| Calcium gluconate is a chemical product that has very important applications in the fields of medicine,food,materials,and chemical industry.Its crystallization process affects the output,quality,and efficiency of the product.However,as of now,the theory of calcium gluconate crystallization However,there are few reports in the research that caused the lack of basic theoretical support for the large-scale production of calcium gluconate,and the low production efficiency of the product.Therefore,it is of great significance to carry out the application research of calcium gluconate crystallization mechanism.The specific research content and results are as follows:This paper studies the vacuum crystallization process of calcium gluconate from three aspects:crystallization thermodynamics,crystallization kinetics and crystallization process.First,the solubility data of calcium gluconate in water at 293.15-333.15 K was measured by the EDTA coordination titration method and the solubility curve was drawn.At the same time,the solubility model-λh equation and Apelblat equation were used to correlate the solubility data.The results show that the solubility of calcium gluconate in water increases with the increase of temperature.The correlation between the two equations and the solubility is the λh equation:In(1+0.0561-x/x)=2933.638 1/T-1/Tm),R2=0.985;Apelblat equation:lnx=-144.72+3875.7/T+21.977lnT,R2=0.993,from the correlation analysis,the Apelblat equation has a better correlation effect on solubility.The conductivity method was used to determine the super-solubility curve and the Apelblat equation was used to correlate it.The law of the metastable zone of calcium gluconate solution with temperature was determined,and the influence of different stirring rates,cooling rates and pH values on the width of the metastable zone was investigated..The results show that the metastable zone of calcium gluconate is wider in the low temperature zone 293.15～313.15K,λT is 5.6-8K,and the high temperature zone is narrower between 313.15～333.15K,λT is 1.8-4.8K.The decrease of the stirring rate and the increase of the cooling rate will widen the calcium gluconate metastable zone by 0.2～0.9K,and the pH value has no obvious influence on the width of the calcium gluconate metastable zone.This is the calcium gluconate industrial crystallization device and industrial crystallization The production operation provides a theoretical basis.The calculated molar dissolution enthalpy ΔHdiss of calcium gluconate is 25898.87 J/mol,a positive number indicates that the dissolution process of calcium gluconate is an endothermic process;the crystallization enthalpy of calcium gluconate ΔHcry is-25898.87 J/mol,a negative number indicates that gluconic acid The crystallization process of calcium is an exothermic process;the molar dissolution entropy ΔSdiss is 33.15 J/mol;the molar Gibbs energy is related to the temperature of the solution system,and is negatively related to the temperature.Exploring the crystallization kinetics of calcium gluconate vacuum crystallization through ASL model,particle number calculation formula and moment transformation method,and obtaining the crystal nucleation rate equation:B0=4.46×1014exp(-58457/RT)MT1.44NP2.21 ΔC1.53,crystal growth rate equation:G0=3.23×10-8exp(-51522/RT)NP0.74ΔC1.72,G=G0(1+0.61L)0.81.The increase of suspension density,supersaturation and stirring rate will promote the nucleation rate of calcium gluconate crystals,and the order of influence on the nucleation rate of calcium gluconate crystals is:stirring rate,supersaturation,and suspension density.An increase in supersaturation will promote crystal growth.The order of supersaturation in the crystal growth rate equation is 1.72.Compared with the nucleation rate equation,the effect on the crystal growth rate is more obvious.Through orthogonal experiment analysis,the influence of temperature,vacuum degree and stirring rate on the crystallization yield is studied,and the experimental data is established by analysis of variance and range analysis,and it is concluded that the degree of influence of the three on the yield of crystallization is from high to low:vacuum degree,Temperature,stirring rate.Among them,the P value of the degree of vacuum is less than 0.05,which is a significant factor.Through the research of the sensitivity analysis module,it is found that the mass flow of calcium gluconate solids under different flashing pressures has a turning point with temperature.This temperature is similar to the boiling point of water under pressure.The evaporation crystallization process is compared with the cooling crystallization process.The mass flow rate of calcium solids is increased by about 25.33%.The change of vaporization fraction with temperature in the flashing process is basically consistent with the change of calcium gluconate solid mass flow rate,and the change of vaporization fraction and calcium gluconate solid mass flow rate is linear.Integrating the effects of flash pressure and flash temperature on the mass flow of calcium gluconate solids,it is found that the flash pressure and flash temperature that significantly increase the mass flow of calcium gluconate solids are generally around the corresponding value of water pressure and boiling point.The simulation results combined with the corresponding relationship between the boiling point of water and the pressure can provide a reference for the design and control of the crystallization process. |
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