A theoretical and experimental investigation of the effects of horizontal barriers in thermal diffusion columns

Abstract

A theoretical and experimental investigation of the effects of horizontal barriers on the separation of binary mixtures attained in thermogravitational thermal diffusion columns was undertaken in an attempt to further the understanding of these effects. The presence of horizontal barriers serves to reduce the internal convective flow and t o divide tht column into a number of smaller columns with interconnecting end feeds. Equations developed from such a model serve to predict the effect of the number of barriers, temperature difference, barrier diameter, and other parameters on the steady state and transient behavior of a batch column and on the manner in which bulk flow through the column influences the steady state separation in continuous-flow columns.Data were taken in both batch and continuous columns to test the theory. Parameters varied experimentally (with an ethanol-water system) were number of barriers, (N = 0, 2, 4, 8, 16, 50).temperature difference, and diameter of the cylindrical barriers. It was found that the theoretical developments were entirely adequate to explain the observed influence o f number of barriers for both types of column operation. The slight dependence of steady state batch separation on temperature difference that was observed is consistent with data of other investigations, and the independence of this type of separation on barrier diameter is in agreement with theoretical predictions. The theoretical predictions with respect to changes in temperature difference and a semitheoretical analysis of the effect of barrier diameter making use of isothermal hydrodynamic determinations proved satisfactory in predicting the influence of changes in these two parameters on both the transient batch and steady state continuous-flow column operation.Thermal diffusion has been the subject of much theoretical and experimental investigation ever since Clusius and Dickel ( 5 ) first introduced their thermogravitational column in 1938. In contrast to an apparatus utilizing the static method of thermal diffusion where there are no convection currents, the thermogravitational column multipIies the separation by means of convection currents in a manner similar to the way a countercurrent extraction cascade produces concentration differences many times greater than the difference for a single stage. As a result, although the degree of separation obtainable in an apparatus utilizing the static method is usually small, a thermogravitational column can produce separations approaching 100% Thus, it is the thermogravitational column that has been of primary interest for the aforementioned theoretical and experimental work.Despite the amount of theoretical and experimental work which has appeared in the literature, industry has not yet applied thermal diffusion as a method for separations. Frazier (11) has developed a number of novel endfeed systems for feeding a group of thermal diffusion columns, and Frazier's co-workers have recently reported (13) versible process and requires a relatively large amount ...

Separation in a thermoelectrogravitational electrophoresis column without reservoirs: Part I. Theoretical development of the transport equation and its application to the analysis of steady state batch operation

“…Moreover, even though it is approximate, it yields a nonlinear differential equation for the transport of a component in a column, which can be further simplified to an ordinary first-order linear differential equation and solved for a variety of cases of column operation. This procedure has been employed in thermal diffusion (Boyer and Powers, 1961;Crownover and Powers, 1962;Fleming and Powers, 1963; Halle ( 1959), and Horne and Bearman (1962). Because of the similarity between thermal diffusion and electrophoresis column operation, the FJO procedure can be adapted to the analysis of the combined effect of electrophoresis and thermal diffusion.…”

Sepration in a thermoelectrogravitational electrophoresis column without reservoirs: Part II. Steady state operation of continuous flow column: Theory and experiment

“…Since the membranes were not mechanically strong and large flow rates of cooling buffer might be required, these membranes were supported by Flexolith filter plates. The membrane spacing was vaned by using plexiglass spacers of different thicknesses as suggested by Fleming ( 1961) and the spacing was measured using liquid displacement as described by Boyer (1961).…”