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Middle Distillate Fuels From Ethanol
ChemCatBio 2022 Technology Brief

This ChemCatBio study bridges biomass and carbon dioxide (CO2) utilization for the production of middle distillate fuels and longer-chain products with ethanol as a critical intermediate, thus providing the scalability of this approach to help address climate change.

This study demonstrates a cost-competitive approach to make middle distillate fuels from renewable ethanol via innovations in catalysis. A market-responsive biorefinery was conceptualized around this C2 platform, where gasoline, jet, diesel, and chemical coproducts can be produced simultaneously. Researchers employed an integrated approach of combining experiments, techno-economic analysis, and life-cycle analysis to assess the economic and greenhouse gas (GHG) emission reduction potential and identify the major cost drivers to prioritize research and development work.

"Production and use of low-carbon intensity middle distillates generated from either biomass or CO2 is considered an effective approach to address the long-term climate impact of the aviation, maritime, and rail sectors."
 

Key Findings

Lewis Acid Zeolite Catalysts Enable Enhanced C3+ Selectivity

When catalyzed by Lewis acid zeolites, the pathway for forming carbon-carbon bonds exhibits much higher C3+ olefin selectivity compared to other direct ethanol-to-butene-rich olefin approaches. This is possible because such catalysts minimize ethanol dehydration to ethelyne through a unique active site combination. These catalysts also avoid significant carbon-carbon cleavage and over-hydrogenation of olefins, thereby preventing the formation of CO2 and light paraffins, respectively.

[CHART]
Ethanol conversion and C3+ olefin selectivity over different pathways and catalyst types.

C3+ Olefins Can Be Upgraded to Longer-Chain Hydrocarbons Over Several Solid Acid Catalysts

C3+ olefins obtained from this one-step ethanol conversion process are further oligomerized to longer-chain hydrocarbons over several solid acid catalysts, including Amberlyst-15, Amberlyst-36, and CT275. Findings suggest that gasoline, jet, and diesel cuts can be adjusted by using different oligomerization catalysts.

[CHART]
Liquid hydrocarbon distributions following oligomerization using Amberlyst-36, Amberlyst-15, and CT275.

The Approach for Making Middle Distillate Fuels From Renewable Ethanol Could Have Cost Advantages

Compared to two-step ethanol to butene-rich olefin processes, this one-step approach can reduce ethanol upgrading costs by as much as 42% ($0.60/gasoline gallon equivalent (GGE) vs $1.04/GGE). When using a pure ethanol feed, the baseline ethanol upgrading cost is $0.60/GGE, with capital expenses contributing 27% and operations 73% of the total cost.

[CHART]
Ethanol upgrading cost distributions for three cases with different ethanol concentrations.

The Approach Could Realize Substantial Reductions in Well-to-Wake GHG Emissions

GHG emissions for this pathway largely depend on the type of biomass feestock, yield of liquid hydrocarbons, and ethanol concentrations. Reducing carbon intensity could lead to significant economic incentives for producing renewable hydrocarbon fuels from ethanol given current and pending low-carbon fuels regulations across the United States.

[CHART]
Well-to-wake (WTWa) GHG emissions (gCO2e/MJ) of nine ethanol to jet (EtOH) cases compared with petroleum jet. GGE equals gasoline gallon equivalent.

Challenges and Next Steps

Risks and Challenges

  1. Integrating all unit operations at a relevant scale—It is important to understand key kinetic and thermodynamic parameters to inform a scale-up model. Integrating unit operations at scale enables researchers to accelerate the scale-up process and give industry partners increased confidence that this technology can advance state, national, and international sustainability goals.
  2. Catalyst production scale-up—Lewis acid zeolite catalysts are synthesized from a combination of metals and components. More research and development is needed to determine the risks and rewards of producing them at scale.
  3. Catalyst stability—To be commercially viable, emerging catalysts must operate smoothly for extended periods of time. More data on the stability and regeneration of Lewis acid zeolite catalysts will better prepare researchers and engineers to design processes accordingly.

Research Needs

Three primary advances are needed to prepare this ethanol-to-SAF production technology for wider commercial adoption:

Integrate all unit operations in series—This allows researchers to analyze the impact of byproducts (and products that do not meet SAF specifications) on downstream conversion

Increase the scale of the reactor—Increasing reactor scale nearly 30 fold—to produce hundreds of milliliters of jet fuel a day from a range of feedstocks—is needed to support fuel specification testing

Prepare for pre-pilot facility—To lower risks for industry, researchers must develop chemistry- and physics-based process models to inform facility scale-up and operations.