Effect of Varying H2S Content on High-Temperature Corrosion of Ferritic and Austenitic Alloys in a Simulated Pyrolysis Process of Post-Consumer Plastics

Abstract

The alloys K90941 and N08811 were tested under conditions simulating a pyrolysis process of post-consumer plastics. Impurities in the plastic feedstock like chlorine containing materials or organic components yield HCl and H2S respectively during the cracking process. The reactor material must be able to withstand these harsh corrosive conditions.In lab-scale test equipment, process conditions of the reactor zone of the pyrolysis process were simulated at temperatures of 420 °C and 580 °C for 72 h. The gas atmosphere consisted of either 200 ppm or 20000 ppm H2S and 3.8 vol% HCl, 1.9 vol% CO2, 0.3 vol% CO, 2.8 vol% H2, bal. N2. After the corrosion experiments, the samples were analyzed by metallography, SEM/EDX, and XRD. Additionally, the mass loss was evaluated. Results show that the ferritic K90941 is more aggressively attacked than the austenitic N08811 and that for both materials the mass loss rises with increasing H2S content in the gas atmosphere and increasing temperature.

High temperature corrosion behavior of alloys in reducing HCl and H2S containing environments: Thermodynamical and experimental assessment

“…SEM/EDX mappings, which show the corrosion structures of the ferritic and austenitic alloys, either can be found in previous studies [ 6,18–22,24,25 ] or for some selected conditions on representative examples of K90941 and N08811 in Figures 7–14. SEM/EDX mappings of K90941 and N08811 for the remaining conditions can be found in the Supporting Information Materials.…”

“…A more detailed analysis of measured corrosion rates and of beneficial alloying elements can be found in previous studies. [ 18,20,21,25 ]…”

“…In the high-H 2 S mixture, chromium was identified to be beneficial by slowing down the corrosive attack at 580°C (Figure 5), among others due to the formation of FeCr 2 S 4 . [21,25] The favored reactions of chromium with the gas phase as indicated in Table 7 and the less pronounced behavior of metal chlorides as indicated by quasi-stability diagrams (Table 8), might explain this behavior. The high corrosion rates of K90941 can be attributed to the nonprotective effect of iron sulfide compared with that of chromium sulfide, whereby the corrosion process can proceed faster.…”

“…x [21,25] x [20,25,29] x [21,25,29] x [19,29] x [25] x [25] x [25] x [21,25] x [25] x [21,25] N06600…”

“…Nevertheless, they are helpful for first estimations of the type of material that may show protective behavior in a particular atmosphere. [23,27,28] The high-temperature corrosion behavior in reducing HCl and H 2 S containing atmospheres of several alloys, ranging from low-alloyed ferritic K90941 up to highly alloyed austenitic N10276, was investigated at various conditions during previous studies [6,[18][19][20][21][22]24,25,29,30] and different corrosion models were generated. [18,20,24,25] In Table 1, an overview of all performed experiments in reducing HCl and H2S-containing atmospheres is presented and corresponding references to the published results are denoted.…”