Carbon dioxide has received a bad rap over recent years, in particular due to greenhouse gas factors associated with global warming, rising oceanic tides, and potentially growing cases of insect-borne diseases such as Malaria - all of which are associated with the increase in greenhouse gas and ambient temperature growing globally.

The end results, are in fact catastrophic, if atmospheric levels of CO2 rise according to some estimates; where over the last 50 years for example, this level has grown over 20% in concentration, and is possibly going to rise geometrically if unabated.

Sequestration of CO2 from all large scale emitting sources including large chemical manufacturing and power (primarily coal fired) plants are the largest targets for sequestration.

However, achieving this end is rather daunting; in part due to retrofit or techniques required for power plant flue gas recovery, as well as capital cost requirements for all sequestration options, and of course proven technologies which best achieve this end.

The other subject reviewed in this article considers a few green applications for carbon dioxide, such as ‘blast cleaning’ with dry ice ‘rice’. A number of friendly applications continue to expand their presence as the drive for green technologies continues; hence this subject is of particular value in our ever-growing drive for cleaner technologies.

Carbon control and reduction methods have been implemented in a number of world markets, with a greater amount of emphasis in the European Zone & Japan than in many regions of the globe; whereas the US, the global economic engine has lagged behind such developed world markets as Europe and Japan.

Much of this is of course political. The US may have been lagging behind but on the other hand, it has active plans (particularly with Obama’s incoming administration) to implement many environmental initiatives, unlike the current administration which has been in place for eight years and largely lagged behind most industrialised nations.

Since the Environmental Protection Administration (EPA) has been unable to regulate CO2, due to political roadblocks in the US, many states, regional state cooperatives, and industries have taken such initiatives, generally in the form of ‘cap and trade’ agreements, whereby a maximum level of emission is placed on certain industries or plants, and emission credits are traded; all of which represents action toward reducing CO2 emissions, but some could argue this as less than actual sequestration of carbon dioxide.

Of course there is terrestrial sequestration via photosynthesis, and the additional planting and growth of trees and algae, for example, are cases of the terrestrial form of sequestration. Sequestration as a man-made mechanism alone can be presented as capturing CO2 from a combustion, chemical manufacturing process or flue gas for example; and in simple terms, tucking it away, and reducing this added carbon burden to the atmosphere.

The task is daunting, expensive, and will require all of us to pay the cost of achieving such an end, in the form of more costly utility bills, or some form of surtax payment; thus the essential task of protecting the globe and the survival of our species and many other life forms from extinction.

Most of the evaluations and practical means of sequestering carbon have been of a geological nature. Geological forms include a number of mechanisms underground, whereby (under high pressure) CO2 is pumped into specific sites or formations. Many offshore initiatives for sequestering carbon have been into the substructure below the ocean, into specific sites compared with pumping CO2 into the ocean alone.

Simply put, pumping CO2 into the ocean is not an alternative, due to an ever-growing acidification of the world’s oceans, and destruction of marine life, some simple life to coral reefs; which leads to loss of larger organisms such as fish, and marine mammals.

Therefore, much of the most viable and successful form of carbon sequestration has been one form or another of geological method.
In the past, many authors including myself have alluded to enhanced oil and enhanced coal bed methane projects as perhaps not a true form of sequestration; due to leakage of the CO2 back into the atmosphere.

This also includes some of the CO2 used in the enhanced oil and coal bed methane projects being returned to the surface, or the oil or gas product being returned to the atmosphere. Perhaps these enhanced energy production methods can be considered a partial form of sequestration, but in certain geologically specific cases this can be true sequestration, in my opinion.

Exceptions to this leakage, and return to the atmosphere in EOR or CBM cases, include the application of CO2 in enhanced energy production projects which incorporate trapping the CO2 in defined rock formations, for example. These can then be a truly green, enhanced energy production project, in conjunction with viable carbon sequestration.

Terrestrial, geological, chemical manufacturing, depleted oil/gas reservoirs, certain enhanced oil and coal recovery, and saline reservoirs are possible sinks for carbon; all of which represent sequestration.

Such goals are conceivable, but much of this is highly sensitive to location and cost; much of this will be shouldered by the consumer in turn, since pipelines for liquid CO2 can often run over $1m per mile.

If CO2 happens to be used in chemical manufacturing, as a feedstock agent, this can be considered a (usually relatively) small form of sequestration by volume. Therefore, the most likely form of carbon sequestration again seems to be geological, from the most practical and feasible apparent options; some of which are attempting a proprietary approach.

However, many of the geological attempts will actually become reality, since due to forthcoming tougher environmental regulations of carbon in the US, and the implementation of the Kyoto Protocol or something which will replace this Protocol, more true action will take place sooner than later.

Many DOE sponsored efforts for geological sequestration projects have been evaluated and implemented on a demo basis in the US; and many such true projects are taking place globally, at least on a planning level.

Green applications for carbon dioxide
We have reviewed numerous green applications for merchant CO2, to include (dry ice) blast cleaning, carbonic acid usage; closed loop applications for supercritical extraction of products such as essential oils; plus possible new thinking about closed loop cryogenic freezing applications, for example.

As for dry ice (rice ice) or small 1/8” dry ice pellets, extruded from a compressed liquid into dry ice; these are delivered via high pressure wands for cleaning or preparing surfaces for a wide range of applications. Such applications can include blast cleaning of paint from surfaces, or preparing surfaces for paint jobs.

Cleaning grease, oils, and debris in chemical plants, refineries, and printing presses are very common with this application of carbon dioxide in the form of small rice-sized dry ice produced (often onsite) or remotely, and then used to blast away dirt, paint, debris, and a wide range of surfaces rather than using sand, or other agents.

The dry ice used in this application sublimates (travels from a solid to gaseous phase) after use, thus not leaving a pile of sand or material, and not raising a cloud of dust or sand when blasting via other methods or materials.

In this respect, the CO2 product is an environmentally-friendly agent and an excellent application, in an extremely wide and sometimes delicate range of environments and applications, such as electronics.

When considering CO2 diffused in water, when producing carbonic acid, this is an excellent weak, self eliminating acid (producing by-products as carbonates and by-carbonates) compared to the application of sulphuric acid, for example, creating sulphate by-products which are not benign as would be the carbonate compounds.

The application of CO2 rather than sulphuric acid is also safer, in terms of handling, and spillage. The application is excellent in some power plant environments, many municipal potable and waste water applications as well.

This represents applications for Ph reduction, controlling calcium carbonate scale formation in the drinking water distribution systems.

Other applications for carbonic acid can be found in chemical plants, and food processing operations, for Ph reduction as well.

Use of CO2 for replacement of perc in dry cleaning environments is small in total merchant volume globally, particularly in the developed world, but an excellent means of eliminating VOC compounds otherwise emitted to the atmosphere, from the use of old time organic solvents.

In terms of closed loop applications for supercritical extraction of essential and vegetable oils, this has been an application found from time to time; however, of a greater size, conceivably could be a closed loop or recovery (re-liquefaction) of spent gases in very large cryogenic applications, and then re-using this liquefied CO2 again and again - perhaps with some purification.

The application has been evaluated in the past, however the long term strategy for the gas suppliers is to sell more and more CO2 for cryogenic service, as well as other applications. Hence, not recover and reuse the CO2 in a large food freezing operation – this is against the marketing goals for the gas companies, as well as other supply industries of commodities; all of whom want to sell more of their product.

In any event, the recovery and re-liquefaction and reuse of this commodity for freezing and food processing is an interesting thought, and essentially an environmentally-friendly improvement in the very large cryogenic applications today.

These are a few green applications for CO2, as well as a conceptual means of making a large volume consuming application becoming green in the world of carbon dioxide.

About the Author
Sam A. Rushing is a chemist, and president of Advanced Cryogenics, Ltd., a CO2 and cryogenics consultant, a supplier of all process, applications, recovey, production, economic, and market related services to allied industries and carbon dioxide / cryogenic projects globally. The company is supported by over 30 years of expertise to all types of

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