Characterization of fouling material by TGA-IR

In ethylene steam cracker facilities, ionic fouling, radical fouling and Diels-Alder fouling occur leading to the formation of solid materials depositing onto equipment. This subsequently hinders heat exchange within the plant resulting in costs in the range of millions of euros. The identification of these residues and quantification of their constituents is considerably challenging due to their very high complexity.

The value of evolved gas analysis techniques (EGA) for polymer and chemical oils characterization is growing year over year. Thermogravimetry (TGA) coupled to Fourier Transform infrared (FTIR) is an example of hyphenated EGA technique that has been widely used in the industrial analytical research for different applications; thermal decomposition pathway of polymers, chemical oils,complex mixtures characterization and understanding of reaction mechanisms. This powerful tool allows not only the identification of the product(s) released by a sample under controlled temperature conditions, but also their quantification. The quantitative analysis by using the relationship of area under the IR curve of one specific band (or band ratio) versus the known amount of gas generated is frequently used.

This study investigates the applicability of TGA-IR to quantify Diels-Alder vs Radical fouling mechanisms in the fouling formation. This information is critical for the optimization of chemical solutions to reduce fouling in a steam cracker. A TGA-IR analytical method has been developed to quantify monomers originating from the retro Diels Alder reactions on fouling samples by a spectroscopy approach. The results of this study have been qualitatively compared with the data obtained by Direct Insertion Probe-Mass Spectrometry analyses (DIP-MS) showing a good alignment between these two techniques. This study shows that TGA-IR is a powerful technique that can be applied for partial quantification of Diels-Alder related fouling.