Sulfonate and sulfate dispersants for the chemical processing industry

The invention provides a method for the inhibition of fouling in petrochemical processes. The method comprises adding from about 0.1 to about 10,000 parts per million sulfonated oils, sulfonated fatty acids, sulfated oils, sulfated fatty acids, or naphthalene sulfonate formaldehyde condensates to a petrochemical process to disperse water insoluble foulant into an aqueous system.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The addition of certain sulfated and sulfonated materials to the aqueous 
streams of a multiplicity of units in the chemical processing industry 
will inhibit the fouling of process hardware. These materials work by 
dispersing the foulant material in the stream and preventing deposition of 
the foulant throughout the system. The usefulness of this invention is 
illustrated by its application in ethylene plant caustic systems, styrene 
monomer production, acrylonitrile recovery systems, and the terephthalic 
acid purification process. 
2. Description of the Prior Art 
In ethylene plants, hydrocarbon feedstocks are thermally cracked with steam 
to produce ethylene. Other hydrocarbon species are also produced along 
with less desirable impurities. Among these impurities are carbon dioxide 
and hydrogen sulfide; the so-called acid gases. These are removed from the 
cracked gas stream in a caustic scrubbing tower. Water soluble salts, 
Na.sub.2 CO.sub.3 and Na.sub.2 S, are formed and are removed in a water 
separator. 
Another by-product produced in the cracking furnace is acetaldehyde. It 
arises from partial oxidation of ethylene. Due to its physical properties, 
acetaldehyde is carried with the cracked gas stream to the caustic 
scrubber tower. In this tower, acetaldehyde reacts with sodium hydroxide 
(caustic) to produce a homopolymer. This polymer is formed by 
self-condensation of acetaldehyde via the Aldol reaction. As the polymer 
grows, it becomes progressively less and less soluble in caustic. It 
eventually precipitates from solution and coats trays and other tower 
internal surfaces. Eventually, scrubbing efficiency is lost and the tower 
must be shut down and cleaned. 
One method of dealing with this problem is described in U.S. Pat. No. 5, 
160,425. This patent discloses use of carbohydrazide to derivatize 
acetaldehyde. This derivative will no longer react with caustic, and hence 
polymerization is stopped. Other compounds have been disclosed for this 
purpose as well. These are ethylenediamine, hydroxylamine salts and ethyl 
acetoacetate. Each of these compounds must be used in a stoichiometric 
ratio to the amount of acetaldehyde present. This is a costly method, 
however, and other more cost effective ways of treating this problem are 
continually being sought. 
Lignosulfonates have been used for over 25 years to disperse polymer of 
this nature into caustic systems. The exact structure of lignin is not 
known, but the basic subunit of the polymeric structure is phenylpropane. 
The water soluble derivative, lignosulfonate helps prevent fouling by 
inhibiting deposition of the homopolymer onto process hardware. We have 
discovered that other, water-soluble dispersants will disperse polymeric 
acetaldehyde in caustic. Since it was not previously known that these 
materials would perform as dispersants for this system, the present 
invention represents a novel technology for this application. 
A process used to purify terephthalic acid is described in volume 17 of the 
Encyclopedia of Chemical Technology. In this process, crude terephthalic 
acid is mixed with water to form a slurry. This slurry is passed through a 
heat exchanger and into a vessel called a dissolver. In the dissolver, the 
slurry is heated to a temperature greater than 250.degree. C. under enough 
pressure to keep water in the liquid phase. Under these conditions, 
terephthalic acid and its impurities are soluble in water. 
In practice, this process leads to fouling of the preheat exchanger. 
Deposit analyses of samples from the exchanger indicate that the foulant 
is terephthalic acid. This means that a small amount of product is not 
being held in the slurry and is simply being deposited on the heat 
exchanger. 
This problem is not successfully treated at this time. Even though 
terephthalic acid is an organic compound and not normally soluble in 
aqueous systems, it exists as an aqueous slurry until it reaches the 
dissolver. Therefore, any treatment must consist of a method of keeping 
terephthalic acid suspended in water. Thus, the addition of a 
water-soluble additive, capable of dispersing organic material into water, 
would be useful for the terephthalic acid process. 
In a styrene manufacturing process, ethylbenzene and steam are fed into a 
reactor. Ethylbenzene is dehydrogenated to form styrene in a catalytic 
process. The temperature is very high, reaching temperatures in excess of 
550.degree. C. From the reactor, crude styrene (containing unreacted 
ethylbenzene, steam and polymer) is cooled by a series of heat exchangers 
and enters an accumulator where condensed water and hydrocarbon are 
separated. Hydrocarbons flow out the top of this separator and are sent to 
the recovery section. Water flows out the bottom of this vessel and is 
sent to a hydrocarbon stripping tower where residual crude styrene is sent 
back to the separator. Water exits the bottom of this tower and is 
convened to steam for use in the reactor. 
In the heat exchanger system, the condensation patterns are such that 
polymer precipitates from the gas stream first. It comes in contact with 
the exchanger walls and adheres to them. Water is next to condense 
followed by crude styrene. Thus, crude styrene is unable to redissolve 
precipitated polymer in this system because of the aqueous interface, 
leading to fouling on the heat exchangers. 
This application is currently treated with an antioxidant. It is injected 
at the high temperature end of the heat exchanger train to help control 
formation of the polymer. However, some polymer is still formed. Addition 
of a dispersant would help move this polymer from the exchanger surface to 
the hydrocarbon layer and greatly improve operation of this unit. 
In one method for the manufacture of acrylonitrile, gaseous reactants from 
the gas phase ammoxidation of propylene are cooled from an initial 
temperature of about 400.degree.-510.degree. C. and are passed 
countercurrent to an aqueous stream of acid such as sulfuric acid, to 
neutralize and recover any ammonia present such as disclosed in U.S. Pat. 
No. 3,404,947 and U.S. Pat. No. 3,408, 157. The resultant gases which 
contain major amounts of nitrogen and acrylonitrile and minor amounts of 
hydrogen cyanide, acetonitrile, carbon dioxide, carbon monoxide, 
propylene, ammonia, water, oxygen, acrolein and certain other carboxylic 
acids, aldehydes, and nitriles, are contacted with water at a temperature 
of 1.degree.-40.degree. C. to form a solution containing less than about 
10 percent by weight acrylonitrile. The acrylonitrile (along with some 
water and hydrogen cyanide) is separated from any acetonitrile present by 
distillation and recovered overhead. Volatiles are separated from the 
resultant aqueous stream in a stripper. The bottoms from the stripper 
contain approximately 1 percent organic material as well as water-soluble 
polymers such as polyacrylic acid and its salts. These materials foul the 
surfaces of heat exchangers in the system, resulting in decreased 
production efficiencies. No technologies are currently practiced to 
alleviate this problem. The addition of an additive to disperse foulant 
material in the process would greatly improve the production of 
acrylonitrile by extending the time between cleanings of heat exchangers. 
SUMMARY OF THE INVENTION 
Materials of the invention include derivatives of oils and fatty acids from 
various natural origins (plant and animal sources). The oils are mostly 
comprised of acids that are primarily oleic (C.sub.18, monounsaturate) and 
linoleic (C.sub.18, polyunsaturate) acids but also include acids with 
carbon lengths of C.sub.16 to C.sub.22. It is shown by example that 
sulfated oils and sulfonated oils both work very effectively. It is also 
demonstrated that single component derivatives (i.e. sulfonated oleic 
acid) are also effective dispersants. Many other sulfur derivatized oils 
and fatty acids perform in a like manner, including carboxylic acids of 
different chain lengths and acids from a wide range of animal fats, fish 
oils, vegetable oils. These acids further include related fatty acids like 
ricinoleic acid (C.sub.18, monounsaturate) and erucic acid (C.sub.22, 
monounsaturate). 
Also included in this invention are materials that are neutralized, 
polymeric condensation products of naphthalene sulfonic acid and 
formaldehyde. These naphthalene sulfonate formaldehyde condensates may 
extend from a molecular weight of about X to about Y. The naphthalene 
portion may be sulfonated in either the 1 or 2 position. Methylene 
linkages typically connect the sulfonated naphthalene rings at positions 5 
or 8. The polymers may be neutralized with a variety of bases or mixture 
of bases including sodium, potassium, calcium, and ammonium hydroxide. The 
general structure of the naphthalene sulfonate formaldehyde condensate is 
--CH.sub.2 [C.sub.10 H.sub.5 (SO.sub.3 M)].sub.n --, where M may be 
Na.sup.+, K.sup.+, Ca.sup.+2, NH.sub.4.sup.+, or the like 
Since it was previously unknown that these materials would behave as 
antifoulants for petrochemical processes, this invention reveals novel 
technology for such applications. The invention is extremely cost 
effective and provides the chemical producer an opportunity to run a more 
economic process. The use of this invention also allows for increased heat 
transfer efficiency, longer run times, and safer operations. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
A method for preventing foulant deposition in petrochemical processes that 
produce water-insoluble foulant materials is disclosed. The method 
comprises dispersing the water-insoluble foulant into an aqueous system, 
wherein the aqueous system includes from about 0.1 to 10,000 parts per 
million sulfonated or sulfated fatty acid. The fatty acid is selected from 
the group consisting of tall oils, fish oils, animal fats, vegetable oils, 
synthetic oils, tall oil fatty acid, castor oil, rapeseed oil, soybean 
oil, oleic acid and linoleic acid. 
In the preferred method, the sulfonated tall oil fatty acids have a carbon 
length range of from about 16 to about 20 carbons. Preferably, the 
sulfonated fatty acids are included in the aqueous system in a 
concentration of from about 0.1 to about 1,000 parts per million. 
Preferably, the aqueous system of the invention is chosen from among 
caustic, quench water, wash water, extraction solvent, hydrocarbon steam 
condensate and terephthalic acid dissolver. Where the aqueous system is an 
extraction solvent, the extraction solvent may be selected from a number 
of such solvents including acrylonitrile extraction solvent, butadiene 
extraction solvent, isoprene extraction solvent and aromatics extraction 
solvent. Alternatively, the extraction solvent may be selected from water, 
water/acetonitrile, 1-methyl-2-pyrrolidinone/water, 
dimethylformamide/2furaldehyde/water, 
3-methoxypropionitrile/2-furaldehyde/water, glycols, and sulfolane. 
Further disclosed is a method for preparing acrylonitrile, the method 
comprising absorbing gaseous acrylonitrile from a gas phase ammoxidation 
reaction into a solvent, the solvent including from about 0.1 to about 
10,000 parts per million of a sulfonated carboxyl compound, recovering the 
acrylonitrile by distillation from the solvent and cooling and recycling a 
portion of the solvent. In the preferred method, the sulfonated carboxyl 
compound is selected from the group consisting of the sulfonated fatty 
acids which are derived from tall oils, fish oils, animal fats and 
synthetic oils. 
Yet another method disclosed by the invention is a method for preparing 
ethylene, the method comprising cracking hydrocarbon feedstocks in a steam 
cracker to produce ethylene and, after cooling and compression, removing 
acid gases from the gaseous products by washing with caustic, the caustic 
containing from about 0.1 to about 10,000 parts per million of a 
sulfonated carboxyl compound recovering ethylene by a series of 
distillations. Preferably, the ethylene preparation method utilizes 
sulfonated carboxyl compounds selected from the group consisting of the 
sulfonated fatty acids which are derived from tall oils, fish oils, animal 
fats and synthetic oils. 
In another embodiment, the invention comprises a method for preventing 
foulant deposition in petrochemical processes that produce water-insoluble 
foulant materials, the method comprising dispersing the water-insoluble 
foulant into an aqueous system, the aqueous system including from about 
0.1 to 10,000 parts per million naphthalene sulfonate formaldehyde 
condensate. Preferably, the condensate is of a molecular weight from about 
1000 to about 1 million daltons and are salts of sodium, potassium, 
calcium, ammonium hydroxide, and/or mixtures thereof. More preferably, the 
condensate is of a molecular weight from about 2500 to about 500,000 
daltons. Most preferably, the condensate is of a molecular weight from 
about 3000 to about 10,000 daltons. In the preferred embodiment, the mixed 
sodium/potassium salts of naphthalene sulfonate formaldehyde condensate 
are included in the aqueous system in the concentration of from about 0.1 
to about 1,000 parts per million. 
Preferably, the aqueous system is chosen from among caustic, quench water, 
wash water, extraction solvent, hydrocarbon steam condensate and 
terephthalic acid dissolver. Where the aqueous system is an extraction 
solvent, the extraction solvent may be selected from a number of such 
solvents including acrylonitrile extraction solvent, butadiene extraction 
solvent, isoprene extraction solvent and aromatics extraction solvent. 
Alternatively, the extraction solvent may be selected from water, 
water/acetonitrile, 1-methyl-2-pyrrolidinone/water, 
dimethylformamide/2-furaldehyde/water, 
3methoxypropionitrile/2-furaldehyde/water, glycols, and sulfolane. 
In another embodiment of the invention a method for preparing acrylonitrile 
is disclosed, the method comprising absorbing gas acrylonitrile from a gas 
phase ammoxidation reaction into a solvent, the solvent including from 
about 0.1 to about 10,000 parts per million of a naphthalene sulfonate 
formaldehyde condensate, recovering the acrylonitrile by distillation from 
the solvent and cooling and recycling a portion of the solvent. 
Preferably, the sulfonated carboxyl compound is of a molecular weight range 
of about 1000 to about 1 million and is the mixed sodium/potassium salt. 
More preferably, the condensate is of a molecular weight from about 2500 
to about 500,000 daltons. Most preferably, the condensate is of a 
molecular weight from about 3000 to about 10,000 daltons. 
Yet another embodiment of the invention comprises a method for preparing 
ethylene, the method comprising cracking hydrocarbon feedstocks in a steam 
cracker to produce ethylene and, after cooling and compression, removing 
acid gases from the gaseous products by washing with caustic, the caustic 
containing from about 0.1 to about 10,000 parts per million of a 
naphthalene sulfonate formaldehyde condensate and recovering ethylene by a 
series of distillations. 
Preferably, the sulfonated carboxyl compound is of a molecular weight range 
of about 1000 to about 1 million and is the mixed sodium/potassium salt. 
More preferably, the condensate is of a molecular weight from about 2500 
to about 500,000 daltons. Most preferably, the condensate is of a 
molecular weight from about 3000 to about 10,000 daltons.

The following examples are presented to describe preferred embodiments and 
utilities of the invention and are not meant to limit the invention unless 
otherwise stated in the claims appended hereto. 
EXAMPLE 1 
Sulfonates as Caustic Tower Dispersants 
Gum dispersancy tests (GDT) were used to evaluate the efficacy of 
dispersants for this application. Normally this test makes use of a 
combination of a solvent for the foulant and a non-solvent which closely 
resembles the stream in which the foulant is to be dispersed. A 
concentrated solution of the foulant is made using the solvent. A small 
amount of this solution is then added to a large amount of the 
non-solvent; causing the foulant to precipitate. Addition of an effective 
dispersant to the non-solvent should delay the onset of precipitation. In 
testing dispersants for caustic systems, it has been found that the best 
method is to grow the polymer in the presence of dispersant which has been 
dissolved in the non-solvent (in this case caustic). The following example 
will illustrate this test. 
Three graduated centrifuge test tubes were charged with 10 mL of a 10% 
aqueous solution of sodium hydroxide. Each tube was dosed with 1000 ppm of 
the appropriate sulfonate, and the tubes inverted 15 times to insure good 
mixing. Vinyl acetate was used as a latent form of acetaldehyde, and 250 
.mu.L of this ester was added to each tube. All three of the centrifuge 
tubes were stoppered and shaken vigorously until the tubes became warm to 
the touch. Ester hydrolysis is exothermic, and thus warm tubes were an 
indication that hydrolysis had taken place. Vinyl acetate hydrolysis 
products (in sodium hydroxide) are sodium acetate and vinyl alcohol which 
tautomerizes to acetaldehyde. 
The centrifuge tubes were then allowed to stand undisturbed as 
polymerization occurred. The results of this testing showed that, in the 
Blank (or untreated sample), the polymer has separated from the caustic 
and has floated to the top of the tube. In the other tubes the polymer was 
still dispersed throughout the caustic liquid. 
After standing for a longer time period, the Blank still showed the polymer 
floating at the top of the caustic. The tubes containing sulfonated oil 
and naphthelene sulfonate/formaldehyde copolymer showed signs of losing 
their dispersancy, while the lignosulfonate was still completely 
dispersing the polymer. The lignosulfonate appears to be effective over a 
longer period of time. However, the other sulfonated products are still 
effective dispersants for use in caustic systems. 
EXAMPLE 2 
Sulfonated Oleic Acid and Sulfates as Dispersants for Caustic Towers 
These products were evaluated in the same manner as the sulfonated oils 
above. In this test, sulfonated and sulfated oleic acid were compared to 
sulfated castor oil, rapeseed oil and soybean oil. As above each 
centrifuge tube was charged with 9 mL of 10% sodium hydroxide and 1 mL of 
a 1% solution of each dispersant. This gave a 10 mL solution containing 
1000 ppm of dispersant. Vinyl acetate was (250 .mu.L) was added to each 
tube. The tubes were capped and shaken to initiate ester hydrolysis. The 
tubes were allowed to stand undisturbed for three hours. Visual 
examination showed that the untreated sample had polymer which had 
agglomerated. All of the other tubes were still dispersing the polymer. 
However, on closer examination it could be seen that the tube containing 
sulfonated oleic acid was not as effective as the other compounds. As seen 
above, the polymer which had agglomerated floated to the top of the 
centrifuge tube rendering quantification difficult. 
EXAMPLE 3 
Sulfonates as Dispersants for the Terephthalic Acid Purification Process 
A gum dispersancy test (GDT) was used to evaluate efficacy of dispersants 
for this application. For this particular test, DMF was chosen as the 
solvent because it is a polar solvent which should dissolve phthalic acid 
and is itself soluble in water. The non-solvent for this test is typically 
the stream from which the deposit precipitates, in this instance water. 
Results of the GDT conducted using deposited phthalic acid from a purified 
terephthalic acid unit showed that the untreated sample (Blank) had just 
over 3 volume percent precipitate. The sample treated with lignosulfonate 
showed almost no precipitate formed in the sample. The sulfonated oil was 
not quite as effective as the lignosulfonate, but did show a good deal of 
dispersancy in this test. 
EXAMPLE 4 
Sulfonates as Dispersants for Styrene Monomer Production 
Since this polymer is absolutely insoluble in water, the 
solvent/non-solvent approach taken with the asphaltene dispersant test 
could not be taken. The polymer simply oils out and adheres to the side of 
the graduated centrifuge tube. Therefore, another approach was taken. 
A sample of polymer of undetermined volume or weight was placed on an 
inside edge of a rectangular 8 ounce glass bottle. A 25 mL aliquot of 
process water was added to the bottle, and it was dosed with 1000 ppm of 
the sulfonated dispersant. The bottle was laid on its side in a shaker 
bath. The bath was operated at low level for four hours. During this time 
the dispersant removed polymer from the side of the bottle and dispersed 
it in the water. Both sulfonated oil and lignosulfonates gave positive 
effects, however, the lignosulfonates were the more effective of the two 
sulfonated products. 
EXAMPLE 5 
Sulfonated Oleic Acid and Sulfates as Dispersants for Styrene Monomer 
Production 
A series of six eight ounce bottles were used for this experiment. In each 
bottle was placed an undetermined quantity of polymer. Aliquots (25 mL) of 
process water were added to each bottle which was then dosed with 1000 ppm 
of dispersant. The dispersants used were sulfonated oleic acid, sulfated 
oleic acid, sulfated castor oil, sulfated rapeseed oil, and sulfated 
soybean oil. As above the bottles were placed in a shaker bath which was 
operated at low level for four hours. In this experiment, the sulfonated 
oleic oil appears to have had the best effect (on a qualitative basis). In 
addition to solubilizing at least some of the polymer in water, this 
product was able to penetrate the deposit and remove it from the surface 
of the glass. Thus, this dispersant allows for better contact between the 
polymer and crude styrene. 
This result is different from that obtained with the sulfated products and 
the lignosulfonate discussed in Example 4. In the above example, 
lignosulfonates remove polymer from the top for the deposit. Visual 
examination showed this phenomenon clearly. In the instant Example, it is 
also clear that sulfonated oleic acid worked by penetrating the deposit 
and lifting it from the surface of the glass. 
EXAMPLE 6 
Sulfonates as Dispersants for Acrylonitrile Recovery 
A sample of stripper bottoms from an acrylonitrile unit was filtered by 
vacuum filtration to remove foulant from the stream. A small amount, about 
2.5 grams, of foulant was dissolved in a dimethylformamide/isopropanol 
solution so that the concentration was about 5% foulant. To three tapered 
centrifuge tubes was added 10 ml of stripper bottoms. Aliquots of an 
aqueous solution of sulfonated fatty acid from tall oil, available from 
Climax Performance Materials Corp., were added to two of the tubes. The 
dosage of antifoulant in tubes 1, 2, and 3 was 0, 50 and 125 ppm, 
respectively. The tubes were shaken to blend the additives in the stripper 
bottoms. Then 0.5 ml of the foulant solution was added to each tube. The 
tubes were capped and shaken. 
After 1 hour and 45 minutes, the foulants began to precipitate from tube 
number 1, (the Blank). No foulant was observed in tubes number 2 or 3. 
This demonstrates that the compound of the invention kept the foulant in 
solution, thus preventing the foulant from precipitating and fouling 
process equipment. 
EXAMPLE 7 
Sulfonated Oleic Acid as a Dispersant for Acrylonitrile Recovery 
An experiment with six graduated centrifuge tubes were set up as previously 
described in Example 6. Each tube contained 10 mL of filtered 
acrylonitrile stripper bottoms and an aliquot of an aqueous solution of 
sulfonated oleic acid, available from Witco. Tubes 1-6 contained 0, 50, 
100, 150, 200, and 250 ppm of the additive solution, respectively. To all 
of the tubes was then added 1 mL of a 1% DMF/isopropanol solution of 
foulant filtered from the stripper bottoms. After 30 minutes, solids began 
precipitating from the Blank (0 ppm). All of the other tubes were clear. 
After 60 minutes, 17 units of solids had settled to the bottom of the tube 
containing the blank solution. The 50 ppm solution contained 2 units of 
settled solids and all other tubes were clear. 
After 120 minutes, the amount of settled solids in the 0, 50, and 100 ppm 
tubes was 11, 9, and 1.5 units, respectively. All other tubes were clear. 
After 270 minutes, the amount of settled solids in the 0, 50, 100, and 150 
ppm tubes was 10, 10, 5.5, and 2.0 units, respectively. All other tubes 
were clear. 
After 20.5 hours, the amount of settled solids in the 0, 50, 100, 150, and 
200 ppm tubes was 9, 8, 3.5, 2.5, and 1.5 units, respectively. The 250 ppm 
tube was clear. 
This example illustrates that sulfonated oleic acid is effective at 
dispersing foulant in acrylonitrile bottoms. 
EXAMPLE 8 
Sulfates as a Dispersants for Acrylonitrile Recovery 
An experiment with five graduated centrifuge tubes was set up as previously 
described in Example 6. Each tube contained 10 mL of filtered 
acrylonitrile stripper bottoms and 100 ppm of one of the following: a 
sulfated castor oil, a sulfated oleic acid, a sulfated rapeseed oil, a 
sulfated soybean oil, all available from Climax Performance Materials, 
Corp. 
To all of the tubes was then added 1 mL of a 1% DMF/isopropanol solution of 
foulant filtered from the stripper bottoms. 
After 60 minutes, 8 units of solids had settled to the bottom of the tube 
containing the blank solution. All other tubes were clear. After 150 
minutes, the amount of settled solids in the blank was 5.5 units. The tube 
containing the sulfated oleic acid contained 0.75 units of settled solids. 
The other three samples remained clear. 
This example illustrates that sulfated oils from various sources are also 
effective as dispersants in the acrylonitrile recovery process. Also, the 
previous example had shown that sulfonated oleic acid is effective at 
dispersing foulant in acrylonitrile bottoms. The present example 
illustrates that the corresponding sulfated material is also effective. 
EXAMPLE 9 
Naphthalene Sulfonate Formaldehyde Condensates as a Dispersants for 
Acrylonitrile Recovery 
An experiment with five graduated centrifuge tubes was set up as previously 
described in Example 6. Each tube contained 10 mL of filtered 
acrylonitrile stripper bottoms and an aliquot of an aqueous mixture of the 
sodium and potassium salts of naphthalene sulfonate formaldehyde 
condensate, available from Hampshire. Tubes 1-4 contained 0, 50, 100, and 
250 ppm of the additive solution, respectively. To a fifth tube was added 
250 ppm of an aqueous solution of sulfonated oleic acid. To all of the 
tubes was then added 0.75 mL of a 1% DMF/isopropanol solution of foulant 
filtered from the stripper bottoms. 
After 30 minutes, solids began precipitating from the Blank (0 ppm). All of 
the other tubes were clear. After 72 hours, solids had precipitated from 
all of the samples except for the one containing 250 ppm of the 
naphthalene sulfonate formaldehyde condensate. Approximately 3 mL of 
solids had precipitated from the blank sample and from the sample 
containing sulfonated oleic acid. The two samples containing 50 and 100 
ppm of the naphthalene sulfonate formaldehyde condensate contained about 1 
mL of precipitated solids. 
Changes can be made in the composition, operation and arrangement of the 
method of the present invention described herein without departing from 
the concept and scope of the invention as defined in the following claims: