Master of Engineering Science
Chemical and Biochemical Engineering
Gasification technologies have been considered as viable avenues for diverting mixed non-recycled plastic waste landfilling. The main objective of this work was to investigate CO2 assistedair gasification with mixed plastic and biomass. High-density polyethylene was co-gasified with Douglas fir in different volumes of CO2 in a semi-batch updraft gasifier. These tests were done in a thermogravimetric analyzer (TGA) to compare the gas, tar and char products of the gasifier with the TGA data. The injection of 10 and 20% CO2 in air gasification with an air to fuel ratio of 0.3 improved carbon conversion from the tar to the gas phase by 20 and 28 carbon wt% respectively. Injecting CO2 was an effective moderator for the H2/CO ratio, beneficial for tar reduction and a key contributor to the energy density of the syngas. From these tests, synergies from the mixed feedstock were identified and discussed for future work.
Summary for Lay Audience
The extensive pollution of mixed plastics in landfilling has garnered considerable attention over the last twenty years and as a result, how to reduce this waste has become a prominent issue. In 2018, the United States alone landfilled 24 million tonnes of plastic waste while only recycling 2.8 million tonnes (8% of all waste plastics) . Alternative approaches to managing non-recycled plastics which would otherwise accumulate in landfills and oceans, need to be researched and developed. Various methods have been investigated to address this problem such as incineration, mechanical, chemical, and thermochemical recycling. The complex composition of these mixed plastic wastes and the consequential environmental effects resulting from some of these proposed solutions have caused greater interest in thermochemical processes such as gasification and pyrolysis. Furthermore, landfilled non-recycled plastics are commonly mixed with biomass residues that decompose into greenhouse gases such as carbon dioxide (CO2) and methane (CH4). Therefore, conversion processes that can accept mixed plastic and biomass wastes would be considered as highly advantageous. While gasification technologies are traditionally used for converting biomass feedstocks into fuels with air, there has been some deliberation whether these technologies could be used with mixed waste biomass and plastic feeds in carbon dioxide (CO2). This work will look to address the possibility of CO2 assisted air gasification of waste plastics with biomass. This is beneficial because it presents an opportunity to utilize CO2, plastic and biomass wastes and convert them into valuable products. Gasification is a high temperature process that can address all of these needs, by converting waste streams into adaptable syngas (synthesis gas), mainly comprised of hydrogen and carbon monoxide (H2 and CO), which can be used for chemical and fuel synthesis. Therefore, the proposed process has the potential to convert plastic, biomass and carbon dioxide waste into valuable fuels and chemicals in a single tunable conversion process. The flexibility of the technology could potentially divert mixed waste plastics from the present archaic waste management infrastructure and carbon dioxide away from current emission pollution.
Cullen, Joshua J., "Co-gasification of Plastic and Biomass Waste" (2022). Electronic Thesis and Dissertation Repository. 8842.