JP4706812B2 - Method for producing dimethyl ether - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing dimethyl ether from hydrocarbons, and more particularly to a method for producing fuel grade dimethyl ether which is improved from the viewpoint of environmental protection and energy saving.
[0002]
[Prior art]
Dimethyl ether is used as a solvent in the chemical industry, but recently, its use is attracting attention as a new fuel for diesel vehicles, fuel cells, and city gas. As a method for producing fuel grade dimethyl ether, for example, Japanese Patent No. 2849475 describes a method of producing dimethyl ether using a catalyst having activity in both methanol synthesis and methanol dehydration of synthesis gas containing hydrogen and carbon oxide. Has been.
[0003]
[Problems to be solved by the invention]
In the method for producing dimethyl ether described in Japanese Patent No. 2849475, an unreacted synthesis gas and a reaction gas containing methanol, dimethyl ether and product water can be obtained from a methanol / dimethyl ether reactor. However, since the boiling point of dimethyl ether is low, it is condensed. A low temperature heat source is required for separation.
Further, in the methanol synthesis, an acidic substance having a low boiling point such as methyl formate is generated and circulated in the reaction system. Acidic substances with a low boiling point such as methyl formate are difficult to separate from dimethyl ether and produced water, are corrosive, and require environmental measures if mixed into wastewater.
Furthermore, when producing synthesis gas, it is necessary to supply water vapor in an amount of 0.6 to 3 times that of the raw material hydrocarbon. However, fuel grade dimethyl ether is often produced from inexpensive natural gas. In particular, water is precious in countries that produce natural gas.
An object of the present invention is to solve the above-mentioned problems in producing fuel grade dimethyl ether and to provide a method for producing fuel grade dimethyl ether which is improved from the viewpoint of environmental protection and energy saving.
[0004]
[Means for Solving the Problems]
As a result of diligent investigations on the production method of dimethyl ether having the above-mentioned problems, the inventors separated methanol synthesis reaction and its dehydration reaction, and synthesized and produced dimethyl ether from crude methanol from which low-boiling substances had been removed in advance by dehydration reaction. It has been found that dimethyl ether improved from the viewpoint of environmental protection and energy saving can be produced by humidifying the hydrocarbon of the raw material with water, and the present invention has been achieved.
[0005]
That is, the present invention comprises (a) a synthesis gas production process in which a hydrocarbon is reacted with water vapor or water vapor and oxygen to generate a synthesis gas mainly composed of hydrogen, carbon monoxide and carbon dioxide, and (b) a methanol synthesis catalyst. A methanol synthesis step for reacting the synthesis gas and recovering the generated crude methanol in liquid form; (c) separating the dissolved gas and low-boiling components from the top of the tower by distillation of the recovered crude methanol; A methanol distillation step for separating from the bottom of the column, (d) a dimethyl ether production step for producing dimethyl ether from the separated aqueous methanol, and (e) a dimethyl ether distillation step for separating the obtained dimethyl ether, produced water and unreacted methanol by distillation. (E) The dimethyl product is characterized in that the produced water separated in step (e) is used for humidifying the hydrocarbon of the raw material. A method for producing ether, and (a) a synthesis gas production process in which a hydrocarbon is reacted with water vapor or water vapor and oxygen to generate a synthesis gas mainly composed of hydrogen, carbon monoxide and carbon dioxide, (b) methanol synthesis A methanol synthesis step of reacting the synthesis gas on a catalyst and recovering the generated crude methanol in liquid form; (c) separating the dissolved gas and low-boiling components from the tower top by distillation of the recovered crude methanol; (b ) A methanol distillation step for separating methanol having a concentration higher than the methanol recovered in the step from the middle stage of the distillation column, (d) a dimethyl ether production step for producing dimethyl ether from the separated methanol, and (e) the obtained dimethyl ether and product water. And a dimethyl ether distillation step in which unreacted methanol is separated by distillation, and separated in step (e). A method for producing dimethyl ether, characterized by using the generated water humidification of the hydrocarbon feedstock.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
As the raw material hydrocarbon in the present invention, gaseous natural gas mainly composed of methane, liquid LPG, naphtha, light oil and the like are used.
In the synthesis gas production process (a), gaseous hydrocarbon or liquid hydrocarbon vaporized and steam or steam and oxygen are reacted in a reformer at 800 to 1050 ° C. in the presence of a nickel-based catalyst. A synthesis gas containing carbon monoxide and carbon dioxide as the main components is produced.
In the methanol synthesis step (b), a copper catalyst is usually used, and crude methanol is produced from synthesis gas at a pressure of 0.5 to 20 MPa and a temperature of 200 to 300 ° C.
[0007]
In the methanol distillation step (c), crude methanol from the synthesis step is supplied to the distillation column, and organic impurities contained in the crude methanol, that is, organic compounds lower than the boiling point of methanol (low-boiling components) and dissolved gas are separated by distillation. Then, methanol and water from the bottom of the column and crude methanol containing an organic compound (high boiling point component) higher than the boiling point of methanol are subjected to a dehydration reaction (dimethyl ether production step (d)). Since an acidic substance is contained in the crude methanol from the synthesis step, it is preferable to add an alkali.
In addition, by extracting a fraction mainly composed of methanol from the middle part of the distillation column and mainly extracting water and high-boiling components from the bottom of the column, methanol having a concentration higher than the methanol recovered in step (b) It can be separated from the stage. Methanol extracted from the middle stage may be subjected to a dehydration reaction.
[0008]
In the dimethyl ether production step (d), a known dehydration catalyst such as γ-alumina catalyst or silica-alumina catalyst can be used. The reaction pressure is 0.5 MPa or more, preferably 1 to 2 MPa. If the reaction pressure is too low, it is difficult to condense dimethyl ether, and it is necessary to condense with cold heat, resulting in an increase in apparatus cost and energy consumption. The dehydration reaction temperature is usually 250 to 400 ° C., and is determined by the catalyst used.
[0009]
In the dimethyl ether distillation step (e), two distillation columns are used, and the product dimethyl ether is separated from the top of the first distillation column, and unreacted methanol is separated from the top of the second distillation column, and water produced by the dehydration reaction is separated from the bottom. It is preferable to separate. In the first distillation column, the pressure at the top of the column is 1-2 MPa in order to separate the product dimethyl ether with air cooling or cooling water, and the pressure at the bottom of the second distillation column is 0 because a heat source such as low-pressure steam is used. .About 1 to 0.2 MPa. Unreacted methanol separated in the second distillation column is recycled in the dimethyl ether production step (d).
[0010]
In the present invention, water produced by the dehydration reaction of methanol is used for humidifying the hydrocarbon of the raw material. There are various types of humidification methods, such as a spray method, a scrubber having a packed bed, and a heat exchange type, and there is no particular limitation, but a heat exchange type is preferred in order to use the generated water for humidification using a heat source as low as possible. . The product water separated in the dimethyl ether distillation step (e) contains trace amounts of organic impurities, which may affect the gas reforming catalyst in the synthesis gas production step (a). It is preferable to further humidify the condensed water in the synthesis gas generated in the synthesis gas production step after humidifying the raw material hydrocarbons using the produced water.
[0011]
In the present invention, in the production of dimethyl ether, the separation of dimethyl ether is facilitated by separating the methanol synthesis reaction and the dehydration reaction. Therefore, condensation separation with an air cooler or cooling water is possible, and no cooling is required. Consumption is reduced. In addition, a large methanol rectification tower is required when rectified methanol is subjected to a dehydration reaction as in the case of dimethyl ether production by a conventional methanol dehydration method. By manufacturing the system, a huge methanol refining tower is not necessary, so that the apparatus cost and energy consumption are reduced. Furthermore, by removing low-boiling substances in the crude methanol and then subjecting it to a dehydration reaction, the influence of methanol on the dehydration reaction is avoided, the production of organic impurities that adversely affect the apparatus is reduced, and the dehydration reaction is stabilized for a long time. Can be done. In addition, by humidifying the raw material hydrocarbons with water generated by the dehydration reaction, the amount of valuable water used in natural gas producing countries is reduced and wastewater containing trace amounts of organic impurities is eliminated. No drainage measures are required.
Therefore, fuel grade dimethyl ether can be produced very advantageously by the method of the present invention in a country where natural gas is produced.
[0012]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples.
[0013]
Example 1
The case where this invention is applied to the dimethyl ether manufacturing apparatus of 5000T / D scale based on the flow of FIG. 1 is shown. In FIG. 1, the raw material hydrocarbon (natural gas) is introduced from the flow path 1 and mixed with the recycle hydrogen (flow path 3) via the flow path 2. The raw material natural gas preheater 4 is preheated to 400 ° C. by exchanging heat with the combustion exhaust gas (flow path 67), and then desulfurized in the hydrogenation reactor 5 and the sulfur adsorption tower 6. The desulfurized raw material natural gas (channel 7) is humidified in the saturator 9, but the saturator feed water (channel 10) includes synthesis gas condensed water (channel 25) and waste water from the methanol rectifier (channel). 64) is used.
After the humidified natural gas (channel 12) is mixed with process steam (channel 13) so that the molar ratio of steam to carbon is 1.8, it is preheated to 630 ° C in the primary reformer inlet gas preheater 14 Then, it is introduced into the reaction tube of the primary reforming furnace 16. Off-gas (flow path 37 and flow path 44) from the natural gas synthesis process is used as fuel for the primary reforming furnace (flow path 65), and combustion air is introduced from the flow path 66.
The primary reforming furnace outlet gas (flow path 17) is further reformed in the secondary reforming furnace 19. The secondary reforming furnace 19 is a partial oxidation reactor using oxygen (flow path 18), and the outlet temperature is 1000 to 1050 ° C. The gas that has exited the secondary reforming furnace is recovered in the heat recovery system 21 as a heat source for high-pressure steam and distillation processes, cooled to room temperature with a synthesis gas cooler 22, and then synthesized gas ( Separated into a flow path 24) and synthesis gas condensed water (flow path 25).
In the methanol synthesis step, the synthesis gas (flow path 24) is pressurized to about 10 MPa by the synthesis gas compressor 26, mixed with the unreacted circulation gas (flow path 29), preheated by the synthesis tower inlet gas preheater 31, Methanol is synthesized in the methanol synthesis tower 32. The synthesis tower outlet gas (flow path 33) is cooled to room temperature by the synthesis tower inlet gas preheater 31 and the cooler 34, and is separated into unreacted gas and crude methanol (flow path 36) by the high pressure separator 35. Most of the unreacted gas is circulated and reused as a methanol synthesis raw material, but a part is purged from the flow path 37 to adjust the system pressure. Crude methanol (flow path 36) removes part of the dissolved gas by the low-pressure separator 38, and is introduced into the crude methanol tank 45 via the flow path 39. Since the low-pressure separator vent gas (flow path 40) contains some methanol, it is recovered by being absorbed into pure water (flow path 42) by the vent scrubber 41, and then passed through the flow path 43 to the crude methanol tank 45. Introduce.
Dissolved gas and low boiling impurities in the crude methanol are separated in the initial flow column 49. In order to facilitate separation by increasing the relative volatility of low boiling impurities, methanol rectification tower drainage (flow path 64) is added from flow path 47. Further, since it contains an acidic component, caustic soda (flow path 48) is added to prevent corrosion. The removed dissolved gas and low boiling impurities are discharged from the flow path 52 and used as fuel for the reforming furnace 16 and the like.
Crude methanol (channel 51) from which dissolved gas and low-boiling components have been removed is mixed with recycled methanol (channel 53), evaporated and heated to 300 ° C in a methanol evaporator 54, and then introduced into a dehydration reactor 56. Synthesize dimethyl ether. The amount of water contained in the crude methanol in the flow path 51 differs depending on the method used for the synthesis gas production process, but when the two-stage reforming method is used as in the example, it is about 21 wt%. Become.
Crude dimethyl ether (flow path 57) from dehydration reactor 56 is rectified by dimethyl ether rectification column 58 to become product dimethyl ether (flow path 60). On the other hand, the mixture of methanol and water at the bottom of the column (channel 61) is separated by the methanol rectification column 62, and the methanol (channel 53) from the top of the column is recycled and reused as a dimethyl ether synthesis raw material. Water containing a small amount of organic impurities (channel 64) is reused as process water for the first distillation column 49 and saturator supply water.
[0014]
Example 2
The synthesis gas production process and the methanol synthesis process are the same as in Example 1. However, in the first distillation column 49, separation into methanol (channel 51) having a low water concentration and waste water (channel 51a) containing a small amount of organic impurities was performed. . By doing so, it is possible to make the devices in the subsequent processes compact and to reduce the required energy. Waste water containing a small amount of organic impurities (flow path 51a) is reused together with the waste water (flow path 64) of the methanol rectifying column 62 for saturator supply water or the like.
[0015]
【The invention's effect】
According to the dimethyl ether production method of the present invention, the separation of dimethyl ether is easy, and a huge methanol purification tower is not required, so that the apparatus cost and energy consumption are reduced. Further, since the low boiling point substance in the crude methanol is removed, the dehydration reaction can be stably performed for a long time without adversely affecting the reaction and the apparatus. Furthermore, by humidifying the raw material hydrocarbons with water generated by the dehydration reaction, the amount of water used is reduced and there is no waste water containing a small amount of organic impurities, so that no drainage measures for environmental conservation are required.
Therefore, fuel grade dimethyl ether can be produced very advantageously in countries producing natural gas.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment of the present invention. Example 1
FIG. 2 is a schematic view showing an example of an embodiment of the present invention. (Example 2)
[Explanation of symbols]
1: Natural gas
2: Raw natural gas
3: Recycled hydrogen
4: Raw material natural gas preheater
5: Hydrogenation reactor
6: Sulfur adsorption tower
7: Desulfurized natural gas
8: Desulfurized natural gas preheater
9: Saturator
10: Saturator supply water
11: Circulating water
12: humidified natural gas
13: Process steam
14: Primary reformer inlet gas preheater
15: Primary reformer inlet gas
16: Primary reforming furnace
17: Primary reformed gas
18: Oxygen
19: Secondary reforming furnace
20: Secondary reformer outlet gas
21: Heat recovery system
22: Syngas cooler
23: Syngas gas-liquid separator
24: Syngas
25: Syngas condensed water
26: Syngas compressor
27: Makeup gas
28: Unreacted circulating gas
29: Circulator
30: Methanol synthesis tower inlet gas
31: Methanol synthesis tower inlet gas preheater
32: Methanol synthesis tower
33: Methanol synthesis tower outlet gas
34: Gas cooler at the outlet of methanol synthesis tower
35: High pressure separator
36: Crude methanol
37: Purge gas
38: Low pressure separator
39: Crude methanol
40: Low pressure separator vent gas
41: Vent gas scrubber
42: Pure water
43: Recovered methanol
44: Vent gas
45: Crude methanol tank
46: Crude methanol supplied to the first distillation column
47: First distillation tower water
48: Caustic soda
49: First tower
50: First tower condenser
51: Low boiling removal crude methanol
52: First tower off-gas
53: Recycled methanol
54: Methanol evaporator
55: Dehydration reactor inlet gas
56: Dehydration reactor
57: Crude dimethyl ether
58: Dimethyl ether fractionator
59: Dimethyl ether fractionator condenser
60: Product dimethyl ether
61: Methanol rectification column supply liquid
62: Methanol fractionator
63: Methanol fractionator condenser
64: Methanol fractionator drain
65: Primary reformer fuel
66: Combustion air
67: Combustion exhaust gas

Claims (3)

(a) a synthesis gas production process in which a hydrocarbon is reacted with water vapor or water vapor and oxygen to generate a synthesis gas mainly composed of hydrogen, carbon monoxide and carbon dioxide;
(b) a methanol synthesis step of reacting the synthesis gas on a methanol synthesis catalyst and recovering the generated crude methanol in a liquid state;
(c) a methanol distillation step in which the recovered crude methanol is distilled to separate dissolved gas and low-boiling components from the top of the tower, and water-containing methanol is separated from the bottom of the tower;
(d) a dimethyl ether production process for producing dimethyl ether from the separated aqueous methanol, and
(e) comprising a dimethyl ether distillation step in which the obtained dimethyl ether, product water and unreacted methanol are separated by distillation,
(e) A method for producing dimethyl ether, wherein the produced water containing organic impurities separated in the step is used for humidifying a hydrocarbon of a raw material. (a) a synthesis gas production process in which a hydrocarbon is reacted with water vapor or water vapor and oxygen to generate a synthesis gas mainly composed of hydrogen, carbon monoxide and carbon dioxide;
(b) a methanol synthesis step of reacting the synthesis gas on a methanol synthesis catalyst and recovering the generated crude methanol in a liquid state;
(c) The recovered crude methanol is distilled to separate dissolved gas and low-boiling components from the top of the column. (b) A methanol distillation step of separating methanol having a concentration higher than the methanol recovered in the step from the middle stage of the distillation column.
(d) a dimethyl ether production process for producing dimethyl ether from the separated methanol, and
(e) comprising a dimethyl ether distillation step in which the obtained dimethyl ether, product water and unreacted methanol are separated by distillation,
(e) A method for producing dimethyl ether, wherein the produced water containing organic impurities separated in the step is used for humidifying a hydrocarbon of a raw material. The method for producing dimethyl ether according to claim 1 or 2, wherein the hydrocarbon is humidified with the produced water separated in step (e) and then humidified with condensed water in the synthesis gas generated in step (a).

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