Note: Descriptions are shown in the official language in which they were submitted.
1082889
Background of the Invention
The present application is concerned with the area
of gaseous effluent pollution control. More particularly,
the invention is concerned with the gaseous effluent resulting
from industrial processes, in particular, the application and
drying of paint on substrates such as transportation vehicles
as automobiles, trucks, and the like.
During various industrlal processes, gaseous effluent
is formed. Due to the increased concern with the atmospheric
environment, various processes have been suggested to control
the gaseous effluent introduced into the environment.
Increased research and development has been undertaken,
especially with
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respect to the effluent resulting from the application
of liquid paints containing organic solvents to
various substrates such as automobiles, trucks and
the like. One such process is that described in
~.S. patent 3,932,151, which relates to paint spray
booth construction and control of excess atomized
paint from the air in the vicinity of a spray-painting
operation.
Another proposed solution to the problem
of gaseous effluent control is a technique where the
gaseous effluent is absorbed onto a high surface area
of carbonaceous substance, such as activated carbon, The
difficulty with such a procedure is that when it came time
to remove the absorbed solvent, a vacuum stripping operat-
ion was employed, which therefore produced a hazardous con-
dition in that the solvent was explosive at such vapor con-
centrations. To overcome this problem, water was applied
to the activated carbon, thereby significantly decreasing
the effectiveness of the activated carbon by substantially
decreasing the surface area of the activated carbon. Such
an approach is highly inefficient for large voIumes of gas-
eous effluent.
In designing a process for the purification
of gaseous effluent one must be particularly conscious of
being able to re-claim the gaseous effluent in order to
make the process economically desirable from an overall
point of view.
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108Z8~39
Summary of the Invention
Broadly speaking the problems of the prior
art are overcome by the present invention which provides
in a process for the purification of gaseous effluent
resulting from the application of liquid paint, wherein
liquid paint is applied to a substrate, thereby forming
a gaseous effluent containing pollutants, said gaseous
effluent containing at least a hydrocarbon solvent or an
; oxygenated solvent and prior to passing effluent to the
- atmosphere, removing the pollutants from the gaseous
effluent, the improvement comprising; in a zone spaced
from that in which the spraying of the substrate takes
place, absorbing the pollutants in the gaseous effluent
by passing the gaseous effluent into a non-reactive
liquid solvent for said gaseous pollutants, wherein said
liquid solvent is substantially water immiscible and
contains only the elements carbon, hydrogen a oxygen.
Brief Description of the Drawings
Fig. 1 is a schematic diagram of the process
of the present invention including the use of the solvent
by-products;
Fig. 2 is a schematic view of a cyclonic
spray scrubber which is a liquid absorber for the gaseous
effluent.
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1~8Z889
Descri tion of Preferred Embodiments
P
Industrial processes that the present
application is directed towards are any processes where
s~aseous effluent is formed, which effluent is deleterious
to the environment. In particular, the most preferred
process is the gaseous effluent formed from the application
of liquid paint.
Liquid paint is used in its broadest terms
to include materials that contain organic film-form~rs
dissolved in organic solvents, with or without pigments~
coating compositions regardless of how formulated,
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whether a latex or an emulsion, a slurry, a suspension and the
like providing the gaseous effluent resulting therefrom
contains hydrocarbon and/or oxygenated paint solvents. The
gaseous effluent formed from the application of paint not only
inclu~es the application of the paint itself but the
volatilization of the solvent from the liquid paint during the
drying of the liquid paint. By "gas" is meant to include not
only a gas phase effluent but also an atomized paint overspray
formed during the application of the paint to a substrate.
10The most preferred gaseous effluent is one that
contains solvents for liquid paint which solvents are a mixture
of substances. In particular, a hydrocarbon substance and an
oxygenated substance.
~iquid paints are normally comprised of a resin
; film-former (natural or synthetic), pigments and a liquid
solvent. Suitable liquid paint solvents are aliphatic
alcohols from 1 to 8 carbon atoms such as methanol, ethanol,
isopropanol, n-butanol, octanol, and the like; aliphatic
ketones such as acetone, methylethyl ketone, methylisobutyl
ketone, diisobutyl ketone cyclohexanone and the like; esters
such as short chain aliphatic acids reacted with short chain
aliphatic alcohols where the total number of carbon atoms of
the acid and the alcohol is approximately 12, such as
ethylacetate, butyl acetate, and the like; hydrocarbon
solvents such as those containing up to 12 carbon atoms, as
hexane, octane, cyclohexane, xylene, toluene, benzene and
the like; aliphatic ethers and the like such as Cellosolve
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(trademark of Union Carbide for ethylene glycol monoethyl
ether), Cellosolve* acetate, butyl Cellosolve*, and butyl
Cellosolve* acetate and the like.
By "oxygenated" is meant organic solvents such as
those ~or paints that contain oxygen in the molecule of the
solvent either as an alcohol, a portion of an acid, an ester,
or an ether.
The paints or coating compositions with which the
present invention is concerned are those cont~ining film-
forming organic and natural resins such as hydrocarbon resins,epoxies (such as the reaction product of bisphenol and
epichlorohydrin), acrylics, polyesters, polyurethanes, alkyds,
vinyls, polyamides, ureas, melamines, polyimides, silicones,
polybenzimidazole and the like.
In the application of liquid paint to a substrate,
the paint is atomized, such as airless, by air or
electrostatically. The paint overspray from the paint spray
booth is collected in a water wash by a water curtain. The
paint applied to the substrate is then dried by passing it
through a heated chamber wherein the solvent is volatilized.
During both the application and the drying of the paint,
gaseous effluent is formed.
Prior to passing the gaseous effluent to the
atmosphere the effluent is then treated according to the
process of the present invention which is to sparge or bubble,
; or pass the gaseous effluent into a liquid absorbing means,
such as a liquid absorber which is a solvent for the gaseous
effluent.
* Trademark
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1013Z889
The liquid absorber with gaseous effluent therein
may be retained in a suitable reservoir or may be subsequently
collected and re-claimed as desired. The advantage of using
a liquid absorbing means is that it can be readily handled,
pumped, stored and reclaimed.
In its broadest aspect, the present invention is
concerned with utilizing in place of the water reservoir for
paint collection or the water curtain as is used currently i~
paint spray booth operations, the liquid absorbing means as is
described further. By having the liquid absorbing means of
the present invention employed as the overspray wash or the
reservoir for collection of paint overspray, one may simplify
the total pollution control of an industrial plant. In this
manner there need be no variation to the organic paint systems
that are currently employed, for one is concerned not with
modification of the paint system itself, bu~ rather the
absorption of the gaseous effluent and the most efficient,
economical reclamation of the liquid absorbing means.
In the normal operation of a paint spray booth
water wash, there is a curtain of water which washes the walls
of a painting zone or spray booth. The water may be sprayed
onto the walls or somehow collect the paint overspray. It is
contemplated by this invention that the water curtain would be
replaced by a curtain of liquid absorbing means described
herein. It is to be appreciated that a curtain of liquid
absorbing means need not be employed bu-t rather any application
technique such as spraying and the like which can collect the
paint overspray.
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32889
The liquid absorbing means of the presentinvention is one that is non-reactive wlth the gaseous
effluent. In addition, the liquid absorbing means
is one that is liquid and is substantially non-volatile
at ambient temperatures and pressures as well as
the temperatures and pressures in which the industrial
process and the reclamation of the organic solvent
is operable. The liquid absorbing means consists only
of carbon, hydrogen and oxygen.
Suitable liquid absorbing ~eans are those
having a vapor pressure of less than 1 mm Hg pressure at
68F. (20C.), most preferably less than 0.01 mm Hg.
Examples of said liquid absorbing means are polyoxyalkylene
glycol, preferably of the structure HO ~ R - O~ H where R
m
contains 2 to 4 carbon atoms and m ranges from 2 to 2000
as polyoxyethylene glycol, polyoxypropylene glycol,
polyoxybutylene glycol; saturated aliphatic polyols
having from 2 to 12 carbon atoms as glyc~rol, ethylene
glycol; dibasic esters such as the dialkyl (up to 8
carbon atoms per group~ esters of saturated aliphatic
polycarboxylic acids (up to 10 carbon atoms per
acid group), such as dialkyl oxalate, dialkyl malonate,
dialkyl succinate, dialkyl glutarate, dialkyl adipate,
dialkyl pimelate, dialkyl suberate, dialkyl azelate,
dialkyl sebacate and the like; saturated aliphatic
ketones such as diacetonealcohol, methyl heptyl ketone;
aromatic dicarboxylic acid esters such as dialkyl
phthalate of from 4 to 13 carbon atoms per alkyl group
as didecyl or dioctyl phthalate and the like; and non-
reactive mixtures thereof. The term "polyoxyalkylene~
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11~8~8~39
is meant to include compounds prepared by reacting ethylene
oxide, propylene oxide and/or butyl oxide together with or
without other co-reac-tants as alcohols, as long as there is
a-t least several ~ R - 0 ~ repeating linkages. It is to be
appreciated that other non-reactive substances may be added as
diluents or viscosity control agents to assist the fluidity
of the liquid. A preferred liquid absorbing means is a 50-50
mixture by volume of didecyl phthalate and a polyoxyalkylene
glycol (Ucon, LB - 65, Trademark of Union Carbide) having a
vapor pressure of less than 0.01 mm Hg pressure @ 68F. (20C,).
It is preferred that the liquid absorbing means
have as low a vapor pressure as possible. This will allow as
little of the liquid to be volatilized as possible during the
absorption of paint spray effluent.
The overall process of the present invention is
- described in Fig. 1 wherein the gaseous effluent is formed
at 10, which effluent is passed into a liquid absorbing means
containing a liquid absorber described herein. The outlet of
said liquid absorber permits the absorbed gaseous effluent to
be passed to a reclamation zone 14. In the reclamation zone,
the liquid absorber is separated from the gaseous effluent.
The liquid absorbing means is then recycled by means of line
16 back to the liquid absorber for subsequent utilization
therein. The gaseous effluent which is primarily solvent from
the liquid paint may then be used and re-processed in the
manufacture of liquid paint 18. If the gaseous effluent
formed at step 10 is other than paint solvent from the
~' application and drying of paint, the product resulting from
reclamation of the liquid absorber would then be disposed.
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One type of liquid absorber apparatus that may be
used in this invention is described and shown in Fig. 2 which
is a schematic diagram of a cyclonic spray scrubber 20 having
an air or yaseous inlet 22. The gas passing through inlet 22
is tangentially passed into the cyclonic chamber 24 which has
a liquid inlet 26 and a liquid outlet 27. The inlet 26 permits
the liquid absorber to be passed through a duct 28 and sprayed
through the spray manifold sections 30 comprised of a plurality
of nozzles. The top of the spray manifold is a core buster
disc 32.
The gas effluent from the industrial process enters
through the inlet 22 and circles around the cyclonic chamber
coming in direct contact with the sprayed liquid absorber 34,
which is a fine division of the liquid absorber permitting
a high surface area for the air to come into contact therewith.
} A very high efficiency is achieved in that substantially all
of the gaseous effluent containing undesirable pollutants is
absorbed in the liquid phase with the remaining gas exiting
through the anti-spin vanes 36. The liquid absorber is then
collected at the outlet 27 for subsequent processing at the
reclamation zone 14. The cyclonic chamber can be manufactured
from any metal stable to the gaseous effluent, e.g., stainless
steel, glass-lined metal chambers and the like. A series of
cyclonic chambers may be used to purify the gaseous effluent
in step-wise fashion by passing the effluent from each
cyclonic chamber to the next.
Cyclonic spray scrubbers described herein are
further described in Chemical Engineers Handbook, Fourth
Edi-tion, at page 18-33 and following.
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1082889
The reclamation zone is primarily directed towards
a means of separating the liquid absorber from the gaseous
effluent which is absorbed therein. Any means may be
employed to form the separation. Two principal techniques
are preferred. One is a vacuum distillation and the second
is the utilization of microfiltration. In the vacuum
distillation, it is highly preferred that there be a large
differential between the boiling point of the liquid absorber
and the gaseous effluent absorbed therein. If the
differential is at least 200F., then a high separation
efficiency can be achieved.
A more efficient technique for separating the
liquid absorber from the gaseous effluent may be through the
utilization of membranes which facilitate a microfiltration
approach. In other words, membranes are inserted in a
~' conduit through which the liquid passes. A low molecular
weight substance will pass therethrough whiLe a higher
molecular weight substance will be prevented from passing
therethrough.
Having described the invention in its broad aspect,
listed below are operative embodiments. All temperatures are
in degrees, Fahrenheit, and all percentages are percentages
by weight, unless otherwise indicated.
Examples
At ambient temperature and pressure, air was
bubbled through a bottle containing a typical acrylic paint
solvent made up of a mixture of Cellosolve* acetate, butyl
Cellosolve* acetate, acetone, aliphatic alcohols (up to C3)
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1082889
and aliphatic hydrocarbons (up to C~). The first bottle was
connected to a second and that to a third bottle with a liquid
absorber in each of the second and third bottles to a level of
2". The air with entrained gaseous effluent from the first
bot:tle was passed into bottles 2 and 3 under the surface of
the liquid therein. Listed on the following page in Table I
is a recital of the various liquid absorbing means used and
the percentage of gaseous effluent recovered at each stage.
* Trademark
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