Recovering valuable products from the aqueous streams of fast pyrolysis

Abstract

<p>Many of the biorefineries found in the world operate on a biochemical or thermochemical platform to produce their fuels and chemicals. However, contaminant removal from bio-refineries process and wastewater streams is a mounting issue that needs to be dealt with. Grain ethanol, cellulosic ethanol, hydroprocessing units, and pyrolysis biorefineries all produce process and wastewater streams that must be cleaned prior to releasing them to sewage systems or purified to sequester all valuable products contained within the aqueous matrix. Two major products are found within the aqueous streams of a pyrolysis reactor: levoglucosan and acetic acid. Separating and purifying these valuable compounds would add these commodity chemicals to a bio-refinery’s portfolio and reduce the cost of wastewater cleanup.</p> <p>Fractionation technology developed at Iowa State University separates bio-oil into water soluble sugars, water insoluble phenolic monomers, dimers, and oligomers, and aqueous phases containing water soluble light oxygenates, and carboxylic acids. Productive use of these fractionated bio-oil streams will be important to the development of a bio-refinery based on the fast pyrolysis of biomass.</p> <p>We have identified a polymeric adsorbent resin that efficiently removes organic contaminants from sugar solutions. It does this by the removal of bio-oil phenolic species which is necessary before the sugars can undergo crystallization or utilization for biological and catalytic upgrading. The resin has high selectivity (affinity) for phenols and other aromatic compounds, high adsorption capacity, low cost, and ease of regeneration. Our results show a marked sugar purity increase and phenol concentration decrease.</p> <p>We have also determined that hydrophobic polymeric resins are suitable candidates for adsorption of acetic acid from the aqueous fractions. Among possible resins for chemical adsorption, debittering and anionic resins were selected due to their affinity for phenolic and acetic acid removal, respectively. Both resins have shown favorable results with almost complete removal of their targeted species.</p> <p>Recovery of acetic acid and other organic species from the aqueous fractions is necessary because it increases the number of chemical products from the bio-oil and reduces the waste water treatment costs associated with the pyrolysis biorefinery. However, the presence of water makes upgrading and simple distillation of this fraction very difficult due to water’s high heat capacity and azeotropic properties. Among possible solvents for liquid-liquid extraction, heptanoic acid was selected because of its low water solubility; high boiling point compared to the acetic acid to be distilled from it; and stability during storage. Heptanoic acid extraction of SF5 has shown favorable results with almost complete removal of acetic acid.</p>