Carbon Dioxide and the Consumer Micell Technologies

Carbon Dioxide (CO2) Natural, cheap, plentiful (too much of it!) 0.04% of atmosphere and apparently rising! Available in >99.9% pure form, £70/$110 per 25kg. By-product of brewing, ammonia synthesis, combustion Non-toxic and properties well understood asphyxiant at high concentrations (excludes oxygen from lungs) Non-flammable Easily removed and recycled, and can be disposed of with no net increase in global CO2

The Consumer Perspective All will have heard of carbon dioxide Has been widely used in consumer applications for many years (carbonated beverages) Supply chain and related technology already established. Relatively good image for consumer ‘Natural’ Probably not thought of as a ‘chemical’ Non-toxic (asphyxiant at high concentrations) Renewable, non-petrochemical sources available Definite benefits over potential alternatives

• • Phase diagram for pure CO2 Pressure (bar) Temperature (ºC) 74 © Monterey Bay Aquarium Research Institute SOLID SUPERCRITICAL Critical FLUID • point Pressure (bar) 74 LIQUID Triple • point 5.1 GAS 1 -78 ºC -56.3ºC 31.1ºC Temperature (ºC)

• • Pressure (bar) Temperature (K) 74 303 SUPERCRITICAL FLUID SOLID point • Pressure (bar) 74 LIQUID GAS Triple point • Temperature (K) 303

• • Pressure (bar) Temperature (K) 74 303 SUPERCRITICAL FLUID SOLID point • Pressure (bar) 74 LIQUID GAS Triple point • Temperature (K) 303

• • Pressure (bar) Temperature (K) 74 303 SUPERCRITICAL FLUID SOLID point Pressure (bar) 74 LIQUID Triple • GAS point Temperature (K) 303

• • Pressure (bar) Temperature (K) 74 303 SUPERCRITICAL FLUID SOLID point • Pressure (bar) 74 LIQUID GAS Triple point • Temperature (K) 303

SCFs are intermediate between liquids and gases

What has carbon dioxide ever done for us?

Current consumer related applications of CO2 technology Carbonated drinks Leavening agents in baking Solvent extraction Surface coating Fumigation (1% in air will eliminate pests in greenhouses) Dry cleaning Surface cleaning Welding pH control (e.g. effluent streams, pulp and paper mills) Refrigeration (dry ice, mechanical systems) Fire extinguishers Life jackets Main raw material for photosynthesis (with water)!

The Future? http://www.nasa.gov/vision/earth/technologies/harvestingmars.html

Dry Cleaning using CO2 Current methods use perchloroethylene 1.5 Million tons used per year (North America) Hazardous air pollutant and suspected carcinogen Contaminates drinking water supplies Contributes to photochemical smog <5% recycled Requires heating to remove solvent residues Characteristic odour Use of PERC in EU to be phased out by 2007 Poly(ether-carbonate) coplymers derived from propylene oxide and CO2.

Dry Cleaning using CO2 New process uses liquid CO2 Requires surfactant (recycled) No unpleasant odours No heat required for drying – energy efficient and kinder on clothes Possible tax credits and reduced regulatory monitoring Utilises same CO2 used by food and drink distributors J.L. Kendall, D.A. Canelas, J.L. Young and J.M. DeSimone, Chem. Rev., 1999, 99, 2663. T. Sarbu, T. Styranec and E.J. Beckman, Nature, 2000, 405, 165.

Dry Cleaning using CO2 Hangers (Micell, NC), DryWash (Global Technologies, CA) Related technology also used for degreasing (e.g. metal parts), semiconductor photoresist removal and spin coating. Franchises now operating in Sweden ICI and Linde now major players Chem. Eng. News, Sept. 2 2002. p12. Micell Technologies

Spray coating using CO2 Union Carbide, Unicarb Technology Replaces 40-90% of VOCs with CO2. Widespread application Coatings on aerospace parts Adhesion promoters on plastics Food Chocolate biscuits Barrier coatings Additives Chem. Eng. News, June 14 1999, 77 (24), 13.

Extraction using scCO2 Extensively used for ‘natural’ coffee decaffeination; alternative uses CH2Cl2 (also tea) Extraction of Hops for Brewing Many other extraction processes Often use liquid rather than supercritical CO2. Spices Essential oils and fragrances Simple product isolation by evaporation, to 100% dryness. No solvent residues or effluent

CO2 Refrigeration Many refrigeration plants currently use fluorine-containing volatile organic compounds which are environmentally persistent and have significant global warming potential Ammonia also used although is toxic and has very strong smell CO2 is rapidly emerging as a viable alternative Area of intense activity for variety of applications (large scale refrigeration, automobile air conditioning, heat pumps, domestic use).

CO2 Refrigeration Large scale units now in operation. ASDA distribution centres in Falkirk and Skelmersdale (2003) Amongst the biggest temperature controlled buildings in the UK (412,000m3) Nestle Coffee freeze drying plant in Hayes, completed in Jan 2002 www.star-ref.co.uk

Chemical Synthesis Fluoropolymer synthesis Dupont $275M facility Replaces CFCs used previously (now banned by Montreal Protocol) Initially used for fluorinated ethylene-propylene and perfluoroalkoxy resins Easy polymer isolation and drying, and minimal waste Replacement for halogenated solvents S.L. Wells amd J. DeSimone, Angew. Chem. Int. Ed., 2001, 40, 518.

Would a consumer prefer to purchase a common pharmaceutical product (e Would a consumer prefer to purchase a common pharmaceutical product (e.g. aspirin) prepared using CO2 as a solvent rather than more harmful VOCs? How much extra would they be prepared to pay?

Conclusion CO2 already has widespread application with more areas under development Very favourable profile for consumer applications Relatively high pressure and energy use may be an issue and needs to be balanced, but can be minimised Has potential as real green technology of the future, as well as the present Use and exploitation of CO2 can only increase.

c.m.rayner@leeds.ac.uk http://www.chem.leeds.ac.uk/People/Rayner.html