What’s the Difference Between Blue, Orange, and White Silica Gel?

Silica gel is a widely used porous material that adsorbs moisture and is frequently used to limit the damaging effects of humidity.  Its widespread use has led to the creation of many different types, colors, and sizes of silica gel.  This article focuses specifically on why silica gel comes in different colors, and the three most frequently seen colors are: blue, orange, and white.  How does the color of silica gel make a difference?

Blue Silica Gel

Blue silica gel is blue because it has cobalt chloride in it.  The reason cobalt chloride is used is because it allows blue silica gel to turn pink once it has reached its adsorption capacity, in other words it’s an indicator for silica gel being full of moisture.  The creation and disposal of blue silica gel is difficult because cobalt chloride is toxic.

Orange Silica Gel

Orange silica gel has methyl-violet in it, which is what gives it an orange color.  Orange silica gel turns green once it has reached its adsorption capacity.  Like blue silica gel orange silica gel is also an indicating type of silica gel, however methyl-violet is not toxic making it safer to create and use.

White Silica Gel

White silica gel is non indicating silica gel.  What this means is as the silica gel adsorbs moisture it does not change colors.  This type of silica gel is most frequently used for preserving items and for reducing humidity for items that are in storage.  White silica gel is the type of gel you find in the little packets you find when you purchase certain products.

A Guide to Determine the Value of Sieve in Ethanol Dehydration

All molecular sieves are not the same.  They are not a commodity and the quality varies from manufacturer to manufacturer, therefore it is important to take the time to examine not only the price of molecular sieve but the value.

 Virtually all molecular sieve manufacturers measure the same characteristics and properties in molecular sieve, and it is the various measurements of these characteristics that allow you to determine the value of your sieve.

Although this list focuses on determining the value of ethanol grade sieve a lot of these measurements can help determine the suitability of a sieve product for any particular application.  Ultimately knowing what makes sieve valuable can make a difficult buying decision less complicated.  Listed below are the sieve properties that can help you determine its value.

1. Density – Knowing the density (when coupled with water adsorption) allows you to figure out the overall water capacity of a vessel in terms of volume or mass. Higher capacity = more water adsorbed.  A more valuable sieve has a higher volumetric capacity.
2. Particle size and distribution – Allows for the calculation of pressure drop, fluidization parameters, and critical velocity through the bed which ultimately effects flow rate.  A higher quality sieve has a tight distribution with less “tails.”
3. Static water adsorption – This refers to the overall capacity of the sieve to adsorb water.  (Do not confuse with working capacity which is much less than static capacity and varies with the operation as well as the sieve).  For more information on working capacity see my previous article on calculating working capacity.  A sieve with a higher static water adsorption capacity is always better.
4. CO2 adsorption – This measures how much ethanol is being adsorbed with the water in your dehydration beds.   Water and (sometimes ethanol) can be adsorbed by 3A sieve because 3A is made from 4A sieve and as a result the sieve bed will not entirely be made up of 3A.  Some of the left over 4A sieve adsorbs CO2 and ethanol therefore the higher the CO2 adsorption rate is the higher the ethanol co-adsorption rate in the bed is.  This ultimately reduces the overall working capacity per cycle in an ethanol plant, look for low CO2 adsorption rates.
5. Crush strength – This one’s simple, the higher the crush strength the higher the durability of the molecular sieve beads in operation.  A higher number here means a higher quality sieve.
6. Attrition – This refers to fryability, which is the tendency of the sieve beads to grind up, which produces dust, thus lowering the overall capacity of the bed.  A lower attrition number is better.
7. Ethanol ΔT (Methanol Delta T) – This is a measurement of the ability of sieve to adsorb ethanol, or a measurement of the co-adsorption characteristics of water and ethanol.  If capacity is being taken up by ethanol then the water capacity suffers, which is why a lower number is better.

Feel free to use this list  as a guide to determine if the sieve you are currently using or or wish to buy is going to be a quality product.  You can find most of, or all of this, information about your sieve  by asking your supplier or manufacturer for a certificate of analysis from their quality control department.

Is the sieve you’re buying valuable?

View Molecular Sieve Comparison Chart By Clicking the Link Below

Molecular Sieve Comparison Chart

Part One of a Two Part Article Dealing with Ethanol Dehydration and Sieve Regeneration and Rotation

Bedded dehydration systems are some of the most frequently used devices for the purification of ethanol.  This article focuses on how bedded dehydration systems distil and purify ethanol to make it over 99% pure.   Ethanol is purified so it can be used as a fuel in automobiles, which currently requires ethanol to be over 99% pure.

The distillation process begins after the fermentation process.  From the beer column, rectified ethanol is pumped into the rectifier column (frequently called the stripper). After distillation occurs in the rectifier column the ethanol mix goes to the condenser.

After ethanol is condensed in the condenser the gaseous ethanol can go to one of two places: the first partial steam of vapors can be sent back to the rectifier column as reflux, or the rest of the vapors are passed through a super-heater before being taken to the molecular sieve units for dehydration.

This part of the process distils the ethanol solution and making it around 95% pure ethanol.  The last 5% of the solution is water still needs to be separated from the mixture in order for ethanol to be use as fuel.  This is done with molecular sieve.

After passing through the super heater the vapor now passes through one of what could be many dehydrating beds of molecular sieve beads. Water in the incoming vapor stream is adsorbed on the molecular sieve material.  Anhydrous ethanol vapor that is now over 99% pure has been created from the sieve loaded dehydration bed, and is now free to be collected.

The process is finalized when the ethanol vapor remaining from the molecular sieve units are condensed in the condenser and cooled down in the product cooler, bringing it closer to its ambient temperature.  The product is then stored in a product tank until it is ready to be sold.

Part two is forthcoming…