Note: Descriptions are shown in the official language in which they were submitted.
1 0 7 2 9 8 8
BACKGROUND OF THE INVENTION
This invention relates to an improved process for producing
cumene from benzene and propylene in the presence of an alkylation cata-
lyst. It also relates to transalkylating di- and triisopropylbenzene
with benzene in the presence of a transalkylation catalyst to produce
; 5 cumene.
The present invention is broadly applicable to the production
of alkylated aromatic hydrocarbons. These compounds are useful in themselves
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and more frequently in subsequent chemical synthesis of other compounds.
The present invention is particularly applicable to the production of
cumene, or isopropylbenzene, which is a reactant finding utility in the
preparation of phenol, acetone, alphamethylstyrene and acetophenone.
Another application of the process of the present invention may be found
in the preparation of p-cymene which may be oxidized to produce p-cresol.
A further application of the process is in the alkylation of a substituted
aromatic compound such as phenol, which when alkylated with isobutylene
forms o-tertiary-butylphenol and p-tertiary-butylphenol, both of which
find utility in the resin field.
As above stated, the present invention finds particular appli-
cation in the preparation of cumene. In the usual commercial process
for the production of cumene, it is the practice to charge liquid benzene
and liquid propylene into a reactor and to react the same therein in one
or more alkylation zones in contact with an alkylation catalyst. In order
to minimize the production of dialkylated products of benzene it has been
the practice to maintain a molar excess of benzene throughout the reaction
zone ranging from about 4:1 to about 16:1, and more preferably about 8:1 of
benzene to propylene. Two competing reactions with the desired production
of isopropylbenzene have created problems in the prior commercial processes
used. One of these as indicated above has been the formation of dialkylated
benzenes such as di- and triisopropylbenzene rather than the desired mono-
alkylated product. This competing reaction has been controlled by means
of employing large molar excesses of benzene as indicated above. The
other competing reaction causing losses in the yield of cumene based on
propylene reactant charged is the formation of oligomers of propylene
such as propylene dimer and trimer which occur to a limited extent even
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with the large molar excesses of benzene present. Propylene trimers
and some of the propylene tetramers boil with cumene. Since the presence
of these olefins interfere with the oxidation reaction used to make
phenol from cumene, this oligomerization side reaction must be minimized
to make a high purity product.
The alkylation reaction of the alkylatable aromatic compound
is exothermic in nature and the temperature within the reactor tends to
increase at a rapid rate. This increase in temperature caused by the
exothermic reaction likewise tends to increase the production of cumene
bottoms products by the competing reactions. In the past it has been
customary to control the temperature rise by catalyzing the reaction in
multiple separate zones and employing a quenching medium between each of
several successive alkylation zones. This quenching has served to control
the ~emperature at which the reaction mixture enters each successive zone
and thus the temperature rise throughout each zone. The temperature rise
from inlet to outlet of the reactor has also been controlled by controlling
the molar excess of benzene charged to the reactor, the benzene acting as
a heat sink to absorb heat released by the alkylation reaction. Accord-
ingly, increasing the molar excess of benzene charged to the reactor,
with a corresponding dilution of the propylene reactant therein, not only
provides more aromatic sites subject to alkylation and a resulting reduc-
tion in oligomers and over alkylated by-products, but also reduces the
formation of undesirable by-products resulting from an excessive temperature
rise across an alkylation zone or zones.
To obtain the desired high molar excess of benzene in the
reactor charge, it has been the practice to separate the reaction zone
effluent to obtain a benzene-rich stream suitable to recycle to the
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107Z98~3
reactor. Since the two principal components of the reaction zone effluent
are benzene and cumene, it is necessary to make a separation of the benzene
and cumene, the latter being the higher boiling component. Consequently,
to obtain a purified stream of benzene relatively free of cumene and suit-
able for recycling to the reaction zone, benzene is vaporized and fraction-
ated, thus requiring consumption of substantial heat to vaporize benzene
and provide adequate reflux in a benzene fractionator, the heat require-
ment being substantially proportional to the ratio of benzene to propylene
desired in the charge to the reactor. At the present time, relatively high
fuel cost necessitates review of processes requiring high utility consump-
tion with the result that alternative processing schemes which previously
were unattractive are becoming more desirable if utility consumption is
reduced.
SUMMARY OF THE INYENTION
An object of the present invention is to provide an improved
process for the alkylation of benzene with propylene to produce cumene
in the presence of an alkylation catalyst. A specific object of this
invention is to reduce utility consumption in a process for the alkyla-
tion of benzene with propylene to produce cumene in the presence of an
alkylation catalyst. A more specific object of this invention is to pro-
vide a process for the alkylation of benzene with propylene to produce
cumene in the presence of a solid phosphoric acid catalyst, the process
requiring a relatively lower molar excess of benzene to propylene than
prior art processes as provided by recycle of excess benzene separated
from the reaction zone effluent.
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One embodiment of the present invention relates to a process
for the production of cumene which comprises: (a) reacting propylene
with an excess of benzene in the presence of an alkylation catalyst at
alkylation reaction conditions in an alkylation reaction zone; (b) divid-
ing the total liquid effluent of said zone into at least two portions oflike composition; (c) recirculating one of said portions of the effluent
to said reaction zone; (d) introducing another of said portions of said
effluent and a transalkylation zone effluent stream, formed as hereinafter
set forth, into a separation zone; (e) separating from the admixed effluents
in the separation zone a benzene-rich stream, a cumene product stream and
a di- and triisopropylbenzene-rich stream; (f) transalkylating the last
named stream with benzene in the presence of a transalkylation catalyst in
a transalkylation zone to form additional cumene; (g) supplying the efflu-
ent of the last mentioned zone to said separation zone as said transalkyla-
tion zone effluent stream; (h) passing at least a portion of said benzene-
rich stream from the separation zone to said alkylation reaction zone; and
(i) recovering said cumene product stream from the separation zone.
In the processing scheme of the present invention, propylene
and excess benzene are reacted in an alkylation reaction zone wherein an
alkylation catalyst is employed, and a portion of the resultant effluent
is recirculated without separation to the inlet of the reaction zone.
A second portion of reaction zone effluent, i.e., net effluent, is passed
into a separation zone in which excess benzene, cumene, di- and triiso-
propylbenzene, and other components are separated. As stated hereinabove,
it is desirable to reduce the quantity of excess benzene separated from
the net effluent stream in order to reduce utility consumption, while at
the same time it is desired to maintain a sufficient quantity of excess
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ioq2988
benzene in the reaction zone to prevent excessive formation of propylene
oligomers. This is accomplished by recirculation of a portion of the
resultant reaction zone effluent without separation. The principal effects
of process operation in the hereinabove described manner include: (1)
a reduction of utility consumption resulting from a reduction of excess
benzene separated from cumene in the net reaction zone effluent stream;
and (2) formation of relatively more di- and trialkylated benzene products
than in processes known~in the prior art. In the separation zone of the
present process, di- and triisopropylbenzenes are concentrated and passed
in admixture with excess benzene into a transalkylation reaction zone,
wherein a transalkylation catalyst is employed in a preferred embodiment.
The cumene-rich transalkylation reaction zone effluent stream is returned
to the separation zone.
DESCRIPTION OF THE DRAWING
This invention can be more clearly described and illustrated
with reference to the attached drawing. While of necessity, certain
limitations must be present in such a schematic description, no intention
is meant thereby to limit the generally broad scope of the invention. As
stated hereinabove, the first step of the process of the present invention
comprises alkylating benzene with propylene in an alkylation reaction zone
in the presence of an alkylation catalyst. In the drawing, this first
step is represented as taking place in alkylation reaction zone 1. How-
ever, a mixture of benzene and propylene must be furnished to this reac-
tion zone. ln the drawing, a propylene-rich feed stream is supplied to
the alkylation zone 1 via conduit 2, benzene is prepared as a recycle
stream as hereinbelow described and furnished to the alkylation zone 1
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via conduit 3, which combines with conduit 2; and an alkylation zone
effluent recirculation stream including principally benzene and cumene
is prepared as described hereinbelow and furnished to the alkylation zone
inlet via conduits 4 and 2. The lastly mentioned stream provides addi-
tional benzene for the purpose of increasing the molar benzene/propyleneratio in the alkylation reaction zone. The combined mixture of propylene
reactant, recycle benzene, and recirculated reaction zone effluent is
then introduced into realction zone 1 via conduit 2. Effluent of the alkyla-
tion reaction zone 1 is withdrawn via conduit 5, a portion is recirculated
via conduit 4 to provide the recirculation stream described hereinabove,
and the remaining portion is passed via conduit 5 into a separation zone
6. Also introduced into the separation zone 6 is an effluent stream
from a transalkylation reaction zone as described hereinbelow, the trans-
alkylation zone effluent stream passing through conduit 7. A benzene feed
stream via conduit 8 is also introduced into the separation zone 6 of the
present process.
The propylene-rich feed stream supplied to the alkylation reac-
tion zone via conduit 2 can be prepared as an effluent stream from various
processes such as fluid catalytic cracking or pyrolysis, and will normally
include non-reactive paraffins, principally propane, but also substantially
smaller quantities of ethane and butane. Olefins other than propylene
result in undesirable products in the alkylation reaction to produce
cumene, therefore propylene normally comprises at least 99 percent of the
olefin content of this stream. The benzene feed stream introduced into
the process in conduit 8 is a high purity stream commonly containing at
least 39.5 percent benzene which is frequently available as an effluent
stream from an aromatics extraction process. Other aromatics are harmful
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in the sense that undesirable by-products result from their presence, and
non-aromatics are normally undesirable because of difficulty in separation
of these non-aromatics from benzene in the separation zone 6. Accordingly,
in the present process, the streams introduced into the separation zone 6
include principally benzene, cumene, propane, and di- and triisopropylbenzene,
with relatively smaller amounts of light paraffins (ethane and butane),
aromatics (toluene and xylene), butylbenzene, and oligomers of propylene.
In the separation zone 6, by suitable combination of flashing,
fractionation, absorption, and stripping, several streams are separated
to withdraw the inlet components stated hereinabove. A propane-rich product
stream including other light paraffins is withdrawn via conduit 9; a
benzene-rich product drag stream including non-aromatic components is
withdrawn via conduit 10; an excess benzene-rich stream is withdrawn via
conduit 3, a portion is recycled to the alkylation reaction zone 1 via
conduit 3 as hereinabove described and a second portion is passed via
conduit 11 to a transalkylation reaction zone as described hereinbelow;
a butylbenzene-rich product stream is withdrawn via conduit 12, a cumene
product stream is withdrawn via conduit 13, a propylene oligomer product
stream is withdrawn via conduit 14; and a di- and triisopropylbenzene-
rich stream is withdrawn via conduit 15.
The di- and triisopropylbenzene-rich stream withdrawn from the
separation zone via conduit 15 is admixed with recycle benzene via conduit
11, and the mixture is passed into a transalkylation reaction zone 16,
which in a preferred embodiment contains a solid phosphoric acid catalyst.
Cumene-rich effluent of the transalkylation reaction zone is passed via
conduit 7 into the separation zone 6, as described hereinabove.
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DETAILED DESCRIPTION OF THE INVENTION
Suitable reactants in the present inventive process to produce
cumene are propylene and benzene. Propylene is normally supplied in ad-
mixture with propane in an effluent stream from a fluid catalytic cracking
unit, a pyrolysis unit, a thermal cracking unit, or other refining unit.
Other light paraffinic hydrocarbons such as ethane and butane may be present
in limited quantity in d propylene-rich feed stream to the present process,
but olefinic compounds other than propylene lead to production of alkyl-
aromatics other than cumene and accordingly are undesirable as a feedstock.
A typical propylene feed stream is illustrated as follows in mole percent:
ethane 0.10, propane 24.80, propylene 74.95, isobutane 0.11, n-butane 0.01,
and butylene 0.03. Benzene is supplied to the present process in high
purity, greater than 99.5 percent, to prevent undesirable side reactions
and to eliminate additional fractionation requirements to separate benzene
and close boiling non-aromatic components within the present process. A
typical benzene feed stream is prepared in an aromatics extraction unit and
contains the following components in mole percent: benzene 99.90, toluene
0.05, and non-aromatics ,0.05. While in the accompanying sketch the benzene
feed stream is introduced into the separation 70ne of the present process,
this stream may also be introduced into the alkylation reaction zone or
the transalkylation reaction zone.
The inlet stream to the alkylation reaction zone of the present
process comprises three streams in admixture: the fresh propylene-rich
feed stream, a recirculated portion of the resultant effluPnt from the
alkylation reaction zone as described hereinbelow, and a benzene-rich
stream which may be supplied to the present process as a fresh feed stream,
or more preferably, as a recycle benzene-rich stream as described hereinbelow.
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Operating conditions in the alkylation reaction zone include an inlet
temperature of about 150~ to 260C. with a preferred temperature of about
195 to 215C.; about 20 to 60 atmospheres pressure, about 0.2 to 2.0
volumes of catalyst per volume/hour of net reaction zone effluent herein-
below defined, about 2 to 6 moles of benzene in the recycle benzene-rich
stream per mole of propylene in the inlet stream to the alkylation reaction
zone, with a preferred molar ratio of recycle benzene tc propylene in the
inlet stream of about 3' and about 1 to 100 moles of benzene in the
recirculated effluent stream per mole of propylene in the inlet stream to
the alkylation reaction zone, with a preferred molar ratio of recirculated
benzene to propylene in the inlet stream of 3 to 20. The process of the
present invention may comprise a single reactor or multiple reactors in
series or parallel flow, flow through each reactor being downflow, upflow,
radial flow, or other, there being no limitation to the inventive concept
of the present process by the configuration of reaction zone design.
The process of the present invention can be effected utilizing
any conventional or otherwise available alkylation catalyst. Such cata-
lysts are typically described as acid-acting catalysts and may be of the
homogeneous or heterogeneous variety. Thus, the catalyst can be a supported
or unsupported Friedel Crafts metal halide, for example anhydrous aluminum
chloride, ferric chloride, stannic chloride, boron fluoride, zinc chloride
and the like. Certain mineral acids, especially sulfuric acid, hydro-
fluoric acid, and phosphoric acid are known for their capacity to catalyze
the alkylation reaction. Sulfuric acid containing less than about 10 wt. %
water, hydrofluoric acid of at least 83% concentration, or liquefied
anhydrous hydrogen fluoride, are suitably employed. Acid-acting inorganic
oxides including phosphorous pentoxide, amorphous silica-alumina, and
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certain crystalline aluminosilicates or zeolites, particularly acid-
extracted mordenite and the Type Y zeolite, are useful as catalysts in
the process of this invention.
The present invention is particularly directed to an alkylation
reaction in the presence of a solid phosphoric acid catalyst. Thus
solid phosphoric acid catalyst which may be utilized in the method of
the present invention may be made by mixing an acid of phosphorous, such
as ortho-, pyro-, or tetraphosphoric acid and a finely divided, generally
siliceous, solid carrier (such as diatomaceous earth, prepared forms of
silica, reactivated clays, and the like) to form a wet paste. The paste
is then calcined at temperatures generally below about 500C. to produce
a solid cake which is thereafter ground and sized to produce particles of
useable mesh. If the calcination is carried out at temperatures above
about 400C., it may be desirable to rehydrate the catalyst granules at
a temperature between about 200C. and 350C., typically 260~C., to produce
an acid composition corresponding to high alkylating activity. The cata-
lyst preparation procedure may be varied by forming particles of the original
paste by extrusion or by pelleting methods after which the formed particles
are calcined and, if necessary, rehydrated. A solid phosphoric acid
catalyst prepared from a major proportion by weight of a phosphoric acid
having at least as large a water content as that of the pyro acid and a
minor proportion of the siliceous carrier, such as kieselguhr, is preferred
for use in the present process. In a preferred embodiment of the present
invention, the alkylation catalyst includes about 50 to 75 percent by
weight phosphoric acid. A further description of a satisfactory solid
phosphoric acid catalyst is available in U.S. Patent No. 1,993,513.
The resultant effluent of the alkylation reaction zone is divided
into two streams, the first being a recirculated effluent stream and the
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second being a net reaction zone effluent stream. An important part of the
inventive concept of the present process concerns recirculating a portion
of the alkylation reaction zone effluent to the inlet of the alkylation
zone to admix with the fresh propylene-rich feed stream and the recycle
benzene-rich stream to form the inlet stream to the alkylation reaction
zone as described hereinabove. Composition of the alkylation zone efflu-
ent is principally benzene with relatively lesser amounts of propane,
cumene, and di- and triisopropylbenzene, and relatively smaller amounts
of butylbenzene, propylene, oligomers, non-aromatics, etc. Propylene is
essentially 100 percent reacted in the alkylation reaction zone, while
benzene forms at least 50 molar percent and preferably 60 to 80 molar
percent of the effluent. Accordingly, recirculation of a portion of the
effluent to the inlet of the alkylation reaction zone increases the benzene/
propylene ratio in the alkylation reaction zone.
Several benefits result as the benzene/propylene ratio increases
in the alkylation reaction zone, including (1) a dilution of propylene
molecules with benzene molecules favoring formation of isopropylbenzene
(cumene) and limiting formation of propylene oligomers; and, (2) a benzene/
propylene ratio greater than one is indicative of the presence of excess
benzene, which acts as a heat sink to absorb heat generated by the exo-
thermic alkylation reaction, and limit the formation of propylene oligomers
and solid hydrocarbon deposits on the catalyst, both of which increase
with higher temperature in the alkylation reaction zone. In prior art
processes, a temperature increase from inlet to outlet of the alkylation
reaction zone of about 20 to 40C. is typical without quench, and in the
present process, a similar temperature increase or lower is desired,
and is attained by suitably increasing the flow rate of recirculated
effluent.
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The recirculated e~fluent stream may be indirectly cooled by
cooling means such as a water cooled exchanger, an air cooled exchanger,
or an exchanger in which another hydrocarbon stream is used as the coolant,
to a temperature of about 150 to 260C., i.e., to a temperature essen-
tially equivalent to the temperature of the reaction zone inlet stream, or
it may be admixed without cooling with a mixture of the propylene feed
stream and the recycle benzene stream, the mixture being at a suitable
temperature to provide an alkylation reaction zone inlet temperature of
about 150 to 260C., and preferably about 195 to 215C. Furthermore, a
third portion of the reaction zone effluent stream may be indirectly
cooled by similar cooling means as stated hereinabove to a temperature of
about 35 to 150C. and passed into the reaction zone at suitable points
to act as quench to cool the reactants and prevent excessive increase of
temperature from inlet to outlet of the alkylation reaction zone. When
the alkylation catalyst employed is a supported catalyst, for example
solid phosphoric acid, suitable quench points may be chosen by dividing
the catalyst bed into several successive separate beds and passing a
portion of the quenching medium between each of the successive beds. In
a preferred mode of operation, a portion of alkylation reaction zone
effluent is cooled to about 35-95C. and introduced into the reaction
mixture as a quenching medium between at least two successive catalyst
beds in an amount sufficient to reduce the temperature of the reaction
mixture to within about -4 C. of the temperature of the reaction mixture
entering the last preceding catalyst bed.
As recirculation of alkylation reaction zone effluent to the
inlet of the reaction zone increases, the concentration of cumene in the
alkylation reaction zone also increases, thus providing more potential
Z988
sites for poly-alkylated benzene products and resulting in increased
production of di- and triisopropylbenzene as compared to prior art pro
cesses. ~Ihereas di- and triisopropylbenzene production in prior art
processes is typically less than 5 mole percent as compared with cumene
production, the present process results in 5 to 20 mole percent or more.
Propane, butane, benzene, and cumene comprises about 90 to
95 mole percent of the alkylation reaction zone effluent, and toluene,
butylbenzene, di- and triisopropylbenzene, propylene oligomers and other
components in trace amounts comprise lO to 5 mole percent. The net
alkylation zone effluent stream withdrawn from the alkylation reaction
zone is passed separately or in admixture with a transalkylation reaction
zone effluent stream set forth hereinbelow into a separation zone, wherein
by means of a combination of fractional distillation, absorption, strip-
ping, and flashing, the des1red components are separated at separation con-
ditions selected to minimize utility consumption. Product streams with-
drawn from the separation zone include a propane-rich stream, a cumene
stream, a butylbenzene-rich stream, a propylene oligomer stream, and a
benzene drag stream, the lastly stated stream serving to remove trace
quantities of non-aromatic components boiling between propane and cumene.
The present inventive concept is not limited by a specific
combination of separation steps, however the separation of excess benzene
and cumene is at present most economically accomplished by fractional
distillation, in which benzene and lighter components are separated into
an overhead fraction and cumene and heavier components are separated
into a bottoms fraction. The separation of excess benzene in prior art
processes has a relatively large capital and utility requirement result-
ing from the greater quantity of excess benzene separated from cumene as
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compared with the present process. While benzene/cumene molar ratios
in the reaction zone net effluent of prior art processes is about 6.5,
this ratio in the present process is about 2 to 5 at constant molar
benzene/cumene ratio in the alkylation reaction zone. Excess benzene
separated from the alkylation reaction zone effluent may be withdrawn from
the process as a product stream, but preferably a first portion is passed
to the inlet of the alkylation reaction zone as a recycle benzene-rich
stream and a second portion is passed into a transalkylation reaction zone
in admixture with a di- and triisopropylbenzene-rich stream, also separated
and withdrawn from the separation zone. The admixture of benzene and di-
and triisopropylbenzene is passed into a transalkylation reaction zone,
wherein the reactants combine to produce cumene.
The inventive process of the present invention is not limited
by the catalyst incorporated in the transalkylation reaction zone. Vari-
ous catalysts are known to one skilled in the art, such as a boron tri-
fluoride-modified inorganic oxide catalyst described in U.S. Patent 3,200,163,
an acid extracted crystalline aluminosilicate catalyst described in U.S.
Patent 3,551,510, or a fluorine containing refractory inorganic oxide
described in U.S. Patent 3,205,277. Preferred as a transalkylation cata-
lyst in the present invention is a solid phosphoric acid catalyst preparedin a similar manner as the one used hereinabove in the alkylation reaction
zone, or especially preferred is a solid phosphoric acid cat~lyst contain-
ing 70 to 90 weight percent phosphorous. The transalkylation zone may be
equipped with heat transfer means, baffles, trays, heating means, pumping
means, etc. The reaction zone is preferably of the adiabatic type, and is
not limited by reactor design or configuration. Conditions utilized in
the transalkylation reaction zone may be varied over a relatively wide
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range; the transalkylation reaction may be effected at temperatures of
from 35 to 370C., at pressures of about 15 to 200 atmospheres, at
molar benzene/polyisopropylbenzene ratio of about 4 to 16, and liquid
hourly space velocity based on reaction zone effluent of 0.1 to 20. With
the preferred solid phosphoric acid catalyst, transalkylation reaction
conditions include a temperature of about 175 to 290C., a pressure of
about 20 to 40 atmospheres, molar benzene/polypropylbenzene ratio of
about 4 to 16, and liquid hourly space velocity based on reaction zone
effluent of 0.5 to 5Ø As described hereinabove, effluent of the trans-
alkylation reaction zone is passed into the separation zone.
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