Silica gel is a hard, porous form of silicon dioxide that is commonly processed into beads or granules and used as a dessicant, and is inside the permeable paper packets marked "DO NOT EAT" that are found inside many products. The substance is made from sodium silicate, and its strong affinity for water molecules causes it to adsorb wetness and prevent mold from forming, which spoils many products. Chemically, silica gel removes water vapor through adsorption of its numerous surface pores rather than by absorption into the gel itself. Most people may be aware of silica gel to some degree, but not everyone knows how it is made.
Silica gelquestion206.htm was invented in the early 1900s. It was first widely used during World War I in gas mask canisters, where it was intended to adsorb dangerous gases. By World War II, its varied uses included keeping penicillin dry and as a fluid cracking catalyst for high octane gasoline. It is currently in widespread use as a dessicant, as a catalyst in chemical reactions, in chromatography and in cat litter. It can also be added to some foods to perform a number of different functions, such as preventing caking and settling.
Contrary to popular belief, silica gel is actually considered safe to eat, and may to be added to foods in concentrations of up to two percent. As with any other food, there are no adverse effects as long as it is consumed in moderation.
In chromatographyChromatography, a mixture of substances is separated out into its components by passing it through a matrix. One way to understand the concept is to think of separating a mixture of pebbles by size, by pouring them through a series of screens. The tiniest pebbles simply pour through the screens and exit first, followed by the small pebbles and then finally the large pebbles manage to work their way through the barriers and exit. In chromatography, silica gel is often used as the matrix, usually called the stationary phase, that delays the passage of various molecules to various degrees allowing them to separate out. Due to the polarity of silica gel, non-polar compounds tend to rapidly pass through the gel. Reverse-phase chromatography uses silica that has had hydrophobic groups attached to it, allowing polar compounds to pass through the gel first.
A thin layer of silica gel is also commonly attached to a solid substrate to produce thin-layer chromatography materials. The dip strips often used in quick urinalysis tests are a prominent example of a medical application, with the silica gel attached to a thin strip of plastic.
Color-changing silica gels have been developed that indicate when they have been exposed to water. A chemical is simply added to the gel in small amounts during preparation. One common color-changing silica gel is prepared by adding cobalt chloride, which renders the gel blue when dry and pink when hydrated. Adding methyl violet makes the gel appear orange when dry and green when hydrated. These color-changing gels can be used to measure moisture exposure and relative humidity because they slowly change color as the amount of water adsorbed into the gel increases.
Silica gel acts as a good catalyst because its hardness translates into high thermal, chemical and deformation resistance. This hardness comes from the silicon dioxide it is made from, which is the same material found in quartz. Water may be the most commonly known substance it can adsorb, but it can adsorb many others as well, and some of them may in turn act as catalysts. A collection of round silica gel granules provide an exceptionally large surface area for adsorption and catalysis -- up to 800 square meters per one gram.
Silica gel is prepared by acidifying solutions of the natural mineral, sodium silicateSodiumsilicate. A clear substance precipitates out, which when dehydrated is the silica gel. The dehydration process is accomplished by heating the gel, and it can also be reconditioned for use after absorbing water by heating it to release the water. Heating the gel to high temperatures changes its properties slightly and increases its adsorption capacity. Many products that use silica gel require extra thermal processing. For example, gas chromatographs that use silica gel that have been processed at 500 degrees Celsius have better separation properties. All silica gel products need to be heated to dehydrate them before use.
The material is gelatinous when it first forms. In order to create round beads instead of a powder, the silicate solution is prepared as an emulsion in a solvent, such as a mixture of hexane and alcohol. In such an emulsion, the silica is present as droplets suspended in the solvent. When gelled by adding acid to the mixture, and while kept in motion by stirring or rotation, the droplets form into spherical blobs of gel suspended in the solvent. The size of the droplets, which regulates the size of the final beads, is controlled by altering the composition of the solvent. The solvent is then washed away and the spheres are heat treated to form solid beads.calcinershell-resized-600
Rotary calcinerscalciners.aspx are ideal process equipment for forming, dehydrating and thermally treating silica gel. This equipment provides indirect heat, and is ideal for a wide range of specialty applications including drying, calcining, chemical reactions and thermal desorptions.
The indirect-heated rotary calciner is a continuous-process device for medium to high temperature applications. Simply designed, the material processed is heated indirectly in a rotating shell. The rotary shell is enclosed and heated from the exterior in a stationary furnace. The heated shell provides the hot surface for heat transfer to the material stream on the shell interior, through a combined radiative and through-wall conductive / convective mode of heat transfer. The rotation and slope of the shell motivate the flow of material through the shell from feed to discharge points, which are located at stationary breechings which enclose the ends of the rotary shell.
Heyl & Pattersonheyl p... inc 29440.htm engineers rotary calciners through its Renneburg Division that are in commercial use to process hundreds of different materials. This equipment can process chemicals that are dusty, combustible, explosive, or thermally sensitive. The heating process is precisely controlled to allow for uniform quality of product. Each rotary calciner is specifically designed for each unique application and is rigorously tested before final manufacture.
Silica Gel and Its Use as an Effective Catalyst
Silica Gel and Its Use as an Effective Catalyst
by David Phillips, Heyl & Patterson, USA
Silica gel is a hard, porous form of silicon dioxide that is commonly processed into beads or granules and used as a dessicant, and is inside the permeable paper packets marked "DO NOT EAT" that are found inside many products. The substance is made from sodium silicate, and its strong affinity for water molecules causes it to adsorb wetness and prevent mold from forming, which spoils many products. Chemically, silica gel removes water vapor through adsorption of its numerous surface pores rather than by absorption into the gel itself. Most people may be aware of silica gel to some degree, but not everyone knows how it is made.
Silica gelquestion206.htm was invented in the early 1900s. It was first widely used during World War I in gas mask canisters, where it was intended to adsorb dangerous gases. By World War II, its varied uses included keeping penicillin dry and as a fluid cracking catalyst for high octane gasoline. It is currently in widespread use as a dessicant, as a catalyst in chemical reactions, in chromatography and in cat litter. It can also be added to some foods to perform a number of different functions, such as preventing caking and settling.
Contrary to popular belief, silica gel is actually considered safe to eat, and may to be added to foods in concentrations of up to two percent. As with any other food, there are no adverse effects as long as it is consumed in moderation.
In chromatographyChromatography, a mixture of substances is separated out into its components by passing it through a matrix. One way to understand the concept is to think of separating a mixture of pebbles by size, by pouring them through a series of screens. The tiniest pebbles simply pour through the screens and exit first, followed by the small pebbles and then finally the large pebbles manage to work their way through the barriers and exit. In chromatography, silica gel is often used as the matrix, usually called the stationary phase, that delays the passage of various molecules to various degrees allowing them to separate out. Due to the polarity of silica gel, non-polar compounds tend to rapidly pass through the gel. Reverse-phase chromatography uses silica that has had hydrophobic groups attached to it, allowing polar compounds to pass through the gel first.
A thin layer of silica gel is also commonly attached to a solid substrate to produce thin-layer chromatography materials. The dip strips often used in quick urinalysis tests are a prominent example of a medical application, with the silica gel attached to a thin strip of plastic.
Color-changing silica gels have been developed that indicate when they have been exposed to water. A chemical is simply added to the gel in small amounts during preparation. One common color-changing silica gel is prepared by adding cobalt chloride, which renders the gel blue when dry and pink when hydrated. Adding methyl violet makes the gel appear orange when dry and green when hydrated. These color-changing gels can be used to measure moisture exposure and relative humidity because they slowly change color as the amount of water adsorbed into the gel increases.
Silica gel acts as a good catalyst because its hardness translates into high thermal, chemical and deformation resistance. This hardness comes from the silicon dioxide it is made from, which is the same material found in quartz. Water may be the most commonly known substance it can adsorb, but it can adsorb many others as well, and some of them may in turn act as catalysts. A collection of round silica gel granules provide an exceptionally large surface area for adsorption and catalysis -- up to 800 square meters per one gram.
Silica gel is prepared by acidifying solutions of the natural mineral, sodium silicateSodiumsilicate. A clear substance precipitates out, which when dehydrated is the silica gel. The dehydration process is accomplished by heating the gel, and it can also be reconditioned for use after absorbing water by heating it to release the water. Heating the gel to high temperatures changes its properties slightly and increases its adsorption capacity. Many products that use silica gel require extra thermal processing. For example, gas chromatographs that use silica gel that have been processed at 500 degrees Celsius have better separation properties. All silica gel products need to be heated to dehydrate them before use.
The material is gelatinous when it first forms. In order to create round beads instead of a powder, the silicate solution is prepared as an emulsion in a solvent, such as a mixture of hexane and alcohol. In such an emulsion, the silica is present as droplets suspended in the solvent. When gelled by adding acid to the mixture, and while kept in motion by stirring or rotation, the droplets form into spherical blobs of gel suspended in the solvent. The size of the droplets, which regulates the size of the final beads, is controlled by altering the composition of the solvent. The solvent is then washed away and the spheres are heat treated to form solid beads.calcinershell-resized-600
Rotary calcinerscalciners.aspx are ideal process equipment for forming, dehydrating and thermally treating silica gel. This equipment provides indirect heat, and is ideal for a wide range of specialty applications including drying, calcining, chemical reactions and thermal desorptions.
The indirect-heated rotary calciner is a continuous-process device for medium to high temperature applications. Simply designed, the material processed is heated indirectly in a rotating shell. The rotary shell is enclosed and heated from the exterior in a stationary furnace. The heated shell provides the hot surface for heat transfer to the material stream on the shell interior, through a combined radiative and through-wall conductive / convective mode of heat transfer. The rotation and slope of the shell motivate the flow of material through the shell from feed to discharge points, which are located at stationary breechings which enclose the ends of the rotary shell.
Heyl & Pattersonheyl p... inc 29440.htm engineers rotary calciners through its Renneburg Division that are in commercial use to process hundreds of different materials. This equipment can process chemicals that are dusty, combustible, explosive, or thermally sensitive. The heating process is precisely controlled to allow for uniform quality of product. Each rotary calciner is specifically designed for each unique application and is rigorously tested before final manufacture.
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