Establishing the Maximum Carbon Number for Reliable Quantitative Gas Chromatographic Analysis of Heavy Ends Hydrocarbons. Part 3. Coupled Pyrolysis-GC Modeling

The purpose of this research work is to determine the maximum single carbon number (SCN) which can be reliably quantified using High Temperature Gas Chromatography (HTGC) analysis of heavy oil hydrocarbons, accounting for (i) thermal cracking risk and (ii) the non/incomplete elution. To that end, an in-house coupled numerical Pyrolysis-GC model has been developed, capable of calculating the degree of elution and of simulating the migration, partitioning, and pyrolysis conversion of a mixture of 11 heavy n-alkanes spanning the range from nC14H30 to nC80H16 throughout the GC column. On the basis of this model and using a commonly used column configuration and temperature program, two conclusions have been made: (i) half of the mass injected of nC80 thermally decomposed before nC70 has eluted, suggesting a possible coelution of both nC70 and the pyrolysis products of nC80 and therefore making the HTGC analysis of nC70 and heavier n-alkanes no longer reliable, and (ii) alkanes heavier than nC70 take progressi...