Industrial Waste Plastic To Green Methanol

Methanol is a fuel source for cars, trucks, marine vessels, boilers, and cookstoves. 200,000 tons of methanol are used daily as a feedstock or fuel, and its demand of 75 million metric tons from 2015 continues to rise. Meanwhile, plastic pollution of landfills is problematic. This project evaluates the feasibility of green methanol production from post-industrial waste plastic and water—a prospective solution for renewable energy and pollution mitigation.

Two possible carbon sources were analyzed: waste plastic and cellulosic biomass. From an overall mass balance, cellulose conversion results in a net release of CO?, while all feed carbon in plastic can potentially be converted into methanol. The plastic route was selected as the more economically and environmentally promising option. Modeled as "CH?" from a material balance perspective, plastic undergoes steam gasification to produce syngas (CO + 2 H?), which is mixed with recycled syngas and sent to a methanol synthesis reactor. The reactor output is then distilled to separate liquid methanol from unreacted syngas for recycle.

Process heat and work requirements were analyzed. The shredder operates adiabatically, requiring 8.14 kJ/mol of electrical work. Gasification requires heat input, with ?h = 160.37 kJ/mol and ?g = 127.34 kJ/mol. Operating at the Carnot temperature of 1447 K allows this heat input to supply process work requirements. The compressor operates isothermally, requiring 20.81 kJ/mol of work to compress syngas from 1 to 16.43 bar, with an equivalent heat rejection to maintain temperature.

Methanol synthesis releases heat, with ?h = ?90.13 kJ/mol and ?g = ?24.79 kJ/mol. Operating at 493 K creates a work deficiency, requiring 10.88 kJ/mol of additional work input. Distillation separates methanol from syngas, releasing heat through condensation (?38.07 kJ/mol). The decompressor operates isothermally, rejecting 0.32 kJ/mol of work while requiring equal heat input.

Heat and work integration was used to reduce energy consumption. The 90.13 kJ/mol of heat released during synthesis was redistributed to meet process needs, including water heating and compressor work.

The total energy requirement is 184.14 kJ/mol, supplied electrically at New Jersey's cost of $0.11/kWh, corresponding to $0.0061 per mole of CH?OH. On a metric ton scale, this results in an operating cost of $190.43 per ton. With a current market price of $700 per ton and a potential $200/ton premium for green methanol, the process yields a profit of $709.57 per ton.

This preliminary feasibility analysis demonstrates that converting industrial waste plastic into methanol is a promising pathway for sustainable fuel production and pollution mitigation.