On-line polyethylene additives
analysis using a diode array uv /visible spectrophotometer andCharm Works
Ron Belchamber
Process Analysis and Automation

Process Analysis & Automation
Fernhill Road, FarnboroughHampshire
GU14 9RX, UK
tel: +44 1252 373000

www.paa.co.uk

Process Analysis & Automation■ Process analysis systems■ Multivariate process analysis software◆ Charm Works■ Sonic product development■ Acoustic emission monitoring systems■ Laboratory automation

Applications - vertical markets■ Antioxidants in polyolefin melts■ Automation of standard tests◆ permanganate time◆ Hazen colour■ Batch processing■ Solvent purity■ Multicomponent stream composition

LabVIEW■ Graphical programming environment■ Designed specifically for instrumentation■ Good graphical user interface■ High connectivity■ Charm Works add on toolkit provides

chemometrics

Charm Works■ Chemometrics for real time process analysis■ LabVIEW tool kit■ PLS, PCA, SIMCA■ Easy to use

Instrument
Instrument
drivers
drivers

SPC
SPC
toolkittoolkitWindowsWindows
DLL,DLL,DDE,DDE,CINSCINS

LabVIEW

SQL
SQL
toolkittoolkitCommunication
Communicationdrivers
drivers
TCP/IP,TCP/IP,serial,serial,ModBus,ModBus,FieldBus
FieldBus

CharmCharmWorks
Works

On-line polyethylene additives
analysis using a diode array uv /visible spectrophotometer andCharm WorksPolyethylene manufacturing

Antioxidants

Additives SpectraRheometric PCR-320

The extruder

Objectives■ Analyse three anti-oxidant additives

concentration in real time
■ On-line in the melt (up to 250°C)■ Manage all of the functions in a single,
integrated, easily maintainable application

Basic approach■ Spectroscopy (proven off-line)■ Probes and optical fibres■ Software environment (connectivity)■ PLS prediction model (1 off-line / 2 on-line)■ Reliable engineering (essential)◆ opto-isolation (analog + digital)◆ watchdog

Technology■ In-line probes (melt) - SpectrAlliance■ Fibre optics as interface(UV Quartz grade 600µm)■ Zeiss MCS500, PDA spectrometer■ National Instruments LabVIEW system■ PLS algorithm (Charm Works)

Zeiss Spectrometer - MCS500

Monitoring system

Polyethylene
extruderColdwaterbath

Optical cell
Sampleopticalfibre opticCutters
ZeissMCS500

Spectrometer functions■ Control and data transfer via RS-422■ Choose averaging time and spectral range■ Initiate scans and down load data
■ Monitor reference spectrum (alarm on 60 %of initial integrated value for 370-400nm)

Communications■ Serial communications with site VAXcomputer◆ incorporation of PLS predicted data into sitedatabase■ Digital alarms to local enunciator panel■ Digital inputs◆ reset alarms◆ rheometer fault

Additional I/O■ Digital outputs◆ analyser fault◆ bad prediction (high Mahalanobis distance)◆ low additive concentration alarm◆ low melt flow or extruder stopped◆ PC Watchdog■ Digital inputs◆sample temperature alarm◆reset low flow

Error detection / correction■ Monitor reference spectrum (alarm on 60 %of initial integrated value for 370-400nm)■ Monitor prediction quality statistics to warnof calibration problems■ To detect flow problems in the rheometer by
signal noise■ Correct for spectral offsets

PLS2 modelling■ X block◆ spectra 243 - 400 nm (180 data points)◆ mean centred scaling■ Y block◆ LC data (concentration of A, B and C)■ 20 samples used initially to build model■ Model extended on-line

600

1400

Additive B - Validation

Additive A - Validation
PLS predicted values (ppm)

500

1000
800
600
400

400

300

200

100200000500

1000

01500

1002002000

Additive C - Validation

1800
1600
1400
1200
1000
800
600
400
20000300

400

500

Liquid chrom atogra phy va lue s (ppm )Liquid chromatography va lue s (ppm)

PLS predicted values (ppm)

PLS predicted values (ppm )

1200

500

1000

1500

Liquid chromatography values (ppm)

2000

600

Conclusions■ The Zeiss MCS500 spectrometer has

produced good spectral results forpolyethylene/polypropylene additives■ PLS modelling has proved effective foranalysing 3 non-resolvable anti-oxidantadditives■ LabVIEW has enabled a fully integrated

process analysis system to be developed in ashort period of time at low costNew developments■ Charm Works 99◆ automatic baseline correction◆ calibration free prediction■ New applications◆ batch processes◆ reacting systems◆ NIR