Saturday, December 15, 2012

Clearing the Air on Solvent Use

The South Coast Air Quality Management District (SCAQMD) is responsible for reducing levels of smog in the Los Angeles basin, a challenge bounded by the nature of atmospheric chemistry and fairness in local politics.
Its Rule 1122 – Solvent Degreasers, limited the capability of aqueous cleaning operations and chased high-technology industry from California. More than a decade later, those who fostered the rule are quietly asking for comments to modify it.
Smog is formed either by a reaction in the troposphere of NOX emissions from automobiles and power plants with ultraviolet (UV) light, or parallel reactions of NOX with volatile organic carbon (VOC) chemicals and UV light. Both reaction paths produce ozone, a precursor of smog.
SCAQMD regulates all emitters of VOCs including cleaning machines that emit dozens and hundreds of pounds per month of VOC chemicals, and other sources such as refineries that emit thousands and tens of thousands of pounds per month.
Search for solutions
Rule 1122 encouraged the option of cleaning with 2.5% VOC in water, an option that was useless for parts that are harmed by contact with water.
Chemicals that the U.S. Environmental Protection Agency (EPA) had exempted from national VOC status because of their low atmospheric reactivity with UV light also were allowed, including HFC-43-10mee, HFE-7100, HFE-7200, and some flammable solvents supplemented by other solvents that were either Class II ozone-depleters or had global warming potential. Enclosed machines that captured and reused solvent emissions—but required considerably more investment than open-top machines—were allowed.
After substantial testing and development, HCFC-225ca/cb—a Class II ozone depleting compound whose manufacture in the United States must, by EPA fiat, cease by 2015 and whose use must cease by 2020—became the favorite cleaning option. There is concern about the toxicity of one of its isomers, which posts a 100-ppm exposure limit.
HCFC-225ca/cb would not rank high on anyone’s list of environmentally preferred cleaning solvents. However, the chlorine atom within its molecular structure turbocharges its cleaning capability, so it has been specified for use in aerospace, military, and other applications, despite its $20 per-pound cost.
The European approach
In Europe, all halogenated solvents except n-propyl bromide are allowed to be used where storage, use, and recovery of solvents is done in automated, fully enclosed machines. The only other limitation on choice is solvents with a certain level of flammability.
It would be in the interest of SCAQMD to support a changeover from current operations to the European approach, and for local operators to revise specifications from a requirement to use HCFC-225ca/cb to another option not threatened by future phase out. I recommend binary azeotropes of an HFC with trans-1,2-dichloroethylene or an HFE with an alcohol.
This "European approach" does not require any invention or a long lead time for implementation, or propose a high risk of an unexpected outcome.

Calculating emissions
Rule 1122 could be modified by requiring operators to form no more than a standard amount of smog with their emissions per reporting time; and to obey all applicable safety and health regulations.
The amount of smog (actually ozone) is calculated by multiplying the product of the emission rate of each chemical by the maximum amount of ozone (MIR) each chemical is expected to produce times the length of the reporting period.
The equation is: 
Smog = [Emissions/Time] x [MIR] x [Reporting Time]
This metric would allow SCAQMD to focus on what is important within their purview, and to treat all emitters on the same standard basis. VOC emissions from small open-top (or enclosed) degreasers could be regulated (and identified) on the same basis as are emissions from smokestacks at refineries and or exhaust vents.
Other alternatives
There are other options. Operators could make their own selection of solvent and pay a negotiated tax based on the amount of emissions and the difference between the relative atmospheric reactivity (MIR value) of the chosen solvent and EPA’s standard for VOC exemption.
Operators could make their own selection of solvent, but be limited to certain negotiated emissions of mass amounts of VOC that they achieve with tailpipe treatment of emissions. Tailpipe treatment, applied to emissions from cleaning or other units, often involves recovery by condensation of solvent vapors, but nearly always involves adsorption of solvent vapor onto activated carbon. Operators would be required to certify compliance with federal and state exposure limitations.
Another option is to allow operators to choose within the expanded population of solvents whose MIR values are outside the current exemption limit. This would enable selection of non-aqueous low volatility solvents such as glymes and glycol ethers in cold cleaning or cosolvent operations.
Operators also could use binary azeotropes, whose cleaning performance would approximate that of HCFC- 225ca/cb.
Whatever options are considered, SCAQMD should not add an exemption for industries or applications deemed critical, and retain the current Rule 1122.
The current rule and contact information for SCAQMD can be found at:

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