Behaviors, product characteristics and kinetics of catalytic co-pyrolysis spirulina and oil shale

Abstract

• Oil shale restrained the thermal decomposition of organic matters in spirulina. • HZSM-5 and CaO promoted the deoxygenization and aromatization of co-pyrolysis. • The minimum E value of catalytic pyrolysis was achieved at 1HZSM-5/3CaO. • A significant synergistic effect was achieved at the percentage of 30% oil shale. The catalytic co-pyrolysis behaviors, kinetics and products distribution of spirulina (SP) and oil shale (OS) were studied by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results indicated that OS delayed the thermal decomposition of organic matters in SP; there existed inhibition for aromatics production under 310 °C and synergistic effects at high temperatures, and a maximum synergistic effect was achieved with 30% OS. HZSM-5 and CaO enhanced the deoxygenation and aromatization reaction, resulting in a prominent decrease of acids and phenols. With the increase of CaO ratio, the relative content of aliphatic hydrocarbons increased from 9.57% to 17.48%, while the relative content of aromatics increased first and then decreased, and the maximum yield of aromatics (15.92%) was obtained at 1CaO/3HZSM-5. The appropriate CaO/HZSM-5 mass ratio contributed to the production of desired pyrolysis product. The kinetic parameters were determined by using Friedman and Flynn–Wall–Ozawa (FWO) method. As the oil shale blending ratio increased, the average activation energy (E) of mixtures decreased from 278.84 kJ/mol to 192.53 kJ/mol (from 265.51 kJ/mol to 189.63 kJ/mol), related to the catalytic decomposition of organic matter by alkaline earth metals in OS ash. The minimum E value of catalytic pyrolysis 5SP/5OS was achieved at 1HZSM-5/3CaO (257.29 kJ/mol and 269.62 kJ/mol). This paper could offer significant pyrolysis knowledge for obtaining high-grade oil from SP and OS with HZSM-5 and CaO.