METHANOL CONVERSION TO HYDROCARBONS OVER ZEOLITE H-ZSM-5 - COMMENTS ON THE FORMATION OF C-4 HYDROCARBONS AT LOW REACTION TEMPERATURES

Pulsed flow microreactor studies are described for the methanol conver sion reaction. The reactor is incorporated into a standard gas chromat ograph injector and this system enables complete analysis of the produ cts exiting the reactor to be made for each pulse. It is found that th e carbon mass balance for the pulse studies are low for microporous ze olites and that it is unsafe to use such a technique to investigate th e nature of the initially desorbed reaction products. Experiments at 1 12 degrees C using 1 mu l pulses of liquid methanol demonstrate that a C-4 hydrocarbon is formed in trace amounts for the initial two pulses (equivalent to 1 methanol per aluminium atom). However, this effect i s not observed for subsequent pulses and it is considered to be the pr oduct of a non-catalytic reaction. Pretreating the zeolite with ethano l is found not to enhance this effect and no hydrocarbons are observed in similar experiments using SAPO-34. Possible mechanisms for the low -temperature formation of C-4 hydrocarbon products are discussed.