TWI410400B - Dual-bed catalytic distillation tower and method for preparing dimethyl ether using the same - Google Patents

Abstract

The present invention relates to a dual-bed catalytic distillation tower and a method for producing dimethyl ether using the same. The dual-bed catalytic distillation tower of the present invention from top to down comprises a low temperature catalytic column and a high temperature catalytic column. When using the dual-bed catalytic distillation tower, the materials may be feed to the tower from the top of the low temperature catalytic column, between the low temperature catalytic column and the high temperature catalytic column or from the bottom of the high temperature catalytic column for dehydration to obtain the dimethyl ether. The dual-bed catalytic distillation tower of the present invention has the advantage of flexible set up depending on various source such as anhydrous or crude methanol and on different grade of dimethyl ether to be obtained.

Description

Twin catalytic distillation column and method for producing dimethyl ether from the same

The present invention relates to a catalytic distillation column for use in the manufacture of dimethyl ether, and more particularly to a two-bed catalytic distillation column having two media beds. The invention also relates to a process for the manufacture of dimethyl ether using such a catalytic distillation column.

Dimethyl ether is generally produced by using various raw materials such as coal, natural gas, petroleum coke or biomass, and methanol is produced by water gas, and further dehydrated to dimethyl ether. The dimethyl ether process can be divided into one-step reaction and two-stage reaction. The one-step reaction synthesis method is to simultaneously produce methanol and dimethyl ether under the action of a catalyst, and the produced methanol is dehydrated to form dimethyl ether; The two-stage reaction synthesis method first produces methanol from water gas, and then dehydrates methanol to synthesize dimethyl ether.

Whether it is a one-step reaction synthesis method or a two-stage reaction synthesis method, the steps of dehydration of methanol are involved. In the reaction of dehydration of methanol, a catalyst is required to assist the reaction, and a solid acid catalyst generally used such as zeolite, lanthanum aluminum oxide, oxidation is generally used. Aluminum, metal phosphates and sulfates, and resin catalysts (Spivey, JJ, 1991), or modified acid catalysts (US 6,740,783). The resin catalyst is a low temperature catalyst (reaction temperature 70-150 ° C), which can obtain almost 100% selectivity, but the disadvantage is that such a catalyst is not resistant to high temperature; while other catalysts are mostly high temperature catalysts, the reaction temperature is self-contained. 200-350 ° C, because methanol and dimethyl ether are oxygenates, will be further dehydrated into C ₂ -C ₄ olefins, so the higher the temperature, the more by-products, the faster the carbon deposition rate, causing contact The decline in media activity reduced the yield and selectivity of dimethyl ether.

In order to reduce the energy consumption of the process, it has been developed to introduce the above solid acid catalyst into the catalytic distillation column, thereby fully utilizing the heat released by the methanol dehydration reaction, reducing the energy consumption, and streamlining the manufacturing process of the dimethyl ether and reducing the equipment. The amount of investment. One of the necessary conditions for the application of catalytic distillation technology is that the reactants and products at the same column pressure, the corresponding column temperature range must be able to promote the occurrence of catalytic reactions.

US 07/0,066,855 discloses the use of catalytic distillation to produce dimethyl ether to take full advantage of the heat evolved from the methanol dehydration reaction for energy savings and equipment simplification. However, in order to make full use of the heat of reaction and overcome the problem of the reaction of the catalytic layer in the catalytic distillation column, the high column pressure used may cause the problem that methanol and water in the stripping layer in the column are not easily separated. Figure 1 shows the relative volatility of methanol and water at different column pressures, thereby estimating the ease of separation of methanol and water at high pressure. The two component parameters of the method are gas-liquid equilibrium data at a pressure of 3-5 bar. (Gmehling et al., 1977), the results show that at 18 bar, the liquid Mohr fraction of water is 0.825, the relative volatility of methanol and water is close to the azeotropic zone of 1, which means dimethyl ether catalysis The high pressure design of the distillation column will spawn new azeotropy problems.

WO 07/014,534 mentions the use of high temperature solid acid in a catalytic distillation column for high temperature gas phase dehydration at a column pressure of 1.8-2.3 MPa and a reaction temperature of 160-180 °C. However, in order to promote the catalytic reaction at high temperatures, the energy consumption of the corresponding condenser and reboiler in the tower tank will increase, which is inconsistent with the principle of reducing energy consumption.

US 5,684,213 mentions a high temperature vapor phase dehydration reaction at a column pressure of 600 psi and a reaction temperature of 350-400 °C. Due to the high temperature in the tower, the carbon deposition effect will cause the catalyst activity to decline, and the olefin by-products will increase and the dimethyl ether yield will decrease. Therefore, hydrogen is injected into the catalytic distillation column to inhibit the catalyst carbon deposition, but this will increase. The cost and complexity of the operation.

There is also a low-temperature liquid phase dehydration reaction with a low-temperature solid acid in a catalytic distillation column having a lower column pressure. For example, WO 07/014,534 discloses a low-temperature solid acid at a column pressure of 10-18 bar and a reaction temperature of 130-158 °C. Liquid phase dehydration is carried out. However, the low temperature limit of the low temperature catalyst is lower (less than 140 ° C), in order to avoid catalyst damage, it needs to operate in low pressure and low temperature environment, but when the tower pressure is too low, the top of the high purity dimethyl ether Dew point will be reduced. For example, when the tower pressure is as low as 9 bar and the dew point of dimethyl ether is 40.3 ° C, it would be a big problem to condense dimethyl ether in the cooling water of the factory where the factory is cheap. The column pressure is adjusted to 12 bar, and the temperature of the catalyst bed under the catalytic layer is higher than 150 ° C, which will cause harmful catalyst life.

The catalytic distillation column used in the above disclosed method uses only a single catalyst system, that is, the catalytic layer is only subjected to a low temperature dehydration reaction or a high temperature dehydration reaction. Therefore, when the methanol grade of the feed is different or when the production of fuel grade and chemical grade dimethyl ether is switched, the prior art single catalyst system configuration mode, the tower height, the column diameter, and the catalyst amount in the catalytic distillation tower are The design requires a high safety factor and the operational flexibility is greatly reduced.

Therefore, the current catalytic distillation method for producing dimethyl ether cannot obtain an appropriate dehydration reaction complementary condition between the catalytic layer catalyst and the tower pressure tower temperature. Even at a low pressure of 8 bar, the methanol saturation temperature reaches 128.3 °C, so that the low temperature acidic catalyst still has the temperature resistance doubt, and the top dimethyl ether dew point is 35.8 ° C low, which makes it impossible to use the 30 ° C cooling water design considerations; When using high pressure conditions above 20 bar, high temperature acidic catalysts have problems such as by-products, low carbon deposition and high yield, high energy consumption, and azeotropy of methanol and water. These problems, in turn, degrade the operational flexibility of the catalytic distillation column and the limitations of different methanol feed concentrations and dimethyl ether product specifications.

Accordingly, it is an object of the present invention to provide a method for compromising the PT-xy relationship between the dimethyl ether, methanol, and water components of the column and the characteristics of the dehydration catalyst when the dimethyl ether is produced by catalytic distillation.

In particular, the present invention relates to a catalytic distillation column having a double bed and a method of producing dimethyl ether using the double bed catalytic distillation column.

The invention provides a catalytic distillation column of double bed, which has two catalyst systems, the upper layer is a low temperature reaction medium bed, the lower layer is a high temperature reaction medium bed, the low temperature reaction medium bed, the low temperature reaction medium bed and the high temperature reaction medium bed. A feed port is disposed between the high temperature reaction medium bed and the low temperature reaction medium bed contains a low temperature dehydration catalyst, and the high temperature reaction medium bed contains a high temperature dehydration catalyst.

Preferably, the low temperature dehydration catalyst is Amberlyst 15 acid resin or Amberlyst 35 acid resin.

Preferably, the high temperature dehydration catalyst is a fluorinated transition metal oxide, a sulfated transition metal oxide, a beta zeolite, and HZSM-5, and the high temperature dehydration catalyst is coated with Teflon to strengthen Its hydrophobic properties.

The present invention also provides a process for producing dimethyl ether, which is dehydrated using the aforementioned two-bed catalytic distillation column, wherein the methanol-containing raw material is at a column pressure of 6-30 bar, from a low-temperature reaction medium bed, and a low-temperature reaction medium bed. The dehydration reaction is carried out with the feed port of the high temperature reaction medium bed or under the high temperature reaction medium bed, and finally dimethyl ether is obtained.

The catalytic distillation column of the present invention has a temperature range of 60-250 ° C. When the temperature is 60-180 ° C, the reaction is carried out with a low-temperature dehydration catalyst, and when the temperature is 110-250 ° C, the reaction is carried out with a high-temperature dehydration catalyst.

Preferably, the column pressure in the catalytic distillation column is 8-14 bar.

Preferably, the flash zone can be reserved between different reaction media beds for use as a feed location or for heat exchange and reflux.

When anhydrous methanol is used as a raw material, it is directly fed from a bed of a low temperature reaction medium.

When syngas is used as a raw material, it is first reacted in a step to a mixture containing dimethyl ether, methanol and water, and then fed between a bed of a low-temperature reaction medium or a bed of a high-low temperature reaction medium.

When the feedstock is crude methanol, the feedstock is fed between a bed of high temperature reaction media or between a bed of high and low temperature reaction media.

From the above, it is understood that the double-bed catalytic distillation column structure of the present invention has better production and operational flexibility than the single-bed catalytic distillation column in the production of dimethyl ether. Moreover, the double-bed catalytic distillation column structure of the invention is suitable for different kinds of methanol feeds, and can also produce dimethyl ether products of different purity grades.

In particular, the catalytic distillation column of the present invention can completely or partially replace the synthesis gas to the step of separating and purifying dimethyl ether, methanol, carbon dioxide and water from the back end of the dimethyl ether process, and the methanol can be reduced to the front end reactor without being refluxed. Process and increase refining.

The technical means adopted by the present invention for achieving the intended purpose of the invention are further described below in conjunction with the drawings and preferred embodiments of the invention.

Figure 2 shows the gas-liquid equilibrium composition of methanol and dimethyl ether, and methanol and water at different temperatures at a pressure of 11 bar. The right half is the gas-liquid equilibrium relationship between methanol and dimethyl ether. When the distance from the top of the tower is higher, the methanol concentration is higher, and the liquid phase concentration is higher than the gas phase. The temperature is close to the saturated liquid temperature of methanol of 140.5 ° C. Therefore, The Z1 region in Figure 2 is suitable for the acidic catalyst for the low-temperature liquid phase dehydration reaction; the left half is the gas-liquid equilibrium relationship between methanol and water. The farther from the bottom of the column, the higher the methanol concentration, but the gas phase concentration instead It is higher than the liquid phase and the temperature is close to the saturated liquid temperature of methanol. Therefore, the Z2 region of Fig. 2 is suitable for use as an acidic catalyst for performing high-temperature vapor phase dehydration reaction. However, the saturated liquid temperature of methanol is related to the column pressure. Therefore, when the column pressure is less than 11 bar, the gas-liquid equilibrium curve of Figure 2 will shift to a low temperature, and the saturated liquid temperature of methanol is less than 140.5 ° C; otherwise, the pressure is greater than 11 bar. The liquid equilibrium curve is shifted to a high temperature, and the temperature of the saturated liquid of methanol is greater than 140.5 °C.

According to the results of the above characteristic analysis, in order to protect the activity and life of the catalyst in the dimethyl ether catalytic distillation column, and to adapt to the operation of different column pressures and different feed compositions, the present invention configures the acidity of different characteristics in different temperature ranges of the catalytic layer. Catalyst to effectively carry out the methanol dehydration reaction. As shown in Fig. 3, the catalytic distillation column of the present invention has two catalyst systems, the upper layer is a low temperature reaction medium bed 7, the lower layer is a high temperature reaction medium bed 11, and the quenching zone 8 above the low temperature reaction medium bed 7 is provided with The quenching zone 1, the quenching zone 9 between the low temperature reaction medium bed 7 and the high temperature reaction medium bed 11 is provided with a feed port 2, a heat exchange and reflux unit 12, and a quenching zone 10 below the high temperature reaction medium bed 11 Feed port 3.

In general, the temperature of the catalytic distillation column of the present invention is in the range of 60-250 ° C. When the temperature is 60-180 ° C, the low-temperature liquid phase dehydration catalyst is disposed in the high methanol liquid concentration region; when the temperature is 110-250 ° C The high-temperature gas phase dehydration catalyst is disposed in the high methanol gas phase concentration region. The critical temperature of the high and low temperature media bed configuration is 110-180 °C.

Preferably, in the upper layer of the catalytic distillation column, a low temperature liquid phase dehydration catalyst is disposed, for example, Amberlyst is configured at 85-110 ° C. 15 acid resin; 110-135 ° C configuration Amberlyst 35 acid resin, but is not limited to this. The lower media bed 11 is provided with a high temperature vapor phase dehydration catalyst, and a suitable catalyst such as a fluorinated transition metal oxide (such as F-alumina), a sulfated transition metal oxide (such as sulfated zirconium dioxide, SO _{4 )} ^2- /ZrO ₂ ), β-type zeolite, and HZSM-5, etc., but are not limited thereto. Such high-temperature dehydration catalysts are coated with Teflon to enhance their hydrophobic properties, thereby greatly reducing the gas phase transfer resistance caused by the surface of the liquid molecules coated with the catalyst.

The tower pressure can vary depending on the conditions, and the general pressure range is 6-30 bar, preferably 8-14 bar. If at high latitudes, consider the operability of conventional 20 ° C industrial cooling water condensation dew point 25.4 ° C dimethyl ether, the pressure can be as low as 6 bar; and at 18 bar high pressure, consider the relative volatility of methanol and water .

Depending on the composition of the methanol mixture and the grade of dimethyl ether desired, the feedstock can be fed from feed port 1, 2 or 3. In general, when the raw material is anhydrous methanol, it is suitable to directly carry out the liquid phase dehydration reaction, and thus is fed from the feed port 1. If a mixture of dimethyl ether, methanol, water and carbon dioxide is produced by a one-step synthesis synthesis method using syngas as a raw material, it is suitable to feed above the low temperature reaction medium bed 7 or between the high and low temperature reaction medium beds, that is, from the feed. Oral 1 or 2 feed. If the raw material is the crude methanol produced by the methanol plant, it needs to be preheated to the saturated gas, so it is fed between the high and low temperature reaction media beds or under the high temperature reaction medium bed 11, that is, from the feed port 2 or 3 material. The quenching zone 9 in the middle of the double-bed catalytic layer may be provided with a heat exchange and reflux unit 12 to temperature-control the reaction temperature of the upper and lower media beds of the catalytic layer and to protect the low temperature dehydration catalyst of the upper media bed.

As shown in FIG. 3, after the action of the catalytic distillation column, the gas phase of the overhead is produced via the condenser at the top of the column, in particular, the methanol mixture containing carbon dioxide is discharged from the condenser outlet 4, and the dimethyl ether is condensed. The outlet 5 is discharged and collected. The unreacted stream is passed from the reboiler outlet 6 via the bottom reboiler and the other streams are returned to the distillation column for continued action.

Figure 4 shows the application of the two-bed catalytic distillation column of the present invention in the dimethyl ether process. Figure 4 (a) shows the use of the catalytic distillation column of the present invention in a one-step reaction process, after a one-step reaction, a mixture of dimethyl ether, methanol, water and carbon dioxide 23, depending on the situation, from different feed ports 1, 2 or 3 The dehydrogenation reaction is carried out to the catalytic distillation column to finally obtain dimethyl ether. Figure 4 (b) shows the use of the catalytic distillation column of the present invention in a two-stage reaction process. The crude methanol 22 after two-stage reaction can be fed with different methanol from the different feed ports 1, 2 or 3 as the case may be. The dehydrogenation reaction is carried out to the catalytic distillation column to finally obtain dimethyl ether.

Example

In the following examples, the verified cryogenic liquid phase dehydration rate (An et al., 2004) and the thermodynamic method NRTL-RK equation, combined with high temperature vapor phase dehydration (Lin et al., 1981; Hayashi, 1982) The kinetic data, theoretical calculation of the dimethyl ether catalytic distillation column in the commercial simulation software Aspen Plus, illustrates the feasibility of the present invention.

Prior art single bed low temperature catalyst catalytic distillation column: the theoretical number of the rectifying layer and the stripping layer are set to 7 plates (including full/or partial condenser and reboiler) in the calculation process, and the methanol is contained at a normal temperature of 30 ° C. The feed of the mixture is heat exchanged with the hot water produced at the bottom of the catalytic distillation column. The heat exchange rate is set to 45 ° C at the heat source side outlet temperature, and the feed temperature after heat exchange is about 40 ° C. The feed position depends on its composition. . Simultaneously adjust the amount of catalyst and the column diameter, that is, change the number of catalytic layers and consider the allowable linear flow rate of the liquid in the catalyst layer (high 24" / plate) 24.4 m / s, so that the weight concentration of dimethyl ether and water are about 99.9 Finally, the operating parameter reflux ratio and D/F were fine-tuned so that the weight concentration of the dimethyl ether and water produced by the catalytic distillation column was 99.9%.

The double-bed high-low temperature catalyst catalytic distillation tower of the invention adopts a low-temperature single-bed catalytic layer as a reference, and according to the result, the tower temperature is adjusted to a boundary point of the high-low temperature double-bed catalytic layer at a temperature of 135 ° C, and the number of catalytic layer plates is synchronously adjusted. And fine-tuning the operating parameter reflux ratio and D/F, so that the catalytic distillation column produces a weight concentration specification of dimethyl ether and water of 99.9%. When producing fuel grade 93 wt% dimethyl ether (including 7 wt% methanol), under the same tower design, due to excessive catalyst catalyst, the amount of refining can be increased to reduce the methanol conversion rate, and the fuel grade is produced from the top of the tower. Dimethyl ether, while the weight concentration of the bottom water is still 99.9%.

Assume the following: low temperature dehydration catalytic layer unit volume = 0.6 theoretical plate unit volume, high temperature dehydration catalytic layer unit volume = 0.85 theoretical plate unit volume (see US 6,045,762 and US 2007/0,095,646). The dehydration rate of the hydrophobic, strong acid type high temperature catalyst is 5 times that disclosed in the literature Lin et al., 1981.

Comparative Example Feeding anhydrous methanol (prior art)

The simulation conditions for the dimethyl ether catalytic distillation column used in US 07/0,066,855 are as follows: tower pressure 12 bar, pressure difference 0.7 bar, reflux ratio 2, D/F weight ratio 0.71773; theoretical plate number 30, feed position 8th plate, Catalyst layer 10-18 plate, catalyst dosage 140 m ³ ; methanol feed amount 5013 tpd, weight concentration 99.88%. The model calculation results showed that dimethyl ether produced 3598 tpd, the weight concentration was 92.35%, and the temperature at the top of the column was 56.1 ° C and 186.9 ° C.

The results obtained in the prior art were as follows: dimethyl ether produced 3598 tpd, the weight concentration was 99.61%, and the top and bottom temperatures were 52 ° C and 190 ° C. Although the tower temperature distribution is not stated, it should not differ from the simulated tower temperature by more than 4 °C. The difference may be due to the thermodynamic method of calculating the gas-liquid equilibrium, and the calculation of the physical property equation of the liquid molar concentration in the methanol dehydration rate formula.

The results show that the number of the two plates at the bottom of the catalytic layer, the temperature of the 17th and 18th plates has reached 151.5 ° C and 156.4 ° C, far exceeding the acid resin catalyst, such as Amberlyst The temperature limit of 35 is 140 °C. Therefore, under a certain tower pressure, such as 12 bar, or even down to 8-12 bar, it is not feasible to use a low-temperature liquid phase dehydration catalyst as a catalyst for the dimethyl ether catalytic distillation column.

Example 1 Using anhydrous methanol as feed

The simulated conditions of the dimethyl ether catalytic distillation column used were as follows: column pressure 11 bar, pressure difference of 0.025 bar per plate, 7th plate at the feed position (above the catalytic layer), initial reflux ratio 4, initial D/F molar ratio 0.4997. The calculation was performed using a prior art single bed low temperature catalyst catalytic layer and a simulated procedure for the double bed high temperature catalyst catalyst layer of the present invention.

The results show that if the conventional single-bed catalytic distillation column is replaced by the double-bed catalytic distillation column of the present invention, the catalytic layer must be increased by 4 plates to increase the methanol conversion rate, because the reaction rate of the high-temperature dehydration catalyst is relatively low, The amount of catalyst used is large, so that the number of plates of the catalytic layer is increased. However, in the present invention, after replacing a part of the low-temperature catalytic layer (17-20 plates) in the single-bed catalytic layer with a high-temperature catalytic layer (17-24 plates), the catalyst is catalyzed by the reaction and separation of the high-temperature catalytic layer. The temperature of the underlying media bed rises and is gentle, and the temperature of the low temperature dehydration catalyst at the end of the bed can be buffered, so that the activity and life of the low temperature dehydration catalyst are protected. Moreover, without changing the column structure and the media bed configuration, the operating variables can be switched to produce the desired grade, such as the production of chemical grade or fuel grade dimethyl ether. The conditions and results of the prior art single bed low temperature catalytic layer and the double bed catalytic layer of the present invention are shown in Table 1, Table 2 and Figure 5.

Table 1 Flow rate of single bed and double bed catalytic layer with anhydrous methanol as feed

Example 2 Feeding crude methanol

The feed composition is referred to US 5,750,799. The stream is derived from a process for producing methanol from syngas, and the crude methanol produced contains about 10-20 mol% of water. Without prior purification of the methanol concentration, the catalytic distillation column of the present invention can be directly used. Dehydration of methanol to produce dimethyl ether. The simulation conditions of the catalytic distillation column were as follows: column pressure 11 bar, pressure difference of 0.025 bar per plate, initial reflux ratio of 4, initial D/F molar ratio of 0.4997. The calculation was performed using a prior art single bed low temperature catalyst catalytic layer and a simulated procedure for the double bed high temperature catalyst catalyst layer of the present invention.

When the feed position is above the catalytic layer, the liquid flow in the column is larger than that in the first embodiment due to the water content of the feed, so the column diameter is relatively large. In addition, the theoretical calculation results of the single-bed and double-bed catalytic distillation columns are The tower temperature distribution of Fig. 5 is similar, and the temperature of the lower bed of the double bed is lower than the temperature of the single bed corresponding to the bed, thereby protecting the resin catalyst.

If the low temperature catalytic layer of the double bed is moved up by one plate number and the feeding position is adjusted to the middle of the double bed, the remaining conditions are unchanged, and under the convergence limit calculated by the program, the reflux ratio is increased to increase the conversion rate of methanol. The weight concentrations of dimethyl ether and bottom water were reduced to 99.3% and 98.9%, respectively.

If the feed position is moved down to the lower of the catalytic layer, for the structure of the single-bed catalytic layer, since the temperature of the medium bed is higher than 160 ° C, the low-temperature dehydration catalyst is destroyed, so only the high-temperature dehydration catalyst can be used.

The results of using the double bed catalytic layer of the present invention and the prior art single bed catalytic layer (high temperature or low temperature dehydration catalyst) are shown in Tables 3, 4, and 6.

* Prior art method, the function of low temperature dehydration catalyst is invalid due to high temperature

** Prior art method using high temperature dehydration catalyst

*** Figure 3 shows the flow rate of the condenser outlet (5) and the reboiler outlet (6)

****The number of feed plates is 7 for the feed above the catalytic layer, the number of feed plates is 9 for the feed between high and low temperature catalyst beds, and the number of feed plates is 16 for the feed under the catalytic layer.

Example 3 A mixture of components such as dimethyl ether, methanol, water, etc.

The feed composition is referred to US 5,908,963. The stream is derived from a one-step reaction process for producing dimethyl ether from a synthesis gas. The product of the test grade dimethyl ether reactor is separated by gas-liquid separation, and the components are carbon dioxide, dimethyl ether, methanol, and water. The weight percentages were 2.8, 49.7, 31.0, 16.5 wt%. Without considering the inert carbon dioxide, the number of feed plates can be located at the upper plate of the catalytic layer or the ninth plate between the upper and lower media beds. The theoretical calculation of the reflux ratio is 0.378, 1.22, and the chemical grade dimethyl ether product can be obtained. The results are detailed in Tables 5 and 6.

Figure 7 shows the temperature change of the catalytic layer. The feed from the feed port between the upper and lower media beds can alleviate the rapid change of the temperature of the upper and lower media beds and protect the catalyst of the upper medium bed. The quenching zone can be reserved in the middle of the double-bed catalytic layer. As an option of the feed port/heat exchange and reflux, the reaction temperature of the upper and lower media beds of the catalytic layer can be controlled by temperature, and the low-temperature dehydration catalyst of the upper medium bed can be protected.

* Prior art method, the function of low temperature dehydration catalyst is invalid due to high temperature

Example 4 A mixture of four components of dimethyl ether, carbon dioxide, methanol and water was used as a feed.

The composition of the feed is referred to US 5,908,963. After the gas phase separation of the test grade dimethyl ether reactor product, the weight percentages of the heavy components carbon dioxide, dimethyl ether, methanol and water are 2.8, 49.7, 31.0, 16.5 wt%. Limited by the column pressure, carbon dioxide cannot be liquefied, and the top of the catalytic distillation column is set as a partial condenser. The calculation conditions and results are shown in Table 7. The dimethyl ether produced contains 1.36 wt% carbon dioxide, which needs to be repurified in a distillation column. The carbon dioxide and dimethyl ether produced in the gas phase are 25 wt% and 75 wt%, respectively. The distillation column was repurified.

1. . . Inlet

2. . . Inlet

3. . . Inlet

4. . . Condenser outlet

5. . . Condenser outlet

6. . . Reboiler outlet

7. . . Low temperature reaction media bed

8. . . Skimming zone

9. . . Skimming zone

10. . . Skimming zone

11. . . High temperature reaction media bed

12. . . Heat exchange and reflux

twenty one. . . Anhydrous methanol

twenty two. . . Crude methanol

twenty three. . . a mixture of dimethyl ether, methanol, water and carbon dioxide

Figure 1 is a graph showing the relative volatility of methanol and water under different column pressures;

Figure 2 is a graph showing the relationship between temperature and gas-liquid equilibrium of methanol and dimethyl ether, and methanol and water at a pressure of 11 bar;

Figure 3 is a schematic diagram of a catalytic distillation column having a two-bed catalytic layer;

Figure 4 is a schematic view showing the application of a two-bed catalytic distillation column to a dimethyl ether process;

Figure 5 is a diagram showing the tower temperature distribution of an anhydrous methanol feed;

Figure 6 is a diagram showing the tower temperature distribution of the crude methanol feed;

Figure 7 is a graph showing the temperature distribution of a media bed using a mixture of dimethyl ether, methanol, water, and the like.

1. . . Inlet

2. . . Inlet

3. . . Inlet

4. . . Condenser outlet

5. . . Condenser outlet

6. . . Reboiler outlet

7. . . Low temperature reaction media bed

8. . . Skimming zone

9. . . Skimming zone

10. . . Skimming zone

11. . . High temperature reaction media bed

12. . . Heat exchange and reflux

Claims (10)

A two-bed catalytic distillation column having two catalyst systems, the upper layer is a low temperature reaction medium bed, and the lower layer is a high temperature reaction medium bed, between the low temperature reaction medium bed, the low temperature reaction medium bed and the high temperature reaction medium bed, and A high temperature reaction medium bed is provided with a feed port, and the low temperature reaction medium bed contains a low temperature dehydration catalyst, and the high temperature reaction medium bed contains a high temperature dehydration catalyst, wherein the temperature of the low temperature reaction medium bed is between 85 ° C and 135 ° C The temperature of the high temperature reaction medium bed is between 135 ° C and 250 ° C. The catalytic distillation column according to claim 1, wherein the low temperature dehydration catalyst is Amberlyst® 15 acid resin or Amberlyst® 35 acid resin. The catalytic distillation column of claim 1, wherein the high temperature dehydration catalyst is a fluorinated transition metal oxide, a sulfated transition metal oxide, a beta zeolite, and HZSM-5. The catalytic distillation column of claim 1, wherein the high temperature dehydration catalyst is coated with Teflon to enhance its hydrophobic properties. A method for producing dimethyl ether using a catalytic distillation column according to any one of claims 1 to 4, wherein the methanol-containing raw material is at a column pressure of 6-30 bar, from a low-temperature reaction medium bed, and a low-temperature reaction medium. The feed port between the bed and the high temperature reaction medium bed or under the high temperature reaction medium bed is subjected to a dehydration reaction, and finally dimethyl ether is obtained. For example, the method of claim 5, wherein the tower pressure is 8-14 bar. For example, in the method of claim 5, the quenching zone may be reserved between different reaction media beds as a feed position or heat exchange and reflux. For example, the method of claim 5, when the raw material is anhydrous methanol When the raw materials are directly fed from the bed of the low temperature reaction medium. For example, in the method of claim 5, when the raw material is syngas, it is first reacted into a mixture containing dimethyl ether, methanol and water, and then passed through a bed of a low-temperature reaction medium or a high-low temperature reaction medium bed. material. As in the method of claim 5, when the raw material is crude methanol, the raw material is fed between the high temperature reaction medium bed or the high and low temperature reaction medium bed.