Handbook of Solvents - George Wypych - ChemTech - Ventech!

854 George Wypych
Table 14.2.2. Total transfers of solvents by the aerospace industry. [Data from ref. 1]
Solvent Amount, kg/year Solvent Amount, kg/year
n-butyl alcohol 2,600 methyl ethyl ketone 500,000
cyclohexane 18,000 methyl isobutyl ketone 17,000
1,2-dichlorobenzene 4,000 tetrachloroethylene 110,000
1,1-dichloro-1-fluoroethane 230 1,1,1-trichloroethane 133,000
dichloromethane 68,000 trichloroethylene 98,000
N,N-dimethylformamide 500 trichlorofluoromethane 3,800
ethylene glycol 14,000 toluene 87,000
methanol 12,000 xylene 12,000
Air emissions result from sealing, painting, depainting, bonding, as well as from leakage
in storage, mixing, drying, and cleaning. The most common solvents involved in coatings
are trichloroethylene, 1,1,1-trichloroethane, toluene, xylene, methyl ethyl ketone, and
methyl isobutyl ketone. Wastewater is generated through contamination by paints and solvents
used for cleaning operations. Solid waste containing solvents comes from paint
overspray intercepted by emission control devices, depainting, cleanup, and disposal of unused
paint. Solvents used for cleaning are usually a mixture of dimethyl-benzene, acetone,
4-methyl-2-pentanone, butyl ester of acetic acid, naphtha, ethyl benzene, 2-butanone, toluene
and 1-butanol. Some solvents used for painting and cleaning are either recycled are
burned to recover energy.
In 1996, 199 aerospace facilities (out of 1885 analyzed in the report) released and
transferred off-site or discharged to sewers about 12,000 kg of 65 toxic chemicals (solvents
in these releases are reported in Table 14.2.1 and transfers in Table 14.2.2).
Methyl ethyl ketone, 1,1,1-trichloroethane, trichloroethylene, and toluene accounted
for 66% of all releases. 70% of all transfers was for recycling purposes. The aerospace industry
released 10,804 tons of VOC in 1997 which constituted 0.61% of the total releases
from 29 industries which were analyzed. Thirteen other industries release more VOC than
the aerospace industry.
Recycling and disposal of solvents in the aerospace industry equals the purchase cost
of the solvents. Therefore reduction of solvent use is very cost effective. Some chemical
stripping operations are now being replaced by cryogenic stripping with liquid nitrogen.
Also, supercritical carbon dioxide has been used in Hughes Aircraft Company in some
cleaning applications. Solvent emissions can be reduced through control of evaporation
(lids, chillers), by dedicating process equipment (reduces cleaning frequency), production
scheduling, immediate cleaning of equipment, better operating procedures, reuse of solvent
waste, and use of optimized equipment for paint application. There are plans to evaluate
powder coatings and water-based paints. 1,2 There are trials to use water as the paint thinner
and to lower viscosity of paints by application of resins which have lower viscosity. 2 Work
is under the way to replace dichloromethane/phenol stripper with benzyl alcohol. 2 The introduction
of an intermediate layer between the primer and the top coat has been proposed.