CONVERSION OF OXYGENATES TO PROPYLENE WITH SELECTIVE HYDROGEN TREATMENT OF HEAVY OLEFIN RECYCLE STREAM

摘要

The average cycle propylene selectivity of an oxygenate to propylene (OTP) process using one or more fixed or moving beds of a dual-function oxygenate conversion catalyst with recycle of one or more C₄+ olefin-rich fractions is substantially enhanced by the use of selective hydrotreating technology on these C₄+ olefin-rich recycle streams to substantially eliminate detrimental coke precursors such as dienes and acetylenic hydrocarbons. This hydrotreating step helps hold the build-up of detrimental coke deposits on the catalyst to a level which does not substantially degrade dual-function catalyst activity, oxygenate conversion and propylene selectivity, thereby enabling a substantial improvement in propylene average cycle yield. The propylene average cycle yield improvement enabled by the present invention over that achieved by the prior art using the same or a similar catalyst system but without the use of the hydrotreating step on the C₄+ olefin-rich recycle stream is of the order of about 1.5 to 5.5 wt-% or more.