REMOVAL AND NEUTRALIZATION OF ACID
CATALYST FROM PRODUCTS OF CUMENE
HYDROPEROXIDE CLEAVAGE
The present invention relates generally to a process for the
production of phenol by the oxidation of cumene and mineral acid-
catalyzed cleavage of cumene hydroperoxide. In particular it relates to
the removal and neutralization of mineral acid catalyst and by-product
organic acids from the cleavage products.
The production of phenol by the oxidation of cumene followed by
the mineral acid-catalyzed cleavage of cumene hydroperoxide is well-
known. The cleavage product contains phenol and acetone as the
principal products together with varying amounts of side-products in the
form of tars and organic substances such as organic acids. Before the
products can be recovered it is necessary to remove or neutralize the
mineral acid catalyst in the cleavage products since the presence of the
acid catalyst in the subsequent distillation interferes with the efficient
recovery of the products and by-products of the reaction in addition to
causing corrosion of the distillation equipment Such neutralization is
accomplished by adding sodium hydroxide or other suitable alkali metal
hydroxide or oxide to the cleavage product mixture. Two immiscible
phases are formed. The top organic phase is the neutralized cleavage
mass and the bottom aqueous phase is the resulting sodium sulfate, or
alkali metal sulfate, solution (higher density). Good separation of the
aqueous phase from the organic phase is essential before the organic
phase is subjected to downstream distillation.
It is taught in US Patent No. 3,931,339 to contact the products of the
mineral acid catalyzed cleavage of cumene hydroperoxide in a first zone
with an aqueous solution comprising an inorganic salt and an excess of an
alkali metal hydroxide or alkali metal phenate over the stoichiometric
quantity required for neutralization of the mineral acid catalyst and
organic acid by-products. The described invention employing an excess
of alkali metal hydroxide or alkali metal phenate to completely remove
the mineral acid catalyst and at least part of the organic acids present as
alkali metal salts is asserted to overcome the disadvantages of the prior art
which attempted to maintain the pH slightly below 7.0 during the catalyst
removal and neutralization step in order to prevent alkali metal phenate
being carried over to the subsequent washing step.
It is further taught in '339 that difficulties are experienced during
commercial operation in maintaining the pH slightly below 7.0 resulting
in the aforementioned disadvantages. Moreover even if the pH is
successfully maintained below 7.0 it is sometimes found that chemical
losses, e.g. loss of methylstyrene, occur under acid conditions.
The pH is preferably maintained by the '339 patented invention in
the range of 7 to 9 to overcome these prior art problems and to minimize
corrosion of downstream equipment which occurs when the acids are not
completely neutralized.
Phenol is itself acidic and will convert to its alkali metal salt above
a pH of 6.5 resulting in an undesirable yield loss. The phenate salt, once
formed, is soluble in the organic layer and carries through in the organic
phase to downstream equipment fouling reboilers and contamination of
tars which must be incinerated or otherwise disposed of in an
environmentally sound manner.
US Patent No. 4,262,150 teaches a different process to recover
phenol from the reaction mixture resulting from the acid cleavage of
cumene hydroperoxide. It broadly embodies effecting the neutralization
of the reaction mixture, and forming a reaction mixture comprising a
phenol, a ketone, a secondary alkylbenzene and a salt of neutralization;
(b) processing an initially salt-free aqueous stream in counter current
contact with the neutralized salt-containing reaction mixture; (c)
progressively saturating the resulting aqueous phase with said salt and
salting out the organic acid cleavage products contained therein whereby
the aqueous phase is recovered containing substantially all of said the and
substantially free of organic products.
One of the more specific embodiments of the 150 invention is a
method for treating a reaction mixture resulting from the sulfuric acid
cleavage of cumene hydroperoxide comprising the steps of (a) effecting
the neutralization of the reaction mixture with sodium phenate, and
forming a reaction mixture comprising phenol, acetone, cumene and a
sodium sulfate salt of neutralization; (b) processing an initially salt-free
aqueous stream in counter current contact with the neutralized sodium
sulfate-containing reaction mixture at a temperature of from about 95° to
about 120° F. and at a pH of from about 2 to about 6; (c) progressively
saturating the resulting aqueous phase with the sodium sulfate and
salting-out the organic acid cleavage products contained therein whereby
the aqueous phase is recovered containing substantially all of the sodium
sulfate and substantially free of organic products.
The process disclosed in the '150 patent is complex with repetitive
cycles requiring substantial energy input and capital investment
A simpler, more controllable process is now required to meet
environmental concerns at a reasonable level of investment
US Patent No. 4,262,151 describes an even more convoluted
approach to solving this critical problem which comprises (a) effecting the
direct neutralization of the acid cleavage reaction mixture and forming a
reaction mixture comprising a phenol, a ketone, a secondary alkylbenzene
and a salt of neutralization; (b) charging the salt-containing reaction
mixture to the mixing stage of the first of a plurality of mixer-settler
means, and admixing the same therein with a salt-containing aqueous
phase charged to a mixing stage in accordance with step (g); (c) separating
an organic phase and an aqueous phase in the settling stage of the first
mixer-settler means; (d) charging the organic phase to the mixing stage of
each succeeding mixer-settler means from the settling stage of the next
preceding mixer-settler means and effecting a progressive decrease in the
salt concentration of the organic phase in contact with an aqueous phase
charged to the mixing stage in accordance with step (g); (c) charging a
substantially salt-free water stream to the mixing stage of the last of the
plurality of mixer-settler means, and admixing the same therein with an
organic phase charged to the mixing stage in accordance with step (d); (0
separating an organic phase and an aqueous phase in the settling of stage
of the last mixer-settler means; (g) charging the aqueous phase to the
mixing stage of each preceding mixer-settler means from the settling steps
of the next succeeding mixer-settler means, and effecting a progressive
increase in the salt concentration of the aqueous phase in contact with an
organic phase charged to the mixing stage in accordance with step (d); (h)
discharging the salt-containing aqueous phase from the settling stage of
the first mixer-settler means substantially free of the organic phase; and (i)
recovering a substantially salt-free organic phase comprising a phenol, a
ketone and unreacted alkyl-substituted aromatic hydrocarbon from the
settling stage of the last mixer-settler means.
In the process of the '151 patent a sodium sulfate-containing
reaction mixture is charged to the mixing stage of the first mixer-settler
means and mixed at a temperature of from about 95° to about 120°F. and
at a pH of from abut 2 to about 4 with a sodium sulfate-containing
aqueous phase as in steps (e), (f) and (g) of the disclosed process. Not
only is this process complex and capital intensive, it is very difficult to
control pH in the highly acidic pH range of 2 to 4. Process reliability is
extremely difficult if a key parameter such as pH is not controlled.
Further, in the pH range of 2 to 4, sulfuric acid exists in the free state and
if it passes downstream in this form, it will cause heavy corrosion which
will severely damage the process equipment and could cause material
spills and environmental and safety hazards.
It has now been discovered that a partial neutralization of the
sulfuric acid, employed as a catalyst in the cleavage of cumene
hydroperoxide, to its half neutral salt sodium hydrogen sulfate, i.e.
sodium bisulfate (NaHS04), results in improved phenol yields,
prevention of downstream equipment corrosion and minimization of ash
content in phenol tars. This partial neutralization is accomplished by
controlling the level of sodium hydroxide, or other suitable alkali metal
hydroxide or oxide added to neutralize the cleavage mass, i.e., the
product of cumene hydroperoxide cleavage, to control the pH of the
aqueous phase during neutralization to the range of from about 4.0, to
about 4.9. Within this pH range the sulfuric acid is converted to NaHSO^
not Na2 SO4, substantially no free H2 SO4 exists and only a small portion
of the organic acids are converted to their basic salts with a major portion
of the organic acids remaining in the free, un-neutralized state. The
substantial absence of free H2 SO4 and the reduction in the level of
organic acids converted to salts results in a surprising reduction in
corrosion of downstream equipment
It has been determined that the sodium salts of the organic acids
are non-volatile and do not distill overhead during the subsequent
distillation processes. Instead they pass to the bottoms of the columns
during distillation and concentrate to high levels in the sumps of the hot
distillation columns where they then decompose due to the heat and
revert to their free acid state. Once formed in this severe environment,
these acids quickly corrode the stainless steel equipment causing severe
damage, and leaching out of chromium, nickel and iron, which is
environmentally undesirable since this metal contamination ultimately
finds its way into the phenolic tar, which must be properly disposed of or
burned in governmental regulated incinerators.
Thus complete neutralization as taught by the prior art only
increases corrosion while partial neutralization with control of pH
between 4.0 to 4.9 preferably about 4.0 to about 4.7 more preferably about
4.0 to about 4.5, and most preferably 4.0 to about 4.2 substantially reduces
corrosion.
In a preferred embodiment only about 60%, preferably less than
50% and more preferably less than 40%, by weight of the organic acids are
converted to their sodium salts during neutralization. Thus a substantial
portion of these acids are allowed to remain in their free acidic state so
that they exist as low-boiling volatile, distillable compounds during
subsequent downstream distillation. In this manner they can be quickly
removed as an overhead distillate cut and not allowed to build-up in
concentration or find their way to the hot sumps of the columns.
Corrosion in the top of the column is minimal because temperatures are
lower and the organic acids are quickly purged from the columns.
Once the organic acids are separated from the phenol containing
product stream, the acids can be treated with sodium hydroxide to fully
neutralize them preferably at a pH of up to 9 or above. Since there is no
phenol present any suitable high pH can now be employed. The organic
acid salts are ultimately purged from the process in a waste water stream.
* As a result of the reduced corrosion in the downstream equipment,
which prolongs equipment life, the process of the present invention also
reduces the level of metals contamination in the phenol tar waste stream
which is disposed of in accordance with government regulations as a
hazardous waste. The reduction in chromium content in this stream is
particularly beneficial in reducing the environmental impact of
disposition of this waste stream. Chromium is one of the elements in the
stainless steel alloy employed in downstream equipment The usual
method of disposition of this tar stream is by incineration.
In a preferred embodiment of the present invention, an amount of
aromatic hydrocarbon effective to facilitate phase separation is added to
the input to the neutralization step. Preferred aromatic hydrocarbons are
those obtained as by-products of the phenol from cumene process or
inputs to the phenol from cumene process. More preferred aromatic
hydrocarbons are alkyl or alkenyl benzenes. Most preferred are cumene,
alpha-methylstyrene or a mixture thereof. Any and all of these
compositions may be found in the recycle streams of the phenol process.
The aromatic hydrocarbons which are water immiscible are added in an
amount of from about 3 to about 15 percent by weight of the total input
stream, preferably from about 4 to about 12 weight percent and most
preferably from about 5 to about 10 weight percent The improved phase
separation reduces sodium salt enrrainment Reduced sodium salt
entrainment reduces heat exchanger fouling and further reduces
corrosion. Fouled heat exchangers cause process downtime and loss of
production. Entrained salts end up in the phenol tar stream and
complicate the disposal of these tars by incineration in compliance with
government environmental regulations. Thus, the improved phase
separation resulting from this embodiment of the invention reduces a
major cause of process downtime, fouled heat exchangers, and lessens the
environmental impact of waste phenol tar disposal.
Figure 1 is a process flow diagram of that portion of the process for
the production of phenol and acetone from cumene which employs the
improvements of the present invention.
Turning now to Figure 1, vessel (1) represents the cumene
hydroperoxide cleavage stage of the process from which the cleavage
mass containing residual sulfuric acid catalyst enters the neutralizer (2)
through line (3). The pH of the neutralizer (2) is carefully controlled
between 4.0 and 4.9, preferably between 4.0 and about 4.7 and more
preferably between 4.0 and about 4.5 and most preferably from 4.0 to
about 4.2, so that the residual sulfuric acid catalyst is converted primarily
to NaHSC>4, preferably at least about 99 percent by weight of sulfuric acid
is converted to NaHSO^ more preferably about 99.9 percent by weight
and most preferably about 99.99 percent by weight In this pH range
substantially no free sulfuric acid remains. A pH of about 4.1 is the target
pH for optimum process operation.
Two phases, organic and aqueous, are formed in the neutralizer (2).
The organic phase leaves the neutralizer (2) and enters the splitter (4)
through line (5) with the aqueous phase containing sulfates leaving the
neutralizer (2) through line (6). Although substantially all of the aqueous
phase exits the neutralizer (2) through line (6) a small amount of water in
minuscule droplets is entrained in the organic phase leaving the
neutralizer in line (5). This entrained water is visible as a faint haze in the
organic phase and contains a high level of salts, including sodium
bisulfate and sodium salts of the organic acids. Elimination of this
entrained salt-containing water before it enters the splitter (4) has a
marked effect on the level of sodium salts corrosion in the splitter and
downstream equipment Installation of a coalescer in line (5) is a most
effective way to reduce this minor amount of aqueous solution of these
various salts substantially and further reduce the corrosion in the bottom
of the splitter and other downstream equipment The sodium levels in
lines (9) and (5) as set forth in the examples were measured with the
coalescer in operation. The sample point in line (5) was between the
coalescer, not shown in the drawing, and the splitter (4). The splitter is a
distillation column. The organic phase is separated in the splitter (4) with
the acetone-rich portion containing the organic acids exiting overhead
through line (7) and the phenol-rich portion containing the tars exiting as
bottoms through line (9). Prior to the present invention the bottom
portion of the splitter (4) was subject to severe corrosion from the organic
acid salts which are soluble in the organic phase and which, when
subjected to the high temperatures in the bottom portion of the splitter (4)
reformed as acids causing heavy damage and requiring frequent repairs
to, and replacement of, splitter (4). The phenol-rich portion is purified
and treated in the phenol purification operation (10) from which phenol
product is taken through line (11) to storage or use and tars and heavy
ends are taken through line (13) to tar cracking (14). In tar cracking (14)
usable products are recycled through line (15) to the neutralizer (2) and
waste tars and residual salts are taken to waste disposal through line (16).
It is in the disposition of these waste tars and residual salts where the
environmental benefit of the low corrosion in the splitter (4) is found. The
reduction in the level of chromium ions in the stream in line (16) lessens
the level of hazardous waste products from the incineration or other
disposal of this stream reducing the environmental impact of such waste
disposition. The overhead from the splitter (4) is taken to the acetone
purification operation (18) through line (7). As noted above, this overhead
stream in line (7) contains the organic acids remaining from the
neutralization according to the process of the present invention in
neutralizer (2). Before the stream enters the acetone purification operation
(18), sodium hydroxide, or other suitable alkali metal hydroxide or oxide,
preferably as an aqueous solution, in an amount sufficient to neutralize all
of the organic acids in the stream, e.g., preferably to raise the pH of the
stream to about 9 is added through line (17). Acetone product is taken
through line (19) to storage or use. Recycle acetone may optionally be
returned through line (21) to the cumene hydroperoxide cleavage stage of
the process (1) but such recycle through line (21) may, under some
circumstances, not be the preferred method of process operation. The
heavy organics including cumene and the aqueous phase containing acid
salts are taken to a separator(20) through line (23). The separator
separates the organic phase from the aqueous phase with the organic
phase taken to a cumene recovery operation through line (24) and the
aqueous phase being split between waste water containing the organic
acid salts being taken to waste disposal through line (25) and recycle
alkaline water returned to the neutralizer (2) through line (26). Because of
the high pH of the recycle alkaline water returned to the neutralizer (2)
through line (26), it is necessary from time to time to actually add sulfuric
acid into line (3), to the neutralizer (2) to keep the pH of the neutralizer (2)
within the 4.0 to about 4.9 range. The key is to monitor the pH of the
cumene hydroperoxide cleavage mass (1) and the recycle alkaline water in
line (26) and add sufficient acid into line (3) to the neutralizer (2) to keep
the pH of the neutralizer (2) in the 4.0 to about 4.9 range.
Example 1 and Comparative Examples 1A and IB
Except as set forth in the following description of these examples
the phenol process was operated under standard operating conditions as
known to the skilled phenol artisan. For periods of one month or more,
the pH of the neutralizer (2) was controlled within the ranges set forth in
Table 1 by monitoring the pH level of the recycle alkaline water and
adding minor amounts of sulfuric acid to the neutralizer (2) through line
(27) and line (3) when the acidity of cumene hydroperoxide cleavage (1)
was running on the high side of the pH range. The composition of the
bottoms stream in line (9) from splitter (4) was monitored for the weight
content of chromium, sodium and total solids with the range of results as
shown in Table 1:
The level of sodium in process stream in line (9) stream, which
indicates the level of sodium salts in the stream, as set forth in Table 1 is
proportional to the amount of sodium hydroxide added to neutralizer (2),
i.e., the less sodium hydroxide added to neutralizer (2) the lower the pH
of neutralizer (2) and the lower the level of sodium in the line (9) stream.
Total solids is the total ash content of the line (9) stream which includes
the sodium salts not exiting the neutralizer (2) through line (6). The key
parameter is the chromium level in the line (9) stream. The chromium
level shows the extent of corrosion of the stainless steel internals of splitter
(4). Below the pH range of 4.2 to 4.7, the level of corrosion is from about 7
to about 20 times greater than within this range. Above the pH range of
4.2 to 4.7, the level of corrosion is from about 5 to about 15 times greater.
The explanation for this minimum corrosion level in the 4.0 to 4.9 pH
range is given above, i.e., the conversion of sulfuric acid to sodium
bisulfate or alkali metal bisulfate, when an alkali metal hydroxide or
oxide other than sodium hydroxide is used, and not converting the
organic acids to unstable salts which revert back to the acids in the bottom
portion of splitter (4). Analysis of the stream in line (16) from the bottom
of tar cracking during the periods of operation of Example 1 and
comparative Examples 1A and IB confirm the low levels of corrosion in
other down stream equipment and the minimization of toxic heavy metals
in this primary waste stream from the process. The difference between
3 ppm by weight of chromium in the phenol tar waste stream and the
lowest level achieved following the best prior art practice which is 5 ppm
constitutes a 40% by weight reduction in chromium content in this waste
stream. Such a reduction allows the phenol tar waste stream to be
incinerated at a 40% higher rate and remain within government imposed
environmental limits a level of about 4 ppm by weight chromium gives a
25% higher rate of incineration. This speeds disposition of this stream and
increases process capacity The range of the results of these analyses by
weight are shown in Table 1 A.
Example 2-5 ,
By adding through line (27) an effective amount of aromatic
hydrocarbons to the input stream in line (3) to the neutralizer (2), operated
at a pH of from 4.0 to about 4.9, separation of the aqueous and organic
phases is greatly enhanced and the level of sodium salts in the organic
phase leaving the neutralizer (2) through line (5) is surprisingly reduced.
The reduction in sodium salts in the organic phase leaving neutralizer (2)
through line (5) also reduces the total solids or ash content in the waste
stream leaving tar cracking (14) through line (16). The effect of added
aromatic hydrocarbons on sodium salt content in the organic phase and
on total solids in the tar cracking waste steam is illustrated in Table 2. All
quantities are based upon weight
of 4.0 to about 4.9. When the level of added aromatic hydrocarbons is in
the range of from about 5% to about 10%, there is a further significant
reduction of sodium salt level in the organic phase as well as a substantial
reduction in total solids in the waste stream from the tar cracking
operation.
All patents cited herein are expressly incorporated in this
specification by reference and are a part of the teaching of this invention.
Unless expressly stated otherwise, all parts, percents or other
expressions of quantity are based upon weight
Although in the description of the present invention, sodium
hydroxide, which is the alkali metal hydroxide most widely used in
commercial manufacture of phenol, has been indicated as the agent to
neutralize the residual acid in the cleavage mass, the skilled artisan will
recognize that any alkali metal oxide or hydroxide can be used in the
practice of the invention since the close control in the neutralizing
equipment of pH in the range of 4.0 to about 4.9 is the key to the invention
not the particular alkali metal hydroxide used to control pH in this range.
We'claim
1. An improved method for the recovery of phenol from a cleavage
mass resulting from the sulfuric acid cleavage of cumene hydroperoxide
comprising neutralizing the cleavage mass, forming an aqueous phase and
an organic phase, separating the organic phase into an acetone-rich stream
and a phenol-rich stream, removing phenol tars from the phenol-rich
stream and cracking the phenol tars wherein the improvement comprises
maintaining the pH of the cleavage mass during neutralization between
4.0 and about 4.9 whereby the sulfuric acid is converted to the bisulfate
salt and substantially no free sulfuric acid remains in the cleavage mass
and corrosion of process equipment is reduced.
2. The method of Claim 1 wherein the method further comprises
purifying the acetone-rich stream and wherein the improvement further
comprises raising the pH of the acetone-rich stream to about 9 after the
stream is separated from the phenol-rich stream but before the acetone-
rich stream is purified whereby organic acids in the acetone-rich stream
are neutralized before the stream is purified and the corrosion of
processing equipment is further reduced.
3. The method of Claim 1 wherein the pH of the cleavage mass in
the neutralizer is between 4.0 and about 4.7.
4. The method of Claim 1 wherein the pH of the cleavage mass in
the neutralizer is between 4.0 and about 4.5.
5. The method of Claim 1 wherein the pH of die cleavage mass in
the neutralizer is between 4.0 to about 4.2.
6. The method of Claim 1 wherein the improvement further
comprises adding to the cleavage mass before it is neutralized aromatic
hydrocarbons in an amount of from about 3% to about 15% by weight of
the cleavage mass whereby the separation of the organic and aqueous
phases is enhanced and the level of salts in die organic phase is reduced.
7. The method of Claim 1 wherein the improvement further
comprises removing from the organic phase substantially all of the
entrained water visible as a faint haze before the organic phase is
separated into an acetone rich stream and a phenol-rich stream whereby
the level of sodium salts in the phenol-rich stream and the phenol tars is
substantially reduced.
8. A phenol tar waste composition produced by cleaving cumene
hydroperoxide to produce a cleavage mass, neutralizing the cleavage
mass at a pH of from 4.0 to about 4.9, forming an aqueous phase and an
organic phase, separating the organic phase into an acetone-rich stream
and a phenol-rich stream, removing phenol tars from the phenol-rich
stream, cracking the phenol tars and removing from the cracked phenol
tars a phenol tar waste composition wherein the phenol tar waste
composition comprises no more than about 4 parts per million by weight
of chromium whereby the phenol tar waste composition can be disposed
of by incineration in compliance with government imposed environmental
elements at about a. 25% increased rate of incineration.
9. The phenol tar waste composition of Claim 8 which comprises
no more than about 3 parte per million by weight of chromium.

This invention relates to an improved method for obtaining phenol
for a cleavage mass resulting from the sulfuric acid cleavage
of cumene hydroperoxide comprising neutralizing the cleavage
mass, forming an aqueous phase and an organic phase, separating
the organic phase into an acetone-rich stream and a phonol-rich
stream, removing phenol tars from the phenol-rich stream and
cracking the phenol tars wherein the improvement comprises
neutralizing by adding alkali metal hydroxide or oxides to the
cleavage product mixture and maintaining the pH of the cleavage
mass during neutralization between 4.0 and about 4.9 whereby
the sulfuric acid is converted to the bisulfate salt and substantially
no free sulfuric acid remains in the cleavage mass and
corrosion of process equipment is reduced.