“Zero-Gravity Distillation Using the Heat Pipe Principle (micro-Distillation)”, 1985-12-01 ():
Separation of ethanol-water and methanol-water mixtures has been accomplished experimentally using a horizontal zero-gravity distillation column. A countercurrent flow between liquid and vapor phases was established using the principle of the heat pipe. The concentration profile along the column has been investigated with various product rates. A high degree of separation was achieved in a relatively short column lined with capillary wicks. The flexible column orientation can also be a tremendous advantage as compared to the necessarily vertical operation of the conventional distillation columns.
Scope: Substantial improvements have been made recently to increase the efficiency of continuous contact distillation. A wetted-wall column has generally been considered to improve its efficiency. However, poor wetting characteristics are still a problem of such a system. Swathed glass tubes, ground glass tubes, and stainless steel mesh tubes have been used as wetted-wall columns with improved wetting properties so that more effective distillation might be achieved (in the range of low reflux rate)
In order to obtain a uniform wetting surface and an enhanced vapor-liquid contacting surface, materials with capillary action, such as wicks and screen meshes, can be used for the distillation. All conventional distillation columns use gravitational force or centrifugal force (eg. the British ICI column) to return the condensed liquid to the evaporator. By employing materials with capillary action, however, the condensed liquid can be transported back to the evaporator in the absence of or even against gravity. Thus the capillary action provides flexibility in column orientation.
The scope of the present study is to investigate the feasibility of microdistillation (using short columns) in the absence of gravity (or in a horizontal position). Both total reflux conditions and steady state with product removal conditions are studied for separation of binary mixtures. As a possible application in outer space, zero-gravity distillation could be used to separate liquid mixtures for recycle of the materials used.
Conclusions and Substance: A new unit operation has been developed for a horizontal distillation column. Experiments were carried out for binary liquid systems using a glass tube and fiberglass as wick material. The temperature of the evaporator was kept just below the boiling temperature of the liquid mixture and an atmospheric pressure was maintained in the vapor phase. Mixture samples were analyzed to determine the concentration profiles along a total reflux column and a steady state column with product removal.
It has been demonstrated that both the most and the least volatile components of a binary mixture of any composition can be separated as highly concentrated products without using gravity forces. In contrast to the tall tower and the vertical operation of conventional distillation, this device permits a short column to achieve the same degree of separation in a horizontal position.
A numerical simulation was developed to obtain the concentration profile along the column. A good agreement is shown between the theoretical and experimental profiles. The performance was characterized by the number of transfer units and height of a transfer unit.