(242f) Insight into the Mechanism of Coke Formation during Cracking of Heavy Residues in a Novel Laboratory Scale Assembly

In the recent past, the share of heavy and extra-heavy crude oils which make up for about 80% of the worldâ??s remaining reserves¹ is steadily increasing in the refinery diet. Refining of these unconventional oils results in the production of increased proportion of residues, in particular vacuum residue² whose processing has become a challenging task. Therefore, it has become very vital for the refiners to have flexible options to deal with these heavy ends (bottom-of-the-barrel) which are obtained by processing unconventional oils.³ One of the critical challenges in processing unconventional oils and in turn bottom-of-the-barrel (BOB) is the formation of coke⁴ at the expense of lighter valuable hydrocarbon fractions. It is, therefore, very important to detect the inception of coke formation while processing heavy residues at different operating conditions. In the present communication, a novel laboratory scale autoclavable reactor has been proposed to address some of the issues associated with processing of heavy residues. The proposed autoclavable reactor is made up of SS-316 having 400 mL capacity. The reactor has internal diameter and outer diameter of 70 mm and 84 mm, respectively, with a provision of simultaneously measuring the temperature of the residual oil near the wall and at the centre of the reactor. An additional thermocouple has been provided to measure the temperature of the gases formed during the course of thermal cracking reactions. Molten tin bath has been used to provide heat to the autoclavable reactor. A double jacketed condenser has been used for the rapid condensation of the gaseous mixture coming out from the reactor at a particular temperature and reaction time. A needle valve has been provided to maintain the pressure during the course of the reaction. It may be pointed out that the temperature-time profile both at the wall and at the centre of the reactor is crucial in predicting the coke forming tendencies of the residual oil in terms of inception, growth, and subsequent saturation of coke formation. One of the additional provisions of this laboratory scale assembly is that it gives the liberty to move the reactor in and out of the molten tin bath during the course of the reaction. The authors believe that the proposed reactor and the methodology has the potential to get some crucial information about how and when the residual oils varying in physico-chemical characteristics, especially in terms of asphaltenes and Conradson carbon residue, give rise to coke when exposed to cracking.

Keywords: heavy crude oil, heavy residue, autoclavable reactor

Literature Cited

1. Hart A, Leeke G, Greaves M, Wood J. Down-hole heavy crude oil upgrading by CAPRI: Effect of hydrogen and methane gases upon upgrading and coke formation. Fuel 2014; 119:226â??235.
2. Sawarkar AN, Pandit AB, Samant SD, Joshi JB. Petroleum residue upgrading via delayed coking: A review. The Canadian Journal of Chemical Engineering 2007;85:1-24.
3. Ancheyta G. Modeling of Processes and Reactors for Upgrading of Heavy Petroleum. Boca Raton, Florida: CRC Press, 2013.
4. Joshi JB, Pandit AB, Kataria KL, Kulkarni RP, Sawarkar AN, Tandon D, Yad Ram, Kumar MM. Petroleum residue upgradation via visbreaking: A review. Industrial and Engineering Chemistry Research 2008;47:8960-8988.