(169c) Two-Phase and Three-Phase Slug Flow Microreactors for Lipase Catalyzed Reactions

We have developed and tested various slug-flow microfluidic systems as microreactors for lipase catalyzed reactions. Our work is motivated by the fact that slug-flow microfluidic systems provide high interphase area, uniform residence time and intensive internal mixing of slugs/plugs. As the lipase catalyzed reactions occur at the oil phase/non-oil phase interface, reduction of transport resistances can lead to substantial decrease of the reaction time. Uniform residence time should provide reproducible composition of reaction products.

                We have developed several microfluidic systems for generation of slug flow and separation of reaction products. We used two types of slug flow generators. A simple microchip with T-cross was developed for formation of two-phase slug flow: oil phase (soybean oil) / non-oil (water, glycerol) phase. This microchip was able to provide stable formation of the water-oil slug flow without enzyme reaction. However, the use of this microchip with the water-oil slug flow in presence of lipase or the glycerol-oil flow lead to unstable and irregular slug flow in reaction capillaries. Hence, we decided to make three-phase slug flow system, where irregularity of the slug flow would be suppressed. In the corresponding microchip, small droplets of a non-oil phase in the oil phase were produced by means of fractal splitting of the non-oil phase microchannel. This emulsion was then lead to a T-cross, where uniform segments of the emulsion and nitrogen gas were formed. This arrangement provides high interphase area even if the oil/non-oil emulsion is unstable.

                We have tested two types of separator in our experiments. First, simple gravity separator was employed at the end of the reaction section due to relative high density difference among the phases. We also successfully tested a microseparator, in which two phases were separated on the base of different surface tensions. This microchip consisted of a central channel and an array of side channels with small characteristic dimensions.

                We have compared our slug-flow microreactors with a classical batch arrangement. Enzyme hydrolysis of soybean oil for fatty acid production was studied in the two-phase arrangement. We have attained similar conversions and time demands for both arrangements. However, the slug flow system will be further optimized.