Method for recovering siloxanes

Abstract

To provide a method for easily recovering siloxanes from hydrophobic organic solvents containing siloxanes.SOLUTION: There is provided a method for recovering siloxanes by extracting the siloxanes from hydrophobic organic solvents containing siloxanes such as dimethylpolysiloxane and cyclic siloxanes (such as saturated hydrocarbons and halogenated hydrocarbons) using concentrated sulfuric acid. In addition, there is also provided a method for recovering siloxanes by hydrating a mixture of concentrated sulfuric acid and siloxanes obtained by extracting siloxanes to obtain siloxanes.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for recovering siloxanes.

Background Art

[0002] Siloxanes such as hexamethyldisiloxane are used for the hydrophobization treatment of silica powder. For example, in the production of silica aerogel, a hydrophobization treatment is performed to prevent pore shrinkage. When drying a wet gel, capillary action due to the surface tension of the solvent and dehydration condensation of surface silanol groups cause drying shrinkage, making it difficult to obtain silica aerogel. To address such problems, by performing supercritical drying, silica aerogel can be obtained by drying under conditions not affected by surface tension. However, since supercritical drying requires high-pressure and high-temperature conditions, it is not a desirable method from an economic perspective. As a method of avoiding supercritical drying and obtaining silica aerogel powder, hydrophobization of the wet gel surface is effective. By replacing the inside of the hydrophobized pores with a solvent having a low surface tension, pore shrinkage can be suppressed even during drying under subcritical conditions, and silica aerogel can be obtained.

[0003] Patent Document 1 discloses a method for producing spherical silica aerogel having a step of subjecting a gelled body dispersed in an aqueous solution to a silylation treatment.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the step of performing the serialization process, the silica surface and the unreacted siloxane are contained in the distillate during the drying in the step of recovering the gelled body after the step of extracting the gelled body with a hydrophobic organic solvent to obtain a powder composed of hydrophobic spherical silica aerogel. As a means for recovering siloxanes from the distillate, industrially, a distillation operation is mentioned. However, when the azeotropy with the extraction solvent or the boiling point difference is small, separation by distillation may be difficult.

[0006] Therefore, an object of the present invention is to recover siloxanes from a hydrophobic organic solvent containing siloxanes by a simple method.

Means for Solving the Problems

[0007] The present inventors have conducted intensive studies to solve the above problems. As a result, it has been found that by mixing a hydrophobic organic solvent containing siloxanes with concentrated sulfuric acid, the siloxanes are extracted into the concentrated sulfuric acid. Furthermore, it has been found that silica powder can be hydrophobized using the concentrated sulfuric acid containing siloxanes obtained by extracting siloxanes, and that by hydrating the concentrated sulfuric acid containing siloxanes, the siloxanes are released from the sulfuric acid solution and become in an isolable state, leading to the completion of the present invention.

[0008] That is, the present invention is a method for recovering siloxanes by extracting siloxanes from a hydrophobic organic solvent containing siloxanes with concentrated sulfuric acid. The present invention also provides a method for recovering siloxanes by adding a mixed solution of concentrated sulfuric acid and siloxanes obtained by extracting siloxanes to water to obtain siloxanes.

[0009] The present invention further provides a method for producing a hydrophobic silica powder in which, after recovering siloxanes by the above method for recovering siloxanes, the recovered siloxanes are used to hydrophobize silica powder. According to the method for producing a hydrophobic silica powder of the present invention, by extracting siloxanes from a hydrophobic organic solvent containing siloxanes with concentrated sulfuric acid, the siloxanes are recovered as a mixed solution with concentrated sulfuric acid, and even using the mixed solution of concentrated sulfuric acid and siloxanes, a hydrophobic silica powder can be obtained.

Advantages of the Invention

[0010] The method for recovering siloxanes of the present invention can recover siloxanes from a hydrophobic organic solvent by a simple method, making it easy to reuse siloxanes.

Embodiments for Carrying Out the Invention

[0011] In the method for recovering siloxanes of the present invention, siloxanes are extracted from a hydrophobic organic solvent solution containing siloxanes with concentrated sulfuric acid to recover the siloxanes.

[0012] <Siloxanes> Siloxanes are not particularly limited as long as they are compounds having a siloxane bond in the molecule. For example, dimethylpolysiloxanes such as hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, and cyclic siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, tetradecamethylcycloheptasiloxane, hexadecamethylcyclooctasiloxane, octadecamethylcyclononasiloxane, eicosamethylcyclodecasiloxane can be mentioned.

[0013] <Concentrated sulfuric acid> As the concentrated sulfuric acid, those with a concentration of 90 to 100% can be used, preferably 95% or more.

[0014] <Hydrophobic organic solvent> A hydrophobic organic solvent that is non-reactive and immiscible with concentrated sulfuric acid can be used. For example, saturated hydrocarbons such as pentane, hexane, heptane, octane, and halogenated hydrocarbons such as dichloromethane, chloroform can be mentioned, and preferably hexane, heptane, octane.

[0015] <Hydrophobic organic solvent containing siloxanes> Scenes where hydrophobic organic solvents containing siloxanes are generated are diverse. For example, after subjecting virgin silica dispersed in a solution containing a hydrophilic organic solvent and water to silylation treatment with siloxanes, the silylated virgin silica is extracted with a hydrophobic organic solvent to recover the silylated virgin silica. The filtrate in the filtration operation of filtering out hydrophobic silica from a slurry in which hydrophobic silica is dispersed in a hydrophobic organic solvent, and the distillate when drying the filtered hydrophobic silica correspond to hydrophobic organic solvents containing siloxanes.

[0016] Specifically, (1) Step of dispersing virgin silica in a solution containing a hydrophilic organic solvent and water (2) Step of subjecting the virgin silica dispersed in the solution containing a hydrophilic organic solvent and water to silylation treatment with siloxanes (3) Step of extracting the virgin silica silylated with a hydrophobic organic solvent (4) Step of recovering the silylated virgin silica to obtain hydrophobic silica It is a hydrophobic organic solvent containing siloxanes generated in the step of (4) recovering the silylated virgin silica to obtain hydrophobic silica in the method for producing hydrophobic silica powder including the above steps. Hereinafter, each step will be described.

[0017] (1) Step of dispersing virgin silica in a solution containing a hydrophilic organic solvent and water Virgin silica is dispersed in a solution containing a hydrophilic organic solvent and water to prepare a slurry.

[0018] <Virgin silica powder> The virgin silica powder, which is the silica powder before treatment, is a silica powder obtained by a known method and is used without particular limitation. Dry silica, wet silica, sol-gel method silica, etc. are representative. Also, these silicas may be silica powders in which part or all are melted. The virgin silica powder includes wet gels obtained at the final stage of the manufacturing process of wet silica and sol-gel method silica. Also, the virgin silica powder may be in a dispersed liquid state.

[0019] The above-mentioned dry silica is generally obtained by burning a silicon compound such as silicon tetrachloride in an oxyhydrogen flame. Generally, it is also referred to as fumed silica. Dry silica can be obtained with a specific surface area in the range of approximately 50 to 500 m 2 / g by changing the manufacturing conditions. The primary particle diameter of the silica calculated from the specific surface area is in the range of approximately 5 to 200 nm, but it usually exists as aggregates of 1 μm or more.

[0020] As for wet silica, precipitated silica obtained by adding a mineral acid to sodium silicate and neutralizing it to precipitate silica in a solution is typical. Generally, it is also referred to as white carbon.

[0021] In addition, gel method silica obtained by similarly adding sodium silicate to an acid, neutralizing it, and suppressing the growth of primary particles under acidic conditions to cause gelation is also a type of wet silica. The pulverized product thereof can be used as the starting silica powder of the present invention. When pulverization is performed, the shape is amorphous, but when it is preferably spherical, it is preferable to perform the gelation of the gel method silica in a W / O emulsion. For example, (A) A step of preparing an aqueous silica sol (B) A step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O type emulsion (C) A step of converting the W / O type emulsion into a dispersion of a gelled product It can be produced by a method including. The W phase composed of an aqueous silica sol is dispersed in an organic solvent phase. After forming a W / O emulsion, the spherical W phase is gelled to produce spherical primary silica. By subjecting this to filtration, washing, and drying, spherical silica powder is obtained. Further, when the primary silica dispersed in a solution containing a hydrophilic organic solvent and water is spherical gel-method silica, after step (C), a step (D) of separating the dispersion into two layers of an O phase and a W phase to obtain the W phase is provided. Hydrophilic organic solvent and water are added to the dispersion to demulsify it and separate it into two layers of an O phase and a W phase. The aqueous layer separated as the W phase may be directly used as a slurry obtained by dispersing the primary silica in a solution containing a hydrophilic organic solvent and water.

[0022] Wet silica can also be obtained in various types by changing the production conditions, and those with a specific surface area in the range of approximately 50 to 1000 m 2 / g have been obtained. Wet silica is considered to be aggregated particles in which fine particles with a primary particle diameter of approximately 3 to 50 nm are aggregated during synthesis, based on its production method. These wet silicas are usually filtered and washed after the neutralization reaction, and after drying, they are pulverized if necessary to obtain a powder. Generally, the average particle diameter of available wet silica particles is 1 to several hundred micrometers.

[0023] Furthermore, sol-gel method silica is produced by hydrolyzing silicon alkoxides such as tetramethoxysilane and tetraethoxysilane in an acidic or alkaline aqueous organic solvent. Although silicon alkoxides are expensive, they have the characteristic that extremely high-purity silica can be obtained because the raw materials can be highly purified by distillation. When hydrolysis is carried out in an acidic or alkaline concentrated solution, bulk silica is obtained, and by pulverizing it, amorphous silica particles with a size of 1 to several hundred micrometers are obtained.

[0024] As the above sol-gel method silica, so-called silica-based composite oxides such as silica-titania, silica-alumina, and silica-zirconia can also be used as the base silica powder of the hydrophobic silica powder of the present invention. These are obtained by co-hydrolyzing a silicon alkoxide and a metal alkoxide such as titanium, aluminum, or zirconium. These silica-based composite oxides can exhibit useful properties not found in ordinary silica depending on the chemical and physical properties of the metal oxides other than silicon used. For example, the refractive index of the silica-based composite oxide can be adjusted by changing the content of the metal oxide.

[0025] In the present invention, as the base silica powder to be hydrophobized, a silica suitable for the application and having a particle size (specific surface area) may be selected and used from among the above-mentioned types.

[0026] <Preparation of Slurry> The slurry is prepared by adding the base silica to an aqueous solution containing a hydrophilic organic solvent, or conversely, adding the aqueous solution to the base silica. This can be carried out by a known method. The silica concentration in the slurry is preferably 2 to 30% by mass, more preferably 4 to 20% by mass.

[0027] From the viewpoint of increasing the solubility of the hydrophobizing agent in the aqueous solution and promoting the reactivity, the concentration of the hydrophilic organic solvent in the aqueous solution is preferably in the range of 15 to 80 wt%. When the final stage in the production process of the base silica itself is an aqueous solution containing a hydrophilic organic solvent, it can also be treated as a slurry. The type of the hydrophilic organic solvent is arbitrary, but it is preferable to use a low-boiling solvent that can be easily distilled off after hydrophobization. Examples of these include acetone, methanol, ethanol, isopropyl alcohol, etc. Among these, isopropyl alcohol can be preferably used.

[0028] (2) Step of silylating the base silica dispersed in a solution containing a hydrophilic organic solvent and water with siloxanes To the slurry in which the starting silica is dispersed, an acid and siloxanes are added, and they are stirred at a predetermined temperature for a predetermined time to perform silylation treatment.

[0029] The amount of siloxanes used depends on the type of siloxane. For example, when performing silylation treatment with hexamethyldisiloxane, with respect to 100 parts by mass of the starting silica, it is preferably 0.03A to 0.15A parts by mass (where A is the specific surface area of the starting silica (m 2 / g)). More preferably, it is 0.04A to 0.13A parts by mass. When it is desired to adjust the remaining silanol groups of the silica after silylation, an amount less than the above range may be used.

[0030] Also, it is preferable to set the pH of the reaction solution to 0 to 1.0 in order to enhance the efficiency of the silylation reaction and shorten the reaction time. These mineral acids and organic acids are preferably sulfuric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, thiocyanic acid, phosphoric acid, formic acid, acetic acid, trifluoroacetic acid, etc., and among them, sulfuric acid and hydrochloric acid are more preferable.

[0031] The temperature during the silylation treatment is preferably 50 to 70°C, and more preferably 60 to 70°C. If it exceeds this range, although it also depends on the types of siloxanes and hydrophilic organic solvents, there is a risk that these will be distilled off and the progress of silylation will be insufficient. When performing at a temperature exceeding the above range, it is preferable to take measures to suppress the distillation off of siloxanes and hydrophilic organic solvents using a condenser.

[0032] The time required for the silylation treatment varies depending on the specific surface area of the silica starting material, the type of siloxanes, the temperature, and furthermore, the hydrophobicity of the target silica powder. The hydrophobicity can be indicated by the methanol concentration in which the silica powder is suspended as the hydrophobicity (M value), and this can also be considered as an index indicating the progress of the silylation reaction. For example, for 100 parts by mass of the starting silica with a specific surface area of 900 to 1000 m 2 / g, using 73 parts by mass of hexamethyldisiloxane, with the treatment temperature at 60°C, the time required to obtain hydrophobic silica with an M value of around 45 Vol% is 1 hour.

[0033] (3) Step of extracting the original silica silylated with a hydrophobic organic solvent When the slurry after silylation contains an acid such as sulfuric acid, it is preferable to remove the acidic component, and known methods such as neutralization treatment and washing with water can be employed. Among them, the method of adding a basic substance for neutralization treatment is suitable. By adding a basic substance, the pH of the slurry is brought to a state of being neutral to weakly acidic. Specifically, the pH of the slurry is preferably 1.0 to 7.5, and more preferably 1.5 to 7.0.

[0034] As the basic substance, any water-soluble substance can be used, and inorganic bases such as hydroxide salts, carbonate salts, bicarbonate salts, and aqueous ammonia, and organic acid salts such as acetate salts can be used.

[0035] Also, the neutralization treatment can be carried out by maintaining the temperature at 35°C to 80°C. Since an acid-base neutralization reaction, which is an exothermic reaction, occurs in this step, this temperature range can be achieved without particularly heating. The time required for adding the basic substance can be appropriately set according to the temperature of the slurry, but it is 0.5 hour to 1 hour.

[0036] After performing the above neutralization treatment, most of the salts can be removed by removing the aqueous layer generated by extracting the silylated original silica into a hydrophobic organic solvent. The hydrophobic organic solvent used for extracting the silylated original silica is arbitrary, but it is preferably a relatively low boiling point that is easily distilled off during drying and is non-reactive with concentrated sulfuric acid used during the recovery of siloxanes. Hexane, heptane, nonane, decane, etc. can be used, and more preferably hexane, heptane, and decane can be used.

[0037] In the silylated original silica dispersion obtained by the above operation, in which the silylated original silica is extracted into a hydrophobic organic solvent, salts remain. Further, when porous silica or silica aerogel is used as the original silica, salts also remain in the pores. When it is necessary to further remove the remaining salts, it is preferable to wash the silylated original silica dispersion with water or an aqueous solution of alcohol. This washing operation can be performed by a known method. In order to increase the washing efficiency, it is preferable to use an aqueous solution of isopropyl alcohol at several tens of wt%. Also, within a range not exceeding the boiling point of the hydrophobic organic solvent, increasing the temperature is preferable for increasing the washing efficiency. Usually, it can be performed in the range of 45 to 70 °C.

[0038] (4) Step of recovering the silylated original silica to obtain hydrophobic silica To obtain hydrophobic silica powder, after performing the above hydrophobization treatment, the silylated original silica is extracted into a hydrophobic organic solvent, and then the hydrophobic silica is filtered off from the silylated original silica dispersion and dried. The temperature during drying is preferably equal to or higher than the boiling point of the solvent and equal to or lower than the decomposition temperature of the surface treatment agent, and the pressure is preferably normal pressure or reduced pressure.

[0039] In the step of recovering the silylated original silica to obtain hydrophobic silica in (4) above, the filtrate obtained when filtering off the hydrophobic silica from the silylated original silica dispersion and the distillate obtained during drying are hydrophobic organic solvents containing siloxanes, and these can be used as the hydrophobic organic solvents containing siloxanes in the present invention.

[0040] <Recovery method> In the method for recovering siloxanes of the present invention, siloxanes are recovered by extracting siloxanes with concentrated sulfuric acid from a hydrophobic organic solvent solution containing siloxanes. By bringing the hydrophobic organic solvent containing siloxanes into contact with concentrated sulfuric acid, for example, by mixing them, the siloxanes can be extracted into the concentrated sulfuric acid and recovered as a mixture of concentrated sulfuric acid and siloxanes.

[0041] The amount of concentrated sulfuric acid for siloxanes depends on the type of hydrophobizing agent. When recovering hexamethyldisiloxane or octamethylcyclotetrasiloxane, from the perspective of improving the recovery rate of siloxanes, it is preferable to use concentrated sulfuric acid in an amount of at least one-fold the mass of the siloxanes contained in the hydrophobic organic solvent, and more preferably at least 1.5-fold the mass of the siloxanes. Although there is no upper limit to the usage amount, using more than 1.5-fold the mass will hardly change the recovery rate of siloxanes even if the amount of concentrated sulfuric acid used is increased, and it is preferable to avoid using more concentrated sulfuric acid than necessary from the perspective of reducing the environmental load. As described later, the siloxanes recovered as a mixed liquid of concentrated sulfuric acid and siloxanes can be used for the purpose of silylating metal oxides wet under acidic conditions. At this time, the acid used during silylation is concentrated sulfuric acid, and the upper limit of the amount of concentrated sulfuric acid used during the extraction of siloxanes can also be determined considering the concentrated sulfuric acid used during silylation.

[0042] The temperature during the above mixing can be carried out in the range of 10 to 90 °C. If it exceeds 90 °C, depending on the type of siloxanes, there is a concern about the influence of volatilization. Furthermore, at higher temperatures, concentrated sulfuric acid acts as an oxidizing substance, and there is a possibility that siloxanes and hydrophobic organic solvents may be oxidized. Also, if it is less than 10 °C, the degree of phase separation between the organic layer and the sulfuric acid layer may deteriorate.

[0043] The degree of extraction of siloxanes can be grasped by measuring the siloxanes in the hydrophobic organic solvent by gas chromatography or liquid chromatography. The time required for extraction varies depending on the conditions. For example, when 80 g of heptane containing 3% of hexamethyldisiloxane and 45 g of concentrated sulfuric acid are used, by stirring for about 5 minutes, the siloxanes contained in the hydrophobic organic solvent can be reduced to the order of several ppm.

[0044] By extracting siloxanes from a hydrophobic organic solvent solution containing siloxanes with concentrated sulfuric acid, the siloxanes are recovered as a mixed liquid with concentrated sulfuric acid. This mixed liquid of concentrated sulfuric acid and siloxanes can also be used to perform silylation treatment of silica powder.

[0045] Furthermore, the siloxanes can also be obtained by isolating them through adding the mixture of concentrated sulfuric acid and siloxanes obtained by extracting siloxanes to water and hydrating the concentrated sulfuric acid. When isolating the siloxanes extracted into the concentrated sulfuric acid, add the mixture of concentrated sulfuric acid and siloxanes to water, and hydrate the sulfuric acid molecules, then the siloxanes will be liberated and separated into two layers. Since the upper layer is the liberated siloxanes, the liberated siloxanes can be separated by decantation.

[0046] The amount of water used for hydration is preferably 1.5 parts by mass or more based on the mass of the concentrated sulfuric acid. If it is 1.5 parts by mass or more, the sulfuric acid molecules will be completely hydrated, and the sulfuric acid layer will lose its ability to dissolve siloxanes, so that the siloxanes can be recovered with good yield.

[0047] The siloxanes obtained by liberation do not maintain the structure before extraction with concentrated sulfuric acid, except when the siloxanes extracted into the sulfuric acid layer are hexamethyldisiloxane. For example, when bringing a hydrophobic organic solvent containing dialkylsiloxane into contact with concentrated sulfuric acid, the structure of the siloxanes extracted into the concentrated sulfuric acid layer is considered to be dissolved in the form of sulfuric acid silyl esters represented by the following formulas (1) and (2).

[0048] RR’2Si-OSO3H (1) RR’Si-(OSO3H)2(2) [In formulas (1) and (2), R represents a hydrophobic group such as a hydrocarbon group; R’ represents hydrogen or a hydrocarbon group, and a plurality of R and R’ may be the same or different.]

[0049] When hydrating the sulfuric acid layer containing the sulfuric acid silyl ester represented by formula (2), the liberated siloxanes are molecules generated by hydrolysis and condensation polymerization of the sulfuric acid silyl ester, and are a mixture of various chain-like and cyclic siloxanes. On the other hand, when hexamethyldisiloxane having no dimethylsilyl group but only trimethylsilyl group is extracted with concentrated sulfuric acid, it is dissolved only in the form of the above formula (1) in the concentrated sulfuric acid layer, and the siloxane obtained by hydration is hexamethyldisiloxane in which trimethylsilyl groups are ether-bonded.

[0050] Although the uses of siloxanes are diverse, the siloxanes obtained by the method for recovering siloxanes of the present invention are suitable, for example, when silylating the surface of silica powder as in the following formula (3) or (4).

[0051] ≡M-O-SiRR’2(3) (≡M-O-)2SiRR’ (4) [In formulas (3) and (4), R represents a hydrophobic group such as a hydrocarbon group; R’ represents hydrogen or a hydrocarbon group, and a plurality of R and R’ may be the same or different.]

[0052] <Method for producing hydrophobic silica powder> In the method for recovering siloxanes of the present invention, the siloxanes are recovered as a mixed solution of concentrated sulfuric acid and siloxanes, or as isolated siloxanes.

[0053] The isolated siloxanes can be used in applications where siloxanes are normally used. For example, in the method for producing hydrophobic silica powder, hydrophobic silica powder can be obtained by using the siloxanes as siloxanes for silylating silica powder.

[0054] In addition, the siloxanes recovered as a mixed solution of concentrated sulfuric acid and siloxanes can be used for the purpose of silylating metal oxides wet under acidic conditions. For example, in the method for producing hydrophobic silica powder, hydrophobic silica powder can be obtained by using the siloxanes as siloxanes for silylating silica powder. Instead of adding an acid and siloxanes for silylation treatment, silylation treatment can be performed by adding a mixed solution of concentrated sulfuric acid and siloxanes, and hydrophobic silica powder can be obtained.

[0055] As an example, in the description of the hydrophobic organic solvent containing the above siloxanes, (1) Step of dispersing the starting silica in a solution containing a hydrophilic organic solvent and water (2) Step of silylating the starting silica dispersed in a solution containing a hydrophilic organic solvent and water with siloxanes (3) Step of extracting the raw silica silylated with a hydrophobic organic solvent (4) Step of recovering the silylated raw silica to obtain hydrophobic silica A method for producing a hydrophobic silica powder including the above can be mentioned.

[0056] (2) In the step of silylating the raw silica dispersed in a solution containing a hydrophilic organic solvent and water with siloxanes, the addition of siloxanes and the adjustment of pH can be carried out by directly adding the mixed solution containing concentrated sulfuric acid and siloxanes obtained by the method for recovering siloxanes of the present invention. When the amount of siloxanes in the mixed solution is insufficient or the pH does not meet the above range, siloxanes or an acid may be added separately. The acid added separately is not limited to sulfuric acid, and any mineral acid or organic acid can be used.

[0057] Also, the siloxanes (mixed solution of concentrated sulfuric acid and siloxanes or isolated siloxanes) recovered by the method for recovering siloxanes of the present invention used for silylation can be used as the hydrophobic organic solvent containing siloxanes. As described above, in the step of (4) recovering the silylated raw silica to obtain hydrophobic silica, the filtrate obtained when filtering off the hydrophobic silica from the hydrophobic silica dispersion or the distillate obtained during drying can be used, and the siloxanes recovered from these can be used.

Example

[0058] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples at all.

[0059] <Method for measuring siloxanes> The concentration of siloxanes in the hydrophobic organic solvent was measured by gas chromatography. The measuring apparatus, measuring conditions, etc. used are shown below.

[0060] Apparatus: Shimadzu GC-2014 Detector: FID (hydrogen flame ionization detector) Capillary column: Agilent J&W DB-1, length: 60 m, inner diameter: 0.32 mm, film thickness: 5 μm Column temperature: 200 °C Inlet pressure: 100 kPa Column flow rate: 0.89 mL / min Split ratio: 8.4 Injection mode: Split (manual injection) Control mode: Pressure control Vaporization chamber: 250 °C Detector: 250 °C

[0061] <Example 1> 100 g of hexamethyldisiloxane and 200 g of heptane were mixed, and 150 g of 95% concentrated sulfuric acid was added to the solution, followed by stirring at 25 °C for 5 minutes. After standing for 1 minute, the concentration of hexamethyldisiloxane in the upper layer of the resulting two liquid phases, i.e., heptane, was 20 ppm or less, and the extraction rate into the sulfuric acid layer was 99% or more.

[0062] <Example 2> The concentrated sulfuric acid containing siloxanes obtained in Example 1 was added to 225 g of pure water to hydrate the sulfuric acid molecules. Then, it was allowed to stand for 1 minute, and the liberated hexamethyldisiloxane was separated by decantation. The obtained amount was 98.5 g, and the recovery rate with respect to the amount of hexamethyldisiloxane used in Example 1 was 99%.

[0063] <Example 3> 5.48 g of hexamethyldisiloxane and 89.9 g of heptane were mixed, and 45.5 g of 95% concentrated sulfuric acid was added to the solution, followed by stirring at 25 °C for 5 minutes. After standing for 1 minute, the concentration of hexamethyldisiloxane in the upper layer of the resulting two liquid phases, i.e., heptane, was 20 ppm or less, and the extraction rate into the sulfuric acid layer was 99% or more.

[0064] <Example 4> Concentrated sulfuric acid containing the siloxanes obtained in Example 3 was added to 50 g of pure water to hydrate the sulfuric acid molecules. Then, it was allowed to stand for 1 minute, and the liberated hexamethyldisiloxane was separated by decantation. The obtained amount was 5.38 g, and the recovery rate with respect to the amount of hexamethyldisiloxane used in Example 1 was 98%.

[0065] <Reference Production Example> While stirring 915 g of 95% concentrated sulfuric acid with a stirring blade, 1029 g of sodium silicate was gradually added to prepare an aqueous silica sol. At this time, the pH was 2.9.

[0066] To 1944 g of the above-prepared aqueous silica sol, 1804 g of heptane was added, and 21.0 g of sorbitan monooleate was added. This solution was stirred for 2.5 minutes at 5400 revolutions per minute using a homogenizer to form a W / O emulsion.

[0067] The obtained W / O emulsion was gelled at 70°C over 10 minutes while stirring with a stirring blade. Subsequently, 992 g of isopropyl alcohol and 812 g of ion-exchanged water were added, and the organic layer and the aqueous layer were separated while stirring with a stirring blade. Subsequently, 135 g of a 0.5 mol / L aqueous sodium hydroxide solution was added. At this time, the pH of the W phase was 7.5. Aging of the gel was performed at 70°C over 10 minutes. The organic layer was removed by decantation to recover a slurry of the gel.

[0068] To the above slurry of the gel, 636 g of 95% concentrated sulfuric acid and 107 g of hexamethyldisiloxane were added, and silylation treatment was performed at 70°C over 1 hour while stirring. After the silylation treatment, 1818 g of a 24% aqueous sodium hydroxide solution was added while stirring with a stirring blade for neutralization treatment. The pH at this time was 2.0.

[0069] Subsequently, 1259 g of heptane was added, the gel was extracted into the organic layer (heptane layer), the aqueous layer was removed by decantation, and the organic layer was recovered. The organic layer was washed twice with 1804 g of 55% isopropyl alcohol.

[0070] The gelled product in the washed organic layer was separated by suction filtration using a suction filter. Drying of the gelled product was carried out by heating at -100 kPa and 150 °C for 16 hours or more to obtain silica aerogel powder composed of hydrophobic spherical silica aerogel. When the gelled product in the organic layer was separated by suction filtration using a suction filter, the filtrate obtained was 1900 g and contained 3.9% of hexamethyldisiloxane.

[0071] The physical properties of the obtained silica aerogel powder are shown in Table 1.

[0072] <Example 5> To 198 g of the filtrate containing 3.9% of hexamethyldisiloxane obtained when performing the suction filtration operation of the gelled product in the organic layer in the reference production example, 45.5 g of 95% concentrated sulfuric acid was added, and the mixture was stirred at 25 °C for 5 minutes. After standing for 1 minute, the organic layer was removed by decantation to obtain a sulfuric acid layer, which is a mixed liquid of concentrated sulfuric acid and hexamethyldisiloxane from which hexamethyldisiloxane was extracted by concentrated sulfuric acid. At this time, the hexamethyldisiloxane remaining in the organic layer was 20 ppm or less. The obtained sulfuric acid layer was added to 70 g of water to hydrate the sulfuric acid molecules. By separating the supernatant liquid liberated by hydration, 7.7 g of hexamethyldisiloxane was recovered. Using the 7.7 g of the recovered siloxane, a silica aerogel powder composed of hydrophobic spherical silica aerogel was obtained in the same manner as the production method of the silica aerogel powder described in the reference production example except that it was on a 1 / 10 scale. The physical properties of the obtained silica aerogel powder are shown in Table 1.

[0073] <Example 6> When performing the suction filtration operation of the gelling agent in the organic layer in the reference production example, 45.5 g of 95% concentrated sulfuric acid was added to 198 g of the filtrate containing 3.9% of hexamethyldisiloxane obtained, and the mixture was stirred at 25 °C for 5 minutes. After standing for 1 minute, the organic layer was removed by decantation, and hexamethyldisiloxane was recovered as a mixture of hexamethyldisiloxane and concentrated sulfuric acid. At this time, the hexamethyldisiloxane remaining in the organic layer was 20 ppm or less. Instead of 95% concentrated sulfuric acid and siloxane, using the entire amount of the obtained mixture of hexamethyldisiloxane and concentrated sulfuric acid, silica aerogel powder composed of hydrophobic spherical silica aerogel was obtained in the same manner as in the reference example except that it was scaled down to 1 / 10. The physical properties of the obtained silica aerogel powder are shown in Table 1.

[0074] <Evaluation method for hydrophobic silica powder> The following tests were conducted on the hydrophobic silica powders produced in the reference production example, Example 5, and Example 6.

[0075] (M value) Hydrophobic silica powder floats in water but is completely suspended in methanol. Utilizing this, the M value measured by the following method was used as an index for the silylation treatment by the hydrophobic group on the silica surface. Silica powder that is suspended in water without adding methanol by the following method is hydrophilic silica powder, and the M value is 0. Silica powder with an M value of 1 or more is hydrophobic silica powder and floats in water without added methanol. The larger the M value, the more methanol is required for the silica powder to be suspended in water, indicating higher hydrophobicity.

[0076] 0.2 g of hydrophobic silica powder was added to 50 ml of water in a 200 mL beaker and stirred with a magnetic stirrer. Methanol was added using a burette, and the addition was stopped when the entire amount of the hydrophobic silica powder was wetted and suspended in the solvent in the beaker. At this time, the methanol was introduced into the solution through a tube so that the methanol did not directly touch the sample. The volume percentage of methanol in the methanol-water mixed solvent at the end point was defined as the hydrophobicity (M value). M value = (methanol dropping amount / (methanol dropping amount + 50 ml)) × 100

[0077] (carbon content) The siloxanes used in the silylation treatment contain carbon atoms, and there is a positive correlation between the progress of silylation and the carbon amount of the hydrophobic silica powder. The increase in this carbon amount suggests the progress of the silylation treatment by the hydrophobic groups present on the silica surface. Using an elemental analyzer (varioMICRO cube) manufactured by Elementar Japan Co., Ltd., the carbon content was measured and used as an index for the progress of the hydrophobization treatment by the hydrophobic groups on the silica surface.

[0078]

Table 1

[0079] The powders obtained in Examples 3 and 4 where silylation treatment was carried out using hexamethyldisiloxane recovered from the filtrate obtained by the suction filtration operation of the silica slurry in the reference production example, or a mixed solution of hexamethyldisiloxane and concentrated sulfuric acid, showed hydrophobicity equivalent to that of the powder obtained in the reference production example. From this result, it can be seen that concentrated sulfuric acid can be used to recover and further reuse siloxanes from a hydrophobic organic solvent solution (hydrophobic organic solvent) containing siloxanes.

Claims

1. A method for recovering siloxanes by extracting siloxanes from a hydrophobic organic solvent containing siloxanes with concentrated sulfuric acid.

2. The method for recovering siloxanes according to Claim 1, wherein a mixed solution of concentrated sulfuric acid and siloxanes obtained by extracting siloxanes is added to water to obtain siloxanes.

3. The hydrophobic organic solvent containing siloxanes is (1) a step of dispersing raw silica in a solution containing a hydrophilic organic solvent and water (2) a step of silylating the raw silica dispersed in a solution containing a hydrophilic organic solvent and water with siloxanes (3) a step of extracting the raw silica silylated with a hydrophobic organic solvent (4) a step of recovering the silylated raw silica to obtain hydrophobic silica The method for recovering siloxanes according to Claim 1, which is a hydrophobic organic solvent containing siloxanes generated in the step (4) of recovering the silylated raw silica to obtain hydrophobic silica in the method for producing a hydrophobic silica powder including

4. The step (1) of dispersing raw silica in a solution containing a hydrophilic organic solvent and water is (A) a step of preparing an aqueous silica sol (B) a step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O type emulsion (C) a step of converting the W / O type emulsion into a dispersion of a gelled product (D) a step of separating the dispersion into two layers of an O phase and a W phase to obtain a W phase The method for recovering siloxanes according to Claim 3.

5. A method for producing a hydrophobic silica powder, wherein after recovering siloxanes by the method for recovering siloxanes according to Claim 1 or 2, the recovered siloxanes are used to hydrophobize silica powder.

6. (1) a step of dispersing raw silica in a solution containing a hydrophilic organic solvent and water (2) a step of silylating the raw silica dispersed in a solution containing a hydrophilic organic solvent and water with siloxanes (3) a step of extracting the raw silica silylated with a hydrophobic organic solvent (4) a step of recovering the silylated raw silica to obtain hydrophobic silica (5) a step of recovering siloxanes by extracting siloxanes from a hydrophobic organic solvent containing siloxanes generated in the step (4) of recovering the silylated raw silica to obtain hydrophobic silica with concentrated sulfuric acid A method for producing a hydrophobic silica powder including.

7. In the step of recovering the silylated starting silica to obtain hydrophobic silica, after recovering the siloxanes in the step of extracting the siloxanes with concentrated sulfuric acid from the hydrophobic organic solvent containing siloxanes generated in this step, the recovered siloxanes are used as at least a part of the siloxanes in the step of subjecting the starting silica dispersed in a solution containing a hydrophilic organic solvent and water to a silylation treatment with the siloxanes. A method for producing a hydrophobic silica powder according to claim 6.

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