Bioslurry as a Fuel. 6. Leaching Characteristics of Alkali and Alkaline Earth Metallic Species from Biochar by Bio-oil Model Compounds

In a bioslurry fuel system, inherent alkali and alkaline earth metallic (AAEM) species can be leached from biochar into the bio-oil phase because of the interaction between biochar and bio-oil [as reported in part 5 (10.1021/ef401888j) of this series]. This paper further investigates the leaching characteristic of these inorganic species from biochar by bio-oil model compounds and the bio-oil water-soluble fraction. The results show that leaching of AAEM species from biochar by bio-oil is mostly attributed to the water-soluble fraction of bio-oil, especially the organic acids and water in bio-oil. The leaching capability of other individual organic compounds (such as methanol, acetone, and guaiacol) in bio-oil appears to be limited because of poor polarity or low dielectric constant. However, in the presence of these organic compounds, the capability of acids and water in leaching the inherent AAEM species from biochar can be significantly influenced. For instance, leaching of AAEM species by water can be hindered in the presence of organic compounds with lower polarity or dielectric constant because of the decrease of salt solubility. However, the presence of phenolic compounds may enhance the leaching of the AAEM species (especially Ca and Mg), likely because of the ability to penetrate into the biochar structure and, thus, increase the accessibility of AAEM species by water or acids.