| Converting calcium carbonate in eggshell to calcium citrate, the paper introduced the method of two-step acid added. The effects of various process sections on the yield and purity were discussed to obtain the optimal process conditions.In addition,the method of one-step acid added(direct neutralization) was compared with the method of two-step acid added.The physico-chemical analysis of products of two-step acid added was fulfiled.At last, the growth of calcium citrate crystal which was the products of two-step acid added was preliminary researched. The main findings are as follows:(1) The technological processing of eggshell membrane separation was studied. the best acids substituted into calcium citrate in the two-step acid added process were screened out.The optimum conditions of eggshell membrane separation were found to be as follows:fineness,80mesh;stirringtime,5min;settingaside time,15min;re placement acid,acetic acid and separate only once.(2) The preparation of calcium citrate process was studied.Take the crude calcium citrate yield as the index to determine the best process conditions.The optimal process parameters were as follows:the fineness of eggshell powder was 100mesh, citrate acid 20%excessive, Solid-liquid ratio of eggshell and acetic acid was 1:19; the reaction temperature of eggshell powder and acetic acid was 50℃for 3h.The crude calcium citrate yield can be more than 88%. The best purification conditions can be obtained by taking the purification yield and the purity as the index.The best purification conditions were as follows:the concentration of sodium hydroxide was 0.30 mol/L,the volum of sodium hydroxide was 400ml,citrate acid 10% excessive.The product purity was 88.21%,the final yield was 86.03% and the utilization ratio of eggshell was about 80.02%.(3) Take the crude calcium citrate yield as the index, the technological parameter of neutralization method has been obtained.The crude calcium citrate yield can be more than 86.20%,when the fineness of eggshell powder was 100mesh,the eggshell 20% excessive, the solid and liquid ration of eggshell and acetic acid was 1:19.0,the reaction time of eggshell powder and acetic acid was 3.5h at 25.4℃,the reaction temperature of citric acid and calcium acetate was 50℃and the citric acid 30% shortfall.The best purification conditions can be obtained by taking the purification yield and the purity as the index.The best purification conditions were as follows:the temperature was 100℃,the concentration of citric acid solution was 0.0070mol/L,the volume of citric acid solution was 500ml.The product purity was 99.27%,the final yield was 84.85% and the utilization ratio of eggshell was about 61%. It can be shows that the purify of the calcium acid products of the two-step acid added was than one-step acid added.The quality of products has met the national standard.Although the utilization ratio of eggshell was less than the latter,the eggshell resource was rich.In addition,the unused eggshell can be recovered to react again.As a result,only the calcium acid which was the products of two-step acid added has been researchd in the chapter4 and chapter5(4) Atomic absorption spectrometry was employed to analysis the calcium citrate which was prepared by the process of 2 acid method.The result shows that the contents of Ca was more than 99.2%,the contents of Mg was less than 0.00371%, the contents of Pb was less than 0.0005% and the contents of As was about 0.000002%. All of them had met the national standards.The crystalline structure and size were examined by XRD and SEM respectively.The results indicated that the purity quotient of the citric calcium products of the two step acid added process was higher than the commercial citric calcium. Besides, the crystallinity was better.(5) The growth of the crystal nucleus of the 2 acid added products was also described by SEM.The mean grain size of calcium citrate was smallest when the concentration of reactants was 1.25 mol/L,the rotate speed was 400 r/min,the recation temperature was 50℃and the recation time was 30min.In the contary,the mean grain size of calcium citrate was biggest when the concentration of reactants was 0.1 mol/L,the rotate speed was 600 r/min,the recation temperature was 80℃and the recation time was 25min. |
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