Crystal size distribution (CSD) of batch salting-out crystallization process for sodium sulfate

The crystal size distribution (CSD) of sodium sulfate from the batch crystallization of sodium sulfate from concentrated sulfuric acid (spent acid) by salting-out with methanol was analyzed. The effects of amount of methanol added, the agitation rate, temperature and residence time (sampling time) on CSD were investigated. The mean crystal size and the coefficient of variation (c.v.) were the criteria used and the Rosin–Rammler distribution model was assumed. The mean crystal size varied from 0.03 to 0.07 mm while the range of c.v. was 5–45%, though most of the runs gave a c.v. of 20% or less, thus a size independent growth rate could be assumed. Larger mean crystal sizes were obtained for the following conditions: small amount of added methanol (low level of supersaturation), low temperature, low agitation rates and longer residence time. Reduction in coefficient of variation was enhanced by the same factors. A 24 factorial design analysis confirmed these findings.