The Willauer technology for producing jet fuel from seawater is economical at $6/gallon

[NNadir]

It's described here: Feasibility of CO2 Extraction from Seawater and Simultaneous Hydrogen Gas Generation Using a Novel and Robust Electrolytic Cation Exchange Module Based on Continuous Electrodeionization Technology Heather D. Willauer, Felice DiMascio, Dennis R. Hardy, and Frederick W. Williams Industrial & Engineering Chemistry Research 2014 53 (31), 12192-12200

The products here are precursors to FT (Fischer Tropsch) chemistry from which any component of petroleum can be manufactured. Dr. Willauer works at the US Naval Research Institute and her goal was for US aircraft carriers to be able to make jet fuel at sea using their nuclear plants.

From the introduction to the paper:

Finding solutions to minimize the anthropogenic levels of carbon dioxide (CO2) in the atmosphere has led to extensive research efforts in the development of technologies specifically designed to capture CO2 from concentrated sources such as fossil fuel burning power plants, cement plants, and refineries. (1, 2) However, these sources are responsible for only roughly half of all anthropogenic carbon dioxide emissions. (1) The other half may be attributed to the transportation industry. These latter sources are mobile in nature, produce relatively low concentrations of CO2 on an individual basis, and are thus difficult to capture on an individual basis. (1) Therefore, a more general approach to CO2 removal from the environment may be needed to minimize anthropogenic CO2 effects.

In the environment, the CO2 in the atmosphere is in constant equilibrium with the ocean, so as anthropogenic CO2 increases in the atmosphere, the world’s oceans absorb more and more CO2 as carbonic acid. Carbonic acid is in equilibrium with carbonate and bicarbonate species which are primarily responsible for buffering and maintaining the oceans’ pH. (3, 4) At seawater pH of less than or equal to 6, the dissolved bicarbonate and carbonate reequilibrate to CO2 gas. This process has been the basis for standard ocean CO2 measurements for over 25 years. (5) Currently the total carbon dioxide concentration of the world’s oceans is about 100 mg/L minimum at all depths, latitudes, and longitudes. Approximately 2–3% of this CO2 is in the form of a dissolved gas, and the remaining 97–98% is in a chemically bound state as bicarbonate and carbonate. (3, 4) Given the total ocean volume of about 1.3 × 1021 L, this means that the CO2 content of the oceans is 1.3 × 105 gigatons (GT) compared to 8.0 × 102 GT in the entire atmosphere. Thus, the oceans are about 175 times greater than the atmosphere as a total carbon reservoir. When the CO2 concentration of the ocean is compared to its concentration in the atmosphere on a weight per volume basis (w/v) (100 mg/L), CO2 in seawater is about 140 times more concentrated than in air (0.77 mg/L). (6) The CO2 in stack gases is about 385 times more concentrated than that found in the atmosphere on a v/v or w/v basis (about 296 mg/L (w/v) for typical stack gas vs about 0.77 mg/L in air (w/v)). (1) In addition, comparing the high seawater concentration on a w/v basis (about 100 mg/L) to that of stack gases (about 300 mg/L) indicates that this is another powerful reason to consider ocean extraction of CO2 rather than air extraction of this important anthropogenic gas. (7-9)

Energy efficient processes to take advantage of the higher w/v concentration of CO2 in seawater would be advantageous from several environmental perspectives. First, CO2 would be indirectly removed from the atmosphere...

The paper contains a photograph and a schematic of the small pilot plant; if I recall correctly, larger scale pilot plants have been built:



The caption:

Figure 2. (a) Labeled photograph of experimental setup. (b) Block diagram of the experimental setup.

Of course, I would rather that we not make petroleum type fuels and prefer the wonder fuel DME; this said, this works.

[hunter]

1. A nuclear power plant might produce fuel, fresh water, and electricity.

It might also extract and sequester atmospheric carbon dioxide.

The sodium hydroxide output of the Willauer technology is interesting.

This kind of science and engineering gives me some hope for the future.

[NNadir]

2. For me - I read this paper when it first came out - the most important point was the recognition...

...was that the path to the removal of carbon dioxide from the atmosphere will most likely succeed via ocean water.

Dr. Willauer's scheme is an electrochemical process, essentially an electrodialysis unit which she calls an "E-CEM" - an electrolytic cation exchange module - apparently not all that far from commercially available systems, but modified in a creative way. It relies on fairly well known organosulfonic acid ion exchange. The neat trick is that it doesn't produce chlorine.

In this paper she describes how she ran the thing using seawater off of Key West.

All this said, electricity is a thermodynamically degraded form of energy in most cases, with the important caveat that if it can be recovered from what is now considered waste heat, then it is acceptable from an efficiency perspective.

I always favor direct thermal processes where possible. I have never found the time and inclination to really sit down for a day or two to study the TEOS-10 equation of state of seawater in any detail, but if I recall from when I peeked into it, it really didn't reach very far into the supercritical state or very high temperatures; most of what has been written in the literature, such as I've been able to uncover in a desultory fashion, actually relates to geological formations, mantle rocks etc. This tends to be qualitative rather than quantitative.

This may be a function of materials science issues. Perhaps very high temperature seawater has not been characterized because viable materials are not readily available or perhaps because no one sees a good reason to go there or because the research has not been funded. This said, I've convinced myself, if somewhat glibly, that there are paths to addressing these issues in materials science. I would be very interested to find the phase diagram for the CO2/H2/molten salt/supercritical water system. It may be out there, but I haven't found it.

Supercritical seawater desalination might prove from an exergy standpoint far superior to electrodialysis; but Dr. Willauer's technology is ready to be scaled.

I am working to put the supercritical CO2/supercritical water/molten brine/H2 system in my son's mind for his career. It's not entirely clear that it would work, but if it does, it would be a remarkable tool. He is already a materials scientist and now is entering into a Ph.D. program in nuclear engineering. I will suggest this as an avenue of research at some point in his career.

To the extent that it would produce electricity as a side product, waste electricity might well be diverted to a system based on Dr. Willauer's elegant approach, for use in off peak hours, if economically justifiable.

She gave the $6 figure for jet fuel in some other paper of hers; I can't off the top of my head remember which one.