Understanding the Adsorption Process

Adsorption is the process of adhesion used by atoms and molecules to attach themselves to a surface.  It is a process that has been capitalized on by many industries and has become essential to producing many of the different everyday products people use.  Below is an, “Industrial Adsorption Course 101,” for people looking to learn more about adsorption and some of the common types of adsorption processes.

Below are some helpful definitions in bold:

Capacity – is defined by temperature and pressure.

Working capacity – in a regenerative process is defined by the difference in the adsorption state (Ta, Pa) and the desorption state (Tr, Pr).

The adsorption and desorption of any material in liquid of vapor phase is a state function.  Adsorption/desorption works the following way, while imaging a Carnot cycle.  The higher the temperature is the lower the adsorption capacity will be; the lower the temperature is, the higher the adsorption capacity will be. The higher the pressure is, the higher the adsorption capacity will be; the lower the pressure is, the lower the adsorption capacity will be.

There must be a change between two states for adsorption and regeneration to work – State 1. The states can be in the vapor or liquid,  but there will be no regeneration of the sieve without a state difference. The working capacity of the sieve is defined as the difference in partial vapor pressure of the two states of the material being adsorbed. Ethanol/water combinations (Daltons Law Pt = p ethanol + p water) are fairly well defined, but other systems with multiple constituents can get a bit more messy.

Liquid phase adsorption can be done, but the vapor pressure variations of most liquids over narrow temperature and pressure ranges are small.  The narrow temperature and pressure ranges decrease the working capacity, rendering the system inefficient.  Most  liquid phase adsorption processes will fit the description of  sacrificial adsorption process (listed below) because it is cheaper to replace the sieve, compared to the cost of energy that will be needed to regenerate it.

There are three basic adsorption processes as well as hybrid systems used for adsorption.  These are listed below:

1)      Sacrificial – you simply dispose of the sieve material after one adsorption cycle: Ta=Tr and Pa = Pr. Expensive solvent recovery would be one example of this.

2)      Pressure Swing Application “PSA” – Isothermal process where Ta=Tr and Pa >>>>>>Pr –Isotherms for the particular adsorbent and process material is used to define the process. Ethanol would be one example of this.

3)      Temperature Swing Application “TSA” – Isobaric process where Ta<<<<<<<<<<<<<<<<Tr and Pa=Pr – Isotherms for the particular adsorbent and process material is used to define the process. Natural gas would be one example of this.

Note One: There do exist hybrid systems which utilizes changes in temperature and pressure with or without vacuum.

Note Two: There are proprietary computer programs written by myself and others to calculate partial pressures for SOME multiple component systems. As you probably remember from thermodynamics fugacities, Van der Waal interactions, viscositys, density changes in multi component systems can get very tricky.

Fukushima Nuclear Disaster Overview

On March 11, 2011 a 9.0 Earthquake, the fourth largest on record since 1900, occurred in the Pacific Ocean causing a series of large tsunamis to strike the eastern coast of Japan.  Now called the Tohoku earthquake, it (and the subsequent tsunamis) caused one of the worst natural disasters on record with over 15,361 people killed, a million buildings damaged or destroyed, and a financial cost of $235 billion dollars (the most expensive natural disaster on record).

In addition to the large amount of damage caused by this natural disaster, it also caused one of the greatest man made disasters on record at Fukushima.  Japan, a country that heavily relies on nuclear power, had a number of nuclear plants that were built near the eastern coast when the tsunamis struck.  Fortunately Japan, a country that sits near two fault lines and has a history with experiencing earthquakes, had containment measures set in place for just such an occurrence.  Once powerful enough earthquake tremors are recorded near Japan’s nuclear plants, they begin to shutdown and cool off.  For the most part this worked, except at Fukushima.

At Fukushima the plants power failed during the earthquake, so the emergency power system along with the emergency cooling condensers had to be used.  Less than half an hour after the emergency systems turned on, tsunamis began to strike the coast near the Fukushima power plant.  A seawall 19 feet high was put in place around the plant to protect it against tsunamis.  The waves from the tsunamis that hit Fukushima were over 46 feet tall, rendering the seawall worthless.  After crashing over the seawall, this wave not only destroyed backup power to the plant but also wiped out key equipment that was part of the emergency core cooling system.

The destruction of key cooling equipment by the tsunami triggered full meltdowns of reactors 1, 2, and 3, thus beginning what we now call the Fukushima Nuclear Disaster.  After the earthquakes subsided, cleanup began and radioactive damage was assessed.  High levels of  Caesium-134, Caesium-137, and some other radioactive isotopes were detected around the nuclear plant and in the ocean.   Currently efforts are on-going to clean up the radioactive waste as a result from the meltdowns.

Molecular Sieve and Zeolites Role in Clean Up

The Fukushima disaster is only the second nuclear disaster (the first was Chernobyl)  to receive a 7 on the International Nuclear Event Scale (INES), the highest disaster rating a nuclear event can be rated.  The clean up process will see new technological developments as well tried and true methods during the clean up of radioactive waste.

One method that’s currently being used, and was used in the past, is using zeolites.  Shortly after the disaster, the Japanese government began to order the dropping of zeolites in the oceans surrounding the disaster site.  The Japanese government is hoping that zeolites (the one’s that the Japanese government are using have specialized in nuclear waste processing), will help to slow down radioactive contamination of the ocean.  Zeolites had previously been used in the clean up of the 1979 Three Mile Island Nuclear Disaster in the United States.

Although dropping zeolite in the ocean seems like a desperate attempt to contain the disaster, Japan is also utilizing  molecular sieve in the clean up process, too.  The molecular sieve in use was specifically designed to capture Caesium, and is being used to treat radioactive wastewater that is on the disaster site. Since the disaster began over 43 million gallons of wastewater have been treated with this molecular sieve at Fukushima.

Experts expect the Fukushima disaster clean up to last decades.  As the clean up continues adsorption technology will continue to play an important role in cleaning up the oceans, environment, and reducing the amount of damage that will be done to our atmosphere.

Sources:

https://share.sandia.gov/news/resources/news_releases/fukushima_cleanup/

http://www.japannewstoday.com/?tag=fukushima-zeolite-absorbs-radiation

http://www.emfnews.org/Fukushima-Decontamination-and-Zeolite.html

http://www.world-nuclear.org/info/fukushima_accident_inf129.html

http://earthquake.usgs.gov/earthquakes/eqarchives/poster/2011/20110311.php

Molecular Sieve is Playing an Important Role in Redefining Contemporary Knowledge of Early Human History

Radioactive carbon dating was a technique developed by Willard Libby in 1949 (a discovery that won him the Nobel Prize in Chemistry over a decade later) that can be used to date carbon based materials up to 60,000 years.  This number is significant because it allows scientists to date all of civilized human history and even some early human history and the history of our common ancestors. Carbon dating can also be used to learn valuable things about what the environment and climate were like in the past, too.

Carbon dating works by measuring the isotopes carbon-14 and carbon-12 or 13 in any fossil.  When people, plants, or anything that is carbon based is alive, it is able to generate carbon-14, when it dies it stops generating carbon-14.

Carbon-14 decays though, while Carbon-12 and 13 do not decay.  Carbon-14 has a half life of 5,730 years, which means due to radioactive decay the amount of carbon-14 in an object will be half of what it was in 5,370 years.  Carbon-12 and 13 do not decay so the ratio of the decaying carbon-14 needs to be compared to carbon-12 or 13  to determine how old the object is.

However, recently studies have shown that samples that go through standard carbon dating tests have accuracy issues when the sample is older than 30,000 years.  This is due to 98% of the carbon-14 already having decayed and because carbon-14 molecules from surrounding soil or other carbon based items start to seep into the fossils.  This combination of events can throw off carbon dating by thousands of years.

Tom Higham, an archeologist working for the University of Oxford, is modifying the carbon dating process.  Tom has been using molecular sieve to remove extra C02 and other carbon chains that are contaminating samples and are distorting the test results.

The graphic below shows how some fossils in Europe have been re-dated using molecular sieve.

Note: 13X molecular sieve is frequently used to remove C02 and other large hydrocarbons from the air, and this is most likely the type of molecular sieve being used to improve fossil dating. 

Using molecular sieve in carbon dating has improved the dating of fossils and items over 30,000 years old.  The improvements in the accuracy of these tests could redetermine historical dates/events that are currently being contested; such as when the first humans entered Europe and whether humans came into contact with neanderthals.  As more carbon dating studies are conducted we may see contemporary knowledge of early human history be redefined.

Sources:

http://www.nature.com/news/archaeology-date-with-history-1.10573

http://planetearth.nerc.ac.uk/features/story.aspx?id=833

http://science.howstuffworks.com/environmental/earth/geology/carbon-142.htm

6 Precautions to Consider While Dehydrating Ethanol

Purifying ethanol requires running your distilled ethanol through molecular sieve beds in order to produce over 99% pure ethanol.  In order to dehydrate ethanol thoroughly most plants require that you have ten’s if not hundred’s of thousands of pounds of sieve installed in your vessels.

Making a significant mistake here could be hazardous to your co-workers and it could cost your plant a lot of money if you end up rolling your beds or if you have to shut down the vessels for awhile so here are six precautions to be aware of when running your sieve beds.

1. Watch the temperature – The adsorption process creates a lot of heat energy; do not let temperatures exceed 600 degrees Fahrenheit at any time.
2. Start the dehydration procedure with 200 proof ethanol, if you do not have 200 proof ethanol available, use extra caution until a stream with low water content is available for recirculation.
3. Avoid massive slugs of liquid, these can stir the bed.  Liquids may need to be drained while you are adding the wet feed.
4. Avoid rapid pressure fluctuations, these can cause bumping or lifting in the bed.  Pressure is normally released in order to control temperature.  Be aware that as sieve and ethanol/water streams are in contact with one another intermolecular frictional heat can occur.  Heat releases of up to 1,800 BTUs/lb of adsorbed water and 700 BTUs/lb  of adsorbed ethanol can occur.
5. Watch out for hot spots on the bed.  This can be avoided by having a recirculating feed rate that is high enough to maintain a vigorous flow throughout the sieve beds.
6. Make sure you purge the air.  Ethanol is a flammable vapor and it is running through your beds at high temperatures and in the presence of oxygen.  Purging the air can prevent fire hazards.

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.