Study On Purifying Three Natural Products By Molecular Distillation And Theoretical Model

Molecular Distillation (MD), also termed as Short Path Distillation (SPD), is a special distillation technology. It has been paid attention to by many people since it had been invented in the 30's of last century. This technique has been gotten more and more applications internationally in the recent decades of years, and especially, it developed very quickly along with the growing-up popularity of natural products.The efficiency of wiped film molecular distillator is very high, and it has been used widely in industries. The material can be distributed into thin liquid film uniformly on the surface of evaporator, which makes the evaporation area of unit volume fluid very large. The thin-film can be renovated continuously when the rotor rotates very quickly, and the flow status in the thin-film develops into turbulent flow as well. Because of these characteristics of wiped film molecular distillator, it can not only avoid the local overheated phenomena, but also strengthen the mass and heat transfer in the liquid thin-film.MD has solved many problems that seem inextricable for conventional distillation because of the high degree of vacuum in the operation of MD. The MD technique is suitable for separating many substances that have following characteristics, low volatility, high molecular weight, high boiling point, high viscosity, heat sensitivity and biological activity, and especially suitable for the purification of natural products.The key purpose of this dissertation is to study the purification of three natural products by wiped film molecular distillation apparatus. The experiments of refining α-linolenic acid, natural Vitamin E and EPA&DHA by the VKL70 wiped film MD equipment have been discussed in this dissertation. The effects of the operating parameters on the purity and yield were studied. The optimum process conditions of refining these three natural products were obtained. This study establishes the foundation of producing these three natural products in industry, and has an important practical value to produce these three natural products massively in the future.The flow process of the liquid thin-film on the surface of the evaporator and the whole material balance in the process of wiped film molecular distillation have been studied in this dissertation. Based on the evaporation theory of Langmuir- Knudsen, the original distillation model has been modified by analyzing and solving the concentration of the liquid film surface. The effects of feed rate, distillation temperature and evaporation speed on the concentration and yield of product have been discussed by using the above modified mathematical model and the newly built multi-theoretical stage model. And also the theoretical stage number in the whole separation process and the required evaporation area in each stage to obtain desired purity of product have been calculated. This study provides the basic theory for new molecular distillator design.