Dispersed‐phase holdup in packed, countercurrent liquid‐liquid extraction columns

Abstract

AbstractThis investigation is a study of the effect of flow rates and packing size and column diameter upon the holdup of a toluene dispersed phase, flowing countercurrent to a continuous water phase in packed liquid‐liquid extraction columns. Six different packings were used: ¼‐, ⅜‐, ½‐, ⅝‐, ¾‐, and 1‐in. nonporous, unglazed‐porcelain Rasching rings. Three extraction columns, 3, 4, and 6 in. I. D., were used in the experimental work.Three types of dispersed‐phase holdup, free, operational, and total, have been investigated. An empirical correlation is presented for the total holdup data below the loading point. A correlation of the effect of packing size on the exponential term r and the coefficient A1 is developed for packing sizes 1/2 in. or larger when the column‐diameter‐to‐packing‐size ratio is at least 8 to 1. The term A1(VD)r in the equation accounts for at least 90% of the total holdup. The small magnitude of the residual term B1(VD) (VC8) did not permit a definite correlation of the coefficient B1 or the exponent s.Observation of the dispersed‐phase holdup during column operation revealed a transitional behavior of the 3/8‐in. rings as compared with that of the 1/4‐ and 1/2‐in. or larger packing. Two, and sometimes three, regimes of flow occur in packed extraction columns. the increase in holdup with increasing continuous‐phase flow rate differed for each zone. In the two zones below the loading zone the holdup was found to increase linearly with the dispersed‐phase flow rate for a constant continuous‐phase flow rate. A new method of randomly packing an extraction column has been found to give reproducible holdup data.