CN114276216A - Method for removing aldehyde impurities in 1, 3-propylene glycol - Google Patents
Method for removing aldehyde impurities in 1, 3-propylene glycol Download PDFInfo
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Abstract
The invention provides a method for removing aldehyde impurities in 1, 3-propylene glycol, which comprises the following steps: mixing the 1, 3-propylene glycol reaction liquid with hydrazine, heating for reaction, adding alkali for continuous reaction to obtain a reduction product, separating the reduction product, removing coke from the obtained reaction kettle material, and performing reduced pressure rectification on the coke-removed fraction to obtain the 1, 3-propylene glycol product. According to the method, hydrazine and alkali are used for reducing aldehyde groups into alkyl according to the characteristics of the aldehyde groups, so that a large amount of aldehyde impurities in the reaction liquid are removed, the total aldehyde content is obviously reduced, the aldehyde groups are converted into the alkyl, the boiling points of corresponding impurities can be obviously reduced, the purification difficulty of the 1, 3-propylene glycol is reduced, and a high-purity product is obtained; in the method, the 1, 3-propylene glycol can be used as a solvent, no new substance is required to be introduced, and the influence on the product quality is reduced; the method has the advantages of simple operation process, simple and convenient operation, low equipment investment and easy industrial implementation.
Description
Technical Field
The invention belongs to the technical field of chemical separation, and relates to a method for removing aldehyde impurities in 1, 3-propylene glycol.
Background
1, 3-propanediol is an important organic chemical raw material, is a raw material for producing unsaturated polyester, a plasticizer, a surfactant, an emulsifier and a demulsifier, is used as a raw material for producing polyester polyol, an initiator for producing polyether polyol, a chain extender for producing polyurethane and the like, can be widely applied to industries such as engineering plastics, garment materials, coatings, cosmetics, pharmacy and the like, and is particularly used as a main raw material for producing 1, 3-propanediol terephthalate (PTT); the PTT fiber is a novel polyester fiber with excellent performance, integrates the characteristics of softness of nylon, bulkiness of acrylic fiber, stain resistance of terylene, inherent elasticity of the PTT fiber, normal-temperature dyeing and the like, integrates the excellent performances of various fibers, and becomes one of the most popular polymer novel materials at present.
The raw materials for PTT synthesis are terephthalic acid and 1, 3-propanediol, and the quality of the 1, 3-propanediol product has a great influence on the characteristics of PTT fibers, for example, the product purity affects the intrinsic viscosity, and the aldehyde content and the color of the product affect the appearance of PTT; therefore, the research on synthesizing high-purity 1, 3-propylene glycol is one of the current hotspots, and the research mainly comprises two major types of chemical methods and biological methods, wherein the former comprises an ethylene oxide carbonylation method and an acrolein hydration hydrogenation method, wherein the acrolein hydration hydrogenation method has the characteristics of low technical difficulty, mild process conditions, high atom utilization rate and the like, and is one of the current industrial routes, but in the method, acrolein and an intermediate product 3-hydroxypropionaldehyde are unstable and are easy to generate polycondensation reaction, so that aldehyde byproducts are generated, more byproducts are generated after hydrogenation, the components of a reaction system are complex, and the aldehyde impurities are important factors influencing the quality of PTT fibers, so that the removal of the aldehyde impurities is a key step when the 1, 3-propylene glycol is purified.
CN 110790636A discloses a refining method for removing trace aldehyde groups in 1, 3-propylene glycol, which comprises the steps of adding sulfonic acid ionic liquid into 1, 3-propylene glycol dehydration concentrated solution containing trace aldehyde group impurities, catalyzing aldehyde groups by the ionic liquid to carry out aldehyde removal reaction, and then carrying out reduced pressure rectification to obtain a product with low aldehyde content and high 1, 3-propylene glycol purity; although the method can obviously reduce the content of aldehyde impurities, the ionic liquid has high cost, complicated preparation process and low product yield, and is not suitable for mass preparation.
CN 112979420a discloses a method for purifying 1, 3-propanediol, which comprises the following steps: adjusting the pH value of a raw material containing 1, 3-propylene glycol and reacting, wherein the raw material contains aldehyde organic matters to obtain a reaction product; carrying out first rectification and second reduced pressure rectification on the reaction product to obtain crude 1, 3-propylene glycol; and (3) subjecting the crude 1, 3-propanediol to resin adsorption and third rectification to obtain the 1, 3-propanediol. The method utilizes the characteristics of aldehyde substances, reactants are added to convert the aldehyde substances into macromolecular substances, but side reactions can also occur, the aldehyde content can be reduced, but the yield of the product is lower, resin adsorption operation is also needed, the operation is complex, and the cost is higher.
In summary, for removing the aldehyde impurities in the 1, 3-propanediol reaction liquid, a proper process and operation need to be selected, so that the yield of the 1, 3-propanediol product is improved, the operation is simplified, and the cost is reduced while the aldehyde impurities are sufficiently removed.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a method for removing aldehyde impurities in 1, 3-propanediol, which adopts Huang Minlon reaction, reduces aldehyde groups into alkyl groups by hydrazine and alkali, greatly removes the aldehyde impurities in the reaction solution, obviously reduces the total aldehyde content, and simultaneously can obviously reduce the boiling points of corresponding impurities by converting the aldehyde groups into the alkyl groups, thus being beneficial to the separation and purification of the 1, 3-propanediol and further preparing a high-purity 1, 3-propanediol product; the method has the advantages of simple operation process, mild condition, low cost and easy industrial implementation.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a method for removing aldehyde impurities in 1, 3-propylene glycol, which comprises the following steps:
(1) mixing the 1, 3-propylene glycol reaction liquid with hydrazine, heating for reaction, adding alkali for continuous reaction to obtain a reduction product, and separating the reduction product to obtain a reaction kettle material;
(2) decoking the reaction kettle material obtained in the step (1) to obtain decoking fraction;
(3) and (3) carrying out reduced pressure rectification on the decoking fraction obtained in the step (2) to obtain a 1, 3-propylene glycol product.
According to the invention, for the separation and purification after the synthesis of 1, 3-propanediol, wherein the removal of aldehyde impurities is a key step, according to the characteristics of aldehyde groups, the Huang Minlon reaction is adopted to react the aldehyde groups with hydrazine to generate hydrazone, then the hydrazone is destroyed to form alkyl, and the aldehyde groups are reduced to the alkyl, so that the aldehyde impurities in the reaction liquid are removed in a large amount, the total aldehyde content is obviously reduced, and the boiling point of the product obtained by the conversion is obviously reduced compared with that of the original aldehyde impurities and the 1, 3-propanediol, so that the purification difficulty of the 1, 3-propanediol is reduced, the reduction product is directly separated by synchronous rectification in the reaction process, and the high-purity 1, 3-propanediol product can be obtained by the purification steps of decoking and reduced pressure rectification;
according to the characteristics of the Huang Minlon reaction, alcohols are also needed to be used as solvents, while the 1, 3-propylene glycol can be used as the solvent, so that new substances are not needed to be introduced, the influence on the product quality is reduced, and the treatment cost is reduced; the method has the advantages of simple operation process, simple and convenient operation, low equipment investment and easy industrial implementation.
The following technical solutions are preferred technical solutions of the present invention, but not limited to the technical solutions provided by the present invention, and technical objects and advantageous effects of the present invention can be better achieved and achieved by the following technical solutions.
As a preferable technical scheme of the invention, the 1, 3-propylene glycol reaction liquid in the step (1) is obtained by acrolein through a hydration hydrogenation process.
Preferably, the 1, 3-propanediol reaction solution in step (1) comprises 1, 3-propanediol, 3-hydroxypropionaldehyde, 3-hydroxymethyltetrahydropyran, 1, 3-dioxane-2-ethanol, 5, 6-dihydropyran-3-formaldehyde, 4-heterooxyheptanediol and water.
Preferably, the 1, 3-propanediol reaction liquid of step (1) has a composition comprising, in terms of mass concentration, 1, 3-propanediol. ltoreq.95.0 wt%, such as 95.0 wt%, 94.0 wt%, 93.0 wt%, 92.0 wt%, 91.0 wt%, or 90.0 wt%, etc., 3-hydroxypropanal. ltoreq.0.1 wt%, such as 0.1 wt%, 0.05 wt%, 0.01 wt%, or 0.005 wt%, etc., 3-hydroxymethyltetrahydropyran. ltoreq.0.1 wt%, such as 0.1 wt%, 0.05 wt%, 0.01 wt%, or 0.005 wt%, etc., 1, 3-dioxane-2-ethanol. ltoreq.0.1 wt%, such as 0.1 wt%, 0.05 wt%, 0.01 wt%, or 0.005 wt%, etc., 5, 6-dihydropyran-3-formaldehyde. ltoreq.0.1 wt%, such as 0.1 wt%, 0.05 wt%, 0.01 wt%, or 0.005 wt%, 0.01 wt%, 0.005 wt%, 0.05 wt%, 0.005 wt%, etc., 5, 0.1 wt%, 0.005 wt%, 0.05 wt%, etc., of heteroheptanedioxy, etc., dialdehyde, etc., 4-heterooxyheptanediol by weight or more, e.g., 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, or 7.0 wt%, etc., and water by weight or less, e.g., 0.2 wt%, 0.19 wt%, 0.18 wt%, 0.16 wt%, or 0.15 wt%, etc.; wherein the total aldehyde concentration is less than or equal to 1000ppm, for example 1000ppm, 800ppm, 600ppm, 500ppm, 400ppm, 200ppm or 100ppm, etc., but is not limited to the recited values, and other unrecited values within the respective numerical ranges are equally applicable.
In the invention, the 1, 3-propylene glycol reaction liquid obtained by the acrolein hydration hydrogenation process contains a plurality of aldehyde by-products, and the aldehyde substances can obviously influence the product performance, so that the total aldehyde content can be generally determined to reflect the purity of the product, and the total aldehyde content is measured by taking formaldehyde as a reference; according to the mass concentration of each component in the invention, the water content is extremely low, which indicates that the reaction liquid has been subjected to concentration treatment.
According to the composition of the 1, 3-propanediol reaction liquid, the aldehyde substances of 3-hydroxypropionaldehyde, 5, 6-dihydropyran-3-formaldehyde and 4-heterooxyheptaldehyde are subjected to aldehyde group reduction reaction to correspondingly generate n-propanol, 3-methyl-5, 6-dihydropyran and n-propyl ether, and compared with the corresponding aldehydes, the respective boiling points of the n-propanol, the 5, 6-dihydropyran and the n-propyl ether are also obviously reduced, thereby being beneficial to the separation of a reduction product.
As a preferred technical scheme of the invention, the hydrazine in the step (1) is added in the form of hydrazine hydrate solution.
Preferably, the hydrazine hydrate solution has a concentration of 50 to 85 wt%, such as 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or 85 wt%, etc., but is not limited to the recited values, and other values not recited within the range of values are also applicable.
Preferably, the mass ratio of the hydrazine hydrate solution to the 1, 3-propanediol reaction solution is 0.01 to 1.0 wt%, for example, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, or 1.0 wt%, but not limited to the recited values, and other values not recited in the range of the values are also applicable, preferably 0.1 to 0.3 wt%.
Preferably, the hydrazine is added in step (1), and the temperature is raised to 90 to 120 ℃ for the reaction, for example, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃ or 120 ℃, but not limited to the recited values, and other values not recited in the range of the values are also applicable, the aldehyde impurities react with the hydrazine to form hydrazone, the reaction time is 1 to 5 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours or 5 hours, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
As a preferred technical solution of the present invention, the base in step (1) comprises any one or a combination of at least two of alkali metal hydroxide, rare earth metal hydroxide or solid superbase, and the combination is typically but not limited to: combinations of alkali metal hydroxides and rare earth metal hydroxides, combinations of rare earth metal hydroxides and solid superbases, combinations of alkali metal hydroxides, rare earth metal hydroxides and solid superbases, and the like.
In the present invention, the alkali metal hydroxide includes sodium hydroxide, potassium hydroxide and the like, the rare earth metal hydroxide includes lanthanum hydroxide, ytterbium hydroxide and the like, and the solid superbase includes K, selected according to the kind of the alkali2O/γ-Al2O3、Na-Na2CO3/γ-Al2O3And the like.
Preferably, the base is added in the step (1) in a mass ratio of 0.01 to 1 wt% to the 1, 3-propanediol reaction solution, such as 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, or 1.0 wt%, but not limited to the recited values, and other non-recited values within the range are also applicable, preferably 0.1 to 0.3 wt%.
Preferably, the reaction after the base is added in the step (1) is that the corresponding functional group of hydrazone is decomposed to generate alkyl under the action of the base, the reaction temperature is 90-180 ℃, such as 90 ℃, 95 ℃, 100 ℃, 110 ℃, 120 ℃, 150 ℃ or 180 ℃, and the like, the reaction temperature is not fixed, and gradually rises along with the reaction, but does not exceed 180 ℃; the reaction time is 1 to 10 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours or 10 hours, but is not limited to the recited values, and other values not recited in the range of the values are also applicable, and preferably 2 to 5 hours.
As a preferred technical scheme of the invention, the reaction in the step (1) is carried out in a reaction rectification device.
Preferably, when the reaction of step (1) is carried out, a rectification process also occurs to separate the reduced product from the 1, 3-propanediol.
Preferably, the reactive distillation apparatus has a theoretical plate number of not greater than 10, e.g., 10, 9, 8, 7, 6, or 5, etc., but not limited to the recited values, and other unrecited values within this range are equally applicable; the reflux ratio is not more than 3, for example 3, 2.5, 2, 1.5 or 1, etc., but is not limited to the recited values, and other values not recited within the numerical range are also applicable.
Preferably, the reactive distillation apparatus has a still temperature of no more than 180 ℃, such as 180 ℃, 178 ℃, 175 ℃, 172 ℃, 170 ℃ or 165 ℃ and the like, but is not limited to the recited values, and other values not recited within the range of values are equally applicable.
As a preferable technical scheme of the invention, decoking in the step (2) is carried out in a decoking tower.
Preferably, the decoking column has a theoretical plate number of no greater than 20, e.g., 20, 17, 15, 12, 10, 8, or 5, etc., but is not limited to the recited values, and other values not recited within the range are equally applicable; the reflux ratio is not more than 3, for example 3, 2.5, 2, 1.5 or 1, etc., but is not limited to the recited values, and other values not recited within the numerical range are also applicable.
Preferably, the decoking column is operated at an absolute pressure of no greater than 5kPa, such as 5kPa, 4kPa, 3kPa, 2kPa, 1kPa, or 0.5kPa, and the like, but is not limited to the recited values, and other values not recited within the range are equally applicable; the operating temperature at the top of the column is, for example, 90 to 135 ℃, such as 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃ or 135 ℃, but is not limited to the values listed, and other values not listed in the range of the values are also applicable.
Preferably, the mass proportion of the decoking fraction extracted from the top of the decoking tower to the entering reaction kettle material is 90-95 wt%, such as 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt% or 95 wt%, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
As a preferred technical scheme of the invention, the vacuum distillation in the step (3) is carried out in a rectifying tower.
Preferably, the number of theoretical plates of the rectification column is not more than 30, for example 30, 28, 25, 22, 20 or 15, etc., but is not limited to the recited values, and other values not recited in the range of values are also applicable; the reflux ratio is not more than 5, for example 5, 4, 3, 2.5, 2 or 1, etc., but is not limited to the recited values, and other values not recited within the numerical range are also applicable.
Preferably, the vacuum distillation is operated at an absolute pressure of no greater than 5kPa, such as 5kPa, 4kPa, 3kPa, 2kPa, 1kPa, or 0.5kPa, but not limited to, the recited values, and other unrecited values within the range are equally applicable.
As a preferable technical scheme of the invention, during the vacuum rectification in the step (3), the front fraction and the main fraction are sequentially extracted from the top of the rectifying tower.
Preferably, the top temperature of the column when the front cut is taken is 90 to 134 ℃, for example 90 ℃, 100 ℃, 110 ℃, 120 ℃, 125 ℃, 130 ℃ or 134 ℃, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the mass proportion of the forecut to the decoking fraction feed is 1 to 10 wt%, such as 1 wt%, 2 wt%, 3 wt%, 5 wt%, 6 wt%, 8 wt%, or 10 wt%, but not limited to the recited values, and other values not recited within this range are equally applicable.
Preferably, the operation temperature at the top of the column when the main fraction is taken is 92 to 135 ℃, for example 92 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 120 ℃, 130 ℃ or 135 ℃, but the operation temperature is not limited to the recited values, and other values not recited in the above range are also applicable.
Preferably, the mass proportion of the main fraction to the decoking fraction feed is 85 to 95 wt%, such as 85 wt%, 86 wt%, 88 wt%, 90 wt%, 92 wt% or 95 wt%, but not limited to the recited values, and other values not recited within this range are equally applicable.
As a preferred technical scheme of the invention, each step of the method is carried out in protective atmosphere, and the pressure of each step of operation is provided by the protective atmosphere.
Preferably, the protective atmosphere comprises nitrogen and/or an inert gas.
In the invention, the protective atmosphere is adopted because oxidation reaction can occur under the air condition, so that heavy components and tar in the tower bottom are increased, and the product yield is reduced.
As a preferred technical scheme of the invention, the method comprises the following steps:
(1) mixing 1, 3-propanediol reaction liquid with hydrazine and then heating up for reaction, wherein the 1, 3-propanediol reaction liquid is obtained by acrolein through a hydration hydrogenation process, and the 1, 3-propanediol reaction liquid comprises, by mass concentration, not more than 95.0 wt% of 1, 3-propanediol, not more than 0.1 wt% of 3-hydroxypropionaldehyde, not more than 0.1 wt% of 3-hydroxymethyltetrahydropyran, not more than 0.1 wt% of 1, 3-dioxane-2-ethanol, not more than 0.1 wt% of 5, 6-dihydropyran-3-formaldehyde, not more than 0.1 wt% of 4-heteroxexy heptanediol, not more than 5.0 wt% of 4-heteroxexy heptanediol, not more than 0.2 wt% of water, and the total aldehyde concentration is not more than 1000 ppm; adding hydrazine in the form of a hydrazine hydrate solution, wherein the concentration of the hydrazine hydrate solution is 50-85 wt%, the addition amount of the hydrazine hydrate solution accounts for 0.01-1.0 wt% of the 1, 3-propylene glycol reaction solution, heating to 90-120 ℃ for reaction, wherein aldehyde impurities and hydrazine react to generate hydrazone, and the reaction time is 1-5 hours;
adding alkali to continuously react, wherein the alkali comprises any one or a combination of at least two of alkali metal hydroxide, rare earth metal hydroxide or solid super alkali, the addition amount of the alkali accounts for 0.01-1 wt% of the 1, 3-propylene glycol reaction liquid, the reaction after the alkali is added is that corresponding functional groups of hydrazone are decomposed under the action of the alkali to obtain alkyl, the reaction temperature is 90-180 ℃, and the reaction time is 2-5 hours, so that a reduction product is obtained; the reaction is carried out in a reaction rectifying device, a rectifying process is carried out while the reaction is carried out, and a reduction product is separated from the 1, 3-propylene glycol to obtain a reaction kettle material; the theoretical plate number of the reaction rectifying device is not more than 10, the reflux ratio is not more than 3, and the temperature of a tower kettle is not more than 180 ℃;
(2) decoking the reaction kettle material obtained in the step (1), wherein the decoking is carried out in a decoking tower, the theoretical plate number of the decoking tower is not more than 20, the reflux ratio is not more than 3, the operating absolute pressure of the decoking tower is not more than 5kPa, the operating temperature at the top of the tower is 90-135 ℃, a decoking fraction is obtained, and the decoking fraction collected at the top of the tower accounts for 90-95 wt% of the mass of the entering reaction kettle material;
(3) performing reduced pressure distillation on the decoking fraction obtained in the step (2), wherein the reduced pressure distillation is performed in a rectifying tower, the theoretical plate number of the rectifying tower is not more than 30, the reflux ratio is not more than 5, and the operating absolute pressure of the reduced pressure distillation is not more than 5 kPa; and sequentially extracting front fraction and main fraction from the top of the rectifying tower, wherein the operation temperature of the top of the rectifying tower is 90-134 ℃ when the front fraction is extracted, the operation temperature of the top of the rectifying tower accounts for 1-10 wt% of the decoking fraction fed material, the operation temperature of the top of the rectifying tower is 92-135 ℃ when the main fraction is extracted, the operation temperature of the top of the rectifying tower accounts for 85-95 wt% of the decoking fraction fed material, and the main fraction is the required 1, 3-propylene glycol product.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to the method, according to the characteristics of aldehyde groups, a Huang Minlon reaction is adopted, and hydrazine and alkali are used for reducing the aldehyde groups into alkyl groups, so that a large amount of aldehyde impurities in a reaction solution are removed, and the total aldehyde content is remarkably reduced;
(2) according to the method, aldehyde groups are converted into alkyl groups, so that the boiling points of corresponding impurities can be obviously reduced, the purification difficulty of the 1, 3-propanediol is reduced, the reduction products are directly separated out through synchronous rectification in the reaction process, and the purity of the obtained 1, 3-propanediol product can reach more than 99.97 wt% through the purification steps of decoking and reduced pressure rectification, and the total aldehyde content can be reduced to be less than 5.0 ppm;
(3) in the method, the 1, 3-propylene glycol can be used as a solvent, no new substance is required to be introduced, the influence on the product quality is reduced, and the treatment cost is reduced;
(4) the method has the advantages of simple operation process, simple and convenient operation, low equipment investment and easy industrial implementation.
Detailed Description
In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the present invention, which is defined by the claims.
The specific embodiment of the invention provides a method for removing aldehyde impurities in 1, 3-propylene glycol, which comprises the following steps:
(1) mixing the 1, 3-propylene glycol reaction liquid with hydrazine, heating for reaction, adding alkali for continuous reaction to obtain a reduction product, and separating the reduction product to obtain a reaction kettle material;
(2) decoking the reaction kettle material obtained in the step (1) to obtain decoking fraction;
(3) and (3) carrying out reduced pressure rectification on the decoking fraction obtained in the step (2) to obtain a 1, 3-propylene glycol product.
The following are typical but non-limiting examples of the invention:
example 1:
this example provides a method for removing aldehyde impurities from 1, 3-propanediol, comprising the following steps:
(1) mixing 1, 3-propanediol reaction liquid with hydrazine and then heating up for reaction, wherein the 1, 3-propanediol reaction liquid is obtained by acrolein through a hydration hydrogenation process, and the 1, 3-propanediol reaction liquid comprises 94.3 wt% of 1, 3-propanediol, 0.08 wt% of 3-hydroxypropionaldehyde, 0.05 wt% of 3-hydroxymethyl tetrahydropyran, 0.04 wt% of 1, 3-dioxane-2-ethanol, 0.03 wt% of 5, 6-dihydropyran-3-formaldehyde, 0.01 wt% of 4-heteroxy heptanediol, 5.4 wt% of 4-heteroxy heptanediol and 0.09 wt% of water by mass concentration, wherein the total aldehyde concentration is 450.8 ppm; the hydrazine is added in the form of hydrazine hydrate solution, the concentration of the hydrazine hydrate solution is 85 wt%, the addition amount of the hydrazine hydrate solution accounts for 0.18 wt% of the mass ratio of the 1, 3-propylene glycol reaction solution, the temperature is raised to 100 ℃ for reaction, aldehyde impurities react with the hydrazine to generate hydrazone, and the reaction time is 3 hours;
then adding sodium hydroxide for continuous reaction, wherein the addition amount accounts for 0.19 wt% of the mass ratio of the 1, 3-propylene glycol reaction liquid, the reaction after adding the sodium hydroxide is that the corresponding functional group of hydrazone is decomposed under the action of the hydrazone to generate alkyl, the reaction temperature is 90 ℃, and the reaction time is 5 hours, so as to obtain a reduction product; the reaction is carried out in a reaction rectifying device, a rectifying process is carried out while the reaction is carried out, and a reduction product is separated from the 1, 3-propylene glycol to obtain a reaction kettle material; the theoretical plate number of the reaction rectifying device is 10, the reflux ratio is 1, and the temperature of the tower kettle is raised to 180 ℃ to finish the reaction rectifying device;
(2) decoking the reaction kettle material obtained in the step (1), wherein the decoking is carried out in a decoking tower, the theoretical plate number of the decoking tower is 20, the reflux ratio is 3, the operating absolute pressure of the decoking tower is 1kPa, the operating temperature at the top of the tower is 100-105 ℃, a decoking fraction is obtained, and the decoking fraction collected at the top of the tower accounts for 94.33 wt% of the mass of the entering reaction kettle material;
(3) performing reduced pressure distillation on the decoking fraction obtained in the step (2), wherein the reduced pressure distillation is performed in a rectifying tower, the theoretical plate number of the rectifying tower is 30, the reflux ratio is 5, and the operating absolute pressure of the reduced pressure distillation is 1 kPa; and sequentially extracting a front fraction and a main fraction from the top of the rectifying tower, wherein the operation temperature of the top of the rectifying tower is 100-103 ℃ when the front fraction is extracted, the mass ratio of the front fraction to the decoking fraction is 7.30 wt%, the operation temperature of the top of the rectifying tower is 103-104 ℃ when the main fraction is extracted, the mass ratio of the front fraction to the decoking fraction is 88.92 wt%, and the main fraction is the required 1, 3-propylene glycol product.
In this embodiment, after the treatment in step (1), the reduction products propanol, 3-methyl-5, 6-dihydropyran, and n-propyl ether can be separated out, the mass concentration of total aldehydes in the reaction kettle material is 24.7ppm, the mass concentration of the 1, 3-propanediol product in the main fraction obtained in step (3) is 99.99 wt%, and the total aldehyde content is only 2.5ppm, which can meet the index requirements of polymer grade 1, 3-propanediol for fibers.
Example 2:
this example provides a method for removing aldehyde impurities from 1, 3-propanediol, comprising the following steps:
(1) mixing 1, 3-propanediol reaction liquid with hydrazine and then heating up for reaction, wherein the 1, 3-propanediol reaction liquid is obtained by acrolein through a hydration hydrogenation process, and the 1, 3-propanediol reaction liquid comprises 94.3 wt% of 1, 3-propanediol, 0.08 wt% of 3-hydroxypropionaldehyde, 0.05 wt% of 3-hydroxymethyl tetrahydropyran, 0.04 wt% of 1, 3-dioxane-2-ethanol, 0.03 wt% of 5, 6-dihydropyran-3-formaldehyde, 0.01 wt% of 4-heteroxy heptanediol, 5.4 wt% of 4-heteroxy heptanediol and 0.09 wt% of water by mass concentration, wherein the total aldehyde concentration is 450.8 ppm; the hydrazine is added in the form of hydrazine hydrate solution, the concentration of the hydrazine hydrate solution is 85 wt%, the addition amount of the hydrazine hydrate solution accounts for 0.15 wt% of the mass ratio of the 1, 3-propylene glycol reaction solution, the reaction is carried out by heating to 95 ℃, aldehyde impurities react with the hydrazine to generate hydrazone, and the reaction time is 4 hours;
then adding potassium hydroxide for continuous reaction, wherein the addition amount accounts for 0.16 wt% of the mass ratio of the 1, 3-propylene glycol reaction liquid, the reaction after adding the potassium hydroxide is that the corresponding functional group of hydrazone is decomposed under the action of the hydrazone to generate alkyl, the reaction temperature is 100 ℃, and the reaction time is 3 hours, so as to obtain a reduction product; the reaction is carried out in a reaction rectifying device, a rectifying process is carried out while the reaction is carried out, and a reduction product is separated from the 1, 3-propylene glycol to obtain a reaction kettle material; the theoretical plate number of the reaction rectifying device is 8, the reflux ratio is 2, and the temperature of the tower kettle is raised to 180 ℃ to finish the reaction rectifying device;
(2) decoking the reaction kettle material obtained in the step (1), wherein the decoking is performed in a decoking tower, the theoretical plate number of the decoking tower is 18, the reflux ratio is 2, the operating absolute pressure of the decoking tower is 3kPa, the operating temperature at the top of the tower is 120-125 ℃, a decoking fraction is obtained, and the decoking fraction collected at the top of the tower accounts for 93.11 wt% of the mass of the entering reaction kettle material;
(3) performing reduced pressure distillation on the decoking fraction obtained in the step (2), wherein the reduced pressure distillation is performed in a rectifying tower, the theoretical plate number of the rectifying tower is 25, the reflux ratio is 4, and the operating absolute pressure of the reduced pressure distillation is 3 kPa; and sequentially extracting a front fraction and a main fraction from the top of the rectifying tower, wherein the operation temperature of the top of the rectifying tower is 120-123 ℃ when the front fraction is extracted, the mass ratio of the operation temperature to the feeding of the decoking fraction is 9.36 wt%, the operation temperature of the top of the rectifying tower is 123-124 ℃ when the main fraction is extracted, the mass ratio of the operation temperature to the feeding of the decoking fraction is 86.00 wt%, and the main fraction is the required 1, 3-propylene glycol product.
In this embodiment, after the treatment in step (1), the reduction products, namely propanol, 3-methyl-5, 6-dihydropyran and n-propyl ether, can be separated out, the mass concentration of total aldehydes in the reaction kettle material is 38.4ppm, the mass concentration of the 1, 3-propanediol product in the main fraction obtained in step (3) is 99.98 wt%, and the total aldehyde content is only 4.8ppm, so that the index requirements of polymer-grade 1, 3-propanediol for fibers can be met.
Example 3:
this example provides a method for removing aldehyde impurities from 1, 3-propanediol, comprising the following steps:
(1) mixing 1, 3-propanediol reaction liquid with hydrazine and then heating up for reaction, wherein the 1, 3-propanediol reaction liquid is obtained by acrolein through a hydration hydrogenation process, and the 1, 3-propanediol reaction liquid comprises 94.3 wt% of 1, 3-propanediol, 0.08 wt% of 3-hydroxypropionaldehyde, 0.05 wt% of 3-hydroxymethyl tetrahydropyran, 0.04 wt% of 1, 3-dioxane-2-ethanol, 0.03 wt% of 5, 6-dihydropyran-3-formaldehyde, 0.01 wt% of 4-heteroxy heptanediol, 5.4 wt% of 4-heteroxy heptanediol and 0.09 wt% of water by mass concentration, wherein the total aldehyde concentration is 450.8 ppm; the hydrazine is added in the form of hydrazine hydrate solution, the concentration of the hydrazine hydrate solution is 85 wt%, the addition amount of the hydrazine hydrate solution accounts for 0.3 wt% of the mass proportion of the 1, 3-propylene glycol reaction solution, the temperature is raised to 90 ℃ for reaction, aldehyde impurities react with the hydrazine to generate hydrazone, and the reaction time is 5 hours;
then adding potassium hydroxide for continuous reaction, wherein the addition amount accounts for 0.3 wt% of the mass ratio of the 1, 3-propylene glycol reaction liquid, the reaction after adding the potassium hydroxide is that the corresponding functional group of hydrazone is decomposed under the action of the hydrazone to generate alkyl, the reaction temperature is 110 ℃, and the reaction time is 2 hours, so as to obtain a reduction product; the reaction is carried out in a reaction rectifying device, a rectifying process is carried out while the reaction is carried out, and a reduction product is separated from the 1, 3-propylene glycol to obtain a reaction kettle material; the theoretical plate number of the reaction rectifying device is 9, the reflux ratio is 3, and the temperature of the tower kettle is raised to 180 ℃ to finish the reaction rectifying device;
(2) decoking the reaction kettle material obtained in the step (1), wherein the decoking is performed in a decoking tower, the theoretical plate number of the decoking tower is 15, the reflux ratio is 2.5, the operating absolute pressure of the decoking tower is 0.5kPa, the operating temperature at the top of the tower is 90-94 ℃, a decoking fraction is obtained, and the decoking fraction collected at the top of the tower accounts for 94.36 wt% of the mass of the entering reaction kettle material;
(3) performing reduced pressure distillation on the decoking fraction obtained in the step (2), wherein the reduced pressure distillation is performed in a rectifying tower, the theoretical plate number of the rectifying tower is 20, the reflux ratio is 4.5, and the operating absolute pressure of the reduced pressure distillation is 0.5 kPa; and sequentially extracting front fraction and main fraction from the top of the rectifying tower, wherein the operation temperature of the top of the rectifying tower is 90-93 ℃ in the front fraction extraction process, the operation temperature of the top of the rectifying tower accounts for 5.32 wt% of the decoking fraction feeding material, the operation temperature of the top of the rectifying tower is 93-94 ℃ in the main fraction extraction process, the operation temperature of the top of the rectifying tower accounts for 93.15 wt% of the decoking fraction feeding material, and the main fraction is the required 1, 3-propylene glycol product.
In this embodiment, after the treatment in step (1), the reduction products, namely propanol, 3-methyl-5, 6-dihydropyran and n-propyl ether, can be separated out, the mass concentration of total aldehydes in the reaction kettle material is 3.5ppm, the mass concentration of the 1, 3-propanediol product in the main fraction obtained in step (3) is 99.99 wt%, and the total aldehyde content is only 0.7ppm, which can meet the index requirements of polymer-grade 1, 3-propanediol for fibers.
Example 4:
this example provides a method for removing aldehyde impurities from 1, 3-propanediol, comprising the following steps:
(1) mixing 1, 3-propanediol reaction liquid with hydrazine and then heating up for reaction, wherein the 1, 3-propanediol reaction liquid is obtained by acrolein through a hydration hydrogenation process, and the 1, 3-propanediol reaction liquid comprises 93.8 wt% of 1, 3-propanediol, 0.1 wt% of 3-hydroxypropionaldehyde, 0.06 wt% of 3-hydroxymethyl tetrahydropyran, 0.05 wt% of 1, 3-dioxane-2-ethanol, 0.05 wt% of 5, 6-dihydropyran-3-formaldehyde, 0.03 wt% of 4-heteroxy heptanediol, 5.75 wt% of 4-heteroxy heptanediol and 0.16 wt% of water by mass concentration, wherein the total aldehyde concentration is 667.8 ppm; the hydrazine is added in the form of hydrazine hydrate solution, the concentration of the hydrazine hydrate solution is 75 wt%, the addition amount of the hydrazine hydrate solution accounts for 0.5 wt% of the mass ratio of the 1, 3-propylene glycol reaction solution, the reaction is carried out by heating to 110 ℃, aldehyde impurities react with the hydrazine to generate hydrazone, and the reaction time is 2 hours;
then adding solid super alkali K2O/γ-Al2O3Continuing the reaction, wherein the adding amount of the solid super base accounts for 0.5 wt% of the mass ratio of the 1, 3-propylene glycol reaction liquid, the reaction after the solid super base is added is that the corresponding functional group of hydrazone is decomposed under the action of the solid super base to generate alkyl, the reaction temperature is 95 ℃, and the reaction time is 4 hours, so that a reduction product is obtained; the reaction is carried out in a reaction rectifying device, a rectifying process is carried out while the reaction is carried out, and a reduction product is separated from the 1, 3-propylene glycol to obtain a reaction kettle material; the theoretical plate number of the reaction rectifying device is 10, the reflux ratio is 2, and the temperature of the tower kettle is raised to 170 ℃ to finish the process;
(2) decoking the reaction kettle material obtained in the step (1), wherein the decoking is performed in a decoking tower, the theoretical plate number of the decoking tower is 20, the reflux ratio is 3, the operating absolute pressure of the decoking tower is 5kPa, the operating temperature at the top of the tower is 131-135 ℃, a decoking fraction is obtained, and the decoking fraction collected at the top of the tower accounts for 93.2 wt% of the mass of the entering reaction kettle material;
(3) performing reduced pressure distillation on the decoking fraction obtained in the step (2), wherein the reduced pressure distillation is performed in a rectifying tower, the theoretical plate number of the rectifying tower is 30, the reflux ratio is 3, and the operating absolute pressure of the reduced pressure distillation is 5 kPa; and sequentially extracting a front fraction and a main fraction from the top of the rectifying tower, wherein the operation temperature of the top of the rectifying tower is 131-134 ℃ when the front fraction is extracted, the mass ratio of the front fraction to the decoking fraction is 6.10 wt%, the operation temperature of the top of the rectifying tower is 134-135 ℃ when the main fraction is extracted, the mass ratio of the front fraction to the decoking fraction is 92.05 wt%, and the main fraction is the required 1, 3-propylene glycol product.
In this embodiment, after the treatment in step (1), the reduction products, namely propanol, 3-methyl-5, 6-dihydropyran and n-propyl ether, can be separated out, the mass concentration of total aldehydes in the reaction kettle material is 6.2ppm, the mass concentration of the 1, 3-propanediol product in the main fraction obtained in step (3) is 99.99 wt%, and the total aldehyde content is only 0.9ppm, which can meet the index requirements of polymer-grade 1, 3-propanediol for fibers.
Example 5:
this example provides a method for removing aldehyde impurities from 1, 3-propanediol, comprising the following steps:
(1) mixing 1, 3-propanediol reaction liquid with hydrazine and then heating up for reaction, wherein the 1, 3-propanediol reaction liquid is obtained by acrolein through a hydration hydrogenation process, and the 1, 3-propanediol reaction liquid comprises 94.5 wt% of 1, 3-propanediol, 0.05 wt% of 3-hydroxypropionaldehyde, 0.04 wt% of 3-hydroxymethyl tetrahydropyran, 0.03 wt% of 1, 3-dioxane-2-ethanol, 0.03 wt% of 5, 6-dihydropyran-3-formaldehyde, 0.02 wt% of 4-heteroxy heptanediol, 5.15 wt% of 4-heteroxy heptanediol and 0.18 wt% of water by mass concentration, wherein the total aldehyde concentration is 375.4 ppm; the hydrazine is added in the form of hydrazine hydrate solution, the concentration of the hydrazine hydrate solution is 50 wt%, the addition amount of the hydrazine hydrate solution accounts for 1.0 wt% of the mass ratio of the 1, 3-propylene glycol reaction solution, the reaction is carried out by heating to 120 ℃, aldehyde impurities react with the hydrazine to generate hydrazone, and the reaction time is 1 h;
adding lanthanum hydroxide to continuously react, wherein the addition amount accounts for 0.6 wt% of the mass ratio of the 1, 3-propylene glycol reaction liquid, the reaction after adding the lanthanum hydroxide is that corresponding functional groups of hydrazone are decomposed under the action of the lanthanum hydroxide to generate alkyl, the reaction temperature is 120 ℃, and the reaction time is 2 hours, so as to obtain a reduction product; the reaction is carried out in a reaction rectifying device, a rectifying process is carried out while the reaction is carried out, and a reduction product is separated from the 1, 3-propylene glycol to obtain a reaction kettle material; the theoretical plate number of the reaction rectifying device is 10, the reflux ratio is 2.5, and the temperature of the tower kettle is raised to 175 ℃;
(2) decoking the reaction kettle material obtained in the step (1), wherein the decoking is carried out in a decoking tower, the theoretical plate number of the decoking tower is 20, the reflux ratio is 3, the operating absolute pressure of the decoking tower is 2kPa, the operating temperature at the top of the tower is 112-116 ℃, a decoking fraction is obtained, and the decoking fraction collected at the top of the tower accounts for 93.58 wt% of the mass of the entering reaction kettle material;
(3) performing reduced pressure distillation on the decoking fraction obtained in the step (2), wherein the reduced pressure distillation is performed in a rectifying tower, the theoretical plate number of the rectifying tower is 28, the reflux ratio is 1, and the operating absolute pressure of the reduced pressure distillation is 2 kPa; and sequentially extracting a front fraction and a main fraction from the top of the rectifying tower, wherein the operation temperature of the top of the rectifying tower is 112-115 ℃ when the front fraction is extracted, the mass ratio of the front fraction to the decoking fraction is 4.32 wt%, the operation temperature of the top of the rectifying tower is 115-116 ℃ when the main fraction is extracted, the mass ratio of the front fraction to the decoking fraction is 92.15 wt%, and the main fraction is the required 1, 3-propylene glycol product.
In this embodiment, after the treatment in step (1), the reduction products, namely propanol, 3-methyl-5, 6-dihydropyran and n-propyl ether, can be separated out, the mass concentration of total aldehydes in the reaction kettle material is 3.15ppm, the mass concentration of the 1, 3-propanediol product in the main fraction obtained in step (3) is 99.99 wt%, and the total aldehyde content is only 0.5ppm, which can meet the index requirements of polymer-grade 1, 3-propanediol for fibers.
Example 6:
this example provides a process for the removal of aldehyde impurities from 1, 3-propanediol, with reference to the process of example 1, except that: in the step (1), hydrazine hydrate solution and sodium hydroxide are added simultaneously, and the reaction time is two-step reaction time addition.
In this embodiment, since the hydrazine hydrate solution and the sodium hydroxide are added simultaneously, the aldehyde impurities do not react sufficiently when the aldehyde group conversion reaction is performed, so as to affect the subsequent alkyl conversion, the mass concentration of the total aldehydes in the reaction kettle material is 60.4ppm, the mass concentration of the 1, 3-propanediol product in the main fraction obtained in step (3) is 99.97 wt%, and the total aldehyde content is 9.82 ppm.
Comparative example 1:
this comparative example provides a process for removing aldehyde impurities from 1, 3-propanediol, which is comparable to the process of example 1, except that: the operation of step (1) is not included.
In the comparative example, because aldehyde group reduction reaction is not carried out, aldehyde impurities in the reaction solution can only be removed by decoking and rectification under reduced pressure, the removal of the aldehyde impurities is limited, and the total aldehyde content in the obtained 1, 3-propylene glycol product is still 58.8 ppm; and because the boiling point difference between the aldehyde impurities and the 1, 3-propylene glycol is small, the 1, 3-propylene glycol loss is large while removing aldehyde, and the yield of the 1, 3-propylene glycol is only 75.5 percent, which is obviously reduced compared with the embodiment 1.
It can be seen from the above examples and comparative examples that the method of the present invention adopts Huang Minlon reaction according to the characteristics of aldehyde group, and hydrazine and alkali are used to reduce aldehyde group into alkyl group, so that a large amount of aldehyde impurities in the reaction solution are removed, and the total aldehyde content is significantly reduced; according to the method, the aldehyde group is converted into the alkyl group, so that the boiling point of corresponding impurities can be obviously reduced, the purification difficulty of the 1, 3-propylene glycol is reduced, the reduced product is directly separated out through synchronous rectification in the reaction process, the purity of the obtained 1, 3-propylene glycol product can reach more than 99.97 wt%, and the total aldehyde content can be reduced to be less than 5.0ppm through the purification steps of decoking and reduced pressure rectification; in the method, the 1, 3-propylene glycol can be used as a solvent, no new substance is required to be introduced, the influence on the product quality is reduced, and the treatment cost is reduced; the method has the advantages of simple operation process, simple and convenient operation, low equipment investment and easy industrial implementation.
The present invention is illustrated in detail by the examples described above, but the present invention is not limited to the details described above, i.e., it is not intended that the present invention be implemented by relying on the details described above. It will be apparent to those skilled in the art that any modifications to the present invention, equivalents of the method of the present invention and additions of ancillary steps, selection of specific means, etc., are within the scope and disclosure of the present invention.
Claims (10)
1. A method for removing aldehyde impurities in 1, 3-propylene glycol is characterized by comprising the following steps:
(1) mixing the 1, 3-propylene glycol reaction liquid with hydrazine, heating for reaction, adding alkali for continuous reaction to obtain a reduction product, and separating the reduction product to obtain a reaction kettle material;
(2) decoking the reaction kettle material obtained in the step (1) to obtain decoking fraction;
(3) and (3) carrying out reduced pressure rectification on the decoking fraction obtained in the step (2) to obtain a 1, 3-propylene glycol product.
2. The method according to claim 1, wherein the 1, 3-propanediol reaction liquid in step (1) is obtained by hydration hydrogenation of acrolein;
preferably, the 1, 3-propanediol reaction solution in the step (1) comprises 1, 3-propanediol, 3-hydroxypropionaldehyde, 3-hydroxymethyl tetrahydropyran, 1, 3-dioxane-2-ethanol, 5, 6-dihydropyran-3-formaldehyde, 4-heterooxyheptanediol and water;
preferably, the 1, 3-propanediol reaction solution in the step (1) comprises, by mass concentration, 1, 3-propanediol less than or equal to 95.0 wt%, 3-hydroxypropionaldehyde less than or equal to 0.1 wt%, 3-hydroxymethyltetrahydropyran less than or equal to 0.1 wt%, 1, 3-dioxane-2-ethanol less than or equal to 0.1 wt%, 5, 6-dihydropyran-3-formaldehyde less than or equal to 0.1 wt%, 4-heteroxy heptanediol more than or equal to 5.0 wt%, and water less than or equal to 0.2 wt%, wherein the total aldehyde concentration is less than or equal to 1000 ppm.
3. The process according to claim 1 or 2, characterized in that the hydrazine of step (1) is added in the form of a hydrazine hydrate solution;
preferably, the concentration of the hydrazine hydrate solution is 50-85 wt%;
preferably, the hydrazine hydrate solution accounts for 0.01-1.0 wt%, preferably 0.1-0.3 wt% of the 1, 3-propanediol reaction solution;
preferably, hydrazine is added in the step (1), and then the temperature is raised to 90-120 ℃ for reaction, wherein the reaction is carried out by reacting aldehyde impurities with hydrazine to generate hydrazone, and the reaction time is 1-5 hours.
4. The process of any one of claims 1 to 3, wherein the base of step (1) comprises any one of an alkali metal hydroxide, a rare earth metal hydroxide, or a solid superbase, or a combination of at least two thereof;
preferably, the addition amount of the alkali in the step (1) is 0.01-1 wt%, preferably 0.1-0.3 wt%, based on the mass of the 1, 3-propanediol reaction solution;
preferably, the reaction after the alkali is added in the step (1) is that the corresponding functional group of hydrazone is decomposed under the action of the alkali to generate alkyl, the reaction temperature is 90-180 ℃, and the reaction time is 1-10 hours, preferably 2-5 hours.
5. The process of any one of claims 1 to 4, wherein the reaction of step (1) is carried out in a reactive distillation apparatus;
preferably, when the reaction in the step (1) is carried out, a rectification process is also carried out, and the reduction product is separated from the 1, 3-propylene glycol;
preferably, the theoretical plate number of the reaction rectification device is not more than 10, and the reflux ratio is not more than 3;
preferably, the still temperature of the reactive distillation apparatus does not exceed 180 ℃.
6. The process of any one of claims 1-5, wherein the decoking of step (2) is carried out in a decoking tower;
preferably, the theoretical plate number of the decoking tower is not more than 20, and the reflux ratio is not more than 3;
preferably, the operating absolute pressure of the decoking tower is not more than 5kPa, and the operating temperature of the top of the decoking tower is 90-135 ℃;
preferably, the mass proportion of the decoking fraction extracted from the top of the decoking tower in the entering reaction kettle material is 90-95 wt%.
7. The process according to any one of claims 1 to 6, wherein the vacuum distillation of step (3) is carried out in a distillation column;
preferably, the theoretical plate number of the rectifying tower is not more than 30, and the reflux ratio is not more than 5;
preferably, the vacuum distillation is operated at an absolute pressure of no greater than 5 kPa.
8. The method according to any one of claims 1 to 7, characterized in that, during the vacuum distillation in the step (3), a front fraction and a main fraction are taken out from the top of the distillation tower in sequence;
preferably, the operation temperature of the tower top is 90-134 ℃ when the front cut fraction is extracted;
preferably, the mass proportion of the front fraction in the decoking fraction feed is 1-10 wt%;
preferably, the operation temperature of the tower top is 92-135 ℃ when the main fraction is extracted;
preferably, the mass proportion of the main fraction in the decoking fraction feed is 85-95 wt%.
9. The method according to any one of claims 1 to 8, wherein each step of the method is carried out in a protective atmosphere, the pressure of each step being provided by the protective atmosphere;
preferably, the protective atmosphere comprises nitrogen and/or an inert gas.
10. Method according to any of claims 1-9, characterized in that the method comprises the steps of:
(1) mixing 1, 3-propanediol reaction liquid with hydrazine and then heating up for reaction, wherein the 1, 3-propanediol reaction liquid is obtained by acrolein through a hydration hydrogenation process, and the 1, 3-propanediol reaction liquid comprises, by mass concentration, not more than 95.0 wt% of 1, 3-propanediol, not more than 0.1 wt% of 3-hydroxypropionaldehyde, not more than 0.1 wt% of 3-hydroxymethyltetrahydropyran, not more than 0.1 wt% of 1, 3-dioxane-2-ethanol, not more than 0.1 wt% of 5, 6-dihydropyran-3-formaldehyde, not more than 0.1 wt% of 4-heteroxexy heptanediol, not more than 5.0 wt% of 4-heteroxexy heptanediol, not more than 0.2 wt% of water, and the total aldehyde concentration is not more than 1000 ppm; adding hydrazine in the form of a hydrazine hydrate solution, wherein the concentration of the hydrazine hydrate solution is 50-85 wt%, the addition amount of the hydrazine hydrate solution accounts for 0.01-1.0 wt% of the 1, 3-propylene glycol reaction solution, heating to 90-120 ℃ for reaction, wherein aldehyde impurities and hydrazine react to generate hydrazone, and the reaction time is 1-5 hours;
adding alkali to continuously react, wherein the alkali comprises any one or a combination of at least two of alkali metal hydroxide, rare earth metal hydroxide or solid super alkali, the addition amount of the alkali accounts for 0.01-1 wt% of the 1, 3-propylene glycol reaction liquid, the reaction after the alkali is added is that the corresponding functional group of hydrazone is decomposed under the action of the alkali to generate alkyl, the reaction temperature is 90-180 ℃, and the reaction time is 2-5 hours, so as to obtain a reduction product; the reaction is carried out in a reaction rectifying device, a rectifying process is carried out while the reaction is carried out, and a reduction product is separated from the 1, 3-propylene glycol to obtain a reaction kettle material; the theoretical plate number of the reaction rectifying device is not more than 10, the reflux ratio is not more than 3, and the temperature of a tower kettle is not more than 180 ℃;
(2) decoking the reaction kettle material obtained in the step (1), wherein the decoking is carried out in a decoking tower, the theoretical plate number of the decoking tower is not more than 20, the reflux ratio is not more than 3, the operating absolute pressure of the decoking tower is not more than 5kPa, the operating temperature at the top of the tower is 90-135 ℃, a decoking fraction is obtained, and the decoking fraction collected at the top of the tower accounts for 90-95 wt% of the mass of the entering reaction kettle material;
(3) performing reduced pressure distillation on the decoking fraction obtained in the step (2), wherein the reduced pressure distillation is performed in a rectifying tower, the theoretical plate number of the rectifying tower is not more than 30, the reflux ratio is not more than 5, and the operating absolute pressure of the reduced pressure distillation is not more than 5 kPa; and sequentially extracting front fraction and main fraction from the top of the rectifying tower, wherein the operation temperature of the top of the rectifying tower is 90-134 ℃ when the front fraction is extracted, the operation temperature of the top of the rectifying tower accounts for 1-10 wt% of the decoking fraction fed material, the operation temperature of the top of the rectifying tower is 92-135 ℃ when the main fraction is extracted, the operation temperature of the top of the rectifying tower accounts for 85-95 wt% of the decoking fraction fed material, and the main fraction is the required 1, 3-propylene glycol product.
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