(239d) Environmental and Economic Analyses of Chemical Recycling Via Dissolution of Polyethylene Terephthalate

Plastics have become an integral part of our day-to-day life owing to their low cost and excellent material properties suitable for multiple applications in several manufacturing industries. High consumption and production of plastics with low collection rates has led to a global plastic waste crisis. Unfortunately, the plastics supply chains globally, and in the U.S., are highly dependent on fossil resources, leading to high greenhouse gas (GHG) emissions and consumption of energy. Polyethylene terephthalate (PET, resin code #1) is one of the important plastic materials and finds applications in production of bottles, fibers (clothes, carpets etc.), films, sheets, and thermoforms. In the U.S., PET waste accounts for ~15% of the total plastic waste produced, most of which is currently being landfilled (66%), incinerated with energy recovery (15%), and the remaining is collected for sorting and recycling (19%). The complete PET supply chain processes in the U.S. released 23 MMT CO₂-eq and consumed 522 PJ of energy in 2019. These emissions represented 1.2% of the total U.S. industry related GHG emissions in 2019¹.

To break this linearity of plastic supply chains, emerging chemical recycling technologies have been proposed to be a part of this solution to implement circular economy by replacing fossil derived plastic resins. These technologies can be broadly classified in 3 main categories: dissolution/purification, depolymerization, and conversion recycling technologies². While the economic and environmental impacts of enzymatic and non-enzymatic depolymerization of waste PET, as well as dissolution of PET using non-green solvents, are known from the literature, these impacts remain unknown for the dissolution process using a green solvent. In addition, none of the previously published studies have evaluated and compared these impacts for PET specific dissolution process with polymer recovery by the evaporation approach. Also, the economic metrics such as net present value, payback period, return on investment, discounted internal rate of return for these processes are not reported in the literature.

Therefore, the purpose of our study was to address these research gaps and compare the environmental and economic performance of dissolution recycling technology for waste PET using a green renewable solvent³, Gamma (γ)-Valerolactone (GVL), with different polymer recovery techniques. Based on our previously published systems analysis framework^{2, 4}, we take a “bottom-up” approach, in which process simulation (ChemCAD) is integrated with life cycle assessment (LCA) and techno-economic analysis (TEA). The first research objective of our study was to conduct process simulation of chemical recycling of waste PET via dissolution process with the solvent GVL. We analyze three different processes that differ in their polymer precipitation techniques, as mentioned above, using the same solvent. The second research objective was to evaluate technoeconomic performance metrics of the simulated recycling processes. We also look at the effect of scaling up the capacity on the total capital costs and minimum selling price. We also couple this economy of scale analysis with a simple transportation model to account for transportation costs over longer distances with increasing capacity, which has been neglected in prior TEA studies for chemical recycling technologies. The third research objective was to evaluate environmental metrics such as GHG emissions and cumulative energy demand (CED) of simulated recycling processes.

Our analysis revealed that the choice of polymer precipitation method affects the overall economic and environmental performance of the process. The MSP of CR-PET, at 8,400 MT/year, was found to range from $1.269 to $1.532/kg of CR-PET, which was lower than fossil derived PET. The “cradle-to-gate” GHG emissions for PET dissolution processes ranged from 1.09-3.56 kg CO₂-eq/kg of CR-PET, with that being the highest for anti-solvent process. Similarly, the total energy consumption was found to range from 17.95 – 56.31 MJ/kg of CR-PET. Overall, dissolution of PET with polymer precipitation via evaporation and cooling methods were found to be economically and environmentally favorable than anti-solvent method as well as fossil derived PET resin.

References

1. Chaudhari, U.S., Johnson, A.T., Reck, B.K., Handler, R.M., Thompson, V.S., Hartley, D.S., Young, W., Watkins, D. and Shonnard, D., 2022. Material Flow Analysis and Life Cycle Assessment of Polyethylene Terephthalate and Polyolefin Plastics Supply Chains in the United States. ACS Sustainable Chemistry & Engineering, 10(39), pp.13145-13155.

2. Chaudhari, U.S., Lin, Y., Thompson, V.S., Handler, R.M., Pearce, J.M., Caneba, G., Muhuri, P., Watkins, D. and Shonnard, D.R., 2021. Systems analysis approach to polyethylene terephthalate and olefin plastics supply chains in the circular economy: A review of data sets and models. ACS Sustainable Chemistry & Engineering, 9(22), pp.7403-7421.

3. Chen, W., Yang, Y., Lan, X., Zhang, B., Zhang, X. and Mu, T., 2021. Biomass-derived γ-valerolactone: Efficient dissolution and accelerated alkaline hydrolysis of polyethylene terephthalate. Green Chemistry, 23(11), pp.4065-4073.

4. Shonnard, D., Tipaldo, E., Thompson, V., Pearce, J., Caneba, G. and Handler, R., 2019. Systems analysis for PET and olefin polymers in a circular economy. Procedia CIRP, 80, pp.602-606.