Sieving and Acid Washing as a Pretreatment to Fast Pyrolysis of a High Ash Hog Fuel

Abstract

Mineral matter can negatively influence liquid yield and product properties from the fast pyrolysis of woody biomass residuals. Biomass pretreatment approaches to reduce the ash content represent a potential pathway to expand the feedstock flexibility of fast pyrolysis. In this work, ash reduction in biomass pyrolysis oil via sieving the fines portion of a hog fuel as well as washing the fractionated hog fuel with nitric acid was investigated prior to the conversion in CanmetENERGY-Ottawa’s 5–10 kg/h fast pyrolysis system. It was found that sieving the material was much less influential on the liquid yield and product properties relative to nitric acid washing. Product analysis showed up to 40% increase in organic liquid yield and up to 30% decrease in biochar yield on a dry, ash-free basis by nitric acid washing the fractionated hog fuel. Pyrolysis reaction water was minimized when nitric acid washing the feedstock, which has important implications for the phase separation of the pyrolysis liquids. Through nitric acid washing, the ash content in the liquid was reduced up to 87% relative to the liquid produced from the pyrolysis of the untreated material. The chemical quantification of the produced pyrolysis liquids demonstrated that the chemical composition was significantly altered after nitric acid washing the hog fuel, indicating that the removal of the ash species impacted the pyrolysis reaction chemistry.

Experimental Evaluation and Empirical Modeling of Cross-Flow Microfiltration for Solids and Ash Removal from Fast Pyrolysis Bio-Oil

“…The vast majority of the FPBOs that were used throughout the experimental work were produced at CanmetENERGY-Ottawa from Canadian forestry biomass residual feedstocks, including hog fuel and sawdust. A description of CanmetENERGY-Ottawa’s bubbling fluidized bed fast pyrolysis system is available in the existing literature . Of relevance to this work is the condensation approach that was used in the fluidized bed fast pyrolysis system for production of the FPBOs.…”

Recent Developments in Understanding Biochar’s Physical–Chemistry

“…The advantages of biomass pretreatments are also related to the formation of solid by-products with specific properties enabling their use in wastewater treatments, air cleaning, soil remediation, and catalytic purposes to facilitate energy production [8,76,[79][80][81][82][83]. In particular, washing biomass prior to pyrolysis with either acidic or basic solutions may remove up to 70% of the initial minerals contained in the feedstock [79,84,85]. However, the use of dilute acid and hot water results in a slight decomposition of hemicellulose.…”

“…Conversely, the application of dilute alkali disrupts lignin structure and solubilizes hemicellulose. As a consequence, the thermal degradation applied after the acid/base treatment achieves a higher yield in liquids (tar) and gases at the expense of the solid residue [79,84,85]. The latter, when obtained after biomass treatment with a 1:1 (v:v) HNO 3 /H 2 O 2 solution, appears to have enhanced adsorption capacity for cadmium from high concentration solutions as compared to biochars obtained from non-pretreated biomasses [86].…”

Experimental Investigation of Fouling Remediation Strategies for Cross-Flow Microfiltration of Fast Pyrolysis Bio-Oil

“…The fast pyrolysis bio-oils that were used throughout this study were produced at CanmetENERGY-Ottawa's 5−10 kg hr −1 bubbling fluidized bed fast pyrolysis system 16 and originated from hardwood flooring sawdust residue. The properties of the hardwood sawdust residue are included in the Supporting Information section.…”

“…For example, MF and UF processes commonly used in wastewater treatment, whey (or other proteins) separation, membrane bioreactor processes, and concentration processes in the food industry have commonalities to FPBO microfiltration. Compared to traditional liquid fuels, fast pyrolysis bio-oil is relatively unique; it is acidic and viscous, is typically a bulk mixture of emulsified hydrophilic and hydrophobic components, and has limitations on preheating due to polymerization, etc. ,− A survey through various publications, books, reviews, and other literature sources shows common fouling remediation strategies that may be considered for use in an FPBO cross-flow microfiltration system to improve performance.…”