Formation of ethene and propene from methanol on zeolite ZSM-5: II. Preparation of Finished Catalysts and Operation of a Fixed-Bed Pilot Plant

Abstract

Conversion of methanol to light olefins in a system with two fixed-bed reactors in series is described. The influence of size and shape of catalyst particles, operating conditions and internal recycle on olefin yield is investigated for a given zeolite as active component. The zeolite is agglomerated by extrusion to cylinders, rings and monoliths; the Bingham-plastic needed for this purpose is prepared without adding materials containing aluminium. The mechanical strength of the agglomerates can be improved by bonding the zeolite crystals with less than 10 wt.% silica. Selectivity of the finished catalysts for olefin production at 300°C is adversely affected by intercrystalline mass transfer if the ratio of volume to external surface of the catalyst grain exceeds 0.5 mm. Overall yields of (ethene+propene) around 60% can be accomplished if conversion of oxygenates at 300°C is restricted to 50% and unconverted reactants are recycled. The use of monoliths as catalysts is not advantageous, due to problems of heat transfer.