JP5162752B2 - Cellulose airgel and method for producing the same - Google Patents

Description

  The present invention relates to a cellulose airgel and a method for producing the same. In particular, the present invention relates to a cellulose airgel having a high specific surface area and a method for producing the same.

Airgel (also aerogel, aerogel, aerogel, etc.) refers to a substance that is a dry solid with a high porosity and maintains a certain shape.
Since airgel has characteristics such as light weight, low thermal conductivity, large specific surface area, and fine pore diameter, it has various uses such as a heat insulating material, a particulate trapping material, a filter, and a catalyst carrier.
Well-known aerogels include inorganic materials such as silica and metal oxides; organic materials such as airgels made of organic polymers; and inorganic-organic composite materials. Inorganic aerogels generally have a problem that they are low in strength and easily crushed. On the other hand, airgel made of organic polymer generally has high strength and can be used as a raw material for carbon airgel by thermal decomposition. As such, an airgel obtained by gelling and drying resorcinol-formalin resin, so-called RF airgel is known.

As an organic airgel, the preparation of airgel from cellulose has been recently studied. For example, project research was conducted in Europe under the name AeroCell (Non-patent Document 1). In this project, N-methylmorpholine oxide (NMMO) and water are used as a cellulose solvent, and the cellulose is dissolved at a high temperature of 80 ° C. or higher. To play. The liquid-containing gel is subjected to carbon dioxide supercritical drying through solvent substitution, whereby a cellulose airgel having a large specific surface area is obtained. The characteristics of the product by this process, 150 to 250 ² / g as a typical value of the nitrogen adsorption specific surface area, results in 300~370m ² / g is shown in a specific condition. Although the maximum value is 420 m ² / g, the conditions are not disclosed. In Non-Patent Document 1, it is mentioned that an airgel can be obtained by using a solution obtained by dissolving cellulose in a caustic alkali aqueous solution, but no specific data is shown.
Innerlohinger 2006.

However, the solvent described in Non-Patent Document 1, that is, hydrated NMMO, is a solvent used in the production of regenerated cellulose fibers. However, since NMMO is a substance having a high melting point (190 ° C.), it is liquid even in a hydrated state. In order to maintain the temperature, a high temperature of 80 ° C. or higher is required. However, at such a high temperature, there is a problem that explosion is likely to occur and there is a danger.
In addition, there is a cost problem that NMMO is expensive. Furthermore, NMMO is easily decomposed at a high temperature at which cellulose is dissolved and difficult to reuse, and has a problem in cost.
Furthermore, the typical value of the nitrogen adsorption specific surface area of the airgel obtained by Non-Patent Document 1 is 150 to 250 m ² / g, and specific conditions are required to obtain an airgel having a larger nitrogen adsorption specific surface area. There was a drawback of being.

Then, the objective of this invention is providing the manufacturing method of the airgel which does not have the said problem.
Specifically, an object of the present invention is to provide a method for producing an airgel using a solvent having an advantage in ease of handling and / or cost, particularly a specific solvent different from NMMO. is there.
Moreover, the objective of this invention is providing the airgel which has a larger nitrogen adsorption specific surface area in addition to the said objective or in addition to the said objective.

As a result of intensive studies to achieve the above object, the present inventors have found the following invention.
<1> An aqueous solution having i) 2-20% by weight of caustic, preferably 4-10% by weight; and ii) 4-20% by weight of urea or thiourea, preferably 6-15% by weight. A cellulose solution is prepared by dissolving cellulose so that the amount is 0.2 to 20% by weight, preferably 0.3 to 10%, and the cellulose solution is immersed in a cellulose non-solvent to prepare a liquid-containing cellulose gel. A cellulose aerogel obtained by preparing and subjecting the liquid cellulose gel to x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying, wherein the ratio of the cellulose aerogel by nitrogen adsorption BET method A cellulose airgel having a surface area of 300 m ² / g or more, preferably 350 m ² / g or more, more preferably 400 m ² / g or more.

<2> In an organic solvent solution containing 5 to 12% by weight, preferably 6 to 10% by weight of an alkali halide, the amount of cellulose is 0.2 to 20% by weight, preferably 0.5 to 10%. A cellulose solution is prepared by dissolving cellulose in the solution, and the cellulose solution is immersed in a cellulose non-solvent to prepare a liquid-containing cellulose gel. The liquid-containing cellulose gel is x) organic solvent substitution dried, y) supercritical drying, or z) A cellulose aerogel obtained by performing subcritical drying, wherein the specific surface area of the cellulose aerogel by nitrogen adsorption BET method is 300 m ² / g or more, preferably 350 m ² / g or more, more preferably 400 m ² / g. This is the cellulose airgel.

<3> In the above <1> or <2>, the cellulose is at least one selected from the group consisting of plant cellulose, microbial-produced cellulose, squirt sac cellulose, and derivatives thereof, and mixtures thereof. Good.
<4> In the above item <3>, the derivative may be a cellulose derivative obtained by esterifying and / or etherifying a hydroxyl group of cellulose to a substitution degree of 1.0 or less.

<5> In any one of the above items <1> to <4>, the liquid cellulose gel may be chemically hydrophobized and then dried x), y) or z).
<6> In any one of the above items <1> to <5>, an inorganic substance may be attached to the liquid-containing cellulose gel, and then x), y), or z) may be dried. In addition, when performing the chemical hydrophobization treatment, the inorganic substance adhesion can be performed before, after or during the chemical hydrophobization process, and preferably the inorganic substance adhesion is performed before the chemical hydrophobization process. .
<7> In any one of the above items <1> to <6>, the cellulose non-solvent is water, a lower alkyl alcohol (such as methanol or ethanol) and an aqueous solution thereof; a lower ketone (such as acetone); a lower fatty acid ester (such as ethyl acetate). ); Acidic aqueous solution (dilute sulfuric acid, dilute hydrochloric acid, etc.); and dilute aqueous solution of salts (sodium sulfate, etc.); and a mixture thereof, preferably pure water, methanol, ethanol, 20% or less dilute sulfuric acid and 20% or less It is preferable to be selected from the group consisting of a sodium sulfate aqueous solution and a mixture thereof.

<8> Any one of the above <1> to <7> x) Organic solvent substitution drying is acetone, ethanol, methanol, propanol, butanol, aromatic hydrocarbons and halogenated lower hydrocarbons, and derivatives thereof and these A solvent selected from the group consisting of a mixture, preferably 2-propanol, t-butanol, benzene, toluene, and a fluorinated lower hydrocarbon may be used.
<9> Any of the above <1> to <7> y) Supercritical drying is performed under conditions of a temperature of 35 to 60 ° C. and a pressure of 75 to 180 kg / cm ² under CO ₂ immersion or CO ₂ atmosphere. Is good.
<10> Any one of the above <1> to <7> z) Subcritical drying is performed at a temperature below the critical point of each solvent, at a temperature lower by 10 ° C. than the boiling point at normal pressure of the solvent, or higher. It is good.

<11> In any one of the above items <2> to <10>, the organic solvent solution containing an alkali halide may contain lithium chloride.
<12> In any one of the above items <2> to <11>, N, N-dimethylacetamide may be used as the organic solvent solution containing an alkali halide.

<13> A) i) An aqueous solution having 2 to 20% by weight of caustic, preferably 4 to 10% by weight; and ii) 4 to 20% by weight of urea or thiourea, preferably 6 to 15% by weight. , A step of preparing a cellulose solution by dissolving cellulose so that the amount of cellulose is 0.2 to 20% by weight, preferably 0.3 to 10%;
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
A method for producing a cellulose airgel, comprising: C) x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel. The above-mentioned method, wherein the cellulose airgel has a specific surface area of not less than 300 m ² / g, preferably not less than 350 m ² / g, more preferably not less than 400 m ² / g by nitrogen adsorption BET method.

<14> A ′) In an organic solvent solution containing 5 to 12% by weight, preferably 6 to 10% by weight of an alkali halide, the amount of cellulose is 0.2 to 20% by weight, preferably 0.5 to 10%. A step of dissolving cellulose so as to prepare a cellulose solution;
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
A method for producing a cellulose airgel, comprising: C) x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel. The above-mentioned method, wherein the cellulose airgel has a specific surface area of not less than 300 m ² / g, preferably not less than 350 m ² / g, more preferably not less than 400 m ² / g by nitrogen adsorption BET method.

<15> In the above item <13> or <14>, the cellulose is at least one selected from the group consisting of plant cellulose, microorganism-produced cellulose, squirt sac cellulose, and derivatives thereof, and mixtures thereof. Good.
<16> In the above item <15>, the derivative may be a cellulose derivative obtained by esterifying and / or etherifying a hydroxyl group of cellulose to a substitution degree of 1.0 or less.

<17> In any one of the above items <13> to <16>, D) a step of chemically hydrophobizing the liquid cellulose gel is performed after step B), and after step D), x) and y ) Or z) is preferably performed.
<18> In any one of the above items <13> to <17>, E) has a step of attaching an inorganic substance to the liquid cellulose gel after step B), and after step E), x), y) or z) It is better to dry. In addition, when performing D) a chemical hydrophobization treatment process, E) an inorganic substance adhesion process can be performed before this D) process or after or during it, Preferably E) an inorganic substance adhesion process is said D) Chemical It is good to carry out before the hydrophobization process.
<19> In any one of the above items <13> to <18>, the cellulose non-solvent is water, a lower alkyl alcohol (such as methanol or ethanol) and an aqueous solution thereof; a lower ketone (such as acetone); a lower fatty acid ester (such as ethyl acetate). ); Acidic aqueous solutions (diluted sulfuric acid, dilute hydrochloric acid, etc.); and dilute aqueous solutions of salts (such as sodium sulfate); and a mixture thereof, preferably pure water, methanol, ethanol, dilute sulfuric acid of 20% or less and 20%. It is preferable to use a solvent selected from the group consisting of the following aqueous sodium sulfate solutions and mixtures thereof.

<20> Any one of the above <13> to <19> x) Organic solvent substitution drying is acetone, ethanol, methanol, propanol, butanol, aromatic hydrocarbons and halogenated lower hydrocarbons, and derivatives thereof and these A solvent selected from the group consisting of a mixture, preferably 2-propanol, t-butanol, benzene, toluene, and a fluorinated lower hydrocarbon may be used.
<21> Any of the above <13> to <19> y) Supercritical drying is performed under conditions of a temperature of 35 to 60 ° C. and a pressure of 75 to 180 kg / cm ^{2 in} a CO ₂ immersion or CO ₂ atmosphere. Is good.
<22> The subcritical drying of any one of the above <13> to <19> is performed at a temperature below the critical point of each solvent, at a temperature lower by 10 ° C. than the boiling point at normal pressure of the solvent, or higher. It is good.

<23> In any one of the above items <14> to <22>, the organic solvent solution containing an alkali halide may contain lithium chloride.
<24> In any one of the above items <14> to <23>, N, N-dimethylacetamide may be used as the organic solvent solution containing an alkali halide.

<25> A cellulose airgel carbide obtained by heat-treating the cellulose airgel according to any one of the above <1> to <12> at 150 ° C. or higher, preferably 200 to 3000 ° C. in a non-oxidizing atmosphere.
<26> A carbide of cellulose airgel obtained by heat-treating the cellulose airgel obtained by any one of the above methods <13> to <24> at 150 ° C. or higher, preferably 200 to 3000 ° C. in a non-oxidizing atmosphere.

<27> A method for producing a carbide of cellulose airgel, comprising the following steps:
A) i) 2-20% by weight of caustic; and ii) 4-20% by weight of urea or thiourea in an aqueous solution so that the cellulose content is 0.2-20% by weight. Step of dissolving and preparing a cellulose solution; or A ′) Cellulose solution by dissolving cellulose in an organic solvent solution containing 5 to 12% by weight of an alkali halide so that the amount of cellulose is 0.2 to 20% by weight. The step of preparing
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
C) The liquid cellulose cellulose gel is subjected to x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel having a specific surface area of 300 m ² / g or more by nitrogen adsorption BET method. And F) a step of heat-treating the obtained cellulose airgel at 150 ° C. or higher in a non-oxidizing atmosphere to obtain a carbide of cellulose airgel;
The above method.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for producing an airgel using a specific solvent different from NMMO, particularly a solvent having ease of handling and / or cost advantages.
Further, according to the present invention, an airgel having a larger nitrogen adsorption specific surface area can be provided in addition to or in addition to the above effects.

Hereinafter, the present invention will be described in detail.
The present invention provides a cellulose airgel having a high nitrogen adsorption specific surface area by the following method.
That is, the process of the present invention comprises A) i) 2-20% by weight of caustic, preferably 4-10% by weight; and ii) 4-20% by weight of urea or thiourea, preferably 6-15% by weight. A step of dissolving the cellulose in an aqueous solution having a weight ratio of 0.2 to 20%, preferably 0.3 to 10% to prepare a cellulose solution;
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
C) The liquid-containing cellulose gel is subjected to x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel.

Alternatively, in the method of the present invention, A ′) an organic solvent solution containing 5 to 12% by weight of an alkali halide, preferably 6 to 10% by weight, and the cellulose content is 0.2 to 20% by weight, preferably 0. A step of dissolving cellulose so as to be 5 to 10% to prepare a cellulose solution;
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
C) The liquid-containing cellulose gel is subjected to x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel.

By the method using the above step A) or A ′), a cellulose airgel having a specific surface area by a nitrogen adsorption BET method of 300 m ² / g or more, preferably 350 m ² / g or more, more preferably 400 m ² / g or more is obtained. be able to.

The cellulose used in the method of the present invention may be at least one selected from the group consisting of plant cellulose, microbial-produced cellulose, squirt sac cellulose and derivatives thereof, and mixtures thereof. In particular, wood cellulose, cotton cellulose, or sea squirt cellulose, or a mixture thereof is preferable.
The cellulose derivatives may be cellulose derivatives obtained by esterifying and / or etherifying a hydroxyl group of cellulose to a substitution degree of 1.0 or less, preferably a substitution degree of 0.1 to 0.8.

Step A) or step A ′) of the method of the present invention is a step of preparing a cellulose solution by dissolving cellulose in a specific solvent.
In order to obtain an airgel having a large specific surface area, which is the object of the present invention, a solvent that forms cellulose fibrils as fine as possible is used in the step B) described below, ie, when cellulose is gelled with a cellulose non-solvent. Is good. Generally, when the fibrils are fine, light is not scattered. Therefore, for the above purpose, a solvent that generates a highly transparent gel as much as possible at the time of liquid-containing cellulose gel generation (hereinafter sometimes referred to as “regeneration”) is suitable. The following is suitable as such a solvent.

The solvent used in step A) is i) 2-20% by weight of caustic, preferably 4-10% by weight; and ii) 4-20% by weight of urea or thiourea, preferably 6-15% by weight. It is the aqueous solution which has.
Here, i) Caustic is NaOH or LiOH, or a mixture thereof. Preferably, it is NaOH. Ii) Of urea or thiourea, urea is preferred.

  The solvent used in step A ′) is an organic solvent, preferably N, N-dimethylacetamide. Further, an alkali halide, preferably lithium chloride is used as the solvent.

  In the case of using either the A) step or the A ′) step, it is considered that the following effects are exhibited by using a specific solvent. That is, the solvent used in any process is easy to handle. In particular, the solvent used in the step A) uses only low-cost, low-toxicity, low-environmental chemicals, and has high practical value.

After step A) or step A ′), the step B) is performed.
Step B) is a step of preparing a liquid-containing cellulose gel by immersing the cellulose solution obtained in step A) or A ′) in a cellulose non-solvent.
The cellulose non-solvent is not particularly limited as long as it does not dissolve cellulose. Cellulose non-solvents include water, lower alkyl alcohols (methanol, ethanol, etc.) and aqueous solutions thereof; lower ketones (acetone, etc.); lower fatty acid esters (e.g., ethyl acetate); acidic aqueous solutions (diluted sulfuric acid, dilute hydrochloric acid, etc.); A dilute aqueous solution of sodium and the like; and a mixture thereof, preferably selected from the group consisting of pure water, methanol, ethanol, 20% or less dilute sulfuric acid and 20% or less sodium sulfate aqueous solution and mixtures thereof. Good.

In the step B), it can be prepared into a liquid-containing cellulose gel having an arbitrary shape. That is, when a cellulose solution is immersed in a cellulose non-solvent, the cellulose solution is injected into a mold having a desired shape, and the mold into which the solution has been injected is immersed in the cellulose non-solvent, thereby obtaining a liquid-containing cellulose having a desired shape. Gels can be prepared. In addition, the specific method described in Non-Patent Document 1 that gives a specific surface area of 300 m ² / g or more is a method of directly dropping high-temperature microscopic droplets into ice-cold water, so that the liquid-containing cellulose having a desired shape A gel or cellulose aerogel cannot be prepared.

  In the state in which the liquid-containing cellulose gel is obtained, the liquid in the liquid-containing cellulose gel can be replaced with any solvent compatible therewith. Solvent used in step A) or A ′), compound used in the step, specifically caustic and urea or thiourea in step A) and / or alkali halide in step A ′) and B) In order to remove the cellulose non-solvent used in the process, it is washed with an appropriate solvent such as water or ethanol, and then replaced with an arbitrary solvent. Note that conventional cellulose solvents such as cellulose solutions such as viscose, copper ammonia, and rhodium calcium often become cloudy during the step B) and are not suitable for the present invention.

After the step B), the step C) is applied.
A step of chemically hydrophobizing the D-containing liquid cellulose gel may be provided after the step B) and before the step C).
Further, after step B) and before step C), E) a step of attaching an inorganic substance to the liquid cellulose gel may be provided. In addition, when providing both D) process and E) process, E) process can be performed before D) process, with D) process, or after D) process, Preferably E) process is said D) chemical It is good to carry out before the hydrophobization process.

Step D) is a step of chemically hydrophobizing the liquid-containing cellulose gel. Specifically, this is a step of treating a liquid-containing cellulose gel with a silylating agent such as hexamethyldisilazane to introduce a silyl group on the surface of the cellulose fibril constituting the gel. More specifically, it is preferable to replace the liquid containing the liquid-containing cellulose gel with an organic solvent having no hydroxyl group before the silylating agent treatment.
By applying this step, the airgel obtained through step C), for example, supercritical drying, becomes hydrophobic. For this reason, it has water repellency and affinity with a synthetic resin, and can be applied as a material having such characteristics.

Step E) is a step of attaching an inorganic substance to the liquid-containing cellulose gel.
By this step, the following effects can be achieved. In other words, the liquid cellulose gel is a three-dimensional network structure having fine cellulose fibrils as constituent elements. Such a structure can be infiltrated and / or impregnated with any solution of a low-molecular substance using a solvent compatible with the contained liquid. If such a solution is used in which a solid is precipitated by a chemical reaction, and the reaction conditions (temperature, order of impregnation, concentration of low molecular weight substance, etc.) are appropriately controlled, fine particles will be formed in the gel network. Can be formed. Such particles adhere to the cellulose fibrils or are retained in the gel in a confined form in the network without adhesion. By drying the liquid-containing cellulose gel to which the inorganic material is adhered in this manner in the subsequent step C), a cellulose airgel in which the inorganic fine particles are retained or the cellulose fibrils are coated with the inorganic thin film can be obtained. Such cellulose airgel can be applied to conductive materials, catalysts, electrodes, and the like.

After step B), step D) and / or step E) are applied as desired, and then step C). Step C) is a step of drying the liquid cellulose gel to obtain a cellulose aerogel.
The drying step in step C) can be performed by x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying.

  x) Organic solvent substitution drying is a step of substituting the liquid contained in the liquid-containing cellulose gel with another solvent, that is, an organic solvent, and then drying the substituted organic solvent. As other solvents, ie organic solvents, acetone, ethanol, methanol, propanol, butanol, aromatic hydrocarbons and halogenated lower hydrocarbons, and their derivatives and mixtures thereof, preferably 2-propanol, t -Selected from the group consisting of butanol, benzene, toluene, and fluorinated lower hydrocarbons, but is not limited thereto. It is preferable to use t-butanol, benzene, or halogenated lower hydrocarbon or a derivative thereof as another solvent, and most preferably t-butanol or fluorinated lower hydrocarbon. In addition, as a drying method in x) organic solvent substitution drying, a freeze drying method or a subcritical drying, preferably a freeze drying method is used.

y) Supercritical drying is a process of drying a liquid-containing cellulose gel in a supercritical atmosphere. Here, as supercriticality, it is good to carry out under conditions of a temperature of 35 to 60 ° C. and a pressure of 75 to 180 kg / cm ² under CO ₂ immersion or CO ₂ atmosphere.
When the liquid contained in the liquid cellulose gel is an organic solvent, ethanol and methanol are suitable for supercritical drying. For subcritical drying, solvents such as ethanol, methanol, aliphatic and aromatic hydrocarbons, halogenated hydrocarbons, ketones and esters are suitable.
When carbon dioxide supercritical drying is performed, it is preferable to wash the liquid-containing cellulose gel and replace the contained liquid with an appropriate intermediate solvent. As the intermediate solvent, an organic solvent compatible with both water and liquid carbon dioxide, such as lower alcohol, acetone, tetrahydrofuran, aprotic polar solvent (N, N-dimethylacetamide, N, N-dimethylformamide, dimethylsulfoxide) Etc.).

z) Subcritical drying is a step of drying a liquid-containing cellulose gel under a subcritical atmosphere. As subcritical conditions, it is good to carry out at the temperature below the critical point of each solvent, the temperature 10 degreeC lower than the boiling point in the normal pressure of this solvent, or more.
When the liquid contained in the liquid-containing cellulose gel is an organic solvent, solvents such as ethanol, methanol, aliphatic and aromatic hydrocarbons, halogenated hydrocarbons, ketones and esters are suitable for subcritical drying.
When carbon dioxide subcritical drying is performed, it is preferable to wash the liquid-containing cellulose gel and replace the contained liquid with an appropriate intermediate solvent. As the intermediate solvent, an organic solvent compatible with both water and liquid carbon dioxide, such as lower alcohol, acetone, tetrahydrofuran, aprotic polar solvent (N, N-dimethylacetamide, N, N-dimethylformamide, dimethylsulfoxide) Etc.).

As described above, the specific surface area of the cellulose airgel, particularly the nitrogen adsorption BET method is 300 m ² / g by passing through the steps A) or A ′), B) and C) and optionally the steps D) and / or E). The cellulose airgel which is the above can be obtained. In particular, a cellulose airgel having a specific surface area by a nitrogen adsorption BET method of preferably 350 m ² / g or more, more preferably 400 m ² / g or more can be obtained.

As described above, since the cellulose airgel of the present invention has characteristics such as light weight, low thermal conductivity, large specific surface area, and fine pore diameter, it has various uses such as a heat insulating material, a particulate trapping material, a filter, and a catalyst carrier.
In particular, the cellulose aerogel of the present invention is significantly superior in mechanical strength and moisture resistance, although it is inferior in transparency and specific surface area as compared to the conventionally known silica aerogel, and may be used as a raw material for pyrolytic carbon. it can. Applications that make use of these characteristics include adsorbents; particulate trapping filters; catalyst carriers; buffer materials; heat insulating materials; In addition, due to carbonization and / or inorganic substance adhesion, electronic materials; electromagnetic wave shielding materials; magnetic materials; various battery materials such as fuel cell materials (particularly electrode materials), lithium ion battery materials (particularly electrode materials), It can be applied to double layer capacitor materials (particularly electrode materials).

The cellulose airgel obtained as described above can be further subjected to a heat treatment step to obtain a carbide of the cellulose airgel. That is, the cellulose airgel can be heat-treated at 150 ° C. or higher, preferably 200 to 3000 ° C. in a non-oxidizing atmosphere to obtain a cellulose airgel carbide.
Here, examples of the non-oxidizing atmosphere include a vacuum, a nitrogen atmosphere, and an argon atmosphere, but the atmosphere is not limited thereto as long as the atmosphere does not include oxygen.

  The thus obtained carbide of cellulose airgel can be applied to conductive materials, electrodes, and adsorbents.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to a present Example.

When 95 g of an aqueous solution containing 7 g of sodium hydroxide and 12 g of urea was cooled to −12 ° C. and 5 g of filter paper pulp (Advantech Toyo) was added and stirred, the cellulose quickly dissolved to give a transparent solution.
About 5 mL of the solution was poured onto a glass plate, and a 0.5 mm-thick solution layer was formed by spreading with a glass rod wound with a wire having a diameter of 0.5 mm at both ends, and immediately immersed in 100 mL of 5% sulfuric acid. After standing for 10 minutes, the solution gelled and could be peeled off from the glass plate to obtain a cellulose gel. The cellulose gel was thoroughly washed with water and then with ethanol, and then carbon dioxide supercritical drying (temperature: 40 ° C .; pressure 90 kg / cm ² ) with a supercritical carbon dioxide drying apparatus (Hitachi HCP-2). -1 was obtained.
The adsorption property of the airgel A-1 was measured with a Quantachrome-Nova4000 type nitrogen adsorption device, and a nitrogen adsorption specific surface area by the BET method: 391.8 m ² / g was obtained. The density obtained from the size and weight of the airgel was 0.20 g / cm ³ , and based on this, the porosity calculated as the density of the cellulose substantial part was 1.5 g / cm ³ was 86.7%.

Airgel A-2 was obtained in the same manner as in Example 1 except that solvent substitution drying into t-butyl alcohol was performed instead of the supercritical carbon dioxide drying in Example 1.
By measuring the properties of the obtained airgel A-2 in the same manner as in Example 1, specific surface area: 366.1 m ² / g, density: 0.22 g / cm ³ , and porosity: 86.9% were obtained. It was.

(Comparative Example 1)
Airgel CA-1 was obtained in the same manner as in Example 1 except that solvent substitution drying into water was performed instead of supercritical carbon dioxide drying in Example 1. Unlike airgel A-1 and A-2, this was a cloudy substance. By measuring the characteristics of the airgel CA-1 in the same manner as in Example 1, specific surface area: 133.3 m ² / g, density: 0.16 g / cm ³ , and porosity: 89.9% were obtained.

In place of sodium hydroxide 7% which is caustic alkali component in Example 1, lithium hydroxide is 4.6%, filter paper pulp charge concentration is 6%, and pure water is used instead of 5% sulfuric acid which is a regeneration bath. Airgel B-1 was obtained by the same method as in Example 1 except that. By measuring the properties of the airgel B-1 in the same manner as in Example 1, a nitrogen adsorption specific surface area: 406 m ² / g, a density: 0.16 g / cm ³ , and a porosity: 89.9% were obtained.

Airgel B-2 was obtained in the same manner as in Example 3, except that 100% ethanol was used instead of pure water as the regeneration bath in Example 3. By measuring the properties of airgel B-2 in the same manner as in Example 1, specific surface area: 410 m ² / g, density: 0.19 g / cm ³ , and porosity: 88.7% were obtained.

Aerogel B-3 was prepared in the same manner as in Example 4 except that the cellulose concentration in Example 4 was 4%, and 90 vol% ethanol (the remaining 10 vol% was water) instead of 100% ethanol as the regeneration bath. Obtained. By measuring the characteristics of the airgel B-3 in the same manner as in Example 1, specific surface area: 416 m ² / g, density: 0.10 g / cm ³ , and porosity: 94.3% were obtained.

Airgel B-4 was obtained by the same method as in Example 5 except that the cellulose concentration in Example 5 was changed to 6%. By measuring the properties of airgel B-4 in the same manner as in Example 1, specific surface area: 389 m ² / g, density: 0.13 g / cm ³ , and porosity: 90.4% were obtained.

Airgel B-5 was obtained in the same manner as in Example 4 except that 100% methanol was used instead of 100% ethanol as the regeneration bath in Example 4. By measuring the characteristics of the airgel B-5 in the same manner as in Example 1, specific surface area: 369 m ² / g, density: 0.16 g / cm ³ , and porosity: 89.8% were obtained.

Airgel B-6 was obtained in the same manner as in Example 4 except that 100% acetone was used instead of 100% ethanol as the regeneration bath in Example 4. By measuring the characteristics of the airgel B-6 in the same manner as in Example 1, a specific table area: 308 m ² / g, density: 0.58 g / cm ³ , and porosity: 61.8% were obtained.

Airgel B-7 was obtained in the same manner as in Example 5, except that 100% 2-propanol was used instead of 90% ethanol which was the regeneration bath in Example 5. By measuring the properties of the airgel B-7 in the same manner as in Example 1, specific surface area: 328 m ² / g, density: 0.33 g / cm ³ , and porosity: 78.7% were obtained.

Airgel B-8 was obtained in the same manner as in Example 7, except that Whatman CF11 was used instead of the filter paper pulp in Example 7. By measuring the properties of the airgel B-8 in the same manner as in Example 1, specific surface area: 452 m ² / g, density: 0.11 g / cm ³ , and porosity: 92.7% were obtained.

Airgel B-9 was obtained in the same manner as in Example 10 except that cotton linter was used instead of Whatman CF11 in Example 10 and the cellulose concentration was 5%. By measuring the properties of airgel B-9 in the same manner as in Example 1, specific surface area: 485 m ² / g, density: 0.13 g / cm ³ , and porosity: 91.3% were obtained.

<Preparation of sea squirt skin cellulose>
The raw material which preserve | saved the maboya sac obtained as a processed food waste of a maboya in 0.2% NaOH at room temperature was defibrated with the mixer. The defibrated material was soaked in 5% NaOH at room temperature overnight, washed with water, and then treated in a 0.3% aqueous sodium chlorite solution at 60 ° C. for 2 hours three times to remove non-cellulose components. The treated product was thoroughly washed with water and then freeze-dried from water to obtain squirt sac cellulose.
<Preparation of squirt cellulose>
Airgel B-10 was obtained in the same manner as in Example 11 except that the above-mentioned sea squirt sac cellulose was used in place of the cotton linter in Example 11 and the cellulose concentration was 3%. By measuring the characteristics of airgel B-10 in the same manner as in Example 1, specific surface area: 392 m ² / g, density: 0.11 g / cm ³ , and porosity: 92.5% were obtained.

Airgel B-11 was obtained in the same manner as in Example 12 except that the cellulose concentration in Example 12 was changed to 0.5%. By measuring the properties of airgel B-11 in the same manner as in Example 1, specific surface area: 481 m ² / g, density: 0.01 g / cm ³ , and porosity: 98.0% were obtained.

5 g of filter paper pulp powder (manufactured by Advantech Toyo Co., Ltd.) was dissolved in an 8.0% N, N-dimethylacetamide (DMAc) solution containing 95 g of lithium chloride (Wako Pure Chemicals, special grade) at room temperature. The solution was made into a 0.5 mm layer in the same manner as in Example 1, then gelled by immersion in 100% ethanol, and thoroughly washed with ethanol. The cellulose gel was supercritically dried with carbon dioxide to obtain an airgel C-1. By measuring the properties of the airgel C-1 in the same manner as in Example 1, a nitrogen adsorption specific surface area: 474 m ² / g, a density: 0.23 g / cm ³ , and a porosity: 85.1% were obtained.

The pure ethanol contained in the liquid cellulose gel obtained in Example 4 was replaced with heptafluorocyclopentane (product name: Zeolora H, manufactured by Nippon Zeon Co., Ltd.), and then freeze-dried under vacuum to obtain an airgel D -1 was obtained. The characteristics of the airgel D-1 were measured in the same manner as in Example 1 to obtain a nitrogen adsorption specific surface area: 389 m ² / g. The heptafluorocyclopentane (manufactured by Nippon Zeon Co., Ltd., trade name Zeorolla H) was also applicable to the preparation of inorganic aerogels such as silica.

After 90% ethanol contained in the liquid-containing cellulose gel obtained in Example 5 was replaced with pure water and sufficiently washed, the cellulose gel was immersed in a 0.17% silver nitrate aqueous solution and allowed to stand for 10 minutes or more. The solution was allowed to penetrate into the gel. When the cellulose gel containing the silver nitrate solution is immersed in a 0.4% sodium borohydride (NaBH ₄ ) solution and left at 25 ° C. for 3 hours, the silver ions are reduced and precipitated in the gel as silver fine particles. It changed. After the gel was sufficiently washed with water, the contained liquid was replaced with ethanol, and CO ₂ supercritical drying was performed in the same manner as in Example 1 to obtain an airgel Ag. By measuring the characteristics of the airgel Ag in the same manner as in Example 1, a nitrogen adsorption specific surface area of 341 m ² / g and a density of 0.11 g / cm ³ were obtained. Nitrogen adsorption specific surface area: 416 m ² / g, density: 0.10 g / cm ³ ).

After 90% ethanol contained in the liquid-containing cellulose gel obtained in Example 6 was replaced with pure water and thoroughly washed, the cellulose gel was immersed in a 2.43% iron chloride (III) (FeCl ₃ ) aqueous solution. The solution was allowed to permeate into the gel for 10 minutes or longer. When the cellulose chloride containing iron chloride solution was immersed in 28% ammonia water and allowed to stand at 21 ° C. for 30 minutes, iron ions were reduced and precipitated as iron hydroxide fine particles in the gel, and the gel was browned. After sufficiently washing the gel with water, the contained liquid was replaced with ethanol, and CO ₂ supercritical drying was performed in the same manner as in Example 1 to obtain airgel Fe. The characteristics of the airgel Fe were measured in the same manner as in Example 1 to obtain a nitrogen adsorption specific surface area of 426 m ² / g and a density of 0.244 g / cm ³ (the value without adhesion of iron hydroxide is Example 6). More specifically, nitrogen adsorption specific surface area: 389 m ² / g, density: 0.13 g / cm ³ ).

After 90% ethanol contained in the liquid-containing cellulose gel obtained in Example 6 was replaced with pure water and thoroughly washed, the cellulose gel was immersed in a 2.21% cobalt (II) chloride (CoCl ₂ ) aqueous solution. The solution was allowed to permeate into the gel for 10 minutes or longer. When the cellulose gel containing the cobalt chloride solution was immersed in 28% ammonia water and allowed to stand at 21 ° C. for 30 minutes, cobalt ions were reduced and precipitated in the gel as cobalt hydroxide fine particles, and the gel was colored light red. After sufficiently washing the gel with water, the contained liquid was replaced with ethanol, and CO ₂ supercritical drying was performed in the same manner as in Example 1 to obtain airgel Co. The characteristics of the airgel Co were measured in the same manner as in Example 1 to obtain a nitrogen adsorption specific surface area: 398 m ² / g and density: 0.324 g / cm ³ (the value without cobalt hydroxide adhesion is Example 6). More specifically, nitrogen adsorption specific surface area: 389 m ² / g, density: 0.13 g / cm ³ )

Ethanol contained in the liquid-containing cellulose gel obtained in Example 4 was solvent-substituted with n-hexane. 1 g of the n-hexane cellulose gel was placed in 50 g of n-hexane, 4 g of hexamethyldisilazane (HMDS, Wako Pure Chemical Industries) was added at room temperature, and the mixture was reacted at 60 ° C. for 12 hours. Thereafter, the hexane-containing cellulose gel was obtained by thoroughly washing with n-hexane to remove unreacted HMDS. The hexane-silylated cellulose gel was subjected to CO ₂ supercritical drying in the same manner as in Example 1 to obtain airgel Si. By measuring the properties of the airgel Si in the same manner as in Example 1, a nitrogen adsorption specific surface area of 328 m ² / g and a density of 0.28 g / cm ³ were obtained.

The airgel B-8 obtained in Example 10 was heat-treated in a muffle furnace (Advantech Toyo FUW210PA) under a nitrogen stream at a heating rate of 10 ° C./minute up to 600 ° C. to obtain a carbon airgel 1 that is an airgel carbide. . By measuring the characteristics of the carbon airgel 1 in the same manner as in Example 1, a nitrogen adsorption specific surface area of 151 m ² / g was obtained.

The airgel Fe obtained in Example 17 was heat-treated in a muffle furnace (Advantech Toyo FUW210PA) under a nitrogen stream at a heating rate of 10 ° C./minute up to 400 ° C. to obtain carbon airgel Fe, which is a carbide of airgel Fe. It was. By measuring the characteristics of the carbon airgel Fe in the same manner as in Example 1, a nitrogen adsorption specific surface area of 166 m ² / g was obtained.

(Comparative Example 2)
3 g of agarose powder (Wako Pure Chemical Industries) was dispersed in 97 g of pure water and dissolved by stirring at 95 ° C. for 10 minutes. About 5 mL of the solution was heated upstream of the glass plate and spread with a glass rod wound with a wire having a diameter of 0.5 mm at both ends to form a solution layer having a thickness of 0.5 mm and then left to cool. Gelled. The agarose hydrogel-containing liquid was replaced with ethanol, and CO ₂ supercritical drying (temperature: 40 ° C .; pressure 90 kg / cm ² ) was performed in the same manner as in Example 1 to obtain an airgel CAA.
By measuring the characteristics of the airgel CAA in the same manner as in Example 1, a nitrogen adsorption specific surface area: 122.1 m ² / g, a density: 0.26 g / cm ³ , and a porosity: 84.7% were obtained.

(Comparative Example 3)
9.8 g of copper (II) hydroxide (Cu (OH) ₂ ) was dissolved in 50 mL of deionized water, and 13.4 mL of ethylene diamine was added with ice cooling and dissolved by stirring. This was diluted with water to make a total volume of 100 mL, and a copper ethylenediamine solution was prepared.
6 g of filter paper pulp powder (manufactured by Advantech Toyo Co., Ltd.) is dispersed in 94 g of the copper ethylenediamine solution obtained above at room temperature, cooled to −30 ° C., frozen, returned to room temperature and stirred for 5 minutes to dissolve the cellulose. Dissolved. The cellulose solution was cast on a glass plate in the same manner as in Example 1, and gelled by immersing in 100 mL of ethanol. This gel was sufficiently washed with ethanol, and dried by solvent substitution with t-butyl alcohol in the same manner as in Example 2 to obtain an airgel CB.
The airgel CB was colored blue and was significantly shrunk and deformed by drying, and density measurement from the dimensions could not be performed. By measuring the nitrogen adsorption specific surface area of the airgel CB in the same manner as in Example 1, 249 m ² / g was obtained.

(Comparative Example 4)
6 g of filter paper pulp powder (manufactured by Advantech Toyo Co., Ltd.) was immersed in 300 g of 16.5% NaOH at 21 ° C. and left to swell for 12 hours. The mixture was squeezed to 18 g, then loosened, and further left to stand at 21 ° C. for 12 hours for aging. Cellulose xanthate was obtained by adding 1.92 g of carbon disulfide CS ₂ to the aged product. By adding 80 g of 4% NaOH aqueous solution to the cellulose xanthate and stirring, a 6% viscose solution was obtained.
The viscose solution was cast on a glass plate in the same manner as in Example 1, and gelled by immersion in 100 mL of 5% sulfuric acid. This gel was sufficiently washed with water, subjected to ethanol substitution, solvent-substituted and dried with t-butyl alcohol in the same manner as in Example 2, and airgel CC was obtained.
The airgel CC was remarkably shrunk and deformed by drying, and the density measurement from the dimensions could not be performed. 202 m ² / g was obtained by measuring the nitrogen adsorption specific surface area of the airgel CC in the same manner as in Example 1.

When compared with the same concentration (6%) of the same cellulose raw material (filter paper pulp), the airgels B-1, B-2, B-4, and B-5 of the present invention are all 300 m ² / g or more, preferably Gives a specific surface area of 350 m ² / g or more, more preferably 400 m ² / g or more, whereas the airgels CB and CC shown in Comparative Examples 3 and 4 give values of 250 m ² / g or less.
The specific surface area value of the airgel according to the present invention does not depend so much on the cellulose concentration, and tends to be strongly influenced by the type of the regeneration bath. And in a suitable condition, the large specific surface area close | similar to 500 m < ² > / g is given like airgel B-9 and airgel G-1. This is due to the fact that by using the solvent defined in the present invention, the behavior of cellulose molecules in the regeneration process is favorable for the preparation of the airgel, that is, the aggregation at the time of drying hardly occurs even though the fibrils are thin.
In addition, it can be observed by transparency of the obtained airgel that aggregation of a cellulose is suppressed and a fibril becomes thin. That is, the airgel of the present invention having a large specific surface area was translucent, whereas the airgel group of the comparative example was strongly cloudy.

Claims (15)

Cellulose is dissolved in an aqueous solution having i) caustic 2 to 20% by weight; and ii) urea or thiourea 4 to 20% by weight so that the amount of cellulose is 0.2 to 20% by weight. A cellulose solution is prepared, and the cellulose solution is immersed in a cellulose non-solvent to prepare a liquid-containing cellulose gel. The liquid-containing cellulose gel is dried by x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying. A cellulose aerogel obtained by carrying out the above, wherein the cellulose aerogel has a specific surface area of 300 m ² / g or more by a nitrogen adsorption BET method. A cellulose solution is prepared by dissolving cellulose in an organic solvent solution containing 5 to 12% by weight of an alkali halide so that the amount of cellulose is 0.2 to 20% by weight, and the cellulose solution is immersed in a cellulose non-solvent. A cellulose aerogel obtained by preparing a liquid-containing cellulose gel and performing x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying of the liquid-containing cellulose gel, A cellulose aerogel having a specific surface area of 300 m ² / g or more by nitrogen adsorption BET method.   The cellulose aerogel according to claim 1 or 2, wherein the cellulose is at least one selected from the group consisting of plant cellulose, microbial-produced cellulose, ascidian sac cellulose and derivatives thereof, and mixtures thereof.   The cellulose aerogel according to claim 3, wherein the derivative is a cellulose derivative obtained by esterifying and / or etherifying a hydroxyl group of cellulose to a substitution degree of 1.0 or less.   The cellulose airgel according to any one of claims 1 to 4, wherein the liquid-containing cellulose gel is chemically hydrophobized, and then the x), y) or z) is dried.   The cellulose airgel according to any one of claims 1 to 5, wherein an inorganic substance is adhered to the liquid-containing cellulose gel, and then the drying of x), y) or z) is performed. A) i) 2-20% by weight of caustic; and ii) 4-20% by weight of urea or thiourea in an aqueous solution so that the cellulose content is 0.2-20% by weight. Dissolving and preparing a cellulose solution;
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
A method for producing a cellulose airgel, comprising: C) x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel. The above-mentioned method, wherein the cellulose airgel has a specific surface area of 300 m ² / g or more by nitrogen adsorption BET method. A ′) A step of dissolving cellulose in an organic solvent solution containing 5 to 12% by weight of an alkali halide so that the amount of cellulose is 0.2 to 20% by weight to prepare a cellulose solution;
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
A method for producing a cellulose airgel, comprising: C) x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel. The above-mentioned method, wherein the cellulose airgel has a specific surface area of 300 m ² / g or more by nitrogen adsorption BET method.   The method according to claim 7 or 8, wherein the cellulose is at least one selected from the group consisting of plant cellulose, microbial-produced cellulose, ascidian sac cellulose and derivatives thereof, and mixtures thereof.   The method according to claim 9, wherein the derivative is a cellulose derivative obtained by esterifying and / or etherifying a hydroxyl group of cellulose to a substitution degree of 1.0 or less.   The method according to any one of claims 7 to 10, further comprising a step of D) chemically hydrophobizing the liquid cellulose gel after the step B) and before the step C).   The method according to any one of claims 7 to 11, further comprising a step of attaching an inorganic substance to the liquid cellulose gel after the step B) and before the step C).   A carbide of cellulose airgel obtained by heat-treating the cellulose airgel according to any one of claims 1 to 6 at 150 ° C or higher in a non-oxidizing atmosphere.   A carbide of cellulose aerogel obtained by heat-treating a cellulose aerogel obtained by the method according to any one of claims 7 to 11 at 150 ° C or higher in a non-oxidizing atmosphere. A method for producing a carbide of cellulose airgel, comprising the following steps:
A) i) 2-20% by weight of caustic; and ii) 4-20% by weight of urea or thiourea in an aqueous solution so that the cellulose content is 0.2-20% by weight. Step of dissolving and preparing a cellulose solution; or A ′) Cellulose solution by dissolving cellulose in an organic solvent solution containing 5 to 12% by weight of an alkali halide so that the amount of cellulose is 0.2 to 20% by weight. The step of preparing
B) A step of preparing a liquid-containing cellulose gel by immersing the cellulose solution in a cellulose non-solvent;
C) The liquid cellulose cellulose gel is subjected to x) organic solvent substitution drying, y) supercritical drying, or z) subcritical drying to obtain a cellulose airgel having a specific surface area of 300 m ² / g or more by nitrogen adsorption BET method. And F) a step of heat-treating the obtained cellulose airgel at 150 ° C. or higher in a non-oxidizing atmosphere to obtain a carbide of cellulose airgel;
The above method.