Effect of n-butanol cofeeding on the deactivation of methanol to olefin conversion over high-silica HZSM-5: A mechanism and kinetic study

Abstract

The co-reaction of methanol and n-butanol that instantaneously dehydrated into 1-butene at the inlet was performed to evaluate the effect of co-feeding olefin on the catalyst deactivation from coke deposition over HZSM-5 with Si/Al = 200 at 460 °C, a practical situation encountered by commercial methanol to propylene (MTP) process. It was revealed that the deactivation was an autocatalytic process depending on both methanol and products. In particular, increasing inlet methanol fraction would dramatically accelerate activity attenuation, and the co-feeding butanol significantly reduces activity loss by promoting methanol conversion. The deactivation is generally non-selective to methanol transformation and product generation, except for methane. A possible deactivation mechanism was proposed with the coke precursor originated from the methylation of lower polymethylbenzenes to higher tardy ones. A deactivation kinetic model was then developed, which gave fairly good prediction to the experimental results in a wide range of feed composition.