JP2004161672A - Method for producing dimethyl ether - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing dimethyl ether at low cost by dehydrating methanol by a gas phase reaction using a hydrous low-purity methanol as raw material. <P>SOLUTION: The method for producing dimethyl ether comprises the following practice: A liquid methanol as the raw material containing e.g. 5-40 wt.% water is vaporized into a gas comprising methanol and water vapor in an evaporator. A refluxing methanol of low water content containing e.g. 1-10 wt.% water is fed in a liquid state to the gas from above the evaporator to effect a countercurrent contact in a gas-liquid contact zone in the evaporator. In this case, part of the water vapor having a higher boiling point than methanol is condensed, while the methanol is vaporized to lower the water vapor concentration of the gas. As a result, the objective dimethyl ether is produced using the hydrous inexpensive methanol as the raw material. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing dimethyl ether by dehydrating methanol by a gas phase reaction to provide a method for reducing the concentration of water contained in a raw material gas supplied to a reactor.
[0002]
[Prior art]
Conventionally, a method for producing dimethyl ether by dehydrating methanol by a gas phase reaction is a catalyst that heats and vaporizes methanol containing almost no impurities in an evaporator, and uses this methanol gas as a raw material to promote a dimethyl ether synthesis reaction. For example, a method is used in which the synthesis reaction of dimethyl ether shown in the reaction formula (1) is advanced in the active region of the catalyst by supplying it to, for example, a continuous flow reaction tower (for example, Patent Document 1). reference.).
2CH ₃ OH → CH ₃ OCH ₃ + H ₂ O ΔH = −23.4 kJ / mol (1)
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 59-199648 [0004]
[Problems to be solved by the invention]
By the way, in order to reduce the production cost of dimethyl ether, it is advisable to use an inexpensive unpurified methanol mixture (crude methanol) as a raw material, but the crude methanol contains, for example, about 5 to 40% by weight of water. ing. When the raw material contains a large amount of water, the reaction rate of the reaction formula (1) decreases due to chemical equilibrium, and the reverse reaction rate increases to lower the reaction yield of dimethyl ether. For this reason, it is necessary to separately provide equipment for removing water, for example, a distillation tower, to separate the water, but in this case, there is a problem that the equipment and operating costs are high, and the manufacturing cost is not greatly reduced.
[0005]
The present invention has been made based on such circumstances, and an object thereof is to provide a technique capable of producing dimethyl ether at low cost by using crude methanol containing water as a raw material and having a low purity.
[0006]
[Means for Solving the Problems]
The method for producing dimethyl ether of the present invention is a method for producing dimethyl ether by dehydrating methanol by a gas phase reaction.
Heating liquid methanol, which is a raw material containing water, and evaporating a part thereof in an evaporator;
Liquid methanol for reflux is supplied to the evaporator, the methanol for reflux and the gas evaporated in the vaporization step are brought into contact with each other, water vapor in the gas is condensed, and liquid methanol for reflux is evaporated. Reducing the moisture concentration in the gas;
And a step of synthesizing dimethyl ether by supplying a gas having a reduced water concentration in the evaporator to the reactor.
[0007]
The reflux liquid methanol is one obtained by separating unreacted methanol contained in the gas distilled from the reactor, and one obtained by separating unevaporated methanol contained in the liquid remaining without being vaporized in the vaporization step. It may contain at least one. The liquid methanol as the raw material may have a water concentration of, for example, 5% by weight to 40% by weight, and the liquid methanol for reflux may have a water concentration of, for example, 0% by weight to 10% by weight. Furthermore, the moisture concentration of the methanol gas whose moisture content has decreased in the evaporator may be, for example, 2 wt% to 15 wt%. Furthermore, the ratio of the liquid methanol for reflux having a water concentration of, for example, 0% by weight to 10% by weight, for example, 20% to 100% with respect to the mass flow rate of the raw material methanol having a water concentration of, for example, 5% to 40% by weight. May be supplied at a mass flow rate of.
[0008]
According to the present invention, methanol (crude methanol) containing water is partially vaporized in an evaporator, and the vaporized gas is brought into contact with refluxing methanol supplied from another location. Can reduce the moisture concentration in the gas. That is, the raw material gas can be supplied to the reactor in a state adjusted to a moisture concentration capable of maintaining the progress of the synthesis reaction of dimethyl ether in the reactor and reducing the volume of the reactor (reaction region). it can. Therefore, inexpensive methanol containing water can be used as a raw material, and the cost of equipment can be reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the method for producing dimethyl ether of the present invention will be described. The main part of this embodiment is in the step of reducing the water concentration in the crude methanol with an evaporator when synthesizing dimethyl ether using unpurified crude methanol containing water. First, the entire system including the evaporator, the reaction tower, and the processing on the downstream side of the reaction tower will be briefly described with reference to FIG.
[0010]
First, liquid methanol (crude methanol) as a raw material is supplied to the evaporator 2 via the pump P1 and the preheater 10. In the evaporator 2, water is removed from the gas to some extent by a method described later, and the vaporized gas is heated to a predetermined temperature by the preheater 40 a and then supplied into the reaction tower 40. The liquid discharged from the bottom of the evaporator 2 is sent to a methanol recovery tower 60 described later.
[0011]
For example, the raw material gas supplied to the above-described adiabatic flow-type reaction tower 40 undergoes the synthesis reaction represented by the reaction formula (1) described in “Conventional Technology” in the catalyst layer 41 of the reaction tower 40, The product gas contains dimethyl ether, water vapor and unreacted methanol. Thereafter, it is cooled to a predetermined temperature by the cooler 40b and supplied to the dimethyl ether purification tower 50.
[0012]
Subsequently, by distilling the outlet gas of the reaction tower 40 in the dimethyl ether purification tower 50, for example, unreacted methanol, water and a small amount of light gas are separated, and dimethyl ether having a desired purity is obtained as a product from the upper stage of the dimethyl ether purification tower 50. can get. At this time, unreacted methanol and water are discharged from the tower bottom and sent to the methanol recovery tower 60, and light gas is discharged from the tower top.
[0013]
On the other hand, the liquid discharged from the bottom of each of the evaporator 2 and the dimethyl ether purification tower 50 is subjected to rectification in the methanol recovery tower 60 to separate water and high-boiling components. It is discharged from the bottom of the tower and processed by a processing facility (not shown). Further, the methanol is liquefied by the condenser 60b, and is supplied to the evaporator 2 as liquid methanol for reflux via the pump P2.
[0014]
Next, an example of the evaporation apparatus 2 which is a main part of this embodiment will be described with reference to FIG. First, as shown in FIG. 2, the evaporation apparatus 2 includes an evaporator (evaporation tower) 20. Inside the evaporator 20, for example, a packing layer 21 made of a large number of packings is provided. Further, a reboiler 3 is provided at the lower stage of the evaporator 20.
[0015]
Subsequently, the process from vaporizing crude methanol with the above-described evaporator 2 to supplying it to the reaction tower 40 will be described in detail. First, for example, crude methanol containing 5 to 40% by weight of moisture and other impurities such as trace amounts of ethanol and paraffinic components is supplied to the evaporator 20 in a liquid state via the crude methanol supply port 25, and a part thereof Vaporize. On the other hand, the liquid methanol for recovery (recovered methanol) returned from the methanol recovery tower 60 includes, for example, crude water having a water concentration lower than that of the crude methanol, for example, 0 to 10 wt%. It is supplied as a reflux liquid from the upper part of the evaporator 20 at a flow rate of, for example, 20 to 100% with respect to the mass flow rate of methanol.
[0016]
Here, when the vaporized gas and the liquid methanol for reflux are brought into countercurrent contact in the gas-liquid contact region, a part of the water vapor having a boiling point higher than that of methanol is condensed, and conversely, Some vaporize. For this reason, the concentration of water (water vapor) contained in the gas is a predetermined water (water vapor) concentration, for example, 2 to 15% by weight. The gas having a reduced moisture concentration is distilled through the gas distillation outlet 27 and then heated to a predetermined temperature, for example, 250 to 350 ° C. by the preheater 40a, and supplied to the reaction tower 40 as a raw material gas. The liquid containing methanol and water at the bottom of the evaporator 20 is discharged through the discharge port 28 and supplied to the methanol recovery tower 60.
[0017]
In such an embodiment, crude methanol is used as a raw material for dimethyl ether, and liquid methanol for reflux is supplied from another location, for example, from the methanol recovery tower 60 to the evaporator 20 in the previous stage of the step of synthesizing dimethyl ether. Since the water concentration in the reactor supply gas is reduced, high-purity methanol is not required for the raw material, and the water concentration can be reduced with simple equipment, thus reducing the cost for synthesizing dimethyl ether. be able to. That is, this embodiment maintains the speed of the synthesis reaction of dimethyl ether by reducing the water in the gas supplied to the reaction tower to a predetermined concentration, thereby reducing the capacity of the reaction tower 40 and separating the water. This is realized by paying attention to reducing the cost of the equipment by performing the above-described moisture adjustment method with an evaporator, instead of providing a distillation column for the purpose.
[0018]
【Example】
Next, examples performed to confirm the effects of the present invention will be described.
Example 1
As shown in FIG. 3, a tower packed with pole rings corresponding to four theoretical plates was used as the evaporator 20 and heated by the reboiler 3 to vaporize a part of the raw raw methanol. The crude methanol (methanol mixture) supplied to the evaporator 20 was 50 kg / h, and its composition was methanol: 74.9% by weight, water: 25.0% by weight, and other impurities: 500 ppm. The recovered methanol sent from the methanol recovery tower 60 was 24 kg / h, and consisted of methanol: 95.0 wt%, water: 5.0 wt%, and other impurities: 400 ppm. Crude methanol was supplied to the position corresponding to the third stage from the top of the column, and liquid methanol for reflux was supplied to the top of the column. Further, a column packed with a pole ring corresponding to 30 theoretical plates was used as the methanol recovery column 60 for separating methanol and water. FIG. 3 also shows the result.
[0019]
(Result of Example 1)
a. Partial vaporization was performed with the top pressure of the evaporator 20 being 2.2 MPa to obtain a gas containing 89.9% by weight of methanol, 10.0% by weight of water, and 500 ppm of other impurities. The flow rate of this gas was 59 kg / h. The amount of heat of the reboiler 3 was 20200 kcal / h calculated from the amount of steam used.
b. The gas obtained from the top of the column was heated to 280 ° C. with the preheater 40a. The amount of heating was 3200 kcal / h.
c. In the reaction tower 40, 70% of methanol was converted to dimethyl ether to synthesize the target product, dimethyl ether. 32 kg / h of a mixture of 49.6% by weight of methanol, 50.4% by weight of water and 400 ppm of other impurities obtained after separation of dimethyl ether in the dimethyl ether purification tower 50, and 47. 7% of methanol not evaporated by the evaporator 20 described above. 15 kg / h of a mixture consisting of 1% by weight, 52.8% by weight of water and 700 ppm of other impurities was mixed and supplied to the methanol recovery tower 60.
d. When the reflux ratio of the methanol recovery tower 60 is 1.0, the tower top temperature is 72 ° C., and the purity of the liquid methanol for reflux obtained as a liquid from the tower top is 95.0% by weight, obtained from the tower bottom as a liquid. The purity of the water obtained was 99.9% by weight, and the amount of heat of the reboiler 60a was 10,000 kcal / h.
e. The heating amount shown here is 33400 kcal / h when the reboiler 3, the preheater 40a, and the reboiler 60a of the methanol recovery tower 60 are combined.
[0020]
(Comparative Example 1)
This example is Comparative Example 1 in the case where the water content of the raw material is adjusted in the methanol recovery tower 60 which is a distillation tower. As shown in FIG. 4, as the distillation raw material, crude methanol (methanol mixture) containing impurities, methanol mainly obtained from the unreacted methanol obtained after separating dimethyl ether from the outlet gas of the reaction tower 40 by the dimethyl ether purification tower 50, and There is a mixture of water. In order to separate the methanol in these raw materials from the water, a column packed with pole rings corresponding to 30 theoretical plates was used as the methanol recovery column 60 in the same manner as in Example 1. Both raw materials were mixed and supplied to the position corresponding to the 10th stage. The crude methanol was 50 kg / h as in Example 1, and the composition was methanol: 74.9% by weight, water: 25.0% by weight, and other impurities: 500 ppm. The unreacted mixture of methanol and water was 32 kg / h, and the composition was methanol: 49.6% by weight, water: 50.4% by weight, and other impurities: 400 ppm. FIG. 4 also shows the results.
[0021]
(Results of Comparative Example 1)
a. Distillation operation was performed with the top pressure of the methanol recovery tower 60 being 0.13 MPa.
b. When the reflux ratio of the methanol recovery tower 60 is 0.4, the top temperature is 74 ° C., the purity of methanol obtained in liquid form from the top is 89.9% by weight, and the purity of water obtained in liquid form from the tower bottom Was 99.9% by weight, and the amount of heat of the reboiler 60a was 20800 kcal / h.
c. The flow rate of recovered methanol containing 89.9% by weight of methanol obtained from the top of the tower, 10.0% by weight of water, and 500 ppm of other impurities is 59 kg / h, and is supplied to the reaction tower 40 by a pump up to 2.3 MPa. After pressurization, it was vaporized by the kettle type evaporator 8 and then heated to 280 ° C. by the preheater 40a. The heating amount was 18900 kcal / h in the evaporator 8 and 3200 kcal / h in the preheater 40a.
d. The heating amount shown here is 42900 kcal / h when the reboiler 60a, the evaporator 8, and the preheater 40a are combined.
[0022]
(Comparative Example 2)
In this example, as shown in FIG. 5, after recovering methanol (liquid methanol used for reflux in the examples) and mixing with crude methanol to lower the water concentration, water and high-boiling components can be extracted from the bottom. It is the comparative example 2 which vaporizes with the possible kettle type | mold evaporator 8, and adjusts source gas. The flow rate and composition of the crude methanol were the same as in Example 1. The recovered methanol sent from the methanol recovery tower 60 was 67 kg / h, consisting of methanol: 95.0 wt%, water: 5.0 wt%, and other impurities: 400 ppm. The two were mixed and supplied to the evaporator 8 and heated to separate into vapor mainly composed of methanol and liquid mainly composed of water and components. A column packed with a pole ring corresponding to 30 theoretical plates was used as the methanol recovery column 60 for separating methanol and water as in Comparative Example 1, and the raw material was supplied to the position corresponding to the 10th plate. FIG. 5 also shows the results.
[0023]
(Results of Comparative Example 2)
a. Partial evaporation was performed with the pressure of the evaporator 8 being set to 2.2 MPa to obtain a gas containing 89.9% by weight of methanol, 10.0% by weight of water, and 500 ppm of other impurities. The flow rate of this gas was 59 kg / h. The amount of heat of the evaporator 8 was 24100 kcal / h.
b. In order to supply the gas obtained from the evaporator 8 to the reaction tower 40, the gas was heated to 280 ° C. by the preheater 40 a. The heating amount was 3200 kcal / h.
c. Dimethyl ether was synthesized in the reaction tower 40. 32 kg / h of a mixture consisting of 49.6% by weight of methanol, 50.4% by weight of water and 400 ppm of other impurities obtained after separation of dimethyl ether by the dimethyl ether purification tower 50, and 82.methanol which has not been evaporated by the evaporator 8 described above. 58 kg / h of a mixture consisting of 9% by weight, 17.1% by weight of water and 400 ppm of other impurities was mixed and supplied to the methanol recovery tower 60.
d. When the reflux ratio of the methanol recovery tower 60 is 0.6, the tower top temperature is 72 ° C., the purity of methanol obtained in liquid from the tower top is 95.0% by weight, and the purity of water obtained in liquid from the tower bottom Was 99.9% by weight, and the amount of heat of the reboiler 60a was 23300 kcal / h.
e. The heating amount shown here is 50600 kcal / h when the evaporator 8, the preheater 40a and the reboiler 60a of the methanol recovery tower 60 are combined.
[0024]
(Comparative Example 3)
This example is the same as Comparative Example 2 in that the water concentration is lowered by mixing recovered methanol (liquid methanol used for refluxing in Example 1) with crude methanol as shown in FIG. An example in which the raw material gas is obtained by evaporating the entire amount with the evaporator 8 without adjustment will be referred to as Comparative Example 3. The flow rate and composition of the crude methanol were the same as in Example 1. The recovered methanol sent from the methanol recovery tower 60 was 17 kg / h, and consisted of methanol: 95.0 wt%, water: 5.0 wt%, and other impurities: 400 ppm. Both were mixed and supplied to the evaporator 8, and the entire amount was vaporized. As the methanol recovery column 60 for separating methanol and water, a column packed with a pole ring corresponding to 30 theoretical plates was used as in Example 1, and the raw material was supplied to a position corresponding to the 10th plate. FIG. 6 also shows the results. In order to convert 70% of methanol to dimethyl ether, the amount of catalyst in the reaction tower 40, which is an adiabatic dimethyl ether synthesis reactor, is high because the moisture concentration of the raw material gas supplied to the reaction tower is high. The catalyst required 2.3 times that of Example 1 was required. In addition, when the experiment was performed with the same catalyst amount as in Example 1 for the reaction tower feed gas of Comparative Example 3, the conversion rate of methanol to dimethyl ether was as low as 21%, which required a large amount of methanol circulation. Processing was impossible with the apparatus used in the examples and comparative examples 1 and 2.
[0025]
(Result of Comparative Example 3)
a. Complete vaporization was performed by setting the pressure of the evaporator 8 to 2.2 MPa, and a gas containing 79.9% by weight of methanol, 20.0% by weight of water, and 500 ppm of other impurities was obtained. The flow rate of this gas was 67 kg / h. The amount of heat of the evaporator 8 was 23200 kcal / h.
b. In order to supply the gas obtained from the evaporator 8 to the reaction tower 40, the gas was heated to 280 ° C. by the preheater 40 a. The heating amount was 3300 kcal / h.
c. Dimethyl ether was synthesized in the reaction tower 40 packed with a catalyst amount 2.3 times that in Example 1, and 40.1% by weight of methanol obtained after separating the dimethyl ether in the dimethyl ether purification tower 50, 59.9% by weight of water, 40 kg / h of a mixture consisting of 400 ppm of other impurities was supplied to the methanol recovery tower 60.
d. When the reflux ratio of the methanol recovery tower 60 is 1.2, the top temperature is 72 ° C., the purity of methanol obtained in liquid form from the top is 95.0% by weight, and the purity of water obtained in liquid form from the tower bottom Was 99.9% by weight, and the amount of heat of the reboiler 60a was 7400 kcal / h.
e. The heating amount shown here is 33900 kcal / h when the evaporator 8, the preheater 40a, and the reboiler 60a of the methanol recovery tower 60 are combined.
[0026]
(Consideration of Example 1, Comparative Example 1 and Comparative Example 2)
In Example 1, Comparative Example 1 and Comparative Example 2, the same raw material (crude methanol) was used to obtain the same gas phase mixture as the raw material of the dimethyl ether synthesis reactor (reaction tower 40), and methanol and water were used. The number of theoretical plates of the distillation column for separation (methanol recovery column 60) was the same, and the purity of the water obtained from the bottom was also the same. Comparing Example 1 and Comparative Example 1, in Example 1, although the evaporator 20 corresponding to four theoretical plates is necessary, the total heating amount is reduced to 78% compared to Comparative Example 1. Understand. Comparing Example 1 and Comparative Example 2, in Comparative Example 2, a large amount of methanol is discharged together with water as a liquid from the evaporator 20 (evaporator 8 in Comparative Example 2) for the purpose of suppressing the moisture concentration in the gas phase. This methanol component is recovered by the methanol recovery tower 60 and supplied again to the evaporator 20 (evaporator 8 in the comparative example 2). In Example 1, although it is necessary to make the evaporator 20 correspond to four theoretical plates, the liquid methanol for reflux supplied from the top of the column plays the role of the reflux liquid in the distillation column, thereby causing the evaporator 20 to It can be seen that the distillation effect is provided, the amount of methanol discharged into the column bottom liquid is reduced to reduce the load on the methanol recovery tower, and the total heating amount is reduced to 66% compared to Comparative Example 2. In other words, it can be seen that the heating amount can be greatly reduced by supplying the liquid methanol for reflux from the top of the column with the evaporator equivalent to four theoretical plates. Further, the cooling amount of the condenser of the methanol recovery tower is similarly reduced.
[0027]
(Consideration of Comparative Example 3)
Comparing Example 1 and Comparative Example 3, in Comparative Example 3, the concentration of water supplied to the reaction tower 40 is high, and the amount of catalyst necessary to obtain an equivalent reaction result is increased 2.3 times. In Comparative Example 3, the load on the methanol recovery tower 60 is larger in Example 1, but in Example 1, it is not necessary to evaporate a large amount of water in the evaporator 20, so the total heating amount is 98 compared with Comparative Example 3. It turns out that it is equivalent to%. In Example 1, although the evaporator 20 corresponding to four theoretical plates is required, the amount of catalyst can be greatly reduced, so that it can be seen that the heating amount is substantially the same and the equipment cost can be reduced.
[0028]
【The invention's effect】
As described above, according to the present invention, in the method for producing dimethyl ether by dehydrating methanol by gas phase reaction, by performing the synthesis reaction of dimethyl ether by reducing the water concentration in the raw material gas supplied to the reactor, Inexpensive methanol containing water can be used as a raw material, and the cost of equipment can be reduced.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing the overall configuration of a dimethyl ether production system incorporating an evaporator equipped with the method of the present invention.
FIG. 2 is a longitudinal sectional view showing an example of an evaporation apparatus provided with the method of the present invention.
FIG. 3 is a characteristic diagram showing an example carried out to confirm the effect of the present invention.
FIG. 4 is a characteristic diagram showing a comparative example performed to confirm the effect of the present invention.
FIG. 5 is a characteristic diagram showing a comparative example performed to confirm the effect of the present invention.
FIG. 6 is a characteristic diagram showing a comparative example performed to confirm the effect of the present invention.
[Explanation of symbols]
2 Evaporator 20 Evaporator 21 Packing Layer 22 Packing Support Portion 24 Reflux Supply Port 25 Crude Methanol Supply Port 3 Reboiler 40 Reaction Tower 50 Dimethyl Ether Purification Tower 60 Methanol Recovery Tower

Claims (6)

In a method for producing dimethyl ether by dehydrating methanol by a gas phase reaction,
Heating liquid methanol, which is a raw material containing water, and evaporating a part thereof in an evaporator;
Liquid methanol for reflux is supplied to the evaporator, the methanol for reflux and the gas evaporated in the vaporization step are brought into contact with each other, water vapor in the gas is condensed, and liquid methanol for reflux is evaporated. Reducing the moisture concentration in the gas;
And synthesize dimethyl ether by supplying a gas having a reduced water concentration in the evaporator to the reactor. Liquid methanol for reflux is at least one of those obtained by separating unreacted methanol contained in the gas distilled from the reactor, and those obtained by separating unevaporated methanol contained in the liquid remaining without being vaporized in the vaporization step. The method for producing dimethyl ether according to claim 1, comprising one of them. The method for producing dimethyl ether according to claim 1 or 2, wherein the liquid methanol as a raw material has a water concentration of 5 wt% to 40 wt%. The method for producing dimethyl ether according to any one of claims 1, 2, and 3, wherein the liquid methanol for reflux has a water concentration of 0 wt% to 10 wt%. The method for producing dimethyl ether according to any one of claims 1 to 4, wherein the moisture concentration of the methanol gas whose moisture concentration has been reduced by the evaporator is 2 to 15 wt%. Supplying liquid methanol for reflux having a water concentration of 0% to 10% by weight at a mass flow rate of 20% to 100% with respect to the mass flow rate of the raw material methanol having a water concentration of 5% to 40% by weight. A process for producing dimethyl ether according to any one of claims 1, 2, and 5.

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