Degradation of polydimethylsiloxane in simulated industrial process environments
Nyman, Oscar (2021)
Nyman, Oscar
2021
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe202102013454
https://urn.fi/URN:NBN:fi-fe202102013454
Tiivistelmä
Polydimethylsiloxane (PDMS) is commonly used in the Kraft process as an anti-foaming agent, which is added during the pulp-washing stage, where the pulp is separated from the black liquor. Crude tall oil (CTO) is later obtained from the process as a by-product and it can be further distilled or upgraded into renewable diesel or other products. However, traces of PDMS have been detected in the CTO and its distillation fractions. This has caused problems in the oil refineries, especially in the hydrotreatment processes, where it causes catalyst poisoning and solid deposits. The purpose of this work was therefore to investigate the fate of PDMS in industrial conditions, such as elevated temperatures and in different fatty acid-based matrices. Experimental work was carried out at Åbo Akademi University, where heating of PDMS in fatty acid-based matrices was carried out in sealed pressure tubes placed in a sand bath on a hot plate equipped with a magnetic stirrer. The effect of an adsorbent and the degradation of PDMS in bio-oil 1 at a slightly larger scale and higher temperature was also tested using an autoclave. The degradation rate of PDMS was analysed using HP-SEC, and the degradation products were analysed using NMR, GC-MS, and GCFID. The fastest degradation of PDMS was observed in the bio-oil 4 matrix, followed by the bio-oil 1 matrix. Somewhat slower degradation was observed in bio-oil 3 and the least degradation in bio-oil 2. The degradation products were found to be cyclosiloxanes ranging from D3–D8, which subsequently suggested the degradation mechanism to be in the form of well-known back-biting reactions seen in the thermal degradation of pure PDMS. Based on results from an experiment and from the composition of the matrices, the catalytic component and driving force behind the degradation of PDMS was suggested to be the fatty and/or resin acids in the matrices.