Effect of mass-transfer control on HY zeolites for dimethoxymethane carbonylation to methyl methoxyacetate

A series of hierarchical HY zeolites were prepared by using sequential acid (H(4)EDTA) and alkaline (NaOH and NH4OH) solution treatments. The nitrogen adsorption-desorption analysis proved that the mesoporous structure was definitely formed with the pore diameter at about 3.5 and 17.5 nm, and the external surface area and mesopore volume significantly increased. The XRD, XRF, and NH3-TPD characterization results disclosed that the relative crystallinity, crystalline sizes, and acidity of as-treated HY zeolites decreased as compared with parent HY although their Si/Al ratios were higher. The zeolites were conducted in vapor phase carbonylation of dimethoxymethane (DMM) to methoxyacetate (MMAc) at 5.0 MPa and different temperatures. As compared with reference HY, the DMM conversion and MMAc selectivity obviously increased from 50.41% to 90.91% and from 34.79% to 84.57% at 383 K, respectively. The DMM conversion were closely related to the medium-strong acid amount and greater amount of medium-strong acid sites resulted in higher DMM conversion. The catalytic stability of HY-DAl0.11-DSiNaOH0.05 was carried out at 393 K and 5.0 MPa for 100 h. The DMM conversion (about 97%) and products selectivity (MMAc: 84%) kept unchanged during the whole carbonylation process, exhibiting excellent catalytic stability, which was also supported by the TG-DTA analysis that the carbon deposition was effectively suppressed. In a word, as-treated HY zeolites with larger external surface area and mesopore volume that contributed to promoting the mass transfer efficiency exhibited much higher DMM conversion, MMAc selectivity and excellent catalytic stability than parent HY.