Analysis in Vinyl Chloride (VCM) Production Process


PVC is a ubiquitous plastic favored in construction, piping, and many other industries due to the properties of the polymer, including light weight, chemical resistance, and versatility. PVC is produced by polymerizing vinyl chloride (VCM), a highly toxic/explosive chemical intermediate which is manufactured strictly for this purpose.

The process of producing VCM from raw materials is sensitive and requires careful monitoring to avoid contaminated products and equipment failure. Typically, VCM is made by thermal cracking of ethylene dichloride (EDC, formally 1,2-dichloroethane), which is produced on site from feed stocks of ethylene and chlorine.

The modern VCM production process sacrifices some efficiency in order to recycle bypoducts and operate at less expense. Maintaining yield purity and conversion efficiency throughout the various stages therefore requires continuous online monitoring of the production stream composition.

Applied Analytics provides a complete, field-proven set of solutions for EDC/VCM production process analysis. Our online chemical concentration monitors provide the real-time readings needed for optimization of the process at various critical analysis points. The OMA-300 Process Analyzer (UV-Vis spectrophotometer) monitors chlorine compounds, with integrated MicroSpec modules for additional measurements, providing a totally solid state, automated solution set.

Multi-Component Chlorine Compound Analysis by OMA

A multi-component analyzer is trusted to accurately measure multiple chemicals simultaneously. Chemicals whose absorbance curves overlap can be de-convoluted by AAI’s multi components algorithm*. Unlike traditional multi-wavelength photometers, the OMA uses a high resolution dispersive UV-Vis spectrophotometer which produces a complete 200-800 nm absorbance spectrum. The light intensity at each integer wavelength in that range is measured by a dedicated photodiode on a 1,024-element array.

This has significant implications for the Cl2 + FeCl3 measurement at AT-1. The OMA is de-convoluting the overlapping UV absorbance curves of the two analytes using many data points (where a simpler photometer might use 2 measurement wavelengths and a reference).

The major advantages here include noise reduction through averaging the modeled concentration from all data points simultaneously as well as expanded dynamic range by access to non-peak absorbance wavelengths in high-concentration scenarios — a critical capability for maintaining accuracy during process upsets.

*Provide sample matrix to AAI for verification.

Spectra FeCl3 and Cl2

Absorbance of FeCl3 and Cl2 in an EDC Background

drawing-OMA for Cl2 and FeCl3 in EDC

Example Arrangement: OMA for Cl2 and FeCl3 in EDC

drawing-MCP-200 for Moisture in EDC / VCM

Example Arrangement: MCP-200 for Moisture in EDC / VCM

The specifications below represent performance of Applied Analytics analyzers in typical EDC/VCM plant applications.

All performance specifications are subject to the assumption that the sample conditioning system and unit installation are approved by Applied Analytics. For any other arrangement, please inquire directly with Sales.

Further Reading