Carbon Dioxide and its practical, green uses

Carbon dioxide — everyone wants to see less of it lying around, but what is it particularly good for?

Our resident Grandmaster of CO2, Sam, Rushing, takes us through the green applications. 

By Sam A. Rushing, president, Advanced Cryogenics, Ltd — special to The Digest

WHEN CO2 is the subject of discussion, outside of those in the gas trade, it is usually associated with greenhouse gases, a gas exhaled endlessly, and soft drinks. As those in the gas industry know all too well, CO2 has many dimensions associated with so many applications, which continue to grow. As related to green applications the range of uses can begin with CO2 usage in solvent technologies; on to high pressure blast cleaning with high density ¼ inch pellets, insect control in grain storage environments, to dry cleaning applications, and Ph reduction usage. The use of CO2 as an aerosol propellant, v. usage of alternate substances can be a green approach to aerosol technologies. Below is a brief review of CO2 uses which I consider to be green.

SOLVENT TECHNOLOGIES include carbon dioxide instead of hydrocarbon compounds (i.e. hexane and acetone); such as extraction of essential oils from plant matter, herbs, seeds, and nuts. All the way around, the green aspect can be noticed from such technology, including disposal issues for the solvent and potential residue and quality for the end product being produced. Decaffeination of coffee can be a popular, safe, environmentally friendly, and more of a natural process v. alternate methods. In the case of solvent technologies, supercritical CO2 is used. In such supercritical technologies CO2 becomes a chemical reagent in production of thermoplastic and fired ceramic materials, for example. Pharmaceuticals may be a long term place for supercritical CO2 in the production of Nano scale particles. In the end, environmentally friendly, green, and low toxicity are key to supercritical CO2 usage.

Supercritical CO2 can be an excellent means of sterilizing medical devices and instruments; and the list continues to grow for supercritical carbon dioxide.

BLAST CLEANING seems to gr growing in popularity in many world markets. When considering some of the alternatives, from a green perspective, CO2 is a cleaner and neater substance than many other blasting materials which are in use, and clean up can be much easier, since sublimation will yield less waste. Media such as plastic beads, solvents and sand have typically been the main stay in terms of blast cleaning options; however CO2 blast cleaning results in minimal abrasion, due to a less transfer of kinetic energy upon impact; due to an almost immediate sublimation of the product upon impact. Rapid change from solid to gas upon impact produces tiny shock waves, which are integral in the removal of the material.

The applications for CO2 blast cleaning are ever-growing, and it must be remembered proper ventilation must be maintained.

INSECT CONTROL can be readily achieved by using CO2 v. alternate fumigants; particularly if hydrocarbon in nature; where some of the fumigants which have been used over the years, may be considered carcinogenic. It is felt the mechanism for insect kill with CO2 is simple desiccation. There are significant advantages over chemical alternatives such as phosphine and methyl bromide, including insects cannot develop immunity to carbon dioxide as they do chemical agents. Further, no residue is left with CO2; and per the EPA registration, CO2 is a non – restricted pesticide, unlike chemicals. Grain silos have been a preferred application in this respect, and liquid CO2 is vaporized, and since 60% atmospheric content is fatal to insects, it is not necessary to seal the silos. Once again, eliminating potentially carcinogenic or otherwise harmful chemical agents for a benign and natural CO2 is entirely green.

DRY CLEANING applications for CO2 are a small part of the overall dry cleaning industry. However, the old standard, namely ‘perc’ (tetrachloroethylene or perchlorethylene) has been closely associated with various forms of cancer and neurological degenerative disease. The more benign symptoms start with irritation of the eyes, nose, throat and skin; and long term exposure is potentially linked to the more severe chronic diseases. Further, perc is a halogenated hydrocarbon solvent, and is everything which is not green by definition. The challenges with CO2 represent a full replacement of the cleaning machines used in the industry; however, long term payback would be invaluable in terms of health gains and environmental benefits.

PHOTOSYNTHESIS can be one of the greenest forms of CO2 applied anywhere. The combination of sun, water, and CO2 yield sugar and oxygen; and we require the oxygen for day to day life. In some greenhouse operations, it was once common to burn fossil fuels such as natural gas, and use the CO2 content in flue gas to enrich the growing environment. Today, it is rather common to find merchant CO2 stored on site, which is vaporized and applied in the greenhouse operation. It is necessary to raise the atmospheric content to 600 ppm in this application.

What is being tested, and soon commercialized, are algae farms which use flue gas from power and other by-product facilities; thus providing a very green carbon sink, and further produce algae, from which the oil is extracted for use in biofuels, often biodiesel. Much of this has been announced in the press; however, commercialization and refinement of algae strains are essential to make the concept truly work. Should this technology work well, it is a logical carbon sink of enormous value.

SEQUESTRATION TECHNIQUES in some forms can be considered very green means of working with carbon dioxide. Of course, CO2 is a most daunting greenhouse gas, from a volume perspective; and as a major constituent in raising global temperatures. The forms of sequestration continue to grow. Of course, there is photosynthesis, where the carbon is captured in plant life, then subterranean forms of sequestration – whether this is applications from enhanced oil recovery methods, plus much more.

In terms of subterranean CO2 disposal with a purpose, assuming there is continuous recycling of the product injected, and the EOR project continues to receive more product for enhanced recovery of oil; this application can be considered quite green, in terms of essentially taking CO2 ‘off the table’. Further, many projects, such as off the North Sea, CO2 is being injected into natural aquifers; and in this respect, perhaps this can also be considered a means of removing CO2 from the equation. Of course, there is a given amount of backlash, that being the horsepower required to compress, process, and transport the CO2 to these ultimate downhole destinations.

There are ongoing efforts to apply CO2 in concrete which is used in industry, apply the product in the manufacture of plastics; thus other possible means of sequestration. In the end, as sequestration techniques continue to develop, more solutions will continue to become a commercial success; and the fight to reduce CO2 content and emissions will gain some ground.

IN SUMMARY carbon dioxide continues to grow in industry, and will continue to grow as green – oriented applications are sought, and as means of sequestering the product becomes ever vital.

About the author: Sam A. Rushing is president of Advanced Cryogenics, Ltd, and a chemist by background. The company offers a full menu of CO2 consulting services from technical, thru market and business related. The company celebrated 25 years last fall, and to make the most of your CO2, from profit and environmental perspectives, please call or write to the contact information as follows: tel. 305 852 2597; e-mail: rushing@terranova.net ; web: www.carbondioxideconsultants.com