FORMATION OF CARBONACEOUS COMPOUNDS FROM PROPENE AND ISOBUTENE OVER A5A ZEOLITE - INFLUENCE OF TEMPERATURE ON THEIR COMPOSITIONS AND LOCATIONS

The formation of carbonaceous compounds (''coke'') from propene and is obutene on a 5A zeolite and their effects on the capacity for nitrogen adsorption were investigated in a microbalance system. The operating conditions of coking were as follows: 100-420 degrees C, pressure of a lkene of 0.97 bar, 0.085 g of the 5A zeolite, and operating time from 5 min to 100 h. At low temperatures (100-150 degrees C), coke constitu ted mainly of oligomers formed on the acid sites of the zeolite. These oligomers located in the ct cages can be removed by thermal treatment in vacuum at high temperatures. The effect on the adsorption capacity was more pronounced for coke formed from isobutene due to the prefere ntial location of oligomers in a cages near the outer surface of the c rystallites. At high temperatures (350-420 degrees C), aromatics and p olyaromatics were formed which cannot be removed by a simple thermal t reatment. The effect of coke on the adsorption capacity showed that wh atever their origin, these coke molecules (most likely the polyaromati c ones) blocked the access of adsorbates to the zeolite pores.