Tuesday, February 06, 2007

Ethanol, Hydrogen and Carbon Dioxide


Wild Grasses - Feedstock of the next industrial revolution?

Over the last week I have been thinking about everything ethanol. (No, this wasn’t a lost weekend). The New York Times had an article on ethanol 3/26/06.

Background – Ethanol is alcohol made from fermenting biological matter. Ethanol along with Bio-Diesel are two promising types of bio-fuels – fuels derived from biological resources. Biofuels are renewable and if the chain of development from planting, through cultivation, harvesting and processing into useable fuel is carefully managed, biofuels can reduce the use of fossil energy, reduce pollution and increase our national security.

Ethanol has been in the news for a variety of reasons. First there have been some studies that show the net energy gain from the manufacture of ethanol is very little or worse yet, negative. Much of this negative chatter has come from conservative talk show hosts bemoaning farm subsidies for the production of ethanol from corn. However there are some new technologies on the horizon.

In their fall 2005 newsletter the Rocky Mountain Institute has a great article on Ethanol and best practices for development of an Ethanol infrastructure. As usual the RMI was ahead of the curve on this development. In their newsletter from the fall of 2005:

Switchgrass Biofuels, and specifically ethanol, have been the subject of a great deal of criticism in recent months by detractors claiming that more energy is required to produce ethanol than is available in the final product, that it is too expensive, and that it produces negligible carbon reductions. These critiques are simply not accurate. State-of-the-art technologies have been competently forecasted—even proven in the market—to produce ethanol that is far more cost-effective and less energy-intensive than gasoline. We'll explore why, and why the critics have gotten it wrong.

When we say biofuels, we mean liquid fuels made from biomass—chiefly biodiesel and ethanol, which can be substituted for diesel fuel or for gasoline, respectively. The technology used to produce biodiesel is well understood, although its biomass feedstocks are limited and production today is fairly expensive. We will instead focus on ethanol, which we believe has significantly greater potential.

....But conventional processes and feedstocks used to make ethanol are not feasible in the United States on a large scale for three reasons: they're not cost-competitive with long-run gasoline prices without subsidies, they compete with food crops for land, and they have only marginally positive energy balances.

Happily, in addition to starch-based feedstocks, ethanol can be produced from "cellulosic" feedstocks, including biomass wastes, fast-growing hays like switchgrass, and short-rotation woody crops like poplar. While not cost-competitive today, already observed advances in technology lead us to believe that in the next few years, ethanol made from these crops will become cost-competitive, won't compete with food for cropland, and will have a sizeable positive energy balance. Indeed, because these crops are expected to have big biomass yields (~10–15 dry tons/acre, up from the current ~5 dry tons/acre), much less land will be required than conventionally thought. Further, cellulosic ethanol will typically have twice the ethanol yield of corn-based ethanol, at lower capital cost, with far better net energy yield.

We can't remember how many times we've been asked the question: "But doesn't ethanol require more energy to produce than it contains?" The simple answer is no—most scientific studies, especially those in recent years reflecting modern techniques, do not support this concern. These studies have shown that ethanol has a higher energy content than the fossil energy used in its production. Some studies that contend that ethanol is a net energy loser include (incorrectly) the energy of the sun used to grow a feedstock in ethanol's energy balance, which misses the fundamental point that the sun's energy is free. Furthermore, because crops like switchgrass are perennials, they are not replanted and cultivated every year, avoiding farm-equipment energy. Indeed, if polycultured to imitate the prairies where they grow naturally, they should require no fertilizer, irrigation, or pesticides either.

So, Cellulosic Ethanol could be a great way to reduce our dependence on Persian Gulf Oil.

A second technology that in my mind is linked to the potential of Cellulosic Ethanol is in development at the University of Minnesota. Dr. Lanny Schmidt has been developing a method of reforming alcohol into hydrogen using a very clever and simple technique. The core idea in his invention is to use a fuel injector to spray a fine spray of ethanol onto a catalyst. Water that naturally occurs in the ethanol turns to steam and this keeps the invention from exploding. (Apparently Dr. Schmidt had many a test rig explode in the lab!) With a carefully crafted catalyst the process runs clean and is very efficient.

Now, on one hand we have a new technology for the conversion of grasses and other agricultural waste into ethanol, and on the other hand we have a new technology for converting ethanol into hydrogen. This makes the possibility of using ethanol as a medium for storing hydrogen, and locally converting ethanol into hydrogen, say at the pump, a possibility. There are a lot of design decisions to make, like how to handle the CO2 that is generated as part of the conversion process. The overall process is close to carbon neutral but if we make high quality CO2 under controlled circumstances, then it seems like a good idea to sequester the CO2.

This leads to the third of the two technologies I wanted to write about today – Supercritical Carbon Dioxide. In the supercritical phase, that is when the pressure is really high, carbon dioxide can be in a phase right on the edge between gas and liquid. It can flow through a lot of materials and it is a highly polar solvent. SCCO2 can be used in some industrial processes as a solvent, or in certain processes it can react with some simple industrial waste products to make a form of carbonate mineral. This process makes a high quality form of pre-cast concrete. It can be used to make concrete block, concrete bricks, pre-cast stone or structural members. The process could sequester a couple of pounds of CO2 in every concrete block made with the process.

So, if you have Cellulosic Ethanol on one hand, a new highly efficient technology for the conversion of Ethanol to Hydrogen which leaves CO2 behind on your other hand, then on your third hand you have the SCCO2 conversion of industrial waste to carbonate minerals, you may have the makings of an entirely environmentally benign manufacturing/ industrial park.

I do plan on covering the SCCO2 process in an upcoming post. It is a lot like pre-cast concrete, only good for the environment.

Check out Cellulosic Ethanol at the Rocky Mountain Institute here.

Check out Dr. Schmidt’s Ethanol to Hydrogen technology here.

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