Note: Descriptions are shown in the official language in which they were submitted.
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REMOVAL OF IMPURITIES FORMED
DURING THE PRODUCTION OF 1,3-PROPANEDIOL
Field of the Invention
This invention relates to a process for the production of 1,3-propanediol
(PDO)
wherein an aqueous solution of 3-hydroxypropanal (HPA) is formed, and the
neutralized HPA is hydrogenated to produce a PDO mixture that is distilled to
produce purified PDO.
Background of the Invention
Several companies have developed technology for the manufacture of PDO
starting with ethylene oxide as the main raw material. The ethylene oxide is
reacted
with synthesis gas (syngas), a mixture of carbon monoxide and hydrogen, which
may
be obtained by steam reforming of natural gas or partial oxidation of
hydrocarbons.
The idealized reaction of ethylene oxide (EO) with syngas to yield PDO is
shown
below:
EO+CO+2H2-~PDO
U.S. Patents 4,873,378, 4,873,379, and 5,053,562 from Hoechst
Celanese describe a single step reaction using 2:1 (molar) syngas at 110 to
120°C and
about 1000 psig (6900 kPa) to give 65 to 78 mole percent yield of PDO and
precursors thereof. The catalyst system used consisted of rhodium, various
phosphines, and various acids and water as promoters.
U.S. Patents 5,030,766 and 5,210,318 to Union Carbide describe the reaction
2 0 of EO with syngas in the presence of rhodium-containing catalysts. At
110°C and
1000 psig (6900 kPa) of 2:1 molar syngas, a selectivity of up to 47 mole
percent was
achieved but the combined rate of formation of PDO and 3-hydroxy propanal was
quite low at 0.05 to 0.07 moles per liter per hour. Better results were
achieved by
increasing the ratio of phosphoric acid promoter to rhodium catalyst.
U.S. Patents 5,256,827, 5,304,686, and 5,304,691 to Shell Oil described PDO
production from EO and syngas utilizing tertiary phosphine-complexed cobalt
carbonyl catalysts. Reaction conditions of 90 to 105°C and 1400 to 1500
psig (9650
to 10,340 kPa) of syngas (1:1 molar ratio) for three hours produced
selectivities in
the range of 85 to 90 mole percent and the EO conversion was in the range of
21 to
3 0 34 percent. Later work reported increased selectivity and EO conversion.
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U.S. Patent 5,527,973 describes a method for the purification of PDO which
contains carbonyl byproducts including acetals. An aqueous solution of a
carbonyl-
containing PDO is formed having a pH less than 7 and then a sufficient amount
of.
base is added to this solution to raise the pH to above 7. The solution is
then heated
to distill most of the water from it and then the remaining basic solution is
heated to
distill most of the PDO from the basic solution providing a PDO composition
having
a lower carbonyl content than the starting composition. This process has
several steps
and it would be a commercial advantage to provide a method which would lower
the
carbonyl content in fewer process steps.
MW 132 acetal of PDO forms as an undesired byproduct of the
hydrofonnylation and hydrogenation reactions. MW132 is difficult to separate
from
PDO by simple distillation because it exhibits volatility similar to that of
PDO. Its
formation lowers the overall recovery of PDO as well as its pL~rity.
Therefore, it
would be highly advantageous to have a process wherein the MW 132 acetal could
be
chemically reacted to other materials which are more easily separated
from.PDO. .
The present invention provides such a chemical method.
Summary of the Invention
In one embodiment, the present invention is an improvement upon the process
for the production of 1,3-propanediol (PDO) wherein an aqueous solution of
2 0 3-hydroxypropanal (HPA) is formed, and the HPA is subjected to
hydrogenation to
produce a crude PDO mixture comprising PDO, water, MW176 acetal (so called
because it is an acetal and has a molecular weight of about 176), and high and
low
volatility materials, wherein the crude PDO mixture is dried, usually by
distillation,
to produce a first overhead stream comprising water and some high volatility
2 5 materials, such as ethanol and/or process solvents, and a dried crude PDO
mixture as
a first distillate bottoms stream comprising PDO, MW176 acetal, and low
volatility
materials, and wherein the dried crude PDO mixture is distilled to produce a
second
overhead stream comprising some high volatility materials, a middle stream
comprising PDO and MW176 acetal, and a second distillate bottoms stream
3 0 comprising PDO and low volatility materials. The major part of the
recoverable PDO
is in the middle stream which is as much as 99.9 %wt PDO. The second
distillate
bottoms stream may contain up to 50 %wt of PDO but this PDO is difficult to
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separate from the low volatility materials. There may be trace amounts of
MW176
acetal in the bottoms stream.
In this embodiment, the improvement comprises contacting 1) the crude PDO
mixture prior to drying and/or 2) the dried crude PDO mixture prior to
distillation
and/or 3) the middle stream (with this third embodiment, another distillation
would
be required to remove the more volatile MW 176 acetal reaction products from
the
PDO) with an acidic zeolite (for example a mordenite clay) at 40 to
150°C to convert
the MW176 cyclic acetal to alternate chemical species which can be more easily
separated from PDO by distillation, in a process where the production of other
color
producing impurities and oligomers of PDO is minimized. In another embodiment
of
this invention, 1) and/or 2) and/or 3) are contacted with an acid form cation
exchange
resin, typically of the sulfonic acid type, at temperatures between ambient
and 150°C.
In another embodiment, soluble acids, such as H2S04, are used to treat the
streams,
preferably in a column which is resistant to corrosion, at a temperature of 20
to
100°C.
The contacting of the crude PDO mixture with the solid acid purifier is done
as
a continuous process, or batchwise,'using standard methods and practice for
contacting a liquid stream with a solid catalyst o"r adsorbent. In this
manner, difficult
to separate impurities such as the MW 176 acetal are largely eliminated, such
that
2 0 PDO may be distilled to high purity with high recovery efficiencies.
In another embodiment, this invention provides a process for producing 1,3-
propanediol comprising the steps of:
a) forming an aqueous solution of 3-hydroxypropanal,
b) hydrogenating the 3-hydroxypropanal to form a first crude 1,3-propanediol
2 5 mixture comprising 1,3-propanediol, water, and MW 132 cyclic acetal,
c) distilling the first crude 1,3-propanediol mixture to remove water and low
boiling impurities and form a second crude 1,3-propanediol mixture,
d) contacting the second crude 1,3-propanediol mixture with an acid form
cationic
exchange resin at a temperature of from 50 to 150°C to convert the
MW132 cyclic
3 0 acetal to more volatile cyclic acetals and/or other degradation products,
and
e) separating the more volatile cyclic acetals and/or other degradation
products
from the 1,3-propanediol by distillation or gas stripping.
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In the most preferred mode of this embodiment, steps d) and e) are carried out
together (such as in the same vessel or column) such that the volatile cyclic
acetals
and/or other degradation products are separated from the 1,3-propanediol as
they are
formed. In another mode of this embodiment, an acidic zeolite can be used in
place
of the cationic acid exchange resin. In such case, the temperature preferably
is from
80 to 200°C.
Brief Descr~tion of the Drawing
Figure 1 is very simple schematic representation of an example of a simplified
distillation scheme.
Detailed Description of the Invention
The 3-hydroxypropanal (HPA) aqueous solution which is the starting material
of the present invention, can be produced by a number of different processes.
The
aforementioned U.S. patents 4,873,378, 4,873,379, 5,053,562, 5,030,766,
5,210,318,
5,256,827, 5,304,686, and 5,304,691, all of which are herein incorporated by '
reference, describe different methods for producing aqueous solutions of HPA.
HPA
can also be produced by hydration of acrolein in the presence of acidic
catalysts.
Processes for accomplishing this result are described in U.S. Patents
5,426,249, .
5,01.5,789, 5,17..1,898, 5,276,201, 5,334,778, and 5,364,987, all of which are
herein
incorporated by reference.
2 0 A preferred method for carrying out the entire process of the present
invention
is described in U.S. Patent No. 5,786,524, which is herein incorporated by
reference,
and is generally as follows. Ethylene oxide (E~) is hydroformylated in a
reactor such
as a bubble column or agitated tank at 200 to 5000 psi (1380 to 34,500 kPa) of
syngas having a ratio of hydrogen to carbon monoxide of 1:5 to 25:1 at 50 to
110°C
2 5 in the presence of a hydroformylation catalyst at a concentration of 0.05
to 15 weight
percent, more preferably 0.05 to 1 percent.
The hydroformylation reaction effluent is preferably extracted with a small
amount of water at water-solvent ratios ranging from 2:1 to 1:20 at 5 to
55°C under
an atmosphere of greater than 50 psi (350 kPa) carbon monoxide. The solvent
layer
3 0 containing more than 90 percent of the catalyst in active form is recycled
back to the
hydroformylation reactor. The HPA is extracted in the water layer at a
concentration
of 10 to 45 weight percent.
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The catalyst may be removed from this aqueous solution of HPA by any
known means including first oxidizing the catalyst and then removing it
utilizing an
acid ion exchange resin. The ion exchange resin may be a weak or strong acid
ion
exchange resin. Examples include AMBERLYST 1 S, 35, and XN-1010,
AMBERLITE IR-118, IRC76, A1200, DOWER 50 x 2-100 and 5 x 8-100, XL-383
and -386, plus BIO RAD AGSOW-X2 and AMBERSEP 252H resins, or other strong
(sulfonic) acid or weak (carboxylic) acid resins (AMBERLYST, AMBERLITE,
DOWER, BIO RAD and AMBERSEP are trademarks).
After neutralization of the aqueous solution of 3-hydroxypropanal, the aqueous
solution is hydrogenated. This may be carried out by hydrogenation over a
fixed bed
of hydrogenation catalyst at typically 100 to 2000 psi (690 to 13,800 kPa) of
hydrogen. The hydrogenation catalyst can be any of those described in U.S.
5,786,524, which is herein incorporated by reference, including catalysts of a
group
VIII metal such as nickel, cobalt, ruthenium, platinum, or palladium. Initial
~ 5 hydrogenation is preferably conducted at 40 to 80°C and the
temperature is
preferably increased to 120 to 175°C to encourage the reaction of
reactive
components such as cyclic acetals to revert back to PDO. Finally, water and ,
entrained light (low boiling) solvent and highly. volatile (low boiling)
impurities,are
distilled (overhead stream) from the crude PDO and the lower volatility
components
2 0 are also separated during distillation as the bottoms stream.
MW132 Acetal
To carry out the second embodiment of this invention, the dried crude product
stream (of the distillation), containing MW132 acetal and PDO, is treated as
described below to recover PDO in high yield and high purity. Crude PDO as
2 5 described above can exhibit high levels of MW 132 cyclic acetal impurity.
This
impurity is undesirable and limits PDO recovery efficiencies during subsequent
distillation. It can form by reaction of PDO with HPA.
Reaction # 1
n
HO~OH + ~ O~~ +HZO
H OH H OH
PDO HPA MW 132 Acetal
5
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The 2-ethylene-1,3-dioxane cyclic acetal (EDCA) formed upon acid catalyzed
decomposition of MW 132 acetal is known to be much more volatile than PDO. The
following formula explains the dehydration of MW132 acetal to form the 2-
ethylene-
1,3-dioxane cyclic acetal (EDCA) that can be readily separated from the PDO by
distillation. Acidic zeolites and acid form cationic exchange resins (such as
used for
cobalt removal) can be used to purify PDO via reaction of MW 132 acetal to
form
EDCA:
Reaction #2
+H O
O O '~ O O
H+ H
H/~~ OH
Acetal 132 EDCA
Thus, the dried crude PDO stream containing the undesirable MW132 cyclic
acetal is contacted with an acid form cationic exchange resin or an acidic
zeolite
under conditions which favor the reaction scheme shown above for the
conversion of
MW 132 acetal to EDCA. This step is combined with removal of the EDCA wia
concerted distillation or via use of a stripping gas such as nitrogen or
steam.
Concerted distillation and reaction, where distillation and reaction are
combined in the same processing unit to separate reactants from products as
they are
formed, may employ any of the well known methods for conducting a "reactive
distillation." Alternatively, an inert gas such as nitrogen may be used to
strip the
reaction mixtures (concerted stripping and reaction) of the more volatile
degradation
product of MW 132 acetal (EDCA), and thus prevent reformation of MW 132 via
2 0 chemical equilibrium. Use of water vapor (steam) is a common commercial
practice
for providing process heat and an inert stripping gas. In this case, the
stripping is
again conducted in the same processing unit as the reaction of MW 132 acetal.
The
reaction products are removed as formed in order to drive the chemical
equilibrium
to eliminate or reduce the presence of MW 132 acetal. In this manner, the
2 5 combination of acid-catalyzed reaction plus stripping in the same
processing step
effects reactant-product separation in the same manner as the "reactive
distillation"
combination of acid-catalyzed reaction and distillation.
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In general, water was found to suppress the reversion of and removal of
MW132 acetal. However, small amounts of water are generally present due to
incomplete removal, sorption in the solid catalyst, or due to the dehydration
reaction
itself (#1 above) and may al ~ a portion of the MW132 removal to proceed via
the
reversal of reaction #l. HPA, if formed in this manner, may then be further
. dehydrated to highly volatile acrolein, which is readily stripped or
distilled from the
reaction mixture. Regardless of which mechanism dominates, the concerted acid-
catalyzed reaction with separation (distillation or stripping) of volatile
reaction
products results in a reduction in the MW 132 impurity of the product PDO.
Concerted distillation or inert gas stripping is required to drive the
chemical
equilibrium away from the thermodynamically favored MW132 cyclic acetal. An
acid formed zeolite can also be used during the procedure described above to
catalyze the degradation of the MW 132 acetal.
Use of the acid form cationic exchange resin with concerted separation
~ produces virtually complete conversion of the MW132 acetal. The reaction is
.preferably carried out at a temperature of from 50 to 150°C, more
preferab~y:at from. , .
80 to 120°C. Contacting with the resin catalyst is either conducted
batchwise, .or in a
continuous column, using well known reactor design methods to insure virtually
° 4
complete conversion of the MW 132 acetal. Batchwise contacting at 80 to
120°C may
2 0 be conducted for 1 to 5 hours with 10 weight percent of acid resin, for
example, to
effect complete conversion. Alternately, the contacting may be effected in a
continuous reaction vessel, preferably a column, with a "weight hourly space
velocity" (weight of impure PDO feed per weight of acid resin per hour-"WHSV")
of 0.1 to 1 per hour.
2 5 With zeolites, the activity for acetal reversion is lower, such that a
higher
temperature or increased contact time with the zeolite is required. The
reaction with
acidic zeolite is preferably carried out at a temperature of from 70 to
250°C, more
preferably at from 90 to 170°C, via batch or continuous contacting.
Similar
contacting times or weight hourly space velocities could be used. For either
system,
3 0 the combination of temperature and contact time with the solid acidic
purifier (acid
form cationic exchange resin or acidic zeolite) must be optimized to limit the
production of undesirable color-imparting impurities and to minimize the
production
of dimer and higher oligomers of PDO.
7
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The preferred catalysts are ion exchange resins with strongly acidic cation
exchange (acid form cationic exchange resins). These include the gel type or
macroreticular (macroporous) ion exchange resins with sulfonic acid functional
groups wherein the sulfonic acid function is bonded directly or indirectly to
an
organic polymer backbone. Examples include Rohm and Haas AMBERLITE or
AMBERLYST A200, A252, IR-118, IR120, A15, A35, XN-1010, or uniform
particle size A1200 resins; Dow MSC-l, M-31, or DOWER 50-series resins,
SYBRON C-249, C-267, CFP-110 resins; PUROLITE C-100 or C-150 resins;
RESINTECH CGB; IWT C-211, SACMP; IWT C-381; or other comparable
commercial strong acid cation exchange resins. Another example of cation
exchange
resins is NAFION acidified perfluorinated polymer of sulphonic acid (SYBRON,
PUROLITE, RESINTECH and NAFION are trademarks).
The suitable zeolite catalysts contain one or more modified zeolites
preferably
in the acidic form. These zeolites should contain pore dimensions large enough
to
. :. admit the entry of the. acyclic or aliphatic compounds. The preferred
zeolites include, ,
' for example, zeolites:ofthe structural types MFI (e.g:, ZSM-5), MEL (e:g.,
ZSM-11), . ...
FER (e.g., ferrierite and ZSM-35),.FAU (e.g., zeolite Y), BEA (e.g.,
beta).,MFS. ~ ' , .. .
(e:g., ZSM-57), NES (e.g.; NU-8.7), MOR (e.g. mordenite) ,CHA (e.g.,
chabazite); ,:. ' _
MTT (e.g., ZSM-23), MWW (e.g., MCM-22 and SSZ-25), EUO (e.g. EU-1, ZSM-
2 0 50, and TPZ-3), OFF (e.g., offretite), MTW (e.g., ZSM-12) and zeolites ITQ-
1, ITQ-
2, MCM-56, MCM-49, ZSM-48, SSZ-35, SSZ-39 and zeolites of the mixed
crystalline phases such as, for example, zeolite PSH-3. The structural types
and
references to the synthesis of the various zeolites can be found in the "Atlas
of
Zeolite Structure Types" (published on behalf of the Structure Commission of
the
2 5 International Zeolite Association), by W.M. Meier, D.H. Olson and Ch.
Baerlocher,
published by Butterworth-Heinemann, fourth revised edition, 1996. Structural
types
and references to the zeolites mentioned above are available on the World Wide
Web
at www.iza-structure.org Such zeolites are commercially available from Zeolyst
International, Inc. and ExxonMobil Corporation. Additional examples of
suitable
3 0 zeolite catalysts can be found in U.S. Patent Nos. 5,762,777; 5,808,167;
5,110,995;
5,874,646; 4,826,667; 4,439,409; 4,954,325; 5,236,575; 5,362,697; 5,827,491;
5,958,370; 4,016,245; 4,251,499; 4,795,623; 4,942,027 and WO99/35087, which
are
hereby incorporated by reference.
8
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MW 176 Acetal
As shown in the exemplary simplified distillation scheme of Figure 1 which is
helpful in describing the first embodiment of this invention, the aqueous PDO
containing MW 176 acetal flows into drying distillation column 2. Water and
some
high volatility materials axe removed in the overhead stream 3 and the dried
PDO
with MW 176 acetal from the distillate bottoms stream flows into distillation
column
5. More high volatility materials are separated and leave through overhead
stream 6
and the distillate bottoms stream 8 contains low volatility materials and some
PDO as
well as trace amounts of MW 176 acetal. The recoverable PDO exits in the
middle
~ stream. Vessels 1, 4, and 7 are optional (although at least one is required
in the
system shown in the figure) acid treatment vessels. The acid catalyst
treatment may
take place before drying in vessel 1 or it may take place after drying in
vessel 4 but
before distillation or it may take place after distillation in vessel 7. When
the last
embodiment is carried out, an additional distillation is required to separate
the more
.15 volatile MW 176 acetal reaction,products from the PDO.
. Crude PD~ as described. above~sometimes exhibits high levels of MW176.
cyclic acetal impurity. This impurity was found to be only marginally less
volatile , .
. ~ ,~~.PDO; which limits PDO recovery efficiencies. Given difficulty in
separation
from PDO, laboratory batch distillation was conducted to assess the relative
2 0 volatilities of MW 176 impurity and PDO. Approximately 85 grams of PDO
tainted
with this impurity and also a CS diol were refluxed at a nominal 10 mm Hg (1.3
kPa)
pressure and 143°C bottoms temperature. Ethylene glycol (EG) and
butanediol
markers were added at about 1 wt% to assist in assignment of relative
volatilities.
The results (Table 1) show both the MW176 acetal and CS diol to be heavier
than
~ 5 PDO. Good agreement was obtained between measured vs. reported relative
volatility of EG vs. PDO which indicates that equilibrium was indeed
approached for
these measurements.
9
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Table 1: Relative Volatilityl
BATCH DISTILLATION
DATA:
Species Distillation Distillation Volatility
bottoms tops ratio:
wt% ~% t/b2
PDO 97.88 98.09 1.00
Ethylene glycol0.369 0.824 2.233
CS diol 0.326 0.280 0.859
MW176 acetal 0.055 0.047 0.855
Butanediol 1.375 0.762 0.554
1 Reported relative volatility EG/PDO at 230°F (110°C) = 2.16
2 t = distillation "tops" or "overhead product"
b = distillation "bottoms"
. The MW 102 acetal formed upon acid catalyzed decomposition of MW 176
acetal is known to be much more volatile than PDO and hence can be readily
separated from PDO with high efficiency. This result was expected basis the
absence
of hydroxyl groups in MW 102 due to condensation elimination. While we do not
wish to be bound by a specific mechanism, the following reactions may explain
the
degradation of MW 176 acetal and formation of, MW 102 acetal (that can be
readily
separated from the PDO by distillation) and also the formation of MW132 acetal
as
observed in the experiments.
to
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TH1778-PCT
O
O O O O + I
OOH
H O H H OH H
Aceta1176 Aceta1132 Acetaldehyde
~n
O~~+~ OH
H
H H
0
+ HO~ OH H O\ / O + H20
H. \ ~H
Aldehyde PDO Acetal 102
"De-ethoxylation" is known to occur under acidic conditions. Aldehydes
readily condense with PDO under acidic conditions to,form thermodynamically
favored cyclic acetals, in this case, MW102 acetal.
An acid form cation exchange resin or an acidic zeolite also facilitates the a
.. .. .~
removal of MW 132 acetal via conversion to 2-ethylene-1,3-dioxane cyclic
acetal
(EDCA) which is a substantially higher volatility material.
+H O
O O H H 2
H/><~ OH
Acetal 132 EDCA
The crude PDO stream containing the undesirable MW 176 acetal is treated
with an acid form cation exchange resin or an acidic zeolite or soluble acid
under
conditions which favor the reaction schemes shown above. Batch or continuous
flow
processes may be used in any mannei providing intimate contacting of the
liquid
stream with the solid acid purifier or the soluble acid. Typically, continuous
contacting in a fixed, fluidized, or expanded bed will be preferred
commercially, in
either downflow or upflow operation or via a horizontal contactor. While the
optimal
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size of the bed will depend upon the particle size and nature of the solid
acid purifier
employed, a typical design will entail a "weight hourly space velocity" (WHSV)
from 0.1 to 10, with WHSV expressed as the mass flowrate of crude PDO per mass
of solid acid purifier per hour. The optimal bed size and operating
temperature are
selected to effect a high level of conversion of MW 176 acetal, while
minimizing the
oligomerization of PDO to other heavy ends components.
When acidic zeolites are employed as the solid acid purifier, a temperature in
the range of 40 to 150°C, preferably 60 to 120°C, is typically
desired. Temperatures
of ambient to 150°C or lower temperatures (as low as ambient
temperature to 100°C)
may be employed with acid form cation exchange resins, which are indicated to
be
more active in removal of the MW 176 impurity. When soluble acids axe used,
the
temperature may be from 20 to 100°C.
The preferred zeolite catalysts contain one or more modified zeolites
preferably
in the acidic form. These zeolites should contain pore dimensions large enough
to
admit the entry of the acyclic or aliphatic compounds. The preferred
zeolites.include, ,
for example, zeolites of the structural types MFI (e.g., ZSM-5), MEL(e.g:, ZSM-
11);
FER (e.g., ferrierite and ZSM-35), FAU (e.g.; zeolite Y)BEA (e.g., beta) ;MFS
' (e.g., ZSM-57), NES (e.g. NU-87), MOR (e.g. morderiite) ,CHA (e.g:;
chabazite);
MTT (e.g., ZSM-23), MWW (e.g., MCM-22 and SSZ-25), EUO (e.g. EU-1; ZSM-
2 0 50, and TPZ-3), OFF (e.g., offretite), MTW (e.g., ZSM-12) and zeolites ITQ-
l, ITQ-
2, MCM-56, MCM-49, ZSM-48, SSZ-35, SSZ-39 and zeolites of the mixed
crystalline phases such as, for example, zeolite PSH-3. The structural types
and
references to the synthesis of the various zeolites can be found in the "Atlas
of
Zeolite Structure Types" (published on behalf of the Structure Commission of
the
2 5 International Zeolite Association), by W.M. Meier, D.H. Olson and Ch.
Baerlocher,
published by Butterworth-Heinemann, fourth revised edition, 1996. Structural
types
and references to the zeolites mentioned above are available on the World Wide
Web
at www.iza-structure.org Such zeolites are commercially available from Zeolyst
International, Inc. and ExxonMobil Corporation. Additional examples of
suitable
3 0 zeolite catalysts can be found in U.S. Patent Nos. 5,762,777; 5,808,167;
5,110,995;
5,874,646; 4,826,667; 4,439,409; 4,954,325; 5,236,575; 5,362,697; 5,827,491;
5,958,370; 4,016,245; 4,251,499; 4,795,623; 4,942,027 and W099135087, which
axe
hereby incorporated by reference.
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Other suitable catalysts include acid form cation exchange resins. These
include the gel type or macroreticular (macroporous) ion exchange resins with
sulfonic acid functional groups in acid form, wherein the sulfonic acid
function is
bonded directly or indirectly to an organic polymer backbone. Examples
include:
Rohm and Haas AMBERLITE or AMBERLYST A200, A252, IR-118, IR120, A15,
A35, XN-1014, or uniform particle size A1200 resins; Dow MSC-1 or DOWER 50-
series resins; SYBRON C-249, C-267, CFP-110 resins; PUROLITE C-100 or C-150
resins; RESINTECH CGB; IWT C-211; SACMP; IWT C-381; and other comparable
commercial resins. Another example of these cation exchange resins is NAFION
acidified perfluorinated polymer of sulphonic acid.
Soluble acids which can be used include H2S04, H3P04, HCI, and soluble
sulfonic acids such as para-toluene sulfonic acid, benzene sulfonic acid, and
methane
sulfonic acid, etc. H2S04 and soluble sulfonic acids are preferred. If these
soluble
acids are used, corrosion-resistant columns are highly preferred. The acid is
removed
' with the heaviest components (heavy ends). The concentration of the acid is
.. preferably 0.1 to 1.0 wt%:
. . EXAMPLES - ' , ~ ~ .. . _ ~ ; t . .
MW176 Examples
' Example 176-1
2 0 The results in Table 2 show that ambient temperature treatment of a PDO
sample contaminated with MW176 acetal with acid-form USY-type zeolite was
ineffective in reverting MW 176 acetal. Room temperature reversion using
strong
acid resin A15 (Rohm and Haas AMBERLYST 15) was demonstrated. High
temperature treatment with the zeolite at 150°C overnight resulted in
elimination of~
MW176 with formation of 2-methyl -1,3-dioxane. However, formation of poly PDO
(di-1,3-propylene glycol) and higher oligomers occurred at higher
concentrations
than the original MW 176 acetal. Overall purity and yield was thus reduced,
though
the more difficult to separate MW176 acetal was eliminated.
Additional timed studies were conducted at 100°C using the USY H+
form
3 0 zeolite. The results show reactive conversion of the MW 176 acetal,
especially the
first gc (gas chromatography peak MW176-1 which reacted to virtual completion
within 5 hours (MW176 acetal shows up as three peaks in gc/mass spec analysis;
the
dominant MW 176-1 peak described in Table 2 readily vanished during acid
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treatment experiments, while a second "isomer" appeared to be unreactive).
Unlike
the earlier test at 150°C, at 100°C the reversion was selective
with no measurable
formation of di- or tri-1,3-propylene glycol via condensation of PDO.
A mordenite sample was inadvertently first tested in sodium form overnight at
150°C, giving copious amounts of new heavy ends byproducts, presumably
via
degradation of PDO. A sample of the acid-form mordenite heated with the same
PDO overnight at 60°C showed, however, essentially complete elimination
of the
MW176 acetal, with formation of the same 2-methyl-1,3-dioxane (MW102 acetal)
and MW132 acetal impurities as observed with the USY type zeolite. The
reversion
was selective as no additional byproducts were observed. The performance of
the
acid-form mordenite was thus comparable with that of the USY acid-form
zeolite.
These results indicate an optimal temperature for complete or partial removal
of the
MW176 acetal, with minimal degradation of PDO to other byproducts.
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O O O O O O O ~ O O O O O O
O O O O O O O O O O O O O O
N
O ~
O O O ~ ~ ~ p O O O d O O O
o p p p ~n O O O O O O O O O O
O O O O O O O O O O O O O O
O O O ~n O O O O O O O O O O
O ~. O O O O O O O O O O
O ~n O O O O O O O O O O
~ Q ~ p p p O O O O O O O O
'G
i
~O N ~--~ N ~n M v~ ~ N oo d' M
o ~ O ~ O ~ O O O O ~ O O O O
p O O O O O O O O O O O
CJ No 000~'o~d~- °~°~°o
° o ~ o ~ o o ~ o o ..
0 0
o ~ O c; 0 0 0 0 0 0 0 0 0 0
O M O O O ~-' M N ,..'~_, o~o M l7~ O OM l~ 'n
o O N O O O d0'.' ~ O d' O N M ~'°~ M
O O O O O O O O O O O O O O O
U
O O~ O~ ~ M O
~-a M M ~ O O
d' O
N O N O N O p p 0 O O O O O
V ~ O O O O O O
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r~ f~ O
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.. j ~ N N "~t~ ~; ~ N N ~ N N N N II
v ~y ' ~ -I- -I- ~ ~ y~ '"i a p w ~.~,
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+~ ~' ~' t~ U U cii -I- ~" U1 t/1 ~ V1 N
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~, x
O
H ~ O N N N O ~ ~ N N O ~ M ~ N
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Example 176-2
MW176 acetal impurity with a strong cation acid ion exchange resin (Rohm
and Haas AMBERLYST A35) at room temperature. The results shown in Table 3
indicate degradation of MW 176 acetal, with formation of MW 102 acetal, MW 18
(H20), and MW132 acetal.
Table 3: Preliminary PDO Treatment Over A35 Resin at Room Temperature
%Wt
Name MW Start End
2-methyl cyclic acetal102 0.00 0.10
cyclic acetal 132 0.05 0.29
cyclic acetal diol 176 0.24 0.01
Water 18 0.02 1.02
PDO 76 99.47 98.39
Other 162 0.02 0.00
ether ' ; 176 0.02 0.01
99.81 99.83
mole balance 1.31 1.35
Solid acid treatment of PDO tainted with MW 176 acetal can degrade this
impurity into lighter components (MW 102 nonhydroxylated acetal) which are
readily
separable via distillation. Strong cation acid ion exchange resins can revert
the
MW 176 acetal at room temperature. Acidic zeolites can also revert the MW 176
acetal at a higher temperature. At still higher temperatures (as demonstrated
for
150°C), PDO is condensed by the acidic zeolites to poly 1,3-propylene
glycols,
leading to yield loss and lower purity.
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MW 132 Examples
Example 132-1 (comparative)
Acid Resin Treatment Prior to Distillation
This experiment entailed treatment of 1500 grams of crude PDO following
water removal, via distillation, with 43.5 grams dry A15 (Amberlyst A15 resin)
strong acid form cationic exchange resin under a nitrogen atmosphere for 3
hours at
100°C with minimal separation (stripping). The treated material was
bright yellow.
MW 132 acetal was reduced only from 3.2 wt% to 2.6 wt%. The treated material
was
distilled and successive distillation cuts showed reduction in MW 132 acetal
from
11% to 2 wt% but formation of up to 2700 ppm acrylate by the final cut.
Excessive
formation of acrylate can be expected because of the strong acid treatment
which
freed 3-hydroxypropionic acid, thus giving maximal ester and ultimately
acrylate
formation. This example illustrates that no significant MW132 acetal removal
was
observed for the resin treatment in the absence of concerted separation
(stripping or
distillation) of the volatile impurities.
Example 132-2
Acid Resin Treatment with Concerted Stripping to, Remove Acetal: -
The results of this experiment are shown in Table 4. 1 gram of vacuum dried
A15 strong acid resin was added to 10 grams of the PDO distillate containing
2 0 1.38 wt% MW 132 cyclic acetal from which a majority of the water had been
removed by distillation. The sample was heated via a metal block heater to
100°C .
with vigorous nitrogen stripping (concerted stripping) as evidenced by an
expansion
of the liquid by about 10 volume percent. MW 132 acetal was readily eliminated
with
formation of significant quantities of di- and tri-PDO via direct PDO self
2 5 condensation.
Table 4
MW 132
Sample Time Acetal di-PDO tri-PDO
Hours wt% wt% wt%
167-9 0 1.3 8 0 0
194-1 1 0.345 0.548 1.356
194-2 3 0.017 3.009 1.934
194-3 5 0.012 6.667 1.997
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This study was repeated with a different distillate. 1 gram of dry A15 resin
was
used to treat 12 grams of PDO distillate. The MW 176 (a higher boiling cyclic
acetal)
and MW 132 acetals were eliminated. Di- and tri-PDO formed in significant
quantities. The results are shown in Table 5.
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'r O
q can
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'
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0 . ~ .;;
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Another similar experiment was carried out using 5 wt% of M31 strong acid
form cationic exchange resin (macroreticular resin). As in the previous
experiments,
the amount of the MW 132 acetal was decreased and PDO dimer was produced with
contacting with acid catalyst and with concerted nitrogen stripping. The
results are
shown in Table 6.
Table 6: Acid Resin + N2 Strip
5% MW 132
resin Time Acetal di-PDO
100C Hours wt% wt%
Catalyst
none 12 2.865 0
A15 12 1.509 10.427
M31 12 1.024 10.316
Example 132-3
Acid Resin Dry Stripping with Subsequent Redistillation ~ y
A twice distilled PDO product sample exhibiting a visible light yellow color
upon testing for color body precursors was contacted with 5 wt% dry A15 strong
acid
form cationic exchange resin with nitrogen stripping for 4 hours at
105°C. MW 132
acetal was virtually eliminated while 1.7 wt% di-PDO was formed (Table 7),
giving a
gc (gas chromatographic) purity of 97.9 wt%. The treated sample was
redistilled at 9
mm Hg (1.3 kPa) in a small 2-ft (0.6 meter) concentric tube column with a
bottoms
temperature of 121 to 123°C. Distillation showed ready separation of di-
PDO from
the PDO distillate. Distillate cuts were substantially reduced in MW 132
acetal with
the gc purity approaching 99.9%. The color test now gave only slightly yellow
tint,
indicating a reduction in the amount of color body precursors.
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Table 7: Acid Stripping With Redistillation
MW 132 PDO di-PDO
grams ppm wt% wt%
Feed 160.44 n.d. 97.933 1.713
Dist cut# 1 17.34 500 99.766 0
2 43.15 200 99.910 0
3 51.19 0 99.894 0
4 43.41 0 99.846 0
Total 155.09
A less pure sample containing 3 wt% MW 132 acetal, which exhibited
significant color when analyzed for color body precursors, was similarly
treated with
wt% strong acid resin (A15) while nitrogen stripping. The resulting PDO
contained
no MW 132 acetal after 4 hours, but it did contain 2.9 wt% di-PDO.
Redistillation at
5 8 mm Hg (1.3 kPa) and 122 to 129°C bottoms temperature in a 2-foot
(0.6 meter)
concentric tube column gave the distillation cuts shown in Table 8. Again,-the
acid-
resin stripping eliminated a significant portion of the MW 132 acetal such
that ~ . .
distillation overhead products free of this impurity could then be produced:
Di-PDO- ~.
formed during the resin treatment was readily separated by distillation. The
parities
of the final distillate cuts would have been quite high if not for progressive
formation
of MW 102 acetal (2-methyl-1,3-dioxane), which is known to be more volatile
than
PDO, during the distillation. Yet another distillation would have rid the
product of
this impurity.
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Table 8: Acid Stripping With Redistillation
2-me-
dioxan
grams MW 132 PDO di-PDO MW 102
Acetal
ppm wt% wt% wt%
Feed 192.66 n.d. 95.204 2.974 0
Dist cut# 1 15.96 460 99.756 0 0.304
2 50.45 0 98.292 0 0.308
3 45.87 0 99.106 0 0.505
4 52:60 0 99.329 0 0.606
10.57 0 98.579 0 1.186
Total 175.45
Example 132-4
Inorganic solid acids such as silica-aluminas or zeolites are more amenable to
commercial use in a nitrogen or steam stripper. However, their activity in
dehydrating
beta-hydroxy cyclic acetals such asIMW 132 is pooier than the activity strong
acid ion
5 exchange resins under comparable conditions (Table 9). The highly active
resins, on the
other hand, make more di- and tri-PDO as byproducts. These oligomers are not
believed
to be color precursors, however, and are more readily separated by
distillation than the
original MW132 acetal. Temperatures and reaction (contacting) times preferably
are
optimally adjusted for the acid form cationic exchange resin vs. the acidic
zeolite to
maximize MW132 acetal reversion to PDO while minimizing the formation of other
heavy impurities.
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Table 9: Inorganic Solid Acids vs. Ion Exchange Resin for Acid Stripping
MW di-
Solid MW 132 132 PDO
Solid Temp Acid Time Initial Final Final
Acid Type C wt% Hours wt% wt% wt%
ASA Amorphous 100 23 3 0.296 0.253 0
silica-alumina
ASA Amorphous 155 22 2 0.296 0.209 0
silica-alumina
Y H+ zeolite 100 5.7 1 0.296 0.323 0
, ZSMS H+ zeolite 100 4 3 2.4 1.5 0
ZSMS H+ zeolite 100 4 3 0.3 0.07 0
A15 Strong acid105 5 4 0.058 0 1.73
ion exchange
resin ,
A15 Strong acid105 5.2 4 3 0 2.97
,
. ~ ion exchange.. .
, ,
resin
A15 Strong acid105 5 12 2.9 1.5 10.3
ion exchange
resin
A15 Strong acid100 10 3 1.38 0.017 3
ion exchange
resin
23
