Insight into the coke precursor in the process of methanol-to-olefins reaction

In this work, formaldehyde formed in the methanol to olefin (MTO) reaction was found to be a coke precursor on SAPO-34 and the amount of formaldehyde during the entire MTO reaction was measured accurately by acetylacetone spectrophotometric method. The mechanism of formaldehyde formation, decomposition and coking in SAPO-34 molecular sieve in methanol to olefin reaction was investigated. It was found that in the MTO reactor, the formed formaldehyde would further condense into coke on the SAPO-34 where formaldehyde created, and traveled onto the downstream SAPO-34 and condensed into coke there. The higher the amount of formaldehyde in the MTO reaction, the higher the coking rate and the shorter the catalytic lifetime of SAPO-34. Physical mixing of MgO and SAPO-34 can slow down the coking rate and prolong the catalytic lifetime of SAPO-34 through decomposing the formaldehyde into CO, CO2 and H2 on MgO.