Process for the manufacture of methyl t-butyl ether

The invention concerns a process for the manufacture of methyl t-butyl ether in which: a hydrocarbon feedstock is cracked to give an ethylene-rich stream; an isobutane-rich stream is separated from C.sub.4 -hydrocarbon stream; the ethylene-rich stream and the isobutane-rich stream are contacted over a transhydrogenation catalyst to give a mixture comprising ethane and isobutene; the isobutene is reacted with methanol to give methyl t-butyl ether; and the residual C.sub.4 -hydrocarbon stream is recycled either to the C.sub.4 -hydrocarbon stream or to the cracker and the ethane is recycled to the cracker. It has been found that combining and interconnecting a hydrocarbon cracker, a transhydrogenation reactor and an etherification reactor results in an integrated, economic process for the production of methyl t-butyl ether.

This invention relates to a process for the manufacture of methyl t-butyl 
ether (MTBE) and in particular to an integrated process for the 
manufacture of MTBE involving the use of a transhydrogenation reaction to 
produce isobutene. 
With legislation in many countries requiring lead-free or reduced lead 
content gasoline there is a need for alternative additives which will 
boost the octane number of gasoline. Methyl t-butyl ether is a 
particularly attractive alternative additive because of its high octane 
number, miscibility with gasoline and its environmental acceptability. 
Methyl t-butyl ether may be readily manufactured by the etherification of 
methanol with isobutene. However, only a limited supply of isobutene is 
available from hydrocarbon cracking and commercial processes have been 
proposed for the isomerization of n-butane from liquid petroleum gas to 
give isobutane and the dehydrogenation of the isobutane to give isobutene. 
In the proposed commercial processes for the preparation of isobutene, and 
subsequently MTBE, the dehydrogenation of isobutane to give isobutene 
severely limits the economics of the overall process as the 
dehydrogenation reaction is thermodynamically unfavourable. The 
dehydrogenation reaction is highly endothermic and therefore requires 
significant expenditure on feed preheating, and the reaction must be 
carried out at high temperatures (typically 540.degree. to 640.degree. C.) 
and at reduced reactant partial pressures (typically under vacuum or with 
steam dilution) to drive the reaction. 
It has now been found that by integrating a cracking facility producing 
ethylene with an etherification facility, isobutene may be produced for 
the manufacture of methyl t-butyl ether in a much more efficient manner by 
the transhydrogenation of isobutane using ethylene as a hydrogen acceptor 
and the recycling to the cracking facility of the ethane formed. 
Accordingly the invention provides a process for the manufacture of methyl 
t-butyl ether which process comprises: 
(i) cracking a hydrocarbon feedstock in a cracking facility to give an 
ethylene-rich stream; 
(ii) separating an isobutane-enriched stream from a C.sub.4 -hydrocarbon 
stream and optionally isomerizing the n-butane and recycling the resulting 
C.sub.4 -hydrocarbon stream for separation; 
(iii) contacting a mixture comprising the ethylene-rich stream from step 
(i) and the isobutane-enriched stream from step (ii) with a 
transhydrogenation catalyst to give a hydrocarbon mixture comprising 
isobutene and ethane; 
(iv) either first separating the hydrocarbon mixture obtained in step (iii) 
into a C.sub.4 -hydrocarbon enriched stream comprising isobutene and a 
C.sub.2 -hydrocarbon enriched stream comprising ethane and second reacting 
said C.sub.4 -hydrocarbon enriched stream comprising isobutene with 
methanol to give methyl t-butyl ether and a residual C.sub.4 -hydrocarbon 
stream; or first reacting said mixture obtained in step (iii) with 
methanol to give methyl t-butyl ether and a residual hydrocarbon stream 
and optionally separating the residual hydrocarbon stream into a residual 
C.sub.4 -hydrocarbon stream and a C.sub.2 -hydrocarbon enriched stream; 
and 
(v) collecting the methyl t-butyl ether and recycling the residual C.sub.4 
-hydrocarbon stream either to the C.sub.4 -hydrocarbon stream or to the 
cracking facility as feedstock and recycling the C.sub.2 -hydrocarbon 
enriched stream to the cracking facility or recycling the unseparated 
residual hydrocarbon stream to cracking facility. 
The process of the present invention is particularly advantageous when the 
cracking facility used is a hydrocarbon cracker designed for the 
production of olefins. It will become clear to those skilled in the art 
that the production of methyl t-butyl ether using such a cracking facility 
has many advantages over prior art methods for the production of methyl 
t-butyl ether. For example, when a cracker based on liquified petroleum 
gas (LPG) feedstock is used in the process of the present invention: 
isobutane may be separated from the LPG to give a source of isobutane and 
an improved (lower isobutane content) feedstock for cracking; the ethylene 
from the cracker and the isobutane may be contacted with a catalyst to 
give isobutene and ethane in a transhydrogenation reaction at 
significantly lower temperatures and higher pressures than those used for 
prior art processes for the dehydrogenation of isobutane to give isobutene 
for methyl t-butyl ether production; the ethane may be separated and, as 
it is a particularly good cracker feedstock, recycled to the cracker; the 
isobutene may be etherified with methanol to give methyl t-butyl ether and 
any residual isobutane may be recycled for transhydrogenation. Thus the 
production of methyl t-butyl ether by the process of the present invention 
not only offers the advantage of lower capital cost because isobutene is 
produced at or above atmospheric pressure at significantly lower 
temperatures, but when integrated into an existing cracker unit enables 
the cracker to be run at design capacity to produce a high value product 
when ethylene demand is low. 
Although the process of the present invention may be used to particular 
advantage when the cracking facility is a cracker designed primarily for 
the production of olefins it may also be used to advantage when the 
cracker is designed primarily for other purposes. For example, refineries 
which crack crude oil for the manufacture of petroleum products such as 
gasoline also produce "light" gas streams which contain ethylene. Such gas 
streams are often used as fuel gas and, because of the large operating 
scale of refineries, offer a convenient and economic source of ethylene 
for use in the transhydrogenation step of the process of the present 
invention. 
Butanes are available in large quantities from liquified petroleum gas 
(LPG) produced during crude oil extraction and during crude oil refining. 
Isobutane for use in the process of the present invention may, for 
example, be obtained by separation from LPG or from a refinery C.sub.4 
-hydrocarbon stream in a deisobutanization column. The remaining n-butane 
may be used as LPG or returned to the C.sub.4 -hydrocarbon stream as 
appropriate. Alternatively, the remaining n-butane may be partially 
isomerized to give an isobutane/n-butane mixture by passage over an 
isomerization catalyst and the mixture returned to the deisobutanization 
column for separation. However, if the cracking facility used in the 
process of the present invention is a cracker designed for olefin 
production the remaining n-butane may be used as cracker feedstock which 
has been improved for cracking by the removal of isobutane. 
Suitable catalysts which may be used in the transhydrogenation step of the 
process of the present invention may be chosen from the dehydrogenation 
catalysts known in the art. Such dehydrogenation catalysts include 
heterogeneous catalysts such as, for example, supported and unsupported 
metals and metal oxides and mixtures thereof and homogeneous catalysts 
such as, for example, organometallic complexes. 
Examples of metals which find use as dehydrogenation catalysts include 
metals from the Groups IVA, VA, VIA, VIIA, VIII, copper, zinc, gallium, 
indium, germanium, tin, lead, antimony, bismuth, tellurium and the oxides 
of certain of these metals. Such metals and their oxides may be used on 
their own as catalysts but are often mixed and used as mixed catalysts. 
Examples of some of the preferred metals which find use as dehydrogenation 
catalysts include the platinum group metals platinum, palladium and 
nickel, the metals iridium, rhodium, cobalt, rhenium, ruthenium, iron and 
copper. These metals may be used as catalysts or their own or in 
combination either in admixture or in the form of alloys. The metals may 
also be used in combination, either in admixture or in the form of alloys, 
with other metals, metal oxides or promotors including, for example, 
metals such as the alkali metals, the alkaline earth metals, the rare 
earth metals and mixtures thereof, either in their elemental state or a 
higher oxidation state. Further the metals, or combinations thereof may be 
modified by poisoning, or reducing the activity thereof, by treatment with 
one of the poisoning agents known in the art. Such poisoning agents 
include, for example sulfur and compounds containing sulfur. 
Examples of some of the preferred metal oxides which find use as 
dehydrogenation catalysts include the oxides of vanadium, chromium, 
molybdenum, copper, tungsten, titanium and zinc. These oxides may be used 
as catalysts on their own or in combination with other metal oxides or 
metals or promotors. 
The metal and metal oxide catalysts which may be used in the 
transhydrogenation step of the process of the present invention may be 
unsupported, for example, in the form of a thin foil, a mesh, sponge, 
granules, pellets, finely divided powder or slurry. Alternatively, the 
metal and metal oxide catalysts which may be used in the 
transhydrogenation step may be supported on a carrier. If the catalysts 
which may be used in the transhydrogenation step are supported on a 
carrier, preferably the carrier is a porous carrier having a large surface 
area. Suitable carriers which may be used as catalyst supports in the 
transhydrogenation step include, for example, alumina, silica, 
aluminosilicates, zirconia, titania, active carbon and mixtures thereof. 
Preferably, the catalysts used in the transhydrogenation step of the 
process of the present invention are non-acidic. Suitable non-acidic 
catalysts may be obtained either by selecting non-acidic catalysts and/or 
catalyst supports or by treating acidic catalysts and/or catalyst supports 
with organic or inorganic bases to poison the acidity of the catalyst 
and/or catalyst support. 
The catalysts used in the transhydrogenation step of the process of the 
present invention may also be treated to alleviate undesirable properties 
and/or to improve the life of the catalyst, the surface area of the 
catalyst or the ease of regeneration of the catalyst. The properties of 
the catalyst may be modified by treating the catalyst or the catalyst 
support with one or more of the modifiers known in the art including, for 
example, sulfur and metals such as lead, tin, arsenic and antimony. 
In the transhydrogenation step of the process of the present invention 
isobutane in the gaseous state may be contacted with the dehydrogenation 
catalyst by passing a gaseous mixture of isobutane and ethylene over a bed 
of dehydrogenation catalyst in an heterogeneous catalytic process. 
Alternatively, a mixture of isobutane and ethylene in the gaseous or 
liquid state may be contacted with a slurry of the dehydrogenation 
catalyst optionally in the presence of an inert solvent, again in an 
heterogeneous catalytic process. In a further alternative process, a 
mixture of isobutane and ethylene in the gaseous or liquid state may be 
contacted with a solution of, for example, an organometallic 
dehydrogenation catalyst in an inert solvent, in an homogeneous catalytic 
process. 
One of the major advantages of the transhydrogenation step of the process 
of the present invention is that it may be carried out with good 
conversion and high selectivity at much lower temperatures and much higher 
pressures than the dehydrogenation processes currently used for the 
preparation of isobutene in the manufacture of methyl t-butyl ether. 
Preferably the transhydrogenation step of the process of the present 
invention is carried out at temperatures below 600.degree. C., more 
preferably between 400.degree. and 550.degree. C., and at pressures close 
to or above atmospheric pressure, more preferably between 1.0 and 10 
atmospheres. 
In the etherification step of the process of the present invention methanol 
may be added to isobutene to give methyl t-butyl ether in an 
acid-catalysed reaction. For example, methyl t-butyl ether may be made in 
high yield by contacting a liquid phase mixture of methanol and isobutene 
with a solid phase acidic catalyst such as a strong acid ion-exchange 
resin.

Referring to FIG. 1 of the drawings, liquified petroleum gas (11) is 
supplied to a deisobutanization unit (27) where it is separated (eg by 
distillation or selective adsorption) into an isobutane stream (13) and an 
n-butane rich stream (12). Optionally, all or part of the n-butane rich 
stream (12) may be fed to an isomerization unit (28) in which the n-butane 
is partially isomerized to isobutane by passage over an isomerization 
catalyst (eg a platinum containing isomerization catalyst at a temperature 
of 150.degree. to 200.degree. C.), and the n-butane/isobutane mixture 
returned to the deisobutanizer column (27). Optionally all or part of the 
n-butane rich stream (12) may be used to form or supplement the make-up 
stream (18) fed to the catalytic cracker (30). 
The isobutane stream (13) drawn from the deisobutanizer column (27) is 
passed through a heat exchanger, mixed with an ethylene-rich stream (20) 
from the cracker (30) and the isobutane/ethylene mixture (14) is fed to 
the transhydrogenation reactor (29). In the transhydrogenation reactor 
(29) the isobutane, or portion thereof, is dehydrogenated to isobutene and 
the ethylene, or portion thereof, is hydrogenated to ethane by passage 
over a transhydrogenation catalyst, for example chromia on alumina, at an 
elevated temperature, for example 450.degree. to 550.degree. C. 
The product stream (15) from the transhydrogenation reactor (29), 
comprising mainly a mixture of isobutene, ethane, isobutane and ethylene, 
is heat-exchanged with the isobutane feed (13), compressed and cooled in 
unit (31) and then fed (16) to debutanizer column (32) where it is 
separated into an ethane-rich C.sub.2 -hydrocarbon stream (17) and an 
isobutene-rich C.sub.4 -hydrocarbon stream (23). 
The ethane-rich C.sub.2 -hydrocarbon stream (17) is recycled to the cracker 
(30), optionally after hydrotreatment to hydrogenate unsaturated 
compounds, and together with the make-up feed (18) is cracked to give the 
ethylene-rich stream (20), fuel gas (19), C.sub.3 and heavier hydrocarbons 
(21) and water (22). 
The isobutene-rich C.sub.4 -hydrocarbon stream (23) from the debutanizer 
column (32) and methanol (25) are fed to the etherification unit (33). In 
the etherification unit (33) methanol and isobutene are reacted, for 
example in the liquid phase over a solid phase strong acid ion-exchange 
resin catalyst, to give methyl t-butyl ether. A mixture of excess methanol 
and methyl t-butyl ether (26) is withdrawn from the etherification reactor 
(33) and distilled to give a methanol/methyl t-butyl ether azeotrope, 
which may be recycled to the etherification reactor, and methyl t-butyl 
ether as product which may be further purified by distillation as 
required. A gaseous mixture (24) mainly comprising isobutane is withdrawn 
from the etherification reactor (33) and recycled to the deisobutanization 
unit (27). 
Table 1 below illustrates typical mass balances required to yield 100 parts 
by weight of methyl t-butyl ether using an isobutane/n-butane feed (11) 
and ethane as the make-up stream (18) to the cracker (30) in the procedure 
illustrated in FIG. 1. 
TABLE 1 
__________________________________________________________________________ 
Contents (parts by weight) of Stream No 
Com- (see FIG. 1) 
ponent 
11 12 13 14 15 16 17 18 
19 
20 22 
23 24 25 26 
__________________________________________________________________________ 
H.sub.2 
-- -- -- -- -- -- -- -- 
2.4 
-- -- 
-- -- -- -- 
CH.sub.4 
-- -- -- -- 0.4 
0.4 
0.4 
-- 
4.4 
-- -- 
-- -- -- -- 
C.sub.2 H.sub.4 
-- -- -- 33.1 
1.0 
1.0 
1.0 
-- 
-- 
33.1 
-- 
-- -- -- -- 
C.sub.2 H.sub.6 
-- -- 0.3 15.8 
47.7 
47.7 
47.4 
9.7 
-- 
15.5 
-- 
0.3 
0.3 
-- -- 
C.sub.3 
-- -- 2.2 3.5 4.4 
4.4 
2.2 
-- 
-- 
1.3 
1.5 
2.2 
2.2 
-- -- 
i-C.sub.4 H.sub.8 
-- 0.1 
0.5 0.5 64.8 
64.8 
0.3 
-- 
-- 
-- -- 
64.5 
0.6 
-- -- 
i-C.sub.4 H.sub.10 
70.4 
2.7 
135.7 
135.7 
69.2 
69.2 
0.6 
-- 
-- 
-- -- 
68.7 
67.9 
-- 0.7 
n-C.sub.4 H.sub.10 
85.8 
85.5 
1.4 1.4 1.4 
1.4 
-- -- 
-- 
-- 1.1 
1.3 
1.3 
-- -- 
C.sub.5+ 
-- -- -- -- -- -- -- -- 
-- 
-- 2.2 
-- -- -- -- 
Coke -- -- -- -- 1.2 
-- -- -- 
-- 
-- -- 
-- -- -- -- 
CH.sub.3 OH 
-- -- -- -- -- -- -- -- 
-- 
-- -- 
-- -- 37.6 
0.7 
MTBE -- -- -- -- -- -- -- -- 
-- 
-- -- 
-- -- -- 100 
__________________________________________________________________________ 
The process of the present invention illustrated in FIG. 1 has many 
advantages over prior-art processes for the manufacture of methyl t-butyl 
ether. Liquified petroleum gas (11) may be used both as a source of 
isobutane (13) and make-up feed (18) for the cracker (30), the essentially 
isobutane-free liquified petroleum gas being better cracker feedstock than 
liquified petroleum gas itself. Moreover, ethane, and most favoured 
feedstock for the production of ethylene, formed during the 
transhydrogenation reaction may be recycled (17) to the cracker (30) as 
feedstock, preferably after hydrotreatment to remove unsaturated 
compounds. Isobutene is usually formed during hydrocarbon cracking and any 
isobutene formed during cracking may be added to the isobutene-rich 
C.sub.4 -hydrocarbon stream (23). Therefore, combining and interconnecting 
a hydrocarbon cracker, a transhydrogenation reactor and an etherification 
reactor results in an integrated, economic process for the production of 
methyl t-butyl ether from liquified petroleum gas. 
Referring to FIG. 2 of the drawings, a gas/liquids mixture (41) from a gas 
field is supplied to a gas/liquids separator (56) and separated into 
natural gas (42) and liquid petroleum gas (43). Optionally, all or portion 
of the natural gas (42) is supplied to a methanol plant (63) for 
conversion to methanol (44). 
Portion of the liquid petroleum gas stream (45) is fed to a deisobutanizer 
column or selective adsorption unit (57) where it is separated into an 
isobutane-rich stream (49) and an n-butane-rich stream (46). The 
n-butane-rich stream (46) is fed to the cracker (62) where it is cracked 
to give an ethylene-rich product stream (47) which is fed to a separation 
stage (61) in which hydrogen, water and condensible hydrocarbons are 
removed (54) to give an ethylene-rich stream (48). Optionally, depending 
on the cracker requirements, portion of the n-butane-rich stream (46) may 
be returned to the liquid petroleum gas product stream (43). 
The isobutane-rich stream (49) and ethylene-rich stream (48) are fed to the 
transhydrogenation reactor (58). In the transhydrogenation reactor (58) 
the isobutane, or portion thereof, is dehydrogenated to isobutene and the 
ethylene, or portion thereof, is hydrogenated to ethane by passage over a 
transhydrogenation catalyst, for example chromia on alumina, at an 
elevated temperature, for example 450.degree. to 550.degree. C. 
The product stream (50) from the transhydrogenation reactor (58), 
comprising mainly a mixture of isobutene, ethane, isobutane and ethylene 
is fed to a debutanizer column (59) where it is separated into an 
ethane-rich C.sub.2 -hydrocarbon stream (52) and an isobutene-rich C.sub.4 
-hydrocarbon stream (51). 
The ethane-rich C.sub.2 -hydrocarbon stream (52) is recycled to the 
gas/liquids separator (56) or, optionally, may be combined with the 
natural gas stream (42). 
The isobutene rich C.sub.4 -hydrocarbon stream (51) and methanol (44) are 
fed into the etherification unit (60). In the etherification unit (60) 
methanol and isobutene are reacted, for example in the liquid phase over a 
solid phase strong ion-exchange resin catalyst, to give methyl t-butyl 
ether. A liquid phase mixture (55) comprising methanol and methyl t-butyl 
ether is withdrawn from the etherification reactor (60) and distilled to 
give a methanol/methyl t-butyl ether azeotrope which may be recycled to 
the etherification reactor and methyl t-butyl ether as product which may 
be further purified by distillation as required. A gaseous mixture (53) 
comprising mainly isobutane is withdrawn from the etherification reactor 
(60) and recycled to the deisobutanization unit (57) or, optionally, added 
to the liquid petroleum gas stream (43). 
Table 2 below illustrates typical mass balances required to yield 100 parts 
by weight of methyl t-butyl ether using a gas/liquids feed (41) in the 
procedure illustrated in FIG. 2. 
TABLE 2 
__________________________________________________________________________ 
Contents (parts by weight) of Stream No 
Com- (see FIG. 2) 
ponent 
41 42 43 44 45 46 47 48 49 50 51 52 53 54 
55 
__________________________________________________________________________ 
H.sub.2 
-- -- -- -- -- -- 2.4 
-- -- -- -- -- -- 2.4 
-- 
CH.sub.4 
1 .times. 10.sup.4 
1 .times. 10.sup.4 
-- -- -- -- 13.2 
13.2 
-- 13.6 
-- 13.6 
-- -- 
-- 
C.sub.2 H.sub.4 
-- -- -- -- -- -- 33.1 
33.1 
-- 1.0 
-- 1.0 
-- -- 
-- 
C.sub.2 H.sub.6 
1805 54 1751 
-- 213 
20.7 
15.5 
15.5 
0.3 47.7 
-- 47.7 
-- -- 
-- 
C.sub.3 
2426 -- 2426 
-- 295 
28.7 
2.8 
2.8 
2.2 5.9 
2.9 
2.9 
2.9 
-- 
-- 
i-C.sub.4 H.sub.10 
1121 -- 1121 
-- 136 
0.6 
-- -- 135.7 
69.2 
68.6 
0.6 
67.9 
-- 
0.7 
i-C.sub.4 H.sub.8 
-- -- -- -- -- -- -- -- 0.5 64.8 
64.5 
0.3 
0.8 
-- 
-- 
n-C.sub.4 H.sub.10 
1678 -- 1678 
-- 204 
19.8 
-- 1.1 
1.4 2.5 
2.5 
-- 2.5 
-- 
-- 
C.sub.5+ 
-- -- -- -- -- -- 2.2 
-- -- -- -- -- -- 2.2 
-- 
Coke -- -- -- -- -- -- -- -- -- 1.2 
-- -- -- -- 
-- 
Methanol 
-- -- -- 37.6 
-- -- -- -- -- -- -- -- -- -- 
0.7 
MTBE -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
100 
__________________________________________________________________________ 
The process of the present invention illustrated in FIG. 2 has essentially 
the same advantages over prior art processes for the manufacture of methyl 
t-butyl ether as those detailed for the process illustrated in FIG. 1. 
However, in addition the process illustrated in FIG. 2 has greater 
flexibility as the ethane produced in the transhydrogenation process (52) 
can be recycled to the gas/liquids separator (56), added to the natural 
gas stream (42) or recycled to the cracker (62) as feedstock. Moreover, 
the isobutane-rich stream (53) from the etherification reactor (60) can 
either be recycled to the deisobutanizer column (57) or added to the 
liquified petroleum gas product stream (43). 
The process of the present invention may also be used to advantage when the 
cracking facility produces ethylene as a by-product only. For example, in 
refining crude oil to manufacture petroleum products such as gasoline, 
"light gas" streams containing ethylene are also produced. Such 
olefin-rich refinery light gases are often reacted with light naphtha or 
low octane streams to give a higher yield of liquid hydrocarbons having a 
higher octane number. The present invention provides a process for more 
effective use of olefin-rich refinery light gases as the preparation of 
methyl t-butyl ether provides a relatively higher yield of liquid products 
and a relatively greater increase in octane number. 
Referring to FIG. 3 of the drawings, a refinery dry gas stream (71) 
comprising hydrogen, carbon oxides, methane, ethane, propane and a 
significant proportion (&gt;10% w/w) of ethylene is fed into a hydrogen 
recovery unit (83) and hydrogen (72) is separated and recycled for 
refinery operations. The olefin-enriched stream (73) is combined with an 
isobutane-rich stream (74) obtained from refinery product streams or by 
separation from liquified petroleum gas and fed into a transhydrogenation 
reactor (84). In the transhydrogenation reactor (84) the isobutane, or 
portion thereof, is dehydrogenated to isobutene and the ethylene, or 
portion thereof, is hydrogenated to ethane as hereinbefore described. 
The product stream (75) from the transhydrogenation reactor (84) is 
combined with any isobutene containing stream (76) from refinery 
operations and fed into a debutanizer column (85) in which it is separated 
into an ethane-rich C.sub.2 -hydrocarbon stream (77), which is recycled 
for further refinery processing or fuel use, and an isobutene-rich C.sub.4 
-hydrocarbon stream (78). 
The isobutene-rich C.sub.4 -hydrocarbon stream (78) is combined with any 
other isobutene-rich stream (79) obtained from refinery operations and 
together with methanol (80) is fed into the etherification unit (86). In 
the etherification unit (86) methanol and isobutene are reacted as 
hereinbefore described to give methyl t-butyl ether. A liquid phase 
mixture (82) comprising methanol and methyl t-butyl ether is withdrawn 
from the reactor and distilled to give a methanol/methyl t-butyl ether 
azeotrope which may be recycled to the etherification reactor and methyl 
t-butyl ether as product which may be further purified by distillation as 
required. A gaseous mixture (81) comprising mainly isobutane is withdrawn 
from the etherification reactor (86) and recycled for recovery and 
combination with the isobutane rich stream (74). 
The transhydrogenation step of the process of the present invention is now 
illustrated by, but in no way limited to, the following Examples. 
EXAMPLES 1 TO 3 
An approximately equimolar mixture of isobutane and ethylene was passed 
through a bed of a standard 19% w/w chromium oxide on alumina 
dehydrogenation catalyst (Harshaw Cr 0221T available from the Harshaw 
Chemical Company) in a tube furnace. The reaction conditions and 
composition of the inlet and outlet gas streams are given in Table 3 
below. 
TABLE 3 
______________________________________ 
Example 
1 2 3 
______________________________________ 
Reaction Conditions 
Temperature (.degree.C.) 
400 450 480 
Pressure atmospheric 
atmospheric 
atmospheric 
Space Velocity 
0.85 0.85 0.85 
Inlet Gas Com- 
position (mole %) 
Ethylene 47.72 48.67 53.84 
Ethane 0.10 0.10 0.11 
Isobutane 52.18 51.23 46.04 
Outlet Gas Com- 
position (mole %) 
Hydrogen 0.41 0.52 0.57 
Carbon Monoxide 
0.01 0.08 0.19 
Carbon Dioxide 
0.04 0.13 0.04 
Methane 0.01 0.16 0.33 
Ethylene 46.47 43.17 42.14 
Ethane 1.17 6.06 12.09 
Propylene 0 0.06 0.13 
Propane 0.01 0.01 0.03 
Isobutane 50.98 44.83 36.23 
Isobutene 0.76 4.78 8.11 
Other C.sub.4 - 
0.07 0.15 0.11 
Hydrocarbons 
Higher 0.06 0.05 0.03 
Hydrocarbons 
______________________________________ 
EXAMPLES 4 TO 6 
An approximately equimolar mixture of isobutane and ethylene was passed 
through a bed of a standard 14.9% w/w molybdenum oxide on alumina 
dehydrogenation catalyst (Harshaw Mo 205-1-R available from The Harshaw 
Chemical Company) in a tube furnace. The reaction conditions and 
composition of the inlet and outlet gas streams are given in Table 4 
below. 
TABLE 4 
______________________________________ 
Example 
4 5 6 
______________________________________ 
Reaction Conditions 
Temperature (.degree.C.) 
400 450 480 
Pressure atmospheric 
atmospheric 
atomspheric 
Space Velocity 
1.4 1.4 1.4 
(wrtsv; h.sup.-1) 
Inlet Gas Com- 
position (mole %) 
Ethylene 50.45 49.36 49.33 
Ethane 0.10 0.10 0.10 
Isobutane 49.45 50.54 50.57 
Outlet Gas Com- 
position (mole %) 
Hydrogen 0.16 2.07 2.02 
Carbon Monoxide 
0.12 0.28 0.43 
Carbon Dioxide 
0.34 0.23 0.06 
Methane 0.08 0.50 0.73 
Ethylene 49.80 42.61 43.74 
Ethane 3.65 6.89 5.52 
Propylene 0.10 0.33 0.37 
Propane 0.02 0.03 0.03 
Isobutane 45.11 44.87 45.16 
Isobutane 0.55 1.65 1.63 
Other 
C.sub.4 -Hydrocarbons 
0.06 0.44 0.31 
Higher Hydrocarbons 
0.02 0.09 0.02 
______________________________________ 
EXAMPLE 7 
An approximately 2:1 molar mixture of isobutane and ethylene was passed 
through a bed of a standard 10% chromia on alumina catalyst (Katalysator 
G-41P available from Nissan Girdler Catalyst Co Ltd) in a tube furnace. 
The reaction conditions and composition of the inlet and outlet gas 
streams are given in Table 5 below. 
TABLE 5 
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Reaction Conditions 
Temperature (.degree.C.) 
500 
Pressure atmospheric 
Inlet Gas Flow Rates 
(cm.sup.3 min.sup.-1) 
Ethylene 6.0 
Isobutene 12.0 
Outlet Gas Composition 
(mole %) 
Methane 0.53 
Ethylene 6.58 
Ethane 25.38 
Propane 0.62 
Isobutane 45.78 
Isobutene 21.11 
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