(147o) A Novel Framework for Design of Net-Zero Chemical Systems: Analysis and Results

Life cycle assessment, operations research, supply chain design, sustainable design and optimization

Anthropogenic greenhouse gas (GHG) emissions must be curbed urgently to limit the ill effects of climate change. Organizations of all magnitudes across the world are committed to driving the transition to net-zero. We argue that the re-invention of material value chains is crucial if such commitments are to be honored.¹ The chemical and materials industry (CMI) is a critical driver of this transition. The CMI embodies 70% of global GHG emissions. It assumes increasingly greater importance as policymakers seek to replace fossil feedstocks and energy sources with chemical energy carriers and feedstocks.² Competing technologies have long claimed to be the sole solutions to our climate crisis. Therefore, the need of the hour is to critically assess the economics, sustainability, material efficiency and robustness of these technologies. Literature has historically focused on assessing net-zero potential of technology combinations for individual products or designing chemical networks for operation under optimal economics and GHG emissions.^{3,4 ,5,6} The uncertainty associated with development of nascent technologies however remains unquantified and unaccounted for in these works. In our study, we bridge this gap by developing a framework capable of designing roadmaps to net-zero, sustainable circular and economic chemical value chains while accounting for stochastic nature of technology development. We also investigate the evolving choice of technologies to fulfill societal chemical demands as technologies and background emissions evolve.

The model of the chemicals and materials industry (CMI) developed by us earlier, serves as the baseline dataset.⁷ This model is supplemented by input side solutions such as renewable power, green hydrogen, biomass, captured carbon-dioxide; process modifications such as electrification, on-demand technologies, utilization of captured carbon dioxide; output side solutions such as carbon capture, incineration, pyrolysis; and recycle options ranging from primary to tertiary recycling, to generate a network superstructure. Additionally, we develop a methodology to calculate the capital and operating costs associated with each technological solution. We formulate a dynamic optimization problem to design the evolution of global chemical and plastic value chains over time. 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. The present formulation uses continuous time Markov chains (CTMCs) to represent technology evolution. However, the formulation can easily accommodate other representations of stochasticity. The availability of biomass is modelled as a dynamic function that represents tree re-growth for multiple species parametrically, generating constraints on biomass feedstock availability. Integrated assessment models (IAMs) are used to estimate background emissions and estimate external inputs such as electricity, energy, material inputs like iron and steel etc. The problem begins with a fixed initial number of facilities for each technology. The commissioning of newer facilities is subject to additional capital costs. The de-commissioning of older facilities is constrained by fixed timelines. The evolving network must meet a growing demand of chemicals and plastics while reducing net GHG emissions to zero within a time frame and maximizing the value addition through chemical products manufactured. The solution to this optimization problem yields a time dependent optimal combination of technologies that enable the transition to net-zero.

Our results point to the need to invest into sequestration and carbon removal technologies at the latest possible time step to minimize total cost. IAM scenarios play a pivotal role in determining these threshold time steps since background emissions also worsen with time. Our 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. The results also emphasize the need to substitute all refinery derived chemicals with on-demand technologies if petrochemical refineries and their products are to be completely bypassed. Finally, mechanical and chemically recycled products emerge as critically important. Such insight can only be derived on the consideration of network effects of this highly interconnected industry in combination with probabilistic evolution of technology evolution and predictive models for other life-cycle inputs. Thus, our study formulates 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, Amrita, George Stephanopoulos, and Bhavik Bakshi. "Mapping Anthropogenic Carbon Mobilization Through Chemical Process and Manufacturing Industries." PSE 2021+ Conference Proceedings (2022). https://pse2021.jp/

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.