Method for producing an alumina gel having a high dispersibility and a specific crystallite size

Abstract

Process for preparing alumina gel in a single precipitation step consisting of dissolving an aluminium precursor, aluminium chloride, in water, at a temperature of 10° C. to 90° C. such that the pH of the solution is from 0.5 to 5, for a period of 2 to 60 minutes, then adjusting the pH to 7.5 to 9.5 by adding a basic precursor, sodium hydroxide, to the solution obtained to obtain a suspension, at a temperature of 5° C. to 35° C., and for 5 minutes to 5 hours, followed by a filtration step, said process not comprising any washing steps. Also, novel alumina gel having a high dispersibility index, in particular a dispersibility index of more than 80%, a crystallite dimension of 0.5 to 10 nm, a chlorine content of 0.001% to 2% by weight and a sodium content of 0.001% to 2% by weight, the percentages by weight being expressed with respect to the total weight of the alumina gel.

1 . An alumina gel having a dispersibility index of more than 80%, a crystallite dimension, obtained by the Scherrer X ray diffraction formula along the crystallographic directions [020] and [120], respectively in the range 0.5 to 10 nm and in the range 0.5 to 15 nm, as well as a chlorine content in the range 0.001% to 2% by weight and a sodium content in the range 0.001% to 2% by weight, the percentages by weight being expressed with respect to the total weight of the alumina gel. 
     
     
         2 . The alumina gel as claimed in  claim 1 , having a dispersibility index in the range 85% to 100%. 
     
     
         3 . The alumina gel as claimed in  claim 2 , having a dispersibility index in the range 88% to 100%. 
     
     
         4 . A process for the preparation of an alumina gel as claimed in  claim 1 , in a single precipitation step (a) consisting of dissolving an acidic aluminium precursor, aluminium chloride, in water, at a temperature in the range 10° C. to 90° C., in a manner such that the pH of the solution is in the range 0.5 to 5, for a period in the range 2 to 60 minutes, then adjusting the pH to a pH in the range 7.5 to 9.5 by adding a basic precursor, sodium hydroxide, to the solution obtained in order to obtain a suspension, at a temperature in the range 5° C. to 35° C., and for a period in the range 5 minutes to 5 hours, and a filtration step b) of the suspension obtained at the end of step a), said process not comprising any steps for washing the precipitate obtained at the end of the filtration step b). 
     
     
         5 . The process as claimed in  claim 4 , in which the acidic aluminium precursor, aluminium chloride AlCl 3 , is dissolved in water, at a temperature in the range 10° C. to 75° C. 
     
     
         6 . The process as claimed in  claim 4 , in which the pH of the solution of aluminium chloride, AlCl 3 , in water, is in the range 1 to 4. 
     
     
         7 . The process as claimed in  claim 4 , in which the pH is adjusted at a temperature in the range 10° C. to 30° C. 
     
     
         8 . The preparation process as claimed in  claim 7 , in which the pH is adjusted at a temperature in the range 10° C. to 25° C. 
     
     
         9 . The preparation process as claimed in  claim 1 , in which the pH is adjusted to a pH in the range 7.7 to 8.8. 
     
     
         10 . The preparation process as claimed in  claim 4 , in which the preparation process also comprises a drying step for the filtered suspension obtained at the end of the precipitation step in order to obtain a powder, said drying step being carried out by drying at a temperature of 100° C. or more or by spray drying. 
     
     
         11 . The preparation process as claimed in  claim 10 , in which the preparation process also comprises a shaping step of the powder obtained in order to obtain a green material. 
     
     
         12 . The preparation process as claimed in  claim 11 , in which the shaping step is carried out by mixing-extrusion or by oil-drop. 
     
     
         13 . The preparation process as claimed in  claim 11 , in which the shaped green material may then undergo a heat treatment step at a temperature in the range 500° C. to 1000° C., for a period in the range 2 to 10 h, in the presence or absence of a stream of air containing up to 60% by volume of water.