Catalytic Performance of HZSM-5 Molecular Sieve for Synthesis of Polyoxymethylene Dimethyl Ethers

Polyoxymethylene dimethyl ethers (PODEn) were synthesized using methanol (MeOH) and trioxymethylene (TRI) as raw materials. Catalytic performance of acidic molecular sieve HZSM-5 catalyst and PODEn selectivity were found to be strongly dependent on silica/alumina ratio, particle size, phosphorus modified and etc. A series of HZSM-5 zeolite samples modified with various contents of phosphorus were prepared by impregnation with an ammonium dihydrogen phosphate. The crystal structure, pore structure, and surface acidity of the catalyst were studied by various characterization techniques such as X-ray diffraction, N-2-adsorption, and temperature-programmed desorption of NH3. Under the mild reaction conditions of 130 degrees C and raw materials mass ratio MeOH/TRI = 2, methanol conversion and the PODEn (n = 2-5) selectivity were 95.2% and 62.9%, respectively, by using the Pd-modified HZSM-5 catalyst with the optimum conditions (molar ratio of Si to Al was 50, particle size was 5 mu m, low-P2O5 content (w = 0-6%) for the preparation). Catalytic performance of HZSM-5 was higher than that of reference commercial catalysts.