8 Useful Guidelines Before Doing a Complete Molecular Sieve Change Out

You have decided to replace your molecular sieve, and now it’s time to load in what may be thousands upon thousands of pounds of molecular sieve in your vessel (of course the amount of sieve you load in depends on the size of your vessel).  What can you do to prepare your vessel before unloading all of this sieve?

In order to help you with that question we have prepared eight useful guidelines that could help prepare your vessel for sieve unloading.

Note: These guidelines are to be carried out before you load the sieve into your vessel.

1)      Before unloading the sieve you should regenerate your vessel by heating and cooling with process gas. Use the same operating conditions that you would normally use when regenerating your bed.

2)       If process gas is not available use nitrogen or another non-toxic gas instead.  Do not use any gas that contains any toxic components at hazardous levels to regenerate your vessel.

3)      After heating the sieve beds, cool them with gas by de-pressurizing the bed to flare.

4)      After using process gas you can start purging the vessel with inert gas at ambient temperature to flare.  It is important that the gas flow rate be sufficient enough to have good distribution inside the bed.

5)      It’s recommended, if you want to be very thorough in the purging process, to pressure up the bed and de-pressure to flare 2 to 3 times.

6)      When outlet gas is 50% below the L. E. L. and free of toxic materials the purging process should be complete.  Once purged the bed is ready to have the molecular sieve dumped inside.

7)      Unloading the sieve is done from the bottom dump port (or manway) with the flow of gravity guiding the sieve to the bottom.

8)      If you decide not to unload the sieve through the bottom dump port then you can unload the sieve with a vacuum hose from the top port.  Bins containers or dumpsters can be used to aid you.

Here are some additional things to consider…

Never enter a vessel that contains used molecular sieve.

During the unloading process the molecular sieve may have adsorbed chemical compounds.  These adsorbed chemicals may be desorbed again when the molecular sieve is exposed to open air, especially if humidity is high or the air is very moist.

These desorbed chemical compounds can create hazards if the desorbed chemical compounds are toxic.   The plant manager or operator has the responsibility to know what chemicals may have be desorbed in this manner and to know what precautions may be necessary to ensure everyone’s safety.

8 Steps to Prepare Your Vessel for Unloading Molecular Sieve 

You have decided to replace your molecular sieve, and now it’s time to load in what may be thousands upon thousands of pounds of molecular sieve in your vessel (of course the amount of sieve you load in depends on the size of your vessel).  What can you do to prepare your vessel before unloading all of this sieve?

In order to help you with that question we have prepared 8 useful guidelines that could help prepare your vessel for sieve unloading.

Note: These guidelines are to be carried out before you load your sieve into your vessel. 

1)      Before unloading the sieve you should regenerate your vessel by heating and cooling with process gas. Use the same operating conditions that you would normally use when regenerating your bed.

2)       If process gas is not available use nitrogen or another non-toxic gas instead.  Do not use any gas that contains any toxic components at hazardous levels to regenerate your vessel.

3)      After heating the sieve beds, cool them with gas by de-pressurizing the bed to flare.

4)      After using process gas you can start purging the vessel with inert gas at ambient temperature to flare.  It is important that the gas flow rate be sufficient enough to have good distribution inside the bed.

5)      It’s recommended, if you want to be very thorough in the purging process, to pressure up the bed and de-pressure to flare 2 to 3 times.

6)      When outlet gas is 50% below the L. E. L. and free of toxic materials the purging process should be complete.  Once purged the bed is ready to have the molecular sieve dumped inside.

7)      Unloading the sieve is done from the bottom dump port (or manway) with the flow of gravity guiding the sieve to the bottom.

8)      If you decide not to unload the sieve through the bottom dump port then you can unload the sieve with a vacuum hose from the top port.  Bins containers or dumpsters can be used to aid you.

Here are some additional things to consider…

Never enter a vessel that contains used molecular sieve.

During the unloading process the molecular sieve may have adsorbed chemical compounds.  These adsorbed chemicals may be desorbed again when the molecular sieve is exposed to open air, especially if humidity is high or the air is very moist.  

These desorbed chemical compounds can create hazards if the desorbed chemical compounds are toxic.   The plant manager or operator has the responsibility to know what chemicals may have be desorbed in this manner and to know what precautions may be necessary to ensure everyone’s safety.

Molecular Sieve Basics: Crystals Help Determine the Pore Size of Molecular Sieve

This article is a kind of a continuation on an article we wrote in 2011 that discusses the pores sizes of molecular sieve.

Molecular sieve are crystalline metal aluminosilicates that belong to the zeolite family.  That means that the molecules and atoms that make up a molecular sieve are made out of alumina, silicon, and oxygen and because they are crystalline they have a strong degree of order in the way they are laid out.

Molecular sieves specialize in separating very small molecules and atoms apart from one another.  Being part of the zeolite family, molecular sieve has a three dimensional network of pores which can adsorb molecules of a specific size.  The pores on a molecular sieve is what makes sieve special, this is because they can separate any substance down to the 1/10,000,000,000th of a meter, or an Angstrom.  There are four standard pore sizes that a molecular sieve can have:

• 3A, 3 Angstrom pore size
• 4A, 4 Angstrom pore size
• 5A, 5 Angstrom pore size
• 13X, 10 Angstrom pore size (depending on the manufacturer the pore size may be either 8 or 9 Angstrom)

The pores on molecular sieve could have one of two structure types: A structure or X structure.  3A, 4A, and 5A are made from an A structure while 13X is made from an X structure.  The A structure is smaller and more square-shaped than the X structure which is larger and circle shaped.

Aluminum Hydroxide, Sodium Hydroxide, Sodium Bicarbonate, and clay are used in the sieve manufacturing process, when the process is created this combination of material will make 4A molecular sieve when created with a type A structure or 13X molecular sieve when created with a type X structure.

3A and 5A molecular sieve are made once they are ion exchanged with the originally cre

ated 4A sieve.  4A molecular sieve is ion exchanged with potassium to create 3A sieve, the potassium molecules are larger than the sodium molecules they were exchanged with shrink the pore size.  5A sieve is created when 4A sieve is ion exchanged with calcium, calcium molecules are exchanged in a 1:2 ratio.  Every calcium molecule removes two sodium molecules thus increasing  the size of the pore.

The various pore sizes of molecular sieve offer a great variety of services to anyone looking to separate different combinations of molecules from one another.

13X Molecular Sieve is Crucial to Making Steel

13X molecular sieve has many different applications and can complete a large variety of tasks.  One industry 13X molecular sieve can be used in is in the steel industry.  Before explaining 13X’s role in the steel industry, here is brief overview that describes how steel is created.

Steel is made from iron and this is done by removing iron’s impurities like silica, phosphorus, and sulfur.  Steel must also have a consistent concentration of carbon (between 0.5% and 1.5%).

Modern steel making has been done using the Bessemer Process (Developed by Henry Bessemer) or one of its modern variants.  The Bessemer Process was developed in 1858 and it was designed to use oxygen to generate steel at a faster rate.  Since separated oxygen was difficult to produce during Bessemer’s time, the patent to this process went mostly unused until the mid 20^th century when new improvements in oxygen generating technology were developed.

The primary modern improvement of Bessemer’s Process uses a basic oxygen furnace instead of a open-hearth furnace to create steel.  A basic oxygen furnace blows high purity oxygen (95%+ pure) through molten iron which lowers carbon, silicon, manganese, and phosphorus levels in iron thus helping to convert it to steel.  The oxygen furnace works approximately 10 times faster than its older counterpart.

Note: Sulfur and phosphorus levels are further reduced by chemical cleaning agents called fluxes in the steel making process.

It’s safe to say that oxygen is a key component to producing steel, and creating pure oxygen is where 13X molecular sieve becomes useful.  Pure oxygen is usually created using the Pressure Swing Process to separate ambient air into two streams.  One stream contains nitrogen, carbon dioxide, and other impurities while the other stream contains over 95%+ pure oxygen.  (The remaining 5% of air in the oxygen stream are noble gases, for example elements like helium).

Pure oxygen that is created from the Pressure Swing Process is then fed into steel furnaces under high pressure to oxidize the impurities inherent in iron.

Cryogenic oxygen generators are also used to purify oxygen for steel production.  These cryogenic generators also require air to be pretreated by molecular sieve in order to remove impurities that are commonly attached to oxygen.

Manufacturing high quality steel requires the use of the Pressure Swing Process or a cryogenic oxygen generator and both require the use of molecular sieve. Without sieve modern high quality steel manufacturing would be impossible today.

Sources:

Smil, Vaclav (2006). Transforming the twentieth century: technical innovations and their consequences, Volume 2. Oxford University Press US

http://science.howstuffworks.com/iron4.htm

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