Increasing Yield from Gasification - A new process can make more fuel from biomass.

[OKIsItJustMe]

http://www.technologyreview.com/computing/24838/

Increasing Yield from Gasification

A new process can make more fuel from biomass.

By Kevin Bullis

Friday, March 19, 2010

Biomass can be converted to fuels via a process called gasification, which uses high temperatures to break feedstock down into carbon monoxide and hydrogen, which can then be made into various fuels, including hydrocarbons. But there's a major drawback--about half of the carbon in the biomass gets converted to carbon dioxide rather than into carbon monoxide, a precursor for fuels. Now researchers in University of Minnesota and the University of Massachusetts, Amherst, have developed a method for gasifying biomass that converts all of the carbon into carbon monoxide.

In the new approach, the researchers gasify biomass in the presence of precisely controlled amounts of carbon dioxide and methane, the main component of natural gas, in a special catalytic reactor that the researchers developed. When they did this, all of the carbon in both the biomass and the methane was converted to carbon monoxide. "In the chemical industry, even a few percent improvement makes a big impact. The increase from 50 percent to 100 percent is profound," says Dionisios Vlachos, the director of the Catalysis Center for Energy Innovation at the University of Delaware.

To increase the yields from gasification, researchers at the University of Minnesota and UMass Amherst added carbon dioxide, which promotes a well-known reaction: the carbon dioxide combines with hydrogen to produce water and carbon monoxide. But adding carbon dioxide isn't enough to convert all of the carbon in biomass into carbon monoxide instead of carbon dioxide. It's also necessary to add hydrogen, which helps in part by providing the energy needed to drive the reactions. It's long been possible to do each of these steps in separate chemical reactors. The researchers' innovation was to find a way to combine all of these reactions in a single reactor, the key to making the process affordable.

The process could both greatly reduce greenhouse gas emissions and increase the amount of fuel that can be made from an acre of biomass using gasification. Many companies are pursuing biological approaches to converting biomass into fuel (using enzymes and yeast, for example), rather than thermochemical methods such as gasification, in part because biological approaches tend to convert more biomass into the desired fuel than thermochemical methods. But biological approaches are each designed to work with just one type of biomass. Gasification has the advantage of being more flexible. The same facility could potentially process grass, wood, and even old tires.

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[Massacure]

1. Gasification is only the first step.

Fischer-Tropsch is the second step.

[OKIsItJustMe]

2. Right

But increasing the efficiency of the first step increases the efficiency of the entire process.

[Massacure]

3. Right.

I'm curious what the economics of gasification + Fischer-Tropsch is like compared to fermentation to ethyl-alcohol or transesterfication to biodiesel.

[NNadir]

4. The reaction they are using is called the Boudouard reaction.

Octave Boudouard, who discovered the reaction, died in 1923.

http://en.wikipedia.org/wiki/Boudouard_reaction

I'm very impressed. I can hardly stand up, I'm so boiling over with optimism.

The Fischer-Tropsch process, which is also almost a century old, is the process using Boudouard products - along with water gas products - to make synthetic alkane mixtures like gasoline.

[Massacure]

5. So if I'm not mistaken,

The Boudouard reaction looks like 2CO + O2 -> 2CO2 + heat below 700 degrees Celsius, but above 700 degrees Celsius 2CO2 + heat -> 2 CO + O2.

The water gas shift reaction looks like CO + H20 -> CO2 + H2 + heat. Can it also be reversed above or below a certain temperature?

So CO2 can be taken from the water gas shift reaction and put through the Boudouard reaction to form CO and O2. The CO from the Boudouard reaction and the H2 from the water gas shift reaction can be used together for the Fischer-Tropsch reaction. I'm betting that the water shift reaction doesn't give nearly enough heat to sustain the Boudouard reaction, so an energy input is probably needed.

Out of curiosity, can the products produced by Fischer-Tropsch be easily controlled? Also, would it be difficult to use the waste heat from a nuclear reactor to sustain these processes for liquid fuels?

[NNadir]

6. These are all good questions.

The Boudouard reaction's condition of equilibrium is very much determined by temperature, particularly since it is a gas phase reaction, and thus entropy plays an important role. The same is true of the water gas shift reaction, which is purely a gas phase reaction usually under conditions in which the form of water is steam or supercritical water.

A reaction is spontaneous whenever the change in the Gibbs free energy, dG is negative. At low temperatures, the direction of the reaction is dominated by the change in enthalpy, but at high temperatures the reaction is dominated by the -TdS term, the change in entropy.

http://2ndlaw.oxy.edu/gibbs.html

Industrially, as these reactions are used in combination, they require a heat input, generally large, and, in fact, can be shown (along with the combustion of hydrogen in oxygen) to sum to combustion of carbon either in the forward sense or backward sense.

The backward sense, owing to the first law of thermodynamics, requires an energy input in the form of heat.

Almost everywhere on earth, where these reactions are used, the heat input is obtained by combusting dangerous fossil fuels and dumping the dangerous fossil fuel waste into the atmosphere.

This is just one of the many reasons why, for instance, Amory Lovins and his hydrogen car ideas are unbelievably stupid and illiterate, particularly because he is a dumb anti-nuke.

Like everything else Amory Lovins says, his scheme is a dangerous fossil fuel greenwashing/three card monty scam.

The "biomass to hydrogen" scheme has been understood as an alternative for about a century and is no "breakthrough." There simply is not enough biomass on this planet to let brazillions of people drive around in brazillions of hydrogen cars.

The products of Fischer Tropsch type chemistry are indeed manipulable via types of catalysts and conditions and one can make any hydrocarbon product that one wants, including FT diesel fuel and FT gasoline. This would be a very bad idea however.

Syn gas is better used to make the remarkable fuel dimethyl ether, and it is being used this way commercially in China using Japanese technology. Regrettably the starting material for this is the worst of the three terrible dangerous fossil fuels, coal. Iran is building a plant that will use dangerous natural gas as a feedstock. That also sucks, although anti-nukes like to pretend that dangerous natural gas is a clean fuel even though they have no fucking idea what to do with the waste.

There have been many schemes to produce hydrogen from nuclear energy, and some are under active development in Asia and Europe, and to a lesser extent in the US.

Usually these reactions do not involve carbon at all. The most famous thermochemical hydrogen cycle is the http://en.wikipedia.org/wiki/Sulfur-iodine_cycle">Sulfur-iodine cycle. It was discovered a long time ago, and was pushed by General Atomics people in order to sell the idea of high temperature gas cooled reactors.

GA reactors however - a few have been built and operated - had a number of problems and did not really become huge commercial players, although British Magnox reactors, which are similar, but not identical, had a long history of operation. The Calder Hall reactor, which was the first nuclear reactor in the Western World to commercially produce electricity, operated from 1956 until 2003.

It was a very small reactor, producing about 50 MWe. Regrettably, this type of reactor is suitable for the production of weapons grade plutonium and Calder Hall was used in this way, to make British nuclear weapons.

Another type of high temperature gas cooled reactor is the pebble bed reactor, which was a German design. It was a better reactor, and modifications of it of various kinds are still discussed. The German scaled up version had some problems and was ultimately shut by German anti-nuke stupidity and replaced by burning dangerous fossil fuels and dumping the dangerous fossil fuel waste into earth's atmosphere. Heckuva job.

The Chinese have built a replica of this type of reactor and have been operating it experimentally since 2003 on a small scale. Either they or the Koreans will be the first to use this type of reactor to make hydrogen using sulfur-iodine chemistry, as it has a suitable outlet temperature, around 950C. I have heard that Korea will using this chemistry commercially in about ten years.

Because of the high operating temperature these types of strategies, coupled to a combined electricity cycle can operate at extraordinary thermodynamic efficiencies, well above 50%. Advances in materials science have probably made these reactors a better bet, but I'm not a gas cooled kind of guy myself, and am fond of alternate high temperature reactor, particularly molten salt types.

http://www.nuc.berkeley.edu/People/Per_Peterson">Per Peterson at UC Berkeley is proposing a reactor that is sort of a hybrid of these two types. He's a great scientist, but I'm not sure I particularly agree with this reactor concept as ideal, although I'm ignorant of the details.

The sulfur iodine cycle is just one kind of thermochemical hydrogen cycle. There are many others.

I have one of my own that is designed to produce syn gas directly and does involve carbon wastes, and water, but I'm treating it as proprietary.