Reconversion of Olefinic Cuts from Fluidized Catalytic Cracking Naphthas

Abstract

The feasibility of reconversion of a highly olefinic cut (OLEF; 60−110 °C), obtained from the bottoms of depentanizer columns used to separate the C5 fraction from fluidized catalytic cracking (FCC) naphtha, was studied under realistic FCC conditions over two equilibrium commercial catalysts. A riser simulator reactor was used at 500 and 550 °C, a catalyst-to-oil ratio of 5.6, and short reaction times of up to 15 s to assess (a) the crackability and the products of the conversion of the cut OLEF, (b) the conversion of a standard vacuum gas oil feed (VGO) to be used as a reference, and (c) the conversion of a mixture with a mass ratio of 20:80 OLEF−VGO. The gas fraction in the conversion of OLEF showed high yields of propene and isobutane, while aromatics and i-paraffins appeared among products with the same range of molecular weights as the feedstock, thus determining a research octane number value in the gasoline cut that is higher than the feedstock's. Olefins showed to be converted selectively. The conversion of the mixture OLEF−VGO showed the following main characteristics that differ from the standard operation (VGO feedstock): (i) an increase in the yield of gasoline, which is higher than the one expected from the separate conversion of equivalent masses of the individual feedstocks, (ii) an increase in the yield of liquified petroleum gas and some individual hydrocarbons, like propene or isoamylenes, and (iii) a better octane-barrel balance in gasoline. The particular characteristics of each catalyst (activity and hydrogen transfer capability) reflected clearly on the product distributions obtained in the conversion of the various feedstocks. This recycling option appears as very interesting because it could contribute to improve the refinery's economy through the improvement of different issues.