CO$_2$ Solubility in Fast Pyrolysis Bio-oil

Preheating and the use of additives, such as alcohols, are common strategies to treat fast pyrolysis bio-oil after production or before its intended use. Such strategies lower the viscosity of bio-oil and slow chemical reactions occurring in bio-oil during storage. Furthermore, they influence the physical-chemical properties, environmental performance, and cost of the final product. This work suggests the use of $CO_2$ as an alternative and environmental strategy. In contrast to other additives, $CO_2$ has the advantage of being a byproduct of the pyrolysis process. To assess $CO_2$ as an additive and solvent for bio-oil, solubility data on $CO_2$ in acetol, pure bio-oil, and mixtures of bio-oil with an added compound are provided. Experiments were conducted at 50 °C and pressures of 20–100 bar. As additional compounds, acetic acid, acetol, furfural, guaiacol, and water are deployed. The results showed that the $CO_2$ solubility is below 0.1 wt % at subcritical pressures but elevated at supercritical pressures. At 95 bar, the $CO_2$ solubility equates to 0.45 wt %. This is below the $CO_2$ solubility of butanol, which accounts for 0.6–0.7 wt % at the same pressure and is generally higher than the solubility in bio-oil. ... mehrThe $CO_2$ solubility in pure fast pyrolysis bio-oil and its mixtures can be well described by the SRK-EoS. This is a basis to draw a connection between the $CO_2$ solubility and its effects on the properties and further treatment.