Propane steam cracking coke formation

The effect of surfaces on the gaseous and solid products of the steam cracking of propane has been studied. The chemical nature of the surface near the reactor inlet has a significant effect on the reaction products while the surface near the exit does not. The material of the reactor tube appears to catalyze gas phase reactions as well as coke formation and gasification. Pretreatment of the reactor tube alters the chemical nature of the surface and, as a result, alters the effect of the material on the reaction products. 

The present studies were initiated in order to investigate the effect of the reactor surface on the product distribution and on the tendency for coke formation during the steam cracking of propane in a tubular reactor. Attention has been focused on correlating various effects which can arise in the system. Previous studies of the pyrolysis of propane has been reviewed recently (17, 18), and the findings of the present work are related to these studies later in this paper. 

Figure 3. Coke formation during steam cracking of propane in the quartz reactor at 850°C on foils made from different materials. Key O, steel V, Co A. Mo , Cu and 0, quartz. Conversion of C3HB — 98%. Feed gas as in Figure 2.

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.

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

Using the quartz liner, coke formation on the foils was substantially less and so were the difference between the coke formation of preoxidized and prereduced foils. Quartz has been found to be catalytically inert and any effect on steam-cracking of propane should not and does not reflect the chemical nature of the surface. Gaseous and solid products obtained in the quartz reactor are shown in Figures 2, 3 and 9. The gas phase product spectrum is typical of a quartz reactor (Figure 2) and is unaffected by the foil material. The initial rate of coke formation on the foil depends on the foil material, but the rate of coke formation on all foils appears to approach a value similar to that for coke formation on coke. 

---