Continuous crystallization of potash alum: MSMPR kinetics

Abstract

The crystallization kinetics of potash alum (aluminium potassium sulphate) from aqueous and aqueous acetone solutions respectively in a continuous mixed‐suspension, mixed‐product‐removal (MSMPR) crystallizer (capacity 4 L) are reported. Growth and nucleation rates are determined by direct model estimation via the population balance analysis of crystal size distribution measured using laser light scattering and sieve analysis. The overall growth rate during drowning‐out precipitation strongly decreases with increasing acetone concentration in the crystallizing solution. Nucleation rates evaluated at zero‐size, however, are virtually unaffected while the “effective” nucleation rates are strongly increased by the presence of acetone with a reduction in the supersaturation order. Magma density dependence is approximately first order during cooling crystallization while a somewhat lower dependence is detected during drowning‐out precipitation.

An Exponential‐Hyperbolic Crystal Growth Rate Model

“…The crystallization kinetics of potash alum from aqueous solutions in a continuous MSMPR crystallizer were recently reported by JONES and MYDLARZ (1990). Figure 5 shows a curved log-cumulative number distribution typical of those obtained in the case of drowning-out precipitation of potash alum with diluted acetone.…”

Slurry filtrability of potash alum

“…mixedproduct-removal draft-tube crystallizer reported recently (Jones and Mydlarz, 1990) indicated that zero-size nucleation rates for cooling crystallization and drowning-out precipitation, however, are approximately the same in both modes of creating supersaturation, indicating that secondary nucleation predominates. mixedproduct-removal draft-tube crystallizer reported recently (Jones and Mydlarz, 1990) indicated that zero-size nucleation rates for cooling crystallization and drowning-out precipitation, however, are approximately the same in both modes of creating supersaturation, indicating that secondary nucleation predominates.…”

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Crystal slurries produced both by cooling and by precipitation with acetone from aqueous solution in a continuous MSMPR crystallizer reported earlier (Jones and Mydlarz, 1990) are analysed in terms of the effect of their crystal size distribution and shape on filtrability characteristics.Crystals produced by precipitation are much smaller but more highly agglomerated than those from cooling crystallization and give rise to lower filter bed permeabilities, a performance which is slightly improved by precipitant dilution. The overall particle size is, however, similar in both modes and is relatively insensitive to crystallizer operating conditions.

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“…Crystal slurries produced both by cooling and by precipitation with acetone from aqueous solution in a continuous MSMPR crystallizer reported earlier (Jones and Mydlarz, 1990) are analysed in terms of the effect of their crystal size distribution and shape on filtrability characteristics.…”

“…The objective of the work reported here is to measure CSD and filtrability of potash alum crystals obtained by cooling and by precipitation respectively from the continuous MSMPR crystallizer reported recently (Jones and Mydlarz, 1990). and to compare the data with the predictions of the Carman-Kozeny model of cake permeability together with recent similar data for the potassium sulfate system (Mydlarz and Jones.…”