Wood Ash Suspensions in Water As a Solvent in CO2 Absorption Processes

Wood ash is a solid waste with organic and inorganic components , obtained from combustion of wood. Its chemical composition may vary according the tree species , soil type , climate and combustion characteristics. The resulting suspension of ash in water has typical properties of high concentrations of carbonates  and high pH values. Together with these qualities , the suspension is an interesting solvent in the study of a CO2 absorption process with low demand of purity and energy. There are studies about the methodology of determining the calcium carbonate equivalence in ashes because in its composition there other substances like alumino-silicates , silicates and iron oxides that can lead to inaccurate results. So the aim of this study is to develop a simple technique to determine the absorption capacity of unknown ash-aqueous suspensions with carbonates The experiments were made with wood fuel ashes from a restaurant furnace and validation tests with water and NaOH. The apparatus have a simple characteristics of dismantle all its parts , including the gas tubes and the electrical wirings , forming a called absorption cell , which could be weighted before and after the absorption process. A simple device was successfully developed that could predict the absorption potential for CO2 of a solvent with unknown composition in ambient conditions of temperature and pressure. The soluble extracted from Pterodon emarginatus Vogel. wood , popularly known in Brazil as Faveiro , had 5.33% of calcium carbonate equivalence. The absorption process with an aqueous solution of this solubles , at aprox. 700 mmHg and 20ºC , absorbed 0.77g CO2 / 100g ashes. Ashes from Eucalyptus has 89.74% of calcium carbonate equivalence and its solubles , 11.01%. The absorption process with the ash-water suspension , at aprox. 700 mmHg and 20ºC , absorbed 12.6g CO2 / 100g ashes. Analyzing the results of pH in function of time suggested that the absorption of CO2 occurred because of the total transformation of the carbonates in bicarbonates. This study suggests that wood fuel ashes are a potential solvent for CO2 absorption.