Yield and Composition of Bio-oil from Co-Pyrolysis of Corn Cobs and Plastic Waste of HDPE in a Fixed Bed Reactor

Abstract

Pyrolysis, a thermal cracking process in inert environment, may be used to produce bio-oil from biomass and plastic waste thus accommodating the use of renewable energy. Abundant amount of biomass wastes in Indonesia are not utilised and plastic wastes are not well processed for clean environment. The aim of present work was to evaluate effect of mass ratio of plastic material to biomass in the feed blend of corn cobs and high density polyethylene (HDPE) of co-pyrolysis on bio-oil yield and chemical composition of bio-oil products. The heating rate of the co-pyrolysis was kept low and residence time was in the order of seconds to accommodate high yield of oil originating from plastic pyrolysis. Corn cobs have high cellulose and hemicellulose content (84%) which is potential to produce bio-oil. The pyrolysis was conducted in a laboratory-scale using a fixed bed reactor with final temperature of 500 °C, heating rate 5 °C/min, flow rate N2 750 mL/min, total weight of biomass and plastic material of 20 g, and hold time after peak temperature of 30 min. Mass ratio of plastics to biomass in the feed blend was varied 0:100, 25:75, 50:50, 75:25 and 100:0. It was found that by increasing HDPE content up to 100% in the feed blend above, the yields of bio-oil decreased, i.e. 28.05, 21.55, 14.55, 9.5, and 6.3 wt%, respectively. Furthermore, for the same variation of the mass ratio, yields of the non-oxygenate mixture of paraffins, olefins and cycloalkanes contained in bio-oil increased, i.e. 0, 28.35, 40.75, 47.17, and 67.05 wt%, respectively. Analysis of the synergetic effect indicates that this effect did work effectively both in bio-oil and non-oxygenate yields due to improper conductive heat transfer from N 2 gas to melting plastics, which contained biomass particles. By increasing composition of HDPE in the feed blend, viscosity and pH of bio-oil changed approaching to those of commercial diesel oil.

Improving the Quality of Pyrolysis Oil from Co-firing High-density Polyethylene Plastic Waste and Palm Empty Fruit Bunches

“…High levels of ash content can cause pyrolysis oil to become corrosive and can reduce its durability. On the other hand, the ash content also influences the capability of external heating in the pyrolysis reactor (Supramono et al, 2016b). Since ash can absorb the heat, the pyrolysis process is not effective.…”

“…The design of the reactor for the slow co-pyrolysis method followed that reported by Supramono et al (2016b). Slow co-pyrolysis was done in a stainless steel reactor of a cylindrical type with a length of 25 cm and a diameter of 6 cm.…”

“…The presence of high lignin may cause the pyrolysis oil to become more viscous, making the product unstable. The viscosity influences the flow ability of pyrolysis oil and ignition delay time (Supramono et al, 2016b), when used as diesel oil.…”

“…The co-pyrolysis method is a more promising way to convert the waste into higher-value oil (Gang & Aimin, 2008). It can reduce the phase separation of pyrolysis oil, and thus it can improve the stability of the oil (Supramono et al, 2016b). This technique can therefore reduce the volume of waste and achieve synergy by coprocessing biomass with plastics and other materials (Gang & Aimin, 2008).…”

“…In addition, copyrolysis has an advantage over pyrolysis of either agricultural waste or plastic waste separately. The co-pyrolysis product yield is higher than when adding the individual pyrolysis oil produced separately by pyrolysis of agricultural or plastic waste, because of the interaction of free radicals during the thermal treatment process (Bhattacharya et al, 2009;Supramono et al, 2016b). The chemical composition of oil from waste agricultural biomass contains significant amounts of oxygenated organic compounds, and therefore results in a high O/C ratio, high moisture causing low energy density, and a low heating-value product.…”