Research On The Crystallization Process Of Rubber Accelerator Of N-Tert-Butylbenzothiazole-2-Sulfenamide

Accelerator NS(N-tert-butylbenzothiazole-2-sulfenamide,TBBS),one of the most important vulcanization accelerators in the rubber industry,performs best compared with other accelerators and consequently possesses broader application.However,the production of TBBS results in the generation of a large amount of wastewater and small particles with wide size distribution.In this paper,the crystallization process of TBBS was systematically studied in order to solve these problems and provide a data basis for the optimization of crystallization process.Firstly,the thermodynamic properties of TBBS of crystallization were investigated.A gravimetric method was applied to measure the solubility of TBBS in six pure solvent systems and in tert-butylamine+water system,in addition,a turbidity method was conducted to measure the solubility of TBBS in tert-butylamine at high temperature.It was observed that the solubility of TBBS increased with the rising temperature and solvent composition of tert-butylamine,and the effect of the solvent composition on the solubility was significantly stronger than the temperature.The experimental solubility data were correlated by the modified Apelblat equation,the van't Hoff equation,the NRTL model and the CNIBS/R-K model.The result showed that the modified Apelblat equation had the best fitting effect.The dissolution thermodynamic parameters of TBBS were calculated by van't Hoff equation,indicating that the dissolving process of TBBS was endothermic,entropy-driven and non-spontaneous.Secondly,a turbidity method was used to determine the metastable zone width(MSZW)of both anti-solvent crystallization and cooling crystallization of TBBS in tert-butylamine.The effects of different operating conditions on MSZW were also discussed.Simultaneously,the Nyvlt's approach,the self-consistent Nyvlt-like equation and the classical 3D nucleation theory approach were employed to correlate the MSZW data of cooling crystallization.As a result,the apparent nucleation order n and the mass nucleation rate constant k_n were calculated,with the value of 1.948 and 1.693,respectively.Finally,the process of the anti-solvent crystallization,the cooling-antisolvent crystallization and the cooling crystallization at high temperature were respectively optimized on the basis of thermodynamics and nucleation kinetics research.Moreover,the products of these optimized processes were characterized and compared.It was found that the anti-solvent crystallization produced much wastewater;the cooling crystallization at high temperature produced large particles which was not benefitial to the post-treatment;and the product of the cooling-antisolvent crystallization had the most centralized particle size distribution,appropriate size and less wastewater generation.The cooling-antisolvent crystallization route was considered as a more feasible crystallization process.