The Crystallization Purification Process And Mathematical Model Of Para-xylene

Para-xylene is an important chemical raw material, commonly known as PX, PX is used for the production of PTA(purified terephthalic acid), Those items are in the most demand on domestic markets, Our foreign dependence ratio of oil is about 50% now. PX is widely used, appeared in the daily life of our daily lives and brings convenient people’s life, In order to solve the problem of high external dependency, we need to increase the capacity of PX production in our country.Px is generally derived from mixed xylene separation, mixed xylene contained in p-xylene and its isomers, the traditional method is difficult to separate, but melt crystallization technology can have a good effect.Melt crystallization technology as a green environmental protection technology, with low energy consumption, good separation efficiency, less equipment investment, higher product purity, and for the separation of azeotrope, heat-sensitive substances have a significant advantage.Because of the particularity of melt crystallization technology, it is hard to say a certain crystallization equipment can be applied to a lot of the separation of many systems, more is in view of the special system, as well as the crystallization of separation condition to design a special equipment. In this work, we use PX- MX system as experimental object, in the tower of homemade crystallizer, by changing various operating conditions, get high purity PX products.The experimental results show that in the crystallizer must have a moderate stirring, without stirring effect can make the crystal suspension uneven density in the bed, can’t get high purity of product, but on the stirring rate remain at a low rate, moderate stirring good crystallization separation effect. Feed concentration on the crystal separation effect is the basic factor of the tower, tower of crystallization can reach the upper limit of the discretion of the separation effect depends on the concentration of the feed, feed concentrations of high purity is prerequisite to obtain high purity products. Crystal tower there is a high degree of crystal bed is the foundation of the crystallization separation conditions, crystallization and purification effect of sweating, countercurrent washing can say most are based on the platform of the crystal bed, as the crystal bed layer increased, the product purity increases, obviously improve the separation efficiency, but high crystal bed will increase equipment cost, in practice, should consider to choose the proper crystal bed. By adjusting the different operation parameters, we get a large amount of data, in the column with the length 1350 mm, the crystallizer of p-xylene can be purified from 93.8% to 99% above, amplified to provide data for equipment improvement.During the experiment, the crystal tower for this experiment has established the mathematical model and its simplified form, and collected a large amount of data in the experiment, obtain the distribution curve of p-xylene concentration along the height, and the mathematical model fitting, in order to validate the correctness of the model, finally from the result of the experiment equipment improvement opinions are put forward.