Process for producing metaboric acid and process for producing secondary alcohol using the metaboric acid and process for producing secondary alcohol

Abstract

The present invention provides a method for stably producing metaboric acid. In addition, the present invention provides a method for producing a secondary alcohol with good production efficiency by providing a continuous method for establishing a reaction with good reactivity. In addition, the present invention provides a reactor for producing metaboric acid. The method for producing metaboric acid includes i) dehydrating orthoboric acid with a dehydrator in the presence of a saturated aliphatic hydrocarbon to obtain a mixture containing metaboric acid, a saturated aliphatic hydrocarbon, and water; ii) separating the saturated aliphatic hydrocarbon and water after distilling the saturated aliphatic hydrocarbon and water from the mixture; and iii) returning the saturated aliphatic hydrocarbon separated in the process ii) to the process i) so that the content of alcohol components in the saturated aliphatic hydrocarbon is less than 2 mass% in the process i). The method for producing a secondary alcohol uses metaboric acid produced by the method for producing metaboric acid, and the reactor includes two or more reactors capable of being switched to batch and continuous modes.

Description

Technical Field

[0001] This invention relates to a method for manufacturing metaboric acid, a method for manufacturing a secondary alcohol using metaboric acid, and a method for manufacturing a secondary alcohol. Background Technology

[0002] (1) Higher secondary alcohol ethoxylates are widely used as nonionic surfactants due to their low pour point and ease of handling. These secondary alcohol ethoxylates are produced by adding epoxides to secondary alcohols as starting materials. The secondary alcohols are obtained by boric acid oxidation, which involves oxidizing saturated aliphatic hydrocarbons in the presence of metaboric acid, esterifying the free alcohol in the oxidation product with orthoboric acid, recovering unreacted saturated aliphatic hydrocarbons by distillation, hydrolyzing the distillation residue, saponifying the resulting organic layer with alkali, and purifying the crude alcohol layer (e.g., Japanese Patent Application Publication No. 56-131531).

[0003] (2) Secondary alcohols are useful as raw materials for the synthesis of detergents, surfactants and plasticizers. Regarding secondary alcohols, the following techniques are known: after an oxidation reaction in which a reaction gas containing molecular oxygen is introduced into a saturated aliphatic hydrocarbon in the presence of metaboric acid, a borate ester compound is obtained, and then, through a hydrolysis process and a saponification process, a secondary alcohol can be obtained (for example, Japanese Patent Application Publication No. 56-131531). Summary of the Invention

[0004] (1) A technology is required to stably manufacture metaboric acid used as a raw material in the above-mentioned boric acid oxidation process.

[0005] Therefore, the first aspect of the present invention was made in view of the above circumstances, and its object is to provide a method capable of stably manufacturing metaboric acid.

[0006] The inventors conducted in-depth research to solve the aforementioned problems. Their findings revealed that by controlling the amount of alcohol contained in the saturated aliphatic hydrocarbons during the dehydration of orthoboric acid in the presence of saturated aliphatic hydrocarbons, the aforementioned problems could be solved, thus completing this invention.

[0007] That is, the above objective can be achieved by a method for manufacturing metaboric acid, the method comprising: i) dehydrating orthoboric acid in the presence of saturated aliphatic hydrocarbons using a dehydrator to obtain a mixture containing metaboric acid, saturated aliphatic hydrocarbons and water; ii) separating the saturated aliphatic hydrocarbons and water by distilling them away from the mixture; iii) returning the saturated aliphatic hydrocarbons separated in step ii) to step i), wherein in step i), the alcohol content in the saturated aliphatic hydrocarbons is less than 2% by mass.

[0008] According to the first aspect of the present invention, metaboric acid can be stably manufactured.

[0009] (2) In addition, Japanese Patent Application Publication No. 56-131531 discloses a technology for performing an oxidation reaction process in an intermittent manner, but in order to increase production, it is desirable to perform the oxidation reaction process in a continuous manner.

[0010] However, it has been established that in previous technologies, even when attempting to connect multiple reactors to achieve a continuous operation, poor reactivity led to reduced production.

[0011] Therefore, the objective of the second aspect of the present invention is to provide a method for producing secondary alcohols with good production efficiency by providing a continuous production method with good reactivity, i.e. good production efficiency.

[0012] One embodiment for solving the above-mentioned problem is a method for producing a secondary alcohol, comprising: a) supplying metaboric acid, saturated aliphatic hydrocarbons, and a reaction gas containing molecular oxygen to a reactor, and, in the presence of metaboric acid, liquid-phase oxidizing the saturated aliphatic hydrocarbons with the reaction gas containing molecular oxygen to obtain a reaction liquid containing oxides; b) esterifying the oxides to obtain a reaction liquid containing borate ester compounds; c) distilling the reaction liquid containing borate ester compounds to separate unreacted saturated aliphatic hydrocarbons and distillation residue; d) hydrolyzing the distillation residue to separate orthoboric acid and an organic layer; e) saponifying the organic layer with an alkali. f) The crude alcohol layer is separated into an alkaline aqueous solution layer and a crude alcohol layer; f) The crude alcohol layer is purified to obtain a secondary alcohol. The reactor includes two or more reactors that can be switched between batch and continuous operation. The method for producing the secondary alcohol also includes the following steps: adding saturated aliphatic hydrocarbons to each of the two or more reactors, adding metaboric acid to the upstream reactor of the two or more reactors, starting to obtain the oxide in the upstream reactor in a batch manner, monitoring the oxygen concentration difference at the inlet and outlet of the upstream reactor, and switching to continuous operation if the oxygen concentration difference reaches 0.5% by volume or more.

[0013] According to a second aspect of the present invention, by providing a continuous production method with good reactivity, i.e. good production efficiency, a method for producing secondary alcohols with good production efficiency can be provided. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the reactor used in Embodiment 1 of the present invention.

[0015] Figure 2 This is a schematic diagram illustrating the manufacturing process of the first secondary alcohol of the present invention.

[0016] Figure 3 This is a schematic diagram illustrating a preferred embodiment of the first oxidation reaction step (a-1) of the present invention.

[0017] Figure 4 This is a schematic diagram illustrating step 2(a) of the present invention.

[0018] Figure 5 This is a schematic diagram of the reactor used in Embodiment 1 of the present invention. Detailed Implementation

[0019] The following describes an embodiment of the first aspect of the present invention. It should be noted that, hereinafter, "the first aspect of the present invention" is sometimes simply referred to as "the present invention." The present invention is not limited to the following embodiments.

[0020] In this specification, the range “X~Y” includes both X and Y, meaning “above X and below Y”. Furthermore, unless otherwise specified, the operation and physical properties are measured at room temperature (20~25°C) and relative humidity 40~50%RH.

[0021] <Method for manufacturing metaboric acid>

[0022] One aspect of the present invention is a method for manufacturing metaboric acid (first aspect), comprising: i) dehydrating orthoboric acid in the presence of saturated aliphatic hydrocarbons using a dehydrator to obtain a mixture comprising metaboric acid, saturated aliphatic hydrocarbons and water (step (i)); ii) distilling off a portion of the saturated aliphatic hydrocarbons and water from the mixture, and separating the saturated aliphatic hydrocarbons and water (step (ii)); and iii) returning the saturated aliphatic hydrocarbons separated in step ii) to step i) (step (iii) wherein, in step i), the alcohol content in the saturated aliphatic hydrocarbons is less than 2% by mass.

[0023] As a method for producing secondary alcohols, the following steps are performed: a) In the presence of metaboric acid, saturated aliphatic hydrocarbons are oxidized in the liquid phase with a gas containing molecular oxygen to obtain a reaction solution containing oxides (step (a-1)); the oxides are esterified to obtain a reaction solution containing borate ester compounds (step (a-2)) (steps (a-1) and (a-2) are also referred to as "step (a)"); b) The reaction solution containing borate ester compounds is distilled to separate unreacted saturated aliphatic hydrocarbons and distillation residue (step (b)); c) The distillation residue is hydrolyzed to separate an aqueous layer containing orthoboric acid and an organic layer (step (c)); d) The organic layer is saponified with alkali to separate an alkaline aqueous solution layer and a crude alcohol layer (step (d)); e) The crude alcohol layer is purified (step (e)). In the above method, unreacted saturated hydrocarbons can be recovered from several steps (e.g., step b above), and it is technologically useful to reuse these unreacted saturated hydrocarbons within the reaction system (e.g., Japanese Patent Application Publication No. 56-131531). Therefore, when producing metaboric acid by dehydrating orthoboric acid in the presence of saturated aliphatic hydrocarbons using a dehydrator, attempts were made to reuse the unreacted saturated aliphatic hydrocarbons recovered during the production of secondary alcohols as described above (recovered saturated aliphatic hydrocarbons). However, if the recovered unreacted saturated aliphatic hydrocarbons are used directly in the reaction, deposits form on the inner wall and piping, resulting in reduced production efficiency, equipment malfunctions, and an inability to stably produce metaboric acid. The inventors have conducted in-depth research on a stable metaboric acid production process using various methods. The results suggest that the unreacted saturated aliphatic hydrocarbons recovered during the secondary alcohol production process (e.g., after oxidation) form borate ester compounds that contribute to the deposits. Therefore, an in-depth study was conducted on the alcohol content of the saturated aliphatic hydrocarbons used in the production of metaboric acid. The results showed that by controlling the alcohol content of the saturated aliphatic hydrocarbons used in the dehydration reaction of orthoboric acid to less than 2% by mass, the formation of borate ester compounds, which are the cause of deposits, can be suppressed and prevented. According to the above method, since deposits do not adhere to the inner walls of the reactor and piping during the dehydration reaction, the increase in stirring power and the blockage of the piping can be effectively prevented. Therefore, metaboric acid can be stably produced according to the above method. In contrast, when unreacted hydrocarbons recovered using the method described in Japanese Patent Application Publication No. 56-131531 are recycled to the above dehydration reaction, deposits adhere to the inner walls of the reactor and piping, potentially causing an increase in stirring power and blockage of the piping. It is presumed that this is because the recovered unreacted saturated aliphatic hydrocarbons contain alcohols formed by the substitution of at least one hydrogen atom of the saturated aliphatic hydrocarbon with a hydroxyl group at a proportion of 2% or more by mass. Therefore, these alcohols react with orthoboric acid in the dehydration process to form borate ester compounds, which are the cause of deposits.It should be noted that the mechanism of action of the above-mentioned effects based on the structure of the present invention is presumptive, and the present invention is not limited to the above presumption.

[0024] The following describes each step of the first aspect.

[0025] (Process (i))

[0026] In this process, saturated aliphatic hydrocarbons (hereinafter referred to as "hydrocarbons") and orthoboric acid are added to a dehydrator to prepare a slurry, and the orthoboric acid is dehydrated in the presence of the saturated aliphatic hydrocarbons. This produces metaboric acid, yielding a mixture (slurry) containing metaboric acid, saturated aliphatic hydrocarbons, water, and, depending on the circumstances, unreacted orthoboric acid.

[0027] In this process, the alcohol content in the saturated aliphatic hydrocarbons (raw material saturated aliphatic hydrocarbons) is less than 2% by mass. If the alcohol content in the raw material saturated aliphatic hydrocarbons is 2% by mass or more, borate ester compounds will be generated during the dehydration reaction of orthoboric acid, inducing the formation of deposits on the inner wall of the reactor and the inner wall of the piping, making it impossible to stably produce metaboric acid. From the viewpoint of more stably producing metaboric acid, the alcohol content in the saturated aliphatic hydrocarbons is preferably 1.5% by mass or less, and particularly preferably less than 1% by mass (lower limit: 0% by mass or less than the detection limit). That is, in the preferred embodiment of the present invention, in the above-described i) process, the alcohol content in the saturated aliphatic hydrocarbons is 1.5% by mass or less. In a more preferred embodiment of the present invention, in the above-described i) process, the alcohol content in the saturated aliphatic hydrocarbons is less than 1% by mass. In this specification, the alcohol content in the saturated aliphatic hydrocarbons is a value determined by gas chromatography. It should be noted that the aforementioned "alcohol component" refers to alcohols (mixtures) formed by replacing hydrogen atoms of saturated aliphatic hydrocarbons with 6 to 30 carbon atoms with hydroxyl groups. Furthermore, the aforementioned "alcohol component" preferably refers to a mixture containing alcohols with 8 to 20 carbon atoms as the main component, more preferably a mixture containing alcohols with 10 to 15 carbon atoms as the main component, and particularly preferably a mixture containing alcohols with 12 to 14 carbon atoms as the main component.

[0028] Here, the saturated aliphatic hydrocarbons are mixtures of saturated aliphatic hydrocarbons (n-alkanes) with 8 to 30 carbon atoms. Preferably, the saturated aliphatic hydrocarbons are mixtures containing saturated aliphatic hydrocarbons (n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, and n-pentadecane) with 10 to 15 carbon atoms as the main component, more preferably mixtures containing saturated aliphatic hydrocarbons (n-dodecane, n-tridecane, and n-tetradecane) with 12 to 14 carbon atoms as the main component. Here, "containing saturated aliphatic hydrocarbons as the main component" means containing saturated aliphatic hydrocarbons with a specified number of carbon atoms in a proportion of more than 90% by mass (preferably more than 95% by mass) (upper limit: 100% by mass) relative to all saturated aliphatic hydrocarbons. Furthermore, the average molecular weight of the saturated aliphatic hydrocarbons is 114 or more and 422 or less, preferably 142 or more and 212 or less, more preferably 170 or more and 198 or less. The saturated aliphatic hydrocarbons can be synthetic or commercially available. Similarly, orthoboric acid can also be synthetic or commercially available.

[0029] In this invention, the mixing ratio of saturated aliphatic hydrocarbons to orthoboric acid is not particularly limited, and the same mixing ratio as in the past can be used. Specifically, the mixing ratio of saturated aliphatic hydrocarbons to orthoboric acid (mass ratio of saturated aliphatic hydrocarbons to orthoboric acid) is 0.5 to 5:1, preferably more than 1:1 and less than 3:1. In addition, the amount of orthoboric acid added in the mixture (slurry) is 15 to 90% by mass, preferably more than 25% by mass and less than 45% by mass, but is not limited thereto.

[0030] In this invention, the dehydration conditions for orthoboric acid in the presence of saturated aliphatic hydrocarbons are not particularly limited, and the same conditions as before can be applied. For example, the dehydration temperature is 100°C or higher and lower than 200°C, preferably 130°C or higher and lower than 180°C. The dehydration time is the time required for substantially all orthoboric acid to be converted to metaboric acid, and can be appropriately selected according to other conditions (e.g., the amount of orthoboric acid added, the mixing ratio of saturated aliphatic hydrocarbons to orthoboric acid, the dehydration temperature, etc.). The dehydration time is, for example, 3 to 7 hours, preferably 4 to 6 hours. If the dehydration time is within the above range, dehydration can be carried out appropriately, and metaboric acid can be produced efficiently. Alternatively, the amount of metaboric acid generated in the reactor can be measured periodically to determine whether substantially all orthoboric acid has been converted to metaboric acid, and the dehydration reaction can be ended when the desired amount of metaboric acid is generated. Here, "substantially all orthoboric acid is converted to metaboric acid" means that more than 0.9 moles (preferably more than 0.95 moles) (upper limit: 1 mole) of metaboric acid are converted relative to 1 mole of orthoboric acid added. The amount of metaboric acid in the mixture can be determined by known methods. In this specification, the amount of metaboric acid is expressed as a value determined by X-ray crystal structure analysis.

[0031] The dehydration reaction described above can be carried out under atmospheric pressure, pressurized conditions, or reduced pressure, but is typically carried out under atmospheric pressure. Furthermore, the dehydration reaction can be carried out while stirring (the reactor can be equipped with a stirrer). Here, the stirring speed during the dehydration reaction is not particularly limited, for example, it is 20–100 rpm, preferably 30–60 rpm. With such a stirring speed, the raw materials (saturated aliphatic hydrocarbons and orthoboric acid) can be uniformly mixed (allowing for a homogeneous dehydration reaction).

[0032] The dehydrator (a reactor for carrying out the dehydration reaction) can be made of any material. Specifically, examples include iron, copper, stainless steel (SUS), nickel alloys (e.g., Hastelloy), ferrochrome nickel alloys, titanium, and titanium dioxide. Among these, stainless steel (SUS), nickel alloys (e.g., Hastelloy), and titanium dioxide are preferred, and stainless steel (SUS) and nickel alloys (e.g., Hastelloy) are more preferred. As detailed below, orthoboric acid separated after the hydrolysis step in the manufacture of secondary alcohols can be reused in this step. In this case, the orthoboric acid contains organic matter (organic acids, organic acid salts, organic acid esters, etc., such as fatty acids, fatty acid esters, sodium fatty acids, potassium fatty acids, etc.), but this organic matter evaporates during the dehydration reaction, sometimes leading to corrosion of the dehydrator. Therefore, at least the gas phase of the reactor is preferably formed of a nickel alloy, particularly Hastelloy, which has excellent heat resistance, pressure resistance, and corrosion resistance. That is, in a preferred embodiment of the invention, at least the gas phase of the dehydrator is formed of a nickel alloy. In a more preferred embodiment of the invention, at least the gas phase of the dehydrator is formed of Hastelloy. Furthermore, in a preferred embodiment of the present invention, the dehydrator is entirely formed of a nickel alloy (more preferably Hastelloy). Examples of Hastelloy include Hastelloy C-22 (composition: Ni 57.0 wt%, Cr 20.5 wt%, Mo 14.2 wt%, Fe 2.3 wt%, W 3.2 wt%, V 0.25 wt%, C 0.01 wt%) and Hastelloy C-276 (composition: Ni 57.0 wt%, Cr 15.5 wt%, Mo 16.0 wt%, Fe 6.0 wt%, W 4.0 wt%, V 0.3 wt%, C 0.01 wt%). Additionally, the "vapor phase section of the dehydrator" refers to the portion of the dehydrator that comes into contact with the vapor of at least one of saturated aliphatic hydrocarbons, orthoboric acid, water, and metaboric acid. Specifically, the gas phase section of the dehydrator is the portion extending from the top of the dehydrator to a point preferably 60% of the total height of the dehydrator (more preferably 30% or more and 60% or less, particularly preferably 40% or more and 50% or less). That is, in a preferred embodiment of the invention, the portion extending from the top of the dehydrator to 60% of the total height of the dehydrator (more preferably 30% or more and 60% or less, particularly preferably 40% or more and 50% or less) is formed of a nickel alloy. Furthermore, the invention also provides a reactor for metaboric acid production, wherein the portion extending from the top of the aforementioned reactor to 60% of the total height of the aforementioned reactor (preferably 30% or more and 60% or less, more preferably 40% or more and 50% or less) is formed of a nickel alloy. In addition, "the dehydrator is formed of material A" includes not only the dehydrator being formed of material A, but also the dehydrator being formed of material B with its inner surface covered by material A.That is, for example, "at least the vapor phase of the dehydrator is formed of nickel alloy" means that the entire dehydrator is formed of nickel alloy; the inner wall of the vapor phase of the dehydrator formed of other materials (e.g., stainless steel) is coated with nickel alloy by means of spraying or lining; the entire inner wall of the dehydrator formed of other materials (e.g., stainless steel) is coated with nickel alloy by means of spraying or lining.

[0033] In this process, orthoboric acid undergoes intramolecular dehydration in the presence of saturated aliphatic hydrocarbons through the following reaction, converting it into metaboric acid. Metaboric acid exists in α- and β-forms depending on its crystal structure; from the viewpoint of thermal stability (anti-coloring effect), β-form metaboric acid is preferred. Such β-form metaboric acid can be manufactured using the method described in Japanese Patent Publication No. 48-37242 and the preferred dehydration conditions described above.

[0034]

Chemical Formula 1

[0035]

[0036] (Process (ii))

[0037] In this process, after distilling off saturated aliphatic hydrocarbons and water from the dehydration reactants obtained in the above process (i), the saturated aliphatic hydrocarbons and water are separated.

[0038] In the dehydration step of step (i) above, saturated aliphatic hydrocarbons and water evaporate (producing a mixed steam of saturated aliphatic hydrocarbon vapor and water vapor). This mixed steam is then extracted from the dehydration reactor and separated. There are no particular limitations on the method used to separate the mixed steam into saturated aliphatic hydrocarbons and water. For example, this can be achieved by extracting the steam from the top of the dehydrator to the outside of the system, condensing the extracted steam into a liquid, and separating the condensate into an aqueous layer (water) and an organic layer (saturated aliphatic hydrocarbons) using a settling tank (separation tank). In this separated aqueous layer (water) and organic layer (saturated aliphatic hydrocarbons), the water is extracted to the outside of the system.

[0039] (Process (iii))

[0040] In this process, the saturated aliphatic hydrocarbons separated in process (ii) are returned to process (i).

[0041] The saturated aliphatic hydrocarbons separated in this process contain almost no or no alcohol components (alcohol components formed by replacing at least one hydrogen atom of a saturated aliphatic hydrocarbon with a hydroxyl group) that cause the formation of boronic acid esters, which are the cause of deposits. Therefore, even if the saturated aliphatic hydrocarbons evaporated in the dehydration reaction of orthoboronic acid are used in the dehydration reaction of orthoboronic acid, the alcohol components hardly react with or completely with orthoboronic acid to form boronic acid esters. Therefore, the formation of deposits on the inner walls of the reactor and piping can be effectively prevented, thus effectively preventing the increase of stirring power and the blockage of piping. Therefore, according to the method of the present invention, metaboronic acid can be stably produced. In addition, since no additional fresh hydrocarbons are required, it is also preferred from the viewpoint of production cost, etc. Here, the content of alcohol components in the saturated aliphatic hydrocarbons separated in the above-described step (ii) is preferably less than 2% by mass, more preferably less than 1.5% by mass, and particularly preferably less than 1% by mass (lower limit: 0% by mass or less than the detection limit).

[0042] <Methods for manufacturing secondary alcohols>

[0043] As described above, the method of the present invention enables the stable and cost-effective production of metaboric acid. Therefore, the metaboric acid produced by the present invention is suitable for the production of secondary alcohols. Specifically, the present invention also provides a method for producing secondary alcohols (a second aspect), comprising: a) liquid-phase oxidation and esterification of saturated aliphatic hydrocarbons with a gas containing molecular oxygen in the presence of metaboric acid to obtain a reaction solution containing a borate ester compound; b) distilling the reaction solution containing the borate ester compound to separate unreacted saturated aliphatic hydrocarbons and a distillation residue; c) hydrolyzing the distillation residue to separate an aqueous layer containing orthoboric acid and an organic layer; d) saponifying the organic layer with an alkali to separate an alkaline aqueous solution layer and a crude alcohol layer; e) purifying the crude alcohol layer to obtain a secondary alcohol, wherein, in step a), the metaboric acid is produced using the method of the present invention.

[0044] The following describes each step of the second aspect. It should be noted that the second aspect is characterized in that the orthoboric acid separated in the hydrolysis step c) of the first aspect is used to produce metaboric acid in the dehydration step, and the metaboric acid is recycled to the a) step of the second aspect. Other steps can be operated in the same way as conventionally known steps or applied with appropriate modifications.

[0045] (Process(a))

[0046] In this process, metaboric acid, saturated aliphatic hydrocarbons, and a gas containing molecular oxygen (the same applies below) are supplied to the reactor. In the presence of metaboric acid, the saturated aliphatic hydrocarbons are oxidized in the liquid phase by the gas containing molecular oxygen to obtain a reaction solution containing oxides (oxidation reaction step (a-1)). Next, the oxides obtained above are esterified to obtain a reaction solution containing borate ester compounds (esterification step (a-2)). That is, the following reaction occurs through this process.

[0047] [Chemical Formula 2]

[0048]

[0049] The metaboric acid used in the above process (a-1) is manufactured using the method of the present invention.

[0050] In the above-described step (a-1), the gas containing molecular oxygen includes not only molecular oxygen (oxygen) but also nitrogen, etc. Preferably, the gas containing molecular oxygen is composed of molecular oxygen (oxygen) and nitrogen. Furthermore, the concentration of molecular oxygen (oxygen) in the gas containing molecular oxygen is 1% (vol%) or more and 10% (vol%) or less, preferably 3% (vol%) or more and 5% (vol%) or less, but not limited thereto. The supply rate of the gas containing molecular oxygen is 100 to 1000 liters / hour per 1000g of saturated aliphatic hydrocarbons, preferably 350 to 600 liters / hour, but not limited thereto.

[0051] In the above-described step (a-1), the reaction mixing ratio of metaboric acid and saturated aliphatic hydrocarbons is not particularly limited. Metaboric acid is preferably 1% or more and 5% or less by mass relative to saturated aliphatic hydrocarbons, more preferably 2% or more and 4% or less by mass, but is not limited thereto.

[0052] There are no particular limitations on the conditions for the liquid-phase oxidation reaction, and the same conditions as before can be applied. For example, the liquid-phase oxidation reaction temperature is 100–250°C, preferably 140–200°C, but it is not limited to this. Furthermore, the liquid-phase oxidation reaction time is, for example, 0.5–5 hours, preferably 1–3 hours, but it is not limited to this. Under such conditions, saturated aliphatic hydrocarbons can be oxidized in the liquid phase with a gas containing molecular oxygen within an appropriate range (e.g., the conversion rate of saturated aliphatic hydrocarbons = 5–30%). The above-mentioned liquid-phase oxidation reaction can be carried out at atmospheric pressure, under pressure, or under reduced pressure, typically at atmospheric pressure to 30 kg / cm³. 2 The reaction is carried out at G (3 MPa). Furthermore, the above liquid-phase oxidation reaction can be carried out while stirring (the reactor can be equipped with a stirrer).

[0053] In the above process (a-1), the liquid-phase oxidation reaction can be carried out in one reactor, or it can be carried out continuously in two or more reactors. Furthermore, the reactor can be, for example, a stirred tank type or a bubble column type.

[0054] In the above-described step (a-1), the liquid-phase oxidation reaction can be carried out in any manner. The liquid-phase oxidation reactor comprises two or more reactors that can be switched between batch and continuous operation. Preferably, it further includes the following steps: adding saturated aliphatic hydrocarbons to each of the two or more reactors; adding metaboric acid to the upstream reactor of the two or more reactors; starting the production of the oxide in the upstream reactor in a batch manner; monitoring the oxygen concentration difference at the inlet and outlet of the upstream reactor; and switching to continuous operation if the oxygen concentration difference reaches 0.5% by volume or more. According to the above method, a continuous operation method with good reactivity and high production efficiency can be provided, and thus a method for producing secondary alcohols with high production efficiency can be provided. That is, in a preferred embodiment of the present invention, a method for producing a secondary alcohol includes the following steps: a-1) supplying metaboric acid, saturated aliphatic hydrocarbons, and a gas containing molecular oxygen (a reaction gas containing molecular oxygen) to a reactor, and in the presence of metaboric acid, oxidizing the saturated aliphatic hydrocarbons in the liquid phase with the gas containing molecular oxygen (a reaction gas containing molecular oxygen) to obtain a reaction liquid containing oxides; a-2) esterifying the above oxides to obtain a reaction liquid containing borate ester compounds; b) distilling the above reaction liquid containing borate ester compounds to separate unreacted saturated aliphatic hydrocarbons and distillation residue; c) hydrolyzing the above distillation residue to separate an aqueous layer containing orthoboric acid and an organic layer; d) using an alkali to react the above organic layer with an alkali. The layer is saponified to separate it into an alkaline aqueous solution layer and a crude alcohol layer; e) the crude alcohol layer is purified to obtain a secondary alcohol, wherein the metaboric acid is manufactured using the method of the present invention, the reactor comprises two or more reactors that can be switched between batch and continuous operation, and the method for manufacturing the secondary alcohol further includes the following steps: adding saturated aliphatic hydrocarbons to each of the two or more reactors, adding metaboric acid to the upstream reactor of the two or more reactors, starting to obtain the oxide in the upstream reactor in a batch manner, monitoring the oxygen concentration difference at the inlet and outlet of the upstream reactor, and if the oxygen concentration difference reaches 0.5% by volume or more, switching to continuous operation.

[0055] The preferred embodiments described above will now be explained. It should be noted that, regarding metaboric acid, it is manufactured in the same manner as described above, and therefore, the description is omitted here. Furthermore, the present invention is not limited to the preferred embodiments described below.

[0056] In the above-described process (a-1), the reactor comprises two or more reactors that can be switched between batch and continuous operation, includes a process of adding saturated aliphatic hydrocarbons to each of the two or more reactors, includes a process of adding metaboric acid to the upstream reactor of the two or more reactors, includes a process of starting to obtain the oxide in the upstream reactor in a batch manner, monitoring the oxygen concentration difference at the inlet and outlet of the upstream reactor, and switching to a continuous operation if the oxygen concentration difference reaches 0.5% by volume or more.

[0057] Figure 3 This is a schematic diagram illustrating a reactor capable of measuring oxygen concentration. (For example...) Figure 3 As shown, reactor 30 consists of two reactors (41, 42). The upstream reactor ( Figure 3 The middle part is reactor 41) and one or more reactors as needed. Figure 3 The volume of reactor 42 can be appropriately determined according to the production quantity of the target material. The two reactors (41, 42) can be switched between batch and continuous operation by means of a connecting pipe 32. Each reactor (41, 42) has: an inlet 33 for adding saturated aliphatic hydrocarbons and metaboric acid, an inlet 34 for introducing gas containing molecular oxygen (reaction gas containing molecular oxygen), and an outlet 35 for discharging gas containing molecular oxygen (reaction gas containing molecular oxygen).

[0058] In one embodiment of the invention, the reaction gas contains molecular oxygen. It may also contain ammonia, etc. The reaction gas can be introduced into each reactor (41, 42) via inlet 34 along with the circulating gas. Examples of circulating gases include inactive gases, such as nitrogen, which is preferred. In one embodiment of the invention, the concentration of ammonia in the reaction gas can be from 10 ppm to 1000 ppm.

[0059] In this preferred embodiment, each reactor (41, 42) has an oxygen concentration measuring device (not shown) at its inlet 34 and outlet 35. The inlet 34 and outlet 35 are each constructed using gas piping. In this preferred embodiment, reactor 41 has one oxygen concentration measuring device at its inlet 34 (gas piping) and outlet 35 (gas piping), and reactor 42 has one oxygen concentration measuring device at its inlet 34 (gas piping) and outlet 35 (gas piping).

[0060] With such a measuring device, the oxygen concentration difference between inlet 34 and outlet 35 can be monitored. In short, a decrease in oxygen concentration at outlet 35 from inlet 34 indicates that an oxidation reaction is underway. In this preferred embodiment, the upstream reactor ( Figure 3 The middle part is reactor 41) and one or more other reactors as needed. Figure 3 The oxygen concentration difference at the inlet and outlet of reactor 42 is monitored. If the oxygen concentration difference reaches 0.5% by volume or more, the reactor switches to continuous operation. In this preferred embodiment, the oxygen concentration difference at the inlet and outlet of each of the two or more reactors is monitored. If the oxygen concentration difference reaches 0.5% by volume or more, the reactor switches to continuous operation. Here, if the oxygen concentration difference is less than 0.5% by volume, the reactivity of the oxidation reaction in continuous operation deteriorates, and a method for producing secondary alcohols with good production efficiency cannot be provided. It should be noted that in this specification, the oxygen concentration difference can be calculated from (oxygen concentration at the inlet (volume%)) - (oxygen concentration at the outlet (volume%)).

[0061] In this preferred embodiment, the upstream reactor ( Figure 3 The middle one is reactor 41) and other one or more reactors ( Figure 3 The oxygen concentration difference at the inlet and outlet of reactor 42 is independently 0.5% by volume or more (preferably 1.0% by volume or more). In one embodiment of the invention, the upstream reactor ( Figure 3 The middle one is reactor 41) and other one or more reactors ( Figure 3 The oxygen concentration difference between the inlet and outlet of reactor 42 is independently 10% by volume or less (preferably 5.0% by volume or less). With this embodiment, the oxidation reaction can be carried out stably.

[0062] In this preferred embodiment, the feedwater is directed to each reactor via inlet 33. Figure 3 Saturated aliphatic hydrocarbons are added to reactors 41 and 42.

[0063] In this preferred embodiment, the reactor has a reactor located on the most upstream side of the reactor ( Figure 3 The process of adding metaboric acid to reactor 41. In one embodiment of the invention, relative to the upstream side of the reactor ( Figure 3Metaboric acid is added to the reactor (41) containing saturated aliphatic hydrocarbons at concentrations below 10% by mass, 7% by mass, 5% by mass, or 3% by mass. If metaboric acid is added to the reactor at a concentration of 10% by mass or more, it may be impossible to maintain an oxygen concentration difference of at least 0.5% by volume between the inlet and outlet of the upstream reactor. In this preferred embodiment, relative to the upstream reactor (… Figure 3 The saturated aliphatic hydrocarbons contained in reactor 41) may be added, for example, metaboric acid at a concentration of more than 0.1% by mass, but not limited thereto.

[0064] In this preferred embodiment, it not only has a reactor on the most upstream side ( Figure 3 The step of adding metaboric acid in reactor 41 is more preferably a step involving one or more other reactors. Figure 3 The process of adding metaboric acid to reactor 42 is carried out by adding metaboric acid in a stepwise manner to each reactor in this way. Figure 3 In reactors 41 and 42, the technology has the effect of suppressing the amount of droplets entrained by metaboric acid, significantly suppressing pipe blockage, and thus improving production efficiency.

[0065] In this preferred embodiment, relative to one or more other reactors ( Figure 3 In reactor 42, each saturated aliphatic hydrocarbon is independently added with metaboric acid at a concentration of less than 10% by mass, less than 7% by mass, less than 5% by mass, or less than 3% by mass. According to this embodiment, the desired effects of the present invention can be effectively achieved. In one embodiment of the present invention, relative to one or more other reactors ( Figure 3 Each saturated aliphatic hydrocarbon contained in reactor 42 is independently added with metaboric acid at a concentration of, for example, 0.1% by mass or more, but not limited thereto.

[0066] In this preferred embodiment, the upstream reactor ( Figure 3 The middle one is reactor 41) and other one or more reactors ( Figure 3 The internal temperatures of reactor 42 are independently set to either above 140°C but below 200°C, 150–190°C, or 160–180°C. If the temperature is below 140°C, it may be impossible to maintain an oxygen concentration difference of at least 0.5% by volume between the inlet and outlet of the upstream reactor. Furthermore, by setting the temperature to above 140°C but below 200°C, the oxidation reaction can proceed stably. Here, "internal temperature" refers to the value measured using a thermometer positioned in contact with the contents of the reactor.

[0067] In this preferred embodiment, the feed is introduced into the reactor at the most upstream side ( Figure 3The middle one is reactor 41) and other one or more reactors ( Figure 3 The temperatures of the reactant gases in reactor 42 are each independently set to either 140°C or 200°C, 150-190°C, or 160-180°C. This embodiment effectively maintains an oxygen concentration difference of 0.5% by volume or more. Furthermore, by setting the temperature to 140°C or 200°C, the oxidation reaction can be carried out stably. Here, the temperature of the reactant gases refers to the value measured using a thermometer positioned in contact with the reactant gases. Additionally, the flow rate of each reactant gas is independently set to 100-1000 liters / hour per 1000g of saturated aliphatic hydrocarbons, preferably 350-600 liters / hour, etc.

[0068] In this preferred embodiment, a reactor is located on the most upstream side. Figure 3 The middle one is reactor 41) and other one or more reactors ( Figure 3 The process of introducing circulating gas into reactor 42) is described in section 42. It should be noted that the preferred temperature range for the circulating gas is the same as the preferred temperature range for the reaction gas.

[0069] In this preferred embodiment, the reactor is repeatedly moved to the upstream side ( Figure 3 The middle part is reactor 41) and one or more other reactors as needed. Figure 3 The reactor (42) intermittently supplies and stops the supply of reactant gas. During this process, monitoring is performed while the intermittent supply is being carried out. That is, the monitoring is performed by repeatedly introducing and stopping the intermittent supply of the reactant gas. A specific operating method will be described, for example, by supplying the reactant gas to the upstream reactor (…). Figure 3 The middle one is reactor 41) and other one or more reactors ( Figure 3 The reactor (42) is introduced with the aforementioned reaction gas at any time. Then, the introduction of the reaction gas is stopped at any time. One cycle of introducing and stopping the reaction gas is considered one cycle, and the reaction gas is supplied in multiple cycles. There is no particular limit to the number of cycles; the above monitoring is performed until the oxygen concentration difference reaches 0.5% by volume or more. As a standard, it is approximately 1 to 10 times, 2 to 7 times, or 3 to 6 times, but it is not limited to these.

[0070] In this preferred embodiment, during the above-described introduction, the material is introduced into the upstream reactor ( Figure 3 The middle one is reactor 41) and other one or more reactors ( Figure 3The oxygen concentration in the reaction gas of the reactor 42 is individually 0.5 vol% or more and 10 vol% or less, preferably 0.5 vol% or more and 2.5 vol% or less, etc.

[0071] In this preferred embodiment, during the above-described introduction, the concentration of molecular oxygen in the reactant gas is monotonically increased. Furthermore, in one embodiment of the invention, during the above-described introduction, the slope of the change in the concentration of molecular oxygen in the reactant gas, calculated using the least squares method, is positive. With such intermittent supply, by allowing the concentration of molecular oxygen in the reactant gas to increase (monotonically) over time (i.e., not decrease, or increase), or by allowing the slope of the concentration change, calculated using the least squares method, to be positive (i.e., the concentration may decrease over time, but if averaged, the concentration increases), a continuous supply can be used while maintaining good reactivity, thereby increasing production capacity.

[0072] In this preferred embodiment, the time interval for each infusion in the intermittent supply is set to 0.5–10 minutes, 0.5–5 minutes, or 0.5–3 minutes. This embodiment effectively achieves the desired oxygen concentration difference.

[0073] In this preferred embodiment, the stopping time for one infusion in the intermittent supply is set to 0.5 to 10 minutes or 1 to 10 minutes.

[0074] In this preferred embodiment, after a predetermined oxygen concentration difference is reached, the intermittent supply of the reaction gas is switched to a continuous supply. In one embodiment of the invention, in Figure 3 In the reactor, reaction gas is continuously supplied from the inlet 34 of at least one of reactors 41 and 42.

[0075] In this preferred embodiment, after the switch to continuous operation, a further step of supplying saturated aliphatic hydrocarbons is performed. In one embodiment of the invention, after the switch to continuous operation, saturated aliphatic hydrocarbons are supplied sequentially. In one embodiment of the invention, after switching the intermittent supply of the reaction gas to continuous supply, saturated aliphatic hydrocarbons are supplied sequentially from the inlet 33 of the reactor 41.

[0076] In this preferred embodiment, the upstream reactor ( Figure 3 The middle one is reactor 41) and other one or more reactors ( Figure 3The reactor (41, 42) is connected in the middle. In this way, a continuous flow (continuous flow) is established from the intermittent process, and a reaction liquid containing oxides (oxidation reaction products) is obtained. Here, the saturated aliphatic hydrocarbons supplied after switching to continuous flow can be the same as or different from the saturated aliphatic hydrocarbons added to the reactors (41, 42) as described above, but are preferably the same.

[0077] In this preferred embodiment, the oxidation reaction process can be carried out under atmospheric pressure, under pressure, or under reduced pressure, typically between atmospheric pressure and 30 kg / cm². 2 The reaction is carried out at G (3 MPa). Furthermore, the above liquid-phase oxidation reaction can be carried out while stirring (the reactor can be equipped with a stirrer).

[0078] In this preferred embodiment, one or more reactors may be, for example, a stirred tank type or a bubble tower type.

[0079] Through the above-described step (a-1), a borate ester compound is generated. In addition, unreacted aliphatic hydrocarbons, free alcohols, and metaboric acid are also present. The boiling point of the free alcohol is close to that of the saturated aliphatic hydrocarbons, making separation difficult. Therefore, in the esterification step (a-2), the alcohol is orthoboronized to convert it into a borate ester compound.

[0080] That is, in step (a-2) above, the free alcohol contained in the oxide obtained in step (a-1) is esterified (orthoboronic acid esterification) to obtain a reaction solution containing borate ester compounds. In this step, the free alcohol present in the oxide obtained in step (a-1) reacts with metaboric acid to convert it into borate ester compounds. Usually, there is residual metaboric acid in the oxide, so it is not necessary to add new metaboric acid here, but sometimes it is added.

[0081] In step (a-2) above, by dehydrating the reaction solution containing oxides under reduced pressure, the free alcohol contained in the oxidation reaction product undergoes orthoboronization and can be converted into a borate ester compound. At this time, the orthoboronization treatment conditions are not particularly limited. For example, the treatment temperature is 100–220°C, preferably 160–180°C, but not limited to these. It should be noted that, in this specification, the temperature in the esterification step refers to the temperature value measured using a thermometer inserted into the liquid in the reactor. The same definition applies throughout this specification. The treatment time is 5–80 minutes, preferably 20–60 minutes, but not limited to these. In this specification, the treatment time in the reaction refers to the residence time in the reactor. Here, residence time generally refers to the time that a substance flowing into a confined space remains in that space. If the volume of the space is denoted as V(m... 3 The volumetric flow rate of the inflowing substance is denoted as θ (m). 3If the residence time (τ) is given by the formula: τ(hr) = V / θ, then the residence time (τ) (hours) is expressed as: τ(hr) = V / θ. The processing pressure is 50–200 hPa, preferably 90–170 hPa, but not limited to this. It should be noted that, in this specification, the pressure in the esterification process refers to the pressure value measured by a pressure gauge installed at the top of the reactor for measuring the pressure of the gas phase. The same definition applies throughout this specification. It should be noted that the orthoboron esterification treatment can be carried out in a nitrogen stream. Under such processing conditions, the alcohol contained in the oxidation reaction product can be orthoboronized efficiently (resulting in borate ester compounds in higher yields).

[0082] (Process (b))

[0083] In this process, the reaction liquid containing borate esters obtained in step (a) above is distilled to separate unreacted saturated aliphatic hydrocarbons (distillate) and distillation residue (bottom residue), and the unreacted saturated aliphatic hydrocarbons are recovered (unreacted saturated aliphatic hydrocarbon recovery process). The boiling point difference between the distillate and the bottom residue is large, so they can be easily separated by distillation.

[0084] In this process, as a method for distilling the borate ester compound, known methods such as simple distillation (e.g., flash distillation) and molecular distillation can be used, but are not particularly limited thereto. The distillation conditions are not particularly limited. The distillation pressure is, for example, under reduced pressure of 1–50 hPa, preferably 3–25 hPa, but is not limited thereto. The distillation temperature (especially the bottom temperature) is 130–250 °C, preferably 150–205 °C, but is not limited thereto. The distillation time is 1–205 minutes, preferably 25–120 minutes, but is not limited thereto. Under such conditions, it is possible to more efficiently separate the distillation residue with a higher boiling point (containing the desired borate ester compound) and the components with a lower boiling point (containing unreacted saturated aliphatic hydrocarbons as the main component, as well as some carbonyl compounds, organic esters, organic acids, alkenes, etc.).

[0085] The unreacted saturated aliphatic hydrocarbons recovered in this process can be reused (recycled) in the oxidation reaction process (a-1) described above. In this case, for example, they can be reused directly in the oxidation reaction process (a-1) after the saturated aliphatic hydrocarbons in the distillate are removed; or the carbonyl compounds and olefins contained in the saturated aliphatic hydrocarbons recovered in this process can be hydrogenated and then reused in the oxidation reaction process (a-1), but are not limited to the above.

[0086] In addition to or instead of the above, the unreacted saturated aliphatic hydrocarbons recovered in this process can also be reused (recycled) in the process (i) of the first aspect described above. It should be noted that the saturated aliphatic hydrocarbons recovered in the above-described recovery process typically contain 2% by mass or more (e.g., about 2 to 5% by mass) of alcohol content. Therefore, in this case, the unreacted saturated aliphatic hydrocarbons recovered in this recovery process can be mixed with unused or separated saturated aliphatic hydrocarbons from the process (ii) of the first aspect described above, such that the alcohol content of the saturated aliphatic hydrocarbons in process (i) is less than 2% by mass (preferably less than 1.5% by mass, more preferably less than 1% by mass), and then reused in the above-described process (i).

[0087] (Process (c))

[0088] In this process, the distillation residue separated in step (b) above is hydrolyzed to separate an aqueous layer and an organic layer containing orthoboric acid (hydrolysis process).

[0089] Specifically, hot water is added to the distillation residue for hydrolysis, separating it into an aqueous layer containing orthoboric acid and an organic layer. Here, the temperature of the hot water (liquid temperature) is 70–150°C, preferably 90–100°C, but not limited to this. Furthermore, the amount of hot water added is 1–20 times the mass of the distillation residue, preferably 2–10 times the mass, but not limited to this. The hydrolysis time is 5–60 minutes, preferably 20–30 minutes, but not limited to this. Under these conditions, the distillation residue can be fully hydrolyzed, and the aqueous layer containing orthoboric acid and the organic layer can be separated more efficiently.

[0090] The aqueous layer containing orthoboric acid separated in this process can be reused in the dehydration step (i) of the method in the first aspect. That is, in one embodiment of the invention, the method of the invention further includes: using the method of the first aspect, producing metaboric acid from the orthoboric acid separated in c) above, and recycling it to a). In this case, after crystallizing the aqueous layer, separation (e.g., centrifugation) is performed, thereby separating the orthoboric acid from the aqueous layer and reusing (recycling) the orthoboric acid in the dehydration step (i) of the method in the first aspect. Here, when the separated orthoboric acid is reused in the dehydration step (i) of the method in the first aspect, the content of organic matter (such as fatty acids, fatty acid esters, sodium fatty acids, potassium fatty acids, organic acid salts, organic acid esters, etc.) in the orthoboric acid is preferably less than 1% by mass, more preferably less than 0.6% by mass (lower limit: 0% by mass or less than the detection limit). This can more effectively suppress the corrosion of the reactor (dehydrating group) in the dehydration reaction. In this specification, the content of organic matter in the orthoboric acid is a value measured using a total organic carbon (TOC) meter. It should be noted that the above method is an example, and the present invention is not limited to the above method.

[0091] (Process (d))

[0092] In this process, the organic layer separated in step (c) above is saponified with alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer (saponification process). This allows for the separation and removal of acids from organic acids and organic acid esters.

[0093] Here, the alkali can be, for example, sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, etc., but is not limited to these. Furthermore, after saponification using the above-mentioned alkali, washing with water can be performed if necessary. There are no particular restrictions on the saponification conditions; the same conditions as before can be applied. For example, the saponification temperature is 120–160°C, preferably 135–145°C, but is not limited to these. The saponification time is 30–120 minutes, preferably 50–90 minutes, but is not limited to these. Under such conditions, the saponification process can be carried out more efficiently.

[0094] (Process(e))

[0095] In this step, the crude alcohol layer separated in step (d) above is purified. This yields the target secondary alcohol (purification step).

[0096] Here, there are no particular limitations on the purification method; known methods can be applied similarly or with appropriate modifications. For example, purification can be performed by distillation or fractionation of the crude alcohol layer. The purification pressure is 1–45 hPa, preferably 4–12 hPa, but not limited to this. Under such conditions, separation can be achieved appropriately based on the boiling point range (e.g., separation into a fraction with a boiling point range of 95–120 °C and a fraction with a boiling point range of 120–150 °C). In the above case, the fraction with a boiling point range of 95–120 °C typically contains small amounts of saturated aliphatic hydrocarbons, carbonyl compounds, and monohydric primary alcohols (monohydrins). Furthermore, the fraction with a boiling point range of 120–150 °C contains trace amounts of carbonyl compounds and secondary alcohols (monohydrins), in which case most of the secondary alcohols are the desired monohydric secondary alcohols.

[0097] It should be noted that between the above-mentioned step (d) and this step (e), at least one step selected from the heavy separation step, the alkali treatment step (especially the potassium hydroxide treatment step) and the light separation step can be performed according to conventionally known methods.

[0098] [Example]

[0099] The following examples illustrate the effects of the present invention. However, the technical scope of the present invention is not limited to the examples provided, and examples obtained by appropriately combining the technical means disclosed in the examples are also included within the scope of the present invention. It should be noted that, unless otherwise specified, the operation in the following embodiments is carried out at room temperature (25°C). In addition, unless otherwise specified, "%" and "parts" refer to "mass %" and "parts by mass," respectively.

[0100] Example 1: Manufacturing of metaboric acid

[0101] exist Figure 1 A mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms (average molecular weight: 184) was introduced into a 5L reactor 1 equipped with a stirrer 2. Figure 1 A mixture M of orthoboronic acid was prepared by mixing 1700g of NP and 1000g of orthoboronic acid. It should be noted that the mixture of saturated aliphatic hydrocarbons as raw materials contains saturated aliphatic hydrocarbons (n-dodecane, n-tetrazane, and n-tetradecane) with a mass ratio exceeding 95% by weight relative to the total mass of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms. Furthermore, the alcohol content in the mixture of saturated aliphatic hydrocarbons was determined by gas chromatography, and the result was below the detection limit (effectively containing no alcohol). As reactor 1, a reactor integrally formed of stainless steel (SUS316) was used, and the upper part 3 ( Figure 1 The slanted section in the diagram; the height of the Hastelloy-coated section / total reactor height = 45%) The inner wall of the reactor is lined with Hastelloy C-22 (composition: Ni 57.0 wt%, Cr 20.5 wt%, Mo 14.2 wt%, Fe 2.3 wt%, W 3.2 wt%, V 0.25 wt%, C 0.01 wt%) with a thickness of 0.5 mm (from the top of the dewatering unit to the upper part of the reactor relative to 45% of the total height of the dewatering unit is covered with Hastelloy).

[0102] The obtained orthoboric acid mixture M was stirred in a mixer 2 at 45 rpm while being heated to 160°C with steam. The orthoboric acid underwent intramolecular dehydration for 5 hours in the presence of a mixture of saturated aliphatic hydrocarbons, converting it to β-type metaboric acid. This yielded 2330 g of a mixture containing 630 g of β-type metaboric acid and 1700 g of saturated aliphatic hydrocarbons (yield of β-type metaboric acid: 1 mole relative to 1 mole of orthoboric acid) (step (i)). It should be noted that X-ray crystal structure analysis confirmed it to be β-type metaboric acid. Additionally, water vapor and saturated aliphatic hydrocarbon vapors were generated during the above dehydration reaction. Figure 1The steam ("water + NP") is drawn from the top of the reactor through pipe 4 to the outside of the system and introduced into condenser 5 to condense the steam. The water and saturated aliphatic hydrocarbons condensed by the condenser are introduced into separation tank (sedimentation tank) 6 to separate the water and saturated aliphatic hydrocarbons (NP) (step (ii)). The water is drawn out of the system, and the saturated aliphatic hydrocarbons (NP) are returned to reactor 1 through pipe 7, while the above dehydration reaction is carried out simultaneously. It should be noted that the content of alcohol in the saturated aliphatic hydrocarbons (NP) separated in separation tank (sedimentation tank) 6 is determined by gas chromatography, and the result is below the detection limit (actually containing no alcohol).

[0103] After the above reaction was completed, the inner wall of the reactor and the inside of the piping were visually inspected. The results showed that almost no deposits were found on the inner wall of the reactor or inside the piping. Furthermore, no corrosion was observed on the inner wall of the reactor (especially the upper inner wall).

[0104] Example 2: Production of secondary alcohols

[0105] The reaction was carried out in the same manner as in Example 1 above, to obtain a mixture containing β-type metaboric acid and saturated aliphatic hydrocarbons.

[0106] Add 932.5g of a mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms (average molecular weight: 184, containing saturated aliphatic hydrocarbons with 12-14 carbon atoms in a proportion exceeding 95% by mass relative to the total mass of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms) to 92.5g of the obtained mixture to obtain 1025g of a mixture containing β-metabolic acid and saturated aliphatic hydrocarbons (composition: 25g β-metabolic acid and 1000g saturated aliphatic hydrocarbons). It should be noted that, for the above-mentioned saturated aliphatic hydrocarbons, the average molecular weight of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms is 184, and it contains saturated aliphatic hydrocarbons with 12-14 carbon atoms in a proportion exceeding 95% by mass relative to the total mass of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms. The mixture was added to a cylindrical reactor with a capacity of 3L, and a mixed gas with an oxygen concentration of 3.5 vol% and a nitrogen concentration of 96.5 vol% was blown in at a ratio of 430L per hour. The liquid phase oxidation reaction was carried out at 170°C under normal pressure for 2 hours to obtain a reaction liquid containing oxides (oxidation reaction mixture) (oxidation reaction process).

[0107] Following the oxidation reaction, the free alcohol is esterified with excess boric acid by reducing the pressure of the reaction solution containing the oxides to obtain a borate ester compound. This esterification is carried out at 105 hPa and 165 °C for 60 minutes (esterification step). Next, the borate ester compound (borate ester mixture) is flash-distilled at 200 °C and 7 hPa for 60 minutes to recover unreacted saturated aliphatic hydrocarbons (unreacted saturated aliphatic hydrocarbon recovery step). Next, the residue is hydrolyzed for 20 minutes with a large volume (twice the mass of the residue) of hot water at 95 °C, separating an aqueous layer containing orthoboric acid and an organic layer (hydrolysis step). The resulting organic layer is saponified and washed with water at 140 °C for 70 minutes using sodium hydroxide to remove organic acids and organic esters (saponification step). The organic layer is fractionated at 7 hPa, with the first fraction yielding a boiling point range of 95–120 °C, and the second fraction yielding a boiling point range of 120–150 °C (purification step). Here, the first fraction (the fraction with a boiling point above 95°C and below 120°C) is 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 between 120°C and 150°C) is a mixture of trace amounts of carbonyl compounds and secondary alcohols (monohydric alcohols), in which the majority of the secondary alcohols are monohydric secondary alcohols.

[0108] Example 3: Production of secondary alcohols

[0109] The procedure was performed in the same manner as in Example 2 above, separating the orthoboronic acid layer into an aqueous layer and an organic layer (hydrolysis step). Next, the aqueous layer was crystallized, centrifuged, and the orthoboronic acid was separated. The alcohol content in the orthoboronic acid obtained above was determined using gas chromatography, and the result was below the detection limit (effectively containing no alcohol). Furthermore, the amount of organic matter (organic acids, etc.) in the orthoboronic acid obtained above was determined using a total organic carbon (TOC) meter, and the result was 0.6% by mass.

[0110] In Example 1 above, instead of using the orthoboric acid obtained above, the same operation as in Example 1 was performed to obtain a mixture containing β-type metaboric acid and saturated aliphatic hydrocarbons. Here, the alcohol content in the saturated aliphatic hydrocarbons (NPs) separated by the separation tank (sedimentation tank) 6 was determined by gas chromatography, and the result was below the detection limit (virtually no alcohol content). In addition, after the dehydration reaction was completed, the inner wall of the reactor and the inside of the piping were visually observed. As a result, almost no deposits were found on the inner wall of the reactor and the inside of the piping. In addition, almost no corrosion was found on the inner wall of the reactor (especially the upper inner wall of the reactor). Based on the above results, it was found that the orthoboric acid recovered in the secondary alcohol manufacturing process (recovered orthoboric acid) contains organic matter such as organic acids that may cause corrosion of the dehydrator, but by using a reactor with a Hastelloy lining in the gas phase section with excellent corrosion resistance, such recovered orthoboric acid can be used for the manufacture of metaboric acid.

[0111] Based on the above results, it is confirmed that, according to the method of the present invention, even if the reaction is carried out continuously until it is substantially completely converted into metaboric acid, no deposits will form on the inner wall of the reactor or inside the piping. Furthermore, based on the above results, it is observed that, according to the method of the present invention, the dehydration reaction can be carried out stably without increasing the stirring power while allowing saturated aliphatic hydrocarbons (NPs) to circulate smoothly.

[0112] Next, in Example 2 above, the same operation as in Example 2 was performed instead of using the mixture containing β-type metaboric acid and saturated aliphatic hydrocarbons obtained above, to produce secondary alcohols.

[0113] Comparative Example 1

[0114] 1000g of a mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms (average molecular weight: 184) and 25g of metaboric acid were added to a 3L cylindrical reactor. A mixed gas with an oxygen concentration of 3.5 vol% and a nitrogen concentration of 96.5 vol% was blown in at a rate of 430L per hour. The oxidation reaction was carried out at 170°C under normal pressure for 2 hours to obtain an oxidation reaction mixture (oxidation reaction step). It should be noted that the mixture of saturated aliphatic hydrocarbons as raw materials contains saturated aliphatic hydrocarbons with 12-14 carbon atoms (n-dodecane, n-tridecane, and n-tetradecane) in a proportion of more than 95% by mass relative to the total mass of the mixture.

[0115] The oxidation reaction mixture was treated at 105 hPa and 165 °C for 60 minutes to esterify the contained alcohols, yielding borate ester compounds (borate ester mixture) (esterification step). Next, the borate ester compounds (borate ester mixture) were flash-distilled at 200 °C (bottom temperature) and 7 hPa for 60 minutes to recover unreacted saturated aliphatic hydrocarbons (unreacted saturated aliphatic hydrocarbon recovery step). The alcohol content in the recovered unreacted saturated aliphatic hydrocarbons (recovered NP) was determined by gas chromatography, and the result was 3.5% by mass. Furthermore, the hydroxyl value of the recovered NP was determined according to the method described in JIS K1557-1 (2007), and the result was 9.0 mg KOH / g.

[0116] exist Figure 1 The recovered NP obtained above was fed into reactor 1, which has a capacity of 5L and is equipped with a stirrer 2. Figure 1 A mixture M of orthoboronic acid was prepared by mixing 1700g of NP and 1000g of orthoboronic acid. It should be noted that reactor 1 was constructed entirely of stainless steel (SUS316).

[0117] The resulting orthoboric acid mixture M was stirred in a mixer 2 at 45 rpm while being heated to 160°C with steam. This caused intramolecular dehydration of the orthoboric acid in the presence of a mixture of saturated aliphatic hydrocarbons for 5 hours, converting it to β-metaboric acid. Thus, a mixture containing β-metaboric acid and saturated aliphatic hydrocarbons was obtained. It should be noted that the above dehydration reaction produces water vapor and saturated aliphatic hydrocarbon vapors (…). Figure 1 The steam ("water + NP") is drawn from the top of the reactor through pipe 4 to the outside of the system and introduced into condenser 5 to condense the steam. The water and saturated aliphatic hydrocarbons condensed by the condenser are introduced into separation tank (sedimentation tank) 6 to separate the water and saturated aliphatic hydrocarbons (NP). The water is drawn out of the system, and the saturated aliphatic hydrocarbons (NP) are returned to reactor 1 through pipe 7, while the above dehydration reaction is carried out at the same time.

[0118] After the above reaction was completed, the inner wall of the reactor and the inside of the piping were visually inspected. The results confirmed a large accumulation of deposits on the inner wall of the reactor and inside the piping. Additionally, corrosion was observed on the upper inner wall of the reactor.

[0119] In Comparative Example 1, which used saturated aliphatic hydrocarbons (recovered NP) recovered after oxidation, deposits formed on the reactor inner wall and inside the piping. Such deposits could potentially increase stirring power and cause piping blockage. Therefore, to remove the deposits, the reaction needs to be stopped, which is undesirable, especially from a large-scale production perspective. Furthermore, the recovered saturated aliphatic hydrocarbons (recovered NP) contain a significant amount of alcohol, suggesting that the aforementioned deposits formed due to the reaction of this alcohol with orthoboric acid to form borate esters.

[0120] Example 4: Manufacturing of metaboric acid

[0121] The same procedure was performed as in Comparative Example 1 above, and unreacted saturated aliphatic hydrocarbons (recovered NP) with an alcohol content of 3.5% by mass were recovered (unreacted saturated aliphatic hydrocarbon recovery process).

[0122] The recovered NP obtained above was mixed with a mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms (average molecular weight: 184) (new NP) at a ratio of 3:4 (recovered NP:new NP mixed mass ratio) to obtain a saturated aliphatic hydrocarbon mixture (NP1) with an alcohol content of 1.5% by mass. The hydroxyl value of this NP1 is 4.0 mg KOH / g.

[0123] In Example 1, NP1 (alcohol content = 1.5% by mass) obtained above was used instead of NP, and all other operations were performed in the same manner. Furthermore, the alcohol content in the saturated aliphatic hydrocarbons separated by the separation tank (sedimentation tank) 6 was determined by gas chromatography, and the result was 1.5% by mass.

[0124] After the above reaction was completed, the inner wall of the reactor and the inside of the piping were visually inspected. The results showed that almost no deposits were observed on the inner wall of the reactor or inside the piping. It should be noted that the amount of deposits observed visually in Example 1 was less. Furthermore, almost no corrosion was observed on the inner wall of the reactor (especially the upper inner wall of the reactor).

[0125] Based on a comparison with the results of Example 1 above, it was found that the alcohol content in the saturated aliphatic hydrocarbons used in the manufacture of metaboric acid is one of the main causes of deposit formation. Furthermore, it was found that controlling the alcohol content in the saturated aliphatic hydrocarbons to below 2% by mass (especially below 1.5% by mass) effectively inhibits the formation of deposits on the reactor inner wall and inside the piping.

[0126] Comparative Example 2: Manufacturing of Metaboric Acid

[0127] The same procedure was performed as in Comparative Example 1 above, and unreacted saturated aliphatic hydrocarbons (recovered NP) with an alcohol content of 3.5% by mass were recovered (unreacted saturated aliphatic hydrocarbon recovery process).

[0128] The recovered NP obtained above was mixed with a mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms (average molecular weight: 184) (new NP) at a ratio of 5:2 (recovered NP:new NP mixed mass ratio) to obtain a saturated aliphatic hydrocarbon mixture (NP2) with an alcohol content of 2.5% by mass. The hydroxyl value of this NP2 is 6.8 mg KOH / g.

[0129] exist Figure 1 The NP2 obtained above was added to a reactor 1 with a capacity of 5L and equipped with a stirrer 2. Figure 1 A mixture M of orthoboric acid was prepared by mixing 1700g of "NP" and 1000g of orthoboric acid (recycled orthoboric acid). It should be noted that reactor 1 was constructed entirely of stainless steel (SUS316).

[0130] The resulting orthoboric acid mixture M was stirred in a mixer 2 at 45 rpm while being heated to 160°C with steam. This caused intramolecular dehydration of the orthoboric acid in the presence of a mixture of saturated aliphatic hydrocarbons for 5 hours, converting it to β-metabolic acid. Thus, a mixture containing β-metabolic acid and saturated aliphatic hydrocarbons was obtained. It should be noted that water vapor and saturated aliphatic hydrocarbon vapors were generated during the above dehydration reaction. Figure 1 The steam ("water + NP") is drawn from the top of the reactor through pipe 4 to the outside of the system and introduced into condenser 5 to condense the steam. The water and saturated aliphatic hydrocarbons condensed by the condenser are introduced into separation tank (sedimentation tank) 6 to separate the water and saturated aliphatic hydrocarbons (NP). The water is drawn out of the system, and the saturated aliphatic hydrocarbons (NP) are returned to reactor 1 through pipe 7, while the above dehydration reaction is carried out at the same time.

[0131] After the above reaction was completed, the inner wall of the reactor and the inside of the piping were visually inspected. The results confirmed the accumulation of deposits on the inner wall of the reactor and inside the piping. It should be noted that the amount of deposits visually observed was greater than that in Comparative Example 1. Furthermore, corrosion was confirmed on the upper inner wall of the reactor.

[0132] A comparison with Comparative Example 1 above shows that even when the recovered saturated aliphatic hydrocarbons (recovered NPs) are used in combination with fresh saturated aliphatic hydrocarbons after the oxidation reaction, if the alcohol content in the saturated aliphatic carbons is 2% by mass or more, deposits will form on the reactor wall and inside the piping. Such deposits can lead to increased stirring power and piping blockage. Therefore, to remove the deposits, the reaction needs to be stopped, which is undesirable, especially from the viewpoint of large-scale production.

[0133] Example 5: Production of secondary alcohols

[0134] The reaction was carried out in the same manner as in Example 1 above, to obtain a mixture containing β-type metaboric acid and saturated aliphatic hydrocarbons.

[0135] To the obtained mixture of 74g, 1946g of a mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms (average molecular weight: 184, containing saturated aliphatic hydrocarbons with 12-14 carbon atoms in a proportion exceeding 95% by mass relative to the total mass of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms) was added, resulting in a mixture of 2020g containing β-metabolic acid and saturated aliphatic hydrocarbons (composition: 20g β-metabolic acid and 2000g saturated aliphatic hydrocarbons). It should be noted that, for the aforementioned saturated aliphatic hydrocarbons, the average molecular weight of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms is 184, and the mixture contains saturated aliphatic hydrocarbons with 12-14 carbon atoms in a proportion exceeding 95% by mass relative to the total mass of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms.

[0136] In such Figure 3 The mixture containing β-type metaboric acid and saturated aliphatic hydrocarbons obtained above was added to each of the two reactors 30 connected in series, namely reactors (41 and 42). It should be noted that the above mixture contains metaboric acid at 1% by mass and 1% by mass relative to the saturated aliphatic hydrocarbons, respectively.

[0137] The internal temperature of each reactor (41, 42) is raised to 170°C. Then, circulating gas (nitrogen: 170°C) is introduced into each reactor (41, 42) through inlet 34.

[0138] Next, the reactors (41, 42) were intermittently supplied with reactant gas, with repeated introduction and cessation of the gas supply.

[0139] More specifically, the temperature of the reactant gases introduced into each reactor (41, 42) is adjusted to 170°C. Furthermore, the oxygen concentration of the reactant gases introduced into each reactor (41, 42) is adjusted to 0.5–10 vol% and 0.5–10 vol%, respectively. The time for each introduction of the reactant gases into each reactor (41, 42) is set to 1–3 minutes. The time for stopping each introduction of the reactant gases is also set to 1–3 minutes. It should be noted that the above introduction is performed with a positive slope calculated using the least squares method for the change in the molecular oxygen concentration in the reactant gases.

[0140] Furthermore, the intermittent supply was implemented while monitoring the oxygen concentration difference at the inlet 34 and outlet 35 of each reactor (41, 42). It was confirmed that one hour after the initial introduction of the reaction gas into each reactor (41, 42), the specified oxygen concentration difference reached 1.0 vol% (i.e., 0.5 vol% or more).

[0141] After the above confirmation, the intermittent supply of reaction gas is switched to continuous supply, and NP is supplied sequentially from inlet 33 of reactor 41 at 50 mL / min, connecting each reactor (41, 42) to carry out the oxidation reaction process in a continuous (continuous flow) manner to obtain oxides (oxidation reaction mixture).

[0142] Following the oxidation reaction, the free alcohol is esterified by adding excess boric acid to the reaction solution containing the oxides under reduced pressure to obtain a borate ester compound. This esterification is carried out at 105 hPa and 165 °C for 60 minutes (esterification step). Next, the borate ester compound (borate ester mixture) is flash-distilled at 200 °C and 7 hPa for 60 minutes to recover unreacted saturated aliphatic hydrocarbons (unreacted saturated aliphatic hydrocarbon recovery step). Next, the residue is hydrolyzed for 20 minutes with a large volume (twice the mass of the residue) of hot water at 95 °C, separating an aqueous layer containing orthoboric acid and an organic layer (hydrolysis step). The resulting organic layer is saponified and washed with water at 140 °C for 70 minutes using sodium hydroxide to remove organic acids and organic esters (saponification step). The organic layer is fractionated at 7 hPa, with the first fraction having a boiling point range of 95 °C to 120 °C, and the second fraction having a boiling point range of 120–150 °C (purification step). Here, the first fraction (the fraction with a boiling point above 95°C and below 120°C) is 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 between 120°C and 150°C) is a mixture of trace amounts of carbonyl compounds and secondary alcohols (monohydric alcohols), in which the majority of the secondary alcohols are monohydric secondary alcohols.

[0143] The method was established in a continuous (continuous flow) manner, with a daily production of 4 kg of secondary alcohol, indicating that the oxidation process has good reactivity.

[0144] It should be noted that the experiment was conducted in a "series" manner in this embodiment, but it was confirmed that the same result could be obtained by setting it to "parallel".

[0145] Explanation of reference numerals in the attached figures

[0146] 1…reactor,

[0147] 2…mixer,

[0148] 3…Upper part of the reactor,

[0149] 4, 7...Piping,

[0150] 5…Condenser,

[0151] 6…Separation tank (sedimentation unit),

[0152] M… mixture,

[0153] 30… (multiple) reactors,

[0154] 41…(1) reactor,

[0155] 42…(1) reactor,

[0156] 32…Piping,

[0157] 33…the entry point for saturated aliphatic hydrocarbons and metaboric acid.

[0158] 34…Inlet for reactant gases and circulating gases

[0159] 35…Outlet for the discharge of reaction gas and circulating gas.

[0160] The above is the first description of the present invention.

[0161] Next, the second aspect of the present invention will be described. It should be noted that the present invention is not limited to the embodiments described below. Furthermore, unless otherwise specified, measurements of operation and physical properties are performed at room temperature (20–25°C). It should be noted that, hereinafter, "the second aspect of the present invention" will sometimes be abbreviated as "the present invention".

[0162] One embodiment of the present invention is a method for producing a secondary alcohol, comprising: a) supplying metaboric acid, saturated aliphatic hydrocarbons, and a reaction gas containing molecular oxygen to a reactor; in the presence of metaboric acid, oxidizing the saturated aliphatic hydrocarbons with the reaction gas containing molecular oxygen in the liquid phase to obtain a reaction solution containing oxides; b) esterifying the oxides to obtain a reaction solution containing borate ester compounds; c) distilling the reaction solution containing borate ester compounds to separate unreacted saturated aliphatic hydrocarbons and distillation residue; d) hydrolyzing the distillation residue to separate orthoboric acid and an organic layer; e) saponifying the organic layer with an alkali to separate... f) Separating an alkaline aqueous solution layer and a crude alcohol layer, the crude alcohol layer is purified to obtain a secondary alcohol. The reactor comprises two or more reactors capable of switching between batch and continuous operation. It includes a step of adding saturated aliphatic hydrocarbons to each of the two or more reactors, a step of adding metaboric acid to the upstream reactor of the two or more reactors, and a step of starting the production of the oxide in the upstream reactor in a batch manner. The oxygen concentration difference between the inlet and outlet of the upstream reactor is monitored, and if the oxygen concentration difference reaches 0.5% by volume or more, the process switches to continuous operation. According to this embodiment, a continuous production method with good reactivity and high production efficiency can be provided, thereby providing a method for producing secondary alcohols with high production efficiency.

[0163] The following is a detailed description of each process.

[0164] (Process(a))

[0165] ((a) Process: Oxidation reaction process)

[0166] In step (a), metaboric acid, saturated aliphatic hydrocarbons and a reaction gas containing molecular oxygen (hereinafter referred to as "oxygen") are supplied to the reactor. In the presence of metaboric acid, the saturated aliphatic hydrocarbons are oxidized in the liquid phase by the reaction gas containing molecular oxygen to obtain a reaction liquid containing oxides.

[0167] Unless otherwise specified, "saturated aliphatic hydrocarbons" in this specification refer to a mixture of saturated aliphatic hydrocarbons (n-alkanes) with 8 to 30 carbon atoms. Preferably, the saturated aliphatic hydrocarbons are mixtures containing saturated aliphatic hydrocarbons (n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, and n-pentadecane) with 10 to 15 carbon atoms as the main component, and more preferably, mixtures containing saturated aliphatic hydrocarbons (n-dodecane, n-tridecane, and n-tetradecane) with 12 to 14 carbon atoms as the main component. Here, "containing saturated aliphatic hydrocarbons as the main component" means saturated aliphatic hydrocarbons containing a specified number of carbon atoms in a proportion exceeding 90% by mass (preferably exceeding 95% by mass) (upper limit: 100% by mass) relative to all saturated aliphatic hydrocarbons. Furthermore, the average molecular weight of the saturated aliphatic hydrocarbons is 114 or more and 422 or less, preferably 142 or more and 212 or less, and more preferably 170 or more and 198 or less. The saturated aliphatic hydrocarbons can be synthetic or commercially available. Similarly, metaboric acid can be synthetic or commercially available. One embodiment of the synthesis method will be described in the section on "Methods for Manufacturing Metaboric Acid" described later.

[0168] In step (a), the reactor comprises two or more reactors that can be switched between batch and continuous operation, and includes a step of adding saturated aliphatic hydrocarbons to each of the two or more reactors, a step of adding metaboric acid to the upstream reactor of the two or more reactors, a step of starting to obtain the oxide in the upstream reactor in a batch manner, monitoring the oxygen concentration difference at the inlet and outlet of the upstream reactor, and switching to a continuous operation if the oxygen concentration difference reaches 0.5% by volume or more.

[0169] Figure 4 This is a schematic diagram illustrating a reactor capable of measuring oxygen concentration. (For example...) Figure 4 As shown, reactor 30 consists of two reactors (41, 42). The upstream reactor (in...) Figure 4 The middle part is reactor 41) and one or more reactors as needed (in Figure 4 The volume of reactor 42 can be appropriately determined according to the production quantity of the target material. The two reactors (41, 42) can be switched between batch and continuous operation by means of piping 32. Each reactor (41, 42) has: an inlet 33 for adding saturated aliphatic hydrocarbons and metaboric acid, an inlet 34 for introducing reaction gas containing molecular oxygen, and an outlet 35 for discharging reaction gas containing molecular oxygen.

[0170] In one embodiment of the invention, the reaction gas contains molecular oxygen. It may also contain ammonia, etc. The reaction gas can be introduced into each reactor (41, 42) via inlet 34 along with the circulating gas. Examples of circulating gases include inert gases, such as nitrogen, which is preferred. In one embodiment of the invention, the concentration of ammonia in the reaction gas can be from 10 ppm to 1000 ppm.

[0171] In one embodiment of the present invention, each reactor (41, 42) has an oxygen concentration measuring device (not shown) at its inlet 34 and outlet 35. The inlet 34 and outlet 35 are each formed by gas piping. In another embodiment of the present invention, reactor 41 has one oxygen concentration measuring device at its inlet 34 (gas piping) and outlet 35 (gas piping), and reactor 42 has one oxygen concentration measuring device at its inlet 34 (gas piping) and outlet 35 (gas piping).

[0172] With such a measuring device, the oxygen concentration difference between inlet 34 and outlet 35 can be monitored. In short, a decrease in oxygen concentration at outlet 35 from inlet 34 indicates that an oxidation reaction is underway. In one embodiment of the invention, the upstream reactor (in...) Figure 4 The reactor is 41) and one or more other reactors as needed. Figure 4 The oxygen concentration difference at the inlet and outlet of reactor 42 is monitored. If the oxygen concentration difference reaches 0.5% by volume or more, the process switches to continuous operation. In one embodiment of the invention, the oxygen concentration difference at the inlet and outlet of each of the two or more reactors is monitored. If the oxygen concentration difference reaches 0.5% by volume or more, the process switches to continuous operation. Here, if the oxygen concentration difference is less than 0.5% by volume, the reactivity of the oxidation reaction in continuous operation deteriorates, and a method for producing secondary alcohols with good production efficiency cannot be provided. It should be noted that in this specification, the oxygen concentration difference can be calculated from (oxygen concentration at the inlet (volume%)) - (oxygen concentration at the outlet (volume%)).

[0173] In one embodiment of the invention, the upstream reactor (in...) Figure 4 Reactor 41) and one or more other reactors (in Figure 4 The oxygen concentration difference at the inlet and outlet of reactor 42 is independently 0.5% by volume or more (preferably 1.0% by volume or more). In one embodiment of the invention, the upstream reactor (in... Figure 4 Reactor 41) and one or more other reactors (in Figure 4The oxygen concentration difference between the inlet and outlet of reactor 42 is independently 10% by volume or less (preferably 5.0% by volume or less). With this embodiment, the oxidation reaction can be carried out stably.

[0174] In one embodiment of the invention, the feedwater is supplied to each reactor (in) via inlet 33. Figure 4 Saturated aliphatic hydrocarbons are added to reactors 41 and 42.

[0175] In one embodiment of the invention, a reactor having a reactor at the most upstream side of the reactor (in Figure 4 The process of adding metaboric acid to reactor 41. In one embodiment of the invention, the reactor (in the uppermost part of the reactor) is used for this process. Figure 4 The saturated aliphatic hydrocarbons contained in reactor 41 are added with metaboric acid at concentrations below 10% by mass, 7% by mass, 5% by mass, or 3% by mass. If metaboric acid is added to the reactor at a concentration of 10% by mass or more, it may be impossible to maintain an oxygen concentration difference of at least 0.5% by volume between the inlet and outlet of the upstream reactor. In one embodiment of the invention, relative to the upstream reactor (in... Figure 4 The saturated aliphatic hydrocarbons contained in reactor 41) may be added, for example, metaboric acid at a concentration of more than 0.1% by mass, but not limited thereto.

[0176] In one embodiment of the invention, not only does it have a reactor at the most upstream side (in) Figure 4 The step of adding metaboric acid in reactor 41 is more preferably a step that includes one or more other reactors (in Figure 4 The process of adding metaboric acid to reactor 42 (in the middle part) involves adding metaboric acid in stages to each reactor. Figure 4 In reactors 41 and 42, the technology has the effect of suppressing the amount of droplets entrained by metaboric acid, significantly suppressing pipe blockage, and thus improving production efficiency.

[0177] In one embodiment of the invention, relative to one or more other reactors (in... Figure 4 In reactor 42, each saturated aliphatic hydrocarbon is independently added with metaboric acid at a concentration of less than 10% by mass, less than 7% by mass, less than 5% by mass, or less than 3% by mass. According to this embodiment, the desired effects of the present invention can be effectively achieved. In one embodiment of the present invention, relative to one or more other reactors (in... Figure 4 Each saturated aliphatic hydrocarbon contained in reactor 42 is independently added with metaboric acid at a concentration of, for example, 0.1% by mass or more, but not limited thereto.

[0178] In one embodiment of the invention, the upstream reactor (in) Figure 4 Reactor 41) and one or more other reactors (in Figure 4 The internal temperatures of reactor 42 are independently set to either above 140°C but below 200°C, 150–190°C, or 160–180°C. If the temperature is below 140°C, it may be impossible to maintain an oxygen concentration difference of at least 0.5% by volume between the inlet and outlet of the upstream reactor. Furthermore, by setting the temperature to above 140°C but below 200°C, the oxidation reaction can proceed stably. Here, "internal temperature" refers to the value measured using a thermometer positioned in contact with the contents of the reactor.

[0179] In one embodiment of the invention, the reactor introduced to the upstream side (in) Figure 4 Reactor 41) and one or more other reactors (in Figure 4 The temperatures of the reactant gases in reactor 42 are each independently set to be above 140°C and below 200°C, 150–190°C, or 160–180°C. This embodiment effectively maintains an oxygen concentration difference of 0.5% by volume or more. Furthermore, by setting the temperature above 140°C and below 200°C, the oxidation reaction can be carried out stably. Here, the temperature of the reactant gases refers to the value measured using a thermometer positioned in contact with the reactant gases. Additionally, the flow rate of each reactant gas is independently set to 100–1000 liters / hour per 1000g of saturated aliphatic hydrocarbons, preferably 350–600 liters / hour, etc.

[0180] In this preferred embodiment, a reactor is located on the most upstream side (in... Figure 4 Reactor 41) and one or more other reactors (in Figure 4 The process of introducing circulating gas into reactor 42) is described in section 42. It should be noted that the preferred temperature range for the circulating gas is the same as the preferred temperature range for the reaction gas.

[0181] In one embodiment of the invention, the reactor is repeatedly moved to the upstream side (in... Figure 4 The reactor is 41) and one or more other reactors as needed. Figure 4 The reactor (42) intermittently supplies and stops the supply of reactant gas. During this process, monitoring is performed while the intermittent supply is being carried out. That is, the monitoring is performed by repeatedly introducing and stopping the intermittent supply of the reactant gas. A specific operating method will be described, for example, by supplying the reactant gas to the upstream reactor (in... Figure 4 Reactor 41) and one or more other reactors (in Figure 4The reactor (42) is introduced with the aforementioned reaction gas at any time. Then, the introduction of the reaction gas is stopped at any time. One cycle of introducing and stopping the reaction gas is considered one cycle, and the reaction gas is supplied in multiple cycles. There is no particular limit to the number of cycles; the above monitoring is performed until the oxygen concentration difference reaches 0.5% by volume or more. As a standard, it is approximately 1 to 10 times, 2 to 7 times, or 3 to 6 times, but it is not limited to these.

[0182] In one embodiment of the present invention, during the above-described introduction, the material is introduced into the upstream reactor (in... Figure 4 Reactor 41) and one or more other reactors (in Figure 4 The oxygen concentration in the reaction gas of the reactor 42 is individually 0.5 vol% or more and 10 vol% or less, preferably 0.5 vol% or more and 2.5 vol% or less, etc.

[0183] In one embodiment of the present invention, during the above-described introduction, the concentration of molecular oxygen in the reactant gas is monotonically increased. Furthermore, in another embodiment of the present invention, during the above-described introduction, the slope of the change in the concentration of molecular oxygen in the reactant gas, calculated using the least squares method, is positive. With such intermittent supply, by monotonically increasing (i.e., not decreasing, or increasing) the concentration of molecular oxygen in the reactant gas over time, or by having a positive slope of the change in concentration calculated using the least squares method (i.e., the concentration may decrease over time, but if averaged, the concentration increases), continuous operation can be employed under conditions of good reactivity, thereby increasing production capacity.

[0184] In one embodiment of the invention, the time interval for each infusion in the intermittent supply is set to 0.5–10 minutes, 0.5–5 minutes, or 0.5–3 minutes. With this embodiment, the specified oxygen concentration difference can be effectively achieved.

[0185] In one embodiment of the present invention, the stopping time for one infusion in the intermittent supply is set to 0.5 to 10 minutes or 1 to 10 minutes.

[0186] In one embodiment of the present invention, after a predetermined oxygen concentration difference is reached, the intermittent supply of the reaction gas is switched to a continuous supply. In one embodiment of the present invention, in Figure 4 In the reactors 41 and 42, reaction gas is continuously supplied from the inlet 34 of reactor 41.

[0187] In one embodiment of the present invention, after the above-mentioned switch to continuous operation, there is a step of further supplying saturated aliphatic hydrocarbons. In one embodiment of the present invention, after the above-mentioned switch to continuous operation, saturated aliphatic hydrocarbons are supplied sequentially. In one embodiment of the present invention, after switching the intermittent supply of the reaction gas to continuous supply, saturated aliphatic hydrocarbons are supplied sequentially from the inlet 33 of the reactor 41.

[0188] In one embodiment of the invention, the upstream reactor (in) Figure 4 Reactor 41) and one or more other reactors (in Figure 4 The reactor (41, 42) is connected in the middle. In this way, a continuous flow (continuous flow) is established from the intermittent process, and a reaction liquid containing oxides (oxidation reaction products) is obtained. Here, the saturated aliphatic hydrocarbons supplied after switching to continuous flow can be the same as or different from the saturated aliphatic hydrocarbons added to the reactors (41, 42) as described above, but are preferably the same.

[0189] In one embodiment of the invention, the oxidation reaction process can be carried out under atmospheric pressure, under pressure, or under reduced pressure, typically at atmospheric pressure (normal pressure) to 30 kg / cm². 2 The reaction is carried out at G (3 MPa). Furthermore, the above liquid-phase oxidation reaction can be carried out while stirring (the reactor can be equipped with a stirrer).

[0190] In one embodiment of the invention, one or more reactors may be, for example, a stirred tank type or a bubble tower type.

[0191] <Method for manufacturing metaboric acid>

[0192] One aspect of the present invention is a method for manufacturing metaboric acid (first aspect), comprising: i) dehydrating orthoboric acid in the presence of saturated aliphatic hydrocarbons using a dehydrator to obtain a mixture comprising metaboric acid, saturated aliphatic hydrocarbons and water (step (i)); ii) distilling off a portion of the saturated aliphatic hydrocarbons and water from the mixture and separating the saturated aliphatic hydrocarbons and water (step (ii)); iii) returning the saturated aliphatic hydrocarbons separated in ii) to i) (step (iii) wherein, in i), the content of alcohol components in the saturated aliphatic hydrocarbons is less than 2% by mass.

[0193] As a method for producing secondary alcohols, a) in the presence of metaboric acid, saturated aliphatic hydrocarbons are oxidized in the liquid phase with a gas containing molecular oxygen to obtain a reaction solution containing oxides (step (a-1)), and the oxides are esterified to obtain a reaction solution containing borate ester compounds (step (a-2)) (steps (a-1) and (a-2) are also referred to as "step (a)"). b) The reaction solution containing borate ester compounds is distilled to separate unreacted saturated aliphatic hydrocarbons and distillation residue (step (b)). c) The distillation residue is hydrolyzed to separate an aqueous layer containing orthoboric acid and an organic layer (step (c)). d) The organic layer is saponified with alkali to separate an alkaline aqueous solution layer and a crude alcohol layer (step (d)). e) The crude alcohol layer is purified (step (e)). In the above method, unreacted saturated hydrocarbons can be recovered from several steps (e.g., step b above), and it is technologically useful to reuse these unreacted saturated hydrocarbons within the reaction system (e.g., Japanese Patent Application Publication No. 56-131531). Therefore, when producing metaboric acid by dehydrating orthoboric acid in the presence of saturated aliphatic hydrocarbons using a dehydrator, attempts were made to reuse the unreacted saturated aliphatic hydrocarbons recovered during the production of secondary alcohols as described above (recovered saturated aliphatic hydrocarbons). However, if the recovered unreacted saturated aliphatic hydrocarbons are used directly in the reaction, deposits form on the inner wall and piping, resulting in reduced production efficiency, equipment malfunctions, and an inability to stably produce metaboric acid. The inventors have conducted in-depth research on a stable metaboric acid production process using various methods. The results suggest that the alcohol contained in the unreacted saturated aliphatic hydrocarbons recovered during the secondary alcohol production process (e.g., after oxidation reaction) forms borate ester compounds, which are the cause of the deposits. Therefore, an in-depth study was conducted on the alcohol content in the saturated aliphatic carbon used in the production of metaboric acid. The results showed that by controlling the alcohol content in the saturated aliphatic hydrocarbons used in the dehydration reaction of orthoboric acid to less than 2% by mass, the formation of borate ester compounds, which are the cause of deposits, can be suppressed and prevented. According to the above method, since deposits do not adhere to the inner walls of the reactor and piping during the dehydration reaction, the increase in stirring power and the blockage of the piping can be effectively prevented. Therefore, metaboric acid can be stably produced according to the above method. In contrast, when unreacted hydrocarbons recovered using the method described in Japanese Patent Application Publication No. 56-131531 are recycled in the above-mentioned dehydration reaction, deposits adhere to the inner walls of the reactor and piping, potentially causing an increase in stirring power and blockage of the piping. It is speculated that this is because the recovered unreacted saturated aliphatic hydrocarbons contain alcohols in a proportion of 2% by mass or more in which at least one hydrogen atom of the saturated aliphatic hydrocarbon is replaced by a hydroxyl group. Therefore, these alcohols react with orthoboric acid in the dehydration process to form borate ester compounds, which are the cause of deposits.It should be noted that the mechanism of action of the above-mentioned effects based on the structure of the present invention is presumptive, and the present invention is not limited to the above presumption.

[0194] The following describes each step of the first aspect.

[0195] (Process (i))

[0196] In this process, saturated aliphatic hydrocarbons (hereinafter referred to as "hydrocarbons") and orthoboric acid are added to a dehydrator to prepare a slurry, and the orthoboric acid is dehydrated in the presence of the saturated aliphatic hydrocarbons. This produces metaboric acid, yielding a mixture (slurry) containing metaboric acid, saturated aliphatic hydrocarbons, water, and, depending on the circumstances, unreacted orthoboric acid.

[0197] In this process, the alcohol content in the saturated aliphatic hydrocarbons (raw material saturated aliphatic hydrocarbons) is less than 2% by mass. If the alcohol content in the raw material saturated aliphatic hydrocarbons is 2% by mass or more, borate ester compounds will be generated during the dehydration reaction of orthoboric acid, inducing the formation of deposits on the inner wall of the reactor and the inner wall of the piping, making it impossible to stably produce metaboric acid. From the viewpoint of more stably producing metaboric acid, the alcohol content in the saturated aliphatic hydrocarbons is preferably 1.5% by mass or less, and particularly preferably less than 1% by mass (lower limit: 0% by mass or less than the detection limit). That is, in the preferred embodiment of the present invention, in i) above, the alcohol content in the saturated aliphatic hydrocarbons is 1.5% by mass or less. In a more preferred embodiment of the present invention, in i) above, the alcohol content in the saturated aliphatic hydrocarbons is less than 1% by mass. In this specification, the alcohol content in the saturated aliphatic hydrocarbons is a value determined by gas chromatography. It should be noted that the above-mentioned "alcohol content" refers to alcohols (mixtures) formed by replacing hydrogen atoms of saturated aliphatic hydrocarbons with 6 to 30 carbon atoms with hydroxyl groups. Furthermore, the aforementioned "alcohol component" preferably refers to a mixture of alcohols containing saturated aliphatic hydrocarbons with 8 to 20 carbon atoms whose hydrogen atoms are replaced by hydroxyl groups as the main component, more preferably refers to a mixture of alcohols containing saturated aliphatic hydrocarbons with 10 to 15 carbon atoms whose hydrogen atoms are replaced by hydroxyl groups as the main component, and particularly preferably a mixture of alcohols containing saturated aliphatic hydrocarbons with 12 to 14 carbon atoms whose hydrogen atoms are replaced by hydroxyl groups as the main component.

[0198] Here, the saturated aliphatic hydrocarbons are mixtures of saturated aliphatic hydrocarbons (n-alkanes) with 8 to 30 carbon atoms. Preferably, the saturated aliphatic hydrocarbons are mixtures containing saturated aliphatic hydrocarbons (n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, and n-pentadecane) with 10 to 15 carbon atoms as the main component, more preferably mixtures containing saturated aliphatic hydrocarbons (n-dodecane, n-tridecane, and n-tetradecane) with 12 to 14 carbon atoms as the main component. Here, "containing saturated aliphatic hydrocarbons as the main component" means containing saturated aliphatic hydrocarbons with a specified number of carbon atoms in a proportion of more than 90% by mass (preferably more than 95% by mass) (upper limit: 100% by mass) relative to all saturated aliphatic hydrocarbons. Furthermore, the average molecular weight of the saturated aliphatic hydrocarbons is 114 or more and 422 or less, preferably 142 or more and 212 or less, more preferably 170 or more and 198 or less. The saturated aliphatic hydrocarbons can be synthetic or commercially available. Similarly, orthoboric acid can also be synthetic or commercially available.

[0199] In this invention, the mixing ratio of saturated aliphatic hydrocarbons to orthoboric acid is not particularly limited, and the same mixing ratio as in the past can be used. Specifically, the mixing ratio of saturated aliphatic hydrocarbons to orthoboric acid (mass ratio of saturated aliphatic hydrocarbons to orthoboric acid) is 0.5 to 5:1, preferably more than 1:1 and less than 3:1. In addition, the amount of orthoboric acid added in the mixture (slurry) is 15 to 90% by mass, preferably more than 25% by mass and less than 45% by mass, but is not limited thereto.

[0200] In this invention, the dehydration conditions for orthoboric acid in the presence of saturated aliphatic hydrocarbons are not particularly limited, and the same conditions as before can be applied. For example, the dehydration temperature is 100°C or higher and lower than 200°C, preferably 130°C or higher and lower than 180°C. The dehydration time is the time required for substantially all orthoboric acid to be converted to metaboric acid, and can be appropriately selected according to other conditions (e.g., the amount of orthoboric acid added, the mixing ratio of saturated aliphatic hydrocarbons to orthoboric acid, the dehydration temperature, etc.). The dehydration time is, for example, 3 to 7 hours, preferably 4 to 6 hours. If the dehydration time is within the above range, dehydration can be carried out appropriately, and metaboric acid can be produced efficiently. Alternatively, the amount of metaboric acid generated in the reactor can be measured periodically to determine whether substantially all orthoboric acid has been converted to metaboric acid, and the dehydration reaction can be ended when the desired amount of metaboric acid is generated. Here, "substantially all orthoboric acid is converted to metaboric acid" means that more than 0.9 moles (preferably more than 0.95 moles) (upper limit: 1 mole) of metaboric acid are converted relative to 1 mole of orthoboric acid added. The amount of metaboric acid in the mixture can be determined by known methods. In this specification, the amount of metaboric acid is expressed as a value determined by X-ray crystal structure analysis.

[0201] The dehydration reaction described above can be carried out under atmospheric pressure, pressurized conditions, or reduced pressure, but is typically carried out under atmospheric pressure. Furthermore, the dehydration reaction can be carried out while stirring (the reactor can be equipped with a stirrer). Here, the stirring speed during the dehydration reaction is not particularly limited, for example, it is 20–100 rpm, preferably 30–60 rpm. With such a stirring speed, the raw materials (saturated aliphatic hydrocarbons and orthoboric acid) can be uniformly mixed (allowing for a homogeneous dehydration reaction).

[0202] The dehydrator (a reactor for carrying out the dehydration reaction) can be made of any material. Specifically, examples include iron, copper, stainless steel (SUS), nickel alloys (e.g., Hastelloy), ferrochrome nickel alloys, titanium, and titanium dioxide. Among these, stainless steel (SUS), nickel alloys (e.g., Hastelloy), and titanium dioxide are preferred, and stainless steel (SUS) and nickel alloys (e.g., Hastelloy) are more preferred. As detailed below, orthoboric acid separated after the hydrolysis step in the manufacture of secondary alcohols can be reused in this step. In this case, the orthoboric acid contains organic matter (organic acids, organic acid salts, organic acid esters, etc., such as fatty acids, fatty acid esters, sodium fatty acids, potassium fatty acids, etc.), but this organic matter evaporates during the dehydration reaction, sometimes leading to corrosion of the dehydrator. Therefore, at least the gas phase of the reactor is preferably formed of a nickel alloy, particularly Hastelloy, which has excellent heat resistance, pressure resistance, and corrosion resistance. That is, in a preferred embodiment of the invention, at least the gas phase of the dehydrator is formed of a nickel alloy. In a more preferred embodiment of the invention, at least the gas phase of the dehydrator is formed of Hastelloy. Furthermore, in a preferred embodiment of the present invention, the dehydrator is entirely formed of a nickel alloy (more preferably Hastelloy). Examples of Hastelloy include Hastelloy C-22 (composition: Ni 57.0 wt%, Cr 20.5 wt%, Mo 14.2 wt%, Fe 2.3 wt%, W 3.2 wt%, V 0.25 wt%, C 0.01 wt%) and Hastelloy C-276 (composition: Ni 57.0 wt%, Cr 15.5 wt%, Mo 16.0 wt%, Fe 6.0 wt%, W 4.0 wt%, V 0.3 wt%, C 0.01 wt%). Additionally, "the vapor phase of the dehydrator" refers to the portion of the dehydrator that comes into contact with the vapor of at least one of saturated aliphatic hydrocarbons, orthoboric acid, water, and metaboric acid. Specifically, the gas phase section of the dehydrator is the portion extending from the top of the dehydrator to a point preferably 60% of the total height of the dehydrator (more preferably 30% or more and 60% or less, particularly preferably 40% or more and 50% or less). That is, in a preferred embodiment of the invention, the portion extending from the top of the dehydrator to 60% of the total height of the dehydrator (more preferably 30% or more and 60% or less, particularly preferably 40% or more and 50% or less) is formed of a nickel alloy. Furthermore, the invention also provides a reactor for metaboric acid production, wherein the portion extending from the top of the aforementioned reactor to 60% of the total height of the aforementioned reactor (preferably 30% or more and 60% or less, more preferably 40% or more and 50% or less) is formed of a nickel alloy. In addition, "the dehydrator is formed of material A" includes not only the dehydrator being formed of material A, but also the dehydrator being formed of material B with its inner surface covered by material A.That is, for example, "at least the vapor phase of the dehydrator is formed of nickel alloy" means that the entire dehydrator is formed of nickel alloy; the inner wall of the vapor phase of the dehydrator formed of other materials (e.g., stainless steel) is coated with nickel alloy by means of spraying or lining; the entire inner wall of the dehydrator formed of other materials (e.g., stainless steel) is coated with nickel alloy by means of spraying or lining.

[0203] In this process, orthoboric acid undergoes intramolecular dehydration in the presence of saturated aliphatic hydrocarbons through the following reaction to convert it into metaboric acid. Metaboric acid has α- and β-type forms depending on its crystal structure; from the viewpoint of thermal stability (anti-fading effect), β-type metaboric acid is preferred. Such β-type metaboric acid can be manufactured using the method described in Japanese Patent Publication No. 48-37242 and the preferred dehydration conditions described above.

[0204]

Chemical Formula 3

[0205]

[0206] (Process (ii))

[0207] In this process, after distilling off saturated aliphatic hydrocarbons and water from the dehydration reactants obtained in the above process (i), the saturated aliphatic hydrocarbons and water are separated.

[0208] In the dehydration step of step (i) above, saturated aliphatic hydrocarbons and water evaporate (producing a mixed steam of saturated aliphatic hydrocarbon vapor and water vapor). This mixed steam is then extracted from the dehydration reactor and separated. There are no particular limitations on the method used to separate the mixed steam into saturated aliphatic hydrocarbons and water. For example, one method involves extracting this steam from the top of the dehydrator to the outside of the system, condensing the extracted steam into a liquid, and separating the condensate into an aqueous layer (water) and an organic layer (saturated aliphatic hydrocarbons) using a settling tank (separation tank). In this separated aqueous layer (water) and organic layer (saturated aliphatic hydrocarbons), the water is extracted to the outside of the system.

[0209] (Process (iii))

[0210] In this process, the saturated aliphatic hydrocarbons separated in process (ii) are returned to process (i).

[0211] The saturated aliphatic hydrocarbons separated in this process contain almost no or no alcohol components (alcohol components in which at least one hydrogen atom of the saturated aliphatic hydrocarbon is replaced by a hydroxyl group) that cause the formation of borate ester compounds. Therefore, even if the saturated aliphatic hydrocarbons evaporated in the dehydration reaction of orthoboric acid are used in the dehydration reaction of orthoboric acid, the alcohol components hardly react with or completely with orthoboric acid to form borate ester compounds. Therefore, the formation of deposits on the inner walls of the reactor and piping can be effectively prevented, and thus the increase in stirring power and the blockage of piping can be effectively prevented. Therefore, according to the method of the present invention, metaboric acid can be stably produced. In addition, since no additional fresh hydrocarbons are required, it is also preferred from the viewpoint of production cost, etc. Here, the content of alcohol components in the saturated aliphatic hydrocarbons separated in the above-described step (ii) is preferably less than 2% by mass, more preferably less than 1.5% by mass, and particularly preferably less than 1% by mass (lower limit: 0% by mass or less than the detection limit).

[0212] (b) Process: Esterification process)

[0213] In step (b), the above-mentioned oxide (oxidation reaction product) is esterified to obtain a reaction solution containing a borate ester compound. In step (b), a borate ester compound is generated, but 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 hydrocarbon, making it difficult to separate the two. Therefore, in the esterification step (b), the alcohol is orthoboronized to convert it into a borate ester compound.

[0214] That is, in step (b) above, the free alcohol contained in the oxidation reaction product obtained in step (a) is esterified (orthoboronic esterification) 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. Usually, there is residual metaboric acid in the oxidation reaction product, so it is not necessary to add new metaboric acid here, but sometimes it is added.

[0215] The method for converting to borate esters is not particularly limited, but it is preferable to subject the reaction solution containing oxides (oxidation reaction product) obtained in step (a) to reduced pressure treatment. This allows for esterification of the free alcohol with excess metaboric acid (or newly added metaboric acid) to obtain the borate ester compound. The esterification conditions are not particularly limited. In one embodiment of the invention, the pressure in step (b) is, for example, 50–200 hPa or 90–170 hPa. In one embodiment of the invention, the temperature in step (b) is, for example, 100–220°C or 160–180°C. In one embodiment of the invention, the processing time in step (b) is, for example, 5–80 minutes or 20–60 minutes. It should be noted that the orthoboration esterification treatment can be carried out in a nitrogen stream. Under such conditions, the alcohol contained in the oxidation reaction product can undergo orthoboration esterification more efficiently (resulting in borate ester compounds in higher yields).

[0216] It should be noted that the following reactions occur in steps (a) to (b) above.

[0217] [Chemical Formula 4]

[0218]

[0219] (Process (c): Recovery of unreacted saturated aliphatic hydrocarbons)

[0220] In step (c), the reaction liquid containing borate esters obtained in step (b) above is distilled to separate unreacted saturated aliphatic hydrocarbons (distillate) and distillation residue (bottom residue), and the unreacted saturated aliphatic hydrocarbons are recovered (unreacted saturated aliphatic hydrocarbon recovery step). The distillate and the bottom residue have a large boiling point difference, so they can be easily separated by distillation.

[0221] In this process, as a method for distilling the borate ester compound, known methods such as simple distillation (e.g., flash distillation) and molecular distillation can be used, but are not particularly limited thereto. The distillation pressure is, for example, under reduced pressure of 1–50 hPa, preferably 3–25 hPa, but is not limited thereto. The distillation temperature (especially the bottom temperature of the column) is 130–250°C, preferably 150–205°C, but is not limited thereto. The distillation time is 1–205 minutes, preferably 25–120 minutes, but is not limited thereto.

[0222] The unreacted saturated aliphatic hydrocarbons recovered in this process can be reused (recycled) in the oxidation reaction step (a) described above. In this case, for example, they can be reused directly in the oxidation reaction step (a) after the saturated aliphatic hydrocarbons in the distillate are removed; the carbonyl compounds and olefins contained in the saturated aliphatic hydrocarbons recovered in this process can be hydrogenated and then reused in the oxidation reaction step (a); or, for example, as described in Japanese Patent Application Publication No. 56-131531, the saturated aliphatic hydrocarbons recovered in this process can be contacted with an alkaline aqueous solution to separate an organic layer and an aqueous layer containing fatty acids and fatty acid esters, the organic layer can be washed with hot water as needed (alkaline treatment step), the unreacted saturated aliphatic hydrocarbons contained in the organic layer can be hydrogenated (hydrogenation treatment step), and the alcohol components contained in the unreacted saturated aliphatic hydrocarbons can be orthoboronized (esterification step) and then reused in the oxidation reaction step (a), but not limited to the above. It should be noted that the saturated aliphatic hydrocarbons recovered in the above-mentioned recycling process contain more than 2% by mass (e.g., about 2 to 5% by mass) of alcohol components.

[0223] (Process (d): Hydrolysis process)

[0224] In this process, the distillation residue separated in step (c) above is hydrolyzed to separate an aqueous layer and an organic layer containing orthoboric acid.

[0225] Specifically, hot water is added to the distillation residue for hydrolysis, separating it into an aqueous layer containing orthoboric acid and an organic layer. Here, the temperature of the hot water (liquid temperature) is 70–150°C, preferably 90–100°C, but not limited to this. Furthermore, the amount of hot water added is 1–20 times the mass of the distillation residue, preferably 2–10 times the mass, but not limited to this. The hydrolysis time is 5–60 minutes, preferably 20–30 minutes, but not limited to this. Under these conditions, the distillation residue can be fully hydrolyzed, and the aqueous layer containing orthoboric acid and the organic layer can be separated more efficiently.

[0226] (Process (e): Saponification process)

[0227] In this process, the organic layer separated in step (d) above is saponified with alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer (saponification process). This removes organic acids and organic acid esters.

[0228] Here, the alkali can be, for example, sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, etc., but is not limited to these. Furthermore, after saponification using the above-mentioned alkali, washing with water can be performed if necessary. There are no particular restrictions on the saponification conditions; the same conditions as before can be applied. For example, the saponification temperature is 120–160°C, preferably 135–145°C, but is not limited to these. The saponification time is 30–120 minutes, preferably 50–90 minutes, but is not limited to these. Under such conditions, the saponification process can be carried out more efficiently.

[0229] (Process (f): Alcohol purification process)

[0230] In this step, the crude alcohol layer separated in step (e) above is purified. Thus, the target secondary alcohol is obtained (purification step).

[0231] Here, there are no particular limitations on the purification method; known methods can be applied similarly or with appropriate modifications. For example, purification can be performed by distillation or fractionation of the crude alcohol layer. The purification pressure is 1–45 hPa, preferably 4–12 hPa, but not limited to this. Under such conditions, separation can be achieved appropriately based on the boiling point range (e.g., separation into a fraction with a boiling point range of 95°C or higher and below 120°C and a fraction with a boiling point range of 120–150°C). In the above case, the fraction with a boiling point range of 95°C or higher and below 120°C typically contains small amounts of saturated aliphatic hydrocarbons, carbonyl compounds, and monohydric primary alcohols (monohydrins). Furthermore, the fraction with a boiling point range of 120–150°C contains trace amounts of carbonyl compounds and secondary alcohols (monohydrins), in which case most of the secondary alcohols are the desired monohydric secondary alcohols.

[0232] It should be noted that between the above-mentioned step (e) and this step (f), at least one step selected from the heavy separation step, the alkali treatment step (especially the potassium hydroxide treatment step) and the light separation step can be performed according to conventionally known methods.

[0233]

Example

[0234] The present invention will be described in more detail below through embodiments and comparative examples. However, the present invention is not limited to these embodiments and comparative examples. Embodiments obtained by appropriately combining the technical means disclosed in the embodiments are also included within the scope of the present invention.

[0235] (Example 1)

[0236] <(a): Oxidation process>

[0237] like Figure 4As shown, 1000 g and 1000 g of a mixture of saturated aliphatic hydrocarbons with 12 to 14 carbon atoms (average molecular weight 184, containing saturated aliphatic hydrocarbons with 12 to 14 carbon atoms (n-dodecane, n-tetrazane, and n-tetradecane) at a proportion of more than 95% by mass relative to the total mass of the mixture) (hereinafter also referred to as NP) are added to each of the two reactors 30 connected in series (41, 42). Next, metaboric acid is added to each of the reactors (41, 42) at a proportion of 1% by mass relative to NP, respectively.

[0238] The internal temperature of each reactor (41, 42) is raised to 170°C. Then, circulating gas (nitrogen: 170°C) is introduced into each reactor (41, 42) through inlet 34.

[0239] Next, the reactors (41, 42) were subjected to intermittent supply of reaction gas, with repeated introduction and cessation of the gas supply.

[0240] More specifically, the temperature of the reactant gases introduced into each reactor (41, 42) is adjusted to 170°C. Furthermore, the oxygen concentration of the reactant gases introduced into each reactor (41, 42) is adjusted to 0.5–10 vol% and 0.5–10 vol%, respectively. The time for each introduction of the reactant gases into each reactor (41, 42) is set to 1–3 minutes. The time for stopping each introduction of the reactant gases is also set to 1–3 minutes. It should be noted that the above introduction is performed with a positive slope calculated using the least squares method for the change in the molecular oxygen concentration in the reactant gases.

[0241] Furthermore, the intermittent supply was implemented while monitoring the oxygen concentration difference at the inlet 34 and outlet 35 of each reactor (41, 42). It was confirmed that the oxygen concentration difference reached 1.0 vol% (i.e., 0.5 vol% or more) 1.0 hour after the initial introduction of the reaction gas into each reactor (41, 42).

[0242] After the above confirmation, the intermittent supply of reaction gas is switched to continuous supply, and NP is supplied sequentially from inlet 33 of reactor 41 at 50 mL / min, connecting each reactor (41, 42) to carry out the oxidation reaction process in a continuous (continuous flow) manner to obtain oxides (oxidation reaction mixture).

[0243] <(b)~(f) Processes>

[0244] Following the oxidation reaction, the alcohol is esterified with an excess of boric acid under reduced pressure in the reaction solution containing the oxide (oxidation product) to obtain a borate ester compound. This esterification is carried out at 105 hPa and 165 °C for 60 minutes (esterification step). Next, the borate ester compound (boronate mixture) is distilled at 200 °C and 7 hPa to remove unreacted saturated aliphatic hydrocarbons (unreacted saturated aliphatic hydrocarbon recovery step). The residue is then hydrolyzed for 20 minutes with a large volume (twice the mass of the residue) of hot water at 95 °C, separating an aqueous layer containing orthoboric acid and an organic layer (hydrolysis step). The resulting organic layer is saponified and washed with water at 140 °C for 70 minutes using sodium hydroxide to remove organic acids and organic esters (saponification step). The organic layer is fractionated at 7 hPa, with the first fraction having a boiling point range of 95 °C to 120 °C, and the second fraction having a boiling point range of 120–150 °C. Here, the first fraction (boiling point range 95–120°C) is a mixture of small amounts of saturated aliphatic hydrocarbons, carbonyl compounds, and monohydric primary alcohols (monohydric alcohols). The second fraction (boiling point range 120–150°C) is a mixture of trace amounts of carbonyl compounds and secondary alcohols (monohydric alcohols), in which the majority of the secondary alcohols are monohydric secondary alcohols.

[0245] The method was established in a continuous (continuous flow) manner, with a daily production of 4 kg of secondary alcohol, indicating that the oxidation process has good reactivity.

[0246] It should be noted that the experiment was conducted in a "series" manner in this embodiment, but it was confirmed that the same result could be obtained by setting it to "parallel".

[0247] (Example 2)

[0248] The reaction gas described above is obtained by mixing air and ammonia instead of air, and otherwise the process is carried out in the same manner as in Example 1. At this time, the ammonia concentration in the reaction gas introduced into each reactor (41, 42) is adjusted to 10 to 1000 ppm and 10 to 1000 ppm, respectively.

[0249] The method was established in a continuous (continuous flow) manner, with a daily production of 4 kg of secondary alcohol, indicating that the oxidation process has good reactivity.

[0250] (Comparative Example 1)

[0251] In Example 1, the internal temperature of all reactors (41, 42) was changed to 140°C. As a result, the oxygen concentration difference was 0.1 vol% (i.e., less than 0.5 vol%). Using this method in a continuous (continuous flow) manner, the daily production of secondary alcohol was 0.7 kg, thus indicating poor reactivity of the oxidation process.

[0252] (Comparative Example 2)

[0253] In Example 1, metaboric acid was added to each reactor (41, 42) at 11% by mass and 11% by mass relative to NP, respectively. As a result, the oxygen concentration difference was 0.1% by volume and less than 0.5% by volume. By establishing this method in a continuous (continuous flow) manner, the production of secondary alcohol was 0.7 kg per day, thus indicating poor reactivity of the oxidation process.

[0254] (Comparative Example 3)

[0255] In Example 1, no intermittent supply was made for 0.5 hours after the initial introduction of the reaction gas into each reactor (41, 42). As a result, the oxygen concentration difference was 0.1 vol% and less than 0.5 vol%. By establishing this method in a continuous (continuous flow) manner, the production of secondary alcohols in one day was 0.7 kg, thus indicating poor reactivity of the oxidation process.

[0256] (Example 3)

[0257] Towards Figure 5 A mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms (average molecular weight: 184) was introduced into a 5L reactor 1 equipped with a stirrer 2. Figure 5 A mixture M of orthoboronic acid was prepared by mixing 1700g of NP and 1000g of orthoboronic acid. It should be noted that the mixture of saturated aliphatic hydrocarbons as raw materials contains saturated aliphatic hydrocarbons (n-dodecane, n-tetrazane, and n-tetradecane) with a mass ratio exceeding 95% by weight relative to the total mass of the mixture of saturated aliphatic hydrocarbons with 12-14 carbon atoms. Furthermore, the alcohol content in the mixture of saturated aliphatic hydrocarbons was determined by gas chromatography, and the result was below the detection limit (effectively containing no alcohol). As reactor 1, a reactor integrally formed of stainless steel (SUS316) and with the upper part 3 ( Figure 5The slanted section in the diagram; the height of the Hastelloy-coated section / total reactor height = 45%) The inner wall of the reactor is lined with Hastelloy C-22 (composition: Ni 57.0 wt%, Cr 20.5 wt%, Mo 14.2 wt%, Fe 2.3 wt%, W 3.2 wt%, V 0.25 wt%, C 0.01 wt%) with a thickness of 0.5 mm (from the top of the dewatering unit to the upper part of the reactor relative to 45% of the total height of the dewatering unit is covered with Hastelloy).

[0258] The obtained orthoboric acid mixture M was stirred in a mixer 2 at 45 rpm while being heated to 160°C with steam. The orthoboric acid underwent intramolecular dehydration for 5 hours in the presence of a mixture of saturated aliphatic hydrocarbons, converting it to β-type metaboric acid. This yielded 2330 g of a mixture containing 630 g of β-type metaboric acid and 1700 g of saturated aliphatic hydrocarbons (yield of β-type metaboric acid: 1 mole relative to 1 mole of orthoboric acid) (step (i)). It should be noted that X-ray crystal structure analysis confirmed it to be β-type metaboric acid. Additionally, water vapor and saturated aliphatic hydrocarbon vapors were generated during the above dehydration reaction. Figure 5 The steam ("water + NP") is drawn from the top of the reactor through pipe 4 to the outside of the system and introduced into condenser 5 to condense the steam. The water and saturated aliphatic hydrocarbons condensed by the condenser are introduced into separation tank (sedimentation tank) 6 to separate the water and saturated aliphatic hydrocarbons (NP) (step (ii)). The water is drawn out of the system, and the saturated aliphatic hydrocarbons (NP) are returned to reactor 1 through pipe 7, while the above dehydration reaction is carried out simultaneously. It should be noted that the content of alcohol in the saturated aliphatic hydrocarbons (NP) separated in separation tank (sedimentation tank) 6 is determined by gas chromatography, and the result is below the detection limit (actually containing no alcohol).

[0259] After the above reaction was completed, the inner wall of the reactor and the inside of the piping were visually inspected. The results showed that almost no deposits were found on the inner wall of the reactor or inside the piping. Furthermore, no corrosion was observed on the inner wall of the reactor (especially the upper inner wall).

[0260] like Figure 4As shown, 973g and 973g of a mixture of saturated aliphatic hydrocarbons with 12 to 14 carbon atoms (average molecular weight 184, containing saturated aliphatic hydrocarbons with 12 to 14 carbon atoms (n-dodecane, n-tetrazane, and n-tetradecane) at a ratio of more than 95% by mass relative to the total mass of the mixture) (hereinafter also referred to as NP) were added to each of the two reactors 1 connected in series. Next, 37g and 37g of a previously synthesized mixture of β-type metaboric acid and NP were added to each of the reactors (41 and 42) respectively (at a ratio of 1% by mass of metaboric acid to NP, respectively), and the secondary alcohol was produced using the same method as in Example 1. The method was established continuously (continuous flow), and the production of secondary alcohol was 4kg per day, indicating that the reactivity of the oxidation process was good. It should be noted that the experiment was conducted in "series" in this embodiment, but it was confirmed that the same results could be obtained by setting it to "parallel".

[0261] Symbol Explanation

[0262] 30: (Multiple) reactors

[0263] 41: (1) reactor,

[0264] 42: (1) reactor,

[0265] 32: Piping,

[0266] 33: The entry point for saturated aliphatic hydrocarbons and metaboric acid.

[0267] 34: Inlet for reactant gases and circulating gases.

[0268] 35: The outlet for reactant gases and circulating gases.

[0269] 1: Reactor,

[0270] 2: Blender

[0271] 3: Upper part of the reactor,

[0272] 4, 7: piping,

[0273] 5: Condenser

[0274] 6: Separation tank (sedimentation device)

[0275] M: Orthoboric acid mixture.

[0276] The above is the second description of the present invention.

[0277] The first and second embodiments of the present invention will be summarized below.

[0278] 1. A method for manufacturing metaboric acid, comprising the following steps: i) dehydrating orthoboric acid in the presence of saturated aliphatic hydrocarbons using a dehydrator to obtain a mixture comprising metaboric acid, saturated aliphatic hydrocarbons and water; ii) separating the saturated aliphatic hydrocarbons and water by distillation of the mixture; and iii) returning the saturated aliphatic hydrocarbons separated in step ii) to step i), wherein, in step i), the alcohol content in the saturated aliphatic hydrocarbons is less than 2% by mass.

[0279] 2. The method for manufacturing metaboric acid according to 1, wherein at least the vapor phase of the dehydrator is formed of a nickel alloy.

[0280] 3. The method for manufacturing metaboric acid according to 1, wherein the portion from the top of the dehydrator to 60% of the total height of the dehydrator is formed of a nickel alloy.

[0281] 4. A method for producing a secondary alcohol, comprising the following steps: a) in the presence of metaboric acid, saturated aliphatic hydrocarbons are oxidized and esterified in the liquid phase using a gas containing molecular oxygen to obtain a reaction solution containing a borate ester compound; b) the reaction solution containing the borate ester compound is distilled to separate unreacted saturated aliphatic hydrocarbons and distillation residue; c) the distillation residue is hydrolyzed to separate an aqueous layer containing orthoboric acid and an organic layer; d) the organic layer is saponified using an alkali to separate an alkaline aqueous solution layer and a crude alcohol layer; and e) the crude alcohol layer is purified to obtain a secondary alcohol, wherein in step a), the metaboric acid is produced using any one of the methods described in 1 to 3.

[0282] 5. The method for manufacturing secondary alcohol according to 4, wherein the method for manufacturing secondary alcohol further comprises the following step: using the method for manufacturing metaboric acid according to any one of 1. to 3, metaboric acid is manufactured from the orthoboric acid separated in step c) above, and recycled to step a) above.

[0283] 6. A method for producing a secondary alcohol, comprising the following steps: a-1) supplying metaboric acid, saturated aliphatic hydrocarbons, and a gas containing molecular oxygen to a reactor, and, in the presence of metaboric acid, oxidizing the saturated aliphatic hydrocarbons with the gas containing molecular oxygen in the liquid phase to obtain a reaction solution containing oxides; a-2) esterifying the oxides to obtain a reaction solution containing borate ester compounds; b) distilling the reaction solution containing borate ester compounds to separate unreacted saturated aliphatic hydrocarbons and distillation residue; c) hydrolyzing the distillation residue to separate an aqueous layer containing orthoboric acid and an organic layer; d) saponifying the organic layer with an alkali to separate an alkaline aqueous solution layer and a crude alcohol layer; and e) saponifying the crude alcohol layer with an alkaline alkali. The alcohol layer is purified to obtain a secondary alcohol. In step a-1), the metaboric acid is manufactured using any one of the methods described in 1 to 3. The reactor comprises two or more reactors that can be switched between batch and continuous operation. The method for manufacturing the secondary alcohol further includes the following steps: adding saturated aliphatic hydrocarbons to each of the two or more reactors; adding metaboric acid to the upstream reactor of the two or more reactors; starting to obtain the oxide in the upstream reactor in a batch manner; monitoring the oxygen concentration difference at the inlet and outlet of the upstream reactor; and switching to continuous operation if the oxygen concentration difference reaches 0.5% by volume or more.

[0284] 7. A reactor for producing metaboric acid, wherein a portion from the top of the reactor to a distance of 60% relative to the total height of the reactor is formed of a nickel alloy.

[0285] 8. A method for producing a secondary alcohol, comprising the following steps: a) supplying metaboric acid, saturated aliphatic hydrocarbons, and a reaction gas containing molecular oxygen to a reactor, and, in the presence of metaboric acid, oxidizing the saturated aliphatic hydrocarbons in the liquid phase with the reaction gas containing molecular oxygen to obtain a reaction liquid containing oxides; b) esterifying the oxides to obtain a reaction liquid containing borate ester compounds; c) distilling the reaction liquid containing borate ester compounds to separate unreacted saturated aliphatic hydrocarbons and distillation residue; d) hydrolyzing the distillation residue to separate orthoboric acid and an organic layer; e) saponifying the organic layer with an alkali to separate it into an alkaline solution. The method for producing the secondary alcohol includes an aqueous solution layer and a crude alcohol layer; and f) purifying the crude alcohol layer to obtain a secondary alcohol. The reactor comprises two or more reactors that can be switched between batch and continuous operation. The method for producing the secondary alcohol further includes the following steps: adding saturated aliphatic hydrocarbons to each of the two or more reactors; adding metaboric acid to the upstream reactor of the two or more reactors; starting to obtain the oxide in the upstream reactor in a batch manner; monitoring the oxygen concentration difference at the inlet and outlet of the upstream reactor; and switching to continuous operation if the oxygen concentration difference reaches 0.5% by volume or more.

[0286] 9. The method for producing secondary alcohol according to 8, wherein the method for producing secondary alcohol includes a step of adding metaboric acid in one or more reactors other than the aforementioned upstream reactor.

[0287] 10. The method for producing secondary alcohols according to claim 9, wherein the method comprises the step of independently adding metaboric acid to each reactor at a concentration of less than 10% by mass relative to each saturated aliphatic hydrocarbon contained in each of the above-described reactors.

[0288] 11. A method for producing a secondary alcohol according to any one of 8 to 10, wherein the method for producing the secondary alcohol includes a step of further supplying saturated aliphatic hydrocarbons after switching to the continuous process described above.

[0289] 12. A method for producing a secondary alcohol according to any one of 8 to 11, wherein the method for producing the secondary alcohol includes monitoring the oxygen concentration difference at the inlet and outlet of each of the two or more reactors, and if the oxygen concentration difference reaches 0.5% by volume or more, switching to a continuous process.

[0290] 13. A method for producing a secondary alcohol according to any one of 8 to 12, wherein the method for producing the secondary alcohol includes a step of independently setting the internal temperature of each of the above-mentioned reactors to 160 to 180°C.

[0291] 14. The method for producing secondary alcohol according to any one of 8 to 13, comprising a step of independently setting the temperature of each of the above-mentioned reaction gases to 160 to 180°C.

[0292] 15. The method for producing a secondary alcohol according to any one of 8 to 14, wherein the monitoring is carried out by repeatedly introducing and stopping the intermittent supply of the reaction gas.

[0293] 16. The method for manufacturing secondary alcohol according to 15, wherein the time for each injection in the intermittent supply is set to 0.5 to 10 minutes.

[0294] 17. The method for manufacturing secondary alcohol according to 15 or 16, wherein the stopping time for one infusion in the intermittent supply is set to 1 to 10 minutes.

[0295] 18. The method for producing a secondary alcohol according to any one of 15 to 17, wherein, during the above-described introduction, the concentration of molecular oxygen in the above-described reaction gas is monotonically increased.

[0296] 19. The method for producing a secondary alcohol according to any one of 15 to 17, wherein, during the above-described introduction, the slope of the change in the concentration of molecular oxygen in the above-described reaction gas, calculated by the least squares method, is positive.

Claims

1. A method for producing a secondary alcohol, comprising the following steps: a-1) Metaboric acid, saturated aliphatic hydrocarbons and a gas containing molecular oxygen are supplied to the reactor. In the presence of metaboric acid, the saturated aliphatic hydrocarbons are oxidized in the liquid phase by the gas containing molecular oxygen to obtain a reaction liquid containing oxides. a-2) Esterify the oxide to obtain a reaction solution containing a borate ester compound; b) Distill the reaction solution containing the borate ester compound to separate unreacted saturated aliphatic hydrocarbons and distillation residue; c) Hydrolyze the distillation residue to separate it into an aqueous layer and an organic layer containing orthoboric acid; d) Saponifying the organic layer with an alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer; and e) Purify the crude alcohol layer to obtain a secondary alcohol; In step a-1), the metaboric acid is manufactured using a method for manufacturing metaboric acid that includes the following steps: i) Dehydrate the orthoboric acid in the presence of saturated aliphatic hydrocarbons using a dehydrator to obtain a mixture containing metaboric acid, saturated aliphatic hydrocarbons and water; ii) After distilling the saturated aliphatic hydrocarbons and water from the mixture, the saturated aliphatic hydrocarbons and water are separated; and iii) Return the saturated aliphatic hydrocarbons separated in step ii) to step i). In step i), the alcohol content in the saturated aliphatic hydrocarbon is less than 2% by mass. The reactor comprises two or more reactors capable of switching between batch and continuous operation. The method for manufacturing the secondary alcohol further includes the following steps: Saturated aliphatic hydrocarbons are added to each of the two or more reactors. In the most upstream reactor among the two or more reactors, metaboric acid is added at a concentration of less than 10% by mass relative to the saturated aliphatic hydrocarbons contained in the most upstream reactor. The internal temperature of the upstream reactor and one or more other reactors is independently set to be above 140°C but below 200°C. The oxide is initially obtained intermittently in the upstream reactor. The oxygen concentration difference between the inlet and outlet of the upstream reactor is monitored. If the oxygen concentration difference reaches 0.5% by volume or more, the process is switched to continuous operation. The process of establishing a continuous reaction from a batch process to obtain a reaction solution containing oxides includes the following steps: The intermittent supply of molecular oxygen-containing gas is repeatedly introduced into and stopped from the upstream reactor and one or more other reactors as needed, while monitoring is performed during the intermittent supply. Once the specified oxygen concentration difference is reached, the intermittent supply of gas containing molecular oxygen is switched to a continuous supply. After switching from an intermittent supply of oxygen-containing gas to a continuous supply, saturated aliphatic hydrocarbons are sequentially supplied from the inlet of the upstream reactor; and The upstream reactor is connected to one or more other reactors.

2. The method for producing secondary alcohols according to claim 1, wherein, The method further includes the following steps: Using the method for manufacturing metaboric acid, metaboric acid is manufactured from the original boric acid separated in step c), and the resulting metaboric acid is recycled to step a), which consists of steps a-1) and a-2).

3. The method for producing secondary alcohols according to claim 1 or 2, wherein, At least the gas phase portion of the dehydrator is formed of a nickel alloy.

4. The method for producing secondary alcohols according to claim 1 or 2, wherein, The portion from the top of the dehydrator to 60% of the total height of the dehydrator is formed of a nickel alloy.

5. A method for producing a secondary alcohol, comprising the following steps: a) Metaboric acid, saturated aliphatic hydrocarbons and a reaction gas containing molecular oxygen are supplied to the reactor. In the presence of metaboric acid, the saturated aliphatic hydrocarbons are oxidized in the liquid phase by the reaction gas containing molecular oxygen to obtain a reaction liquid containing oxides. b) Esterify the oxide to obtain a reaction solution containing a borate ester compound; c) Distill the reaction solution containing the borate ester compound to separate unreacted saturated aliphatic hydrocarbons and distillation residue; d) Hydrolyze the distillation residue to separate it into orthoboric acid and an organic layer; e) The organic layer is saponified with alkali to separate it into an alkaline aqueous solution layer and a crude alcohol layer; as well as f) The crude alcohol layer is purified to obtain a secondary alcohol. The reactor comprises two or more reactors capable of switching between batch and continuous operation. The method for manufacturing the secondary alcohol further includes the following steps: Saturated aliphatic hydrocarbons are added to each of the two or more reactors. In the most upstream reactor among the two or more reactors, metaboric acid is added at a concentration of less than 10% by mass relative to the saturated aliphatic hydrocarbons contained in the most upstream reactor. The internal temperature of the upstream reactor and one or more other reactors is independently set to be above 140°C but below 200°C. The oxide is initially obtained intermittently in the upstream reactor. The oxygen concentration difference between the inlet and outlet of the upstream reactor is monitored. If the oxygen concentration difference reaches 0.5% by volume or more, the process is switched to continuous operation. The process of establishing a continuous reaction from an intermittent process to obtain a reaction solution containing the oxide includes the following steps: The process involves repeatedly introducing and stopping the supply of a reactive gas containing molecular oxygen to the upstream reactor and one or more other reactors as needed, while monitoring is performed during the intermittent supply. Once the specified oxygen concentration difference is reached, the intermittent supply of the reactive gas containing molecular oxygen is switched to a continuous supply. After switching the intermittent supply of the reactive gas containing molecular oxygen to a continuous supply, saturated aliphatic hydrocarbons are sequentially supplied from the inlet of the upstream reactor; and The upstream reactor is connected to one or more other reactors.

6. The method for producing secondary alcohols according to claim 5, wherein, The method for producing the secondary alcohol includes a step of adding metaboric acid in one or more reactors other than the upstream reactor.

7. The method for producing secondary alcohols according to claim 6, wherein, The method for producing the secondary alcohol includes the step of independently adding metaboric acid to each reactor at a concentration of less than 10% by mass, relative to the saturated aliphatic hydrocarbons contained in each reactor.

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