Paraffins fluid catalytic cracking

The olefins ethylene and propylene are highly important synthetic chemicals in the petrochemical industry. Large quantities of such chemicals are used as feedstock in the production of polyethylene, polypropylene, and so on [31]. The prime source of lower olefins is the olefin-paraffin mixtures from steam cracking or fluid catalytic cracking in the refining process [32]. Such mixtures are intrinsically difficult to... 

Zeolite catalysts provide the cracking function in many hydrocracking catalysts, as they do in fluid catalytic cracking catalysts. Zeolites are crystalline aluminosilicates, and among all commercial catalysts, the zeolite used at present is faujasite. Pentasil zeolites, including silicalite and ZSM-5 are also used for their ability to crack long chain paraffins selectively. 

Dupain, X., Krul, R.A., Schaverien, C.J., Makkee, M., Mouhjn, J.A., 2006. Production of clean transportation fuels and lower olefins from Fischer—Tropsch synthesis waxes under fluid catalytic cracking conditions. The potential of highly paraffinic feedstocks for FCC. Applied Catalysis B 63, 277—295. 

Olefins crack more readily than paraffins since double C=C bonds are more friable under reaction conditions. Iso-paraffins and naphthenes are cracked more readily than normal paraffins, which in turn are cracked more readily than aromatics. In fact, aromatic ring compounds are very resistant to cracking, since they readily deactivate fluid cracking catalysts by blocking the active sites of the catalyst (see the next part). The reactions postulated for olefin compounds apply principally to intermediate products within the reactor system, since the olefin content of catalytic cracking feedstock is usually very low. 

The high influence of cracking catalyst on PE conversion was confirmed by Aguado et al. [11] in a continuous screw kiln reactor. The application of a sophisticated laboratory Al-MCM-41 cracking catalyst and process temperature of 400-450°C led to 85-87% yield of gas and gasoline fractions (C1-C12). Besides olefins and n- and iso-paraffins some quantity of aromatics, 5 wt% was determined in the process products. In the same reactor system with a noncatalytic process the gas yield was halved while similarly as in case of the fluid reactor system yields of gas oil and heavy waxes fraction (C13-C55) attained values of 62% (compared with 4 wt% in catalytic process) [12]. 

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