April 17, 2007

Converting Biomass to Hydrogen

It is pretty clear that whatever exists as an energy paradigm today will be replaced in the future. Wood gave way to coal, whale oil made way to petroleum and petroleum distillates, and gasoline is ceding ground to ethanol. What will follow ethanol?

Many suspect that ethanol will give way to hydrogen - hydrogen produced using biomass conversion processes. Hydrogen from electrolysis and other ways runs the risk of using more energy to produce it than it creates. Gasification produces syngas which is predominantly carbon monoxide and hydrogen. So the energy in the feedstock is used for both providing the heat to break its chemical bonds while the hydrogen atoms are released for isolation.

The reason we cannot skip ethanol and proceed directly to hydrogen is because we need to transition our infrastructure, energy storage, and vehicle technology at the same time. Ethanol is easy - made far simpler because it is blendable in gasoline - acting as both an oxygenate (to burn cleaner) and an extender.

Hydrogen sounds irresistible because it's emissions are so clean (drops of water) as it propels our automobiles. But implementation will require that many new technologies advance concurrently. One question is how can we transport compressed hydrogen? One prominent answer is - ethanol could be the carrier! If that is the direction hydrogen distribution is taking then the infrastructural transition from ethanol to hydrogen will be so much easier.

Here are excerpts from an article about the bioconversion of feedstock into "biohydrogen" that appeared this week on Biopact. They preface a story about a British company, Biohydrogen, that is advancing technology in this area.

New company called 'Biohydrogen' to make H2 from sugar

The problem with hydrogen is that it is merely an energy carrier and needs a primary energy source from which the gas can be obtained. If this first source is a fossil fuel, then hydrogen isn't really a clean energy carrier. If the gas is made from the electrolysis of water, which is a rather energy-intensive process, then electricity is needed, and the dilemma remains: where do we get the electricity from?

Biohydrogen is probably the most competitive of the non-fossil fuel production routes. There are roughly three main ways of obtaining the gas from biological sources: (1) biochemical conversion (diagram, click to enlarge): chemotrophic or phototrophic micro-organisms are allowed to ferment sugars, under anaerobic or aerobic conditions (depending on the micro-organism) during which hydrogenase or nitrogenase enzymes produce hydrogen directly (on H2 production from cyanobacteria and micro-algae see the last section of our post on biofuels from algae), (2) thermochemical conversion: biomass in solid form (wood, straw, etc) is transformed through gasification into a hydrogen-rich gas, from which the H2 is then separated, or (3) indirectly from biogas: biomass is anaerobically fermented into biogas, the methane of which is further converted into hydrogen (similar to H2 production from natural gas); combinations between biohydrogen and biomethane production are being researched as well.

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1 comment:

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