CN112225649B - Method for preparing high-purity polymethoxy dimethyl ether - Google Patents
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Abstract
The invention relates to a method for preparing high-purity polymethoxy dimethyl ether, which mainly solves the problems of easy tower blockage, difficult circulation and easy waste liquid generation of formaldehyde in the purification process for separating polymethoxy dimethyl ether by a rectification method in the prior art, and comprises the following steps: the aldehyde-containing feed liquid and entrainer enter a first rectifying tower, the tower top material is separated into a first light fraction and a first rectifying tower kettle liquid after passing through a condenser, and the first rectifying tower kettle liquid can be separated into PODE 3‑4 Or PODE 3‑5 The method comprises the steps of carrying out a first treatment on the surface of the The first light fraction enters a entrainer recovery tower, and the top of the entrainer recovery tower separates out a second light fraction; the side offtake material of the entrainer recovery tower enters a pervaporation membrane assembly, and after water is separated from the permeation side, the recycle material returns to the entrainer recovery tower; the technical proposal of recycling the bottom liquid of the recovery tower to the PODE synthesizing unit solves the problem well and can be used in the industrialized production of the polymethoxy dimethyl ether.
Description
Technical Field
The invention relates to a method for separating and refining 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 very strongThe ideal component of the diesel fuel additive with the prospect can be used for partially replacing diesel fuel, and the combustion efficiency of the diesel fuel 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 or formaldehyde 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 coolThe white solid is accumulated on the condenser and accumulated 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 that in the purification process of separating polymethoxy dimethyl ether by a rectification method, a tower is easy to be blocked, the recycling is difficult and waste liquid is easy to generate in the process of separating formaldehyde, and provides a method for preparing high-purity polymethoxy dimethyl ether by separation and refining.
In order to solve the technical problems, the invention adopts the following technical scheme: a method for separating and refining polymethoxy dimethyl ether, which comprises the following steps:
(a) The aldehyde-containing feed liquid 1 and entrainer 2 enter a first rectifying tower 3, and a tower top material is separated into a first light fraction 5 and a first rectifying tower bottom liquid 6 after passing through a condenser 4; the first rectifying tower bottom liquid 6 is optionally separated into PODE through one-stage or two-stage conventional rectification 3-4 Or PODE 3-5 A product;
(b) The first light fraction 5 enters a entrainer recovery tower 7, and a second light fraction 8 is separated from the top of the entrainer recovery tower;
the side offtake material 10 of the entrainer recovery tower 7 enters a pervaporation membrane module, and after moisture 11 is separated from the permeation side, a recycle material 12 returns to the entrainer recovery tower 7; the recovery tower bottom liquid 9 is recycled to the PODE synthesis unit.
In the technical scheme, the aldehyde-containing feed liquid in the step (a) comprises formaldehyde and PODE 2-6 The formaldehyde content is 0.1-6%.
In the above-mentioned technical scheme, the acid value (calculated as acetic acid) of the aldehyde-containing liquid in the step (a) is preferably not more than 0.6%, more preferably not more than 0.4%. When the acid value is too high, the adjustment may be performed by selecting a base or an ion exchange resin.
In the above technical solution, the aldehyde-containing feed solution in step (a) is prepared by separating DMM from a reaction balance of a PODE synthesis unit, wherein the separation process is as follows: the reaction balance of the PODE synthesis unit is firstly fed into a light component removal tower for normal pressure rectification, and after the light component containing methylal is separated from the tower top, aldehyde-containing feed liquid is obtained from the tower bottom, wherein the DMM content in the 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 embodiment, the entrainer in step (a) is preferably a mixed liquid comprising methanol and water, and the mass percentage of water in the entrainer is preferably 0 to 90%, more preferably more than 0.
In the above embodiment, the amount of the entrainer used in step (a) is preferably 1 to 10 times, more preferably 1 to 5 times, most preferably less than 5 times the mass of formaldehyde.
In the above technical solution, the operating pressure of the first rectifying tower in the step (a) is preferably 0.05-0.1 MPa; the temperature of the tower bottom is preferably 100-160 ℃, the temperature of the tower top is preferably 60-90 ℃, and the reflux ratio of the tower top is preferably 0.5-5.
In the above technical solution, the operating temperature of the condenser (4) in the step (a) is preferably 10-50 ℃.
In the technical proposal, PODE in the first rectifying tower kettle liquid in the step (a) 2-6 Preferably not less than 99%, formaldehyde content preferably not more than 0.1%, and water content preferably not more than 0.1%.
In the above technical scheme, the theoretical plate number of the entrainer recovery tower in the step (b) is preferably 15-30; the distance between the side line extraction position and the tower kettle position is preferably 0-5 theoretical plates; the temperature of the tower kettle is preferably 80-120 ℃;
in the above technical solution, the membrane in the pervaporation membrane module in the step (b) is preferably a molecular sieve membrane; the membrane module is preferably operated at a temperature of 80 to 120℃and the permeate side pressure is preferably 0 to 30kPa.
In the above technical scheme, the content of methanol in the bottom liquid of the recovery tower in the step (b) is preferably not more than 2%, and the content of water is preferably not more than 1%.
In the above technical scheme, the overhead fraction 8 of the entrainer recovery column and the permeate side water 11 can be recycled in whole or in part; the entrainer recovery tower bottom liquid is preferably directly circulated and returned to the PODE reaction synthesis unit.
In the above technical solution, the conventional rectification in the step (a) includes one or two 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.
The process uses methanol/water mixed solution as entrainer, and carries out special rectification with PODE mixed material containing formaldehyde, and the tower top does not find signs of formaldehyde polymerization by controlling process conditions, so that the problem of tower blockage of formaldehyde is avoided due to the mixed entrainer, and the continuous separation process of formaldehyde can be realized; the first rectifying tower overhead fraction containing formaldehyde is further rectified by coupling with a vaporization permeable membrane component, methanol and water are separated from different positions, formaldehyde in tower kettle materials can be recycled, and entrainer can be recycled. The process is relatively simple to operate, no new impurities are introduced, no waste liquid is generated in the whole process, the pollution and the influence on the environment are reduced, and the expansion of production is facilitated.
By adopting the technical scheme of the invention, the methanol/water mixed solution is used as the entrainer to carry out special rectification with the PODE mixed material containing formaldehyde, and the tower top does not find the sign of formaldehyde polymerization by controlling the process conditions, thereby avoiding the problem of blocking the tower by formaldehyde and realizing the continuous separation process of formaldehyde; the first rectifying tower overhead fraction containing formaldehyde is further rectified by coupling with a vaporization permeable membrane component, methanol and water are separated from different positions, formaldehyde in tower kettle materials can be recycled, and entrainer can be recycled. The process is relatively simple to operate, no new impurities are introduced, no waste liquid is generated in the whole process, the pollution and influence on the environment are reduced, the expansion of production is facilitated, and a better technical effect is achieved.
Drawings
Fig. 1 is a process flow diagram of an embodiment of the present invention.
In the figure, aldehyde-containing feed liquid 1 and entrainer 2 enter a first rectifying tower 3, and a material at the top of the tower is separated into a first light fraction 5 and a first rectifying tower kettle liquid 6 after passing through a condenser 4. The first light fraction 5 enters a entrainer recovery tower 7, and a second light fraction 8 is separated from the top of the entrainer recovery tower; the side offtake material 10 of the entrainer recovery tower 7 enters a pervaporation membrane assembly 11, water 12 is separated from the permeation side, and a recycle material 13 returns to the entrainer recovery tower 7; the entrainer recovery tower bottom liquid 9 is recycled to the PODE synthesis unit. The first rectifying tower bottom liquid 6 can separate PODE through one-stage or two-stage conventional rectification 3-4 Or PODE 3-5 And (5) a product.
Detailed Description
[ example 1 ]
The aldehyde-containing feed solution with the formaldehyde content of 2.8% and the entrainer respectively enter a first rectifying tower, the entrainer is methanol, the dosage of the entrainer is 3 times of the formaldehyde mass (calculated by the aldehyde-containing feed solution, the dosage of the entrainer is 8.4%), the operation pressure is 0.1MPa, the temperature of a tower bottom is 129 ℃, the temperature of a tower top is 83 ℃, the temperature of a reflux ratio is 3, the temperature of a condenser at the tower top is 30 ℃, and a first light fraction is separated from the tower top.
The first light fraction enters a entrainer recovery tower containing 30 theoretical plates, is rectified under the conditions of normal pressure operation, tower bottom temperature of 100 ℃, tower top temperature of 64.5 ℃ and reflux ratio of 2, methanol is separated from the tower top, and the distance from the tower bottom is about 3 theoretical platesThe side line of the plate is discharged, the side line is discharged into a pervaporation membrane system containing NaA molecular sieve membranes for further dehydration treatment, the temperature of a membrane component is 90 ℃, the osmotic side pressure is 30kPa, the dehydrated circulating materials are returned to a entrainer recovery tower, the formaldehyde content in the kettle liquid pumped from the kettle of the entrainer recovery tower is 6.17%, the water content is 0.85%, and the circulating materials can be directly returned to a PODE synthesis unit; PODE in first rectifying column bottom 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
The formaldehyde-containing feed liquid with the formaldehyde content of 6.3 percent and methanol directly enter a first rectifying tower respectively, the methanol dosage is 3 times of the formaldehyde mass, the rectification is carried out under the conditions that the operating pressure is 0.1MPa, the temperature of a tower kettle is 129 ℃, the temperature of a tower top is 83 ℃, the reflux ratio is 3, the temperature of a tower top condenser is 30 ℃, a first light fraction is separated from the tower top, the first light fraction enters a entrainer recovery tower, the rectification is carried out under normal pressure, white solid polymer is observed to appear in the tower kettle in the rectification process, the tower blockage phenomenon occurs, the test is stopped, and the formaldehyde is difficult to recover.
Comparative example 2
The formaldehyde-removing feed liquid with the formaldehyde content of 2.8% directly enters into a tower for rectification under the conditions of the operating pressure of 0.1MPa, the temperature of a tower kettle of 129 ℃, the temperature of the 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 tower blockage phenomenon occurs, and the test is stopped.
[ example 2 ]
The aldehyde-containing feed solution with the formaldehyde content of 6% and the aqueous solution of the entrainer methanol respectively enter a first rectifying tower, the water content of the entrainer is 10%, the amount of the entrainer is 1 time of the mass of formaldehyde (calculated by the aldehyde-containing feed solution, the amount of the entrainer is 6%), the rectification is carried out under the conditions that the operating pressure is 0.06MPa, the temperature of a tower bottom is 125 ℃, the temperature of a tower top is 79 ℃, the reflux ratio is 2, the temperature of a tower top condenser is 40 ℃, and a first light fraction is separated from the tower top.
The first light fraction enters a entrainer recovery tower containing 15 theoretical plates and is operated at normal pressure,Rectifying at 100 ℃ at the tower bottom temperature of 64.5 ℃ under the condition of reflux ratio of 3, separating methanol at the tower top, discharging from the side line of the tower bottom, feeding the side line of the discharged material into a pervaporation membrane system containing NaA molecular sieve membranes for further dehydration treatment, dehydrating at 100 ℃ of a membrane component and 10kPa of a permeation side pressure, wherein the formaldehyde content in the dehydrated material is 11.36% and the water content is 0.5%, and directly returning to a PODE (pre-oxidation catalyst) synthesis unit; PODE in first rectifying column bottom 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.
[ example 3 ]
The aldehyde-containing feed solution with the formaldehyde content of 0.99% and the methanol aqueous solution of the entrainer respectively enter a first rectifying tower, the water content of the entrainer is 50%, the amount of the entrainer is 2 times of the mass of formaldehyde (calculated by the aldehyde-containing feed solution, the amount of the entrainer is about 2%), the rectification is carried out under the conditions of the operating pressure of 0.05MPa, the tower bottom temperature of 100 ℃, the tower top temperature of 70 ℃ and the reflux ratio of 5, the temperature of a tower top condenser of 20 ℃ and the first light fraction is separated from the tower top.
The first light fraction enters a entrainer recovery tower containing 20 theoretical plates, is rectified under the conditions of normal pressure operation, the temperature of a tower kettle is 100 ℃, the temperature of the tower top is 64.5 ℃ and the reflux ratio is 4, methanol is separated from the tower top, side line discharge is carried out from the position of the tower kettle, the side line discharge enters a pervaporation membrane system containing molecular sieve membranes for further dehydration treatment, the temperature of a membrane component is 95 ℃, the side pressure of the permeate is 5kPa for dehydration, the formaldehyde content in the dehydrated material is 2.66%, the water content is 0.3%, and the dehydrated material can be directly returned to a PODE synthesis unit; PODE in first rectifying column bottom 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 ]
The aldehyde-containing feed solution with the formaldehyde content of 5.78% and the methanol aqueous solution of the entrainer respectively enter a first rectifying tower, the water content of the entrainer is 90%, the amount of the entrainer is 4 times of the mass of formaldehyde (calculated by the aldehyde-containing feed solution, the amount of the entrainer is 23.12%), the rectification is carried out under the conditions of the operating pressure of 0.1MPa, the temperature of a tower bottom is 150 ℃, the temperature of a tower top is 85 ℃ and the reflux ratio is 1, the temperature of a condenser at the tower top is 25 ℃, and a first light fraction is separated from the tower top.
The first light fraction enters a entrainer recovery tower containing 20 theoretical plates, is rectified under the conditions of normal pressure operation, the temperature of a tower kettle is 105 ℃, the temperature of the tower top is 64.5 ℃ and the reflux ratio is 2, methanol is separated from the tower top, the side line is discharged from the position which is about 5 theoretical plates away from the tower kettle, the side line is discharged into a pervaporation membrane system containing molecular sieve membranes for further dehydration treatment, the temperature of a membrane assembly is 120 ℃, the osmotic side pressure is 1kPa for dehydration treatment, the dehydrated circulating material returns to the entrainer recovery tower, the formaldehyde content in the kettle liquid pumped from the tower kettle is 10.76%, the water content is 0.02%, and the circulating material can directly return to a PODE synthesis unit; PODE in first rectifying column bottom 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 ]
The aldehyde-containing feed solution with the formaldehyde content of 5.29% and the methanol aqueous solution of the entrainer respectively enter a first rectifying tower, the water content of the entrainer is 30%, the amount of the entrainer is 5.6 times of the mass of formaldehyde (calculated by the aldehyde-containing feed solution, the amount of the entrainer is 29.62%), the rectification is carried out under the conditions of the operating pressure of 0.08MPa, the temperature of a tower bottom of 135 ℃, the temperature of a tower top of 87 ℃ and the reflux ratio of 0.5, the temperature of a condenser at the temperature of the tower top of 10 ℃ and a first light fraction is separated from the tower top.
The first light fraction enters a entrainer recovery tower containing 25 theoretical plates, is rectified under the conditions of normal pressure operation, the temperature of a tower kettle is 105 ℃, the temperature of the tower top is 64.5 ℃ and the reflux ratio is 5, methanol is separated from the tower top, the side line is discharged from the position which is about 5 theoretical plates away from the tower kettle, the side line is discharged into a pervaporation membrane system containing molecular sieve membranes for further dehydration treatment, the temperature of a membrane assembly is 110 ℃, the osmotic side pressure is 5kPa for dehydration treatment, the dehydrated circulating material returns to the entrainer recovery tower, the formaldehyde content in the kettle liquid pumped from the tower kettle is 9.61%, the water content is 0.13%, and the circulating material can directly return to a PODE synthesis unit; first rectifying tower kettle liquidMiddle PODE 2-6 The content is 99.1%, 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. A method for separating and refining polymethoxy dimethyl ether, which comprises the following steps:
(a) Feeding aldehyde-containing feed liquid (1) and entrainer (2) into a first rectifying tower (3), and separating a first light fraction (5) and a first rectifying tower kettle liquid (6) from tower top materials through a condenser (4); optionally separating PODE from the first rectifying tower bottom liquid (6) by optional one-stage or two-stage conventional rectification 3-4 Or PODE 3-5 A product; the entrainer in the step (a) is a mixed liquid containing methanol and water, and the methylal content in the aldehyde-containing liquid is not higher than 10%;
(b) The first light fraction (5) enters a entrainer recovery tower (7), and a second light fraction (8) is separated from the top of the entrainer recovery tower; the side-draw material (10) of the entrainer recovery tower (7) enters a pervaporation membrane assembly (11), water (12) is separated from the permeation side, and the recycle material (13) returns to the entrainer recovery tower (7); the recovery tower bottom liquid (9) is circulated back to the PODE synthesizing unit.
2. The method for separating and purifying polymethoxy dimethyl ether according to claim 1, wherein the aldehyde-containing liquid in the step (a) contains formaldehyde and PODE 2-6 Formaldehyde content is 0.1-6%; or the aldehyde-containing feed liquid is derived from a reaction balance, the method further comprises the steps of: the reaction balance obtained by the PODE reaction synthesis unit is firstly removed from the light ends containing methylal in a light ends removal tower, and a kettle liquid containing formaldehyde is obtained from the kettle of the tower, namely the aldehyde-containing feed liquid (1).
3. The method for separating and purifying polymethoxy dimethyl ether according to claim 1, wherein the entrainer in the step (a) has a water content of 0 to 90% by mass.
4. The process for separating and purifying polymethoxy dimethyl ether according to claim 1 or 3, wherein the entrainer in the step (a) is used in an amount of 1 to 10 times by mass of formaldehyde.
5. The method for separating and purifying polymethoxy dimethyl ether according to claim 4, wherein the entrainer in the step (a) is 1 to 5 times the formaldehyde.
6. The method for separating and purifying polymethoxy dimethyl ether according to claim 5, wherein the entrainer in the step (a) is less than 5 times the formaldehyde.
7. The method for separating and purifying polymethoxy dimethyl ether according to claim 1, wherein the first rectifying tower in the step (a) has an operating pressure of 0.05-0.1 MPa; the temperature of the tower bottom is 80-160 ℃, the temperature of the tower top is 60-90 ℃, and the reflux ratio of the tower top is 0.5-5.
8. The method for separating and purifying polymethoxy dimethyl ether according to claim 1 or 2, wherein the condenser (4) in the step (a) is operated at a temperature of 10 to 50 ℃.
9. The method for separating and purifying polymethoxy dimethyl ether as recited in claim 1, wherein the first rectifying tower still liquid in the step (a) is PODE 2-6 The percentage of the formaldehyde is not less than 99%, the formaldehyde content is not more than 0.1%, and the water content is not more than 0.1%.
10. The process for separating and purifying polymethoxy dimethyl ether according to claim 1, wherein the theoretical plate number of the entrainer recovery column in the step (b) is 15 to 30; the side line extraction position is 0 to 5 theoretical plates away from the tower kettle position; the temperature of the tower kettle is 80-120 ℃.
11. The method for separating and purifying polymethoxy dimethyl ether according to claim 1, wherein the membrane used in the pervaporation membrane module in the step (b) is a molecular sieve membrane; the operating temperature of the membrane component is 90-120 ℃, and the osmotic side pressure is 0-30 kPa.
12. The method for separating and purifying polymethoxy dimethyl ether according to claim 1, wherein the water content in the bottom liquid of the recovery tower in the step (b) is not more than 1%.
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