Activated carbon catalysts hydrocracking

Coprocessing of waste plastics with heavy petroleum fractions have considerable interest in feedstock recycling. In this study, we aimed to investigate the processing of municipal waste plastics (MWP) in presence of conventional and non-conventional catalysts in a refinery stream. For this purpose, the hydrocracking of MWP in vacuum gas oil (VGO) over metal loaded active carbon and conventional acidic catalysts (HSZM-5, DHC-8) was carried out to obtain liquid fuel. 2 refs. 

In hydrocracking of HVGO alone the reason for decreased gas formation over Co-AC catalyst (compared with a thermal run) may be the fact that the activated carbon leads to the formation of more H or HS which terminates the radical degradation pathy-ways. However, in the case of a blend, in the absence of catalytic activity, hydrocarbon quenching (with radicals from derivated plastics) may be more pronounced than hydrogen quenching (with H ). 

As a result, MWP sorted from municipal solid wastes can be processed in a refinery, which has a dechlorination unit installed prior to the hydrocracking unit. Even though commercial catalysts showed satisfactory performance at high temperatures, neutral catalysts based on activated carbon can also be utilized for this purpose. 

Figure 4 shows that the relative activity for n-pentane Isomerization drops linearly with the amount of carbon deposited on the acid function of the catalyst. This is so because isomerization of n-pentane is a typical bifunctional reaction controlled by the acid function of the catalyst. Hydrocracking to propane shows... 

Fig. 4 (left). Relative catalytic activity for the n-pentane reactions at 500 C on commercially coked catalysts as a function of carbon content. A, isomerization. , hydrocracking. , dehydrocyclization. o hydrogenolysis... 

By this time we were doing about as well as had been done previously with a molybdenum oxide alumina catalyst, but with considerably less carbon formation. So now things became more serious, but not serious enough to get people very excited about it. After all, we had been using a 3% platinum on silica catalyst, and even in those days 3% platinum was pretty expensive. Platinum on silica-alumina did much better with respect to octane number but we could not control the hydrocracking very well, so we switched to alumina which had an intermediate activity. The results looked pretty good, particularly because we could run for days without much loss in activity. 

The reforming process consists of exothermic reactions (isomerization, hydrocracking) and endothermic reactions (dehydrogenation, dehydrocyclization). In summary the process is endothermic. Several parallel and sequential reactions with diEFerent rates and equilibrium limitations take place (Table 6.9.1). In addition, coke formation occurs, which leads to a gradual decrease of the activity of the catalyst To minimize coke formation hydrogen is added in a large excess to the feed, that is, H2 formed by dehydrogenation and dehydrocydization is recycled. Nevertheless, coke must be burned off after a certain carbon load has been reached. 

A metal, a metal oxide, a metal sulfide, or a combination of these compounds may supply the metal function of the catalyst. The key requirement for the metal function is that it must activate hydrogen and catalyze dehydrogenation and hydrogenation reactions. In addition, metal-catalyzed hydrogenolysis (carbon-carbon breaking) is undesirable because the distribution of the hydrogenolysis products is less desirable relative to hydrocracking. 

These results are interpreted as an influence of the liquid-vapour equilibrium leading to increased effective residence times of products. These residence times depend on the nature of the interface gas-solution or gas-liquid-solid. The contact time of the products with the active metal increases very rapidly with carbon number (e.g. 1 hour for octane in the liquid phase) due to the existence of a condensed phase solution or product in the pore structure of the catalyst. This effect, in addition to the corresponding increase in concentration of heavy hydrocarbons in the condensed phase, modifies the formal kinetic scheme of this complex reaction by the interference of secondary hydrocracking heavy hydrocarbons are converted to methane and linear or branched light hydrocarbons. The simulation of this kinetic network has led to selectivities in excellent accordance with the experimental results. 

The first Y-zeolite hydrocracking catalysts contained residual sodium ions in the sodalite cages that were mobile during operation and they entered the supercage. This led to a loss of cracking activity. Treatment of the zeolite with an anunonium salt solution removed the mobile sodium ions and restored acidity. The redistribution of palladium with ammonia solution could be combined with an exchange of sodium ions to rejuvenate the catalyst in one step. This was done before reactivation by burning off the carbon deposits. 

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