Process formed coke

Comparing the overall concentrations of these different carbons designated generally as structural patterns , measured before and after a process such as FCC or hydrocracking (see Chapter 10), enables the conversion to be monitored the simple knowledge of the percentage of condensed aromatic carbon of a feedstock gives an indication of its tendency to form coke. 

Influence of the type of process fluid coking", compared to delayed coking" makes a harder coke that contains less volatile matter and forms finer grains. 

Refinery Production. Refinery propylene is formed as a by-product of fluid catalytic cracking of gas oils and, to a far lesser extent, of thermal processes, eg, coking. The total amount of propylene produced depends on the mix of these processes and the specific refinery product slate. For example, in the United States, refiners have maximized gasoline production. This results in a higher level of propylene production than in Europe, where proportionally more heating oil is produced. 

In the fluid coking process, part of the coke produced is used to provide the process heat. Cracking reactions occur inside the heater and the fluidized-bed reactor. The fluid coke is partially formed in the heater. Hot coke slurry from the heater is recycled to the fluid reactor to provide the heat required for the cracking reactions. Fluid coke is formed by spraying the hot feed on the already-formed coke particles. Reactor temperature is about 520°C, and the conversion into coke is immediate, with... 

Zeolites have led to a new phenomenon in heterogeneous catalysis, shape selectivity. It has two aspects (a) formation of an otherwise possible product is blocked because it cannot fit into the pores, and (b) formation of the product is blocked not by (a) but because the transition state in the bimolecular process leading to it cannot fit into the pores. For example, (a) is involved in zeolite catalyzed reactions which favor a para-disubstituted benzene over the ortho and meso. The low rate of deactivation observed in some reactions of hydrocarbons on some zeoUtes has been ascribed to (b) inhibition of bimolecular steps forming coke. 

Carbon Deposition. The processing of hydrocarbons always has the potential to form coke (soot). If the fuel processor is not properly designed or operated, coking is likely to occur. Carbon deposition not only represents a loss of carbon for the reaction but more importantly also results in deactivation of catalysts in the processor and the fuel cell, due to deposition at the active sites. 

Metallurgical coal coal that meets the requirements for use in the steelmaking process to manufacture coke it must be low in ash and sulfur and form coke that is capable of supporting the charge of iron ore and limestone in a blast furnace. 

Microcat-RC process (M-Coke process) a catalytic hydroconversion process operating at relatively moderate pressures and temperatures using catalyst particles, containing a metal sulfide in a carbonaceous matrix formed within the process, that are uniformly dispersed throughout the feed because of their ultra small size (10-4 inch diameter) there are typically several orders of magnitude more of these microcatalyst particles per cubic centimeter of oil than is possible in other types of hydroconversion reactors using conventional catalyst particles. 

The results show that the specificities of catalyst deactivation and it s kinetic description are in closed connection with reaction kinetics of main process and they form a common kinetic model. The kinetic nature of promotor action in platinum catalysts side by side with other physicochemical research follows from this studies as well. It is concern the increase of slow step rate, the decrease of side processes (including coke formation) rate and the acceleration of coke transformation into methane owing to the increase of hydrogen contents in coke. The obtained data can be united by common kinetic model.lt is desirable to solve some problems in describing the catalyst deactivation such as the consideration of coke distribution between surfaces of metal, promoter and the carrier in the course of reactions, diffusion effects etc,. 

While originally designed for cracking the overhead stream from vacuum distillation units, known as vacuum gas oil (4), most FCC units currently operate with some higher boiling vacuum distillation bottoms (Resid) in the feed. Table 5.1 illustrates the difficult challenges faced by refiners, process licensors and FCC catalysts producers the resid feeds are heavier (lower API gravity), contain many more metals like Ni and V as well as more polyaromatic hydrocarbons prone to form coke on the catalysts (Conradson Carbon Residue, or CCR). 

Immediately after cracking, the cracked gases are reduced in temperature as quickly as possible to stop the cracking processes and prevent the cracked gases forming coke. This quenching is often referred to as the transfer-line-heat-exchange (TEE). Excess steam is condensed and the water recycled (not shown). Heat from the TEE is recovered as process steam. 

Carbonization refers to the heating of bituminous coal in ovens or retorts sealed from air to form coke. The process involves thermal decomposition of the coal with distillation of the products. Various technologies are used which perform the process at (i) low temperature (500-750 C), (ii) medium temperature (750-900°C) and... 

The other cause is the catalytic disproportionation of two normal adjacent carbenium ions to yield a paraffin and a site-spanning di-ion which deactivates two sites. This is a minor catalytic process it can form coke, but at the same time it yields valuable complex products, notably aromatics. In fact, this process can in principle be engineered not to form coke if an appropriate reaction environment can be arranged. 

Acidic zeolites are known for their excellent catalytic activity in cracking and isomerization of hydrocarbons (75). In the absence of metal, however, these catalysts rapidly deactivate due to the formation of carbonaceous products, usually referred to as coke. The carbonaceous residues are mainly formed via alkylaromatics and polyaromatics, which are the result of dehydrogenation, cyclization, and further alkylation processes. The coke deposits lower the catalytic activity by site poisoning and eventually also by pore blocking, which inhibits access of hydrocarbon molecules to the acid sites (286). 

Hydrogen is also formed in large quantities as a byproduct in petrochemical processes, refineries, coking plants (coke oven gas) and in chemical and electrochemical processes e.g. chloralkali-electrolysis. Other processes such as the photochemical production of hydrogen or thermal dissociation of water are only used in special applications and are currently industrially unimportant. 

Formed coke Based on a presentation by Langhoff, Figure 409 shows a generally valid schematic into which all formed coke processes can be fitted... 

Figure 409. Block diagram of the different processes for formed coke manufacturing ...

A predominant number of formed coke processes use roller briquetting. This is due to the fact that relatively coarse coal particles can be agglomerated at widely variable conditions and that, ultimately, roller briquetting equipment can be easily scaled up to handle large tonnages of coal. 

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