Purdue University Mark

Purdue University

Liquid Fuels Research Group
School of Chemical Engineering

Research

Background

In order to achieve energy security for the United States and to create long-lasting jobs that enhance the economic development of the rural economy, it is essential to develop biomass to liquid fuel (biofuel) technologies that would be sustainable and co-exist harmoniously with other uses of biomass.  Since the driver for biomass growth is energy from the sun, we begin our search for a suitable biomass-to-fuel conversion technology by examining a future scenario where solar energy is the prime driver of our energy economy.   While we are currently analyzing this dynamic interaction to identify resource availability, technology needs, economics, environmental footprint for harmonious coexistence of all the end uses, we focus on the use of biomass to produce transportation fuels.

Historically, all the solutions for biomass to liquid fuel have relied solely on biomass and have ignored possible interaction with other resources and associated technologies.  We start our analysis by first identifying a synergistic interaction across technologies that has a potential to supply much larger quantities of biofuel from a given quantity of biomass.  As shown in the figure above, for a biomass growth rate between 1 kg/m2/yr to 3.75 kg/m2/yr, the net energy efficiency of solar photons to biomass conversion is 0.3 to about 1%   The traditional methods such as fermentation, gasification followed by conversion to liquid fuel, fast-pyrolysis etc. that solely use biomass will lead to further reduction in Sun- to-biofuel efficiency due to conversion process inefficiencies.  Generally, this means that the overall efficiency from sun photons to biofuel is in the range of 0.12 to 0.5%.  Such overall low-conversion efficiencies directly translate into large land area requirements to meet all the liquid fuel need for the U.S. transportation sector. 

On the other hand, processes to convert solar photons to electricity using photovoltaics or solar-thermal power easily have efficiencies of about 15%.  With use of such electricity and an electrolyzer, one can produce hydrogen with an overall efficiency from sun-to-hydrogen of about 7.5% (based on lower heating value, LHV).  This efficiency is an order of magnitude higher than the sun-to-biomass growth efficiency. 

A long term goal of our work is to suggest and develop novel long-term sustainable solutions that will synergistically use solar hydrogen with biomass to yield a much higher overall sun-to-biofuel conversion efficiency processes.

 

The H2CAR process

Based on the analysis above, we recently proposed a hybrid H2-Carbon (H2CAR) process.  In the H2CAR process, H2 from a carbon-free energy source such as solar, nuclear etc. is reacted with biomass to provide liquid fuel for the transportation sector.  Since all the carbon in the biomass is converted to liquid fuel in this process, only one-third the biomass needed to produce the same quantity of liquid fuel. 

The most significant finding of the H2CAR process is that 1.366 billion tons of sustainable biomass available per year is capable of providing the 13.8 million bbl/day of liquid fuel needed for the entire U.S. transportation sector!  This is in contrast to literature estimates that 1.366 billion ton biomass is sufficient to meet 30% of the U.S. transportation fuel need.

 

The H2Bioil process

There are three main challenges in the recently published H2CAR process [1, 2]; the estimated amount of supplementary H2 needed at 0.33kg/l of oil produced is quite large, the cost competitiveness due to the usage of a gasifier and a FT reactor and the infeasibility to transport biomass over large distances to feed large size liquid fuel plants [3, 4]. In order to reduce the levels of supplementary H2 while still providing high recoveries of biomass carbon as liquid fuel, a novel process based on the biomass fast hydropyrolysis and hydrodeoxygenation is developed: Hydrogen Bio-Oil (H2Bioil) [5].  Since all the carbon in the biomass is converted to liquid fuel in this process, only one-third the biomass needed to produce the same quantity of liquid fuel.

The H2Bioil process integrates the well understood higher efficiency and yield of a fast- pyrolysis based process with hydrogen from an external source, and is capable of producing deoxygenated oil, suitable to replace petroleum based fuels.

Thus, H2Bioil has the potential to play a major role in providing transportation fuel! In the United States with the 1 billion tons of annual sustainable biomass and solar H2, H2Bioil process has the potential to produce 8.7 million bbl/d of biofuel, providing 63% of the fuel requirement of the entire US transportation sector. This process (see fig. below), requiring only 27% of the hydrogen requirement of the H2CAR process, can be built at small to medium size and distributed over relatively short distances to avoid transportation of biomass over long distances [3, 5].

H2BioilTM process  

We propose to run biomass using fast-hydropyrolysis instead of the ordinary fast-pyrolysis because the presence of during pyrolysis in the H2Bioil process is expected to decrease the char formation. Furthermore, Hydrodeoxygenation is essential for lowering the oxygen content of the fuel in order for these bio-oils to blend in more easily with petroleum products.

 

Synergistic Integrations of Biomass with Coal and Natural Gas

However, currently, the cost of H2 from solar or nuclear energy is quite high. Hence, during this transition period, we propose that supply of Hydrogen can be provided by integration of with coal gasification (H2Bioil-C) and H2bioil with Natural Gas Reforming (H2Bioil-NG).  

 Process flowsheet for H2bioil integration with coal and natural gas  

This novel concept proposed a direct usage of hot gas from a coal gasifier or methane reformer containing along with CO, CO2 and H2O to be used for fast hydropyrolysis and HDO. This has the potential to make the overall process more energy efficient and will also eliminate equipment and associated cost needed to purify H2 before the fast hydropyrolysis/HDO.

For the H2Bioil-C process, our calculations suggest that we expect to obtain an increase by a factor of 2.6 in bio-fuel production by this process! s for the process, we present a scenario where it is synergistic to use H2 gas directly from the exhaust of steam-methane reformer for biomass fast hydropyrolysis/HDO. In this simplest version of the process, no gas turbine, etc will be used to coproduce electricity. Our modeling calculations estimate the synergistic gain from H2Bioil-NG process will increase the yield by a factor of 1.6 as compared to stand-alone Biomass-to-Liquid (BTL) and Natural Gas-to-Liquid (GTL) processes! Therefore, H2Bioil-C and H2Bioil-NG process serves as a transition pathway for the H2bioil process when hydrogen from carbon-free energy source will be available in the future!

 

References

1. Agrawal, R.; Singh, N. R.; Ribeiro, F. H.; Delgass, W. N., Sustainable fuel for the transportation sector. PNAS 2007, 104, (12), 4828-4833.

2. Rakesh Agrawal; Navneet R Singh, System and Process for producing synthetic liquid hydrocarbon. US Patent 20080115415 2008.

3. Agrawal, R.; Singh, N. R., Synergistic Routes to Liquid Fuel for a Petroleum deprived future AIChE Journal 2009, 55, (7), 1898-1905.

4. Rakesh Agrawal; Navneet R Singh, Novel integrated gasification-pyrolysis process. US Patent 20090084666 2009.

5. Rakesh Agrawal; Manju Agrawal; Navneet R. Singh, Novel process for producing liquid hydrocarbon by pyrolysis of biomass in presence of hydrogen from a carbon-free energy source. US Patent 20090082604 2009.