Hydrogen from Bio-Derived Liquids

Bio-derived liquid fuels can be produced from renewable agricultural products, such as wood chips.

Background

Bio-derived renewable fuels are attractive for their high energy density and ease of transport. One scenario for a sustainable hydrogen economy considers that these bio-derived liquid fuels will be produced at plants close to the biomass resource, and then transported to distributed hydrogen production centers (e.g., hydrogen refueling stations), where the fuels will be reformed via the steam reforming process, similar to the current centralized production of hydrogen by the steam reforming of natural gas.

Hydrogen produced by reforming these fuels must first be purified and compressed to appropriate storage and dispensing pressures. Compressing hydrogen is energy intensive, however, and it can consume a significant fraction of the fuel’s heating value. One promising option for producing pressurized hydrogen from bio-derived liquids is to perform the steam reforming reaction at high pressure.

Pressurized reforming is not without its challenges, however. Calculations of thermodynamic equilibrium predict that high-temperature reforming will lead to lower hydrogen and higher methane yields. Also possible is an increased tendency for the formation of coke deposits, which interfere with catalyst performance. 

Argonne’s Research

Argonne researchers are investigating ways to overcome the challenges of high-pressure reforming of bio-derived liquids by studying the reaction using ethanol and glycerol as surrogates for such fuels in general. To identify suitable processing conditions, they are examining preferred catalysts, higher temperatures, various steam-to-carbon molar ratios, and hydrogen separating membranes.

Accomplishments to date include:

• Design and fabrication of a palladium-alloy membrane reactor and apparatus to study the effectiveness of hydrogen extraction on reaction kinetics and hydrogen yield during the steam reforming of ethanol at pressures up to 1000 psig.
• Measurement of the hydrogen transported across a membrane to establish the hydrogen flux as a function of temperature and pressure difference.
• Development of mathematical models of steam reforming reactors, with and without a hydrogen separation membrane. Use of the reactor models to define process configurations and conditions needed to meet process targets, such as system efficiency.

Because injecting liquid feeds into a pressurized reactor requires very little energy, it is advantageous to conduct the hydrogen production step (reforming) in a pressurized reactor, thereby producing hydrogen at high pressure and reducing the energy needed to compress the hydrogen to storage or delivery pressures. Producing hydrogen at high pressure would also offer flexibility in the selection of hydrogen purification/separation technologies. More compact systems (for greater reactivity) and higher driving forces for pressure-based separation and purification systems are additional expected advantages.

If the initial results from the pressurized reforming in a membrane reactor are promising, the concept may be demonstrated at the pilot scale in collaboration with industrial partners. Successful high-pressure distributed reforming of bio-derived liquid fuels will expand hydrogen production options and it will help to develop capabilities critical for progress towards reduced reliance on fossil fuels.

Funding

This work is funded by the Fuel Cell Technologies Program of the DOE Office of Energy Efficiency and Renewable Energy.

December 2009