One of the most popular desiccants present in the industry, silica has many applications that spread throughout food and pharmaceuticals to manufacturing and experimentation.
Silica Gel has seen a rise in use in the past decade and has a history of application in wars worldwide as filters in gas masks to adsorb toxic gases.
The pharmaceutical industry in India has seen a rapid rise in silica usage as a desiccant. This might be a byproduct of the massive growth of the global silica gel whose market value is estimated to reach about 750 million dollars by 2030.
Being highly moisture absorbent, they are used as a cost-effective method of maintaining closed environments dry. Silica Gel is also used to thicken liquid solutions and create a dull surface for paint and films.
Silica gel is the amorphous and porous form of silica. An irregular framework consisting of oxygen and silicon atoms form its structure with many pores present inside.
Since silica has a strong affinity for water, it is widely used in many pharmaceutical and food industries as a desiccant. The large surface area present due to an increased number of pores to help create a strong force of adsorption.
This makes an affinity for water molecules present in the surrounding atmosphere to get sucked into the framework’s pores. Hence, silica acts as one of the best moisture absorbers.
Types of Silica Gel:
A Type: Transparent clear pellets that have a diameter of about 2.5 nanometers. They are mostly used as adsorbents or catalyst carriers.
B Type: Almost white with a diameter ranging from 4.5 nanometers to 7 nanometers. Mainly used as perfume carriers and adsorbents, also used as a catalyst carrier.
C Type: Used as a raw material for the making of cat litter silica gel. Can be converted into macro pored silica to be used as an adsorbent or as a catalyst carrier
Silica Alumina: Yellow and chemically stable. Used for applications of thermal stability. Can be dissolved only in alkali or hydrofluoric acid. Resistant to flames and much more useful than silica with delicate pores.
Stabilizing Silica: Micro-pored powdery substances. Used in breweries to remove micro-organic constituents. Also resistant to flames and non-toxic.
How it’s Made
Acidified sodium silicate forms a gelatinous precipitate which is then dehydrated after washing. The dehydration process results in the formation of colorless silica that is collected to produce industrial-grade silica gel.
Since silica gel is almost transparent, indicators are added to indicate moisture content’s presence to make industrial applications easier.
Cobalt chloride or Ammonium Tetrachlorocobaltate is used as an indicator to visibly display the amount of moisture content present in the silica. Blue indicates dryness and pink marks the point of maximum saturation.
The gel can be reused by the process regeneration where the silica gel is heated for an hour or two to a temperature of about 120 degrees Celsius. The regeneration process removes all the moisture content and brings the silica back to its original dry state.
In its dry form, silica gel is powdery and greasy to touch while in its saturated form is solid and bulky. Many silica pellets break when fully saturated or exposed to water as the silica surface film cannot handle the extra moisture content.
Advantages Of Using Silica Gel:
Having superior chemical properties, silica gel has found itself in many applications throughout the country.
Silica is also used as a catalyst in many chemical reactions that may produce a lot of water due to silica’s moisture retention. It is also used as a dehydration agent during ethanol formation and various hydrogenation processes.