Study On The Preparation Of Tin-containing Silicalite-1 Zeolite And Its Catalytic Performance In Transforming Ethylenediamine To Triethylenediamine

Triethylenediamine is the most widely used tertiary amine foaming agent in polyurethane materials.The traditional strong acidic ZSM-5 zeolite catalyst for synthesis of triethylenediamine from ethylenediamine faced challenges such as producing many by-products and rapid deactivation of the catalyst.Therefore,the preparation of tin-modified defective S-1 zeolite catalyst and the synthesis of triethylenediamine with ethylenediamine were systematically studied in this paper.The main research contents are as follows:Firstly,three types of stannous catalysts were prepared on defective S-1 zeolite,S-1 zeolite with low content of hydroxyl nests and amorphous SiO₂?fumed SiO₂?by means of deposition and precipitation with tin dichloride as the tin source.Through the characterizations of hydroxyl vibration and pyridine adsorption FT-IR spectroscopy and NH₃-TPD,it was found that the Lewis acid sites in the tin-containing S-1 zeolite was mainly derived from the interaction between the nanometer tin oxide clusters and the hydroxyl nests inside the zeolite.The evaluation results of fixed bed reactor indicated that the Sn6-S-1 catalyst prepared by the defective S-1 zeolite showed excellent catalytic performance in the synthesis of triethylenediamine from ethylenediamine.The conversion of ethylenediamine was86%and the selectivity of triethylenediamine was 56%.The conversion of ethylenediamine was more than 8 times higher than that of defective S-1 zeolite parent.Based on this,the defective S-1 zeolite catalysts with different tin loadings were prepared by solid--state ion-exchange method with tin dichloride and tin oxide as tin sources.Through the characterizations of hydroxyl vibration and pyridine adsorption FT-IR spectroscopy and NH₃-TPD,it was found that when the catalyst was prepared by solid-state ion-exchange method,tin dichloride was more likely to interact with the hydroxyl nests inside the zeolite,resulting in the production of a large number of Lewis acid sites.Results showed that when the tin loading was 3%,the catalytic performance of the tin-containing defective S-1 zeolite catalyst was the best,and its ethylenediamine conversion and triethylenediamine selectivity were 86%and 57%,respectively.Finally,the results of continuous reaction obtained with fixed bed reactor indicated that the tin-containing defective S-1 zeolite catalyst prepared by both deposition precipitation method and solid-state ion-exchange method showing good activity stability in the ethylenediamine to triethylenediamine reaction,as indicated by the fact in the 70-80-h time-on-stream no significant catalyst deactivation phenomenon was observed.This indicates that the tin-containing defective S-1zeolite catalyst has good anti-coking deactivation ability due to its weak acid sites.