MICROCARBON RESIDUE YIELD AND HETEROATOM PARTITIONING BETWEEN VOLATILES AND SOLIDS FOR WHOLE VACUUM RESIDS AND THEIR LIQUID-CHROMATOGRAPHIC FRACTIONS

Five petroleum >1000-degrees-F resids were separated into compound type fractions using liquid chromatography. The coking tendency of each compound type was assessed using the microcarbon residue (MCR) test (ASTM D 4530). Heteroatom (N, S, Ni, V) partitioning between MCR solids versus volatiles was determined through analysis of the starting fractions and the corresponding MCR solids. The weighted sum of MCR solid yields over all compound types in a given resid was typically in good agreement with the MCR yield of the whole resid. This finding agrees with prior studies indicating coke yield to be an additive property. Sulfur partitioning was also an additive property, was predictable from MCR yield, and was nearly independent of the initial form (sulfide, thiophenic, sulfoxide) present. Nitrogen and nickel partitioning was nonadditive and therefore composition dependent. Partitioning of vanadium into solids was essentially quantitative for all resids and their fractions. MCR solid yield was generally dependent only on H/C ratio. However, there is some evidence indicating secondary dependence on hydrocarbon structure, i.e., that naphthenic rings reduce MCR in proportion to H/C by virtue of their effective hydrogen-transfer properties. Deposition of N and Ni into MCR solids over the fractions was often appreciably less than that of the whole resids, thereby indicating that interaction among various compound types was required for maximum incorporation of those elements into coke.