Microwave-assisted pyrolysis of HDPE using an activated carbon bed

Abstract

Plastics play an enormous role in modern manufacturing, but the extraction and refining of raw materials, followed by the synthesis of plastics themselves, represents an enormous energy investment into a product that is all too often simply "thrown away" into a landfill after a single use. Microwave-assisted pyrolysis is a recycling technique that allows the recovery of chemical value from plastic waste by breaking down polymers into useful smaller hydrocarbons using microwave heat in the absence of oxygen. This dissertation examines the use of a catalytic activated carbon bed in this procedure, using high density polyethylene (HDPE) as a model plastic. Initial tests with the batch input of HDPE produced a condensed pyrolysis oil comprising 35.5-45.3% aromatics, with the remainder primarily short-chain aliphatics. This oil was approximately three times lighter than that produced in the absence of catalyst, with a narrower range of molecular masses that matched those of the liquid transport fuels petrol and diesel (C 5-C 21). The non-condensable gases that resulted were short-chain aliphatics that could be used as feedstock for the creation of new chemicals (such as virgin HDPE), or fuels such as natural gas and LPG. The development of apparatus capable of adding sample in a continuous fashion enabled the processing of larger quantities of HDPE, and resulted in condensed products with a significantly higher aromatic content (>80% at 450°C), and which I owe a debt of thanks to many people for the support and kindness they have shown me throughout my time in Cambridge. I would like to thank my supervisor, Professor Howard Chase, for his generous provision of tutelage, expertise, and support throughout the production of this work. A further thank you to my colleagues and the department support staff for their extremely skilled time and advice. I would also like to acknowledge the generous financial support that I have received from the Cambridge Commonwealth Trust, The Higher Education Funding Council for

Catalytic microwave pyrolysis of waste engine oil using metallic pyrolysis char

“…As previously observed by others in microwave pyrolysis studies [17,18,23,45,46], the interaction of the electromagnetic microwave field with particular types of carbon (e.g., metallic-char) generates "microplasmas" (i.e., electrical discharges resulting from the rapidly oscillating electromagnetic microwave field) which create charge imbalances that are restricted by the physical boundaries of the carbon particles. The temperature of these microplasmas is considerably higher than that of the bulk carbon bed, and consequently waste oil exposed to these microplasmas will be cracked to a greater extent.…”

“…The use of microwave radiation as a heat source is known to offer additional advantages over traditional thermal heat sources [13,14], and the combination of carbon-based material and the novel use of microwave heating in pyrolysis processes is of increasing interest as reflected by considerable recent research reported in the literature [15][16][17][18]. Microwave systems show a distinct advantage in providing a rapid, energy-efficient, and targeted heating process compared to conventional technologies, thus facilitating increased production rates and decreased production costs.…”

Polymer Degradation Under Microwave Irradiation

“…Recently, Russell et al [76] performed microwave-assisted pyrolysis of HDPE using a reactor bed of catalytic activated carbon. As activated carbon is an excellent microwave absorbent, it served two primary functions: as a catalyst in the pyrolytic cracking of HDPE and also as the enveloping and energy transferring agent necessary for processing microwave-transparent material.…”

Production of Pyrolyzed Oil from Crude Glycerol using a Microwave Heating Technique

“…A microwave pyrolysis method has been successfully used to pyrolyze a variety of feedstock including waste engine oil (Lam et al, 2010;Lam et al, 2016), wheat straw (Budarin et al, 2009), scrap tires (Appleton et al, 2005;Undri et al, 2013), oil palm biomass waste (Salema & Ani, 2011) and waste plastic (Russell et al, 2012). Valliyappan et al (2008) performed a study on the pyrolysis of glycerol for the production of hydrogen or syngas by using a conventional heating method.…”