A mechanistic study of Layered-Double Hydroxide (LDH)-derived nickel-enriched mixed oxide (Ni-MMO) in ultradispersed catalytic pyrolysis of heavy oil and related petroleum coke formation

Heavy oil contains a significantly lower H/C ratio and higher quantity of organic heteroatoms and organo-metallic complexes than conventional light oil. Consequently, novel catalytic materials are needed to aid in heavy oil upgrading to remove the deleterious components and support the higher demand for low sulfur and higher value fuels. Heavy oil upgrading was studied using an inexpensive nickel-aluminum Layered Double Hydroxide (LDH)-derived Ni-enriched Mixed Metal Oxides (Ni-MMO) dispersed catalyst in a Baskerville autoclave. The conditions were set at 425 °C, initial pressure of 20 bar, 0.02 Catalyst-To-Oil (CTO) ratio, and a residence time of 30 min to mimick previously optimized conditions for in situ upgrading processes. The extent of the upgrading following catalytic pyrolysis was evaluated in terms of a solid, liquid, and gaseous phase mass balance, liquid viscosity reduction, desulphurization, and True Boiling Point (TBP) distribution. A typical in situ activated CoMo-alumina commercial hydroprocessing catalyst was used as a reference. It was found that the produced oil from dispersed ultrafine Ni-MMO exhibited superior light oil characteristics. The viscosity decreased from 811 to 0.2 mPa·s while the light naptha fraction increased from 12.6% of the feed to 39.6%, with respect to the feed. Using a thorough suite of analytical techniques on the petroleum coke product, including Thermogravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM), a reaction mechanism has been hypothesized for the upgrading by dispersed Ni-MMO under both N ₂ and H ₂ atmospheres. Under a N ₂ atmosphere, the Ni-MMO, generated by the in situ thermal decomposition of the LDH, demonstrate a preferential asphaltene and poly aromatic adsorption mechanism, generating a poly aromatic mixed oxide-coke precursor. While using Ni-enriched mixed oxides under a reducing H ₂ atmosphere, hydrogenation reactions become more significant.