Breaking of Butyric Acid–Water Azeotrope: Experimental Analysis on Air Gap Membrane Distillation

In this study, the feasibility of using air gap membrane distillation (AGMD), a type of membrane distillation, to separate butyric acid and water from azeotropic mixtures is experimentally investigated. The azeotropic feed solution was run through the AGMD experimental setup, which was fitted with a microporous hydrophobic PTFE membrane. The impact of process parameters such as flow rate of feed solution and flow rate cooling water on total permeate flux, butyric acid selectivity, and permeate and retentate concentration has been investigated. The diffusivity of butyric acid and water in air was estimated using a combination of kinetic theory and corresponding state arguments, while the vapour pressure of butyric acid and water in air was determined using the Antoine equation. The experimental outcome shows that total permeate flux increases from 7.93 to 8.80 kg/m2 h and selectivity of butyric acid increases from 0.35 to 0.53 on increasing feed flow rate from 1 to 5 L/min at 3 mm air gap thickness. In addition, no effect on the total flux and selectivity of butyric acid was observed when the cooling water flow rate is increased from 2 to 6 L/min at air gap of 3 mm. The experimental results indicate that butyric acid/water azeotrope breaks in both permeate and retentate. Therefore, it is concluded that a strong possibility of using the AGMD technique for the breaking of the azeotrope.