Process of Catalytic Reforming

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. 

Depending on the type of regeneration (coke bum-off), reforming processes are classified into three types (i) semi-regenerative, (ii) cychc regenerative, and (iii) continuously regenerative. 

In cyclic processes regeneration is achieved by swinging one of several reactors (typically 4—6) off-line for coke bum-off while the others continue to operate. 

In 1992, 74% of the commercial reforming plants operating in the USA, Japan, and Europe were semi-regenerative, 11% cyclic, and 15% continuous (Farrauto and Bartholomew, 1997). 

The reforming reactor(s) must be designed to cope with the variety of reactions that take place. To optimize each of the different reactions, a series of separate reactors, usually three, is used. The liquid hourly space velocity (LHSV) is in a range of 1-3 m liquid feed per m catalyst bed volume and hour. Initially, the reactors had 

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The process of catalytic reforming is utilized for the production of high-octane-number compounds from lower-octane-number fractions. It is an endothermic process which requires heat and a catalyst in order to maintain a constant reaction rate. Hydrogen is also produced in significant quantities through the reforming process. 

However, the major source of these hydrocarbons is now petroleum. Although aromatic compounds do occur naturally in petroleum, they are mainly obtained by the process of catalytic reforming, in which aliphatic hydrocarbons are aromatized through dehydrogenation, cyclization and isomerization. The process, which is also known as hydroforming, is carried out under pressure at 480-550 °C in the presence of a catalyst, typically chromium(III) oxide or alumina. Benzene is thus produced from... 

Finally, by the process of catalytic reforming (Sec. 12.4) enormous quantities of the aliphatic hydrocarbons of petroleum are converted into aromatic hydro... 

Still larger quantities of aromatic hydrocarbons are needed, and these are synthesized from alkanes through the process of catalytic reforming (Sec. 9.3). This can bring about not only dehydrogenation as in the formation of toluene from methylcyclohexane, but also cyclization and isomerization as in the formation of toluene from //-heptane or 1,2-dimethylcyclopentane. In an analogous way, benzene is obtained from cyclohexane and methylcyclopentanc, as well as from the hydrodealkylation of toluene. 

The process of catalytic reforming introduces chains, and catalytic cracking introduces double bonds. Not only do these two processes increase the amount of gasoline that s produced, but they also improve the quality of the gasoline s burning characteristics. Also notice that benzene, an aromatic compound, has an octane value of 106. Its burning characteristics are better than isooctane. Other substituted aromatic compounds have octane ratings of almost 120. However, benzene and some related compounds are health hazards, so they re not used. 

For many years benzene was made from coal tar even as late as 1949, when all of it was made by this old process. New processes began to take over in the 1950s, which were used for 50% of the benzene in 1959, 94% in 1972, 96% in 1980, and near 100% in the 1990s. These new processes consist of catalytic reforming of naphtha and hydrodealkylation of toluene in a 70 30 capacity ratio. 

The Platforming-Udex process for catalytic reforming of naphtha is also used for toluene. The feedstock should be rich in seven carbon naphthenes such as dimethylcyclopentanes, methylcyclohexane, and ethylcyclopentane... 

The first suggestions concerning the mechanism of catalytic reforming were based on studies with hydrocarbon mixtures that permitted only observation of composition changes.91,98,120 It was observed, for example, that about 30% of the Ci—C4 product consisted of methane and ethane. These, however, are not common products in catalytic cracking processes. In fact, when n-heptane was hydrocracked, less methane and ethane were formed than expected, according to the stoichiometry of Eqs. (2.15) and (2.16). Therefore, C5 and C6 hydrocarbons were not considered... 

A number of refinery processes require the use of a fixed-bed catalyst These processes include catalytic reforming, hydrodesulfurization, hydrotreating, hydro-cracking, and others. These catalysts become inactive in six months to three years and are eventually replaced in the reactors with fresh catalyst during a unit shutdown. Many of these catalysts contain valuable metals which can be recovered economically. Some of these metals, such as platinum and palladium, represent the active catalytic component other metals such as nickel and vanadium are contaminants in the feed which are deposited on the catalyst during use. After valuable metals are recovered (a service usually performed by the outside companies), the residuals are expected to be disposed of as solid waste. 

Early reported studies on the application of bifunctional catalysts to the foregoing reactions were those of Haensel and Donaldson (H2), Ciapetta and Hunter (C2, C4, C5), Heinemann and co-workers (H3), and Hettinger and co-workers (H7). These reactions form the heart of catalytic reforming and have been exploited commercially in a number of processes, including the following ... 

For many years benzene (benzol) was made from coal tar, but new processes that consist of catalytic reforming of naphtha and hydrodealkylation of toluene are more appropriate. Benzene is a natural component of petroleum, but it cannot be separated from crude oil by simple distillation because of azeotrope formation with various other hydrocarbons. Recovery is more economical if the petroleum fraction is subjected to a thermal or catalytic process that increases the concentration of benzene. 

The fifth chapter discusses the catalytic reforming of hydrocarbons from the point of view of the individual types of chemical reactions involved in the process and the nature of the catalysts employed. Some consideration is also given to technological aspects of catalytic reforming (103 references). 

Such two-step processes are also referred to as cracking-catalytic reforming (CCR) processes. The catalytic reforming stage of the primary oil product ensures high-quality diesel or gasoline products are obtained. The catalytic reforming step improves the RON and the contents of isomer, cycloparafflns and aromatics. 

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