JP3474382B2 - Method for producing dimethyl ether - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing dimethyl ether using a hydrocarbon as a main raw material. 2. Description of the Related Art Dimethyl ether has low toxicity and is stable, and is used as a propellant in place of chlorofluorocarbon, an intermediate material for synthetic gasoline, an alternative fuel for LPG, and a fuel for a diesel engine. [0003] Conventionally, as a commercial production method of dimethyl ether, methanol is once synthesized from carbon monoxide and hydrogen, and then, using the obtained methanol as a raw material, one molecule of water is dehydrated from two molecules. The method of obtaining by this is taken. On the other hand, recently, a technique for preparing a synthesis gas containing carbon monoxide and hydrogen as a make-up gas and causing it to undergo a catalytic reaction to directly synthesize dimethyl ether in a single-stage reactor is being developed.
As a method for directly synthesizing dimethyl ether from carbon monoxide and hydrogen as described above, a method in which a synthesis raw material gas is passed through a fixed bed catalyst layer to cause a reaction (for example, Japanese Patent Laid-Open No. 2-28)
No. 0836) and a method of passing a synthesis raw material gas through a slurry reactor in which catalyst fine particles are suspended in a medium oil having a high boiling point (for example, Japanese Patent Application Laid-Open No. 5-810069). I have. When dimethyl ether is directly synthesized from carbon monoxide and hydrogen by any of the above methods, the following reactions (1), (2) and (3) are represented.
Methanol synthesis, dimethyl ether synthesis generated by dehydration reaction from synthesized methanol, and three types of reactions in which water produced as a byproduct of dimethyl ether synthesis reacts with carbon monoxide to generate hydrogen are produced in one reactor. Progress simultaneously. 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 reactions (1) to (3) are summarized, dimethyl ether (hereinafter, referred to as DME) and carbon dioxide represented by the reaction (4) are used as raw materials. Equivalent amounts are produced from hydrogen and carbon monoxide. 3CO + 3H ₂ → CH ₃ OCH ₃ + CO ₂ (4) However, the above reactions (1) to (3) are equilibrium reactions governed by temperature and pressure. In the actual synthesis process, 100% of the above three reactions do not proceed. Therefore, the reaction (4), which is a summary of the above three reactions, is also 100%
Does not progress. Therefore, as represented by reaction (4), 100% of the raw material hydrogen and carbon monoxide are not converted,
The gas at the reactor outlet always contains unreacted hydrogen and carbon monoxide. Therefore, usually, the unreacted hydrogen and carbon monoxide are not discarded, but are separated from other products and then recycled to a dimethyl ether synthesis reactor for use as a part of a raw material gas, thereby being effectively used. Is done. FIG. 2 is a flow sheet showing an example of a production apparatus used for directly synthesizing dimethyl ether from the above-mentioned synthesis raw material gas composed of carbon monoxide and hydrogen. This production apparatus is a reactor R for dimethyl ether synthesis.
1. and reformer R for preparing makeup gas
2, a methanol / water separator S1, an unreacted gas separator S2, and a CO ₂ separator S3. [0008] Hydrocarbon 15 'and steam 16' are supplied to a reformer R2. In reformer R2, hydrocarbon 15 'is reformed with steam 16' (reforming)
Then, a makeup gas 1 'is prepared, and a recycle gas 11' mainly containing unreacted carbon monoxide and hydrogen is mixed with the makeup gas 1 '. Thus, the synthesis raw material gas 2 ′ of dimethyl ether is prepared. The reactor R1 is supplied with the synthesis raw material gas 2 '. From the reactor R1, the reaction product gas 3 'flows out and enters the methanol / water separator S1. Here, the reaction product gas 5 'from which methanol and water 4' have been separated enters the unreacted gas separator S2. Here, unreacted gas (CO and H
₂ ) is separated into a recycled gas 7 '. Unreacted gases DME and CO ₂ 6 separated 'enters CO ₂ separator S3, where CO ₂ is separated, DME is recovered. The recycled gas 7 'is appropriately purged to the purge line 10 in the middle of the recycled gas line 7', and the remaining recycled gas 11 'is recycled to the recycled gas line 11'.
And mixed with the makeup gas 1 ′, and supplied to the reactor R1 as the synthesis raw material gas 2 ′ as described above. As described above, in the conventional one-step method of DME synthesis, unreacted CO and H ₂ are recycled to the reactor R1 to improve the utilization efficiency of the raw material gas. In addition, methanol is recovered and used, but carbon dioxide is usually
Has been discarded. When dimethyl ether is directly produced from synthesis gas as described above, the carbon monoxide and hydrogen are usually produced by reforming natural gas. For example, steam reforming with methane, which is a main component of natural gas, is performed in reaction (5). CH ₄ + H ₂ O → 3H ₂ + CO (5) Thus, the gas reformed from natural gas H
_{The 2} : CO molar concentration ratio is usually about 3: 1. However, for the synthesis of dimethyl ether, as can be seen from the above reaction (4), the molar ratio of H ₂ : CO of the synthesis raw material gas is desirably 1: 1 of the stoichiometric ratio. Therefore, the hydrogen in the synthesis source gas 2 'becomes excessive with respect to carbon monoxide. [0013] As described above, when hydrogen becomes excessive with respect to carbon monoxide, for example, the compressor power of the recycle gas 7 'of the dimethyl ether synthesis line becomes excessively necessary, or the amount of generated hydrogen is increased. The capacity of the separation device (unreacted gas separator S2) must be increased. As the number of times the recycle gas 7 'is circulated (recycled) increases, the surplus degree of hydrogen tends to increase more and more. Therefore, the amount of gas purged from the recycled gas 7 'must be increased. Therefore, there is a disadvantage in the process economy. Therefore, in the whole process, the surplus hydrogen is discharged from the dimethyl ether synthesis reaction step as, for example, a heat source of the process. This is a problem from the viewpoint of effective utilization of raw material resources. Therefore, in producing a raw material gas for the synthesis of dimethyl ether by reforming a saturated hydrocarbon gas such as natural gas, a technique is desired that is advantageous in terms of process economics of dimethyl ether synthesis and effective utilization of the raw material resources. ing. The reason why the saturated hydrocarbon gas is selected as the reforming target substance is that it is easily available as a natural resource. By the way, the present inventor has taken up, as an examination subject, whether or not it is possible to use coal bed methane, which is considered to be the cheapest, among the saturated hydrocarbon gases. Coalbed methane is methane gas generated in coal mines during coal excavation and contains a large amount of air. The air content is said to range from 30 to 90%. When coalbed methane is reformed and used as a raw material gas for dimethyl ether, a problem arises in that nitrogen remains in the unreacted gas and nitrogen accumulates in the recycled gas. As described above, no study on the process in the case where a large amount of nitrogen is contained in the synthesis raw material gas of dimethyl ether has been found at all. As described above, when a hydrocarbon, for example, natural gas is reformed with steam as in the conventional method,
The H ₂ / CO molar concentration ratio of the reformed makeup gas is too large than an appropriate value of 1. Therefore, the amount of the purge gas 10 'must be increased. On the other hand, if coalbed methane is used as an inexpensive raw material, the accumulated amount of nitrogen in the recycled gas is remarkable, so that coalbed methane cannot be used in practice. An object of the present invention is to solve the above-mentioned problems, prepare coal synthesis methane by reforming coalbed methane, streamline the entire production process of dimethyl ether synthesis, and efficiently obtain inexpensive dimethyl ether. It is to provide a method. From the above-mentioned viewpoints, the present inventor has found that the coal gas methane is reformed by adding oxygen or air or oxygen to the oxygen contained therein, if necessary. We have conducted intensive research to develop a method for producing dimethyl ether at a low cost using. Therefore, the present inventors have focused on the following points. First, in the reforming of hydrocarbons, by using oxygen instead of steam, the molar ratio of H ₂ / CO of the make-up gas is reduced to 1%.
We focused on being able to approach ("first focus point"). Thus, for example, reforming of methane with oxygen is represented by reaction (6). CH ₄ + (1/2) O ₂ → 2H ₂ + CO (6) The reaction (6) is carried out by the reaction of the methane of the reaction (5). It can be seen that the H ₂ / CO molar concentration ratio of the produced gas is greatly reduced and approaches 1 compared with the steam reforming by the method described above, which is advantageous in the DME synthesis process. Second, coalbed methane is inexpensive as a raw material for synthesis, but cannot be recycled as a recycled gas as a raw material gas in a DME synthesis system for the reasons described above. However, it was noted that carbon monoxide and hydrogen contained in the recycled gas can be used as a heat source. That is, the present inventors focused on using a recycled gas containing a large amount of nitrogen as a heat source of a reformer (second viewpoint). By doing so, the accumulation of nitrogen in the dimethyl ether synthesis system can be completely solved. Third, recovering the carbon dioxide that has been discarded in the conventional dimethyl ether synthesis line, and supplying the recovered carbon dioxide to a coalbed methane reformer. Then, the reaction (7) is performed by the reformer (third viewpoint). CH ₄ + CO ₂ → 2H ₂ + 2CO (7) By doing so, the raw material resources are effectively used. Furthermore, by doing so, the H ₂ / CO molar ratio of the reformed synthesis raw material gas approaches 1 as can be seen from the reaction (7), and the DME synthesis process becomes more industrially advantageous. . Although the reaction (7) is an endothermic reaction, replenishment of heat with a recycle gas is effective. The present invention is a method for producing dimethyl ether based on the above findings, and is characterized by the following. A method for producing dimethyl ether by using a mixed gas containing at least carbon monoxide and hydrogen as a synthesis raw material gas obtained by reforming a gas containing hydrocarbons with a reformer, and subjecting the synthesis raw material gas to a catalytic reaction. It is characterized in that the gas is prepared by the following steps (a) to (e). (I)
The steps (e) to (e) are steps of (a) separating and recovering carbon dioxide generated in the dimethyl ether production step, and then circulating the recovered carbon dioxide to obtain circulating carbon dioxide; ) A step of preparing coal-bed methane containing air, (c) a step of preparing pure oxygen or air as required, and (d) separating and recovering unreacted gas generated in a process of producing dimethyl ether, and then reforming. And a heat source for the reformer, and
(E) mixing the circulating carbon dioxide obtained in (b) above, the coalbed methane prepared in (b) above, and the pure oxygen or air prepared in (c) above, and then obtaining In this step, the mixed gas is supplied to a reformer, and the mixed gas is reformed to prepare a synthesis raw material gas. Next, the present invention will be described with reference to the drawings. FIG. 1 shows a flow sheet of an example of an apparatus for producing dimethyl ether for carrying out the method of the present invention.
This manufacturing apparatus includes a reactor R1 for DME synthesis, a reformer R2 for preparing a synthesis raw material gas 2 ', a methanol / water separator S1, and an unreacted gas separator S
2 and a CO ₂ separator S3. This manufacturing apparatus is significantly different from the flow sheet of the conventional manufacturing apparatus shown in FIG. 2 in the following two points. That is, CO
CO ₂ 8b flowing out from the ₂ separator S3 'was collected without discarding circulating the reformer R2, and recycle gas 7 containing N ₂ flowing out from the unreacted gas separator S2' to the reactor R1 Without circulation, reformer R2
To be used as a heat source of the reformer R2. Is for the effective use of CO _2, which results in the effective use of the raw material carbon resources. This is for avoiding the accumulation of N ₂ in the dimethyl ether synthesis system and for effectively utilizing the recycled gas 11 ′ containing unreacted CO and H ₂ as a heat source for the reformer R 2. The coalbed methane 12 ', pure oxygen or air 13' if necessary, and the circulating carbon dioxide 8b 'are mixed, and the reforming mixed gas 14' is supplied to the reformer R2. In the reformer R2, the coalbed methane 12 ′ is converted into H ₂ and C by the following reactions (6) and (7).
It is reformed to O. CH ₄ + (１ ／) O ₂ → 2H ₂ + CO ---------------- (6) CH ₄ + CO ₂ → 2H ₂ + 2CO -------------- (7) However, the circulating carbon dioxide 8b 'is generated in a dimethyl ether synthesis line. The synthesis raw material gas 2 ′ reformed in the reactions (6) and (7) is an example of a conventional reforming reaction of a saturated hydrocarbon gas with water vapor, and the H ₂ / CO molar concentration of the gas obtained in the reaction (5) is H ₂ / CO significantly smaller than the value of the ratio and close to 1
It can be seen that it has a molar ratio. CH ₄ + H ₂ O → 3H ₂ + CO (5) Note that N ₂ contained in coalbed methane 12 ′ is an unreacted gas Remains in the synthesis raw material gas 2 ′. The reaction (7) is an endothermic reaction, and the energy of the recycled gas 7 'replenishes the heat source of the reformer R2. As for the use of the unreacted gas, since the reformer is usually operated at a temperature of about 1000 ° C., both the raw material gas and the recycle gas are used as heat sources for raising the temperature to this temperature. Reaction (6) is an exothermic reaction, although CO ₂
When a large amount of is reformed, since the reaction (7) is an endothermic reaction, the entire reformer becomes an endothermic reaction,
External heat supply is required. The heat source. As described above, the H ₂ / C of the synthesis raw material gas 2 ′ is
Since the O molar concentration ratio approaches 1 and is optimized as compared with the conventional method, even if N ₂ is contained in the synthesis raw material gas, the CO conversion rate is improved. The raw material gas 2 'is supplied from the bottom of the reactor R1. The main components of the synthesis source gas 2 ′ are CO, H ₂ and N ₂ . The synthesis raw material gas 2 ′ adjusted to a predetermined H ₂ / CO molar concentration ratio enters the reactor R 1, where dimethyl ether and CO ₂ , which are reaction products generated by the reactions (1) to (3), and the reaction intermediate It becomes methanol and water as a body, and further, each part of carbon monoxide and hydrogen as unreacted gas, and the entire amount of nitrogen remain, and becomes a reaction product gas 3 '. Next, the reaction product gas 3 ′ enters the methanol / water separator S1, where methanol and water are separated into a reaction product gas 5 ′. Reaction product gas 5 'then goes into DME · CO ₂ separator S2, dimethyl ether and CO ₂ is liquefied and separated. Recycle gas 7 ', which is an unreacted gas from which dimethyl ether and CO ₂ have been separated, is circulated and used as a heat source for reformer R2. On the other hand, dimethyl ether and CO ₂ 6 ′
Is CO ₂ 8b 'enters ₂ separator S3 are separated. CO ₂
8b 'is circulated to form circulating carbon dioxide, mixed with coalbed methane 12' and, if necessary, pure oxygen or air 13 ', then enters the reformer R2 to be used as the synthesis feed gas 2'. Dimethyl ether flowing out of the separator S3 is recovered as a product. The type of the reformer R2 and the reforming conditions may be performed according to a conventional method, and need not be special. The type of the reactor R1 may be any of a fixed bed type, a fluidized bed type and a slurry bed type. In particular,
In the slurry bed type, the temperature inside the reactor is uniform,
It is desirable because there are few by-products. As for the catalyst, a methanol synthesis catalyst and a methanol dehydration catalyst are used, and an aqueous shift reaction catalyst is appropriately added in order to proceed with the above-mentioned reactions (1) to (3) to synthesize DME. These catalysts are mixed and used. As the methanol synthesis catalyst, copper oxide-zinc oxide, zinc oxide-chromium oxide, copper oxide-zinc oxide / chromium oxide, copper oxide-zinc oxide / alumina, etc., which are usually used industrially, are used. As a methanol dehydration catalyst, acid-base catalysts such as γ-alumina, silica, silica
Alumina, zeolite, or the like is used. Here, as the metal oxide component of the zeolite, oxides of alkali metals such as sodium and potassium, and alkaline earth oxides such as potassium and magnesium 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 both a methanol dehydration catalyst and a water gas shift catalyst. The mixing ratio of the above three catalysts does not need to be particularly limited, and may be appropriately selected according to the type of each component or reaction conditions. However, the methanol dehydration catalyst is usually about 0.1 to 5 and preferably about 0.2 to 2 with respect to the methanol synthesis catalyst 1 in terms of weight ratio, and the water gas catalyst is 0.1 to 0.2.
About 2 to 5, preferably about 0.5 to 3 are mixed.
When the methanol synthesis catalyst and the water gas shift catalyst are made of the same substance, and the methanol synthesis catalyst also serves as the water gas shift catalyst, the total amount of both catalysts is used. Regarding the form of the catalyst, when a slurry bed type reactor is used, the average particle size is 300 μm or less, preferably 1 to 200 μm, more preferably 10 to 150 μm.
What is crushed to the extent is good. In order to use it more effectively, the above-mentioned mixed powder is appropriately compacted and molded, and pulverized again,
Use the one prepared to the above particle size. When a slurry bed reactor is used, the medium oil must maintain a stable 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 can be appropriately determined depending on the type of the solvent, the reaction conditions, and the like.
About 1 to 50% by weight based on the solvent is desirable. As the reaction conditions in the slurry bed type reactor, the reaction temperature is preferably in the range of 150 to 400 ° C.,
In particular, the temperature is 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 decreases. The reaction pressure is 1
Within the range of 0 to 300 Kg / cm ² G, particularly preferably 2
The range is preferably from 0 to 70 Kg / cm ² G. Reaction pressure is 1
0 kg / cm ² less the conversion of CO is less than G, whereas if greater than 300 Kg / cm ² G, except that the reactor becomes a special, since it takes a great deal of energy for Noborinetsu economic Not. The space velocity (the supply rate of the raw material gas in a standard state per kg of the catalyst) is 100 to 500.
00Nl / kg · h is desirable, especially 500-3000
Nl / kg · h is desirable. Space velocity is 50,000Nl
/ Kg · h, the conversion rate of CO decreases,
On the other hand, if it is less than 100 Nl / kg · h, the reactor becomes extremely large and is not economical. Thus, the composition of the reaction product gas 3 'obtained in the reactor R1 is DME: 5 to 30 vol.
_{2:. 5~30vol%, CO:} . 0~50vol%, H 2: 0
_{. ~50vol%, CH 3 OH:} . 0~10vol%, H 2 O:
_{. 0~10vol%, N 2:.} 0~70vol%, and Others:
It is about 10 vol.% Or less. As described above, according to the present invention,
Coalbed methane is reformed with oxygen contained in itself, pure oxygen or air if necessary to prepare synthesis gas,
Since dimethyl ether can be produced from this synthesis gas, and the molar ratio of hydrogen and carbon monoxide in the synthesis gas supplied to the dimethyl ether synthesis reactor is optimized,
A revolutionary method has been developed in which large feed conversions can be obtained despite the fact that the synthesis gas contains nitrogen. Furthermore, since the carbon dioxide generated in the dimethyl ether synthesis line is recycled without being discarded and reformed to be a part of the synthesis gas, it contributes to prevention of environmental destruction and can effectively utilize carbon resources. .
Further, dimethyl ether can be produced at low cost because coalbed methane can be used as a main raw material.
The present invention can provide such a method for producing dimethyl ether, and has an industrially useful effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow sheet showing an example of a production apparatus for carrying out the method for producing dimethyl ether of the present invention. FIG. 2 is a flow sheet showing an example of a production apparatus for carrying out a conventional method for producing dimethyl ether. [Description of Signs] 1 Makeup gas line 1 'Makeup gas 2 Synthetic material gas line 2' Synthetic material gas 3 Reaction product gas line 3 'Reaction product gas 4 Methanol / water line 4' Methanol and water 5 Reaction product gas line (Including DME, CO ₂ ) 5 ′ reaction product gas (including DME, CO ₂ ) 6 DME / CO ₂ line 6 ′ DME and CO ₂ 7 recycling gas line (including N ₂ ) 7 ′ recycling gas (including N ₂ ) 8a CO ₂ waste line 8a'CO ₂ 8b CO ₂ recycling line 8b'CO ₂ 9 DME line 9'DME 10 Purge line 10'Purge gas 11 Recycle gas line 11'Recycle gas (including N ₂ gas) 12 Coal bed Methane line 12'Coal bed Methane 13 Pure oxygen or air line 13 'Pure oxygen or air 14 Reforming mixed gas line 14' Reforming mixing Scan 15 hydrocarbon line 15 'hydrocarbon 16 steam line 16' steam R1 reactor (DME synthesis) R2 reformer S1 methanol-water separator S2 DME-CO ₂ separator S3 CO ₂ separator

Continuation of the front page (72) Inventor Keiji Tomura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-10-182533 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) C07C 41/01 C07C 41/09 C07C 43/04

Claims (1)

(57) [Claim 1] A mixed gas containing at least carbon monoxide and hydrogen obtained by reforming a gas containing hydrocarbons with a reformer is used as a synthesis raw material gas. A method for producing dimethyl ether by a catalytic reaction of a gas, wherein the synthesis raw material gas is prepared by the following steps (a) to (e). (A) separating and recovering carbon dioxide generated in the dimethyl ether production process, and then circulating the recovered carbon dioxide to obtain circulating carbon dioxide; (b) preparing coal-bed methane containing air (C) a step of preparing pure oxygen or air if necessary; (d) separating and collecting unreacted gas generated in the dimethyl ether production step, and then supplying the unreacted gas to the reformer, And (e) the circulating carbon dioxide obtained in (a), the coalbed methane prepared in (b), and the pure oxygen or air prepared in (c). Mixing, and then supplying the mixed gas thus obtained to the reformer and reforming the mixed gas to prepare the synthesis raw material gas.