Note: Descriptions are shown in the official language in which they were submitted.
" 10~'7066
The invention relates to a process for the direct
obtaining of isobutylene. The process is equally suitable
for the removal of isobutylene from gas mixtures having a
high butadiene content or from gas mixtures containing
only butenes and butane, by means of selective reaction
with methanol. The formed methyl tert.butyl ether (NTBE)
can be easily separated from the C4 hydrocarbons. Most parts
of the isobutylene used in the art originate from the C4
fraction obtained via pyrolysis or out of butane-de-
hydrogenation processes. However, these processes do not
yield pure isobutylene and the product contains also other
olefins and diolefins in addition to saturated hydrocarbons.
A more purified compound can be obtained only by using
expensive equipments and complicated operations.
The C4 fraction arising from the pyrolysis of
hydrocarbons and gas mixtures prepared by dehydrogenation
processes could not serve hitherto as direct sources of iso-
butylene, due to their high butadiene contents. In the known
processes at first butadiene is extracted and after iso-
butylene is separated generally by means of absorption with
sulphuric acid (G. D. Hobson: Modern Petroleum Techn. p.
460). Tert. butanol is formed in the course of the
absorption which after purification is dehydrated and yields
pure isobutylene.
Isobutylene can be reacted also with methanol in
the presence of acidic catalysts when MTBE is formed.
According to the British Patent Specification No. 1.165.479
e.g. MTBE can be easily decomposed over an A1203 catalyst
to methanol and pure isobutylene. A further advantage is that
the formed MTBE may be used preferably as a component having
1 ~07706~;
high octane number in motor gasolines.
A requirement of environmental protection is to re-
duce the lead content of gasolines. This requires in
turn a posslbly cheap method for the production of gasoline
components having high octane number. In this field the
production of MTBE from isobutene-containing gas mixtures
represents a significant technical progress.
The freaction of isobutene with methanol in the
presence of acidic catalysts has been described by
T. E. Evans (Ind. Eng. Chem. 28 /N 10/ 1186). Sulphuric acid
is the most efficient catalyst of this reaction. In the
process according to the U.S. Patent Specification No.
2.721.222 (Esso Res. Eng. Co.) similarly sulphuric acid
is used as catalyst. The reaction is carried out in a
heterogeneous phase, then the reaction mixture is diluted
with a great amount of methanol in order to decrease the de-
composition during distillation. Accord$ng to the U.S. Patent
Specification No~ 2.720.547 (Standard Oil Co.) the reaction
is carried out similarly in a heterogeneous phase and 80 %
sulphuric acid or alkane-sulphonic acid is applied as
catalyst ln order to decrease decomposition during
distlllation as a consequence of using a catalyst of lower
activity. However, up to the present it was not possible
to solve by means of a simple method the problem of the
separation and recirculation of the catalyst. Thus, the
recently applied processes are using in general solid
heterogeneous catalysts. In the majority of processes one
operates with an ion exchanger catalyst of a sulphonated type
of styrene-divinylbenzene base. Processes of this type
are e.g. those described in the Belgian Patent Specification
107'~06!~
No. 612.33B (Bayer), in the U.S. Patent Specification No.
3.170.000 (Sinclair Res. Inc.) or in the British Patent
Specification No. 1.176.620 (Shell). However, these catalysts
have essentially lower activities and are extremely
sensitive to even small contaminations of the raw materials.
In general, these processes lend themselves only to the
conversion of pure isobutylene because in this case the low
conversion can be increased by recirculating the butane and
the amount of detrimental contaminants such as butadiene is
small. The processing of mixtures of isobutylene and
n-butylene is limited because of the low cqnversion.
According to the latest processes, German Patent Specification
No. 2.246.004 (Sun Oil Co.) only a part of isobutylene is
allowed to react and the gas mixture with the residual
isobutylene content is then used for other purposes.
The prerequisite of the economic production of MTBE
out of isobutylene and methanol is the possibility of
producing MTBE by the direct extraction of the isobutylene
content of gases of various origin. For this purpose the
best suitable raw material is the C4 fraction of the gasoline
pyrolysis. However, the isobutylene content of the mixture
of C4 hydrocarbons which contains about 40 % of butadiene
could not be obtained economically by known processes.
Namely, butadiene polymerizes readily under the action of
strong acids and reacts also with methanol. This is shown
in the U.S. Patent Specification No. 2.922.822 (Esso Res.
Eng. Co.) according to which unsaturated ethers are proced
from butadiene-containing gases and from methanol under
conditions similar to those of the reaction of isobutylene.
In the course of our experimental work we examined
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thoroughly the behaviour of butadiene under the conditions
under which MTBE is being produced. It was found in these
experiments that isobutylene can be selectively reacted in
the presence of butadiene provided the amount of sulphuric
acid applied as catalyst is below 20 Z by weight calculated
on the reaction mixture and the reaction is carried out at
a temperature between 50 and 120 C in a homogeneous liquid
phase with an excess of methanol. Under such conditions the
polymerization of butadiene can be reduced to a neglibible
extent.
The methanol addition of isobutylene takes place
under these conditions in a thousand times higher rate than
the reaction rate of butadiene and methanol. According to
the process of invention isobutylene reacts completely
selectively with methanol even in the case if the raw
material contains 40 to 60 Z of butadiene.
The environmental protection necessitates the de-
crease of the amount of sulphuric acid involved in the
process. This can be accomplished in the present invention
by a recirculation of the catalyst. Investigations were
carried out to establish the dissolving capacity of the re-
action mixture having a different composition relating to
sulphuric acid. It has been recognized that under particular
conditions after a reaction carried out at a temperature
between 50 and 120 C in a homogenous liquid phase, the
reaction mixture when cooled to room temperature, a major
part of the catalyst forms a separate phase with a part of
the excess methanol. The separated lower phase contains
10 to 50 % of sulphuric acid and can be directly employed
as a catalyst of the synthesis. The separation of this
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catalyst phase after the reaction is influenced by the
proportion of methanol to isobutylene and by the
sulphuric acid content. In Fig. l the values of the
maximum concentration of sulphuric acid in per cent by
weight are plotted against the contents of methanol at
90 C and 30 C. These data relate to a raw material
having 95 % of isobutylene content. In the case of an
identical methanol content the amount of dissolved
sulphuric acid decreases parallely to the decrease of the
isobutene content whereas the amount of dissolved sulphuric
acid increases with the increase of the molar ratio of
methanol, as shown by Fig. 1. The deviation between the two
curves shows the separating efficiency of the catalyst
which takes place on the effect of cooling. The initial
molar ratio of methanol to isobutylene is apparently re-
duced by the amount of methanol entering the sulphuric
acid phase, increasing in this way the amount of separated
sulphuric acid.
It has been found that the separation of the
catalyst can be promoted by recirculating after the
reaction mixture free of methanol or the C4 fraction
set free from isobutylene which fraction leaves the
process. The surprising efficiency of recirculating
is illustrated by Fig. 2 which shows the amount of the
separated phases plotted against the amount of hydro-
carbons recirculated. The amount of hydrocarbons
which have been recirculated are given in per cent
referred to the initial hydrocarbon content of the
reaction mixture. The curve on Fig. 2 relates to
the product of the reaction of a hydro-
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carbon mixture having 27 % of isobutylene content, carried
out at a 3.5 molar ratio of methanol to isobutylene and
in the presence of 3.2 % by weight of sulphuric acid as
catalyst up to a 90 % conversion of isobutylene. As shown
by the curve on Fig. 2, the amount of the separated phase
is remarkably influenced by already small amounts of re-
circulated material whereas the recirculation of greater
amounts of material did not influence significantly the
amount of separated phase.
The two effects referred to namely the decrease of
temperature and the decrease of methanol content make
possible either alone or combined a separation of the
sulphuric acid in a rather simple way. The separated phase
having high sulphuric acid content can be preferably
employed directly as catalyst. It is of advantage that the
costs of recovering excess methanol is reduced because
the recovery of methanol content of the catalyst phase
can be easily carried out.
The flow scheme of the claimed process is shown on
Fig. 3.
The isobutylene-containing mixture of hydrocarbons
is fed through pipeline 1 and methanol through pipeline
2 into reactor 4. Fresh sulphuric acid catalyst is
introduced into reactor 4 through pipeline 3 whereas the
catalyst solution separated from the reaction mixture
through pipeline 9. The reaction takes place in a
homogeneous liquid phase. The reaction mixture leaving
reactor 4 through pipeline 5 is cooled in condenser 6.
Simultaneously with the cooling of the batch a part of
the hydrocarbon fraction from which isobutylene has been
~077()66
removed and is recirculated through pipeline 7 and/or
a part of the reaction mixture free from methanol is re~
circulated as well through pipelines 7 and 14. Under the
effect of cooling and recirculating the homogeneous reaction
mixture is decomposed in two phases which are subsequently
separated in separator 8. The lower phase having a high
sulphuric acid content and serving as catalyst is trans-
ferred from separator 8 through pipeline 9 into reactor 4.
The upper phase with a decreased sulphuric acid content is
conducted in turn through pipeline 10 into washing tank 11
whereto water containing if necessary alkali is fed through
pipeline 12 in order to remove traces of catalyst. me
washing water leaving the tank 11 through pipeline 13
contains the excess of methanol used in the reaction. This
excess of methanol can be separated in a known way by
distillation and ~hen recirculated in the reaction system.
The reaction mixture after having removed the methanol,
leaving the system through pipeline 15 is partly re-
circulated through pipelines 14 and 7 to the separation of
the catalyst. The residual part is transferred through
pipeline 15 into distilling column 16 where the unreacted
hydrocarbons are separated from MTBE. The hydrocarbon
mixture after removing the isobutylene leaves the column
at the top through pipeline 18. However, a part of the
leaving mixture is recirculated to the separation step of
the catalyse through pipeline 7. The MTBE formed from
the isobutylene present originally in the raw material
leaves the column at the bottom through pipeline 17.
The MTBE obtained here can be used directly or eventually
after an adequate purification as a component of motor fuels
~77()~6
or can be decomposed to isobutylene and methanol.
It can be seen from the abovementioned process that
it is suitable in a wider concentration range for the
conversion of the isobutylene content of gaseous mixtures of
hydrocarbons in to MTBE even in case of raw materials
having a high butadiene content. A further advantage is that
sulphuric acid can be applied in the process as a catalyst
having high activity and low price and that a considerable
part of the sulphuric acid can be separated after the
reaction and recirculated.
The process is illustrated by the Examples given
below:
Example 1
Into a 0.5 liter autocalve lined with polypropylene
259.8 ml. of liquid isobutylene of 95 % purity, 140.2 ml.
of methanol and 9.5 g. of sulphuric acid are fed at -20 C.
The reaction is carried out at 90 C, the reaction mixture
is homogeneous and 87 % of isobutylene is converted into
MTBE in 20 minutes. On cooling the reaction mixture, a
phase of higher specific gravity is separating from the
product. This phase contains beside methanol more than
80 % of the sulphuric acid catalyst introduced. On re-
circulating the catalyst phase and calculaeing the amount
thereof in a concentration corresponding to its content
of sulphuric acid and methanol, no difference was
observed carrying out the reaction and the separability of
the catalyst phase from the reaction product remained as
good as in the previous step.
Example 2
Into a reactor kept under a pressure of 20 atm
_ g _
~077()66
and at a temperature of 90 C continuously 5 literslhour of
a liquid C4 fraction (containing 25 % of isobutane and 41 %
of butadiene) originating from gasoline pyrolisis, 1.22
liter of methanol, 15 ml. of sulphuric acid and 0.75 liter
of catalyst solution containing sulphuric acid are intro-
duced. The isobutylene content of the raw material in the
homogeneous reaction mixture leaving the reactor is
converted in a rate of 93.8 % into MTBE. The reaction
mixture is colled and at the same time 1 liter/hour of C4
fraction free from isobutylene added. The catalyst
solution containing 26.9 % of sulphuric acid which is
separating from the reaction mixture owing to its higher
specific gravity is recirculated to the entry of the
reactor whereas the upper phase is introduced into an
aqueous washing vessel kept under pressure of 5 atm in
order to remove excess methanol. The washing water contained
2 % of sodium hydroxide which serves for the removal of
traces of the catalyst. The reaction mixture after re-
moval of methanol is decomposed in an apparatus for
continuous distillation to NTBE and to fractions con-
taining C4 hydrocarbons under a pressure of about 4 atm.
A part of these C4 hydrocarbons is recirculated to the
separation step of the catalyst. me capacity of the
apparatus of the amount to 3.~3 liter/hour of liquid C4
hydrocarbons having 2 % of isobutylene and 52 % of
butadiene content.
Example 3
Into the reactor described in Example 2,
continuously 5.0 liters/hour of a liquid C4 fraction
containing 20 % of isobutene which fraction originates
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~077066
from catalytic cracking, 1.0 liter of methanol, 10 ml. of
98 % sulphuric acid and 0.65 liter of catalyst solution are
introduced. To the reaction mixture leaving the reactor
1.2 literlhour of reaction mixture already free from
methanol is recirculated and at the same time the reaction
mixture is cooled to room temperature. The separated
catalyst phase contains 25.4 % of sulphuric acid. Then
methanol is removed from the reaction mixture by washing
it with water and a part o the reaction mixture containing
MTBE and C4 hydrocarbons is recirculated for the separation
of the catalyst. The residual part is fed into a ~ !
distilling apparatus where the residual C4 hydrocarbons are
separated from MTBE. 94.6 % of the introduced isobutylene
was converted. The C4 gas leaving the system contained more
than 98 % of the introduced n-butylenes.
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