Alonized Incoloy

The coke formed on the alonized Incoloy 800 surface was amorphous, and it could be scraped from the surface rather easily. Amorphous coke, as defined here, is sometimes referred to as polycrystalline coke. Other examples of amorphous coke are shown in Figure 6. 

Figure 1. Coke formed from acetylene at about 410°-460°C. (Left) Incoloy 800 (right) alonized Incoloy 800.

Figure 3 shows an example of needle or arrowhead coke. This coke is produced from ethylene, propylene, and butadiene on Incoloy 800 surfaces in the temperature range from about 365°C up to at least 600° C. The size of needles as shown in Figure 3 was smaller than that observed in most other photographs this coke was magnetic because of the iron present in it. The coke produced on alonized Incoloy 800 at comparable conditions was amorphous, however, as shown in Figure 3. 

Figure 6 indicates that amorphous coke was formed from acetylene, ethylene, propylene, and butadiene at 600°C on alonized Incoloy 800 surfaces. These cokes were in all cases nonmagnetic in character and contained no detectable iron. They did contain a trace of aluminum, probably as alumina. 

Figure 6. Coke formed at 600°C on alonized Incoloy 800 with four unsaturated hydrocarbons. (Top left) acetylene (top right) ethylene (bottom left) propylene (bottom right) butadiene.

Figure 8. Various surface on alonized Incoloy 800. (Top,) new (or unused) surface (bottom left,) partially decoked (first acetylene and then oxygen treatment) (bottom right) partially decoked (first acetylene and then steam treatment).

The pyrolysis reactors were similar to those used earlier (1,2) they were 1.1 to 1.26-cm i.d. tubes that were heated in an electrical resistance furnace over a length of about 48 cm. The materials of construction in the four reactors used in this investigation were as follows Incoloy 800, stainless steel 304, Vycor glass, and alonized Incoloy 800. The latter reactor was prepared by Alon Processing, Inc. of Tarentum, Pennsylvania. 

The results for Run 19 (Vycor glass reactor), Run 21 (alonized Incoloy 800 reactor), and Run 14 (coke-covered Incoloy 800 reactor) were similar to both the kinetics and type of products obtained. Although neither oxygen or hydrogen pretreatments were tried in Vycor glass or alonized Incoloy 800 reactors prior to acetylene pyrolyses, it is thought that such pretreatments would have little or no effect on acetylene reactions. This conclusion is based on such pretreatments prior to pyrolysis with other hydrocarbons in these two reactors. It has been concluded that all increases in acetylene conversions above those of Runs 14, 19, and 21 were in some way caused by surface reactions. Based on this assumption, surface reactions were of major importance in Runs 15, 18, and 23. 

Butadiene reacted in Incoloy 800, alonized Incoloy 800, and Vycor glass reactors to give quite similar results. Butadiene conversions increased from about 60%-80% at 500°C to about 94%-97% at 700°C. The main products formed were liquids (i.e., products that condensed... 

Methane was formed in significant amounts in such cases it is thought that hydrogen reacts with the surface coke or metal carbides on the surface, such as has been shown earlier to occur (1). At the same temperatures (600°-700°C), little or no reactions occurred in the Vycor glass or in the alonized Incoloy 800 reactors. Clearly the Incoloy 800 surfaces were promoting significant coking reactions at these temperatures. 

A series of runs was made in the alonized Incoloy 800 reactor by using ethylene, ethane, propylene, and propane. These runs were com-... 

Although more information is needed to determine details concerning factors that favor inactive coke formation, relatively high levels of surface sulfides probably promote formation of such coke. On the other hand, metal oxides on the surface likely favor production of active coke. Sulfiding the reactor tube immediately upon completion of the decoking step would form metal sulfides. An aluminized surface, such as provided by the alonized Incoloy 800 reactor, also has been found to be an effective way to prevent the production of active coke. Quite possibly, the initial type of coke formed on the just-cleaned tube would have an important effect on the length of time a reactor tube could be used in a commercial plant before decoking would be required. 

B, alonized Incoloy 800, panoramic view C, round columns on Incoloy 800 surfaces D, other columns on Incoloy 800 surfaces E, face of round column and F, area of Incoloy 800 surface near base of round column. 

Figure 9. Coke deposition vs. time (10% C2Hi at 800°C). Key O, Incoloy 800 and 0, alonized Incoloy 800.

Treatments of aluminized (or alonized> Incoloy 800 coupons with helium, oxygen, or steam at 700°C in general resulted in only rather small changes in appearance, as shown in both Figures 3 and 4 for the unpolished and the polished coupons, respective The findings with the polished aluminized coupons must however be considered less reliable. The objective had been to remove only the outer layer that in places was almost pure aluminum and polish until the depth was reached at which aluminum had alloyed with the Incoloy 800. For some coupons, too much or perhaps too little metal was removed, such as for the rough portion of the steam-treated coupon shown in Figure 4C. 

Figure 4. Gaseous treatments of polished alonized Incoloy 800 at 700°C for 4 h.

Figure 6. Gaseous treatments of alonized Incoloy 800 surfaces at 900°C for 4 h.

Figure 9. Coke deposited on various alonized Incoloy 800 surfaces. Conditions 5% C2H, 900°C for 1 h.

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