JP6427644B1 - Method for producing alumina hollow fiber - Google Patents

Abstract

The present invention provides a method for stably producing an alumina hollow fiber excellent in mechanical strength characteristics. SOLUTION: A step of preparing a slurry of pH 9.5 to 14 containing a ceramic raw material compound containing aluminum as a main component, an organic fiber and an alkaline solution, and the obtained slurry at 100 ° C 0.3 to 1 A step of obtaining a composite consisting of the organic fiber and the boehmite covering the organic fiber by subjecting it to a hydrothermal reaction under temperature and pressure conditions of 4 MPa, and the obtained composite at a temperature of 60 to 1200 ° C. in an oxygen atmosphere And subjecting to a calcination reaction for 10 minutes to 10 hours to obtain an aluminous hollow fiber. 【Selection chart】 None

Description

  The present invention relates to a method for producing an aluminous hollow fiber useful as a heat insulating material, a filter medium, an adsorbent, a catalyst carrier and the like.

Fibers (alumina fibers) consisting of crystalline alumina (Al ₂ O ₃ ) and mullite (Al ₆ O ₁₃ Si ₂ ), which are artificial mineral fibers mainly composed of alumina, are also used as a catalyst carrier support material, For example, a catalyst for purifying automobile exhaust gas is supported, and is stored in a catalytic converter in an automobile exhaust pipe.

  Furthermore, a hollow fiber is developed in which both ends of the alumina fiber are open, for example, in Patent Document 1, a paste obtained by filling a ceramic powder with a polymer binder composition is extruded to form a hollow fiber, and bonding thereof A process is disclosed for producing ceramic hollow fiber membranes for microfiltration, ultrafiltration, gas separation, etc., wherein the agent composition is removed by thermal diffusion prior to sintering the powder particles.

  Also, for example, in Patent Document 2, after forming a metal oxide film having a thickness of 0.1 μm or more deposited from a solution containing a metal compound to be a precursor on the outer peripheral surface of organic fibers, the organic A method is disclosed for producing a ceramic hollow fiber product in which fibers are removed by firing or the like to form pores having an internal shape corresponding to the shape of the organic fibers, thereby increasing the specific surface area.

Japanese Patent Publication No. 8-510159 JP 2001-248024 A

However, in the production method using extrusion of the ceramic powder paste of Patent Document 1 described above, it is difficult to produce small diameter hollow fibers, and it is necessary to add a binder composition to the ceramic raw material, and the raw material cost becomes high. It will In the liquid phase deposition method of Patent Document 2, when the metal oxide is alumina, gibbsite (Al (OH) ₃ , density: 2.42 g / cm ³ ) is obtained as a precursor thereof. Since gibbsite has a large volume change due to dehydration at the time of obtaining alumina, the resulting hollow alumina fibers are likely to have structural defects and may be inferior in mechanical strength characteristics.

  Therefore, an object of the present invention is to provide a method for stably producing an alumina hollow fiber excellent in mechanical strength properties.

The present inventors have variously studied, and by forming boehmite (AlOOH, density 3.07 g / cm ³ ) as a precursor of alumina around an organic fiber used as a template, excellent mechanical strength characteristics can be obtained. It has been found that an alumina-based hollow fiber can be obtained, and the present invention has been completed.

  That is, the present invention comprises the steps of preparing a slurry containing a ceramic raw material compound containing aluminum as a main component, an organic fiber, and an alkaline solution, and subjecting the obtained slurry to a hydrothermal reaction to obtain the organic fiber Alumina, comprising the steps of: obtaining a composite comprising boehmite coating the organic fibers; and subjecting the obtained composite to a calcination reaction to obtain an aluminous hollow fiber. The present invention provides a method for producing hollow fibers.

  In the method for producing an alumina hollow fiber according to the present invention, the pH of the slurry is preferably set to 9.5 to 14.

  Moreover, it is preferable to perform the said hydrothermal reaction at the temperature of 100 degreeC or more, and the pressure of 0.3-1.4 Mpa.

  Moreover, it is preferable to perform the said baking reaction for 10 minutes-10 hours in the oxygen atmosphere of the temperature of 600-1200 degreeC.

  Preferably, the firing reaction is carried out by raising the temperature to a firing temperature of 5 ° C./min or more to the firing temperature for subjecting the composite to the firing reaction.

  Moreover, it is preferable that the said organic fiber is a cellulose nanofiber.

  In addition, the ceramic raw material compound is at least one of aluminum and aluminum-containing metal compounds, sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, halides, organic acid salts, and alkoxides. It is preferable that it is what consists of 1 type (s) or 2 or more types selected from the group which consists of.

  According to the present invention, boehmite, which is a precursor of alumina, is formed around an organic fiber used as a mold for an alumina hollow fiber, and when this is fired, the organic fiber is burned off and alumina having excellent mechanical strength characteristics A hollow fiber is obtained.

It is a X-ray-diffraction pattern of the precursor of the alumina obtained by Example 1 and Comparative Example 1. FIG. It is an optical microscope photograph which shows the state which pressurized the alumina hollow fiber obtained in Example 1 with the hand press machine, FIG. 2 (a) is before pressurization, FIG.2 (b) is after pressurization. . It is an optical microscope photograph which shows the state which pressurized the alumina hollow fiber obtained in Example 2 with the hand press machine, FIG. 3 (a) is before pressurization, FIG.3 (b) is after pressurization. . It is an optical micrograph which shows the state which pressurized the alumina hollow fiber obtained by the comparative example 1 with the hand press machine, FIG. 4 (a) is before pressurization, FIG.4 (b) is after pressurization. . It is a figure which shows a mode that the alumina hollow fiber obtained in Example 1 was observed with a transmission electron microscope (TEM), FIG. 5 (a) is the TEM photograph, FIG.5 (b) is FIG. It is a schematic diagram for showing the hole position of the edge part in the TEM photograph of a).

Hereinafter, the present invention will be described in detail.
The method for producing an alumina hollow fiber according to the present invention comprises the following steps (I) to (III).

(I) A step of preparing a slurry containing a ceramic raw material compound containing aluminum as a main component, an organic fiber, and an alkaline solution.
(II) A step of subjecting the obtained slurry to a hydrothermal reaction to obtain a composite composed of the organic fiber and boehmite coating the organic fiber.
(III) A step of subjecting the obtained composite to a calcination reaction to obtain an aluminous hollow fiber.

  According to the method for producing an alumina hollow fiber having the above-described structure, an alumina hollow fiber excellent in mechanical strength characteristics can be easily obtained by using a hydrothermal method. The mechanism is that boehmite formed as a precursor of alumina by the hydrothermal reaction contains less hydroxyl groups than the gibbsite formed by the liquid phase deposition method, and has a relatively minute and uniform particle structure. Since the particle structure continuously forms a covering structure around the organic fiber used as a template and as a mold, the volume change due to dehydration is small also in the subsequent firing to obtain alumina, and the mechanical strength characteristics are excellent. It is believed that alumina hollow fibers will be obtained.

  In step (I), a slurry containing a ceramic raw material compound containing aluminum as a main component and an organic fiber to be a template for the desired alumina hollow fiber is prepared.

  The metal element contained in the ceramic raw material compound is mainly composed of aluminum, but may contain an element other than aluminum in an amount of 30 mol% or less in 100 mol% of all metal elements including aluminum. As elements other than aluminum, for example, elements of Group IA such as Li, Na and K; elements of Group IIA such as Mg, Ca, Sr and Ba; Y, La, Ce, Nd, Sm, Dy, Eu Elements of group IIIA such as Ti; elements of group IVA such as Zr; elements of group VA such as V, Nb, Ta etc; elements of group VIA such as Cr, Mo, W etc; VIIA such as Mn Elements of group VIII such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, etc. elements of group IB such as Cu, Ag, Au etc .; group II B of Zn, Cd etc. Elements; elements of Group IIIB such as B, Ga, In, Tl; elements of Group IVB such as Si, Ge, Sn, Pb etc; elements of Group VB such as P, As, Sb, Bi etc; Te, Po And other elements of Group VIB. Among them, metal elements such as Fe, Co, Ni, Cu, Zn, Ga, Tb, Si, Ge, Sn, Ti, Zr, Mn, Eu, Y, Nb, Ce, Ba and the like are preferably included. As such ceramic raw material compounds, specifically, sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, halides of aluminum or a metal compound comprising aluminum and the above metal element , Organic acid salts, alkoxides and the like can be suitably used.

  Since the resulting alumina hollow fiber uses an organic fiber as a mold, an organic fiber having an appropriate size is selected according to the required length and inner diameter of the alumina hollow fiber. The outer diameter (thickness) of the alumina hollow fiber can be controlled in the hydrothermal reaction of step (II) described later.

  The organic fiber is not particularly limited as long as it forms boehmite on the surface in the hydrothermal reaction of step (II) described later and burns off in the calcination reaction of step (III) described later. Cellulose, cellulose nanofibers, wool, cotton, hemp, silk and the like can be used, and as synthetic fibers, aramid, polyamide, polyester, polyethylene, acrylic, rayon and the like can be used.

  In addition, in preparation of the said slurry, use of the cellulose nanofiber (CNF) as an organic fiber is preferable from a viewpoint of having favorable dispersibility to water. Cellulose nanofibers are skeletal components that occupy about 50% of all plant cell walls, and are lightweight, high-strength fibers that can be obtained by disaggregating plant fibers constituting such cell walls to micron size or nano size. The average fiber diameter is 10 nm to 30 μm, and the average length is 100 nm to 100 μm.

In the step (I), when a slurry is prepared by mixing the ceramic raw material compound and the organic fiber, a polar solvent or the like which can dissolve or disperse these well is used as the dispersion medium. For example, water can usually be used. Then, an appropriate alkali agent is appropriately added to obtain a pH-adjusted slurry, and a metal component dissolved or dispersed in the slurry is made to be a metal hydroxide by a neutralization reaction. In the addition of the alkali agent, it is preferable to drop a sufficient amount of the pH-adjusted slurry so as to maintain 9.5 to 14 from the viewpoint of suppressing by-products. If the pH is less than 9.5, NaAl ₃ (SO ₄ ) ₂ (OH) ₆ tends to be by-produced as an impurity, and the efficiency of producing an alumina precursor by hydrothermal reaction may deteriorate.

  As the alkali agent, for example, sodium hydroxide, lithium hydroxide, ammonia and the like are preferable, and they are preferably added in the form of an aqueous solution. Alternatively, when the slurry is prepared, the dispersion medium at the time of preparing the slurry is previously made to have a desired pH or to approach a desired pH without adding an additional alkali agent. An alkaline agent may be added.

  When the slurry is prepared by mixing the ceramic raw material compound and the organic fiber, the pH adjusted dispersion medium (for example, water), that is, the amount of the alkaline solution used is the solubility or dispersion of each raw material. From the viewpoints of properties, easiness of stirring, efficiency of hydrothermal reaction, etc., 0.5 to 1000 g is preferable to 1 g of the ceramic material compound, and 0.5 to 800 g is more preferable. Further, the content of the organic fiber in the slurry is preferably 0.05 to 20 g, preferably 0.05 to 10 g based on 1 g of the ceramic raw material compound in the slurry, from the viewpoint of supporting alumina on the surface. Is more preferred.

  The above slurry is preferably stirred to sufficiently advance the neutralization reaction from the viewpoint of generating a metal hydroxide well by the neutralization reaction. The temperature of the slurry during the neutralization reaction is preferably 5 ° C. or higher, more preferably 10 to 60 ° C. Moreover, 2-120 minutes are preferable and, as for the stirring time of the slurry in the neutralization reaction, 5-90 minutes are more preferable.

  In step (II), the slurry obtained as described above is subjected to a hydrothermal reaction to obtain a composite in which the organic fiber is coated with boehmite (hereinafter sometimes referred to as "boehmite-coated composite"). Get The temperature during the hydrothermal reaction is preferably 100 ° C. or higher, and more preferably 100 to 200 ° C. The hydrothermal reaction is preferably carried out in a pressure-resistant vessel, and when the reaction is carried out at 100 ° C. or more, the pressure at this time is preferably 0.3 MPa or more, and the pressure is 0 when the reaction is carried out at 100 to 200 ° C. It is preferable that it is .3-1.4MPa. The hydrothermal reaction time is preferably 0.1 to 12 hours, and more preferably 0.2 to 6 hours. When the temperature of the hydrothermal reaction is less than 100 ° C. and the time of the hydrothermal reaction is less than 0.1 hours, the crystal growth of the alumina precursor does not occur sufficiently, and the mechanical strength of the aluminous hollow fiber may be inferior. is there. In addition, when the temperature of the hydrothermal reaction exceeds 200 ° C. and the time of the hydrothermal reaction exceeds 12 hours, there is a possibility that the organic fiber is dissolved and the boehmite-coated composite can not be obtained.

  In the case where the thickness of the coating of the boehmite coating the organic fiber is increased, that is, in the case of obtaining a thick alumina hollow fiber, the mass ratio of the ceramic material compound / organic fiber in the slurry is set large. Specifically, the mass ratio of the ceramic material compound to the organic fiber is made larger than 0.5. And in the hydrothermal reaction, the low temperature and pressure environment is continued for a long time so as to promote the crystal growth of the individual crystals of boehmite. Specifically, for example, a hydrothermal reaction may be performed at 130 ° C. and 0.3 MPa for 12 hours.

  After the hydrothermal reaction, the surface of the organic fiber is coated with boehmite, which is separated from the dispersion medium by filtration or the like, preferably washed with water or the like, and then dried or the like, as will be described later. The boehmite coated composite can be isolated for subjecting to the calcination reaction of (III). When washing the boehmite-coated composite with water, it is preferable to use 5 to 50 parts by mass of water based on 1 part by mass of the boehmite-coated composite from the viewpoint of removing by-products. Moreover, as a drying means, lyophilization, vacuum drying, warm air drying etc. are used, and lyophilization or warm air drying is preferable.

  In step (III), the boehmite-coated composite obtained as described above is further subjected to a calcination reaction. As a result, the organic fibers contained in the boehmite-coated composite obtained in the above step (II) can be burned off, and at the same time, the cylindrical boehmite can be subjected to a firing reaction to obtain an aluminous hollow fiber. Here, from the viewpoint of densifying the obtained alumina, the firing temperature is preferably 600 to 1200 ° C., and more preferably 700 to 1200 ° C. in an oxygen atmosphere. The baking time is preferably 10 minutes to 10 hours, and more preferably 30 minutes to 5 hours. When the firing temperature is less than 600 ° C. or the firing time is less than 10 minutes, the formation of alumina accompanied by dehydration from the alumina precursor and the crystal growth of alumina become insufficient, and the mechanical strength of the alumina hollow fiber becomes inferior There is. In addition, when the firing temperature exceeds 1200 ° C. and the firing time exceeds 10 hours, sintering of alumina occurs remarkably, and there is a possibility that a hollow form can not be obtained.

  The atmosphere oxygen concentration for the firing reaction is not special, and a normal atmosphere may be used. As the firing means, an electric furnace, a roller hearth kiln, a batch kiln, a pusher kiln, a mesh belt kiln, a rotary kiln or the like is used, and an electric furnace, a pusher kiln or a mesh belt kiln is preferable.

  The alumina hollow fiber according to the production method of the present invention may be in the form of a tube having an open fiber end, or may be in the form of a tube having a closed fiber end. The end of the closed hole may be in the form of a tube in a mixed state. Whether the end of the fiber is open or closed can be controlled by the firing conditions. Specifically, when the temperature raising rate to reach the firing temperature for subjecting the boehmite-coated composite to the firing reaction is large, the gasification of the organic fiber to carbon dioxide rapidly occurs, so the fiber It tends to be a tube with an open end, for example, when the temperature rise rate is 2.5 ° C./min, a tube with an open fiber end is generated, and at a temperature rise rate of 5 ° C./min or more, almost all The end of the fiber is open. Also, if the temperature rise rate is less than 2.5 ° C./min, gasification of organic fibers occurs gradually, so after the gas escapes from the interstices of primary particles of boehmite, sintering of boehmite causes many fibers to end. The part is hollow and closed.

  In addition, since the alumina hollow fiber by the manufacturing method of the present invention can be arbitrarily controlled by the mold used, the fiber diameter and length can be made into an aggregate of alumina hollow fibers of uniform size, or the fiber diameter and length can be It may be an aggregate of different aluminous hollow fibers, and may be an aggregate of two or more kinds of aluminous hollow fibers having different chemical compositions.

  The alumina hollow fiber obtained by the production method of the present invention can be suitably formed into a useful heat insulating material, a filter medium, an adsorbent, a catalyst carrier, etc., or a component thereof, etc. by an ordinary ceramic fiber processing method etc. It is possible to process.

  EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Example 1
0.79 g of Al ₂ (SO ₄ ) ₃ · 16H ₂ O, 2.31 g of cellulose nanofibers (PC manufactured by Daicel Finechem, PC 110 T, water content 65 mass%), and 72.3 mL of water are mixed for 60 minutes to obtain a slurry A ¹ Was produced. To the resulting slurry ^{A 1,} was added aqueous NaOH 3.0g of 10% strength by weight, to prepare a slurry ^{B 1} of pH10 was mixed for 5 minutes.
Slurry B ¹ was charged into an autoclave and subjected to a hydrothermal reaction at 140 ° C. and 0.3 MPa for 1 hour. The resulting hydrothermal reaction product is allowed to cool, then filtered, washed with water, and dried with warm air at 80 ° C. for 4 hours to obtain a composite C ¹ comprising an alumina precursor and cellulose nanofibers. The The obtained composite C ¹ was placed in an electric furnace and fired under an air atmosphere at 700 ° C. for 1 hour to obtain an alumina hollow fiber (BET specific surface area: 220 m ² / g).

Example 2
An alumina hollow fiber (BET specific surface area: 210 m ² / g) was obtained in the same manner as in Example 1 except that 0.81 g of cotton was used instead of cellulose nanofibers.

Comparative Example 1 (Method of Patent Document 2)
Aqueous ammonia was added to a 0.04 mol / L Al ₂ (SO ₄ ) ₃ aqueous solution to prepare an aqueous solution D ² having a pH of 3. To the resulting solution D ^2, by immersing the cotton 60 ° C. 24 hours, on cotton fibers, to precipitate a precursor of alumina, after hot-air drying for 4 hours at 80 ° C., 500 ° C. 1 hour under an air atmosphere firing Thus, an alumina hollow fiber (BET specific surface area: 240 m ² / g) was obtained.

(Test Example 1)
X-ray diffraction analysis was performed on the alumina precursors obtained in Example 1 and Comparative Example 1. The obtained XRD pattern (device used: D8-ADVANCE manufactured by Bruker AXS Co., Ltd.) is shown in FIG.
As shown in FIG. 1, an XRD pattern characteristic of boehmite (AlOOH) was obtained in Example 1, and an XRD pattern characteristic of Gibbsite (Al (OH) ₃ ) was obtained in Comparative Example 1.

(Test Example 2)
The alumina hollow fibers obtained in Examples 1 and 2 and Comparative Example 1 were pressurized at 1 MPa for 10 seconds using a hand press in order to evaluate the mechanical strength. The optical microscope images before and after pressing are shown in FIG. 2 (before (a) pressing and after (b) pressing) for Example 1, and before (FIG. 3 ((a) pressing) for Example 2. FIG. 4 ((a) before pressurization, (b) after pressurization) is shown for (b) after pressurization and for Comparative Example 1 respectively.
As a result, as shown in FIGS. 2 and 3, in Examples 1 and 2, while the shape of the fiber is maintained even after pressing, as shown in FIG. It was destroyed after the pressure and became small pieces.

Furthermore, with respect to the alumina hollow fibers obtained in Examples 1 and 2 and Comparative Example 1, the residual amount (% by mass) with a 212 μm sieve before and after pressing was measured.
The measurement results are shown in Table 1.

As a result, as shown in Table 1, while the weight loss of Examples 1 and 2 was less than 10%, in Comparative Example 1, the sieve residue after pressing was reduced by 40% or more.
From the above, it became clear that the alumina hollow fibers obtained in Examples 1 and 2 are superior in mechanical strength to Comparative Example 1.

(Test Example 3)
The alumina hollow fiber obtained in Example 1 was observed by a transmission electron microscope (TEM) (using apparatus: JEM-3200FS manufactured by JEOL Ltd.). The TEM observation image is shown in FIG.
As a result, as shown in FIG. 5, in the alumina hollow fiber obtained in Example 1, the hole 2 was formed at the end 1 thereof, and an open-hole alumina hollow fiber was obtained. It became clear.

1 end 2 hole

Claims (7)

Preparing a slurry containing a ceramic raw material compound containing aluminum as a main component, an organic fiber, and an alkaline solution;
Subjecting the obtained slurry to a hydrothermal reaction to obtain a composite comprising the organic fiber and a boehmite coating the organic fiber;
And b. Subjecting the resulting composite to a calcination reaction to obtain an aluminous hollow fiber. In the method of producing an alumina hollow fiber according to claim 1,
The pH of the said slurry shall be 9.5-14, The manufacturing method of the aluminous hollow fiber characterized by the above-mentioned. In the method for producing an aluminous hollow fiber according to claim 1 or 2,
The method for producing an aluminous hollow fiber, wherein the hydrothermal reaction is carried out at a temperature of 100 ° C. or higher and a pressure of 0.3 to 1.4 MPa. In the method of producing an aluminous hollow fiber according to any one of claims 1 to 3,
The method for producing an aluminous hollow fiber, wherein the firing reaction is carried out in an oxygen atmosphere at a temperature of 600 to 1200 ° C. for 10 minutes to 10 hours. In the method of producing an aluminous hollow fiber according to any one of claims 1 to 4,
A method for producing an alumina-based hollow fiber, comprising: carrying out the firing reaction by raising the temperature of the composite to the firing reaction at a temperature rising rate of 5 ° C./min or more to the firing temperature for subjecting the composite to the firing reaction. In the method of producing an aluminous hollow fiber according to any one of claims 1 to 5,
The method for producing an aluminous hollow fiber, wherein the organic fiber is a cellulose nanofiber. In the method of producing an aluminous hollow fiber according to any one of claims 1 to 6,
The ceramic raw material compound is composed of sulfate, nitrate, carbonate, acetate, oxalate, oxide, hydroxide, halide, organic acid salt, and alkoxide of at least one of aluminum and aluminum-containing metal compound A method for producing an aluminous hollow fiber, characterized in that it comprises one or more selected from the group consisting of