Experimental demonstration of rotating spiral microchannel distillation

A prototype device using a rotating spiral microchannel to produce multistage distillation has been designed and used to separate 2,2-dimethylbutane from an initial 50:50 mixture with 2-methyl-2-butene. Distillation or other phase-contacting processes in microchannels requires a strategy for handling surface forces so that the phases can interact in a controlled manner and efficient mass transfer can take place. The rotating spiral approach uses centrifugal force to maintain segregation of the phases into parallel-flowing liquid and vapour layers. When centrifugal force is opposed by pressure gradient along the channel, these layers can flow counter currently. Changing rotation rate and pressure allows adjustment of the phase flow rates and the contacting layer thicknesses. Thus, it is possible to control the phase contacting and take full advantage of the rapid mass transfer that is potentially available for small microchannel dimensions. This efficient contact can be maintained over long channel distances, allowing a large number of separation stages to be reached. A further advantage of the rotating spiral approach is that the mass transfer is augmented by secondary motions produced by Coriolis force. The paper describes the design of the prototype device, including flow and thermal aspects, and presents results for a simple binary distillation. The results obtained demonstrate the practical feasibility of rotating spiral contacting and provide initial quantitative data that are used to evaluate the performance achieved by the prototype device.