Pyrolysis of Waste Packaging & Marine Plastic Catalyzed by Commercial and Coal-fly-ash-synthesized Zeolites

In the first chapter, the plastic film residue (PFR) of a plastic waste recycling process was selected as pyrolysis feed. Both thermal and catalytic pyrolysis experiments were performed and coal fly ash (CFA) and X zeolites synthesized from CFA (X/CFA) were used as pyrolysis catalysts. The main goal is to study the effect of low-cost catalysts on yields and quality of pyrolysis oils. NaX/CFA, obtained using the fusion/hydrothermal method underwent ion exchange followed by calcination in order to produce HX/CFA. Firstly, thermogravimetry and differential scanning calorimetry (TG and DSC, respectively) analyses evaluated the effect of catalysts on the PFR degradation temperature and the process energy demand. Subsequently, pyrolysis was carried out in a bench scale reactor adopting the liquid-phase contact mode. HX/CFA and NaX/CFA reduced the degradation temperature of PFR from 753 to 680 and 744 K, respectively, while the degradation energy from 2.27 to 1.47 and 2.07 MJ·kg-1, respectively. Pyrolysis runs showed that the highest oil yield (44 wt%) was obtained by HX/CFA, while the main products obtained by thermal pyrolysis were wax and tar. Furthermore, up to 70% of HX/CFA oil was composed by gasoline range hydrocarbons. Finally, the produced gases showed a combustion energy up to 8 times higher than the pyrolysis energy needs. In the second chapter, a Marine Plastic Litter (MPL) sample, collected during a beach clean-up campaign, underwent thermal and catalytic pyrolysis to demonstrate that valuable hydrocarbon oil and gas can be produced from a heterogeneous plastic waste, partly aged and not mechanically recyclable. A low-cost H-X zeolite lab-synthesized from coal fly ashes (CFA) was tested and compared with two commercial zeolites (H-USY and H-ZSM5) commonly used in the industrial cracking field. MPL characterization revealed it is mainly composed of PE and PP (52 and 45wt%, respectively) and it has ideal physicochemical properties as feed for pyrolysis processes. Thermogravimetric analyses demonstrated that catalysts can reduce the degradation temperature of MPL from 472 to 450, 421, 342 and 380 °C for H-ZSM5, H-X/CFA and H-USY, respectively. These results were confirmed by thermal and catalytic pyrolysis tests performed in a bench-scale reactor. All the catalytic tests were carried out at 450 °C with liquid-phase contact mode. In particular, H-X/CFA, avoiding tar and wax formation, produced up to 87wt% of light-oil with high content of short-chain aliphatic hydrocarbons, obtaining results very similar to those gained with the expensive commercial H-USY. For all the catalytic pyrolysis tests, the produced gases proved to be more than sufficient to sustain the process heat requirement. In the third chapter, the assessment of acid properties of proton form of X zeolite, synthesized from coal fly ash, named H-X/CFA, was carried out using thermal decomposition of NH4+ into ammonia and H-form of the zeolite. The described thermal decomposition method (TDM) allows the measurement of two properties: (i) total acidity [µmolNH3·g-1] and (ii) acid strength [kJ·molNH3-1]. The measurement of aforesaid properties were carried out using a thermogravimeter couple with FT-IR Spectrometer. TDM was calibrated using a set of commercial zeolites set with silica-to-alumina (SAR) ratio varying from 1 up to 200. Total acidity showed a decreasing trend vs zeolite’s SAR whereas, instead, acid strength increased. With the TDM calibrated, the characterization was carried out on synthesized X/CFA zeolite that showed similar properties to 13-X commercial zeolite. A mathematical model, regressed over the commercial zeolites set data, was used to estimate structural SAR of X/CFA which was found equal to 1.92 .