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Hydrocarbons from Spirulina Pyrolysis Bio-oil Using One-Step Hydrotreating and Aqueous Extraction of Heteroatom Compounds

Yaseen Elkasabi, Bruna M. E. Chagas, Charles A. Mullen, Akwasi A. Boateng
Energy & Fuels 2016 v.30 no.6 pp. 4925-4932
Spirulina, algae, biofuels, biomass, carbon, catalysts, distillates, feedstocks, gases, hydrocarbons, hydrochloric acid, pyrolysis, reproduction, ruthenium, temperature
Biomass feedstocks such as algae and cyanobacteria are highly sought after because of their high reproduction rates and growth densities, but their high concentrations of O and N heteroatoms are problematic for biofuel applications. Mild upgrading processes are necessary for producing fungible fuels from these renewable sources. We developed a process to upgrade spirulina-based bio-oil from tail-gas reactive pyrolysis (TGRP), using a combination of catalytic hydrotreatment and purification of the upgraded product. The TGRP bio-oil was distillated at high organic yields, and the distillates served as the feedstock for catalytic upgrading. Simultaneous hydrodeoxygenation and hydrodenitrogenation (HDO/HDN) was carried out in one step using a commercial ruthenium catalyst on carbon support. Using bio-oil distillates as feedstocks for hydrotreatment produced hydrocarbons at high space velocities. Reactor temperature was the critical variable, wherein the optimal temperature compromised between excessive yields loss and catalyst inactivity. While the HDO/HDN product contained relatively significant amounts of residual O and N (∼1 wt % each), the remaining O and N-containing compounds were removed via single aqueous-phase extraction with hydrochloric acid. The extraction step serves as a milder alternative to deep HDO/HDN processes that diminish final product yields.