Degradation processes of polydimethylsiloxane under thermal cracking conditions of hydrocarbons in an experimental pilot plant followed by size exclusion chromatography coupled to inductively coupled plasma high resolution mass spectrometry

In the oil and gas industry, silicon coming from antifoaming agents, is recognized to be an emergent contaminant for hydrotreatment catalyst due to its negative effect on their performance. Using a pilot plant, representative samples of the thermal degradation of antifoaming agent such as polydimethylsiloxanes (PDMS) were produced under evaluated thermal cracking of hydrocarbons with the presence or absence of steam. Micro size exclusion chromatography hyphenated to inductively coupled plasma high resolution mass spectrometry was used to characterize these samples. Under low temperature processing conditions at around 250 °C, PDMS was not degraded in the presence of hydrocarbons. Under thermal cracking of hydrocarbons at 500 °C, PDMS is degraded and formed intermediate polymers and low molecular weight compounds. A small amount of the initial PDMS can be present following the different operating conditions. The percentage of steam has a great influence on the degradation of intermediate polymers probably following a hydrolysis to produce low molecular weight species. The results presented bring preliminary results and a new insight on the degradation of PDMS under thermal cracking conditions. This work indicates that the different molecular weight silicon compounds can distillate in the various petroleum cuts and could be responsible for catalyst poisoning.

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► The understanding of antifoaming degradation is essential for silicon speciation.
► Representative degradation samples were produced on a pilot plant at 500 °C.
► A SEC-ICP-HR/MS method to characterize silicon degradation products.
► Three different distributions: PDMS, intermediate PDMS, low molecular weigh silicon compounds.
► A real advance for silicon speciation and catalyst poisoning.