Determining the sequence of extracting Pinus radiata bark to maximize the total yield of extractives–towards the development of a bark-based biorefinery

Tree bark is an abundantly available resource that is a waste product of the timber processing industry. It is rich in chemicals that require sequential treatment with solvents of differing polarities to extract said compounds. The success of such an approach, i.e. biorefinery, depends on the individual yields of the extraction processes influenced by multiple parameters like solvent type, temperature, time etc. However, research into determining the optimal order of using these solvents is scarce, which is the core focus of this work. Pinus radiata bark was sequentially extracted using two solvents- water and hexane, to study the combined impact of the extraction order and particle size on total yield and product quality. Total extractives were highest when water was used first (11.74% and 9.45%) compared to hexane (10.53% and 6.53%). The individual yields of hexane extractives were in the range of 2.4% – 2.9% while those of water were 4.30% – 9.24%. Chemical analyses of the extracts and residues showed no qualitative differences, indicating the order in which bark is extracted does not alter the extract composition. Moreover, the results have successfully established that extracting bark with water first followed by hexane will increase the total yield of extractives that increasing particle size decreases the total yield of the sequential extraction.