Methods of separating lignin solids and black liquor from tall oil fatty acids

The separation of black liquor, containing lignin, from tall oil is enhanced by the addition of a separation aid. The separation aid is an alkylphenol-formaldehyde resin alkoxylate, a poly (proplyene oxide) ethoxylate, an alkanol amine condensate, or combination thereof.

FIELD OF THE INVENTION 
The present invention relates to improvements in the production of tall oil 
fatty acids from crude tall oil soap skimmings. More particularly, the 
present invention relates to a method of improving the separation of 
lignin solids and black liquor from tall oil fatty acids through addition 
of a separation aid to crude tall oil soap skimmings. 
BACKGROUND OF THE INVENTION 
In the production of paper by the kraft process, black liquor results from 
the cooking of pulp wood in an alkaline solution. The black liquor is a 
source of lignin and tall oil. These materials are recovered from the 
black liquor by acidification of soap skimmings, cooking and separation. 
The skimmed soap separated from black liquor consists of a mixture of 
emulsified tall oil soaps and lignin. This mixture is cooked, in the 
presence of an acid, and is separated by decantation or centrifuge. 
The use of water soluble, typically anionic dispersants such as condensed 
naphthalene sulfonic acid sodium (available as Tamol SN from Rohm & Haas), 
short-chain acetylenic glycols, tannic acids, lignosulfonates, and 
hexametaphosphates is known to aid the separation of the tall oil and the 
lignin. Such a process is described in U.S. Pat. No. 2,802,845. In this 
process, the dispersant by dispersing the soap into the acid, accelerates 
its acidification and thereby enhances the separation process. 
However, it has been found that such prior processes do not provide for a 
complete separation of the black liquor lignin mixture from the tall oil. 
The carryover of black liquor lignin into the tall oil decreases the 
quality of tall oil produced. 
SUMMARY OF THE INVENTION 
The present inventor discovered that the separation of tall oil from lignin 
solids and black liquor could be enhanced by the addition of specific 
non-dispersing oil or water soluble surfactants into the system. It was 
discovered that the addition of specific classes of nonionic, oil soluble 
surfactants or cationic water soluble surfactants to a tall oil separator 
system enhanced the separation of lignin solids and black liquor from the 
tall oil. The surfactants used in the method of the present invention 
include alkyl phenol-formaldehyde resin alkoxylates, poly (propylene 
oxide) ethoxylates and alkanol amine condensates. The surfactants can be 
added to a tall oil separator system at the evaporators, the acidulator, 
the cooker or any other appropriate feedpoint. The surfactants of the 
methods of the present invention can be employed alone or in combination 
with prior art tall oil separator treatments such as water soluble, 
anionic dispersants. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a paper mill which employs the kraft process, tall oil can be recovered 
from the black liquor by a continuous acidification of the soap skimming. 
The soap skimmings separated from the black liquor consist of a mixture of 
emulsified tall oil soaps and lignin. In the prior art, water soluble, 
anionic dispersants were added to such emulsions to aid separation. Such 
dispersants were added to the acidic aqueous phase to preferentially water 
wet and intensify the repulsive anionic change on the lignin fraction 
allowing an improved separation of the tall oil from the lignin, now 
dispersed in the aqueous black liquor. The present inventor discovered 
that specific classes of water or oil soluble surfactants markedly 
improved the separation of the tall oil from the aqueous black liquor when 
added to a tall oil recovery system. The oil or water soluble surfactants 
of the present invention can be added at any point in a tall oil recovery 
process including but not limited to the soap/black liquor mixture, at the 
acidification stage or prior to separation. The oil or water soluble 
surfactants of the present invention may be employed alone or in a 
combination as well as with prior art treatments such as dispersants or 
napthalene sulfonate condensates. 
The oil soluble, nonionic surfactants of the present invention include 
alkyl phenol-formaldehyde resin alkoxylates and poly (propylene oxide) 
ethoxylates. The water soluble, cationic surfactants include alkanol amine 
condensates. The alkyl phenol-formaldehyde resin alkoxylates useful in the 
present invention can include t-butyl, t-amyl and nonylphenol-formaldehyde 
resin ethoxylates preferably in the 1000 to 5000 MW range made from the 
acid or base catalyzed condensation of alkylphenol and formaldehyde 
followed by base catalyzed reaction with 25-75% ethylene oxide. The poly 
(propylene oxide) ethoxylates useful in the method of the present 
invention can include propylene oxide/ethylene oxide block copolymers 
preferably in the 2000 to 10,000 MW range made from the base catalyzed 
reaction of propylene oxide with propylene glycol, glycerine, 
trimethylolpropane or ethylene diamine followed by further reaction with 
20-60% ethylene oxide. The alkanol amine condensates useful in the method 
of the present invention can include condensates of mono-, di- or 
tri-ethanolamine. These classes of surfactants, alone and in combination, 
were found to enhance the separation of lignin and black liquor from tall 
oil in a kraft paper mill tall oil recovery process. 
The oil or water surfactants used in the method of the present invention 
are added to a tall oil recovery process in an amount sufficient to 
provide the desired separation of ligniniblack liquor from the tall oil. 
It has been found that effective separation can be accomplished by 
treatment amounts ranging from about 50 to 1000 parts treatment per 
million parts total fluid. Preferably treatment amounts from about 410 to 
1000 parts per million when added to the soap skimmer and 50-200 parts per 
million when added to the cooker. The temperature of the treatment can 
range from about 30.degree.-300.degree. F., preferably 
1500.degree.-300.degree. F. 
The present invention will now be further described with reference to a 
number of specific examples which are to be regarded solely as 
illustrative and not as restricting the scope of the present invention.

EXAMPLE 1 
Samples from the soap skimmer outlet of a tall oil separator process at a 
Southern U.S. kraft paper mill were gathered. Seventy-five milliliter 
portions were treated with the treatments as set forth in Table 1. The 
treated samples were mixed, heated to 190.degree. F., shaken, and then let 
stand to determine the rate at which soap rose to the top of the black 
liquor. The samples were then centrifuged for ten minutes. The volume of 
sediment, black liquor and brown soap was recorded. The results are 
tabulated in Table 1. (Total volume exceeds 75 mL because of air entrained 
in the soap.) 
TABLE 1 
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Dose Break Rate 
Volume After Centrifuge (mL) 
Treatment 
(ppm) (min) Sediment 
Liquor Soap 
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A 1000 &gt;10 0.15 39.5 50 
B 1000 1 0.30 40.0 50 
C 1000 &gt;10 N/T N/T N/T 
D 1000 3 N/T N/T N/T 
Control -- &gt;10 0.13 39.0 50 
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N/T = not tested 
The data of Table 1 shows that surfactants of the present invention can 
accelerate the rate of separation of black liquor and improve the 
sedimentation of lignin from saponified tall oil soaps. 
EXAMPLE 2 
Samples of soap fed to the cooker of a tall oil separator process at a 
Southern U.S. kraft paper mill were gathered. Seventy-five milliliter 
portions were treated with the treatments as set forth in Table 2. These 
samples were heated to 210.degree. F. then shaken at high speed for 2.5 
hours with a 16% sulfuric acid solution at a 3:1 soap:acid ratio. The 
clarity of the phases and the rate at which they separated was recorded. 
The samples were centrifuged for two minutes at 210.degree. F. The amount 
of sediment, free water and tall oil continuous layers were recorded. The 
clarity of the water and apparent cleanness (absence of lignin) of the 
sulfuric acid/tall oil interface was recorded. The quality of the tall oil 
was checked by thiefing 6.25 mL from the middle of the oil phase, cutting 
50/50 with toluene and centrifuging for 10 minutes at high speed. The 
residual sediment and water were recorded. Table 2 summarizes the results. 
TABLE 2 
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Dose Acid 
Break Rate 
Sed. 
Acid 
Oil 
I/F Res. 
Treatment 
(ppm) 
Clarity 
(min) (mL) 
(mL) 
(mL) 
Clean. 
Sed. + H.sub.2 O 
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A 100 Lt. 1 3 43 27 2 1.0 
B 40 Dk. 5 3 43 25 4 not run 
B 80 Dk. 2.5 3 45 24.5 
2.5 0.8 
B 96 Dk. 2 2 43 26 4 1.6 
C 150 Lt. 4 4.5 
45 22.5 
3 0.5 
D 75 Lt. 2 5 45 24 1 0.4 
D 150 Lt. 1 6 45 23 1 0.35 
D 180 Lt. 2 4 44 25 2 0.6 
control 
-- Dk. 4 3 45 23 4 1.33 
D/B 120/32 
Lt. 1 3 43 28 1 0.6 
D/B 90/48 
Lt. 1 3 44 26 2 0.6 
D/B 90/105 
Lt. 1 4 44 26 1 0.6 
D/B/E 
60/32/70 
Lt. 1 2 44 27 2 0.8 
B/E 48/105 
Dk. 3 3 44 25 3 1.6 
E 210 Dk. 4 3 44 25 3 1.6 
__________________________________________________________________________ 
Sed.=sediment; I/F clean=interface cleanness (mL of lignin); Res. 
Sed.+H.sub.2 O=thiefed residual sediment and water (mL), Lt.=light, 
Dk.=dark. 
The data of Table 2 shows that the surfactants of the present invention 
significantly accelerated the rate, increased the amount, and improved the 
interfacial quality of the separation of black liquor and lignin from tall 
oil fatty acid in sulfuric acid solutions. 
Table 3 summarizes the treatments tested. 
TABLE 3 
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Treatment 
Description 
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A poly(propyleneglycol) ethoxylate, water or oil solvent base 
B ethanolamine condensate, water solvent base 
C nonylphenol-formaldehyde resin ethoxylate, oil solvent base 
D blend of nonylphenol-formaldehyde resin ethoxylates and 
poly(propylene glycol) ethoxylates, oil solvent base 
E naphthalene-formaldehyde sodium sulfonate salt (Tamol SM, 
available from Rohm & Haas) 
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While the present invention has been described with respect to particular 
embodiments thereof, it is apparent that numerous other forms and 
modifications of this invention will be obvious to those skilled in the 
art. The appended claims and this invention generally should be construed 
to cover all such obvious forms and modifications which are within the 
true spirit and scope of the present invention.