Bayer Aktiengesellschaft

Werner Ludovici

Hans-Dieter Block

Hans-Heinrich Moretto

Peter Schmidt

Uwe Brekau

Peter Schober

Alex Burger

Hans Guth

Andreas Nickel

Hermann Rohe

Hermann Kaiser

A process is provided for the preparation of aqueous silica sols having a particle size of 27 to 72 nm. by adding fresh acidic silica sol into the reactors of a multi stage cascade reactor wherein the reactors contain aqueous solution of colloidal silica sol of a pH of 8 or above. Each successive stage of the cascade reactor is supplied with overflow from the preceding stage. Alkaline compounds, such as alkaline sodium silicate solution, alkaline potassium silicate solution, sodium hydroxide solution or potassium hydroxide solution, are introduced into the first reactor or first reactors so that a pH value in the range of 8 to 12.5 is established in the reactors.

Continuous preparation of silica sols which contain large particles

Process for the production and concentration of alkaline silica sols containing nonaggregated, spherical SiO.sub.2 particles with a diameter of .gtoreq.1 nm starting with SiO.sub.2 concentrations of 4-8% by weight, using microporous membrane filters.

Process for the production and concentration of silica sols

In the production of activated carbon by passing a preheated gaseous activation medium through a zone containing a bed of carbon-containing material while indirectly heating to maintain a temperature of about 500.degree. to 1100.degree. C., supplying carbon-containing material to the bed, and removing activated carbon from the bed, the improvement which comprises introducing the activation medium and the carbon-containing material co-current near the bottom of the zone at a rate such that gaseous products are formed in a quantity sufficient to maintain in the zone a lower static layer and an upper fluidized layer in particular proportions, the rate of supply of the carbon-containing material and withdrawal of activated carbon being related so as to convert about 30 to 55% by weight of the carbon-containing material to gaseous products. The average residence of the carbon-containing material is from about 0.2 to 6, preferably 1 to 4, hours. A suitable apparatus for carrying out the process is described.

Production of activated carbon in a reactor having a lower static layer

In the production of break-resistant and abrasion-resistant shaped structures of active carbon, comprising the steps of molding a finely divided, carbon-containing starting material with a binder, hardening the molding, eliminating volatile constituents from the molding composition and activating the moldings at a temperature of about 700.degree. to 1200.degree.C with at least one of steam and carbon dioxide, the improvement which comprises molding the carbon-containing material with a binder comprising a mixture of a phenol and an aldehyde or a condensation product thereof. The carbon-containing starting material may contain volatiles and hardening is effected in two stages with elimination of volatiles, the first stage up to about 150 to 200.degree.C and the second stage up to about 600 to 700.degree.C. The moldings are characterized by a benzene-adsorption capacity in excess of about 25 %, a methylene blue number of at least about 10, an abrasion of less than about 0.6 %, a breakage of less than about 0.8 % and a compression hardness of at least about 15 kp.

Production of strong active carbon moldings

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Odenthal, Germany

Werner Ludovici