Particle analysis makes solid progress

June 1, 2008
Plants benefit from real-time online measurements

The ability to both collect and use data in real time increasingly is driving process efficiency improvements and bolstering process optimization efforts. This is particularly true for particle characterization. The days of the off-line “snapshot” measurement and its labor-intensive methodology are drawing to a close.

Instead, fully automated, online analysis is becoming the technology of choice for the chemical industry. The benefits are numerous, including easier identification of changes in process conditions and far better product consistency.

Evolution of established particle measurement technologies is spurring much of the action, but there are some new wrinkles, too.

Laser diffraction

One well-established method is laser diffraction. For over three decades, Malvern Instruments, Malvern, U.K., has been a driving force in the development of the technology. Many of the world’s leading chemical companies rely on its Insitec analyzer during plant start-ups, shut-downs and operational changes. The Insitec can handle the multiple scattering that takes place at the high particle concentrations encountered in a process line — via a patented multiple scattering algorithm that ensures accurate particle size measurement regardless of process loading.

“We originally developed Insitec about seventeen years ago. In the face of our biggest ever challenge, the need for an intrinsically safe device for both the chemical and the pharmaceutical industries, a new Insitec was required” explains David Pugh, marketing manager for Malvern.

So the company developed a new version to keep up with evolving regulatory and other demands. The Insitec X sensor can be used in hazardous locations (e.g., ATEX Zone 20). Described by Malvern as the world’s first intrinsically safe online particle size analyzer, this real-time device can handle particle sizes ranging from 0.1–1,000 μm.

Figure 1. Plant trials using this easy-to-install unit have convinced companies to switch to online analysis. Source: Malvern Instruments.

However, a new consulting service that provides a five-day plant trial of the Insitec Voyager model (Figure 1) is generating even more interest. This mobile analyzer connects to the process when and where real-time measurements are needed. It suits dry processes with particles in the 1–1,000 μm range. Installation usually takes only a few hours. So, the bulk of the trial time is spent generating particle size data, allowing the plant to thoroughly explore the potential for improved control and to properly quantify the benefits.

“The consultancy is a low cost way of ‘seeing is believing,’” says Pugh. “In general, customers report payback times of around six months, but this approach delivers process-specific information. A trial also gives the user confidence that the technology will deliver the projected benefits.” More than 85% of potential customers, including several of the largest chemical companies, who have used the consultancy service have now switched to online analysis.

The burgeoning interest in online particle analysis also is spurring increased demand for training. “Fully trained customers get the most out of their instruments, which is what we want. However, we are seeing a high turnover in jobs and so today you often only get one specialist in charge of an instrument. Ideally we would like to see more than this,” notes Pugh.

New drivers

Meanwhile, Quantachrome Instruments, Boyton Beach, Fla., points to changing markets for much of its growth. “Essentially we are in the business of surface-area and pore-size measurement. It’s still a traditional business, so we are selling a lot to the petroleum and petrochemical industries — for use right from exploration through to catalysts and feedstocks. However, there has been a big resurgence in the last few years, driven by China and increasing demand generally,” says Martin A Thomas, Quantachrome Instruments’ director of business development.

A substantial part of this demand is now “green-driven,” he adds, for example from companies involved in carbon dioxide sequestration. Sometimes the gas is used as a feedstock to grow algae or else stored in old coal mines and oil fields. “The technological challenge for us is to measure very specific gas/solid interactions,” he explains. It’s a similar story with the synthetic porous materials currently being designed for both carbon dioxide sequestration and hydrogen storage.

Thomas credits Quantachrome’s success to its ability to nimbly adapt its existing technologies to changing demands. This means not just dealing with different feedstocks but also with different temperature ranges and more downstream applications — “hybridizing, or hyphenating techniques,” he says.

One important role is in analyzing catalysts. The active surface of many catalysts is often found deep within pores of individual particles. This has a tremendous impact on catalyst performance because, even for a single solid, not all surfaces are created equal. Real surfaces are heterogeneous and their properties vary from exterior to interior as well as from one surface site to another. Thomas maintains that textural (surface area, pore size and pore volume) properties and surface reactivity/heterogeneity can most fully be quantified and qualified via a complete gas sorption analyzer such as the Autosorb-1-C with its optional thermal conductivity detector (TCD).

That unit integrates catalyst characterization with flow and vacuum volumetric techniques to provide information such as meso- and micropore size distribution, active surface area, degree of metal dispersion, and heats of adsorption. Temperature-programmed techniques can be automatically performed via user-programmable pretreatment and analysis procedures while a flow-based pulse titration method rapidly determines active surface area.

Thomas echoes Pugh’s comments: “Training is very big now and attendances have doubled in the last year. This is about protecting the investment, too, as customers can be spending anything from $3,000 to $110,000 on their instruments,” Thomas explains. “A whole generation of people with the sort of knowledge needed to use this technology have taken early retirement, so there is a generation gap developing. Many of the younger people often don’t understand the science involved and so don’t know whether the data they are getting is any good. Therefore we do encourage training.”

More options

Malvern and Quantachrome certainly aren’t alone in responding to the chemical industry’s demand for online real-time particle characterization data. For instance, Sympatec, Clausthal-Zellerfeld, Germany, is another long established vendor. Its line of products rely on laser diffraction, image analysis and ultrasonics extinction. Mytos analyzers, which combine proven laser diffraction sensors and dry dispersers, are the state-of-the-art in-line laser diffraction units for dry powders from 0.25–3,500 µm, claims the company. For granulates or very fragile particles, Mytis units team the laser diffraction technology with a gravity disperser in a single instrument that covers 0.5–10,000 µm range.

Mettler Toledo, Columbia, Md., certainly believes in the value of in-situ particle measurement. Its Lasentec FBRM and PVM analyzers are in-process, real-time technologies said to be suitable for crystallization or virtually any solids or dispersed-phase concentration testing. Models of both are available for use from lab through scale-up to production, ensuring consistent data throughout the life of a process.

Figure 2. Portable unit provides performance that reportedly rivals larger and more expensive FTIR spectrometers. Source: A2 Technologies.

For A2 Technologies, Danbury, Conn., portability is key. The company’s new Exoscan FTIR spectrometer, launched in March at Pittcon, is designed for non-destructive, on-site surface and bulk analysis (Figure 2). Claimed to be the most compact FTIR spectrometer on the market, Exoscan weighs less than seven pounds. Yet, says A2, its analytical performance rivals far larger and more expensive traditional FTIR spectrometers.

A2’s CEO Jon Frattaroli explains the rationale behind the product: FTIR spectroscopy is a powerful analytical tool that has been primarily used in the laboratory due to its size, complexity and lack of instrument stability. However, for increased numbers of applications, a sample can’t be brought to the laboratory or put into a traditional FTIR bench because of the size of the material. So, there’s a need for an analyzer that offers the power of FTIR spectroscopy with the portability of a handheld instrument.

Shaping up

While the benefits of online analysis are obvious, the basis for many modern particle characterization techniques — the equivalent spherical diameter (ESD) — still poses something of a problem. While the ESD allows a single number to be used to quantify the “size” of particles of any shape, particles rarely are homogeneous but instead exhibit a variety of different shapes. Knowing the actual length and width of particles — their shape in fact — in chemical formulations can be critical to product effectiveness.

This is why FlowCAM, a continuous imaging fluid particle analyzer from Fluid Imaging Technologies, Edgecomb, Me., is attracting attention. “FlowCAM was originally developed for the analysis of waste water, but is now moving into the chemicals, pharmaceutical and even food sectors,” says Lew Brown, manager of marketing and sales. Chemical applications to date include paints, printing inks, ink jet toners, plus assorted dispersions, emulsions and mixtures. One major chemical customer has five FlowCAMs, one working 24/7 in the quality control laboratories, with the others shortly going into the production process.

“The main difference here is that we can differentiate between shapes. Everybody knows that the ESD basically involves taking a volume, scrunching it up into a sphere and then finding the volume of that sphere. This tells you nothing about the particle and its shape, unless you’ve got a homogeneous solution.”

Figure 3. Windows provide various details about the classes of particles — here, agglomerates, rounds or longs — in a sample. Source: Fluid Imaging Technologies.

FlowCAM can record up to 26 different parameters for each particle and then uses a pattern recognition algorithm to find out how many there are of a particular shape in each sample (Figure 3).

This gives FlowCAM substantial advantages over other analysis techniques, according to Brown. For example, the device reportedly requires far less set-up and maintenance time and, using different-sized flow cells, allows for particles ranging from 1 micron to 3mm to be analyzed. Also, a patented optical element within the objective lens extends the system’s depth of field, greatly increasing the clarity of imaging the instrument is capable of at higher magnifications. The enhanced depth of field allows the device to be used at higher flow rates (up to 10 ml/s) than other instruments, he notes. In addition, measurements such as length/width (not just ESD), area and aspect ratio are easily calculated on the fly, and the images are available for both visual and computational post-processing.

“Our big challenge is that people are stuck in their ways. We have lost a number of potential contracts because people have said that they really like what we can do, but ‘this is the way we do it.’ However, we are getting known around the chemical industry now,” says Brown.

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