Catalytic Cracking and Reforming

Since 1938, the development of methods of applying or handling catalysts in the production of gasoline has become fundamentally important to all chemical industry as well as to the petroleum industry. The approximate capacities of such plants during 1955 were  

Catalytic cracking constitutes about 60 per cent of all cracking capacity, and catalytic reforming about 70 per cent of all reforming capacity. 

Theory. Porous adsorbent catalysts of the silica alumina type are widely used. The fact that one or more hydrous metallic oxides are present in all successful catalysts suggests that water in some way is important in this type of catalysis. Nevertheless, completely satisfactory explanations of the mechanism of catalytic cracking have not been presented. Greensfelder and associates have studied the cracking of dozens of paraffinic, naphthenic, and aromatic hydrocarbons. They find that 

Paraffins crack preferentially at such linkages that fragments containing three or four carbon atoms are produced. Normal paraffins tend to crack at the gamma carbon-carbon bonds or still nearer the center of the molecule so that yields of methane and two-carbon-atom gases are low. Long chains tend to crack simultaneously at several places. 

Naphthenes also tend to yield fragments of three or four carbon atoms, and they crack both in the ring and in the chain especially if the chain contains more than three carbon atoms. 

---

Catalytic cracking and reforming. The polymer chains are broken down by the effect of a catalyst, which promotes cleavage reactions. 

While many studies have been carried out aimed at the feedstock recycling of rubber wastes by pyrolysis and hydrogenation processes (see Chapters 5 and 7), little information is found on the catalytic cracking and reforming of rubber alone. Larsen35 has disclosed that waste rubber, such as used tyres, can be degraded in the presence of molten salt catalysts with properties as Lewis acids, such as zinc chloride, tin chloride and antimony iodide. The decomposition proceeds at temperatures between 380 and 500 °C to yield gases, oil and a residue, in proportions similar to those obtained by simple thermal decomposition. 

Five main methods of feedstock recycling have been considered in this book, classified according to the degradation conditions and the products obtained chemical depolymerization, gasification, thermal treatments, catalytic cracking and reforming, and hydrogenation. 

As more complex operations, such as catalytic cracking and reforming were introduced, more complex instrumentation and controls were needed to operate the plants safely and economically. Pneumatic units replaced manual controllers as operations became more complex. These were subsequently replaced by electronic controllers, then by programmed smart controllers, and eventually by computerized systems. Each evolution required that operators, instrument technicians, and analyzer technicians have more and more technical training to understand process operations and perform their Job safely and profitably. A gradual evolutionary process occurred and many employees evolved into technicians. They were no longer just blue collar workers. 

These equations show that the hydrogenation process can be likened to the processes of catalytic cracking and reforming of petroleum in which a variety of saturated, unsaturated, aromatic and naphthenic compounds are produced [Macrae, 1966b],... 

The presence of unsaturated and aromatic compounds indicate that the severe reaction conditions for the hydrogenation process [Anagho et al., 2004] led to further breakdown and re-arrangement of the oils produced. This process could be likened to the processes of catalytic cracking and reforming. 

The current raw material base for the production of nylon 66 is benzene, which is derived almost entirely from catalytic cracking and reforming of petroleum. Catalytic reduction of benzene to cyclohexane followed by catalyzed air oxidation gives a... 

Ethylene glycol for the synthesis of PET is obfained by air oxidation of ethylene to ethylene oxide (Section 11.8A) followed by hydrolysis to the glycol (Section 11.9A). Ethylene is, in turn, derived entirely from cracking eifher petroleum or ethane derived from natural gas (Section 2.9A). Terephthalic acid is obtained by oxidation of p-xylene, an aromatic hydrocarbon obtained along with benzene and toluene from catalytic cracking and reforming of naphtha and other petroleum fractions (Section 2.9B). 

The main types of feedstock recycling processes can be summarised as chemical depolymerisation, gasification and partial oxidation, thermal degradation, catalytic cracking and reforming, and hydrogenation [852663]. The current advanced thermal treatments are as follows [a.372]. 

Phases of processing other than heavy-oil distillation processes are discussed in many chapters, particularly under treating (Chaps. 10-11), dewaxing (Chap. 12), thermal cracking (Chap. 19), chemical manufacture (Chap. 20), catalytic cracking and reforming (Chap. 21), and natural gasoline (Chap. 22). 

---