Inert Coating Transfer of Sulphur in Petrochemical Applications with Inert Surface Coatings

Author / Editor: MARTIN HIGGINS / Dominik Stephan

Inert coating technology, such as SilcoNert 2000 of SilcoTek Corp., allows petrochemical operators to obtain accurate sulphur data every time without any delay, sample errors or false readings. By adopting this technology, petrochemical plants can save thousands of rupees through improved yields, better test cycle times and improved system reliability.

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Passivation can alter the results of sulphur samplings in petrochemical applications - an effect that can be overcome by using inert coartings. (Source: / Nikolay Zaburdaev)
Passivation can alter the results of sulphur samplings in petrochemical applications - an effect that can be overcome by using inert coartings. (Source: / Nikolay Zaburdaev)

Accurate analysis of part-per-million and part-per-billion levels of sulphur containing compounds like hydrogen sulfide (H2S) and methyl mercaptan in petrochemical streams are critical to meeting new regulations for low level sulphur, and for profitable or accurate grading of feedstock. Many organosulphur compounds like H2S get adsorbed to metal surfaces. Adsorption problems in sample pathways often can be traced to tubing, fittings and valves used to transfer the sample to the analytical instrument. Petrochemical plant operators often attempt to minimize sulphur adsorption effects by priming or passivating the analytical pathways. Priming often leads to poor or unreliable sample results. Comparative testing demonstrates the effectiveness of inert coatings over passivation. Chemically inactive or inert coatings greatly reduce maintenance cycles, improve test reliability, increase test speed and process feedback. Reliable sampling results in improved process yields, lower operating costs and improved environmental compliance.

For maximum reliability of analytical systems used in sampling and transfer of sulphur containing species, we must address surface inertness when stainless steel components are used. In most refining and petrochemical streams, analysis in the ppm level is required. Figure 1, demonstrates that even at concentrations of 50ppm, hydrogen sulphide sampling requires inert surfaces. In this analysis, sample cylinders tested were either sourced from the manufacturer, non-coated, or treated with a carboxy-silane, commercial name Dursan. The inert surface significantly outperformed the bare stainless steel surface, and allowed for

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longer sample stability and integrity during storage and transport.

Passivcation: A Debated Effect

Figure 2 demonstrates the need for coating during the sampling, storage and analysis of part-per-billion levels of hydrogen sulphide. In critical applications, the ultimate inertness of components is enhanced using silicon-based coatings. In figure 1 and 2, the degradation of hydrogen sulphide on bare stainless steel is rapid and irreversible, both at 50ppm and 17 ppb levels, H2S is lost within 24 hours. The effect of passivation on sulphur storage and transport reliability is debated. Passivation is a technique that is based on the assumption that – if all active areas of a transport vessel or storage vessel are taken up by sulphur compounds, they are made inert to sulphur compounds. There have been studies to support this at low temperature for gas phase transport through low surface area regulators. It was demonstrated that purging a component with clean

gas can reduce the inertness of the passivation with measurable impact occurring within one day and complete within one week. Additional data in the same study also demonstrated that heated stainless does not passivate, and complete adsorption of sulphurs will occur – no matter the conditions and previous exposure to sulphur compounds.