Monday, May 19, 2008

Replacing Fossil Fuels

If you follow the public debate over global warming, you get the impression that generating electricity is the only problem. Actually, electricity is the easy part of the problem because we can generate all the electricity we need from non-fossil energy sources. Considering the externalized costs of fossil fuels, the non-fossil sources are even cost-effective.

The hard part of the problem is motor fuels. We don't have a good substitute in place. Biofuels won't ever supply a major part of our motor fuels, for reasons we've discussed before. But take heart. Two chemists at Los Alamos National Laboratory have devised a process using current technology that could replace petroleum as as source. F. Jeffrey Martin and William L. Kubic have published Green Freedom: A Concept for Producing Carbon-Neutral Synthetic Fuels and Chemicals (Patent Pending).

A Simple Description

As you can imagine, turning atmospheric CO2 into gasoline takes a huge amount of energy. In this process, the energy inputs are in the form of heat and electricity. Lots of both.

The electricity could come from a number of sources, but the process is most effective if the electricity supply is steady, which effectively limits it to nuclear. That's just as well, though, because the CO2 capture requires spraying a potassium-carbonate solution into an air stream. That requires something very much like a wet cooling tower, so the wet cooling tower for the nuclear plant can do double duty as a CO2 collector.

Once the CO2 is collected, it can be extracted from the solution by an electrolytic process, originated by Martin and Kubic. They claim that this is their chief innovation and that all the other features of the process are standard to the chemical industry. The electrolytic process is more energy-efficient than other means of separating the CO2, and generates hydrogen at the same time, reducing the amount of hydrogen that has to be generated elsewhere.

In their baseline design, Martin and Kubic propose to use water electrolysis for generating the additional hydrogen needed. They chose this because nuclear plants in the US are all capable of providing the electricity needed. As they point out, more-recent technology can improve efficiencies substantially. Steam electrolysis consumes less energy and advanced nuclear reactors can generate hydrogen thermochemically; this last technique can be essentially 100% efficient, since the leftover heat can generate electricity.

Once the hydrogen is generated, commercially-tested processes can be used for converting CO2 and hydrogen into methanol, and for converting methanol into gasoline. Alternatively, hydrogen, CO2, and steam can be combined over catalysts in the Fisher-Tropsch process to produce any kind of hydrocarbon compound, including diesel oil and aviation fuel.


As the authors take pains to make clear, the process depends only on equipment in commercial use today. There are no technological barriers to implementing it. There is a cost consideration, however. Their calculations show that the gasoline could be sold at the pump for $4.60 per gallon. Since we're dealing here with known technology they probably are not understating it by much, taking into account that projects of all kinds end up costing more than the planners expected.

But there are ample reasons for believing the actual costs would be lower. As they explain, newer technology will improve efficiencies considerably. Moreover, their analysis assumes their nuclear plant, which comprises the main capital cost, would be dedicated to producing hydrocarbon fuel. In practice, the nuclear plant will sell electricity during times of peak demand, especially when renewable energy is in short supply. This will become more apparent when fossil-fired power plants are phased out and all electricity depends on renewable and nuclear sources. We can look forward to an economy in which nuclear plants produce all our hydrocarbon fuels during off-peak hours. This sharing of costs will greatly reduce the cost of producing liquid fuels.

Looking Ahead

What we can say for sure is that it will take a massive energy investment to free the world from dependence on petrofuels. Straight hydrogen doesn't look promising because of the difficulty of onboard storage and because the inevitable leaks will threaten the ozone layer. Batteries for powering freight-hauling trucks don't seem like a reasonable hope, given the paltry improvements batteries have seen in the last few decades. Biofuels won't do the job, as discussed earlier. Since this process is already practical, it's not much of a stretch to predict that something very similar will be our fuel source in the future.