JPH01317515A - Alkali resistant filter medium - Google Patents

Abstract

PURPOSE:To improve alkali resistance by adding bonding agents comprising activated xMgO.yAl2O3 to a porous sinter whose composition is represented by a general formula of xMgO.yAl2O3 wherein the crystal structure thereof includes 95% or more of spinel type MgO.Al2O3 and sintering them together. CONSTITUTION:An activated substance having composition of xMgO.yAl2O3 is added, as a bonding agent 2, to an aggregate 1 comprising spinel type MgO.Al2O3, whereto dextrin and water are added to be mixed therewith, and thereafter they are molded, dried and sintered. After being sintered, they are aged and cooled naturally to produce an alkali resistant filter medium comprising porous sinter whose composition is represented by a general formula of xMgO.yAl2O3 wherein the crystal structure thereof includes 95% or more of spinel type MgO.Al2O3. The filter medium has an improved alkali resistance and is effective in filtering substances containing alkali in the form of powder, liquid or gas.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a ceramic filter that has excellent filtration performance and resistance to chemical deterioration when it comes to filtering powdery, liquid, and gaseous substances containing alkaline components. It is used in chemical plants, chemical treatment processes, chemical separation and purification processes, basic slag treatment processes, condensable gas separation and purification processes, alkaline vapor separation membranes, and fermenters that can withstand alkali treatment. It is intended for use in filters, diffuser elements for gas diffusion in alkaline solutions, filters for high temperature gas, filters for alkaline waste liquid treatment, various diaphragms used in electrochemical reactions, etc.

Mgo has strong durability in harsh thermal and chemical environments.
- Aztos spinel is sintered into a porous body and used as a filter material.

(Prior Art) Metal filters that are said to have durability against alkaline solutions, filters made of carbon, fluororesin, and the like have been used. Although metal filters such as stainless steel are durable, they are expensive, and they are difficult to manufacture with minute pores, and there are also restrictions on their shapes. Carbon filters have the disadvantages of arbitrary molding shape, uniformity of pores, and difficulty in forming micropores. Filters made of fluororesin are expensive and have a large contact angle with aqueous solutions, which affects the filtration yield in filtration operations and limits the fields in which they can be put to practical use. On the other hand, although various conventional ceramic filtration materials are available, there is none that can withstand use in an alkaline environment and is available at an industrially acceptable price. For example, the most commonly used alumina filter gradually erodes in hot alkaline water.
The deterioration in strength is significant. The 5in2 system cannot be used in alkaline solutions.

(Problems to be Solved by the Invention) Many conventional ceramic materials are corroded by alkaline solutions and deteriorate in strength. This is because there is a problem with the composition of the main raw material aggregate and binder that make up the filter material, and the alkali decomposes it and creates salt. For example, additives and impurities include Tie, , Sin, , Fe2 o,
, MgO, Cab, Na2O, K, O, etc. are often included. In addition, many aggregates themselves are affected by alkali. These most commonly used materials, such as silica, mullite, silicon carbide, and alumina, are themselves not durable against alkaline solutions. There are reports that α-alumina itself has resistance to alkali, but when an actual erosion test is carried out, the strength gradually deteriorates.

The level of erosion and deterioration varies depending on the structural form of the ceramic body. Normally, most of the so-called alkali-resistant materials are discussed in terms of dense bodies. For example, magnesium silicate, calcium silicate, etc. prevent corrosion while forming a film of alkali metal salts, but when made into porous materials, the deterioration is noticeable. be. Furthermore, porous materials such as filter media are affected by the concentration of the target liquid, temperature, and time, and large differences in erosion and deterioration are recognized depending on the porosity and pore diameter of the filter media.

Until now, there have been no materials that can be used for a wide range of purposes, as some materials are not stable. The present invention aims to provide a filtration material that solves these problems.

(Means for solving the problem) In order to achieve this problem, we focused on the high-temperature refractory properties and crystal structure of ceramic materials.
Focusing on MgO/h1203 spinel, which has the above-mentioned high content, we proceeded with development, and through repeated experiments, we found that MgO/Al and Os spinel had sufficient durability against alkaline solutions, and decided to create a filter material using this substance. It was a success.

The filter medium of the present invention has Mg O-AA! upon completion of sintering. t O
Conditions are required in which spinel has a main component of 95% or more, and the aggregate raw material is Mg0A120. Some porous materials can be made by mixing spinel powder and a starting material that assumes the crystalline structure of MgO·hltos spinel upon completion of sintering, and can be used as is. %MgO・γU, Os described in the claims
The binder for the active particles is xMgO-YA, which constitutes the porous body.
This is used for the purpose of strongly sintering ltos, and by adding this binder, the sintering temperature can be lowered and a porous structure can be created. The active particles of xMgO.yhltos are effective whether they are spinelized particles, hydrated particles, or particles at a pre-spinelization stage. The more easily these active particles can be sintered at low temperatures, the more effectively they act on the porous body of this patent. In other words, compared to aggregate particles with a particle size of micron order or more, active particles with a particle size of submicron order complete sintering at a temperature lower than the sintering start temperature of the aggregate particles. Unlike sintering of ceramics, this method does not cause large shrinkage, and it is easy to create porous bodies with high porosity.

At present, the crystal structure of MgO/Altos spinel has not been sufficiently elucidated academically, and although the reason is not clear, an excess of Altos may be more suitable for the purpose of use, depending on the molding method. It is also recognized that excess MgO is clearly superior in durability when used for basic slag and the like. As a result of various experiments, the present invention has concluded that a sintered body made of at least 95 inches of MgO-Al2O and spinel is suitable as a filtration material to be used in an environment with severe usage conditions. It has been found that preferably all the components have a spinel crystal structure, which expands the field of use except in special cases.

The filter medium according to the present invention is xMg O-y AA! 20s
However, chemical substances added in the manufacturing process that disappear upon completion and whose existence cannot be recognized are within the scope of this patent. included. For example, organic matter that disappears, low-temperature decomposable inorganic matter that disappears after contributing to crystal growth, etc., and an operation method that does not contain components other than Mg0-AltOs at the time of completion by sintering 2''' process, etc. Chemical substances that disappear include LiC1, Li
Alkali metals such as F, chlorides and fluorides of alkaline earth metals such as Mg C12, MgF, B20. There are borides such as

An example of a filter medium according to the present invention is manufactured as follows. MgO/Altos spinel-containing powder with a molar ratio determined according to the purpose is ground in a ball mill, pickled, and washed with water.
After ensuring purity, it passes through a classifier to adjust the particle size, and then performs operations that set multiple particle size distribution levels depending on the application. 75 of the cumulative distribution, especially when it is necessary to adjust uniformly.
% average particle diameter: D7. It is preferable that the ratio of 25 cm average particle diameter = D0 be smaller than the following value.

D) The binder is preferably an activated powder whose molar ratio is adjusted and which undergoes spinelization at a sintering temperature of around 1000°C. The active particles usually have a particle size on the submicron order, and have a high surface energy as the specific surface area increases. Typical examples of the method for producing active particles according to the present invention include coprecipitation, colysis, etc. Generally, buffers, peptizers, flocculants are used as adjusting agents, water or water-organic systems are used as solvents, and precipitants are used as precipitants. cations, anions,
Used in the form of nitrates and hydrochlorides as complex compounds and raw material salts.

By controlling the concentration of the aqueous solution, fine crystals are precipitated through a precipitation operation, followed by filtration, drying, and rapid thermal decomposition to create a powder. The co-decomposition method is a method in which a magnesium solution and an aluminum solution are mixed, and there are various other similar methods. As a synthesis method different from the wet method, high purity Mg-AA! When an alloy pellet is placed in pure water and a spark is discharged using an electrode, a fine alloy hydrate is obtained, and this powder is rapidly calcined at a temperature of around 1000°C to produce an active powder. There is also.

In this method, hydrates of magnesium and aluminum may be made separately by spark discharge in the same manner as above, and the hydrates may be mixed and sintered. Mg0-h12, which is the skeleton of the filter medium of the present invention
0. The spinel is preferably of a stable type with suppressed activity, and the MgO-A40s spinel particles to serve as the bonding layer are preferably highly active particles having a highly purified submicron particle size.

10 parts by weight of the aggregate thus obtained.
Add ~40 parts by weight of a binder, add purified water to make a slurry, mix thoroughly, and then pass through a dryer to dry it.
Adjust the formulation according to the molding method. The shape can be freely formed into a plate shape or a pipe shape. The glue used is generally organic, and one with a low content of impurities such as inorganic compounds is selected. For example, starch, dextrin, PVA.

These include PVB, CMClMC, PEG, and EC. Combustible and dissipative substances such as various plastics and wood flour are used as pore regulators. Depending on the molding method, deflocculants, lubricants, antifoaming agents, etc. are added. It may also be used in the form of granulated powder in the pretreatment process. As the forming method, a press method, an air static press method, a mud casting method, a tape molding method, a doctor blade method, a paper forming method, an extrusion method, etc. are applicable. After molding, each molded product is dried and sintered using a drying method suitable for the molded product. The maximum sintering temperature is set at 1,100 to 1,700°C, which is the temperature range in which practical strength is achieved; at temperatures below 1,100°C, the amount of active powder added may be increased, or the thickness of the product may be increased. Therefore, it becomes necessary to provide external assistance with supports such as sheets or nets that reinforce the strength of the material.

Although high sintering temperatures exceeding 1,700°C are effective for porous materials with large particle sizes, microporous filter media will shrink more, resulting in lower porosity, more sophisticated firing equipment, and higher energy costs. This is not preferable because it increases the cost increase factor. Preferred practical sintering temperature is 1300-1500
°C is appropriate.

In this way, for the filtration of powdery, liquid, and gaseous substances containing alkaline components, the crystal structure of the sintered porous body created with the composition represented by the general formula
Mg O-AA more than Chi! Composed of 20s spinel,
xMgO・yAA as a binder! To produce an alkali-resistant filter material characterized by sintering using an activated substance, which is used in the related fields listed in the section of industrial application fields, and which solves the problems of the conventional technology. It is.

(Function) An example of a process in which submicron particles are used in a binder with inert particles and active particles having similar or identical chemical compositions as the temperature increases is shown in the drawing. Conceivable. FIG. 1 shows a state in which active particles of binder 2 are sprinkled on inert particles of aggregate 1. The standard packing state has a coordination number of around 8. This state is in the early stage of firing, where organic additives such as glue disappear due to combustion, the binding force between the active particles of the binder is weak, and there are many pores within the active particle layer. Even in this state, "bridging" is performed between the aggregates 1 and 1. In Figure 2, as the temperature rises further, the sintering driving force due to the release of surface energy of the active particles in the "bridge" part between aggregates 1 and 1 is applied to the center of the bonding bridge where many active particles are accumulated. The aggregate 1 acts toward the surface of the aggregate 1 while attracting active particles located away from the bonding bridges, thereby increasing the density while filling the pores of the bonding bridges. At the same time, the distance between the aggregates 1 and 1 becomes narrower, and the aggregates tend to shrink. Figure 3 shows that the reaction and sintering of the bond bridges that are in contact with the surface of aggregate 10 progresses, and the particles that make up the bond bridges continue to grow crystals, reaching a level where they maintain a surface energy similar to that of aggregate 1. Then, a stable state is reached and sintering is completed, and pores 3 are created in the area surrounded by the aggregate 1 and the binder 2.

Example 1゜MgO・AA! 20. Spinel was ground in a steel ball mill, pickled, and washed repeatedly, and a powder was obtained by wet classification. (Dys: 75% average particle diameter in cumulative distribution, D
2. : 25-inch particle size in cumulative distribution, Dlo.

According to the method of expressing the maximum particle size as 10091+. ) The active particles of the binder are MgO-Al2O by the spark discharge method.

Spinel particles were used. The active particles were adjusted to an average particle diameter of 0.2 μm, and the aggregate Mg0-AJ120s spinel aggregate (Mg0A40a spinel) 100 parts by weight Active particles (MgO, V2O, spinel) 20 parts by weight Dextrin 4 parts by weight Water (purified) Water) 4 parts by weight After mixing, this mixture was pressed at a molding pressure of 200 kli/Crn2, molded into a mold with a diameter of 60 mtxφ and a wall thickness of 2×φ, dried and fired at a maximum temperature of 1400'C. The temperature increase rate is 100℃/hr
After aging at the maximum temperature for 5 hours, the temperature was lowered to room temperature by natural cooling to obtain a sintered body.

Example 2゜The aggregate was the same as Example 1. The Mg0-AltOs spinel used in Example 1 was used, and the active particles of the binder were the same as in Example 1. 40 parts by weight of the material used in the above were added to 100 parts by weight of aggregate (MgO.AJ, O, spinel). The composition of each material for press molding is shown below.

Aggregate (Mg()AI!203 spinel) 100 parts by weight Active particles (MgOA40s spinel) 40
Parts by weight Dextrin 4 parts by weight Water (purified water) 5 parts by weight This formulation was mixed and prepared in Example 1. It was molded into the same shape under the same molding pressure and fired at a maximum temperature of 1300°C.

The temperature increase rate was 100℃/hr, and after aging at the maximum temperature for 5 hours,
The temperature was lowered to room temperature by a cooling method using natural cooling, and a sintered body was obtained.

Example 3 An extruded product was produced in the following manner. The formulation is as shown below.

Aggregate (MgO・h120. Spinel) 100 parts by weight Active particles (MgO・hltos spinel) 30
Parts by Weight Plastic Glue Paste 52 Parts by Weight Aggregate and Activator MgO・)d120s spinel was prepared using Example 1. It was prepared in the same manner as above and used as the main constituent material. The particle size is also similar to that of Example 1. is the same as

The plastic cross material is made by blending 15 parts by weight of wheat flour, 78 parts by weight of water (purified water), and 7 parts by weight of aqueous ammonia (commercially available as a reagent), and while mixing, 52 parts by weight are mixed into 130 parts by weight of the wheat raw material. The mixture was then kneaded using a kneader to form a rice cake shape.

This kneaded product was extruded into a circular pipe with an outer diameter of 10 m and an inner diameter of 8 mm using a vacuum extruder and cut into a length of 150 mm. 9 Maximum temperature after drying 1450℃, heating rate 70℃/br up to 800℃, 100℃ from 800℃ to 1450℃
/hr.

At 1450℃. After aging for a period of time, the mixture was allowed to cool naturally to obtain a sintered body.

Example 3゜Grain size of aggregate +220 (JI, SR6001-19
It was classified and used according to the classification distribution based on 73. The molding method is a press method and the formulation is as follows.

Aggregate (Mg O-AJ2 o, spinel +220)
100 parts by weight active particles CMgO"klzOs spinel)
40 parts by weight water (purified water)
4 parts by weight of dextrin and 3 parts by weight were added. The shape is a disc with a diameter of Zoomφ and a wall thickness of 10+mφ. After drying, the mixture was aged for 5 hours at a maximum temperature of 1500°C and a temperature increase rate of 150°C/hr1, and then cooled by natural cooling to obtain a sintered body.

Example 5 A powder having an average particle diameter of about 20 μm was produced by classifying Mg 0-Al, O, and spinel. The particle size distribution was determined by using Sha as an aggregate and kneading it in the following formulation to create an extrusion molded product.

Aggregate (Mg()A40g spinel with 20μm particles) 10
0 parts by weight active particles (MgO”fiJgos spinel)
30 parts by weight plastic glue included
52 parts by weight on plastic glue Example 3. It was made in the same manner as above, and the extruded shape has an outer diameter of 50 mwφ and an inner diameter of 30 mm. Since the length is an extrusion method, it can be set arbitrarily, but
A test sample was cut into a length of 150+m and used for testing.

The MgO AJ203 spinel active particles were prepared by a coprecipitation method and adjusted to a powder having an average particle diameter of 0.211 m.

After extrusion molding, it was fired after a drying process. Maximum temperature 1
The mixture was aged at 350°C for 5 hours at 1400°C at a heating rate of 80°C/hr. After the ripening was completed, the product was cooled by natural cooling to obtain a sintered body.

(Effect of the invention) The bond bridge made of active particles has intricate grain boundaries, and the bond bridge becomes strong. In addition, the grain boundaries between the active particles that are in contact with the aggregate are merged by the aggregate particles, and the crystals on the bonding bridge side grow along the uneven surfaces of the aggregate particles.
As the surface energy decreases, the aggregate and bonding bridges become a stable structure resembling the same crystal. Bonding bridges are the most important for supporting the strength of porous materials, and are influenced by the purity of active particles. By constructing the bond bridge with a highly purified material, it has the effect of lowering the concentration of impurities that would otherwise be concentrated at the grain boundaries with the aggregate. Manufactured in this way, orientation 0-A
A! 20s spinel filter material has a melting point of 10
Because it is able to take advantage of the properties of materials with high bonding energy at temperatures above 0°C, it produces revolutionary effects that are unaffected by chemical solutions such as alkaline solutions.

[Brief explanation of the drawing]

The sintering process is sequentially illustrated in FIGS. 1, 2, and 3 by modeling the process of heating and aging due to the thermal history. 1... Aggregate particles made of xMgO . Pores formed by Patent applicant: Mitsui Grinding Wheel Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] Regarding the filtration of powdery, liquid, and gaseous substances containing alkaline components, the crystal structure of the sintered porous body composed of the general formula xMgO・yAl_2O_3 is 95% or more.
Composed of gO・Al_2O_3 spinel, with x as a binder
An alkali-resistant filter material characterized by being sintered using an activated substance of MgO.yAl_2O_3.