A new open-access study published in Proceedings of the National Academy of Sciences (PNAS) finds that Vertimass’ integrated, cost-efficient process to convert ethanol into a blend-stock consisting of a mixture of C₃ – C₁₆ hydrocarbons containing paraffin, iso-paraffins, olefins, and aromatic compounds can reduce greenhouse gas emissions between 40 and 96 percent. Vertimass originally licensed the technology from Oak Ridge National Laboratory (ORNL) in 2014. (Earlier post.)

A team from Vertimass LLC, Thayer School of Engineering at Dartmouth College, Argonne National Laboratory (ANL), Boeing, the Brazilian Bioethanol Science and Technology Laboratory (CTBE), the Brazilian Center for Research in Energy and Materials (CNPEM), the Federal Aviation Administration (FAA), Imperial College, Oak Ridge National Laboratory (ORNL), the National Renewable Energy Laboratory (NREL), Pennsylvania State University, and the University of California Riverside contributed to the report.

Unlike prior processes for converting alcohols into hydrocarbons with multiple steps for dehydration, oligomerization, and hydrogenation, the Vertimass consolidated alcohol dehydration and oligomerization (CADO) conversion is accomplished in a single reactor system using a metal exchanged zeolite catalyst.

Block flow diagram illustrating (top) water removal from wet ethanol vapor above the feed tray to produce pure fuel grade ethanol or (bottom) CADO of the same wet ethanol to fungible blendstocks. HE = heat exchangers. Hannon et al.

Through the ability to process vapor containing about 40% ethanol in water that is released when fermentation streams are volatilized, overall CADO costs for conversion of wet ethanol into the hydrocarbon blendstocks are estimated at $2.00/GJ today with the potential to drop to $1.44/GJ in the near future.

These predicted unit energy costs are similar to those estimated for removing water from the same ethanol vapor to meet fuel grade requirements ($1.46/GJ). Increased oil prices or current production incentives make Vertimass fuel cost competitive, and CADO-derived hydrocarbon blendstocks pass on greenhouse gas emission reductions of the ethanol feedstock.

Vertimass’ catalytic conversion of ethanol to fungible hydrocarbon fuel blendstocks was greatly accelerated through cost sharing by the BioEnergy Technology Office (BETO) of the Energy Efficiency and Renewable Energy Office (EERE) within the US Department of Energy.

To understand the full-scale impacts of CADO, the researchers evaluated the environmental impacts of the system via life-cycle analysis. Researchers also evaluated the technical and economic impacts of the approach.

Argonne researchers used the Greenhouse Gases, Regulated Emissions, and Energy use in Transportation (GREET) model to calculate the life cycle GHG emissions produced by hydrocarbon fuels made from different raw materials and conversion methods. Some of the feedstocks analyzed were corn and sugarcane, which are first generation feedstocks, as well as sugarcane straw and corn stover, which are non-food biomass, or the second generation feedstocks.

Variations in the feedstock used to make ethanol and pathways used to convert it, yield different levels of GHG emissions.

—Argonne energy systems analyst Pahola Thathiana Benavides, co-author

The analysis showed that hydrocarbon blends made using the CADO conversion process reduced greenhouse gas emissions anywhere from between 40% up to 96% depending on the feedstock and the conversion pathway. GHG emissions fell by 40% with corn grain, 70% with sugarcane juice and 70-96% with cellulosic biomass such as sugarcane straw and corn stover.

In order to move towards more sustainable development, we will need fuels that can generate fewer emissions and that are economically feasible. This work is an exciting indicator that building such a future is possible.

—Pahola Thathiana Benavides

This work was funded by the Bioenergy Technologies Office within DOE’s Energy Efficiency and Renewable Energy Office (EERE), by Vertimass LLC, and by the Center for Bioenergy Innovation, a DOE Bioenergy Research Center supported by the Office of Biological and Environmental Research within DOE’s Office of Science.

Resources

• John R. Hannon, Lee R. Lynd, Onofre Andrade, Pahola Thathiana Benavides, Gregg T. Beckham, Mary J. Biddy, Nathan Brown, Mateus F. Chagas, Brian H. Davison, Thomas Foust, Tassia L. Junqueira, Mark S. Laser, Zhenglong Li, Tom Richard, Ling Tao, Gerald A. Tuskan, Michael Wang, Jeremy Woods, Charles E. Wyman (2019) “Technoeconomic and life-cycle analysis of single-step catalytic conversion of wet ethanol into fungible fuel blendstocks” Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1821684116