Solvent polarity control in direct liquefaction of eucalyptus wood

Abstract

In 2015, with the conclusion of the Paris Agreement, the world has begun to move toward the achievement of the IPCC RCP2.6 Scenario. One of the keys is the large-scale deployment of afforestation. The afforestation tree absorbs CO₂ as it grows. The carbon is stocked on the ground if arid land without vegetation becomes forest and the equivalent amount of CO₂ in the atmosphere decreases. However, the mature forest absorbs very little CO₂. Therefore, it is necessary to harvest the tree regularly and to use it effectively for CO₂ reduction such as the alternatives to fossil fuel. By reducing the amount of fossil fuel used, CO₂ emission into the atmosphere is reduced. The authors considered the arid land of Australia is expected to be afforested with eucalyptus. Since woody biomass is a non-uniform solid, it has poor handleability, and since it contains oxygen in its structure, it has a low calorific value. However, by liquefying woody biomass, handleability and calorific value are improved. The liquefaction method is roughly divided into direct liquefaction and indirect liquefaction, but the authors focused on the direct liquefaction under mild reaction conditions. In the process of direct liquefaction, some solvent is required to transport the solid sample and to transfer heat uniformly to it. The previous study reported that the use of an alkaline aqueous solution as a solvent increases liquefaction rate. The liquefied oil is assumed to be used as a diesel oil mixed fuel, but the problem is that the liquefied oil and diesel oil phase separate due to the high polarity of the liquefied oil. On the other hand, another previous study reported that by the use of diesel oil as a solvent, the homogeneous liquefied oil can be obtained. However, the problems are the residue yield is high and the liquefied oil, low. Therefore, to obtain a low polarity liquefied oil with high yield, the authors used a diesel oil solvent added with alkaline aqueous solution. The present result showed that the higher yield of liquefied oil was obtained with alkaline aqueous solution mixed with diesel oil as a solvent than that without it. Furthermore, the liquefied oil separated from aqueous phase was found to form a single phase with more yield than the diesel oil used as the solvent.