Hydrocarbons from spirulina pyrolysis bio-oil using one-step hydrotreating and aqueous extraction of heteroatom compounds

Authors: Elkasabi, Yaseen; CHAGAS, BRUNA - Universidade Federal Do Rio Grande Do Norte (UFRN); Mullen, Charles; Boateng, Akwasi

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2016
Publication Date: 5/18/2016
Publication URL: https://handle.nal.usda.gov/10113/62683
Citation: Elkasabi, Y.M., Chagas, B.M., Mullen, C.A., Boateng, A.A. 2016. Hydrocarbons from spirulina pyrolysis bio-oil using one-step hydrotreating and aqueous extraction of heteroatom compounds. Energy and Fuels. 30:4925-4932.

Interpretive Summary: Fast pyrolysis is the high-temperature breakdown of biomass in the absence of oxygen, which produces a liquid crude product resembling petroleum (“bio-oil”). However, bio-oil must be further refined into a finished fuel. Although pyrolysis is not generally influenced by biomass type, some biomass types can exhibit unique issues. For example, spirulina is a biomass that shows promise since it grows in water and has a very high growth rate compared with land crops. However, one unique aspect is that spirulina bio-oil contains high levels of nitrogen and oxygen, both of which must be removed efficiently. This work examined the process conditions necessary for the removal of both nitrogen and oxygen from spirulina bio-oil, such that a significant fuel product can be obtained. Using ruthenium based catalysts, it was found that the catalyst can effectively remove oxygen and nitrogen (down to < 1%) and produce a significant amount of fuel product. This was accomplished in one reactive step, which is in contrast to the multistep reactions typically used with multiple catalysts. After reaction, we also used water-based mixtures to remove the remaining oxygen and nitrogen-containing compounds from the fuel, such that the oxygen and nitrogen left is undetectable with standard equipment.

Technical Abstract: Biomass feedstocks such as algae and cyanobacteria are highly sought after due to their high reproduction rates and growth densities, but their high concentrations of O and N heteroatoms are problematic for biofuels applications. The development of mild upgrading processes is necessary for producing fungible fuels from these renewable sources We developed a process to upgrade produced hydrocarbons by catalytically upgrading Spirulina bio-oil from tail-gas reactive pyrolysis (TGRP), with 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 distillates for hydrotreatment ensured upgrading 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 residual O and N heteroatoms (approximately 1 wt% each), 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 which can diminish final product yields.