Thermo-catalytic pyrolysis of marine debris: A waste to wealth conversion study for energy recovery

•Maximum liquid yield observed in non-catalytic cracking of PMD at 550 °C.•Synergistic effect observed during degradation of PMD.•Details of compositional analysis of liquid and gaseous pyrolysis products.•Effect of 10 %Ni/Al2O3 and AlNaO6Si2 on the distribution of product yield.•Discussion on the variation of hydrocarbons composition during catalytic cracking. The rapid increase in marine waste has resulted in the accumulation of plastic marine debris (PMD), which is of concern to the scientific community due to the need for its safe disposal worldwide. PMD primarily consists of non-degradable polymeric waste, namely thermoplastics, which contain a substantial amount of energy as they are made from petroleum-based sources. Proper disposal and energy reclamation of this waste have become pressing topics. This study aimed to investigate PMD through thermogravimetric analysis followed by pyrolysis in the temperature range of 450–600 °C. Additionally, two catalysts, 10% nickel impregnated activated alumina (10% Ni/Al2O3) and sodium aluminosilicate (AlNaO6Si2), were incorporated (non-contacting method) to evaluate their effect on product yield and quality. During the non-catalytic process, the highest yield (∼78%) was achieved at a temperature of 550 °C while the presence of a catalyst had a minimal effect on oil density (0.74–0.76), and the percentage yield decreased to ∼ 58 and ∼ 62% using AlNaO6Si2 and 10% Ni/Al2O3 at 550 °C. The catalyst had a significant effect on the fraction of oxygenated compounds in the oil, reducing it by ∼ 18% from the non-catalytic process. AlNaO6Si2 resulted in a higher fraction of gasoline-range compounds, while 10% Ni/Al2O3 showed a higher similarity towards diesel fractions. Gas chromatography-mass spectrometry (GC–MS) analysis identified the presence of alkanes, alkenes, aromatics, alcohols, and other compounds in the oil product, with variations observed depending on the catalyst used. The results showed that among all hydrocarbons, propane had the maximum fraction, followed by ethane, methane, and butane in the gaseous compounds. Based on the degradation mechanism, yield distribution, and component evolution, the dissociation mechanism for both processes was explained.