Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to the isomerization,
especially skeletal isomerization of alkenes, for example, n-
butene to isobutene employing a gamma alumina catalyst.
It is well known that acid solids such as alumina,
silica-alumina, TiO2 and other metal oxides ard phosphates
can catalyze various reactions such as cracking, polymerization
and isomerization. The degree to which each reaction will be
catalyzed depends on reaction conditions and catalyst properties,
such as surface acid strength, acid site concentration and site
distribution, hydrophobicity, pore volume and size distribution,
and surface area. Thus it is important that the surface
properties of the catalyst be effectively and accurately
controlled.
It has been reported in the literature that the
enhancement of alumina acidity can be achieved by incorporat-
ing F and Cl through various methods.
In U.S. Patent No. 4,038,337 the skeleton isomeri-
zation of alkenes is reported using alumina which has been
reacted with a silicon compound of the general formula:
X
Y - si - w
z
wherein X, Y, Z and W can be -R, -OR, -Cl, Br, SiH3, -COOR,
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-SinClm; R being hydrogen or a hydrocarbon group of 1 to 30
carbon atoms, m and n being 1-3, preferably an ester of
silicic acid, with from 0.5% to 12% by weight of silica being
deposited on the alumina.
The isomerization is equilibrium limited. In the
case of n-butene isomerization to isobutene, the yield in a
single pass is limited by thermodynamic equilibrium to about
40 weight percent (conversion X selectivity). According to
the present invention, yields of up to about 33 weight % per
pass have been obtained.
Isobutene is of significant value having diverse
applications, such as for example being one of the comonomers
for butyl rubber, for use in alkylations and for dimerization
to diisobutene which is an intermediate in the preparation
of detergents.
~ particular feature of the present isomerization
is the high conversions and selectivities obtained with
unmodiied gamma alumina. These and other advantages and
features will become apparent from the following.
SUMMARY OF THE INVENTION
It has been discovered that alumina with a very low
sodium content, i.e., less than 0.01 weight percent cal-
culated as Na2O, is a superior catalyst for use as an alkene
isomerization catalyst.
The catalysts of the present invention are gamma
alumina, A12O3 having a sodium content o~ less than 0.01 wt.
as Na2O.
The catalysts as described are employed in an iso-
merization process comprising feeding alkenes having at
least four carbon atoms and preferably 4 to 12 carbon atoms,
in vapor phase at a temperature in the range of 300C. to
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600C., preferably 450C. to 550C. through a bed of said low
sodium content gamma alumina, an LHSV (LHSV - Liquid Hourly
Space Velocity in hr l-liquid volumes of alkene to be iso-
merized per ~olume of isomerization zone containing catalyst
per hour) in the range of .5 to 12, preferably 1 to 8 to
produce an isomer, especially a skeletal isomer of said alkenes.
It has also been found that the presence of water
in the isomerization feed improves the operation of gamma
alumina in the isomerization process, i.e., an amount of
water from a water saturated alkene to about 1 mole of water
per mole of alkene.
The presence of water in the alkene feed to be iso-
merization also results in an improved process of isomerization
using unmodified gamma alumina.
Thus, in accordance with the invention there is pro-
vided a process for the isomerization of alkenes comprising
feeding a stream containing alkenes having at least four
carbon atoms and from about 0.01 to 1.0 mole of water per
mole of alkenes, in vapor phase, at a temperature in the
range of 300C. to 600C at an LHSV in the range of 0.15 to
12,-through a fixed bed of gamma alumina having a sodium
content of less than 0.01 weight percent, calculated as Na2O.
In particular the isomerization is skeletal iso-
merization and the gamma alumina is in particulate form.
DETAILED DESCRIPTION OF THE INVE~TION
AND PREFERRED EMBODIMENTS
Gamma alumina is employed because of its desired
high surface area, generally in the range of 100-350 m2/gram
preferably the gamma alumina has a surface area of greater
than 150 m 2 /gram up to about 300 m 2 /gram.
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It has been found the level of sodium impurity in
the gamma alumina is an important consideration. Sodium,
measured as Na2O is less than 0.01 wt. % to provide suitable
catalysts for the isomerization of alkenes.
The alumina is normally in granular form of 12 to
20 standard U.S. mesh. Other shapes and sizes may be used,
depending on the process to be utilized.
The presence of dienes such as butadiene in a C4 feed
results in rapid coking of the catalyst and loss of activity.
Hence, the feed to-the isomerization should contain as little
diene as possible, preferably less than 0.05 mole %. It has
also been found that the complete absence of water from the
feed to the isomerization results in more rapid deactivation
of the catalyst. Thus, in the preferred operation of this
process, water is present. This has been obtained by passing
the gaseous reactants through a water bath to provide a
vapours stream which was saturated with water (approximately
0.03 mole of water per mole of n-butene) under the conditions
of temperature and pressure present. Water may also be added,
e.g., as steam, in amounts of up to one mole of water per mole
of alkene. Thus from about 0.01 to 1.0 mole, preferably about
0.02 mole to 0.5 mole of water per alkene, e.g., n-butene, is
present during the isomerization. The presence of these amounts
of water also greatly improves the functioning of unmodi-
fied alumina of the type described and silicon modified
alumina according to the present invention by increasing both
'iF~
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63
conversion and selectivity to the isomerized product.
It has been observed that as the catalyst is deacti-
vated with a loss in total activity, however, the drop in
activity is due solely to a drop in conversion, whereas
selectivity increases.
The feed to the isomerization may be substantially
pure alkene, however, it is more likely that the feed will be
a refinery cut, generally containing both allcenes and alkanes
of the same chain length and some materials, both higher and
lower boiling. The alkanes are substantially inert in the
isomerization and serve as diluents. The process is carried
out in vapor phase, and in addition to the hydrocarbons pre-
sent, diluent gases such as nitrogen may be present.
The isomerization is carried out by feeding the
alkene containing stream (preferably the stream is free of
organic compounds other than hydrocarbons), in vapor phase to
a reactor containing the unmodified gamma alumina or silicon
modified catalysts of the present invention at temperatures in
the range of 300C. to 600C. and LHSV of 0.5 to 12, preferably
about 450C. to 550C. and LHSV about 1 to 8, higher tempera-
tures being preferred for higher L~SV.
The feed of the isomerization will preferably con-
tain only one skeletal isomer, i.e., a normal alkene or iso-
alkene. Although the skeletal isomer of the alkene (or iso-
alkene) may be present, it will be present in less than an
equilibrium amount otherwise, even though the isomerization
occurs the product will be substantially the same as the feed.
Generally during use of the present catalyst, con-
version dropped from 43% to 30% while selectivity improved from
83% to 89% with more than 30 hours of continuous running, the
result of carbon deposition. The catalyst regeneration para-
meters studied were temperature, length of time, regeneration
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feed composition, moisture and moisture level. Briefly, it
was found that a regeneration sufficient for 24 hours of con-
tinuous running of the isomerization was obtained by feeding
a stream of oxygen containing gas (e.g. air) at a temperature
of 550C. to 600C. for 1 to 3 hours, e.g., one hour at 575C.,
depending on the degree of coking. Higher oxygen content and
flow rates shortened the regeneration period. The use of small
amounts of water in the regeneration has been found to be
beneficial. The water tends to reduce the temperature increase
in the catalyst bed during the regeneration. The dilution of
the regenerataive air with an inert, e.g., nitrogen, reduces
the temperature rise in the bed. Several methods of
regeneration were evaluated and the one best suited for a
particular operation should be selected.
The following examples are intended to illustrate
the invention and various permutations thereof and not to
limit the scope thereof.
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ISOMERIZATION
The isomerizations were carried out in a fixed
reactor constructed of 316 stainless steel tubing with a 2 ~1
O.D. and a 3/8" I.D. An 1/8" thermowell is located in the
middle of the reactor. The reactor temperature is controlled
by a two zone furnace. The first zone of 4 inches is a pre-
heater. The second zone of 8 inches is the reactor section.
The catalyst volume for length was 5 inches (with no inerts)
to provide a bed length to diameter ratio over 8Ø The
catalysts were tested under flow conditions of 500C., LHSV=
1.35, Flow rate n-C4=/N2 of 60/~0 ml/min. and atmospheric
pressure. The feed had the following composition:
Component Mole %
n-butene 15
N-butene-l
trans n-butene-2 ) 85
cis n-butene-2
The results of each run are reported on the average
of 24 hours on stream, except for the poorer results, which
are not usually continued. The 24 hour average is after
several regenerations. The product analysis was by gas chroma-
tography. Small amounts, less than 25 mol ~ of C3 and C5 were
detected in the product. Some cracking products, CH4 0.3
mole ~ and H2, 0.3 to 0.6 mole % were detected.
EXAMPLE 1
This example demonstrates the improvement in the
skeletal isomerization of alkenes for unmodified alumina when
water is added to the feed. The alumina employed was Harshaw
Al-3438 (surface area 202 sq. m/g and Na content < 0.01%).
The alumina was unmodified. A feed of the type described
was employed and water added to the feed as steam at two
.,...., J
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levels 0.1 ml and 0.2 ml (liquid) per minute. The con-
ditions and results are shown in Table I. The same
apparatus as previously described was used. The temperature
was 500C. and LHSV was 2.94. The mole ratio of water/n-C4
run B was 0.08/1 and Eor run C, 0.17/1.
EXAMPLE 2
This example illustrates the excellent results
achieved in an isomerization using unmodified alumina having
a sodium content of less than 0.01% (measured as Na2O) when
water is present as part of the feed to the isomerization.
The LHSV was high (4.2). Conversions were high with excellent
selectivity. The data is reported in Table II.
EXAMPLE 3
This example illustrates the effect of the sodium
content of the catalyst on the isomerization. The data is
reported in Table III.
TABLE I
RUN FLOW RATE, ml/min. ON STREAM CONV. SEL.
n-butene Water-liq. Hrs. Mole % Mole %
A 1600 0.0 - 42.7 15 86
B 1600 0.1 44.5 24 88
C 1600 0.2 41.1 25 89
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TABLE II
Catalyst: Al--3438 of Harshaw (alumina, low sodium level,
< 0.01%)
Conditions: LHSV - 4.2
Temp. C. = 515
Water (ml/min~) = 0.4
Feed Composition: 84% n-Butenes, 16% n-Butene
Test Results: Time on stream Conv. Select.
Hours mole % mole %
10.2 39 86
2.3 35 87
18.6 30 88
21.6 28 88
TABLE III
Catalyst: Al-4028 of Harshaw (alumina~ sodium level, 0.02%)
Conditions: LHSV = 1.35
Temp. C. = 500
Bubbled through water
n-Butene/nitrogen = 1.0
Feed Composition: 84% n-Butenes, 16% n-Butane
Test Results: Time on stream Conv. Select.
Hours mole %mole %
.1 10 89
2.5 5.8 92
20.1 5-3 93
