2.3. Cracking Product Characterization

Detailed analysis of the cracking product was conducted by gas chromatography with mass spectrometry using a Perkin Elmer Clarus 600 gas chromatograph (Shelton, CT, USA) equipped with a 30 m long and 0.25 mm diameter capillary chromatographic column and an Elite 5 MS low-polarity film of 0.5 µm thickness, along with a Clarus 600 MS spectrometer with quadrupole mass analyzer and photomultiplier. The chromatograph injector temperature of 350 °C was retained. The GC oven was programmed to hold at 40 °C for 10 min, then ramp to 320 °C at 6 °C/min and hold for 10 min. Helium was used as a carrier gas with a constant flow rate of 0.8 mL/min. A 1.0 µL sample injection and a split of 50 were used. Liquid samples were injected directly; solid and semi-solid samples were injected as 1% wt. solutions in carbon disulphide (CS2). The mass spectrometer electron energy was 70 eV, and the ion source and transfer line temperature were 200 °C. The detector was turned off in the time range of 0–2.4 min to allow the solvent to leave the spectrometer. The built in TurboMass v. 6.1.2 software from Perkin Elmer was used for data collection. Automatically integrated peaks with a calculated minimum concentration of 0.1% wt. were analyzed and counted. Chromatographic peaks were identified by means of the NIST mass spectral data library. When detailed identification was not possible due to the low probability of the proposed species, additional evaluation by characteristic ion was considered. Characteristic ions for specific hydrocarbon groups are listed in ASTM D2425 and in several studies [40,41,42,43]. The concentration of each component was calculated by dividing the proper peak height or area by the sum of all peak heights or areas, respectively, and multiplying by 100%.

The boiling range of each sample was analysed by simulated distillation (SIMDIS) following ASTM D7500 [44]. A Perkin Elmer Clarus 580 (Shelton, CT, USA), equipped with a 5 m long capillary chromatographic column with an internal diameter of 0.53 mm and a 0.1 µm thick, non-polar Col C stationary phase, in combination with an flame ionization detector (FID), was used. The temperature of the on-column injector was ramped from 40 °C to 430 °C at 20 °C/min. The final temperature was held for 9.5 min. The temperature of the oven was ramped from 35 °C to 430 °C at 15 °C/min, and the final temperature was held for 2.67 min. The detector temperature was 450 °C. Then, 1% wt. solutions of samples in carbon disulphide were injected in quantities of 0.4 µL. Helium was used as a carrier gas with a constant flow rate of 14 mL/min. For the FID, synthetic air with a flow rate of 450 mL/min and hydrogen with a flow rate of 45 mL/min were used. The built in TotalChrom v. 6.3.2 and Dragon v. 1.2.0 software from Perkin Elmer were used to collect the data and automatically calculate the boiling range.

The bromine number was analysed according to ASTM D1159 [45]. The weighted sample (around 4 g) was dissolved in the solvent. The solvent was created by mixing 714 mL of glacial acetic acid, 134 mL of dichloromethane, 134 mL of methanol and 18 mL of sulphuric acid solution (1 volume of concentrated sulphuric acid was mixed with 5 volumes of distilled water). The sample solution was then cooled down and maintained at 0–5 °C, then titrated with 0.25 M standard bromine-bromate solution. The endpoint was indicated by a sudden change in potential on an electrometric apparatus, after which the addition of 0.2 mL of bromine-bromate solution did not cause an increase of more than 5–10 mV.

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