Isomerization hydrocracking

Aluminum chloride has extensive commercial applications. It is used primarily in the electrolytic production of aluminum. Another major use involves its catalytic applications in many organic reactions, including Friedel-Crafts alkylation, polymerization, isomerization, hydrocracking, oxidation, decarboxylation, and dehydrogenation. It is also used in the production of rare earth chlorides, electroplating of aluminum and in many metal finishing and metallurgical operations. 

Reforming Gasolines, naphthas High-octane gasolines, aromatics 850-1000°F 455-535°C Dehydrogenation, dehydroisomerization, isomerization, hydrocracking, dehydrocyclization... 

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... 

The acidity reached with this promotion is enough to catalyze skeletal isomerization, hydrocracking and other reactions important in reforming. 

It does not influence the dehydrogenating activity but affect the isomerization, hydrocracking and, dehydrocyclization reactions. 

Catalytic reforming Catalytic cracking Naphtha b.p. 30-190°C H, (6 1) Fractions b.p. 220-540°C 0.3-0.5% Pt on y-AI2O3 promoted by 1% chlorine. Zeolite or + SiO 500-525°C 23.3 atm 500-550°C 1 atm Dehydrogenation Isomerization (Hydrocracking) Carbonium ion reactions (acidic sites) Aromatics Alkanes Gasoline (high olefin content)... 

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. 

LHSV, h per reactor isomerization 5.5 isomerization, hydrocracking, dehydrocyclization 2.4 1.7... 

Catalysis. As of mid-1995, zeoHte-based catalysts are employed in catalytic cracking, hydrocracking, isomerization of paraffins and substituted aromatics, disproportionation and alkylation of aromatics, dewaxing of distillate fuels and lube basestocks, and in a process for converting methanol to hydrocarbons (54). 

Catalytic conversion processes include naphtha catalytic reforming, catalytic cracking, hydrocracking, hydrodealkylation, isomerization, alkylation, and polymerization. In these processes, one or more catalyst is used. A common factor among these processes is that most of the reactions are initiated hy an acid-type catalyst that promotes carhonium ion formation. 

Catalytic reformers are normally designed to have a series of catalyst beds (typically three beds). The first bed usually contains less catalyst than the other beds. This arrangement is important because the dehydrogenation of naphthenes to aromatics can reach equilibrium faster than the other reforming reactions. Dehydrocyclization is a slower reaction and may only reach equilibrium at the exit of the third reactor. Isomerization and hydrocracking reactions are slow. They have low equilibrium constants and may not reach equilibrium before exiting the reactor. 

Detergent manufacturing Catalytic cracking and hydrocracking Xylene isomerization, benzene alkylation, catalytic cracking, catalyst dewaxing, and methanol conversion. 

It should be noted that many practically important catalytic transformations (such as isomerization of or hydrocracking of paraffins), which are presumed to proceed via consecutive mechanisms, are performed on multifunctional catalysts, with which the coupling of reactions in the sense just discussed may not necessarily occur. The problem of the selectivity of some models of polystep reactions on these catalysts has been discussed in detail by Weisz (56). 

Production of p-xylene via p-xylene removal, i.e., by crystallization or adsorption, and re-equilibration of the para-depleted stream requires recycle operation. Ethylbenzene in the feed must therefore be converted to lower or higher boiling products during the xylene isomerization step, otherwise it would build up in the recycle stream. With dual-functional catalysts, ethylbenzene is converted partly to xylenes and is partly hydrocracked. With mono-functional acid ZSM-5, ethylbenzene is converted at low temperature via transalkylation, and at higher temperature via transalkylation and dealkylation. In both cases, benzene of nitration grade purity is produced as a valuable by-product. 

Figure 4.17 Cracking and isomerization pathways of paraffins in hydrocracking (M, metallic site A, acidic site).

Catalytic processes (finid catalytic cracking, catalytic hydrocracking, hydro-treating, isomerization, ether manufacture) also create some residuals in the form of spent catalysts and catalyst fines or particulates. The latter are sometimes separated from exiting gases by electrostatic precipitators or filters. These are collected and disposed of in landfills or may be recovered by off-site facilities. The potential for waste generation and hence leakage of emissions is discussed below for individual processes. 

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