Crystal Growth Phenomena of Methacrylic Acid under the Presence of Maleic Acid in Melt Crystallization

Crystal growth phenomena were investigated in the suspension melt crystallization of an organic acid. Methacrylic acid was used as the target material, a certain amount of methanol was used as the solvent, and the effect of a small amount of the maleic acid byproduct formed during the methacrylic acid synthesis was focused on. Batch crystallizations were carried out on a laboratory scale using various concentrations of maleic acid. In the presence of maleic acid, it was observed that the mother liquor compositions did not attain equilibrium. Moreover, the quantity of crystal deposition in the presence of maleic acid was smaller than in the absence of maleic acid; nevertheless, the final temperature in the crystallizer was the same. It was suggested that the amount of saturated deposition decreased in the presence of maleic acid. Furthermore, it was observed that the ratio of the growth rate of the minor axis to the growth rate of the major axis varied; the average aspect ratio of the obtained crystal particles gradually decreased over time concurrently with crystal growth. The variation of this growth rate ratio depended on the concentration of maleic acid and it was observed that the crystal size obtained was smaller in the presence of maleic acid than in the absence of maleic acid; maleic acid seemed to suppress the growth rate of the crystals. In addition, the relationship between the aspect ratio and crystal length suggested that aspect ratios of crystals deposited under lower supersaturation conditions will be small and this allows for the potential to decrease the surface washing load of the crystal particles.