Study On The Erythritol Membrane Assisted Antisolvent Crystallization Process

Antisolvent crystallization is more environmentally friendly and novel skill,antisolvent crystallization has irreplaceable advantages for the products,which include some thermosensitive materials,fine particles,special morphologies and crystal species.At present,the main method of conventional antisolvent crystallization is batch dropping skill,the focus of people’s research has been optimizing the antisolvent adding method and solution micro-mixing,to improve the crystal quality.However,the problems of burst nucleation in the drop point and inhomogeneous supersaturation have been unable to be solved,mixing efficiency and control precision of supersaturation need to be improved.Antisolvent crystallization is usually used in drug production,most of the drugs are organic,high viscosity and macromolecules,the batch production process leads to agglomeration and tube blockage,which makes the antisolvent crystallization is difficult to be industrialized in drug production.In order to solve the problems,this paper builds single/multi stage hollow fiber membrane modules assisted antisolvent crystallization process,which changed the way of antisolvent adding and mixing fundamentally.Provide liquid membrane renewal theory,combine with Bernoulli equation and fully use membrane advantages,the burst nucleation and inhomogeneous mixing are solved.The process is stable,easy controlled,has no membrane fouling and adapts different production.During continues production,there is no reunited crystal and tube blockage when the crystal is flowing out of the device.The research firstly use NaCl as template,which is easy to observe and stable,to explore single stage membrane assisted antisolvent crystallization.Choose lipophilic polyethersulfone(PES)hollow fiber membrane to be module core.By comparing the crystals,find the quality of crystal have been greatly improved,which prove the membrane assisted antisolvent crystallization is usability and has control advantage.Provide liquid membrane renewal theory which is accord with membrane assisted process,combine with Bernoulli equation,to build a method which use membrane to control antisolvent adding rate.Based on the single stage membrane assisted antisolvent crystallization process,it is used in erythritol production,by researching operation parameters,when the shell side velocity is 0.021m/s,tube side velocity 0.1079m/s,stirring rate is 100r/min,the crystal size distribution and morphology are ideal.The structure of the crystal is complete spindle,aspect ratio is between 1.4-1.6,and the primary nucleus has obvious structure.The crystal size distribution is narrow,the average size variation coefficient decreases by 19.3%,which compared with the conventional.Various operating conditions have effect on antisolvent permeation rate and shell side velocity promotes surface renewal,reduce the liquid membrane thickness and transfer resistance efficiently,tenability and sensitivity are higher.The interface mass rate is 0.02 times than conventional process,the control precision is strengthened greatly,and interface mass rate is the primary cause of membrane process.This paper furtherly developed the single stage into a multistage membrane assisted process to produce erythritol,to make the process more perfect.The parameters of multistage process is researched.It is found that influence of shell velocity and the process theory is not changed,multistage process could screen the crystal.The shell velocity and process stages have effect on the antisolvent permeate rare and addition,and influence the crystal production rate,change residence time and effect the morphology and size distribution of crystal.