At constant temperature and concentration, the chemical
effect of IPA became a factor. It hindered the formation of DHSA
crystal embryos and re-dissolved the DHSA crystal nuclei, delaying
the propagation of the crystallization process from nucleation
to crystallization, ripening, agglomeration and finally separation.
When the crystallization was terminated at the 720th minute, there
was a high probability that the crystal growth had only achieved the
early stage of agglomeration. These very fine crystals formed a cake
with low porosity and permeability during filtration. This ‘agglomeration’
led to partial inclusion of the mother liquor. The mother
liquor (with impurities) adsorbed within the DHSA crystals and/or
remained between individual crystals, compromising the purity of
the final product. This liquid entrainment phenomenon was also
observed when DHSA was solvent crystallized with ethanol (Abidin
et al., 2009; Sumaiya et al., 2010).