JPH04164853A - Production of hardened extrusion molded material - Google Patents

Abstract

PURPOSE:To simplify preparation of materials and to obtain an hardened extrusion molded material having high strength by blending a material consisting essentially of gypsum dihydrate with water to give a blend, extrusion molding the blend, treating the blend with a solution of an alkali potassium salt and hardening. CONSTITUTION:Gypsum dihydrate as a main component is optionally mixed with a thickening agent such as methyl cellulose and other additives, blended with water to give a blend, which is extrusion molded by an extrusion molding machine. Then, the extrusion molded article is treated with a solution of an alkali potassium salt, gypsum dihydrate is subjected to reactions shown by formula I and formula II to simultaneously form crystal syngenite [K2Ca(SO4)2 H2O] and slaked lime [Ca(OH)2]. Consequently, acicular syngenite crystal is complexly entangled to form a hardened material and slaked lime can be produced. Therefore, addition of slaked lime for denitration is not required and an hardened extrusion molded material can be produced by simple and ready preparation action.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing an extrusion-molded cured body using a material whose main component is dihydrate gypsum.

(Background of the invention) Conventionally, water is added to gypsum hemihydrate (CaSO4・1/211.0) or anhydrous gypsum (CaSO4) and kneaded, the kneaded product is extruded using an extrusion molding machine, and then the mixture is hardened. A method of obtaining an extrusion-molded hardened body of gypsum is known. This is due to water hardening of anhydrous (or raw water) gypsum.
It takes advantage of the fact that it becomes water gypsum (CaSO, 211.0).

However, it is difficult to obtain a good extrusion-molded cured body of gypsum. The reason is as follows.

In other words, when anhydrous or hemihydrate gypsum is kneaded with water and extruded, the mixing and extrusion operations require a very long time, during which time the kneaded material undergoes a hydration hardening reaction, making it possible to extrude it without any problems. This is because it is extremely difficult to do so.

Therefore, various studies have been conducted to delay the hydration and hardening of the kneaded material by adding a curing retarder (dihydration retardant) to the kneaded material.

However, when a large amount of such a retardant is added or blended, since the retardant is originally surplus,
It is unavoidable that the strength of the obtained extrusion molded product will decrease or the properties will deteriorate. For example, when the extrusion-molded cured product is used as a catalyst carrier, it has been reported that the addition of a retarder reduces the catalyst activity.

In addition, when adding a retarder to delay the hardening of the kneaded product, it is necessary to select the amount of the retarder to be added so that the curing reaction occurs in an appropriate amount of time. It is extremely difficult to maintain a proper viscosity for a long period of time, and water hardening inevitably occurs during work, resulting in an increase in viscosity over time.

Alternatively, even if extrusion molding can be performed in a soft state, it takes a long time for the extruded molded product to complete the hydration hardening reaction, so the soft molded product may deform or break during that time. On the other hand, a method has been proposed in which dihydrate gypsum is used as a raw material and extrusion molded (JP-A-55-236).

Since this method uses dihydrate as the raw material, there is no concern that a curing reaction will occur during the extrusion process, but the molded product obtained is simply an aggregation of raw material powder. Since it is not a cured product, there is a problem that its strength is insufficient. Therefore, in this method, a thickener is added to the raw material to improve strength.

Although a reinforcing agent is added, sufficient strength cannot be expected from the action of such a thickening agent alone. Also, even with this method, thickeners, enhancers, and other additive components must be blended and the viscosity of the kneaded product must be precisely adjusted.
There are problems that are difficult to reconcile.

Therefore, the present applicant filed an earlier patent application (Japanese Patent Application No. 2-72985).
No. 3), the method is characterized by extruding a kneaded product obtained by adding water to a material containing dihydrate gypsum as a main component, and treating the extruded product with a treatment liquid containing a potassium salt to harden it. A method for producing extrusion-molded cured products was proposed.

This method utilizes the fact that when a material whose main component is dihydrate gypsum is treated with the above treatment liquid, the dihydrate causes a reaction and produces needle-like crystals, which form a hardened body in which they are intricately intertwined. It is something that has been done. Although the extrusion-molded hardened body obtained by this method can no longer be called gypsum, it is similar in properties to the extrusion-molded hardened body of gypsum, and therefore can be used for similar purposes and uses.

When an extrusion-molded cured body is produced according to this method, curing is completed in a very short time, so there is no need to keep the extrusion-molded body in a soft state for a long time, and therefore the molded body does not change during that time. Deformation and breakage can be avoided.

In addition, since the molded product is cured by reacting with the potassium salt in the processing liquid, there is no need to strictly adjust the viscosity and other properties of the kneaded product before extrusion, and the blending adjustment can be rough to some extent. There is also the advantage that things can be easily adjusted.

By the way, it is being considered that this extrusion-molded cured product may be used as a catalyst carrier or catalyst for air purification by forming it into a honeycomb shape or the like. At that time, if the extrusion-molded cured product contains slaked lime (Ca(Oll), ), the denitration effect can be performed (Ca
(Oll) - has the effect of reacting with NOx and removing it). However, in order to perform such a denitrification effect, it is necessary to add and mix Ca (Oll) into the material in advance and knead it into the material, which poses the problem of complicating the mixing process. .

(Means for Solving the Problems) The present invention has been made to solve the above problems, and its gist is to provide a kneaded product obtained by adding water to a material whose main component is dihydrate gypsum. The method consists of extrusion molding, and then treating the extruded molded body with an alkaline potassium salt solution to harden it.

(Operation and Effects of the Invention) In the present invention, gypsum dihydrate (CaSO, .21(,O) is the main component, and thickeners such as activated carbon and methyl cellulose and other additives are added and blended as necessary. Above, water is added and kneaded, and the kneaded product is extruded using an extrusion molding machine and molded into the desired shape.Then, the molded product is treated with an alkaline potassium salt solution.For example, KOII is used as the alkaline compound, and potassium When treated with So as a salt, dihydrate gypsum reacts as follows.

C, aso, ・2H, O+2KO11<a(OH),
+, SO4+28,0-(1)CaSO,・2H,O
+ to SO, @ to Ca (SO4), ・II, O+H,
0-(2) As is clear from the above equations (1) and (2), when dihydrate gypsum is treated with an alkaline potassium salt solution, syngenite crystals (K, Ca (So, )t
・H, O) and slaked lime (Ca(O)l)-) are generated simultaneously. In the formula (2), a hardened body is formed by generating needle-shaped syngenite crystals and by intricately intertwining the needle-shaped syngenite crystals.

As described above, according to the present invention, the extrusion molded body is cured and Ca(
Oll), is generated at the same time. Therefore, there is no need to add Ca(011) to the material in advance for denitrification, etc., which simplifies the preparation of the material and reduces the time and effort required for compounding. This facilitates the compounding action.

Furthermore, when (lea (OH)) is contained in the cured product according to the present invention, such Ca(011) is preferentially generated in the surface layer portion of the cured product that is in direct contact with air, so that it is different from the conventional method. Unlike the case where Ca (OH) is kneaded into the raw material in advance, the same Ca (011)
, the advantage of higher denitrification effect can be obtained. When Ca(011) is kneaded into the material, Ca(011) will be contained and dispersed evenly in the surface layer and inside, but in the case of the above reaction, it will be mixed with the treatment liquid. This is because Ca (Oll.

In the present invention, KOj1 is used as an alkaline compound.
Besides, it is also possible to use other substances such as Na0Il, and it is also possible to use MCI, Co, and other substances as potassium salts.

Furthermore, other conditions such as hydroxide ion concentration and potassium salt concentration can be appropriately selected depending on the required strength of the cured product.

However, according to the inventor's experiments, Ca (011) is easily generated when the hydroxide ion concentration is 0.5 mol/1 or more, and conversely, K z Ca (""4) *・H, O is hydroxylated If the ion concentration becomes too high, the generation will be suppressed, and 1.0 m
It has been confirmed that when the amount exceeds ol/l, the amount produced becomes particularly small. Therefore, the desirable range for the hydroxide ion concentration is from 0.5 mol/I to 1.0 mol/I.

(Example) Next, in order to further clarify the characteristics of the present invention, examples thereof will be described in detail below.

70 parts of dihydrate gypsum, 30 parts of activated carbon, and 8 parts of methyl cellulose were mixed, and 95 parts of water was added and kneaded. Note that the activated carbon here is used as an adsorption catalyst. The kneaded product was put into an extrusion molding machine, and as shown in Fig. 1, the cell angle was 1.5 mm, and the cell J! (A honeycomb-shaped extrusion molded body 10 of 0.5 aun was obtained. The molded body 10 obtained was immersed in various treatment solutions shown in Table 1 for 2 hours to generate slaked lime and at the same time, the molded body After that, the cured product was taken out of the liquid and air-dried.The resulting cured product was subjected to X-ray analysis to measure the amounts of syngenite, slaked lime, and other components, and to measure the compressive strength. This is also shown in Table 1.

(Margin below) From the results in Table 1, we can see that Fuki.

As can be seen from the results of (b) No.] to No.3,
The higher the potassium concentration, the more easily syngenite is formed;
When immersed for hours, it is efficiently generated at 2M (mol/l) or more.

(D) As can be seen from the results of No. 4 to No. 7, a hydroxide ion concentration of 0.5 to 1.0 M is good, and 0.5 M is particularly good for syngenite formation. Ta.

(A) In the hydroxide ion concentration range of 0.5 to 1.0 M, increasing the potassium concentration promotes the formation of syngenite. Furthermore, if the hydroxide ion concentration is increased, the amount of Ca(011) produced increases.

By adjusting the hydroxide ion concentration and the potassium concentration within this hydroxide ion concentration range, the composition of the product can be well adjusted.

(d) Compressive strength clearly increases due to the formation of syngenite. From this, it was confirmed that the formation of syngenite greatly contributed to improving the strength of the extruded product.

Although the embodiments of the present invention have been described in detail above, these are merely examples of the present invention, and the present invention can be implemented in various modified forms without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a honeycomb extrusion molded body obtained according to an embodiment of the present invention. lO: Honeycomb extruded product patent applicant Inax Co., Ltd.

Claims (2)

[Claims] (1) An extrusion-molded cured product characterized by extruding a kneaded product obtained by adding water to a material whose main component is dihydrate gypsum, and treating the extruded product with an alkaline potassium salt solution to cure it. manufacturing method. (2) The extrusion-molded cured product according to claim (1), wherein the alkaline potassium salt solution has a hydroxide ion concentration adjusted to 0.5 mol/l to 1.0 mol/l. manufacturing method.