(422c) Sustainability Assessment of a Global High-Trl Renewable Carbon Syncrude Economy

Refinery products are currently responsible for 15 % of global greenhouse gas (GHG) emissions. Given that demand is expected to grow a further 20 % towards 2050, more sustainable alternatives will be needed to meet climate targets [1]. However, frequently discussed solutions, such as electrification, green hydrogen, or a methanol-mediated economy, despite showing promise, face major challenges regarding scalability and cost. If implemented on a larger scale, these technologies would be disruptive to the value chain of transport and chemical products [2]. Hence, a high technology readiness level (TRL) solution could accelerate the shift away from crude oil, mitigating climate impacts while enhancing circularity and resilience.

Here we shall explore the Fischer Tropsch (FT) technology as the backbone of a high TRL solution that could provide a drop-in solution for the petrochemical industry, where the infrastructure downstream of the refinery could remain intact. Several FT plants operated by companies Shell and Sasol are currently running in Malaysia, Qatar, and South Africa [3] [4]. These production plants produce naphtha, kerosene, and diesel with production volumes up to 18 % of large conventional refineries. However, the main raw material fed to these plants currently comes from fossil sources such as natural gas or coal, while here we study the feasibility and performance of similar plants based on renewable carbon instead.

Literature has shown the technical feasibility of a so-called middle distillate synthesis plant (MDS) from fossil feedstocks [5]. In essence, the MDS is a combination of a Fischer Tropsch reactor and subsequent downstream upgrading. Much work has been done in recent years on producing sustainable aviation fuel (SAF) or naphtha from synthesis gas. Indeed, through downstream upgrading and refining, a Fischer Tropsch system could be tuned to maximize the yield of a single product[6]. To our knowledge, MDS plants using sustainable feedstocks and their economic and environmental impact on the petrochemical industry remain unexplored.

This work evaluates the potential benefits and challenges of integrating large-scale Fischer Tropsch plants in the petrochemical industry, co-producing naphtha, kerosene, and diesel. We use process simulation (Aspen HYSYS v12), techno-economic analysis and life cycle assessment (LCA) to evaluate the performance of the production of synthetic crude oil (syncrude) from several sources (biogas, biomass and direct air captured (DAC) CO₂ with wind electrolytic hydrogen) and compare them to the business-as-usual (BAU) from fossil crude oil.

Our results show that the cost per barrel of product is mainly driven by the cost of feedstock but is also heavily influenced by regional conditions for industrial heating and power. More specifically, biogas-based syncrude could be competitive to crude oil if large biodigesters are installed and energy costs are low. Syncrude from biomass and natural gas could also be produced at costs close to the breakeven point. However, for syncrude produced from DAC CO₂ and electrolytic H₂, the high cost of green hydrogen results in costs five to six-fold the price of fossil crude. Large quantities of manure, agricultural waste, and foresting residues could further boost the potential of bio-based syncrude.

The life cycle assessment (LCA) highlights negative GHG emission refinery operations for all the renewable syncrude scenarios. Moreover, the end-of-life analysis shows that capturing CO₂ in biogas upgrading and the biomass gasification processes could offset the direct emissions of diesel and kerosene combustion, leading to overall net-negative cradle-to-grave emissions.

Beyond the feasibility and potential of stand-alone FT refineries, this work also focuses on what changes would need to be made to a conventional crude oil refinery to facilitate FT-syncrude. As syncrude mainly consists of linear alkanes and alkenes, without many heteroatoms such as sulfur and oxygen, hardly any hydrotreating is required. Instead, the refinery would function more as an upgrader, where isomerization, cracking, and reforming are the reactions that yield products with the correct specifications. Utilizing existing infrastructure increases the profitability of the MDS and allows for an even faster drop-in solution.

All in all, this work explores a promising alternative to shift away from crude oil towards more sustainable production. Petrochemical products are vital in keeping the economy running and connecting citizens and goods to the rest of the world. At the same time, the corresponding GHG emissions place a large burden on the environment. FT-syncrude based on renewable carbon seems to offer an appealing compromise solution between the economy and the environment, where current oil and gas companies could find a way to diversify their businesses more sustainably. Moreover, when using biogenic sources, it could be produced at competitive costs while keeping emissions low. An economy based on a blend of crude oil and syncrude could, therefore, operate more independently, at similar costs while bringing their environmental footprint down. Such a solution would also make economies more resilient against the volatility in crude oil prices. All in all, we could envision a hybrid way forward based on the gradual replacement of fossil carbon with renewable carbon sources using FT as a key enabler, where both feedstocks should coexist temporarily until full circularity is eventually reached.

References

[1] OPEC World Oil Outlook 2024. https://publications.opec.org/woo/chapter/129/2356

[2] R.P. Lee & A. Scheibe. (2020). The politics of a carbon transition: An analysis of political indicators for a transformation in the German chemical industry. Journal of Cleaner Production, 244, 118629. https://doi.org/10.1016/j.jclepro.2019.118629

[3] J.E. Apolinar-Hernández, S.L. Bertoli, H.G. Riella, C. Soares & N. Padoin (2023). An Overview of Low-Temperature Fischer–Tropsch Synthesis: Market Conditions, Raw Materials, Reactors, Scale-Up, Process Intensification, Mechanisms, and Outlook, Energy & Fuels, 38. https://doi.org/10.1021/acs.energyfuels.3c02287

[4] R.L. Espinoza, A.P. Steynberg, B. Jager & A.C. Vosloo. (1999). Low temperature Fischer–Tropsch synthesis from a Sasol perspective. Applied Catalysis A: General, 286. https://doi.org/10.1016/S0926-860X(99)00161-1

[5] M.J. v.d. Burgt, C.J. van Leeuwen & J.J. del'Amico, S.T. Sie (1988). The Shell Middle Distillate Synthesis Process, Studies in Surface Science and Catalysis, 36. https://doi.org/10.1016/S0167-2991(09)60541-3

[6] A. De Klerk (2008). Fischer–Tropsch refining: technology selection to match molecules, Green Chemistry, 10. https://doi.org/10.1039/B813233J