间歇冷却结晶中硫酸铵晶体粒度及形态调控

Regulation of size and morphology of ammonium sulfate crystals in batch-cooling crystallization

在间歇冷却结晶器中,采用激光法测定了(NH_4)_2SO_4溶液的介稳区宽度。讨论了冷却速率以及搅拌速率对(NH_4)_2SO_4晶体粒度和形态的影响,给出了优化操作条件。得到平均长度8.0 mm和宽度1.0 mm的针状(NH_4)_2SO_4晶体。此外,研究了添加CaCO_3颗粒对(NH_4)_2SO_4晶体粒度和形态的改变。当CaCO_3添加量(质量分数)为2.0%时,(NH_4)_2SO_4晶体由针状变为均匀颗粒状,平均粒度1.7 mm。研究了CaCO_3对(NH_4)_2SO_4晶体粒度和形态的影响机理。由结果可知:Ca CO3颗粒充当了(NH_4)_2SO_4非均相成核的催化剂,诱导(NH_4)2_SO_4在比均相结晶更低过饱和度下结晶,减少了(NH_4)_2SO_4(001)晶面的生长时间。此外,Ca CO3颗粒表面优先占据了(NH_4)_2SO_4(001)晶面的活性生长点位,抑制了(001)晶面的生长,从而使(NH_4)_2SO_4晶体粒度和形态改变。

A laser monitoring observation technique was used to measure the metastable zone width of（NH4）2SO4solution in a batch-cooling crystallizer. The effects of cooling rate and stirring rate on the size and morphology of（NH4）2SO4product crystal were discussed,and the optimized operating conditions were provided. The acicular crystals with a length of 8. 0 mm and a width of 1. 0 mm on average were obtained. Moreover,the size and morphological modification of（NH4）2SO4crystals added CaCO3 particles were studied. When 2. 0%（ mass fraction） CaCO3 was added,（NH4）2SO4crystals shape changed from acicular to uniformly granule-like with the average size 1. 7 mm. The mechanism of the effect of CaCO3 on the size and morphology of（NH4）2SO4crystals was studied. The results show that CaCO3 particles act as heterogeneous nucleation catalyst for（NH4）2SO4,and those induce（NH4）2SO4to crystallize at a lower supersaturation than in homogeneous crystallization,the growth time of（NH4）2SO4（ 001） face decreases. Moreover,the CaCO3 particles surface prefers to occupy the active growth sites of（NH4）2SO4（ 001） face,which suppresses the growth of（ 001） face. As a result,the size and morphology of（NH4）2SO4crystals are changed.