Note: Descriptions are shown in the official language in which they were submitted.
1139;~17
0154
Method
for
Preparing p-Aminophenol
This inVention relates to the field of oxganic
chemistry, and more paxticularly, to a method for the pre-
paration of _-Aminophenol.
p-Aminoph.enol (.PAP) is an important chemical
intermediate used in the preparation of the analgesic,
acetaminophen t~PAP~. A number of other derivatives having
a wide variety of industrial applications may also be
prepared from PAP.
An i~poxtant commercial method for the preparation
lQ of PAP involves the catalytic hydrogenation of nitrobenzene
in an acid aqueou$ ~edium. Conventionally, the hydrogenation
i5 caxxied out in the presence of a 10%-13% sulfuric acid
solution containing a small amount of a surfactant, such as
dodecyltximethylammonium chloride, and utilizing a platinum-
lS on-caxbon catalyst. The reaction is complex and yields, in
addition to the pxincipal product, PAP, a significant amount
of aniline and smaller amounts of other impurities.
~'
1139~17
0154
In any commercial process which utilizes a platinum
catalyst, recovery of the paltinum from the spent catalyst
is an important economic factor. While the carbon-supported
platinum catalysts commonly used in the nitrobenzene/PAP
process are reasona~ly satisfactory from the point of view
of their primary function, i.e., the conversion of nitrobenzene
to PAP, they leave much to be desired from the point of view
of platinum recovery fxom the spent catalyst. As a rule, such
recovery depends on combustion of the carbon to separate it
from the platinum. Experience has shown such recovery to be
only about 60-65% efficient. In addition, the spent
carbonaceour catalyst is rather unpleasant to handle.
In accordance with the above, it is an object of
this invention to provide a method for the preparation of
~A~ from nitxo~enzene utilizing a supported platinum catalyst
ha~ing performance chaxacteristics essentially equivalent to
those of a good platinum-on-carbon catalyst but which is
adapted to the reco~ery of platinum in high yield therefrom.
Othex o~jects and features will be in part apparent and in
2Q pa~t po~nted out hereinafter.
The present invention is directed to a method for
preparing p-a~inophenol which comprises hydrogenating nitrobenzene
in an acid~c aqueous reaction medium in the presence of a
catalyst comprising platinum supported on gamma-alumina.
''
1135~;~17
0154
The term "alumina" covers a considerable variety
of specific entities having varying physico-chemical properties.
The chemical compositions of various types of alumina run
from trihydrates, Al(OH)3, through monohydrates, AlOOH, to
the anhydrous oxide, A1203. The matter is further complicated
by the existence of different crystalline forms having
essentially the same gross chemical composition. Further,
in addition to the three more or less well defined degrees
of hydration suggested by the chemical formulas given above,
1~ there exist a number of "transition aluminas", identifiable
by crystallographic and other physico-chemical criteria.
The matter is still further complicated by the intermingling
of two or more systems of nomenclature. To illustrate, one
crystalline entity having the nominal composition of Al(OH)3
is known variously as alpha-alumina trihydrate, gibbsite and
hydrargyllite. S~milaxly, one crystalline entity having the
nominal composition repxesented by AlOOH is known as alpha-
alumina oxide hydroxide, alpha-alumina monohydrate or boehmite.
The end product of the thermal degradation of all the forms
2Q of h~dxated ~lumina i$ A1203, known as alpha-alumina or
coxundum. The tex~"acti~ated alumina" has ~een applied
broadly to the tran~ition aluminas. The whole matter of the
interrelationships of the various types of "alumina" is
discussed in the Kirk-~thmer "Encyclopedia of Chemical
Technology", 3rd Ed. Vol. 2, pp. 218-244 (John Wiley &
50ns, Ne~ Yoxkl 1978.
.~
~ 1 3~
0154
Alumina-supported platinum catalysts have been
used in such large scale applications as oxidation catalysts
in automobile mufflers and as dehydrogenation/hydrogenation
catalysts in gasoline reforming. However, only a few general
references have been made to the use of such catalysts in
processes involving hte hydrogenation of nitrobenzene. For
example, U.S. Patent 3,715,397 suggests that platinum supported
- on alpha-alumina may be a useful catalyst in the hydrogenation
of nitrobenzene to P~P in an aqueous sulfuric acid reaction
10 medium. Similarly, U~S. Patent 3,694,509 suggests that a
catalyst consisting of platinum supported on alumina is
useful in the catalytic hydrogenation of nitrobenzene to
phenylhydroxyla~ine in a neutral aqueous/alcoholic medium.
U.S. Patent 3,472,897 suggests the use of a catalyst consisting
of platinum supported on pure eta-alumina in the preparation
of aniline by the hydrogenation of nitrobenzene in glacial
acetic acid. Similarly, U.S. Patent 3,253,039 suggests the
use of a cat~lyst consisting of platinum supported on activated
alumina in the same reaction.
N ~ Popo~a, et al. CChem. ~s. 72: la4294b/1~7
used a catalxst consisting of mixed platinum and palladium
~uppo~ted on alu~inum oxide in the hydrogenation of nitrobenzene
in water or ethanol.
il3~;~17
0514
In accordance with the present invention, the
hydrogenation of nitrobenzene to PAP in an acidic aqueous
medium is carried out utilizing a supported platinum catalyst
in which the support is the transition alumina known as
gamma-alumina. Gamma-alumina is the first transition phase
encountered in the calcination of boehmite (alpha-alumina
monohydrate~ to alpha-alumina (corunduml. It is formed by
calcining boehmite at temperatures in the range of 500-
850C. Preferably. the gamma-alumina support has a specific
surface area of at least 200 m2/g. Preferably, the supported
catalyst should contain about 3-5% Pt. However, such catalysts
containing Pt in the range of about 1-10% may be used.
Platinum i5 readily recoverable from spent Pt/
gamma-alumina catalysts by immersing the spent catalyst in a
strongly alkaline solution, such as a solution of sodium
hydroxide, to dissolve the gamma-alumina. The undissolved
platinum may then be filtered off. Recovery yields of about
8~-85% are oxdinarily achievable. Alpha-alumina is not
xeadily s~lufile under the sa~e conditions.
2Q T~e invention is further illu~trated by the following
example.
113~;~17
0154
EXAMPLE
Supported platinum catalysts were prepared using as supports
alpha-alumina and gamma-alumina. The gamma-alumina was
prepared by calcining boehmite powder (48% less than 45
microns, 9% larger than 90 microns) at 1100F (593C) for
two hours. The cooled product was screened through a U.S.
Standard No. 325 sieve.
The characteristics of this gamma-alumina and of the
alpha-alumina also used as a support are set forth in Table 1.
Table 1
Ch~;x~ctexistic~ of Alumina Supports
Charactexiatic ~lpha-Alumina Gamma-Alumina
Sp~ci~ic surface area 5.7 230
(m /gl(BET~
Bulk Density ~g~ccl Q.83 0.62
Loss on Ign~tion (%1 Q.16 7.77
rron OEe) C%~ o.aQl Q.OQ3
Sul~ur (S~ Q.Q07 0.009
Filter Speed Csec) 143 191
2Q Proportion Passing U.S.
No. 325 Sieve All All
Ave. Particle Size 23 23
(microns)
.~,
113~17
0154
II.
Platinum was deposited on the alpha- and gamma-alumina
supports by the following method.
A portion of the alumina (48.5g) was slurried in water (500
ml) at 22C. Chloroplatinic acid solution (lOOml. containing
1.5 g Pt) was added dropwise to the stirred slurry during a
period of 10 minutes. The slurry was stirred an additional
10 minutes, then vacuum filtered. Without washing, the
filter cake was dried 16 hours at 150C.
III.
The platinum deposit was reduced to metallic platinum as
follow~. The dry platinum/alumina composition was packed
into a quartz tube (1" diameter) and the tube was purged
with hydrogen (100 ml/min.) for 10 minutes. Hydrogen (100
ml/min) was then passed through the tube at 350C for 30
minutes. The catalyst was cooled under hydrogen, then the
tube ~ pur~ed ~th nltrogen (lQaml/min~ for lQ minutes,
and the catal~st was d~scharged from the tube under nitrogen.
A second batch of Pt/gamma-alumina catalyst (B~ was prepared
2Q b~ the procedure described above for the first batch (A).
The supported cataly~ts had the characteristics tabulated in
Table 2.
113~
0154
Table 2
Characteristics of Supported Catalysts
Support
Alpha--Al~mina Gamma-Alumina
Characteristic A B
Pt. ~/w? 2.93 2.88
Pt. Dispersion (%? 10.5 53.1 36.4
Sp~cific Surface Area (m /g) 7 229 229
Iron tFe~(.%? 0-004 0.448
Mean particle diameter
(micxons) 25 32
Loss on I~nition (%) 0.33 2.71 7.01
IV.
The. catalysts d~scr~ed above ~ere. u~ed in th.e catalytic
~ydxogenation of nitrob.enzene to PAP by the method described
below, the hydrogenation being interrupted prior to the
condu~ption of all the nitrobenzene, as descxibed by R.G.
Bennex QU.S. ~atent 3,383,416?.
A ~xtuxe of di$tilled watex (65~ ml?, dodecyltrimethyl-
2a ammonium chloride, (2ml~ and Pt/alumina catalyst containg
7.5 mg of Pt, in a 2 liter reaction vessel equipped for pressure
h~drogenation, ~as ~lushed with nitrogen then heated to
70~C. under hydrogen.
~r
.
1139;~7
0154
With vigorous agitation, sulfuric acid (80 g of 95-98% reagent
grade/Sp.Gr. 1.84) was added during a period of 2-3 minutes,
the temperature rising to 87-77C. Nitrobenzene (108g) was
added rapidly, and hydrogenation was carried out a 87-90C.
at pressures slightly above atmospheric (6-10 inches of water).
After 5-6 hours the hydrogenation was interrupted and the
aqueous and nitrobenzene phases were separated, the catalyst
remaining suspended in the nitrobenzene phase. The concentrations
of p-aminophenol and aniline, respectively, in the aqueous phase
1~ were determined by high pressure liquid chromatography. Signi-
ficant data are tabulated in Table 3.
8a
~?.
31`7
0154
P
P P
p ,_ ,_
u~
P P
O ~n : : W t
~ P P
P 1-- P
N
It
O
.~b ~ Ul ~ w ~ I--
O O
rt ~ .
1~. ~D
O O P
~ 8 ~,
o ~ ,
~h P ~
J.
U~
~ o~ ~ o
o P~ P.
o
1- ~ tn
P tD
~ O
~t ~. P
o'
~D I Y ~
O ~ ~ ~ ~ ~3
N ~S Ui
~D ~ ~ tJ- ID
0~ ~S O W
~ . ~
P _, O
P ~
1-- ~
P
Ul
r~ O
lt 00 CO CO 00 1--
~ N Ul ~ Ul ~ 1
p .... .. ~ O O
~ O O ~ æ
P ~D ~ 1~.
~ o ~
U~ ~ g o
o~
P ~ N
C
~D ~ ~
O 1~ ~ 1~- P ~D
O ~ ~ ~ ~ I_
~- ~
O O ~ 1-- ~ ~ ~ O
(D
~D ~
t 1~ ~.
O
~D
~,r
113~ 7
0154
Experience has shown that the performance of a
catalyst, as evaluated by the method outlined above, may be
considered acceptable if the yield of PAP exceeds 50 mg/ml
and the PAP/aniline ratio is greater than 3Ø
In view of the above, it will be seen that the
objects of the invention are achieved and other advantageous
reslults obtained.
As various changes could be made in the above
methods without departing from the scope of the invention,
it is intended that all matter contained in the above desceiption
shall be interpreted as illustrative and not in a limiting
sense.
lQ
,~
