A Method for the Quantification of Alkali and Alkaline Earth Metallic Species in Bioslurry Fuels

Abstract

This study reports a method for the quantification of alkali and alkaline earth metallic (AAEM) species in bioslurry fuels. The so-called evaporation–ashing–digestion–ion chromatography (IC) method consists of four steps, including evaporation that converts bioslurry into solid-like residue, ashing that converts the residue into ash, acid digestion that dissolves the ash into a solution, and IC analysis that quantifies the AAEM species in the solution. The novelty of the method is the combination of the evaporation step with the existing ashing–digestion–IC method that is developed for solid fuels but not suitable for bioslurry fuels. The evaporation step consists of multi-steps of slow heating and holding at various segment temperatures corresponding to the boiling points of the major compounds in bio-oil, resulting in progressive evaporation of bio-oil vapors with little carry-over of biochar particles. The method has been successfully applied for quantifying AAEM species in bioslurry fuels with various biochar loading levels (5–20 wt %), with small relative standard errors (within ±3%) and low limitations of quantification (0.4–3.0 ppm). It also overcomes the biochar incomplete oxidation issue associated with the microwave–digestion-based methods, which considerably underestimate the concentrations of AAEM species in bioslurry fuels.