How can I separate carbon monoxide from wood gas?

Question

I am thinking about using open source wiki designs from allpowerlabs to construct a wood gas generator. The motivation came from experiencing a 10 day power outage after super storm Sandy. The utility company could not provide power due to damaged transformers, power lines, and other grid infrastructure. Most of the gasoline service stations did not have backup power to run the pumps and meters and those that did had huge queues to wait through.

Meanwhile there was tons of biomass available in my 2 acre yard. I used some of the wood in our wood stove for heating and some cooking but did not have a way of getting the energy stored in wood and other biomass to electrical energy.

The solution is a wood gas generator that converts the stored solar energy in wood to a gas that can be combusted in a hacked generator to provide electrical power. Allpowerlabs.com has a turn key solution all ready to go but it is beyond my budget, but they offer the open source build it yourself GEK (Gasifier Electricity Kit), mentioned earlier, that I would like to build.

Instead of using the wood gas to run a hacked Briggs and Stratton generator, I would prefer to route it to a BIY (Build It Yourself) fuel cell. Wood gas consists of hydrogen, carbon monoxide, carbon dioxide, water vapor, and small amounts of other. For fuel considerations hydrogen(H2) and carbon monoxide(CO) are usable.

While molten carbonate and solid oxide fuel cells can use CO, the operating temperatures are too high to be practical and we want to sequester the carbon instead of releasing to atmosphere. I would like to separate the carbon oxides from the wood gas and use the H2 directly into a fuel cell or store it for later use.

I know that we can remove CO2 from the wood gas or exhaust with low cost or Brew it yourself sodium hydroxide (NaOH), via caustic scrubbing.

My question is: How can we cost effectively separate the CO from the wood gas? I am not sure how NaOH reacts with hydrogen gas and CO.

Answer 1

This master's thesis by Dahiru Rufai Ahmed at the university of Oulu provides a comprehensive background into the removal of CO2 from wood gas.

On pages 36-37 it mentions the water-gas shift (WGS) reaction as a method of adjusting the hydrogen/carbon monoxide mixture or removing CO entirely to get pure H2. "The WGS reaction is an exothermic reaction (∆Hr = -41.1 kJ/mol) that converts excess carbon monoxide into hydrogen."

CO + H2O --> CO2 + H2 + heat

"At low temperature the reaction can be catalyzed by catalysts based on copper, aluminum and zinc oxides. (Basu, P. (2010). Biomass gasification and pyrolysis: Practical Design and Theory. 1st ed., Elsevier Inc. 365pp. ISBN: 9780123749888.)

However, in recent times, interest has been shifted to a catalyst-membrane system that incorporates the WGS reaction and H2 separation via a hydrogen selective membrane (Mendes, D., Chibante, V., Zheng, J-M., Tosti, S., Borgognoni, F., Memdes, A. and Madeira, L. M. (2010). Enhancing the production of hydrogen via water-gas shift reaction using Pd-based membrane reactors. Inter J Hydrogen Energy. 35 (22), 12596–12608.)."

This article describes a membrane based catalyst for the WGS reaction. The catalyst in the membrane uses Palladium alloys with Silver and Copper due to their higher selectivity and permeability to Hydrogen.

Since Palladium is an expensive noble metal and since catalytic converters for automobiles already use Palladium for CO oxidation, I am considering using an automobile catalytic converter (CAT) for this purpose. The CAT uses oxidation rather than WGS to convert CO, so I am concerned that it would also oxidize the hydrogen. However, I think the CAT would perform WGS if the input gas mixture is lacking oxygen which would be the case for wood gas. Any useful comments and feedback appreciated.

Answer 2

If you are going to use wood gas to run a generator, don't bother removing the CO. Burn it.

https://www.youtube.com/watch?v=X3KipK49v7g is a vid on making a woodgas powered truck.

That said: Consider getting a manual transfer switch, and a gas or diesel powered generator. While the power may have been off for 10 days this time, I found in our (shorter) outages that a 2 kW genset could keep the sump pump running, the fridge and freezer running, and by changing the extension cords I could refill the water tank from the well. It took about 5 gallons of gas a day. So a drum of fuel would get you through a 10 day outage.

Ideally such a generator is hooked up to natural gas. (In 20 years here we have had several half day to day and a half power outages a year, but have yet to have a gas outage.) No storage issues. Second best of propane, which is a pain to fill, keeps indefinitely. Gas and diesel both have limited storage spans. There are tricks you can use to lengthen this.

Your project makes a lot of sense for someone who was going off grid. But the total cost of this is way over what a generator, switch and fuel storage would cost.