Saturday, May 12, 2007

And I Shall Call You, Patriot Fuel.

This post has very little to do with farming, directly at least. I'm going to talk about how to make ethanol. Every politician has their own biofuels agenda and everyone is talking about ethanol. Most of the time, the focus is on the feedstock, rather than the conversion technology, but the right technology could vastly improve society's potential gains.

Engineers can make ethanol in a variety of different ways, each of which has advantages and disadvantages, all of which have complicated names. The two most promising technologies for producing low impact biofuels are integrated gasification combined cycle with Fischer-Tropsch (IGCC-FT) and cellulosis. The goal of this post is to demystify the ethanol conversion technologies and to find if a longer name really does add up to a better technology.

Amazingly enough, I found an article in readily understandable English discussing IGCC-FT, so that will be my first subject. See Heidi Ledford, Making It Up As You Go Along, 444 Nature 677-78 (Dec. 2006). IGCC-FT is not a new technology. Countries facing embargos, such as World War II Nazi Germany and Apartheid South Africa used IGCC FT to liquefy coal to be used as gasoline and diesel. South Africa still relies on coal syfuels for 30% of its fuel supply (called "synfuels" because they are synthetic). While IGCC-FT may be popular with the wrong crowd, it shows promise as a conversion technique. Currently the U.S. is hot to convert coal into fuel via IGCC-FT, particularly states such as Montana and Pennsylvania. The President has joined the coal liquefecation bandwagon as well. He refers to the technology as "coal to liquid" or CTL. As far as I can tell IGCC-FT and CTL are the same thing. However, IGCC-FT can be used to convert biomass into synfuels, a more attractive option if one is worried about carbon dioxide emissions.

IGCC-FT has 2 basic steps. The first step is gasification. Engineers use heat and pressure to break the hydrocarbon chains in the coal or biomass. This yields carbon monoxide and hydrogen. Under Fischer Tropsch, the gas is liquefied using catalysts. This yields several different hydrocarbons, including diesel and petrol. Both steps release carbon dioxide int the atmosphere, which is more problematic if your feedstock is coal.

IGCC-FT provides an efficiency advantage over cellulitic methods. Tilman et al. report that converting grassland biomass via IGCC-FT would yield 28.4 GJ/ha-1. Cellulitic methods would yield less than 18 GJ/ha-1. See David Tilman et al., Carbon-Negative Biofuels from Low-Impact High-Diversity Grassland Biomass, 314 Science 1598 (Dec. 2006). Unfortunately, the technology is not up-to-speed. Currently, Germany is the only nation to have a commercial scale plant. Furthermore, IGCC-FT will not be economical unless oil reaches $70-80/barrel.

Making cellulosic ethanol is kind of like making beer, which might account for its greater popularity. Pretreatment exposes cellulose by freeing it from lignin (woody type material). Hydrolysis is then used to break the cellulose into sugars. This can be done with acid treatment or enzymatically. Acid creates more toxic byproducts, so companies such as Iogen are developing bigger and better enzymes for this step. Next the brew is fermented and distilled.

Cellulosic ethanol suffers from the same technology and cost problems that plague IGCC-FT. According to most sources, it will not be commercialy viable on a grand scale for about 10 years, although Iogen is on the verge of breaking ground on the first American plant and the Bush administration just gave 385 million in grants to 6 demonstration plants. Nonetheless, cellulosic plants are just blips on the horizon for now. Plus, cellulosic ethanol costs about 3 times as much as corn ethanol. Of course, this would go down with economies of scale.

It sounds to me like IGCC-FT has a slight edge over cellulitic methods based on the Tilman data. I'm thinking its main obstacle is its name. I would like to propose renaming IGCC-FT something like the "patriot method." Then we could call the synfuels "unity fuel" or "peace fuel." Note that the President refers to IGCC-FT with coal feedstock as "coal to liquid." Sadly, he has left it to me to come up with a new name for biomass conversion. Actually, I'm not sure who came up with CTL, but it does beat IGCC-FT.

Even if IGCC-FT doesn't take flight with a new name, there is hope for cellulosic ethanol. New research at North Carolina State University would improve efficiency of the hydrolosis step by 50%. This sounds very promising. Unfortunately, the researchers decided to name their process "atmospheric pressure plasma-enhanced soft hydrolysis." Uh oh.

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