Developing a Robust Sampling and Measuring Unit for At-Line NIR Analysis of Esters

Abstract

The use of Near Infrared (NIR) Spectroscopy as a tool for routine chemical process control has often revealed the differences between laboratory and process analysers. In-line applications are usually preferable because they can be integrated easily with the control system for direct monitoring. However, for some special applications, inherent technical problems brought by in-line measurement have still not been solved in practice. At-line analyses on the plant site can then be the first step towards continuous process control. In addition to a reliable spectrometer, these types of application demand accessories rugged enough to be used in a plant environment. The analysis procedure must also be operator-friendly. However, up to now, most of the commercial NIR sampling accessories have been developed for laboratory equipment and still require analytical skills to operate them. A sampling unit for transmittance NIR measurement of esters has been constructed using commercially available parts, making it a cost-effective device. Inspired from the “flow cell” used for in-line applications, the normal cleaning procedure between two analyses uses the sample to be measured itself. It does not require additional solvents, thereby reducing significantly chemical handling and waste disposal. Cross-contamination has been extensively tested, using esters of various viscosity. As indicated by all results, the sampling and measuring unit presented in this paper simplifies both analysis and maintenance procedures and is thus especially well-suited to a factory environment. Last but not least, with its fixed path length and its accurate temperature control, it has proven to be a valuable tool for research studies.