(86a) Use of Process Analytical Technology (PAT) for Monitoring and Optimizing Powder Mixing Processes

Use of Process
Analytical Technology (PAT) for monitoring and optimizing powder mixing
processes

The Process Analytical
Technology (PAT) approach, which is well established in the pharmaceutical and
chemical industry, was successfully applied on food manufacturing. PAT is about
the IDENTIFICATION of critical process parameters in the manufacturing process
as well as in-line sensors enabling real time process MONITORING and CONTROL
for the continual improvement of quality and costs.

A food manufacturing process was
analyzed in view of critical unit operations and process parameters. A strategy
to assess and develop in-line sensors to monitor and control the critical unit
operations was put in place. Sensors were used to make the invisible visible,
which further improved our process understanding and enabled the optimization
of the manufacturing process. The advantages and limitations of PAT will be
discussed for powder mixing, which is one of the most important unit operations
when producing powdery products. During mixing, the foundation of a compliant
and consistent product is laid. But the homogeneity does not only effect
product quality but quite often also the asset intensity of downstream unit
operations. For a given installation and recipe, the homogeneity of the mixed
mass is mainly influenced by the mixing time, the speed of the mixing devices
as well as the filling degree of the mixer. Traditionally, the analysis of the
powder mixer performance is quite time intensive, which makes the studies of parameter
variations difficult.  Several samples
are taken after different mixing times, analyzed with off-line analytics and
the variance is calculated to assess the mixing progress with time [1]. 

In his PhD thesis “Continuous dynamic mixing of cohesive
powders” [2], Kehlenbeck has already shown the power of near-infrared (NIR)
spectroscopy to access continuous and batch powder mixing processes [3]. An
industrial application of the developed self-cleaning near-infrared probe (air
flushing) was not possible as a contact between probe and product was required:

·        
In contrast to the model ingredients maize
starch and calcium carbonate used in the framework of the PhD thesis, most food
powders are moisture as well as temperature sensitive and tend to form layers
in the mixer. After a short time of operation, a layering on the measuring
window of a near-infrared spectrometer would occur, which cannot be removed by
air flushing and would cause an incorrect measuring result.

·        
Furthermore, industrial mixers do not have
openings allowing an immersion of near-infrared probes in the fluidized mass
without drilling holes.

In the meantime, powerful near-infrared spectrometers for a
contactless measurement in distances of up to 60 cm were commercially
available. The assessment of this technology for process monitoring and
optimization was successfully restarted in pilot and industrial scale.

The following topics will be covered:

·        
Process Analytical Technology in general

·        
Impact of the mixer filling degree on the mixing
homogeneity

·        
Impact of the sample size on the measuring
result

·        
Use of near-infrared spectroscopy for monitoring
continuous and batchwise working powder mixers in pilot and industrial scale
(time and trajectory plots)

·        
Comparison of off-line reference and in-line near-infrared
measurements

·        
Until the World Congress on Particle Technology
(WCPT8), it is expected that the impact of the particle size on the mixing
result was also investigated and can be discussed.

[1] Kehlenbeck, V.; Sommer, K.: Different methods to
determine the mixing performance of a batchwise working screw mixer; Powder
handling & processing Vol. 15 (2003) No. 5, pp. 318-327

[2] V. Kehlenbeck: Continuous dynamic mixing of cohesive
powders; PhD Thesis Technical University Munich 2016

[3] V. Kehlenbeck: Use of Near Infrared Spectroscopy for in-
and off-line performance determination of continuous and batch powder mixers:
opportunities & challenges; Procedia Food Science 1 (2011) pp. 2015 – 2022