Cumene

Ascorbic acid, AIBN (2,2′-azobis (2-methylpropionitrile)), AAPH ((2,2′-azobis (2-methylpropionamidine) dihydrochloride), PMHC (2,2,5,7,8-pentamethyl-6-chromanol), DPPH• (2,2-diphenyl-1-picrylhydrazyl), Chelex^® 100 sodium form, cumene, styrene, and tetrahydrofuran (unstabilized) were commercially available (Sigma-Aldrich, Milan, Italy). Solvents were HPLC or spectrophotometry grade and were used without further purification. THF was distilled under vacuum and stored under argon at 5 °C; the content in hydroperoxides was < 50 ppm (μg g^–1), as determined spectrophotometrically (262 nm) by detection of Ph₃P=O after titration with triphenylphosphine (Ph₃P) in iso-propanol. cumene and styrene were percolated through silica and through activated alumina to remove traces of peroxides and were stored under nitrogen. AIBN was recrystallized from methanol and stored at −18 °C. Halloysite nanoclay was purchased from Sigma-Aldrich: it had an average tube diameter of 70 nm and inner lumen diameter of 15 nm. Typical specific surface area of this halloysite is 65 m² g⁻¹, pore volume of ~1.25 cm³ g⁻¹, refractive index 1.54, and specific gravity 2.53 g cm⁻³.

Styrene (≥99%, Sigma-Aldrich Co, Steinheim, Germany) and cumene (98%, Sigma-Aldrich) were percolated on alumina and silica before the experiments in order to remove traces of stabilizer (4-tert-butylcatechol). Initiator, α,α’-Azobisisobutyronitrile (AIBN, >98% GC, Fluka Chemika, Buchs, Switzerland) was recrystallized from methanol before use. Solvents, chlorobenzene (99.9% HPLC grade, Sigma-Aldrich, St. Louis, MO, USA) and acetonitrile (≥99.9% HPLC grade, Sigma-Aldrich, Steinheim, Germany) were of the highest grade commercially available and used as received. 2,2,5,7,8-pentamethylchroman-6-ol (1c, PMHC, ≥99%, Sigma-Aldrich, St. Louis, MO, USA), an autoxidation inhibitor in the reference flask (see Section 2.2.3), was used as received.

n-Octane (99+%), n-hexadecane (99%) and 1-hexene (97%) were received from Acros (Belgium). Cumene, 1-methylnaphthalene and toluene (99.5%) were received from Sigma Aldrich. N-heptane was received from Alfa Aesar. Pyrolysis liquids were kindly supplied by Urbaser, Spain. All chemicals were used as received. Table 2 shows the composition of the model mixture used in this study, whereas the chemical composition of the real pyrolysis mixture is given in Table 3.