In 1974, Sherwood Rowland and Mario Molina discovered that chlorofluorocarbons (CFCs) were depleting the ozone layer, and in 1995, they received the Nobel Prize in Chemistry for this work. In response, the United Nations Environment Programme called an international conference to discuss the issue. Shortly thereafter, the US banned all non-essential uses of CFCs as propellants in aerosols. The Montreal Protocol required all developed countries to begin the phase-out of CFCs in 1993 and reduce CFCs to 50% of the baseline by 1998. A timeline for the phase out of hydrochlorofluorocarbons (HCFCs) was created in 1997. To meet the 90% total reduction requirement for all HCFCs by 2015, HCFC-225 is now being phased out.
HCFC-225 (also called “AK-225”), a precision cleaning solvent, is a mixture of two isomers, HCFC-225ca and HCFC-225cb. A common source of HCFC-225 is from Asahi Glass Company as Asahiklin AK-225. AK-225 has many unique properties, including its ability to form azeotropes, good solvency, and thermal stability, which makes it good for use in vapor degreasing. AK-225 is nonflammable, has a low acute toxicity, low viscosity, high density, and low surface tension. However, it is now being phased out.
How Is the Phase-Out Defined?
The Clean Air Act addresses the phaseout of HCFC-225 in section 605(a). The first part covers the restriction of use and states: “Effective January 1, 2015, it shall be unlawful for any person to introduce into interstate commerce or use any class II substance unless such substance – has been used, recovered, and recycled; is used and entirely consumed (except for trace quantities) in the production of other chemicals; or is used as a refrigerant in appliances manufactured prior to January 1, 2020.”
In this case “use” refers to the use of the controlled substance (i.e., HCFC- 225). In 40 CFR 82.3, the U.S. Environmental Protection Agency (EPA) defines a controlled substance as follows: “…any substance listed in appendix A or appendix B to this subpart [both HCFC-225ca and HCFC-225cb are listed in appendix B], whether existing alone or in a mixture, but excluding any such substance or mixture that is in a manufactured product other than a container used for the transportation or storage of the controlled substance.”
The exclusions (in italics) are a source of misunderstanding. Neat (without additives) HCFC-225 in bulk packaging (gallon and multi-gallon containers) meets the definition of controlled substance. A blend is considered a mixture of chemicals in a container, so it is also a controlled substance. An aerosol, however, is a chemical blend in a manufactured product and is excluded from the definition of controlled substance. End-users may use and continue to purchase aerosols containing HCFC-225 made before January 1, 2015. Be gin ning on January 1, 2015, HCFC-225 can only be used in the manufacture of cleaning products if it has been used, recovered, and recycled, as per the Clean Air Act 605(a).
What Are the Replacements?
To date, the EPA has approved more than 300 substitutes for over 60 different uses. Potential substitutes for HCFC-225 include DuPont Vertrel Solvents, Techspray’s Precision-V Solvents, n-Propyl Bromide(nPB), Trichloroethylene (TCE), 3M hydrofluoroethers (HFEs), and Honey well’s Solstice Performance Fluid.
DuPont Vertrel Solvents have characteristics similar to HCFC-225 but are much more environmentally friendly and have no use restrictions. Solvents containing nPB work well for difficult precision cleaning, but they are not considered environmentally friendly. From a health and environmental standpoint, TCE is not a good replacement as it has been a suspected carcinogen for years. TCE is an aggressive cleaner; this makes it unsuitable for use with most plastics and elastomers. From an environmental standpoint 3M HFEs are great as they have been granted VOC exemption. Honeywell’s HFO-1233zd(E) is a low global warming potential, non-flammable solvent. The EPA has recently found it to be acceptable as a substitute for HCFC- 225ca and HCFC-225cb, and blends thereof for use as an aerosol solvent. It also has low toxicity characteristics.
Because HCFC-225 is commonly used in high end, class 3 applications, like aerospace, medical, and biotech, qualification of replacement solvents is a long, arduous process. It is not too early to start the process, and there are many choices to meet most every requirement.
This article was written by Lindsey Shehan, Chemist, R&D, Techspray, a division of Illinois Tool Works, Amarillo, TX. For more information, visit https://info.hotims.com/49742-162.