TWI417275B - A method of producing dimethyl ether - Google Patents

Description

Method for producing dimethyl ether by reactive distillation

The present invention relates to a method for producing dimethyl ether by reactive distillation, and more particularly to a method for combining a reactor and a distillation column into a single process equipment, in particular, under a column pressure of less than 8 Bar, ie Dimethyl ether can be produced by dehydration of methanol, which can save space requirements and equipment costs, and at the same time improve the conversion rate of raw material methanol and reduce the effect of energy waste.

Dimethyl Ether (DME) has the chemical formula CH ₃ OCH ₃ and has a boiling point of -25 ° C at normal pressure. It can be liquefied at room temperature to 5.4 bar (Bar) for storage, transportation and use. Dimethyl ether is currently used in chemical sprays, and according to statistics, the world's production capacity in 2009 exceeded 5 million tons, which is evident in the vast economic opportunities. Because the nature of dimethyl ether is close to that of liquefied petroleum gas, it can be directly added to the partial replacement of liquefied petroleum gas, which has the advantages of energy diversity. It is also called one of the new energy carriers in the 21st century. Ether combustion is also cleaner than diesel, which is environmentally friendly and belongs to clean fuels.

The preparation of dimethyl ether by dehydration of methanol is currently widely used in many countries in the world for the production of dimethyl ether, and there are quite a number of commercial processes. In the current commercial process, more than two process equipments are required, that is, at least one reactor and one dimethyl ether separation and purification device are required, and most of the dimethyl ether separation and purification devices are distillation towers or packed towers. . When the system is produced, the raw material (methanol) is firstly dehydrated in the reactor. After the dimethyl ether and water are formed, the dimethyl ether is recovered and purified from the recovered stream by using a dimethyl ether separation and purification device. . However, this traditional dimethyl ether production technology is limited by the balance of its dehydration reaction, so the conversion rate of methanol is mostly only between 80% and 90%. In other words, about 10% to 20% of methanol is wasteful. Whether it is necessary to use another separation and purification device for recovery and purification of methanol, it can be recycled.

Furthermore, the dehydration of methanol to form dimethyl ether is an exothermic reaction, and the conventional process of dehydrating methanol to produce dimethyl ether is less likely to recycle the heat released by the reaction, so that energy is also wasted.

In view of this, in recent years, a reactive distillation method has been developed, the characteristics of which are based on the chemical equilibrium and the Le Chatelier's principle. For chemical reactions with chemical equilibrium restrictions, after the reactants react in the system, The reactants and products were immediately separated. The method is characterized in that the product obtained by the reaction is different in relative volatility, so that the reaction distillation column not only has the effect of material separation, but also is continuously removed from the liquid phase due to the relatively high volatility product. The reaction is more favorable to the formation of the product, and the chance of occurrence of side reactions in the system will be relatively reduced, which shows that the production technology of this new state is extremely economical.

At present, the patent information retrieval system of the Republic of China has not found any patent for reactive distillation technology for dimethyl ether production. However, similar patents can be found in the US Patent and Trademark Office (USPTO), such as US 2007/0066855 A1, US 2009/0048468 A1, and US 2009/0069607 A1, but the technical contents of these similar patents are It is shown that the reaction distillation column needs to be operated at a higher pressure (>8 Bar) before the methanol can be dehydrated to produce dimethyl ether; however, when the operating pressure is higher, the required equipment cost, operating cost and energy consumption will follow. The higher.

In addition, a paper on the European Symposium (Stanislao et al., 2007) was also found in the literature. It also uses reactive distillation technology to produce dimethyl ether from methanol dehydration under the operating tower pressure of 8 to 12 Bar. The technical problems displayed in this conference paper are also the same as the above patents. Because of the higher operating tower pressure, the equipment cost, operating cost and energy consumption will be higher. Therefore, the general practitioners cannot meet the needs of the user in actual use.

The main object of the present invention is to overcome the above problems encountered in the prior art and to provide a process equipment (reactor and dimethyl ether separation and purification device) which can be realized by only one process equipment (reaction distillation column). The purpose is to combine the reactors and distillation towers that are common in traditional chemical processes into a process method, which can effectively save space requirements and equipment costs, and at the same time, can improve the conversion rate of raw materials methanol and reduce energy waste, thereby improving existing The commercial process makes the production process of dimethyl ether more economical and has the effect of saving energy and saving carbon.

In order to achieve the above object, the present invention is a process for producing dimethyl ether by reactive distillation, which is produced by using a methanol as a raw material by a reactive distillation method. The reactive distillation method is carried out in a single process equipment, and at the same time, the chemical reaction of the raw materials and the separation and purification of the products are carried out, and the methanol can be dehydrated to produce dimethyl ether under a column pressure of less than 8 Bar.

Please refer to FIG. 1 for a schematic diagram of the process for producing dimethyl ether from a reactive distillation column of the present invention. As shown in the figure: The present invention is a method for producing dimethyl ether by reactive distillation, using methanol as a raw material to produce dimethyl ether (Dimethyl Ether, DME/CH ₃ OCH ₃ ) by reactive distillation (Reactive Distillation) method. . The reactive distillation method of the present invention is carried out in a single process equipment, and at the same time, the chemical reaction of the raw materials and the separation and purification of the products are carried out, which at least comprises the following steps:

(A) Establishing a reactive distillation column 1 having a column top and a bottom, the temperature at the top of the column is between -25 and 40 ° C, and the temperature at the bottom of the column is between 84.6 and 170 ° C. Three sections of the distillation zone 11, the reaction zone 12 and the stripping zone 13, each zone is provided with a plurality of sieve plates (not shown), and in the reaction distillation column 1, the reaction zone 12 is filled with a catalyst, and the catalyst The reaction distillation column 1 further comprises a condenser 14 at the upper end of the tower and a reboiler 15 at the lower end of the tower bottom;

(B) introducing the raw material methanol into the reactive distillation column 1 having a column pressure of less than 8.0 bar (Bar), and feeding the liquid from the reaction zone 12 to the bottom of the column, and contacting the catalyst. A methanol dehydration reaction occurs, and the resulting product is dimethyl ether and water. Wherein, since dimethyl ether has high volatility, it is a gas in the above operating temperature and pressure range, so that an overhead stream containing dimethyl ether flowing in the top direction of the column is generated in the reactive distillation column 1, and the bottom portion is included The effluent water and the bottoms stream of methanol, the remaining methanol unreacted in the bottoms stream will be heated by the bottom reboiler 15 to be gasified upwards to the top of the column and condensed to the condenser 14 In contact with the catalyst, the ruthenium can be continuously circulated and reacted in the reactive distillation column 1, thereby increasing the conversion rate of the raw material methanol;

(C) Finally, high-purity dimethyl ether can be recovered at the top of the reaction distillation column 1, and most of the mixture recovered from the bottom outlet is water, and the balance is trace amount of methanol.

In the above step (A), the catalyst packed in the reaction zone 12 in the distillation column 1 may be one or more solid catalysts having dehydration, such as alumina, cerium oxide, cerium oxide, zirconium oxide, calcium phosphate, aluminum. Acid zinc, Al ₂ O ₃ -SiO ₂ , Al ₂ O ₃ -Cr ₂ O ₃ , Al ₂ O ₃ -MgO/SiO ₂ , MgO-Al ₂ O ₃ , cadmium oxide (CdO), zinc oxide (ZnO), ZSM-5, molecular sieves and acidic anion exchange resins.

In the above step (A), the rectification zone 11 and the stripping zone 13 in the distillation column 1 are provided with several sieve plates or filled with irregular inert materials, such as Rasching, Lessing or abalone. Pall, etc., to provide several distillation theoretical plates, to promote the separation of dimethyl ether from the reaction after the reaction.

The above step (B) allows the purity of the raw material methanol to be only 90% or more. The chemical reaction of the methanol dehydration to form dimethyl ether and water is as follows:

2CH ₃ OH CH ₃ OCH ₃ +H ₂ O;

This reaction is a reversible reaction. If dimethyl ether or water is removed from the reaction system, the reaction is continued in the direction of dimethyl ether formation, which improves the yield of dimethyl ether.

When utilized, the present invention is based on an engineering simulation in a preferred embodiment, the feed being 99% methanol and 1% water, fed to the reactive distillation column 1 at a feed rate of 114 tons per hour, as in Figure 1 shows. The reactive distillation column 1 has a total of 20 theoretical theoretical plates, and the top condenser 14 is the first plate, the bottom reboiler 15 is the 20th plate, and the rectification zone 11 in the column is the second plate to the first plate. 4 plates, the reaction zone 12 is the 5th plate to the 15th plate, and the stripping zone 13 is the 16th plate to the 19th plate. When the reactive distillation column 1 is operated at 6 Bar, the overhead condenser 14 is sufficient to completely condense the overhead gas stream into a liquid stream by using only normal room temperature water, and the methanol dehydration reaction rate is fast, and the dehydration reaction is in the reaction zone. Each of the plates in 12 is chemically balanced. When the material is fed from the eighth plate and the reflux ratio is 0.188, and the ratio of the outlet flow rate at the top of the column to the feed flow rate is 0.49, a purity of 99.5 mole% of dimethyl ether can be collected at the top of the column, and the temperature is 25.6. °C, the bottom discharge composition is about 97.6 mole% water, 2.4 mole% methanol and trace dimethyl ether, the temperature is 154 ° C; wherein the top condenser 14 power is -10.9 megawatts (MW), the tower The bottom reboiler 15 has a power of 10.4 MW and can achieve a methanol conversion rate of 98.597%.

Please refer to the "Fig. 2 and Fig. 3" for the change of the purity of the dimethyl ether and the methanol conversion rate of the feed position of the present invention and the effect of the feed position of the present invention on the power of the condenser and the reboiler. As shown in the figure: the performance of the reactive distillation column and energy consumption will be affected due to different feed locations. Therefore, the present invention illustrates the ratio of the fixed reflux ratio and the top outlet flow rate to the feed flow rate (as described above) in the above examples, and discusses the change in methanol conversion rate and the purity of the overhead product (ie, dimethyl ether) with different feed positions. . As shown in Tables 2 and 2 below, when the raw material methanol is fed between the eighth plate and the eleventh plate, the dimethyl ether purity curve 21 and the methanol conversion rate curve 22 are shown in the figure, and the collected two are obtained. Methyl ether has the highest purity and the highest conversion rate. In addition, it can be observed from Tables 1 and 3 below that when the raw material methanol is fed from the eighth plate to the eleventh plate, it can be seen from the condenser heat load curve 31 and the reheater heat load curve 32 in the figure. Not only does the condenser need to remove less heat, but the amount of heat that the reboiler needs to supply is also less; thus, it can be seen that the feedstock from the reaction zone is more advantageous for reactive distillation column performance and energy consumption.

As can be seen from the above, the present invention proposes a novel reactive distillation process which can achieve the purpose of two process equipments (reactor and dimethyl ether separation and purification device) by using only one process equipment (reaction distillation column), that is, It is a process method that combines the common reactor and distillation tower in the traditional chemical process. Since the catalyst is generally used to accelerate the progress of the chemical reaction, it can also be called Catalytic Distillation. The invention proposes that the dimethyl ether can be produced by dehydration of methanol under the operating tower pressure of less than 8 Bar. Compared with the conventional technology, the invention can save the space requirement and the equipment cost, and at the same time, can improve the conversion rate of the raw material methanol and reduce the conversion rate of the raw material methanol. Energy waste can improve existing commercial processes (methanol dehydration to produce dimethyl ether), make the production process of dimethyl ether more economical, and have the effect of energy saving and carbon saving.

In summary, the present invention is a method for producing dimethyl ether by reactive distillation, which can effectively improve various disadvantages of the conventional use, and uses methanol as a raw material to produce dimethyl ether by using reactive distillation (Dimethyl Ether). , DME / CH ₃ OCH ₃ ), the reaction distillation method is in a single process equipment, while the chemical reaction of the raw materials and the separation and purification of the product, the methanol can be dehydrated to produce dimethyl ether under a column pressure of less than 8 Bar It can effectively save space demand and equipment cost, and at the same time, can improve the conversion rate of raw material methanol and reduce energy waste, and can improve the existing commercialization process, make the production process of dimethyl ether more economical, and have energy saving and carbon saving. The efficacies, in turn, make the invention more progressive, more practical, and more in line with the needs of the user, and indeed meet the requirements of the invention patent application, and file a patent application according to law.

However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto; therefore, the simple equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the invention are modified. All should remain within the scope of the invention patent.

1. . . Reactive distillation column

11. . . Rectification zone

12. . . Reaction zone

13. . . Stripping zone

14. . . Condenser

15. . . Reboiler

twenty one. . . Dimethyl ether purity curve

twenty two. . . Methanol conversion curve

31. . . Condenser heat load curve

32. . . Reheater heat load curve

Fig. 1 is a schematic view showing the flow of a dimethyl ether produced by a reactive distillation column of the present invention.

Fig. 2 is a schematic view showing the change of the purity of the dimethyl ether and the methanol conversion rate in the feed position of the present invention.

Figure 3 is a graphical representation of the effect of the feed position of the present invention on the power of the condenser and reboiler.

1. . . Reactive distillation column

11. . . Rectification zone

12. . . Reaction zone

13. . . Stripping zone

14. . . Condenser

15. . . Reboiler

Claims (6)

A method for producing dimethyl ether by reactive distillation is carried out in a single process equipment, and a chemical distillation reaction of the raw material and separation and purification of the product are simultaneously carried out by a reactive distillation method, which comprises at least the following steps: (A) establishing At the top of the column and the bottom of the reaction distillation column, the temperature at the top of the tower is between -25 and 40 °C, and the temperature at the bottom of the column is between 84.6 and 170 °C. The structure in the column is divided into a rectification zone and a reaction zone. Three sections of the stripping zone, each section is provided with a plurality of sieve plates, and the reaction zone is filled with a catalyst in the reaction distillation column; (B) methanol is introduced into the reaction distillation column having a column pressure of less than 8.0 bar (Bar), Feeding from the reaction zone in the column and flowing to the bottom of the column, contacting the catalyst to form an overhead stream comprising dimethyl ether (Dimethyl Ether, DME/CH ₃ OCH ₃ ) and a bottoms stream comprising water and methanol; (C) recovering dimethyl ether having a purity higher than 99 mole% or more at the top of the reaction distillation column. A method for producing dimethyl ether by reactive distillation according to the first aspect of the patent application, wherein the reaction distillation column can be equipped with a plurality of sieve plates or filled with an irregular inert material. A method for producing dimethyl ether by reactive distillation according to the first aspect of the patent application, wherein the irregular inert material may be Rasching, Lessing or Pall ring (Pall) ). The method for producing dimethyl ether by reactive distillation according to the first aspect of the patent application, wherein the catalyst system may be one or more solid catalysts having dehydration, and may be alumina, cerium oxide or cerium oxide. , zirconia, calcium phosphate, zinc aluminate, Al ₂ O ₃ -SiO ₂ , Al ₂ O ₃ -Cr ₂ O ₃ , Al ₂ O ₃ -MgO/SiO ₂ , MgO-Al ₂ O ₃ , cadmium oxide (CdO ), zinc oxide (ZnO), ZSM-5, molecular sieves and acidic anion exchange resins. A method for producing dimethyl ether by reactive distillation according to the first aspect of the patent application, wherein the purity of the methanol is 90% or more. The method for producing dimethyl ether by reactive distillation according to the first aspect of the patent application, wherein the reaction distillation tower further comprises a condenser at the top of the tower and a reboiler at the bottom of the tower for The unreacted residual methanol in the bottom stream is heated, gasified upwards, and then condensed and liquefied to contact the catalyst, and the ruthenium is continuously circulated and reacted in the column.