Understanding the Enhanced Lifetime of SAPO-34 in a Direct Syngas-to-Hydrocarbons Process

In a hybrid catalyst process, syngas is converted, via a methanol intermediate, into a mixture of short-chain hydrocarbons over a combined methanol synthesis catalyst and molecular sieve. It operates under process conditions where the hydrogen partial pressure is relatively high vs the (intermediate) methanol partial pressure. We show that, under these conditions, the lifetime of the molecular sieve (SAPO-34) is greatly enhanced and the amount and type of carbon on the spent catalyst are vastly different as compared to those in a methanol to olefins (MTO) process. The impact of the hydrogen partial pressure, temperature, and methanol partial pressure is studied, leading to a conceptual model of coke deposition and removal. This allows the identification of process conditions that lead to a stable and long lifetime of SAPO-34 in a direct syngas-to-hydrocarbons process.