Note: Descriptions are shown in the official language in which they were submitted.
METHOD FOR PRODUCING DIMETHYL OXALATE
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Field of the Invention
The present disclosure relates to a method for producing dimethyl oxalate, and
further relates to a method for producing dimethyl oxalate, and dimethyl
carbonate as
a byproduct.
Back2round of the Invention
Dimethyl oxalate (DMO) is an important intermediate product of considerable
significance in the chemical engineering industry. It can be used to produce
oxalic
acid through hydrolysis, and ethylene glycol through hydrogenation. Dimethyl
oxalate
can be synthesized substantially through two procedures. In one procedure,
methanol
and oxalic acid are used to produce dimethyl oxalate through esterification.
Such a
procedure is subject to the defects of a large amount of wastewater emissions
and
severe environmental pollution. The other procedure is completed through a
coupling
reaction between carbon monoxide and methyl nitrite in the presence of a
platinum
catalyst. In recent years, due to rapid growth of the coal chemical industry,
the latter
procedure has drawn wide attention as an intermediate step in the production
of
ethylene glycol from coal through a synthesis gas. In such a procedure, a
coupling
reaction occurs between carbon monoxide, under the action of a supported
catalyst of
Pd/a-A1203, and methyl nitrite at atmospheric pressure, to generate dimethyl
oxalate
and nitrogen monoxide, wherein the main reaction equation is as follows:
2C0 +2CH3ONO ¨>(COOCH3)2 +2N0.
Date recue / Date received 2021-11-29
CA 02896290 2015-07-03
In such a synthesis procedure, the following side reactions substantially
occur.
Carbon monoxide reacts with methyl nitrite to produce nitrogen monoxide and
dimethyl carbonate (C3H603), wherein the methyl nitrite decomposes to generate
nitrogen monoxide, methyl formate (C2H402), and methanol, while carbon
monoxide
and nitrogen monoxide react with each other to produce nitrogen and carbon
dioxide.
The equations of the above reaction are as follows:
CO+ 2 CH30 NO --> 2 NO+ C3H603 ,
4 CH3ONO --> 4 NO+ C2H402 + 2 CH30 H , and
2 CO+ 2 NO --> N2 + 2 CO2 =
Currently, a pure dimethyl oxalate product can be obtained typically through
absorption with methanol, followed by separation of methanol, dimethyl
carbonate,
and dimethyl carbonate with each other. That is, purification of dimethyl
oxalate
needs to be performed through an alcohol washing column and an alcohol
recovery
column. The pure dimethyl oxalate product obtained can be directly used as a
product
or as raw material for synthesis of ethylene glycol. Because an azeotropic
phenomenon would occur between dimethyl carbonate and methanol, a liquid
mixture
of methanol and dimethyl carbonate obtained should go through a procedure of
membrane separation, variable pressure rectification, or extractive
distillation for
separation, so as to obtain a pure dimethyl carbonate product.
UBE INDUSTRIES's patent application US 4453026A discloses reaction of
carbon monoxide and methyl nitrite or ethyl nitrite in the presence of a
platinum-group noble metal catalyst. The reaction products are condensed and
separated to obtain a condensate and a non-condensable gas, wherein during a
condensing step, a specific amount of methanol or ethanol is added, so as to
prevent
the dimethyl oxalate or diethyl oxalate from being mixed with the non-
condensable
gas, which would otherwise lead to crystallization. The condensate enters a
primary
rectifying column to generate a crude dimethyl oxalate or diethyl oxalate
product.
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CN 101993367A, CN 101993365A, CN 101993369A, CN 101993361A, CN
101492370A, and CN 101381309A each disclose performing gas-liquid separation
on
the reaction products of carbon monoxide and nitrites to obtain a gas-phase
distillate
and a liquid-phase distillate, and further performing separation and
purification on the
liquid-phase distillate containing oxalates to obtain a crude oxalate product.
CN 202643601U discloses separating dimethyl oxalate through a primary flash,
a washing column, and dimethyl oxalate rectifying column. Crystallization of
dimethyl oxalate occurs easily in the washing column due to low-temperature
washing
with methanol.
CN 101462961A discloses reacting carbon monoxide with methyl nitrite in
contact with a platinum-group noble metal catalyst, to obtain a product
containing
both dimethyl oxalate and dimethyl carbonate. The product is fed into a
condenser to
contact with methanol and then condensed, thus generating a non-condensable
gas,
and a liquor condensate comprising dimethyl oxalate, dimethyl carbonate,
methyl
formate, and methanol. The liquor condensate is then fed to a distillation
column to be
distillated, to produce an azeotrope of the dimethyl carbonate and the
methanol in a
top of the column, and a stream containing the dimethyl oxalate in a bottom of
the
column. These process steps are complex. In addition, dimethyl oxalate, due to
a
relatively high condensation point thereof, will easily crystallize on a wall
of the
condenser, which would finally block the condenser.
To conclude the above, in the prior art, coupling products of carbon monoxide
and methyl nitrite are all condensed before entering successive procedures.
The
process steps are complex. Moreover, dimethyl oxalate easily crystallizes in a
device
and a pipe. Thus, heat preservation or heat tracing is required, in order to
prevent
blockage of the device and pipe by crystallized dimethyl oxalate. Meanwhile,
crystallization of dimethyl oxalate in the device and the pipe also reduces
the yield of
dimethyl oxalate.
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In addition, as discussed above, in the process of producing dimethyl oxalate
by
coupling reactions between carbon monoxide and methyl nitrite, dimethyl
carbonate
can be inevitably generated more often than not. As is well known, an
azeotropic
phenomenon occurs between dimethyl carbonate and methanol. Besides, methanol
.. requires huge latent heat in vaporization thereof. Consequently, separation
of dimethyl
carbonate, especially low-concentrated dimethyl carbonate, from methanol
requires
complex process steps, long time, and high energy consumption.
Shanghai Coking & Chemical Corporation's patent application CN 101190884A
discloses a method for synthesizing dimethyl oxalate and a byproduct dimethyl
carbonate. The method comprises first absorbing dimethyl carbonate along with
dimethyl oxalate that are contained in a coupling reaction product with a
large
quantity of methanol, then separating methanol from dimethyl carbonate with
dimethyl oxalate through extractive distillation, and finally separating
dimethyl
oxalate from dimethyl carbonate. Because the absorption step requires a large
amount
of methanol, a large amount of dimethyl oxalate is also required for
extraction of the
dimethyl carbonate from the methanol through extractive distillation.
Meanwhile, the
large amount of methanol has to be recycled by being steamed out from a top of
the
column, which requires high energy consumption.
East China University of Science and Technology's patent application CN
101381309A discloses a method for separating low concentrated dimethyl
carbonate
through a double-column procedure during synthesis of dimethyl oxalate. The
method
comprises first separating methanol and dimethyl carbonate from dimethyl
oxalate,
.. and then separating methanol from dimethyl carbonate through variable
pressure
rectification. The problem of complex process steps and high energy
consumption
during separation of methanol from dimethyl carbonate still stay unsolved.
In a word, in the prior art, separation of dimethyl carbonate, either through
variable pressure rectification or through extractive distillation, is subject
to use of a
large amount of methanol, thereby leading to complex process steps and high
energy
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CA 02896290 2015-07-03
consumption.
Summary of the Invention
One purpose of the present disclosure is to provide a new method for producing
dimethyl oxalate, so as to solve the problems of complex process steps, easy
blockage
of devices and pipes by crystallization of dimethyl oxalate I, high
consumption of
material and energy, and the like in the prior art during production of
dimethyl oxalate.
The method of the present disclosure has the features of simple process steps,
low
energy consumption, high yield of dimethyl oxalate, etc.
Another purpose of the present disclosure is to provide a method for producing
dimethyl oxalate, and meanwhile dimethyl carbonate as a byproduct. The method
has
the features of simple process steps and low energy consumption, and can
produce
high-purity dimethyl oxalate, and dimethyl carbonate as a byproduct. In
addition, with
this method, it will be unnecessary to separate dimethyl carbonate from
methanol.
According to a first aspect of the present disclosure, a method for producing
dimethyl oxalate is provided, comprising the following steps:
step a): feeding, into a coupling reactor, a reaction material containing
carbon
monoxide and methyl nitrite, which react in the presence of a platinum-group
metal
catalyst, to obtain a dimethyl oxalate-containing gas-phase stream; and
step b): feeding the dimethyl oxalate-containing gas-phase stream into a
dimethyl
oxalate separation column, and enabling counter-current contact of the
dimethyl
oxalate-containing gas-phase stream with a methanol-containing stream entering
the
separation column from a top thereof, so as to obtain crude methanol from the
top of
the column and a dimethyl oxalate product from a bottom of the column,
wherein the dimethyl oxalate-containing gas-phase stream is not cooled before
being fed into the dimethyl oxalate separation column.
According to a preferred embodiment of the present disclosure, the dimethyl
oxalate-containing gas-phase stream does not go through an alcohol washing
column
before being fed into the dimethyl oxalate separation column. That is, the
dimethyl
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CA 02896290 2015-07-03
oxalate-containing gas-phase stream does not have to be washed by an alcohol
in any
alcohol washing column.
As described above, a reaction stream flowing out from the coupling reactor is
often condensed in the prior art. During such a step, dimethyl oxalate would
be
partially separated out, while the rest dimethyl oxalate flows into successive
sections
for further separation and purification. However, in such a process, dimethyl
oxalate
would easily crystallize in a device or a pipe. Moreover, the condensed
dimethyl
oxalate does not have a high purity. In addition, more often than not, the
reaction
stream flowing out from the coupling reactor needs to be washed by an alcohol
in the
prior art, which requires a large quantity of methanol.
In the method for producing dimethyl oxalate according to the present
disclosure,
however, the gas-phase stream from the coupling reactor enters directly into
the
dimethyl oxalate separation column for separation without being cooled. In
addition,
an alcohol washing step is omitted in the method of the present disclosure.
This not
only eliminates a risk for dimethyl oxalate to be crystallized and
precipitated, but also
simplifies process devices and steps.
The platinum-group metal catalyst used in the method of the present disclosure
is
known in the art, and can be any proper catalyst used in catalyzing reactions
between
carbon monoxide and methyl nitrite to produce dimethyl oxalate.
According to the method provided by the present disclosure, the dimethyl
oxalate
product obtained in step b) generally has a purity higher than 99.85%.
According to a preferred embodiment of the present disclosure, the dimethyl
oxalate separation column comprises: an absorbing and rectifying section,
which is
arranged between a feed inlet for the methanol-containing stream and a feed
inlet for
the dimethyl oxalate-containing gas-phase stream, and is provided with a
column
plate or a filler; and a stripping section, which is arranged between the
inlet for the
dimethyl oxalate-containing gas-phase stream and the bottom of the column, and
is
provided with a column plate or a filler.
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Preferably, a height ratio of the absorbing and rectifying section to the
stripping
section is in the range from 0.2:1 to 5:1, more preferably 0.5:1 to 3:1.
Further
preferably, the height ratio of the absorbing and rectifying section to the
stripping
section is in the range from 1:1 to 2:1. Tests have shown that the
aforementioned
ranges of height ratio enable better effects of absorption and separation of
dimethyl
oxalate and methanol.
In a preferred embodiment of the present disclosure, the top of the dimethyl
oxalate separation column has a temperature in the range from 0 C to 60 C,
preferably 25 C to 45 C, and a pressure in the range from 0.1 MPa to 0.3
MPa,
preferably 0.15 MPa to 0.2 MPa. And preferably, the bottom of the dimethyl
oxalate
separation column has a temperature in the range from 161 C to 210 C,
preferably
176 C to 195 C, and a pressure in the range from 0.1 MPa to 0.35 MPa,
preferably
0.12 MPa to 0.24 MPa.
In the present disclosure, the pressures mentioned are all absolute pressures.
According to the method for producing dimethyl oxalate of the present
disclosure,
the filler can be structured or bulk packed, and the column plate can be in
the form of
a float valve tray, a sieve plate, a double pass tray, a bubble-cap tray, or a
Thorman
tray.
Preferably, the stripping section has a theoretical plate number in the range
from
5 to 40.
According to the present disclosure, operation conditions of the coupling
reactor
include a reaction temperature in the range from 50 C to 200 'V, preferably
60 C to
180 C, and a pressure in the range from 0.1 MPa to 2.0 MPa, preferably 0.1
MPa to
1.0 MPa.
Preferably, heat tracing is performed on a pipe arranged between the coupling
reactor and the dimethyl oxalate separation column.
Preferably, heat tracing is performed on a discharge pipe arranged in the
bottom
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CA 02896290 2015-07-03
of the dimethyl oxalate separation column.
In the method for producing dimethyl oxalate provided in the present
disclosure,
carbon monoxide is first used to synthesize dimethyl oxalate. Raw material
gasses
containing carbon monoxide and methyl nitrate are fed into a reactor filled
with a
solid platinum-group metal catalyst for gas-phase catalytic reactions.
The coupling reactor can be preferably selected as a tubular, fixed bed
reactor,
which adopts circulating hot water for heat removal and produces steam as a
byproduct.
The raw material gasses, before entering the reactor, are usually diluted with
inert gasses such as nitrogen or carbon dioxide. The concentration of methyl
nitrite in
the raw material gasses may vary in a relatively large range. However, in
order to
obtain a proper reaction rate, the concentration of methyl nitrite in the raw
material
gasses cannot be lower than 3 vol%, and preferably be in the range from 5 vol%
to 30
vol%. The concentration of carbon monoxide in the raw material gasses may vary
in a
relatively large range also, generally in the range from 10 vol% to 90 vol%.
The
reaction can be performed at a relatively low temperature and a relatively low
pressure. The residence time of the gas-phase reactants in a catalyst bed is
generally
no more than 12 s, properly in the range from 0.2 s to 6 s.
In the method for producing dimethyl oxalate according to the present
disclosure,
a second step is separation of the dimethyl oxalate. In this step, the
reaction product at
an outlet of the coupling reactor directly enters the dimethyl oxalate
separation
column in the intermediate section thereof without being cooled, wherein
counter-current contact is enabled between the reaction product and the
methanol
entering the column from the top thereof, to produce crude methanol and
non-condensed gases from the top of the column, and the dimethyl oxalate
product
.. from the bottom of the column.
The absorbing and rectifying section is provided between the feed inlet of the
methanol-containing stream and the feed inlet of the coupling reaction product
stream,
and is provided with the column plate or the filler, preferably a highly
efficient and
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IOW resistant, structured or bulk packed filler. The absorbing section
meanwhile
functions as a rectifying section. A section between the feed inlet of the
methyl
oxalate-containing stream and the bottom of the column is the striping
section, which
can be in the form of a float valve tray, a sieve plate, a double pass tray, a
bubble-cap
tray, or a Thorman tray, or can be a filler.
After condensation at the top of the dimethyl oxalate separation column, a
non-condensed gas is subject to subsequent treatment, while a condensed liquid
is
partially discharged as the crude methanol product for subsequent treatment,
and
partially recycled and to be mixed a feedstock of methanol to form the
methanol-containing stream, which enters the dimethyl oxalate separation
column.
The pipe from the outlet of the coupling reactor to the dimethyl oxalate
separation column, and the discharge pipe arranged at the bottom of the
dimethyl
oxalate separation column are both preferably to be trace heated, preferably
with
steam, hot water, electricity, and the like, so as to prevent the dimethyl
oxalate from
being crystallized in the devices or in the pipes.
When the method for producing dimethyl oxalate provided by the present
disclosure is used, cooling and alcohol washing devices are unnecessary, and
absorption of the coupling product in a cooling device and rectification of
the
coupling product in a distillation device in the prior art can be completed in
one
dimethyl oxalate separation column, thereby reducing energy consumption and
simplifying devices. Moreover, crystallization of the dimethyl oxalate in the
cooling
device can be prevented, thereby increasing yield of dimethyl oxalate. In
addition,
investment in equipment and floor space can be saved. Meanwhile,
simplification of
process steps renders costs of tracing heat significantly reduced. When the
method for
producing dimethyl oxalate according to the present disclosure is used, the
yield of
dimethyl oxalate can reach higher than 99.5%, with largely reduced energy
consumption of a recovery system for dimethyl oxalate, which is a very obvious
technical effect.
According to a second aspect of the present disclosure, a method for producing
dimethyl oxalate, and dimethyl carbonate as a byproduct is provided,
comprising the
9
following steps:
step a): feeding, into a coupling reactor, a reaction material containing
carbon
monoxide and methyl nitrite, which react in the presence of a platinum-group
metal
catalyst, to obtain a gas-phase stream containing both dimethyl oxalate and
dimethyl
carbonate;
step b): feeding the gas-phase stream containing both dimethyl oxalate and
dimethyl carbonate into an ester separation column, and enabling counter-
current
contact of the gas-phase stream containing both dimethyl oxalate and dimethyl
carbonate with a methanol-containing stream entering the ester separation
column
from a top of the column, and an extraction agent stream containing dimethyl
oxalate
and entering the ester separation column from an intermediate section thereof,
so as to
obtain crude methanol from the top of the column and a mixture containing both
dimethyl oxalate and dimethyl carbonate from a bottom of the column; and
step c): feeding the mixture into a dimethyl oxalate refining column, to
obtain a
dimethyl carbonate product from a top of the refining column and a dimethyl
oxalate
product from a bottom of the refining column,
wherein the gas-phase stream containing both dimethyl oxalate and dimethyl
carbonate is not cooled before being fed into the ester separation column.
The ester separation column refers to a separation column in bottom of which
dimethyl oxalate and dimethyl carbonate are obtained.
Preferably, the gas-phase stream containing both dimethyl oxalate and dimethyl
carbonate does not go through an alcohol washing column before being fed into
the
ester separation column. That is, the gas-phase stream containing both
dimethyl
oxalate and dimethyl carbonate does not have to be washed by an alcohol in any
alcohol washing column.
According to a preferred embodiment of the present disclosure, the ester
separation column comprises: an absorbing section, which is arranged between a
feed
inlet for the extraction agent stream and a feed inlet for the methanol-
containing
stream, and is provided with a column plate or a filler; an extracting
section, which is
arranged between a feed inlet for the gas-phase stream and the feed inlet for
the
extraction agent stream, and is provided with a column plate of a filler; and
a stripping
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CA 02896290 2015-07-03
section, which is arranged between the feed inlet for the gas-phase stream and
the
bottom of the ester separation column, and is provided with a column plate or
a filler.
The gas-phase product from the coupling reactor is fed into the ester
separation
column from between the extracting section and the stripping section thereof,
moves
upward to the extracting section, and get into counter-current contact with
the
liquid-phase dimethyl oxalate flowing downward. The liquid phase in the bottom
of
the extracting section flows downward to the stripping section and is
separated therein,
to obtain the mixture of dimethyl oxalate and dimethyl carbonate in the bottom
of the
column. The gas-phase stream in the top of the extracting section, after
contacting
with an extraction agent, moves upward to the absorbing section and gets into
counter-current contact with methanol stream flowing downward from the top of
the
ester separation column. The methanol stream further absorbs dimethyl oxalate
carried in the gas phase. Thus, a gas-phase stream substantially containing no
dimethyl oxalate or dimethyl carbonate obtained from the top of the ester
separation
column can be recycled to an oxidation and esterification unit for
regeneration of
methyl nitrite.
Preferably, a height ratio of the absorbing section to the extracting section
is in
the range from 1:0.5 to 1:5, preferably 1: 1.5 to 1:3.5.
Preferably, a height ratio of the absorbing section to the stripping section
is in the
range from 1:0.2 to 1:5, preferably 1: Ito 1:2.
In the same way, the filler used in the ester separation column can be
structured
or bulk packed, and the column plate can be in the form of a float valve tray,
a sieve
plate, a double pass tray, a bubble-cap tray, or a Thorman tray.
Preferably, the stripping section has a theoretical plate number in the range
from
5 to 40, more preferably from 10 to 25. In the prior art, merely methanol is
used as an
absorbing agent in a dimethyl oxalate separation column. The ester separation
column
of the present disclosure, however, is added with the extracting section,
wherein
dimethyl oxalate not only works as the extraction agent for separation of
dimethyl
carbonate and methanol, but also works as an absorbing agent for absorption of
the
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gas-phase dimethyl oxalate. Addition of dimethyl oxalate as the absorbing
agent
enables the amount of methanol used to be reduced, and meanwhile ensures
substantially complete absorption of the dimethyl carbonate and dimethyl
oxalate that
are contained in the gas-phase product from the coupling reactor. Thus, the
liquid
obtained in the bottom of the ester separation column will contain no
methanol. This
can reduce energy consumption and loss of methanol in the subsequent
separation
system.
According to the present disclosure, 50-90%, preferably 60-85%, and more
preferably 60-70% of the dimethyl oxalate product obtained in step c) is
recycled to
the ester separation column as the extraction agent. Preferably, the
extraction agent
has a temperature in the range from 55 C to 210 C, more preferably 60 C to
150 C.
The dimethyl oxalate used as the extraction agent is cooled to a temperature
in the
above ranges before entering the ester separation column. A low temperature is
favorable for reduction of the amount of dimethyl oxalate used as the
extraction agent.
However, since the freezing point of dimethyl oxalate at atmospheric pressure
is 54 C,
too low a temperature thereof would lead to a risk of blockage of the pipe by
crystallized dimethyl oxalate.
During the tests of the present disclosure, the influences of the
concentration of
dimethyl oxalate in the extraction agent upon the relative volatility of
methanol to the
dimethyl carbonate have been studied. It has been discovered that, in the
method
according to the present disclosure, a liquid phase in the extracting section
of the ester
separation column has a concentration of dimethyl oxalate equal to or higher
than 20
mol%, e.g., 20-90%. Within the above ranges, an azeotropic point of methanol
and
dimethyl carbonate can be avoided, so that they can be readily separated from
each
other. The molar concentration of dimethyl oxalate in the liquid phase in the
extracting section of the ester separation column can be adjusted through
adjustment
of flow of the extraction agent and adjustment of the flow of the methanol-
containing
stream added in the top of the column.
According to a preferred embodiment of the present disclosure, the top of the
ester separation column has an operation pressure in the range from 0.1 MPa to
0.4
MPa, preferably 0.11 MPa to 0.25 MPa, and a temperature in the range from 0 C
to
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60 C, preferably 20 C to 40 C. Too high an operation pressure in the ester
separation column would be unsuitable, because a higher pressure in the column
would lead to a higher temperature in the bottom of the column, which is
unfavorable
for stability of dimethyl oxalate in the bottom of the column. In the top of
the ester
separation column, however, positive pressure operation would be preferred
since the
operation pressure thereof is subject to restriction by the recycling gas
system.
According to a preferred embodiment of the present disclosure, a volume ratio
of
the methanol-containing stream to the extraction agent stream fed into the
ester
separation column is in the range from 1:1 to 1:5, preferably from 1:1 to 1:3.
According to a preferred embodiment of the present disclosure, the dimethyl
oxalate refining column has an operation pressure in the range from 0 MPa to
0.3
MPa, preferably 0.1 MPa to 0.2 MPa, and a temperature in the top thereof in
the range
from 20 C to 130 C, preferably 80 C to 110 C.
Preferably, the dimethyl oxalate refining column has a theoretical plate
number
in the range from 10 to 60, preferably 25 to 50, and a reflux ratio in the
range from 2
to 200, preferably 5 to 50.
As a reactant stream in the method of the present disclosure, the reaction
material comprises 5-40 mol% of carbon monoxide, 5-30 mol% of methyl nitrite,
1-10 mol% of nitrogen monoxide, 0.1-10 mol% of methanol, and inert gasses,
such as
nitrogen, as a balance. Preferably, the gas-phase material entering the
coupling reactor
comprises 10-30 mol% of carbon monoxide, 5-20 mol% of methyl nitrite, 2-8 mol%
of nitrogen monoxide, 1-8 mol% of methanol, and nitrogen as a balance. The
methyl
nitrite can be supplied by an oxidation and esterification device.
Preferably, the reaction temperature in the coupling reactor is in the range
from
90 C to 150 C, and the reaction pressure therein is in the range from 0.1
MPa to 1
MPa. Preferably, the reaction temperature in the coupling reactor is in the
range from
110 C to 130 C, and the reaction pressure therein is in the range from 0.2
MPa to 0.5
MPa. In the methods of two aspects according to the present disclosure, the
reaction
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conditions in the coupling reactors can be the same. Due to strong
exothermicity of
the coupling reactions, a higher concentration of methyl nitrate would lead to
stronger
reactions. On the one hand, if reaction heat cannot be effectively removed, it
would
cause temperature runway in the reactor. On the other hand, too low a
concentration
of methyl nitrite in the reactor would increase the concentration of the inner
gases
therein, thereby increasing energy consumption of the system. Moreover,
existence of
nitrogen monoxide would restrain the reaction rate of coupling reactions.
Hence, it
may be unfavorable to have too high a concentration of nitrogen monoxide in
the
coupling reactor. However, the concentration of nitrogen monoxide is
correlated to the
oxidation and esterification reaction, and therefore must be kept excessive to
ensure
complete reaction of oxygen. Because methanol is needed for regeneration of
methyl
nitrite in the oxidation and esterification reactor, the gas-phase stream from
the
oxidation and esterification reactor and entering the coupling reactor
contains
methanol at an amount that enables a gas-liquid equilibrium state. Although
methanol
may be unfavorable for the coupling reactions, cooling a product of the
regeneration
of methyl nitrite down to a lower temperature in order to reduce the amount of
methanol contained in the coupling reactor would inevitably increase energy
consumption of the system.
According to a preferred embodiment of the present disclosure, the coupling
reactor is selected in the form of a tubular, fixed bed reactor. Reaction
materials flow
within the tubes, and saturated water flow between and among the tubes. The
coupling
reaction of carbon monoxide in preparation of dimethyl oxalate is a strong
exothermic
reaction. Reaction heat can be effectively released through the tubular, fixed
bed
reactor. Besides, vaporization of the saturated water also absorbs a large
amount of
heat, and meanwhile produces low-pressure stream as a by produce. Thus, the
amount
of circulating water used can be reduced, and the temperature of the water can
be
constantly maintained. At the same time, boiling water can provide a
relatively large
heat transfer coefficient and benefit removal of the reaction heat.
According to a preferred embodiment of the present disclosure, the ester
separation column comprises a reboiler at the bottom and a condenser at the
top
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thereof. With the condenser at the top, the amount of complementary methanol
from
outside and used for absorption can be reduced, while the reboiler at the
bottom can
remove the methanol contained in the liquid stream in the bottom of the
extracting
section. Thus, methanol can be avoided from being withdrawn along with
dimethyl
carbonate, which would otherwise cause methanol loss.
According to a preferred embodiment of the present disclosure, the liquid at
the
bottom of the ester separation column comprises 0.05-5%, preferably 0.1-3% of
dimethyl carbonate, and methyl oxalate substantially as a balance.
In the method provided according the second aspect of the present disclosure,
the absorbing section of the ester separation column, while being used for
absorbing
gas-phase dimethyl oxalate, can also be used as the rectifying section at the
same time,
which restricts movement of dimethyl oxalate toward the top of the column. The
extracting section also plays a role of the absorbing section, wherein liquid-
phase
dimethyl oxalate first absorbs gas-phase dimethyl oxalate and dimethyl
carbonate that
are contained in a rising gas phase. This can significantly reduce the amount
of
methanol, the absorbing agent, used in the absorbing section. When the amount
of
methanol used is reduced, the loads of the reboiler and the condenser can both
be
reduced.
In the method for producing dimethyl oxalate, and dimethyl carbonate as a
byproduct provided by the present disclosure, a cooling device and an alcohol
washing device can be both omitted. And absorption of coupling products in a
cooling
device and rectification of the coupling products in a distillation device in
the prior art
can be completed in one ester separation column, thereby reducing energy
consumption and simplifying devices. Besides, dimethyl oxalate can be
prevented
from being crystallized in the cooling device, thus improving yield of
dimethyl
oxalate. In addition, investment into equipment and floor space can be
reduced.
Meanwhile, simplification of process steps also enables reduced costs in heat
preservation. At the same time, the liquid-phase dimethyl oxalate used as the
extraction agent and circulated in the system destroys the azeotropic balance
between
methanol and dimethyl carbonate, and thus facilitates separation of the
methanol from
the dimethyl carbonate. Subsequently, dimethyl oxalate and dimethyl carbonate
can
CA 02896290 2015-07-03
be separated from each other, thereby not only reducing energy consumption in
separation of dimethyl carbonate, but also obtaining dimethyl oxalate and
dimethyl
carbonate products at required purities. In addition, since dimethyl carbonate
is
separated from methanol, the methanol flowing out of the separation column can
be
further used without being influenced by any accumulation of dimethyl
carbonate.
When the technical solution for producing dimethyl oxalate, and dimethyl
carbonate as a byproduct is used, the recovery rate of dimethyl oxalate can be
higher
than 99.5%, and the removal rate of dimethyl carbonate reaches higher than
99%,
with significantly reduced amount of steam consumption in separation of
dimethyl
carbonate, which are rather beneficial technical effects.
Brief Description of the Drawings
Fig. 1 schematically shows a flow chart of a method for producing dimethyl
oxalate according to the present disclosure;
Fig. 2 schematically shows a flow chart of a method for producing dimethyl
oxalate, and dimethyl carbonate as a byproduct according to the present
disclosure;
and
Fig. 3 shows distribution curves of the concentration of dimethyl oxalate and
the
relative volatility of methanol to dimethyl carbonate in an ester separation
column.
Detailed Description of the Embodiments
The present disclosure will be further explained through examples with
reference
to the accompany drawings. It should be understood that the scope of the
present
disclosure is not to be limited thereto.
As Fig. 1 shows, a nitrogen feedstock 1, a carbon monoxide feedstock 2, a
methanol feedstock 3, and a methyl nitrite feedstock 4 are mixed, preheated,
and then
fed into a coupling reactor R-101 for coupling reaction therein. After the
coupling
reaction, the material stream 6 discharged out of the coupling reactor as
reaction
16
CA 02896290 2015-07-03
product directly enters a dimethyl oxalate separation column in an
intermediate
section thereof. A methanol 7 as an absorbing agent, and a reflux liquid 10 of
the
dimethyl oxalate separation column are mixed with each other to form a
methanol-containing stream which enters a top of the dimethyl oxalate
separation
column. In an absorbing and rectifying section of the dimethyl oxalate
separation
column, countercurrent contact and thus reaction between the material stream 6
and
the methanol-containing stream are enabled. A liquid phase that has absorbed
dimethyl oxalate contained in the material stream 6 moves downward to enter a
stripping section, wherein the dimethyl oxalate is separated, to obtain a
dimethyl
.. oxalate product 12 which is withdrawn from a bottom of the column. A gas 8
from the
top of the dimethyl oxalate separation column is condensed through a condenser
arranged in the top of the dimethyl oxalate separation column, whereby a
non-condensed gas 9 is subject to subsequent treatment, while a crude methanol
product 11 is partially withdrawn and partially works as the reflux liquid 10
of the
dimethyl oxalate separation column. The pipes for the streams 6 and 12 are
heat
traced, so as to prevent the dimethyl oxalate from being crystallized in the
device or
pipes.
As shown in Fig. 2, a gas-phase raw material containing carbon monoxide and
.. methyl nitrite enters a coupling reactor 21 through a pipe 25. A material
discharged
from the coupling reactor enters an ester separation column 22 in an
intermediate
section thereof between an extracting section 22b and a stripping section 22c
through
a pipe 26, wherein countercurrent contact is enabled between the material and
dimethyl oxalate that enters a top of the extracting section 22b of the ester
separation
column through a pipe 33 and flows downward. Thus, a stream is obtained in a
bottom of the extracting section 22b of the ester separation column and flows
into the
stripping section 22c of the ester separation column. After stripping is
performed in
the stripping section 22c, a liquid mixture of dimethyl oxalate and dimethyl
carbonate
is obtained in a bottom of the tripping section 22c of the ester separation
column. The
liquid mixture enters a refining column 23 through a pipe 29. A gas-phase
stream
obtained in a top of the extracting section 22b comes in countercurrent
contact with a
methanol stream entering a top of the absorbing section 22a of the ester
separation
column through a pipe 28 and flowing downward, wherein the methanol stream
further absorbs dimethyl oxalate carried in the gas-phase stream. Thus, a gas-
phase
17
CA 02896290 2015-07-03
stream in a pipe 27 substantially containing no dimethyl oxalate or dimethyl
carbonate
in the top of the ester separation column enters an oxidation and
esterification reactor
for regeneration of methyl nitrite.
Dimethyl carbonate separated from a top of the dimethyl oxalate refining
column
23 is withdrawn through a pipe 30. High-purity dimethyl carbonate is obtained
from a
bottom of the refining column 23, wherein the dimethyl oxalate stream
partially enters
a dimethyl oxalate condenser through a pipe 32, is condensed therein, and then
recycled to the ester separation column 22 as the extraction agent, while the
rest
dimethyl oxalate is withdrawn through a pipe 31.
Example 1
A nitrogen feedstock 1, a carbon monoxide feedstock 2, a methanol feedstock 3,
and a methyl nitrite feedstock 4 were mixed, preheated, and then fed into a
coupling
reactor R-101 at a flow rate of 30 t / h for coupling reaction therein. After
the coupling
reaction, a material stream 6 discharged out of the coupling reactor as
reaction
product directly entered a dimethyl oxalate separation column from an
intermediate
section thereof. A methanol 7 at a flow rate of 20 t / h, after being mixed
with a reflux
liquid 10 of the dimethyl oxalate separation column, entered the dimethyl
oxalate
separation column from a top thereof. A gas 8 in top of the column was
condensed in
a condenser arranged in the top of the dimethyl oxalate separation column,
whereby a
non-condensed gas 9 was subject to subsequent treatment, while a crude
methanol
product 11 was withdrawn. A dimethyl oxalate product 12 was withdrawn from a
.. bottom of the column. The yield of dimethyl oxalate was higher than 99.99%.
The height of a bulk packed filler provided in the dimethyl oxalate separation
column was 10 m; the theoretical plate number in the stripping section was 10;
and
the height ratio of the absorbing and rectifying section to the stripping
section was 2:1.
The operation temperature in the top of the column was 32 C, and the
operation
pressure in the top of the column was 0.14 MPa; while the operation
temperature in
the bottom of the column was 185 C, and the operation pressure in the bottom
of the
column was 0.185 MPa. A thermal load of a reboiler of the column was 4.0435 MW
18
CA 02896290 2015-07-03
The compositions of feedstocks fed into the reactor and those of the main
streams were shown in Table 1.
Table 1
Stream
Parameter
6 7 9 11 12
Temperature, C 110 120 40 20 20 185
Pressure, MPa 0.33 0.21 0.95 0.14 0.14 0.185
N2 44.30% 44.30% 0 50.15% 180 ppm
0
CO 19.08% 10.17% 0 11.51% 171 ppm 0
NO 5.23% 15.07% 0 17.06% 134 ppm 0
CO2 0 30 ppm 0 34 ppm 307 ppm 0
Methyl
29.74% 9.72% 0 11.01% 1.03% 0
nitrite
Content of
Methyl
composition 0 0 0 0 346 ppm 0
formate
by weight
Methanol 1.65% 1.7% 99.78% 9.59% 94.40% ()
Dimethyl
0 0.57% 0.217% 0.627% 4.48% 0.144%
carbonate
Water 0 0 50 ppm 0 14.7 ppm 16 ppm
Dimethyl
0 18.41% 0 0 0 >99.85%
oxalate
5
Example 2
The steps of Example I were repeated except that compositions of the
feedstocks
and parameters of the columns were different from those of Example 1.
1.0
The height of a bulk packed filler provided in the absorbing and rectifying
section of the dimethyl oxalate separation column was 15 m; the theoretical
plate
number of the stripping section was 20; and the height ratio of the absorbing
and
rectifying section to the stripping section was 1.5:1. The operation
temperature in the
top of the column was 29 C, and the operation pressure in the top of the
column was
0.12 MPa; while the operation temperature in the bottom of the column was 178
C,
and the operation pressure in the bottom of the column was 0.15 MPa. A thermal
load
of a reboiler of the column was 3.680 MW. The yield of dimethyl oxalate was
higher
than 99.99%.
19
CA 02896290 2015-07-03
The compositions of the main streams were shown in Table 2.
Table 2
Stream
Parameter
6 7 9 11 12
Temperature, C 110 120 40 15 15 178
Pressure, MPa 0.31 0.21 0.95 0.11 0,11 0.15
N2 44.30% 44.30% 0 140 ppm 50.63%
0
CO 15.61% 6.59% 0 90 ppm 7.53% 0
NO 8.71% 18.79% 0 150 ppm 21.47%
0
CO2 0 50 ppm 0 0 60 ppm 0
Methyl
29.74% 9.22% 0 0.88% 10.52% 0
nitrite
Content of
Methyl
composition 0 730 ppm 0 490 ppm 830 ppm
0
formate
by weight
Methanol 1.65% 1.72% 99.77% 91.96% 8.85% 0
Dimethyl
0 0.88% 0.22% 7.07% 0.89%
0.14%
carbonate
Water 0 0 50 ppm 10 ppm 0 20 ppm
Dimethyl
0 18.41% 0 0 0 >99.85%
oxalate
5
Example 3
The steps of Example 1 were repeated except that compositions of the
feedstocks
and parameters of the columns were different from those of Example 1.
The height of a bulk packed filler provided in the absorbing and rectifying
section of the dimethyl oxalate separation column was 20 m; the theoretical
plate
number of the stripping section was 30; and the height ratio of the absorbing
and
rectifying section to the stripping section was 1.35:1. The operation
temperature in the
top of the column was 34 C, and the operation pressure in the top of the
column was
0.16 MPa; while the operation temperature in the bottom of the column was 187
C,
and the operation pressure in the bottom of the column was 0.2 MPa. A thermal
load
of a reboiler of the column was 4.801 MW The yield of the dimethyl oxalate was
higher than 99.99%.
CA 02896290 2015-07-03
The compositions of the main streams were shown in Table 3.
Table 3
Stream
Parameter
6 7 9 11 12
Temperature, C 110 110 40 15 15 189
Pressure, MPa 0.31 0.21 0.95 0.14 0.14 0.20
N2 46.86% 46.87% 0 190 ppm
53.42% 0
CO 17.51% 9.42% 0 160 ppm 10.74% 0
NO 9.35% 18.38% 0 180 ppm 20.95% 0
CO2 0 50 ppm 0 0 6 ppm 0
Methyl
24.49% 6.12% 0 0.72% 6.96% 0
nitrite
Content of
Methyl
composition 0 600 ppm 0 490 ppm 680 ppm
0
formate
by weight
Methanol 1.77% 1.83% 99.77% 92.58% 7.17% 0
Dimethyl
0 0.72% 0.22% 6.58% 0.67%
0.14%
carbonate
Water 0 0 50 ppm 10 ppm 0 20 ppm
Dimethyl
0 16.58% 0 0 0 >99.85%
oxalate
5
Example 4
The steps of Example 1 were repeated except that compositions of the
feedstocks
and parameters of the columns were different from those of Example 1.
1.0
The height of a bulk packed filler provided in the absorbing and rectifying
section of the dimethyl oxalate separation column was 25 m; the theoretical
plate
number of the stripping section was 40; and the height ratio of the absorbing
and
rectifying section to the stripping section was 1.25:1. The operation
temperature in the
top of the column was 36 C, and the operation pressure in the top of the
column was
0.18 MPa; while the operation temperature in the bottom of the column was 192
C,
and the operation pressure in the bottom of the column was 0.22 MPa. A thermal
load
of a reboiler was 4.769 MW. The yield of dimethyl oxalate was higher than
99.99%.
The compositions of the main streams were shown in Table 4.
21
Table 4
Stream
Parameter
6 7 9 11 12
Temperature, C 110 110 40 15 15 192
Pressure, MPa 0.31 0.21 0.95 0.16 0.16 0.22
N2 46.86% 46.86% 0 220 ppm
53.97% 0
CO 17.52% 9.42% 0 190 ppm
10.85% 0
NO 9.35% 18.38% 0 200 ppm
21.17% 0
CO2 0 50 ppm 0 0 60 ppm ..
0
Methyl
24.49% 6.12% 0 0.83% 7.03% 0
nitrite
Content of
Methyl
composition 0 600 ppm 0 560 ppm
0.07% 0
folinate
by weight
Methanol 1.77% 1.83% 99.78% 92.03% 6.27% 0
Dimethyl
0 0.72% 0.22% 7.02% 0.63%
0.14%
carbonate
Water 0 0 50 ppm 10 ppm 0 20 ppm
Dimethyl
0 16.59% 0 0 0 >
99.85%
oxalate
Comparative Example 1
5
A coupling reaction product was first cooled through a
heat exchanger, wherein a part of dimethyl oxalate was condensed. A gas phase
and a
liquid phase from the heat exchanger both entered a gas-liquid separator,
wherein
dimethyl oxalate that can be directly used was obtained in a bottom of the gas-
liquid
separator. The rest dimethyl oxalate contained in a non-condensed gas phase
from the
gas-liquid separator was fed into an absorbing column, to be absorbed by
methanol. A
resulting liquid from the absorbing column was finally separated through
distillation
to obtain dimethyl oxalate.
The gas-liquid mixture was cooled down to 60-70 C in the heat exchanger. The
height of a packed filler in the absorbing column was 25 m. The amount of
methanol
used for absorption was the same as the amount of the methanol that entered
the top
of the dimethyl oxalate separation column in Example 4. For other conditions,
22
Date recue / Date received 2021-11-29
CA 02896290 2015-07-03
reference can be made to CN 202643601U. The theoretical plate number in the
refining column of the dimethyl oxalate was 40. A required thermal load of a
reboiler
was 11.849 MW, which was obviously higher than the thermal load of the
reboiler of
Example 4, i.e., 4.769 MW.
Example 5
A gas-phase feedstock containing carbon monoxide and methyl nitrite entered a
coupling reactor 21 through a pipe 25, and a coupling reaction product entered
an
ester separation column 22 in an intermediate section thereof between an
extracting
section 22b and a stripping section 22c through a pipe 26, and came into
countercurrent contact with dimethyl oxalate as an extraction agent that
entered a top
of the extracting section 22b of the ester separation column and flowed
downward. A
liquid stream obtained in a bottom of the extracting section 22b of the ester
separation
column flowed into the stripping section 22c of the ester separation column,
wherein
after stripping was performed, a liquid mixture of dimethyl oxalate and
dimethyl
carbonate was obtained in the bottom of the tripping section 22c. This liquid
mixture
entered a refining column 23 through a pipe 29. A gas-phase stream obtained
from the
top of the extracting section 22b came into countercurrent contact with
methanol
zo entering a top of an absorbing section 22a of the ester separation
column through a
pipe 28 and flowing downward, wherein the methanol further absorbed dimethyl
oxalate carried in the gas phase. As a result, a gas-phase stream in pipe 27
substantially containing no dimethyl oxalate or dimethyl carbonate from the
top of the
ester separation column entered an oxidation and esterification reactor for
regeneration of methyl nitrite.
Dimethyl carbonate separated from a top of a refining column 23 was withdrawn
through a pipe 30. High-purity dimethyl carbonate was obtained in a bottom of
the
refining column 23, wherein the dimethyl oxalate stream partially entered a
dimethyl
oxalate condenser (e.g., a heat exchanger) through a pipe 32, was condensed
therein,
and then recycled to the ester separation column 22 as an extraction agent,
while the
rest dimethyl oxalate was withdrawn through a pipe 31.
The temperature in the coupling reactor was 120 C, and the reaction pressure
23
CA 02896290 2015-07-03
thereof was 0.3 MPa.
The ratio of the absorbing section of the ester separation column to the
extracting
section thereof was 1:3, and the theoretical plate number of the stripping
section was
10. The operation pressure in the ester separation column was 0.16 MPa. The
operation temperature in the top of the column was 38 C, while the operation
temperature in the bottom of the column was 177 C. The volume ratio of the
extraction agent stream (dimethyl oxalate) to the absorbing agent stream
(methanol)
was 1.2:1.
As to the dimethyl oxalate refining column, it had a theoretical plate number
of
40, a reflux ratio of 6, an operation pressure of 0.12 MPa, and operation
temperatures
of 95 C in the top thereof and 176 C in the bottom thereof. The ratio of the
dimethyl
oxalate circulated as the extraction agent to the dimethyl oxalate product
withdrawn
out was 1.3:1. The dimethyl oxalate as the extraction agent was cooled to 80
C
through the heat exchanger.
In this example, the relationship between the concentration of dimethyl
oxalate
and the relative volatility of methanol to dimethyl carbonate in the ester
separation
column was studied, with the result as shown in Fig. 3, which indicates
distribution
curves of the concentration of dimethyl oxalate and the relative volatility of
methanol
to dimethyl carbonate in the ester separation column. In Fig. 3, the values as
indicated
in the position of theoretical plates, from small to large, respectively
represent the
theoretical plate numbers successively arranged from the top to the bottom of
the ester
separation column. In the extracting section which was located below the
theoretical
plates of the feed inlet of the extraction agent, when the concentration of
dimethyl
oxalate in the liquid phase was increased to 28 mol%, i.e., the molar
concentration of
dimethyl oxalate in the extracting section of this example, dimethyl oxalate
obviously
functioned as an extraction agent, such that the relative volatility of
methanol to
dimethyl carbonate was increased from 0.7 as in the absorbing section (above
the
theoretical plates of the feed inlet of the extraction agent) to 1.8, crossing
an
azeotropic point where the relative volatility of methanol to dimethyl
carbonate is 1.
At this point, methanol cannot be separated from dimethyl carbonate. The
dimethyl
carbonate was altered from a light component which formed azeotropy with
methanol
24
CA 02896290 2015-07-03
to a heavy component, and moved toward the bottom of the column, while the
methanol moved toward the top of the column, such that the dimethyl carbonate
could
be readily separated from the methanol.
The recovery rate of dimethyl oxalate was higher than 99.99%, and the removal
rate of dimethyl carbonate was 99.6%. The loads of the reboilers in the ester
separation column and the dimethyl oxalate refining column were 7.667 MW and
1.256 MW, respectively.
The compositions of the feedstocks into the reactor and those of the streams
in
the pipes were as shown in Table 5.
Table 5
Stream in pipe
Parameter
25 27 29 30 31 33
Temperature, C 100 27 177 40 176 80
Pressure, MPa 0.30 0.14 0.19 0.12 0.14 0.14
N2 36.10% 39.43% 0.00 0.00 0.00 0.00
CO 20.05% 13.84% 0.00 0.00 0.00 0.00
NO 4.30% 13.52% 0.00 0.00 0.00 0.00
Content of Methyl
34.96% 20.24% 0.00 0.00 0.00 0.00
compositio nitrite
n by Methanol 4.59 % 12.97 % 0.01 0.92 % 0.00 0.00
weight Dimethyl
0.00 237 ppm 1.47% 99.08% 7 ppm 7 ppm
carbonate
Dimethyl
oxalate 0.00 0.00 98.52% 0.00 > 99.9% >
99.9%
Example 6
The steps were the same as those in Example 5, with different reaction
conditions and parameters of columns.
The reaction temperature in the coupling reactor was 120 C, and the reaction
pressure thereof was 0.3 MPa.
The height ratio of the absorbing section of the ester separation column to
the
extracting section thereof was 1:1.5, and the theoretical plate number of the
stripping
CA 02896290 2015-07-03
section was 25. The operation pressure in the ester separation column was 0.16
MPa.
The operation temperature in the top of the column was 38 C, while the
operation
temperature in the bottom of the column was 180 C. The volume ratio of the
extraction agent stream (dimethyl oxalate) to the absorbing agent stream
(methanol)
was 2.2:1.
As to the dimethyl oxalate refining column, it had a theoretical plate number
of
40, a reflux ratio of 8.5, an operation pressure of 0.12 MPa, and operation
temperatures of 96 C in the top thereof and 176 C in the bottom thereof. The
ratio of
the dimethyl oxalate as an extraction agent to the dimethyl oxalate product
withdrawn
out was 2.3:1. The dimethyl oxalate as the extraction agent was cooled to 100
C
through the heat exchanger. The concentration of dimethyl oxalate in the
liquid phase
in the extracting section of the ester separation column was 42 mol%.
The recovery rate of dimethyl oxalate was higher than 99.99%, and the removal
rate of dimethyl carbonate was 99.5%. The loads of the reboilers in the ester
separation column and the dimethyl oxalate refining column were 8.945 MW and
1.543 MW, respectively.
The compositions of the feedstocks into the reactor and those of the streams
in
the pipes were shown in Table 6.
Table 6
Stream in pipe
Parameter
27 29 30 31 33
Temperature, C 100 27 180 40 176 100
Pressure, MPa 0.30 0.14 0.19 0.12 0.14 0.14
N2 36.10% 39.43% 0.00 0.00 0.00 0.00
CO 20.05% 13.84% 0.00 0.00 0.00 0.00
NO 4.30% 13.52% 0.00 0.00 0.00 0.00
Methyl
Content of 34.96% 20.24% 0.00 0.00 0.00 0.00
nitrite
composition
Methanol 4.59% 12.97% 0.00 0.00 0.00 0.00
by weight
Dimethyl
0.00 299 ppm 1.07% > 99.9% 5 ppm 5 ppm
carbonate
Dimethyl
0.00 0.00 98.93% 0.00 > 99.9% > 99.9%
oxalate
26
CA 02896290 2015-07-03
Example 7
The steps were the same as those in Example 5, with different compositions of
feedstocks, reaction conditions, and parameters of columns.
The reaction temperature in the coupling reactor was 130 C, and the reaction
pressure thereof was 0.4 MPa.
The ratio of the absorbing section of the ester separation column to the
extracting
section thereof was 1:2, and the theoretical plate number in the stripping
section was
15. The operation pressure in the ester separation column was 0.2 MPa. The
operation
temperature in the top of the column was 42 C, while the operation
temperature in the
bottom of the column was 186 'C. The volume ratio of the extraction agent
stream
(dimethyl oxalate) to the absorbing agent stream (methanol) was 1.8:1.
As to the dimethyl oxalate refining column, it had a theoretical plate number
of
30, a reflux ratio of 8.8, an operation pressure of 0.20 MPa, and operation
temperatures of 113 C in the top thereof and 193 C in the bottom thereof.
The ratio
of the dimethyl oxalate as an extraction agent to the dimethyl oxalate product
withdrawn out was 1.9:1. The dimethyl oxalate as the extraction agent was
cooled to
60 C through the heat exchanger. The concentration of dimethyl oxalate in the
liquid
phase in the extracting section of the ester separation column was 36 mol%.
The recovery rate of dimethyl oxalate was higher than 99.99%, and the removal
rate of dimethyl carbonate was 99.5%. The loads of the reboilers in the ester
separation column and the dimethyl oxalate refining column were 9.459 MW and
1.741 MW, respectively.
The compositions of the feedstocks into the reactor and those of the streams
in
the pipes were shown in Table 7.
Table 7
Stream in pipe
Parameter
25 27 29 30 31 33
Temperature, 'V 100 25 186 40 193 80
27
Pressure, MPa 0.4 0.14 0.23 0.20 0.22 0.22
N2 47.21% 51.85% 0.00 0.00 0.00 0.00
CO 16.86% 9.98% 0.00 0.00 0.00 0.00
NO 4.52% 14.33% 0.00 0.00 0.00 0.00
Methyl
Content of 27.56% 11.20% 0.00 0.00 0.00 0.00
nitrite
composition
Methanol 3.86% 12.64% 0.00 0.00 0.00 0.00
by weight
Dimethyl
0.00 355 ppm 1.34% >99.9% 7 ppm 7 ppm
carbonate
Dimethyl
oxalate 0.00 0.00 98.66% 0.00 > 99.9%
> 99.9%
Comparative Example 2
The same scale and similar reaction conditions of Example 5 above.
A coupling reaction product was absorbed with a large
quantity of methanol in an alcohol washing column, to obtain a liquid in a
bottom of
the column containing 40 wt% of methanol, 1.1 wt% of dimethyl carbonate, and
58.9
wt% of dimethyl oxalate. An alcohol recovery column had a total theoretical
plate
number of 80, and a reboiler load of 28.134 MW. An ester separation column had
the
same number of theoretical number as that in Example 5, and a reboiler load of
1.872
MW. Such reboiler loads were obviously higher than the reboiler loads of the
ester
separation column and the dimethyl oxalate refining column of Example 5 of the
present disclosure.
In addition, the investment in equipment according to CN 101190884A is higher
than the investment in equipment for carrying out the method according to the
present
disclosure.
Although the present disclosure has been explained in detail, modifications
within the spirit and scope of the present disclosure would be apparent for
those
skilled in the art. Moreover, it should be understood that various aspects,
and parts of
different, specific embodiments recited in the present disclosure, and various
features
as listed can be combined or partially or completely exchanged with each
other. In
addition, those skilled in the art can understand that, the descriptions above
merely
28
Date recue / Date received 2021-11-29
CA 02896290 2015-07-03
constitute exemplary implementing manners of the present disclosure, but are
not
intended to limit the present disclosure.
List of references
R-I01. coupling reactor;
C-101. dimethyl oxalate separation column;
D-102. reflux tank of the dimethyl oxalate separation column;
1. nitrogen feedstock;
2. carbon monoxide feedstock;
3. methanol feedstock;
4. methyl nitrite feedstock;
5. material fed into to the coupling reactor;
6. material stream discharged out of the coupling reactor;
7. methanol feedstock as an absorbing agent;
8. gas from a top of the dimethyl oxalate separation column;
9. non-condensed gas from the top of the dimethyl oxalate separation column;
10. reflux liquid of the dimethyl oxalate separation column;
11. crude methanol product;
12. liquid stream from a bottom of the dimethyl oxalate separation column
(dimethyl oxalate product);
21. coupling reactor;
22. ester separation column;
22a. absorbing section;
22b. extracting section;
22c. stripping section;
23. dimethyl oxalate refining column;
24. dimethyl oxalate condenser;
25. material inlet pipe of the coupling reactor;
26. material outlet pipe of the coupling reactor;
27. gas-phase pipe in a top of the ester separation column;
28. methanol inlet pipe;
29. liquid pipe in a bottom of the ester separation column;
30. dimethyl carbonate pipe in a top of the dimethyl oxalate refining column;
29
CA 02896290 2015-07-03
31. outlet pipe for dimethyl oxalate products;
32. pipe for circulation of dimethyl oxalate; and
33. pipe for circulation of cooled dimethyl oxalate.
