JP4344846B2 - Method and apparatus for producing dimethyl ether - Google Patents

Description

  The present invention relates to a method and an apparatus for producing dimethyl ether using carbon monoxide and hydrogen as main raw materials.

  As a technology for directly producing dimethyl ether (DME) from synthesis gas mainly composed of carbon monoxide and hydrogen, the raw material gas passes through a slurry reactor in which catalyst fine particles are suspended in a high boiling point medium oil. And a technique for synthesizing dimethyl ether in a high yield by reacting them (see, for example, Patent Document 1).

  In the method of directly synthesizing dimethyl ether from carbon monoxide and hydrogen, synthesis and synthesis of methanol produced from hydrogen and carbon monoxide represented by the following formulas (1), (2) and (3) are performed. Furthermore, dimethyl ether synthesis produced by the dehydration reaction from methanol and three types of reactions in which water produced by the synthesis of dimethyl ether reacts with carbon monoxide to produce hydrogen simultaneously proceed.

CO + 2H ₂ → CH ₃ OH ---------- (1)
2CH ₃ OH → CH ₃ OCH ₃ + H ₂ O ---------- (2)
H ₂ O + CO → H ₂ + CO ₂ ---------- (3)

  When the formulas (1) to (3) are summarized, as represented by the reaction formula of the following formula (4), dimethyl ether and carbon dioxide are produced in equal amounts from hydrogen and carbon monoxide.

3CO + 3H ₂ → CH ₃ OCH ₃ + CO ₂ ---------- (4)

  However, the reactions of the above formulas (1) to (3) are equilibrium reactions, and in many cases, sufficient reaction time is not taken until the input raw material gas reaches equilibrium in the reactor. In the process, the above three reactions do not proceed 100%. Therefore, the reaction of the formula (4), which is a summary of the above three reactions, does not proceed 100%. Therefore, 100% conversion of the raw material hydrogen and carbon monoxide as represented by the formula (4) does not occur, and the reaction products DME and carbon dioxide are generated in the gas flowing out from the reactor. In addition, methanol and water as reaction intermediate products are produced as by-products. The gas flowing out from the reactor contains unreacted hydrogen and carbon monoxide.

  Conventionally, the methanol produced is separated from dimethyl ether and then further purified or incinerated as a product.

  However, it is difficult to ship a small amount of methanol produced as a product from a dimethyl ether production plant built in a natural gas or coal production area, and an increase in the yield of dimethyl ether has been desired.

  For this reason, as a method of effectively using the generated methanol, the present applicant returns a liquid mainly composed of methanol and water obtained by cooling the gas flowing out from the reactor to the reactor, thereby increasing the yield of dimethyl ether. The method of making it proposed (refer patent document 2).

Japanese Patent Laid-Open No. 10-182528 JP-A-10-182529

However, it is difficult to separate a liquid mainly composed of methanol by controlling the cooling temperature, and the liquid obtained by cooling always contains dimethyl ether, water, and carbon dioxide in addition to methanol. Table 1 shows each component ratio of methanol (MeOH), dimethyl ether (DME), water (H ₂ O), and carbon dioxide (CO ₂ ) transferred to the recovered liquid at 5 MPaG and 30 ° C. (ratio to the total amount of gas before cooling). ).

  Dimethyl ether liquefies as much as 20 to 30% of the produced amount at 30 ° C. When the reaction products dimethyl ether, carbon dioxide and water are returned to the reactor as they are, the reaction is inhibited. When components other than methanol are separated and discarded, dimethyl ether and carbon dioxide are lost (water may be taken out of the system).

  Moreover, when water contained in the liquid is returned to the reactor, not only the reaction is inhibited, but also the dimethyl ether synthesis catalyst is deteriorated.

  The present invention has been made to improve the above-described problems, and provides a method for producing dimethyl ether that can effectively use methanol produced as a by-product and can increase the yield of dimethyl ether. Objective.

In order to solve the above-mentioned problem, the invention of claim 1 introduces a raw material gas containing carbon monoxide and hydrogen into a reactor and causes the raw material gas to undergo a catalytic reaction to produce dimethyl ether and at least carbon dioxide, In the method for producing dimethyl ether that produces methanol and water as by-products, the product gas from the reactor is cooled to a liquid (1) containing dimethyl ether, carbon dioxide, methanol and water, and a gas containing unreacted gas components. Separate carbon dioxide from the obtained liquid (1), dimethyl ether from the liquid (2) from which carbon dioxide has been separated, and methanol from the liquid (3) from which carbon dioxide and dimethyl ether have been separated. The separated methanol is returned to the reactor, and the product gas is converted into a liquid (2) from which carbon dioxide is separated, and carbon dioxide. The liquid (3) which fine dimethyl ether are separated, and wherein the contacting.

The invention according to claim 2 is a reactor in which a raw material gas containing carbon monoxide and hydrogen is subjected to a catalytic reaction to produce dimethyl ether and at least carbon dioxide, methanol and water as byproducts, and a product gas from the reactor , And separates carbon dioxide from the resulting liquid (1) by separating the liquid (1) containing carbon dioxide, dimethyl ether, methanol and water into a gas (1) and a gas containing unreacted gas components. A CO ₂ purification device, a DME purification device for separating dimethyl ether from a liquid (2) from which carbon dioxide has been separated, a methanol purification device for separating methanol from a liquid (3) from which carbon dioxide and dimethyl ether have been separated, and separation A recycle line for returning the methanol to the reactor, and in the gas-liquid separation device, the product gas is converted into the CO ₂ purification device. The liquid (2) from which carbon dioxide has been separated by contact with the liquid (3) from which dimethyl ether has been separated by the DME purification apparatus is brought into contact.

  According to the present invention, the by-produced methanol can be effectively used to increase the yield of dimethyl ether. Further, the reaction products dimethyl ether, carbon dioxide and water are less likely to be returned to the reactor, and the reaction is not hindered.

Further, according to the invention of claim 1 or claim 2 , the recovery rate of dimethyl ether and carbon dioxide can be increased.

Next, the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment (flow diagram) of an apparatus for producing dimethyl ether (hereinafter referred to as DME) of the present invention. In FIG. 1, 1 is a reformer that generates carbon monoxide gas (hereinafter referred to as CO) and hydrogen gas (hereinafter referred to as H ₂ ) from natural gas, and 2 is a DME synthesis that generates dimethyl ether from a source gas containing CO and H _2. The reactor. Carbon dioxide (hereinafter referred to as CO ₂ ), DME, and methanol (hereinafter referred to as MeOH) are sequentially separated from the liquid obtained by cooling the reaction gas flowing out from the reactor 2 in three separation towers 3, 4, and 5. -Purified. The purified MeOH is returned to the reactor 2 via the recycle line 6.

  Hereinafter, this apparatus will be described along the flow from the reformer 1 through the reactor 2 to the recovery of the purified and separated DME.

Natural gas is reacted with CO ₂ , O ₂ and steam in the reformer 1 to produce a reforming reaction product. The reforming reaction product is cooled and dehydrated upstream of the synthesis gas compressor 7 (not shown), and the reforming reaction product flowing out of the synthesis gas compressor 7 is decarboxylated in the CO ₂ recovery tower 8.

The synthesis gas generated by the reformer 1 is dehydrated and decarboxylated to become a DME synthesis reaction raw material gas (DME synthesis makeup gas). Next, the makeup gas for DME synthesis is mixed with unreacted gas (CO and H ₂ ) -based recycle gas flowing through the recycle gas line 10 and MeOH flowing through the recycle line 6 to form DME source gas. become.

  The source gas is supplied from the bottom of the reactor 2. In the reactor 2, the raw material is subjected to a catalytic reaction to perform a DME synthesis reaction. The medium oil flowing out from the reactor is recovered and returned to the reactor 2 by the pump 11.

  Hereinafter, the reactor 2 will be described in detail. The system of the reactor 2 may be any of a fixed bed type, a fluidized bed type, and a slurry bed type. In particular, the slurry bed type is desirable because the temperature in the reactor is uniform and there are few by-products.

  As for the catalyst, a methanol synthesis catalyst and a methanol dehydration catalyst are used in order to synthesize DME by proceeding with the reactions (1) to (3) above, and an aqueous shift reaction catalyst is appropriately added. A catalyst having these functions is appropriately combined and used.

  As the methanol synthesis catalyst, industrially used copper oxide-zinc oxide, zinc oxide-chromium oxide, copper oxide-zinc oxide / chromium oxide, copper oxide-zinc oxide / alumina and the like are usually used. As the methanol dehydration catalyst, γ-alumina, silica, silica-alumina, zeolite, and the like, which are acid-base catalysts, are used. Here, as the metal oxide component of zeolite, alkali metal oxides such as sodium and potassium, alkaline earth oxides such as potassium and magnesium, and the like are used. In addition, since the methanol synthesis catalyst has a strong shift catalytic activity, it can also serve as a water gas shift catalyst. As described above, an alumina-supported copper oxide catalyst can be used as a methanol dehydration catalyst and a water gas shift catalyst.

  The mixing ratio of the three catalysts is not particularly limited, and may be appropriately selected according to the type of each component or reaction conditions. However, the weight ratio is usually about 0.1-5, preferably about 0.2-2 for the methanol dehydration catalyst and about 0.2-5 for the water gas catalyst, preferably about 0.2. About 5 to 3 are mixed. In the case where the methanol synthesis catalyst and the water gas shift catalyst are the same substance and the methanol synthesis catalyst also serves as the water gas shift catalyst, the total amount of the methanol synthesis catalyst is used.

  As for the form of the catalyst, when a slurry bed reactor is used, the average particle diameter is preferably 300 μm or less, desirably 1 to 200 μm, more desirably about 10 to 150 μm. In order to use it more effectively, the mixed powder is appropriately compacted and molded, pulverized again, and prepared to the above particle size.

  In the case of using a slurry bed type reactor, the medium oil must stably maintain a liquid state under the reaction conditions. For example, aliphatic, aromatic and alicyclic hydrocarbons, alcohols, ethers, esters, ketones and halides, and mixtures of these compounds are used. The amount of the catalyst to be present in the solvent is appropriately determined depending on the kind of the solvent and the reaction conditions.

As reaction conditions in the slurry bed type reactor, the reaction temperature is preferably in the range of 150 to 400 ° C, and particularly preferably in the range of 250 to 350 ° C. Even if the reaction temperature is lower than 150 ° C. or higher than 400 ° C., the conversion rate of CO in the raw material gas is lowered. The reaction pressure is preferably in the range of 10 to 300 kg / cm ² G, particularly preferably in the range of ^{20 to} 70 kg / cm ² G. If the reaction pressure is lower than 10 kg / cm ² G, the CO conversion is low. On the other hand, if the reaction pressure is higher than 300 kg / cm ² G, the reactor becomes special, and a large amount of energy is required for pressurization. Not economical. The space velocity (feeding rate of the raw material gas per kg of catalyst) is preferably 100 to 50000 Nl / kg · h, and particularly preferably 500 to 7500 Nl / kg · h. If the space velocity is greater than 50000 Nl / kg · h, the CO conversion is low, while if it is less than 100 Nl / kg · h, the reactor becomes extremely large and not economical.

Thus, the reaction gas obtained in the reactor ₂ includes DME and CO ₂ as reaction products, CH ₃ OH and H ₂ O as reaction intermediate products, unreacted H ₂ and CO, and raw material gas. Impurities etc. that have been included are included. The component composition of the reaction gas, _{typically, DME: 3~25%, CO 2} : 3~25%, CO: 20~50%, H 2: 20~50%, CH 3 OH: 0.5~3%, H ₂ O: 0.1 to 0.5%, and other: about 5% or less.

Next, the product gas from the reactor 2 is cooled by the heat exchanger 12, and the liquid (1) containing DME, CO ₂ , MeOH and H ₂ O and the unreacted gas component are contained by the gas-liquid separator 13. Separated into gas. These heat exchanger 12 and gas-liquid separator 13 constitute a gas-liquid separator. By this cooling, the liquid (1) containing DME, MeOH and H ₂ O is condensed, and CO ₂ is dissolved in the condensed DME. The cooling temperature is about −10 ° to −60 ° C., preferably about −40 ° C. to −50 ° C., and the pressure at that time is about 1 to 30 MPa, preferably about 1.5 to 15 MPa.

FIG. 2 shows a detailed view of the gas-liquid separator 13. A gas-liquid separator 13 is connected to the outlet side of the heat exchanger 12 that is a cooler. The gas-liquid separator 13 has packing layers 14 and 14 such as Raschig rings arranged in two stages, and a lower part is a liquid reservoir. In the space above each of the packing layers 14, 14, a nozzle is disposed so as to spray substantially uniformly on the upper surface of the packing layer. The space between the liquid reservoir of the gas-liquid separator 13 and the lower packed bed 14 is provided with an inlet for a product gas cooled by a heat exchanger, and a liquid phase containing DME, CO ₂ and MeOH at the bottom. A gas-phase outlet containing unreacted gas is provided at the top, respectively. A methanol supply pipe is connected to the nozzle in the space above the upper packing layer 14, and a DME supply pipe is connected to the nozzle in the space above the lower packing bed 14.

From the nozzle of the gas-liquid separator 13, lower liquid (CO ₂ separating column liquid (2 CO ₂ is separated by), i.e. the crude DME) in the CO ₂ separation column 3 to be described later, and described later DME separation column 4 The lower liquid (liquid (3) from which DME is separated, ie, crude MeOH) is ejected, and these absorbing liquids are brought into contact with the product gas. The supply timing of the crude DME and the crude MeOH may be before or during the condensation of the DME in the product gas, but it is efficient to supply the product after the condensation so that it contacts the gas phase containing the unreacted gas. is there. Either DME or MeOH may be supplied first or simultaneously. Further, the mixture may be supplied by mixing in advance. However, when processing the product gas after DME condensation using an absorption tower as shown in FIG. 2, it is desirable to first contact with DME and then MeOH, because this will reduce the DME concentration in the exhaust gas. .

By bringing the CO ₂ separation tower lower liquid (crude DME) and the DME separation tower lower liquid (crude MeOH) into contact with the gas in the gas-liquid separator 13, the CO ₂ and DME recovery rates are increased. In order to lower the DME concentration in the gas recycled to the reactor 2, MeOH containing no CO ₂ or DME is required. The presence of the DME separation tower 4 makes it possible to supply the MeOH absorbing solution and supply the MeOH containing no CO ₂ and DME to the reactor, thereby increasing the amount of DME recovered and generated.

The separated unreacted gas mainly composed of CO and H ₂ and a gas containing a small amount of impurity gas become a recycle gas. Most of the recycle gas passes through the recycle gas line 10 and is mixed with the makeup gas of DME synthesis. The mixed raw material gas is supplied from the bottom of the reactor 2.

The liquid (1) mainly composed of MeOH, H ₂ O, CO ₂ and DME is put into the CO ₂ separation tower 3 (CO ₂ purification apparatus), and CO ₂ is first separated. In the CO ₂ separation tower 3, CO ₂ is separated and purified by distillation, for example.

The liquid (2) from which CO ₂ has been separated by the CO ₂ separation tower 3 is charged into the DME separation tower 4 (DME purification apparatus), and DME is separated. The DME separation column 4 separates and purifies DME, for example, by distillation. The purified high purity DME is recovered as a product through the DME line.

The liquid (3) from which CO ₂ and DME are separated is mainly composed of MeOH and H ₂ O. This liquid is put into the methanol separation tower 5 (methanol purification apparatus), and MeOH is separated. The methanol separation column 5 separates and purifies MeOH having a purity of 95% by mass or more by, for example, distillation.

  The separated high-purity MeOH is introduced into the makeup gas for DME synthesis through the recycle line 6 and vaporized. Thus, the raw material gas mixed with MeOH is supplied from the bottom of the reactor 2.

According to this embodiment, since MeOH is purified and H ₂ O is not charged into the reactor 2, there is no deterioration of the catalyst. Further, since H ₂ O, CO ₂ and DME are not charged into the reactor, there is an advantage that the DME production reaction is not inhibited. In addition, an efficient process is established in which crude MeOH (3) is circulated through the gas-liquid separator 13, high purity MeOH is supplied to the reactor, and MeOH is not discharged out of the system.

  FIG. 3 shows an experimental apparatus for examining the composition of the product when MeOH is returned to the reactor. The experimental apparatus is smaller than an actual DME manufacturing apparatus.

The reactor is supplied with CO and H ₂ as source gases. As shown in Table 2 below, the slurry in the reactor is composed of 388 g of catalyst and 1552 g of medium oil.

  As shown in Table 3 below, the reaction conditions in the reactor 2 are a temperature of 260 ° C. and a pressure of 5 MPaG.

The product gas from the reactor is cooled to 30 ° C. by a heat exchanger, and is converted into a liquid containing MeOH and H ₂ O as main components and a gas containing unreacted gas components, CO ₂ and DME, in a gas-liquid separator. To be separated. The liquid recovered by the gas-liquid separator was extracted from the gas-liquid separator through a pressure reducing valve and brought to normal pressure, and CO ₂ and DME were volatilized to obtain MeOH and H ₂ O as liquids. The gas generated at the time of depressurization was analyzed for composition by a gas chromatograph after measuring the flow rate using a gas meter. The composition of the obtained liquid was analyzed by gas chromatography after weighing. The gas separated by the gas-liquid separator was measured for the composition using a gas chromatograph after measuring the flow rate using a gas meter.

  In this experiment, the gas obtained from the gas-liquid separator and the amount corresponding to the total amount of MeOH contained in the liquid are returned to the reactor. Here, the source gas is preheated to 110 ° C., and MeOH is preheated to 120 ° C. MeOH sprayed into the raw material gas under this experimental condition was completely vaporized.

Note that the flow rates of CO and H ₂ supplied to the reactor as raw material gases are about 18 NL / min, respectively, and the product does not have an amount sufficient to stably operate the distillation column. Absent.

  Table 4 shows a comparison of the product composition when no MeOH was added to the reactor (Comparative Example) and when MeOH was added to the reactor (Example).

The raw material H ₂ and CO flow rate were measured with a mass flow meter. MeOH was converted to a gas flow rate from the weight speed charged by the micropump. The product was calculated from the results of gas flow rate measurement and gas chromatographic analysis, and the weight measurement of recovered liquid and the results of gas chromatographic analysis. The “water-cooled recovered liquid MeOH concentration” is a MeOH concentration obtained by cooling the product gas to 30 ° C. and evaporating DME · CO ₂ under normal pressure and analyzing the remaining H ₂ O · MeOH by gas chromatography. . In the collected liquid, 20-25% of the produced DME is dissolved.

In the comparative example and the example, the flow rates of the raw material CO and H ₂ are the same. In the examples, since the load of the catalyst is increased by adding MeOH, it is possible to reduce the flow rates of the raw material CO and H ₂ , but the flow rate of the comparative example was kept. If increasing CO and the flow rate of H ₂ product in Example, but there will be material did not change in DME, CO of the flow rate of H ₂ in the product hardly changes. Rather, the total flow rate of CO and H ₂ in the product was reduced when MeOH was added. Further, the amount of DME in the product was increased by adding MeOH, and the amount of MeOH in the product was not increased. In this experiment, all the methanol in the reactor is processed in the reactor. From this experiment, without reducing the flow rate of CO and H ₂ of the raw material to be introduced, also the flow rate of CO and H ₂ in the product nor increase, it was found that it is not necessary to increase the purge gas to be discarded .

That is, according to the experiment, even when all the amount of MeOH discharged from the reactor 2 was added, the conversion rate of CO and H ₂ hardly changed, and DME corresponding to the amount corresponding to the added MeOH was increased. . On the other hand, the amount of MeOH discharged from the reactor 2 hardly changes. Furthermore, even if more MeOH than the amount to be discharged was added, the amount of DME corresponding to the added MeOH was increased. Thus, since MeOH can be processed excessively, it is also possible to process MeOH carried in from outside the system.

MeOH is an intermediate product of the DME synthesis reaction, and it was also considered that adding this would inhibit the reaction and not increase the DME yield. In other words, the amount of DME that can be produced by the reactor was limited, and it was thought that CO and H ₂ would not react and remain as unreacted gas as much as MeOH was added. However, when MeOH is introduced from the reactor inlet, the amount of DME produced increases even with the same amount of catalyst.

This seems to be because the methanol dehydration catalyst has sufficient capacity in the lower part of the reactor 2 and this portion is effectively used. The reactor 2 of the slurry reaction bed has a vertically long structure, and there is a portion in which the above formulas (1) to (3) are advanced on the upper side and the lower side. In the lower part of the reactor 2, MeOH is generated from H ₂ and CO according to the above equation (1), and a dehydration catalyst that advances the equation (2) and a shift catalyst that advances the equation (3). May be playing. When MeOH is introduced into the lower part of the reactor 2, the above formulas (2) and (3) are advanced by the dehydration catalyst and the shift catalyst, and the production amount of DME is considered to increase.

FIG. 4 shows the change over time in the CO conversion rate when the MeOH purity of MeOH charged into the reactor 2 is changed. Distilled water (H ₂ O) was mixed with MeOH to obtain MeOH having a predetermined purity. The amount of raw material input is the same as in the example. However, the amount of MeOH was the amount of MeOH component in H ₂ O + MeOH. The amount of raw material input is the same as in the example. When the MeOH purity decreases, the flow rate of H ₂ · CO · MeOH does not change, but the amount of H ₂ O increases. The CO conversion rate is a value indicating how much CO in the raw material has been changed to a product. It was found that the CO conversion rate hardly decreased when the MeOH purity was 95% by mass, whereas the CO conversion rate slightly decreased when the MeOH purity was 80% by mass. That is, the change with time can be ignored when the MeOH purity is 95% by mass, but the deterioration with time cannot be ignored when the MeOH purity is 95% by mass.

In addition, this invention is not restricted to the said embodiment, A various change is possible. For example, the present invention is not limited to the production method using the general reaction of the above formula (4) in which DME and CO ₂ are produced in equal amounts, and production in which MeOH is produced as a by-product with the synthesis of DME. The method can be generally applied.

Further, in the above embodiment, the one-stage gas-liquid separation device separates the liquid containing DME, CO ₂ , MeOH, and H ₂ into the gas containing the unreacted gas component. You may isolate | separate with a separation apparatus. In this case, first, the product gas is cooled to, for example, about 30 ° C. in the first-stage gas-liquid separator to obtain a liquid mainly composed of MeOH and H ₂ O. Next, the product gas is cooled to, for example, about −30 to −50 ° C. in the second stage gas-liquid separation device to obtain a DME liquid in which CO ₂ is dissolved. Then, MeOH may be purified from a liquid mainly composed of MeOH and H ₂ O separated by the first-stage gas-liquid separator, and the MeOH may be returned to the reactor.

The flowchart of an example of a DME manufacturing apparatus. Detailed view showing a gas-liquid separator. Experimental apparatus for examining the composition of the product when MeOH is returned to the reactor. The graph which shows the time-dependent change of CO conversion rate when changing MeOH purity.

Explanation of symbols

2 ... reactor 3 ... CO ₂ separation column (CO ₂ purification apparatus)
4 ... DME separation tower (DME purification equipment)
5 ... Methanol separation tower (methanol purification equipment)
6 ... Recycling line

Claims (2)

In a method for producing dimethyl ether, a raw material gas containing carbon monoxide and hydrogen is introduced into a reactor, and the raw material gas is subjected to a catalytic reaction to produce dimethyl ether and at least carbon dioxide, methanol and water as by-products.
The product gas from the reactor is cooled and separated into a liquid (1) containing dimethyl ether, carbon dioxide, methanol and water, and a gas containing unreacted gas components,
Carbon dioxide is separated from the obtained liquid (1), dimethyl ether is separated from the liquid (2) from which carbon dioxide is separated, and methanol is separated from the liquid (3) from which carbon dioxide and dimethyl ether are separated,
The separated methanol is returned to the reactor, and the product gas is brought into contact with the liquid (2) from which carbon dioxide is separated and the liquid (3) from which carbon dioxide and dimethyl ether are separated. A method for producing dimethyl ether.   A reactor for catalyzing a raw material gas containing carbon monoxide and hydrogen to produce dimethyl ether and at least carbon dioxide, methanol and water as by-products;
  A gas-liquid separator that cools the product gas from the reactor and separates the liquid (1) containing carbon dioxide, dimethyl ether, methanol, and water, and a gas containing unreacted gas components;
  CO to separate carbon dioxide from the resulting liquid (1) ₂ A purification device;
  A DME purifier for separating dimethyl ether from the liquid (2) from which carbon dioxide has been separated;
  A methanol purifier for separating methanol from the liquid (3) from which carbon dioxide and dimethyl ether are separated;
  A recycling line for returning the separated methanol to the reactor,
  In the gas-liquid separator, the product gas is converted into the CO. ₂ An apparatus for producing dimethyl ether, comprising contacting a liquid (2) from which carbon dioxide has been separated by a purification apparatus and a liquid (3) from which dimethyl ether has been separated by the DME purification apparatus.

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