Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11'~2554
Process for obtaining isobutene from C4-hydrocarbon mixtures
containing isobutene
The present invention relates to a process for
obtaining isobutene from a C4-hydrocarbon mixture containing
isobutene, by reacting the mixture with a primary C3- or C4-
alcohol, isolating the tertiary ether formed and decomposing
it at an elevated temperature.
It is already known to obtain isobutene from a
C4-hydrocarbon mixture by means of a sulfuric acid extraction
process. In this process, highly concentrated sulfuric acid
must be used and consequently expensive materials must be employed
for the equipment. Since, furthermore,-side-reactions of iso-
bu'tene, for example dimerization, polymerization, hydration and
the like, occur during the extraction, the sulfuric acid extrac-
tion process is not satisfactory in respect of yield, and of
quality of the products.
A process for obtaining isobutene is also known,
for example from German Patent 1,216,865 published on May 18,1966
or German Application DAS 1,934,422 published on January 15,1970
or DAS 2,011,826 published on October 1, 1970 in which a C4-
hydrocarbon mixture containing isobutene is reacted with methanol
in a first stage and the resulting methyl tert.-butyl ether is
decomposed into methanol and isobutene in a second stage. However,
the known processes have the disadvantage that methanol forms
azeotropic mixtures with the C4-hydrocarbons. For example it
is known from Germain-Laid-Open Application DOS 2,629,769
published January 5, 1978 and German Published Application DAS
1,934,422 that in the preparation of methyl tert.-butyl ether,
when the unconverted
1~ 5~
- 2 - o.z. 0050/033~51
hydrocarbons are removed from the reaction mixture by
distillation they contain about 2 % of methanol, due to
the hydrocarbon/methanol azeotropes, and this methanol
can only be reco~ered by expensive methods, for example
by interpolating a water wash. It is a particular
disadvantage that on separating by distillation the
reaction mixture obtained from the decomposition s.tage
and containing isobutene and methanol, the methanol and
isobutene form an azeotropic mixture so that an expensive
waterwash mustalso beint~lat~d into the decomposition
stage (cf., for example, German Published Application n~-~
1,934,422) in order to m1ni~;7-e the loss of methanol and
obtain a met~nol-fre~ isobutene, as is re~uired for.most
applications.
It is true that in addition to the use of meth-
anol and possibly ethanol as alc.ohols for the etherifica-
tion reaction, primary alcohols in general ha~e previously
been referred to as possible reactants for the conversion
to the tertiary ether (cf., for exa le, German Patent
1,216,865 and German Published Applications DAS 1,934,422
and 2,011,826, already referred abo~e). However, there
was a subst~ntial prejudice against the use of higher
primary alcohols, for example C3- or C4-alcohols, si~ce
it was known that such higher prim~ry alco~ols can easily
be dehydrated to olefins under the reaction conditions of
the decomposition stage, in the presence of an acid
ca ~lyst. For example, German Published Application
DAS 1,934,422, already referred to, expressly points out,
in column 3, 1st paragraph, that methanol, which cannot
ilf~255~
be dehydrated, should be used as the alcohol in order to
avoid the undesirable formation of olefins in the decom-
position stage.
A further substantial prejudice against the use
of higher primary alcohols resulted from the fact that
it was known, for example from U.S. Patent 3,170,000,
especially Table I and dolumn 3, lines 20 to 31, that methanol
and ethanol give substantially higher yields in the ether-
ification reaction than do the higher primary alcohols, eg.
the C3- or C4-alcohols.
Because of the disadvantages and prejudices des-
cribed above, the conventional process for obtaining iso-
butene by decomposing the tertiary ether obtained in a first
etherification stage have not found industrial use but have
only remained prior art on paper, and hence the industrial
production of isobutene had to depend on the use of the
sulfuric acid extraction process, with all the shortcomings
and disadvantages inherent in the said process.
It is an object of the present invention to provide
a process for obtaining isobutene from a C4-hydrocarbon
mixture containing isobutene, which does not suffer from the
disadvantages of the conventional processes.
We have found that this object is achieved by a
simple process for obtaining isobutene from a C4-hydrocarbon
mixture containing isobutene, which comprises
(a) reacting the mixture continuously with a primary
C3- or C~-alcohol in the presence of an ion exchanger in its
acid form as a condensing agent to form the corresponding
C3- or C4-alkyl tert-butyl ether by feeding the primary C3-
or C4-alcohol and the C4-hydrocarbon mixture with or without
prior mixing, to an etherification rcaction zone which contains
the ion exchanger, while maintaining the exit temperature
- 3 -
l~ tZ551~
of the reaction mixture from the etherification reaction zone
at from 25 to 65C and the quotient of the volume of the
etherification reaction zone and the throughput of the C4-
hydrocarbon mixture and the primary C3- or C4-alcohol at
from 0.01 to 5 hours;
(b) distilling the reaction mixture obtained from the
etherification reaction zone in a first distillation zone,
taking off as the top product without water washing a C4-
hydrocarbon mixture comprising the unconverted hydrocarbons
and not more than 1,000 ppm by weight of the primary C3- or
C4-alcohol and taking off as the bottom product the resulting
C3- or C4-alkyl tert-butyl ether, which may contain therein
primary C3- or C4-alcohol which may have been added in excess;
(c) feeding the bottom product to a second reaction
zone containing an acid catalyst, in which the C3- or C4-
alkyl tert-butyl ether is decomposed at an elevated temperature
- to give isobutene and primary C3- and C4-alcohol;
(d) feeding the mixture of isobutene and primary
C3- and C4-alcohol produced in step (c) to a second distil-
lation zone, taking off as the top product without a waterwash isobutene containing not more than 500 ppm by weight of
primary C3- or C4-alcohol ancl taklng orf as ~hc ~ottom procluct
the remaining primary C3- or C4-alcohol produced in step (c);
and
(e) recycling the primary C3- or C4- alcohol
which is the bottom product of step (d) to the etherification
reaction zone.
Using the novel process, a C4-hydrocarbon .
A
ll'~Z55 ~
-- 5 -- ~.Z. OGSO/C33951
raffinate which is virtually free from C3- or C4-alcohol
is isolated from the reaction mixture obtained after the
etherification stage, by simple distillation without
interpolating a water wash, since un ~nverted primary
C3- or C4-alcohol surprisingly does not form an azeotrope
with the C4-hydrocarbons. In general, a C4-hydro-
carbon raffinate containing not more than 1,000 ppm by
weight of C3- or C4-alcohol, preferably at most 500 ppm
by weight, in particular at most 100 ppm by weight, is
lo taken off as the top product of the distillation.
Again, when the reaction mixture, obtained on decomposing
the C3- or C4-alkyl tert.-butyl ether, is separated by
distillation-into isobutene and the C3- or C4-alcohol,
azeotropesof the alcohol are not formed. The C3- or
C4-alcohol can therefore be recovered, without interpol-
ation of a water wash, in a simple manner and virtually
without losses, and be recycled to the etherification
stage.
Surprisingly, the process according to the inven-
tion gives isobutene in high yield, for example in a
yield of more than 97 %, based on the isobutene contained
in the C4-hydrocarbon mixture employed. This was
unexpected since U.S. Patent 3,170,000, already referred
to, states in column 3 that on using C3- or C4-alcohols
only very poor yields of tertiary ether are obtained.
It is also known from U.S. Patent 3,634,535, especially
column 6,that the reaction of isobutene with propanol
gives the tertiary ether in a yield of only about 50 %,
whilst the corresponding reaction of isobutene and
ZS5i~
- 6 - O.Z. oOSo/033951
methanol gives yields of from about 90 to 95 ~. It was
therefore surprising that yields of tertiary ether of
more tha~ 95 % are obtained by the process according to
the invention.
Isobutene-containing C4-hydrocarbon mixtures suit-
able for the process of the invention are obtained, for
example, from ~he thermal or catalytic cracking of petroleum
products, from the manufacture of ethylene by pyrolysis of
liquefied petroleum gas (LPG), naphtha, gas oil or the like,
lo or from the catalytic dehydrogenation of n-butane and/or
n-butene. These C4-hydrocarbon mix~ires as a rule
contain-olefinic and paraffinic C4-hydrocarbons in addition
to the isobutene and may also contain butadiene, for
example in amounts of up to 70 per cent by weight, and
higher acetylenes, eg. but-l-yne and butenyne. Butadiene-
containing C4-hydrocarbon mixtures may be employed as such
or after first removing the butadiene from the C4-hydrocarb~
m;xture~ for example by extraction with aselective solvent.
The C4-hydrocarbon mixtures may in addition contain C3-
hydrocarbons, eg. propane, propene and propyne, for examplein amounts of up to 10 per cent by weight, In general,
the C4-hydrocarbon mixtures contain from 5 to 95 per cent by
weight, preferably from 10 to 90 per cent by weight, in
particular from 20 to 70 per cent by weight, of isobutene.
Preferably, C4-hydrocarbon mixtures are used which in addi-
tion to isobutene contain n-butane, isobutane, but-l-ene,
trans-but-2-ene and cis-but-2-ene, with or without buta-1,3-
diene.
The primary C3- or C4-alcohols (ie. alcohols of 3
il~2S5~
or 4 carbon atoms) to be used according to the invention
are in general n-propanol, n-butanol or isobutanol, prefer-
ably n-propanol or isobutanol, and especially isobutanol.
The alcohols are used, for example, as technical-grade
products of conventional purity, for example of a purity of
at least 95%, preferably at least 98%.
The acid condensing agents used for the etherifi-
cation which represents the first stage are ion exchangers
in the acid form. Examples of suitable ion exchangers are
sulfonated coal, sulfonated phenol-formaldehyde resins,
sulfonated resins derived from coumarone-indene condensation
products and, in particular, sulfonated polystyrene resins,
eg. nuclear-sulfonated crosslinked styrene-divinylbenzene
copolymers. The amount of the ion exchanger is in general
from 0.01 to 1 liter of bulk volume per liter of reactor
volume. The ion exchangers may be used as such or on a
carrier. Examples of suitable carriers are alumir,a, silica,
active charcoal and plastics, eg. styrene polymers. The
etherification may be carried out in, for example, stirred
kettles or fixed bed reactors, the latter being preferred.
The exit temperature of the reaction mixture from
the etherification zone is from 25 to 65C, preferably from
30 to 60C, ~specially from 30 to 50C. Preferably, exit
temperatures which are lower than the mean temperature in the
etherification stage are employed. In general, the ether-
ification reaction results in not less than 90%, preferably
n
A
1~ 55~
- 8 - 0.2. ~O50/033951
less than 95 %, in particular not less than 96 %,
conversion of the isobutene, contained in the C4-
hydrocarbon mixture, to the C3- or C4-alkyl tert.-
butyl ether.
The etherification according to the Ln~e~tion can
be carried out under atmospheric pressure, However, it
is advantageous to' wor~ under slightly superatmospheric
pressure, for example at from 1.01 to 30 bar, especially
from 2 to 20 bar. The isobutene-containing C4-hydro-
lo carbon mixture can, depending on the pressure and tempera-
ture, be employed for the reaction as a liquid or a gas.
Preferably, liquid isobutene-containing C4-hydrocarbon
m;xtures are employed. ~he etherification can be
carried out batchwise. In that case, the reaction
times are in general from 1 minute to 5 hours. Prefer-
ably, however, the etherification is carried out continu-
ously, in which case the quotient of the volume of the
rsaction zone (in volume units) and the throughput in
volume units per hour is in general from 0.01 to 5 hours,
preferably from 0 02 to 1 hour, especially from 0.03 to
1 hour.
~or the etherification reaction, the weight ratio
of primary C3- or C4-alcohol to the isobutene contained in
the C4-hydrocarbon mixture is in general from 100 : 1 to
1 : 1, preferably from 20 : 1 to 1.2 : 1, especially from
4 : 1 to 1.3 : 1.
- The reaction mixture which is obtained from the
etherification reaction zone and which as a rule still
contains excess primary C3- or C4-alcohol which had been
t ~. 'S' ' r~ ~
_ 9 ~ 33 3 ~: 5 1
added for the etherificat~on reaction ls separated by
distiilation, without ~nterpolating a water wash, and
the top product taken off is a C4-hy8rDcarDon raf-
firAte substantially free from isobutene, the isobutere
content in general being not more than 5 percent by weight,
preferably not more than 2.5 percent by weight, especially
not more than 1.5 percert by weight. Preferably, the
top product taken off is a C4-hydrocarbon raf~inate con-
taining not more than 200 ppm by weight of ~3- or C4-
alkyl tert.-butyl ether and/or di-C3-aLkyl or di-C4-alkyl
ether.
The bottom product from the distillation of the
reaction mixture obtained after the etherification con-
sists of the C~- or C4-alkyl tert.-butyl ether which may
or may not still contain excess primary C3- or C4-alcohol.
Advantageously, a bottom product cor~taining ~ot more thar.
1,000 ppm by weight, preferably not more than 500 ppm ~y
weight, especially not more than 100 ppm by weight, of
C4-hydrocarbons is taken off.
mereafter, in the second stage of the process,
the tertiary ether obtained is decomposed into isobutenG
and primary C3- or C4-alcohol in the p-esence o an acid
catalyst at ele~ated temperatures. The starting material
for the decomposition can be a tertia~ ether ~hich is
virtually free from C3- or C4-alcohol and which has been
obtained, for example, by using, for the etherlfication, an
amount of C3- or C4-alcohol corresponding to at most the
stoichiometrically required amount of alcohol, or ~y remov-
ing (for example by distillation) excess added pri~ary C -
10 ~ 33 ~`'
or C4-alcohol from ~he bottom product obtained after distil-
lation of the etherification reaction mixtu~e. Prefer-
ably, howe~er, ~e tertiary ether obtained as the bottom
product after remc~ing the ~4-hydrocarbon raffinate by
distillation is employed for the decomposition without
further removal of any excess C3- or C4-alcohol which may
be present. Alternatively, it is ~lso possible to rem-
ove only a part of the excess C~- or C4-alcohol. In
general, the C3- or C4-alkyl tert.-butyl ether formed is
o used in the decomposition stage without addition of water.
To carry-Qut the decomposition, the tertiary ether
is ~aporized and brought into contact with the acid catalyst
in the vapor phase. Examples of suitable acid catalysts
are ion exchangers in the acid form,
eg. sulfonated coal, sulfonated phenol-formaldehyde resins,
sulfonated resins derived from coumarone-indene condensation
products and, in particular,sulfonated polystyrene resins,
eg. nuclear-sulfonated, crosslir~ed styrene-divinylbenzene
copolymers.
Other catalysts which may be used advantageously are
solid phosphoric acid catalysts which comprise monophospho-
ric acid or preferably polyphosphoric acid on a solid
carrier. Ex~mples of suitable carriers for the ~hos-
phoric acid catalysts are alumina, silica, active charcoal,
kieselguhr or pumice. Silica gel is the prefe~red
carrier .
Other suit~ble acid catalysts are acid metal sul-
fates, eg, sodium bisulfate, calcium bisulfate, alum~num
sulfates, nickel sulfate, copper sulfate, cobalt sulfate,
- 11 - 3.~ C50~3~951
c~dmium sulfate and stron~ium sulfate. These acid
sulfates ~ay ~e used unsupported but are prefer-
ably used on a carrier. Examples of cuitable carriersare silica gel, active charcoal, alumina and pumice.
Further suitable catalysts for the decompositior~
are silica gel and alumina used by themsel~es.
In a further embodiment of th~ process according to
the invention, a metal phosphate, especially a metal hydro-
gen phosphate, is used as the acid decomposition catalyst.
lo These phosphates may also contain phosphoric acid i~ excess
over the amount corresponding to the stoich~ometric compo-
sition of the acid metal phosphate, for example in anexcess of up to 6~%, preferably from l +o 50 ~, in particular
fromlO to 20 %. Examples of such metal phosphates are mag-
nesium phosphates, calcium phosphates, strontium phosphates,
barium phosphates, manganese phosphates, nickel phosphates,
copper phosphates, cobalt phosphates, cadmium phosphates,
iron(II) phosphates, chromium phosphates ~nd in ~articular
aluminum phosphates, ~he metal phcspnate cat21ystca~beused as
such or on a carrier. Examples of suitable carriers
are alumina, silica, acti~e charcoal and zinc oxide.
The amount of the acid catalyst is ln Oeneral ~rom
about O.Olto lkg,preferably from aboutO.03 toO.3 k~, ~e~
kg of tertiary ether passed thh~ough the reactor per hour.
- Preferably, fixed bed reactors are used cr ~he decomposi-
- tion of the tertiary ether.
me decomposition temperature of the ~ertiary ether
varies wi+~h the nature of the acid catalyst and with the
contact time, but is Ln general from 50 to 350QC, preferably
from 80 to 30QC, in particular from 100 to 250C. Tf a
metal phosphate or phosphoric acid catalyst ls used as the
decomposition catalyst, the decomposition is in general
carried out at from 80 to 350C, preferably from 90 to 260C,
especially from 170 to 210C.
me contact time of the vaporized tertiary ether is
advantageously from 0 1 to 20 seconds, preferably ~rom 1 to
lo 10 seconds.
~he decomposition of the tertiary e~her c~n be
carried out under atmospheric pressure, but is i~ general
carried out u~der superatmospheric pressure, for example
at up to ~0 bar, preferably up to 20 bar. Advantage-
ously, the decomposition of the tertiary ether is carried
out under pressures of from 2 to 15 bar, preferably from
3 to 12 bar, especiaily from 4 to 12 bar. H~wever, the
decomposition can also be carried out under reduced
pressure.
The decomposition of the terliary ether ~ay be
carried out batchwise but is preferabiy carried out con-
tinuously.
me reaction mixture obtained from the decompo-
sition, which contains isobutene and primary C3- or C4-
alcohol as the reaction products, is fed to a second
distillation zone, in which isobutene containing not more
than 500, prefer2bly no~ more than 100, especially not
more than 50, ppm by weight of primary C3- or C~-alcohol
is taken off as the top product~ wit~out inter?olati~.g
1 1 ~ >'~
- 13 - o.~. o~o~o33? 1
a water wash. AdvantageousiyJ a top product which is
` not less than 99.3 ~ by weight pure) preferably not less
than ~9.5 ~ by weight pure, especially not less ~han
99.7 % by weight pure, and which contains the di-C3-alkyl
ether or di-C4-alkyl ether, which may be formed in very
small amounts as a by-product, and/or the C3- or C4-alkyl
tert.-butyl ether, in an amour.t of at most 100 ppm by
weight, preferably at most 50 ppm by weight~ especially
at most 20 ppm by weight, is taken off. ~he pr~ ary
lo C3- or C4-alcohol obtai~ed as the bottom product from the
second distillation zone is recycled to the etherification
reaction zone. Preferably, the content of di-C3-aL~yl
ether or di-C4-alkyl ether, which may be formed in very
small amounts a~ a by-product but accumulates in the
recycled prima-y C3- or C4-alcohol, is restricted to from
2 to 20 % by weight in the latter.
In the novel process, it can be advantageous, if
isobutanol is used as the C4-alcohol, to bleed off a
part of the stream of isobutanol in order to remove any
impurities which may have accumulated, in whi~h case the
ble~stream is advantageouslytakenfrom the side of '~he
second distillation zone, or from the bo~tom product
+æken off the second distillation zone. Advantageously,
the isobutanol ~leed-stream is in general from 0.1 to
10 ~ by weight, preferably from 0.5 to 5 % by weight, of
the total isobutanol stream. ~he isobutanol bleed-
stream taken off to remove any diisobutyl ether formed
advantageously contains from 3 ! 0 40 % by weight, prefer-
ably ~rom 5 to ~ ~ by weight, especi~lly ~rom 10 to 30 ~
- 14 - ~ J
by weight, of diisobutyl ether.
In an advantageous embodiment of the process,
the isobutano~ ble ~ stream is dehydrated in the con~en-
tional manner in ~he presence of a denydrating catalyst,
resulting in the dehydration of not only the isobutanol
but also the diisobutyl ether, &nd thereby additionally
increasing the yield of isobutene.
Advantageously, the dehydration is carried out in
the gas phase over a catalyst. Examples of suitable
catalysts are silica gel, thorium oxide, tit ium(lV~
oxide ànd especially all~mina. In general, the dehydra-
tion is carried out at from 250 to 450C, preferabl~ from
300 to 400C. It can be advantageous to carry out
the dehydration in the presence of water, which may or
may not be added for the purpose.
The Figure diagrammatically shows a~ illustrative
embod~ment of the process according to the invention.
The isobutene-containing C4-hydrocarbon mixture (fed
through line 1) and the primary C3- or C4-alcohol (fed
through line 2) are mixed, and the resulting mixture is
passed through line 3-to the etherification reaction 4,
which contains the ion exchanger. Advantageously,
tAe reactor is a fixed bed reactor, eg. a flow
t~be or a loop reactor or a combination of both types.
However, other types of reactor, for example a stirred
kettle or astirred kettle cascade, can also be used.
The reaction mixture obtained is taken from the reactor
- through line 5 and fed to a first distillat on colu~Ln 6.
At the top of the distillation column, substæ~tially
- 15 - ~ . O~SCfO339~1
isobutene-free C4-hydrocarbon raffinate is taken off through
!ine 7. The tertiary ether which is obtained as
the bottom product of the distillation column 6 and which
may contain excess primary C3- or C4-alcohol is next fed to
the vaporizer 9 through line 8, and after vaporization is
passed through line 10 into the reactor 11 which contains
the acid catalyst. This reactor is in general a fixed
bed reactor. The mixture of isobutene and primary C~- or
C4-alcohol taken from reactor 11 is passed through line 12
lo into the distillation column 13 where very pure isobutene is
obtained as the top product, which is taken off through
line 14. The C3- or C4-alcohol obtained as the bottom
product is returned to the etherification reactor 4 through
lines 15 and 2, where necessary after replenishing the C~-
or C4-alcohol through line 16. Advantageously, a small
pleed-stre~ontainirg C3- or C4-alcohol is taken off
through line 17 to remove any impurities formed, eg. diiso-
butyl ether, diisobutene or triisobutene. If isobutanol
is used as the C~- or C4-alcohol, thisbleed-stream can be
fed to a dehydration reactor, where additional isobutene is
obtained,
Using the process according to the invention, very
pure isobutene is obtained, which in particular is suitable
for the manufacture of high molecular weight polymers of
isobutene.
The Examples which follow illustrate the lnvention,
EXAMPLE 1
- me etherification ~ carried out using a C4-hydro-
carbon mixture which consis~d of the residue (raffinate) of
- - 16 - o.~. O~S0/v339~1
a C4-fraction~ obtained from an ethylene production instal-
lation, from which the butadiene had been ex~racted .
After the extraction of the butadiene, the C4-hydrocarbon
mixture had the following composition:
isobutane 1 9 % by volume
n-butane 8.1 % by ~olume
isobutene 46.o % by volume
but-l-ene 26.7 % by volume
trans-but-2-ene 10.1 % by volume
cis-~ut-2-ene 7.0 % by volume
buta-1,3-diene 0.2 % by volume
Per hour, a mixture of 258 g of this C4-hydrocarbon
mixture and 320 ml of isobutanol was introduced into a
stainless steel tubular reaction vessel which contained
254 ml of a sulfonated
styrene-divinylbenzene copolymer resin in the hydrogen
form (Lewatit SPC 118, particle size 0.8 - 1 mm). A
temperature of 40C and a pr~ssure of 12 bar were maintained
in the reaction vessel. ~he reaction mixture obtained
2c was fed to a distillation column, and at the top of the
column a butene/butane raffinate containing less than
2 per cent by weight of isobutene was obtained. The
raffinate was -rirtually free from isobutanol ard could
therefore be used directly, without additional purification
operations (for example without interpolation of a
water was~, as the starting material for further reactions.
At the bottom of the column, 500 ml per hour of isobutyl
tert~-butyl ether, which still contained 24 3 per cent by
weight, based on the mixture, of excess isobutanol, were
* (trademark)
- 17 - ~ 050JC3~9~1
taken off and fed to a vaporizer. The vaporized iso-
butyl tert.-butyl ether, heated to lgOC, was cracked by
pàssing it into a tubular crack~ng reactor which contaired
ph~sphoricacid on silica (20 %excess ofbhosph~ic acid)as the
cracking catalys~; cracking took place at 190C, giving iso-
butene and isobutanol. ~he crac~ed reaction product W2S
passed into a second distillation column, at the top of
which 115 g per hour of ~ery pure isobutene of the following
composition were obtained;
isobutene 99.85 % by weight
isobutane 730 ppm by weight
butane 3 ppm by weight
but-l-ene 420 ppm by weight
trans-but-2-ene 190 ppm by weight
cis-but-2-ene 160 ppm by weight
buta-1,3-diene 19 ppm by weight
me yield of isobutene, based on isobutene origin-
ally contained in the C4-hydrocarbon mixture em~loyed,
was 97.7 %. At the bottom of the second distillat on
column, 320 ml per hour of isobutanol were obtained, and
this material was recycled to the etherification reaction.
It proYed possible to effect a 4-fold increase in
the throughput of C4-hydrocarbon mixture and isobut&nol
through the etherification reactor, with virtually no
change in the purity of the butene/butane raffinate obtained
on distillation, and of the product, containing isobutyl
- tert.-butyl ether, obtained at the bottom of the distil-
lation column.
-- 18 ~ 050fO33951
COMP.~RA~IVE E~PLE1
The etherification was carried out as described in
Example 1, at 40C, but employing the corresponding stoichi-
ometric amountof methanol instead of isobutanol With a
throughput, of starting mixture, of 2 liters/h per liter
of reactor volume, the residual content of isobutene in
the bute~e/butane raffinate obtained after distillation was
more than 30 per cent by weight. In addition, this
raf~inate contained more than 1.5 mole ~ of methanol, which
was washed out of the raffinate by treatment with water.
The methanol was recovered from the methanol-water mixture
obtained a~ter the water wash, and was recycled to the
etherification reaction. ~e butene/butaneraffinatewas
thendried inorder to remove the entrained water.
In contrast, when using isobutanol (as described in
Example 1) Lnstead o~ methanol, a butene/butane raffinate
containing less than 1 ppm of isobutanol is obtained by
simple distillation.
COMPARATIVE EXAMPLE 2
The ether cleavage was carried out as described
in Example 1, but instead of isobutyl-tert.-butyl ether,
methyl tert,butyl ether was used.
Impure isobutene having the following composition was
obtained at the top of the distillation column:
isobutene 97.0 ~ by weight
othe~ hydrocarbons 0.15 ~ by weight
methanol 2.45 % by weight
dimethyl ether 0.4 X by weight
me isobutene obtained contained 2.45 ~ by weight
of methanol and, in addition, 0.4 ~ by we'ght of d~methyl
- 19 ~ 050/033951
ether, whilst in the isobutene obtained according to
Example 1 the content of isobutanol and of diisobutyl
ether wasbelow the limit of detectability (4 ppm).
For many applications, for example for use as a
starting material for cationic polymerization with boron
fluoride, the isobutene obtained in the Comparative
Example must be subjected to additional purification
operations, whilst the very pure isobutene obtained
accordLng to Example 1 can be employed directly. In
lo order to obtain, from the isobutene produced in Comparati~e
Example 2, an isobutene of similar purity to that
obtained in Example 1, it would be necessary, for example,
to carry out the following additional process steps.
1. Distillation of the isobutene to remove the
dimethyl ether.
2. Subsequent extraction of the isobutene with water
to remove methanol.
3. Drying the resulting moist isobutene.
4. Distillation of the methanol-water mixture,
obtained from the extraction, in order to recover the
methanol.
EXAMPLE 2
~he etherification was carried out using the C4-cut
from an ethylene production installation. The C4-hydro-
carbon mixture had the following composition:
butane 3.65 % by weight
isobutane 1.41 % by weight
but-l-ene 20.44 ~ by weight
isobutene 23.52 ~ by weight
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trans-but~2-ene 4.95 % by weight
cis-but-2-ene 3.15 ~ by wei~ht
buta-1,3-diene 42.31 % by weight
buta-1,2-diene 0.10 % by weight
but-l-yne 0.11 % by weight
butenyne 0.36 % by weight
Per hour, a mixture of 457 g of this hydrocarbon cut
and 320 ml of isobutanol was reacted as described in
Example 1. me isobutene content of the butene/butane
raffir~te obtained after distillation was 1.0 per cent by
weight.
The bottom product from the first distillation was
vaporized and then passed Lnto a tubular cracking reactor,
where the isobutyl tert.-butyl ether was cracked, at 190C,
to give isobutene and ~sobutanol. me isobutene (107 g
per hour) taken of~ at the top of the downstream distil-
lation stage had the following composition:
butane 0.012 % by weight
isobutane ~.041 % by weight
but-l-ene 0.042 % by weight
isobutene 99.332 % by weight
trans-but-2-ene0.09 % by weight
cis-but-2-ene 0.11 % by weight
buta-1,3-diene0.36 % by weight
buta-1,2-diene0.007 % by weight
but-l-yne 0.0032% by weight
butPnyne 0.0028 % by weight
In spite of the C4-hydrocarbon mixtur_ used as the
starting material having a buta-1,3-diene content of
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42.31 per cent by weight, the content of buta-1,3-diene in
the isobutene product was only 0.~6 per cent by weight.
Equally, the concentrations of buta-1,2-diene, but-l-yne
and butenyne were greatly reduced.
Th~ yield of isobutene, based on isobutene contained
in the C4-hydrocarbon mixture employed, was 96.5 %. The
isobutanol, which was recovered virtually completely from
the bottom of the second distillation column, was recycled
to the etherification reaction.
EXAMPT`~ 3
The etherification was carried out using a C4-hydro-
carbon mixture which c ~ isted of the residue (raffinate) of
a C4-fraction, obtained from an ethylene production instal-
lation, from which the butadiene had been extracted.
After the extraction of ~he butadiene, the C4-hydrocarbon
mixture had the following composition:
isobutane 1 9 % by volume
n-butane 8.1 % by volume
isobutene 46.0 % by volume
but-l-ene 26.7 ~ by volume
trans-but-2-ene 10.1 % by volume
cis-but-2-ene 7.0 % by volume
butadiene 0.2 % by volume
Per hour, a mixture of 250 g of this C4-hydrocarbon
mixture and 266 ml of n-propa~ol was introduced into a
stainless steel tubular reaction vessel which contained
138 ml o~ a sulfonated
styrene-divinylbenz2~e copolymer resin in the hydroge~
form (Lewatit SPC 118, particle size 0 8 - 1 mm). A
-- 22 -- ~ . 0050/03 3a.~ 1
temperature of 40C and a pressure of 12 bar were maintained
in the reaction vessel. me reaction mixture obtained
was fed to a distillation colllmn, and at the top of the
column a butene/butane raffinate contai~ing
2 per cent by weight of isobutene was obtained. ~he
raffinate was virtually free from propanol a~d could
therefore be used directly, without additional purification
operations (for example without interpolation of a
water wa~, as the starting material for further reactions.
At the bottom of thedis~llatior cn~l~,428ml perhour ofpropyl
tert.-butyl ether, which still contained 27 per cent by
weight, based on the mixture, of excess propanol, we~ taken
off and fed to a vaporizer. The vaporized propyl tert.-
butyl ether, heated to 170C, was cracked by passing it
irto a tubular crac~ing reactor which contained 20 % of H3P04
on heat-treated silica gel as the cracking catalyst;
cracking took place at ~rom 180 to 200C, gi~ing isobutene
and propanol. The cracked reaction product was passed
i~to a second distillation column, at the top of which
95.7 g per hour of very pure isobutene of the following
composition were obtained:
isobutene 99.9 % by weight
isobutane 300 ppm by weight
butane 100 ppm by weight
but-l-ene 100 ppm by weight
trans-but-2-ene 100 ppm by weight
cis-but-2-ene 100 ppm by weight
buta-1,3-diene 100 ppm by weight
At the bottom of the second distillation column,
-- 23 -- ~ . C~S0/033~51
287 ml per hour of propanol, containing 7~2 % of propyl
tert.-butyl ether, were obtained. It was possible to
recycle this mixture to the etherification reaction, where-
by the amou~t of isobutene obtained could be Lncreased to
112 g per hour.
The yield of isobutene, based on isobutene cont~lned
in the C4-hydrocarbon mixture employed, was 97.5 ~ if the
entire bottom product was recycled to the second di~t l-
lation column.
Drawing
