CN111087287A - Method for separating polymethoxy dimethyl ether - Google Patents
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Abstract
The invention relates to a separation method of polymethoxy dimethyl ether, mainly solve the technical problem that the pipeline that is apt to produce is blocked and problem that the intermediate product recycles in the course of separating formaldehyde, through adopting the tower bottom supplies obtained after removing unreacted methylal of the first rectifying column, enter the catalytic rectifying column, the catalytic rectifying column is divided into four sections, second section and third section contain solid acid catalyst, collect PODE2 fraction containing water from second section top, return to the catalytic rectifying column after the membrane separation system dehydrates; extracting light fraction containing methanol from the upper part of the third section, and recycling the fraction at the top of the tower to a feed inlet below the second section; the technical proposal that the bottom liquid of the catalytic rectification tower enters a product tower and PODE3-4 or PODE3-5 products are extracted from the top of the product tower better solves the problem and can be used in the industrial production of separating the polyoxymethylene dimethyl ethers.
Description
Technical Field
The invention relates to a separation method of polyoxymethylene dimethyl ethers, in particular to a method for preparing and purifying high-purity PODE (polyoxymethylene dimethyl ether) from a reaction mixture containing polyoxymethylene dimethyl ethers obtained from a reaction taking polyformaldehyde as a raw material3-5The method of (1).
Background
With the rapid increase of energy consumption in modern society, the petroleum resources are increasingly tense, the environmental pressure is also increased, and the development of new clean diesel fuel is urgently needed. The oxygen-containing compound is used as the diesel additive, and no additional device or engine structure change is needed, so that the method is a convenient and effective measure and becomes a new idea for development of the petroleum industry.
Polyoxymethylene dimethyl ethers (PODE) are oxygen-containing compounds of the general formula CH3O(CH2O)nCH3Wherein n is an integer ≧ 1 (generally, the value is less than 10, and for PODE of different n, hereinafter, PODEN is expressed). PODE, particularly polymer with n being 3-5, not only has proper melting point and boiling point, but also has higher oxygen content (47% -49%) and cetane number (78-100), which is beneficial to improving the combustion condition of diesel oil in an engine, improving the thermal efficiency and reducing the pollutant emission; thus, PODE3～5The diesel fuel additive is an ideal component with great application prospect, can be used for partially replacing diesel oil, and improves the combustion efficiency of the diesel oil. At the same time, PODE2Has good solubility and is a potential high-quality solvent.
In recent years, the production of PODE has attracted much attention, and a large number of patents have been reported. In the process for synthesizing PODE from formaldehyde and methanol, water is inevitable as a reaction product, which is also a fatal disadvantage of the synthetic route. The reason is that the presence of water under acidic conditions tends to cause hydrolysis of PODE to form a hemiacetal, which is difficult to remove from PODE, making isolation and purification of PODE more complicated.
A method for controlling moisture from a source is to prepare PODE by taking methylal (DMM) and trioxymethylene or cheap paraformaldehyde as raw materials. US2449269 and US5746785 describe the synthesis of PODE from methylal with paraformaldehyde (or concentrated formaldehyde solution) in the presence of sulfuric acid and formic acid. European patent EP1070755A1 discloses a process for preparing PODE by reacting methylal with paraformaldehyde in the presence of trifluorosulfonic acid, the conversion of methylal being 54%, PODE E2～5The yield of (b) was 51.2%. CN103664549A and CN103880614A adopt paraformaldehyde as raw material and solid super acid as catalyst to synthesize PODE, the product contains unreacted raw material methylal and paraformaldehyde, and the composition of the reaction mixture contains 8.3% of unreacted paraformaldehyde besides methylal and PODE.
With the progress of research, in addition to paying attention to the selection of raw material routes and catalysts, more and more attention is paid to the subsequent separation and purification. In the preparation method of PODE, not only products, unreacted raw materials, formaldehyde (or paraformaldehyde) dissolved in a system, and even by-products such as methanol exist in a reaction mixture, and in order to obtain pure PODE for adding diesel, the reaction mixture needs to be separated and purified, and particularly, the separation problem of by-products such as formaldehyde and water becomes a technical bottleneck influencing the continuous and stable operation of the PODE separation process.
The PODE preparation processes introduced in CN101048357A and CN102786397A both adopt a multi-stage series rectification tower to prepare the PODE3～4Being a target product, PODE2The distillate is directly recycled to the reaction unit as a recycled material after rectification, so that the separation of formaldehyde (or trioxymethylene) is avoided. Chinese patent CN103333060B discloses a method for refining and refining polymethoxy dialkyl ether, which comprises adding 40-50 wt% sodium hydroxide aqueous solution into equilibrium reaction product, and performing condensation reflux treatment at 50-60 deg.C to achieve the purpose of eliminating formaldehyde reaction. CN103333061, CN103319319 and CN104672067 respectively describe that solid sulfite, sodium percarbonate and excessive ammonia gas are added into the reaction product in several times, and then condensation reflux treatment is carried out, and finally solid-liquid separation is carried out to obtain the PODNN refined product without aldehyde. The methods are all methods for removing formaldehyde by adding other substances into the product to perform chemical reaction with formaldehyde, so that the problem of formaldehyde polymerization in the rectification process is avoided, the loss of a certain proportion of reaction products is caused, the removed formaldehyde cannot be recycled, and the utilization rate of raw materials is reduced. CN104725198 introduces a method for dehydrating a polyoxymethylene dimethyl ether gas phase material flow, in which water in the gas phase material is removed by a two-stage adsorption tower alternate flow adsorption and regeneration method, so as to ensure the production continuity, but the adsorption and desorption method has high energy consumption and complex process and can cause more waste.
Our long-term study of the separation by distillation of the reaction mixture obtained by reacting methylal with paraformaldehyde found that PODE was isolated2During the rectification process, formaldehyde is easy to be aggregated on a condenser into white solid and accumulated along with the operation of the deviceThe blockage of the reflux pipe and the discharge pipe causes the shutdown for maintenance, and the continuous production operation for a long time is difficult.
Disclosure of Invention
The invention aims to solve the technical problems of pipeline blockage and intermediate product recycling easily caused in the separation process of formaldehyde in the existing refining process of polymethoxy dimethyl ether, and provides a separation method of polymethoxy dimethyl ether, which avoids the problems of pipeline blockage and the like easily caused in the separation process of formaldehyde, avoids the negative influence of water on a catalyst, and has the advantages of high PODE rectification efficiency and high yield of a target product.
In order to solve the technical problems, the technical scheme of the invention is as follows: the separation method of the polymethoxy dimethyl ether comprises the following steps:
(a) a material 1 to be separated containing DMM (methylal), formaldehyde and PODE2-6 firstly enters a first rectifying tower 2, a first light fraction 3 containing DMM is obtained at the top of the tower, and a first tower bottom liquid 4 containing formaldehyde and PODE2-6 is obtained at the bottom of the tower;
(b) the first tower bottom liquid 4 enters a catalytic rectifying tower 5 comprising four sections, a second light fraction 6 is obtained from the top of the catalytic rectifying tower 5, a material 7 containing byproducts such as methanol and the like is extracted from a side line of a third section 5-3, and a side line material 8 is extracted from a space between the second section and the third section; obtaining catalytic rectification tower bottoms 9 containing PODE3-6 from the tower bottom; the second light fraction 6 is circularly returned to the rectifying tower through the feed inlet; the side material 8 is dehydrated by a dehydration system 10 and then returns to the catalytic rectification tower;
(c) and (3) feeding the catalytic distillation tower bottoms 9 into a product tower 13, and collecting PODE3-4 or PODE3-5 products 14 from the top of the tower.
In the technical scheme, the theoretical plate number of the first rectifying tower in the step (a) is 10-30, the operation pressure is normal pressure, and the tower top temperature is 39-42 ℃.
In the above technical scheme, the catalytic distillation column in the step (b) is divided into four sections, wherein the first section 5-1 is a stripping section, the second section 5-2 and the third section 5-3 are reaction sections filled with acidic solid catalysts, and the fourth section 5-4 is a rectifying section.
In the above technical solution, the stripping section and the rectifying section in step (b) are preferably packed with close-packed packing or structured packing; the reaction zone is preferably packed with structured packing containing catalyst.
In the above technical solution, the solid acid catalyst in step (b) is selected from any one of a molecular sieve catalyst, a solid super acid, a sulfonic acid type cation exchange resin and a modified sulfonic acid type cation exchange resin; preferably HZSM-5 molecular sieve catalyst, sulfonic acid type cation exchange resin and metal ion modified sulfonic acid type cation exchange resin; more preferably sulfonic acid type cation exchange resin, and the inventors have surprisingly found that when the solid acid catalyst is preferably sulfonic acid type cation exchange resin, the total yield of PODE3-4 can be improved by about 10 percentage points or more under the same conditions.
In the technical scheme, the theoretical plate number of the catalytic distillation tower in the step (b) is 40-70, wherein the theoretical plate number of the first section 5-1 is 5-20; the theoretical plate number of the second section 5-2 is 10-25; the theoretical plate number of the third section 5-3 is 10-30; the theoretical plate number of the fourth section 5-4 is 5-15.
In the technical scheme, the operating pressure of the catalytic distillation tower in the step (b) is 0.1-0.5 MPa; the temperature of the tower top is 40-90 ℃; the temperature of the tower kettle is 150-250 ℃; the temperature of the first section is 120-180 ℃; the temperature of the second section is 100-130 ℃; the temperature of the third section is 60-110 ℃; the temperature of the fourth section is 40-90 ℃.
In the above technical solution, the membrane separation system 10) in step (b) includes a membrane separator, a vacuum system and a temperature control system; the membrane in the membrane separator is selected from one of an inorganic molecular sieve membrane, an organic polymer membrane or an organic-inorganic composite membrane.
In the technical scheme, the operating temperature of the membrane separator in the step (b) is 80-150 ℃, and the operating pressure of a vacuum system is 0-30 KPa.
In the technical scheme, the side material 8 in the step (b) is a gas-phase material, and the extraction position is between the second section 5-2 and the third section 5-3; the feed position is between the first section 5-1 and the second section 5-2.
In the above technical scheme, the position of the material 7 extracted in the step (b) is preferably a side line extraction above the third section 5-3.
In the technical scheme, the theoretical plate number of the product tower in the step (c) is 5-20, the operating pressure is 0.01-0.05 MPa, the tower top temperature is 70-135 ℃, and the reflux ratio is 0.1-1;
in the above technical solution, the content of PODE3-5 or PODE3-4 in the product fraction 14 of step (d) is 98-99.9% by weight.
Under the condition that the technical scheme is disclosed, a person skilled in the art can adjust the product composition into PODE3-4 or PODE3-5 according to the market demand condition.
Unless otherwise specified,% referred to in the present invention means weight percent or weight percent content.
We surprisingly found that the process mainly comprises rectification, an intermediate product PODE2 and formaldehyde are converted into PODE1-5 by catalytic rectification, a high-boiling PODE3-5 product is transferred to a tower bottom, PODE1-2 and a byproduct formaldehyde and the like are further separated and circulated in a rectification tower, and the balance is achieved in the catalytic rectification tower; through the coupling of rectification process conditions and reaction conditions, the further reaction of formaldehyde with PODE2 and DMM is promoted to produce PODE3-5, and the problems of pipeline blockage and the like easily generated in the separation process of formaldehyde are avoided; by combining membrane separation and rectification, the negative influence of water on the catalyst is avoided, and the rectification efficiency of PODE and the yield of target products are greatly improved.
By adopting the technical scheme of the invention, the purity of PODE3-4 or PODE3-5 in the obtained product fraction reaches more than 98 percent, and the separation and continuous rectification of paraformaldehyde can be ensured to be carried out smoothly.
Drawings
FIG. 1 is a process flow diagram of an embodiment of the present invention.
Firstly, a material 1 to be separated containing DMM, formaldehyde and PODE2-6 enters a first rectifying tower 2, a first light component 3 is obtained at the top of the tower, and a first tower bottom liquid 4 containing formaldehyde and PODE2-6 is obtained at the bottom of the tower; the first tower bottom liquid 4 enters a catalytic rectifying tower 5 containing four sections of fillers, a second light fraction 6 is obtained from the top of the catalytic rectifying tower 5, a first side material 7 containing byproducts such as methanol and the like is extracted from the side above a third section 5-3, and a second side material 8 is extracted from the space between the second section and the third section; the second side line material 8 enters a membrane separation system 10 for dehydration; and obtaining catalytic rectification tower bottoms 9 containing PODE3-6 from the tower bottom. The material passing through the membrane separator is converged with the second light fraction 6 and circularly returned to the rectifying tower through the feed inlet of the catalytic rectifying tower; and (3) feeding the catalytic rectification tower bottoms 9 into a product tower 13, and extracting PODE3-4 or PODE3-5 products 14 from the tower top, wherein the product tower bottoms 15 are materials containing high polymers.
Detailed Description
[ example 1 ]
The reaction mixed liquid from the synthesis reaction unit is used as a material to be separated and firstly enters a first rectifying tower, the number of the first rectifying tower is 30, a first light component is obtained under the conditions that the operation pressure is normal pressure and the temperature of the top of the tower is 40.7 ℃, and a first tower bottom liquid is obtained when the temperature of the bottom of the tower is 102 ℃; the first tower bottom liquid enters a catalytic rectifying tower containing four sections of fillers, the catalytic rectifying tower has 60 theoretical plates, the operation pressure is normal pressure, and the temperature of a tower kettle is 168 ℃; 15 theoretical plates are arranged in the stripping section, and the temperature is 120 ℃; 15 theoretical plates are arranged in the second section, the operation temperature is 95 ℃, and the filler containing the sulfonic acid type cation exchange resin catalyst is filled in the second section; the third stage has 20 theoretical plates, and is filled with filler containing sulfonic acid type cation exchange resin catalyst at 66 deg.C; the number of 10 theoretical plates in the rectifying section is total, the temperature at the top of the rectifying section is 42 ℃, a second light fraction is obtained from the top of the catalytic rectifying tower, a first side line material is collected from a 10 th theoretical plate, a second side line material is collected from a 30 th theoretical plate, the second side line material enters a membrane separation system, a membrane in a membrane separator is an inorganic molecular sieve membrane, the operating temperature is 100 ℃, the pressure at a permeation side is 10Kpa, the material passing through the membrane separator is converged with the second light fraction, and the second light fraction returns to the catalytic rectifying tower through a feed inlet at a 45 th theoretical plate for cyclic utilization; and (3) feeding the catalytic distillation tower bottom liquid obtained from the catalytic distillation tower bottom into a product tower, rectifying the product tower under the conditions that the operating pressure is 0.01MPa, the tower top temperature is 161 ℃ and the reflux ratio is 1, collecting PODE3-4 products from the tower top, and returning the product tower bottom liquid to the synthesis unit for recycling. Sampling each material flow, analyzing by gas chromatography, improving the total yield of PODE3-4 by 33.41%, and the quality purity of the product reaches 99.34%, and the analysis of each component is shown in Table 1.
TABLE 1
| Percent (b)% | DMM | PODE2 | PODE3-4 | PODE5-6 | Methanol | Water (W) | Formaldehyde (I) |
| To be separated | 48.5 | 26.55 | 15.9 | 3.37 | 2.53 | 0.15 | 3 |
| First tower bottoms | 0.10 | 52.21 | 31.27 | 6.63 | 3.73 | 0.29 | 5.89 |
| Second tower bottoms | 0.15 | 82.39 | 17.46 | ||||
| Product(s) | 0.18 | 99.34 | 0.48 | ||||
| Product kettle liquid | 1.75 | 98.25 |
[ COMPARATIVE EXAMPLE 1 ]
The first rectifying tower has 30 theoretical plates in total, the first light component is obtained under the conditions that the operating pressure is normal pressure and the tower top temperature is 40.7 ℃, and the first tower bottom liquid is obtained under the tower bottom temperature of 102 ℃; the first tower bottom liquid enters a rectifying tower containing four sections of fillers, the catalytic rectifying tower has 60 theoretical plates, the operating pressure is normal pressure, and the temperature of a tower kettle is 168 ℃; 15 theoretical plates are arranged in the stripping section, and the temperature is 120 ℃; the second section has 15 theoretical plates, the operation temperature is 95 ℃, and common fillers are filled in the second section; the third section has 20 theoretical plate numbers, common fillers are filled in the third section, and the operation temperature is 66 ℃; the number of 10 theoretical plates in the rectifying section is totally, and the temperature at the top of the tower is 42 ℃; and (3) extracting a first side line material from the 10 th theoretical plate, finding white solid aggregation at the position of the first side line extraction and the tower top, blocking the rectifying tower, and stopping the test.
[ COMPARATIVE EXAMPLE 2 ]
The reaction mixed liquid from the synthesis reaction unit is used as a material to be separated and firstly enters a first rectifying tower, the number of the first rectifying tower is 30, a first light component is obtained under the conditions that the operation pressure is normal pressure and the temperature of the top of the tower is 40.7 ℃, and a first tower bottom liquid is obtained when the temperature of the bottom of the tower is 102 ℃; the first tower bottom liquid enters a catalytic rectifying tower containing four sections of fillers, the catalytic rectifying tower has 60 theoretical plates, the operation pressure is normal pressure, and the temperature of a tower kettle is 168 ℃; 15 theoretical plates are arranged in the stripping section, and the temperature is 120 ℃; 15 theoretical plates are arranged in the second section, the operation temperature is 95 ℃, and the filler containing the sulfonic acid type cation exchange resin catalyst is filled in the second section; the third stage has 20 theoretical plates, and is filled with filler containing sulfonic acid type cation exchange resin catalyst at 66 deg.C; the number of 10 theoretical plates in the rectifying section is total, the temperature at the top of the rectifying section is 42 ℃, a second light fraction is obtained from the top of the catalytic rectifying tower, a first side line material is collected from a 10 th theoretical plate, a second side line material is collected from a 30 th theoretical plate, the second side line material enters a molecular sieve dehydration system, the material dehydrated by the molecular sieve is converged with the second light fraction, and the material returns to the catalytic rectifying tower through a feed inlet at a 45 th theoretical plate for cyclic utilization; and (3) feeding the catalytic distillation tower bottom liquid obtained from the catalytic distillation tower bottom into a product tower, rectifying the product tower under the conditions that the operating pressure is 0.01MPa, the tower top temperature is 161 ℃ and the reflux ratio is 1, collecting PODE3-4 products from the tower top, and returning the product tower bottom liquid to the synthesis unit for recycling. Sampling each material flow, and carrying out component analysis by gas chromatography, wherein the total yield of PODE3-4 is improved by 9.17%, and the yield of PODE3-5 is lower under the same specific conditions as example 1.
[ example 2 ]
The reaction mixed liquid from the synthesis reaction unit is used as a material to be separated and firstly enters a first rectifying tower, the number of the first rectifying tower is 30, a first light component is obtained under the conditions that the operation pressure is normal pressure and the temperature of the top of the tower is 40.7 ℃, and a first tower bottom liquid is obtained when the temperature of the bottom of the tower is 102 ℃; the first tower bottom liquid enters a catalytic rectifying tower containing four sections of fillers, the catalytic rectifying tower has 60 theoretical plates, the operation pressure is normal pressure, and the temperature of a tower kettle is 168 ℃; 15 theoretical plates are arranged in the stripping section, and the temperature is 120 ℃; 15 theoretical plates are arranged in the second section, the operation temperature is 95 ℃, and the filler containing the HZSM-5 molecular sieve catalyst is filled in the second section; the third section has 20 theoretical plates, and is filled with filler containing HZSM-5 molecular sieve catalyst at 66 deg.C; the number of 10 theoretical plates in the rectifying section is total, the operating temperature is 42 ℃, a second light fraction is obtained from the top of the catalytic rectifying tower, a first side line material is collected from a 10 th theoretical plate, a second side line material is collected from a 30 th theoretical plate, the second side line material enters a membrane separation system, a membrane in a membrane separator is an inorganic molecular sieve membrane, the operating temperature is 100 ℃, the pressure of a permeation side is 10Kpa, the material passing through the membrane separator is converged with the second light fraction, and the second light fraction returns to the catalytic rectifying tower through a feed inlet at a 45 th theoretical plate for cyclic utilization; and (3) feeding the catalytic distillation tower bottom liquid obtained from the catalytic distillation tower bottom into a product tower, rectifying the product tower under the conditions that the operating pressure is 0.01MPa, the tower top temperature is 161 ℃ and the reflux ratio is 1, collecting PODE3-4 products from the tower top, and returning the product tower bottom liquid to the synthesis unit for recycling. Sampling each material flow, analyzing by gas chromatography, improving the total yield of PODE3-4 by 24.55 percent, and the quality purity of the product reaches 99.14 percent, and the analysis of each component is specifically shown in Table 2.
TABLE 2
| Percent (b)% | DMM | PODE2 | PODE3-4 | PODE5-6 | Methanol | Water (W) | Formaldehyde (I) |
| To be separated | 48.5 | 26.55 | 15.9 | 3.37 | 2.53 | 0.15 | 3 |
| First tower bottoms | 0.10 | 52.21 | 31.27 | 6.63 | 3.73 | 0.29 | 5.89 |
| Second tower bottoms | 0.66 | 81.97 | 17.37 | ||||
| Product(s) | 0.79 | 99.14 | 0.07 | ||||
| Product kettle liquid | 1.01 | 98.99 |
[ example 3 ]
The reaction mixed liquid from the synthesis reaction unit is used as a material to be separated and firstly enters a first rectifying tower, the number of the first rectifying tower is 20, the first rectifying tower obtains a first light component under the conditions that the operation pressure is normal pressure and the temperature of the top of the tower is 40.7 ℃, and the temperature of the bottom of the tower is 104 ℃ to obtain a first bottom liquid; the first tower bottom liquid enters a catalytic distillation tower containing four sections of fillers, the catalytic distillation tower has 70 theoretical plates, the operating pressure is 0.2MPa, and the tower bottom temperature is 204 ℃; the number of 10 theoretical plates in the stripping section is total, and the temperature is 140 ℃; the second section has 20 theoretical plates, the operation temperature is 117 ℃, and the filler containing the modified sulfonic acid type cation exchange resin catalyst is filled in the second section; the third section has 25 theoretical plates, and is filled with filler containing modified sulfonic acid type cation exchange resin catalyst at an operation temperature of 81 ℃; 15 theoretical plates are arranged in the rectifying section, and the temperature of the tower top is 61.5 ℃; obtaining a second light fraction from the top of the catalytic rectifying tower, collecting a first side line material from a 15 th theoretical plate, collecting a second side line material from a 40 th theoretical plate, feeding the second side line material into a membrane separation system, wherein a membrane in a membrane separator is an inorganic-organic polymer composite membrane, the operating temperature is 120 ℃, the pressure on a permeation side is 2Kpa, and the material passing through the membrane separator returns to the catalytic rectifying tower from a feed inlet at a 50 th theoretical plate for cyclic utilization; and the second light fraction returns to the catalytic rectifying tower through a feed inlet at the 60 th theoretical plate, the bottom liquid of the catalytic rectifying tower enters a product tower, the product tower is rectified under the conditions that the operating pressure is 0.02MPa, the temperature of the tower bottom is 200 ℃, the temperature of the tower top is 95 ℃ and the reflux ratio is 0.5, PODE3-4 products are collected from the tower top, and the bottom liquid of the product tower returns to the synthesis unit for recycling. Sampling each material flow, analyzing by gas chromatography, improving the total yield of PODE3-4 by 36.64%, and the quality purity of the product reaches 99.14%, and the analysis of each component is shown in Table 3.
TABLE 3
| Percent (b)% | DMM | PODE2 | PODE3-4 | PODE5-6 | Methanol | Water (W) | Formaldehyde (I) |
| To be separated | 55.15 | 23.08 | 11.58 | 2.08 | 3.11 | 0.38 | 4.62 |
| First tower bottoms | 0.13 | 52.42 | 26.30 | 4.72 | 5.30 | 0.85 | 5.89 |
| Second tower bottoms | 0.03 | 84.75 | 15.22 | ||||
| Product(s) | 0.03 | 99.95 | 0.02 | ||||
| Product kettle liquid | 0.01 | 99.99 |
[ example 4 ]
The reaction mixed liquid from the synthesis reaction unit is used as a material to be separated and firstly enters a first rectifying tower, the first rectifying tower comprises 10 theoretical plates, the operating pressure is normal pressure, the tower top temperature is 42 ℃, a first light component is obtained, and the tower bottom temperature is 104 ℃, so that a first tower bottom liquid is obtained; the first tower bottom liquid enters a catalytic distillation tower containing four sections of fillers, the catalytic distillation tower has 50 theoretical plates, the operating pressure is 0.3MPa, and the tower bottom temperature is 230 ℃; the total number of 7 theoretical plates in the stripping section is 150 ℃; 25 theoretical plates are arranged in the second section, the operation temperature is 125 ℃, and the filler containing the sulfonic acid type cation exchange resin catalyst is filled in the second section; the third stage has 10 theoretical plates, and is filled with filler containing sulfonic acid type cation exchange resin catalyst at 95 deg.C; the number of the rectification sections is 8 theoretical plates, and the temperature of the top of the tower is 75 ℃; obtaining a second light fraction from the top of the catalytic rectifying tower, collecting a first side line material from the 8 th theoretical plate, collecting a second side line material from the 18 th theoretical plate, feeding the second side line material into a membrane separation system, wherein a membrane in a membrane separator is an inorganic-organic polymer composite membrane, the operating temperature is 125 ℃, the pressure on a permeation side is 20Kpa, and the material passing through the membrane separator and the second light fraction are converged and returned to the catalytic rectifying tower for cyclic utilization; and (3) feeding the catalytic distillation tower bottoms into a product tower, rectifying the product tower under the conditions that the operating pressure is 0.03MPa, the tower bottom temperature is 200 ℃, the tower top temperature is 110 ℃ and the reflux ratio is 0.8, collecting PODE3-4 products from the tower top, and returning the product tower bottoms to the synthesis unit for recycling. Sampling each material flow, analyzing by gas chromatography, improving the total yield of PODE3-4 by 20.42 percent, achieving the product quality purity of 99.22 percent, and specifically analyzing each component as shown in Table 4.
TABLE 4
| Percent (b)% | DMM | PODE2 | PODE3-4 | PODE5-6 | Methanol | Water (W) | Formaldehyde (I) |
| To be separated | 55.15 | 23.08 | 11.58 | 2.08 | 3.11 | 0.38 | 4.62 |
| First tower bottoms | 0.13 | 52.42 | 26.30 | 4.72 | 5.30 | 0.85 | 5.89 |
| Second tower bottoms | 0.11 | 84.68 | 15.21 | ||||
| Product(s) | 0.13 | 99.22 | 0.65 | ||||
| Product kettle liquid | 1.43 | 98.57 |
[ example 5 ]
The method comprises the following steps of (1) taking reaction mixed liquid from a synthesis reaction unit as a material to be separated, firstly, feeding the material to be separated into a first rectifying tower, wherein the number of theoretical plates of the first rectifying tower is 15, a first light component is obtained under the conditions that the operation pressure is normal pressure and the temperature of the top of the tower is 41 ℃, and a first tower bottom liquid is obtained under the condition that the temperature of a tower bottom is 101 ℃; the first tower bottom liquid enters a catalytic rectifying tower containing four sections of fillers, the catalytic rectifying tower contains 40 theoretical plates, the operating pressure is 0.4MPa, and the tower bottom temperature is 250 ℃; the number of 10 theoretical plates in the stripping section is total, and the temperature is 165 ℃; the second section has 10 theoretical plates, operation temperature is 140 ℃, and filler containing modified sulfonic acid type cation exchange resin catalyst is filled in the second section; the third stage has 15 theoretical plates, and is filled with filler containing modified sulfonic acid type cation exchange resin catalyst at 108 deg.C; the rectification section has 5 theoretical plate numbers in total, and the tower top temperature is 87 ℃; obtaining a second light fraction from the top of the catalytic rectifying tower, collecting a first side line material from a 5 th theoretical plate, collecting a second side line material from a 20 th theoretical plate, feeding the second side line material into a membrane separation system, wherein a membrane in a membrane separator is an inorganic-organic polymer composite membrane, the operating temperature is 140 ℃, the pressure on a permeation side is 25Kpa, and the material passing through the membrane separator and the second light fraction are converged and returned to the catalytic rectifying tower for cyclic utilization; and (3) feeding the catalytic distillation tower bottoms into a product tower, rectifying the product tower under the conditions that the operating pressure is 0.05MPa, the tower bottom temperature is 250 ℃, the tower top temperature is 130 ℃ and the reflux ratio is 0.3, collecting PODE3-4 products from the tower top, and returning the product tower bottoms to the synthesis unit for recycling. Sampling each material flow, analyzing by gas chromatography, improving the total yield of PODE3-4 by 16.53 percent, achieving the product quality purity of 98.25 percent, and specifically analyzing each component as shown in Table 5.
TABLE 5
| Percent (b)% | DMM | PODE2 | PODE3-4 | PODE5-6 | Methanol | Water (W) | Formaldehyde (I) |
| To be separated | 55.15 | 23.08 | 11.58 | 2.08 | 3.11 | 0.38 | 4.62 |
| First tower bottoms | 0.13 | 52.42 | 26.30 | 4.72 | 5.30 | 0.85 | 5.89 |
| Second tower bottoms | 0.78 | 84.11 | 15.11 | ||||
| Product(s) | 0.91 | 98.25 | 0.84 | ||||
| Product kettle liquid | 2.75 | 97.25 |
Claims (10)
1. A method for separating polymethoxy dimethyl ether, comprising:
(a) firstly, a material (1) to be separated containing DMM, formaldehyde and PODE2-6 enters a first rectifying tower (2), a first light fraction (3) containing DMM is obtained at the top of the tower, and a first tower bottom liquid (4) containing formaldehyde and PODE2-6 is obtained at the bottom of the tower;
(b) the first tower bottom liquid (4) enters a catalytic rectifying tower (5), a second light fraction (6) is obtained from the top of the catalytic rectifying tower (5), a material (7) is extracted from the side line of a third section (5-3) of the catalytic rectifying tower (5), and a material (8) is extracted from the side line between the second section and the third section; obtaining catalytic rectification tower bottoms (9) containing PODE3-6 from the tower bottom; the second light fraction (6) is circularly returned to the rectifying tower through the feeding hole; the side material (8) is dehydrated by a dehydration system (10) and then returns to the catalytic rectification tower;
(c) and (3) feeding the catalytic distillation tower bottoms (9) into a product tower (13), and collecting a PODE3-4 or PODE3-5 product (14) from the top of the tower.
2. The method for separating polymethoxy dimethyl ether according to claim 1, wherein the number of theoretical plates of the first rectifying tower in the step (a) is 10 to 30, the operation pressure is normal pressure, and the temperature at the top of the tower is 39 to 42 ℃.
3. The method for separating polymethoxy dimethyl ether according to claim 1, wherein the catalytic distillation column of the step (b) comprises at least four stages, the first stage (5-1) is a stripping stage, the second stage (5-2) and the third stage (5-3) are reaction stages packed with an acidic solid catalyst, and the fourth stage (5-4) is a rectifying stage.
4. The method according to claim 1 or 3, wherein the acidic solid catalyst in the step (b) is at least one selected from the group consisting of a molecular sieve catalyst, a solid super acid, a sulfonic acid type cation exchange resin, and a modified sulfonic acid type cation exchange resin.
5. The method for separating polymethoxy dimethyl ether according to claim 3, wherein the number of theoretical plates of the catalytic distillation column in the step (b) is 40 to 70; wherein the theoretical plate number of the first section (5-1) is 5-20; the theoretical plate number of the second section (5-2) is 10-25; the theoretical plate number of the third section (5-3) is 10-30; the theoretical plate number of the fourth section (5-4) is 5-15.
6. The method for separating polymethoxy dimethyl ether according to claim 1, wherein the operating pressure of the catalytic distillation column of the step (b) is 0.1 to 0.5 MPa; the temperature of the tower top is 40-90 ℃; the temperature of the tower kettle is 150-250 ℃; the temperature of the first section is 120-180 ℃; the temperature of the second section is 100-130 ℃; the temperature of the third section is 60-110 ℃; the temperature of the fourth section is 40-90 ℃.
7. The separation method of polymethoxy dimethyl ether according to claim 1, wherein the dehydration system (10) of step (b) comprises a membrane separation system consisting of a membrane separator, a vacuum system and a temperature control system; the membrane in the membrane separator is at least one of an inorganic molecular sieve membrane, an organic polymer membrane or an organic-inorganic composite membrane.
8. The method for separating polymethoxy dimethyl ether according to claim 7, wherein the membrane separator of step (b) has an operating temperature of 80 to 150 ℃ and an operating pressure of 0 to 30KPa in a vacuum system.
9. The method for separating polymethoxy dimethyl ether according to claim 1, wherein the side stream (8) in step (b) is a gas phase stream, and the withdrawal position is between the second section (5-2) and the third section (5-3); the feed position is between the first section (5-1) and the second section (5-2).
10. The method for separating polymethoxy dimethyl ether according to claim 1, wherein the number of theoretical plates of the product column in the step (c) is 5 to 20, the operation pressure is 0.01 to 0.05MPa, the overhead temperature is 70 to 135 ℃, and the reflux ratio is 0.1 to 1; the content of PODE3-5 or PODE3-4 in the product fraction (14) is 98-99.9%.
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| CN112174816A (en) * | 2020-09-10 | 2021-01-05 | 天津大学 | Method and device for reactive distillation and membrane coupling in backpack tower |
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