Experimental Study On The Purification Of Citric Acid By Supercritical Fluid Chromatography

Citric acid is one of the main products of organic acid. It is widely applied in the field of food, pharmaceutical and cosmetics industry. The conventional separation used in the industry is the precipitation as a calcium salt, using calcium carbonate and sulfuric acid. This conventional process includes a lot of batch steps which increase the production cost and generate considerable amount of an environmental harmful waste.Many new separation techniques, i.e., ion exchange separation, have been developed. But the problems mentioned above were not absolutely solved. In recent years, Supercritical fluid chromatography (SFC), which is environment-friendly and high-efficiency technology of separation and purification, is widely used in refining of nature drugs and food.In this paper, SFC was first introduced into the purification of citric acid from simulated fermentation. In the SFC separation for citric acid, polar column ZoxBax SB-CN (250×9.4mm I.D.,5μm) was used as the stationary phase, and SC-CO2/C2H5OH was used as the mobile phase and the content of ethanol was 9.7% (wt.%). The velocity of CO2 is 15g·min-1, temperature 313.15K, pressure 13MPa and injected volume 0.05mL. Under the above conditions, the purity of collected citric acid reached 99.6%, removal rate of glucose reached 93% and the yield reached 87.2%.This paper focused on adsorption equilibria of citric acid from supercritical fluid on a cyano column as stationary phase. MD method of molecular simulation was used to predict the density of SC-CO2/C2H5OH binary mixture in the range of pressure 13MPa to 19.8MPa and at T=313.15K and T=321.15K. Under the conditions, the method of elution by characteristic point (ECP) was used to determine adsorption isotherm of citric acid from supercritical fluid on the ZorBaxSB cyano column. The results indicated that the loading of citric acid on the stationary phase decreased with increasing temperature and density of binary mobile phase.The Hill adsorption isotherm was applied to relate the experiment data. Agreement of results was good. The saturated capacity of citric acid was in the ranges of 40-65mg·cm-3.