New Frontiers

Bio-Prospecting for a Hydrogen Economy

When the "hydrogen economy" was first presented to the public as a "green" alternative to hydrocarbons, most scientists and engineers scoffed - knowing that the vast majority of hydrogen was manufactured from natural gas made it a sham. On the other hand, the same group would sit up and take note if a way were found to manufacture hydrogen on an industrial scale by harnessing nature's ability to split water molecules using only the sun's energy. The industrial application of such an approach remains only a theoretical possibility, but rapid progress in bioengineering is advancing the science, and Colorado School of Mines is making some important contributions.

Photosynthesis typically involves two discrete steps. First, light powers the oxidation of water in the presence of chlorophyll, stripping electrons and hydrogen ions from oxygen. In the second step, the liberated electrons are combined with carbon dioxide to create a simple carbohydrate. The challenge for molecular biologists is to intercept the energy generated after the water-splitting step of this process, before it is chemically bound up with carbon, channeling that energy toward the manufacture of hydrogen gas instead.

And there are organisms that have naturally evolved the ability to do this. Mathew Posewitz, a research professor at Mines who works in collaboration with the National Renewable Energy Laboratory, describes how certain algae, when deprived of oxygen or exposed to other unusual conditions, will switch from fixing carbon dioxide to manufacturing hydrogen gas. The problem is that for industrial-scale production of hydrogen, they need an organism that will do this under normal conditions, and none has yet been found. "We would prefer to use a naturally occurring organism. We've been looking for a while, and the search will go on," says Posewitz. "But it may not be out there. We may be looking at bioengineering."

To this end, the Mines-NREL collaboration made an important contribution in 2004, when they published a paper on how the enzyme hydrogenase can be transferred from one species to another. Hydrogenase is the catalyst that enables the creation of hydrogen gas from the electrons and protons freed by water oxidation. In labs around the world, numerous previous attempts to transfer active hydrogenase into other organisms had been unsuccessful, so the group's findings represented a major breakthrough.

With this bioengineering roadblock removed, the Mines-NREL research group is now focusing on what they call "bio-prospecting." They are continuing to search for an organism that will generate hydrogen naturally, but they are also looking for robust biological traits that they can genetically engineer. "We want to find the right photosynthetic organism that can efficiently harvest photons of light and oxidize water, and then find the right hydrogenase that can reduce the protons to hydrogen gas, and get those traits into the same critter," says Posewitz. "We want the best photo system and the best hydrogenase combined into a single organism."

Their hunt for appropriate biological traits is focused on some quite extreme environments, including the Great Salt Lake and the hot pools in and around Yellowstone National Park. Posewitz explains, "If bio-energy production is ever going to be a reality, we are talking about a very large-scale production, and we aren't going to have adequate freshwater resources or arable land to devote to it. Algae in the Great Salt Lake have evolved to tolerate extremely saline water, and we have plenty of that."

The reason for sampling high-temperature environments is to find the most stable hydrogenase. "When we transfer traits to our organism of choice, we want to impart robust qualities that aren't going to break down," says Posewitz, who points out that organisms adapted to high-temperature environments tend to have more stable enzymes and proteins.

Although great strides have been made in recent years, there is much left to be done. Posewitz estimates that if they are lucky, in 10 or 15 years they may have an organism that can do everything they are aiming for. After that, rolling out production in a way that makes economic sense will be incremental and could take many forms.

Jon Meuser, a graduate student at Mines who works with Posewitz, believes that biological hydrogen production ay be just one component of a larger industrial operation. "The same infrastructure created to farm algae for hydrogen could also support algae that produce other useful products, such as lipids for biodiesel, or lactate for bioplastics," he says. "The 'biorefinery' of the future could one day produce many products we currently get from oil."

For now, Posewitz and his colleagues continue to work on the biochemistry of hydrogen production: "There are many obstacles to overcome. We are working upstream against billions of years of evolution - photosynthetic organisms want to use the energy they capture for themselves. We have to tinker with those systems and make them do what we want them to do. It's sort of like trying to get your children in line - it's not always easy to get biology to do what you want."

 

High-Tech Rock Abuse

Geophysicists are masters of uncertainty. Armed only with theories, algorithms, and a few snippets of information about the rock they are studying, they interpret sound-wave data and formulate highly detailed predictions about the subsurface. By and large, these predications are remarkably accurate, but geophysicists are rarely 100 percent certain until a hole is bored into the ground and samples are brought up for analysis. More often than not, there is a degree of guesswork that goes into interpreting seismic data.

Mike Batzle, who heads up Mines' Center for Rock Abuse (CRA) explains: "Predictions from seismic data are based on theories," he says. "But theories have adjustable knobs. If you don't know where the right settings are, then you have to make a guess."

The CRA is helping provide the right "settings" for geophysicists by analyzing rock samples in the lab. Taking a fist-sized column of rock, they can calibrate changes in seismic signature under a variety of different conditions - this is where the "abuse" comes in. "We will often squeeze the rock, exerting pressures that mimic the sample's native environment. Then we might inject either a liquid or a gas and calibrate the speed that sound moves through the sample under those conditions," says Batzle. "Then we'll inject a different gas or liquid and test again. We might do this with methane, carbon dioxide, water, oil or a mixture of two or more of these, each time registering the change in seismic signature. "

With the CRA's results in hand, geophysicists can be much more certain of their interpretations. "They can point to a given signature and be pretty sure of what that signal means - whether the rock transitions from natural gas to water, or natural gas to oil, or oil to water, or even water to a mixture of carbon dioxide and petroleum."

The lab's results are not only useful for interpreting seismic surveys from the region where the sample originated. They can also be used to interpret seismic data from any area where a similar rock is found. Manika Prasad, the lab's co-director, points out that with each new kind of rock they test, they add to their database. "With some rocks we get in, we can simply go to data from previous tests of similar rock. As our database of seismic signatures grows, we can extrapolate more and more," she says.

In addition to seismic analysis, the lab also tests porosity, permeability and strength of samples. This can provide valuable baseline information for predicting how fast fluids and gas will flow under certain conditions, how much gas or oil is contained in a given formation and how best to fracture rock to increase flow rates.

In addition to calibrating rocks, the lab also analyzes liquid and gaseous hydrocarbons in isolation. "There is a lot of interest in heavy oils right now because they are so plentiful," says Batzle. "But they are thick and hard to extract. Heating the oil-bearing strata can lower its viscosity, allowing oil to flow more easily. When this is done, seismic imaging can be used to monitor the production process remotely, but to do this accurately - to translate seismic wiggles into materials and conditions - the seismic signatures of the various materials must be known. That's what we can provide."

The laboratory is home to eight graduate students, one full-time technician and several visiting scholars. Much of the work is done in collaboration with other departments and universities, particularly the Rock Physics Lab at the University of Houston.

Indicative of their high profile, the CRA client list includes a raft of blue chip oil and gas corporations and service companies from around the world, including Anadarko, BP, British Gas, Chevron, EnCana, Shell, Petrobras, StatoilHydro, ExxonMobil, Devon, Japan Oil and Minerals, Chinese National Oil, Schlumberger, CggVeritas, Paradigm and others. Batzle says, "There aren't many other labs doing what we do. We've got a lot of toys and can recreate just about any kind of underground condition. It's fun. We get paid to play, and we're building up a very valuable database of information.