U.S. patent application number 15/155746 was filed with the patent office on 2016-11-03 for method for producing dimethyl ether and device suitable therefor.
This patent application is currently assigned to THYSSENKRUPP INDUSTRIAL SOLUTIONS AG. The applicant listed for this patent is THYSSENKRUPP INDUSTRIAL SOLUTIONS AG. Invention is credited to Melanie BAUER, Harald KOMPEL, Alexander SCHULZ.
Application Number | 20160318834 15/155746 |
Document ID | / |
Family ID | 49209317 |
Filed Date | 2016-11-03 |
United States Patent
Application |
20160318834 |
Kind Code |
A1 |
BAUER; Melanie ; et
al. |
November 3, 2016 |
METHOD FOR PRODUCING DIMETHYL ETHER AND DEVICE SUITABLE
THEREFOR
Abstract
An apparatus for producing dimethyl ether by catalytic
dehydration of methanol and by distillation of the dehydration
product includes a first DME reactor having at least a first
reaction stage and a last reaction stage connected in series, the
first reaction stage being configured to at least partially perform
catalytic dehydrogenation of methanol. A cooling apparatus is
disposed between at least the first reaction stage and the last
reaction stage and is configured to cool a reaction mixture
conveyed from the first reaction stage disposed upstream of said
cooling apparatus. A DME column is disposed downstream of, and
operatively coupled to, the last reaction stage and is configured
to separate dimethyl ether from the reaction mixture conveyed from
the last reaction stage. A methanol column is also operatively
coupled to a bottom of the DME column and is configured to separate
the dimethyl-free reaction mixture into methanol and water.
Inventors: |
BAUER; Melanie; (Essen,
DE) ; KOMPEL; Harald; (Bad Vilbel, DE) ;
SCHULZ; Alexander; (Frankfurt, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THYSSENKRUPP INDUSTRIAL SOLUTIONS AG |
Essen |
|
DE |
|
|
Assignee: |
THYSSENKRUPP INDUSTRIAL SOLUTIONS
AG
Essen
DE
|
Family ID: |
49209317 |
Appl. No.: |
15/155746 |
Filed: |
May 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14428298 |
Mar 13, 2015 |
9422213 |
|
|
PCT/EP2013/002702 |
Sep 10, 2013 |
|
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15155746 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 19/245 20130101;
B01J 8/0457 20130101; B01J 2208/00256 20130101; B01D 3/009
20130101; B01D 3/002 20130101; Y02P 20/127 20151101; B01D 3/143
20130101; B01J 2208/065 20130101; B01J 2219/00006 20130101; C07C
41/09 20130101; Y02P 20/10 20151101; B01J 2219/00103 20130101; B01J
2219/24 20130101; C07C 41/42 20130101; C07C 41/09 20130101; C07C
43/043 20130101 |
International
Class: |
C07C 41/09 20060101
C07C041/09; C07C 41/42 20060101 C07C041/42; B01D 3/14 20060101
B01D003/14; B01J 8/04 20060101 B01J008/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2012 |
DE |
102012018341.0 |
Claims
1. An apparatus for preparing dimethyl ether by catalytic
dehydrogenation of methanol, comprising: a first DME reactor having
at least a first reaction stage and a last reaction stage connected
in series, said first reaction stage being configured to at least
partially perform catalytic dehydrogenation of methanol; a cooling
apparatus disposed between at least said first reaction stage and
said last reaction stage and configured to cool a reaction mixture
conveyed from said first reaction stage disposed upstream of said
cooling apparatus; a DME column disposed downstream of, and
operatively coupled to, said last reaction stage and configured to
separate dimethyl ether from the reaction mixture conveyed from
said last reaction stage; and a methanol column operatively coupled
to a bottom of said DME column and configured to separate the
dimethyl-free reaction mixture into methanol and water.
2. The apparatus of claim 1, wherein said first reaction stage is
configured to operate adiabatically.
3. The apparatus of claim 1, wherein said DME reactor is an
adiabatically operated DME reactor having a first upstream catalyst
bed operatively connected in series to a second downstream catalyst
bed, and wherein said cooling apparatus is disposed between said
first and second catalyst beds and is configured to provide
intermediate cooling of the reaction mixture conveyed from the
first catalyst bed located upstream.
4. The apparatus of claim 3, wherein said DME reactor is a vertical
shaft reactor.
5. The apparatus of claim 1, wherein said cooling apparatus is at
least one of a heat exchanger or an apparatus for introducing
cooling liquid into the reaction mixture.
6. The apparatus of claim 1, wherein said methanol column is
configured to recirculate methanol separated from the reaction
mixture back to the first adiabatically operated reaction stage of
said DME reactor.
7. The apparatus of claim 1, wherein said cooling apparatus is a
heat exchanger through which vapor of the methanol used for
dehydration is conveyed as a cooling medium.
8. The apparatus of claim 1, wherein said first reaction stage is
configured to operate non-adiabatically.
9. The apparatus of claim 1, wherein said first reaction stage of
said first DME reactor is a separate first stage DME reactor,
wherein said second reaction stage of said first DME reactor is a
separate last stage DME reactor, wherein said cooling apparatus is
operatively coupled to, at least said first stage DME reactor,
wherein said last stage DME reactor is disposed downstream of, and
operatively coupled to, said cooling apparatus and configured to
further react the reaction mixture conveyed from said cooling
apparatus, and wherein said DME column is configured to distill the
reaction mixture conveyed from said last DME reactor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional Application of U.S. patent
application Ser. No. 14/428,298, filed Mar. 13, 2015, which is a
U.S. National Stage Entry of International Patent Application
Serial Number PCT/EP2013/002702, filed Sep. 10, 2013, which claims
priority to German patent application no. DE 102012018341.0, filed
Sep. 15, 2012, the entire contents of each of which is hereby
incorporated by reference herein.
FIELD
[0002] The invention relates to a process for preparing dimethyl
ether and a reactor suitable for this purpose.
BACKGROUND
[0003] Dimethyl ether (hereinafter also referred to as "DME") is
used in many fields in industrial production and by the private
consumer. Examples are the use as propellant, e.g. for hair spray,
or as starting material for chemical syntheses, e.g. for the
preparation of dimethyl sulfate or light olefins (ethylene,
propylene, butenes). In addition, DME is a low-emission fuel which
is used as an alternative to liquefied petroleum gas from crude oil
("LPG") and can replace the latter in the long term. The use as
low-emission fuel for diesel vehicles has also been tested
successfully in a number of countries. DME is usually prepared from
synthesis gas (H.sub.2 and CO) obtained by reforming of natural gas
or by gasification of coal or solids.
[0004] The preparation of dimethyl ether is then effected either by
direct synthesis from synthesis gas or in two stages via the
synthesis of methanol and subsequent conversion of the methanol
into DME and water. The DME produced worldwide today is prepared
virtually exclusively from methanol. The second stage of this
"indirect" DME synthesis, viz. the preparation of DME from
methanol, is based on the known reaction design basis of conversion
of methanol into DME and water in the gas phase over an acid
catalyst, for example over Al.sub.2O.sub.3, in a single-stage
fixed-bed reactor. The following chemical reaction takes place
here:
2CH.sub.3OHCH.sub.3OCH.sub.3+H.sub.2O, .DELTA.H=-24kJ/mol
[0005] The heat of the exothermic reaction is either removed by
cooling in the reactor or the gaseous feed methanol is, in the case
of adiabatic operation of the reaction, superheated by the heat of
the reaction product in a feed heat exchanger. In the case of a
cooled reactor, this is typically designed as a tube reactor, with
the chemical reaction taking place in the catalyst-filled tubes and
the reaction at the same time being cooled by the gaseous feed
methanol which is conveyed to the shell side of the reactor and is
further preheated there by the heat of reaction.
[0006] The version of the methanol-based DME process which is
described below as "prior art DME process" is based on the use of a
DME reactor. The DME reactor is usually followed by a product
work-up using two rectification columns, an DME column and a
methanol column for separating off unreacted feed methanol from
water, and also an offgas scrubber. This DME process is shown in
FIG. 1.
[0007] The prior art DME process usually comprises a complicated
heat integration, with the hot reaction product being utilized for
heating the feed methanol and for operating boilers or for heating
streams which are circulated by pumping in the vicinity of the
bottom of one of the columns.
[0008] There is a continual search for improving the process
economics of industrial processes. Possible improvements can relate
to the energy efficiency, low purity requirements of the starting
materials, higher product purity, productivity and/or the
apparatuses used.
[0009] The earlier DE 10 2011 114 228 A1, which is not a prior
publication, discloses a cooled reactor for preparing dimethyl
ether from methanol by heterogeneously catalyzed dehydration. A
reactor in which adiabatic heating by means of the heat of reaction
liberated in the start zone is firstly carried out, by which means
the reaction rate is increased to industrially acceptable values,
is used. One of the reactor designs presented comprises a plurality
of catalyst beds connected in series. The work-up of the reaction
product dimethyl ether is not disclosed.
[0010] US 2009/0023958 A1 discloses a process for preparing
dimethyl ether from methanol in an adiabatically operated reactor
in which two catalyst beds are arranged in series. The process is
characterized by the use of selected catalysts in the catalyst
beds.
[0011] U.S. Pat. No. 4,560,87 A discloses a further process for
preparing dimethyl ether and also working up the product obtained.
The resulting dimethyl ether is formed in good yield and is
obtained in high purity.
[0012] It is an object of the present invention to provide an
improved process and a plant suitable for this purpose for
preparing dimethyl ether, which give a high productivity.
[0013] The DME synthesis is an equilibrium reaction. It is
independent of or only insignificantly dependent on the pressure.
The equilibrium can be shifted in the direction of DME formation by
a low working temperature. However, the kinetics of the catalytic
reaction at the same time require a minimum working temperature for
the chemical reaction to light-off and proceed in a stable
manner.
[0014] To achieve a high conversion of the equilibrium reaction, it
is thus advantageous to work at the lowest possible reactor
temperature, which results in a relatively low reactor outlet
temperature.
[0015] Small DME plants, e.g. for preparing pure DME as propellant,
mostly have one cooled reactor. Such plants usually have capacities
of from 10 000 to 40 000 metric tons per year. The cooled reactor,
designed as a tube reactor with cooling by methanol vapor on the
shell of the apparatus, is economically feasible at small to medium
plant capacities.
[0016] Larger DME plants for producing fuel-grade DME as LPG or
diesel substitute usually have capacities of more than 100 000
metric tons per year. The design of such large plants has been
known for about ten years, while small plants for producing pure
DME have been built for over thirty years. At the construction
scale of fuel-grade DME plants, tube reactors are very expensive
because of the large number of tubes and because two tube reactors
have to be provided in parallel at the largest capacities.
Industrially, an adiabatic fixed-bed reactor, which can have, for
example, the form of a shaft reactor, is therefore used at such
large plant capacities for reasons of lower capital costs.
[0017] A disadvantage of the adiabatic mode of operation is that
the temperature of the reaction mixture typically increases by more
than 100.degree. C. within the reactor. This shifts the reaction
equilibrium to a lower methanol conversion compared to a cooled
reactor which has a lower outlet temperature. As a result, more
unreacted methanol has to be recovered in the methanol column,
which significantly increases the capital costs and the operating
media costs of this column.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The present invention is described in detail below with
reference to the attached drawing figures, wherein:
[0019] FIG. 1 is a schematic diagram depicting a DME process;
[0020] FIG. 2 is a schematic diagram of an embodiment of a process
of the present disclosure.
DETAILED DESCRIPTION
[0021] To provide a remedy here, the conventional concept of an
adiabatic reactor has been improved according to the invention by
carrying out the reaction in at least two reaction stages connected
in series, of which at least the first is operated adiabatically
and the reaction product is cooled between the two reaction
stages.
[0022] The present invention provides a process for preparing
dimethyl ether by catalytic dehydration of methanol and work-up of
the dehydration product by distillation, which is characterized in
that the catalytic dehydration is carried out in at least two
reaction stages connected in series, of which at least the first
reaction stage is operated adiabatically and cooling of the
reaction product is carried out at least between the first reaction
stage and the second reaction stage.
[0023] The process of the invention is thus carried out in at least
two reaction stages connected in series, of which the first
reaction stage or preferably the first and second reaction stages
is/are operated adiabatically.
[0024] However, it is also possible to provide a larger number of
reaction stages connected in series, of which at least one,
preferably two and very particularly preferably all, reaction
stages are operated adiabatically.
[0025] In a preferred process variant, at least one reaction stage
consists of a plurality of reactors connected in parallel.
Particular preference is given to using a plurality of reactors
connected in parallel in all of the reaction stages connected in
series.
[0026] As an alternative, the process of the invention can also
comprise at least two reaction stages, with the first reaction
stage being operated adiabatically and one or more downstream
reaction stages being operated nonadiabatically, for example
isothermally.
[0027] Cooling of the reaction mixture is carried out at least
between the first reaction stage and the second reaction stage.
When more than two reaction stages are present, cooling of the
reaction mixture preferably takes place between each reaction
stage.
[0028] The temperature in the reaction stages of the process of the
invention is lower compared to the temperature in the adiabatically
operated reactors of the prior art. The temperature in the reaction
stages connected in series according to the invention is typically
in each case in the range from 200 to 400.degree. C., preferably
from 250 to 370.degree. C.
[0029] The process of the invention is preferably operated using
two adiabatic reaction stages connected in series.
[0030] Between the individual reaction stages, the reaction mixture
is cooled. Within an adiabatic reaction stage, the reaction
temperature increases since the process is exothermic. In general,
the reaction mixture is cooled after passage through an adiabatic
reaction stage to such an extent that its temperature corresponds
approximately to the temperature at which the reaction mixture
enters the preceding adiabatic reaction stage. In the case of a
reaction stage which is not operated adiabatically, for example an
isothermally operated reaction stage, the reaction mixture is
cooled to below the entry temperature and DME formation is promoted
in this way. The temperature of the reaction mixture is preferably
decreased to from 200 to 300.degree. C. between the reaction
stages.
[0031] Cooling of the reaction mixture can be carried out by use of
heat exchangers and/or by introduction of cooling liquid directly
into the reaction mixture ("quenching").
[0032] Suitable cooling liquids are methanol, DME and/or water,
with liquid methanol preferably being used in the first reaction
stages and liquid DME or a DME-containing liquid preferably being
used in the last reaction stage. The cooling liquid is introduced,
e.g. sprayed, into the gaseous reaction mixture between the
reaction stages and, as a result of vaporization, brings about
effective cooling of the reaction mixture.
[0033] Suitable heat exchangers are of all known types, for example
helically coiled heat exchangers, shell-and-tube heat exchangers
and plate heat exchangers. These are preferably supplied with
liquids which originate from the DME plant and can effect cooling
of the hot reaction mixture. Thus, for example, methanol from the
methanol column can be used as coolant for the heat exchanger or
exchangers.
[0034] The various reaction stages of the process of the invention
can be realized by means of at least two reactors connected in
series, of which at least the first is operated adiabatically.
Cooling of the reaction mixture is carried out at least between the
first two reactors.
[0035] In an alternative variant of the process of the invention,
the various reaction stages can be realized in one reactor, with at
least the first of the reaction stages being operated
adiabatically. Preference is given to using an adiabatically
operated reactor which has at least two catalyst beds connected in
series. A heat exchanger for intermediate cooling of the reaction
mixture from the catalyst bed located upstream is arranged at least
between the first and second catalyst beds, preferably between all
catalyst beds, and/or cooling liquid is sprayed into the reaction
mixture between at least the first two catalyst beds, preferably
between all catalyst beds.
[0036] Preferred reactors are adiabatically operated fixed-bed
reactors.
[0037] In the case of nonadiabatic operation, preference is given
to using shell-and-tube reactors or fluidized-bed reactors.
[0038] As heat exchangers, it is possible to use all known types.
Examples are shell-and-tube heat exchangers, helically coiled heat
exchangers or plate heat exchangers.
[0039] In a preferred variant of the process of the invention, the
cooling of the reaction product between the reaction stages is
effected by means of a heat exchanger through which vapor of the
methanol used for the dehydration is conveyed as cooling
medium.
[0040] In a particularly preferred variant of the process of the
invention, three adiabatically operated reaction stages connected
in series are provided and liquid methanol is introduced as coolant
into the reaction mixture between the first and second reaction
stages and the cooling of the reaction mixture between the second
and third reaction stages is effected by means of a heat exchanger
through which vapor of the methanol used for the dehydration is
preferably conveyed as cooling medium.
[0041] This embodiment of the process of the invention is
preferably carried out in an adiabatically operated reactor which
has three catalyst beds connected in series, a device for
introducing liquid methanol into the reaction mixture between the
first and second catalyst beds and a heat exchanger, preferably a
plate heat exchanger, between the second and third catalyst beds in
order to cool the reaction mixture before it enters the third
catalyst bed.
[0042] In the process of the invention, it is possible to employ
the conventional catalysts used for the dehydration of methanol.
Preference is given to using an acidic and solid catalyst,
preferably aluminum oxide, for the dehydration. As an alternative
to aluminum oxide, it is also possible to use other solid acidic
catalysts, for example aluminosilicates such as zeolites or
titanium dioxide or aluminotitanates.
[0043] As a result of the above-described way of carrying out the
reaction, the reaction equilibrium is set at a low reactor exit
temperature comparable to that of a cooled reactor and a higher
methanol conversion and a lower amount of recirculated methanol are
thus achieved. The throughput through the methanol column is
significantly reduced thereby.
[0044] In a preferred embodiment of the process of the invention,
the reaction mixture coming from the last reaction stage is worked
up in a DME column in which dimethyl ether is separated off from
the reaction mixture by distillation to leave a bottom product
which is transferred from the DME column into a methanol column
where it is separated by distillation into a methanol stream and a
water-containing bottom product. The methanol stream obtained is
preferably recirculated to one or more of the DME reaction
stages.
[0045] The process of the invention has a number of advantages
compared to the prior art DME processes. In the process of the
invention, up to about 30% less methanol is distilled off in the
methanol column of the two-stage reaction concept. The amount of
recirculated methanol is thus reduced by up to about 70% of the
value obtained in the prior art DME processes because of the higher
methanol conversion in the two-stage reaction. As a result, the
diameter of the methanol column can be reduced in the process of
the invention and costs incurred for operating media in the
materials separation can be saved.
[0046] The process of the invention results in a lower reactor
outlet temperature compared to other adiabatic processes and
therefore permits a higher methanol equilibrium conversion, for
example up to 88%.
[0047] In summary, the process of the invention thus leads to:
[0048] a smaller amount of circulated methanol (about 30% smaller)
[0049] and thus smaller equipment (for example, the diameter of the
methanol column becomes about 17% smaller) [0050] and to lower
operating costs for materials separation (saving of cooling water
of about 20%, saving of steam of about 40%).
[0051] Additional costs are incurred as a result of the use of a
second reactor and as a result of a somewhat greater amount of
catalyst needed.
[0052] Looking at the overall economics of a large DME plant of 800
000 metric tons per year, on the basis of a comparison of capital
costs and operating costs of the plant over a life of 20 years, the
two-stage reaction is more economical than the "standard" DME plant
having one adiabatic reactor.
[0053] Product income and raw materials costs are the same in both
variants since the amounts of DME and methanol are identical. The
improved economics thus result from the lower total costs.
[0054] The invention also provides an apparatus for preparing
dimethyl ether by catalytic dehydrogenation of methanol, which
comprises the elements: [0055] A) at least two DME reactors (1a,
1b) connected in series, of which at least the first DME reactor is
operated adiabatically, [0056] B) a cooling apparatus (2) arranged
between at least the first DME reactor and the second DME reactor
for cooling the reaction mixture from the reactor (1a) located
upstream of the cooling apparatus (2), [0057] C) a DME column (3)
connected to the last reactor (1b) for separating the dimethyl
ether from the reaction mixture, and [0058] D) a methanol column
(4) connected to the bottom of the DME column (3) for separating
the reaction mixture which has been freed of the dimethyl ether
into methanol and water.
[0059] An alternative embodiment of the invention provides an
apparatus for preparing dimethyl ether by catalytic dehydrogenation
of methanol, which comprises the elements: [0060] A') at least one
DME reactor in which at least two reaction stages connected in
series, of which at least the first reaction stage is operated
adiabatically, are arranged, [0061] B') a cooling apparatus (2)
arranged between at least the first reaction stage and the second
reaction stage for cooling the reaction mixture from the reaction
stage located upstream of the cooling apparatus, [0062] C') a DME
column (3) connected to the last reaction stage for separating the
dimethyl ether from the reaction mixture, and [0063] D) a methanol
column (4) connected to the bottom of the DME column (3) for
separating the reaction mixture which has been freed of the
dimethyl ether into methanol and water.
[0064] In a preferred embodiment, the apparatus of the invention
has an adiabatically operated DME reactor in which two catalyst
beds connected in series are provided and a cooling apparatus which
serves for intermediate cooling of the reaction mixture from the
catalyst bed located upstream. The adiabatically operated reactor
is, in particular, a vertical shaft reactor. The cooling apparatus
(2) is a heat exchanger and/or an apparatus for introducing cooling
liquid into the reaction mixture.
[0065] In a further preferred embodiment of the apparatus of the
invention, methanol from the methanol column (4) is recirculated to
the first adiabatically operated DME reactor (1a) or to the first
adiabatically operated reaction stage of the DME reactor.
[0066] In a further preferred embodiment of the apparatus of the
invention, a heat exchanger through which vapor of the methanol
used for the dehydration is conveyed as cooling medium is used as
cooling apparatus (2).
[0067] The capital costs in the case of a two-stage reaction can be
reduced further by the two reaction stages not being formed by two
apparatuses (two reactors) but being realized in one reactor. Such
an integrated vertical shaft reactor comprises two or even more
catalyst beds and one or more intermediate cooling stages using one
or more built-in heat exchangers, preferably plate heat exchangers,
or by introducing cooling liquid, preferably methanol. The heat
exchangers are particularly preferably supplied with vapor of the
feed methanol as cooling medium.
[0068] FIGS. 1 and 2 describe, by way of example and schematically,
a process according to the prior art and a variant of the process
of the invention.
[0069] FIG. 1 schematically shows the known DME process. The feed
methanol (6) is vaporized and superheated and then fed into the DME
reactor (1) at a temperature of at least 250.degree. C. The
equilibrium reaction of methanol to form DME and water takes place
over an acid catalyst, at a pressure of about 12-14 bar(a) and with
a methanol conversion of about 83%. The reaction product (7) leaves
the DME reactor (1) at about 370.degree. C. and is cooled by heat
integration, for example firstly by heat exchange with the feed
methanol vapor and then by heating of a boiler or by heating of
streams which are circulated by pumping in the vicinity of the
bottom of one of the columns. The reaction product (7) which has
been cooled in this way is introduced into the DME column (3). In
this DME column (7), the DME is separated off as liquid overhead
product at a pressure of about 10-12 bar(a) using cooling water in
the overhead condenser and fed into a runback vessel (11). Liquid
DME product (10) is taken off from this and discharged from the
plant or part thereof is recirculated to the DME column. The gas
phase from the runback vessel (11) is fed into a DME absorber (5).
In addition, part of the feed methanol (6) is fed into the DME
absorber (5). In the DME absorber (5), incondensable gases (13)
consisting of a small amount of dissociation gas (H.sub.2, CO,
CO.sub.2 and CH.sub.4) and DME are scrubbed with methanol in order
to recover the DME, and the liquid product (14) from the DME
absorber (5) is fed to the DME reactor (1). The bottom product (8)
from the DME column (3) is separated into methanol (12) and water
(9) in the methanol column (4) which is operated at a slight
superatmospheric pressure. In the methanol column (4), the
unreacted methanol (12) is recovered and this is fed back into the
process. The remaining amount of water in the recirculated methanol
is subject matter of optimization since it has effects on the costs
of methanol column (4) and DME reactor (1). A higher water content
in the circulated methanol has an unfavorable influence on the
conversion of methanol via the reaction equilibrium and in addition
means that the chemical reaction has to be operated at a higher
entry temperature, which in turn has unfavorable effects on the
equilibrium since the methanol conversion decreases at higher
temperature.
[0070] The process indicated is described in Ullmann's Encyclopedia
of industrial Chemistry, Fifth Completely Revised Edition, Volume
A6, pages 541 to 544, of 1987 and also in numerous patent documents
such as U.S. Pat. No. 4,802,958 and EP 0 270 852 A2.
[0071] FIG. 2 schematically shows a variant of the process of the
invention. The feed methanol (6) is vaporized and superheated and
then fed into a first DME reactor (1a) at a temperature of about
250.degree. C. The equilibrium reaction of methanol to form DME and
water takes place over an acid catalyst, at a pressure of about
12-14 bar(a) and with a methanol conversion of about 83%. The
reaction product from the first reaction stage is cooled by heat
integration from about 370.degree. C. to 250.degree. C., e.g. in a
heat exchanger (2) which cools the product and at the same time
superheats the feed methanol vapor (6). The cooled reaction product
is fed at 250.degree. C. into the second DME reactor (1b) where
further methanol is reacted as a result of the more favorable
position of the equilibrium at lower temperature. The reaction
product (7) leaves the second DME reactor (1b) at a temperature of
about 260.degree. C. As a result of the use of the second DME
reactor, the total methanol conversion is now increased to about
88%. The amount of unreacted methanol is at the same time reduced
by 30%.
[0072] After cooling (not shown in FIG. 2) of the DME product (7)
from the second reaction stage by heat exchange, once again using
feed methanol (6) and/or by heating of a boiler or by heating of
streams which are circulated by pumping in the vicinity of the
bottom of one of the columns, this is fed into the DME column (3).
In this DME column (3), the DME is separated off as liquid overhead
product using cooling water in the overhead condenser at a pressure
of about 10-12 bar(a) and fed into a runback vessel (11). Liquid
DME product (10) is taken off from this and discharged from the
plant or part thereof is recirculated to the DME column. The gas
phase from the runback vessel (11) is fed to a DME absorber (5). In
addition, part of the feed methanol (6) is fed into the DME
absorber (5). In the DME absorber (5), incondensable gases
consisting of a small amount of dissociation gas (H.sub.2, CO,
CO.sub.2 and CH.sub.4) and DME are scrubbed with methanol in order
to recover the DME, and the liquid product (14) from the DME
absorber (5) is fed to the first DME reactor (1a). The bottom
product (8) from the DME column (3) is separated into methanol (12)
and water (9) in the methanol column (4) which is operated at a
slightly superatmospheric pressure. In the methanol column (4), the
unreacted methanol (12) is recovered and this is fed back into the
process.
* * * * *