(23c) Life Cycle Analysis and Techno-Economic Assessment of Emerging Sustainable Polymer Processes

Of the 350 million tonnes of plastic waste generated worldwide in 2018, only 18% was recycled, while a majority 58% was landfilled or lost to environment.^1,2The remaining 24% was incinerated, which emits greenhouse gases. In this context, the design of sustainable polymers that contribute less solid waste and less greenhouse gas emissions have arisen as a priority. Design of sustainable polymers can entail the use of renewable raw materials (like biomass), incorporating recyclability and/or degradability to benign compounds, and reducing energy and water consumption in the production of polymers, among other strategies. We evaluated three polymers designed to incorporate sustainability attributes including production from biomass and biodegradability with techno-economic and life cycle analyses. The goal was to analyze benefits/disadvantages of implementing these processes at different scales, compared to the similar baseline systems in use today.

The first process explores the synthesis of caprolactone monomers from biomass via the production on an intermediate p-cresol.³ This was compared to the conventional method of producing petroleum derived caprolactone monomers. Caprolactone monomers are essential as they are the building blocks of polycaprolactones which are subsequently employed in the production of polyurethanes. A preliminary cradle-to-gate life cycle analysis revealed the comparative advantage of such a process in terms of greenhouse gas emissions, water use and energy use. The second process employs biomass-derived cellulose nanocrystals (CNCs)⁴ as nano-fillers to reinforce polylactic acid (PLA), which is a biodegradable polymer. The biodegradability of these nanofillers is important to ensure the biodegradability of the polymer composite. The process of producing a piece of cutlery (fork) from this entirely biodegradable material was compared against two scenarios: (1) where the polymer is PLA with a non-biodegradable nanofiller (like graphene, titanium dioxide, calcium carbonate, silica etc.) and (2) where the polymer itself is non-biodegradable, like polypropylene, along with a non-biodegradable nanofiller. In the third process, the production of b-cyclodextrin polymers⁵ (which can be sourced from biomass cellulose) for the adsorption of micropollutants (especially PFAS and PFOA) in primary treated wastewater was explored for their environmental and economic footprint. This was compared with the production of conventional adsorbents like activated carbon for similar functional performance of micropollutant removal.

Impact categories explored in all the life cycle analysis included greenhouse gas emissions, water use and energy intensity. Argonne National Laboratory’s GREET model was employed to conduct the life cycle analyses. In the case of the cyclodextrin adsorbents, aquatic toxicity was also investigated as an impact category and the U.S. Environmental Protection Agency’s AQUATOX model was used as a means to establish the toxicity of baseline PFAS/PFAO emissions. For the techno-economic analysis, a discounted cash flow approach method was employed to evaluate a minimum selling price of the concerned product.

For large-scale applications of these emerging processes, these environmental and economic analyses can serve as an integral tool to identify possible bottlenecks and subsequently guide the direction of future research efforts.

References:

1. Geyer, R., Jambeck, J. R. & Law, K. L. Production, use, and fate of all plastics ever made. Sci. Adv. 3, e1700782 (2017).
2. A circular economy for plastics – Insights from research and innovation to inform policy and funding decisions, European Commission. https://op.europa.eu/en/publication-detail/-/publication/33251cf9-3b0b-1... (2019).
3. Lundberg, D. J., Lundberg, D. J., Hillmyer, M. A. & Dauenhauer, P. J. Techno-economic Analysis of a Chemical Process To Manufacture Methyl-ε-caprolactone from Cresols. ACS Sustain. Chem. Eng. 6, 15316–15324 (2018).
4. Calvino, C., Macke, N., Kato, R. & Rowan, S. J. Development, processing and applications of bio-sourced cellulose nanocrystal composites. Prog. Polym. Sci. 103, 101221 (2020).
5. Ling, Y., Alzate-Sánchez, D. M., Klemes, M. J., Dichtel, W. R. & Helbling, D. E. Evaluating the effects of water matrix constituents on micropollutant removal by activated carbon and β-cyclodextrin polymer adsorbents. Water Res.173, 115551 (2020).