Catalytic Upgrading of Pyrolysis Vapors from Scenedesmus sp. Microalgae towards Renewable Hydrocarbons using a Low-Cost Zeolite Synthesized from Rice Husk Ash and Diatomite Residue

The present study aims to investigate the potential for producing an aromatic hydrocarbon-enriched fuel from Scenedesmus sp. microalgae using low-cost zeolite in catalytic flash pyrolysis. The methodology adopted in this study involved the use of an analytical micropyrolyzer coupled with a gas chromatograph/mass spectrometer at 500 ºC to assess the effectiveness of the low-cost HZSM − 5 catalyst in deoxygenation, denitrogenation, and aromatization activities of volatile reaction products. The HZSM − 5 catalyst was synthesized using the hydrothermal method, employing low-cost precursor materials, rice husk ash, and diatomite residue as alternative silicon and aluminum sources. The oxygenated and nitrogenated volatile products in non-catalytic flash pyrolysis constituted 51.7% and 15.3%, respectively. Catalytic upgrading of pyrolysis vapors from Scenedesmus sp. microalgae was demonstrated by significant deoxygenation and denitrogenation activity, reaching up to 99%, while chemical industry-relevant classes experienced increased proportions: aromatic hydrocarbons by 5.8-fold, and aliphatic hydrocarbons by 1.7-fold. Around 78% selectivity for aromatic hydrocarbons was achieved, predominantly yielding BTEX (benzene, toluene, ethylbenzene, and xylene). Another significant finding is that 89.8% of the renewable hydrocarbons produced fall within the gasoline range (C₅ − C₁₂). This study conclusively indicates that the low-cost HZSM − 5 catalyst shows significant promise for producing high-quality bio-oil through the flash pyrolysis of Scenedesmus sp. microalgae.