CN106866369B - Separation method of polyol mixture - Google Patents
Separation method of polyol mixture Download PDFInfo
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- CN106866369B CN106866369B CN201510915692.7A CN201510915692A CN106866369B CN 106866369 B CN106866369 B CN 106866369B CN 201510915692 A CN201510915692 A CN 201510915692A CN 106866369 B CN106866369 B CN 106866369B
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- C07C29/80—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation
- C07C29/84—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation by extractive distillation
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Abstract
The invention discloses a separation method of a polyol mixture with similar boiling points, which takes glycol containing dihydric fusel (1, 2-propylene glycol and 1, 2-butanediol) as the feed of a vacuum rectification tower, and improves the relative volatility between the 1, 2-propylene glycol with the same weak polarity, the 1, 2-butanediol and the glycol with the stronger polarity by introducing a weak-polarity gaseous extractant into the bottom of the tower, thereby improving the separation efficiency of rectification. The invention provides a novel rectification method for separating dihydric fusel in ethylene glycol, wherein the boiling point of the used gaseous extracting agent is far lower than that of the dihydric alcohol, and the gaseous extracting agent is easy to separate and can be recycled, so that the material consumption and the energy consumption in the separation process are reduced. The invention can separate 1, 2-propylene glycol and 1, 2-butanediol from ethylene glycol, and obtain high purity ethylene glycol and concentrated by-products of 1, 2-propylene glycol and 1, 2-butanediol.
Description
Technical Field
The invention relates to a chemical separation technology for removing 1, 2-propylene glycol and 1, 2-butanediol from ethylene glycol.
Background
Ethylene glycol is a basic chemical raw material for mass production, and can be used for producing polyester fibers (terylene), polyethylene terephthalate, explosives, solvents, antifreeze agents, plasticizers, moisture absorbents and the like. At present, ethylene is mainly used as a raw material in industry, ethylene glycol is produced by an ethylene oxide hydration method, and a large amount of non-renewable petroleum and natural gas resources are consumed. Since 2002, the proportion of the imported ethylene glycol in the demand of China is always maintained to be more than 70%. Wherein the glycol consumed by the polyester industry accounts for more than 80 percent. The biomass raw material rich in cellulose is cheap and easy to obtain, and the renewable biomass is used as the raw material to produce the ethylene glycol, so that the dependence on petroleum and coal can be reduced, the emission of carbon dioxide can be reduced to the greatest extent, the greenhouse effect is weakened, and the method has a good industrial prospect. In addition, the technology for preparing ethylene glycol from coal is suitable for the national situation of rich coal and little oil in China, has wide development prospect and is partially industrialized.
However, the ethylene glycol crude product synthesized by using biomass or coal as a raw material contains a certain amount of by-products such as 1, 2-propanediol, 1, 2-butanediol and the like. The boiling point of the by-products is close to that of ethylene glycol, the conventional rectification and separation are difficult, and the separation energy consumption and cost are high; and the downstream polyester industry generally requires that the mass fraction of ethylene glycol reach 99.9%. Therefore, efficient separation of ethylene glycol, 1, 2-propylene glycol and 1, 2-butanediol is a challenging subject, and is a key technical problem to be solved urgently for energy conservation and consumption reduction in industrial production of biomass-based and coal-based ethylene glycol.
Patent CN103772146A and patent US4966658A use one of ketal, ethylbenzene, 3-heptanone, p-xylene, o-xylene, mesitylene, cumene, diisobutyl ketone, etc. as an entrainer, and extract ethylene glycol from the top of the column by azeotropic distillation. The azeotrope formed by the entrainer and ethylene glycol used in the two patents is difficult to further separate by rectification, and most of the entrainers form azeotrope with ethylene glycol with the highest content, so the amount of the entrainer and the energy consumption are high. The patent US8143458B2 discloses an extractive distillation method for separating 1, 2-propylene glycol, 1, 2-butanediol and 2, 3-butanediol from ethylene glycol, all the extracting agents (such as water, methanol and ethanol) used in the patent are strong polar extracting agents, and the related method belongs to the category of liquid extractive distillation, and has almost no promotion effect on the separation of 1, 2-butanediol.
Disclosure of Invention
The invention provides a technical scheme for separating 1, 2-propylene glycol and 1, 2-butanediol from ethylene glycol by gas extractive distillation. The method is characterized in that a crude product of ethylene glycol containing one or two of 1, 2-propylene glycol and 1, 2-butanediol is used as a raw material, wherein the total mass concentration of the 1, 2-propylene glycol and the 1, 2-butanediol in the polyhydric alcohol mixture in the ethylene glycol solution is 0.5-50%. Introducing gaseous substances serving as an extracting agent from the lower part of a rectifying tower, extracting one or two of light components 1, 2-propanediol and 1, 2-butanediol from ethylene glycol and gasifying the light components simultaneously in a gas extraction and rectification mode, condensing one or two of the gasified 1, 2-propanediol and 1, 2-butanediol at a partial condenser at the top of the tower, partially extracting, and condensing and recycling most of the gaseous extracting agent at the partial condenser through a full condenser without condensing at the partial condenser; the purification of the ethylene glycol is realized while one or two of the 1, 2-propylene glycol and the 1, 2-butanediol are extracted and gasified; the used extracting agent is an organic matter with a normal-pressure boiling point of 0-170 ℃, and comprises one or a combination of more than two of alcohols, esters, ethers, halogenated hydrocarbons, alcohol amines and amines with the carbon number more than 3, and comprises ethyl acetate, ethyl butyrate, propyl ether, butyl ether, n-butyl alcohol, n-amyl alcohol, isobutyl alcohol, ethanolamine, n-pentylamine, dichloromethane and 1-chloropentane. The extractant acts as an extraction in the form of a gas. The extractant used cannot form an azeotrope with 1, 2-propanediol or 1, 2-butanediol glycol.
When the ethylene glycol crude product is separated by gas extraction and rectification, the liquid temperature in the tower kettle is 115-150 ℃, and the gas phase pressure at the top of the tower is 3-20 kPa absolute pressure. Before the extractant enters the rectifying tower or is completely gasified or partially gasified in the rectifying tower to be gaseous extractant. Extracting one or two of 1, 2-propanediol and 1, 2-butanediol to the top of the tower by a gaseous extracting agent, condensing the 1, 2-propanediol and 1, 2-butanediol at the top of the tower in a partial condenser mode, and refluxing and extracting part of the condensate; most of the gaseous extractant is not condensed by the partial condenser, then the gaseous extractant is condensed by the full condenser with lower temperature, and the extractant condensed by the full condenser can return to the rectifying tower for reuse. Due to the partial pressure of the gaseous extractant, the overall vacuum degree of the rectifying tower can be reduced on the premise of maintaining the temperature of the tower bottom unchanged. The temperature of the partial condenser is higher than the boiling point of the gaseous extracting agent in the partial condenser and lower than the boiling point of the 1, 2-propylene glycol or the 1, 2-butanediol in the partial condenser.
The method comprises the following specific steps:
(1) adding a proper amount of dihydric alcohol mixture into a tower kettle, starting a kettle bottom heating and vacuum unit, keeping the temperature of the tower kettle of the rectifying tower at 115-150 ℃, and keeping the pressure of the tower top at 3-20 kPa. After the condensate liquid appears in the overhead condenser 1, the temperature of the condenser 1 is adjusted, so that the set temperature of the partial condenser is higher than the boiling point of the gaseous extracting agent in the partial condenser and lower than the boiling point of the 1, 2-propanediol or the 1, 2-butanediol in the partial condenser, thereby enabling the extracting agent to be in a gaseous state on the surface of the condenser 1, and simultaneously enabling the 1, 2-propanediol and the 1, 2-butanediol to be condensed on the surface of the condenser 1, namely the condenser 1 essentially belongs to the partial condenser. While the condenser 2 is switched on. The total reflux is carried out for a period of time, so that the rectification system and the vacuum system are stable;
(2) the gaseous extractant directly enters the rectifying tower without preheating; the liquid extractant is preheated by the evaporating pipe to gasify all or most of the extractant, and the rest of the extractant is gasified at the bottom of the tower. The gaseous extractant enters the rectifying tower and contacts with descending liquid flow in a reverse direction, the tower plate or the filler provides a gas-liquid mass transfer interface for rectification and gas extraction at the same time, and the 1, 2-propylene glycol and the 1, 2-butanediol are condensed and partially refluxed at the condenser 1. The gaseous extractant enters the condenser 2 to be condensed and can return to the rectifying tower for recycling; 1, 2-propylene glycol and 1, 2-butanediol with a small amount of extractant can be extracted at the condenser 1, and the low-boiling point extractant can be removed by one or two of distillation, extraction, adsorption and gas stripping. In addition, high-purity ethylene glycol is extracted from the bottom of the rectifying tower;
preferably, the extractant is ethyl butyrate;
preferably, when ethyl butyrate is used, the temperature of the condenser 1 is set to be 95-110 ℃, and the pressure at the top of the condenser is adjusted to be 15 kPa;
preferably, the volume flow rate ratio of the liquid ethyl butyrate to the liquid glycol raw material is 5: 1;
preferably, the overhead reflux ratio is set to 10: 1;
preferably, the temperature of the condenser 2 is set to 10 ℃ at an absolute pressure of 15kPa, when ethyl butyrate is used.
The equipment needed for realizing the invention mainly comprises: a reduced pressure rectifying tower, a vacuum unit, a condenser, a flash tank, a pump and the like.
The principle of separating 1, 2-propylene glycol and 1, 2-butanediol from ethylene glycol is as follows:
at higher temperature, the rectification column is in a gas-liquid equilibrium state, and Gibbs free energy of gas-liquid phase molecules is equal to Gibbs free energy of liquid-liquid phase molecules. When the extractant gas is introduced, the extractant molecules interact with the 1, 2-propanediol and 1, 2-butanediol molecules in the gas phase or on the liquid surface, so that the Gibbs free energy of the 1, 2-propanediol and 1, 2-butanediol in the gas phase or on the liquid surface is reduced. Therefore, the 1, 2-propylene glycol and the 1, 2-butanediol in the liquid are easier to enter a gas phase, namely, the gas extraction promotes the mass transfer of the 1, 2-propylene glycol and the 1, 2-butanediol with low boiling points from a liquid phase to the gas phase, but simultaneously has no obvious or inhibiting effect on the liquid-gas mass transfer of the ethylene glycol, so macroscopically, the concentration of the 1, 2-propylene glycol and the 1, 2-butanediol in the product extracted from the tower top is increased, namely, the separation effect is improved.
Compared with the prior art, the invention has the advantages that:
the rectification separation of the 1, 2-propylene glycol and the 1, 2-butanediol is promoted, the mass fraction of the 1, 2-propylene glycol in a product at the top of the tower can be increased by 10-30%, and the mass fraction of the 1, 2-butanediol can be increased by 4-12%, so that the number of tower plates and energy consumption of a rectification tower can be reduced on the premise of finishing the same separation task, and the fixed investment and the operation cost of a rectification device are reduced.
Due to the introduction of the extractant gas, the partial pressure of the glycol steam can be reduced, and the vacuum degree of the rectifying tower can be reduced on the premise of keeping the temperature at the bottom of the tower constant, so that the high-performance requirements on the rectifying tower and vacuum unit equipment are reduced.
Drawings
FIG. 1 is a flow chart of batch type pressure-reducing gas extraction rectification of the present invention.
FIG. 2 is a flow chart of continuous vacuum gas extraction and rectification according to the present invention.
FIG. 3 is a flow diagram of a conventional batch vacuum distillation.
FIG. 1: 1. a vacuum pump 2, a vacuum degree regulating valve 3, a condenser 2 (a complete condenser) 4, a gaseous extractant 5, a condenser 1 (a partial condenser) 6, an emptying valve 7, a buffer tank 8, a flash tank 9, a dihydric alcohol product 10, a digital thermometer 11, a gas extraction rectifying column 12, a digital pressure gauge 13, a glycol mixed solution 14, a digital thermometer 15, a rectifying still 16, an extractant storage tank 17 and an evaporating pipe
FIG. 2: 1. vacuum pump 2, vacuum degree regulating valve 3, condenser 2 (whole condenser) 4, gaseous extractant 5, condenser 1 (partial condenser) 6, glycol steam and superheated extraction gas 7, blow-off valve 8, buffer tank 9, flash tank 10, 1, 2-propanediol (or 1, 2-butanediol) 11, mixture 12 of ethylene glycol and 1, 2-propanediol (or 1, 2-butanediol), gas extraction-rectification tower 13, extractant storage tank 14, evaporation pipe 15, reboiler 16, ethylene glycol product
FIG. 3: 1. a vacuum pump 2, a vacuum degree regulating valve 3, a condenser (a complete condenser) 4, glycol steam 5, 1, 2-propylene glycol (or 1, 2-butanediol) 6, a mixture 7 of ethylene glycol and 1, 2-propylene glycol (or 1, 2-butanediol), a rectifying tower 8, a reboiler 9, an ethylene glycol product
Detailed Description
The invention is described in detail below with reference to the figures and examples.
Example one
As shown in figure 1, 200mL of a mixed solution of 1, 2-propylene glycol and ethylene glycol was added to the bottom of a batch-type rectification column, wherein the mass fraction of 1, 2-propylene glycol was 22% and the mass fraction of ethylene glycol was 78%. The absolute pressure of the gas phase at the top of the rectifying tower is kept at 13kPa, and the liquid phase temperature in the tower bottom is 120 ℃. The rectifying tower uses a triangular spiral packing, and the number of theoretical plates is 55. The temperature of the condenser 1 was adjusted to 100 ℃ and the temperature of the condenser 2 was adjusted to 10 ℃. The total reflux is carried out for 0.5h, so that the system is stable;
the reflux ratio was set to 10: 1. Ethyl butyrate was injected from a storage tank into an evaporation tube having an inner surface temperature of 105 ℃ at a flow rate of 0.78mL/min, and the ethyl butyrate was completely vaporized in the evaporation tube. The gaseous extractant enters the rectifying tower and contacts with the descending liquid flow at the top of the tower. The ascending gas flow is condensed at the condenser 1 and partially extracted, ethyl butyrate carried in the product at the top of the tower is removed through a flash tank, and the evaporated ethyl butyrate enters the condenser 2 to be totally liquefied and returns to the rectifying tower. The flash tank was operated at atmospheric pressure and the flash temperature was 160 ℃. 45mL of 1, 2-propylene glycol with the mass fraction of 80% can be obtained at the early stage of batch rectification, and then 155mL of ethylene glycol product with the mass fraction of 93.6% can be obtained;
example two
As shown in FIG. 1, 200mL of a mixed solution of 1, 2-butanediol and ethylene glycol, wherein the mass fraction of 1, 2-butanediol is 10% and the mass fraction of ethylene glycol is 90%, was added to the bottom of a batch-type rectification column. The absolute pressure of the gas phase at the top of the rectifying tower is kept at 14.5kPa, and the temperature of the liquid phase in the tower bottom is 110 ℃. The rectifying tower uses pall ring packing, and the number of theoretical plates is 60. The temperature of the condenser 1 was adjusted to 90 ℃ and the temperature of the condenser 2 was adjusted to 3 ℃. The total reflux is carried out for 0.5h, so that the system is stable;
the reflux ratio was set to 10: 1. Propyl ether was injected from a storage tank into an evaporation tube having an inner surface temperature of 95 ℃ at a flow rate of 1.1mL/min, and most of the propyl ether was vaporized in the evaporation tube and a small amount was vaporized at the bottom of the column. The gaseous extractant enters the rectifying tower and contacts with the descending liquid flow at the top of the tower. The ascending gas flow is condensed at the condenser 1 and partially extracted, propyl ether carried in the product at the top of the tower is removed through a flash tank, and the evaporated propyl ether enters the condenser 2 to be totally liquefied and returns to the rectifying tower. The flash tank was operated at atmospheric pressure and the flash temperature was 160 ℃. 50mL of 1, 2-butanediol with the mass fraction of 36% can be obtained at the early stage of batch rectification, and then 150mL of ethylene glycol product with the mass fraction of 99% can be obtained;
EXAMPLE III
As shown in figure 1, 200mL of a mixed solution of 1, 2-propylene glycol and ethylene glycol was added to the bottom of a batch type rectification column, wherein the mass fraction of 1, 2-propylene glycol was 50%, and the mass fraction of ethylene glycol was 50%. The absolute pressure of the gas phase at the top of the rectifying tower is kept at 19.8kPa, and the liquid phase temperature in the tower bottom is 150 ℃. The rectification column uses Raschig ring packing, and the number of theoretical plates is 83. The temperature of the condenser 1 was adjusted to 137 ℃ and the temperature of the condenser 2 was adjusted to 20 ℃. The total reflux is carried out for 0.7h, so that the system is stable;
the reflux ratio was set to 8.5: 1. Isobutanol was injected from a storage tank into a vaporizing tube having an inner surface temperature of 143 c at a flow rate of 1mL/min, and most of isobutanol was vaporized in the vaporizing tube and a small amount of isobutanol was vaporized at the bottom of the column. The gaseous extractant enters the rectifying tower and contacts with the descending liquid flow at the top of the tower. The ascending gas flow is condensed at the condenser 1 and partially extracted, isobutanol carried in the product at the top of the tower is removed through a flash tank, and the evaporated isobutanol enters the condenser 2 to be totally liquefied and returns to the rectifying tower. The flash tank was operated at atmospheric pressure and the flash temperature was 174 ℃. 100mL of 1, 2-propylene glycol with the mass fraction of 97.1 percent can be obtained at the early stage of batch rectification, and then 100mL of glycol product with the mass fraction of 97.5 percent can be obtained;
example four
As shown in fig. 2, the total theoretical plate number of the continuous plate-type rectification column is 30. And injecting a mixed solution of 1, 2-propylene glycol and ethylene glycol into the rectifying tower at a flow rate of 2t/h by taking the 12 th plate as a feeding plate, wherein the mass fraction of the 1, 2-propylene glycol is 5%, and the mass fraction of the ethylene glycol is 95%. The absolute pressure of the gas phase at the top of the rectifying tower is kept at 3kPa, and the liquid phase temperature in the tower bottom is 115 ℃. The temperature of the condenser 1 was adjusted to 90 ℃ and the temperature of the condenser 2 was adjusted to 3 ℃. The total reflux is carried out for 1h, so that the system is stable;
the reflux ratio was set to 8: 1. 1-chloropentane was injected from a storage tank at a flow rate of 2t/h into an evaporation tube having an inner surface temperature of 92 ℃ and most of the 1-chloropentane was vaporized in the evaporation tube and a small amount was vaporized at the bottom of the column. The gaseous extractant enters the rectifying tower and contacts with the descending liquid flow at the top of the tower. The ascending gas flow is condensed at a condenser 1 and partially extracted, 1-chloropentane carried in a product at the top of the tower is removed through a flash tank, the flash tank is operated at normal pressure, and the flash temperature is 151 ℃.1, 2-propylene glycol with the mass fraction of 97 percent is extracted at the bottom of the flash tank at the yield of 0.1t/h, and the 1-chloropentane which is flashed out enters a condenser 2 to be completely liquefied and returns to the rectifying tower; collecting an ethylene glycol product with the mass fraction of 99% at the bottom of the rectifying tower;
EXAMPLE five
As shown in FIG. 2, the total theoretical plate number of the continuous packed column was 45. And injecting a mixed solution of 1, 2-propylene glycol and ethylene glycol into the rectifying tower at a flow rate of 10t/h by taking the 22 nd plate as a feeding plate, wherein the mass fraction of the 1, 2-propylene glycol is 15%, and the mass fraction of the ethylene glycol is 85%. The absolute pressure of the gas phase at the top of the rectifying tower is kept at 10kPa, and the liquid phase temperature in the tower bottom is 123 ℃. The temperature of the condenser 1 was adjusted to 90 ℃ and the temperature of the condenser 2 was adjusted to 3 ℃. The total reflux is carried out for 1h, so that the system is stable;
the reflux ratio was set to 13: 1. N-pentylamine was injected from a storage tank into an evaporation tube having an inner surface temperature of 92 ℃ at a flow rate of 9t/h, and most of the n-pentylamine was vaporized in the evaporation tube and a small amount thereof was vaporized at the bottom of the column. The gaseous extractant enters the rectifying tower and contacts with the descending liquid flow at the top of the tower. The ascending gas flow is condensed at a condenser 1 and partially extracted, and n-pentylamine carried in a product at the top of the tower is removed by a flash tank, wherein the flash tank is operated at normal pressure and the flash temperature is 150 ℃.1, 2-propylene glycol with the mass fraction of 90 percent is extracted at the bottom of the flash tank at the yield of 1.2t/h, and the n-pentylamine which is flashed out enters a condenser 2 to be completely liquefied and returns to the rectifying tower; collecting an ethylene glycol product with the mass fraction of 95% at the bottom of the rectifying tower;
the following comparative tests were made in the present invention with respect to the rectification flow and the separation effect of the present invention.
Comparative example 1
As shown in FIG. 3, the conventional batch vacuum distillation is adopted, and a triangular spiral packing is used in a rectifying tower, and the number of theoretical plates is 55. 200mL of 1, 2-propylene glycol and ethylene glycol mixed solution is added into the tower kettle, wherein the mass fraction of the 1, 2-propylene glycol is 22%, and the mass fraction of the ethylene glycol is 78%. The absolute pressure of the gas phase at the top of the rectifying tower is kept at 8kPa, and the liquid phase temperature in the tower kettle is 120 ℃. The temperature of the condenser 1 was adjusted to 100 ℃ and the temperature of the condenser 2 was adjusted to 10 ℃. The total reflux is carried out for 0.5h, so that the system is stable;
the reflux ratio was set to 10:1 and the product was taken off at the top of the column. 45mL of 1, 2-propylene glycol with the mass fraction of 72% can be obtained at the early stage of batch rectification, and then 155mL of ethylene glycol product with the mass fraction of 91% can be obtained. Both the light product extracted from the top of the tower and the main product of the ethylene glycol have the main components with the mass fraction (purity) 2.7-10% lower than that of the corresponding product in the first embodiment of the invention, namely, the separation effect of the invention is obviously better than that of the conventional rectification;
comparative example No. two
As shown in FIG. 3, the conventional batch type vacuum distillation is adopted, the rectification tower uses pall ring packing, and the number of theoretical plates is 60. 200mL of 1, 2-butanediol and ethylene glycol mixed solution is added into the tower kettle, wherein the mass fraction of the 1, 2-butanediol is 10%, and the mass fraction of the ethylene glycol is 90%. The absolute pressure of the gas phase at the top of the rectifying tower is kept at 8.7kPa, and the liquid phase temperature in the tower bottom is 110 ℃. The temperature of the condenser 1 was adjusted to 90 ℃ and the temperature of the condenser 2 was adjusted to 3 ℃. The total reflux is carried out for 0.5h, so that the system is stable;
the reflux ratio was set to 10:1 and the product was taken off at the top of the column. 50mL of 1, 2-butanediol with the mass fraction of 30% can be obtained at the early stage of batch rectification, and then 150mL of ethylene glycol product with the mass fraction of 96.7% can be obtained. Both the light product extracted from the top of the tower and the main product of the ethylene glycol have the mass fraction (purity) of the main components which is 2.3 to 16.7 percent lower than the corresponding product of the second embodiment of the invention, namely the separation effect of the invention is obviously better than that of the conventional rectification; in addition, comparison shows that under the premise that the temperature of a liquid phase in a tower kettle is kept unchanged, the absolute pressure of a gas phase at the top of the rectifying tower is 5-6 kPa higher than that of a gas phase in a corresponding comparative example, namely the required vacuum degree of the rectifying tower is lower than that of a conventional vacuum rectification method in the comparative example, so that the performance requirements on vacuum devices and equipment are reduced.
The above embodiments are only effective implementations, and besides, many similar methods may be used to implement the present invention, and all technical solutions adopting equivalents or equivalent substitutions are within the scope of the present invention.
Claims (8)
1. A process for separating a polyol mixture, characterized by: taking a crude product of ethylene glycol containing one or two of 1, 2-propylene glycol and 1, 2-butanediol as a raw material, taking a gaseous substance as an extracting agent, introducing the extracting agent from the lower part of a rectifying tower, extracting and simultaneously gasifying one or two of light components of 1, 2-propylene glycol and 1, 2-butanediol in the crude product of ethylene glycol in a gas extraction and rectification mode, condensing and partially collecting one or two of gasified 1, 2-propylene glycol and 1, 2-butanediol at a partial condenser at the top of the tower, wherein most of the gaseous extracting agent is not condensed at the partial condenser, condensed by a full condenser and recycled; the purification of the ethylene glycol is realized while one or two of the 1, 2-propylene glycol and the 1, 2-butanediol are extracted and gasified; the extractant plays an extracting role in a gas form;
the used extractant and 1, 2-propylene glycol and 1, 2-butanediol ethylene glycol can not form an azeotrope;
the extractant is one or more of ethyl acetate, ethyl butyrate, propyl ether, butyl ether, n-butylamine, n-pentylamine, dichloromethane and 1-chloropentane.
2. The method of claim 1, wherein: the total mass concentration of 1, 2-propylene glycol and 1, 2-butanediol in the polyhydric alcohol mixture in the ethylene glycol solution is 0.5-50%.
3. The method of claim 1, wherein: when the ethylene glycol crude product is separated by gas extraction and rectification, the liquid temperature in the tower kettle is 115-150 ℃, and the gas phase pressure at the top of the tower is 3-20 kPa absolute pressure.
4. The method of claim 1, wherein: before the extractant enters the rectifying tower or is completely gasified or partially gasified in the rectifying tower to be gaseous extractant.
5. The method of claim 1, wherein: extracting one or two of 1, 2-propanediol and 1, 2-butanediol to the top of the tower by a gaseous extracting agent, condensing the 1, 2-propanediol and 1, 2-butanediol at the top of the tower in a partial condenser mode, and refluxing and extracting part of the condensate; while the vast majority of the gaseous extractant is not condensed by the partial condenser, after which the gaseous extractant is condensed by the lower-temperature partial condenser.
6. The method of claim 1, wherein: due to the partial pressure of the gaseous extractant, the overall vacuum degree of the rectifying tower can be reduced on the premise of maintaining the temperature of the tower bottom unchanged.
7. The method of claim 1, wherein: the temperature of the partial condenser is higher than the boiling point of the gaseous extracting agent in the partial condenser and lower than the boiling point of the 1, 2-propylene glycol or the 1, 2-butanediol in the partial condenser.
8. The method of claim 6, wherein: the extractant condensed by the full condenser can be returned to the rectifying tower for reuse.
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