Using ammonia to upgrade pyrolytic bio-oils to value-added chemicals

Biomass is a promising, sustainable alternative option to fossil fuels, as it is naturally carbon storing. However, one challenge is that the bio-oil produced from biomass pyrolysis contains large amounts of water and acids (>40 wt%), making it difficult to store and transport. Here, we have produced natural, pyrolytic bio-oils from a pine-hardwood mixture, and then successfully upgraded the bio-oils to aqueous and organic phases using ammonia gas. The aqueous phase, which contained water, ammonium, acetic acid, sugars, and other water-soluble compounds, was used as a fertilizer for ryegrass. The bio-oil based fertilizer significantly improved grass growth compared to a no-fertilizer control and was comparable to commercial fertilizers optimized for grasses, resulting in a grass coverage of double that of the no-fertilizer control. The organic phase contained many aliphatic, aromatic, and oxygenated hydrocarbons. It was tested for combustibility, yielding a heating value of 25.3 ± 1.3 MJ/kg, and upgrading to common hydrocarbon compounds using ZSM-5 catalysts. The upgraded organics contained a mixture of acetonitrile and common crude oil sourced aromatics, with a typical carbon length of between seven and eight carbons, which could be used in fuels or separated for other uses. Overall, this work has demonstrated that upgrading real pyrolytic bio-oils using ammonia is viable, further opening possibilities for biomass to partially replace fossil fuels as a sustainable alternative.