Filtration of Liquefied Gases & Caesar’s Last Breath

liquified gases
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On the heels of my blog about “The Business of Breathing,” it’s time to talk about gas. I recently finished reading the Sam Kean book “Caesar’s Last Breath.”  For those of you who have not read Kean, his specialty is writing science books in an exciting and entertaining fashion.  His three other books focus on the elements in the periodic table, genetics, and the brain.  Meanwhile, Caesar’s Last Breath looks at gases and both how the atmosphere has shaped human beings and how human beings have shaped the atmosphere.

The word “gas” actually comes from the Greek word “Khaos” for chaos or empty space between the Greek gods and the earth. To the Greeks, gases were the least understood component and the most “wildest” of spirits that no one could tame.

liquified gases

Today we know gases can become liquids, solids or stay as gases.  The book is a survey of the history of the earth explored through the air that we breathe and the scientists that made major discoveries of gaseous properties.

Believe it or not, there are good guys and bad guys and conflicts in the book.  Kean covers the earth’s early days, atomic tests at Bikini Atoll, details of UFO sightings in Roswell, New Mexico, and the truth behind the US Air Force tests.  There is a whole chapter on nitrous oxide (laughing gas) as well as the Manhattan Project and the development of ammonia gas and fertilizers.  Of course, there is a discussion of ice seeding for rain, which I am am keenly interested in as well (remember my blog on the Cat’s Cradle and the Vonnegut family?).  Finally, Caesar’s Last Breath concludes with alien life, new planets, greenhouse gases and other crazy ideas for other civilizations. All of these chapters are a lot of fun to read.

Relating my Reading to Filtration Tech

Yet, while all of this is very interesting, especially Kean’s scientific data, the question remains for my blog readers: how does BHS handle liquified gases?  Knowing that gases, under pressure, act as a liquid The BHS Rotary Pressure Filter can conduct filtration, washing, and drying of slurries continuously under pressure to keep the gas as a liquid. We also have installed units for Dimethyl Ether (DME) with specialty containment; contact me  for further information or discuss your critical filtration applications.

In the meantime, what have you been reading lately that you might suggest I pick up? I’m always on the lookout for new must-reads with a scientific bent. Or anything you can share that offers a new perspective on liquified gases.

Best Practices for Filtration Testing for Solid-Liquid Separation

filtration testing
Photo by Pacific Northwest National Laboratory – PNNL on Foter.com / CC BY-NC-SA

Testing in school has a negative connotation. Students dread tests. Parents bemoan “teaching to the test.” Teachers chafe against the curriculum parameters defined by testing expectations. Yet, the word “testing” should resonate much more positively with process engineers. After all, testing is the key for selecting the most suitable filtration tech for any individual solid-liquid separation task.

Although there is only limited theoretical background available, and even specialized engineering education at universities leaves many theoretical questions open, it is beneficial to have a minimum understanding of the theory of filtration itself. By identifying the role of each influencing part, the process engineer gains a potential tool to work with when it comes to understanding testing findings and developing a path forward in determining the best filtration procedure.

Just from experience, and for the benefit of engineers, some overview observations are necessary:

  • Don’t stop testing just because the first results suit your target
  • Don’t accept samples without verifying the parameters in the description
  • Never change more than one parameter at a time
  • One result is no result => verification is a must
  • Take a break and check the conformity of the results before you call it a day

Filtration Testing Requires Decision Making

In testing it’s essential to train yourself to stop and repeat. Don’t succumb to perceived certainty. After all, many parameters of the liquid and the solids have an influence on the filtration process.

  • Form and size of particles
  • Particle size distribution (PSD)
  • Agglomerate building behavior
  • Deformability
  • Compressibility
  • Liqiud viscosity
  • Solid content
  • Zeta-potential

While all of the above may not be known for all filtration applications, the final target is to find a theoretical approach together with a practical method of testing.

Sampling in Filtration Testing

Filtration tests need to be done with a “representative sample” defined as a sample “as close as possible” to the real production product.  Yet the specific characteristics of a slurry from the point of filtration are not obvious to everyone. That’s where testing comes in: the list of parameters is quite extensive and in many cases only a few are available.

Still, the more you can get the better. Although for the first tests, the ph-value, temperature, particle shape, size distribution, etc. are not necessary right from the beginning, these parameters are normally quickly measured and complete the picture of the suspension. It is obvious that solid content and viscosity do have an impact on the filterability.

“Suspending” Judgment in Filtration Testing

The characteristics of suspensions are not only caused by the liquid phase but also by the particles, the other half of a slurry. The solids can be of crystalline nature or amorphous, which means their structure is not really defined. They can also be organic (i.e. cell debris), fibrous, in-organic, compressible or incompressible, generate agglomerates or not, may have a zeta potential or not…. there are many possibilities.

An easy way to verify the type of solids is a sample check. If possible, the original suspension should be checked under the microscope. Then, the behavior of the solids can also be seen:

  • Do they tend to build agglomerates or stay on their own?
  • How is the distribution of the solids?
  • Is the structure of the solids needle-shape, potato shape, snow crystal or even fibrous?

The best practice in filtration testing is to consider all of these angles thoroughly before deciding on a filtration procedure.

I am a big fan of Sherlock Holmes who always warns “don’t jump to conclusions.”  This is one of the biggest risks we face during tests in the daily work of process engineering.  Let me know if you need help!

Cookies are yummy, but avoid cookie-cutters.

filtration tests
Photo credit: Amy Loves Yah / Source / CC BY

We can all agree that cookies are yummy. Cookie monster is not the only creature out there who loves to chow down on a tasty chocolate chip or oatmeal raisin (my favorite are Thin Mints).

What is not so good, though, is using a cookie-cutter approach to problem solving and filtration tests.

In filtration testing and scaling-up to commercial size, it’s important to not “jump to conclusions” that the familiar approach is going to work best.

Laboratory/bench top filtration testing is critical in the problem analysis, technology selection, and pilot and demonstration scale-up stages.

As I’ve blogged about, and discuss at length in my Practical Guide to Solid-Liquid Filtration, we can learn a lot from sleuths Holmes and Watson. They would argue it’s important to train yourself to be a better decision maker. Your best bet is to use checklists, formulas, and structured processes.

It’s also essential to train yourself to stop and repeat. Don’t succumb to certainty. Discuss your options with technology suppliers that can provide different filtration solutions. Partnering with suppliers with a proven track record in similar applications will shorten your technology scale-up cycle.

Ultimately, what matters are your premises (process definition, requirements and testing objectives) how the testing unwinds the crucial from the incidental (what is the critical process parameter) and ending up with a logical conclusion (optimum process filtration solution). With caution and clear thinking you can better manage the stress of a scale-up.

This blog marks the one year anniversary of “Perlmutter Unfiltered.”  I would like to thank everyone for their feedback and responses.  Let me know your ideas and thoughts; guest bloggers are always welcomed, whether it’s about filtration tests or something else for our industry.