Formation of coke from propene over 5A adsorbents - influence of the binder on the coke composition, location and removal

Coke formation from propene was investigated at 623 K and P-propene = 100 k Pa on a pure 5A zeolite and an industrial adsorbent (5A zeolite 80 wt.%-bin der 20 wt.%). The composition and location of coke molecules were determine d as a function of time on stream. Coking on the pure zeolite was faster th an on the industrial adsorbent. This result is mainly due to the trapping o f coke precursors by the binder, and consequently a significant decrease in the amount of coke on the zeolite present in the adsorbent. While the coke deposited on the binder is very polyaromatic, the carbonaceous compounds f ormed on the zeolite and on the adsorbent are constituted at low coke conte nt by mono-, bi-, tri- and tetra-alkyl aromatic components, and these compo unds are sterically blocked in the alpha -cages of the 5A zeolite. At high coke content, very heavy polyaromatic compounds appear and are certainly lo cated on the external surface of the zeolite crystallites. Adsorption measu rements of both samples show that coke is heterogeneously distributed in th e zeolite pores. Whatever be the adsorbent, the partial oxidation of coke o n highly coked samples caused an increase in the adsorption capacity. The f irst few steps of regeneration of coked samples remove the heavy polyaromat ic molecules responsible for the pore blockage and thus liberate the pores which are not occupied by coke molecules. (C) 2000 Elsevier Science B.V. Al l rights reserved.