Catalytic transformation of the gases evolved during the thermal decomposition of HDPE using acid-activated and pillared clays

Abstract

HDPE was thermally decomposed in a thermobalance and the evolved gases were passed through a bed of catalyst. Two acid activated clays of different structure were used, i.e. sepiolite (SEP), which is a fibrous clay mineral, and smectite (K10) which is a layered mineral. In addition two pillared smectites were studied one which was pillared with an Al species (AZA) and the other with an Al/Fe-species (FAZA). The thermal and catalytic decomposition of HDPE was studied under dynamic (35 to 650 °C at 10 °C min^–1) and isothermal (60 min at 420 °C) conditions. The evolved gases were analysed using TG-OTM-GC-MS. The thermal decomposition of HDPE yielded characteristic quartets of peaks assigned to n-alkanes, alk-1-enes, alk-x-enes and α,ω-dienes in the range C₄-C₂₀. Species of higher molecular weight than C₂₀ were not detected. All four catalysts converted the alkenes present in the thermally generated off gases into light gases and aromatic species including respectable quantities of toluene, xylenes, tri- and tetra-methylbenzenes. Ethylbenzenes and naphthalenes were produced to a lesser extent. AZA and FAZA produced the largest yield of aromatics and sepiolite is considered to produce significant quantities of low molecular weight gases in the isothermal process. The product distribution over sepiolite suggested that there were fewer dehydrocyclisation sites on this catalyst. None of the catalysts used was capable of cracking the saturated alkanes.

References

1. K. Liu and H. Meuzelaar, Fuel Process. Technol., 1996, 49, 1.
2. W. Ding, J. Liang and L. Anderson, Fuel Process. Technol., 1997, 51, 47.
3. M. Uddin, K. Koizumi, K. Murata and Y. Sakata, Polym. Degrad. Stab., 1997, 56, 37.
4. W. McCaffrey, M. Kamal and D. Cooper, Polym. Degrad. Stab., 1995, 47, 133.
5. Y. Uemichi, A. Ayame, Y. Kashiwaya and H. Kanoh, J. Chromatogr., 1983, 259, 69.
6. Y. Uemichi, Y. Kashiwaya, M. Tsukidate, A. Ayame and H. Kanoh, Bull. Chem. Soc. Jpn., 1983, 56, 2768.
7. R. Mordi, R. Fields and J. Dwyer, J. Anal. Appl. Pyrolysis, 1994, 29, 45.
8. X. Xiao, W. Zmierczak and J. Shabtai, Div. Fuel Chem., 1995, 40, 4.
9. G. Audisio, A. Silvani, P. Beltrame and P. Carniti, J. Anal. Appl. Pyrolysis, 1984, 7, 83.
10. P. L. Beltrame, P. Carniti, G. Audisio and F. Bertini, Polym. Degrad. Stab., 1989, 26, 209.
11. T. Yoshida, A. Ayame and H. Kanoh, Bull. Jpn. Petroleum Inst., 1975, 17, 218.
12. C. Vasile, P. Onu, V. Barboiu, M. Sabliovschi, G. Moroi, D. Ganju and M. Florea, Acta Polym., 1988, 39, 306.
13. C. Vasile, P. Onu, V. Barboiu, M. Sabliovschi and G. Moroi, Acta Polym., 1985, 36, 543.
14. C. L. Thomas, J. Hickey and G. Stecker, Ind. Chem. Eng., 1950, 42, 866.
15. Pillared Layered Structures: Current Trends and Applications, ed. I. V. Mitchell, Elsevier, Barking, 1990.
16. S. Chevalier, R. Franck, J. F. Lambert, D. Barthomeuf and H. Suquet, Appl. Catal. A: General, 1994, 110, 153.
17. B. Nagy and W. F. Bradley, Am. Mineral., 1955, 40, 855.
18. K. Brauner and J. Preisinger, Tschermaks. Mineral. Petrogr. Mitt., 1956, 6, 120.
19. R. M. Barrer, N. Mackenzie and D. M. McLeod, J. Phys. Chem., 1954, 58, 568.
20. J. de D. Lopez-Gonzalez, A. Ramirez-Saenz, F. Rodriguez-Reinoso, C. Valenzuela-Calahorro and L. Zurita-Herrera, Clay Miner., 1981, 16, 103.
21. J. L. Bonilla, J. de D. Lopez-Gonzalez, A. Ramirez-Saenz, F. Rodriguez-Reinoso, C. Valenzuela-Calahorro and L. Zurita-Herrera, Clay Miner., 1981, 16, 173.
22. A. Corma, V. Fornes, A. Mifsud and J. Perez-Pariente, Clay Miner., 1984, 19, 673.
23. T. Curlee and S. Das, Resour. Conserv. Recycl., 1991, 5, 343.
24. J. A. Ballantine, P. Graham, I. Patel, J. H. Purnell, K. Williams and J. M. Thomas, Proc. Int. Clay Conf. Denver, 1987, 311.
25. C. Breen, Clay Miner., 1991, 26, 473.
26. V. Haensel, Adv. Catal., 1951, 3, 194.
27. Y-H. Lin, P. N. Sharrat, A. A. Garforth and J. Dwyer, Thermochim. Acta, 1997, 294, 45.
28. Y. Ishihara, H. Nanbu, T. Ikemura and T. Takesue, Fuel, 1990, 69, 978.
29. H. Ohkita, R. Nishiyama, Y. Tochihara, T. Mizushima, N. Kakuta, Y. Morioka, A. Ueno, Y. Namiki, S. Tanifuji, H. Katoh, H. Sunazuka, R. Nakayama and T. Kuroyanagi, Ind. Eng. Chem. Res., 1993, 32, 3112.
30. W. O. Haag, R. M. Largo and P. B. Weisz, Faraday Discuss Chem. Soc., 1981, 72, 317.
31. A. R. Songip, T. Masuda, H. Kuwahara and K. Hashimoto, Appl. Catal. B: Environ., 1993, 2, 165.
32. A. R. Songip, T. Masuda, H. Kuwahara and K. Hashimoto, Energy Fuels, 1994, 8, 136.
33. H. Ming-Yuan, L. Zhongui and M. Enze, Catal. Today, 1988, 2, 321.
34. S. A. Bagshaw and R. P. Cooney, Chem. Mater., 1993, 5, 1101.
35. S. Bodoardo, F. Figueras and E. Garrone, J. Catal., 1994, 147, 223.
36. S. Perathoner and A. Vaccari, Clay Miner., 1997, 32, 123.