Silica gel comprising guanidine carbonate
a technology of guanidine carbonate and silicon gel, which is applied in the field of silicon sols, can solve the problems of high aluminum content in some applications, unstable fresh sol, and unstable bet surface area, and achieves high stability and large specific surface area.
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example 1
[0076]An apparatus which consists of three glass overflow reactors arranged in series and connected to one another was used.
[0077]The content of each reaction vessel is thoroughly mixed with a propeller stirrer. The reactor content is heated indirectly by means of steam. For this purpose, heating coils through which steam flows are mounted in the interior of the reaction vessel. The vapors are passed over a water condenser and are condensed and the volume of the condensate is then measured.
[0078]In the first of the three overflow reactors, an aqueous solution of acidic fresh sol, prepared according to U.S. Pat. No. 2,244,325, was added by means of a feed apparatus. The feed apparatus was chosen so that the addition could also be effected into individual, selected reactors. The addition of the guanidine carbonate solution and optionally of a solution of a further base was likewise possible by means of a metering apparatus.
[0079]In order to increase the shelf life, i.e. the duration o...
example 2
[0085]A steady state was established in the apparatus described in example 1, with an average residence time of 14 min in the 1st reaction vessel, 16 min in the 2nd reaction vessel and 20 min in the 3rd reaction vessel, by adding 1600 ml of fresh sol containing 5.6% by weight of SiO2 per hour to the first reaction vessel and 128 ml of alkaline guanidine carbonate solution per hour likewise to the 1st reaction vessel and by evaporating 390 ml of water. The alkaline guanidine carbonate solution contained 45.7 g of guanidine carbonate and 8.4 g of KOH per 945 ml of water.
[0086]During the steady state, 85° C. was established in the 1st reaction vessel, 100° C. in the 2nd reaction vessel and likewise 100° C. in the 3rd reaction vessel. The SiO2 concentration changed from 5.6% by weight in the 1st reaction vessel to 6.1% by weight in the 2nd reaction vessel.
[0087]After an operating time of 3 hours in the steady state, a silica sol containing 6.1% by weight of SiO2 and having a pH of 8.71 ...
example 3
[0088]In this example, an aqueous guanidine carbonate solution which contained no additional base was used.
[0089]The reaction was carried out in the apparatus described in example 1. A steady state was established, with an average residence time of 14 min in the 1st reaction vessel, 16 min in the 2nd reaction vessel and 20 min in the 3rd reaction vessel. For this purpose, 1600 ml of fresh sol containing 5.6% by weight of SiO2 per hour and 128 ml of aqueous guanidine carbonate solution per hour were added to the 1st reaction vessel and 1160 ml of water were evaporated in the downstream reaction vessels.
[0090]The aqueous guanidine carbonate solution contained 50 g of guanidine carbonate per 950 g of water.
[0091]During the steady state, 87° C. was established in the 1st reaction vessel, 100° C. in the 2nd reaction vessel and likewise 100° C. in the 3rd reaction vessel. The SiO2 concentration changed from 5.6% by weight in the 1st reaction vessel to 5.8% by weight in the 2nd reaction ve...
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Abstract
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