Catalyst screening for conversion of Chlorella sp. to aromatic fuel additives: A sustainable strategy for CO2 capture

Abstract

Developing biofuels with characteristics similar to current fossil fuels and compatibility with existing petroleum infrastructure (drop-in biofuels) is gaining prominence, aligning with global efforts towards carbon-neutral economies and decarbonization of the transportation sector. The originality of the current study involves two directions: first, the use of Chlorella sp. microalgae, cultivated under simulated post-combustion gas, as a raw material for producing drop-in biofuel precursors; and second, an investigation of the catalytic activity of hierarchical zeolites in the deoxygenation and denitrogenation of volatile pyrolysis products, enhancing hydrocarbon content. To accomplish this, a micro-furnace-type temperature-programmable pyrolyzer coupled with chromatographic separation and mass spectrometry detection (Py-GC/MS) was utilized to assess the upgrading effectiveness of distinct zeolites (faujasite-type, MFI-type, and mordenite-type) on volatile pyrolysis products. All tested zeolites effectively reduced oxygenated and nitrogenated compounds in the volatile pyrolysis products, enhancing their suitability for producing renewable fuel. This supports sustainable development goals by promoting affordable, clean energy and climate action. HMor yielded the highest hydrocarbon content (98.5 %), followed by HZSM-5 (97.6 %) and HY (85.5 %). Catalytic upgrading significantly increased the concentration of aromatic hydrocarbons (at least 66.3 %), with MFI-type zeolites showing the highest selectivity for valuable BETX compounds (benzene, ethylbenzene, toluene, xylene). Hydrocarbons in the gasoline range, with up to 91.7 %, predominantly align with the needs of the transportation fuel market. The principal component analysis illustrates that using MFI-type zeolites promoted the lowest selectivity for PAHs, constituting precursors for coke formation, which is advantageous for ensuring a longer catalyst lifespan. Our results are promising and encourage the conversion of microalgal biomass into renewable fuel additives for formulating drop-in biofuels, as hydrocarbon-rich volatile pyrolysis products could be directly integrated into existing biorefineries. Thus, microalgal biomass cultivated using flue gas as the carbon source can be viewed as a versatile and promising resource for producing renewable fuel additives, contributing to developing a sustainable, low-carbon future.