Cracking of long chain n-paraffins on silica—alumina and rare earth exchanged Y zeolite
✍ Scribed by R.V. Shendye; R.A. Rajadhyaksha
- Publisher
- Elsevier Science
- Year
- 1992
- Tongue
- English
- Weight
- 725 KB
- Volume
- 47
- Category
- Article
- ISSN
- 0009-2509
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✦ Synopsis
The present work reports for the first time a study of cracking of model parafIinic compounds in the boiling range of vacuum gas oil. The cracking reactions are investigated on commercial silica-alumina catalysts and rare earth exchanged Y zeolite (REY) using the ASTM procedure for microactivity test. Effect of alumina content, temperature and hydrothermal treatment on activity and product selectivity is studied. Increase in alumina content results in higher activity without significant difference in product selectivity. Hydrothermal treatment results in decrease in the quantity of Cl-C+ products. RE-Y exhibited higher activity as compared to silica-alumina. The yield of gasoline and middle distillate range products was found to be higher on RE-Y. The product patterns are analysed on the basis of a detailed mechanism in the following paper. WTRODUCTION Catalytic cracking of normal partins is a reaction of considerable importance due to its relevance to ffuidtied-bed catalytic cracking (FCC) which is the largest scale catalytic process practised in industry. Cracking of' n-paraffins is of special relevance to FCC due to various reasons. n-Par&ins have low crackability as compared to most other components of the vacuum gas oil. The distribution of products obtained from cracking of n-paraffins is of even greater importance to refiners. n-Paraffins in the high boiling range of diesel increase the pour point of diesel and hence are undesirable. n-Paraffins are also undesirable in the gasoline range due to their lower octane rating. In view of this, cracking of n-paraffins has been extensively investigated on a wide variety of catalysts (Wojciechowski and Corma, 1986). However, most of the studies have been carried out using low molecular weight compounds. Although these studies are very helpful in discerning the mechanism of paraffin cracking, they offer little information regarding the distribution of products obtainable from cracking of larger molecules. The reported studies on cracking of long chain paraffins have been very limited (Greensfelder and Voge, 19&a, b; Higbtower and Emmett, 1965; Nate, 1969a. b). Greensfelder and Voge have studied cracking of a series of n-paraffins in the C,-C2,+ range on a commercial silica-aluminazirconia catalyst. Hightower and Emmett studied mechanistic aspects of cracking of n-hexadecane using radioactive tracer compounds on silica-alumina catalysts. Nate (1969a, b) has reported cracking of Rhexadecane and Cs-Cla olefins on silica-alumina and rare earth exchanged zeolite X.