撞击流-共沉淀法制备三水碳酸镁的工艺优化及结晶动力学

Process optimization and crystallization kinetics for preparation of nesquehonite by impinging stream-coprecipitation technology

采用新型撞击流技术结合共沉淀法制备三水碳酸镁(MgCO_(3)·3H_(2)O)晶体,对MgCO_(3)·3H_(2)O制备的工艺条件及其结晶动力学进行了研究。实验以长径比为指标讨论了反应物浓度c、反应温度T、循环撞击流量Q和循环撞击时间t对MgCO_(3)·3H_(2)O晶体形貌及结构的影响。实验的最佳工况为:反应物浓度0.25 mol/L、反应温度50℃、循环撞击流量500 L/h、循环撞击时间50 min,在该工况下可得到长径比为20、晶体平均长度为57.3μm的MgCO_(3)·3H_(2)O晶体。运用粒数衡算模型分析晶核粒数密度、生长速率以及成核速率。最佳工况下晶体成核速率为2.061×10^(6)#/(mL·min)、生长速率为0.148μm/min。得出了撞击流-共沉淀法反应体系下各因素的成核、生长动力学方程,确定了各因素对晶体生长影响的敏感系数i。各影响因素得到的敏感系数呈现的关系为iQ<iT<0<it<ic,循环撞击流量和反应温度可促进晶体生长。

Impinging stream is a technique to enhance heat and mass transfer in process engineering.Due to the characteristics of its high and uniform supersaturation,it is widely used in powder preparation.Nesquehonite(MgCO_(3)·3H_(2)O)can be used to combine with materials and increase the strength and toughness of materials because of its special rod-like structure.In this work,MgCO_(3)·3H_(2)O crystal was prepared from magnesium chloride and sodium carbonate by a new impinging stream technology combined with co-precipitation method,and the preparation process conditions and crystallization kinetics of MgCO_(3)·3H_(2)O were studied.The effects of reactant concentration c,reaction temperature T,cyclic impact flow rate Q and cyclic impact time t on the crystal morphology and structure of MgCO_(3)·3H_(2)O were discussed by taking the aspect ratio of rod-like MgCO_(3)·3H_(2)O as the index.The optimal conditions were as follows:the reactant concentration was 0.25 mol/L,the reaction temperature was 50℃,the cyclic impact flow rate was 500 L/h,and the cyclic impact time was 50 min.Under these conditions,the MgCO_(3)·3H_(2)O crystal with the aspect ratio of 20 and an average crystal length of 57.3μm can be obtained.The particle size distribution data under different conditions were measured by laser particle size meter,and the crystal nucleus number density,growth rate and nucleation rate of the product were analyzed according to the population balance model.Under the optimal conditions,the nucleation rate of the crystals was 2.061×10^(6)#/(mL·min)and the growth rate was 0.148μm/min.The nucleation and growth kinetic equations of each factor in the system of impinging stream-coprecipitation reaction were obtained,and the sensitivity coefficient i of each factor on crystal growth was determined.iQ<iT<0<it<ic is the relationship of sensitivity coefficients obtained by each influencing factor.Cyclic impact flow rate and reaction temperature can promote crystal growth.