Amorphous coke

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 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. 

Acetylene at 800°C on alonized surface both knobby and amorphous cokes. 

Butadiene at 460°C on alonized surfaces both amorphous and a semiknobby, almost filament-type coke. The latter coke appears to be on top of the amorphous coke. The filaments, if they are filaments, are quite different in appearance to filaments shown in Figures 1 and 2. 

The model proposed assumes reversible formation of amorphous coke (Ccm) and simultaneous formation of whiskers (Ccw) on the catalytic surface. The amount of monolayer coke at infinite time (Cc ax) depends on the operating conditions (e.g. temperature) and is governed by values of the rate constant for... 

Peak 5 can be assigned on the basis of previous work with Ni and Ru catalysts to amorphous coke or Cp. The formation of a hydrogen-containing carbon species during CO hydrogenation has been verified on Ru [18] and iron catalysts [13]. While Dwyer observed no polymethylene, as he calls it, on K-fiee iron after reaction for 8 hours at 7 atm, H2/CO = 3 and 540 K, identical treatment of a catalyst promoted with potassium produced a multilayer coverage of Cp. Accordingly, the area of Peak 5 should increase with K addition. Indeed, upon the addition of K... 

To avoid putting a coke drum in such a vulnerable position, an overhead temperature of 780°F or higher should prevail when the drum is almost full. This will eliminate the potential for carrying over an amorphous mass of partially coked resid. The black "glass" found in plugged lines is solidified amorphous coke. 

Amines color, 90, 92-93 salts, 98 strength, 102-104,110 flow control, 104 dehydration, 104 104 dehydration, 104 Ammonia, 82, 98, 227, 301, 310 water washing, 310 Ammonium hydrosulfide, 423 Amorphous coke, 42 Analyzer control, 114 Annular flow, 77 Anode material, 48 Antifoam agents, 40, 100 Anti-foulant chemicals, 27 Antimony, 164, 171 flow loss (catalyst), 171... 

Although Raman spectroscopy is very useful for identification and quantitation of carbonaceous species in various matrices, carbon is the most problematical filler. Common carbon fillers (amorphous coke or graphite) are strong Raman scatterers, but they also strongly absorb the Raman scattered light from the polymer. Thus, a carbon-filled polymer often displays only the spectrum of carbon, or if excessive laser power is used, the sample is burnt by laser absorption. When using 1064 nm excitation (FT-Raman) carbon-filled samples are strongly heated and will incandesce. 

Fluid coke is produced in a fluidized bed reactor where the heavy oil feedstock is sprayed onto a bed of fluidized coke. The oil feedstock is cracked by steam introduced into the bottom of the fluidized bed reactor. Vapor product is drawn off the top of the reactor while the coke descends to the bottom of the reactor and is transported to a burner where a portion of the coke is burned to operate the process. Fluid coke reactors are operated at about 510 - 540°C (950 - 1000 F). Flexicoke is a variant cm fluid coke, where a gasifier is added to the process to increase coke yields. Fluid coker installations tend to have yields that are lower than delayed coker installations, while flexicoker installaticms have yields that can be significantly greater than delayed coker installations. Fluid cokers produce layered and non-layered cokes. Both delayed and fluid coke installations produce amorphous, incipient, and mesophase cokes with the amorphous cokes having higher volatility and mesophase cokes having the lowest volatility. 

Metal dusting is a special form of catastrophic corrosion that takes place in carbon-containing environments where the carbon activity exceeds a value of 1 [26,27]. For Fe-based materials the principles are shown schematically in Figure 13.17. The catalytic effect of the metal or cement-ite surface leads to a dissociation of the carbon-containing gaseous species (CO , C ,Hy) with the effect of carbon uptake into the metal subsurface zone and carbon deposition (amorphous coke) on the surface. This mechanism is evidently influenced by the crystallographic situation of the metal grains on the material surface [28]. For carbon monoxide (CO) adsorbed on metal... 

Amorphous Silica—Alumina Based Processes. Amorphous siHca—alumina catalysts had been used for many years for xylene isomerization. Examples ate the Chevron (130), Mamzen (131), and ICI (132—135). The primary advantage of these processes was their simpHcity. No hydrogen was requited and the only side reaction of significance was disproportionation. However, in the absence of H2, catalyst deactivation via coking... 

Coke deposition is essentially independent of space velocity. These observations, which were developed from the study of amorphous catalysts during the early days of catalytic cracking (11), stiU characteri2e the coking of modem day 2eohte FCC catalysts over a wide range of hydrogen-transfer (H-transfer) capabihties. 

The activation energy for burning from a coked zeoHte has been reported as 109 kj/mol (29) and 125 kj/mol (30 kcal/mol) has been found for coke burning from a H-Y FCC catalyst. Activation energies of 167 kJ/mol (40 kcal/mol) (24) and 159 kJ/mol (25) have been reported for the burning of carbon from a coked amorphous siUca-alumina catalyst. 

The CF and GF represent the coke- and gas-forming tendencies of an E-cat compared to a standard steam-aged catalyst sample at the same conversion. The CF and GF are influenced by the type of fresh catalyst and the level of metals deposited on the E-cat. Both the coke and gas factors can be indicative of the dehydrogenation activity of the metals on the catalyst. The addition of amorphous alumina to the catalyst will tend to increase the nonselective cracking, which forms coke and gas. 

Graphite is a denser crystalline form of carbon. Graphite anodes are prepared by heating calcined petroleum coke particles with a coal tar pitch binder. The mix is then shaped as required and heated to approximately 2 800°C to convert the amorphous carbon to graphite. Graphite has now superseded amorphous carbon as a less porous and more reliable anode material, particularly in saline conditions. 

In addition to graphite, diamond, and Cso, carbon exists in several "amorphous" forms. These include charcoal, soot, lampblack, and coke, some of which have important industrial uses. 

These forms of carbon are also known to have some order, so they are not completely amorphous. When appropriately prepared (so-called activated charcoal), charcoal has an enormous surface area, so it is capable of adsorbing many substances from both gases and solutions. As was described in Chapter 11, coke is used on an enormous scale as a reducing agent in the production of metals. The "amorphous" forms of carbon can be transformed into graphite by means of the Acheson process, in which an electric current heats a rod of the "amorphous" form. 

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