GB818219A - Improvements in or relating to a process for the catalytic cracking of hydrocarbon oils - Google Patents

Abstract

A hydrocarbon oil boiling essentially above the gasoline range is cracked to give gasoline by: (1) introducing it as vapour into a narrow first reaction zone together with 5-15 parts by weight (per part of oil) of a freshly regenerated finely-divided cracking catalyst and passing them as a suspension through the zone for a contact time of 1-4 seconds at a velocity (defined below) of 2.4-18 metres per sec. and above that at which the catalyst will fluidize, the conversion being at least 40 per cent; (2) separating hydrocarbon vapours and catalyst and passing the former together with hydrocarbon vapours from the second reaction zone (see below) to a fractionating zone where there are separated gasoline product and oil boiling essentially above gasoline; (3) part of the oil boiling above gasoline from the fractionating zone such that the combined feed ratio (defined below) is between 1.5 and 2.8 is passed to the second reaction zone, the remainder being withdrawn as product; (4) passing partially used catalyst from the first reaction zone to the second reaction zone where conditions are maintained for a contact period of at least 2 minutes and a conversion of 10-40 per cent, the temperature being below that in the first reaction zone; (5) separating catalyst from the hydrocarbon vapour effluent which latter is then passed to the fractionating zone. The velocity is defined as the arithmetic average of the velocities at the beginning and end of the first reaction zone; the combined feed ratio is the ratio of the volume of feed passed to both reaction zones to that passed to the first reaction zone; first stage and total conversion are defined as 100 minus the percentage of oil recovered boiling above 232 DEG C. (450 DEG F.) from the first stage and total reaction products respectively, the difference between these being the second stage conversion. The catalyst is conventional, e.g. silica-alumina or activated clay, it is preferably fluidized in the second reaction zone and may thereafter be regenerated and returned to the first reaction zone. First stage reaction temperature is preferably at least 510 DEG C. and may be up to 580 DEG C. The feed preferably contains less than 0.5 per cent boiling below 232 DEG C.