Background:
Alkali metal silicates (having silica as a main constituent) are a family of chemicals with a wide range of physical and chemical properties and have major application in the detergent, pigment, adhesives, cement & building materials, pulp and paper, catalyst and silica gel producing industry. Silicates are produced either by the dry process or the wet process. In the dry process, the solid silicate product is made at temperatures in the range from 900 °C to 1500 °C. But the dry process is highly expensive both in terms of investment and maintenance costs and in terms of energy consumption and, further, it causes considerable air pollution. In the wet process, reaction takes place in a high-pressure reactor at a temperature of 180 °C to 250 °C. Although this process is comparatively less expensive than dry process in terms of investment cost, still the silicate production cost is high. Another disadvantage of wet process is that the conversion reaction is sluggish and does not take place quantitatively and results in low modulus sodium silicate:
Technology Details:
Accordingly, it is an object of the present invention to prepare powdered alkali metal silicate employing energy efficient process which obviates the drawbacks as mentioned above. A primary object of the present invention is to provide a process for obtaining powdered alkali metal silicate using rice husk/ rice husk ash as a source of amorphous silica, or using commercially available amorphous silica. It is a further object of the present invention to provide a method of producing powdered alkali metal silicate by a less energy intensive process than current processes for producing alkali silicates:
Another object of the present invention is to provide a process for obtaining powdered alkali metal silicate by precipitation after mixing alkali metal silicate solution with water miscible low boiling point organic solvent:
The present invention, discloses a process for obtaining powdered alkali metal silicate from rice husk (RH) or rice husk ash (RHA) or from commercially available amorphous silica. It comprises three specific principal stages, in which alkali metal silicate solutions of low modulus are initially produced from RH/RHA, that can be further processed to yield an alkali metal silicate solution of high molar ratio. Alkali metal silicate of high modulus can also directly be prepared by using commercially available amorphous silica. The third stage of the present invention comprises treating high modulus alkali metal silicate solution with water miscible low boiling point recyclable organic solvent, and precipitating and drying to produce high modulus alkali metal silicate in powder form.