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Патент USA US3051772

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United States Pater
Patented Aug. 28, 1962
reaction temperature at which it was for-med (usually
Gordon MacBeth and Robert G. Heitz, Concord, Calif.,
assignors to The Dow Chemical Company, Midland,
Mich., a corporation of Delaware
N0 Drawing. Filed June 2, 1958, Ser. No. 738,936
2 Claims. (Cl. 260-623)
about 240° C.) and under a pressure at least suf?cient to
maintain it in the liquid state (usually about 250-600
p.s.i.) while any liquid or solid organic phase (uncon
verted hexachlorobenzene) is mechanically separated and
the solution is acidi?ed by the addition of a suitable acid,
such as sulfuric, hydrochloric or the like. The liberated
pentachlorophenol promptly separates as a clean-cut
This invention relates to the production of pentachloro
lower layer and can be mechanically separated from the
phenol by the alkaline hydrolysis of hexachlorobenzene. 10 aqueous brine layer. Suitably, it can be led directly to
The alkaline hydrolysis of hexachlorobenzene to pro
duce pentachlorophenol is a well known process. A pre
- to ‘form a solid product having the desired physical form.
ferred mode of conducting the hydrolysis comprises heat
Since pentachlorophenol is somewhat heat-sensitive under
?aking rolls, spray towers or other means ‘for cooling it
ing hexachlorobenzene with an excess of aqueous caustic
the conditions inherent in the process and darkens in
at a temperature of about 240° C. and a pressure of about 15 color if held in the molten state for long periods, it is
500-600 p.s.i., effective contact between the two phases
preferred that the temperature and time in the molten
being obtained by use of vigorous agitation and/or a
state be held to a practical minimum.
surface-active dispersing agent. This yields an aqueous
The practice of the invention is illustrated by the fol
alkaline reactor e?luent solution of alkali metal penta
lowing example.
chlorophenate from which pentachlorophenol is com 20 The aqueous alkaline solution of sodium pentachloro
monly liberated by ‘acidifying the cooled aqueous solu
phenate from the conventional hydrolysis of hexachloro
tion. A ?ltration step may precede the acidi?cation.
benzene was received from the reactor at 240° C. and
The product is thus obtained as a solid precipitate which
575 p.s.i. This was partially ?ashed to reduce it to 208°
may then be isolated by ?ltration, extraction by use of
C. ‘and 250 p.s.i. and was then clari?ed by ?ltration. The
an organic solvent, or similar means. All of these meth 25 calculated amount of concentrated hydrochloric acid to
ods for the isolation of the product from the reactor
reduce the pH to about 4.9 was then added with adequate
e?luent have been unsatisfactory in that they are tedious
agitation. After acidi?cation the agitation was stopped,
and expensive or they yield an impure product or both.
whereupon a prompt, clean-cut separation into a lower
Accordingly, it is an object of this invention to pro
oil-phase and an upper brine-phase occurred. The
vide simple, economical and effective methods for iso 30 former was bled off and fed directly to a water-cooled
lating pentachlorophenol from the aqueous alkaline re
?aking roll, after which the brine layer was ?ashed to
actor e?iuent solutions in which it is obtained by the
produce process steam. The ?aked product assayed 100
hydrolysis of hexachlorobenzene. Other objects will ap
percent by titration, and chloride analysis showed only
0.04 percent as sodium chloride. The yield in this step
pear hereinafter.
According to the invention, pentachlorophenol is ob 35 was 92 percent of the theoretical. The residual brine,
tained in good purity, ‘and in a physical form easily
after ?ashing and cooling to room temperature, contained
handled and used, by acidifying the aqueous alkaline re
a precipitate which was ?ltered out and ‘found to be penta
actor e?luent liquor while the latter is at a temperature
chlorophenol (8 percent of theory). This could be used
above the melting point of the product. In this way, the
as such or recycled to the neutr-alizer ‘for conversion to
product is obtained as a molten organic layer that is 40 ?aked form.
easily separated from the accompanying aqueous brine
without necessity of ?ltration, solvent extraction or other
We claim:
1. In a process for making pentachlorophenol by the
expensive process step. The molten pentachlorophenol
alkaline hydrolysis of hexachlorobenzene wherein there
thus obtained may be ?aked on suitable rolls; solidi?ed
is formed an aqueous alkaline solution of pentachloro
in mass; with or without subsequent grinding to the de 45
phenol at a temperature above about 190° C. and a pres
sired degree of ?neness; sprayed into a stream of cool
sure at least suf?cient to maintain the materials in the
gas to solidify it in the form of discrete particles; dropped
liquid state, the steps comprising isolating the pentachloro
into a body of cool, non-solvent liquid; or otherwise re
phenol from the aqueous solution by acidifying said solu
duced to the desired physical form.
Any unconverted hexachlorobenzene, being insoluble 50 tion, thus to form a molten pentachlorophenol phase and
an aqueous brine phase, and separating said phases.
in aqueous caustic, is present in the reactor effluent as a
2. A process as de?ned in claim 1 wherein the tem
separate phase which is liquid above about 225° and
perature is about 190 to 240° C. and the pressure is
solid below that temperature. It may be separated from
about 250 to ‘600 p.s.i.
the caustic liquor by suitable mechanical means; e.g., by
?ltration at temperatures below about 225° or by de 55
References Cited in the ?le of this patent
cantation at higher temperatures.
In a preferred embodiment of the invention, the aque
ous alkaline solution of pentachlorophenol formed in the
Bruce _______________ __ Aug. 14, 1951
reactor is maintained at a temperature between the melt
Nicolaisen ___________ __ July 17, 1956
ing point of pentachlorophenol (about 190° C.) and the 60 2,755,307
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