Naphtha Cracking Kinetics and Process Chemistry on Y and ZSM5 Type Catalysts

A deeper understanding of naphtha catalytic cracking is required for on-purpose propylene production in downflow HS-FCC. A study was conducted wherein olefinic and paraffinic naphthas were cracked in a MAT (microactivity test) reactor over various blends of Y- and ZSM5-based catalysts. Reaction kinetics was tracked in order to gain insights into the process chemistry of naphtha catalytic cracking. It was found that olefins rapidly crack in olefinic naphthas while the other components crack at a much slower rate. The ultimate conversion of paraffinic naphtha is approximately equal to the total paraffin content. Naphthenes can either crack or convert to aromatics depending on temperature and ZSM5 content in the mixture. The formation of dry gas (H2, C1, and ethane) is due to carbonium-ion cracking and not thermal cracking. The relative important of carbonium- or carbenium-ion cracking is determined by process conditions and by catalyst composition.