Study On Separation And Purification Of Glutaric Acid From Mixed Dicarboxylic Acids

During the production process of adipic acid,other kinds of dicarboxylic acids,i.e,glutaric acid and succinic acid,are coupled with formation.The amount of the by-product increases with the increasing production capacity of adipic acid.At present,the mixed dicarboxylic acids are mainly used to produce DBE,but its economic value is not high enough.The glutaric acid in the mixed dicarboxylic acids has an important application prospect,therefore it would has highly economic value to separate and purify the glutaric acid from the mixed dicarboxylic acids.In order to improve the utilization of the mixed dicarboxylic acids,more and more attention has been paid to the separation and purification of the three kinds of dicarboxylic acid.In this paper,the separation and purification of glutaric acid from the mixed dicarboxylic acids are mainly investigated.After comparing the advantages and disadvantages of some present separation methods,the aqueous crystallization method was chosen to separate glutaric acid from the mixed dicarboxylic acids.Due to lack complete solubility data of glutaric acid and adipic acid,the solubility data of three kinds of dicarboxylic acid contained in the mixed dicarboxylic acids need to be measured before to conduct the crystallization separation experiment.By comparing the experimental solubility data of succinic acid with the solubility data in the Chemical Data Manual,the method for solubility measuring used in this paper was proved to be reliable.Based on the experimental measuring solubility data of three kinds of dicarboxylic acid,and water as the solvent,the primary separation of glutaric acid was achieved after dissolving,crystallization,vacuum filtration,atmospheric distillation and so on.A high performance liquid chromatographic method was established to determine the composition of mixed dicarboxylic acids(nitric acid,succinic acid,glutaric acid and adipic acid).By applying the single factor experiment method,the factors which impacted the performance of the crystallization separation were investigated,such as crystallization time,crystallization temperature,the ratio of feedstock to water,stirring rate and so on.The proper crystallization conditions were determined as follows: the crystallization time was about 4 hours and the ratio of feedstock to water was 1.43,the crystallization temperature was 5℃ and stirring at a suitable rate during the crystallization process.Under the proper conditions,the purity of glutaric acid in the obtained product was 81.66 wt.%,and the recovery rate of glutaric acid was 83.46% in primary crystallization process.In order to further enhanced the purity of glutaric acid,secondary crystallization experiment was carried out,and the crude product of the primary crystallization was used as the feedsock of the secondary crystallization experiment.The experimental results demonstrated that the amount of glutaric acid in the crystals of the secondary crystallization was higher than that in the filtrate,it was different with the primary crystallization,and thus the crystals were collected as the product of the secondary crystallization.By the single factor experimental method,the proper conditions of secondary crystallization process was determined as follows: the crystallization time was 4h,the crystallization temperature was 15℃,the ratio of feedstock to water was 1.7 and stirring at the proper rate during the crystallization process.The purity of glutaric acid in the obtained product was 95.17 wt.%,and the recovery rate of glutaric acid in the secondary crystallization process was 27.67%.The recovery rate of glutaric acid was very low during the secondary crystallization process,more than 70 wt.% of glutaric acid in the feedstock of the secondary crystallization process was left in the filtrate.In order to separate and recover more glutaric acid from the filtrate of secondary crystallization process,two methods were applied.The first was to dry the filtrate of secondary crystallization process and then to recrystallize,and another method was to crystallize the filtrate of secondary crystallization process by gradient-cooled.This product could be crystallized and separated under the suitable conditions of secondary crystallization to obtain a product with purity of glutaric acid more than 90 wt.%.,and the filtrate of secondary crystallization process could be effectively reused by the first method.By using the gradient-cooled crystallization of the filtrate of secondary crystallization process,the highest purity of glutaric acid in the product obtained at 0℃,but it was only about 80 wt.%.Taking into account of energy consumption and economic benefits,the first method was superior.Then,the product with more than 90 wt.% purity of glutaric acid was tertiary crystallized under the crystallization time of 4h,the crystallization temperature of 15℃ and the 1.6 ratio of feedstock to water,a product with glutaric acid purity exceeding 99 wt.% could be obtained.If the crystallization filtrate was not considered for recycling,the total recovery rate of glutaric acid with three times of crystallization was only 12.62%.If the filtrate of secondary crystallization process was recycled once,the total recovery rate of glutaric acid would be high to 20.23%.