On Site Carbon Dioxide Generation
Commercial use of carbon dioxide (CO2) depends largely on compressed CO2 or “dry ice”, both inconvenient sources for small users, since dry ice sublimates uncontrollably and compressed CO2 requires heavy, thick-walled containers, in addition to valves and regulators. A more convenient, on-site, source of CO2 would benefit users for applications such as green house growers, hydroponics/aquaponics, as an attractant to monitor/manage various insects including mosquitoes and for the “on-site” production of CO2 for the creation/maintenance of anaerobic environmental conditions in cell culture chambers or as a gas source to dispense a variety of fluids, such as fragrances, repellants, insecticides, etc.
Med-e-Cell has developed technology and products that are specifically suited for these applications. The technology is based on the electrochemical stripping of CO2 from carboxylated organic acids. A preferred chemical is oxalic acid, a stable solid, containing 97.8wt% of CO2. It is virtually pure CO2 without the inconvenience of uncontrolled sublimation. It can be stored for long time periods.
(The annual world production of oxalic acid is about 300,000 metric tons. The product is quoted fob production factory at 700-800 USD/ton).
The electrolytic process can be carried out at current densities exceeding 2 amp/cm2, at single cell voltages of less than 1.5 volts, corresponding to generation rates of about 0.1 kg CO2/cm2-day. The CO2 stripping process is conducted to completion i.e. the solid oxalic acid progressively disappears until a clear solution remains. Since there are no side reactions the total weight of CO2 produced can be predicted from the start-up weight of the oxalic acid feed or from the expanded amp-hours.
Since the cell voltages are stable, the CO2 generation rate can be either voltage- or current-controlled. Start-up is instantaneous and the generation rate responds instantaneously to current changes. A considerable advantage over compressed CO2 is that no gas metering is required, the correlation between current and generation rate being always respected.
The energy consumption is less than 0.6 kilowatt-hours per kilogram of CO2. The same process can be applied for the generation of minute amounts of CO2 (cc/hr) as well as much larger quantities (tons/day).
Med-e-Cell has developed a process to manufacture single cells up to 10 cm2 in active surface area and to assemble multiple cells in stacks operating at up to 10 amps and DC voltages of 3, 6 and 12 volts.
Developed initially to provide a convenient CO2 source for monitoring/managing mosquitoes, the generators have been tested by USDA/ARS as a tool for vector control. The product, Moustiq-air™, capable of producing CO2 at a rate up to 300 cc/minute, can be viewed on the Internet. It was first introduced to vector control professionals at the American Mosquito Control Association, 2011, Austin, Texas. The same technology can be implemented in commercial mosquito abatement products to replace conventional propane combustion burners.
Currently, Med-e-Cell is developing a product, SuperGroCO2, (see Internet) aimed at providing simple, easy-to-use, CO2 sources for enhanced plant growth, i.e. by increasing/maintaining the CO2 concentration at a 1250 ppm level in greenhouse enclosures. Prototypes will be available during the first quarter of 2013.
These “on-demand” systems can competitively replace conventional compressed CO2 stored in high-pressure cylinders. Similarly to bench-top oxygen and hydrogen sources they can be also developed as bench-top “on-demand” CO2 sources for anaerobic chambers.
For additional technical information, please refer to “On-site Generation of Carbon Dioxide”, H. Maget, Gases and Technology, July/September 2006, pp.18-20.
Attached files:idea connection images, CO2.pdfSuperGro-CO2=flyer=.pdfPatents:
US 6,387,228 issued 2002-05-14 [MORE INFO
US 8,168,048 issued 2012-05-01 [MORE INFO
US 7,785,459 issued 2010-08-31 [MORE INFO
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