Date of Award

7-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Chemical Engineering

First Advisor

M. Toufiq Reza

Second Advisor

Maria Pozo de Fernandez

Third Advisor

Mirmilad Mirsayar

Fourth Advisor

Manolis Tomadakis

Abstract

In 2019, waste plastic production in the United States (U.S.) amounted to approximately 73 million metric tons. Projections indicate that by 2030, the generation of waste plastic in the U.S. will increase to nearly 90 million metric tons, and by 2060, it is expected to surpass 140 million metric tons. One prominent type of waste plastic is polyvinyl chloride (PVC), characterized by its high chlorine content, making it a halogenated plastic. This dissertation presents a comprehensive investigation of the dechlorination of waste PVC (WPVC) through various hydrothermal liquefaction (HTL) methods to produce environmentally friendly solid and liquid products. In this purpose, first, the catalytic HTL (ca-HTL) experiments explored the influence of noble metal catalysts (Ru/C, Pt/C, and Pd/C), residence time (0.5, 1, 2, and 4 h), reaction temperature (300, 325, and 350 °C), and catalyst loading (0, 5, and 10 wt%) on dechlorination of WPVC. Notably, the highest dechlorination efficiency (DE) of 99.01% was achieved at 350 °C and 1 h with a 10 wt% Pd/C loading. The chlorine content in the solid residue decreased significantly from 568.8 g/kg (WPVC) to 5.64 kg/g (solid residue) under these conditions. Second, the focus shifted to acidic HTL (A-HTL) of WPVC using the acidic process fluid (PF) obtained from the hydrothermal carbonization (HTC) of orange peel. The A-HTL experiments were conducted at temperatures ranging from 300 to 350 °C and residence times from 0.25 to 4 h. The findings revealed a high DE of up to 97.57 wt%, achieved at 350 °C and 1 h. The A-HTL method enhanced the higher heating value (HHV) of the resulting solid (char) and liquid (oil) products, reaching values of 33.07 and 34.60 MJ/kg, respectively. Third, co-hydrothermal treatment (co-HTL) of WPVC using an acidic hydrochar (AHC) produced from pineapple waste was investigated. The co-HTL experiments involved varying temperatures (300-350 °C), residence times (0.25-4 h), and AHC loadings (0-20 wt%). The addition of 5% AHC at 325 °C and 1 h significantly enhanced the DE of WPVC (99.46%). The co-HTL solid products exhibited low slagging index, fouling index, alkali index, and low/medium chlorine contents. The resulting liquid product contained no chloride and exhibited a high HHV of up to 36.43 MJ/kg. Finally, a simulation and exergy analysis of the hydrothermal process of WPVC were performed. The simulation considered experimental data from HTL, A-HTL, and ca-HTL methods at 325 °C for 1 h. The energy consumption per fuel product were determined as 10.16, 12.41, and 12.93 MJ/kg for HTL, A-HTL, and ca-HTL, respectively. The reactor accounted for the majority of the energy consumption. The total exergy efficiency ranged from 79.82% to 82.84% for the different hydrothermal methods. The results of this dissertation provided valuable insights into the effectiveness of different hydrothermal liquefaction approaches to dechlorinate WPVC and their associated parameters.

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