Melt Crystallization with Direct Contact Cooling Techniques

TLDR: In this paper, direct contact cooling was used for the separation of an n -decanol- n -dodecanol mixture. Butane was used as the main cooling agent and three coolants, air, water and butane, were employed.

Abstract: Melt crystallization using direct contact cooling techniques has been examined for the separation of an n -decanol- n -dodecanol mixture. Additionally, the heat transfer of melt crystallization by direct contact of coolants has been investigated. Three coolants, i.e. air (as a gas), water (as a liquid) and butane (as a liquefied gas) were employed. Volumetric heat transfer coefficients obtained by direct contact cooling in the melt crystallizer are in the range between 0.1 and 100kW/(m 3 K) and increased roughly with the 1.5 to 1.8 power of the linear superficial velocity of coolant. The volumetric production rate was found to be in the range between 0.01 and 0.2kg/(m 3 s) for the coolant air, 0.05 to 1.4kg/(m 3 s) for the coolant water and butane. The linear growth rate of crystals was proportional to the second power of subcooling. The quality of the crystals produced by this direct contact cooling technique was good, and the crystals are significantly larger than those obtained using scraped-surface crystallizers. A comparison between the effective distribution coefficient obtained before and after wiping has shown that the core of crystals is very pure and the impurity is concentrated in the outer layer of crystals. The described melt crystallization also shows the advantage of continuous operating, high thermal economy and no encrustation in spite of high mean temperature difference.