TWI262896B - Process for preparing porous silica xerogel - Google Patents

Abstract

The present invention discloses a process for preparing silica xerogel including 2-step acid-base catalyst procedures, a surface modification with trimethylchlorosilane, and a heat treatment at a high temperature. The 2-step acid-base catalyst procedures includes mixing tetraethoxysilane, isopropanol, water and acid to form a sol solution, and adding an aqueous solution of ammonium hydroxide to start gelation.

Description

1262896 IX. Description of the invention: The technical field to which the invention belongs, and the present invention relates to a method for preparing a porous two-gas fossil shower gel, in particular to a porous cerium oxide using a sol-gel method and surface modification. Dry gel of the radix lozenge lL. p & preparation method. This porous ceria xerogel can be used as a thermal insulating material. The main process of the prior art is that the sol-gel method is prepared by a sol-gel method. Basically, the sol-gel method is a chemical reaction mechanism of a liquid phase, and the inorganic salt (inorganie saIts) is used for hunting. Organic salt (. ah k, burnt oxide (10) 〇xide) 'metal oxide (metal 〇xides) before lying with a variety of different solvents, various drugs according to different ratios (concentration, purity), mixing and stirring for a certain period of time , get our fossil sol solution. However, the sol-gel block body is easy to be broken due to the different process methods, and the block material is broken and the process parameters are not easy to control. Therefore, the preparation of the cerium oxide gel will need to be considered in different states, and it is determined that it is suitable for the rubber glue process. In order to obtain high performance gel insulation.

When glass or ceramics are generally produced by a lyotropic method, siloxane is most commonly used as a precursor, and the chemical H of the decane oxide is represented by Si(〇R)4, which represents an alkyl group. The lyophilization process is mainly divided into three steps of hydrolysis and condensation polymerization: '' I Hydrolysis Reaction One of the decane oxides reacts with hydrazine and reacts with water. These substances are large VIII ~ 刀容1262896 a hydroxide, one of the water molecules OH group is substituted with an OR group to form a decyl oxide containing a 0H group, and the alcohol is released, and the precursor is stirred with water ((11)4) with acid or alkali. Hydrolysis is carried out under catalysis, and the chemical reaction mechanism is as follows:

(R0)3SiOR + 4//20 <=> HOSi(OR)3^R〇H ^>Si(OH)A +4R0H (1) Uranium flooding with tetraethoxy zebra burning $ζ·... (tetraethylorthosilicate, or tetraethoxysilane, referred to as TEOS)

Si(OC2H5)4 +4H20 Si(OH)4 +4C2H5OH (2) 2·Condensation Reaction The hydrolyzed Si(OR)4 will condense with another si(〇R)4 to form (OH) 3Si-0-Si(OH)3 and one molecule of water is removed, wherein, by the condensation reaction of monosilicic acid in the above formula (2), a cerium oxide wet gel··nSi{OH can be formed. , * —> viSiO0 + ILyiH^O (3) 3. Polymerization I-reaction in nucleophilic substitution, nucleophilic due to hydroxyl or alkoxy attack Addition), wherein the oxane oxide containing a hydroxyl group is easily reacted with an alkoxy group or a hydroxyl group in another alkoxide to form a bridging oxygen to release an alcohol or a water, such as the following reaction As shown in the formula, (0H)3Si-0-Si(0H)3 will be polymerized with other si(〇H)4 to form a polymer of ceria network. All reactions can be catalyzed by acid or base 1262896. Something is different in different catalytic conditions. The lyogel produced under the structure will also be H〇--·Si^-q-Si- Oil II ^ 〇OH 1,0—ψ一O—si—0—Si— OH i LI HO—〇HH 〇一sj_ 0II — plus ου , "有:和.. The size, structure, and degree of cross-linking of the bulk particles have a very deep relationship with the degree of the sol. The reaction rate of the gel is cut and the spleen is controlled. In the meantime, if any of the above changes, the composition of the starting solution will be changed to phase VIII and become a smear. Let the original homogeneous solution be sputum, 嬗, 、, The concentration of the reactants of the six I m ^ phantom B is a change, apparently: the length of a room and the microstructure of the gel. The process parameters of the I/旋胶 are mainly precursors, solvents, The relative molar ratio of water and different modifiers is also the result of the thermal properties of the gel. However, the following problems are often found during the preparation process: The surface potential and the degree of the solution using different solvents will be affected. No, the shirt is ringing, thus causing an important parameter for gelation in the gel preparation process. _ 2· S (0R) 4 has a different alkyl (R) Gelation time, when the choice of non-burning base, the chain lengthening or complex shape will reduce the condensation: the machine should be 卩 ♦ low to form the proportion of the network structure polymer. 3. Early Kistler et al. Water washes the salt in the gel

0H

0H H0 —Si—〇一si~〇H

0H

0H 'η H20 1262896 Remove the hydrazine and replace the water father with alcohol, and finally evaporate the alcohol, so that six can produce a condensate. However, because the solvent in the wet oxidized oxide gel is removed by simple: thermal drying, the condensed skeleton will shrink and the gel will be broken. This phenomenon is caused by the collapse of the hole in the gel porous body when the solvent evaporates and cannot withstand the strong surface tension of the interface. ‘ Agent! The amount of 'will cause the concentration of the reactants in the solution to change' severely affects the gel time and microstructure. Good Britain (4) 682574 (AD 1952) reveals a hydrophobic second-generation reform institute. I will have one or two d The -C4 alkyl-based gasification stone is reacted with the cerium oxide particles in an inert solvent. SUMMARY OF THE INVENTION The present invention is directed to (iv) gel process parameters such as precursors, solvents == change! The type of agent and their relative molar ratio are adjusted. The efficiency of yttria/rotation and aging treatment, the occurrence of rupture caused by the surface tension of the pores and the decrease of the pores. Preparation of reticular cerium oxide xerogel/inclusion·Using crushed 惫仏rb 槪屯 knowing that one of the ruthenium compounds is reacted with water, using citric acid as an acid catalyst, and hydrolyzed into ruthenium Hydroxide (ruthenium sol), then ammonia water as a base catalyst, argon condensation reaction to form -Si-O-Si- and release water knife, thus obtaining -& agent (dissolved in the positive appearance ^ fossil) Xixi wet gel, and then modified with a trimethyl chlorite cherished two children A h * 兀, surface modification, the introduction of the required functional based on the aphid surface, the use of high temperature calcination, the formation of heat insulation Sexual network structure 1262896 oxidized pulverized gel. The cerium sol of the present invention is prepared by using a molar ratio of 丨:X: 2: 1.8X10-3 tetraethoxy decane (by (1) 匕仏) 4), A mixture of isopropanol (ch3ch(qh)3oh), deionized water and hydrochloric acid, wherein χ is between 2 and 12. The amount of ammonia (molar) is approximately equal to the amount of hydrochloric acid. Since the present invention uses tetraethoxyl money, the gel time of the process of the present invention can be substantially shortened compared to other long chain oxides. The present invention uses isopropyl alcohol as a solvent, since it has a suitable vapor pressure (25 (a) at 10C (10), avoiding gel shrinkage caused by surface tension on the gel structure. From 2 to 12, the isopropanol to tetraethoxy decane has a sigma-like knee time, and too much or too little isopropanol solvent will cause the gelation time to be too long. The surface of the wet gel is modified by using a modifier (dissolved in n-hexane) to prevent the cracking of the cerium dioxide wet gel during the high-temperature treatment of the subsequent performance. The cerium oxide xerogel has a Βετ specific surface area of 100 to 600 m 2 /g. Embodiments The present invention provides a method for preparing _ ^ -7 VA ^ species of porphyrin gasification dry gel comprising the following steps: Preparing a wet gel comprising: hydrolyzing a tetraethoxy decane, isopropanol, water and a compound, and forming a wet gel in the presence of a catalyst to form a wet gel, wherein The molar ratio of the tetraethoxy zebra to 1262896 isopropanol is between 1:2 and Hl2 · 11) immersing the wet gel in a modified or modified solution containing Φ, 隹7 modified agent and an inert solvent, 苴m Cl Γ4 ^ A AA - /, ~ Wenbei agent is a gasified decane reactivity with one or two C 1-C4 :!: elementary groups; ""The bathing agent is not modified by heat treatment of the surface modification agent.矽 矽 矽 。 。 以 以 以 以 以 一 一 一 一 一 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 较佳 矽 矽 矽 矽Preferably, the modified solution of step ii) has dimethylhethane having 1-20% by volume of trimethyl decane, and the wet gel is immersed in the chloroform or chloroform. The modified solution is 12-72 hours. The preferred 'step-out' heat treatment is carried out at a price of from lining for 24-96 hours; and at (10) Cn〇〇〇c is heated for 〇 〇 hours. Preferably, stepping out) The porous silica dioxide dry gel produced has a BET specific surface area of 100 to 600 m 2 /g. According to a preferred embodiment of the present invention, a network of knots is performed. The preparation method of the composition of the dioxide dioxide dry gel is as follows: (4) Dissolving 1 mole of tetraethoxylate in isopropyl alcohol. 1.8X10·3 molar hydrochloric acid and 2 molar Deionized water mixed with the above two solutions in the reaction tank, homogenized for 20 minutes at 3 rpm. (b) Then take 8.12x1 〇·3 moles of ammonium hydroxide with 2 moles The sol added to the step (a) prepared by ionized water was searched for 3 262 minutes with 3〇〇RpM homogenization 10 1262896. (C) The reaction tank was insulated from the outside air by a gas-tight membrane, and placed in ^(8) to warm. Gel at ion procedure. When the molar ratio X was 3, gelation was allowed to stand for 40 hours; when x was 6, the waist was allowed to stand for 10 hours; when X was 9, gelation was allowed to stand for 126 times. However, if X is 1.5, the gelation standing time is as long as about 76 〇 J. Yuancheng 4 gelation and aging treatment directly form wet coagulation veins. (d) A solvent exchange/surface modification procedure was carried out in a 6% by volume ratio of trimethylchloromethane in n-hexane, including static solution of the wet gel in a 6 % by volume solution of trimethylchloromethane in n-hexane. 36 hours in the middle. (e) After the modification is completed, it is dried at room temperature for 48 hours. (f) The modified gel was subjected to water removal adsorption for 4 minutes in a 4 (rc oven). (g) The gel after water removal was dried at a fixed temperature of 6 ° C for 48 hours. The dried ruthenium gel is placed in a crucible, and then calcined in a high-temperature furnace, and air is introduced to raise the temperature from room temperature to 2 ° C per minute rc, and then to 200 ° C at 3 ° C per minute. After heating to 600 ° C and holding the temperature for 2 hours, a network structure of cerium oxide xerogel can be obtained. When X is 3-6, the obtained network structure cerium oxide xerogel has a density of 0 · 36 g/cm3, a BET specific surface area of 7〇8·2 m2/g, a pore volume of 1·8 cm / g, an average pore size of 1618 Egypt heat transfer coefficient 0.089 W/mk 〇

Claims (1)

1262896 X. Patent application scope: The following steps are included: 1. Preparation method of a porous cerium oxide xerogel: i) preparing a wet gel comprising a 7' element, isopropanol, containing a tetraethylene group, The water and acid mixture is subjected to a hydrolysis reaction, and a polycondensation reaction is carried out in the presence of a base #1 hydrating agent to form a wet gel, wherein the molar ratio of the ethoxylated decane to the isopropyl alcohol is between 1:2 to 1:1 2; ii) immersing the wet gel in a modified solution containing a modifier 盥 左 κ ^ inert solvent for surface modification, wherein the modifier is a female y , one or two c 1-C4 :): the complete chlorinated stone smoldering, the inert solvent is not suitable for the p and the shelling agent; for a long time to form a porous dioxygen iii) heat treatment The surface modified wet gelled dry gel. 2. The method of claim i, wherein the step Η) is a trimethylchloromethane. The method of claim 3 or 2, wherein the monthly solvent of step 1) is n-hexane, acetone, toluene, dichloromethane or chloroform. 4. The method of claim 3, wherein the inert solvent is the method of claim 4, wherein the modified 12 1262896 solution of step Η) has 1 to 20% by volume of trimethylchlorodecane, And the wet gel is immersed in the modified solution for 12-72 hours. 6. The method of claim 1, wherein the heat treatment of step i i i) is carried out at 45 ° C to 10 (TC is heated for 24-96 hours; and heated at 100 ° C to 800 ° C for 1-10 hours). 7. The method of claim 1, wherein the porous ceria xerogel prepared in step iii) has a BET specific surface area of from 100 to 600 m2/g. 13