Pyrolysis of waste plastic fish bags (polyethylene and polypropylene) to useable fuel oil

Rahman, Shofiur and Hawboldt, Kelly and Helleur, Robert J. and MacQuarrie, Stephanie (2018) Pyrolysis of waste plastic fish bags (polyethylene and polypropylene) to useable fuel oil. Research Report. Memorial University of Newfoundland, St. John's, Newfoundland and Labrador.

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Abstract

The objective of this study is to determine the feasibility of pyrolysis of waste plastic fish feed bags to heating oil. Pyrolysis is a thermal treatment without oxygen and produces three products (gas, oil, and solid), the yields depend on the feedstock and operating conditions. The fish feed bags are polyethylene (PE) or polypropylene (PP) and are typically contaminated with a small amount of residual fish feed. This limits the treatment and disposal options. Thermal decomposition of the bags to their original oil base could potentially produce a fuel for use in heating and possibly power for the plant. Unused and used bags were pyrolyzed and compared to determine the impact of the fish feed on the oil and the residual solids and gas evolved during the process. The temperature for the pyrolysis temperature is a function of the feed material. For waste plastic the temperature can range between 400−550°C depending on the type of plastic. In this work a series of pyrolysis experiments were performed where key factors that would impact the oil quality produced, were varied including; temperature of pyrolysis 400−550°C) type of bag (PE, PP, and mixtures of the two), mass of residual fish feed retained in bag (0-40% by mass of feedstock) and gas residence time. Based on these experiments the optimum operating conditions were obtained. A temperature of 500°C produced the maximum wax/oil yields, 69-75wt% of feedstock with a solids (residue) between 6-7wt%, and gas between 23-25wt%, depending on the feedstock. The melting point of wax/oil samples varied between 53-62°C. The melting point of the wax/oil samples decreased slightly with increasing amounts of fish feed. The increase in wax/oil yield is likely a result that the FF pyrolysis products are predominantly lipids, this would both add to the overall oil content and possibly decrease the uncondensable gas content through co-pyrolysis. The heating values of the wax/oil samples varied from 42.8- 45.7 MJ/kg. The pure fish feed heating value was 25.47 MJ/kg. The heating values of all waxes are comparable to standard fuels, 44-46 MJ/kg petrol/gasoline, 43 MJ/kg for diesel, and from 43-44 MJ/kg for fuel oil. Although, the wax/oil samples are solid (wax) at temperatures below 50oC, heating to above 60oC produces a liquid oil with a high heating value. The gas produced in 2 the pyrolysis, largely methane and ethane, could be used as a fuel gas. Based on 100 metric tonnes of waste bags per year this translates to 2.8 MJ/yr from the oil and 1.38 MJ/yr from the gas.

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