Method for producing crotonaldehyde

Abstract

To provide a method for industrially and efficiently producing high-quality crotonaldehyde with a low degree of coloration.SOLUTION: The method for producing crotonaldehyde of the present disclosure is a method for producing crotonaldehyde in which purified crotonaldehyde is obtained by distilling crude crotonaldehyde containing crotonaldehyde, water, and hue-deteriorating components, wherein purified crotonaldehyde with a Hazen color number of 150 or less is obtained from the upper layer by separating the overhead vapor condensate of a distillation column into two layers and controlling the reflux ratio of the lower layer to 2.7 or less. Purified crotonaldehyde having a Hazen color number of 100 or less may be obtained from the upper layer by setting the reflux ratio of the lower layer to 1.2 or less. The crude crotonaldehyde may contain at least one selected from the group consisting of aldols, aldoxanes, aldehydes (excluding crotonaldehyde), and carboxylic acids or salts thereof.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for producing crotonaldehyde.

Background Art

[0002] Crotonaldehyde is useful as a raw material and an intermediate for various chemicals such as butyraldehyde, butanol, 3-methoxybutanol, crotyl alcohol, crotonic acid, and sorbic acid. As a method for producing crotonaldehyde, a method of subjecting acetaldol or an acetaldol derivative such as aldoxane or para-acetaldol to a dehydration reaction is known.

[0003] JP-A-57-163333 discloses a method for obtaining crotonaldehyde by dehydrating acetaldol and its derivatives using a cation exchange resin as a catalyst. In this document, the reaction solution is batch-distilled under normal pressure to distill off the whole amount to obtain crotonaldehyde. The yield of low molecular weight polymers (oily substances) in the distillate is described as 0.1 - 0.2%, and the yield of crotonaldehyde is described as 97 - 98%. However, this document does not describe the distillation conditions, nor does it describe the quality and impurities of the obtained crotonaldehyde.

[0004] Japanese Patent Publication No. 62-195341 discloses a method for producing crotonaldehyde from acetaldehyde in a single step, rather than the usual two-step method (via acetaldol). Specifically, it describes a method in which acetaldehyde is dimerized and dehydrated at a reaction temperature of 80-200°C in the presence of at least one metal salt catalyst selected from alkali metal salts or alkaline earth metal salts of higher alcohols having 5 or more carbon atoms, and the reaction product containing crotonaldehyde and water is evaporated from the reaction area and collected in vapor form. More specifically, the vapor from the reaction vessel is fed into a first distillation column, and the reaction products such as unreacted acetaldehyde, crotonaldehyde, and water are distilled from the top of the column. The vapor is then led to a partial condenser, where the acetaldehyde is not condensed but extracted as a gas and recycled back into the reaction vessel. Then, the crotonaldehyde and water are condensed in the aforementioned partial condenser, and these are separated into two liquid phases in a decanter. A portion of the upper phase (organic phase) is refluxed to the top of the column, and the majority is distilled off and supplied to the second distillation column. The product water is extracted from the lower phase (aqueous phase) of the first distillation column, and the high-boiling point components are extracted from the bottom of the column. The second distillation column is operated under conditions for rectification of crotonaldehyde, and the low-boiling point components and water are distilled off from the top of the column, and the product crotonaldehyde is obtained from the side flow. The bottom liquid is recycled back to the first distillation column to recover the crotonaldehyde. However, this document does not describe the distillation conditions for either the first or second distillation column, nor does it describe the quality of the obtained crotonaldehyde, or the specific contents of the high-boiling point and low-boiling point components. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 57-163333 [Patent Document 2] Japanese Unexamined Patent Publication No. 62-195341 [Overview of the project] [Problems that the invention aims to solve]

[0006] Crotonaldehyde is increasingly used as a raw material or intermediate in various chemical products, and there is a growing demand for products with low coloration and high purity. However, the aforementioned literature does not describe the purification conditions for obtaining crotonaldehyde, nor does it describe the high-boiling and low-boiling point components produced as by-products in the reaction. Furthermore, the literature does not address the challenge of improving the quality of the crotonaldehyde product. Therefore, it is not possible to learn from these documents how to industrially and efficiently produce high-quality crotonaldehyde with low coloration. Furthermore, the quality of the crotonaldehyde is preferably such that the Hazen index (APHA) is 150 or less, and particularly preferably 100 or less. In addition, the purity is preferably 86% or higher, and particularly preferably 88% or higher.

[0007] Therefore, the object of this disclosure is to provide a method for industrially and efficiently producing high-quality crotonaldehyde with low coloration. [Means for solving the problem]

[0008] To achieve the above objective, the inventors diligently investigated the relationship between the distillation conditions of a crotonaldehyde purification column and the degree of coloration of the crotonaldehyde product. As a result, they discovered that in a crotonaldehyde rectification column, by setting the reflux ratio of the lower layer (aqueous phase) of the top vapor condensate to below a specific value, or by setting the content of specific impurity components in the upper layer (organic phase; crotonaldehyde phase) to below a specific value, the amount of color-degrading components mixed into the crotonaldehyde product can be reduced, thereby reducing the degree of coloration of the crotonaldehyde obtained from the upper layer. Based on these findings, the inventors have completed this disclosure.

[0009] In other words, this disclosure provides a method for producing crotonaldehyde to obtain purified crotonaldehyde by distilling crude crotonaldehyde containing crotonaldehyde, water, and color-degrading components, wherein the top vapor condensate of the distillation column is separated into two layers, and the lower layer is distilled at a reflux ratio of 2.7 or less, thereby obtaining purified crotonaldehyde with a Hazen color number of 150 or less from the upper layer (hereinafter sometimes referred to as "Production Method 1").

[0010] In the above manufacturing method 1, purified crotonaldehyde with a Hazen color number of 100 or less may be obtained from the upper layer by distilling the lower layer at a reflux ratio of 1.2 or less.

[0011] Furthermore, in the above manufacturing method 1, the crude crotonaldehyde may contain at least one selected from the group consisting of aldols, aldoxanes, aldehydes (excluding crotonaldehyde), and carboxylic acids or their salts.

[0012] This disclosure also provides a method for producing crotonaldehyde, comprising distilling crude crotonaldehyde containing crotonaldehyde, water, a color-degrading component, a crotonaldehyde dimer, and 2,4,6-octatrienal to obtain purified crotonaldehyde, wherein the top vapor condensate of the distillation column is separated into two layers, and the total content of crotonaldehyde dimer and 2,4,6-octatrienal in the upper layer is reduced to 3.9% or less, thereby obtaining purified crotonaldehyde with a Hazen color number of 150 or less from the upper layer (hereinafter sometimes referred to as "Production Method 2").

[0013] In the above manufacturing method 2, purified crotonaldehyde with a Hazen color number of 100 or less may be obtained from the upper layer by reducing the total content of crotonaldehyde dimer and 2,4,6-octatrienal in the upper layer to 3.6% or less.

[0014] Furthermore, in the above manufacturing method 2, the crude crotonaldehyde may contain at least one selected from the group consisting of aldols, aldoxanes, aldehydes (excluding crotonaldehyde, crotonaldehyde dimers, and 2,4,6-octatrienal), and carboxylic acids or salts thereof. [Effects of the Invention]

[0015] According to this disclosure, in a distillation column for rectifying crotonaldehyde, high-quality crotonaldehyde with low coloration can be industrially and efficiently produced by simple means such as keeping the reflux ratio of the lower layer of the top vapor condensate below a certain value, or keeping the content of specific impurity components in the upper layer of the top vapor condensate below a certain value. Furthermore, the purity of the product crotonaldehyde can also be improved.

[0016] Traditionally, it was common knowledge among engineers involved in distillation that increasing the reflux ratio improved product quality. However, in this disclosure, the unexpected result was that product quality was improved by lowering the reflux ratio. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram of a distillation apparatus used in one embodiment of the method for producing crotonaldehyde according to the present disclosure. [Figure 2] This is a schematic diagram of a distillation apparatus used in another embodiment of the method for producing crotonaldehyde according to the present disclosure. [Figure 3] This is the gas chromatogram (GC chart) of purified crotonaldehyde (product crotonaldehyde) in Comparative Example 1. [Figure 4] This is the gas chromatogram (GC chart) of the lower reflux liquid in Comparative Example 1. [Modes for carrying out the invention]

[0018] In the method for producing crotonaldehyde of the present disclosure, crude crotonaldehyde containing crotonaldehyde, water, and a hue deterioration component (hereinafter sometimes simply referred to as "crude crotonaldehyde") is distilled to obtain purified crotonaldehyde. Hereinafter, the method for producing crotonaldehyde of the present disclosure will be described while referring to the drawings. In the following, the distillation column for distilling crude crotonaldehyde may be referred to as a "crotonaldehyde purification column". The "hue deterioration component" means a causative substance (coloring causative substance) that increases the degree of coloring of crotonaldehyde. It can be said that the larger the value of the Hazen index of the crude crotonaldehyde, the more the hue deterioration component is contained.

[0019] FIG. 1 is a schematic diagram of a distillation apparatus used in one embodiment of the method for producing crotonaldehyde of the present disclosure. In one embodiment of the method for producing crotonaldehyde of the present disclosure, crude crotonaldehyde (X-1) is supplied to a crotonaldehyde purification column A, and a vapor mainly composed of an azeotropic mixture of crotonaldehyde and water is extracted from the top of the column and condensed by a condenser (A-1), and then separated into two liquid layers by a decanter (separator and reflux tank) (A-2). Crotonaldehyde (X-2) as a product is obtained from the upper layer of the decanter. The lower layer liquid mainly contains water and is refluxed to the top or near the top of the crotonaldehyde purification column A (for example, between the top of the column and the crude crotonaldehyde charging stage). From the bottom of the column, a bottoms liquid (X-3) (water containing high-boiling components) is withdrawn. The description of a heater or the like for heating and evaporating the bottom liquid is omitted.

[0020] Figure 2 is a schematic diagram of a distillation apparatus used in another embodiment of the method for producing crotonaldehyde according to the present disclosure. In another embodiment of the method for producing crotonaldehyde according to the present disclosure, crude crotonaldehyde (X-1) is supplied to a crotonaldehyde purification column A, and a vapor mainly consisting of an azeotrope mixture of crotonaldehyde and water is extracted from the top of the column. This vapor is condensed in a condenser (A-1), and before being introduced into a decanter, a portion of the condensate is refluxed back into the crotonaldehyde purification column A. The reflux location is preferably at or near the top of the crotonaldehyde purification column A (for example, between the top of the column and the crude crotonaldehyde feeding stage). The remainder of the condensate is separated into two liquid layers in a decanter (separator and reflux tank) (A-2). Crotonaldehyde (X-2), which is the product, is obtained from the upper layer of the decanter. The lower layer liquid, whose main component is water, is refluxed to crotonaldehyde purification column A. The reflux position of the lower layer liquid is preferably below the middle of crotonaldehyde purification column A (for example, between the crude crotonaldehyde charging stage and the bottom of the column). The bottom liquid (X-3) (water containing high-boiling point components) is removed from the bottom of the column. Note that the description of heaters, etc., for heating and evaporating the bottom liquid has been omitted.

[0021] In the method for producing crotonaldehyde of the present disclosure, the crude crotonaldehyde is not particularly limited as long as it is a liquid containing crotonaldehyde, water, and a hue deterioration component. For example, as the crude crotonaldehyde, (i) a crude crotonaldehyde containing crotonaldehyde obtained by subjecting acetaldol and / or its derivative (e.g., aldoxane which is a cyclic trimer of acetaldehyde, para-acetaldol which is a cyclized dimer of acetaldol, etc.) generated by aldol condensation of acetaldehyde to a dehydration reaction can be mentioned. Further, as the crude crotonaldehyde, (ii) a crude crotonaldehyde containing crotonaldehyde generated as a side reaction product in a process for producing various chemicals such as 1,3-butanediol (1,3-butylene glycol) by hydrogenating acetaldol and / or its derivative (e.g., aldoxane which is a cyclic trimer of acetaldehyde, para-acetaldol which is a cyclized dimer of acetaldol, etc.) generated by aldol condensation of acetaldehyde can be mentioned. Furthermore, as the crude crotonaldehyde, (iii) a crude crotonaldehyde containing crotonaldehyde generated by subjecting acetaldehyde to a dimerization-dehydration reaction and containing crotonaldehyde and water can be mentioned.

[0022] The above (i) will be explained in more detail. The aldol condensation of acetaldehyde is generally carried out in the presence of a basic catalyst (alkaline catalyst) such as sodium hydroxide. The condensation reaction product (aldol condensate) is usually neutralized with an acid such as dilute acetic acid, and the neutralized liquid is introduced into an acetaldehyde separation column (distillation column). Unreacted acetaldehyde is recovered from the top of the acetaldehyde separation column and recycled to the aldol condensation reactor. The bottom liquid of the acetaldehyde separation column can be used as "crude crotonaldehyde" in the method for producing crotonaldehyde of this disclosure. In addition to crotonaldehyde and water, this bottom liquid of the acetaldehyde separation column usually contains acetaldehyde, aldoxane, sodium acetate, acetic acid, and color-degrading components. Crotonaldehyde is produced in the acetaldehyde separation column described above, but it can also be produced in the crotonaldehyde purification column during the aldol condensation reaction step of acetaldehyde, or if acetaldehyde or its derivatives (see above) are present in the crude crotonaldehyde.

[0023] The above (ii) will be explained in more detail. Similar to (i) above, two molecules of acetaldehyde are subjected to aldol condensation using a small amount of basic catalyst (alkaline catalyst) such as sodium hydroxide, and then neutralized, usually with an acid such as dilute acetic acid. The neutralized liquid is introduced into the acetaldehyde separation step to recover unreacted acetaldehyde and recycled to the aldol condensation reactor. In the acetaldehyde separation step, acetaldehyde may be separated by the acetaldehyde separation column (distillation column) described above, but an evaporation step may be provided before introducing the liquid into the distillation column to obtain a flow rich in acetaldehyde. In that case, the distillate from the evaporator used in the evaporation step is introduced into the acetaldehyde separation column to recover unreacted acetaldehyde and recycled to the aldol condensation reactor. In any case, the bottom liquid of the acetaldehyde separation column can be used as "crude crotonaldehyde" in the method for producing crotonaldehyde of this disclosure. The bottom liquid of this acetaldehyde separation column typically contains acetaldehyde, water, and other substances besides crotonaldehyde, as described in (i) above, such as acetaldehydedol, aldoxane, sodium acetate, acetic acid, and color-degrading components. However, if an evaporation step is provided, most of the sodium acetate is separated and removed in the evaporation step before being charged into the acetaldehyde separation column. Crotonaldehyde is produced in the aldol condensation reaction step of acetaldehyde, in the evaporator, and in the acetaldehyde separation column. In addition, if acetaldehyde or its derivatives (see above) are present in the crude crotonaldehyde, it can also be produced in the crotonaldehyde purification column.

[0024] In this disclosure, the crotonaldehyde content in the crude crotonaldehyde subjected to the crotonaldehyde purification column is not particularly limited and can take on a wide range of values. The crotonaldehyde content in the crude crotonaldehyde is, for example, 0.2 to 90% by weight, preferably 0.3 to 60% by weight, more preferably 0.5 to 40% by weight, and even more preferably 0.8 to 15% by weight. Similarly, the water content in the crude crotonaldehyde is not particularly limited and can take on a wide range of values. The water content in the crude crotonaldehyde is, for example, 10 to 99.8% by weight, preferably 15 to 99.7% by weight, more preferably 20 to 99.5% by weight, and even more preferably 25 to 99.2% by weight. The total content of crotonaldehyde and water in the crude crotonaldehyde is, for example, 15 to 99.9% by weight, preferably 20 to 99% by weight, and even more preferably 40 to 98% by weight.

[0025] The crude crotonaldehyde mentioned above, depending on the acquisition route of the crude crotonaldehyde, usually contains crotonaldehyde (CR) and water, as well as acetaldehyde (AD), paraaldehyde (P-AD), 2-vinylcrotonaldehyde (2-VCR), 2,4-hexadienal, crotonaldehyde dimers, 2,4,6-octatrienal, acetaldol (AAD) (=3-hydroxybutanal), and aldoxane (ADX The crude crotonaldehyde contains impurities such as 2,4-dimethyl-1,3-dioxan-6-ol, paraacetaldol (PAAD) [2-(2-hydroxypropyl)-4-methyl-1,3-dioxan-6-ol], 2,5-dihydrofuran, diethyl ketone, 2,4-dimethyl-1,3-dioxane, carboxylic acids [acetic acid (AC), crotonic acid, sorbic acid, 3-hydroxybutanoic acid, etc.] or their salts (carboxylates). In addition, the crude crotonaldehyde may also contain aldehydes, aldols, ketones, alcohols, or carboxylic acid esters, which have 5 or more carbon atoms, may or may not have carbon-carbon unsaturated bonds, may or may not have side chains, and may or may not have a cyclic structure. It is thought that these components react or polymerize (condense) sequentially at the bottom and / or inside the crotonaldehyde purification column to produce high-boiling-point components and color-deteriorating components (substances that cause discoloration). Furthermore, some of the above impurities can also be generated in the stages preceding the crotonaldehyde purification process, such as the aldol condensation reaction of acetaldehyde or in subsequent purification steps.

[0026] The Hazen color number (APHA) of the crude crotonaldehyde subjected to the crotonaldehyde purification column is, for example, greater than 50, or greater than 100, preferably greater than 150, and more preferably greater than 200. The upper limit of the Hazen color number (APHA) of the crude crotonaldehyde is not particularly limited, but for example, it is 5000 or 1000.

[0027] The theoretical number of stages in a crotonaldehyde purification column is, for example, 1 to 100 stages, preferably 5 to 80 stages, and more preferably 20 to 70 stages. The supply position of the feed liquid (crude crotonaldehyde) is, for example, 10 to 90%, preferably 20 to 80%, more preferably 30 to 70%, and even more preferably 40 to 60% of the column height, downwards from the top of the column. In a crotonaldehyde purification column, the top pressure is usually atmospheric pressure (0.1 MPa), but distillation can also be performed under reduced pressure or pressurized pressure.

[0028] In the manufacturing method 1 of this disclosure, the top vapor condensate of the crotonaldehyde purification column is separated into two layers, and purified crotonaldehyde with a Hazen color number (APHA) of 150 or less is extracted from the upper layer (organic phase) by distillation with a reflux ratio of 2.7 or less in the lower layer (aqueous phase). The reflux ratio of the lower layer means (reflux flow rate of the lower layer to the distillation column) / [distillation volume (amount of top vapor condensate withdrawn from the distillation column)]. Note that the separation into two layers may be limited to a portion of the top vapor condensate of the crotonaldehyde purification column. That is, for example, a portion of the top vapor condensate of the crotonaldehyde purification column may be refluxed directly to the crotonaldehyde purification column without being separated into two layers.

[0029] The reflux ratio of the lower layer is preferably 2.0 or less, more preferably 1.5 or less, even more preferably 1.0 or less, and particularly preferably 0.9 or less. The lower limit of the reflux ratio of the lower layer is, for example, 0.01, or 0.03 or 0.05. The Hazen color number (APHA) of the purified crotonaldehyde removed from the upper layer is preferably 120 or less, more preferably 100 or less, even more preferably 80 or less, particularly preferably 60 or less, and most preferably 50 or less. The purity of the purified crotonaldehyde removed from the upper layer is, for example, 86.0% by weight, preferably 86.5% by weight or more, and more preferably 88.0% by weight or more.

[0030] Generally, increasing the reflux ratio of a distillation column improves the quality of the product obtained as distillate. However, when distilling crude crotonaldehyde, increasing the reflux ratio of the lower layer (aqueous phase) increases the amount of water circulating in the distillation column. It is thought that high-boiling-point components and color-degrading components (substances that cause discoloration) present in the bottom liquid of the column are azeotropically mixed with water and boiled up to the top of the column, causing these components to be mixed into the crotonaldehyde product, increasing its coloration and decreasing its purity. It is highly unexpected that the quality of the crotonaldehyde product can be improved by lowering the reflux ratio of the lower layer (aqueous phase).

[0031] Furthermore, as shown in Figure 2, if a portion of the top condensate of the distillation column is refluxed to the crotonaldehyde purification column before being introduced into the decanter, the reflux ratio of the condensate (hereinafter sometimes referred to as the "top reflux ratio") is, for example, 0.01 to 5.0, preferably 0.1 to 3.0, more preferably 0.3 to 2.0, and even more preferably 0.5 to 1.6. The top reflux ratio refers to [the amount of the top condensate (before separation) refluxed to the distillation column] / [the amount of distillate (the amount of top vapor condensate withdrawn from the distillation column)].

[0032] In the manufacturing method 2 of this disclosure, the top vapor condensate of the crotonaldehyde purification column is separated into two layers, and the total content of crotonaldehyde dimer and 2,4,6-octatrienal in the upper layer (organic phase; crotonaldehyde phase) is reduced to 3.9% by weight or less, thereby obtaining purified crotonaldehyde with a Hazen color number (APHA) of 150 or less from the upper layer.

[0033] Crotonaldehyde dimers are represented by the following formulas (1a) and (1b). 2,4,6-Octatrienal is represented by the following formula (2). [ka]

[0034] The content (%) of crotonaldehyde dimer and 2,4,6-octatrienal in the upper layer can be determined by gas chromatography analysis (3% FFAP / Chromosorb 101 packed column, FID detector). Details of the analytical conditions will be described later.

[0035] The total content of crotonaldehyde dimers and 2,4,6-octatrienal in the upper layer is preferably 3.6% by weight or less, more preferably 3.0% by weight or less, even more preferably 2.0% by weight or less, and particularly preferably 1.0% by weight or less. Although the details of the color-deteriorating components (substances causing discoloration) are not clear, as a result of examining the relationship between the type and content of impurities in the upper layer and the Hazen color number (APHA) of the upper layer, it was found that there is a correlation between the total content of crotonaldehyde dimers and 2,4,6-octatrienal in the upper layer and the Hazen color number (APHA) of the upper layer, and that by setting the total content of crotonaldehyde dimers and 2,4,6-octatrienal in the upper layer to 3.9% by weight or less, the Hazen color number (APHA) of the upper layer can be set to 150 or less. The total content of crotonaldehyde dimers and 2,4,6-octatrienal in the upper layer can be reduced, for example, by lowering the reflux ratio of the lower layer (aqueous phase), as described above.

[0036] In the manufacturing method 2 of this disclosure, the reflux ratio of the lower layer (aqueous phase) is, for example, 2.7 or less, preferably 2.0 or less, more preferably 1.5 or less, even more preferably 1.0 or less, and particularly preferably 0.9 or less. The lower limit of the reflux ratio of the lower layer is, for example, 0.01, or 0.03 or 0.05. The Hazen color number (APHA) of the purified crotonaldehyde removed from the upper layer is preferably 120 or less, more preferably 100 or less, even more preferably 80 or less, particularly preferably 60 or less, and most preferably 50 or less. The purity of the purified crotonaldehyde removed from the upper layer is, for example, 86.0% by weight, preferably 86.5% by weight or more, and more preferably 88.0% by weight or more.

[0037] In the manufacturing method 2 of this disclosure, as shown in Figure 2, a portion of the condensate at the top of the distillation column may be refluxed to the crotonaldehyde purification column before it is introduced into the decanter. In this case, the reflux ratio of the condensate (top reflux ratio) is, for example, 0.01 to 5.0, preferably 0.1 to 3.0, more preferably 0.3 to 2.0, and even more preferably 0.5 to 1.6.

[0038] The following diagram outlines the generation mechanisms of various impurities in the acetaldehyde aldol condensation reaction, the crotonaldehyde production reaction by dehydration of acetaldehyde, and the purification process [acetaldehyde separation process (evaporation process, acetaldehyde separation column), crotonaldehyde purification process]. In the diagram, AD is an abbreviation for acetaldehyde, AAD is an abbreviation for acetaldehyde, CR is an abbreviation for crotonaldehyde, PAAD is an abbreviation for paraacetaldehyde, ADX is an abbreviation for aldoxane, and 2-VCR is an abbreviation for 2-vinylcrotonaldehyde. As described above, the compounds represented by formulas (1a) and (1b) are crotonaldehyde dimers, and the compound represented by formula (2) is 2,4,6-octatrienal.

[0039] [ka]

[0040] Each embodiment disclosed herein can be combined with any other features disclosed herein. Furthermore, each configuration and combination thereof in each embodiment is merely an example, and additions, omissions, and other modifications are permitted as appropriate, without departing from the spirit of this disclosure. This disclosure is not limited by the embodiments, but is limited only by the claims. [Examples]

[0041] The present disclosure will be described in more detail below based on examples. Unless otherwise specified, "%" as a unit of concentration refers to weight.

[0042] <Measurement of color intensity> In Table 2 below, the Hazen color number was measured using a TZ7700 colorimeter manufactured by Nippon Denshoku Industries Ltd., after creating a calibration curve using a standard solution prepared by diluting APHA (Hazen) colorimetric stock solution (No. 500) reagent with distilled water.

[0043] <Moisture content measurement (water analysis)> In Tables 2-4 below, moisture content was measured using a volumetric titration type moisture analyzer (KF method) MKV-710S manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0044] <Oil content measurement> In Tables 2-4 below, the acidity was determined by titration with 0.1 mol / L alcoholic potassium hydroxide normal solution using phenolphthalein as an indicator, and the corresponding amount of acetic acid was calculated by gravimetric method.

[0045] <Measurement of the concentration of each component and the purity of crotonaldehyde> The concentration of each component was measured using two types of gas chromatography (GC analysis). The gas chromatography analysis conditions are shown below. Gas chromatography analysis condition 1 can be used for the analysis of crotonaldehyde and major impurities. Gas chromatography analysis condition 2 can be used for the analysis of acetaldehyde, crotonaldehyde, acetaldol, aldoxane, paraacetaldol, etc.

[0046] (Gas chromatograph analysis conditions 1) Analytical column: 3% FFAP / Chromosorb101 packed column (length 2.1m, inner diameter 2.6mm) Column heating conditions: 80°C → 10°C / min → 200°C Sample introduction temperature: 200℃ Carrier gas: Nitrogen Column gas flow rate: 63 mL / min Detector and detection temperature: Flame ionization detector (FID), 230°C

[0047] Under the gas chromatography analysis conditions 1 described above, the retention times of crotonaldehyde and major impurities, and the relative retention times of major impurities when the retention time of crotonaldehyde is set to 1.0, are shown below. Retention time (minutes) Relative retention time Crotonaldehyde: Approximately 10.5g, 1.0g Acetaldehyde: approximately 3.4 0.30~0.34 Acetone: Approximately 6.3g, 0.57-0.62g Acetic acid: approximately 8.7 0.82~0.86 Paraaldehyde: Approximately 14.9 1.38~1.45 Crotonic acid: approximately 16.5g, 1.54-1.61g 2-Vinylcrotonaldehyde: Approximately 18.0 1.69~1.75 2,4-Hexadienal approx. 21.0 1.96~2.03 Crotonaldehyde dimer: approximately 29.8 2.78~2.88 2,4,6-Octatrienal approx. 31.6 2.95~3.07 The acetone used is for cleaning the microsyringes used during gas chromatography analysis, and the measurement is performed to confirm whether or not contamination is present.

[0048] Acetaldehyde, acetone, paraaldehyde, acetic acid, and 2,4-hexadienal were quantified using calibration curves created with standard samples (absolute calibration curve method). The concentrations of impurities other than those listed above were calculated by multiplying the area percentage of the peak of each component by {100 - water content (%)} / 100, taking into account the water content. For example, the concentration of impurity X (concentration after water correction) was calculated using the following formula. Concentration of impurity X (concentration after moisture correction) (%) = {(peak area of ​​impurity X) / (sum of peak areas of all peaks)} × {100 - moisture (%)} / 100 The concentration (content) of crotonaldehyde dimer and 2,4,6-octatrienal in purified crotonaldehyde can be determined by the above formula.

[0049] (Gas chromatograph analysis conditions 2) Analytical column: HP-5 capillary column (liquid layer thickness 1.00 μm, length 60 m, inner diameter 0.25 mm) Column heating conditions: 70°C (hold for 5 minutes) → 5°C / min → 100°C (hold for 1 minute) → 10°C / min → 130°C (hold for 15 minutes) → 20°C / min → 250°C (hold for 24 minutes) Sample introduction temperature: 220℃ Carrier gas: Helium Column gas flow rate: 1.72 mL / min Detector and detection temperature: Flame ionization detector (FID), 280°C The samples were analyzed after being treated with TMS (trimethylsilylation).

[0050] Under the gas chromatography analysis conditions 2 described above, the retention times for crotonaldehyde and major impurities, and the relative retention times of major impurities (with the retention time of crotonaldehyde set to 1.0) are shown below. Note that these retention times and relative retention times are after the sample has been treated with TMS. Retention time (minutes) Relative retention time Crotonaldehyde: approximately 28.9g, 1.0g Acetaldehyde: approximately 3.9g, 0.12-0.15g Acetic acid: approximately 9.0 0.29~0.33 Acetaldol: Approximately 38.0 1.26~1.33 Aldoxane: Approximately 34.0 1.04~1.30 Paraacetaldol: Approximately 39.5g (1.35-1.39g) 3-HBE approx. 40.9 1.39~1.44 n-decane (internal standard) approx. 20.8 0.71~0.74

[0051] Acetaldehyde, crotonaldehyde, acetic acid, paraacetaldol, and 3-HBE (1,3-butylene glycol ester of 3-hydroxybutanoic acid) were quantified using calibration curves created with standard samples (internal standard method). For acetaldol and aldoxane, calibration curves were created using paraacetaldol standard samples (internal standard method), and quantification was performed using the same factors. n-decane was used as the internal standard.

[0052] (Purity of crotonaldehyde) In the analysis results of the product crotonaldehyde shown in Table 2, the purity of crotonaldehyde was determined from the analysis results of water analysis and gas chromatography analysis under condition 1 using the following formula. Purity (%) = 100 - {Moisture content (%) + Sum of each impurity concentration according to gas chromatography analysis condition 1 (%)} Here, the concentration of each impurity, except for components that were quantified by creating a calibration curve using the above-mentioned standard, is the concentration after correcting for moisture content.

[0053] (Analysis of Tables 2-5) In Table 2, the concentrations of impurities such as acetaldehyde are the results of analysis under gas chromatography analysis conditions 1 and 2 (for acetaldehyde, aldoxane, and paraacetaldehyde). In Tables 3 and 4, the concentrations of crotonaldehyde and acetaldehyde are the results of analysis under gas chromatography analysis condition 2. In Table 5, the concentrations of paraaldehyde, 2-vinylcrotonaldehyde, 2,4-hexadienal, HB-a, HB-b, HB-c, and HB-d are the results of analysis under gas chromatography analysis condition 1. In Table 5, the concentrations of acetaldehyde, crotonaldehyde, acetaldehyde, aldoxane, and paraacetaldehyde are the results of analysis under gas chromatography analysis condition 2. Note that "Other" in Table 5 includes impurities that cannot be detected by gas chromatography.

[0054] Comparative Example 1 Distillation was performed using the apparatus shown in Figure 1 and under the conditions shown in Table 1. A 40mmφ Oldershaw glass column with 55 stages was used as the distillation column. The predetermined amount of feed liquid was charged to the 27th stage from the top of the distillation column and heated to a predetermined temperature at the top of the column. The lower layer liquid was withdrawn so that the interface with the decanter (constantly controlled at 10°C) remained constant, and refluxed to the top of the distillation column. The upper layer liquid was withdrawn by overflow from the withdrawal port at the top of the decanter, and the product crotonaldehyde was distilled off. The bottom liquid was withdrawn (bottom extraction) so that the bottom liquid level remained constant. The operation was carried out at atmospheric pressure at the top of the column. The results are shown in Tables 2 to 5. Table 2 shows the analysis results of the product crotonaldehyde, Table 3 shows the analysis results of the lower layer reflux liquid, Table 4 shows the analysis results of the bottom extraction liquid, and Table 5 shows the analysis results of the feed liquid. "ND" indicates below the detection limit. In Table 2, HB-a, HB-b, HB-c, and HB-d are high-boiling point impurities. GC-MS analysis confirmed that HB-a and HB-b are crotonaldehyde dimers and 2,4,6-octatrienal, a condensation product of crotonaldehyde, respectively. Furthermore, HB-c and HB-d are likely aldehydes, aldols, ketones, alcohols, or carboxylic acid esters with 8 to 10 carbon atoms, respectively.

[0055] In the distillation column for rectifying crotonaldehyde shown in Figure 1, the top vapor is condensed in a condenser and then entirely introduced into a decanter. The condensate is not refluxed to the top of the column before being introduced into the decanter. Therefore, as shown in Table 1, the top reflux ratio, which is the weight-based ratio of top reflux flow rate to distillate volume, is zero. After separation into two liquid layers in the decanter, the lower liquid is refluxed to the top of the distillation column for rectifying crotonaldehyde, and the crotonaldehyde product is distilled from the upper layer. Table 1 shows the weight-based ratio of lower reflux flow rate to distillate volume as the lower reflux ratio.

[0056] Distillation was performed with a lower reflux ratio of 3.00. As shown in Table 2, the Hazen color number of the upper distillate, the product crotonaldehyde, was 166 and the purity was 85.3%. The concentrations of HB-a (crotonaldehyde dimer) and HB-b (2,4,6-octatrienal) were 3.0% and 1.0%, respectively. The concentration of components other than crotonaldehyde, acetaldehyde, water, and acid was 5.9%.

[0057] Furthermore, the dimer of crotonaldehyde, 2,4,6-octatrienal, is highly reactive, and it is thought that in the crotonaldehyde manufacturing process, it undergoes sequential reactions with itself and / or with acetaldehyde, crotonaldehyde, 2-vinylcrotonaldehyde, 2,4-hexadienal, etc., to form higher aldehydes, thus worsening the coloration. In addition, it is thought that higher aldehydes, aldols, ketones, alcohols, and carboxylic acid esters are present in the process liquid during the crotonaldehyde manufacturing process as impurities that cannot be detected by gas chromatography. For example, 2,4,6,8,10-dodecapentaenal is a substance that causes coloration, although it has not been detected by gas chromatography. If the concentrations of HB-a (crotonaldehyde dimer) and HB-b (2,4,6-octatrienal) are high, the reaction rates with HB-c, HB-d, and other higher-grade impurities are thought to increase, leading to higher concentrations of color-causing substances and a further deterioration of quality.

[0058] Figure 3 shows a gas chromatogram of the components of the product crotonaldehyde obtained from the upper layer of the decanter of a distillation column for rectification of crotonaldehyde. As mentioned above, the Hazen color number of the product crotonaldehyde was 166, and it was colored yellow. Figure 4 shows a gas chromatogram of the components of the lower layer liquid of the decanter. The lower layer liquid was a colorless and transparent liquid, and compared to Figure 3, there were fewer high-boiling point components (including HB-a and HB-b) after a retention time of 17 minutes, confirming that most of the color-causing substances had been distributed to and concentrated in the upper layer liquid. Note that the gas chromatograms shown in Figures 3 and 4 were obtained under gas chromatographic analysis condition 1. HB-4, HB-5, HB-6, and HB-7 in Figures 3 and 4 correspond to HB-a, HB-b, HB-c, and HB-d, respectively. AC is acetic acid.

[0059] Comparative Example 2 Distillation was performed using the apparatus shown in Figure 2 under the conditions shown in Table 1. A 40mmφ Oldershaw glass column with 55 stages was used as the distillation column. A predetermined amount of the charge was placed in the 27th stage from the top of the column and heated to a predetermined top temperature. After condensing the top vapor, a reflux timer was used to reflux a portion of the condensate to the top of the column at a predetermined reflux ratio. The remaining condensate was introduced into a decanter, and the lower layer was withdrawn so that the interface with the decanter (constantly controlled at 10°C) remained constant, and refluxed to the 33rd stage from the top of the column. The upper layer was withdrawn by overflow from the withdrawal port at the top of the decanter, and the product crotonaldehyde was distilled off. The bottom layer was withdrawn (bottom extraction) so that the bottom liquid level remained constant. The operation was carried out at atmospheric pressure. The results are shown in Tables 2 to 5. The analytical method is the same as in Comparative Example 1.

[0060] Distillation was performed with a top reflux ratio of 0.25 and a bottom reflux ratio of 3.85. The resulting product, crotonaldehyde, had a Hazen color number of 175 (yellow) and a purity of 85.8%. The concentrations of HB-a (crotonaldehyde dimer) and HB-b (2,4,6-octatrienal) were 3.0% and 1.1%, respectively. The concentration of components other than crotonaldehyde, acetaldehyde, water, and acid was 6.0%.

[0061] Examples 1 to 5 Similar to Comparative Example 1, the apparatus shown in Figure 1 was used. Distillation was performed under the conditions shown in Table 1. The results are shown in Tables 2 to 5. The analytical method was the same as in Comparative Example 1. By reducing the lower reflux ratio at a top reflux ratio of 0, the Hazen color number and purity of the product crotonaldehyde were improved. In Example 4, distillation was performed with the lower reflux ratio reduced to 0.31, resulting in a Hazen color number of 32 (almost colorless and transparent) and a purity of 91.1% for the upper distillate product crotonaldehyde, yielding high-quality crotonaldehyde. The concentration of HB-a (crotonaldehyde dimer), an impurity in the product crotonaldehyde, was 0.2%, and HB-b (2,4,6-octatrienal) was detected by gas chromatography, but only at trace levels (below the limit of quantification). The concentrations of components other than crotonaldehyde, acetaldehyde, water, and acid were also 0.7%, which was significantly lower than in Comparative Example 1.

[0062] Example 6 The procedure was carried out using the apparatus shown in Figure 2, similar to Comparative Example 2. Distillation was performed under the conditions shown in Table 1. The results are shown in Tables 2 to 5. The analytical method was the same as in Comparative Example 1. Distillation was performed with the lower reflux ratio reduced to 0.82. As a result, the Hazen color number of the upper distillate, the product crotonaldehyde, was 41 (almost colorless and transparent), and the purity was 89.6%, indicating that high-quality crotonaldehyde was obtained. The concentrations of impurities HB-a (crotonaldehyde dimer) and HB-b (2,4,6-octatrienal) in the product crotonaldehyde were 1.4% and 0.3%, respectively. The concentration of components other than crotonaldehyde, acetaldehyde, water, and acid was 2.9%, which was significantly reduced compared to Comparative Example 2.

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] [Table 4]

[0067] [Table 5] [Explanation of Symbols]

[0068] A Distillation Column A-1 Condenser A-2 Decanter (separator and reflux tank) X-1 Crude Crotonaldehyde X-2 Refined Crotonaldehyde (Product Crotonaldehyde) X-3 Canned liquid

Claims

1. A method for producing crotonaldehyde, comprising distilling crude crotonaldehyde containing crotonaldehyde, water, and color-degrading components to obtain purified crotonaldehyde, wherein the top vapor condensate of a distillation column is separated into two layers, and the lower layer is distilled at a reflux ratio of 2.7 or less to obtain purified crotonaldehyde with a Hazen color number of 150 or less from the upper layer.

2. A method for producing crotonaldehyde according to claim 1, wherein purified crotonaldehyde with a Hazen color number of 100 or less is obtained from the upper layer by distilling the lower layer at a reflux ratio of 1.2 or less.

3. The method for producing crotonaldehyde according to claim 1 or 2, wherein the crude crotonaldehyde comprises at least one selected from the group consisting of aldols, aldoxanes, aldehydes (excluding crotonaldehyde), and carboxylic acids or salts thereof.

4. A method for producing crotonaldehyde, comprising distilling crude crotonaldehyde containing crotonaldehyde, water, a color-degrading component, a crotonaldehyde dimer, and 2,4,6-octatrienal to obtain purified crotonaldehyde, wherein the top vapor condensate of the distillation column is separated into two layers, and the total content of crotonaldehyde dimer and 2,4,6-octatrienal in the upper layer is reduced to 3.9% or less, thereby obtaining purified crotonaldehyde with a Hazen color number of 150 or less from the upper layer.

5. The method for producing crotonaldehyde according to claim 4, wherein the total content of crotonaldehyde dimer and 2,4,6-octatrienal in the upper layer is 3.6% or less, thereby obtaining purified crotonaldehyde with a Hazen color number of 100 or less from the upper layer.

6. The method for producing crotonaldehyde according to claim 4 or 5, wherein the crude crotonaldehyde comprises at least one selected from the group consisting of aldols, aldoxanes, aldehydes (excluding crotonaldehyde, crotonaldehyde dimers, and 2,4,6-octatrienal), and carboxylic acids or salts thereof.

7. A method for producing crotonaldehyde according to claim 4 or 5, wherein the total content of crotonaldehyde dimer and 2,4,6-octatrienal in the upper layer is 3.9% or less by distillation at a reflux ratio of 2.7 or less in the lower layer.

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