EFFECT OF DIELECTRIC-CONSTANT, CAVITIES IN SERIES, AND CAVITIES IN PARALLEL ON THE PRODUCT DISTRIBUTION OF THE OLIGOMERIZATION OF METHANE VIA MICROWAVE PLASMAS

The use of microwave-induced plasmas as a method to oligomerize methan e to higher hydrocarbons has been studied. The pressure range used was 10-20 Torr and the applied power was 60 W. The microwave power is cou pled to the plasma by means of either an Evenson or a Beenakker cavity , the Beenakker being the most effective. We explored the effect of th e presence of a dielectric material on the product distribution for th is reaction. The values of the dielectric constants for these material s varied from 2.6 for Pb(Ac)(2) to 10 000 for MnO2 relative to the vac uum. No direct correlation was found, but in some cases the selectivit ies toward C-6s, to C-8s, were enhanced. TiO2 and Li2CO3 increased the selectivities toward C-6s. SnO2 was the best for selectivities to C-7 s and C-8s. When a coating of Si/SiC on the reactor walls was present in the plasma zone, the selectivities toward C-6s and C-7s increased w ith respect to both materials (Si and SiC) by themselves. We also stud ied the effect of cavities in series and cavities in parallel on the o ligomerization of methane with and without dielectric material in betw een the cavities. When methane and iodine are activated separately and then recombined, it seems that the oligomerization of methane is enha nced toward higher hydrocarbons. Ww found that when a dielectric mater ial is placed in between and when the distance between the two cavitie s in series is the largest, the oligomerization of methane toward high molecular weight hydrocarbons is maximized.