Production of value-added liquid fuel via microwave co-pyrolysis of used frying oil and plastic waste Wan Adibah Wan Mahari a , Cheng Tung Chong b , Chin Kui Cheng c , Chern Leing Lee d , Kristian Hendrata d , Peter Nai Yuh Yek a, e , Nyuk Ling Ma f , Su Shiung Lam a, * a Eastern Corridor Renewable Energy Group (ECRE), School of Ocean Engineering, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia b China-UK Low Carbon College, Shanghai Jiao Tong University, Lingang, Shanghai 201306, China c Faculty of Chemical and Natural Resources Engineering, University Malaysia Pahang, Lebuhraya Tun Razak, 26300 Gambang, Pahang, Malaysia d Chemical Engineering Discipline, Monash University Malaysia, Jalan Lagoon Selatan, 47500 Bandar Sunway, Selangor, Malaysia e School of Engineering and Technology, University College of Technology Sarawak, Lot 88, Persiaran Brooke, 96000 Sibu, Sarawak, Malaysia f School of Fundamental Sciences, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia article info Article history: Received 2 December 2017 Received in revised form 28 July 2018 Accepted 1 August 2018 Available online 6 August 2018 Keywords: Pyrolysis Co-pyrolysis Microwave Oil Plastic Waste Fuel abstract The production of household wastes such as used frying oil (UFO) and plastic waste (PW) are increasing each year, thus representing potential feedstocks for conversion into an energy source. Microwave co- pyrolysis was investigated for its potential to transform a mixture of UFO and polyolefinic-based plas- tic waste into fuel product with desirable properties. The co-pyrolysis approach demonstrated positive synergistic effects in providing fast heating rate (up to 50  C/min) and a lower reaction time (25 min), and generated up to 81 wt.% yield of liquid oil and 18 wt.% yield of pyrolysis gases for use as potential fuels. The liquid oil showed promising green properties comprising low oxygen content, free of nitrogen and sulphur and higher energy content (42e46 MJ/kg). The oil product also demonstrated improved stability and desirable fuel properties nearly similar to transport-grade diesel, thus indicating the great potential of microwave co-pyrolysis as an approach for transforming household wastes into value-added liquid fuel. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction The fossil fuel is a limited non-renewable energy source and it is unable to satisfy the world's growing energy demand. Therefore, research on production of alternative energy source has been intensified in recent years. Currently, waste materials such as agricultural waste, used frying oil, waste engine oil and plastic waste have shown potential as renewable resource to generate alternative fuel source [1e4]. Transforming waste materials into an energy source has become an attractive way to completely utilize the waste in order to fulfil the increased energy requirement. Many researchers have reported the potential of thermochemical con- version processes such as pyrolysis, gasification and combustion to produce alternative fuel from waste materials [5e8]. Nevertheless, the fuel products possess undesirable properties such as high water content, acidity and oxygenated compounds compared to tradi- tional fossil fuels such as gasoline and diesel [9, 10]. These proper- ties could lead to high viscosity, reducing the combustion efficiency and limiting their application as fuel source. Owing to these problems, co-processing of waste materials us- ing microwave pyrolysis technique has attracted attention due to its potential to simultaneously treat and convert several wastes to produce cleaner fuel [11e 13]. Microwave pyrolysis is a microwave- heated thermal process performed in an inert environment from which oxygen is excluded from the heating process. This pyrolysis process heats and thermally decomposes waste and biomass ma- terials to produce pyrolysis products in the form of gases, liquid oil and char products. These products can further be used in petro- chemical industries, refineries and boiler for energy or power * Corresponding author. E-mail addresses: adibah.mahari@gmail.com (W.A. Wan Mahari), ctchong@mail. fkm.utm.my (C.T. Chong), chinkui@ump.edu.my (C.K. Cheng), lee.chernleing@ monash.edu (C.L. Lee), kristian.hendrata@monash.edu (K. Hendrata), peter.yek@ ucts.edu.my (P.N. Yuh Yek), nyukling@umt.edu.my (N.L. Ma), lam@umt.edu.my (S.S. Lam). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy https://doi.org/10.1016/j.energy.2018.08.002 0360-5442/© 2018 Elsevier Ltd. All rights reserved. Energy 162 (2018) 309e317