Spectral Sensors by Carl Zeiss

ON-LINE ANALYSIS OF AROMATIC
HYDROCARBONS IN PROCESS WATERINTRODUCTION

Aromatic Hydrocarbons such as benzene and its derivatives, toluene and xylene often referred as BTX
are used as starting materials in a multitude ofproducts from pharmaceuticals, dyes, polymers toagrochemicals.
These aromatics are known to cause health effects
from chronic exposure and even benzene is listed as acancer causing substance. In production processes
cooling water and condensed water can becomecontaminated with these compounds. It is therefore
necessary to have reliable and fast methods todetermine and control the amount of these compounds
as well as effective methods for treatment and removal.
Figure 1: BTX solvents

Gas chromatography is the most commonly usedmethod for measurement. However, there is demand
for alternative methods utilising fast on-line analysis
with lower running costs.

THE METHOD
Aromatic hydrocarbons show good absorption
characteristics in UV-VIS region due to the high levelof conjugated bonds present. Figure 1 gives an example
of different concentrations of a benzene, toluene, xylene
mixture in water.
A method using absorbance characteristic of aromatics
in the region 190–300 nm was developed to measurethese compounds in the ppm range.
A PLS algorithm is used to determine the concentrationof individual and total aromatics.
Figure 2: LabView screenshot

Application Note 1/99

Spectral Sensors by Carl Zeiss

THE SYSTEM
The industrial diode array system MCS 500 UV based on the established ZEISS MCS polychromator technology
provides the spectral information in the UV range required for the developed method.
High sensitivity, high wavelength stability and low straylight guarantee excellent reliability of the determined values.
Pre-aligned flow cell, 2-channel plug-in multiplexer to measure two streams or sample/reference, industrial standard
outputs (RS 422, 4-20 mA) and an easy-to-use on-line software package complete the system.
Systems can be cascaded and controlled via one Host PC to measure compounds in different streams.
THE SOFTWAREThe DM1 software package is designed to run under WINDOWS®NT and includes the PLS/IQ module from
GALACTIC to work with any PLS model designed under GRAMS 5.
The programm allows to display the results of up to 4 channels including the measured absorbance spectra.
Concentrations of the compounds can be displayed, saved and/or sent via analog output.
Digital controlled devices like valves, shutter etc. to switch streams or references can be included in the automatedsignal processing.
THE BENEFITS
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Analysis and response time greatly reduced
Fast and continuous monitoring
Established and proved system and method
High reliability, low maintananceEasy to use software
Speed and full spectrum advantage of photodiode array detection
Possibility to combine systems to monitor various streams
Fiber optics allow flexibility in installation and location of the system

SYSTEM SPECIFICATIONS
Wavelength range
Wavelength resolution
Wavelength reproducibility
Measurement time
PC Interface
Distance between PC and System
Analog output (4 – 20 mA)
Optical Fiber (Probes-System)
Housing

Carl Zeiss
Spectral Sensors

200 – 620 nm (190–1020 nm optional)
0,8 nm/diode (2,4 nm Rayleigh)< 0,05 nm< 2s
RS422up to 80 m with standard cable
Up to 2,5 km with waveguide transmission
4 channels (standard)
NI PC ISA card
Quartz, 600 µm core, SMAMaximum distance 10 m
19” slide-in rack
19” protective housing

D-07740 Jena
Telefon:(03641)64 33 85
Telefax:(03641)64 33 11
E-Mail:info.spektralsensorik@zeiss.de
Internet:
http:\\www.zeiss.de