Chemical Engineering July 2023 - 37

Engineering Practice
Real-Time Particle-Size Analysis
Technologies: Overview and Case Study
Monitoring particle sizes in real time can improve product quality and reduce costs
in chemical processes. Presented here is an overview of available technologies for
particle-size analysis and an example involving suspension polymerization
Sebastian Maass
Sopat GmbH
E
ffective measurement, in real
time, of particle sizes and
particle-size distributions in
chemical processes can offer
potentially significant improvements
in process efficiency and reductions
in waste and energy consumption.
This is true for wet or dry processes
handling solid or fluid particles (like
droplets or bubbles). A number of
technologies available may be able
to accomplish this task, including
laser diffraction [1, 2], photosedimentometry,
ultrasound attenuation
spectroscopy [3],
laser backscattering
[4, 5] and inline microscopy
[6]. In addition to their differing operating
principles, these technologies
are often categorized according
their measurement position relative
to the process - namely offline, atline,
online and inline (Figure 1). Inline
measurements are taken directly
in the flow of the product, providing
real-time feedback on process parameters.
Online measurements are
similar to inline measurements, but
are taken from a separate location
that is connected to the process.
Online measurements are very often
bypass solutions, and there are associated
advantages and challenges
for such technologies, which are discussed
here.
There remains a significant level
of confusion over measurement
positions of instruments. For example,
bypass solutions are still often
C. Minnich
Shutterstock
wrongly considered
to be inline technologies.
A bypass is
a common feature
in many process
measurement systems,
and it can be
used to divert a portion
of the process
flow away from the
main line to allow
for measurement
or analysis. While a
bypass can provide
a solution when the
process is too hot,
too cold, or too corrosive for the
measurement instrument, it also introduces
additional complexity and
cost to a process measurement system,
and there is a risk of contamination
or cross-contamination.
To help improve understanding of
the tools available for real-time particle
sizing and to clear up confusion
over how measurement positions
of the devices are considered, this
article provides information about
the five technologies used for inline
particle measurement, and further
defines the different possible measurement
positions.
To illustrate the use of inline realtime
particle sizing, a case study is
presented for measuring particle size
in the suspension polymerization of
expanded polystyrene (EPS). The
case study demonstrates how the use
of real-time particle sizing in suspension
polymerization has proven to be
FIGURE 2. Online measurement of particle size is a key part of the emulsion
polymerization process at this plant in Russia
a valuable tool for the improvement of
polymer production processes, leading
to higher polymer product quality
and more efficient and cost-effective
processes (Figure 2).
Particle sizing technologies
The following sections provide an
overview of five technologies used
for particle-size measurement: laser
diffraction, photosedimentometry,
ultrasound attenuation spectroscopy,
laser back scattering and inline
microscopy.
FIGURE 1. The diagrams represent the various measurement-position terminology (adapted from Ref. 9)
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JULY 2023
Despite the clear potential for optimized
production processes of, for
example, EPS (discussed later), and
the availability of several inline particle
sizing technologies available for
monitoring of EPS particles in production,
no industrial " gold " standard
has been established in the chemical
engineering community. The most
reliable technology will depend on
several factors, including the specific
requirements of the production
process, the size of the particles, the
operating conditions, and the desired
level of accuracy and precision.
Laser diffraction. Laser diffraction
(LD) is the most commonly used
technology in particle characterization.
Here, a light (laser) beam is
37

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Chemical Engineering July 2023

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