Process for producing secondary alcohol

Abstract

The present invention provides a method for producing secondary alcohols that can significantly suppress the production of unsaturated aliphatic hydrocarbons that may be produced during the distillation of a reaction liquid containing a borate ester compound and significantly reduce unrecovered residual saturated aliphatic hydrocarbons. The method comprises: a) subjecting a saturated aliphatic hydrocarbon to liquid-phase oxidation using a molecular oxygen-containing gas in the presence of metaboric acid to obtain a reaction liquid containing an oxide; b) esterifying the oxide to obtain a reaction liquid containing a borate ester compound; c) distilling the reaction liquid containing the borate ester compound to separate it into unreacted saturated aliphatic hydrocarbons and a distillation residue; d) hydrolyzing the distillation residue to separate it into orthoboric acid and an organic layer; e) saponifying the organic layer with an alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer; and f) purifying the crude alcohol layer to obtain a secondary alcohol, wherein the distillation in step c) is carried out in two stages, with the second distillation temperature being higher than the first distillation temperature and the second distillation pressure being lower than the first distillation pressure.

Description

Technical Field

[0001] The present invention relates to a method for producing secondary alcohols. Background Art

[0002] Secondary alcohols are useful as raw materials for synthetic detergents, surfactants, plasticizers, and the like. Regarding secondary alcohols, the following technology is known: in the presence of metaboric acid and a saturated aliphatic hydrocarbon, an oxidation reaction step involving the introduction of a molecular oxygen-containing gas is performed to obtain a borate ester compound, which is then subjected to a hydrolysis step and a saponification step to obtain the secondary alcohols (e.g., Patent Documents 1 to 3).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 56-131531

[0006] Patent Document 2: Japanese Patent Publication No. 50-25447

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 48-34807 Summary of the Invention

[0008] However, it has been found that according to the prior art, the produced secondary alcohols and the secondary alcohol alkoxylates produced using the same as raw materials may cause coloring, contamination, and the like.

[0009] The present inventors have conducted in-depth research to find out the above reasons (especially the reasons for coloration). As a result, it was found that the cause of the above phenomenon is due to the unsaturated aliphatic hydrocarbons produced by the decomposition of the borate compound in the distillation for recovering unreacted saturated aliphatic hydrocarbons after the saturated aliphatic hydrocarbons are oxidized in the presence of metaboric acid. If described in more detail, after the oxidation reaction step is implemented, borate compounds, unreacted saturated aliphatic hydrocarbons, etc. are mixed in its product. Then, it was found that although the distillation of the reaction solution containing the borate compound is carried out to recover unreacted saturated aliphatic hydrocarbons, in the prior art, the borate compound is decomposed in large quantities in the distillation, thereby producing unsaturated aliphatic hydrocarbons in large quantities. This problem is a problem peculiar to secondary alcohols and is not a problem for primary alcohols. It is believed that this is because the hydrogen at the β position relative to the addition position of the hydroxyl group is more easily captured by secondary alcohols than by primary alcohols, and double bonds are easily generated.

[0010] Therefore, the problem to be solved by the present invention is to significantly suppress the generation of unsaturated aliphatic hydrocarbons that may be generated during the distillation of a reaction liquid containing a borate ester compound for the purpose of recovering unreacted saturated aliphatic hydrocarbons, thereby significantly reducing the amount of unrecovered residual saturated aliphatic hydrocarbons.

[0011] One embodiment for solving the above-mentioned problems is a method for producing a secondary alcohol, comprising: a) supplying metaboric acid, a saturated aliphatic hydrocarbon and a molecular oxygen-containing gas to a reactor, and in the presence of metaboric acid, liquid-phase oxidizing the saturated aliphatic hydrocarbon with the molecular oxygen-containing gas to obtain a reaction liquid containing an oxide; b) esterifying the above-mentioned oxide to obtain a reaction liquid containing a borate ester compound; c) distilling the above-mentioned reaction liquid containing the borate ester compound to separate it into unreacted saturated aliphatic hydrocarbon and a distillation residue; d) hydrolyzing the above-mentioned distillation residue to separate it into orthoboric acid and an organic layer; e) saponifying the above-mentioned organic layer with an alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer; and f) purifying the above-mentioned crude alcohol layer to obtain a secondary alcohol, wherein, in the above-mentioned step c), the above-mentioned distillation is carried out in two stages, and is carried out under the conditions that the temperature of the second distillation is higher than the temperature of the first distillation and the pressure of the second distillation is lower than the pressure of the first distillation.

[0012] According to the present invention, the generation of unsaturated aliphatic hydrocarbons that may be generated during the distillation of a reaction liquid containing a borate compound for recovering unreacted saturated aliphatic hydrocarbons can be significantly suppressed, and the amount of unrecovered residual saturated aliphatic hydrocarbons can be significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram showing the process in step (c). DETAILED DESCRIPTION

[0014] The present invention will be described below. It should be noted that the present invention is not limited to the following embodiments. Unless otherwise specified, operations and measurements of physical properties were performed at room temperature (20 to 25°C).

[0015] One embodiment of the present invention is a method for producing a secondary alcohol, comprising: a) supplying metaboric acid, a saturated aliphatic hydrocarbon, and a molecular oxygen-containing gas to a reactor, and subjecting the saturated aliphatic hydrocarbon to liquid-phase oxidation with the molecular oxygen-containing gas in the presence of metaboric acid to obtain a reaction liquid containing an oxide; b) esterifying the oxide to obtain a reaction liquid containing a borate ester compound; c) distilling the reaction liquid containing the borate ester compound to separate it into unreacted saturated aliphatic hydrocarbon and a distillation residue; d) hydrolyzing the distillation residue to separate it into orthoboric acid and an organic layer; e) saponifying the organic layer with an alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer; and f) purifying the crude alcohol layer to obtain a secondary alcohol, wherein, in the above step c), the distillation is carried out in two stages, with the temperature of the second distillation being higher than the temperature of the first distillation and the pressure of the second distillation being lower than the pressure of the first distillation. According to this embodiment, the generation of unsaturated aliphatic hydrocarbons that may be generated during the distillation of the reaction liquid containing the borate compound for recovering unreacted saturated aliphatic hydrocarbons can be significantly suppressed, and the unrecovered residual saturated aliphatic hydrocarbons can be significantly reduced.

[0016] Hereinafter, each step will be described in detail.

[0017] (Step (a))

[0018] ((a) Step: Oxidation Reaction Step)

[0019] In step (a), metaboric acid, saturated aliphatic hydrocarbons, and a molecular oxygen-containing gas are supplied to a reactor. In the presence of metaboric acid, the saturated aliphatic hydrocarbons are liquid-phase oxidized by the molecular oxygen-containing gas to obtain a reaction liquid containing oxides.

[0020] Saturated aliphatic hydrocarbons are mixtures of saturated aliphatic hydrocarbons (normal paraffins) having 8 to 30 carbon atoms. Preferably, the saturated aliphatic hydrocarbons are mixtures containing saturated aliphatic hydrocarbons having 10 to 15 carbon atoms (n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane and n-pentadecane) as the main components, and more preferably, mixtures containing saturated aliphatic hydrocarbons having 12 to 14 carbon atoms (n-dodecane, n-tridecane and n-tetradecane) as the main components. Here, “containing saturated aliphatic hydrocarbons as the main component” means that the saturated aliphatic hydrocarbons having a specified number of carbon atoms are contained in a ratio exceeding 90% by mass (preferably exceeding 95% by mass) (upper limit: 100% by mass) relative to all saturated aliphatic hydrocarbons. In addition, the average molecular weight of the saturated aliphatic hydrocarbons is greater than 114 and less than 422, preferably greater than 142 and less than 212, and more preferably greater than 170 and less than 198. The saturated aliphatic hydrocarbons may be synthetic or commercially available. Similarly, metaboric acid may also be synthetic or commercially available.

[0021] In step (a), the molecular oxygen-containing gas contains nitrogen in addition to molecular oxygen (oxygen). Preferably, the molecular oxygen-containing gas is composed of molecular oxygen (oxygen) and nitrogen. Furthermore, the concentration of molecular oxygen (oxygen) in the molecular oxygen-containing gas is, but is not limited to, 1% by volume (vol%) or higher and 10% by volume (vol%) or lower, preferably 3% by volume (vol%) or higher and 5% by volume (vol%) or lower. The molecular oxygen-containing gas is supplied at a rate of, but is not limited to, 100 to 1000 liters / hour, preferably 350 to 600 liters / hour, relative to 1000 g of saturated aliphatic hydrocarbons.

[0022] In the above-mentioned step (a), the reaction mixing ratio of metaboric acid and saturated aliphatic hydrocarbon is not particularly limited. The amount of metaboric acid relative to the saturated aliphatic hydrocarbon is preferably 1% by mass or more and 5% by mass or less, more preferably 2% by mass or more and 4% by mass or less, etc., but is not limited thereto.

[0023] There are no particular restrictions on the liquid phase oxidation reaction conditions, and the same conditions as before can be applied. For example, the liquid phase oxidation reaction temperature is 100 to 250°C, preferably 140 to 200°C, etc., but not limited thereto. In addition, the liquid phase oxidation reaction time is, for example, 0.5 to 5 hours, preferably 1 to 3 hours, etc., but not limited thereto. Under such conditions, saturated aliphatic hydrocarbons can be liquid-phase oxidized using a gas containing molecular oxygen within an appropriate range (for example, the conversion rate of saturated aliphatic hydrocarbons = 5 to 30%). The above-mentioned liquid phase oxidation reaction can be carried out under atmospheric pressure (normal pressure), under pressure or under reduced pressure, usually at atmospheric pressure (normal pressure) to 30 kg / cm 2 G. In addition, the liquid phase oxidation reaction may be carried out while stirring (the reactor may be equipped with a stirrer).

[0024] In the above step (a), the liquid-phase oxidation reaction may be carried out in a single reactor or may be carried out continuously in two or more reactors. The reactor may be, for example, a stirred tank type or a bubble column type.

[0025] ((b) Step: Esterification Step)

[0026] In step (b), the oxide (oxidation reaction product) is esterified to obtain a reaction solution containing a borate ester compound. While the borate ester compound is produced in step (b), unreacted aliphatic hydrocarbons, free alcohol, and metaboric acid are also present. The boiling point of the free alcohol is close to that of the unreacted saturated aliphatic hydrocarbons, making separation of the two difficult. Therefore, in the esterification step (b), the alcohol is orthoborated to convert it into a borate ester compound.

[0027] Specifically, in step (b), the free alcohol contained in the oxidation reaction product obtained in step (a) is esterified (orthoborated) to obtain a borate ester compound. In this step, the free alcohol present in the oxidation reaction product obtained in step (a) is reacted with metaboric acid to convert it into a borate ester compound. However, since residual metaboric acid is usually present in the oxidation reaction product, it is not necessary to newly add metaboric acid. However, it may be added in some cases.

[0028] The method for converting to a borate compound is not particularly limited, and it is preferred that the reaction solution containing the oxide obtained in step (a) be subjected to a decompression treatment. Thus, a borate compound can be obtained by esterification using free alcohol and excess metaboric acid (or newly added metaboric acid). The conditions for the esterification are not particularly limited. In one embodiment of the present invention, the pressure in step (b) is, for example, 50 to 200 hPa, preferably 90 to 170 hPa, etc. It should be noted that, in this specification, the pressure in the esterification process refers to the value of the pressure measured by a pressure gauge provided on the upper part of the reactor to measure the pressure of the gas phase. In this specification, the same definition applies to all. In one embodiment of the present invention, the temperature in step (b) is, for example, 100 to 220°C, preferably 160 to 180°C, etc. It should be noted that, in this specification, the temperature in the esterification process refers to the value of the temperature measured using a thermometer inserted into the liquid in the reactor. In this specification, the same definition applies to all. In one embodiment of the present invention, the treatment time in step (b) is, for example, 5 to 80 minutes, preferably 20 to 60 minutes, etc. In this specification, the processing time in the reaction refers to the residence time in the reactor. Here, the residence time generally refers to the time that a substance flowing into a limited space stays in the space. If the volume of the space is set to V (m 3 ), the volume flow rate of the inflowing material is set to θ(m 3 / hr), the residence time (τ) is expressed by the following formula.

[0029]

Mathematical formula 1

[0030] τ(hr)=V / θ

[0031] It should be noted that the above-mentioned steps (a) to (b) include the following reactions.

[0032]

Chemical Formula 1

[0033]

[0034] (Step (c): Recovery of Unreacted Saturated Aliphatic Hydrocarbons)

[0035] In step (c), the reaction liquid containing the borate ester compound is distilled to separate unreacted saturated aliphatic hydrocarbons and a distillation residue. Specifically, the reaction liquid containing the borate ester compound obtained in step (b) is distilled to separate unreacted saturated aliphatic hydrocarbons (distillate) and a distillation residue containing the borate ester compound (bottoms), and the unreacted saturated aliphatic hydrocarbons are recovered.

[0036] In one embodiment of the present invention, the distillation in c) is performed twice (in two stages). Distillation may be combined with condensation or the like. Figure 1 The schematic diagram of step (c) is shown. Figure 1 As shown, the reaction liquid 3 containing the borate ester compound obtained in the above step (b) is introduced into the distillation apparatus 1 for the first distillation. It should be noted that the distillation apparatus 1 may have a condenser, etc., not shown in the figure. In the first distillation, a distillate 5 and a residual liquid at the bottom of the tower can be obtained. The residual liquid at the bottom of the tower is introduced into the distillation apparatus 2 as a distillation residue 4 for the second distillation. It should be noted that the distillation apparatus 2 may have a condenser, etc., not shown in the figure. In the second distillation, a distillate 5 and a distillation residue 6 can be obtained. The distillation residue 6 is transported to the hydrolysis step of the step (d) described later.

[0037] In the present invention, in step (c), the temperature of the second distillation is higher than that of the first distillation, and the pressure of the second distillation is lower than that of the first distillation. As described above, secondary alcohols produced by conventional secondary alcohol production methods, and secondary alcohol alkoxylates produced using them as raw materials, are susceptible to coloration and contamination. Therefore, by setting the temperature of the second distillation higher than that of the first distillation and the pressure of the second distillation lower than that of the first distillation, the production of unsaturated aliphatic hydrocarbons can be significantly suppressed, significantly reducing the amount of unrecovered residual saturated aliphatic hydrocarbons. It should be noted that the present invention is not limited to performing further distillation after the above-mentioned second distillation.

[0038] In one embodiment of the present invention, the pressure conditions during the first distillation are, for example, 50 hPa or less, 45 hPa or less, less than 45 hPa, 30 hPa or less, less than 30 hPa, 25 hPa or less, 24 hPa or less, 21 hPa or less, or 20 hPa or less. In one embodiment of the present invention, the pressure conditions during the first distillation are, for example, greater than 7 hPa, 8 hPa or more, 10 hPa or more, 12 hPa or more, 13 hPa or more, 15 hPa or more, or 18 hPa or more. In this specification, the distillation pressure refers to the pressure value measured using a pressure gauge installed at the top of the column to measure the pressure of the gas phase. The same definition applies throughout this specification.

[0039] In one embodiment of the present invention, the distillation temperature in the first distillation is, for example, preferably greater than 130°C and less than 200°C, more preferably greater than 145°C and less than 180°C, even more preferably 155-175°C, and even more preferably 160-170°C. In this specification, the distillation temperature refers to the value measured by a thermometer inserted into the liquid at the bottom of the column. The same definition applies throughout this specification.

[0040] In one embodiment of the present invention, the residence time (distillation time) in the first distillation is preferably 10 to 125 minutes, more than 15 minutes and less than 120 minutes, 20 to 100 minutes, more than 30 minutes and less than 90 minutes, or more than 45 minutes and less than 75 minutes. In this specification, the distillation residence time related to the liquid at the bottom of the column refers to the amount of liquid (volume of liquid) (m 3 ) divided by the amount of liquid extracted from the bottom of the distillation tower (m 3 In this specification, the same definitions apply to all.

[0041] In one embodiment of the present invention, the residual liquid after the first distillation (in Figure 1 The ratio of unreacted saturated aliphatic hydrocarbons in the distillation residue 4) is more preferably 10% by mass or less, and further preferably 6% by mass or less. It should be noted that the lower limit is also not particularly limited, and is, for example, 0.1% by mass or more, or 1% by mass or more.

[0042] In one embodiment of the present invention, the pressure conditions during the second distillation are, for example, less than 20 hPa, 15 hPa or less, 13 hPa or less, 12 hPa or less, less than 12 hPa, 10 hPa or less, or 9 hPa or less. In one embodiment of the present invention, the pressure conditions during the second distillation are 1 hPa or more, 2 hPa or more, 2.5 hPa or more, 3 hPa or more, 3.5 hPa or more, 4 hPa or more, 4.5 hPa or more, or 5 hPa or more.

[0043] In one embodiment of the present invention, the distillation temperature in the second distillation is preferably, for example, less than 250°C, 240°C or less, 230°C or less, 220°C or less, less than 220°C, or 215°C or less. In one embodiment of the present invention, the distillation temperature in the second distillation is preferably, for example, 180°C or more, 185°C or more, 190°C or more, or 195°C or more.

[0044] In one embodiment of the present invention, the residence time (distillation time) in the second distillation is preferably 80 minutes or less, less than 80 minutes, 75 minutes or less, 60 minutes or less, less than 60 minutes, 45 minutes or less, or 35 minutes or less. In one embodiment of the present invention, the residence time (distillation time) in the second distillation is preferably 1 minute or more, 3 minutes or more, 5 minutes or more, 10 minutes or more, 15 minutes or more, more than 15 minutes, or 20 minutes or more.

[0045] In the second distillation, the decomposition of the boric acid ester is suppressed by performing the distillation at a high temperature, low pressure, and short time as much as possible. In particular, performing the distillation at a high temperature as much as possible has the effect of suppressing the production of unsaturated aliphatic hydrocarbons.

[0046] In one embodiment of the present invention, the ratio of the temperature in the second distillation to the temperature in the first distillation is preferably greater than 1 and 1.5 or less, more preferably 1.1 to 1.4, and even more preferably 1.1 to 1.3. This allows the desired effects of the present invention to be efficiently exhibited.

[0047] In one embodiment of the present invention, the ratio of the distillation pressure in the first distillation to the distillation pressure in the second distillation is greater than 1 and is 30 or less, 1.1 to 7, 1.2 to 4.5, 1.5 to 3.5, or 2.0 to 3.2. This allows the desired effects of the present invention to be efficiently exhibited.

[0048] In one embodiment of the present invention, the ratio of the residence time in the first distillation to the residence time in the second distillation is 1 to 90, 1.1 to 25, 1.2 to 12, 1.3 to 8, 1.4 to 5, or 1.5 to 4. The desired effects of the present invention can be efficiently exhibited.

[0049] In one embodiment of the present invention, as the methods for the first distillation and the second distillation, known methods such as simple distillation (eg, flash distillation) and molecular distillation may be used independently, but are not particularly limited thereto.

[0050] In one embodiment of the present invention, the simple distillation apparatus is composed of an evaporation tank, a condenser, a distillate receiver, a liquid feeding pump, and the like.

[0051] In one embodiment of the present invention, the first distillation is performed by simple distillation (eg, flash distillation), and the second distillation is also performed by simple distillation (eg, flash distillation).

[0052] In one embodiment of the present invention, the first distillation is performed by simple distillation (eg, flash distillation), and the second distillation is performed by molecular distillation.

[0053] In one embodiment of the present invention, the distillation residue (i.e., the second distillation residue ( Figure 1 The iodine value of the distillation residue (6) or the distillation residue in the case of further distillation) is lower than 6.4. Such an embodiment, that is, the iodine value is lower than 6.4, means that the unsaturated aliphatic hydrocarbons in the distillation residue are significantly less. Therefore, high-quality secondary alcohols with little or no coloration and pollution can be obtained, and high-quality secondary alcohol alkoxylates produced using the same as raw materials can be obtained. In one embodiment of the present invention, the iodine value of the above-mentioned distillation residue is 6.3 or less, 6.2 or less, 6.1 or less, 6.0 or less, 5.9 or less, or 5.8 or less. With this embodiment, the above-mentioned technical effects become more significant. In one embodiment of the present invention, the iodine value of the above-mentioned distillation residue is actually greater than 2.0 or greater than 4.0. Here, the iodine value is measured by the Wigers method (JIS K 0070 1992). This method is also used for measurement in the examples.

[0054] In one embodiment of the present invention, the distillation residue (i.e., the second distillation residue ( Figure 1 The content of unreacted saturated aliphatic hydrocarbons in the distillation residue (6) or, if further distillation is performed, the distillation residue (d) is less than 1.3% by mass. By setting the content of unreacted saturated aliphatic hydrocarbons to less than 1.3% by mass in this embodiment, contamination is reduced and the yield of the target product is improved. Furthermore, by setting the content of unreacted saturated aliphatic hydrocarbons to less than 1.3% by mass and sending the distillation residue to the hydrolysis step (d), the load in the subsequent purification step is reduced, resulting in the technical effect of obtaining high-quality secondary alcohols. In one embodiment of the present invention, the content of unreacted saturated aliphatic hydrocarbons in the distillation residue is 1.2% by mass or less, 1.1% by mass or less, 1.0% by mass or less, 0.9% by mass or less, 0.8% by mass or less, 0.7% by mass or less, 0.6% by mass or less, 0.5% by mass or less, 0.4% by mass or less, or 0.3% by mass or less. This embodiment further enhances the above-mentioned technical effects. In one embodiment of the present invention, the content of unreacted saturated aliphatic hydrocarbons in the distillation residue is substantially 0.01% by mass or greater, or 0.1% by mass or greater. The content of unreacted saturated aliphatic hydrocarbons in the distillation residue is essentially the ratio of the unreacted saturated aliphatic hydrocarbon content to the content of the distillation residue after the second distillation. When three or more distillations are performed, it may be the ratio of the unreacted saturated aliphatic hydrocarbon content to the content of the distillation residue after the final distillation. The content of unreacted saturated aliphatic hydrocarbons in the distillation residue is measured by gas chromatography. This method is also used in the Examples.

[0055] It should be noted that the unreacted saturated aliphatic hydrocarbons recovered in this step can be reused (circulated) in the oxidation reaction step (a). In this case, for example, after removing the saturated aliphatic hydrocarbons from the distillate, the unreacted saturated aliphatic hydrocarbons can be directly reused in the oxidation reaction step (a); after hydrogenating the carbonyl compounds and olefins contained in the saturated aliphatic hydrocarbons recovered in this step, the unreacted saturated aliphatic hydrocarbons can be reused in the oxidation reaction step (a); or, as described in Japanese Patent Application Laid-Open No. 56-131531, the unreacted saturated aliphatic hydrocarbons recovered in this step can be contacted with an alkaline aqueous solution to separate into an organic layer containing fatty acids and fatty acid esters and an aqueous layer, and the organic layer can be washed with hot water as needed (alkali treatment step), the unreacted saturated aliphatic hydrocarbons contained in the organic layer can be hydrogenated (hydrogenation step), and the alcohol components contained in the unreacted saturated aliphatic hydrocarbons can be orthoborated (esterification step) before being reused in the oxidation reaction step (a). However, the present invention is not limited to the above.

[0056] (Step (d): Hydrolysis Step)

[0057] In this step, the distillation residue is hydrolyzed and separated into orthoboric acid and an organic layer.

[0058] Specifically, hot water is added to the distillation residue to hydrolyze it and separate it into an aqueous layer containing orthoboric acid and an organic layer. Here, the temperature (liquid temperature) of the hot water is 70 to 150°C, preferably 90 to 100°C, etc., but not limited to this. In addition, the amount of hot water added is 1 to 20 times the mass of the distillation residue, preferably 2 to 10 times the mass of the distillation residue, etc., but not limited to this. The hydrolysis time is 5 to 60 minutes, preferably 20 to 30 minutes, etc., but not limited to this. Under such conditions, the distillation residue can be fully hydrolyzed, and the aqueous layer containing orthoboric acid and the organic layer can be separated more efficiently.

[0059] (Step (e): Saponification Step)

[0060] In this step, the organic layer separated in the above step (d) is saponified with an alkali to separate into an alkaline aqueous solution layer and a crude alcohol layer (saponification step). This can remove organic acids and organic acid esters.

[0061] Here, as the alkali, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc. can be used, but are not limited to these. In addition, after the above-mentioned saponification treatment with alkali, water washing can be performed if necessary. The saponification conditions are not particularly limited, and the same conditions as in the past can be applied. For example, the saponification temperature is 120-160°C, preferably 135-145°C, etc., but are not limited to these. The saponification time is 30-120 minutes, preferably 50-90 minutes, etc., but are not limited to these. Under these conditions, the saponification treatment can be carried out more efficiently.

[0062] (Step (f): Alcohol Purification Step)

[0063] In this step, the crude alcohol layer separated in the above step (e) is purified to obtain the target secondary alcohol.

[0064] Here, the purification method is not particularly limited, and known methods can be used in the same manner or with appropriate modifications. For example, purification can be performed by distilling or fractionating the crude alcohol layer. The purification pressure in this case is 1 to 45 hPa, preferably 4 to 12 hPa, but is not limited thereto. Under these conditions, appropriate separation can be achieved based on boiling point range (for example, into a fraction with a boiling point range of 95°C to below 120°C and a fraction with a boiling point range of 120 to 150°C). In this case, the fraction with a boiling point range of 95°C to below 120°C generally contains small amounts of saturated aliphatic hydrocarbons, carbonyl compounds, and monohydric primary alcohols (monohydric alcohols). Meanwhile, the fraction with a boiling point range of 120 to 150°C contains trace amounts of carbonyl compounds and secondary alcohols (monohydric alcohols). In this case, the majority of the secondary alcohols are the desired monohydric secondary alcohols.

[0065] It should be noted that between the above-mentioned step (e) and the step (f), at least one step selected from a heavy component separation step, an alkali treatment step (particularly a potassium hydroxide treatment step), and a light component separation step can be carried out according to a conventionally known method.

[0066] [Example]

[0067] The present invention will be described in more detail below with reference to Examples and Comparative Examples. However, the present invention is not limited to these Examples and Comparative Examples, and examples obtained by appropriately combining the technical means disclosed in the Examples are also within the scope of the present invention.

[0068] (Examples 1 to 19, Comparative Examples 1 and 2)

[0069] 1000 g of a mixture of saturated aliphatic hydrocarbons having 12 to 14 carbon atoms and 25 g of metaboric acid were added to a 3 L cylindrical reactor, and a mixed gas having an oxygen concentration of 3.5 vol% and a nitrogen concentration of 96.5 vol% was blown into the reactor at a rate of 430 L per hour. An oxidation reaction was carried out at 170° C. under normal pressure for 2 hours to obtain a reaction solution containing an oxide (oxidation reaction step). It should be noted that the average molecular weight of the mixture of saturated aliphatic hydrocarbons is 184, and the mixture contains saturated aliphatic hydrocarbons having 12 to 14 carbon atoms (n-dodecane, n-tridecane, and n-tetradecane) at a ratio exceeding 95% by mass relative to the total mass of the mixture.

[0070] After the oxidation reaction, the reaction solution containing the oxide is decompressed and esterified with alcohol and excess boric acid to obtain a borate ester compound. This esterification is carried out at 105 hPa, 165° C., and 60 minutes (esterification step).

[0071] (First paragraph (first time))

[0072] Next, if Figure 1 As shown in FIG. 1 , this liquid (reaction liquid containing a borate ester compound) was introduced into distillation apparatus 1 (simple distillation column) as reaction liquid 3 containing a borate ester compound, and a first distillation was performed at the temperature, pressure, and residence time shown in the table below. Most of the saturated aliphatic hydrocarbons contained in reaction liquid 3 containing a borate ester compound introduced into distillation apparatus 1 (simple distillation column) were distilled from the top of the column as distillate 5 (recovery step of unreacted saturated aliphatic hydrocarbons). The residual saturated aliphatic hydrocarbon concentration in the bottom fraction was approximately 5% by mass.

[0073] (Later part (second time))

[0074] Next, this bottom fraction was introduced as distillation residue 4 into distillation apparatus 2 (simple distillation column) and subjected to a second distillation at the temperature, pressure, and residence time shown in the table below. Approximately 90% by mass of the saturated aliphatic hydrocarbons contained in distillation residue 4 introduced into distillation apparatus 2 (simple distillation column) were distilled overhead as distillate 5 (unreacted saturated aliphatic hydrocarbon recovery step). The saturated aliphatic hydrocarbon concentration of distillation residue 6, the bottom fraction, was measured, and the results are shown in the table below.

[0075]

Table 1

[0076]

[0077] (Example 20)

[0078] The same operation as in Example 1 was carried out except that the distillation apparatus 2 (simple distillation column) was replaced with the distillation apparatus 2 (molecular distillation column) and the temperature, pressure and residence time were changed as shown in the following table.

[0079]

Table 2

[0080]

[0081] Example

[0082] As shown in Tables 1 and 2, by continuously performing the distillation twice under the conditions where the second (latter) distillation temperature is higher than the first (first) distillation temperature and the second distillation pressure is lower than the first distillation pressure, a high-quality distillation residue with a low concentration of residual saturated aliphatic hydrocarbons and a low iodine value is obtained. This ultimately allows for the production of high-quality secondary alcohols.

[0083] <Steps (d) to (f)>

[0084] The distillation residue obtained in Example 1 was hydrolyzed with a large amount (twice the mass of the residual liquid (distillation residue)) of 95°C hot water for 25 minutes, separating it into an aqueous layer containing orthoboric acid and an organic layer (hydrolysis step). The resulting organic layer was saponified with sodium hydroxide at 140°C for 80 minutes and then washed with water to remove organic acids and organic acid esters (saponification step). The organic layer was fractionally distilled at 7 hPa to obtain a first fraction with a boiling point range of 95-120°C and a second fraction with a boiling point range of 120-150°C. The first fraction (the fraction with a boiling point range of 95°C to below 120°C) was a mixture of small amounts of saturated aliphatic hydrocarbons, carbonyl compounds, and monohydric primary alcohols (monohydric alcohols). The second fraction (the fraction with a boiling point range of 120-150°C) was a mixture of trace amounts of carbonyl compounds and secondary alcohols (monohydric alcohols), with the majority of the secondary alcohols being monohydric alcohols. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] 1: First distillation unit,

[0087] 2: Second distillation unit,

[0088] 3: Reaction solution containing borate compound,

[0089] 4: Distillation residue,

[0090] 5: Distillate,

[0091] 6: Distillation residue.

[0092] Hereinafter, aspects of the present invention will be summarized.

[0093] 1. A method for producing a secondary alcohol, comprising the following steps:

[0094] a) supplying metaboric acid, a saturated aliphatic hydrocarbon, and a molecular oxygen-containing gas to a reactor, and subjecting the saturated aliphatic hydrocarbon to liquid-phase oxidation with the molecular oxygen-containing gas in the presence of metaboric acid to obtain a reaction solution containing an oxide;

[0095] b) esterifying the oxide to obtain a reaction solution containing a borate compound;

[0096] c) distilling the reaction solution containing the borate ester compound to separate it into unreacted saturated aliphatic hydrocarbons and a distillation residue;

[0097] d) hydrolyzing the distillation residue to separate it into orthoboric acid and an organic layer;

[0098] e) saponifying the organic layer with alkali and separating it into an alkaline aqueous solution layer and a crude alcohol layer; and

[0099] f) purifying the crude alcohol layer to obtain a secondary alcohol,

[0100] In the step c), the distillation is performed in two stages, under the conditions that the temperature of the second distillation is higher than the temperature of the first distillation and the pressure of the second distillation is lower than the pressure of the first distillation.

[0101] 2. The method according to item 1, wherein the temperature of the first distillation is higher than 130°C and lower than 200°C.

[0102] 3. The method according to 1 or 2, wherein the pressure of the first distillation is lower than 45 hPa.

[0103] 4. The method according to any one of 1 to 3, wherein the residence time of the first distillation is more than 15 minutes and less than 120 minutes.

[0104] 5. The method according to any one of 1 to 4, wherein the pressure of the second distillation is lower than 20 hPa.

[0105] 6. The method according to any one of 1 to 5, wherein the residence time of the second distillation is less than 80 minutes.

[0106] 7. The method according to any one of 1 to 6, wherein the temperature of the second distillation is lower than 250°C.

[0107] 8. The method according to any one of 1 to 7, wherein the iodine value of the distillation residue is lower than 6.4.

[0108] 9. The method according to any one of 1 to 8, wherein the content of unreacted saturated aliphatic hydrocarbons in the distillation residue is less than 1.3% by mass.

[0109] 10. The method according to any one of 1 to 9, wherein in the step c), the first distillation and the second distillation are each independently simple distillation or molecular distillation.

Claims

1. A method for producing a secondary alcohol, comprising the following steps: a) supplying metaboric acid, a saturated aliphatic hydrocarbon, and a molecular oxygen-containing gas to a reactor, and subjecting the saturated aliphatic hydrocarbon to liquid-phase oxidation with the molecular oxygen-containing gas in the presence of metaboric acid to obtain a reaction liquid containing an oxide; b) esterifying the oxide to obtain a reaction solution containing a borate ester compound; c) distilling the reaction solution containing the borate ester compound to separate it into unreacted saturated aliphatic hydrocarbons and a distillation residue; d) hydrolyzing the distillation residue to separate it into orthoboric acid and an organic layer; e) saponifying the organic layer with alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer; as well as f) purifying the crude alcohol layer to obtain a secondary alcohol, In the step c), the distillation is carried out in two stages, with the temperature of the second distillation being higher than the temperature of the first distillation and the pressure of the second distillation being lower than the pressure of the first distillation. The temperature of the first distillation is higher than 130°C and lower than 200°C, The pressure of the first distillation is lower than 45hPa, The residence time of the first distillation is more than 15 minutes and less than 120 minutes, The pressure of the second distillation is lower than 20hPa, The residence time of the second distillation is less than 80 minutes, The temperature of the second distillation is lower than 250°C.

2. The method according to claim 1, wherein The pressure of the first distillation exceeded 7 hPa.

3. The method according to claim 1, wherein The pressure of the second distillation is above 1 hPa.

4. The method according to claim 1, wherein The residence time of the second distillation is more than 1 minute.

5. The method according to claim 1, wherein The temperature of the second distillation is above 180°C.

6. The method according to claim 1, wherein The pressure of the first distillation exceeds 7 hPa, the pressure of the second distillation is 1 hPa or more, the residence time of the second distillation is 1 minute or more, and the temperature of the second distillation is 180° C. or more.

7. The method according to claim 1, wherein The iodine value of the distillation residue is lower than 6.

4.

8. The method according to claim 1, wherein The content of unreacted saturated aliphatic hydrocarbons in the distillation residue is less than 1.3% by mass.

9. The method according to claim 1, wherein In the step c), the first distillation and the second distillation are each independently simple distillation or molecular distillation.

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