Production of high yields of light olefins from heavy hydrocarbons

A process for conversion of hydrocarbon feedstock into light olefins of C2-C4 carbons in the presence of a catalyst system, the process comprising:

• cracking of the hydrocarbon feedstock in a temperature of range of 550° C. to 650° C., weight hourly space velocity (WHSV) in a range of 100-300 hr−1 and a pressure in a range of 1-4 kg/cm2 g in a concentric downflow reactor,
• wherein the catalyst system comprises 7-10 wt % of an ultra-stable Y zeolite;
• 4-8 wt % of a shape selective pentasil zeolite;
• 2.5-5 wt % of a bottom selective material, wherein the bottom selective material is mesoporous acidic alumina;
• 0.5-2 wt % of rare earth metals;
• and 75-88 wt % of a support material,
• wherein the hydrocarbon feedstock comprises feedstock selected from the group consisting of C4, reduced crude oil, Vacuum Residue, Hydrotreated Vacuum Gas Oil (HDT-VGO) and hydrocracker bottom,
• wherein the catalyst is present in the range 25-40 wt. % of the hydrocarbon feedstock, and
• recycling 0 to 50% of products from the concentric downflow reactor
• to yield 40-65 wt % of fresh hydrocarbon feedstock as light olefins of C2-C4 carbons.