Note: Descriptions are shown in the official language in which they were submitted.
1040~59
This invention relates to a process for the production of
hydroquinone by the hydrogenation of nltrobenzene to an amino product and
the hydrolysis o~ the amino product to hydroquinone.
Hydroquinone is a widely used organic reducing agent. It
has the characteristic o~ being easily oxidized to quinone and the quinone-
like products. The principal large scale use of hydroquinone is as a
photographic developer. Hydroquinone also inhlbits the autoxidation of
various materials and is used as an antioxidant for substances such as
ats, oils, whole milk powders, vitamins, and the like.
Hydroquinone has been produced heretofore commercially by
the oxidation of aniline in sulfuric acid with manganese dioxide or sodium
dichromate to quinone and the reduction of the quinone with iron dust in
water to hydroquinone. Other suggested methods of production have included
the hydrolysis of p-halogenated phenols with aqueous alkali metal hydro-
xide solutions and the electrolytic oxidation of benzene to quinone in
sulfuric acid and the later reduction of the quinone to hydroquinone.
According to this invention hydroquinone ls made from nitro-
benzene by hydrogenating the nitrobenzene in an aqueous acid medium and in
the presence of an acid resistant reducing catalyst at an elevated tempera-
ture of 130 to 160 C. with hydrogen at an elevated pressure until hydrogen
absorption by the reaction ceases, the acid and nitrobenzene being present
in at least effective molar quantities; steam distilling the reaction
medium to remove residual nitrobenzene; filtering the catalyst from said
reaction medium; adding sufficient water to provide 40 to 90 moles of
water per mole of nitrobenzene initially present; maintaining the aqueous
reaction medium at a temperature of 200 to 300C. ~preferably from 200 to
260C.) for a time sufflcient to hydrolyze the hydrogenated product to
hydroquinone; cooling the aqueous reaction medium; and extracting the
hydroquinone from the cooled aqueous product solution with an organic
water-immiscible ~olvent.
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1(~4~659
The start~ng ~te~al ~or uSe ln the present inVention is
nitrobenzene. Two grades of nitrobenzene are commerclally available:
Nitrobenzene (a technical undistilled product) and oil of mirbane (distilled
nitrobenzene). The small amounts of hydrocarbons, both benzene and -
paraffins, and traces of m-dinitrobenzene, nltrophenol, and water that
constitute the impurities in the technical grade do not appreciably affect
the process. The oil of mirbane grade has a purity (by freezing point)
better than 99.5%.
The acid characteristic of the acid medium may be provided
by either phosphoric acld, sulfuric acid, or ammonium bisulfate and either
may be of commercial grade. ~monium bisulfate has the advantage that`the
ammonium compound that results from the hydrolysis may be regenerated
and reused. The acld producing ingredient, phosphor~c acid, sulfuric acid,
or ammonium bisulfate, is diluted with water to a concentration of in- -
grçdient which may range from }0 to 50% by weight of the aqueous medium.
The effective molar quantity of the ingredient is normally about 1.2 to
10 moles based upon the moles of nitrobenzene.
The nitrobenzene is most.effectively dispersed in the
aqueous medium by agitation. Initially, the nitrobenzene-aqueous medium
system in the reaFtor is a two-phase system; but when the solid catalyst
is added, the system becomes a three-phase system. The nitrobenzene can
be either the upper liquid phase or the bottom liquid phase, depending
upon the concentration of the ingredient employed. For example, concentra-
tions of ammonium bisulfate above 20% have a speclfic gravity greater than
that of nitrobenzene. As the nitrobenzene hydrogenates, the resulting
aniline, para-aminophenol, and other compounds dissolve in the aqueous
acid solution so that at the completion of hydrogenation only a single
liquid phase is present. This single liquid phase is a water white
~olutio~ that 910wly darkens in the presence of air.
The catalytic hydrogenation of nitrcbenzene in acidic
aqueous mediums is known and is believed to involve the formation of an
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1040659
intermediate product beta-phenylh~droxyla~ine which is rearranged to form
para-amlnophenol and anlllne. The catalyst, of course, must be an acld
resistant hydrogeneration catalyst. Sultable catalysts include the
platinum and platinum on carbon that are conventionally used in the con-
version of nitrobenzene to p-aminophenol, platinum sulfide on carbon,
molybdenum sulfide on carbon, and molybdenum sulfide. While the conven-
tional catalysts such as platinum catalysts are well sulted for the pre-
paratlon of commercially significant quantities of p-aminophenol, they are
capable of further hydrogenating the p-aminophenol to alicyclic compounds
which are undesirable by-products; particularly where hydrogenation takes
place in the presence of a high quantity of platinum catalysts, and the
nitrobenzene usually cannot be hydrogenated to completion wlthout over-
hydrogenatlon by use of platinum catalysts. Thus, the process should be
stopped prlor to completion to avoid the formation of undesired alicyclic
compounds. Conventional platinum catalysts are easily poisoned and
generally are not reusable. One catalyst which ls suitable in the process
of this invention comprises molybdenum sulfide-on-carbon. This catalyst
(a) is capable of complete hydrogenatlon of nitrobenzene without the
possibllity of over-hydrogenation and with the consequential ellmination of -
the usual nitrobenzene recovery step, (b) ls not readily poisoned during
the preparation of p-aminophenol and (c) is reusable many times before
loss of activity. Also a molybdenum sulfide-on-carbon catalyst permits
the higher temperatures to be employed during hydrogenation that are -
preferable, e.g. 155 C. and above, since the rearrangement of the inter-
mediate b-hydroxylamine to p-aminophenol is not only endotharmic but is
significantly accelerated at the higher temperatures. ~cceleration of
the rearrangement is important, for if it does not take place, anillne
is produced.
The amount of catalyst to be used appears to be a matter
o~ economics. The more of the catalyst that is used, the faster the re-
action proceeds. Since the catalyst is expensive only small quantities are
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used ln practice. It has been found, fox example, that 0.050 percent by
weight of catalysts based upon the weight of nitrobenzene may be used
when the catalyst is 1.0% by weight of platinum on carbon.
The hydrogenation is carried out at temperatures of from
130C. to 160C., the elevated hydrogen pressure generally being from
about 50 to 500 pounds per square inch gauge. The completion of the re-
action is noted by the decrease in the consumption of hydrogen. Generally,
the hydrogenation will require from about 3 to 18 hours. The time is
dependent upon the type and concentration of catalysts and the temperature
and pressures of the reaction.
At the conclusion of the hydrogenation step, from 90 to 98
percent of the nitrobenzene is generally converted to hydrogenation ~ -
products; which products are a mixture of para-aminophenol, hydroquinone
precursors, and anillne. It is desirable in each instance to hydrogenate ~ -
at those conditions that favor the optimum production of para-aminophenol
as this is believed to be the main compound ~hich undergoes hydrolysis to
hydroquinone. The aniline seems to remain unchanged by the hydrolysis.
The optimum conditions can be Feadily determined by one skilled in the
art when he is using a particular catalyst, temperature, pressure, acid ;
medium, and reaction vessel.
As an example, when it was found that when 91% of the charge
of nitrobenzene had been converted to hydrQgeneration products, an aliquot
product analysis showed a yield based upon the amount o~ nitrobenzene
consumed o~ 72% para-aminophenol and 15% aniline. The resulting yield
after hydrolysis to the product hydroquinone was a 93% yield of hydro
quinone based upon the para-aminophenol content and a 67% yield ba~ed upon
j the amount of consumed nitrobenzene. The aniline appeared to remain un-
` changed. It is believed that the high yield based upon the para-aminophenol
is due to some undetermined hydrogenation products which also hydrolyze
~- 30 to hydroquinone. As further illustrations, nitrobenzene was hydrogenated
with a conversion o~ 94% of the nitrobenzene to amino products which
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104~659
provlded a yield of 70% par~-Aminophenol and 16% aniline based upon the
weight of consumed nitrobenzene using 0.03% by weight, based upon the
weight of the nitrobenzene, of a catalyst constituted o~ 5% platinum on
a carbon carrier at 250 pounds per square inch gauge of hydrogen for six
hours' reaction time at 130C. and using a mole ratio of one mole of
nitrobenzene and one mole of sulfuric acid which sulfurlc acid had been
diluted with water to a concentration of 13%. In a like manner, one mole
of nitrobenzene was hydrogenated ln an aqueous medlum containing two moles
of phosphoric acid dlluted with water to a 40% concentration at a pressure
of 150 pounds per square inch gauge of hydrogen and at à temperature of
135C. for six hours in the presence of 0.03% by weight, based ~pon the
weight of nitrobenzene, of the above mentioned platinum-on-carbon catalyst
to give a yleld of 64% of para-aminophenol and 21% of aniline based upon
100% converslon of the nitrobenzene. Also, a 94% conversion of nitro- -~
benzene was obtalned using a salt comprlsed of 3.5 moles of ammonium bl-
sulfate and 0.35 moles of ammonium sulfate dissolved in a hundred moles
of water wlth 0.11%, based upon the weight of nitrobenzene, of a catalyst
co~prised of 1% platinum-on-carbon at a temperature o~ 135C. for 3 hours
and a pressure of 100 pounds per square inch gauge of hydrogen to give a
.
product which was found to provlde a yield of 75% of para-aminophenol and
13% of aniline based upon the conversion of the nitrobenzene.
Any nitrobenzene that remains after the hydrogenation is
readily removed by steam distillation. The nitrobenzene so recovered can
, be recycled for use in the next hydrogenation sequence. A~ter the nitro-
benzene removal, the aqueous reaction mass is then filtered to remove the
, catalyst. When molybdenum sulfide on carbon is used as the catalyst, the
catalyst can be reused for subsequent reductlon reactions. After the
catalysts removal, the reaction medium is ready for the hydrolysis reaction.
The composition of the aqueous acid reaction medium becomes
impo~tant ~or th~ hydrolysis. Such co~position ca~ be readlly determined
by analysis. The minimum requirement is that there be at least an effectlve
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~040659
molar quantity o~ an acid p~ovlding ~ngred~ent per mole o~ nltrobenzene
originally present in the reaction.
The hydrolysis can be carried out ln one step or it can be
carried out in two or more steps. It can be continued sequentiall~ by
terminating the reaction, cooling, extracting the hydrolysis product and
reheating the hydrolysis mixture without further addition of reactants.
A one-step hydrolysis is desirable from the standpoint of ease and
efficiency of operation. Usually, an lncrease in yieid can be achieved
by a second hydrolysis of the reaction mixture after the product of the
first hydrolysis has been extracted. From the standpoint of obtaining
high yields in a single hydrolysis step, high concentrations of the acid ~ -
producing ingredient, in the case of ammonium bisulfate up to the point
of saturation of the aqueous solution, is desirable. The point of satura-
.,; -. ., :
tion of the solution when ammonium bisulfate is used is dependent upon
the amount of water present and upon the temperature at which the ammonium
bisulfate is added to the water.
When ammonium bisulfate is belng used, the overall useful
range of ammonlum bisulfate concentration, as an effective molar quantity,
varies between 1.2 and 12 moles of ammonium bisulfate per mole of nitro-
benzene originally present with the preferred range being between 3.5 and
5 moles. If less than 1.2 moles of ammonium bisulfate are present, ~a)
insufficient converslon results; (b) the reaction time is unduly prolonged;
and (c) large amount of starting material remains in the aqueous solution.
1 If more than about 12 moles are used, a practical problem arises from the
; standpoint of handling large quantities of salt.
Water must be present in an amount sufficient to provide
for hydrolysis and also to act as solvent for the salts of the hydroquinone
precursors, hydroquinone, ammonium bisulfate, the ammonium sulfate, and/or
the ammonium phosphate for~ed during the course of the reaction. As an --
example, at least 40 moles o~ water per ~ole of nitrobenzene originally
charged should be present to dissolve suf~icient quantities of ammonium
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1040659
bisulfate; and as the concent~ation o~ ammonium blsulate is increased,
more water up to about 120 moles, is required. ~xcess water raises the
practical problem of water removal during the ammonium bisulfate regenera-
tion step.
The temperature for the hydrolysis can vary over a wide
range of from about 200 to 300 C. If temperatures below about 200 C.
are used, an unduly long reaction tlme is required and the yields are not
generally good. As the temperature is lncreased, the pressure must be
correspondingly increased to maintain the reaction medium in the aqueous
phase. At temperatures as high as 300C., a steam pressure of up to about
1250 psig is required to maintain an aqueous phase and thère is danger of
resin formation if the contact time is too long. No advantage is obtained
by increasing or decreasing the pressure to a value other than that which
is sufficient to malntain a liquid phase. To avoid the use of considerable
pressure, with the correspondlng equlpment requlreménts, temperatures in
the range of 200 to 260C. are preferred.
~, The reaction time or residence time of the reactants during
hydrolysis varles wlth the temperature and to a lesser extent wlth the
mole ratlo of the reactants. At minimum temperature, e.g., 200 C., a per
pass reaction tlme of 8 hours is ordinarily required. ~t 220C., effective
results from the standpoint of yield are obtalned using a two-pass hydrolysis
.- reaction and a reaction time of three hours per pass. At 220C., satis-
factory results can be obtained in a single pass hydrolysis step if the
, reaction ti~e is extended to 7 or 8 hours. Dependlng upon the choice of
` the reactants, hydrolysis can occur at temperatures above 250C, in five
minutes to a half hour. From a practical standpoint, the overall time per
pass for hydrolysis can be considered to be from 5 minutes to 8 hours.
Both the hydrogenation and the hydrolysis should be carried
out in a zone ~hich is resistant to any substantial attack by the ammonium
bisulfate, ammonium phosphate, sulfuric ~cid~ phosphoric acid, nltro-
i benzene, hydrogen, hydroquinone, or aminophenol. ~t very low temperatures
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1040659
within the useful range, an o~dinary glass~lined P~audler kettle can be
used, ~hen hlgher temperatures and pressurlzed equipment are requlred,
other construction materials become necessary. ~t temperatures up to
220 to 230C., ~eflon reactors are ef~ectl~e. The higher temperature
ranges require the use of more durable equipment such as tantalum-llned
reactors.
After the period of hydrolysls, the length of time of which
is dependent to some e~tent on whether a single or multiple pass hydrolysis
is used~ the reaction mixture ls cooled. Coollng is required to prevent
resinification of the product in the acidic aqueous reaction mixture and
to enable the separation of the by-product by organic solvent extraction. - ~-
- Any substantially water-immiscible solvent which will dissolve the product
hydroquinone is useful. The preferred solvent is ethyl ether.
In the extraction, the organic solvent phase is then sepa-
rated from the reaction mixture by decantation and the product is removed
from the solvent by distillation or other means. Distillation provides a
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high purity hydroquinone as a product.
, As examples of the acid hydrolysis, analyses have shown
that an 82% yield of hydroquinone based upon the analyzed para-aminophenol
content are obtained by a two-pass hydrolysis carried on at a temperature
of 240C. for 3 hours for each pass using a mole ratio of one mole of
sulfuric acid and 80 moles of water per mole of para-aminophenol. When
using phosphoric acid, a yield of 90% of hydroquinone based upon the
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analyzed para-aminophenol content was obtained by hydrolysis carried out
at 240C. for 2 hours in one pass using a mole ratio of 2 moles of phosphoric
acid and 60 moles of water per mole of para-aminophenol. A two-pass
i hydrolysis using ammonium bisulfate at a temperature of 240C. for 3 hours
1 for each pass with a mole ratio of 2 moles of ammonium bisulfate and 60
i moles of water per mole of the analyzed para-aminophenol content gave a
yield of 82~ of hydroquinone based upon the para-aminophenol.
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10~59
The by-product aniline is not hydrolyzed under the conditions
used to hydrolyze the para-amlnophenol to hydroqulnone. The anlline can
be recovered, after the hydroquinone has been removed from the aqueous
reaction medium, by neutralizing the aqueous reaction medium with ammonia
and steam distilling the aniline from the reactlon medium.
After removal of the hydroquinone and the aniline, the
resulting aqueous effluent reaction mixture can be reheated to the hydro-
lysis temperature for a second or even a third hydrolysis step. The second
and subsequent hydrolysis steps are carried out as before; i.e., by heat-
ing the reaction mixture to the appropriate temperature of hydrolysis for
the desired period of time, cooli~g and removing the hydroquinone product
by solvent extraction.
Ammonium bisulfate is regenerated for reuse in the process
by removing the residual water from the remaining reaction mixture and
heating the molten salt, primarily mixed ammonium sulfate, and ammonium
bisulfate at atmospheric pressure at a temperature between 310 and 450 C.
An unduly long time is required to effect decomposition at temperatures
below 310C., and no practical advantage ls seen in using temperatures
higher than 450C.; especially as the bisulfate tends to decompose at
temperatures higher than 450C. At 330C., 75 to 95 percent of the
ammonium sulfate is converted within a few minutes to ammonium bisulfate.
Slightly higher conversions are obtained at higher temperatures, but this
advantage of higher conversion is offset by the increased equipment cost
required. ~uring the decomposition of the ammonium sulfate, residual
organic materials may be pyrolyzed to black granules resembling activated
charcoal but such granules can be removed by dissolving the product in
water and flltering it. The ammonia formed during the decomposition can
be recovered and used in other chemical processes. The clear, filtered
salt solutlon, the salt portion of which 75 to 95 percent is ammonium
bisulfate, may be ad~usted to the desired concentration and be recycled
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to the reaction mixtu~e ~o~ hyd~olysls of additional hydrogenation of
nitrobenzene or hydrolysis of the hydrogenera$ion product.
Without ~urther elaboration, lt is belleved that one skilled
in the art can, by following the preceding description, utilize the present
invention to its fullest extent. The following specific embodiments are,
therefore, to be construed as merely illustrative, and not limitative of -
the disclosure.
EXAMPLE I
To a 30-gallon glass-lined Pfaudler autoclave was charged
nitrobenzene (8.30 lbs.), NH4HS04 (27.00 lbs.), (NH4)2S04 (3.14 lbs.), H20
(121.50 lbs.), 1% Pt/C catalyst (4.00 g.), and 150 drops of Igepal 60
emulsifying agent. After a nitrogen purge the autoclave was heated to
~ 135C. under 10 psi o~ H2. The hydrogen pressure was purposely kept low
during heat-up so that no hydrogenation would take place until reaction
temperature was reached because hydrogenation at a lower than reaction
temperature has beeD found to favor aniline formation. Then the agitator
speed was adjusted to 170 rpm and the hydrogen pressure raised to 120 psi
of 1l2. The hydrogen abs,orption rate was maintained at a pressure of 170
to 140 psi/hr. for 2-1/2 hrs. and 12 psi/hr. for the last 1/2 hour. The -~
- 20 hydrogen pressure was purposely adjusted to maintain an absorption rate
that would extend the hydrogenation to a period of 3 hours.
At the end of the hydrogenation reaction period, any un-
reacted nitrobenzene was steam distilled from the aqueous reaction medium
in the autoclave. Nitrobenzene (350 g.) was collected; this indicated a
con~ersion of 91% of the nitrobenzene to hydrogenated products. ~ster
` equal to the water distllled over with the nitrobenzene was returned to
the autoclave to maintain the original concentration of water.
~ - The hydrogenate was fil$ered of catalyst through double
'j layers of paper on a Nutsche type filter. A sample of the filtrate was
~'t
-~l 30 ta~en for analysis; and it showed that based upon the amount of consumed ;
or converted nitrobenzene, there was a yield of 15 mole % aniline and 75
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104~659
mole % para-aminophenol.
The filtrate was returned to an acid ~esistant autoclave
(tantalum lined). After a nitrogen purge, the autoclave was heated to
250C. for 1/2 hour and maintained at this temperature of 1-1/2 hours.
After cooling to room temperature, 118.5 g. of solids were filtered from
the hydrolyzate. The filtrate was extracted with ethyl ether. The ethyl
ether was neutralized with sodium bicarbonate, filtered and distilled.
The residue o~ crude hydroquinone was 2190 g. (81.~%). Distillation of
the crude product gave 1949 g. (72.7%) based on nitrobenzene consumed of
hydroquinone, b.p. 192 to 194C./40 mm., and 162 g. (6.1%) of a non- -
distillable residue.
The aqueous reaction medium that remained from the process
as illustrated above was regenerated to provide bisulfate for recycling.
., .
To this end, the water was evaporated to provide a dry salt that was about
an equal mixture of ammonium bisul~ate and ammonium sulfate. This dry i~
salt was heated in an oil bath. The salt was stirred easily after it
reached the temperature of 146C., the melting point of ammonium bisulfate.
As heating was continued to a temperature of 312C., ammonium evolved.
The melt was held at this temperature of 312 C. for 12 minutes. After
this time, analysis revealed the ~nonium bisulfate content to be 95~
During the heating of the melt, the organic material in the melt changed
I to fine carbonaceous particles. Dissolving the thermally treated salt
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mixture in water and filtering it produced a clear filtrate solution.
Evaporation of the water from the filtrate yielded light yellow ammonium
, bisulfate crystals. The ammonium bisulfate so produced was suitable for- recycling for use in the hydrogenation or hydrolyzing step, to produce
l~ more amino product to hydroquinone.
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`f~ The following is a tabulation wherein the mol ratios and
~-~ yields in the hydrogenation step are by weight based upon the weight of
3~ nitrobenzene originally charged. The yield based on para-aminolphenol is
based upon the analyzed result. The yield and mol ratios in the hydrolysis
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reaction are based upon the amount o~ nitrobenzene actually consumed inthe hydrogenatlon reaction. The acid ingredlent used was ammonium
bisulfate.
HYDROGENATION
Acid Mol Ratio 3.5
Acid Concentration % 17.7
Catalyst Type 1% Pt/c
Catalyst Concentration % 0.107 -
Time, hours 3.0 - ~ ~
Temp., C. 135 -
Pressure, psig Hydrogen 120 ~ ~-
Para-aminophenol Yield % 75
Anillne Yield % 16
Nitrobenzene Consumed, % of Charge 91
HYDROLYSIS
Acid Mol Ratio 3.8
Water Mol Ratlo 114
No. of Passes 2
Time/Pass, Hours 1-1/2
Temp., C. 250
Hydroquinone Yield based on Para-aminophenol % 92
Hydroquinone Yield based on Nitrobenzene % 67
Aniline Yield % 16
EXA~LE II
,, .The procedure of Example II was repeated except that
sulfuric acid was used to provide the acid characteristic to the aqueous ~ -
medium. The resulting products were hydroquinone, aniline and ammonium
- bisulfate. The results are tabulated below on the same basis as described
for Example I.
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1041~659
HYDROGENATION
Acid Mol Ratio 1.0
Acid Concentration 13%
Catalyst Type 5% P/c
Catalyst Concentration % .015
Time, hours 8
Temp., C. 130
Pressure, psig Hydrogen 250
Para-aminophenol Yield % 6
Aniline Yield % 14
Nitrobenzene Consumed, % of Charge 65
The reaction medium was analyzed and the acid and water ratios adjusted.
I~YDROLYSIS
Acid Mol Ratio l.O
~ater Mol Ratio 80.0
No. of Passes 2
Time/Pass, Hours 3
Temp., C. 240
Hydroquinone Yields based on Para-aminophenol % 91.2
~ydroquinone Yields based on Nitrobenzene % 62 - -
Anlline Yield % 14
`~ The by-product ammonium sulfate is convertable to ammonium
~ bisulfate as described in Example I.
- EXAMPLE III
` The procedure of Example I was repeated except that phos-
phoric acid was used to provide the acid characteristic to the acid
medium. The resulting products were hydroquinone, aniline and a~monium
: phosphate compounds. Ammonium phosphate compounds cannot be reused as
; can the ammonium sulfate compounds but can be used for other purposes as,
for example, for fertillzers. The results are tabulated below on the same
~ basis as described for Example ~.
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HYDROGEN~TION
Acid Mol Ratio 2.0
Acid Concentration 23
Catalyst Type 5% Pt/c
Catalyst Concentration % 0.021
Time, hours 8
Temp., C. 135 -
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Pressure, psig Hydrogen 115-150
Para-aminophenol Yield % 55
Anilihe Yield % 16
Nitrobenzene Consumed, % o~ Charge 96.7
The reaction medium was analyzed and the acid and water ratios adjusted.
HYDROLYSIS
Acid Mol Ratio 4
~ater Mol Ratio 120
No. of Passes 2
Time/Pass, Hours 3
Temp., C. 240
.
Hydroquinone Yield based on Para-aminophenol % 118 -
Hydroquinone Yield based on Nitrobenzene % 65.1
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Aniline Yield % 16 ~
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