Extraction of N-methylpyrrolidone-2

Water or acidified water can be used to extract N-methylpyrrolidone from a mixture containing phenol and N-methylpyrrolidone. In one embodiment of this invention water or acidified water can be used to extract N-methylpyrrolidone from the kettle bottoms of the N-methylpyrrolidone recovery column of a poly(phenylene sulfide) polymerization process.

This invention relates to the extraction of N-methylpyrrolidone from a 
mixture containing phenol and N-methylpyrrolidone. An embodiment of this 
invention relates to the treatment of the kettle bottoms of an 
N-methylpyrrolidone recovery distillation column with water or acidified 
water to extract N-methylpyrrolidone. 
BACKGROUND 
The preparation of poly(phenylene sulfide) can be accomplished by heating 
p-dichlorobenzene in the presence of a partially dehydrated mixture of 
sodium sulfide and N-methylpyrrolidone as disclosed in U.S. Pat. No. 
3,354,129. U.S. Pat. No. 3,354,129 is incorporated by reference into this 
disclosure. After completion of the polymerization reaction, the 
poly(phenylene sulfide) can be recovered by flash evaporation of the 
volatile components, i.e., N-methylpyrrolidone, water, unreacted 
p-dichlorobenzene and volatile by-products of the polymerization reaction. 
U.S. Pat. Nos. 4,056,515 and 4,060,520 teach such a process and are 
incorporated by reference into this disclosure. A significant volatile 
by-product of the polymerization reaction is phenol. Other by-products 
include diphenyl ether and N-methyl-succinimide. 
In order to recover N-methylpyrrolidone the flashed volatiles are 
fractionated in two successive distillation processes. The flashed 
volatiles are first passed to a "lights column" where water, unreacted 
p-dichlorobenzene and the more volatile by-products are removed overhead. 
The less volatile by-products (including phenol, diphenyl ether and 
N-methyl-succinimide) and N-methylpyrrolidone accumulate at the bottom of 
the "lights column." These kettle bottoms are subsequently fed into an 
"N-methylpyrrolidone recovery column" which generally operates at a 
temperature higher than that of the first column. 
The overhead of the second recovery column is relatively pure 
N-methylpyrrolidone. Phenol, an impurity, accumulates at the bottom of the 
column so long as the phenol concentration in the kettle bottoms remains 
low (generally less than about 20 weight percent) and the temperature of 
the kettle bottoms remains low (generally below about 460.degree. F.). 
Above these levels the phenol codistills with N-methylpyrrolidone. Because 
N-methylpyrrolidone is recycled to the polymerization step and because 
phenol adversely affects polymerization, codistillation of the phenol is 
highly undesirable. 
It is well known that N-methylpyrrolidone (also called 
N-methyl-.gamma.-butyrolactam) and phenol form a 1:1 adduct as disclosed 
in the Journal of Organic Chemistry 29, 3122-3124 (1964) incorporated by 
reference herein. This adduct formation apparently explains why phenol 
accumulates in the kettle bottoms even though it has a lower boiling point 
than N-methylpyrrolidone. Under the distillation conditions of the 
"N-methylpyrrolidone recovery column" a considerable excess of 
N-methylpyrrolidone relative to the amount of phenol must be present in 
the column in order to preserve the thermal stability of the adduct. For 
this reason, a significant amount of N-methylpyrrolidone (about four times 
the amount of phenol) cannot be recovered by distillation since it must 
remain in the kettle bottom to bind phenol and thus prevent the phenol 
from distilling overhead and contaminating the N-methylpyrrolidone. This 
incomplete recovery is costly in that a valuable reagent is lost and 
kettle bottom disposal problems are magnified. 
SUMMARY OF THE INVENTION 
In brief summary, this invention resides in the use of water or acidified 
water to extract N-methylpyrrolidone from a mixture containing phenol and 
N-methylpyrrolidone such as the above-described kettle bottoms. 
OBJECTS OF THE INVENTION 
Accordingly it is an object of this invention to extract 
N-methylpyrrolidone from the kettle bottoms of an "N-methylpyrrolidone 
recovery column." 
More generally it is an object of this invention to extract 
N-methylpyrrolidone from a mixture containing phenol and 
N-methylpyrrolidone. 
These objects and other objects and advantages of the invention will be 
made apparent from a study of this disclosure and the appended claims. 
DETAILED DESCRIPTION OF THE INVENTION 
I have discovered a method whereby a substantial portion of the 
N-methylpyrrolidone content of the kettle bottoms of an 
"N-methylpyrrolidone recovery column" can be recovered by extraction with 
water or acidified water. As compared to phenol and the other by-products 
or impurities, a disproportionately larger percentage of 
N-methylpyrrolidone is dissolved in the water. In other words, after 
extraction, comparison of the resultant aqueous phase to the resultant 
organic (or oil) phase reveals that the weight percentage ratio of 
N-methylpyrrolidone to phenol and other impurities is greater in the 
aqueous phase than in the organic (or oil) phase. Separation of water and 
N-methylpyrrolidone can be accomplished by fractional distillation in the 
"lights column" or by extraction with a suitable organic material not 
miscible with water. 
The scope of this invention is not limited to application in a 
poly(phenylene sulfide) process but includes the extraction of 
N-methylpyrrolidone from any mixture comprising phenol and 
N-methylpyrrolidone. 
By using acidified water, more N-methylpyrrolidone can be extracted per 
unit of extracted phenol, i.e., the weight percentage ratio of extracted 
N-methylpyrrolidone to extracted phenol can be increased. The acidified 
water generally extracts more of the other by-products or impurities and 
as a result the overall weight percentage of N-methylpyrrolidone in the 
extracted aqueous phase may be slightly less than with non-acidified 
water. This, however, may not be an unacceptable price to pay for 
improving, i.e., increasing, the N-methylpyrrolidone to phenol ratio in 
the extracted aqueous phase because phenol is the least desirable impurity 
and is believed to be the most difficult to separate from 
N-methylpyrrolidone. 
If it is desired to use acidified water it is currently preferred to 
acidify the water with acetic acid because this acid is a weak acid and is 
readily available. Persons of ordinary skill in the art will easily 
recognize other suitable acids. Accordingly, the scope of this invention 
is not limited to any specific acid but rather embraces all acids 
recognized by those skilled in the art to be useful for the intended 
purpose. 
The invention can be successfully practiced by using conventional 
liquid-liquid extraction techniques. Since extraction utilizes differences 
in the solubilities of the components it is desirable that the water and 
the N-methylpyrrolidone and phenol-containing solution be brought into 
good contact to permit transfer of material. The extraction may be 
conducted batchwise or continuously. Examples of suitable extraction 
equipment include mixer-settlers, spray columns, packed columns, 
perforated-plate columns, baffle columns, and agitated towers. 
The amount of water used will depend upon the extraction technique and 
equipment employed and upon other constraints and objectives. It is 
generally contemplated that the weight percentage ratio of water to 
N-methylpyrrolidone will range from about 20:1 to about 1:2 but the scope 
of this invention is not limited thereby. The presently preferred range is 
about 8:1 to about 2:1. 
Successful practice of the invention is contemplated at, but not limited 
to, extraction temperatures ranging from about 50.degree. F. to about 
250.degree. F. and extraction pressures ranging from about 0 to about 200 
psig. Given this disclosure, optimum temperature, pressure and other 
operational parameters can be determined by a skilled practitioner of the 
art. The essence of this invention is found in the use of water or 
acidified water to extract a disproportionately greater percentage of 
N-methylpyrrolidone from a mixture containing phenol and 
N-methylpyrrolidone.

The following examples illustrate the practice of my invention and 
demonstrate its operability. 
EXAMPLE I 
The experimental runs of this example involve the extraction of the kettle 
bottoms of an "N-methylpyrrolidone recovery column" with water. The 
results demonstrate that the weight percentage ratio of extracted 
N-methylpyrrolidone to extracted by-products or impurities in the aqueous 
extraction phase is greater than in the kettle bottoms. This is 
particularly significant with respect to the N-methylpyrrolidone to phenol 
weight percentage ratio. 
A sample of the "N-methylpyrrolidone recovery column" kettle bottoms of the 
Ryton.RTM. polyphenylene sulfide plant of Phillips Petroleum Company was 
analyzed employing a Perkin Elmer Sigma 3 gas chromatograph filled with 6% 
K20M (Carbowax poly(ethylene glycol)) on 35/60 mesh Chromasorb T (See run 
1). Subsequently, 100 ml of the oily kettle bottom content was added to 
various amounts of water. After stirring the system for 15 minutes and 
allowing it to settle, the aqueous layer was decanted from the oil layer 
through a filter and also analyzed by a Perkin Elmer Sigma 3 gas 
chromatograph. 
The peak areas obtained by employing a gas chromatography detector not 
responsive to water were used to calculate the weight percentages of the 
principal impurities in N-methylpyrrolidone. This data is summarized in 
Table I. The data clearly show that the weight percentage of 
N-methylpyrrolidone in the water extract was greater than in the oil 
phase. Conversely, the weight percentage of phenol and other impurities in 
the water extract was less than in the oil phase. It therefore follows 
that the affinity of water for N-methylpyrrolidone is greater than the 
affinity of water for phenol and the other impurities. 
TABLE I 
__________________________________________________________________________ 
1 2 3 4 5 
Run (Control) 
(Invention) 
(Invention) 
(Invention) 
(Invention) 
__________________________________________________________________________ 
Amount of added water, ml 
0 100 200 300 500 
Amount of N--methylpyrrolidone 
in water phase, weight %.sup.(a) 
-- 82.02 85.13 85.19 87.50 
in oil phase, weight % 
66.24 
-- -- -- -- 
Amount of Phenol: 
in water phase, weight %.sup.(a) 
-- 13.61 12.38 12.43 9.61 
in oil phase, weight % 
16.91 
-- -- -- -- 
Amount of Diphenyl ether: 
in water phase, weight % 
-- 0.59 0.35 0.34 0.43 
in oil phase, weight % 
1.94 -- -- -- -- 
Amount of N--Methylsuccinimide: 
in water phase, weight %.sup.(a) 
-- 0.29 0.23 0.17 0.35 
in oil phase, weight % 
0.51 -- -- -- -- 
Amount of Others, mainly Unknowns: 
in water phase, weight %.sup.(a) 
-- 3.49 1.91 1.87 2.11 
in oil phase, weight % 
14.40 
-- -- -- -- 
Weight % ratio 3.92 6.03 6.88 6.85 9.11 
of N--methylpyrrolidone 
to phenol 
Weight % ratio of 1.96 4.56 5.72 5.75 7.00 
N--methylpyrrolidone to 
all impurities 
(including phenol) 
__________________________________________________________________________ 
.sup.(a) determined on a waterfree basis, i.e., as weight percentage of 
solutes in water 
EXAMPLE II 
Runs 6 and 7 of this example relate to the extraction of 
N-methylpyrrolidone from the kettle bottom content of an 
"N-methylpyrrolidone recovery column" with acidified water. In both cases 
acetic acid was added to the aqueous extractant. Extraction and analysis 
procedures were the same as in Example I. 
The data in Table II indicate that although slightly less 
N-methylpyrrolidone, on a weight percentage basis, was extracted in runs 6 
and 7 (acidified water) than in run 5 (non-acidified water) the 
N-methylpyrrolidone to phenol weight percentage ratio was improved (i.e., 
increased) in the latter runs. Because phenol is the most difficult 
impurity to separate from N-methylpyrrolidone, especially in a subsequent 
fractionation step, the acid serves a useful purpose. 
TABLE II 
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1 5 6 7 
Run (Control) 
(Invention) 
(Invention) 
(Invention) 
__________________________________________________________________________ 
Amount of added water, ml 
0 500 500 500 
Amount of acetic acid in water, ml 
-- 0 5 10 
Amount of N--methylpyrrolidone 
in water phase, weight %.sup.(a) 
-- 87.50 87.43 87.13 
in oil phase, weight % 
66.24 
-- -- -- 
Amount of Phenol: 
in water phase, weight %.sup.(a) 
-- 9.61 8.82 8.96 
in oil phase, weight % 
16.91 
-- -- -- 
Amount of Diphenyl ether: 
in water phase, weight %.sup.(a) 
-- 0.43 0.50 0.52 
in oil phase, weight % 
1.94 -- -- -- 
Amount of N--Methylsuccinimide: 
in water phase, weight %.sup.(a) 
-- 0.35 0.30 0.30 
in oil phase, weight % 
0.51 -- -- -- 
Amount of Others, mainly unknowns: 
in water phase, weight %.sup.(a) 
-- 2.11 2.95 3.09 
in the oil phase, weight % 
14.40 
-- -- -- 
Weight % ratio of 3.92 9.11 9.91 9.72 
N--methylpyrrolidone to 
phenol 
Weight % ratio of 1.96 7.00 6.96 6.77 
N--methylpyrrolidone to 
all impurities 
(including phenol) 
__________________________________________________________________________ 
.sup.(a) determined on a waterfree basis, i.e., as weight percentage of 
solutes in water 
The examples have been given to illustrate the practice of my invention and 
should not be interpreted to limit its scope. 
Reasonable variation from and modification of my invention as herein 
disclosed and not departing from the essence thereof are contemplated to 
be within the scope of patent protection desired and sought.