Novel Filtration Technologies for Pharmaceutical Hydrogenation

pharmaceutical hydrogenation
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When it comes to removing catalyst fines from pharmaceutical hydrogenation reactions, BHS Filtration has come up with a novel approach.

Currently, most hydrogenation slurries are clarified with the use of manual plate or nutsche filters, bag filters, or cartridge filters. All of these require manual operations for cake discharge and cleaning between batches or campaigns. At the same time, these units suffer from high labor, maintenance and disposal costs as well as the exposure of the operators and the environment to toxic and hazardous solvents and solids, used and contaminated filter cloth, bag filters, and filter cartridges.  

A new approach uses candle filters which are batch-operated, pressure-filtration systems.

Understanding Candle Filters

A candle filter is a pressure vessel filled with tubular filters called candles. The candle is comprised of:

  • filtrate pipe —  runs the length of the candle and ensures high liquid flow, as well as maximum distribution of the gas during cake discharge.
  • perforated core with supporting tie rods —  the tie rods create an annular space between the filter sock and the perforated core, which helps to maintain a low pressure drop during operation and promotes efficient expansion of the filter sock during cake discharge
  • filter sock — installed over the candle, and made of various synthetic materials, the filter sock is capable of removing particles smaller than 1 micron (μm). As the cake builds during operation, the candle filter’s removal efficiency increases, enabling removal of particles as small as approximately 0.5 μm.

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Candle Filter in Action

During operation, pressure from the reactor forces the slurry into the bottom of the pressure vessel. The solids build up on the outside of the filter sock, while the liquid filtrate flows into the candle, through the registers, and out of the vessel. This process continues until the maximum pressure drop, design cake thickness, minimum flow, or filtration time is reached. The cake is then washed to remove impurities and residual mother liquor. Finally, the cake is dried. 

For cake discharge, low-pressure gas enters in the reverse direction through the registers and into the individual candles and expands the filter socks. This process breaks apart the dry cake, which detaches from the filter sock and falls into the vessel cone. The cake can also be discharged as a concentrated slurry. 

Pharmaceutical Hydrogenation Application 

In the pharmaceutical catalytic hydrogenation application, the current process after the reactor is metal bag filters for slurry discharge into manual nutsche “clamshell” filters for vacuum filtration and drying.  The process was time-consuming and required handling of liquids and solids including final “manual dig out” of the filters.  The process solvent was tetrahydrofuran (THF) and ethanol.

Lab testing was conducted to develop a new, one-step process for filtration and drying.  The BHS candle filters with pharma designed candles and cGMP compliance allowed for a revamp of the operation with two filters, one-on/one-off for continuous operation.  Read the full article and let me know what you think!

Become a Filtration Tech Troubleshooting Expert

filtration tech troubleshooting
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Recently I addressed the too-familiar telephone call that the “filtration system is not working.” When the call comes in — and so seldom during regular business hours —  filtration tech experts have to react quickly to solve the problem.

Now, the question is how do you avoid getting these types of calls in the first place?  Well, you can turn off your cell phone, but maybe isn’t the best idea.  Instead, the better approach is proactive troubleshooting. 

Proactive Filtration Tech Troubleshooting Ideas

As you know, I’m a big fan of Sherlock Holmes. The great sleuth talks about checklists and separating the consequential from the inconsequential facts. This systematic approach works perfectly for troubleshooting — take a systematic approach with a comprehensive set of questions and logic charts.  After all, we all know that most problems, maybe 90% or more, that arise with the filtration system have been experienced before.  

A different approach involves “walking around” or random analysis.  Sherlock and Dr. Watson are also very good at this. They see what’s not there to uncover the facts. This observation approach can help with the unique problems. I’ve written before also about the Japanese approach of “Genchi Genbutsu,” which further explains this option.

Becoming an Expert Troubleshooter

Becoming an Expert Troubleshooter, though, requires developing several “soft” skills over and above your technical expertise and great depth of knowledge in many areas. These characteristics include:

  • Critical thinking: Ask probing questions to everyone at the plant from operators, mechanics, to process and R&D engineers to encourage conversations
  • Excellent communication: Listen to the answers and ask the same questions in a different way or use the answers to formulate different questions and keep an open mind.
  • Empathy: Try to understand potential frustrations.
  • Motivational: Praise everyone who provided you with the answers, ideas, etc. to inspire the plant
  • Ability to teach: Look for teaching moments so problem-solving permeates through the organization.

In the future of work, we’re going to be looking more at talents in addition to expertise. Cultivate your troubleshooting chops. Keep walking around and keep learning. In the meantime, let me know your area of expertise; maybe I can use your skills.

Filtration of Liquefied Gases & Caesar’s Last Breath

liquified gases
foter.com

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!