Coke formation preoxidized steel reactor

Figure 7. Coke formation during steam cracking of propane at 840°C on a steel foil (Sandvik ISRelO) in a preoxidized steel reactor. The reactor surface and the foil were preoxidized for 95 min using 46% Ot in Nt at 840°C. Conversion of C3Hs 89%. Feed gas as in Figure 4.

It is seen that coke formation on the sample of foil is dependent on the material of the tubular reactor as is the product gas composition. With the steel reactor, preoxidation leads to a substantial increase in the coke formation on the steel foil (Figures 6 and 7). The effect of preoxidation is even more pronounced with Ni as the foil material (Figure 8). On the other hand, preoxidation does not lead to a high rate of coke formation on the steel foil if a quartz liner is used in the tubular reactor (Figure 9). 

Figure 9. Coke formation during steam cracking of propane at 850°C on steel foils (Sandvik 15RelO) in a preoxidized quartz reactor.

With a steel reactor it is shown that preoxidation of the foil and the reactor surface results in much higher coke formation on the foil compared with prereduction of the reactor system (Figures 6 and 7). This is not surprising since Fe and Ni present on the oxidized surface are known to be good catalysts for carbon formation (21). Prereduced foils, which contain mostly Cr and Mn on the surface, produce much less coke. In agreement with this, the coke deposit from the preoxidized foil surface contains Fe (characteristic of catalytic coke formation) whereas the deposit on the prereduced foils contains effectively no Fe (20). 

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