The Promiscuous, the Selective, and Biofuels

by Jim Lane (Biofuels Digest) ...Promiscuous, because a zillion organisms know how to use photosynthesis, under a zillion set of circumstances, to turn simple and abundant molecular compounds — like carbon dioxide and water — into longer-chain and useful molecules for structure, protection or energy.

With fossil fuels — just like biomass, Nature will do the work for free. Just not at the speed we need, nor with a particularly high yield (consider, for example, the amount of biomass created by Nature over the history of the plant, and how little of that actually became a fossil fuel – the yield is something like 1 ton of hydrocarbons for every 100 million tons of biomass, and Nature is on average producing something on the order of 150,000 tonnes of fossil fuels per year, enough to run one city the size of West Covina, California on a renewable basis).

The problem with fossil fuels is that we’ve had no Neolithic Revolution — we’re still hunting and gathering hydrocarbons, and we’ve figured out no particularly effective way to speed up, industralize, or densify the way in which Nature produces them. Something that was worked out with, say, wheat and barley several thousands of years ago. That’s why we’re running low — the problems of selectivity and rate.

Newt Gingrich once famously pointed out, you can’t fill up a car and run it on algae; less usefully, he neglected to mention that you can’t fill up a car and run it on kludgy Venezuela crude, either.

We take those biomass or fuel precursors and turn them into useful products — one way is through fermentation, but the more traditional path is through chemistry and catalysis — the science of making useful reactions happen better, faster and cheaper.

Here are the challenges with biomass. First, you have to get the oxygen out in order to get a hydrocarbon. Second, you want the molecular chains to be longer so that they have the boiling points that work in combustion engines and they have sufficient energy density.

Here’s another set of problems. Catalysts are designed, traditionally, to be selective, and you lose a lot of yield that way. Worse, the reactions that result in hydrocarbons work better under high temp, high pressure conditions (one reason why you find hydrocarbons forming underground where those conditions are abundant, and why oil refineries need special permits for the intense conditions).

Well, making furan aldehydes from C6 and C5 sugars (e.g. glucose and xylose) is a known art.

Better? It’s been known for some time that under certain intense conditions (e.g. 300 degrees celsius, and about 50 times the standard atmospheric pressures), you can use catalysis to make hydrocarbons, non-selectively, from tetrahydrofuran intermediates.

But how how do you achieve this without blowing out the energy input budget with a whole bunch of high temperatures and high pressures? Until now, impossible.

A group of collaborators from Los Alamos and The University of Guelph in Canada (Andrew Sutton, Fraser Waldie, Rulian Wu, Marcel Schlaf, Pete Silks and John Gordon) published an article in Nature Chemistry last month — titled “The hydrodeoxygenation of bioderived furans into alkanes“.

But it describes how to take building blocks that are derived from glucose or cellulose and couple them with other bio-derived building blocks to give new molecules that have between eight and fifteen carbons in a row. This work describes a completely new approach, an alternative route to convert this class of molecules to hydrocarbons that uses much less energy and has a very high degree of conversion to provide pure products.

Well, imagine accomplishing the same result without the 60 million years, the high temps and pressures, or having to frack your way to recovering hydrocarbons from the shales Nature is known to hide them in. You make the biomass in a season (or less, if you are using photobioreactors) and make hydrocarbons on the spot. READ MORE and MORE