Study On Solid-phase Solvent-free Synthesis Of Molecular Sieves And Catalytic Degradation Of Xanthate In A Cheap System

Zeolite have been valued by researchers since their discovery,and their synthetic methods are mainly hydrothermal synthesis and isomeric substitution.Hydrothermal synthesis method due to the use of a large number of solvents in the preparation of molecular sieve is easy to cause environmental pollution.Homogeneous crystal substitution method is more complex and reproducible.The solvent-free synthesis method is a new molecular sieve synthesis method.It has the advantages of simple operation,safety of the system and no large amount of waste water after the reaction.Therefore,this study has selected this solvent-free synthesis method for the synthesis of zeolite.Nano-silica and silica fume were used as the silica source to synthesize Si-ZSM-5,X-ZSM-5 and titanium silicalite TS-1.Not only to achieve the high value of the use of silica source,but also provide a more moderate synthesis method of MFI-type molecular sieve.The Si-ZSM-5 samples were obtained by heating at 180℃ for 48 h with tetrabutylammonium bromide(TPABr)as template and ammonium chloride as mineralizer.And the crystallization temperature and crystallization time of Si-ZSM-5 were studied.The results showed that synthesis temperature range can be extended from 120℃ to 180℃ for the synthesis of Si-ZSM-5 with nano-silica as silicon source.Meanwhile,titanium silicalite TS-1 were synthesized by using ammonium fluoride instead of ammonium chloride as mineralizer.The effects of crystallization temperature and crystallization time on the synthesis of titanium silicalite TS-1 were also investigated.The results showed that the titanium silicalite TS-1 with high crystallinity can be synthesized in the range of 120℃-180℃.When temperature was 120℃,the crystallinity of the sample prepared for 60 h was the highest,while when the temperature was 180℃,the sample prepared for 36 h has the highest crystallinity.Based on the characterization of titanium silicalite TS-1 and its crystallization kinetics,the synthesis regular of titanium silicalite TS-1 by solvent-free synthesis method was obtained.The synthesis time was longer at low temperature,and the high temperature could greatly shorten the synthesis time.But there is a period of induction in the early crystallization process of all the synthesized samples prepared at different temperatures.The crystallinity of the sample increased rapidly after the induction period,and then after the maximum value it decreases with the increasing of the synthesis time.Meanwhile,in this system,the nucleation activation energy of the reaction is higher and the activation energy of crystal growth is lower,so the crystal nucleation rate is slower and the crystal growth rate is faster.In this study,titanium silicalite TS-1 synthesized by solvent-free synthesis method was also used as the catalyst and H2O2 was used as the oxidant to catalyze the degradation of the xanthate solution.The results showed that the removal rate of the xanthate was greatly improved after titanium silicalite TS-1 added.It was found to be that the main product after degradation is carbon disulfide.Moreover,the higher the reaction temperature,the higher the removal efficiency of xanthate.When the temperature is 55℃,the removal efficiency of xanthate was 95.5%after 10 min.At the same time,the reaction products of xanthate degradation were different in acidic and alkaline conditions.The main product is carbon disulfide in acidic conditions,and in alkaline conditions the main product is thiosulfate.