Aligned with our theme this month, Sam A. Rushing discusses the environmentally-friendly applications of CO2 and the need for mitigation of atmospheric CO2.

During my series of articles in gasworld, a wide variety of subjects surrounding carbon dioxide have been evaluated and reported on; some of which have brushed environmental consequences and issues.

This piece shall review some of the applications for carbon dioxide which have an environmentally friendly and positive result on the environment; while on the other hand, the subject of attempting and often achieving positive means of handling CO2 or even reducing emissions of carbon dioxide in today’s world with greenhouse gas concerns.

I will review a few major applications for CO2 of an environmentally friendly nature in this article; and the subject of CO2 mitigation is also an ever growing subject, which is more commonly mentioned in the press today, in part due to efforts behind a reduction in emissions, and the pros and cons associated with global warming.

Sourcing of CO2 has changed over the years, and in North America this change has been at a dramatic and rapid rate, due to grain availability, energy self-sufficiency; which are both highly associated with the ethanol market.

It will become ever-more important to both utilise CO2 in environmentally friendly environments and mitigate carbon dioxide emissions in the future; both of which are on track; however they require both political forces and industry cooperation, in order to best implement such actions.

Environmentally friendly uses for carbon dioxide – common and useful applications.
I have reviewed carbonic acid use in the past during the article covering applications for CO2; however, this is one of the most important and often common environmentally friendly uses for the product.

More specifically, carbonic acid renders harmless by-products as carbonates and by-carbonates when used in a wide variety of applications compared with the use of mineral acids such as sulfuric acid. Much of the obvious benefit in this application is the by-product from sulphuric being sulphate compounds rather than the harmless carbonate compounds.

Next, would be the safer application of CO2 versus a dangerous sulfuric acid, such as in the event of spillage and leakage, both in the application of and the storage of mineral acids compared to CO2. Carbon dioxide is self eliminating at a mild Ph, thus the application of CO2 as an acid can not be in excess.

CO2 is common in municipal water and waste water plants, some power plants, and some food plants; and this application should be evaluated in cases where mineral acids are used, particularly the more hazardous mineral acid, that being sulphuric acid.

CO2 as a solvent, such as the replacement of ‘perc’ in dry cleaning operations is an excellent application thus reducing organic residues and emissions when compared to a safe and viable method of dry cleaning. Use of CO2 in supercritical extraction applications is another use as a solvent.

There has been an ever-growing trend for use of CO2 in ‘blast cleaning’ as opposed to sand blasting, blasting with other materials, and the use of certain solvents, often petroleum based or mineral acids.

The advantage from an environmental perspective can be eliminating a run-off when using the solvents and acids rather than CO2 rice pellets, and the lack of residue in the form of sand piling up or other blasting agents accumulating at the job site.

Management and mitigation of atmospheric carbon dioxide; an ever-growing requirement, debate, and ultimately a point of implementation
The US never became an active part of the Kyoto Protocol, in part due to political forces claiming there was no substance or proof behind global warming; which was driven by big business favoring the incumbent party and reciprocity in turn has been supporting big oil and related industries in the US.

The tone of this support in favour of greenhouse gas abatement, particularly that of CO2 is changing in the US, in part on a state level rather than the Federal Government, since the EPA has not ruled on carbon dioxide.

Of course, the challenge is enormous in terms of reducing and ultimately attempting mitigation of great excess exports to the atmosphere of CO2 from industry, cars on the road, and all forms of combustion and manufacturing.

Given the incremental steps being taken by private and public industry toward CO2 emissions reduction efforts, it is interesting and rather extraordinary to note some of the state initiatives in terms of defining CO2 from an emission perspective, and making positive efforts to implement mitigation plans and positive action; this is particularly noticeable in California, one of the world’s single leading economies, and a leading economy in the US.

From a regional level, Northeastern, Southwestern, and Midwestern groups of states have taken positive steps in the area of plans for ‘cap and trade’ when concerning carbon dioxide, along with efforts surrounding electric utility companies, in their greater plans to handle a carbon dioxide emission subject, which must be handled in due time, like it or not.

Of course, when considering many of these initiatives, perhaps short of ‘cap and trade’ which does not really reduce emissions, but accounts for, defines limits, and trades credits; the consumer of an electric utility and a state resident is ultimately going to pay for elimination or handling of CO2 mitigation via charges on their electric power bill, or taxes by government agencies.

With regard to the former, American Electric Power, a holding company for a great number of US electric power companies and power plants has evaluated the options for CO2 mitigation, cap and trade, and sequestration; and in one case, they are evaluating the use of mechanical refrigeration of flue gas, and this process (which I am dubious of) is then being considered for subsequent application in sequestration.

I am dubious of their planned concentration and sequestration, since, via a planned demo project the CO2 contains a small fraction by volume of CO2, thus all prior successful methods of carbon dioxide recovery have required concentration of the CO2 extracted from flue gas, compared to trying to refrigerate the flue gas and thus have ample concentration for sufficient removal and sequestration.

In the end, historically many forms of CO2 recovery from flue gas, usually running from 3-12% by volume, with only amine (MEA) as the practical method of recovering via a solution method. In the past hot potassium carbonate was used for concentrating CO2 from flue gas, but in treating natural gas by-product, or a few turbine off-gas recovery processes from cogeneration for the merchant markets, MEA has been the agent of choice.

Globally, an estimated 75 million tpd of CO2 is emitted to the atmosphere, of which maybe 25 million tons is absorbed via natural oceanic processes, the greatest natural sink for CO2; however, this leaves up to 50 million tons daily which are in excess, and which are raising the already burdened atmosphere and greenhouse like atmosphere with more CO2.

This process must be dealt with in a successful and probably incremental manner over time, otherwise catastrophic results are likely, and such great rises in oceanic levels anywhere from 20-40 feet in added height are possible. As per many forecasts, this would be attributable to enormous levels of water released from the poles and Polar Regions.

Furthermore, as the global temperatures rise, and warmth creeps up the globe to once cold climates, the potential for insect-borne diseases such as Malaria are ever more threatening.

In terms of the methods for stalling the CO2 greenhouse gas crisis, places such as North American states, corporations, and utilities are adopting so-called ‘cap and trade’ systems, allowing for an eventual cap in the amount of CO2 emitted, and the opportunity to trade carbon credits with other nations.

Some industrial projects such as The AES Corporation have in the past implemented carbon offsets such as planting forests in Latin America, which are an uptake for CO2. Offsets such as this are a practical means to an end, which are a little more than simply staving off the need to actually reduce emissions, such as pure sequestration methods - of which many are unproven, expensive, and in a stage of infancy.

Simply put, we have a long way to go in terms of practically and efficiently managing CO2 emissions, and truly reducing CO2 threats from a greenhouse gas perspective.

From a sequestration perspective, I mentioned The AES Corporation planting forests in Latin America, during the boom days of cogeneration, as a carbon offset; this type of carbon uptake is at large considered to be one of today’s practical major alternatives for reducing the carbon footprint. Toward this end, algae farms are a practical method of sequestration, whereby certain strains of blue-green algae are an excellent sink for CO2, such as from ethanol plants, and even power facilities; one such power facility is trying this technique in Israel.

The algae method is a sink being evaluated, as would be seaweed, and other oceanic or marine environment based options for sequestration.

CO2 pumped deep into the oceans is not a practical or even an ethical method for disposal of this product, since, the end result is ‘oceanic acidification’, thus lowering the Ph further, and further damaging marine life, like the coral reefs.

Instead, a wide variety of geological formats for CO2 injection and placement have been evaluated, including the concept of pumping CO2 into abandoned mines and aquifers, the latter has been successfully handled by Norwegian oil producers.

As to the evaluation of using enhanced oil recovery (EOR) as a means of sequestering the product, when considering the process of enhanced oil recovery, and perhaps CBM or coal bed methane (enhanced), some of the oil or methane could be brought up in the recovery process.

Therefore, in part these methods may serve as a partial form of sequestration, since some of the CO2 would be left underground, but not in full. In the end, both EOR and CBM are means of using CO2 for practical and energy self sufficiency purposes; but not true forms of sequestration.

The road to truly reducing carbon emissions, making an impact on greenhouse CO2 content in the atmosphere and saving our planet will depend highly on cooperation among nations, politicians, and industry. All of us as individuals must also play a daily role in thinking about how we cam impact this ever-growing problem; hence save the planet from catastrophic consequences.

The answers will include some of what I have mentioned, refinements in these processes; and new developments for energy efficient CO2 concentration from flue gas, and implementation of new and improved technologies.

About the Author
Sam A. Rushing, a chemist, is president of Advanced Cryogenics, Ltd., a CO2 consulting organization in business for almost 2 decades; which supplies all forms of CO2 consulting expertise to all sources of CO2 and projects surrounding the commodity, on a global basis.
Tel: 001 305 852 2597