Note: Descriptions are shown in the official language in which they were submitted.
rrhe present invention relates to a process for the
production of methyl tert-bu-tyl ether.
Tert alkyl ethers are prepared by reacting a primary
alcohol with olefines having a double bond on a tertiary carbon
atom~ ~or instance methanol reac-ts with isobutylene or iso-
amylenes (2-methyl 1- or 2-pentene)to ~orm respectively methyl
tert-butyl ether (MT~E) or methyl ter-amyl ether. (MTAE).
Since the reaction is selective with respect to
tertiary olefins, it can thus be utilized for removing such
olefins from olefinic streams wherein linear unreactive olefins
are also present. The reaction has an equilibrium which is
shifted towards the synthesis of the ether when the reaction
temperature is lowered, in accordance with its negative enthalpy.
The reaction is catalyzed by Lewis acids (alumini~n
trichloride, boron trifluoride), mQneral acids (sulphuric
acid) or organic acids ~alk~l and aryl sulphonic acids~ ion-
exchange resins). Ion exchange resins in their acid form have
been found -to be particularly suitable to this end, and the
best results are obtained in fact with macroreticular resins
of the "Amberlyst*15" -type. ~y means o~ such catalysts, it is
possible to reach the therm~dynamic equilibrium with industrially
acceptable contact times, at temperatures of 50-60C. At lower
temperatures, which thermodynamically are more favourable, the
kinetics is not sufficiently high to permit in practice to
reach equilibrium. This fact thus limits the conversions; in
the particular case of isobutylene and methanol used in eguimole-
cular ratios, the conversions reached are not higher -than 92%~
The conversion of a reagent can of course be increased
by increasing in the feed the content oL the other reagent but
this involves a lowering of the conversion of -the reagent in
excess. This can cause some dra~backs as, for instance, occurs
in the synthesis of llTBE starting from methanol and isobutylene
* Trademark
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contained in an olefinic stream. The use of an excess of
isobutylene involves as consequence that the olefinic stream,
after separation of the MTBE, still contains 5-10% isobutylene
and this constitutes a drawback when such stream is utilized for
the production of maleic anhydride or butadiene; vice-versa, an
excess of methanol renders the purification of MTBE very difficult
because of the formation of azeotropes.
The present invention proposes to provide a process
by means of which a high conversion for both reagents can be
obtained, even when these are maintained globally in stoichio-
metric ratios.
According to the subject invention, there is provided
a process for the production of methyl tert-butyl ether by
reacting isobutylene with methanol at a pressure sufficient to
maintain the liquid phase in the presence of a catalyst consisting
of an acid ion exchange resin, which comprises the steps of:
(a) reacting in a first reactor in the presence of the
catalyst at a temperature of from 60-70C (i) methanol.and (ii)
a mixture comprising isobutylene, linear olefins and methanol,
the total quantity of methanol being in stoichiometric excess of
the quantity of isobutylene;
~ b) subjecting the product of step (a) to distillation to
obtain an off gas comprising linear olefins and less than 2 percent
of isobutylene and a bottoms product comprising methanol and tert-
butyl ether;
(c) reacting in a second reactor in the presence of thecatalyst at a temperature of from 60 to 70C the bottoms product
of step ~b) with a mixture comprising isobutylene and linear
olefins, the space velocity of the mixture being in the range of
20 to 50 LHSV and the respective total quantities of methanol and
isobutylene reacted in steps (a) and (c) being stoichiometrically
equivalent; and
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(d) subjecting the product of step (c) to distillation
to produce an off gas comprising isobutylene, linear olefins
and methanol, and a bottoms product comprising methyl tert-
butyl ether, the off gas being recycled as feed to the reactor
in step (a).
In a preferred embodiment of the invention, the mixture
comprising isobutylene, linear olefins and methanol in step (a)
consists essentially of the off gas from step (d) and a portion of
a mixture comprising isobutylene and linear olefins, the remainder
of this mixture being introduced in step (c).
The ratio by weight of isobutylene to methanol in step
(a) is preferably from about 0.62 to 0.72 while that in step (c)
is preferably from about 2.35 to 2.8.
According to a furtheradvantageous embodiment, the space
velocity of the mixture in step (a) is 5 LHSV.
The present invention will now be better understood
by means of the following description of embodiments, followed
by non-restrictive working examples, reference being made to
the appended drawings, wherein:
Fig. 1 is a flow diagram illustrating the synthesis of
methyl tert-butyl ether in accordance with an embodiment of the
invention; and
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62
~ ig- 2 i3 a flow diagram illus-tra-ting the synthesis
of methyl -tert-butyl ~her in accordance with another embodiment
of the invention.
Methanol 1 is fed to a reactor R-1 together with the
effluent stream 3 coming from the top of column C-2, constituted
by an olefinic stream free of isobutylene. The reaction mixture
contains an excess of metha~ol such that the isobutylene
converslon will be very high.
~ he e~fluent stream 4 discharged from R-1 is sent to the
distillation column C-1, from the top of which an olefinic
fraction 6 is recovered having an isobutylene content lower
than 2~ and from the botto~ of which a mixture 5 of methanol
and MTBE is obtained. ~he bottom stream 5 together with an
olefinic feed 2 are introcluced into reactor R-2. The reaction
mixture in R-2 contains an excess of isobutylene so that the
methanol conversion is high.
'~he product 7 leaYing reactor R-2 is sent to the
distillation column C2, from the bottom of which MT~æ 8 having a
high degree o~ purity is discharged and from the top of which an
olefinic stream 3 free of isobutylene is discharged ana is
recycled to R-1.
I~ reactor R-2, a strong excess of isobutylene is
present and it is possible to have secondary oligomerization
reactions of isobu-tylene; this effectively occurs when working
at 60-70C and space velocities of 5-10. ~he phenomenon can be
minimized by distributing the olefin ~eed both to reactor R-1
and to reactor R-29 as best shown in fig. 2. It has been
moreover found that it is possible to obtain high selectivities
also in presence of an e~cess of isobutylene, by working at a
3 temperature of 60C and a space velocity of 40, without lowe~ing
the conversion to M~æ.
~ ~ _
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r~he operation was carried out in accordance with
figure 1. 21.11 parts by weight of methanol 1 were joi~ed to
the stream 3 leaving the top of column C-2, constituted by
23~38 parts of isobutylene, 43.43 parts of linear olefines and
0.35 parts of methanol. '~he mixture, in which the isobutylene-
methanol molar ratio - was 0. 62, was fed to reactor R-1 in which
it was reacted in presence of Amberlyst*15 at a temperature of
60c with a space velocity of 5 volumes per hour and per volume
f catalyst and at a pressure sufficient to maintain the system
in liquid phase.
'~he effluent stream 4 from reactor R-1, which contained
8.46 parts of methanol, 35.76 parts of MTEE, 0.62 parts of
isobutylene and 43.43 parts of linear butenes was then fed to
the distillation column C-1; from the top o~ column C-1 (line
6) were obtained 44.95 parts of a fraction having the following
composition:
isobutylene (~0 by weight) - 1.4
methanol (% by weight) - 2.0
linear olefines (% by weight) = 96.6
- ~rom the bot-tom of column C-1 (line 5), 35.76 parts
of M~B~ and 7.56 parts of methanol were discharged and, together
with 37.00 parts of isobutylene and 43~.43 parts of linear butenes
2, were fed to reactor R-2 in which the reaction was effected
in thepresence of Amberlyst*159 at a temperature of 60C and
a space velocity of 40. '~he isobutylene-methanol molar ratio
was 2.8 in the reactor R-2.
'l'he effluent stream 7 from reactor R-2 which was
constituted by 55. 60 parts of M~EE, O.35 parts of methanol,
23.38 parts of isobutylene, 53.43 parts of linear butenes and
0.99 parts of diisobutylene was fed to the distillation column
C-2~ from the top of which (line 3) 23.38 parts of isobutylene,
* Trademark
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3L0~ 2
43.43 parts OI linear butenes and 0.~5 ~par-ts of me-thanol were
discharged a~d recycled to reactor R 1, and from l;he bottom of
which (line 8) 56.59 parts of MTEE having a purity of 98.25%
were withdrawn.
The total conversion of methanol was 960to ~vith a
selectivity of 100%' while the isobutylene conversion was 98
with a selectivity of 97%~
This example ~as carried out in accorda~ce with figure 2.
32.12 parts by weight o methanol 1 were joined with the effluent
stream 3 from the top o~ colwnn C-2, constituted by 0.98 parts
of methanol, 40.73 parts o:~ linear butenes and 23.94 parts of
isobu-tylene, ~d with a portion 4 ofi the feed olefines 2. This
portion was constituted by 16.44 parts of isobutylene and 16.77
parts of linear butenes.
The reaction mixture in which the isobutylene-methanol
ratio was 0.72 was fed to reactor R-1 at a space ~elocity of 5,
' wherein the reaction was effected in the presence of Amberlyst*
15, at a temperature of 60C and a pressure sufficient to maintain
the system in the liquid state.
The reaction product 6 which was constituted by 10.67
parts of methanol9 1.11 parts of isobutylene, 57.50 parts of
linear butenes and 61.70 parts of MT~ was fed to the distillation
column C-1" from the top of which (line 10) were obtained 59.67
parts of a fraction having the following composition:
isobutylene (% by weight) ~ 1.9
methanol (% by weight) = 1.8
linear butenes (% by weight) =96.3
~rom the bottom of column C 1 were obtained 9.61
parts of methanol and 61.70 parts of MT~E. The bottom product
7, together with 39.66 parts of isobutylene and 40.73 parts of
linear butenes constituting the remaining portion of the olefinic
* Trademark
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~eed 2, were reacted in reactor R-2 at 60~ and a space velocity
of 40. ln this reactor, the isobu-~lene/methanol ratio was
2.35. The reaction product 8 which ~s cons-tituted by 0.98
parts of methanol, 85.45 parts of M~E 9 23.94 parts of iso-
butylene, 40.73 parts of linear butenes and 0.88 parts of
diisobutylene was sent to the distillation column C-2; 0.98
parts of methanol, 23.94 parts o~ isobutylene and 40.73 parts
of llnear butenes were obtained as overhead products 3 which
were recycled to reactor R~ rom the bottom of column C-2
(line 9) were recovered 86.33 parts of I~Eæ having a purity of
99%-
The total conversion o~ methanol was 96.7~ with a
selec-tivity of 100%; the isobutylene conversion was 98% with
a selectivity of 98%.
The feed to reactor ~o2 of the preceding example
was reacted at t~ dif~erent tempexatures and at three different
~pace velocities; the results obtained were the following:
Temperature 60 C 70 C
~HSV . 3 8.5 40 3 8.5 40
.
~otal conversion
of isobutylene 61 55 44 63 55 45.5
Conversion o~ isobuty-
lene to M~BE 41.5 46.5 41 43 42-5 37
Selectivity 68 83 93 68 77-5 82
IHSV - space veloci-ty expressed as volumes of liquid ~eed per
volume o~ catalyst per hour.
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