JP2001342160A - Method for producing dimethyl ether - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably producing dimethyl ether in higher yield from a synthesis gas. SOLUTION: This method for synthesizing dimethyl ether from a feedstock gas comprising carbon monoxide and hydrogen is characterized by involving <=0.35 wt.% in the moisture content of the feedstock gas. Another version of this method for synthesizing dimethyl ether from a feedstock gas comprising carbon monoxide and hydrogen is characterized by involving <=5 wt.% in the carbon dioxide content of the feedstock gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing dimethyl ether (DME) using synthesis gas as a raw material.

[0002]

2. Description of the Related Art Heretofore, there have been known several methods for producing dimethyl ether from a mixed gas of carbon monoxide and hydrogen in the presence of a catalyst suspended in a medium oil.

For example, JP-A-2-9833, JP-A-3-181435, JP-A-3-52835, JP-A-4-264046, and JP-A-5-810
No. 069 (WO93 / 10069) discloses a method for producing dimethyl ether or a mixture of dimethyl ether and methanol by catalyzing a synthesis gas in a mixture of a methanol synthesis catalyst and a methanol dehydration catalyst suspended in an inert liquid. I have.

[0004] The method disclosed in Japanese Patent Application Laid-Open No. 2-9833 discloses a method of contacting a synthesis gas composed of hydrogen, carbon monoxide and carbon dioxide with a solid catalyst and reacting the synthesis gas in the presence of the solid catalyst. In the direct synthesis of dimethyl ether, the method comprises contacting the synthesis gas in the presence of a solid catalyst system, wherein the solid catalyst is a single catalyst suspended in a liquid medium or a three-phase (liquid phase) reactor system. A mixture of a plurality of catalysts, wherein the three-phase reactor system is a process for the direct synthesis of dimethyl ether from synthesis gas consisting of at least one three-phase reactor.

The method disclosed in Japanese Patent Application Laid-Open No. 3-181435 discloses a method for producing dimethyl ether from a mixed gas of carbon monoxide and hydrogen or a mixed gas further containing carbon dioxide and / or steam. A method for producing dimethyl ether, wherein a catalyst is suspended in a medium oil and used in a slurry state.

[0006] The method disclosed in Japanese Patent Application Laid-Open No. 3-52835 is to react methanol in the presence of a solid methanol synthesis catalyst to produce methanol, and to react the produced methanol in the presence of a solid dehydration catalyst. To produce dimethyl ether. In a method of synthesizing dimethyl ether from a synthesis gas consisting of hydrogen, carbon monoxide and carbon dioxide, the synthesis gas is brought into contact with and reacted in the presence of a solid catalyst system comprising a methanol synthesis component and a dehydration (ether formation) component. A solid catalyst or a mixture of catalysts in a liquid medium in a three-phase (liquid-phase) reactor system in said solid catalyst system, operating said reactor system to reduce the minimum effective methanol rate to at least one hour A dimethyl ether synthesis method characterized by maintaining methanol at 1.0 g mole per 1 kg of a catalyst.

[0007] The method disclosed in Japanese Patent Application Laid-Open No. Hei 5-810069 discloses a method for producing a mixed gas containing carbon monoxide and one or both of hydrogen and water vapor, or a mixed gas further containing carbon dioxide. In a method for producing dimethyl ether, at least zinc oxide,
This is a method for producing dimethyl ether, characterized in that a mixed catalyst containing copper oxide or chromium oxide and aluminum oxide is pulverized, adhered under pressure, and then the pulverized catalyst is suspended in a solvent and used in a slurry state.

The reaction for synthesizing dimethyl ether from carbon monoxide and hydrogen proceeds as follows. CO + 2H ₂ → CH ₃ OH (1) Methanol synthesis reaction 2CH ₃ OH → CH ₃ OCH ₃ + H ₂ O (2) Dehydration reaction CO + H ₂ O → H ₂ + CO ₂ (3) Shift reaction

That is, in this reaction, first, methanol is produced from carbon monoxide and hydrogen on a methanol synthesis catalyst, and then methanol is transferred onto a methanol dehydration catalyst, and dimethyl ether and water are produced by dehydration condensation. Further, water moves to the water gas shift catalyst and / or the methanol synthesis catalyst and reacts with carbon monoxide to produce carbon dioxide and hydrogen.

In a DME direct synthesis process from a synthesis gas in which at least a methanol synthesis catalyst and a methanol dehydration catalyst are arranged in a single reactor as described above, conventionally, the water (ie, steam and water mist) in the raw material gas is particularly reduced. There was no purposeful management, and therefore, a relatively high concentration of water was actually supplied to the DME synthesis reactor while being contained in the raw material gas.

[0011] Similarly, the CO ₂ concentration in the source gas has not conventionally been managed with a particular purpose, and therefore, the DME synthesis reaction has been actually carried out while the relatively high concentration of CO ₂ is contained in the source gas. Was supplied to the vessel. Also, some researchers have reported that CO ₂ in the feed gas provides catalyst stability.

[0012]

In a process for producing dimethyl ether from a synthesis gas as a raw material, it is always required to increase the yield of dimethyl ether and to use the catalyst stably without deactivating the catalyst.

An object of the present invention is to provide a method capable of stably producing dimethyl ether from a synthesis gas at a higher yield.

[0014]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the moisture in the raw material gas has been reduced to D
They have found that the activity of the ME synthesis catalyst can be reduced quickly, and that the stability of DME synthesis can be increased by controlling the water concentration in the raw material gas to be low.

Further, CO ₂ in the raw material gas is found to reduce the reaction efficiency of DME synthesis, also CO ₂ in the raw material gas is found that they had no involvement in the stability of the catalyst, therefore the raw material gas It has been found that the efficiency of DME production can be increased by controlling the CO ₂ concentration of the DME at a low level.

The present invention has been made based on this finding. In a method for synthesizing dimethyl ether from a raw material gas containing carbon monoxide and hydrogen, the raw material gas has a water content of 0.35% or less. In the method for synthesizing dimethyl ether, and the reaction method for synthesizing dimethyl ether from a raw material gas containing carbon monoxide and hydrogen, CO ₂ contained in the raw material gas is 5% or less. A synthesis method.

If the raw material gas for the DME synthesis reaction contains a high concentration of water, the long-term stability of the DME synthesis reaction is impaired. In particular, in a slurry bed DME synthesis reaction,
The amount of water that can be dissolved in the solvent that supports the catalyst in the slurry is low and limited, and the ability to convert water by a water gas shift reaction or the like is also limited. Therefore, when the raw material gas contains a certain amount of water or more, the water concentration in the reactor rises, which leads to a decrease in the activity due to, for example, sintering of copper, which is a catalytically active component, and as a result, the long term Impairs stability. The reduction of the moisture contained in the raw material gas can be achieved by, for example, installing a pretreatment reactor that causes a water gas shift reaction of the moisture immediately before the supply to the DME synthesis reactor.

Also, CO ₂ in the raw material gas behaves like an inert gas rather than behaving as a raw material for MeOH synthesis before the DME synthesis in the reactor.
Has little involvement in OH synthesis. Therefore, CO
_The presence of ₂ causes a decrease in the partial pressure of H ₂ and CO, which are the raw materials for MeOH synthesis, so that the conversion rates of H ₂ and CO are reduced and the DME synthesis efficiency is reduced. The reduction of the concentration of CO ₂ in the source gas is achieved by, for example, removing CO ₂ by an absorption method or the like before supplying it to the DME synthesis reactor. Further, in the stage of producing the synthesis gas, for example, by appropriately setting the reaction conditions of the autothermal reforming of methane, CO ₂
Can be reduced to some extent.

[0019]

DETAILED DESCRIPTION OF THE INVENTION The source gas to which the present invention is applied is
Ratio of hydrogen and carbon monoxide 0.5 with _H 2 / CO molar ratio
Those having a mixing ratio of 3.0, preferably 0.8 to 2.0 can be used. On the other hand, the ratio of hydrogen and carbon monoxide (H ₂ / CO
Ratio) is extremely small (for example, 0.5 or less) or in the case of carbon monoxide containing no hydrogen, steam is supplied separately to partially remove carbon monoxide in the reactor with steam and hydrogen and carbon dioxide. It needs to be converted to carbon.
The amount of water vapor is equimolar to the amount of carbon monoxide to be converted (equal to the amount of missing hydrogen). Also, the amount of carbon dioxide is the same as the number of moles of the converted carbon monoxide. Examples of such a source gas include coal gasification gas, synthesis gas from natural gas, and coalbed methane.

In the present invention, the amount of water contained in the raw material gas is set to 0.35% by volume or less, preferably 0.3% by volume or less. The method for reducing the water content to 0.35% by volume or less is not particularly limited, and a desiccant may be used.
A preferred method is to carry out a water gas shift reaction prior to the dimethyl ether synthesis reaction to convert water to hydrogen.
That is, the water gas shift reactor is installed on the upstream side of the dimethyl ether synthesis reactor, and the water contained in the raw material gas is reacted with carbon monoxide by the water gas shift catalyst to convert it into hydrogen.

Examples of the water gas shift catalyst include copper oxide-zinc oxide, copper oxide-chromium oxide-zinc oxide, and iron oxide-chromium oxide. Since the methanol synthesis catalyst has a strong shift catalytic activity, it can also serve as a water gas shift catalyst. An alumina-supported copper oxide catalyst can be used as a catalyst that also functions as a methanol dehydration catalyst and a water gas shift catalyst. Water gas shift reaction is about 100 ~ 500 ℃,
It is suitable to carry out the reaction preferably at about 150 to 450 ° C. and about 1 to 30 MPa, preferably about 1.5 to 15 MPa. The water concentration is monitored by installing a water concentration meter at the inlet side of the DME synthesis reactor, and taking measures such as replacing the catalyst when the water concentration increases.

The amount of carbon dioxide contained in the raw material gas is set to 5% by volume or less, preferably 4.5% by volume or less. The method for reducing the amount of carbon dioxide to 5% by volume or less is not particularly limited, but for example, an amine absorption method such as diethanolamine, a membrane separation method and the like are suitable.

As the dimethyl ether synthesis catalyst, a mixture of a methanol synthesis catalyst and a methanol dehydration catalyst is used, and in some cases, a water gas shift catalyst is further added. These may be used in a mixed state, or the water gas shift catalyst may be cut off to form a two-stage reaction.

Examples of the methanol synthesis catalyst include copper oxide-zinc oxide, zinc oxide-chromium oxide, copper oxide-zinc oxide / chromium oxide, and copper oxide-zinc oxide / alumina, which are usually industrially used for methanol synthesis. Examples of the methanol dehydration catalyst include γ-alumina, silica, silica / alumina, and zeolite, which are acid-base catalysts. Examples of the metal oxide component of zeolite include oxides of alkali metals such as sodium and potassium, and alkaline earth oxides such as calcium and magnesium. The water gas shift catalyst can be selected from those described above, and can also be used as a methanol synthesis catalyst.

The mixing ratio of the above-mentioned methanol synthesis catalyst, methanol dehydration catalyst and water gas shift catalyst is not particularly limited, and may be appropriately selected according to the type of each component or the reaction conditions. The methanol dehydration catalyst is about 0.1-5, preferably about 0.2-2, and the water gas shift catalyst is about 0.2-5, preferably about 0.5-3, based on the methanol synthesis catalyst 1. The range is often appropriate. When the methanol synthesis catalyst also serves as the water gas shift catalyst, the amount of the water gas shift catalyst is added to the amount of the methanol synthesis catalyst.

The above-mentioned catalyst is used in a powder state, and has an average particle size of 300 μm or less, preferably about 1 to 200 μm.
Particularly preferably, about 10 to 150 μm is appropriate. For that purpose, it can be further pulverized if necessary.

Any medium oil can be used as long as it exhibits a liquid state under the reaction conditions. For example, aliphatic, aromatic and alicyclic hydrocarbons, alcohols, ethers, esters, ketones and halides,
A mixture of these compounds and the like can be used. Preferred are those containing a hydrocarbon as a main component. Further, light oil from which sulfur content has been removed, vacuum gas oil, high-boiling fraction of hydrogenated coal tar, Fischer-Tropsch synthetic oil, high-boiling edible oil and the like can also be used. The amount of the catalyst to be present in the solvent is appropriately determined depending on the type of the solvent, the reaction conditions and the like, but is usually 1 to 50% by weight, preferably about 2 to 30% by weight based on the solvent.

The reaction conditions in the slurry reaction include:
The reaction temperature is preferably from 150 to 400 ° C, especially from 250 to 400 ° C.
A range of 350 ° C. is preferred. If the reaction temperature is lower than 150 ° C. or higher than 400 ° C., the conversion of carbon monoxide is low. The reaction pressure is suitably from 10 to 300 kg / cm ² , more preferably from 15 to 150 kg / cm ² , particularly preferably from 20 to 70 kg / cm ² . Reaction pressure is 1
If it is lower than 0 kg / cm ^2, the conversion of carbon monoxide is low,
On the other hand, if it is higher than 300 kg / cm ^{2, the} reactor becomes special, and a large amount of energy is required for pressurization, which is not economical. The space velocity (supply rate of the mixed gas in a standard state per kg of the catalyst) is 100 to 500
00L / kg · h is preferable, and especially 500 to 30,000
L / kg · h. Space velocity is 50,000L / kg ・
h, the conversion rate of carbon monoxide is low.
If it is less than 00 L / kg · h, the reactor becomes extremely large and is not economical.

The method of separating dimethyl ether from the synthesis reaction product gas can be carried out by the inventor of the present invention, which has been previously developed, and which is disclosed in a publication or a known method.

[0030]

Example 1) Effect of moisture in raw material gas An experimental apparatus equipped with a reactor having an inner volume of 100 ml
A methanol synthesis catalyst (copper oxide-zinc oxide-alumina) and a methanol dehydration catalyst (alumina) were mixed at a ratio of 2: 1, and a catalyst slurry to which paraffin oil was further added was used for the experiment. As the raw material gas, a gas obtained by adding moisture to a gas of H ₂ and CO at a ratio of 1: 1 was used. The reaction temperature was 260 ° C. and the pressure was 5 MPa. The ratio of catalyst weight to feed gas is
4 g of catalyst was used per 1 mol / hr of raw material gas. In the reaction experiment, water was not added for 30 hours after the start of the experiment, water was added for 25 hours from 30 hours after that, the addition of water was stopped, and the reaction was continued for another 25 hours.
The results are shown in the table.

[0031]

[Table 1]

As a result, when the water concentration was 0.88% or more, the efficiency of DME synthesis was significantly impaired by the water addition. On the other hand, when the content is 0.35% or less, the decrease rate is reduced, and the content is reduced to 0.
At 15%, almost the same result as without water addition was obtained. When the water addition was 0, the stability of DME synthesis was most excellent. In each case, methanol was 1 of DME.
By-products were produced at a rate of just under 0%.

2) Water gas shift reaction of water in raw material gas A gas shift catalyst (copper oxide-
Zinc oxide) and a mixed gas of H ₂ and CO containing water was passed. H ₂ / CO was 1. The reactor was a fixed bed. The reaction temperature was 200 ° C. The ratio of the catalyst weight to the raw material gas was 3 g of the catalyst per 1 mol / hr of the raw material gas. The reaction results are shown in the table.

[0034]

[Table 2]

As a result, it was found that the water concentration in the gas can be reduced to 0.1% or less by the water gas shift reaction. Further, in the continuous experiment for 100 hours, no deterioration of the reaction was observed.

3) Shift and DME Process For example, when a gas shift reactor is arranged immediately before a DME synthesis reactor, the raw material gas supplied to the gas shift reactor is heated using the heat of the gas exiting the DME synthesis reactor. You can do it. Reaction temperature of DME synthesis reactor is 260 ° C
In this case, the temperature of the raw material gas supplied to the gas shift reactor can be raised to around 200 ° C.

4) Influence of CO _{2 in} the raw material gas An experimental apparatus equipped with a reactor having an inner volume of 100 ml
A methanol synthesis catalyst and a methanol dehydration catalyst were mixed at a ratio of 2: 1 and a catalyst slurry to which paraffin oil was further added was used for the experiment. As the raw material gas, a gas obtained by mixing H ₂ and CO in a ratio of 1: 1 with CO ₂ at a predetermined concentration was used, and the reaction temperature was 260 ° C. and the pressure was 5 MPa. The ratio of the catalyst weight to the raw material gas was 4 g of the catalyst per 1 mol / hr of the raw material gas. In the reaction experiment, the yield of DME 6 hours after the start of the experiment is shown in the table.

[0038]

[Table 3]

As a result, the DME yield decreased monotonically with increasing CO ₂ concentration. 0% CO ₂ concentration
At that time, the highest yield was obtained. The CO ₂ concentration is 5%
In the following, the STY exceeded 20, and was significantly lower at 10% and 15%. When the long-term reaction stability was compared between the case where the CO ₂ concentration was 0% and the case where the CO ₂ concentration was 10%, no difference in the reaction stability was observed at the time point of 100 hours after the start of the experiment. In each case, methanol was by-produced at a rate of less than 10% of DME.

[0040] 5) Process CO ₂ removed, for example, upstream of the DME synthesis reactor, by placing the CO ₂ absorption column with an aqueous alkaline solution such as sodium hydroxide, the CO ₂ in the feed gas of DME synthesis to 0 Can be lowered.

[0041]

According to the present invention, by controlling the water concentration in the raw material gas for DME synthesis below a certain value,
In addition, by constructing a process for realizing this, the long-term stability of DME synthesis can be improved as compared with the related art.

Further, by controlling the CO ₂ concentration in the raw material gas for DME synthesis to be lower than a certain value, and by establishing a process for realizing the same, the D
The efficiency of ME synthesis can be improved.

[Brief description of the drawings]

FIG. 1 shows a water gas shift reactor according to the present invention.
It is a flow sheet which shows the example provided in the upstream of the E synthesis reactor.

FIG. 2 is a flow sheet showing an example in which a CO ₂ absorption tower is provided on the upstream side of a DME synthesis reactor according to the present invention.

Continuing on the front page (72) Inventor Keiji Tomura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Takashi Ogawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock Inside the company (72) Inventor Masami Ono 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Kenichi Okuyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Seiji Aoki 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 4H006 AA02 AC29 AC41 AC43 BA05 BA07 BA09 BA30 BA66 BA69 BB11 BC10 BC11 BC18 BC31 BC32 BC36 BD10 BE20 BE40 GN05 GP01 4H039 CA60 CA61 CB20 CL25 CL35

Claims (5)

[Claims] 1. A method for synthesizing dimethyl ether from a source gas containing carbon monoxide and hydrogen, wherein the moisture contained in the source gas is 0.35% or less. 2. The method according to claim 1, wherein the synthesis is carried out in the presence of a methanol synthesis catalyst and a methanol dehydration catalyst. 3. A method for synthesizing dimethyl ether from a source gas containing carbon monoxide and hydrogen, wherein CO ₂ contained in the source gas is 5% or less. 4. The method according to claim 3, wherein the synthesis is carried out in the presence of a methanol synthesis catalyst and a methanol dehydration catalyst. 5. The synthesis method according to claim 1, wherein CO ₂ contained in the raw material gas is 5% or less.