季戊四醇在反应液中的结晶动力学研究

甲醛、乙醛在碱性条件下合成季戊四醇,反应液中含有大量杂质,结晶是实现季戊四醇提纯和关键杂质组分二季戊四醇回收的主要手段。文章用筛析法对工业季戊四醇反应液中的季戊四醇和二季戊四醇结晶动力学特性进行了研究。考察浓缩反应液从80℃降到30℃,结晶时间为8 h,搅拌速度为60 r/min条件下,测得二季戊四醇与季戊四醇的成核速率分别为3.32×106,5.1×105个/(h.L),比值为6.51;季戊四醇与二季戊四醇晶体生长速率分别为0.032 9,0.006 5 mm/h,比值为5.05,以三维体积计为128倍。理论上证明了季戊四醇晶体粒径大、密度小,二季戊四醇晶体粒径小、密度大的原因,与镜检结果一致。为制备高纯季戊四醇工艺提供理论依据,表明可以根据产品的纯度和收率要求,设计相应的工艺条件。

Crystallization kinetics of pentaerythritol in reaction solution

Formaldehyde and acetaldehyde were used to synthesize pentaerythritol under alkaline condition with a large number of impurities.Crystallization was considered as main means to realize the purification of pentaerythritol and the recovery of dipentaerythritol which is the key component in impurities.The characteristics of crystallization kinetics of pentaerythritol and dipentaerythritol were studied by sieve separating.Under the conditions of temperature dropping from 80 ℃ to 30 ℃,crystallization time of 8 h,mixing speed of 60 r/min,the number of crystal nucleus of dipentaerythritol and pentaerythritol was measured respectively as 3.32×106,5.1×105 per hour and per liter,with a ratio of 6.51;crystal growth rate of pentaerythritol and dipentaerythritol is 0.032 9,0.006 5 mm/h,with a ratio of 5.05 which is 128 times as three-dimensional volume.It theoretically proves that the pentaerythritol crystal has large size,low density;dipentaerythritol crystal has small size,high density.The results are consistent with those by microscope examination,and also provide the theoretical basis for preparation of high purity pentaerythritol.The appropriate process conditions can be determined in design according to the requirements for product purity and yield.