Purdue University scientists Rakesh Agrawal, Navneet Singh, Fabio Ribeiro, and Nicholas Delgass have proposed a hybrid system of hydrogen and carbon that can produce a sufficient amount of liquid hydrocarbon fuels to power the entire U.S. transportation sector. The H2CAR process uses carbon produced by biomass and hydrogen supplied from carbon-free energy. The following is summarized and paraphrased from the online publication of their report cited above.
The process has several advantages:
- The land area needed to grow the biomass is <40% of that needed by other routes that solely use biomass to support the entire transportation sector.
- Prior known processes were estimated to be able to produce 30% of the United States transportation fuel from the annual biomass of 1.366 billion tons, while the H2CAR process shows the potential to supply the entire United States transportation sector from that quantity of biomass.
- The synthesized liquid provides H2 storage in an open loop system.
- Reduction to practice of the H2CAR route has the potential to provide the transportation sector for the foreseeable future, using the existing infrastructure.
In their proposal, the primary purpose of either coal or biomass is to provide carbon atoms needed for the production of liquid hydrocarbons. Thus, the goal is to accomplish the complete transformation of every carbon atom contained in either of the feed stocks to liquid fuel by supplementing the conversion process with a carbon-free energy source. They propose to generate H2 from a carbon-free primary energy source such as solar, nuclear, wind, etc. and then use it to supply the hydrogen atoms needed for the chemical transformation.
There are a number of important consequences of the process. First, there is no CO2 emission from the chemical processing system, and the only CO2 released to the environment is from the transportation engine. Therefore, for coal, it eliminates the need to sequester CO2 produced in the liquefaction process. Second, an associated benefit of the absence of CO2 release from the chemical processing system is that 40% of the amount of coal or biomass is needed to deliver the same quantity of liquid fuel. Third, by providing open-loop H2 storage, this solution addresses one of the grand challenges of the H2 economy. Fourth, on a carbon atom basis, the energy content of the liquid fuel is higher than that of coal or biomass.
Making the concept economically competitive with gasoline and diesel fuel would require research in two areas: finding ways to produce cheap hydrogen from carbon-free sources and developing a new type of gasifier needed for the process.
Many more details are included in the referenced report. The report states numerous advantages for producing the carbon from biomass rather than from coal. Even though it is too early to estimate costs, the process efficiencies are very good as indicated in table I of the report.