Citric acid-modified beta zeolite for polyoxymethylene dimethyl ethers synthesis: The textural and acidic properties regulation

Abstract

Beta zeolite exhibits satisfactory catalytic activity in the synthesis of polyoxymethylene dimethyl ethers. However, the microporous channels of beta zeolite have adverse effects on mass transfer of macromolecules. In this work, it was found that the textural and acidic properties of catalysts could be improved by citric acid treatment. Extensive characterization confirmed that citric acid induced significant pore-expanding on catalysts, and its dealumination and realumination effect could lead to reduced amount of total acid sites and increased amount of Brønsted acid sites (BAS). Meanwhile, a good positive correlation was found between amount of external weak BAS and initial reaction rate. It was speculated that BAS with relatively weak acid strength might be the primary active sites in this reaction. Compared with the blank sample, the initial reaction rate of optimal catalyst was increased by 100 %, and the conversion of trioxane was increased by 86.5 %, indicating a significantly improved catalytic activity.