An invovative green technology to produce green precipitated silica from rice husk ash

• Process Of Making Silica

• Silica is manufactured by using rice husk ash as a source of silicate or silica and this ash is then reacted with sodium hydroxide which yields the sodium silicate, which on further reacting with sulphuric acid gives silica along with by-product sodium sulphate. The basis of the advantages for this proposed process is first the rice husk ash with higher silica content.
• The process to extract all the silicate content from the rice husk is just by burning the rice husk under controlled conditions of air and temp. By this condition, we can get the clear white ash in the furnace. The basic steps in the production of precipitated silica are • Obtaining silica from rice husk                  • Dissolution of silica in alkali • Preparation of silica from silicate solution
• Flowchart of production of Silica from Rice Husk Ash
• Process Description
• The initial step is extraction of silica from ash as sodium silicate using caustic soda. This reaction is carried out at a temperature in the range 180ºC-200ºC and pressure ranging from 6-8 atmospheres. But high reaction temperature and pressure can be avoided if ash obtained by burning rice husk at 650ºC is used. This ash is mostly amorphous silica which is reactive around 100ºC with NaOH solution at atmospheric pressure to yield sodium silicate.
• A viscous, transparent, colourless sodium silicate solution (~15%w/w) is obtained after filtration of the reacted slurry (consisting of residue digested ash, sodium silicate, water and free sodium hydroxide). In the second step of the process, silica is precipitated from sodium silicate using sulphuric acid. This step requires controlled conditions of addition rate of sulphuric acid and temperature of reacting mass in a neutralizer. The temperature is in the range of 80-90ºC and pressure is the normal atmospheric pressure. The reaction is as follows:
• The addition of sulphuric acid is done very slowly (otherwise the chemistry of such mass may change along with physical properties) until acidic conditions are reached. The acidic conditions indicate approximately complete precipitation of silica from sodium silicate. A white precipitate of silica in solution of sodium sulphate is obtained.
• The silica (wet impure silica) obtained above is filtered. Purification of this silica for removal of sulphate impurities constitutes the third step of process. For this successive demineralized water washings are given in the filter process itself. The conductivity of the effluent follows a decreasing trend owing to removal of sodium sulphate. Thus, conductivity can be used as the criteria to decide the number of washings for obtaining silica of desired purity.
• Silica after removal of sulphates (wet silica) is generally spray dried to obtained the amorphous powder form in the final step of the process. The purification and drying produce silica in while amorphous powder form. Sodium sulphate from the effluent water and good quality bricks from ash residue are other recoveries.
• Rice husk is not just a waste material but more than that. Thus, instead of just disposing it off, one can add value to it by effectively utilizing silica content present in it and to produce precipitated silica from it. It has been observed that approximately more than 90% of SiO2 can be recovered from rice husk ash under ideal conditions.
• The main advantage of this process is that waste disposal problem of rice husk is eliminated and also valuable product is obtained. The amorphous silica obtained using this method have many application, e.g. as filter in rubber products and paper, anti- sticking agents. It is an important catalyst in chemical industry and also serves as the raw material for the production of silicon. Also byproduct thus obtained has industrial importance to produce different derivatives.

• Uses of Silica

• Reinforcement of elastomeric products like shoe soles. Brisil is a leading manufacturer of Silica; addressing the problem of rice husk ash utilization. Brisil engages with rice husk & rice husk ash-producing industries and sets up the plants based on the technology. Brisil produces & supplies rice husk ash based green precipitated silica, highly dispersible silica and other chemicals for all major applications including tires, rubber, toothpaste, paints, plastics etc.
  •  Reinforcement of silicone rubber.
  •  Reinforcing material in tires.
  •  In sheathing compounds for cables.
  •  A constituent of adhesives in for bonding of unvulcanized rubber to textiles or steel tire cord.
  •  In thermoplastics, used to act as anti-blocking agents and to prevent plate out effects in films and film.
  •  To improve the mechanical properties of PVC flooring.
  •  As carrier silica for materials and as free flow agents for powder formulation, particularly of hygroscopic and adhesive substances.
  •  As adsorbent.
  •  In toothpaste to control rheological properties and as a cleansing agent.
  •  Hydrophobic precipitated silica is used in mineral oil and silicone oil antifoaming effect.
  •  Purification and stabilization of beer.
  •  Analysis of blood.
  •  Cosmetics.
  •  The food industry as an anti-caking agent.
  •  Specially prepared silica gels from silica are used for making thermal insulation material.
  •  As a dehumidifying agent for air and other gases. 
  •  As a filtering agent to clarify juices.
• Brisil produces industry-specific silica for all major applications. We can provide customized specifications to meet the requirement of its clients. We work closely with our clients to develop silica to meet their silica requirements. Contact Brisil for Precipitated Silica and Highly-Dispersible Silica today!
  

Source : https://www.slideshare.net/brisiltechnology/preparation-of-silica-from-rice-husk-ash