Kinetic analysis of vacuum residue hydrocracking in early reaction stages

In this work, a lumped kinetic model for the hydrocracking of vacuum residue (VR) from Maya crude oil was developed. A preliminary kinetic analysis based on the conversion of VR was performed. Next, ten models with increasing level of complexity were proposed and solved sequentially using Matlab® software. All models included four lumps: products with boiling point >450 C (L+), products with boiling point <450 C (L-), gas and coke. Kinetic parameters were estimated from the experimental data obtained in a microbomb batch reactor at three temperatures (400, 425 and 450 C) and four holding times (10, 30, 60 and 90 min). Two catalysts, NiMo/Al₂O₃ and NiMo/Al₂O₃-Cr (alumina doped with chromium), were tested. Kinetic results showed that gas was mainly produced from the decomposition of L- at low temperatures, whereas at 450 C gas is predominantly formed from cracking of L+. Moreover, coke was found to be exclusively produced from L+ at all temperatures. In general, NiMo/Al₂O₃ gave rise to higher yields of L- than NiMo/Al₂O₃-Cr. Nevertheless, NiMo/Al₂O₃-Cr was able to retain greater activity at higher temperatures.