CN112225648B - Aldehyde removing method in polymethoxy dimethyl ether separation process - Google Patents
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Abstract
The invention relates to a dealdehyding method in a polymethoxy dimethyl ether separation process, which mainly solves the technical problems of separating formaldehyde and co-producing formate in a polymethoxy dimethyl ether preparation process, adopts the dealdehyding method in the polymethoxy dimethyl ether separation process, and comprises the following steps: (a) After the aldehyde-containing feed liquid (4) is contacted with a first aldehyde removing agent (5) in an aldehyde removing kettle (6), respectively obtaining a solid byproduct (7) and aldehyde-removing feed liquid (8) through solid-liquid separation equipment; (b) Feeding the aldehyde removing feed liquid (8) and the second aldehyde removing agent (13) into a separation rectifying tower (9), separating a first light fraction (10), feeding into a purification rectifying tower (12), and separating a second aldehyde removing agent (13); the technical proposal of the PODE synthesis unit after the purification rectifying tower kettle liquid (14) is optionally dehydrated further solves the problem well, and can be used in the industrial production of the polymethoxy dimethyl ether.
Description
Technical Field
The invention relates to an aldehyde removing method in the separation process of polymethoxy dimethyl ether, in particular to a method for preparing high-purity PODE from polymethoxy dimethyl ether-containing reaction mixture obtained in the reaction of paraformaldehyde as a raw material 3～4 Products or PODE 3～5 A method of producing the product.
Background
With the rapid increase of energy consumption in modern society, the petroleum resources are increasingly stressed, the environmental pressure is also increasing, and the development of new clean diesel fuels is urgently needed. The use of the oxygen-containing compound as the diesel additive does not need to additionally increase devices or change the structure of the engine, is a convenient and effective measure, and becomes a new idea of the development of the petroleum industry.
Polymethoxy dimethyl ether (PODE) is an oxygen-containing compound with the general formula of CH 3 O(CH 2 O)nCH 3 Where n is an integer not less than 1 (generally having a value of less than 10, and for PODE of different n, the PODEn is hereinafter referred to as PODEn). The polymethoxy dimethyl ether, especially the polymer with n=3-5, has proper melting point and boiling point, and has relatively high oxygen content (47% -49%) and cetane number (78-100), and is favorable to improving the combustion condition of diesel oil in engine, raising heat efficiency and reducing pollutant discharge; thus, PODE 3～5 Is firewood with great application prospectThe ideal component of the fuel additive of the oil machine can be used for partially replacing diesel oil, and the combustion efficiency of the diesel oil is improved.
In recent years, the preparation of PODE has received a great deal of attention and has been reported in a number of patents. In the method of synthesizing PODE using formaldehyde and methanol as raw materials, water is unavoidable as a reaction product, which is also a fatal disadvantage of the synthetic route. The reason is that under the acidic condition, the existence of water is easy to cause the hydrolysis of the polymethoxy dimethyl ether to form the hemiacetal, and the hemiacetal is difficult to remove from the polymethoxy dimethyl ether, so that the separation and purification of the polymethoxy dimethyl ether are more complicated.
The method for controlling the water from the source is to prepare the polymethoxy dimethyl ether by taking methylal and trioxymethylene or cheap paraformaldehyde as raw materials, however, most patent reports pay attention to the raw material route selection and catalyst selection, and no intensive research report is made for subsequent separation and purification. U.S. Pat. nos. 2449269 and 5746785 describe a process for the synthesis of polymethoxy dimethyl ether from methylal and paraformaldehyde (or concentrated formaldehyde solution) in the presence of sulfuric acid and formic acid. EP1070755A1 discloses a process for preparing polymethoxy dimethyl ether by reacting methylal with paraformaldehyde in the presence of triflic acid, the conversion of methylal being 54%, PODE 2～5 The yield of (2) was 51.2%. CN103664549a and CN103880614a adopt paraformaldehyde as raw material and solid super acid as catalyst to synthesize polymethoxy dimethyl ether, the product contains unreacted raw material methylal and paraformaldehyde, and the reaction mixture contains 8.3% of unreacted paraformaldehyde besides methylal and polymethoxy dimethyl ether.
In the preparation method of the polymethoxy dimethyl ether, not only products, unreacted raw materials, formaldehyde (or paraformaldehyde) dissolved in a system, but also byproducts methanol and the like are contained in a reaction mixture, and the reaction mixture needs to be separated and purified in order to obtain pure PODE for adding diesel oil.
We have found that, in a long-term study of the separation by rectification of a reaction mixture obtained by reacting methylal with paraformaldehyde, PODE is isolated 2 In the rectification process of (2), formaldehyde is easy to gather into white on a condenserThe solids accumulate along with the running of the device, so that the blockage of the return pipe and the discharge pipe causes shutdown maintenance, and long-term continuous production running is difficult.
Chinese patent CN103333060B discloses a method for refining and purifying polyoxymethylene dialkyl ether, which achieves the purpose of eliminating formaldehyde reaction by adding 40-50wt% aqueous sodium hydroxide solution to the reaction equilibrium product for condensation reflux. However, the sodium hydroxide solution dosage of the method is 10-40%, the recovery rate of the product is low, a large amount of high-concentration salt-containing waste liquid is formed after aldehyde removal, the recycling and the post-treatment are very complex and troublesome, and the method is unfavorable for expanding production.
Therefore, the separation problem of formaldehyde is a technical bottleneck affecting continuous and stable operation of the polymethoxy dimethyl ether separation process.
Disclosure of Invention
The invention aims to solve the technical problems of tower blocking in the process of separating the polymethoxy dimethyl ether by a rectification method and a large amount of waste liquid generated by dealdehyding of chemical treatment liquid, and provides a dealdehyding method in the process of separating the polymethoxy dimethyl ether.
In order to solve the technical problem of formaldehyde separation, the technical scheme of the invention is as follows: the formaldehyde removing method in the polymethoxy dimethyl ether separation process comprises the following steps:
(a) After the aldehyde-containing feed liquid 4 is contacted with a first aldehyde removing agent 5 in an aldehyde removing kettle 6, respectively obtaining a solid byproduct 7 and aldehyde-removing feed liquid 8 through solid-liquid separation equipment;
(b) The aldehyde removing feed liquid 8 and the second aldehyde removing agent 13 enter a separation rectifying tower 9 to separate a first light fraction 10, enter a purification rectifying tower 12 to separate a second aldehyde removing agent 13; the purified rectifying tower kettle liquid 14 is returned to the PODE synthesizing unit after being dehydrated further.
In the technical scheme, the aldehyde-containing feed liquid in the step (a)Comprises formaldehyde and PODE 2-8 The formaldehyde content is preferably not higher than 15%, more preferably 5 to 15%, still more preferably 6 to 12%.
In the above technical scheme, the aldehyde-containing liquid in the step (a) is preferably derived from the reaction equilibrium mixture 1, and can be prepared by separating DMM from the reaction equilibrium mixture 1 of the PODE synthesis unit, wherein the separation process is as follows: firstly, removing light fraction 3 containing methylal in a first separation tower 2 from a reaction equilibrium mixture 1 of a PODE synthesis unit, and obtaining a kettle liquid containing formaldehyde from a tower kettle, namely aldehyde-containing feed liquid 4; the DMM content in the resulting aldehyde-containing feed liquid is preferably not higher than 10%, more preferably not higher than 5%, and most preferably not higher than 1%.
In the above technical scheme, the first separation tower is preferably a prefractionator, the separation process is normal pressure rectification, and the aldehyde-containing feed liquid is obtained from the rectification tower kettle after the methylal-containing light component is separated from the tower top.
In the above technical scheme, the first aldehyde removing agent in the step (a) is preferably sodium hydroxide solution and/or potassium hydroxide solution, and the solid byproduct is the corresponding formate solid.
In the above technical scheme, the mass concentration of the sodium hydroxide solution and the potassium hydroxide solution is preferably not less than 40%, more preferably 40% -60%, and even more preferably 45% -50%.
In the technical scheme, the dosage of the first aldehyde removing agent in the step (a) is preferably 0 to 1.5 times of the mass of formaldehyde; more preferably 0.1 to 1.5 times, most preferably 0.5 to 1.4.
In the technical scheme, the temperature of the aldehyde removing kettle in the step (a) is preferably 30-60 ℃, more preferably 45-55 ℃; the contact time is preferably 5 to 60 minutes, more preferably 20 to 40 minutes; the formaldehyde content in the aldehyde removal feed liquid corresponding to the aldehyde removal kettle is preferably 0.1-6%, and formaldehyde is partially removed to obtain a solid byproduct.
In the above technical solution, the solid-liquid separation device in step (a) is preferably, but not limited to, a centrifugal separator, a pressurized filter, and a vacuum pump.
In the above technical solution, the second aldehyde removing agent in the step (b) is preferably at least one of methanol and water, and the dosage of the second aldehyde removing agent is preferably 0.5-7 times of the formaldehyde in the aldehyde removing liquid, and more preferably 1-5 times of the formaldehyde in the aldehyde removing liquid.
In the above technical scheme, the operation pressure of the separation rectifying tower in the step (b) is preferably 0.05-0.1 Mpa; the temperature of the tower kettle is preferably 100-120 ℃; the reflux ratio is 0.5-5.
In the above-mentioned embodiments, the dehydration treatment in the step (b) is preferably, but not limited to, at least one of dehydration methods such as rectification, drying, and evaporation-permeation membrane separation.
In the above technical solution, it will be understood by those skilled in the art that the dehydration treatment in step (b) may be selected from those commonly used in the art, such as, preferably but not limited to, distillation, drying, evaporation and permeation membrane separation, etc.;
in the above-mentioned embodiment, the dehydration treatment in the step (b) is more preferably separation by a vaporization permeable membrane coupled in a column.
In the technical scheme, the top fraction of the purifying rectifying tower is completely or partially recycled; the dehydrated purifying rectifying tower bottom liquid can be directly circulated and returned to the PODE reaction synthesis unit.
In the technical proposal, PODE in the bottom liquid of the separation rectifying tower in the step (b) 2-6 Not less than 99%.
In the technical proposal, the PODE can be further separated from the bottom liquid of the separation and rectification tower 3-4 Or PODE 3-5 The product, then the method further comprises the following step (c): the PODE is separated from the bottom liquid 11 of the separating and rectifying tower by one-stage or two-stage conventional rectification 3-4 Or PODE 3-5 A product; it is further preferable that the conventional rectification is one or two selected from the group consisting of normal pressure rectification and reduced pressure rectification. Under the condition of disclosing the technical proposal, the technical personnel in the field can reasonably adjust the operating pressure of the rectifying tower, the temperature at the top of the tower and other process conditions according to market demand conditions, and select the product fraction as PODE 3～4 Or PODE 3～5 。
Unless otherwise indicated, all percentages stated herein refer to weight percentages or weight percentages.
Surprisingly, we find that the process mainly comprises chemical dealdehyding and special rectification, firstly, partial formaldehyde is converted into solid formate and removed from the system by reacting with a first dealdehyding agent and controlling process conditions, the operation is simple, the influence of formaldehyde on the rectification process is greatly reduced, and the obtained solid formate as a byproduct can be used as a byproduct; after the formaldehyde is fed into a separation rectifying tower through a second aldehyde removing agent to be specially rectified, formaldehyde remained in the system is separated from PODE 3-6 The material liquid is separated, and then can be recycled to the reaction system of the PODE synthesis unit along with the bottom liquid of the purifying and rectifying tower, thereby improving the utilization rate of the material. The whole process has no waste liquid, reduces the pollution and influence on the environment, and is beneficial to expanding production.
By adopting the technical scheme of the invention, firstly, partial formaldehyde can be converted into solid formate to be removed from the system by reacting with the first aldehyde removing agent and controlling the process conditions, the operation is simple, the influence of formaldehyde on the rectification process is greatly reduced, and the obtained solid formate can be used as a byproduct; the formaldehyde remained in the system is separated from PODE by the special rectification of a separation rectifying tower 3-6 The material liquid is separated, and then can be recycled to the reaction system of the PODE synthesis unit along with the bottom liquid of the purification rectifying tower, so that the utilization rate of the material is improved; the whole process has no waste liquid, reduces the pollution and influence on the environment, is beneficial to expanding production, and achieves better technical effect.
Drawings
Fig. 1 is a process flow diagram of an embodiment of the present invention.
After the aldehyde-containing feed liquid 4 contacts with a first aldehyde removing agent 5 in an aldehyde removing kettle 6, solid-liquid separation is carried out to respectively obtain a solid byproduct 7 and aldehyde-removing feed liquid 8; the aldehyde removing feed liquid 8 and the second aldehyde removing agent 13 respectively enter a special rectifying tower 9 to separate a first light fraction 10, enter a purifying rectifying tower 12 to separate a second aldehyde removing agent 13; the purifying rectifying tower kettle liquid 14 can be returned to the PODE synthesizing unit after further dehydration treatment; the special rectifying tower kettle liquid 11 can separate PODE3-4 or PODE3-5 products through one-stage or two-stage conventional rectification.
FIG. 2 is another process flow diagram of an embodiment of the present invention.
FIG. 3 is a solid by-product of example 1 of the present invention, a white solid salt.
FIG. 4 shows the viscous liquid material obtained in comparative example 1 as dark brown-red waste.
The reaction equilibrium mixture 1 obtained by the reaction synthesis unit is firstly removed from the light fraction 3 in the first separation tower 2, and aldehyde-containing feed liquid 4 is obtained from the tower kettle; after the aldehyde-containing feed liquid 4 contacts with a first aldehyde removing agent 5 in an aldehyde removing kettle 6, solid-liquid separation is carried out to respectively obtain a solid byproduct 7 and aldehyde-removing feed liquid 8; the aldehyde removing feed liquid 8 and the second aldehyde removing agent 13 respectively enter a special rectifying tower 9, a first light fraction 10 is separated, the first light fraction enters a purifying rectifying tower 12, the second aldehyde removing agent 13 is separated, a side-draw material enters a pervaporation membrane system, and moisture 15 is removed and then the side-draw material returns to the purifying rectifying tower 12; the purifying rectifying tower kettle liquid 14 can be directly returned to the PODE synthesizing unit for recycling; and (3) feeding the special rectifying tower kettle liquid 11 into a product tower 17 for reduced pressure rectification, and extracting a product 18 from the tower top or a side line, wherein the tower kettle liquid 19 is PODEn heavy components with n > 5.
The invention is further illustrated by the following examples.
Detailed Description
[ example 1 ]
Obtaining a reaction equilibrium mixture with formaldehyde content of 3.3% in a reaction synthesis unit, and firstly removing a first light fraction in a first separation tower to obtain aldehyde-containing feed liquid with formaldehyde content of 6.5%; feeding aldehyde-containing feed liquid into an aldehyde removal kettle, wherein 40% sodium hydroxide is first aldehyde-removing liquid, the dosage of the sodium hydroxide is 1 time (3.3% calculated by reaction balance products) of the formaldehyde mass, stirring at a constant temperature of 50 ℃ for 20min, and performing solid-liquid separation by vacuum suction filtration to obtain solid byproducts and aldehyde-removing feed liquid with formaldehyde content of 2.8% respectively; a picture of the solid by-product is shown in figure 3.
The aldehyde-removing feed liquid and methanol respectively enter a special rectifying tower, the methanol dosage is 3 times of the formaldehyde mass, the operating pressure is 0.1MPa, the tower bottom temperature is 120 ℃, the tower top temperature is 83 ℃, the first light fraction is separated under the condition of reflux ratio 3, the first light fraction enters a purifying rectifying tower, and the strip with reflux ratio 2 is operated at normal pressure and the tower bottom temperature of 100 ℃, the tower top temperature of 64.5 DEG CRectifying under the piece, separating methanol from the tower top, feeding the tower bottom feed liquid into a pervaporation membrane system containing a molecular sieve membrane for further dehydration treatment, returning the dehydrated circulating material with the formaldehyde content of 5.28% to a PODE (point of sale) synthesis unit, and ensuring that the formaldehyde recovery rate is 50%; PODE in special rectifying tower kettle liquid 2-6 The content is 99.5%, the material enters a product tower for reduced pressure rectification, and PODE can be smoothly separated 3-4 Or PODE 3-5 And (5) a product.
Comparative example 1
Obtaining a reaction equilibrium mixture with formaldehyde content of 3.3% in a reaction synthesis unit, and firstly removing a first light fraction in a first separation tower to obtain aldehyde-containing feed liquid with formaldehyde content of 6.5%; the aldehyde-containing feed liquid enters an aldehyde removing kettle, 40% sodium hydroxide is used as a first aldehyde removing liquid, the dosage is 3 times (about 10% based on the reaction balance product) of the formaldehyde, the mixture is stirred at the constant temperature of 50 ℃ for 20min, red liquid appears, and layering and no solid phase generation are caused after standing. The formaldehyde removal rate of the feed liquid on the upper layer reaches 100% through analysis, and formaldehyde can not be recovered at all; and the lower layer is a viscous liquid material (see fig. 4), which is difficult to treat and generates process waste liquid.
Comparative example 2
The formaldehyde-containing feed liquid with the formaldehyde content of 6.3% is not treated by a first aldehyde removing agent, directly enters a special rectifying tower with methanol, the methanol dosage is 3 times of the formaldehyde mass, a first light fraction is separated under the conditions that the operating pressure is 0.1MPa, the tower kettle temperature is 120 ℃, the tower top temperature is 83 ℃ and the reflux ratio is 3, the first light fraction enters a purifying rectifying tower, rectification is carried out under normal pressure, white solid polymer is observed to appear in the rectifying process, the tower blocking phenomenon occurs, the test is stopped, and formaldehyde is difficult to recover.
[ comparative example 3 ]
Obtaining a reaction equilibrium mixture with formaldehyde content of 3.3% in a reaction synthesis unit, and firstly removing a first light fraction in a first separation tower to obtain aldehyde-containing feed liquid with formaldehyde content of 6.5%; the aldehyde-containing feed liquid enters an aldehyde removing kettle, 40% sodium hydroxide is used as first aldehyde removing liquid, the dosage is 1 time (3.3% calculated by reaction balance products) of the formaldehyde, the mixture is stirred for 20 minutes at the constant temperature of 70 ℃, a small amount of red liquid appears, and layering and no solid phase formation are generated after standing. The formaldehyde removal rate of the feed liquid at the upper layer is about 90% through analysis, but the feed liquid at the lower layer is a viscous liquid material, so that the feed liquid is difficult to treat, and the process waste liquid is generated.
The upper layer liquid is aldehyde removing feed liquid with formaldehyde content of 0.82%; the aldehyde-removed feed liquid and methanol respectively enter a special rectifying tower, and the PODE containing formaldehyde can be smoothly separated under the other conditions same as those in the example 1 2 The feed liquid returns to the PODE synthesis unit, and the recovery rate of formaldehyde is only 8%.
[ comparative example 4 ]
Obtaining a reaction equilibrium mixture with formaldehyde content of 3.3% in a reaction synthesis unit, and firstly removing a first light fraction in a first separation tower to obtain aldehyde-containing feed liquid with formaldehyde content of 6.5%; the aldehyde-containing feed liquid enters an aldehyde removing kettle, 40% sodium hydroxide is used as first aldehyde removing liquid, the dosage is 1 time (3.3% calculated by reaction balance products) of the formaldehyde, the mixture is stirred at the constant temperature of 50 ℃ for 70 minutes, red liquid appears, and layering and no solid phase generation are realized after standing. The formaldehyde removal rate of the feed liquid at the upper layer is about 70% through analysis, but the feed liquid at the lower layer is a viscous liquid material, so that the feed liquid is difficult to treat, and the process waste liquid is generated.
Comparative example 5
Obtaining a reaction equilibrium mixture with formaldehyde content of 3.3% in a reaction synthesis unit, and firstly removing a first light fraction in a first separation tower to obtain aldehyde-containing feed liquid with formaldehyde content of 6.5%; feeding aldehyde-containing feed liquid into an aldehyde removal kettle, wherein 40% sodium hydroxide is first aldehyde-removing liquid, the dosage of the sodium hydroxide is 1 time (3.3% calculated by reaction balance products) of the formaldehyde mass, stirring at a constant temperature of 50 ℃ for 20min, and performing solid-liquid separation by vacuum suction filtration to obtain solid byproducts and aldehyde-removing feed liquid with formaldehyde content of 2.8% respectively; a picture of the solid by-product is shown in figure 1. The aldehyde-removed feed liquid directly enters into a tower for rectification under the conditions of the operating pressure of 0.1MPa, the temperature of a tower bottom of 120 ℃, the temperature of a tower top of 83 ℃ and the reflux ratio of 3, and white solid polymer is observed at the cold of the tower top after continuous rectification for about 2 hours, so that the phenomenon of tower blockage occurs. The test was discontinued.
[ example 2 ]
Feeding aldehyde-containing feed liquid with formaldehyde content of 6.3% into an aldehyde removing kettle, taking 45% sodium hydroxide as first aldehyde removing liquid, taking 0.1 time of formaldehyde mass, stirring at a constant temperature of 60 ℃ for 10min, performing solid-liquid separation by vacuum suction filtration, and separating out solid byproducts to obtain aldehyde-removing feed liquid with formaldehyde content of 5.87%.
The formaldehyde-removing feed liquid and the methanol respectively enter a special rectifying tower, the methanol consumption is 1 time of the formaldehyde mass, the first light fraction is separated under the conditions that the operating pressure is 0.1MPa, the tower bottom temperature is 120 ℃, the tower top temperature is 83 ℃ and the reflux ratio is 3, the first light fraction enters a purifying rectifying tower for rectification under normal pressure, the methanol is separated from the tower top, the tower bottom feed liquid enters a pervaporation membrane system containing a molecular sieve membrane for further dehydration treatment, the formaldehyde content in the dehydrated circulating material is 11.36 percent, and the circulating material returns to a PODE (pre-oxidation de) synthesis unit, and the formaldehyde recovery rate is 93 percent; PODE in special rectifying tower kettle liquid 2-6 The content is 99.3%, the material enters a product tower for reduced pressure rectification, and PODE can be smoothly separated 3-4 Or PODE 3-5 And (5) a product.
[ example 3 ]
Feeding aldehyde-containing feed liquid with formaldehyde content of 12.3% into an aldehyde removing kettle, taking 45% sodium hydroxide as first aldehyde removing liquid, taking 1.4 times of formaldehyde (7.5% calculated by reaction balance product), stirring at constant temperature of 40 ℃ for 30min, and then carrying out solid-liquid separation by using a fully-closed pressure filter to obtain solid byproducts and aldehyde-removing feed liquid with formaldehyde content of 0.99% respectively; feeding the aldehyde removing feed liquid and water of a second aldehyde removing agent into a special rectifying tower, wherein the dosage of the second aldehyde removing agent is 0.5 times of the mass of formaldehyde, separating a first light fraction under the conditions of operating pressure of 0.05MPa, tower kettle temperature of 100 ℃, tower top temperature of 70 ℃ and reflux ratio of 5, feeding the first light fraction into a purifying rectifying tower, dehydrating by a pervaporation membrane system of a molecular sieve membrane coupled with the tower kettle, operating at normal pressure, tower kettle temperature of 100 ℃, and pervaporation membrane assembly temperature of 95 ℃, wherein the formaldehyde content in the dehydrated material is 1.74%, and returning the dehydrated material to a PODE (pre-oxidation de) synthesizing unit, and the formaldehyde recovery rate is 10%; PODE in special rectifying tower kettle liquid 2-6 The content is 99.9%, the material enters a product tower for reduced pressure rectification, and PODE can be smoothly separated 3-4 Or PODE 3-5 And (5) a product.
[ example 4 ]
Feeding aldehyde-containing feed liquid with formaldehyde content of 12.3% into an aldehyde removing kettle, wherein 50% of potassium hydroxide is first aldehyde removing liquid, the dosage is 1.05 times of the formaldehyde mass, stirring for 40min at the constant temperature of 45 ℃, and then carrying out solid-liquid separation by using a fully-closed pressure filter to respectively obtain solid byproducts and aldehyde removing feed liquid with formaldehyde content of 5.78%; feeding the dealdehyded feed liquid and 80% methanol aqueous solution into a special rectifying tower, wherein the dosage of the formaldehyde aqueous solution is 4 times of the mass of formaldehyde, separating first light fraction under the conditions of the operating pressure of 0.1MPa, the tower kettle temperature of 149 ℃, the tower top temperature of 85 ℃ and the reflux ratio of 1, feeding the first light fraction into a purifying rectifying tower, rectifying under the conditions of normal pressure operation, the tower kettle temperature of 100 ℃, the tower top temperature of 64.5 ℃ and the reflux ratio of 2, separating methanol from the tower top, feeding the tower kettle feed liquid into a pervaporation membrane system containing a molecular sieve membrane for further dehydration treatment, wherein the formaldehyde content in the dehydrated circulating material is 10.76%, and returning the circulating material to a PODE (point of gravity) synthesizing unit, and the formaldehyde recovery rate is 42%; PODE in special rectifying tower kettle liquid 2-6 The content is 99.8%, the material enters a product tower for reduced pressure rectification, and PODE can be smoothly separated 3-4 Or PODE 3-5 And (5) a product.
[ example 5 ]
Obtaining a reaction equilibrium mixture with the formaldehyde content of 4.3% in a reaction synthesis unit, and firstly removing a first light fraction in a first separation tower to obtain aldehyde-containing feed liquid with the formaldehyde content of 8.2%; feeding aldehyde-containing feed liquid into an aldehyde removing kettle, wherein 50% sodium hydroxide is first aldehyde-removing liquid, the dosage of the sodium hydroxide is 0.5 times of the formaldehyde mass (1.9% based on a reaction balance product), stirring at a constant temperature of 30 ℃ for 60min, and performing solid-liquid separation by vacuum suction filtration to obtain a solid byproduct and aldehyde-removing feed liquid with formaldehyde content of 5.29% respectively; the dealdehyding feed liquid and methanol respectively enter a special rectifying tower, the methanol dosage is 7 times of formaldehyde mass, the operating pressure is 0.08MPa, the tower bottom temperature is 135 ℃, the tower top temperature is 87 ℃, the reflux ratio is 0.5, the first light fraction enters a purifying rectifying tower, the rectification is carried out under the conditions of normal pressure operation, the tower bottom temperature is 95 ℃, the tower top temperature is 64.5 ℃ and the reflux ratio is 2, the methanol is separated from the tower top, and the tower bottom feed liquid enters a further dehydration position of a molecular drying systemAnd (3) the formaldehyde content in the dehydrated circulating material is 9.61%, and the circulating material returns to the PODE synthesis unit, so that the formaldehyde recovery rate is 62%; PODE in special rectifying tower kettle liquid 2-6 The content is 99%, the material enters a product tower for reduced pressure rectification, and PODE can be smoothly separated 3-4 Or PODE 3-5 And (5) a product.
Claims (12)
1. The formaldehyde removing method in the polymethoxy dimethyl ether separation process comprises the following steps:
(a) After the aldehyde-containing feed liquid (4) is contacted with the first aldehyde removing agent (5) in the aldehyde removing kettle (6), the aldehyde-containing feed liquid passes through solid-liquid separation equipment,
respectively obtaining a solid byproduct (7) and an aldehyde removal feed liquid (8); the first aldehyde removing agent comprises one of sodium hydroxide solution and/or potassium hydroxide solution; the dosage of the first aldehyde removing agent is 0.1-1.5 times of the formaldehyde; the temperature of the formaldehyde removing kettle is 30-60 ℃ and the contact time is 5-60 min;
(b) Feeding the aldehyde removing feed liquid (8) and the second aldehyde removing agent (13) into a separation rectifying tower (9); separating out a first light fraction (10), entering a purifying and rectifying tower (12), separating out a second aldehyde removing agent (13), and optionally further dehydrating a purifying and rectifying tower kettle liquid (14) and returning to the PODE synthesizing unit; the second aldehyde removing agent is at least one of methanol and water.
2. The method for removing aldehyde in a process of separating polymethoxy dimethyl ether according to claim 1, wherein the aldehyde-containing liquid in the step (a) contains formaldehyde and PODE 2-8 Formaldehyde content is 5-15%; or the aldehyde-containing feed liquid is from the reaction equilibrium mixture (1), then the method further comprises: and (3) removing the light fraction (3) containing methylal from the reaction balance mixture (1) obtained in the PODE reaction synthesis unit in a first separation tower (2), and obtaining a kettle liquid containing formaldehyde from the tower kettle, namely the aldehyde-containing feed liquid (4).
3. The method for removing aldehyde in a process of separating polymethoxy dimethyl ether according to claim 1, wherein the mass concentration of the first aldehyde removing agent is not lower than 40%, and the solid byproduct is the corresponding formate.
4. The method for removing aldehyde in the process of separating polymethoxy dimethyl ether according to claim 1, wherein the dosage of the first aldehyde removing agent is 0.5-1.4 times of the formaldehyde.
5. The method for removing formaldehyde in a polymethoxy dimethyl ether separation process according to claim 1, wherein the formaldehyde content in the formaldehyde-removing feed liquid is 0.1-6%.
6. The method for removing aldehyde in a polymethoxy dimethyl ether separation process according to claim 1, wherein the solid-liquid separation equipment comprises at least one of a centrifugal separator, a pressurized filter and a vacuum suction filter.
7. The method for removing aldehyde in the process of separating polymethoxy dimethyl ether according to claim 1, wherein the dosage of the second aldehyde removing agent is 0.5-7 times of the formaldehyde content in the aldehyde removing feed liquid.
8. The method for removing aldehyde in the process of separating polymethoxy dimethyl ether according to claim 1, wherein the operation pressure of the separating and rectifying tower is 0.05-0.1 MPa; the temperature of the tower kettle is 100-150 ℃; the reflux ratio is 0.5-5.
9. The method for removing aldehyde in the process of separating polymethoxy dimethyl ether according to claim 1, wherein the dehydration treatment comprises at least one of rectification, drying and vaporization osmotic membrane separation.
10. The method for removing aldehyde in the process of separating polymethoxy dimethyl ether according to claim 1, characterized in that the PODE in the bottom liquid of the separating and rectifying tower 2-6 Not less than 99%.
11. The process for dealdehyding in a polymethoxy dimethyl ether separation process according to any one of claims 1 to 10, characterized in that the process further comprises the following step (c): the separation rectifying tower bottom liquid (11) is optionally subjected to one-stage or two-stage conventional rectification to separate PODE3-4 or PODE3-5 products.
12. The method for removing aldehyde in the process of separating polymethoxy dimethyl ether according to claim 11, wherein the conventional rectification is one or two selected from normal pressure rectification and reduced pressure rectification.
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Citations (6)
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