Introduction
Chlorine (Cl2) is one of the most important industrial gases used in chemical manufacturing, water treatment, and specialty gas applications. In many industrial processes, controlling chlorine concentration is critical for process efficiency, product quality, environmental compliance, and operational safety. Unlike chlorine detection systems designed only for leak alarms, online chlorine gas analyzers provide continuous quantitative measurement of chlorine concentration in process streams, exhaust gases, and specialty gas mixtures. Industrial chlorine analysis covers a very wide concentration range, the required measurement range depends on the process location and the purpose of analysis.
This article summarizes major industrial applications of online chlorine (Cl2) analysis, including:
ppm-Level Chlorine (Cl2) Analysis: Chlor-Alkali, PVC, Phosgene and CEMS Applications
Percentage-Level Chlorine (Cl2) Analysis: Industrial Process Applications
Chlorine (Cl2) Analyzer Applications in Chlor-Alkali and PVC Production
1. Why Is Online Chlorine (Cl2) Analysis Required?
In industrial processes, chlorine concentration is rarely constant. Variations may affect:
reaction efficiency
product purity
equipment corrosion
downstream process stability
environmental emissions
Traditional laboratory sampling cannot provide the continuous information required for modern process control.
Online chlorine analyzers allow operators to:
monitor real-time chlorine concentration
optimize chlorine feed ratio
detect excess or insufficient chlorine
improve process efficiency
reduce chlorine losses
comply with emission regulations
2. Chlorine Measurement Ranges in Industrial Applications
Industrial chlorine analysis can generally be divided into two categories:
| Measurement Range | Typical Application | Main Purpose |
|---|---|---|
| ppm-level Cl2 | PVC HCl synthesis, phosgene production, chlorine CEMS | Safety, quality control, environmental compliance |
| Percentage-level Cl2 | HCl synthesis, chlorine liquefaction, specialty gases | Process optimization and production control |
3. Chlorine (Cl2) Online Analysis Applications
3.1 PVC Production: Residual Chlorine in HCl Synthesis
Process Background
In calcium carbide-based PVC production, hydrochloric acid (HCl) is produced by reacting hydrogen and chlorine:
H2+Cl2→2HCl
After synthesis, residual chlorine may remain in the HCl gas stream.
Typical Measurement Point
HCl synthesis outlet
HCl gas main line
Typical Measurement Range
ppm-level chlorine
commonly controlled below hundreds of ppm
Why Online Analysis Is Required
Residual chlorine can affect:
hydrochloric acid quality
downstream PVC process stability
corrosion risk
Continuous chlorine measurement provides real-time process information for quality and operational control.
3.2 Chlorine Emission Monitoring (CEMS)
Process Background
Industries using chlorine-containing processes may generate exhaust gases containing trace chlorine.
After gas treatment systems such as scrubbers, chlorine concentration may be continuously monitored before discharge.
Typical Measurement Point
treated exhaust gas line
stack emission monitoring system
Typical Measurement Range
ppm-level Cl2
Why Online Analysis Is Required
Continuous chlorine monitoring helps:
verify scrubber performance
maintain environmental compliance
provide continuous emission data
UV-based differential absorption techniques are commonly used for chlorine emission monitoring because chlorine has strong absorption characteristics in the ultraviolet range.
3.3 Phosgene Production: Residual Chlorine Monitoring
Process Background
Phosgene is produced by reacting carbon monoxide and chlorine:
CO+Cl2→COCl2
The reaction requires precise control of chlorine conversion.
Typical Measurement Point
phosgene reactor outlet
solvent wash vent
Typical Measurement Range
ppm-level residual chlorine
Why Online Analysis Is Required
Residual chlorine measurement supports:
reaction completion monitoring
purification control
operational safety
UV photometric analyzers are used for continuous chlorine measurement in phosgene-related processes.
3.4 HCl Synthesis: Excess Chlorine Measurement
Process Background
During HCl synthesis, chlorine may be intentionally controlled at a slight excess level to ensure complete hydrogen conversion.
Typical Measurement Point
HCl synthesis furnace outlet
dry HCl gas stream
Typical Measurement Range
percentage-level chlorine
Why Online Analysis Is Required
Online measurement helps control:
hydrogen/chlorine ratio
reaction efficiency
free chlorine concentration
This application is different from ppm-level residual chlorine measurement. The purpose is not only product quality but also reaction optimization.
3.5 Chlorine Liquefaction Tail Gas Analysis
Process Background
In chlorine production plants, gaseous chlorine is compressed and liquefied.
Not all chlorine is condensed, and the remaining tail gas may contain significant chlorine concentration.
Typical Measurement Point
chlorine liquefaction unit tail gas
Typical Measurement Range
high percentage-level chlorine concentration
Why Online Analysis Is Required
Continuous chlorine analysis helps:
evaluate liquefaction efficiency
reduce chlorine losses
optimize recovery systems
3.6 Specialty Gas Mixtures: Excimer Laser Gas Analysis
Process Background
Excimer lasers such as KrCl systems use carefully controlled gas mixtures containing chlorine.
Typical Measurement Point
laser gas mixing system
specialty gas supply system
Typical Measurement Range
percentage-level chlorine
Why Online Analysis Is Required
Precise chlorine concentration control is required to maintain:
laser performance
gas mixture consistency
product quality
4. Chlorine Measurement Technology
UV Absorption Spectroscopy
UV spectroscopy is widely applied for chlorine analysis because chlorine molecules strongly absorb ultraviolet radiation.
Advantages include:
direct chlorine measurement
fast response
continuous operation
minimal chemical consumption
suitability for corrosive gas applications
Common configurations include:
UV photometers
UV-DOAS systems
fiber-optic UV analyzers
5. Online Chlorine Analyzer Selection Considerations
When selecting a chlorine analyzer, key factors include:
5.1 Measurement Range
The analyzer must match the application:
ppm-level residual chlorine
percentage-level process chlorine
5.2 Gas Composition
Industrial chlorine streams may contain:
HCl
nitrogen
oxygen
hydrocarbons
reaction products
Interference resistance is essential.
5.3 Sampling System Design
Because chlorine is highly reactive and corrosive, the sampling system is often as important as the analyzer itself.
Important considerations:
material compatibility
sample conditioning
response time
maintenance requirements
Conclusion
Online chlorine (Cl2) gas analysis is used across a wide range of industrial processes, from ppm-level residual chlorine monitoring to percentage-level process control.
The major application categories include:
| Application Category | Examples |
|---|---|
| ppm-level chlorine analysis | PVC HCl synthesis, chlorine emission monitoring, phosgene production |
| percentage-level chlorine analysis | HCl synthesis control, chlorine liquefaction tail gas, specialty gas mixtures |
For industrial users, selecting the correct chlorine analyzer requires matching the measurement technology, concentration range, and process objective.
Continuous chlorine analysis provides critical information for improving process efficiency, maintaining product quality, and ensuring reliable operation in chlorine-based industries.
For product information, please visit:
Ultraviolet photometry analyzer.
For further technical consultation or application support, please contact us at sales@mzdd.de .