EFFECT OF HEAT-TREATMENT ON THE CHARACTER OF COKE DEPOSITED ON HZSM-5 AND HY ZEOLITES IN ACETONE CONVERSION

HZSM-5 and HY zeolites were coked at 350-degrees-C during acetone conversion under on-stream conditions at atmospheric pressure, in some cases also in a static arrangement at lower pressures. The character of the carbonaceous residues deposited on both zeolites under the above conditions and the influence of pyrolysis as well as of partial oxidation were examined using infrared and C-13 cross-polarization magic angle spinning nuclear magnetic resonance spectroscopies together with the mass spectrometric detection of the volatile products. The coke on HY zeolites was found to be composed of more condensed aromatics and branched aliphatic chains than that on HZSM-5. The pyrolysis removed the aliphatic chains, and on HZSM-5, the less condensed aromatic rings. Both these coke components were also preferentially oxidized. The partial oxidation led to a substantial increase in the void volumes compared with the parent coked zeolites. Oxidized intermediates were observed on the zeolite surfaces.