| Domestic factories of producting 2-cyanoguanidine due to the backward production technology, not only the products has wide particle size distribution, low-yield, and unstable crystal form, but also the production process was run with energy consumption and pollution. Therefore, this paper aims to study crystallization process of 2-cyanoguanidine using salting-out crystallization systematically.2-Cyanoguanidine is one of the fundamental chemical compounds; which is used in the printing, dyeing and electronic industries widely. In this paper, mole fraction solubility (103xe) of 2-cyanoguanidine in different mixed solvent (methanol+water) was determined using static method at (283.15-343.15) K, it increased from 4.14 to 72.62 with the mass fraction of methanol increased from 0.100 to 0.600. Three salting-out effects of three salts on 2-cyanoguanidine dissolved in water were investigated. Mole fraction solubility data (103xe) of 2-cyanoguanidine in three kinds of alkali metal chloride salts (sodium chloride, potassium chloride, lithium chloride) aqueous solution was determined by same method from 298.15 to 328.15 K, it increased from 2.4236 to 14.9933 (NaCl), from 2.7058 to 14.9912 (KCl) and from 2.0026 to 14.3697 (LiCl) with three kinds of metal salt solution concentration (mass fraction) varying from 0.01 to 0.25. The corresponding salting-out yield of three kinds of alkali metal chloride salts ranged from 0.89% to 46.69% (NaCl), from 0.87% to 35.61%(KCl),4.9%-52.34%(LiCl)。Considering the price of three salts and corresponding salting-out effects, sodium chloride was choosed as salting-out agent finally in crystallization of 2-cyanoguanidine.In addition, the metastable zone widths of 2-cyanoguanidine in methanol and ethanol were obtained by the polythermal method as a function of cooling rate at (283.15-323.15) K. MSZW data of 2-cyanoguanidine in water increased from 1.98 to 5.14℃, and it increased from 1.24 to 3.94℃ in methanol, from 0.82 to 2.37℃ in ethanol. Apparent nucleation orders were computed by Self-consistent Nyvlt-like approach and Kubota’s model, which suggests that the nuclei are formed by instantaneous nucleation in methanol and ethanol, while the 2-cyanoguanidine nucleate in water shows the occurrence of progressive nucleation mechanism.In order to optimize the traditional purification process of 2-cyanoguanidine, this paper got the best process conditions of cooling and salting-out coupling crystallization of 2-cyanoguanidine through the single factor experiment, orthogonal experiment, and verification and test. The temperature of crystallization is 50℃, stirring rate is 250r·min-1, cooling rate is 0.4 K·min-1, seed amount is one-tenth of theoretical output, salting-out reagent amount is 0.75 g (0.75% of saturated liquid quality theoretical output). Under the optimal conditions, the indicators of product were obtained:average particle size is 602.13 μm,M.S. value is 760.10 μm, C.V. value is 0.58, and average yield is 93.49%.In production process of pharmaceutical grade of 2-cyanoguanidine, concentration of calcium ions in the mother liquor was so high that limited application of products. In this paper, chemical precipitation and solvent extraction method were ued to remove calcium ions from mother liquor, respectively. Two methods were all able to achieve the goal.The results in this paper not only provided essential data and theoretical basis for traditional industrial purification of 2-cyanoguanidine to research thermodynamics, dynamics and crystallization process of 2-cyanoguanidine, but also it had a certain guiding significance for developing production technology of high-purity 2-cyanoguanidine, realizing industry of calcium carbide specialization, greening, high added-value to study on them. |
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