(310g) Roadmapping to Net-Zero Chemicals and Plastics: Analysis and Results

Humankind is faced with threats of irreversible climate change and its ill effects in the near future. To combat this, policymakers across institutions, organizations and nations seek to steer the global economy to operate with net-zero emissions. Despite an overwhelming majority of current research focusing on delivering cleaner energy with minimum emissions to industrial and residential systems, we emphasize that “net-zero” cannot be reached unless material value-chains are reinvented.¹ The direct and indirect emissions from the chemicals sector account for only 7% of the global emissions. However, as chemical energy carriers like hydrogen and methanol become increasingly important to bridge the intermittency issues associated with renewable energy solutions, eliminating emissions from this hard-to-decarbonize sector becomes critical.² The emissions from the global chemicals industry may be abated by the deployment of any number of emerging technologies. The development of modelling techniques however, is critical to assess and select the most economic, sustainable, circular and robust of these. There are instances of assessing the net-zero potential of technology combinations for individual product systems and designing the overall chemical network for net-zero emissions while accounting for economic drivers, in current literature.^{3, 4} Zibunas et al. also quantify capital investments and their role in roadmappping for a net-zero chemical industry.⁵ However, such formulations for steady-state analysis and design do not account for nascent innovations or the uncertainties associated with technology development.⁶ In this study, we bridge this research gap by developing a framework to design roadmaps to net-zero, sustainable, circular and economic chemical value chains while satisfying the growing need for chemical products and accounting for the probabilistic nature of technology development. We calculate metrics to estimate environmental and economic impact. The problem seeks to minimize the network costs while steering the chemical process network to net-zero life cycle emissions. We also investigate the evolving choice of technologies to fulfill chemical demands as technologies and background emissions evolve.

The model of the chemicals and materials industry (CMI) developed by us earlier, serves as our baseline dataset.⁷ This model is supplemented by input side solutions such as renewable power, green hydrogen, biomass, captured carbon-dioxide; process upgradations such as process electrification, transformative technologies; output side solutions such as carbon capture, incineration, pyrolysis; and recycle options ranging from primary to tertiary recycling. Additionally, we develop a methodology to calculate the capital and operating costs associated with each technological solution. We formulate the road-mapping problem to design the evolution of global chemical and plastics value chains over time as a dynamic optimization problem. The Sustainable Circular Economy (SCE) framework developed earlier is used to accommodate circular flows within the LCA framework. ^8,9,10 The temporal evolution of emerging technologies is modelled as a stochastic process. Our present formulation uses continuous time Markov chains (CTMCs) to represent technology evolution. However, the general framework is amenable to other representations of their stochasticity. The availability of biomass is modelled as a dynamic function that represents tree re-growth for multiple species parametrically. This allows us to constrain the availability of biomass to be used as feedstock. We estimate the evolution of background emissions from integrated assessment models (IAMs). The dependence of life-cycle processes on economic sectors like electricity, energy, material inputs like iron and steel etc. incorporates the effects of dependence of parallelly evolving sectors. The problem begins with a fixed number of facilities for each technology at the initial time step. The commissioning of newer facilities is allowed, subject to additional capital costs. The de-commissioning of older facilities is enforced according to fixed timelines. The problem is constrained to meet a growing demand of chemicals and plastics. The formulation seeks to reduce net greenhouse gas emissions from the network to zero within a time frame while maximizing the value addition through chemical products manufactured. The solution to this optimization problem yields the time dependent optimal combination of technologies that enable the transition to net-zero.

Our results instruct the investment into sequestration and carbon removal technologies at the latest possible time step to minimize total cost. The IAM scenarios play a pivotal role in determining these threshold time steps since background emissions also worsen with time. Our key findings indicate that carbon-negative solutions such as biofuels, biomass derived chemicals, and end-of-life upgradation to value added chemicals are preferably adopted as they become available. Lower TRL technologies such as electrochemical conversion of carbon dioxide to platform chemicals, emerge as robust solutions since their low TRL values imply their maturity only when the electricity grid has significantly shifted to being renewably powered, as indicated by IAMs. The results also emphasize the need to substitute all refinery derived chemicals using on demand technologies if petrochemical refineries and their products are to be completely bypassed. Finally, the need to incorporate mechanically and chemically recycled products becomes apparent to leverage higher value addition with minimum emissions. Such insight cannot be derived unless the network effects of this highly interconnected industry are considered in combination with probabilistic evolution of technology evolution and predictive models for other life-cycle inputs. Thus, our study puts forth a method to evaluate and optimize the adoption of uncertainty ridden emerging technologies to support transition to a more sustainable, circular future.

References

1. Circle Economy (2020) The circularity gap report

2. Wevers, J. B., Shen, L., & Van der Spek, M. (2020). What does it take to go net-zero-CO2? A life cycle assessment on long-term storage of intermittent renewables with chemical energy carriers. Frontiers in Energy Research, 8, 104.

3. Sen, A., Stephanopoulos, G., & Bakshi, B. R. (2022). Mapping Anthropogenic Carbon Mobilization Through Chemical Process and Manufacturing Industries. In Computer Aided Chemical Engineering (Vol. 49, pp. 553-558). Elsevier.

4. Gabrielli, P., Gazzani, M., & Mazzotti, M. (2020). The role of carbon capture and utilization, carbon capture and storage, and biomass to enable a net-zero-CO2 emissions chemical industry. Industrial & Engineering Chemistry Research, 59(15), 7033-7045.

5. Kätelhön, A., Meys, R., Deutz, S., Suh, S., & Bardow, A. (2019). Climate change mitigation potential of carbon capture and utilization in the chemical industry. Proceedings of the National Academy of Sciences, 116(23), 11187-11194.

6. Meys, R., Kätelhön, A., Bachmann, M., Winter, B., Zibunas, C., Suh, S., & Bardow, A. (2021). Achieving net-zero greenhouse gas emission plastics by a circular carbon economy. Science, 374(6563), 71-76.

7. Sen, A., Stephanopoulos, G., & Bakshi, B. R. (2022). Mapping Anthropogenic Carbon Mobilization Through Chemical Process and Manufacturing Industries. In Computer Aided Chemical Engineering (Vol. 49, pp. 553-558). Elsevier.

8. Thakker, V., & Bakshi, B. R. (2021). Toward sustainable circular economies: A computational framework for assessment and design. Journal of Cleaner Production, 295, 126353.

9. Thakker, V., & Bakshi, B. R. (2021). Designing Value Chains of Plastic and Paper Carrier Bags for a Sustainable and Circular Economy. ACS Sustainable Chemistry & Engineering, 9(49), 16687-16698.

10. Thakker, V., & Bakshi, B. R. (2023). Ranking Eco-Innovations to Enable a Sustainable Circular Economy with Net-Zero Emissions. ACS Sustainable Chemistry & Engineering.