Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for preparing
tetrahydrofuran which comprises heating a carboxylic acid
monoester of 1,4-butanediol in the presence of a dehydro-
acyloxylation catalyst.
It is known in the art that tetrahydrofuran may be
made by a number of different methods, the more prominent
methods are by the catalytic hydrogenation of furan or by the
dehydration of 1,4-butanediol.
In practice, the tetrahydrofuran is most often
produced by a series of reactions starting with the reaction
of formaldehyde and acetylene in the presence of a cuprous
acetylide complex to form butynediol. Butynediol is converted
on hydroyenation to butanediol. The 1,4-butanediol is con-
verted to tetrahydro~uran as indicated boave.
Additionally, tetrahydrofuran is prepared from maleic
acid, its esters, maleic anhydride, fumaric acid, its esters,
succinic acid, its esters, succinic anhydride, ~ -butyrolactone,
or mixtures of these compounds, by hydrogenation over a
hydrogenation catalyst.
However, these methods involve considerably
expensive equipment and the handling of hazardous materials.
Also, catalysts in some cases may be e~pensive, and in other `
instances may be easily poisoned
Tetrahydrofuran is a useful solvent for natur~ and
synthetic resins, particularly vinyls. Also, it is used as
an intermediate in the manufacture of nylon, 1,4-dichlorobutane
and polyurethanes.
It has been discovered that tetrahydrofuran may be
inexpensively prepared from a carboxylic acid monoester of
1,4-butanediol by heatin~ it in the presence of a heterogeneous
dehydroacyloxylation catalyst. By this method, tetrahydrofuran
is produced in essentially quantitative yields. Also, the
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dehydroacyloxylation catalyst of the instant invention is
stationary and permanent and therefore may be continually
reused~
Another object of t~is invention is to produce
tetrahydrofuran from inexpensive starting materials, i.e.,
propylene, carbon monoxide, hydrogen and oxygen, by way of
several intermediate steps.
The dehydroacyloxylation catalysts which may be
employed in the practice of this invention are those which
promote ring closure and evolution of the carboxylic acid.
In the case of the acetate ester, the catalyst is a de-
hydroacetoxylation catalyst. Suitable dehydroacylo~ylation
catalystsinclude zeolites, silica, alumina, silica-aluminas,
silica-magnesias, acidic clays and t~e like.
The zeolite dehydroacyloxylation catalysts which `; i
may be used in the instant invention include the synthetic
and natural zeolites, also known as molecular sieves. These
zeolites are well kno~n in t~e art and are detailed in
Molecular Sieves, Charles ~. ~ersh, Reinhold Publishing -
Company, Mew York (1961). Preferably, representative natural
zeolites which may be employed in the instant invention
include those in Table 3-1, on page 21, of the ~ersh reference ~
while representative molecular sieves include those in Table ;
5-1, on page 54, of the Hersh reference. Ad~tional zeolite
catalysts are set forth in Orqanic Catalysts Over Crystalline
.
Aluminosilicates, P B Venuto and P S Landis, ~dvances in
Catalysis, Vol. 18, pp. 259 to 371 (1968).
The silica-alumina dehydroacyloxylation catalysts
which may be used vary in composition from pure silica to pure
alumina whereas the silica-magnesias vary in composition from
pure silica to predominantly magnesia.
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The acidic clay dehydroacyloxylation catalysts which
may be used in the instant inve~ion include clays containing
the minerals kaolinite, halloysite, montmorillonite, illite,
quartz, calcite, liminomite, gypsum, muscavite and the like,
either in naturally acidic forms or after treatment with acid.
The catalyst is preferably used in the form of a
bed through which the reactants are passed.
The carboxylic acid monoesters of 1,4-butanediol
which are suitable in the instant invention preferably contain
2 to 8 carbon atoms. A preferred carboxylic acid monoester of
1,4-butanediol is 4-acetoxybutanol. -~
The temperature at which the process can be carried
out varies widely. Temperatures ranging from about 125C. to
about 300C. are generally adequate although higher temperature~
can be used. Preferably, the reaction is carried out at a
temperature of from about 150C. to about 250C. The maximum
depends upon destruction of the product, olefin formation
occurring under too rigorous conditions.
Although only atmospheric pressure is normally
required, it will be of course apparent to those skilled in the
art that superatmospheric pressure or subatmospheric pressure
may be used where conditions and concentrations so dictate.
The process may be illustrated, taking 4-acetoxy-
butanol as an example, by the following equation:
O
HO(CH2)40CCH3 ~ CH2 CH2 + CH3COH
.~ C~ ~CH2 ,,
... ~
In Canadian application Serial No . ~03, a/~ of
William E. Smith, filed ~ne ~y, /~ and assigned to the
same assignee as the present invention, there is disclosed
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and claimed a process for ma~ing butanediols by reacting
propylene, oxygen and a carboxylic acid to produce an allyl
carboxylate which is then hydroformylated to produce the
mixture of the corresponding aldehydes. Hydrogenation of the
mixture produces a mixture of the esters of the corresponding
diols. In Canadian application Serial No. 195,892 of William
E. Smith, filed March 25, 1974 and assigned to the same
assignee as the present invention, there is disclosed and
claimed a process wherein the hydrogenation is accomplished
concurrently with the hydroformylation reaction. De-
esterification of the diol ester mixture produces the desired
butanediols which can be separated by distillation.
In carrying out the preparation of tetra~ydro~uran
starting ~rom propylene, oxygen and a car~oxylic acid, the
procedures disclosed in the above Canadian applications may
be used to obtain the carboxylic acid esters of 1,4-butanediol. ;`
These involve ~a) reacting propylene, oxygen and a carboxylic
acid to form the corresponding allyl carboxylate; (b) con-
verting the allyl carboxylate under hydroformylation-hydrogenation
conditions to a mixture comprising the carboxylic acid esters
of 1,4-butanediol, 1,2-butanediol and 2-methyl-1,3-propanediol;
(c~ heating the diol esters in the presence of a dehydro-
acyloxylation catalyst to form tetrahydrofuran and the
carboxylic acid; and (d) isolating the carboxylic acid in a
form suitable for recycling to (a).
To varying extents, depending on reaction
conditions, the 1,4-butanediol diester is formed in this
sequence, either by disproportionation of the monoester (which
affords the diester and diol) or by further esterification of
the monoester with the carboxylic acid present as a decomposition
.. . ..
product.
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Specifically, this overall process for preparing
tetrahydrofuran comprises (a) reacting propylene, oxygen and
a carboxylic acid in the presence of a catalyst comprising a . :
Group VIII noble metal, or its salts, or its oxide~ or :-
mixtures thereof at a temperature sufficiently high to provide ~.
the desired rate of formation of the corresponding allyl
carboxylate but below the temperature at which substantial ~ :
deg.radation of khe allyl carboxylate occurs; (b) converting
the allyl carboxylate under hydro-formylation-hydrogenation `~
conditions to a mixture comprising the carboxylic acid esters -
of 1,4-butanediol, 1,2-butanediol and 2-methyl-1,3-propanediol;
(c) heating said mixture in the presence of a dehydroacyloxy-
lation catalyst to convert the 1,4-butanediol monoester
present, as well as any diol, to tetrahydrofuran and the
carboxyllc acid; and (d) isolating the carboxylic acid in a
form suitable or recycling to (a).
More specifically, the process of producing tetra- .
hydrofuran comprises (a) reacting propylene, oxygen and acetic
acid in the presence of a catalyst comprising a Group VIII
noble metal, or its salts or its oxides or mixtures thereof at ~:~
a temperature sufficiently high to provide the desired rate of
formation of allyl acetate but below the temperature at which -~
substantial degradation of allyl acetate occurs; (b) con~
verting the allyl acetate under hydrogenation-hydroformylation
conditions to a mixture comprising 1,4-butanediol monoacetate,
1,4-butanediol diacetate, 1,4-butanediol and the corresponding
derivatives of 2-methyl-1,3-propanediol and 1,2-butanediol;
(c) heating said mixture in the presence of a dehydroacetoxy-
lation catalyst to convert the monoacetate of l,4-butanediol :
as well as the diol present to tetrahydrofuran and acetic
acid; (d) i~olating the acetic acid in a form suitable for
recycling to (a)
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The conditions under which the carboxylic acid
esters of 1,4-butanediol, 1,2-butanediol and 2-methyl-1,3-
propanediol are formed from propylene, oxygen and carboxylic
acids by way of intermediate steps are disclosed in Canadian
applications discussed above.
The instant process is carried out in the vapor
phaseO All of the carboxylic acid monoester is converted
directl~ to tetrahydrofuran and the carboxylic acid, the
addition of water being unnecessary. The tetrahydrofuran ;
can be easily isolated by distillation. In contrast, the
methods in which water is produced or is otherwise present ,
afford the tetrahydrofuran-water azeotrope, which must be
dealt with in another operation to provide anhydrou~ t~tra-
hydrouran. ;~
Additionally, if the li~uid phase and strong acid
catalyst are used, a side reaction occurs, i.e., the following
disproportionation:
o O o ;~
HO(CH2)40CCH3- ~ OH(CH2)40H ~ C~3CO(CH2)40CCH
This process competes with tetrahydrofuran formation.
The diol formed is easily converted to tetrahydrofuran but the
diacetate formed is not. Therefore, a considerable excess of `
water must be present to hydrolyze the diacetate to the mono-
acetate so it can eliminate acetic acid and form tetrahydro- ;
furan.
The dehydroacyloxylation mixture can be passed over
the catalyst in the liquid phase, vapor phase or liquid-vapor
phase. Preferably, it is used in the vapor phase.
For most instances, the reaction is carried out by
passing a carboxylic acid monoester of 1,4-butanediol through ~ ;
a heated catalyst bed. Thereafter, the product is distilled - ~
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to effect isolation o~ the carboxylic acid and tetrahydro~uran. ;
Well-known techniques of purification of the fractions can be
used to obtain the maximum yield of tetrahydrofuran and the
carboxylic acid
The following examples are set forth to illustrate
more clearly the principle and practice of this invention to
those s~illed in the art. Unless otherwise specified, where
parts or percents are mentioned, they are parts or percents
by weight.
Apparatus - A vertical hot tube reactor (16 mm ID x
.
70 cm effective length) is constructed from heavy wall glass,
with 24/40 male and female joints. Vigreaux points are
idented just above the male joint to support catalyst pellets.
Thermocouple leads are fastened into three other Vigreau~
indentations at points along t~e lengt~. Thr~e 4 ~t. x 1 in.
Briskheat glass insulated heating tapes are wound onto the
tube, covered with glass wool and glass tape, and connected
to separate variable transformers. The tube exit is connected
by a gooseneck (also heated) to an efficient condenser and
collection vessel. A three necked flask serves as the
evaporator, with the reactants added from an additional funnel
in a side neck. ~itrogen carrier gas is passed through to
provide residence times on the order of 3 to 10 seconds.
Example 1 - The tube reactor described above is
charged with 89 grams of silica-alumina catalyst (87% silica -
13% alumina, 3/16" x 3/16" pills, Davison Chemical Grade 970)
and i9 maintained at 220-250C. while 50.0 grams of a crude
oxo product mixture containing, as indicated by ~uantitative
glpc analysis, 31.7 grams of 4-acetoxybutanol, 10.2 of 1,4-
butanediol diacetate, a very small amount of 1,4-butanediol,
and oxo by-products (about 6 grams of acetate derivatives of
2-methyl~1,3-propanediol and 1,2-butanediol) is flash
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evaporated and passed through over one ~our. Quantitative glpc
analysis (propionic acid internal standard) of the effluent
shows that no 4-acetoxybutanol remains unconverted, and that
- 17.3 grams of tetrahydrofuran (100% yield based on the 4-
acetoxybutanol initially present) and 17.6 grams of acetic
acid have been collected. The 1,4-butanediol diacetate ard
! OXO by-products pass through the tube essentially unchanged.
Example 2 - A 50.0 gram portion of the same crude
oxo product mixture described in Example 1 is passed th~ ugh
the tube containing 85 grams of silica-magnesia catalyst ~70%
silica - 30% magnesia, 3/16" x 3/16" pills, Davison Chemical),
again at 220-2S0 C. and over a one hour period. The results,
as indicated by quantitative glpc analysis of the eEfluent,
are substantially the same as in Example 1 - 16.3 grams of
tetrahydrofuran (94% yield) and 16.5 grams of acetic acid ;
are collected.
Example 3 - The tube reactor is charged with 110 '
grams of alumina catalyst (1/8" pellets, ~Iarshaw Al-0104T),
is
which/subsequently subjected to pretreatment at 200C. with
50O/o aqueous acetic acid. Then 50.0 gr~ s of a crude oxo
product mixture containing, as indicated by quantitative glpc
analysis, 24.3 grams of 4-acetoxybutanol, 8.2 grams of 1,4-
butanediol diacetate, and oxo by-products (about 5 grams of
3-acetoxy-2-methyl propanol, 6 grams of 2-acetoxybutanol,
small amounts of the corresponding diacetates and acetic acid)
is flash evaporated and passed through at 200-220C over 30
minutes. Quantitative glpc analysis of the effluent shows
that no 4-acetoxybutanol remains unconverted and that 12.2 ;
grams of tetrahydrofuran (92% yield based on the 4-acetoxy-
butanol) and 17.1 grams of acetic acid have been collected.
~he 1,4-butanediol diacetate passes through the tube unchanged
under these conditions.
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~ xample 4 - The tu~e reactor is char~ed with 91
grams of Linde 13X zeolite (1/8" pellets) and maintained at
250-300 C. Four successive 50 gram portions of 4-acetoxybutanol
(containing minor amounts of the disproportionation products
1,4-butanediol and 1,4-butanediol diacetate) are passed through
over 30 minute periods. The individual effluents are subjected
to ~uantitative glpc analysis; the results are summarized in
Table I.
Example 5 - A miniplant is constructed and operated
for the production of tetrahydrofuran from propylene via the
disclosed cyclic process. An 8 ft. x 1 in. diameter stainless
steel tube is charged with one liter (lO00 grams) of ca~alyst
com~osed o~ alumina impregnated with palladlum (0.3%) and
potassium acetate (3%). The reactor temperature is maintained
at 180C. (circulating oil jac~et) while a mixture per hour of
2000 grams of propylene, 600 grams of acetic acid, 170 grams
of oxygen and 900 grams of water is passed through. The output
per hour is a mixture of about 960 grams of allyl acetate and
1050 grams of water, in addition to 18 grams of carbon dioxide
and t~e excess propylene and~oxygen, which are recycled. The
allyl acetate phase, which contains about 0.1% acetic acid, is
separated and used directly in the second stage of the process.
A two liter stirred autoclave heated at 125C. is
pressurized wit~ 3000 psi of 2:1thydrogen/carbon monoxide and
charged with a mixture of 400 grams of the allyl acetate, 8.0
grams of cobalt octacarbonyl and 400 ml. o~ benzene. ~n exo-
thermic reaction and gas uptake ensue. ~fter 15 minutes at
125-145 C., the product mixture is pumped from the autoclave,
cooled and vented. It is then decobalted by heatin~ at 110C.
for lO minutes in a closed ~essel, the addition of acetic acid
being unnecessary because of its presence as a decomposition
product. (The cobaltous acetate w~ich forms is iltered off
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and transformed to cobalt octacarbonyl by subjection to
hydrogen/carbon monoxide at elevated temperature and pressure
([160 C., 3000 Psl ). The benzene solution is concentrated
.. . . .
and the products are flash distilled, affording 474 grams (91% '~
yield~ of oxo aldehydes containing minor amounts of the
butanediol acetate compounds. A glpc analysis indicates the
presence of 4-acetoxybutyraldehyde, 3-acetoxy-2-methylpropion-
aldehyde and 2-acetoxybutyraldehyde in 7 : 1.5 : 1.5 ratio.
The aldehyde mixture is combined in a stirred auto-
clave with 50 grams of a 13% cobalt on silica catalyst,
subjected to 3000 psi of hydrogen, and heated for 30 minutes
at 150 C. Reduction to the diol derivatives is complete, in
essentially quantitative yield. ~ ,
After removal of the hydrogenation catal~st ~y
filtration, the product mixture is examin~d ~y glpc and ~ound
to contain 4-acetoxybutanol, 3-acetoxy-2-methylpropanol and
2-acetoxybutanol, and small amounts of their respective
diacetate and diol disproportionation products. ;
The acetate mixture is passed directly through an
8 ft. x 1 in. diameter tube containing one liter of the --~
catalyst described in Example 1, at 220 C. and over a 30
minute period (contact time 3-10 seconds). Distillation of
t~e effluent affords 184 grams of tetrahydrofuran (64% yield
in the conversion from allyl acetate) and 173 grams of acetic
acid (72%). The higher boiling components of the effluent
include minor amounts of the respective diol diacetates and
the by-product monoacetates, from which acetic acid could be
derived in a hydrolysis operation. ~o 4-acetoxybutanol remains
unconverted.
The acetic acid produced in the final step is
recycled to the propylene oxidation stage for production of
allyl acetate.
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.The process as described is operated semi-
continuously to provide tetrahydrofuran at about one pound per .
hour.
It should, of course, be apparent to those skilled
in the art that changes may be made in the particular
embodiments of the invention described which are within the
full inté~ded scope of the invention as de~ined by the appended
claims.
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