JP2001039911A - Production of methanol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for minimizing the amount of organic substances discharged to the atmosphere by recovering dissolved gas, organic impurities and accompanied methanol in crude methanol discharged from an initial boiling tower. SOLUTION: This method for producing methanol comprises the following processes: (a) reacting hydrocarbons with steam to generate synthesis gas; (b) recovering crude methanol in a liquid state which is formed by reacting the synthesis gas; (c) separating a mixed gas comprising dissolved gas, low boiling point component and methanol accompanied by the low boiling point component from the recovered crude methanol by distillation in an initial boiling tower 2 first and discharging the mixed gas from the overhead part of the tower 2, followed by feeding the residue into a rectifying tower where the residue is separated into purified methanol, high boiling component and water by distillation. The mixed gas is scrubbed in a flushing tower 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing methanol from hydrocarbons, and more particularly to a method for reducing the amount of gas discharged from a methanol producing apparatus and improving methanol from the viewpoints of environmental protection, air pollution prevention and energy saving. Related to manufacturing method.

[0002]

2. Description of the Related Art As a method for producing methanol from hydrocarbons, for example, as disclosed in Japanese Patent Publication No. 3-31694, generally, (a) reacting hydrocarbons with water vapor to produce hydrogen, A synthesis gas production step of generating a synthesis gas containing carbon oxides and carbon dioxide as main components, (b) a synthesis step of reacting the synthesis gas on a methanol synthesis catalyst, and recovering the generated crude methanol in a liquid state, (c) From the recovered crude methanol, first, in a first distillation column, a mixed gas containing a dissolved gas, a low-boiling component and methanol accompanying the low-boiling component is separated, and the mixed gas is discharged from the top of the first distillation column. Then, the remaining components are introduced into a rectification column, in which a distillation step of separating the residual components into purified methanol, high-boiling components and water is performed.

In the synthesis gas production process, usually, it is necessary to supply steam having about three times the number of carbon atoms of the raw material hydrocarbon, and a large amount of steam is required in the production of methanol. For this reason, the steam generated by using the heat generated in each manufacturing process is collected, and the collected steam is used in the synthesis gas manufacturing process. In the synthesis process, methanol and hydrogen are produced from hydrogen and carbon monoxide in the synthesis gas, and methanol and water are produced from hydrogen and carbon dioxide. This water is contained in the crude methanol along with the methanol.

[0004] In the distillation step, the crude methanol produced in the above synthesis step is purified using distillation towers such as an initial distillation tower, a rectification tower and a recovery tower, and facilities such as a reboiler and a condenser. In the first distillation column, organic impurities contained in the crude methanol, that is, organic compounds (low-boiling components) lower than the boiling point of methanol and dissolved gases are concentrated and separated by distillation.
The concentrated organic compound and dissolved gas are discharged from the final condenser to the atmosphere through an air discharge pipe.

[0005]

The above purification method by distillation is an effective method for removing impurities in crude methanol, but the final condenser completely separates methanol from low-boiling components. Since it is difficult to discharge the organic compound or dissolved gas out of the system, methanol is also discharged out of the system together with the exhaust gas, resulting in a loss of methanol. In addition, since a small amount of organic substances is emitted into the atmosphere, there is a risk of air pollution. From the viewpoint of air pollution prevention, early treatment of this organic substance treatment is awaited. An object of the present invention is to minimize the amount of organic substances released into the atmosphere by recovering dissolved gas, organic impurities and methanol accompanying these in crude methanol discharged from a discharge pipe at the top of the first distillation column. It is an object of the present invention to provide a method for producing methanol that can be used effectively and efficiently use the recovered material.

[0006]

Means for Solving the Problems As a result of diligent studies on a methanol distillation apparatus having the above-mentioned problems, the present inventors have found that when purifying crude methanol in an initial distillation column at normal pressure,
The organic impurities and methanol released along with the dissolved gas discharged from the first distillation tower are efficiently washed in the washing tower, and the washing liquid is recovered as a raw material steam and a hydrocarbon source in the synthesis gas production process. It has been found that methanol and organic impurities discharged from the distillation column can be reduced and effectively recovered as a process raw material. The present invention has been completed based on such findings.

That is, the present invention provides: (a) a synthesis gas producing step of reacting a hydrocarbon with water vapor to generate a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide as main components;
(b) reacting the above synthesis gas on a methanol synthesis catalyst,
A synthesis step of recovering the generated crude methanol in a liquid state, and (c) first separating a dissolved gas, a low-boiling component, and a mixed gas containing methanol accompanying the low-boiling component in the first distillation column from the recovered crude methanol. Then, the mixed gas is discharged from the top of the first distillation column, and then the residual components are introduced into the rectification column, where the residual components are separated into purified methanol, high-boiling components and water. The present invention also provides a method for producing methanol, which comprises washing the mixed gas in a washing tower.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, gaseous natural gas containing methane as a main component, liquid LPG, naphtha, light oil and the like are used as hydrocarbons as raw materials. In the synthesis gas production step (a), a gaseous hydrocarbon or a liquid hydrocarbon is vaporized and steam is passed through a reforming furnace.
The reaction is performed at 800 to 1000 ° C. in the presence of a nickel-based catalyst to produce a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide as main components. In the reaction in the synthesis step (b), a copper-based catalyst is usually used as a methanol synthesis catalyst,
By reacting the above synthesis gas under the conditions of a pressure of 50 to 200 kg / cm ² G and a temperature of 200 to 300 ° C., crude methanol is produced. Note that a methanol catalyst other than the copper catalyst, for example, a zinc catalyst, a chromium catalyst, or the like may be used.
The pressure and temperature conditions are not limited to the above ranges, and may be appropriately selected.

In the distillation step (c), the crude methanol obtained in the synthesis step is supplied to the first distillation column, and organic impurities contained in the crude methanol, that is, an organic compound having a boiling point lower than the boiling point of methanol (low boiling point component) ) And the dissolved gas are separated from the crude methanol by distillation, and methanol and water remaining at the bottom of the first distillation column, and organic impurities including organic acids, that is, organic compounds having a boiling point higher than methanol (high-boiling components) are rectified. Feed to tower. In the rectification column, purified methanol is separated from the top of the column, and high-boiling components and water are separated from the side and bottom of the column. Separately, a recovery tower is installed, and the components separated from the side and bottom of the rectification tower are distilled in the recovery tower to recover methanol.

According to the present invention, in the above-mentioned methanol production apparatus, the gas separated from the top of the first distillation column in the distillation step (c) is washed by a washing tower. As a washing tower for washing gas separated from the top of the first distillation tower,
Generally, a packed tower or a spray tower is used, but it is preferable to use a washing tower having a spray and a packed layer for diffusing gas and washing water separated from the first distillation tower. By using such a washing tower, the concentration of methanol in the gas discharged from the washing tower can be reduced to 20 ppm or less, and the amount of organic substances released to the atmosphere can be significantly reduced.

In the present invention, the washing liquid containing the low-boiling component and methanol discharged from the washing tower is brought into contact with the raw material hydrocarbon and evaporated to humidify the low-boiling component. And a washing solution containing methanol are introduced into the synthesis gas production step (a). In a process water evaporator in which the raw material hydrocarbon is brought into contact with the washing liquid and the washing liquid is evaporated, high boiling components and water separated from the side and bottom of the rectification column are treated in addition to the washing liquid. You can also. By using such a process water evaporator, methanol and organic impurities discharged from the distillation column can be effectively recovered as process raw materials, so that gas discharged from the distillation column to the atmosphere can be reduced. . Also, the condensed water separated in the synthesis gas production process can be treated in the process water evaporator,
The amount of water vapor used in the synthesis gas production process can be reduced.

As a heat source of the process water evaporator, a high-temperature synthesis gas or a combustion gas generated from a reforming furnace in a synthesis gas production process, a methanol synthesis reactor outlet gas generated in a synthesis process, or the like can be used. . Using a packed tower or a spray tower also for the process water evaporator, the process water as described above is circulated to a heat exchanger installed outside, and the process water can be effectively recovered by a packed tower evaporator. If a heat exchange type evaporator is used and heating is performed using a high-temperature gas, process water can be more efficiently evaporated. At this time, it is necessary to blow a part of the process water in order to avoid the influence of the process water concentration.However, heat exchange between the high-temperature blow wastewater from the process water evaporator and the cleaning solution containing the low boiling point component and methanol is performed. By doing so, the temperature of the wastewater from the process water evaporator is lowered, and the cleaning liquid containing the low boiling point component and methanol is heated before being introduced into another process water evaporator. The heat source used in the water evaporator can be reduced. By performing such heat exchange, it is possible to reduce energy consumed in the methanol production apparatus and also reduce cooling water. In the process water evaporator as described above, the washing liquid containing low-boiling components and methanol discharged from the washing tower, and the discharge liquid from the rectification tower,
Alternatively, by bringing the condensed water separated in the synthesis gas production step into contact with the hydrocarbons of the raw material, the hydrocarbons of the raw material are humidified and the amount of process steam is reduced, so that the thermal efficiency of the methanol production apparatus is improved. The humidified hydrocarbon is sent to the synthesis gas production step (a), mixed with a shortage of steam, and introduced into the reforming furnace.

[0013]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples.

Embodiment 1 A case where the present invention is applied to a 2500 T / D scale methanol production apparatus based on the flow of FIG. 1 will be described. As shown in FIG. 1, crude methanol from the synthesis process
Will be introduced. In the first distillation column 2, the crude methanol is separated into a dissolved gas, a mixed gas containing a low-boiling component and methanol accompanying the low-boiling component, and methanol, water, and a high-boiling component. The mixed gas is discharged and separated from the flow path 3 of the first fractionation tower, and methanol, water and high-boiling components are separated and introduced into the rectification tower from the flow path 4 at the bottom of the first distillation column 2. The low-boiling components and dissolved gas in the mixed gas discharged from the top of the first distillation column 2 are cooled by the condenser 5 in the cooling water 7.
And the uncondensed gas comprising the dissolved gas, the low-boiling component and methanol obtained by the cooling.
The water is sent to a washing tower 8 having a spray and a packed bed. In the washing tower 8, the uncondensed gas is washed by the washing water from the flow path 9, and the exhaust gas is released from the flow path 10 to the atmosphere.

The washing liquid containing low-boiling components and methanol discharged from the washing tower 8 to the flow path 11 is supplied from the flow path 11 to the heat exchanger.
The water is introduced into the process water evaporator 14 through the flow path 13 through the flow path 12. The process water evaporator 14 is a heat exchange evaporator,
Heat is exchanged with the high-temperature syngas introduced from 17 and discharged from the flow path 18 to be heated. In the process water evaporator 14,
The raw material hydrocarbon introduced from the flow path 15 is humidified, and the humidified hydrocarbon is discharged from the flow path 16, mixed with a shortage of steam, and introduced into the reforming furnace in the synthesis gas production process.
The humidification of the hydrocarbons is performed by the washing liquid discharged from the washing tower 8 and containing low-boiling components and methanol, or by the condensed water separated in the synthesis gas production step and introduced into the process water evaporator 14 from the flow path 21. You. Therefore, the hydrocarbon sent out from the flow path 16 to the reforming furnace contains the evaporated washing water and low-boiling components, methanol, and the like. In addition to saving water vapor for use, low boiling components and methanol in the cleaning liquid are used as raw materials, and the yield of hydrocarbons as raw materials is improved.

Among the components in the cleaning liquid supplied to the process water evaporator 14, those that have not evaporated are circulated to the process water evaporator 14 through a flow path 19 and reused. It is discharged from the flow path 20 as blow water to avoid it. By exchanging heat in the heat exchanger 12 between the high-temperature effluent and the cleaning liquid supplied to the process water evaporator 14, energy can be recovered and cooling water for cooling the effluent can be saved. Can be. When the above flow is applied to a 2500 T / D-scale methanol production apparatus, the amount of uncondensed gas supplied from the channel 6 to the washing tower 8 is about
500 Nm ³ / hr, the composition of which is 55% by volume of CO ₂ ,
35% by volume of methanol, 10% by volume of low boiling components and water. The uncondensed gas is introduced into a packed tower having a spray at the top of the tower, and washed with about 5 m ³ / hr of washing water, so that the methanol concentration in the washing tower exhaust gas discharged from the channel 10 is 20 ppm (based on volume). ), And the methanol in the uncondensed gas supplied to the washing tower 8 and the approximately
99.9% is recovered and can be used effectively as a raw material for methanol production. Further, by using the condensed water separated in the synthesis gas production process in the process water evaporator 14, the process steam can be reduced by 56 T / H (about 30%).

Example 2 An example in which the present invention is applied to a 2500 T / D scale methanol production apparatus based on the flow of FIG. 2 will be described. As shown in FIG. 2, crude methanol from the synthesis process
Will be introduced. In the first distillation column 32, the crude methanol is separated into a dissolved gas, a mixed gas containing a low-boiling component and methanol accompanying the low-boiling component, and methanol, water, and a high-boiling component. The mixed gas is discharged from the flow path and separated, and methanol, water and high-boiling components are separated from the flow path at the bottom of the first distillation column 32 and introduced into the rectification column. The low-boiling components and dissolved gas in the mixed gas discharged from the top of the first distillation column 32 are cooled by cooling water in the condenser 33, and the non-condensed gas obtained by cooling is composed of the dissolved gas, low-boiling components and methanol. The gas is sent to a wash tower 35 having a spray and packed bed. Channel 36 in the washing tower 35
The uncondensed gas is washed by the washing water introduced from the outside, and the exhaust gas is released from the flow path 37 to the atmosphere.

As shown in FIG. 2, the raw material hydrocarbon is humidified in two stages, a first process water evaporator 41 and a second process water evaporator 44. The first process water evaporator 41 is a direct cooling tower, is provided with an external heat exchanger 48, and is heated by high-temperature synthesis gas from the external heat exchanger 48. First process water evaporator 41
Is separated from the side and bottom of the rectification column
The high-boiling components and water introduced through 46 are brought into contact with the raw material hydrocarbons and evaporated to humidify the raw material hydrocarbons. High-temperature wastewater remaining after evaporating the high-boiling components and water is sent to the heat exchanger 39. The second process water evaporator 44 is a heat exchange evaporator, and is heated by exchanging heat with a high-temperature synthesis gas introduced from the flow path 49 and discharged from the flow path 50. In the second process water evaporator 44, the effluent from the washing tower 35 and the condensed water separated from the synthesis gas production step and introduced from the flow path 47 are treated. The washing liquid containing low-boiling components and methanol sent from the washing tower 35 is introduced into the second process water evaporator 44 from the flow path 38 via the heat exchanger 39.
At this time, in the heat exchanger 39, heat exchange is performed between the cleaning liquid containing the low-boiling component and methanol and the high-temperature wastewater sent from the first process water evaporator 41, and the cleaning liquid is heated.
The raw material hydrocarbon is introduced into the second process water evaporator 44 from the passage 43 through the first process water evaporator 41 from the passage 42, humidified and sent out from the passage 45, and mixed with the shortage of steam. Is introduced into the reforming furnace.

By finally humidifying the raw material hydrocarbons with the condensed water separated in the synthesis gas production process, the hydrocarbons introduced into the reforming furnace have the effect of being washed, and the reforming catalyst is Has a positive effect. First process water evaporator
The blow water from 41 and the second process water evaporator 44
After the heat is recovered by the heat exchanger 39 via 40, it is discharged. When the above flow is applied to a 2500 T / D-scale methanol production apparatus, the uncondensed gas supplied to the washing tower is the same as in Example 1.
The washing liquid containing low-boiling components and water sent from the washing tower 35 is separated from the condensed water (32 T / H) separated in the synthesis gas production process and from the side and bottom of the rectification tower. High boiling components and water (24 T / H) can be treated in a process water evaporator. Therefore, the methanol and the low-boiling components in the uncondensed gas supplied to the washing tower and the organic components from the rectification column are effectively used as raw materials for producing methanol, and the process steam is reduced to 5%.
6T / H (about 30%) can be saved.

[0020]

According to the present invention, the following effects are obtained by washing the gas discharged from the top of the first distillation column with a washing tower and using the washed water liquid for humidifying the hydrocarbons of the raw material. can get. (1) Almost all of methanol and organic compounds excluding carbon dioxide released from the first distillation column discharge pipe are recovered, which contributes to prevention of environmental pollution. (2) The washing liquid in which the organic substance introduced into the washing tower is dissolved is reused as a part of the process steam, and the organic substance is effectively used as a raw material hydrocarbon. (3) Washing liquid containing low-boiling components and methanol discharged from the washing tower, high-boiling components and water separated from the tower side and lower part of the rectification tower, and condensation separated in the synthesis gas production process By treating water in a process water evaporator, process water vapor is reduced and significant energy savings are achieved. (4) The amount of steam generated in the process water evaporator can be increased by exchanging heat between the cleaning liquid supplied to the process water evaporator and the blowdown water of the process water evaporator.

[Brief description of the drawings]

FIG. 1 is a flowchart of an initial distillation tower, a washing tower, and a process water evaporator in Example 1.

FIG. 2 is a flowchart of an initial distillation tower, a washing tower, and a process water evaporator in Example 2.

[Explanation of symbols]

 1: Crude methanol introduction flow path 2: Initial distillation tower 5: Condenser 8: Rinse tower 9: Wash water introduction flow path 10: Release gas discharge flow path 12: Heat exchanger 14: Process water evaporator 15: Raw material hydrocarbon Introducing channel 16: Humidifying hydrocarbon discharging channel 31: Crude methanol introducing channel 32: First distillation column 33: Condenser 35: Washing tower 36: Washing water introducing channel 37: Emission gas exhaust channel 39: Heat exchanger 41: First process water evaporator 42: Raw material hydrocarbon introduction channel 44: Second process water evaporator 45: Humidified hydrocarbon discharge channel

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C07B 61/00 300 B01J 23/74 321 (72) Inventor Masatoshi Yamaguchi 3500 Matsuhamacho, Niigata City, Niigata Mitsubishi (72) Inventor Kazuhiro Morita 2-5-1 Marunouchi, Chiyoda-ku, Tokyo In-house Sanshu Heavy Industries Co., Ltd. (72) Shuichi Miyamoto 2-5-1 Marunouchi, Chiyoda-ku, Tokyo F term (reference) in Mitsubishi Heavy Industries, Ltd.

Claims (6)

[Claims] 1. A synthesis gas production step of: (a) reacting a hydrocarbon with water vapor to generate a synthesis gas containing hydrogen, carbon monoxide and carbon dioxide as main components; (b) synthesizing the above on a methanol synthesis catalyst A synthesis step of reacting the gas and recovering the generated crude methanol in a liquid state; and (c) first, from the recovered crude methanol, in a first distillation column, dissolve gas, a low-boiling component and methanol accompanying the low-boiling component. The mixed gas is separated, and the mixed gas is discharged from the top of the first distillation column. Then, the remaining components are introduced into the rectification column, where the residual components are purified methanol and high boiling components. And a distillation step of separating the mixture gas and water, wherein the mixed gas is washed in a washing tower. 2. The method for producing methanol according to claim 1, wherein the washing tower has a spray for diffusing washing water and a packed bed. 3. A method for producing methanol, wherein a washing liquid obtained by washing in a washing tower contains a low-boiling component and methanol, and the washing liquid is introduced into the synthesis gas producing step. 4. The method of introducing a cleaning liquid containing a low-boiling component and methanol into a synthesis gas production step includes bringing the cleaning liquid into contact with a raw material hydrocarbon in a process water evaporator and evaporating the hydrocarbon to humidify the hydrocarbon. 4. The method for producing methanol according to claim 3, wherein the methanol is introduced into the synthesis gas production step together with the hydrocarbon from the process water evaporator. 5. The method for producing methanol according to claim 4, wherein the high-temperature discharge water discharged from the process water evaporator is heat-exchanged with a cleaning solution containing a low-boiling component and methanol. 6. The process further comprising contacting the high-boiling components and water discharged from the rectification column with hydrocarbons as a raw material in another process water evaporator and evaporating the hydrocarbons to humidify the hydrocarbons. The method for producing methanol according to claim 4, wherein heat exchange is performed between the high-temperature wastewater discharged from the evaporator and a cleaning solution containing a low-boiling component and methanol.