Influence of retention time and catalyst concentrations on catalytic pyrolysis yields of polyethylene and polystyrene

ABSTRACT

The present work focuses on enhancing the liquid fraction yields having hydrocarbons in the diesel fuel range from pyrolysis of PS/PE (1:1 wt.%) under the influence of ZSM–5 catalysts in an autoclave reactor. The pyrolysis product yields and their compositions were investigated for varied catalyst concentrations (0%, 5%, 7.5%, and 10%), reaction temperatures (250–500°C), and retention times (20–60 min). The physical and chemical characterization of the feedstocks, catalysts, and thermally and catalytically derived oils were carried out along with elemental analysis of the liquid products. It was observed that 7.5% catalyst concentration exhibited the maximum liquid fraction yields (71.2 wt.%) at 350°C and a retention time of 30 min. Catalytic cracking with a retention time of 20–30 min produced maximum liquid yields with aromatic, aliphatic, and isomerized hydrocarbon contents of 42.9%, 30.15%, and 14.3%, respectively. Expedite weakening of the catalytic activity of the ZSM-5 catalyst was observed with process retention time higher than 30 min. The calorific values of catalytically derived oils were found to be in the range of 44.2–44.8 MJ/kg, and their carbon numbers were between C₁₁ and C₁₉. Thus, these characteristics make these oils a potential candidate to be used as an alternative to diesel fuel. Further, the higher proportions of aromatics and aliphatic compounds present in catalytically derived oils compared to that obtained from thermal pyrolysis affirmed its superiority as a potential diesel substitute.

KEYWORDS:

• Plastic
• environment
• pollution
• pyrolysis
• Zeolite
• degradation

Acknowledgements

The author greatly thanks the assistance from the Engine Research laboratory, National Institute of Technology Silchar for providing the autoclave pyrolysis unit and the physical characterization facilities. The authors also gratefully acknowledge SAIC Iasst Guwahati, SAIC Tezpur University, and SAIF IIT Bombay for GC–MS, TG, FT–IR, SEM –EDX, and CHNO analyses, respectively.

Disclosure statement

No potential conflict of interest was reported by the author(s).

CRediT authorship contribution statement

Amarendra Deka: Conceptualization, Methodology, Investigation, Writing – original draft. Rahul Dev Misra: Research guidance, Conceptualization, supervision, review, and editing.

Additional information

Notes on contributors

Amarendra Deka

Amarendra Deka is pursuing Ph.D program in Mechanical Engineering from National Institute of Technology Silchar, Assam, India. His research interests include Alternative fuels, Renewable energy, Fuel additives, and IC engines.

Rahul Dev Misra

Rahul Dev Misra received his Ph.D degree in Mechanical Engineering from IIT Roorkee. He is currently working as a Professor in the Mechanical Engineering Department, National Institute of Technology Silchar, Assam, India. His research interests include Thermoeconomics, Refrigeration, Air-conditioning, Biofuels, and IC engines.