CN108440493B - Method for separating trioxymethylene by extractive distillation - Google Patents
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Abstract
The invention provides a method for separating trioxymethylene by extractive distillation, which takes the combination of one or more ionic liquids as an extracting agent and purifies and separates trioxymethylene from a trioxymethylene aqueous solution by extractive distillation; wherein the mass ratio of the extracting agent to the trioxymethylene aqueous solution is 0.1-20: 1; the temperature of the separation process is 90-200 ℃. The method for extracting, rectifying and separating trioxymethylene provided by the invention can break the azeotropic point of trioxymethylene and water, and the saturated vapor pressure of the used ionic liquid extractant is low, and the ionic liquid extractant completely exists in a liquid phase and cannot escape into a gas phase along with trioxymethylene; meanwhile, the ionic liquid extractant has good thermal stability and can not be pyrolyzed under the conditions of long time and high temperature.
Description
Technical Field
The invention relates to a method for separating trioxymethylene by extractive distillation, belonging to the technical field of trioxymethylene separation.
Background
Trioxymethylene is an important chemical product, and is widely applied to the preparation of products such as anhydrous formaldehyde, pesticides, molding materials, binders, disinfectants and the like, and particularly, when polyformaldehyde engineering plastics are prepared, a high-purity trioxymethylene raw material is needed, so that the rapidly-increased demand of national economy on the polyformaldehyde engineering plastics is increased day by day, and therefore, the provision of more high-purity trioxymethylene becomes a technical problem which needs to be solved urgently in the field.
Trioxymethylene is synthesized by reactive distillation of formaldehyde, gas phase distillate of reactive distillation mainly contains trioxymethylene, water, formaldehyde and other impurities, and at present, three methods mainly exist in the industry for purifying trioxymethylene from the system: namely a reduced pressure distillation process, a crystallization process and an extraction process. The trioxymethylene and water have azeotropic points, the azeotropic composition of the trioxymethylene and the water is 69.8 percent and 30.2 percent, the azeotropic point of the trioxymethylene and the water can be broken through reduced pressure distillation, but the reduced pressure distillation has higher requirements on distillation equipment and a control system. The crystallization process and the extraction process have high energy consumption, can not be continuously operated, and are not suitable for industrial continuous large-scale production. In conclusion, the methods for purifying trioxymethylene which are industrially used at present have a great problem.
The method breaks through common organic extractants with azeotropic points in industry, such as dimethyl sulfoxide and dimethylformamide, the boiling points of which are about 200 ℃, so that serious evaporation loss exists in the extraction and rectification process, and the organic extractants also exist in gas phase distillate, so that the separation efficiency of trioxymethylene is reduced; meanwhile, the organic solvent has poor thermal stability under the continuous high-temperature industrial condition and can be gradually thermally decomposed.
Therefore, providing a new method for separating trioxymethylene by extractive distillation has become a technical problem to be solved in the art.
Disclosure of Invention
In order to solve the disadvantages and shortcomings, the invention aims to provide a method for separating trioxymethylene by extractive distillation.
In order to achieve the aim, the invention provides a method for separating trioxymethylene by extractive distillation, which takes the combination of one or more ionic liquids as an extracting agent and purifies and separates trioxymethylene from a trioxymethylene aqueous solution by extractive distillation;
wherein the mass ratio of the extracting agent to the trioxymethylene aqueous solution is 0.1-20: 1;
the temperature of the separation process is 90-200 ℃.
In one embodiment, the mass ratio of the extracting agent to the aqueous trioxymethylene solution is preferably 1 to 10: 1.
In a specific embodiment, preferably, the ionic liquid is a neutral ionic liquid or a basic ionic liquid.
In one embodiment, preferably, the cation of the ionic liquid comprises
wherein, R, R1、R2Is an alkyl group.
In one embodiment, preferably, the anion of the ionic liquid comprises Cl-、Br-、NO3 -、CH3COO-、CF3COO-、CH3SO3 -、CF3SO3 -One or more of benzene sulfonate, p-methyl benzene sulfonate, p-chlorobenzene sulfonate, p-nitrobenzene sulfonate, bis-trifluoromethyl sulfonyl imide and phosphate anions.
Wherein the structural formula of the phosphate anions is shown as formula 1;
in the formula 1, R3、R4Is an alkyl group.
In one embodiment, preferably, the ionic liquid comprises:
In one embodiment, the concentration of trioxymethylene is preferably 0.1 wt% to 70.0wt% based on the total weight of the aqueous trioxymethylene solution being 100%.
In one embodiment, the concentration of trioxymethylene is preferably 0.1 wt% to 60.0wt% based on the total weight of the aqueous trioxymethylene solution being 100%.
In one embodiment, it is preferable that the aqueous trioxymethylene solution contains impurities in a concentration of 0 to 50.0wt% based on the total weight of the aqueous trioxymethylene solution taken as 100%. Wherein the impurities comprise formaldehyde, methyl formate, methanol and the like.
The method for extracting, rectifying and separating trioxymethylene adopts the device for extracting, rectifying and separating trioxymethylene to evaluate the separation effect of different ionic liquids on trioxymethylene, and the device comprises an improved Othmer gas-liquid equilibrium kettle, a first Pt electrode temperature sensor 2, a second Pt electrode temperature sensor 4, a heating belt 3, a condensing pipe 5 and a heating device 9 (a temperature-controllable oil bath with magnetic stirring); the Othmer gas-liquid equilibrium kettle is provided with a feed inlet 1, a gas phase sampling port 6, a valve 7 and a liquid phase sampling port 8; and a rotor 10 is arranged in the Othmer gas-liquid equilibrium kettle and the temperature-controllable oil bath 9. The device adopted by the invention has the advantages of accurate measurement and simple operation.
The method for separating trioxymethylene by extractive distillation provided by the invention adopts the ionic liquid as the extractant, the saturated vapor pressure of the ionic liquid is low, the thermal stability is good, the ionic liquid replaces the traditional organic solvent to be used as the extractant, the evaporation loss and the pyrolysis loss of the extractant can be reduced, and the trouble of further separating the extractant from the gas-phase distillate is avoided.
In the method for separating trioxymethylene by extraction, rectification and purification, which is provided by the invention, the most key point for extracting, rectification and purification of trioxymethylene is breaking the azeotropic point of trioxymethylene and water, the ionic liquid extracting agent adopted by the method can form strong hydrogen bond action with water, but has no obvious hydrogen bond action with trioxymethylene, and further, the relative volatility of trioxymethylene and water is obviously changed by adding the ionic liquid extracting agent, and the azeotropic point of trioxymethylene and water is broken.
In conclusion, the method for extracting, rectifying and separating trioxymethylene provided by the invention can break the azeotropic point of trioxymethylene and water, and the saturated vapor pressure of the used ionic liquid extractant is low, and the ionic liquid extractant completely exists in a liquid phase and cannot escape into a gas phase along with trioxymethylene; meanwhile, the ionic liquid extractant has good thermal stability and can not be pyrolyzed under the conditions of long time and high temperature.
Drawings
FIG. 1 is a schematic structural diagram of an apparatus for separating trioxymethylene by extractive distillation used in the examples of the present invention;
FIG. 2 is a diagram showing the results of gas chromatography detection provided in example 1 of the present invention.
The main reference numbers illustrate:
1, a feeding hole;
2. a first Pt electrode temperature sensor 2;
3. heating the tape;
4. a second Pt electrode temperature sensor;
5. a condenser tube;
6. a gas phase sampling port;
7. a valve;
8. a liquid phase sampling port;
9. a heating device;
10. and a rotor.
Detailed Description
In order to clearly understand the technical features, objects and advantages of the present invention, the following detailed description of the technical solutions of the present invention will be made with reference to the following specific examples, which should not be construed as limiting the implementable scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; the materials, reagents and the like used are commercially available unless otherwise specified.
The structure schematic diagram of the device for separating trioxymethylene by extractive distillation used in the following examples is shown in fig. 1, but not limited thereto, and as can be seen from fig. 1, it includes a modified Othmer gas-liquid equilibrium kettle, a first Pt electrode temperature sensor 2, a second Pt electrode temperature sensor 4, a heating belt 3, a condenser pipe 5, and a heating device 9 (specifically, a temperature-controllable oil bath with magnetic stirring); the Othmer gas-liquid equilibrium kettle is provided with a feed inlet 1, a gas phase sampling port 6, a valve 7 and a liquid phase sampling port 8; and a rotor 10 is arranged in the Othmer gas-liquid balance kettle and the temperature-controllable oil bath 9;
wherein, the purpose of arranging the heating belt 3 is to prevent trioxymethylene from condensing at the section, and the voltage of the heating belt can be properly adjusted according to the actual situation;
the temperature of the circulating water used by the condensation pipe 5 is 40-60 ℃, and the temperature can ensure that the gaseous trioxymethylene can be condensed into liquid drops without being condensed to stick to the wall.
The method for separating trioxymethylene by extraction, rectification and separation comprises the following specific experimental steps: adding a trioxymethylene aqueous solution and an ionic liquid extracting agent in a certain ratio into an Othmer kettle, then opening an oil bath and a heating belt, properly adjusting the temperature of the solution at the bottom of the kettle (measured by a first Pt electrode temperature sensor 2) and the temperature of the heating belt as required, fully heating and refluxing for 1h to achieve gas-liquid phase balance, and starting timing after the gas phase temperature is stable; and sampling from the gas and liquid phase sampling ports by using a needle tube, and analyzing the content of trioxymethylene and impurities in each sample by using gas chromatography.
The ionic liquid extractants used in the following examples are as follows:
example 1
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of water and 5mol/(kg of aqueous solution) of ionic liquid a are added into an Othmer kettle through a feeding hole, the oil bath temperature is controlled at 100 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature (measured by a second Pt electrode temperature sensor 2) is stabilized, gas and liquid phase compositions are analyzed by gas chromatography (ethanol is used as an internal standard, see figure 2), and the water content is measured by a Karl Fischer moisture tester.
The measurement result shows that: the vapor phase trioxymethylene concentration was 86.17 wt%, the vapor phase water content was 13.83 wt%, and the liquid phase trioxymethylene concentration was 51.64 wt%.
Example 2
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of 20 wt% aqueous formaldehyde solution and 5mol/(kg of aqueous solution) of ionic liquid a are added into an Othmer kettle through a feed inlet, the temperature of an oil bath is controlled at 140 ℃ for gas-liquid balance, sampling and analyzing are carried out 30min after the gas phase temperature is stable, the gas phase and the liquid phase are analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture tester.
The measurement result shows that: the concentration of the gas-phase trioxymethylene was 87.89 wt%, the content of the gas-phase formaldehyde was 4.48 wt%, the content of the gas-phase water was 7.63 wt%, and the concentration of the liquid-phase trioxymethylene was 51.85 wt%.
Example 3
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of water and 5mol/(kg of aqueous solution) of ionic liquid b are added into an Othmer kettle through a feed inlet, the oil bath temperature is controlled at 140 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature is stable, the gas-liquid phase composition is analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture meter.
The measurement result shows that: the gas-phase trioxymethylene concentration was 82.69 wt%, the gas-phase water content was 17.31 wt%, and the liquid-phase trioxymethylene concentration was 53.47 wt%.
Example 4
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of water and 5mol/(kg of aqueous solution) of ionic liquid c are added into an Othmer kettle through a feed inlet, the oil bath temperature is controlled at 140 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature is stable, the gas-liquid phase composition is analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture meter.
The measurement result shows that: the concentration of trioxymethylene in the gas phase was 78.38 wt%, the water content in the gas phase was 21.62 wt%, and the concentration of trioxymethylene in the liquid phase was 54.66 wt%.
Example 5
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of water and 10mol/(kg of aqueous solution) of ionic liquid d are added into an Othmer kettle through a feed inlet, the oil bath temperature is controlled at 150 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature is stable, the gas-liquid phase composition is analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture meter.
The measurement result shows that: the concentration of the gas-phase trioxymethylene was 76.42 wt%, the water content of the gas phase was 23.58 wt%, and the concentration of the liquid-phase trioxymethylene was 55.25 wt%.
Example 6
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of water and 10mol/(kg of aqueous solution) of ionic liquid e are added into an Othmer kettle through a feed inlet, the oil bath temperature is controlled at 180 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature is stable, the gas-liquid phase composition is analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture meter.
The measurement result shows that: the concentration of the gas-phase trioxymethylene was 76.42 wt%, the water content of the gas phase was 23.58 wt%, and the concentration of the liquid-phase trioxymethylene was 55.25 wt%.
Example 7
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of water and 5mol/(kg of aqueous solution) of ionic liquid f are added into an Othmer kettle through a feed inlet, the oil bath temperature is controlled at 160 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature is stable, the gas-liquid phase composition is analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture meter.
The measurement result shows that: the concentration of the gas-phase trioxymethylene was 80.66 wt%, the water content of the gas phase was 19.34 wt%, and the concentration of the liquid-phase trioxymethylene was 53.96 wt%.
Example 8
The embodiment provides a method for separating trioxymethylene by extractive distillation, which comprises the following steps:
60g of trioxymethylene, 40g of water and 3mol/(kg of aqueous solution) of ionic liquid a and 2mol/(kg of aqueous solution) of ionic liquid b are added into an Othmer kettle through a feed inlet, the oil bath temperature is controlled at 150 ℃ for gas-liquid balance, sampling and analyzing are carried out 30min after the gas phase temperature is stable, the gas and liquid phase compositions are analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture tester.
The measurement result shows that: the gas phase trioxymethylene concentration was 87.56 wt%, the gas phase water content was 12.44 wt%, and the liquid phase trioxymethylene concentration was 50.97 wt%.
Comparative example 1
The present comparative example provides a method for separating trioxymethylene, which comprises the following steps:
60g of trioxymethylene and 40g of water are added into an Othmer kettle through a feeding hole, the oil bath temperature is controlled at 150 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature is stable, the gas-liquid phase composition is analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture tester.
The measurement result shows that: the gas-phase trioxymethylene concentration was 69.54 wt%, the gas-phase water content was 30.66 wt%, and the liquid-phase trioxymethylene concentration was 56.87 wt%.
Comparative example 2
The present comparative example provides a method for separating trioxymethylene, which comprises the following steps:
60g of trioxymethylene, 40g of water and 5mol/(kg of aqueous solution) of dimethyl sulfoxide are added into an Othmer kettle through a feeding hole, the oil bath temperature is controlled at 150 ℃ for gas-liquid balance, sampling analysis is carried out 30min after the gas phase temperature is stable, the gas-liquid phase composition is analyzed by gas chromatography, and the water content is measured by a Karl Fischer moisture meter.
The measurement result shows that: the concentration of vapor-phase trioxymethylene was 71.36 wt%, the vapor-phase water content was 20.95 wt%, the concentration of liquid-phase trioxymethylene was 56.02 wt%, and the concentration of vapor-phase dimethylsulfoxide was 7.69 wt% as determined by the normalization method.
The above examples 1 to 8 and comparative examples 1 to 2 were summarized as the results shown in Table 1 below.
TABLE 1
As can be seen from Table 1, the extractant is not added in the comparative example 1, the azeotropic point is 69.54 wt%, and the experimental data of the examples 1 to 8 and the comparative example 1 show that the azeotropic balance of the trioxymethylene and the water can be broken through after the ionic liquid is added as the extractant, so that the separation effect of the trioxymethylene is obviously improved; from the experimental data of examples 1-8 and comparative example 2, it can be seen that with ionic liquid as the extractant, the gas phase is completely free of ionic liquid, and the used organic solvent, dimethyl sulfoxide, escapes into the gas phase; from the experimental results of examples 1, 3 and 8, it is clear that the ionic liquid can obtain the effect of "1 +1> 2" when used in combination.
In conclusion, the invention provides a method for separating trioxymethylene by extractive distillation, wherein the ionic liquid is used as an extracting agent in the extractive distillation, so that the azeotropic point of the trioxymethylene and water can be broken, and the separation effect of the trioxymethylene is obviously improved; the saturated vapor pressure of the ionic liquid extractant is low, and the gas phase hardly contains the ionic liquid; in addition, the ionic liquid has good thermal stability, and the separation effect of the ionic liquid cannot be influenced even if the ionic liquid is used for a long time.
Claims (2)
1. A method for extracting, rectifying and separating trioxymethylene is characterized in that an ionic liquid is used as an extracting agent, and trioxymethylene is purified and separated from a trioxymethylene aqueous solution through extraction and rectification;
wherein the mass ratio of the extracting agent to the trioxymethylene aqueous solution is 1-2.22: 1;
the temperature of the separation process is 90-180 deg.CoC；
The ionic liquid is
The total weight of the trioxymethylene aqueous solution is 100 percent, and the concentration of the trioxymethylene is 0.1 to 70.0 weight percent;
the concentration of impurities contained in the aqueous trioxymethylene solution is 0 to 50.0wt% based on the total weight of the aqueous trioxymethylene solution as 100%.
2. The method according to claim 1, wherein the concentration of trioxymethylene is 0.1 wt% to 60.0wt% based on the total weight of the aqueous trioxymethylene solution being 100%.
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| CN1524006A (en) * | 2001-03-20 | 2004-08-25 | �����ɷ� | Ionic liquids as selective additives for separation of close-boiling or azeotropic mixtures |
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| CN1978438A (en) * | 2005-12-09 | 2007-06-13 | 中国科学院兰州化学物理研究所 | Method for synthesizing tripoly aldehyde by ionic liquid catalysis of aldehyde |
| CN101311154B (en) * | 2007-05-22 | 2010-08-11 | 富艺国际工程有限公司 | Process for synthesizing triformol using ionic liquid |
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| "反应萃取生产三聚甲醛的新工艺";刘继泉等;《青岛科技大学学报（自然科学版）》;20140228;第35卷(第1期);第39-42页 * |
| "离子液体的工业应用研究进展";李臻等;《化工进展》;20121231;第31卷;第2113-2123，2182页 * |
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