JPS5855331A - Hydrophobic silica gel and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a hydrophobic surface having prescribed heat of adsorption of wate by hydrothermally treating silica hydrogel or silica xerogel immersed in an alkaline aqueous soln. of a prescribed pH. CONSTITUTION:Silica hydrogel or silica xerogel is immersed in an alkaline aqueous soln. of 10-11.2pH such as 0.001N aqueous NaOH soln., hydrothermally treated, taken out, and dried. The resulting silica gel has <=10.6kcal/mole heat of adsorption during adsorption of water on the surface. The heat is smaller than heat of condensation of water. The surface of the silica gel is hydrophobic, and the silica gel is widely used as hydrophobic and organophilic silica gel for org. paint, plastics and printing ink.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel hydrophobic silica gel and a method for producing the same.

Conventional yy gels are hydrophilic and organophobic, except for those that have been surface-modified with organic substances or groups thereof, and their usage and applications have been limited.

If hydrophobic and organophilic silica gel is present, it can be used to improve the dispersibility of finely divided silica used in organic paints, desnaxes, printing inks, adhesives, etc., as well as as fillers and catalysts for chromatography. As a carrier, it can be used in a wide range of applications as a material with properties different from those of conventional silica gel.

Therefore, the present inventor conducted research to produce hydrophobic silica gel, and investigated the hydrothermal treatment and surface properties of silica hydrogel, especially Q.
Various studies have been conducted regarding the relationship with the H group. As a result, they discovered that when hydrothermally treated under special conditions that had not been done before, unique QH groups with hydrogen bonding properties appeared on the surface and a hydrophobic silica gel was obtained, and the present invention was completed.

That is, the gist of the present invention is to prepare hydrophobic silica gel having a surface on which the heat of adsorption when water is adsorbed is smaller than the heat of condensation of water, 10.6 kcal/mol, and silica hydrogel or silica xerogel at pH 10.0 to 11.0. 2. A process for producing hydrophobic silica gel characterized by immersing it in an alkaline solution, hydrothermally treating it, and drying it.

The present invention will be described in detail below. In order to produce the silica gel of the present invention, it is first necessary to produce silica hydrogel or silica xerogel. There are no particular restrictions on the method for producing V-sca and drogel, but for example -) A dilute aqueous alkali silicate solution is poured into excess acid with strong stirring to obtain a gel-like glue drogel. Method,(
b) Neutralize the alkaline silicate aqueous solution with a dilute aqueous acid solution [
, by forming a relatively stable lyohydrosol and then heating or standing the silica gel to form a particulate silica hydrogel, by extruding the lyohydrosol into a hot liquid medium that is immiscible with water. Any method may be used. t/T) 11 There are no particular restrictions on how to produce xerogel, but it may be done by subjecting the silica hydrogel to W, S, etc. to remove the moisture in the V-lyca v-ya gel and replacing it with a gas such as air. Next, the produced silica hydrogel or V9tl xeroge #
is immersed in an alkaline aqueous solution with a pH of 10.0 to 11.2. Examples of the alkali to be used include sodium hydroxide and ammonia.
A concentration of 0.004% by weight (0.001 normal) is used. If the pH is lower than 10.0, it will not be hydrophobic but will be hydrophilic, and if it is higher than 11.2, silica will dissolve. From water to heat treatment
The 9★ glue was pulled up and dried by leaving it in a dryer at a temperature of 150° C. for 6 hours to obtain a hydrophobic silica gel.

The average particle size of the silica gel thus obtained was 2000-7.
000μ, specific surface area is 100-500〆/-, and pore area is 0.4-L2d/f. In addition, for this silica gel of the present invention, the differential heat of adsorption was measured by the adsorption isotherm of water and methanol using the following method using the following Cracilus-Clapeyron equation. : Gas constant q: Heat of adsorption T: Absolute temperature P: Pressure method: For example, take adsorption isotherms at two temperatures, such as 10°C and 30°C, and calculate the differential heat of adsorption by applying the Cracilus-Clapeyron equation.Water heat of condensation, i.e. 10.
It will be smaller than 6 kcal/mot. In other words, the silica gel surface is hydrophobic. Furthermore, compared to the heat of wetness per surface area for water molecules of silica gel, which mainly has free OH groups, is 190×10-'J/cd, that of silica gel produced by the above method is 11:0.
X10-'J/d, and this value is smaller than the energy of the ice surface.

This result also shows that these surfaces are hydrophobic.

The exact reason why hydrophobic silica gel can be obtained by the above method is unknown, but the hydrogen-bonding OH groups of the silica gel, which has some OH groups and microdea on the silica substrate surface, are formed by hydrothermal treatment after immersion in an alkaline aqueous solution. It is presumed that this is because an OH group that is completely different from that is generated.

The hydrophobic silica gel of the present invention is expected to be used for applications completely different from those of the conventional hydrophilic silica gel as described above.

The present invention will be explained in more detail below using Example C, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example 1 Tetraethylsilicic acid was hydrolyzed at pH 2, 0, and 80° C. for 100 minutes to prepare a silica hydrogel. The hydrogel was dissolved in water adjusted to pH 11.2 with sodium hydroxide for 1 hour.
Hydrothermally treated at 00°C for 110 hours (heated to 110°C in an oil bath, drained after 110 hours of treatment), and then gently dried to obtain silica gel. The differential heat of adsorption of water and methanol to this Vlikage/I/IC was measured by the Clasillus Clapeyron method described above, and curve A in FIG. 1 was obtained.

The results were as follows, and it was confirmed that the gel was hydrophobic.1. Example 2 Silica gel was produced in the same manner as in Example 1, except that the hydrothermal treatment time was 2 hours, and the differential heat of adsorption of water was When measured, the results were as shown in curve B in Figure 1, confirming that it was hydrophobic.

Comparative Example V licagel was produced in the same manner as in Example 1, except that the hydrothermal treatment was carried out at pH 8 and 9 for 2 hours, and the differential heat of adsorption of water and methanol was measured, as shown in curves CI and C in Figure 1. This result confirmed that it is hydrophilic.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the differential heat of adsorption of licagel obtained in Examples and Comparative Examples. Agent Patent attorney Tsutomu Ashioki Procedural amendment (spontaneous) October 16, 1980 Commissioner of the Patent Office Haruki Shimada 1, Indication of the case 1981 Patent application No. 150091y 2, Title of invention Hydrophobic silica gel and its Manufacturing process 3. Relationship with the case of the person making the amendment Patent applicant 4, agent 8, contents of the amendment as shown in the attached sheet

Claims (1)

[Claims] 1. The heat of adsorption when water is adsorbed on the surface is the heat of condensation of water 10
．． Hydrophobic silica gel with surface texture less than 6 keil/mol. PHi silica hydrogel or silica xerogel
A method for producing hydrophobic silica gel, which comprises immersing it in an alkaline aqueous solution of o to 11.2, hydrothermally treating it, and drying it.