CN107286002B

CN107286002B - Method for refining polymethoxy dimethyl ether 2

Info

Publication number: CN107286002B
Application number: CN201610223987.2A
Authority: CN
Inventors: 张彬; 刘文杰
Original assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Current assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Priority date: 2016-04-12
Filing date: 2016-04-12
Publication date: 2020-09-04
Anticipated expiration: 2036-04-12
Also published as: CN107286002A

Abstract

The technical scheme of the invention is as follows: the refining method of the polymethoxy dimethyl ether 2 comprises the following steps: (a) selected from the following steps (a1) or (a 2); (a1) rectifying raw materials to be refined in a PODE2 separation tower to obtain a tower top material and a tower bottom material which is basically PODE 2; the raw material to be refined is PODE2 crude material; (a2) rectifying raw materials to be refined in a PODE2 separation tower to obtain tower top materials and tower bottom materials which are basically PODE2 and DMM; the raw material to be refined contains the PODE2 crude material and introduced DMM material; (b) feeding the tower top material obtained in the step (a) into a methanol/water rectifying tower; separating the methanol/water rectifying tower to obtain tower top material and tower bottom material of low pressure rectifying heavy component basically comprising methanol and water; (c) returning the overhead material obtained in the step (b) to a PODE2 separation tower; the crude PODE2 material contained PODE2, water and methanol.

Description

Method for refining polymethoxy dimethyl ether 2

Technical Field

The invention relates to a method for refining polymethoxy dimethyl ether 2.

Background

Polyoxymethylene dimethyl ether (PODE) is a generic term for a class of substances, whose brief formula can be represented as CH₃O(CH₂O)_nCH₃. PODE has high oxygen content (42-51% is different) and cetane number (more than 30), can improve the combustion condition of diesel oil in an engine, improve the thermal efficiency, and simultaneously reduce the emission of solid pollutants, COx and NOx. It is reported that 5-30% of CH is added₃OCH₂OCH₃Can reduce NOx emission by 7-10% and PM by 5-35%. Thus, PODE is considered to be a novel methanol derivative with great application prospect and can be used for diesel oil blending.

PODE can be synthesized from methanol and formaldehyde by acid-catalyzed dehydration. The industrial synthesis of synthesis gas from coal gasification, methanol from synthesis gas and formaldehyde from methanol oxidation are all relatively mature routes. The addition amount of PODE in diesel oil can be very high (up to 30%), and the addition of PODE can not only replace part of diesel oil, but also improve the combustion efficiency and emission performance of diesel oil. In 2006, the diesel consumption of China is 1.16 million tons, and if 30% of diesel is replaced by PODE, the import dependence of China's petroleum can be reduced by 3400 ten thousand tons, which is a very considerable number. Therefore, the research on the synthesis of PODE has great significance for relieving the environmental protection pressure of China, developing and utilizing coal resources and further on national energy safety.

The discovery of PODE was earlier, but only recently has it started to attract the interest of experts and scholars. At present, the synthesis of PODE is researched by BP, BASF and other companies internationally, and a small amount of patents are applied. From the reports of published documents, the reaction route has not received attention of foreign academic circles, and related basic or application researches are few, and no industrialization reports are seen. Under the situation that petroleum resources are increasingly scarce, compared with the routes of preparing olefin from coal through methanol, preparing ethylene glycol from coal through synthesis gas and the like, the synthesis of coal-based PODE is a novel coal chemical industry route with great application potential.

Domestic related PODE_nThe research on the synthesis technology of (2) has been gradually carried out in recent years, and the research on PODE (PODE-based pod) by the national institute of chemistry and physics, Shanghai institute of petrochemical engineering, Shanxi institute of coal chemical engineering, and the university of eastern China_nThe synthesis of (2) was studied in the related art and a few patents were filed. From the reports of published documents, the reaction route has started to be concerned by academia, but related basic or application researches are few, and the problems of low catalyst activity, difficult regeneration, low product selectivity, complex process and the like exist.

Currently, only Shandong (Neze) Xin new energy company and Zhongkojie Langhua institute are seen as industrialized reports to build ten-thousand-ton PODE_nThe device, its hundred tons class device, in 2012 completed the pilot test at gansu silver pilot base. The technology takes methanol as raw material and ionic liquid as catalyst to synthesize PODE (potassium iodide) by trioxymethylene_n. The related research mainly focuses on a homogeneous reaction system taking ionic liquid as a catalyst, and the process has the inherent defects of homogeneous catalytic reaction, such as high price of the ionic liquid catalyst, difficulty in complete separation of the ionic liquid catalyst and a product in the recycling process and the like.

Since in the synthesis of PODEn, individual components of n-1-6 are produced. When the value of n is 1, the polymethoxy dimethyl ether is methylal (DMM), and the methylal serving as the vehicle fuel additive component can improve the energy utilization rate and reduce the exhaust emission, but can still cause air resistance. When n is 2, the flash point of polyoxymethylene dimethyl ether (namely polyoxymethylene dimethyl ether 2 or PODE2 for short) is too low to facilitate compression ignition, so that the n is a component of 3-6 in common use.

Synthesis and isolation of PODE was first reported in patents, but until recently, attention was drawn due to the rising price of petroleum and the stricter requirements for environmental protection. As can be seen from the international patent that has been filed, the patents filed after 1998 are the most important. Most patents obtain PODE through dehydration reaction of methanol and formaldehyde, but the presence of water in the system can increase the separation energy consumption, cause hydrolysis reaction of hemiacetal as an intermediate product of the reaction, and reduce the yield of PODE products.

In the presence of an acid catalyst, methylal and trioxymethylene (and/or paraformaldehyde) are used as raw materials to produce PODE, a reaction product is firstly separated into a top component containing DMM, PODE containing n more than 2 and a small amount of water through a DMM separation tower at the operation pressure of 100-150 kPa, the tower bottom temperature of 90-120 ℃ and the tower top temperature of 40-50 ℃, the method comprises the following steps of (1) obtaining a DMM tower bottom material containing a small amount of methanol and a small amount of trioxymethylene, wherein the DMM tower bottom material passes through a PODE product separation tower at the operation pressure of 35-60 kPa to obtain a PODE2 crude material (the raw material to be refined is obtained after the DMM is added) which is a component containing PODE2, a small amount of water (1-3%) (w) and a small amount of methanol (1-4%) (w) (sometimes containing negligible DMM) at the top of the PODE separation tower, and a product component containing n being 3-6 at the bottom of the PODE separation tower. In order to reduce cost and increase efficiency, PODE2 and/or DMM in the top component of the PODE separation column needs to be returned to the reactor for further reaction, but water and methanol in the top component of the PODE separation column are unfavorable for the reaction process, and water and methanol need to be removed.

CN 104447221a (purification method of polyoxymethylene dimethyl ether) specifically discloses a method for removing methanol in PODE2 by using cyclohexane, n-hexane, methyl formate, ethyl acetate, methyl propionate or n-heptane as an azeotropic solvent. But no specific disclosure is made of the removal of water from light component materials including DMM, PODE2, water and methanol.

Disclosure of Invention

The invention aims to solve the technical problem of providing a novel refining method of polymethoxy dimethyl ether 2, which has the advantage of simultaneously removing methanol and water.

In order to solve the technical problems, the technical scheme of the invention is as follows: the refining method of the polymethoxy dimethyl ether 2 comprises the following steps:

(a) selected from the following steps (a1) or (a2):

(a1) rectifying the raw material to be refined in a PODE2 separation tower A to obtain a tower top material 7 and a tower bottom material 3 which is basically PODE 2; the raw material to be refined is PODE2 crude material 1;

(a2) rectifying raw materials to be refined in a PODE2 separation tower A to obtain a tower top material 7 and a tower bottom material 3 which is basically PODE2 and DMM; the raw material to be refined contains the PODE2 crude material 1 and introduced DMM material 2;

by way of non-limiting example, wherein in step (a) the bottoms of substantially PODE2 and DMM are by weight: PODE2 content 70-100%, DMM content 5-40%; preferably, the content of PODE2 is 75-100%, and the content of DMM is 10-30%; more preferably, the PODE2 content is 80-100%, and the DMM content is 10-20%.

(b) Feeding the tower top material 7 obtained in the step (a) into a methanol/water rectifying tower B; separating the methanol/water rectifying tower B to obtain a tower top material 6 and

tower bottom materials

4 and 5 which are low-pressure rectifying heavy components of methanol and water basically; by way of non-limiting example, the substantially methanol and water lower pressure distillation heavy components 4 have by weight: the content of methanol is 20-80%, and the content of water is 20-80%; preferably, the content of methanol is 30-70%, and the content of water is 30-70%; more preferably, the content of the methanol is 40-60%, and the content of the water is 40-60%;

(c) returning the overhead material 6 obtained in the step (b) to the PODE2 separation tower A;

the crude PODE2 material 1 contains PODE2, water and methanol; the operating pressure of the PODE2 splitter a is higher than the operating pressure of the methanol/water rectifier B. By adopting the scheme, the content of water and methanol in PODE2 material can be reduced.

In the above embodiment, the operating pressure of the separation column a of PODE2 is preferably at least 450 kPa. The higher the operation pressure of the PODE2 separation tower A is, the better the effect is for removing water in the PODE2 crude material, but 450-700 kPa is preferred in consideration of equipment material and operation difficulty.

In the above-described embodiment, the operating pressure of the methanol/water rectifying column B is preferably 200kPa or lower. The lower the pressure, the better the separation effect of DMM material from water and methanol, but the lower the pressure operation reaches negative pressure, the equipment investment is increased, so 100-200 kPa is preferred.

By adopting the operation of high-pressure rectification and the operation of low-pressure rectification, the water and the methanol in the PODE2 material can be further removed on the basis of pure high-pressure rectification, and the process loss of DMM can be reduced.

In the above technical scheme, the raw material to be refined preferably contains PODE2 and the following components in percentage by mass:

H₂ O 1～4％；H₂o is more preferably 1.3-4%;

0.7-3% of methanol;

0-40% of DMM. Preferably, the DMM is greater than 0, and the DMM content can be, for example, but not limited to, 5%, 10%, 20%, 30%, etc. The higher the DMM content is, the more thorough the water and methanol removal is, but the higher the DMM content is, the higher the energy consumption is, and the comprehensive consideration can be, for example, 10-30%.

In the above technical solution, the raw material to be refined after the DMM material 2 and the crude material 1 of the PODE2 are mixed is fed into the PODE2 separation tower a, or the DMM material 2 and the crude material 1 of the PODE2 are fed into the PODE2 separation tower a respectively and mixed in situ to obtain the raw material to be refined.

In the technical scheme, the theoretical plate number of the PODE2 separation column A is preferably 20-60, the reflux ratio is preferably 1.5-8, the operation temperature at the top of the column is preferably 90-96 ℃, and the operation temperature at the bottom of the column is preferably 150-170 ℃.

In the technical scheme, the theoretical plate number of the methanol/water rectifying tower B is preferably 15-70, the reflux ratio is preferably 1-6, the tower top operation temperature is preferably 37-58 ℃, and the tower bottom operation temperature is preferably 80-110 ℃.

In the above technical solution, the top material of the PODE2 separation column a preferably provides heat load for the methanol/water rectification column B. At the moment, the energy integration design is effectively carried out by utilizing the temperature difference between the high-pressure tower and the low-pressure tower, and the energy consumption and the operating cost of the system are reduced. More preferably, at least a portion of the bottoms stream 5 of step (B) is heated by the PODE2 splitter a heat exchanger and returned to the methanol/water rectification column B;

in the above technical solution, the rectifying tower comprises at least one PODE2 separating tower a and at least one methanol/water rectifying tower B, and it is within the scope of the present invention as long as the combined operation of high pressure rectification and low pressure rectification can be achieved.

By adopting the technical scheme of the invention, the contents of methanol and water in PODE2 material can be simultaneously reduced, and the methanol and water can be completely removed under the process conditions of the specific implementation mode of the invention, thereby obtaining beneficial technical effects and being used in the refining production of PODE 2.

The invention is further illustrated by the following examples in conjunction with the accompanying drawings.

Drawings

FIG. 1 is a schematic flow diagram of one embodiment of the present invention.

In fig. 1: the raw material feed of PODE2 is 1, the material feed of DMM is 2, the high-pressure rectification heavy components of PODE2 and DMM are 3, the low-pressure rectification heavy components containing methanol and water are 4, the overhead condenser of a PODE2 separation tower A is 5, the methanol/water rectification tower B provides heat load materials, the overhead distillate of the methanol/water rectification tower B returns to the material of the separation tower A, and the high-pressure PODE2 separation tower A rectifies light components is 7.

A is PODE2 knockout tower, B is methanol/water rectifying tower, C is PODE2 knockout tower condenser, D is methanol/water rectifying tower condenser, E is PODE2 knockout tower reboiler.

Detailed Description

[ example 1 ]

The operation is carried out according to the flow shown in figure 1, wherein heavy components containing the polyoxymethylene dimethyl ether and the DMM are separated out by a PODE2 separation tower and returned to the original system for reaction, and the overhead distillate enters a methanol/water rectifying tower B to separate out impurities such as methanol, water and the like. Carrying out high-pressure rectification on a raw material to be refined containing DMM, PODE2, water and methanol by a PODE2 separation tower to obtain a high-pressure rectification heavy component containing PODE2 and DMM and a high-pressure rectification light component containing DMM, water and methanol; the operating pressure of the high-pressure rectification of the PODE2 separation column A is 505 kPa; the high-pressure rectification light component of the PODE2 separation tower A is preferably further subjected to low-pressure rectification by a methanol/water rectification tower B to obtain a low-pressure rectification light component containing DMM and a low-pressure rectification heavy component containing methanol and water; the operating pressure of the low-pressure rectification of the methanol/water rectifying tower B is 102 kPa; the raw material to be refined preferably contains PODE2 and the content of the components in percentage by mass is shown in Table 1; two rectifying towers are selected and connected in series, the distillate at the top of the former rectifying tower enters the next rectifying tower which is respectively a PODE2 separating tower A and a methanol/water rectifying tower B, the high-pressure rectification is carried out in the PODE2 separating tower A, and the low-pressure rectification is carried out in the methanol/water rectifying tower B; mixing DMM material and PODE2 material containing methanol and water to obtain raw material to be refined, and rectifying in PODE2 separation column A under high pressure; at the moment, the theoretical plate number of the PODE2 separation tower A is 20, the reflux ratio is 2.5, the operation temperature of the tower top is 94 ℃, and the operation temperature of the tower kettle is 145 ℃; the theoretical plate number of the methanol/water rectifying tower B is 20, the reflux ratio is 1.9, the operation temperature of the top of the tower is 42 ℃, and the operation temperature of the bottom of the tower is 87 ℃; in operation the overhead of the methanol/water rectification column B is preferably returned to the PODE2 splitter column a; while the overhead condenser of the PODE2 splitter a preferably provides the heat load for the methanol/water rectification column B.

The feed composition and separation effect of the feed in example 1 are shown in tables 1 and 2. From tables 1 and 2, it can be seen that the returned material is almost free of methanol and water, and in the conventional operation, the methanol content of the returned PODE2 is generally limited to 2% or less, while the water content is 1% or less. Therefore, the method of the invention completely meets the separation requirement required by the system and has obvious advantages.

[ COMPARATIVE EXAMPLE 1 ]

Cyclohexane was used instead of DMM, and a single-column operation was used, similar to the operating conditions of patent CN 104447221A (refining method of polyoxymethylene dimethyl ether). In this case, in FIG. 1, there was no returned material 6, the overhead product was 7, the bottom product was 3, the theoretical plate number of the column was 20, the reflux ratio was 6.8, the operating pressure was 103kPa, the top temperature was 66 ℃ and the bottom temperature was 105 ℃. The feed is shown in Table 3, and from the separation results in tables 3 and 4, it can be seen that although methanol can be removed by adding the azeotropic agent, water contained in the feed cannot be completely removed efficiently.

[ COMPARATIVE EXAMPLE 2 ]

Cyclohexane was used instead of DMM, still using a single column operation, i.e. similar to the operating conditions of patent CN 104447221A (refining method of polyoxymethylene dimethyl ether). In this case, in FIG. 1, there was no returned material 6, the overhead product was 7, the bottom product was 3, the theoretical plate number of the column was 20, the reflux ratio was 6.8, the operating pressure was 505kPa at a high pressure, the temperature at the top of the column was 105 ℃ and the temperature at the bottom of the column was 159 ℃. The feed is shown in Table 5, and from the separation results in tables 5 and 6, it can be seen that although methanol can be removed by adding the entrainer, it is still not completely effective for removing water contained in the feed at high pressure operation.

[ COMPARATIVE EXAMPLE 3 ]

Except that cyclohexane was used in place of DMM, and the other steps were performed in the same manner as in example 1 using a high-pressure column and a low-pressure column, as follows:

the operation is carried out according to the flow shown in fig. 1, wherein heavy components such as polymethoxy dimethyl ether, trioxymethylene and the like are separated out by a PODE2 separation tower, and are returned to the original system to react, and the overhead distillate enters a methanol/water rectifying tower B to separate out impurities such as methanol, water and the like. Carrying out high-pressure rectification on a raw material to be refined containing DMM, PODE2, water and methanol to obtain a high-pressure rectification heavy component containing PODE2 and DMM and a high-pressure rectification light component containing DMM, water and methanol; the operating pressure of the high-pressure rectification of the PODE2 separation column A is 505 kPa; the PODE2 separation column A had a theoretical plate number of 20, a reflux ratio of 0.2 and an operating pressure of 505 kPa; the high-pressure rectification light component is preferably further subjected to low-pressure rectification by a methanol/water rectification tower B to obtain a low-pressure rectification light component containing DMM and a low-pressure rectification heavy component containing methanol and water; the theoretical plate number of the methanol/water rectifying tower B is 20, the reflux ratio is 0.15, and the operating pressure is 102 kPa; the raw material to be refined preferably contains PODE2 and the content of the components in percentage by mass is shown in Table 7; two rectifying towers are selected and connected in series, the distillate at the top of the former rectifying tower enters the next rectifying tower which is respectively a PODE2 separating tower A and a methanol/water rectifying tower B, the high-pressure rectification is carried out in the PODE2 separating tower A, and the low-pressure rectification is carried out in the methanol/water rectifying tower B; mixing DMM material and PODE2 material containing methanol and water to obtain raw material to be refined, and introducing into the high-pressure PODE2 separation column A; at the moment, the operation temperature of the top of the PODE2 separation tower A is 91 ℃, and the operation temperature of the bottom of the tower is preferably 132 ℃; the tower top operating temperature of the methanol/water rectifying tower B is 51 ℃, and the tower bottom operating temperature is 106 ℃; in operation the overhead of the methanol/water rectification column B is preferably returned to the PODE2 splitter column a; while the overhead condenser of the PODE2 splitter a preferably provides the heat load for the methanol/water rectification column B.

The feed composition and separation effect of the feed in comparative example 1 are shown in tables 7 and 8. From tables 7 and 8, it can be seen that although the introduction of the entrainer recovered PODE2 and removed water, the methanol content in the returned PODE2 did not decrease but rather increased, and the requirement of the methanol content in the returned material being less than 2% was not met, and that the new impurity entrainer was also introduced in the returned PODE2 and that part of the entrainer was also carried away in the bottom distillate of the low pressure methanol/water rectification column B, which is not acceptable.

[ COMPARATIVE EXAMPLE 4 ]

Consider the PODE2 splitter A pressure employed at 450kPa and the methanol/water rectifier B pressure at 102 kPa. Considering the feed as in table 9, the separation effect of PODE2 separation column a will be poor at this time, while methanol/water rectification column B cannot accomplish the separation task due to the inability of high pressure PODE2 separation column a to accomplish the separation task due to the inability of high pressure PODE2 separation column a, the separation effect of PODE2 separation column a bottom is shown in the last column of table 10, it can be seen that water is still in the returned PODE2, and much DMM is lost in the returned PODE2, i.e. the related DMM is not fully utilized. It is found that the column pressure of the high-and low-pressure column, PODE2 separation column A, is strictly required, and it is recommended to perform the separation operation at 500KPa or more.

[ example 2 ]

Similar to example 1, consider another feed scenario having feed specific values, see table 11, for a high pressure PODE2 splitter a with theoretical plate number of 20, reflux ratio of 1.7, and operating pressure of 555 kPa; the light distillation component of the high-pressure PODE2 separation tower A is preferably further rectified by a low-pressure methanol/water rectification tower B to obtain a low-pressure rectification light component containing DMM and a low-pressure rectification heavy component containing methanol and water; the number of theoretical plates of the low-pressure methanol/water rectifying tower B is also 20, the reflux ratio is 1.3, and the operating pressure is still 102 kPa; the raw material to be refined preferably contains PODE2 and the content of the components in percentage by mass is shown in Table 11; two rectifying towers are still selected and connected in series, the distillate at the top of the former rectifying tower enters the next rectifying tower which is respectively a PODE2 separating tower A and a methanol/water rectifying tower B, the high-pressure rectification is carried out in the PODE2 separating tower A, and the low-pressure rectification is carried out in the methanol/water rectifying tower B; mixing DMM material and PODE2 material containing methanol and water to obtain raw material to be refined, and introducing into high-pressure PODE2 separation column A; at the moment, the operation temperature of the top of the PODE2 separation tower A is 98 ℃, and the operation temperature of the bottom of the separation tower A is 151 ℃; the tower top operating temperature of the methanol/water rectifying tower B is 42 ℃, and the tower bottom operating temperature is 84 ℃; the other related operations are similar to those of example 1.

The separation effect corresponding to the system is shown in table 11 and table 12, and it can be found from the table that the expected separation effect can be achieved by selecting the method of the present invention according to different feeding requirements in a proper operation range, and the requirement of returning the PODE2 to the raw material is met.

In the data of the table in the present specification, E represents × 10, and the numerical value following E represents the corresponding power of 10.

TABLE 1 Material Mass composition Structure

TABLE 2 Material Mass fraction composition Structure

TABLE 3 Material Mass composition Structure

TABLE 4 composition of mass fractions of materials

TABLE 5 Material Mass constitution Structure

TABLE 6 composition of mass fractions of materials

TABLE 7 Material Mass constitution Structure

TABLE 8 composition of mass fractions of materials

TABLE 9 Material Mass constitution Structure

TABLE 10 composition of mass fractions of materials

TABLE 11 Material Mass constitution Structure

TABLE 12 composition of mass fractions of materials

Claims

1. The refining method of the polymethoxy dimethyl ether 2 comprises the following steps:

(a) selected from the following steps (a1) or (a2):

(a1) rectifying the raw material to be refined in a PODE2 separation tower (A) to obtain a tower top material (7) and a tower bottom material (3) which is basically PODE 2; the raw material to be refined is PODE2 crude material (1);

(a2) rectifying the raw material to be refined in a PODE2 separation tower (A) to obtain a tower top material (7) and a tower bottom material (3) which is basically PODE2 and DMM; the raw material to be refined contains the PODE2 crude material (1) and the introduced DMM material (2);

(b) feeding the tower top material (7) obtained in the step (a) into a methanol/water rectifying tower (B); separating the methanol/water rectifying tower (B) to obtain a tower top material (6) and tower bottom materials (4, 5) which are basically methanol and water and have low-pressure rectification heavy components;

(c) returning the overhead material (6) obtained in the step (b) to the PODE2 separation tower (A);

said PODE2 separation column (A) is operated at a pressure of at least 500 kPa;

the operating pressure of the methanol/water rectifying column (B) is 200kPa or less.

2. The purification process as claimed in claim 1, wherein the operating pressure of the methanol/water rectification column (B) is 100 to 200 kPa.

3. The refining method of claim 1, wherein the raw material to be refined contains PODE2 and the following components in percentage by mass:

H₂O 1～4％；

0.7-3% of methanol;

DMM，0～40％。

4. the purification process as claimed in claim 1, wherein the PODE2 separation column (A) has a theoretical plate number of 20 to 60, a reflux ratio of 1.5 to 8, an operation temperature at the top of the column of 90 to 96 ℃ and an operation temperature at the bottom of the column of 150-170 ℃.

5. The refining process as claimed in claim 1, wherein the theoretical plate number of the methanol/water rectifying column (B) is 15 to 70, the reflux ratio is 1 to 6, the operation temperature at the top of the column is 37 to 58 ℃ and the operation temperature at the bottom of the column is 80 to 110 ℃.

6. The purification process as claimed in claim 1, wherein the overhead from said PODE2 separation column (A) provides a heat load to said methanol/water rectification column (B).

7. Refining process according to claim 6, characterized in that at least part of the bottom stream (5) of step (B) is heated by the PODE2 knockout column (A) heat exchanger and returned to the methanol/water rectification column (B).