Y. Boucheffa et al., FORMATION OF CARBONACEOUS COMPOUNDS FROM PROPENE AND ISOBUTENE OVER A5A ZEOLITE - INFLUENCE OF TEMPERATURE ON THEIR COMPOSITIONS AND LOCATIONS, Industrial & engineering chemistry research, 36(8), 1997, pp. 3198-3204
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.