การผลิตเชื้อเพลิงและสารเคมีมูลค่าสูงจากกระบวนการไพโรไลซิสของขยะพลาสติก

Abstract

Plastic wastes have become one of the most concerning environmental issues in Thailand.High-density polyethylene (HDPE), Low-density polyethylene (LDPE) and Polypropylene (PP) equal 46%, 25%, and 16% of total plastic wastes in Thailand. They are produced from petroleum chemicals and are not biodegradable. The majority of plastic wastes which are sent to landfills end up in environments. Polylactide (PLA) is one of the most popular biodegradable polymers which trends to increase in usage. However, due to poor waste management, the biodegradable and traditional plastic wastes have disposed of in the same waste streams. Pyrolysis is a very viable and sustainable process of waste management to recovery chemicals and energy from wastes. In this study, virgin plastics (HDPE, LDPE, PP and PLA) and synthetic plastic waste (HDPE:LDPE:PP:PLA at 1:1:1:1) were investigated by a fixed-bed reactor. The effect of temperatures (400, 450, 500, 550, and 600 °C), the effect of heating method (conventional and stepwise) and the effect of catalysts (LTA zeolite, spent FCC, and MgO) were determined. From the results, thermal stability of studied polymers showed as HDPE>LDPE>PP>PLA depended on the structure of polymer and chain. Thermal degradation of petroleum-based polymers presented around 450-500 °C and that of PLA around 350-400 °C. The synthetic plastic waste presented two steps of thermal decomposition. The first step was the thermal decomposition of PLA, while the second step was the decomposition of petroleum-based polymers. The highest yield of pyrolysis liquid of HDPE, LDPE, PP and PP obtained from the pyrolysis at 600 °C, 500 °C, and 550 °C, respectively. While the pyrolysis of PLA at 400 °C produced the highest yield of liquid products. However, the pyrolysis at temperature 400 °C could not decompose the petroleum-based polymers, melted polymer remained in the reactor. There over two form of pyrolysis liquid as pyrolysis oil and wax, classified by their pouring ability. Each studied catalyst influenced the production of different chemicals by pyrolysis process of petroleum-based polymers at 600 °C with spent FCC obtained high C8-C12 hydrocarbons (gasoline range), high aromatics, and iso-alkane, which can apply for fuels production. The pyrolysis of PLA at 400 °C with LTA zeolite catalyst gave high yield of lactide and L-lactic acid at 78.87% and 0.04 %, respectively. While the of PLA with spent FCC gave high propanoic acid production at 52.85 %. The yield of pyrolysis liquid obtained from synthetic plastic waste was lower than those of virgin plastics because the complex decomposition of various polymer in synthetic plastic waste supported the gases production. Both conventional and stepwise pyrolysis led to similar yield of pyrolysis liquid. However, the stepwise pyrolysis could separate products of PLA from the products from petroleum-based polymers. In first step, lactide, L-lactic acid, and oxygenated compounds were the main products. Long chain hydrocarbons without oxygen were the major product of the second step. This work demonstrated the production of gasoline hydrocarbons, was, aromatics, lactide, L-lactide, and propanoic acid. These chemicals and fuels perusers can be further upgraded and used in several application. In addition, these in formation can apply for the plastic waste management by catalytic pyrolysis process.