E.F.A. I
Chronology and Use of Chlorinated Solvents
Introduction
Chlorinated solvents are organic-solvent/compounds containing at least one covalently bonded chlorine atom in
their molecular structure. Due to their wide structural variety and divergent chemical properties chlorinated
solvents have found a broad range of application in a variety of day to day process, rendering them the capacity to
harm/contaminate the environment. Chlorinated solvents are one of the most frequently encountered
contaminants in environmental investigations (Siegrist, 1993). Trichloroethylene (TCE) and tetrachloroethylene
(PCE), for example, were detected in 945 groundwater-supplied drinking systems in an Environmental Protection
Agency survey of drinking wells in the United States. In September 1997, TCE and PCE were detected at 852 and
771, respectively, of the 1420 National Priority List (NPL) or Superfund sites in the United States (Butler and
Hayes, 1999). As a result of the frequency of detection and toxicity of chlorinated solvents, millions and often
billions of dollars are alleged in litigation associated with their investigation and remediation.
Chronology
The global production and use of chlorinated solvents began after World War II, with volumes gradually increasing
through the 1950s and 1960s. In the early years of solvent use, the military was the primary consumer. From 1978
through 1988, the total production of chlorinated solvents in the United States declined modestly, by about 11%.
After 1988, the decline was more substantial, amounting to about 45% between 1978 and 1985.
The decrease in the demand of chlorinated solvents during 1978 to 1985 reflects the production ban on 1,1,1-
trichloroethane (1,1,1-TCA, or TCA) and Freon-113 (1,1,2-trichloro-1,2,2-trifluoroethane). Another factor in this
decrease was the increased regulations on TCA, tetrachloroethylene (PCE), and methylene chloride (MC). The total
global capacity for chlorinated solvents in 1994 was about 1.7 million metric tons, with the U.S. accounting for
about 36% of the total, followed by Western Europe and Japan at 40% and 23%, respectively.
The primary use of chlorinated solvents is vapor degreasing. In vapor degreasing, solvents are boiled (150 to
2500F), thereby producing a heated vapor zone within the degreaser. A single-chamber vapor degreaser contains
heating coils at the bottom to boil the liquid solvent, and cooling coils surround the top to contain the vapor. Metal
parts are lowered into the solvent vapor zone for cleaning, usually in a metal basket. The warm solvent condenses
on the colder parts, dissolving the contaminants or oil into the solvent. In some instances, a spray wand is manually
used to spray the solvent vapor on the parts in the basket. The vapor zone height is limited by the cooling coils that
condense the solvents and return them to the liquid at the bottom of the degreaser. The mixture drains to a
water/solvent separator, where the heavier solvent sinks to the bottom and the condensed water and dissolved
solvent are disposed. While many vapor degreasers are more sophisticated, with vacuum systems, multiple
chambers, attached distillation units for removing the soils from the solvent, ultrasonics, and mechanized basket
trays, the general operating principle is the same.
Cold cleaning is another degreasing technique. Cold cleaning is similar to vapor degreasing, except that the solvent
is maintained at room temperature or is heated to a temperature below the solvent’s boiling point. Like vapor
degreasing, metal parts are dipped into the liquid solvent, and the contaminants are dissolved and removed from
the metal. Cold cleaning is less effective than vapor degreasing because the solvent is not boiled clean. The heated
1 Chronology and Use of Chlorinated Solvents| Environmental Forensic Analysis I
, E.F.A. I
solvent used in vapor degreasing is also more effective in degreasing than the same solvent used at room
temperature for the same purpose. The dominant cold cleaning solvent is 1,1,1-TCA.
Equipment related to vapor degreasers includes distillation or evaporation stills used to recover solvents. The two
types of stills are batch and continuous. In a batch still (also differential, Raleigh, or pot distillation), a fixed amount
of spent solvent is placed inside a heated evaporation chamber from which the condensed vapor is withdrawn.
Continuous, multistage distillation (also fractional distillation) is used when there is a need for a high degree of
distillation purity, if the amount of spent solvent to be recovered is large, or when differences in solvent volatility
are small. Continuous distillation is accomplished in a column equipped with trays or packing materials to facilitate
contact between the liquid and vapor phases. Liquid is introduced continuously into the column at the top while
the vapor moves upward, becoming more enriched with the more volatile compounds. The high boiling
compounds thereby become concentrated in the liquid. Chlorinated solvents are used in the electronics
manufacturing industry, especially in the production of semiconductors. Applications include:
• Semiconductor wafer fabrication and assembly
• Printed circuit board fabrication and assembly
• In situ generation of etchants
• Miscellaneous critical electronic applications
Chlorinated solvents used in the semiconductor industry include 1,1,2-trichloro- 1,2,2-trifluoroethane (Freon-
113); 1,1,1-trichloroethane (TCA); methylene chloride (MC); trichloroethene (TCE); and tetrachloroethylene (PCE).
Freon-113 and TCA applications include removal of flux from printed circuit boards after the various electronic
components are soldered to the board. TCA is frequently combined with alcohol because alcohol is an effective flux
remover. TCA and methylene chloride are also used in the photoresist process. In the early 1990s, all photoresist
solutions were solvent, aqueous, or semi-aqueous solutions. In the photoresist process, dryfilm photoresist is
applied to the copper substrate of the electronic board and the desired circuitry is imprinted by shining a high-
intensity light through a photomask.
If a negative photoresist is used, the areas of the film exposed to the light polymerize, whereas the unexposed areas
do not. After the developer carries away the unpolymerized material, the photoresist is then developed with a
solvent such as TCA, which is followed by the etching step. The remaining photoresist is then stripped, often with
methylene chloride.
In environmental litigation, the most commonly encountered solvents are Trichloroethylene (TCE),
Tetrachloroethylene (PCE), 1,1,1-Trichloroethane(TCA), Carbon Tetrachloride( TC), Chloroform(TCM) and
Methylene Chloride(MC).
Information about the specific applications and historical production of these solvents is summarized below
Trichloroethylene (TCE, Trichloroethene)
Trichloroethylene is used as a metal degreaser and has been available worldwide for about 50 years.
Trichloroethylene was first prepared by Fisher in 1864 during experiments on the reduction of hexachloroethane
with hydrogen. Trichloroethylene production began in Austria and the United Kingdom in 1908; Germany, in 1910;
the U.S., 1925; and Japan, 1935. Trichloroethylene is manufactured by the catalytic oxidation of 1,1,2,2-
tetrachloroethane and the catalytic chlorination of acetylene.
2 Chronology and Use of Chlorinated Solvents| Environmental Forensic Analysis I
Chronology and Use of Chlorinated Solvents
Introduction
Chlorinated solvents are organic-solvent/compounds containing at least one covalently bonded chlorine atom in
their molecular structure. Due to their wide structural variety and divergent chemical properties chlorinated
solvents have found a broad range of application in a variety of day to day process, rendering them the capacity to
harm/contaminate the environment. Chlorinated solvents are one of the most frequently encountered
contaminants in environmental investigations (Siegrist, 1993). Trichloroethylene (TCE) and tetrachloroethylene
(PCE), for example, were detected in 945 groundwater-supplied drinking systems in an Environmental Protection
Agency survey of drinking wells in the United States. In September 1997, TCE and PCE were detected at 852 and
771, respectively, of the 1420 National Priority List (NPL) or Superfund sites in the United States (Butler and
Hayes, 1999). As a result of the frequency of detection and toxicity of chlorinated solvents, millions and often
billions of dollars are alleged in litigation associated with their investigation and remediation.
Chronology
The global production and use of chlorinated solvents began after World War II, with volumes gradually increasing
through the 1950s and 1960s. In the early years of solvent use, the military was the primary consumer. From 1978
through 1988, the total production of chlorinated solvents in the United States declined modestly, by about 11%.
After 1988, the decline was more substantial, amounting to about 45% between 1978 and 1985.
The decrease in the demand of chlorinated solvents during 1978 to 1985 reflects the production ban on 1,1,1-
trichloroethane (1,1,1-TCA, or TCA) and Freon-113 (1,1,2-trichloro-1,2,2-trifluoroethane). Another factor in this
decrease was the increased regulations on TCA, tetrachloroethylene (PCE), and methylene chloride (MC). The total
global capacity for chlorinated solvents in 1994 was about 1.7 million metric tons, with the U.S. accounting for
about 36% of the total, followed by Western Europe and Japan at 40% and 23%, respectively.
The primary use of chlorinated solvents is vapor degreasing. In vapor degreasing, solvents are boiled (150 to
2500F), thereby producing a heated vapor zone within the degreaser. A single-chamber vapor degreaser contains
heating coils at the bottom to boil the liquid solvent, and cooling coils surround the top to contain the vapor. Metal
parts are lowered into the solvent vapor zone for cleaning, usually in a metal basket. The warm solvent condenses
on the colder parts, dissolving the contaminants or oil into the solvent. In some instances, a spray wand is manually
used to spray the solvent vapor on the parts in the basket. The vapor zone height is limited by the cooling coils that
condense the solvents and return them to the liquid at the bottom of the degreaser. The mixture drains to a
water/solvent separator, where the heavier solvent sinks to the bottom and the condensed water and dissolved
solvent are disposed. While many vapor degreasers are more sophisticated, with vacuum systems, multiple
chambers, attached distillation units for removing the soils from the solvent, ultrasonics, and mechanized basket
trays, the general operating principle is the same.
Cold cleaning is another degreasing technique. Cold cleaning is similar to vapor degreasing, except that the solvent
is maintained at room temperature or is heated to a temperature below the solvent’s boiling point. Like vapor
degreasing, metal parts are dipped into the liquid solvent, and the contaminants are dissolved and removed from
the metal. Cold cleaning is less effective than vapor degreasing because the solvent is not boiled clean. The heated
1 Chronology and Use of Chlorinated Solvents| Environmental Forensic Analysis I
, E.F.A. I
solvent used in vapor degreasing is also more effective in degreasing than the same solvent used at room
temperature for the same purpose. The dominant cold cleaning solvent is 1,1,1-TCA.
Equipment related to vapor degreasers includes distillation or evaporation stills used to recover solvents. The two
types of stills are batch and continuous. In a batch still (also differential, Raleigh, or pot distillation), a fixed amount
of spent solvent is placed inside a heated evaporation chamber from which the condensed vapor is withdrawn.
Continuous, multistage distillation (also fractional distillation) is used when there is a need for a high degree of
distillation purity, if the amount of spent solvent to be recovered is large, or when differences in solvent volatility
are small. Continuous distillation is accomplished in a column equipped with trays or packing materials to facilitate
contact between the liquid and vapor phases. Liquid is introduced continuously into the column at the top while
the vapor moves upward, becoming more enriched with the more volatile compounds. The high boiling
compounds thereby become concentrated in the liquid. Chlorinated solvents are used in the electronics
manufacturing industry, especially in the production of semiconductors. Applications include:
• Semiconductor wafer fabrication and assembly
• Printed circuit board fabrication and assembly
• In situ generation of etchants
• Miscellaneous critical electronic applications
Chlorinated solvents used in the semiconductor industry include 1,1,2-trichloro- 1,2,2-trifluoroethane (Freon-
113); 1,1,1-trichloroethane (TCA); methylene chloride (MC); trichloroethene (TCE); and tetrachloroethylene (PCE).
Freon-113 and TCA applications include removal of flux from printed circuit boards after the various electronic
components are soldered to the board. TCA is frequently combined with alcohol because alcohol is an effective flux
remover. TCA and methylene chloride are also used in the photoresist process. In the early 1990s, all photoresist
solutions were solvent, aqueous, or semi-aqueous solutions. In the photoresist process, dryfilm photoresist is
applied to the copper substrate of the electronic board and the desired circuitry is imprinted by shining a high-
intensity light through a photomask.
If a negative photoresist is used, the areas of the film exposed to the light polymerize, whereas the unexposed areas
do not. After the developer carries away the unpolymerized material, the photoresist is then developed with a
solvent such as TCA, which is followed by the etching step. The remaining photoresist is then stripped, often with
methylene chloride.
In environmental litigation, the most commonly encountered solvents are Trichloroethylene (TCE),
Tetrachloroethylene (PCE), 1,1,1-Trichloroethane(TCA), Carbon Tetrachloride( TC), Chloroform(TCM) and
Methylene Chloride(MC).
Information about the specific applications and historical production of these solvents is summarized below
Trichloroethylene (TCE, Trichloroethene)
Trichloroethylene is used as a metal degreaser and has been available worldwide for about 50 years.
Trichloroethylene was first prepared by Fisher in 1864 during experiments on the reduction of hexachloroethane
with hydrogen. Trichloroethylene production began in Austria and the United Kingdom in 1908; Germany, in 1910;
the U.S., 1925; and Japan, 1935. Trichloroethylene is manufactured by the catalytic oxidation of 1,1,2,2-
tetrachloroethane and the catalytic chlorination of acetylene.
2 Chronology and Use of Chlorinated Solvents| Environmental Forensic Analysis I
