Micro-scale distillation for the separation of methanol-water mixture

Abstract

Separation of methanol-water mixture has been executed experimentally using a micron scale distillation device. Microchannel was patterned on PDMS (Polydimethylsiloxane) elastomer using soft lithography and was covered by glass substrate. Since distillation is a boiling point operation, Peltier device was used as a microheater. PDMS micro-distillation device consisted of two parts, feed evaporation i.e. vapor generation and vapor-liquid separation .Because of high heat and mass transfer and large surface area to volume ratio, it is easy to achieve evaporation in microchannels but it is not less than a challenge to separate vapor-liquid mixture on micron scale. A small microchamber was proposed having 4 to 10 mm diameter with 4 to 12 mm height and the vapor and liquid were drawn at the top and bottom of the chamber for successful separation of vapor and liquid. Distillation efficiency and methanol recovery were chosen as performance criteria and the effect of different parameters such as flow rate, suction pressure, temperature, and geometry of microchannel and microchamber were investigated. Device performances were compared with and without Teflon membrane as a separation media and greater efficiency was obtained without membrane. Greater distillation efficiency and recovery were observed at low flow rate, at low suction pressure, near equilibrium temperature, with deeper microchannel and with larger diameter and higher microchamber. The distillation efficiency using micro-distillation device was more than 90% with single and two stage recoveries almost 50 and 70 % respectively. It is illustrated that both the more and less volatile component of a binary mixture (methanol-water) can be separated into highly concentrated products with negligible gravity effects. In contrast to the tall tower and vertical operation of a conventional distillation column, this device permits a short microchannel and a microchamber to achieve the same degree of separation in a hori...