Octane enhancement by the selective separation of branched and linear paraffins in naphthas using a PVDC-PVC carbon molecular sieve

Silicalite-1 samples and PVDC based Carbon Molecular Sieve (CMS-IMP12) material were compared in the separation of linear and multi-branched paraffins present in a real feedstock by fixed bed adsorption experiments. The CMS-IMP12 material was obtained from the pyrolysis of a poly-(vinylidene choride-co-vinyl chloride) (PVDC-PVC) polymer commercially known as Saran™. Material balances of the breakthrough experiments showed higher adsorption capacities for the CMS-IMP12 (5.4–8.8 g/100 g-adsorbent) than for silicalite-1 (1.2–3.4 g/100 g-adsorbent) at the temperature range studied (175–325 °C). Additionally, the octane number increment for the CMS-IMP12 was at least 4 units higher for the same amount of recovered non-adsorbed fraction (1.5 g/100 g-adsorbent). In order to simplify the description of the hydrocarbon mixture, the alkanes were classified according to their degree of branching as: linear, monomethyl, dimethyl (non-gem), dimethyl (gem) and trimethyl alkanes. Similarly, cycloalkanes as: non-branched (cyclopentane and cyclohexane), monomethyl, dimethyl (non-gem), dimethyl (gem) and trimethyl cycloalkanes, where gem refers to the relationship between two methyl groups that are attached to the same carbon atom. The CMS-IMP12 was able to separate gem-dimethylalkanes, gem-dimethylcycloalkanes and trimethylalkanes, while silicalite-1 was less selective.