Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a method for the
oxidation of propane to produce valuable oxygenated
products. The method is a liquid phase process for
the oxidation of propane to useful oxygenated products,
which comprises contacting oxygen with a liquid reaction
medium comprising propane and a liquid organic material
that is a solvent for propane and which is non-reactive
with oxygen under the conditions of the process, wherein
the process is carried out in an enclosed reaction zone
that is maintained under superatmospheric pressure, and
at an elevated temperature and for a period of time
sufficient to produce oxygenated products. The principal
products of the reaction are acetone and isopropyl alcohol.
Any organic liquid that-does not react readily
with oxygen under the conditions used for the oxidation
process can be employed as a solvent in the process of
the invention. Of course, the liquid must also be a
solvent for propane. Such organic liquids include
aromatic materials such as benzene, nitrobenzene, and
chlorobenzene, and aliphatic materials such as acetonitrile.
The organic liquid must also remain liquid under the con-
ditions of the reaction.
The exact proportion of organic liquid to
propane that is employed in the process is not narrowly
critical. For example, the solvent: propane ratio can
be in the range of from about 1:5 to 1:1. Higher ratios
than 1:1 can be employed, although the productivity of
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the reaction tends to decrease as the dilution of the
propane becomes greater. At weight ratios of solvent
to propane of less than 1:5, the amount of solvent tends
to become insufficient to dissolve st of the propane
present in the reaction zone.
The reaction is carried out at an elevated
temperature sufficient to oxidize the propane to valuable
oxygenated products, including acetone and/or isopropyl
alcohol. For example, a temperature within the range of
from about 160 to about 220C. can be employed. Preferred
temperatures are found within the range of from about
180 to about 200C. Below 160C., the reaction rate
tends to become impracticably slow, and at temperatures
above 220C., the incidence of undesired side reactions
tends to become greater.
The reaction is carried out under superatmospheric
pressure. Because the temperatures employed in the reaction
are above the critical temperature of propane, the auto-
geneous pressure of the reaction is high. Thus, the normal
minimum pressure of the reaction will be about 700 p.s.i.
The reaction can be carried out at pressures of up to
2000 p.s.i. or higher, if desired.
The reaction time is not narrowly critical. If
the process is carried out as a batch operation, there will
usually be an induction period before the oxidation begins.
In such a case, the residence time of the reactants in the
reaction zone may vary from about 1 to about 8 hours, and
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preferably from about 2 to about 5 hours. If the
reaction is carried out as a continuous reaction, with
reaction mixture being constantly withdrawn as fresh
reactants are added to the reaction zone, the residence
time in the reaction zone may be as short as 5 minutes to
as long as 1 hour or more. Preferred residence times in
such a case would be from about 10 to about 30 minutes.
With reaction times longer than those indicated
above, the incidence of undesired side reactions tends to
become greater, with the result that the efficiency of the
reaction to the desired acetone and isopropyl alcohol pro-
ducts is reduced. With very short reaction times, the
amount of propane oxidized tends to become so low that
the operation becomes economically unattractive.
Oxygen is employed in the reaction, either as
pure oxygen or as an oxygen-containing gas such as air.
The oxygen concentration in the gas phase of the reaction
zone is controlled so that it is below the explosive range
of the organic material-oxygen mixture present. If the
reaction is carried out in a continuous manner, the desired
amount of oxygen and propane, along with the liquid solvent
for the propane, are continuQusly fed to the reaction zone.
At the same time, reaction mixture is continuously drawn
off in order to maintain a constant amount of material in
the reaction zone. If the reaction is carried out as a
batch process, an initial quantity of oxygen, propane, and
solvent are charged to the reaction zone, and after the
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induction period when oxygen begins to be consumed (as
i6 evidenced by a drop in pressure), additional oxygen
can be fed to the reaction zone as needed.
The total amount of oxygen employed is
preferably an excess of stoichiometric. (The stoichio-
metric proportion is i mole of 2 per mole of propane.)
In order to avoid an explosive mixture in the gas phase
of the reaction zone, the amount of oxygen at all times
in said gas phase should be not more than about 11 per-
cent, by volume.
The process may be carried out in a vessel
such as an autoclave, equipped with means for heating,
cooling, pressure regulation, agitation, and the like.
The material of construction can be stainless steel,
Hastelloy C, titanium, tantalum, or other material that
is inert to the reactants and is capable of withstanding
the elevated pressures attained in the process.
The products of the reaction can be recovered
by conventional procedures. For example, the products
can be separated by fractional distillation, and un-
reacted propane as well as the organic solvent can be
recycled to the reaction.
The following example illustrates the practice
of the invention:
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EXAMPLE
Liquid-Phase Oxidation of Propane in Benzene Solvent
The reaction vessel was a stainless steel
autoclave equipped with a stirrer, temperature indicator,
gas inlet line, and safety device for accommodating
sudden pressure increases. The autoclave contained
an internal coil through which steam could be passed
for heating or water for cooling. To the vessel were
charged 780 grams of benzene (10 moles) and 900
grams of propane (20.5 moles). The mixture was heated
to 182C. At that temperature, the autogeneous pressure
was 720 p.s.i. Oxygen was then added to raise the
total pressure to 810 p.s.i., and the reaction mixture
was stirred. After an hour, the pressure on the system
began to drop slowly, indicating that the consumption
of oxygen had started. Periodically, additionaly oxygen
was added to maintain the total pressure at 810 p.s.i.
At the end of 3 hours, no re oxygen was consumed. The
reaction mixture was cooled, and the gas and liquid por-
tions of the product were analyzed by gas chromatograph.
The conversion of the propane charged was 3.7 percent.
Of the propane that reacted, 55.3 percent formed acetone,
10.7 percent formed isopropyl alcohol, and 3.6 percent
formed normal propanol.
A complete analysis of the products is displayed
in the table below.
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TABLE I
LIQUID-PHASE OXIDATION OF PROPANE
BENZENE SOLVENT
Reaction Conditions
180C.
810 psi max pressure
4 hours reaction time
2-gallon stainless steel autoclave
Product Composition
Liquid
Component Weight Percent
Propane 4.13
Acetaldehyde 0.02
Propylene Oxide 0-04
Acetone 2.26
Methanol 0.23
Isopropanol 9l 2l
n-Propanol 0.16
Water 0.27
Unknown 0.41
Acetic Acid 0.07
Propylene Glycol (tentative) 0.60
Gas
Component Weight Percent
Carbon Dioxide 0.9
Oxygen 6.8
Nitrogen 7.36
Carbon Monoxide 1.05
Propane 808 4321
Propane Impurities o 49
Benzene 1.35
Charge
Benzene 780 g
Propane 900 g
