| Citric acid, a kind of metabolic intermediate, is widely used in food industry,pharmaceutical industry, cosmetics and toiletries, chemical industry, and so on due toits excellent physical and chemical properties. Calcium citrate is a calciumsupplement, and can be used as buffer, organization coagulant, calcium supplementsand food emulsifying salt in food industry. This paper mainly studied granularitycontrol of citric acid and polymorphs and crystal transformation of calcium citrate.First the influence of spontaneous nucleation temperature, seeding temperature,cooling way and amount of seed on particle size distribution of citric acid werestudied in order to achieve the granularity control of citric acid. Then the preparationof small size of citric acid was studied. In cooling crystallization of citric acid, theeffect of size of seed, amount of seed, mixing and cooling rate on particle sizedistribution of citric acid were investigated. Finally the possibility of preparation ofsmall size of citric acid from solvent-out crystallization was studied.The thermodynamic data of calcium citrate was measured. First the solubility ofcalcium citrate tetrahydrate in water at temperatures ranging from (20to80)?weredetermined by a static method. Then the thermodynamic stable polymorph wasdetermined. Finally the supersolubility of calcium citrate was determined in thereaction system of sodium citrate and calcium chloride using FBRM. The effect oftemperature, adding rate and adding way on supersolubility of calcium citrate wasinvestigated.Calcium citrate was prepared by reactive crystallization of sodium citrate andcalcium chloride system and citric acid and calcium hydroxide system respectively.The effect of temperature, addition rate and adding way on polymorphs and crystalhabit of calcium citrate were investigated. Raman and FBRM were used to monitorthe experiment process to determine why crystal transformation occurs. The productsobtained from experiment were analyzed by thermal gravimetric analysis, and effectof temperature, adding rate and adding way on the particle size distribution and bulkdensity of products were investigated.Finally, transformation of calcium citrate anhydrate was measured offline byusing XRD to measure the solid polymorph and online by using Raman and FBRM.The effect of temperature and stirring rate on the transformation rate of calcium citrateanhydrate was determined and the transformation mechanism and the control step were determined.The above research has not been reported in the literature. |
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