American chemists investigate sequestering CO2 in natural gas brines.

[NNadir]

As we all know by now, nobody knows what to do with fossil fuel waste, the result being that it is simply dumped into the air and water with fatal consequences through the agency of global climate change and toxicity. One of the most important constituents of this waste is represented by carbon dioxide, followed by in importance by acidic species such as nitrogen oxides, and sulfur oxides. Heavy metals from ash, notably mercury, uranium, thorium and the elements of the radiaoctive decay series including radon, and radium are also of some importance.

Rather than stop the production of these dangerous wastes, many schemes have been proposed for dumping them, including the injection of the gaseous forms into rock formations.

In the ASAP section of the journal Energy and Fuels a study has been published examining the carbon dioxide properties of natural gas brines.

In 2001, United States CO2 emissions accounted for 1.57 GtC, which was 24% of the total global carbon releases from CO2.1 Of that 1.57 GtC, 36% was from energy- and industry-related coal combustion. It is also projected that by the year 2025 coal consumption by U.S. electricity generators will increase by 48% from the 2001 level.1 Carbon sequestration, along with increases in efficiency and the advancement of clean-coal technologies, may serve to minimize the environmental impact of coal. With the proximity of U.S. electricity generators to deep saline aquifers of large estimated capacity, geologic sequestration is proposed as a suitable method to reduce CO2 emissions. Capability exists in the technologies currently being explored by energy industries regarding concentrating and transporting CO2 from flue gas, fluid injection into subsurface media, and the characterization of geologic formations. U.S. deep saline aquifers are estimated to provide storage for approximately 130 GtC equivalent, which is approximately 80 times the United States’ total carbon emissions in 2001.1,2 Geologic sequestration in saline aquifers is a complex process with multiple mechanisms for carbon storage. Saline aquifers are deep porous rock formations that are saturated with brine, which is typically rich in various metals. Following the injection of CO2 into the subsurface below a typical depth of 800 m, the mechanism for CO2 storage is initially hydrodynamic as the CO2 is stored as a dense supercritical fluid...

...Conclusions
Calcite formation was induced at temperatures of 150 °C and pressures ranging from 600 to 1500 psi by reacting CO2 with a natural gas well brine of low iron content. The most favorable initial brine pH for calcite formation was approximately 9.0, as opposed to the lower values investigated. During the reactions, the system pH immediately dropped following the introduction of high-pressure CO2 due to the formation of carbonic acid. An experimental reaction time of 18 h revealed little change in system pH following the initial decrease. At the start of the reactions, the liquid-phase composition of various metals, such as Na, Ca, Mg, and Sr, was inversely related to the adjusted pH as minerals have a lower solubility at a high pH. Throughout the course of the reactions, compositional trends in the metals most important for mineral carbonate formation were not identified. Large fluctuations indicate that the system did not reach steady state. ICP-AES data cannot be used to correlate changes in brine composition with pH changes and the precipitation of carbonates using a reaction time of 18 h. XRD has verified that calcite was most abundantly present in the solid products for the reactions with an initial pH of approximately 9.0. No other carbonate minerals, such as magnesite or dolomite, were detected despite the significant brine concentrations of magnesium...

Not surprisingly, the ability of these brines to absorb CO2 and precipitate is carbonates is pH dependent. None of this will of course have any insight into the long term stability of these systems and their possible consequences for future generations.

The most important conclusion is this sentence from the "too little too late heading:"

...Feasibility for an industrial-scale operation to sequester carbon in natural gas well brine is currently limited by the extent that pH needs to be raised and maintained to promote the rapid formation of carbonates...

People may or may not be aware that the raising of pH under these circumstances will involve the input of energy.


The abstract is found here: http://pubs.acs.org/cgi-bin/abstract.cgi/enfuem/asap/abs/ef050115u.html

The full article requires a fee or subscription.

[acmejack]

1. Do you think sequestration is a viable strategy?

on a Giga ton scale?

[NNadir]

2. No.

There may be some solutions that palliate the problem, and others that dump it on future generations. But I do not believe that it is possible to permanently sequester CO2.

It is a gas. It is very difficult to contain gases because they are extremely low viscosity fluids.

One would like to imagine that we could sequester CO2 via biological means, however with global climate instability is is not a good bet to imagine that the biosphere will be very reliable in the future.

[NV Whino]

3. Plant more trees

and stop cutting the rain forests. Have these idiots forgotten about photosynthesis?

[NNadir]

5. Actually no.

Everybody knows photosynthesis works. This has done little to change the concentration of CO2 in the atmosphere however.

In fact global climate change is likely to change the ability of plants to sequester carbon dioxide, since many existing forests will suddenly find themselves in places where the climate is no longer suitable. This is especially the case with water flows, but diseases, insects, and invasive species will also effect the CO sequestering ability of these plants.

I note in passing that agriculture and the destruction of forests for biofuels (cf Brazil and Maylasia) is actually making things worse.

[Odin2005]

6. Photosynthesis has nothing to do with GLOBAL CO2 levels.

Almost all our planet's carbon is trapped in limestone rock and regulated by volcanism and erosion. Rainwater disolves calcium ions weathered from rock, the calcium ions react with dissolved CO2 to form calcium carbonate, which is deposited in the ocean as limestone. the limestone si eventually subducted and is released by volcanoes. and the cycle repeats. Warming will increase rainfall, which increases erosion, absorbing more CO2 than is released in volcanoes, and the climate cools down again. Land plants make this cycle more efficent, bit not because of photosynthesis. it is because of plants pumping CO2 into the groundwater as a result of the aerobic metabolism in thier roots. A better way to reduce CO2 levels is to enourage the growth of marine algae with calcium carbonate "armor" by dumping iron in the ocean, which acts as a fertilizer. the armor eventually falles to the seabed when the algae die and become limestone, removing CO2 from the air.

[formercia]

4. for every atom of carbon, a molecule of oxygen is sequestered

Plants do a better job of sequestering carbon and return Oxygen back to the atmosphere.