Experimental studies on a two-step fast pyrolysis-catalytic hydrotreatment process for hydrocarbons from microalgae (Nannochloropsis gaditana and Scenedesmus almeriensis)

Two microalgae species (marine Nannochloropsis gaditana, and freshwater Scenedesmus almeriensis) were subjected to pyrolysis followed by a catalytic hydrotreatment of the liquid products with the objective to obtain liquid products enriched in hydrocarbons. Pre-dried microalgae were pyrolyzed in a mechanically stirred fluidized bed reactor (380 and 480 °C) with fractional condensation. The heavy phase pyrolysis oils were hydrotreated (350 °C and 15 MPa of H₂ pressure for 4 h) using a NiMo on alumina catalyst. The pyrolysis liquids after pyrolysis and those after catalytic hydrotreatment were analyzed in detail using GC–MS, GC × GC–MS, and 2D HSQC NMR. The liquid products are enriched in aromatics and aliphatic hydrocarbons and, as such have a considerably lower oxygen content (1.6–4.2% w/w) compared to the microalgae feeds (25–30% w/w). The overall carbon yield for the liquid products was between 15.6 and 19.1% w/w based on the initial carbon content of the algae feedstock.