Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Great quantities of paints, lacquers, varnishes, base
coats and clear coats are used in the automobile, appliance,
and allied industries to coat finished products. These paints,
lacquers, varnishes, base coats and clear coats hereinafter
referred to as paints, are generally solvent-based. In the use
of these materials, generally in enclosed areas called paint
spray booths, substantial quantities of solvent and oversprayed
paint solids are discharged into the booth atmosphere. These
materials represent environmental hazards which have to be
controlled. Current paint spray booths comprise a chamber, a
duct system for passing air down through such chamber to
remove volatile organic paint carriers and oversprayed paint
particles present in the chamber into a sump containing a cir-
culating hydr~philic liquid located at the bottom of the cham-
ber which has been adapted to remove volatile organic paint
carriers and paint particles from the air containing them.
This system has generally been satisfactory for removing paint
particles but has not been effective for removing the volatile
organic components present as paint carriers.
Paint spray booths generally represent major items of
capital expense and, as such, replacing paint spray booths with
more effective systems which would enable removal of volatile
organic carriers would be prohibitively expensive. Consequent-
ly, it is important to find a method for modifying existing
equipment so that this existing equipment can recover volatile
organic paint carriers rather than discharge these volatile
organic paint carriers into the atmosphere.
The prior art shows the use of various materials to
be employed as fluids in the sump of paint spray booths which
will trap paint particles and which act as solvents for vola-
.
.~" 1
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tile organic carriers. References employing oil-in water emul-
sions for this purpose include Japanese Kokai 52990, United
States patent No. 4,265,642, and ~,378,235, and commonly
assigned United States Patent No. 4,378,235.
In the Japanese reference,an oil-in-water emulsion of
a purified white oil mixed with a detergent such as alkyl ben-
zene sulphonic acid is used to scrub volatile organic carriers
from contaminated air. The emulsion is used in an absorption
tower to trap volatile organic carriers. While systems of this
type could be effective, no mention is made of reusing this
emulsion Since materials of this type, which include petrol
leum products, are expensive without reuse of this emulsion,
procedures of this type tend to be impractical.
n United States patent No. 4,265,542 there is
disclosed a method for the removal of volatile organic carriers
from the air in paint spray booths using an oil-in-water
emulsion. While the oil-in-water emulsion is reusable,
ultrafiltration is used to separate the components of the
emulsion to allow recovery of a solvent or oil phase from which
volatile organic carriers can be distilled. Ultrafiltration
techniques for handling large volumes of continuously
recirculated liquid present in paint spray booths are
impractical. Large paint spray booths of this type generally
employ circulation of up to 10,000 gallons per minute of liquid
and the ultra-filtration of even a small fraction of this
amount is economically impractical.
United States Patent No. 4,396,405 discloses a pH
sensitive oil-in-water emulsion which may be used in a process
to recover volatile organic materials from paint spray booths.
The paint solids in this case are filtered off and discarded.
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rrhe emphasis in this reEerence is to recover volatile organic
materials from the oil-in-water emulsion by wreaking the
oil-in-water emulsion and then distilling the volatile organic
materials from the oil phase of the emulsion. This oil phase
may then be recombined with the aqueous phase to reform the
emulsion.
United States patent 4,378,235 discloses a process
for the removal of volatile organic paint carriers from paint
spray booth sumps using an oil-
f 2a -
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in-water emulsion. In this case paint solids are filtered, and the
volatile organic material is recovered as in the previously mentioned
application by distillation from the oil phase of the oil-in-water
emulsion.
While the above two references provide an advance in the art,
a continuous process of this type requires expensive equipment such as
distillation units and oil-in-water separators, and while recovering volatile
organic materials, are not as efficient as desired.
The subject invention seeks to provide a process for the
recovery of oversprayed paint solids from paint spray booth systems and
secondarily, and to provide for the recovery of volatile organic carriers
assoc-~ated with the paint from paint spray booth systems. The process of
thus invention calls fox the use of an oil-in-water emulsion which will
detackify the paint solids so as to allow for their ready separation from
the oil-in-water emulsion, but which will also, in the case of certain
types of paints, trap or capture the volatile organic paint carrier in the
oversprayed paint particles. By the use of this invention detackified
oversprayed paint or lacquer solids carryingthe volatile organic carrier
are easily separated from the oil-in-water emulsion. The detackified paint
material containing the solvent may then.be used as a fuel, or further
treated to recover the volatile organic material. The oil-in-water emulsion
may be reused.
Accordingly, this invention seeks to provide to the art a
method for the detackification of oversprayed paint and/or lacquer solids.
Further, this invention seeks to provide to the art a method
for the detackification of oversprayed paint solids and the recovery of
volatile organic paint carriers.
Still further, this invention seeks to provide a method for the
recovery of volatile organic paint carriers from paint spray booths by
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removing from the oil-in-water emulsion used as the hydrophilic liquid
in the base or sump of the paint spray booth detackified oversprayed paint
solids having entrained therein the volatile organic paint carriers.
Thus in its broadest aspect this invention provides a method
for the detackification of oversprayed paint solids which comprises con-
tacting the oversprayed paint solids with an oil-in-water emulsion.
This invention is directed to a method for the detackification
of paint solids and the recovery o-f volatile organic paint carriers from
paint spray booth systems. The paint spray booths of the type for which
this invention is designed may be of a wet wall, center draft, or other
canstruction. Paint spray booths of these types operate, in a sense, as
large gas scrubbers with air passing through the booth picking up substan-
tial quantities of volatile organic carriers, and paint particles that do
not meet the object being painted. The air, after picking up the materials,
passes inta a sump or the like where it isintimately contacted with the
hydrophilic fluid which is generally recirculated throughout the paint
spray booth. The hydrophilic fluid serves to trap oversprayed paint
particles to prevent their release into the atmosphere and, also, has
served to some extent, to trap the organic vapors collected from the booth.
The organic vapors that are generally encountered inpaint
spray booths of the type described are those commonly used
?7 2
as organic carriers in industrial finishes such as paints and
lacquers and may consist of aromatic materials such as benzene,
xylene, toluene, low-boiling ethers, esters, ketones such as
methyl isobutyl ketone, methyl amyl ketone, and mixtures
thereof. Accordingly, the hydrophilic liquid scrubblng medium
which is employed must act as a solvent for these types of
volatile organic paint carriers. It is also important in the us
of this invention that the oversprayed paint solids be
detackified. This means essentially that the individual
particles must not stick to the sides of the booth, process
equipment, or agglomerate with themselves to form materials which
cannot be easily handledO Ideally, the oversprayed paint solids !
should be detackified to the point where they can be readily
separated from the hydrophilic liquid being employed. This
separatlon step may be done by filtration, flotation,
coagulation, or the like.
We have found that when certain oil-in-water emulsions
are employed, suitable paint detackification is obtained. In
addition, the detackified paint solids often contain substant1al
quantities of the oversprayed volatile organic paint carriers.
These solids may be readily removed by separating the oversprayec
paint solids from the hydrophilic liquid.
The hydrophilic liquid chosen for use in this invention
is an oil-in-water emulsion system which comprises an organic
liquid having a boiling point of at least 150 C., an
oil-in-water emulsifier, and water.
efore briefly describing the process in which the
oil-in-water emulsions of this invention are utililzed, the
following explanation is presented for each of the components of¦
the oil-in-water emulsions of this invention.
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The Organic Liquid
The organic liquid component of the oil-in-water emulsions of
this invention should be a non-volatile, water-immiscible, hydrocarbon
material which has the further characteristic of acting as a solvent for
volatile organic paint carrier used in the paint or lacquer being employed
in paint spray booth. Organic liquids employed may be primarily aliphatic,
paraffinic, aromatic or mixtures thereof. The organic liquids may either
be halogenated or non-halogenated and should generally having a boiling
point greater than lS0F. and, preferably 200F., and most preferably,
above 300F. Viscosities of materials used may range from that of a 100
SEC primarily aliphatic petroleum process oil tothat of a highly chlorinated
paraffinic material having a viscosity in excess of 20,000 cps. Thus,
the only criteria for materials of this type are those stated above.
Typical materials which can be employed include Telura 323, a
process oil manufactured by Exxon Company, United States of America, which
is categorized as having a boiling point of from 545-88~E., negligible
solubility in water, a specific gravity of.~O3 at 60F., a Cleveland open
cup flash point of 330 F. and a viscosity at 100 F, of 105-115. This oil
is believed to be a complex mixture of aliphatic and aromatic petroleum
hydrocarbons. Also useful are various chlorinated paraffinic materials
such as those designated Kloro 6000, Kloro 7000, CW 52, CW 170, CW 8560
Erom the Keil Chemical Division of the Ferro Corporation; as well as
Isopar M , a branched paraffinic material available from the Humble Oil
Refinery Company; LOPS , a low odor paraffinic solvent purchased from the
Exxon Company, United States of America; and Marcol* 82, a highly aliphatic
viscous white oil available from Exxon Company, United States of America.
* Trade Marks
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For safety purposes, the organic liquid employed in
the oil-in-water emulsion of this invention should be substanti-
ally non-toxic and have a flash point greater than 250 F. A
preferred organic liquid for use in this invention is Telura 323
described above.
It will be seen however, that substantial variations
in organic liquids can be accomplished without varying from the
spirit and intent of this invention. As an example, 10 weight
motor oil has been satisfactorily employed in laboratory experi-
ments as the oil phase of the oil-in-water emulsion.
The Oil-In-Water Emulsifiers
The oil-in-water emulsifiers useful in this invention
are those capable of forming a relatively stable oil-in-water
emulsion with the organic liquid selected Generally these mate-
rials will have an HLB value ranging from about 6 to about 40
and most preferably from about 10 to 30. The HLB system is de-
fined in the Atlas HLB Surfactant Selector. Since the oil-in-
water emulsions of this invention do not have to be broken, ease
of breakability is not an important criteria. The emulsifier
may be any water-soluble anionic, cationic, nonionic, or mixture
o emulsifiers falling within the above criteria. Preferred
emulsifiers for use in this invention are saturated and unsatu-
rated fatty acids and alkali metal salts thereof containing
12-30 and, preferably, 16-24 carbon atoms. Other oil-in-water
emulsifiers such as the condensation proauct of cocoamine
reacted with 2 moles of ethylene oxide may be used. The prefer-
red emulsifiers of the invention form emulsions which break when
made acidic. It is expected, however, that oil-in-water emulsi-
fiers other than those specifically enumerated herein may be
employed. An especially preferred emulsifier for use in this
invention is oleic acid.
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Water
The water used to form the oil-in-water emulsions of
this invention should preferably not contain more than 150 ppm
hardness as Ca 2 or Mg +2. It has been found that excessive
hardness in water being used creates soap scum with the prefer-
red fatty acid emulsifiers. If hard water is encountered, how-
ever, chelating agents such as NTA and/or EDTA may be added to
the water on a 1:1 molar basis to combat hardness.
Formation of the_Emulsion
The components of the emulsion used in this invention
are used in the following weight percentages:
A. Hydrocarbon Oil
Generally 1-250,000 ppm by weight of
the emulsion
Preferably 2-125,000 ppm by weight of
the emulsion
Most Preferably 10-75,000 ppm by weight of
the emulsion
B. Emulsifier
Generally .1-30~ by weight of the
hydrocarbon oil
Preferably 1-20% by weight of the
hydrocarbon oil
Most Preferably 1.5-10~ by weight of the
hydrocarbon oil
C. Water balance
The emulsion is formed by simply mixing the above-
mentioned ingredients together. In formulating the emulsions
of the subject invention we have generally found that emulsions
having an alkaline aqueous phase of from pH 7.5-12 and prefer-
ably a pH 8-11 are preferred due to their greater ability to
detackify the paint materials used. pH adjustment of the emul-
sion can be accomplished by merely adding a small quantity of an
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alkaline metal hydroxide, preferably sodium or potassium
hydroxide to water prior to mixing to form the emulsion.
Once the emulsion has been formed, it may be used in
the spray booth as the hydrophilic liquid to capture the vola-
tile organic paint carrier materials and oversprayed paints pre-
sent in the paint spray booth. We have found that at the levels
mentioned above the oversprayed paint and/or lacquer particles
are detackified. These detackified materials, which we have
found to additionally contain the bulk of the volatile organic
paint carrier present in the spray booth, are then separated
from the oil-in-water emulsion. Due to the fact that the paint
carrier will also carry with it some of the oil-in-water emul-
sion, it has been found generally that additional quantities of
the hydrocarbon oil and emulsiier may optionally be added to
maintain the composition of the oil-in-water emulsion.
The oil-in~water emulsion may be reused indefinitely
and continuously recirculated in the paint spray booth so long
as additional quantities of materials are added to replace what
is lost with the oversprayed paint particles.
The detackified oversprayed paint particles are re-
moved from the oil-in-water emulsion by flotation, skimming, or
the like. We have found that when the subject invention is
operating properly the detackified paint or carrier overspray
generally floats on the surface of the emulsion allowing for
ready removal. This removal is accomplished by skimming using
known means. Saturation is, of course, also allowable, and may
be employed. The method of separation employed is not critical
to
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this invention and other means known to those skilled in the art may be
employed.
As stated above J the separation of the detackified paint
particles from the oil-in-water emulsions can be accomplished by a
variety of means. When the process of this inventionis employed on enamel
and/or base coat/clear coat materials, oily sludges are produced which
disperse in the emulsion. These sludges tend to sink to the bottom of
the sludge removal system. Accordingly, when employing this invention
in a spray booth utilizing these particular types of paints, or similar
materials, means for removing sludge from the bottom of the sludge removal
system should be provided.
The recovered detackiEied oversprayed paint particles in this
invention may be further treated to recover the volatile organic component,
pigment and other paint components, or may simply be used as a high B.T.U.
fuel. Due to the fact that only minor amounts of the hydrocarbon oil are
employed in forming the oil-in-water emulsion of this invention, the
process is economical, and hydrocarbon oil losses are kept at a minimum
level. The emulsion employed need not be breakable, and does not have to
be subjected to complicated processing steps to recover the volatile
2~ organic material or the oversprayed paint solids.
While substantial amounts generally 6-9%) of volatile organic
paint carrier may be recovered in the detackified paint sludge by the
method of this invention when certain types of paints are being treated,
sludges from certain paint types, notably enamels and/or base and clear
coats, will generally contain less than one percent by weight volatile
organic carrier.
In order to further illustrate the use and practice of this
invention the following examplesarepresented:
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1;2~372~L~
Example 1
In order to determine the effectiveness of the
oil-in-water emulsions of the subject invention, a system
containing a Binks spray booth, emulsion feed system, and Nordsor
airless paint spray system was
assembled.
About 3-5 gallons of premixed paint is placed in a
stainless steel paint pot sitting on a weighing scale. The
suction line for the Nor~son spray system is placed in the pot.
The paint pot is well covered with aluminum foil during the
tests. The paint spray rate during the test can be obtained by
observing the loss of weight in the pot per unit time. The air
pressure to the Nordson unit is maintained at 14-16 psi.
A paint filter ~4 and paint tip tO16-~02) was used. the
spray gun was positioned in the front of the spray booth and was
aimed toward the water curtain. Air flow over the spray gun is
approximately 100-150 ft/min. The air flow through the booth is
about 3000-3300 CFM.
The paint spray booth is a Binks Dynaprecipitor model
with a water capacity of 350 gallons. Air movement in the booth
is directed toward the water curtain and enters the
Dynaprecipitor unit through an opening at the top of the water
curtain where it passes through the first of four washes. The
recirculation rate to the header is about 150 gal/min.
The spray booth has a beach and a trough in the front to
allow for the skimming and recovery of floating paint solids.
There is no mechanism provided to recover sinking paint sludge.
The paint spray booth is equipped with a level control
so that makeup water is added automatically.
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A metering pump and mixing device is used to feed the
oil-in-water emulsion. A lQ gpm centrifugal pump is used to feed¦
booth water to the pump of the metering pump and mixing device.
A 0-3 gpm gear pump supplies oil to the mixing chamber of the
metering pump and mixing device. It is in the special mixing
chamber that the oil is emulsified in the booth water.
Oil-in-water emulsion made in the metering pump and mixing device
passes through a static mixer for additional mixing prior to
entering the header in the spray booth.
A pH controller connected to a tank probe controls
additions of caustic in the booth. Additions of acid are rarely ¦
requiced and are made with graduated cylinders as required.
Experimental Procedure
The sequence of events for running the detackification
tests done in this study is outlined below.
1. The paint to be used is well mixed with an air
operated mixer.
2. The booth is filled with water and the pH is then
adjusted The oil is charged via a metering pump
and mixing device. The pH is optimized with
respect to foam and emulsion stability. The
emulsions used tended to foam more at higher pH
values.
3. Begin spraying paint at 40-70 grams/minute.
4. Observe the condition of the paint sludge in the
spray booth. The oversprayed paint sludge is
consideced tacky if it adheres to metal surfaces orl
sticks to the skin when rolled between the fingers.
.,,'
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S. No adjustments to the system are made as long as
the paint sludge is detackified.
6. If the paint sludge floats it ls removed
periodically by skimming the sludge onto the beach
and into the trough and collected in a 5-gallon
pail. Free water is allowed to separate and is
drained before the paint sludge is weighed.
7. When tacky sludge is observed, additional soluble
oil is charged to the spray booth. Normally, the
booth i5 initially charged at a low concentration
which means that additions of soluble oil may be
required a short time after painting begins.
Additions of oil are made until the paint sludge
formed becomes detackified.
When additions of oil are made and the paint sludge
becomes detackified, then spraying should continue
until the tackiness is again obtained. In this
manner, paint overspray to detackifier ratios are
obtained. These ratios are equivalent to the
maintanance dosages required to keep the
detackified program working properly. The run
times for these tests vary between 1-5 hours.
8. Foaming with the oil-in-watec emulsion programs can
be controlled by lowering the pH of the system or
by using Nalco 71-D5 Antifoam or Nalco
2WP-546, available from Nalco Chemical Company, Oak
Brook, Illinois.
lZ~i7217
9. Sludge samples are taken and analyzed for BTU and I¦
oil, % water, and % solids. A determination on the
condition of sinking paint sludge is made at the
time the booth is dtai,ned. Observations are made
as to whether or not sludge sticks to the bottom
pan or if it can be easily hosed with water.
10. Samples of the emulsion are taken at regular
intervals and are analyzed for total volatile
organic carrier, oil, BOD, COD, TOC and hardness.
The following compositions were tested:
Composition I
93.3% Telura 323
7% Oleic Acid
Composition II
70.0% Oil, Napthenic 100 sec neutral
3~7~ Tall oil, fatty acid, 26% rosin
1.3~ Chlorinated paraffin wax
10.7~ Sodium petroleum sulfonate
4.7~ Sulfonated castor oil
3.7~ Fatty acid (waste stream) -
3.3~ Isopropanol amine (mixed)
1.4% Biocide
.001~ Anti-foam
Based on the above examples, the oil-in-water emulsions
used in this invention satisfactorily detackify paint and organic
solids and also allow removal of the volatile organic carrier
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72~7
associated with the paint or carrier. The removed sversprayed
solids or sludge is readily disposable and may be employed as a
. high BTU fuel.
: The compositions were tested according to the procedure
outlined above, results are found in Tables I - V. Data found i
: Tables VI-VIII was obtained using a pilot center draft spray
: booth designed by the Flakt Company having similar capacities anc
air flow to the Binks booth used in Table I-IV.
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