Note: Descriptions are shown in the official language in which they were submitted.
CA 02248359 2005-07-08
PROCESS FOR PREPARING 1,3-PROPANEDIOL
This invention relates to the preparation of 1,3-propanediol. In one aspect,
the invention
relates to a cobalt-catalyzed process for manufacturing 1,3-propanediol in
high yields
without the use of a phosphine ligand for the cobalt catalyst. In a specific
aspect, the
invention relates to improving the degree of recovery and recycle of the
cobalt catalyst
in such a process.
1,3-propanediol (PDO) is an intermediate in the production of polyesters for
fibers and
films. It is known to prepare PDO in a two-step process involving ( 1 ) the
cobalt-
catalyzed hydroformylation (reaction with synthesis gas, H2 /CO) of ethylene
oxide to
intermediate 3-hydroxypropanal (HPA) and (2) hydrogenation of the HPA to PDO.
The
initial hydroformylation step can be earned out at temperatures greater than
100°
C. and at high syngas pressures to achieve practical reaction rates. The
resulting product
mixture is, however, rather unselective for HPA.
In an alternate hydroformylation method, the cobalt catalyst is used in
combination with
a phosphine ligand to prepare HPA with greater selectivity and at lower
temperature and
pressure. However, the use of a phosphine ligand adds to the cost of the
catalyst and
increases the complexity of catalyst recycle.
It would be desirable to prepare HPA in a low temperature, selective process
in which
cobalt catalyst recovery was inexpensive but essentially complete.
The present invention seeks to provide, in a process for the preparation of
1,3-
propanediol which does not require the use of a phosphine-ligated catalyst for
preparation of the HPA intermediate, essentially complete recovery and recycle
of the
cobalt catalyst.
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2
According to the invention, 1,3-propanediol is prepared in a process
comprising the
steps of
(a) contacting ethylene oxide with carbon monoxide and hydrogen in an
essentially non-
water-miscible solvent in the presence of an effective amount of a non-
phosphine-
ligated cobalt catalyst and an effective amount of a catalyst promoter, under
reaction
conditions effective to produce an intermediate product mixture comprising
less than
about 15 wt % 3-hydroxypropanal;
(b) adding an aqueous liquid to said intermediate product mixture and
extracting into
said aqueous liquid a major portion of the 3-hydroxypropanal to provide an
aqueous
phase comprising 3-hydroxypropanal in greater concentration than the
concentration of
3-hydroxypropanal in said intermediate product mixture, and an organic phase
comprising a major portion of the cobalt catalyst or a cobalt-containing
derivative
thereof;
(c) separating the aqueous phase from the organic phase;
(d) adding fresh non-water miscible solvent to said aqueous phase and
extracting into
said fresh solvent at least a portion of any cobalt catalyst or cobalt-
containing derivative
thereof present in such aqueous phase, to provide a second aqueous phase
comprising 3-
hydroxypropanal and a second organic phase comprising the cobalt catalyst or a
cobalt-
containing derivative thereof;
(e) separating the second aqueous phase from the second organic phase;
(f) passing the first organic phase and the second organic phase to the
reaction of step
(a);
(g) contacting the second aqueous phase comprising 3-hydroxypropanal with
hydrogen
in the presence of a
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hydrogenation catalyst under hydrogenation conditions to
provide a hydrogenation product mixture comprising
1,3-propanediol; and
(h) recovering 1,3-propanediol from said hydrogenation
product mixture.
The process enables the production of 1,3-propanediol
in high yields and selectivity without the use of a
phosphine-ligated cobalt catalyst in the hydroformylation
step, with enhanced recovery and recycle of the cobalt
catalyst.
FIGURE 1 is a schematic flow diagram of one
embodiment of the invention 1,3-propanediol preparation
process with enhanced cobalt recovery.
The invention 1,3-propanediol preparation process can
be conveniently described by reference to Figure 1.
Separate or combined streams of ethylene oxide 1, carbon
monoxide and hydrogen 2 are charged to hydroformylation
vessel 3, which can be a pressure reaction vessel such as
a bubble column or agitated tank, operated batchwise or
in a continuous manner. The feed streams are contacted in
the presence of a non-phosphine-ligated cobalt catalyst,
i.e., a cobalt carbonyl composition which has not been
prereacted with a phosphine ligand. The hydrogen and
carbon monoxide will generally be introduced into the
reaction vessel in a molar ratio within the range of 1:2
to 8:1, preferably 1.5:1 to 5:1.
The reaction is carried out under conditions
effective to produce a hydroformylation reaction product
mixture containing a major portion of 3-hydroxypropanal
(HPA) and a minor portion of acetaldehyde and
1,3-propanediol, while maintaining the level of
- 3-hydroxypropanal in the reaction mixture at less than
15 wt%, preferably within the range of 5 to 10 wt%. (To
provide for solvents having different densities, the
desired concentration of HPA in the reaction mixture can
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be expressed in molarity, i.e., less than 1.5M,
preferably within the range of 0 . 5 to 1~I. )
The hydroformylation reaction is carried out at
elevated temperature generally less than 100 °C,
preferably 60 to 90 °C, most preferably 75 to 85 °C, and
at a pressure within the range of 3.4 to 34.5 MPa (500 to
5000 psig), preferably (for process economics) 6.9 to
24.1 MPa (1000 to 3500 psig), with higher pressures
preferred for greater selectivity. The concentration of
3-hydroxypropanal in the intermediate product mixture can
be controlled by regulation of process conditions such as
ethylene oxide concentration, catalyst concentration,
reaction temperature and residence time. In general,
relatively low reaction temperatures (below 90 °C) and
relatively short residence times (20 minutes to 1 hour)
are preferred. In the practice of the invention method,
it is possible to achieve HPA yields (based on ethylene
oxide conversion) of greater than 80%, with formation of
greater than 7 wt% HPA, at rates greater than 30 h-1.
(Catalytic rates are referred to herein in terms of
"turnover frequency" or "TOF" and are expressed in units
of moles per mole of cobalt per hour, or h-1.) Reported
rates are based on the observation that, before a
majority of EO is converted, the reaction is essentially
zero-order in ethylene oxide concentration and
proportional to cobalt concentration.
The hydroformylation reaction is carried out in a
liquid solvent inert to the reactants. By "inert" is
meant that the solvent is not consumed during the course
of the reaction. In general, ideal solvents for the
phosphine ligand-free process will solubilize carbon
monoxide, will be essentially non-water-miscible and will
exhibit low to moderate polarity such that the
3-hydroxypropanal intermediate will be solubilized to the
desired concentration of at least 5 wto under
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hydroformylation conditions, while significant solvent
will remain as a separate phase upon water extraction.
By "essentially non-water-miscible" is meant that the
solvent has a solubility in water at 25 °C of less than
25 wto, so as to form a separate hydrocarbon-rich phase
upon water extraction of HPA from the hydroformylation
reaction mixture. Preferably this solubility is less
than 100, most preferably less than 5 wto. The
solubilization of carbon monoxide in the selected solvent
will generally be greater than 0.15 v/v (1 atm, 25 °C),
preferably greater than 0.25 v/v, as expressed in terms
of Ostwald coefficients.
The preferred class of solvents are alcohols and
ethers which can be described according to the formula
R2-O-R1 (1)
in which R1 is hydrogen or C1_20 linear, branched,
cyclic or aromatic hydrocarbyl or mono- or polyalkylene
oxide and R2 is C1-20 linear, branched, cyclic or
aromatic hydrocarbyl, alkoxy or mono- or polyalkylene
oxide. The most preferred hydroformylation solvents can
be described by the formula
R3
R4 C-O-R1 ( 2 )
R5
in which R1 is hydrogen or C1-g hydrocarbyl, and R3, R4
and R5 are independently selected from C1_g hydrocarbyl,
alkoxy and alkylene oxide. Such ethers include, for
example, methyl-t-butyl ether, ethyl-t-butyl ether,
diethyl ether, phenylisobutyl ether, ethoxyethyl ether,
diphenyl ether and diisopropyl ether. Blends of solvents
such as tetrahydrofuran/toluene, tetrahydrofuran/heptane
and t-butylalcohol/hexane can also be used to achieve the
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desired solvent properties. The currently preferred
solvent, because of the high yields of HPA which can be
achieved under moderate reaction conditions, is methyl-t-
butyl ether.
The catalyst is a non-phosphine-ligated cobalt
carbonyl compound. Although phosphine-ligated catalysts
are active for hydroformylation reactions, the invention
process is designed to achieve good yield and selectivity
without the additional expense of the ligand. The cobalt
catalyst can be supplied to the hydroformylation reactor
in essentially any form including metal, supported metal,
Raney-cobalt, hydroxide, oxide, carbonate, sulfate,
acetylacetonate, salt of a carboxylic acid, or as an
aqueous cobalt salt solution, for example. It may be
supplied directly as a cobalt carbonyl such as
dicobaltoctacarbonyl or cobalt hydridocarbonyl. If not
supplied in the latter forms, operating conditions can be
adjusted such that cobalt carbonyls are formed in situ
via reaction with H2 and CO, as described in J. Falbe,
"Carbon Monoxide in Organic Synthesis," Springer-Verlag,
NY (1970). In general, catalyst formation conditions
will include a temperature of at least 50 °C and a carbon
monoxide partial pressure of at least 0.7 MPa (100 psig).
For more rapid reaction, temperatures of 120 to 200 °C
should be employed, at CO pressures of at least 3.4 MPa
(500 psig). Addition of high surface area activated
carbons or zeolites, especially those containing or
supporting platinum or~palladium metal, can accelerate
cobalt carbonyl formation from non-carbonyl precursors.
The resulting catalyst is maintained under a stabilizing
atmosphere of carbon monoxide, which also provides
protection against exposure to oxygen. The most
economical and preferred catalyst activation and
reactivation (of recycled catalyst) method involves
preforming the cobalt carbonyl under H2/CO from cobalt
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hydroxide in the presence of a small amount of seed
cobalt carbonyl. The conversion of Co2+ to the desired
cobalt carbonyl is carried out at a temperature within
the range of 75 to 200 °C, preferably 100 to 140 °C and a
pressure within the range of 6.9 to 34.5 MPa (1000 to
5000 psig) for a time preferably less than 3 hours. The
preforming step can be carried out in a pressurized
preforming reactor or in situ in the hydroformylation
reactor.
The amount of cobalt present in the reaction mixture
will vary depending upon the other reaction conditions,
but will generally fall within the range of 0.01 to
1 wt%, preferably 0.05 to 0.3 wt%, based on the weight of
the reaction mixture.
The hydroformylation reaction mixture will preferably
include a catalyst promoter to accelerate the reaction
rate. Suitable promoters include sources of mono- and
multivalent metal cations of weak bases such as alkali,
alkaline earth and rare earth metal salts of carboxylic
acids. Also suitable are lipophilic promoters such as
lipophilic phosphonium salts and lipophilic amines, which
accelerate the rate of hydroformylation without imparting
hydrophilicity (water solubility) to the active catalyst.
As used herein, "lipophilic" means that the promoter
tends to remain in the organic phase after extraction of
HPA with water. The promoter will generally be present
in an amount within the range of 0.01 to 0.6 moles per
mole of cobalt. Suitable metal salts include sodium,
potassium and cesium acetates, propionates and octoates;
calcium carbonate; and lanthanum acetate. The currently
preferred metal salt, because of its availability and
demonstrated promotion of ethylene oxide
hydroformylation, is sodium acetate. The currently
preferred lipophilic promoters are dimethyldodecyl amine
and tetrabutylphosphonium acetate.
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It is generally preferred to regulate the
concentration of water in the hydroformylation reaction
mixture, as excessive amounts of water reduce (HPA + PDO)
selectivity below acceptable levels and may induce
formation of a second liquid phase. At low
concentrations, water can assist in promoting the
formation of the desired cobalt carbonyl catalyst
species. Acceptable water levels will depend upon the
solvent used, with more polar solvents generally being
more tolerant of higher water concentrations. For
example, optimum water levels for hydroformylation in
methyl-t-butyl ether solvent are believed to be within
the range of 1 to 2.5 wto.
Following the hydroformylation reaction,
hydroformylation reaction product mixture 4 containing
3-hydroxypropanal, the reaction solvent, 1,3-propanediol,
the cobalt catalyst and a minor amount of reaction by-
products, is cooled and passed to extraction vessel 5,
wherein an aqueous liquid, generally water and optional
miscibilizing solvent, are added via 6 for extraction and
concentration of the HPA for the subsequent hydrogenation
step. Liquid extraction can be effected by any suitable
means, such as mixer-settlers, packed or trayed
extraction columns, or rotating disk contactors.
Extraction can, if desired, be carried out in multiple
stages. The water-containing hydroformylation reaction
product mixture can optionally be passed to a settling
tank (not shown) for resolution of the mixture into
aqueous and organic phases. The amount of water added to
the hydroformylation reaction product mixture will
generally be such as to provide a water: mixture ratio
within the range of 1:1 to 1:20, preferably 1:5 to 1:15.
The addition of water at this stage of the reaction may
have the additional advantage of suppressing formation of
undesirable heavy ends. Extraction with a relatively
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small amount of water provides an aqueous phase which is
greater than 20 wt% HPA, preferably greater than 35 wt%
HPA, permitting economical hydrogenation of the HPA to
PDO and recovery of PDO product. The water extraction is
preferably carried out at a temperature within the range
of 25 to 55 °C, with higher temperatures avoided to
minimize condensation products (heavy ends) and catalyst
disproportionation to inactive, water-soluble cobalt
species. In order to maximize catalyst recovery, it is
optional but preferred to perform the water extraction
under 0.3 to 1.4 MPa (50 to 200 psig) carbon monoxide at
25 to 55 °C.
The organic phase containing the reaction solvent and
the major portion of the cobalt catalyst can be recycled
from the extraction vessel to the hydroformylation
reaction via 7. According to the invention, aqueous
extract 8 is passed to second extraction vessel 9,
wherein a fresh quantity of the non-water-miscible
solvent such as methyl-t-butyl ether used for the
hydroformylation reaction is added via 10 for extraction
of cobalt carbonyl or cobalt-containing derivatives
thereof remaining in the aqueous phase. It is desirable
for process economics to recover and recycle to the
hydroformylation step as much of this cobalt catalyst as
possible. This second extraction step typically has been
found to recover more than 30 wto, and optimally recover
more than 75 wt%, of the cobalt otherwise lost to the
aqueous 3-hydroxypropanal phase following water
extraction when used in combination with distillation or
other means to concentrate cobalt in this recycle stream
to the hydroformylation reaction. The process
facilitates reaching the overall process objective of
recovering and recycling at least 99.6 wt% of the cobalt
present in the hydroformylation reaction.
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The solvent for this second extraction step can be any of those previously
described for
the hydroformylation reaction step; however, the preferred solvent will be the
same as
that chosen for the hydroformylation step, most preferably methyl-t-butyl
ether. The
solvent can be fresh "makeup" solvent or can be solvent recovered from
downstream
distillation.
This second-stage extraction is most efficiently carried out at a temperature
within the
range of about 25 ° to about 55 °C and a preferable but optional
carbon monoxide
pressure within the range of 0.3 to 1.4MPa ( 50 to 200 psig. The process can
be carried
out by introducing the solvent into the aqueous phase with agitation, in the
same or
different vessel as for the water extraction step, and then allowing the
organic and
aqueous phases to resolve. In such a process, the solvent can be used in an
amount
within the range of about 3 to about 300 wt %, based on the amount of the
liquid phase
to be treated, depending on the process options available for recycling
catalyst and
solvent to the reaction. Alternatively, the cobalt-containing aqueous phase
can be
countercurrently contacted with the added solvent in a multi-staged vessel
under the
above conditions. 'The solvent phase from second-stage extraction containing
recovered
cobalt is recycled via 1 l, with optional concentration of cobalt by
distillation or other
means, to the hydroformylation reaction.
The decobalted aqueous product mixture 12 is passed to hydrogenation vessel 13
and
reacted with hydrogen 14 in the presence of a hydrogenation catalyst to
produce a
hydrogenation product mixture 15 containing 1,3-propanediol. The hydrogenation
step
may also revert some heavy ends to PDO. The solvent and extractant water 17
can be
recovered by distillation in column 16 and recycled to the water extraction
process via a
further
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distillation (not shown) for separation and purge of
light ends. PDO-containing product stream 18 can be
passed to distillation column 19 for recovery of PDO 20
from heavy ends 21.
Hydrogenation of the HPA to PDO can be carried out in
aqueous solution at an elevated temperature during at
least a portion of the hydrogenation step of 40 °C,
generally within the range of 50 to 175 °C, under a
hydrogen pressure of at least 0.7 MPa (100 psig),
generally within the range of 1.4 to 13.8 MPa (200 to
2000 psig). The reaction is carried out in the presence
of a fixed-bed hydrogenation catalyst such as any of
those based upon Group VIII metals, including nickel,
cobalt, ruthenium, platinum and palladium, as well as
copper, zinc and chromium and mixtures and alloys
thereof. The preferred catalysts are particulate nickel-
based compositions. Hydrogenation is preferably carried
out in three sequential temperature stages: a first
stage at 50 to 70 °C; a second stage at 70 to 100 °C; and
a third, high-temperature stage at greater than 120 °C
for reversion of heavy ends to 1,3-propanediol. Highest
yields are achieved under slightly acidic reaction
conditions.
Exam 1p a 1
This experiment was performed to determine if
residual cobalt carbonyl hydroformylation catalyst could
be removed from an aqueous solution of 3-hydroxypropanal
obtained by water extraction of 3-hydroxypropanal from
the reaction product mixture of cobalt carbonyl catalyzed
ethylene oxide hydroformylation.
Two parts fresh methyl-t-butyl ether were added with
agitation to one part of the aqueous 3-hydroxypropanal
solution at room temperature under 4.I MPa (600 psi)
1:1 (CO:H2) syngas. The phases were allowed to resolve.
The "new" aqueous phase was removed, and both phases were
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analyzed by cobalt-specific colorimetry for cobalt. 60%
of the cobalt in the original water phase was removed.
E~ple 2
A series of experiments was conducted in which
aqueous intermediate product was sampled directly from
3.8 1 (one-gallon) batch ethylene oxide hydroformylation
reactions, following water extraction in the reactor at
25-45 °C and 3.4-9.0 MPa (500-1300 psi) 1:1 syngas. The
aqueous product was transferred to a nitrogen-capped jar
of nitrogen-sparged methyl-t-butyl ether. Off-gassing of
syngas provided a syngas blanket over the jar. The jar
was shaken to provide thorough contact of the aqueous
phase with the MTBE, and the phases were allowed to
separate. The cobalt content of each phase was assessed
by colorimetry following acid digestion. Results are
shown in Table 1. Cobalt recoveries by solvent re-
extraction ranged from 5-80 percent, depending upon
conditions employed.
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WO 97/33851 PCT/EP97/01172 -
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example 3:
Aqueous product from the first extraction stage of
a continuous pilot plant PDO preparation process
containing 25 wta 3-hydroxypropanal intermediate and 67
ppm cobalt at a flow of 7.08 grams/minute was extracted
with countercurrent fresh MTBE at 0.67 grams/min flow
in a 76.2 cm (30-inch) tall by 2.54 cm (one-inch)
inside diameter extractor packed with plastic rings.
Extraction was carried out at 40 °C under 9.7 MPa
(1400 psi) 3:1 H2:C0. The cobalt level of the aqueous
effluent from the second extractor was 43 ppm, giving
35o recovery of cobalt from the original feed. MTBE
solvent exiting the top of the column contained 254 ppm
cobalt. The flow rate of MTBE employed matched that
required for makeup of MTBE lost from the
hydroformylation system via the aqueous product.
Higher extraction efficiencies would be expected from
increased MTBE flow rates, with separation of catalyst
and MTBE to recycle a more concentrated cobalt/MTBE
stream, as desired to maintain MTBE solvent inventory
in the hydroformylation system.
