Date of Award
Master of Science in Chemical Engineering - (M.S.)
George C. Keeffe
Jerome J. Salamone
C. L. Mantell
To determine the effects of reduced pressure on pressure drop and holdup in distillations seven different liquids were distilled at varying rates at atmospheric pressure and under vacuum at pressures down to 50 mm Hg, using protruded stainless steel packing. Pressure drop and holdup were found to vary exponentially with masste at each pressure. At constant mass rate pressure drop was higher for decreased head pressure. Use of material of higher molecular weight led to lower pressure drop at same rate and pressure. Greatest effect of pressure on pressure drop was observed below 300 mm Hg. Liquid holdup was not affected greatly by pressure or molecular weight with the packing used.
Data for the seven liquids at all pressures tested, correlated by a plot at log Δρ vs. log G/φ, defined a straight line within reasonable limits. This line, however, had a slope too steep to be used for design work with much accuracy. Correlation of the data by a plot of loge ρΔρ vs. log 0 also gave a straight line within about the same limits. This has a slope approximately the same as the G/φ curve and is not recommended for design work.
Modification of the Reed-Fenske equation to use liquid instead of vapor viscosities appeared to yield abetter correlation of data for the individual liquids and gave closer agreement among all the liquids. The curve, defined by (ρΔρ /µ2 = 0.0001 (G/µ1)2.4, should be useful for approximating expected pressure drop for any liquid at any rate for the size and type packing used.
Evidence pointy to diffusion concepts as a baste for correlation of distillation data. A new relationship is presented to predict the change in pressure drop at constant rate produced by a material of different molecular volume. The data is shown in the form:
(log Δρ)G/φ = a - 3/4 Vm
Use of the curves obtained permitted estimation of pressure drop of a liquid with molecular volume greater than twice those used here to within thirty percent over a tenfold change in pressure drop. The curves should apply at any pressure since G/φ includes the effect of pressure on vapor density.
Cummins, Joseph Peter, "The effect of reduced pressure on variables in distillation" (1955). Theses. 2286.