(354h) Environmental and Economic Analyses of Liquid Fed Pyrolysis Process for Waste Polyethylene Films

About 71% of total plastics production in the U.S. are polyethylene terephthalate (PET, resin code #1) and polyolefin plastics such as high-density polyethylene (HDPE, resin code #2), linear low-density polyethylene (LLDPE, resin code #4), low-density polyethylene (LDPE, resin code #4), and polypropylene (PP, resin code #5). These types of plastics also represent 79% of the total plastic waste generation in the U.S., with 77% being landfilled, 16% incinerated for energy recovery, and only 7% collected for recycling¹.

To break this linearity and dependence on limited fossil resources of plastic supply chains, emerging chemical recycling technologies have been proposed to replace fossil derived plastic resins. These technologies can be broadly classified in 3 main categories: dissolution/purification, depolymerization, and conversion recycling technologies². Conversion recycling technologies convert plastic waste into intermediate hydrocarbon products such as specialty chemicals, waxes, lubricants, fuels, and gases. Pyrolysis, gasification, hydrothermal liquefaction, hydrogenolysis are some of the examples of thermal conversion recycling technologies. In this work, we look the environmental and economics analyses of a novel liquid-fed pyrolysis process that was developed at the Michigan Technological University^3,4. We look at three different scenarios for technology, first, co-locating this process with a petrochemical facility (“integrated facility” scenario), and second, locating this process remotely and away from a petrochemical facility (“non-integrated facility” scenario), and third, increasing the yield of wax at a non-integrated facility. Based on our previously published systems analysis framework^{2, 5}, we take a “bottom-up” approach, in which process simulation 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 liquid fed pyrolysis processes. The second research objective was to evaluate technoeconomic performance metrics of the simulated recycling processes and compare these different scenarios mentioned above. We also look at the effect of scaling up the capacity on the total capital costs and minimum selling price of liquid naphtha, the main pyrolysis product. We also couple the 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 the 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 and compare it against their fossil counterparts.

Our results revealed that the economic feasibility of this process depends on the capacity, location, product distribution, and price of pyrolysis products. For the integrated facility scenario, sales from pyrolysis gas product to the petrochemical facility favors the economics, whereas that for the non-integrated facility with high yield of wax, favors the economics. The MSP of pyrolysis oil produced at an integrated and non-integrated facility ranged from $1.019 to $1.918/kg of pyrolysis oil and was the highest for the remote facility. Preliminary LCA results revealed that the GHG emissions and CED impacts for the processes compare well with their fossil counterparts. The “cradle-to-gate” GHG emissions of pyrolysis oil ranged from 0.56-0.68 kg CO₂-eq/kg of pyrolysis oil, whereas those for pyrolysis gas ranged from 0.57-0.7 kg CO₂-eq/kg of pyrolysis gas. Similarly, the energy demand for pyrolysis oil ranged from 8.2-10.58 MJ/kg of pyrolysis oil, whereas that for pyrolysis gas ranged from 8.45-10.91 MJ/kg of pyrolysis gas.

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. Kulas, D.G., Zolghadr, A., Chaudhari, U.S. and Shonnard, D.R., 2023. Economic and environmental analysis of plastics pyrolysis after secondary sortation of mixed plastic waste. Journal of Cleaner Production, 384, p.135542.

4. Zolghadr, A., Kulas, D. and Shonnard, D., 2022. Evaluation of Pyrolysis Wax as a Solvent in Polyolefin Pyrolysis Processing. Industrial & Engineering Chemistry Research, 61(30), pp.11080-11088.

5. 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.