Adsorptive Recovery Of Related Substances From The Mother Liquors Of Gallic Acid

The coarse mother liquor of gallic acid is resulted from the crystallization process of the crude product of gallic acid,which is a"refractory organic wastewater" due to its high organics content,high salinity and low pH value.Another wastewater,commonly known as refined mother liquor of gallic acid,is generated in the gallic acid refining process,which is worthy of recovery because of its high content of gallic acid.These two wastewaters put seriously environmental pressure on the enterprises and also cause the loss of gallic acid,so it is urgent to get effective recovery.Food grade tannic acid,which is widely used in the productive process of beer and beverage as clarifying agent or stabilizer,is usually produced by extraction with ethyl acetate,but the purity of this tannic acid is insufficient due to the excessive content of gallic acid.The effective removal of gallic acid from tannic acid product is still a technical problem.Due to the advantages of simple operation,high treatment efficiency and good selectivity,resin adsorption process has been widely used in wastewater treatment and purification of natural products.This dissertation focuses on the problems existing in the productive process of gallic acid and tannic acid.The main contents are as following:According to the characteristics of the coarse mother liquor of gallic acid,hyper-crosslinked resin was used in adsorptive recovery of gallic acid and tannic acid from the coarse mother liquor,and the process for recovering of quinic acid was tried.The results showed that AM-35 resin with appropriate pore size and high specific surface area could be used as the target resin.Dynamic experiments showed that the single column treatment capacity of the resin reached 10BV,and the resin could be regenerated by 8%sodium hydroxide solution.However,quinic acid could not be adsorbed and recovered due to the existence of inorganic salts.According to the characteristics of the refined mother liquor of gallic acid,AM-7 was used in adsorptive recovery of gallic acid from the refined mother liquor of gallic acid.The results showed that the AM-7 resin has good adsorption properties,the single column treatment capacity of the resin reached 30BV,and the resin could be regenerated by 6%sodium hydroxide solution.When the eluent was received by some hydrochloric acid solution,the loss of gallic acid can be avoided and the recovery rate of gallic acid is above 87%.In order to resolve the problems existing in the productive process of food grade tannic acid,we proposed a solution by combining resin adsorption process with solvent extraction process to produce high purity food grade tannic acid.The results showed that AM-8 resin could adsorb gallic acid selectively from tannic acid aqueous solution,and the selectivity was based on the size sieving effect.Technical study showed that the efficiency of removing gallic acid by using static adsorption was higher than that by using dynamic adsorption.After treatment of 25BV(bed volume)industrial tannin acid aqueous solution,which mass concentration was 5%,by static adsorption with mechanical stirring for 6-8 hours,more than 75%gallic acid was removed from industrial tannin acid aqueous solution.Through static adsorption treatment,gallic acid content existing in food grade tannin acid declined from 6%to under 1%,which meet the quality requirements of high purity tannic acid.