RU2282613C2 - High-purity dimethyl ether production process - Google Patents

Abstract

FIELD: industrial organic synthesis.

SUBSTANCE: high-purity dimethyl ether is obtained via dehydration of methanol in presence of sulfo-ionite catalyst at 110-150^°C and pressure 4.9-13.2 atm gauge in combined reaction-rectification apparatus composed of two rectification zone and one middle reaction zone filled with catalyst. Methanol is fed to catalyst zone or to lower rectification zone. It is possible to dispose reaction and rectification zone both inside the same apparatus and separately in two or three apparatuses so to conduct a single reaction-rectification process. Desired ether is recovered from the top of apparatus. A part of dimethyl ether containing impurities is discharged from lower part of higher reaction zone in side withdrawal point corresponding to 1-10 theoretical plate (going from the bottom of rectification column).

EFFECT: improved quality of product.

2 cl, 3 dwg, 3 ex

Description

The present invention relates to the field of production of dimethyl ether, which finds application as a refrigerant, extractant, as a component of diesel fuel, household and cosmetic products.

High purity dimethyl ether (DME) is known to be an excellent propellant widely used in aerosol containers. A mandatory requirement for dimethyl ether used in household and cosmetic aerosols is its high concentration (above 99.99%), the presence of methanol not more than 0.0001% and, in certain cases, the absence of any foreign smell.

Currently, the main source of dimethyl ether is the production of methanol from synthesis gas, where dimethyl ether is formed as a by-product in the amount of 2-5% wt. Such processes are described in patents DE 2362944, DE 2757788 and DE 3220547.

Processes for the purification of DME from methanol, water and impurities by rectification are described in patents EP-A 0124078, EP-A 0270852, US 4802956, US 5037511.

The absence of extraneous odor in the purified DME is the main indicator of its quality when used, for example, in the manufacture of cosmetics. There are a number of impurities that are present in DME at the level of one ten thousandth percent, but give an unsuitable smell to the purified ether. These impurities have boiling points close to the boiling point of DME, which greatly complicates their separation by distillation. So, in the patent US 5037511, the presence of impurities such as methyl formate, hydrocarbons, carboxylic acids, esters, amides, acetals, etc. in the crude DME is noted.

Many processes are known in which dimethyl ether is obtained by the dehydration of methanol using various catalysts. According to DE 680328, aliphatic esters are obtained by heating alcohols in the presence of zinc chloride.

Patents GB 322756, GB 350010, GB 403402, US 1873537 and FR 701335 disclose a number of catalysts for the production of esters from alcohols, namely, compositions based on ferric chloride, tin chloride, manganese chloride, aluminum chloride and aluminum sulfate, alum, aluminum oxide titanium oxides, barium oxides, silica and aluminum phosphate.

The use of the above catalysts has a number of disadvantages, the main of which are:

- low processability associated with the need for frequent replacement, addition or regeneration of catalysts;

- the use of high temperatures and pressures;

- the need to use expensive equipment designed to work in conditions of high temperatures and pressures.

In patents DE 2818831, DE 3201155, EP-A 0124078, EP-A 0099676, more technologically advanced catalysts based on modified alumina, doped or undoped aluminosilicates are claimed. Thus, in patent DE 2818831 an aluminosilicate catalyst is indicated for producing dimethyl ether from methanol. US Pat. No. 5,037,511 describes a method according to which pure DME is obtained by catalytic dehydration in a separate reactor at a temperature of 140-500 ° C and a pressure of 1-50 ata, followed by isolation of DME by distillation.

The disadvantages of the above methods include the need to have a high temperature (up to 500 ° C) and pressure (up to 50 ata) in the DME synthesis reactors, as well as the tendency of the catalysts to coke formation at operating temperatures.

A method for producing dimethyl ether in a reactive distillation reactor is described (article “Obtaining dimethyl ether using the combined chemorectification technology” Chemical technology, No. 2, 2004, p. 34-41). According to the method, low-temperature catalysts of the Amberlyst-15W type, compositions based on Al ₂ O ₃ and copper compounds are used to dehydrate methanol in DME. The maximum pressure in the column apparatus is declared 3500 mm RT. column (4.6 ata), which corresponds to a cube temperature of 145-148 ° C, a reaction zone of 105-109 ° C, and a top of about 15 ° C. The total number of stages of separation, including the catalyst zone, does not exceed 20, and the reflux ratio is 2.6. On top of the target product concentration of 97 mol%. (98% wt.). The specified product is intended for use as motor fuel.

The disadvantage of this method is the low purity of the obtained DME, which limits the scope of its application.

Closest to the proposed technical solution is a method for producing dimethyl ether from a methanol-containing stream by contacting it with a dehydrating catalyst (RF Application No. 20022132017, published on July 10, 2004). The method is carried out in a reactive distillation system in which the reaction zone is connected by countercurrent flows of liquid and steam with exhaustive and strengthening distillation zones. The methanol-containing stream is fed to the reaction zone, and / or to the upper part of the exhaustive distillation zone, and / or to the lower part of the strengthening distillation zone. A stream containing predominantly DME is discharged from above the reinforcing zone, and a stream containing predominantly water is discharged from below the specified exhaustive zone. As the catalyst, a sulfonic ion catalyst is used with a particle size of at least 3 mm, preferably in the form of cylinders or mass transfer nozzles, in particular rings. Dehydration is carried out at a temperature of from 100 to 160 ° C and the concentration of water in the methanol stream returned to the reaction zone (s) is less than 12 wt%, preferably less than 5%.

The disadvantage of this method is, as in the above method, a low content of DME (not higher than 99.5%) with a methanol content of 0.5%. In addition, this method involves a two-reactor scheme for dehydration (Figs. 3 and 4), the selected stream of dimethyl ether is supposed to be subjected to water washing from methanol, and the water-methanol mixture is fed into the distillation zone from water and / or into the exhaustive distillation zone of the reaction-distillation system (item 13). VAT product of the distillation apparatus containing up to 5-12% wt. methanol, will require the separation of methanol from it, which will also lead to a complication of the technological scheme.

The present invention is to improve the quality of DME, which will expand the scope of its use: from motor fuels to cosmetics. In the latter case, increased requirements are imposed on DME both in terms of purity (above 99.99%) and in the absence of extraneous unsuitable odors. The methanol content is especially tightly regulated - less than 0.0001%. In addition, simplification of the technology is achieved while maintaining the high quality of the target product.

The indicated result is achieved by the method of producing high purity dimethyl ether by methanol dehydration in the presence of a sulfoionite catalyst at elevated temperature and pressure in a combined reaction-distillation apparatus, which consists of three zones: two distillation and a middle one — reaction, filled with a catalyst, and the target ether is removed from the top of the combined reactor, according to which dehydration is carried out with lateral selection of a portion of dimethyl ether enriched in impurities from the lower part of the upper rectum fication zone from 1-10 theoretical plates (counting from the bottom of the specified distillation zone), preferably from 3-5 theoretical plates.

Figure 1 shows the concentration profile of the reaction-distillation apparatus for impurities. To obtain DME, methanol of a concentration of 99.96% was used, the content of “light” impurities was 0.007773%, “heavy” was 0.001685%, and water was 0.03%. A survey of the concentration profile of the reaction-distillation apparatus indicates the concentration of so-called “light” impurities boiling in the temperature range above the boiling temperature of DME and below the boiling temperature of methanol in the lower part of the upper distillation zone. “Heavy” impurities boiling above the boiling point of methanol are concentrated in the region belonging to the reaction (catalyst) zone. The data on the distribution of impurities along the height of the reaction-distillation apparatus make it possible to determine the positions for removing accumulated impurities in order to avoid their entry into the selected DME and thus ensure its high purity and lack of smell.

The inventive method is illustrated by a variant of the technological scheme shown in figure 2.

The source methanol is heated in the heat exchanger 1 and fed to the apparatus 2. The reaction-distillation apparatus 2 includes three zones:

- the upper distillation zone for the separation of dimethyl ether from methanol;

- the average reaction zone filled with catalyst;

- a lower distillation zone for separating methanol from water formed as a result of the reaction.

In apparatus 2, dimethyl ether is synthesized and products are isolated. Pairs of pure DME are removed from the top of the apparatus, which are condensed in the condenser 3. The condensate is partially returned to the apparatus 2 as reflux, and the balance surplus is removed to the warehouse. Lateral sampling of a part of DME enriched with impurities contained in methanol and formed in the process is carried out along line 4. Water is taken from the cube of apparatus 2. The reaction-distillation apparatus is heated through a remote boiler 5.

Methanol is supplied either under the catalyst bed or in the upper part of the lower distillation zone.

It is possible to place the reaction and distillation zones both inside one column apparatus, and separately in two or three apparatuses in such a way that they together carry out a single reaction-distillation process.

The proposed method is illustrated by the following examples.

Example 1

The synthesis of dimethyl ether was carried out in a continuous mode in a reaction-distillation apparatus, made in the form of a collet column. The column consisted of 6 tsars with an inner diameter of 32 mm and was equipped with a heated cube and a reflux condenser. The two lower and two upper drawers were filled with an irregular nozzle in the form of a spiral with a diameter of 2 mm, made of nichrome wire. The effectiveness of each drawer was about 10 theoretical plates. The two middle shells were filled with a KIF catalyst, which is the product of sulfonation of a molded mixture of polyethylene and a copolymer of styrene with divinylbenzene, taken in a ratio of 30 to 70. The catalyst was made in the form of cylinders with a diameter of 2 mm and a length of 2 ÷ 5 mm.

The amount of loaded catalyst is 250 ml. The amount of methanol supplied was determined by the onset of equilibrium in the column, preventing its withdrawal from the bottom product.

Methanol in an amount of 60 ml / h was supplied to the lower part of the third drawer (score from the cube). The synthesis was carried out under the following conditions:

- top pressure - 8.7 ata;

- top temperature - 39 ° C;

- the temperature of the catalyst layers is 133 ÷ 127 ° C;

- the temperature of the cube is 174 ° C.

Pure dimethyl ether was selected from the top of the column with a basic substance concentration of more than 99.99% wt., Methanol content less than 0.0001% wt. in the amount of 41.6 ml / h. 13.5 ml / h of water was taken from the cube of the column. From the lower part of the sixth drawer (counting from a cube), lateral selection of DME enriched with undesirable impurities was carried out. The amount of selection was 10 ml / h. Lateral selection contained the following impurities (% wt.): Acetone - 0.00126; methyl ethyl ketone - 0,00070; methanol - 0.0010; methyl isopropyl ketone - 0,00040; ethanol - 0.00017.

The service life of the catalyst is about 5000 hours.

Example 2

The synthesis of dimethyl ether was carried out in the reaction-distillation system described in example 1. Amberlyst-15 sulfocationion was used as a catalyst. The amount of loaded catalyst is 250 ml.

Methanol in an amount of 60 ml / h was supplied to the lower part of the second drawer (score from the cube). The synthesis was carried out under the following conditions:

- top pressure - 8.7 ata;

- top temperature - 39 ° C;

- the temperature of the catalyst layers -133 ÷ 127 ° C;

- the temperature of the cube is -174 ° C.

From the top of the column was taken dimethyl ether with a concentration of the main substance of more than 99.99% wt. and the absence of extraneous odor (methanol content less than 0.0001% wt.) in the amount of 41.6 ml / h. 13.5 ml / h of water was taken from the cube of the column. From the lower part of the sixth drawer (counting from a cube), lateral selection of DME enriched with undesirable impurities was carried out. The lateral selection point corresponded to the tenth theoretical plate of the upper distillation zone. The amount of selection was 10 ml / h. Lateral selection contained the following impurities,% wt .: acetone - 0.00128; methyl ethyl ketone - 0,00065; methanol - 0.0098; methyl isopropyl ketone - 0,00039; ethanol - 0.00018.

The service life of the catalyst is about 5000 hours.

Example 3

The synthesis of dimethyl ether was carried out in the reaction-distillation system described in Example 1. Amberlyst sulfocationion - 15 was used as a catalyst. The amount of loaded cation exchange resin was 250 ml.

Methanol in an amount of 40 ml / h was fed into the upper part of the second drawer (count from the cube). The synthesis was carried out under the following conditions:

- top pressure - 4.9-5.0 at;

- top temperature - 20 ° C;

- the temperature of the catalyst layers -115 ÷ 110 ° C;

- cube temperature - 157 ° C.

Dimethyl ether was selected from the top of the column with a basic substance concentration of more than 99.99% wt., Methanol content of less than 0.0001% wt. in an amount of 29.4 ml / h. Water was taken from the cube of the column in an amount of 9 ml / h. From the bottom of the fifth drawer (counting from the cube), lateral selection of DME enriched in undesirable impurities was carried out. The side sampling point corresponded to the first theoretical plate of the upper distillation zone. The amount of selection was 5 ml / h. Lateral selection contained the following impurities,% wt .: acetone - 0.00214; methyl ethyl ketone - 0.00126; methanol - 1.58; methyl isopropyl ketone - 0,00097; Thanol - 0.00032.

The service life of the catalyst is about 5000 hours.

Example 4

The synthesis of dimethyl ether was carried out in a reactive distillation system, placed in three separate apparatuses, connected so that they formed a single reactive distillation system. The technological scheme is presented in figure 3. Each of the devices consisted of two tsars. Two apparatuses (1 and 3) were used as the lower and upper distillation zones and were filled with an irregular nozzle in the form of a spiral with a diameter of 2 mm made of nichrome wire. The third apparatus (2) was used as a reaction zone. As a catalyst, Purolite S-275 sulfocationionite was used. The amount of loaded cation exchanger is 250 ml.

Methanol in the amount of 70 ml / h was fed into the middle of the second drawer (score from the cube). The synthesis was carried out under the following conditions:

- top pressure - 13.2 ata;

- top temperature - 50 ° C;

- the temperature of the catalyst layers -140 ÷ 150 ° C;

- the temperature of the cube is 190-192 ° C.

Pure dimethyl ether was selected from the top of the column with a basic substance concentration of more than 99.99% wt., Methanol content less than 0.0001% wt. in the amount of 61 ml / h. 16 ml / h of water was taken from the cube of the column. From the middle part of the fifth drawer (counting from a cube), lateral selection of DME enriched with undesirable impurities was carried out. The lateral selection point corresponded to the fourth theoretical plate of the upper distillation zone. The selection amount was 7 ml / h. Lateral selection contained the following impurities,% wt .: acetone - 0.00263; methyl ethyl ketone - 0.001264; methanol - 0.0687; methyl isopropyl ketone - 0,00042; ethanol - 0,00022.

The service life of the catalyst is about 3000 hours.

As can be seen from the above examples, the stated process conditions make it possible to obtain DME of a high concentration of 99.99% and higher and without any foreign unsuitable odor (methanol content less than 0.0001% by weight), which significantly expands the scope of DME using a simpler technology.

It should also be noted that the use of a coarse granular sulfonated ionized catalyst in the process will make it easy to implement the process on an industrial scale.

Claims (2)

1. A method of producing high purity dimethyl ether by dehydration of methanol in the presence of a sulfoionite catalyst at elevated temperature and pressure in a combined reaction-distillation apparatus, consisting of three zones: two distillation and an average reaction, filled with catalyst, and the target ether is removed from the top of the apparatus with methanol supply or in the catalyst zone, or in the lower distillation zone, while it is possible to place the reaction and distillation zones both inside one apparatus, and separately in two or three devices in such a way that they together carry out a single reaction-distillation process, characterized in that the dehydration is carried out at a temperature of 110-150 ° C, a pressure of 4.9-13.2 atm with a side selection of part of dimethyl ether enriched with impurities , from the lower part of the upper distillation zone at the point of lateral selection corresponding to 1-10 theoretical plates (counting from the bottom of the specified distillation zone). 2. The method according to claim 1, characterized in that the lateral selection is carried out at a point of lateral selection corresponding to 3-5 theoretical plates.

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