Reactor hydrogen sulfide treatment

Hydrogen sulfide treatment of reactor surfaces produced a relatively durable, passive, metal sulfide layer. The oxide layer is probably converted to sulfides either entirely or at least to a sufficient depth that very little catalytic oxides are exposed. 

After each hydrogen sulfide treatment of the stainless steel reactor, oxygen was passed through the reactor and Initially most of the oxygen was adsorbed on the reactor surface. For example, the Inlet flow rate of oxygen was adjusted to 13 cc/mln. after the second hydrogen sulfide treatment Initially the outlet flow was almost zero for about 50 minutes. Subsequently, the exit flow Increased In amount during the next three hours, and the... 

Figure 4. Concentration profile for Incoloy 800 reactor used for pyrolysis of ethane and propane after hydrogen sulfide treatment...

A reactor constructed of stainless steel 410 was used for pyrolysis since it contained no nickel. The coke layer formed during pyrolysis was usually thin and greyish. Less frequently, a piece of black coke was found on the surface. The metal surface (Surface C) was always grey. Figure 5 shows the two types of coke formed at Surface A in the stainless steel 410 reactor. The black (less frequent) coke appeared to be a floe of fine filaments, about 0.05 / m in diameter, with occasional 0.4- m filaments. The predominant deposit seems to be platelets of coke that include metal crystallite inclusions, the lighter area. The metal particles in the coke deposits, as detected by EDAX, were chromium rich compared with the bulk metal, as reported in Table III. Some sulfur also was present in the deposit the sulfur was present, no doubt, because of the prior treatment of the surface with hydrogen sulfide. Surfaces B and C for the stainless steel 410 reactor are also shown in Figure 6. Surface B indicated porous coke platelets. Surface C was covered mostly with coke platelets, and cavities existed on the surface. Metal crystallites rich in iron apparently were pulled from the metal surface and were now rather firmly bound to Surface B. Surface C was richer in chromium than the bulk metal. 

The inner surface of the stainless steel reactor was deactivated by the following procedure. The tube was cleared by passing air at the rate of 1-2 L/min. for 30 min while maintaining a temperature of 575°C. Hydrogen sulfide was then passed for 30 min at the rate of 250 mL/min. Finally, hydrogen was passed for 30 min at the rate of 3 L/min. To equilibrate the surface a small amount of the liquid hydrocarbon was pumped before starting the experiment. This treatment apparently eliminates any major catalytic effects of the reactor surface, as indicated by the lack of carbon deposits in all runs. 

The Strong surface effects observed after oxygen treatment of the reactors are probably caused by oxygen adsorption and/or reaction of the oxygen with the reactor walls to form complex metal oxides. Transformations in the structure of these oxides can occur due to change in temperature, exposure to a reducing atmosphere, or attack by another chemical such as hydrogen sulfide. 

Two oxidation runs were made using oxygen In the stainless steel reactor after It was treated with pure hydrogen sulfide at 800 C first for 2 hours after 30 oxidation-reduction sequences and then for 18 hours after 35 sequences. After the first treatment, the amount of oxygen reacted Increased by about 20-25%. 

All residual sulfur compounds in tail gas are hydrogenated in a bed of co-balt/molybdate/alumina catalyst, operated at 300°C, after the addition of a suitable volume of hydrogen to the Claus reactor tail gas. The hydrogen sulfide formed can then be recycled to the Claus process furnace. This treatment improves conversion up to 99.9%. 

Sulfiding All catalysts were passivated with diluted H2S before the accelerated deactivation tests and before the coking reaction in order to suppress the initial hyperactivity usually found in fi esh Pt-Re/Ab03 catalysts. Such passivation treatment was performed in a fixed bed reactor at 500 C under flowing of a 1 % H2 H2 mfacture (30 cmvmin, 90 min, atmospheric pressure). The samples were then stabilized in pure hydrogen (500 °C, 5 h) in order to remove the S reversibly adsorbed (10). 

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