limonene, high feed concentration would be more appropriate, however with the expense of lower PSI values for the other compounds. The most suitable conditions for separation of D-limonene are at 75-fold of original orange juice feed concentration, high feed temperature of 45 °C and low permeate pressure of 5 mmHg. Whereas the appropriate conditions to separate ethyl butyrate, trans-2-hexenal and 1-hexnol is operated with real orange juice concentration, feed temperature 45 °C and permeate pressure 5 mmHg.