My Thoughts on Filtration and Separation Trends and Practices

 

filtration forecasting
Image source

I recently had the opportunity to share my ideas on filtration and separation trends and practices with World of Chemicals magazine. My favorite part may have been the headline, “Aging with perfection in filtration technology.” I like to think they were talking about me — ha ha!

filtration forecasting
Image source

In the meantime, I thought I’d excerpt some of the thoughts I shared in that interview.

Talking about global trends in filtration & separation equipment market, I noted, as the world’s population grows, there is a need for cleaner energy, improved water & food and advanced health care….Advances in healthcare and pharmaceuticals and nutraceuticals [are also allowing] people to live longer, healthier and more productive lives.

This means, “filtration and separation technology suppliers must continually improve their products to meet these needs. The trends in the filtration market space are two-fold: moving towards continuous filtration (which is more efficient) as well as moving towards finer and finer particle size removal.”

I suspect we’ll see high demand for filtration and separation products in “pharmaceuticals with smaller batches, cleanability and multipurpose operations.” Also, “for increased food supply, we see growth in the agrochemical market including fertilizers, pesticides, herbicides and insecticides.” Plus, “cleaner water is driving the specialty chemicals for resins and catalysts.”

As chemical and pharmaceutical manufacturers adapt to more multipurpose facilities, filtration and separation equipment must be cleanable and avoid cross-contamination between products. Batch sizes are also smaller, and we demand for finer filtration and separation to 0.5 microns as well as automatic operation for safety, efficiency etc.

Automation trends & more

Automation technology is one of the most important aspects for customers today. It is critical for filtration and separation products for preventative maintenance, efficient operation, mechanical troubleshooting and process analysis. Applying improved automation technology greatly reduces the energy usage and improves accuracy and precision to the overall process.

Automation also provides for optimum operations, time monitoring systems, report generation and recipe management.

We’re also going to have to incorporate R&D to meet market demands. At BHS, we’re working with clients to combine technologies for full turnkey responsibility to minimize lifecycle costs and reduce operating costs. So, overall, we are focused on innovation, automation, continuous processing, cleanability and overall reliability to 99 percent uptime. We strive to provide complete process solutions with spare parts, service and continually to improve the client’s operation.

This requires testing — of course. “Testing provides the collaboration with the client to provide innovative and cost-effective process solutions.”

At the same time, one big challenge in our market is the need for speed. Speed of innovation is impacting our clients who are developing new processes very quickly using micro-reactors, new chemistry, and new products.

The speed at which the filtration and separation suppliers must operate to meet the clients is even faster. Successful companies must fulfill this “speed” objective without sacrificing any core values of safety, efficiency, quality, and service.

Troubleshooting When the Filtration System is Not Working

 

troubleshooting filtration technology
Image source

These are five dreaded words that no engineer wants to hear on a Saturday night or Sunday morning: “The filtration system is not working.” Of course, we never seem to get this call at 10 in the morning on a work day!

No matter the time of day, let’s not panic, take a deep breath and begin the analysis.  

There are normally three main areas that must be examined when you learn the filtration system is not working:

  1. The filter itself for mechanical reasons
  2. The equipment around the filter is not working
  3. The filter operational procedures are not correct.  

To fully understand the problem, it’s necessary to separate the symptoms from the causes. So, let’s examine each of these groups in more detail.

Troubleshooting Filter Problems

The first thing that should be checked is the filter itself. There could be a failure of the equipment mechanics such an internal components, seals, etc. Many of these issues will be described normally in the preventative maintenance section of the filter’s O & M manual. 

Second, keeping in mind, the filtration system is part of the entire process it’s important to examine the upstream and downstream equipment. For example, you might check:

  • Are the reactors performing correctly in terms of agitation, temperature control, etc. in order to produce the specified crystals?  
  • Are the precoat and body feed systems in tune for mixing, feeding, flow rates, solids loading, etc.?  
  • Are the valves and instruments operating correctly and reading the correct variables (calibrations), etc.?  

Next, take a look at the pumps that feed the slurry and washing liquids as well as the compressors the feed the gas streams for drying and cake discharge.  The pumps must produce the required pressure, flow rates, etc.  The compressors must also produce a certain gas flow at a specific pressure for a certain amount of time.  Are their interlocks in the control system or a control communication problem that are not being recognized that are causing the filter problem.  Finally, if flocculants and chemicals are being used, have these changed?  

Process Engineering Problems? 

The last place to look is the process or operational procedures. These could be responsible for the filtration problems.  For example, the particle size distribution may have changed, the amount of solids in the slurry may have changed, the cake compressibility may have changed, etc.  In terms of the operation, has the filtration pressure changed, timers changes, speed changed, etc.?  Finally, determine whether or not a process parameter has changed.  

Trouble shooting is not easy, but solving the problem brings a great sense of satisfaction. 

Let me know some of your troubleshooting horror stories! I’d love to share some in a future blog. Together, we can make it easier to handle the situation next time we hear those five dreaded words.  

troubleshooting filtration technology
Image source

Selecting and Designing Combination Filtration for Solid-Liquid Separation

Filtration technology
Photo by uptownguydenver on Foter.com / CC BY-NC-ND

Filtration experts, over the years, have discussed combination filtration and debated its definition.

  • In the realm of cartridge filtration, simply defined, a combination filter is one that does at least one other processing job at the same time as filtering a suspension.  For example, this could be carbon canister which removes both suspended and dissolved components.
  • In water applications, a combination filter removes bacteria, sediment, chlorine taste and odor, and scale.
  • In lubrication oil filtration, combination filtration refers to full-flow and by-pass flow filtration.
  • For small scale process filtration, combination filtration is installing bag and cartridge filtration systems in series.

There is, however, a new definition of combination filtration that transcends the standard approach and will assist process engineers with trouble shooting and idea-generation.  The approach relies upon the slurry analysis and testing to uncover the “process symptom” and then develop a process solution called “combination mechanical slurry conditioning and filtration.”

Filtration Technology in Combination

There are, without doubt, many technologies already existing in the marketplace that can be applied in combination, including the use of chemicals such as flocculants and coagulants.  However, from a practical viewpoint, let me review general operating conditions at chemical plants and illustrate creative idea-generation when examining a process problem.

In this first case, we have a high solids slurry with a wide particle size distribution.  What should you do?  My idea is to provide filtration for the slurry with a continuous technology and let the fines bleed through; capture theses fines with clarification.  Yes, more filtration but a much more reliable system.

 

filtration procedure

This new definition of combination filtration will provide process engineers a framework for idea generation when analyzing an operating bottleneck.  Complete my application data sheets for new and existing application data for filtration for solid-liquid separation. Let us start the process.

Filtration of Liquefied Gases & Caesar’s Last Breath

filtration tech
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.

Screen Shot 2018-02-13 at 12.07.13 PM

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 liquefied gasses?  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.

Innovation Grown from Oranges

Innovative technology
Photo credit: photoschafl via Foter.com / CC BY-NC-ND

I have written over the years about sustainability; you may remember Ford & Jose Cuervo. Today, I’m writing about a new idea grown from the rinds and seeds of Sicily’s most famous citrus fruit — the orange.

The orange, which Sicily harvests several hundred thousand tons each year, is being used in a wide range of greener and healthier business initiatives.

The innovation is as impressive as the filtration technology used to give consumers the pulp-free OJ they drink at breakfast on a given morning!

Oranges & Textiles

In 2011, Adriana Santonocito was a design student in Milan and had an idea to make sustainable textiles from Sicilian oranges. People already knew how to extract cellulose from orange rinds, but Adriana developed a process to make fiber which could be blended and the color-dyed with other textiles such as cotton or polyester. She and her classmate Enrica Arena founded Orange Fiber in 2014 and are now selling the silk-like material to the famous Italian fashion designer Salvatore Ferragamo. 

fiber innovation
Source: Ferragamo

 

What else from the oranges?

They are also making baked goods healthier, and stay fresher, thanks to a new procedure which transforms them into an innovative fat-free flour /citrus paste. Pastazzo is flour made from the orange rinds, seeds and part of the pulp not used for juice. The “brioche” from this flour has the same taste and look of brioche made with butter/fats/oils but much healthier.

innovative technology
Source: La Sicilia

Although we’ve yet to be employed working with oranges, BHS has applied its leadership  in sustainability to feedstocks and applications including:

  • Corn cobs and stovers
  • Wood chips
  • Bagasse / Sugar cane
  • Dairy waste and chicken renderings
  • Algae and microbial for PHA
  • Fish Oils
  • Biocatalysts

I’d be happy to tell you more about our technology for filtration, cake washing and drying of these natural products with the BHS vacuum belt filter and rotary pressure filter.

Or, let us know your feedstocks and we can brainstorm new ideas. In the meantime, be aware you may be wearing something that you can eat!

4 Key Differences between Filtration and Centrifugation

I’m always looking to collaborate and explore ideas with others in our filtration technology business. Happily, director of Oriental Manufacturers Jigar Patel, has offered this guest blog discussing differences between filtration and centrifugation. I hope you enjoy Patel’s perspective:

filtration technology
Photo by gemmerich on Foter.com / CC BY-SA

Filtration and centrifugation are two distinct separation techniques used for isolating the required components from the mixture. The major difference between the techniques is the nature of the force employed and the separation method used. While filtration uses a sieve or filter media to strain undesired constituents, centrifugation leverages the power of the centrifugal force for the separation.

What is Filtration?

Filtration is a physical separation technique, by pressure, vacuum or gravity, used for segregating one or more components from a mixture for different applications. Depending on the application, the process may employ one or multiple metal perforated layers or filter mesh for solid-liquid separation. 

What is Centrifugation? 

Centrifugation is a process that employs a centrifugal force to separate the elements of the liquid slurry.  The remaining liquid (supernatant) is then transferred from the centrifuge tube or removed without disturbing the precipitate. The precipitating particles left behind depend on the speed of the machine, the shape and size of the particles and their volume, viscosity, and density.

4 Major Differences between Filtration and Centrifugation

#1 Nature of Operation 

  • Filtration 

Large particles in a mixture are unable to pass through the perforated layers of the filter. Yet fluids and small particles easily pass through the filter mesh under the pressure, vacuum, or gravitational force. 

  • Centrifugation 

The centrifugal machine forces the heavier solids to the bottom creating a firm cake. The lighter mixture that stays above the cake is then decanted. 

#2 Separation Techniques

  • Filtration 

Filtration uses different techniques depending on the expected outcome which can be classified as pressure, vacuum, or gravitational.

  • Centrifugation 

Centrifugation techniques can be classified as micro-centrifuges, high-speed centrifuges and ultra-centrifugations. Microcentrifuge is typically used for research studies that require the processing of biological molecules in very small volumes. High-speed centrifugal machines are designed to handle bigger batches and are mainly used for processing industrial mixtures on a large scale. The ultra-centrifugation technique is used to study the properties of biological particles.

#3 Function 

  • Filtration 

The main function of filtration is getting the desired output by eliminating impurities from any given liquid or isolating solids from a mixture. 

  • Centrifugation 

The main purpose of centrifugation is fast, efficient separation of solids from a liquid solution or slurry.

#4 Efficiency 

  • Filtration 

Simple filtration techniques take time separating the desired materials, which makes the separation method less efficient. 

  • Centrifugation 

Centrifugation techniques employ machines that run with the aid of power, so the separation method is faster and more efficient. 

Both filtration and centrifugation are solid-liquid separation techniques that use different equipment and have different applications.

My two cents: Deciding which one is best suited to your process will take work. No matter the process in question, engineers are well served by taking the time to gather the information, make their own comparisons, and then develop a process solution.

Thanks to Jigar Patel. The director of Oriental Manufacturers believes in the power of good functional designs and their ability to boost productivity and drive growth. Fueled by his passion for innovation and all things EPC, Jigar writes on topics related to process plant equipments, process machinery production, turnkey solutions, best industry practices, and his personal insights!‌

Keep the sharing going — let me know what you want to write about in this spot next!

What Are Process Engineering Responsibilities in Technical Sales

process engineer
Image source

With graduation season coming there will be many chemical engineers on the market looking for their first jobs.  There are many opportunities with operating companies, engineering companies, startups, venture capitalists (yes, engineers in the financial industry), and consulting firms. Nevertheless, my first choice is technical sales.

Why technical sales? It’s an interesting field for process engineers for several reasons as you get the opportunity to:

  • Combine technical expertise with people skills  and business knowledge to help customers solve problems
  • Define customer’s technical requirements
  • Explain, test, and demonstrate the company’s products to meet the requirements and solve the customer’s problems
  • Employ a flexible approach to technical/commercial situations
  • Interact with a variety of people and positions

The best process engineers for technical sales possess a desire to get involved in the business aspects of many different industries/application and are willing to cultivate long-term selling relationships with varied types of people.

But Will I Still be a Process Engineer?

In school you learned all of the technical skills. Now, in technical sales, you use all of your process engineering skills. How so?

  • Selling requires logical analysis and documentation to the client to make them feel comfortable with the product
  • Performing calculations allows you to be successful in risk taking and feel confident in your decisions
  • Continuing to trouble shoot the process and solve difficult problems even after you have sold the equipment

Graduating with the technical skills under control, there are certain attributes that can help you transition to a technical sales role as a process engineer. Those looking to hire you for technical sales will want to see:

  • Are you a good listener?
  • Are you motivated?
  • Do you have thick-skin so that if the client is not satisfied you can accept criticisms?
  • Can you be part of a team?
  • Are you a good writer?
  • Do you like to be in front of people making presentations?
  • Are you both curious and creative?

My Path to Technical Sales

I embarked on this career path with degrees in chemistry and environmental science and technology.  I joined the US Environmental Protection  Agency in 1976 when we were a young agency.  I did air sampling (clean shaven and no beard) and rule development and was able to learn about many industries and applications.  After getting by MBA at night (over four long years), I joined Pall Corporation in technical marketing.  This role was fun, creative but now here I am working with BHS-Sonthofen. Some 35 years later, technical sales and marketing are ingrained in my psyche.

Let me know if I can help you with your career decisions and training.  Good hunting.

The Business of Breathing

process engineer Charlotte
Photo credit: Sole Treadmill via Foter.com / CC BY

As loyal readers already know, I sometimes mention my yoga practice, which includes headstands, shoulder stands, tripod stands, etc. Another important component of yoga is the breathing.

Yoga involves controlled breathing, while the high-risk world of freediving involves holding your breath — these are two different ends of the spectrum with benefits for practitioners of either (or both). BusinessWeek discussed the need for conscious breathing in two 2017 articles.

Patrick Scott, in his June 19, 2017 article “Free Falling,” connects diving and holding one’s breath to a feeling of euphoria unlike any other. Freedivers talk about how the mind and body are altered. Surface cares dissolve — replaced by a profound immersion in the present.

The Guinness World Record for holding one’s breath underwater is 24 minutes and 3 seconds. However, most freedivers plan for 3 – 5 breathless minutes. The key is to relax and override the urge to breathe underwater by learning to embody the energy the flows throughout the universe.

Controlled breathing in Yoga

In yoga, there are many types of breathing all of which focus on the individual. One is Ujjayi breathing. This “victorious breath” has a balancing influence on the entire cardiorespiratory system, releases feelings of irritation and frustration, and helps calm the mind and body. With Ujjayi, there are many benefits:

  • Increases the amount of oxygen in the blood
  • Builds internal body heat
  • Relieves tension and regulates blood pressure
  • Builds energy
  • Detoxifies mind and body

Another yoga breathing exercise is Sitali (or Sitkari) Pranayama, which literally means “to extend the vital life force.” There are three practices:

  • Gentle “extended exhale” breathing
  • Cooling breath
  • Long exhale

A third type is Breath of Fire. You’ll breathe 2-3 times/second through the mouth and up to 120 -180 times/minute.

Lastly, there is alternative nostril breathing. In this case, breathing through the left nostril is calming and breathing through the right nostril has an energizing effect.

Take a Deep Breath by Jennifer Miller outlines five classes explaining the art of inhaling. After all, whether you breathe deeply or hold your breath, the right breath technique can lead to “physical and emotional release.” In the non-stop environment we all work in today — pressured to perform, to innovate, to respond, to deliver, to compete — it’s not a bad idea to take a breath and find the right path with intention.

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!

Chemical Process Optimization needs Out of the Box Thinking

Actual Unit -- Figure 2. This continuous vacuum belt filter with 9.0-m2 filter area was installed in 2016.
A continuous vacuum belt filter with 9.0-m2 filter area.

Loyal readers of this blog know how much I value innovation and creativity. So, you can’t be surprised that I want to share with you a success story in which we partnered with a client to develop an optimized filtration process for a zinc oxide product.

As discussed in a coauthored article for Chemical Processing, Madison Industries and BHS-Sonthofen Inc. worked together on laboratory and field pilot testing. Engineers from both firms showed creativity and “outside-the-box” thinking in looking at the process from new vantage points in their quest to find a better option than the installed batch filter press.

Our efforts led to the selection of continuous vacuum filtration. The continuous filter, which was installed in 2016, provides maximum filtration efficiency and improves product quality while increasing yield and reducing operating and maintenance costs.

Schematic Operation Of Filter -- Figure 1. Technology, based on fixed vacuum trays, features step-wise movement of filter media.
Figure 1. Technology, based on fixed vacuum trays, features step-wise movement of filter media.

Case Background

Madison Industries, based in Old Bridge, N.J., supplies copper and zinc compounds such as copper sulfate, copper carbonate, zinc sulfate, zinc chloride, zinc orthophosphate and phosphoric acid as well as other chemical products containing copper and zinc. Applications include animal feed, water treatment, dairy farming, food and pharmaceutical processing, and pool and wood preservative chemicals, among others.

The Madison facility was using a plate-and-frame filter press to filter a zinc oxide slurry made from a mix of various zinc feedstocks. The solids were mixed with water to form a slurry of 20% solids and then filtered. The cake was bagged in 2,000-lb totes, moved to another area of the plant and reslurried in sulfuric acid for further processing.

Madison wanted to expand production and replace the present labor-intensive process with a continuous operation.

Crucial Tests

BHS process engineers began laboratory evaluation of the process. Madison was open to all ideas and formed a team to brainstorm different approaches.

BHS conducted several weeks of testing and evaluated both pressure and vacuum filtration based upon the specific characteristics of the solids and slurries. The testing led to the following observations:

• Filtrate clarity: The most-appropriate filter cloth is a double-weave 12-micron polypropylene.
• Filtration rate: Vacuum filtration produced the maximum filtration flux rate at a cake thickness of 6 mm.
• Cake washing: Maximum displacement washing was achieved with wash ratios of 2.6:1.
• Cake moisture: Although not a critical parameter because the cake is reslurried, cake moisture is approximately 35%.

Based on its creative testing, BHS’s process engineers recommended continuous-indexing vacuum filtration as the optimum option.

Why Continuous Indexing

The BHS continuous-indexing vacuum belt filter provides for vacuum filtration, cake washing, pressing and drying of high solids slurries. The technology is based upon fixed vacuum trays, a continuously feeding slurry system and indexing or step-wise movement of the filter media (see Figure 1). In practical terms, the belt filter operates similarly to a series of Buchner funnels.

At each indexed belt position, washing and drying efficiencies are maximized with the stopped belt and the mechanism of plug flow for gases and liquids. Cake pressing and squeezing further enhance drying. Finally, the fixed trays allow for the mother liquor and the wash filtrates to be recovered individually and recirculated/recovered/reused for a more efficient operation. The design also can integrate steaming as well as counter-current washing.

Successful Switch

Madison and BHS installed the vacuum belt filter in 2016. The unit has met all product quality specifications. Madison has realized a 50% savings in wash liquids per batch as well as a reduction in labor and operating costs because the vacuum belt filter operation is fully automatic. Since the installation, Madison has optimized the operation, improving yields and minimizing costs.

The Madison and BHS collaboration illustrates a successful relationship between client and technology supplier. The BHS approach of lab and pilot testing, coupled with idea-generation, fosters identifying the optimal option for critical and difficult solid/liquid separations.