Application of modified molecular sieve in the quality upgrading of ethylene glycol
Biomass-and-coal-based ethylene glycol contains 1,2-butanediol and other vicinal diols.The acidity of molecular sieve was modulated through ion exchange,and the treated molecular sieve was used to catalyze the dehydration reactions of diols,which could be transformed into separable aldehydes.Therefore,the purity of ethylene glycol was improved.The molecular sieve was dispersed in a sodium-acetate solution,and the ion exchange proceeded for 1 h.After calcination,the molecular sieve was added to diols for reactions at 185 ℃ for 2.5 h.Meanwhile,the products were isolated via evaporation.The molecular sieve with an exchange ratio of 17.1％showed high catalytic activity in the dehydration reactions of miscellaneous vicinal diols and weak catalytic activity for acetalization reactions,significantly reducing the loss of ethylene glycol due to the reactions.Under the preferable conditions,the mass concentration of ethylene glycol in the mixed diols was increased from 65％to 96％after the reactions.From the perspective of reaction selectivity,for example,the selectivity to 2-propyl-1,3-dioxolane,which was the product of acetalization reaction,was decreased from 62.8％to 14.5％due to modification.This result indicates that the reaction between butanal and ethylene glycol was suppressed,thereby reducing the consumption of ethylene glycol.The NH3-TPD measurement results show that the numbers of acid sites with weak and medium strength in the molecular sieve are reduced,while that of strong acid sites remains almost unchanged during the ion-exchange process.Therefore,mere strong acid is indispensable in the dehydration reactions,while acetalization reactions are dependent on the total number of acid sites.
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