A new catalyst and process developed by researchers at PNNL will improve the efficiency and decrease the cost of converting ethanol to gasoline, jet fuel, or diesel. The ethanol also can be converted to valuable chemicals used for a variety of products—such as latex gloves, synthetic plastics, automobile tires, and more. The co-production of value-added chemicals offers the potential to improve overall economics, as well as provide feedstock flexibility for commercial operation, both of which are being investigated by researchers in tandem with fuel products. The patented process would enable biorefineries to convert ethanol as a feedstock sourced from renewable biomass—such as corn, switchgrass, and algae—or industrial waste gasses from steel mills into biofuels and value-added chemicals.
Faster and Cheaper Process for Producing Renewable Fuels and Commodities
PNNL’s single-step chemical conversion streamlines what is currently a costly, multi-step process. The patented catalyst converts biofuel (ethanol) directly into a versatile “platform” chemical called n-butene.
N-butene currently is produced from petroleum-based feedstocks using the energy-intensive cracking—or breaking down—of large molecules. The global production of ethanol using this method is about 29 billion gallons per year. The United States alone produces about half of that amount per year in nearly 200 distributed facilities. By comparison, PNNL’s new technology reduces emissions of carbon dioxide by using renewable or recycled carbon feedstocks. Using renewably derived n-butene as a starting point, existing processes can further refine the chemical for multiple commercial uses, including diesel and jet fuels. The monomer also is the building block for just about every major synhetic plastic or rubber, such as tires (styrene-butadiene), fuel hoses (nitrile-butadiene), legos (acrylonitrile butadiene), and much more.
Research focused on producing n-butene from ethanol has existed for years. However, achieving high yields at industrial scale is challenging and costly. PNNL’s novel catalytic process bridges this gap. A highly active, multifunctional catalyst comprising silica as a support material, with silver nitrate powder and zirconium nitrate as the catalytic material, enables the single-step conversion process. The invention produces n-butene with greater than 90 percent ethanol conversion and greater than 60 percent selectivity (other products predominantly being other olefins). This pathway provides an economic route to jet- and diesel-range hydrocarbons over the current state-of-the-art technology, with elimination of a unit operation. Additional energy savings are achieved by coupling exothermic and endothermic reactions.
The process works by ripping hydrogen off the ethanol molecules, creating acetaldehyde—a compound that typically occurs naturally in coffee, bread, and ripe fruit. Carbon-to-carbon bonds follow, producing crotonaldehyde, which occurs in a variety of foods like soybean oils. The crotonaldehyde is then converted to crotyl alcohol, which undergoes dehydration, resulting in butadiene. Butadiene then is selectively hydrogenated to n-butene. A more recent catalyst formulation produces n-butene through butyraldehyde instead of butadiene intermediate. This discovery is advantageous because butadiene is a coke precursor, both uses lead to higher levels of catalyst deactivation. Instead, this new catalyst formulation produces three times less coke formation, leading to significantly improved catalyst stability.
PNNL's invention offers many benefits, including a lower production cost.
- A new catalyst system for direct conversion of ethanol to n-butene-rich olefins.
- A total olefin selectivity of 85 to 90 percent was demonstrated (~60 percent selectivity to butenes), thus, providing a more economic route to jet- and diesel-range hydrocarbons over current technology. The current state of the art for the ethanol-to-distillates process requires four steps: ethanol to ethylene, oligomerization of ethylene to butenes, oligomerization of butenes to distillate-range hydrocarbons, and hydrotreating to saturate olefins.
- A single-step conversion process demonstrated for greater than 90 percent ethanol conversion and 75 percent selectivity to n-butene (with total olefins up to 90 percent selectivity).
- Catalyst stability has been a focus of improvement, and catalyst regeneration has been demonstrated.
- The co-production of value-added chemicals (e.g., n-butene; 1,3-butadiene) also has been shown to improve overall economics, as well provide feedstock flexibility for commercial operation, and this is being investigated in tandem with fuel products.
State of Development
PNNL’s single-step process for converting ethanol to n-butene is available for licensing in some fields of use.