Enhanced stability of bio-oil and diesel fuel emulsion using Span 80 and Tween 60 emulsifiers

Abstract

Bio-oil (biomass pyrolysis oil) has some undesirable properties (e.g., low heating value, high corrosiveness, and high viscosity) that restrain its direct use as a transportation fuel. The emulsification of bio-oil and diesel is an effective and convenient method to use bio-oil in the present transportation fuel infrastructure. The addition of an emulsifying agent (emulsifier or surfactant) to two immiscible liquids of diesel and bio-oil is an important step in emulsification. The hydrophilic–lipophilic balance (HLB) value, according to the chemical structure and characteristics of the emulsifier, is a key parameter for selecting a surfactant. In this study, an ether treatment of raw bio-oil was carried out to separate the ether-soluble fraction of bio-oil from its heavy (dark brown and highly viscous) fraction, and the ether-extracted bio-oil (EEO) was processed further for emulsification into diesel fuel. The effects of the HLB value of the emulsifier and the contents of EEO, diesel, and emulsifier on the stability of the EEO/diesel emulsion were investigated. To optimize the HLB value of the emulsifier, different HLB values (4.3–8.8), which were prepared by mixing different amounts of Span 80 and Tween 60 as surfactants, were used for the EEO and diesel emulsification. A HLB value of 7.3 with diesel, EEO, and emulsifier contents of 90, 5, 5 wt%, and 86, 7.4, 6.6 wt% resulted in EEO/diesel emulsions (without phase separation) stable for 40 and 35 days, respectively. Measurement of the high heating value (HHV) of the emulsified fuels gave a 44.32 and 43.68 MJ/kg values for the EEO to emulsifier mass ratios of 5:5 and 7.4:6.6, respectively. The stability of emulsified EEO and diesel was verified by TGA and FT-IR methods.