Traditionally, vehicle, equipment, aircraft, and ship maintenance operations utilize organic solvents containing hazardous air pollutants (HAP), such as MIL-PRF-680, xylene, and methyl ethyl ketone (MEK), to remove dirt, grease, soot, paint debris, and burned-on carbon from various parts. Tertiary butyl acetate (TBAC), a HAP-Free and volatile organic compound (VOC) exempt solvent, can enable the Department of Defense (DoD) to demonstrate compliance with National Emission Standards for Hazardous Air Pollutants (NESHAP) and VOC regulations without performing the extensive record keeping required when using HAP and VOC containing solvents.
The objective of this project was to demonstrate the efficacy and to validate the economic and process impact of TBAC in DoD solvent applications as a replacement for HAP and VOC containing solvents.
TBAC (CAS 540-88-5) is a natural gas-derived ester solvent originally developed in the 1950’s by Texaco as a fuel additive to improve cetane and reduce harmful exhaust emissions. However, it was never commercialized for that purpose. Until recently, it had found limited commercial use as a pharmaceutical intermediate. In 1997, Lyondell Chemical identified TBAC as a chemical with negligible photochemical reactivity and petitioned the U.S. Environmental Protection Agency (EPA) to add it to their list of VOC exempt compounds. TBAC is also not a HAP, ozone depleter, greenhouse gas, particulate matter precursor, or Superfund Amendments Reauthorization Act (SARA) 313 chemical. TBAC is inherently biodegradable, has low bioaccumulation potential (Bio Concentration Factor [BCF] <5), low tendency to partition to water and soil, and low toxicity. TBAC is also Significant New Alternatives Program (SNAP)-approved as a replacement for ozone depleting chloroflourocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in cleaning and other applications.
TBAC can be used in coatings, inks, adhesives and for cleaning, paint thinning and cleanup, and adhesive residue removal where these flammable solvents and blends are currently being used. It can also be used instead of toluene, xylene, methyl ethyl ketone (MEK), and other esters to reduce the HAP and VOC content of chemical agent resistant coatings (CARC) without negatively affecting cost or performance.
TBAC is also a potential replacement for acetone, methyl acetate, and PCBTF (parachlorobenzotrifluoride or Oxsol 100), three VOC-exempt solvents used in cleanup and CARC paints. Acetone and methyl acetate have low flash points and TBAC provides an additional margin of safety and can reduce solvent usage because of its lower evaporation rate. PCBTF is relatively expensive and dense, has an unpleasant odor, and is not as good a viscosity reducer as TBAC. TBAC can reduce procurement costs, solvent usage, and potential soil and water contamination issues compared to PCBTF.
TBCA solvent has low water content and meets urethane grade specifications for use in two-component urethane coatings. It is stable indefinitely under normal storage conditions in unopened, factory-sealed containers. It is resistant to oxidation, hydrolysis and aminolysis, three common decomposition pathways for other ester solvents such as methyl-, ethyl-, propyl- and nbutyl acetates.
TBAC was evaluated for cleaning applications in several process lines. Based on the process parameters developed in the laboratory evaluation and bench scale testing, full scale demonstration programs were performed at three sites, one each from the Army, Navy and Marine Corp. The demonstration sites were Corpus Christi Army Depot (CCAD), Texas; Norfolk Naval Shipyard (NNSY), Virginia; and Marine Corp Logistics Base Albany (MCLB), Georgia. These demonstrations showed that TBAC can replace the currently used solvents in some applications. Furthermore, cost analysis shows that such replacements are economically feasible.
The impact of TBAC on the overall coating process was evaluated. The impact of cleaning with TBAC on coating integrity was evaluated per the requirements of ADS-61A-PRF, “Aeronautical Design Standard Performance Specification for Army Aircraft Cleaners, Aqueous and Solvent”. Coating adhesion and sealant peel strength are included in the laboratory test plan. The NNSY demonstration evaluated the effect of TBAC on paint quality by painting with the demonstration paint equipment and evaluating coating quality per documented paint application procedures.
For TBAC to be qualified as an alternative to current solvents in the cleaning process, it must meet all the requirements of those processes, including all environmental, occupational safety, and health, chemical properties, materials compatibility and performance requirements. For those successful demonstration and validation tests, TBAC could be substituted for the current solvents in the cleaning process steps of similar coating application operations DoD maintenance facilities and depots.
TBAC has a flash point of 40°F. It is a flammable liquid as defined under SARA Title III, section 311/312 hazard category, but is not subject to the reporting requirements of SARA Title III, section 313. The flashpoint of TBAC was a consideration in the selection of the demonstration applications. Applications were selected where flammability was not a primary consideration or where the flashpoint of TBAC did not change the flammability classification of the process.