New news on renewables
POSTED AUG 30, 2002

 

1. A sweet idea

2. Smokin' grass

 

When this little tube is heated, glucose in the reactor at the center releases hydrogen, which leaves through the top. Those black tubes bring water to cool the hydrogen.

 

A 6-inch steel cylinder with pipes at top and bottom. The simplest element
Take an atom. Trash all the non-essential parts. Eventually you'll wind up with one lousy proton and one measly electron.

Chemists call this bare-bones set-up a hydrogen atom.

And while it may be more stripped than a chopped and channeled Harley-Davidson, hydrogen atoms could represent the future of clean energy.

Consider the advantages: All fossil fuels contain carbon, which when burned makes carbon dioxide and global warming. Hydrogen, on the other hand, oxidizes (burns) to make hydrogen oxide, AKA water.

(Now, we recognize that global warming is not on the table at the Johannesburg summit on sustainable development, apparently at the request of the United States and similarly oil-obsessed nations. But we agree with those who argue that sustainable development would be a meaningless benefit to a southern-fried planet...)

As a fuel, hydrogen could power modified internal combustion engines. More important, it's the fuel of choice for fuel cells, the up-and-coming method for powering green vehicles. Fuel cells make electricity without combustion, and without making nitrogen and sulfur oxides, both sources of acid rain.

But there are stumbling blocks. The simple gas is hard to store, and no infrastructure exists to distribute or sell it.

More fundamentally, hydrogen is almost always bonded to other atoms. In methane, the main component of natural gas, four hydrogen atoms are bonded to one carbon atom. Burn methane, and you get water -- and carbon dioxide, which returns us to that all-the-globe's-a-skillet snafu.

Sure, hydrogen is the most abundant element in the universe, but to get hydrogen's environmental advantage, you gotta separate it from carbon. That's expensive.

John points at the lugged metal piece, with some apparatus in background.
Grad student John Shabaker points to the assembly that captures hydrogen generated by the low-temperature reactor.

Sweet!
So any time there's a better way to strip away hydrogen molecules, we Why Filers are listening. This week's Nature carries a report of a rather simple, and potentially cheap, process that could help turn agricultural waste into hydrogen energy. Since the research was happening just down the hill from the high-tech Why Files newsroom, we hopped on our low-tech bicycle to take a gander.

When we walked into the lab, we couldn't immediately identify where hydrogen was being generated. The reactor, it turned out, was purring quietly along, courtesy of the little pump that moves a solution of water and hydrocarbon through the reactor chamber. The chamber was hidden inside a metal cylinder, connected to a couple of hoses and the odd wire or two.

Inside that chamber, a solution of water and hydrocarbon was exposed to a platinum catalyst (a compound that facilitates a chemical reaction without itself being consumed). When glucose (or other compounds with approximately equal ratios of carbon to oxygen) molecules touch the catalyst, they break down, releasing atomic hydrogen and a different type of hydrocarbon, the alkanes.

a row of numerous, small bottles on a shelf
These bottles hold candidate catalyst materials. Reducing the cost of the catalyst would go a long way toward making the hydrogen generator economically feasible.

Now, what's special here is the large amount of hydrogen released, and the low pressure and temperature (about 200 degrees Celsius) required, says James Dumesic, a professor of chemical engineering. Dumesic collaborated with UW-Madison scientist Randy Cortright and graduate student Rupali Davda on the project. "This is the first time," he says, "that a solid catalyst has made high concentrations of hydrogen at rather modest conditions."

Existing techniques for separating hydrogen require more energy, higher temperatures, or both. The usual method, heating petroleum products with steam, is energy-intensive. Other methods are just inefficient (although some researchers have used biological processes to get hydrogen from algae).

However, even though the apparatus is simple, Dumesic doesn't envision it being used to generate hydrogen aboard a car. Instead, it's more likely to generate hydrogen for storage and sale at what would literally be "gas stations."

What's the big deal?
A key advantage of the new process concerns the feedstock, the chemical from which hydrogen is separated. The glucose or other hydrocarbon could be extracted from agricultural trash -- straw, sugar-beet waste, potato peels -- left over from food harvesting or processing.

Since the hydrocarbons contains – you guessed it – carbon, the extraction would yield carbon dioxide, but since the same amount of carbon would be removed from the atmosphere by the next crop, there would be no net increase in greenhouse gas. The present method of getting hydrogen from petroleum, remember, transfers large quantities of carbon from Earth to the atmosphere.

Energy flows from left to right: Sun ------ Green plant ---- Waste product ------ Chemical feedstock ------ Hydrogen generator ----- fuel cell
Energy flows clockwise from top left: Sun ------ Green plant ------ Waste product ------ Chemical feedstock ------ Hydrogen generator ----- fuel cell

The identity of the raw material remains uncertain. "It's an open question what's the most appropriate feedstock," says Dumesic. When fermentation (microbial decomposition) is used to make methane fuel from biomass, "you need a fairly specific carbohydrate. We feel our process is fairly insensitive to the type of carbohydrate." Glucose, sorbitol, glycerol, ethylene glycol and methanol all worked with the same process and apparatus, although the smaller molecules produced higher yields, Dumesic says.

It's even possible -- but unproven -- that blended feedstocks would work. That would minimize the cost of raw material.

Still, hurdles remain. For one thing, the catalyst is a precious metal, platinum. For another, too much hydrocarbon decomposes in the hot water before contacting the catalyst.

Both problems are being attacked in the lab, says Dumesic, using standard chemical engineering techniques.

Hydrogen ahead?
Advances like this would help usher in a "hydrogen economy" when concerns about global warming and fossil-fuel shortages cause hydrogen to replace coal, oil and gas. The changeover depends, however, on improvements in generating and storing the gas. It also depends on cheaper fuel cells, something many major car manufacturers are attempting.

In the meantime, the little reactor purrs along, making gas week after week, anticipating a day when cars burn hydrogen and spew clouds of pure water vapor.

Needed. A big bunch of biomass.

 

 

 

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Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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