Process analytics in PI plant
– the challenges
David Littlejohn
University of Strathclyde/CPACT
PROCESS INTENSIFICATION: Meeting the Business and Technical
Challenges, Gaining Competitive Advantage
The Royal Institution of Great Britain, London: 19th November 2003
Reasons for process analysis
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Monitor progress of a reaction
Know when end-point is reached
Check reaction kinetics
Impurity detection
Monitor/control blending or mixing
Used for decision making or direct control
Requires timely qualitative or quantitative
analysis
Increased profits through on-line
process analysis & control
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Better yield of product
Greater purity of product
More consistent production
Less re-work
Lower energy usage
Improved use of raw materials
etc. etc.
Terminology
Off-line
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At-line
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On-line
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Manual sampling and
analysis at a separate
laboratory
Manual sampling and
analysis at the process
Automatic sampling and
analysis; process - analyser
interface
On-line analysis
True on-line
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In-line
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Non-invasive
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Some of the process
liquors are passed
through an on-line
analyser
No sampling; analyser
probe inserted into
reactor or pipe
No sampling; no direct
contact required between
process liquors and
analyser
Features of process analysis in
conventional plant
• Kit is comparatively large
• Probes in sampling loops or insertion devices
• Reaction/operation times are 10s min to hours
• Measurement times are seconds to minutes
• Measurements repeated during process
• Calibration/validation measurements included
Process analysis
• Spectroscopy techniques - NIR, mid-IR,
UV-visible, Raman, MS, NMR, XRF
• Gas chromatography and mass spectrometry
• Fast response times
• Information rich
• Chemical composition monitoring
• From process development to production
Checklist for implementation of
process analysis techniques
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Decide information required
Decide frequency
Consider sampling issues
Select technique
Decide measurement technology
Consider calibration/modelling
Schematic of a dye manufacturing process
Monitoring dye process by
visible spectrometry
• Dye content - 200 g/l
• Effluent - 0.1 g/l
• Optimum path lengths are 0.00025 and 0.5
cm, respectively.
• Use “transmission” for effluent and “ATR”
for concentrate
Transmission Probe
2
1
Attenuated Total Reflection Probe
3
Experimental arrangement for attenuated total reflection
Challenges in signal processing
and calibration
• Usually measure “mixed” spectra
• Spectra often broad-band
• Some parts of spectra are more useful than
others
• Samples change composition with time
• Lab-prepared standards may not be
representative
Features of process analysis
in PI plant
• Kit is small and may be a continuous process
• Reaction/operation times are seconds to minutes
• Access for probes may be limited
• Measurement times must be short e.g. seconds
• Need robust transferable calibration procedure or
methods that are calibration-free
• Forward control of rapid multi-step processes
may be desirable
Innovative Reactors
Innovative Technologies
Static Mixers
Innovative Technologies
FlexReactor from BHR Group
FlexReactor - Features
Features
 Simple but effective
static mixer technology
 Highly flexible package
 Wide range of materials
of construction
• Benefits
– Use for wide range of processes
– Flexibility to cope with undefined
chemistry
Measurement characteristics in PI
• In-situ measurements better than extractive
sampling
• Can flow-cells be built-in to continuous PI
processes?
• Non-invasive measurements avoid
disturbing process dynamics
Features of techniques for PI
Gas chromatography
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Possible for gaseous processes
Extractive sampling required
Good sensitivity range
Compact systems now available
Fast analysis possible
Micro machined GC system analytical module (c) Siemens
Micro machined GC
system - module
assembled to basic
unit (c) Siemens
Multi- and in-line detection
(c) Siemens
Laboratory GC
Injector
Conventional Process GC
Injector
Column
Detector
Column
Column
Backflush
Column
Distribution
Detector
Column
Distribution
Column
Column
Process-GC with Parallel Chromatography Approach
Injector
Column
Backflush
Column
Detector
Features of techniques for PI
Mass spectrometry
• Extractive sampling required
• Rapid and sensitive analysis possible
• Requires chemometrics to deconvolute
fragmentation patterns
• Improvements to design required for PI
applications?
Features of techniques for PI
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NIR spectrometry
Not particularly sensitive
Fast measurement times <1 s, but…..
Used for liquids and powders
Flow-cells possible
Compatible with silica fibres
Chemometric calibration required
Transmission and reflection options
Non-invasive use possible (needs window)
Zeiss Corona 45 NIR
Aspect software used to acquire spectra through PC link
Powder blending
glass
mixing
vessel
transducer
attached
here
Zeiss Corona
(non-invasive
NIR spectrometer)
Features of techniques for PI
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Raman scattering
Fundamentally a fast event
Not a sensitive technique
Measurement times may be too long
Fluorescence can be a problem
Compatible with silica fibres
Can be non-invasive
Sharper spectra than NIR
Kaiser HoloProbe Raman
Spectrometer
Non-invasive Raman
• Non-contact optic attached to probe head
• Probe to bottle distance = 5.5 cm
• Measurement time = 3 min
Features of techniques for PI
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Mid-infrared spectrometry
Can be relatively sensitive
Good at molecular identification
Flow-cell for gases, ATR probe for liquids
Not easy to interface with plant
Special materials/fibres required
Multivariate or univariate calibration
SpectraProbe Linx 5-10
Acoustic measurements
• Passive
transducer
• Active
pulse-echo
pitch-catch
Acoustic impedance
incident transmitted
reflected
material 1
impedance Z1
material 2
impedance Z2
• If Z1 and Z2 are very different (e.g. air and water)
most of the incident wave will be reflected
• If Z1 and Z2 are similar (e.g. oil and water) most of
the incident wave will be transmitted
Impact on measurements
passive – yes
active - no
e.g. granular solid material
passive – yes
active - yes
e.g. solid in liquid
passive – no
active - no
glass
air
glass
vessel wall
passive – yes
active - yes
glass
oil
glass
vessel wall
Acoustic emission
• Can measure and process the data to give
spectrum that is based on “frequency of
event” or acoustic frequency
• Non-invasive and relatively inexpensive
• Responds to changes in physical form
• Not a molecular technique
• Not particularly sensitive
• Requires sophisticated signal processing
Acoustic emission event frequency
Plant
Sensor and
preamplifier
Data acquisition
and prediction
DC signal
envelope
Amplified AC
signal
AC to RMS
conversion
log10(intensity/a.u.)
Event frequency spectrum
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Stirring of heterogeneous mixture
0
5
10
15
20
frequency of event/Hz
25
30
Nano 30 broadband transducer
(150-750 kHz)
pre-amplifier
and filters
transducer
power
supply
oscilloscope
GPIB/USB
computer
Matlab
Broadband
transducer
Linked directly to
oscilloscope
Agilent Infiniium oscilloscope
Data acquired in C-program using GPIB
link
Signal processing
Fourier
transform
process
time
time
sum
frequency
frequency
Passive acoustic spectrum of
aspirin in avicel – Nano 30
0.14
intensity/a.u.
0.12
0.1
0.08
0.06
0.04
0.02
0
50
150
250
frequency/kHz
350
200 g of itaconic acid in toluene
Stir rate = 250 rpm
Oil temp = 20 °C
6000
intensity/a.u.
5000
4000
3000
2000
1000
0
0
100
200
300
frequency/kHz
400
500
Chip-based approach to LC
• Fast analysis times
• Micro-machined capillary column
– Ideal column geometries realizable
– High fabrication uniformity
• Integrated injector and detector
– No extra-column dispersion
• No column packing
– low operating pressures
Technological challenges
• Reproducible sample injection
• Interfacing the macro-world with a
microfluidic chip
• Continous flow sampling
• Avoidance of sample carry-over between
measurements
2nd generation LC chips
© Crystal Vision Microsystems
Sample inlet
Buffer inlet
Sample outlet
Electrode
contact
pads
20mm
Outlet
Details of chip mount
© Crystal Vision Microsystems
Conception of analytical module
© Crystal Vision Microsystems
Analytical module
Schematic of module and deployment
Some final thoughts
• Most current process analysers are not designed
for PI plant in size, sampling interface etc.
• Techniques that you think could be good
chemically may be difficult to implement
• Sensitivity limitations could be a problem
considering short process times
• Combinations of techniques may be required
• Curve resolution chemometrics will be
important to achieve calibration-free analysis
Some final thoughts (continued)
• Analysers must be built-in if possible
• On-line optimisation and control will be
required in many processes
New approaches to the design and
operation of process analysers are
required