The Aqueous Phase Reforming (APR) process, invented by J. A. Dumesic and co-workers at the University of Wisconsin, is a unique process that can produces carbon-neutral hydrogen, fuel gas, liquid fuels or value added chemicals from a wide range of oxygenated compounds, such as ethylene glycol, biomass-derived glycerol, sugars and sugar-alcohols. Specifically, Virent, a company founded by Dumesic and others is developing a system to generate hydrogen from aqueous solutions of these compounds in a single step reactor process as compared to the three or more reaction steps required for hydrogen generation via conventional processes that utilize non-renewable fossil fuels.
In January the company announced that in a system purchased by Madison, Gas & Electric (MGE), it has successfully started up a demonstration system capable of directly converting sugars and glycerin into power. The system (see schematic below) has demonstrated the ability to deliver a minimum of 10kW of clean power to the MGE grid since its startup at the beginning of 2006 The system is utilizing the waste heat from the ICE to provide the limited amount of process heat required for the reactor.The system currently operates on pure glycerin. In the future, the Company will use a lower grade of glycerin that is generated as a byproduct of the biodiesel production process.
The process (US. Patent No. 6,699,457) will enable localized production of hydrogen using readily available sugar-based feedstocks effectively eliminating hydrogen transport, storage and safety roadblocks that impede adoption of hydrogen fueled power systems. Due to the low temperature operation of APR, the economics are scalable to small home and office use applications. Depending on the feedstock, the process is capable of producing green hydrogen at a total cost of between $1.80-$4.00/kg. This is dramatically less than alternative renewable sources, such as wind and solar, and very competitive with mature, capital intensive hydrogen production methods such as natural gas reformation, coal gasification or electrolysis.
For comparison the energy contained in a kg of hydrogen is comparable to the energy in a gallon of gasoline, thus the cost to operate an internal combustion engine (ICE) on this hydrogen, produced from a distributed production system would be competitive to an ICE running on gasoline and the cost of operating a fuel cell would be about one-third that of an ICE.
Contained in a single reactor vessel, APR is a combined process whereby a catalyst reforms oxygenated hydrocarbons to produce relatively clean hydrogen which is then passed to a second-stage ultra-shift catalyst where carbon monoxide is removed and the hydrogen made even more pure.
Dumesic and his team tested more than 300 catalysts to find a nickel-tin-aluminum combination that reacts with biomass-derived oxygenated hydrocarbons to produce hydrogen and carbon dioxide without producing large amounts of unwanted methane.
When the sugar or alcohol molecules touch the surface of the catalyst, chemical reactions break and rearrange many of the carbon bonds, causing the atoms to be “reformed” into new configurations and liberating hydrogen in the process. In fact, about half the product is hydrogen gas. The researchers estimate that, if the system is fully developed, it will be able to turn a liter of biomass into about 1,000 watts of power.
Dumesic and coworkers found a room-temperature substitute for the entire water-gas procedure: letting CO react with a liquid “oxidizing” compound, at room temperatures. The compound, made from tiny clusters of molybdenum oxide, containing 12 molybdenum atoms, 40 oxygen atoms as well as a central phosphorous atom is an environmentally benign polyoxometalate (POM) compound. When CO mixed with this agent in the presence of nano-gold particles about 1,000 times thinner than a human hair, nearly every carbon monoxide molecule was converted to CO2. The compound not only removes CO from gas streams for fuel cells, but also converts the energy content of CO into a liquid that subsequently can be used to power a fuel cell. The advance will make possible a new generation of inexpensive fuel cells operating with solutions of reduced POM compounds. While higher current densities can be achieved in fuel cells using electrodes containing precious metals, the researchers found that good current densities can be generated using a simple carbon anode.
The remaining byproducts consist of carbon dioxide and methane (or other readily combustible hydrocarbons). In a commercial application, the hydrocarbons could be separated and burned to provide all the heat needed to run the reactor, making the whole process energy-neutral.
Because the process occurs in a liquid phase at low reaction temperatures (e.g., 225oC), the hydrogen is made without the need to vaporize water. That represents a major energy savings compared to ethanol production or other conventional methods for producing hydrogen from fossil fuels based on vapor-phase, steam-reforming processes.
- Capability to generate hydrogen from renewable biomass-derived feedstocks
- Capability to provide on-demand hydrogen with low capital requirements
- Significantly lower operating temperatures (220 ○C v 800 ○C) enabling easier assimilation into heat sensitive environments
- Fuel-cell grade hydrogen is made in a single-step process
- Ability to use conventional distribution infrastructure to deliver feedstocks with little or no safety concerns
- Generation of 10 times more hydrogen per gram of catalyst than steam reforming processes
Virent has developed a cost model to develop cost projections for production of hydrogen and alkane fuels. The following assumptions were made to arrive at these projections:
- An APR reforming unit that generates roughly 500 kg of gas per day
- Capital cost which includes the cost of precious metal catalyst for the ultra-shift catalyst
- Operation and maintenance expenses are included
- 10% return on investment with system depreciation over 15 years
- For H2, reactor thermal efficiency of 70% and catalyst performance of 6 watts per gram
- For mixed alkanes, reactor thermal efficiency of 85% and 100% (less heat should be required) and catalyst performance of 6 watts per gram
- There is no consideration of carbon or renewable tax credits, which can have significant impact on overall economics in Kyoto geographies
The chart below shows preliminary cost projections for APR production of H2 from glycerol.
Because of the tremendous cost and energy advantages that the APR process has shown, Virent is targeting smaller (< 10 KW) H2ICE, SOFC, and PEM FC applications. The process also offers a compelling alternative to ethanol production by squeezing 60% more net energy out of each sugar molecule than the energy intensive fermentation/dewatering process.
Dumesic and Dr Randy Cortright, a UW-Madison College of Engineering researcher, formed Virent Energy Systems to move the technology from the engineering laboratory to the marketplace. The Wisconsin Alumni Research Foundation (WARF) is pursuing two additional patents based on the technology and has granted Virent Energy Systems an exclusive license. In lieu of licensing fees, WARF has taken an equity stake in Virent.
Virent Energy Systems, Inc., Madison, WI
Successful Startup for 10kW Virent System that Generates Power from Biomass, Press Release, January 26, 2006
Biomass to Power, APR Virtual tour, Energy Center of Wisconsin
Raney Ni-Sn catalyst for H2 Production from biomass-derived hydrocarbons, Dumesic, Science, 2075 (2003)