Beneficiation of sawdust: chemical fractionation of lipophilic extractives.

Abstract

Lipophilic extractives are generally known to be those compounds in wood that cause pitch problems in the pulp and paper industry. However, these compounds are advantageous to the biorefining industries as they contain a selection of valuable components. According to theory like dissolves like non-polar solvents dissolve the lipophilic compounds. In this study it was found that the non-polar solvent, cyclohexane, as a mixture with a polar solvent, acetone or ethanol, showed better extracting abilities as opposed to pure non-polar solvents. Many past researches looked at extraction from pine sawdust, but not specifically focussing on the lipophilic extractives and its composition, making it difficult to compare this work with others. This study focusses on the viability of solid-liquid extractions on pine sawdust residues, of various ages, for the potential conversion of its useful compounds to value-added products. A potential product is the conversion of α-pinene to pine oil. Alpha pinene is the main terpene contained in pine wood sawdust, and pine oil is known to be a product with various uses in various industries. However, it is currently not locally produced. When carrying out solvent extractions, it is important to know the composition of the extracts and not only focus on the total extractive contents. In this study, the terpene contents in the extracts were closely studied as it is seen to contain components that could be used to produce the most valuable compounds. Experiments were conducted to determine the effects of operating variables such as; temperature, extraction time, extracting solvents, particle size as well as the effect of storage time on the composition of the extracts. A preliminary study was conducted using a 6-hour extraction time. The results produced a maximum of 1,75% α-pinene, and a maximum of 3,7% of the total terpene content of the extractives, which is a significant but low quantity of terpenes. The ASE extraction method uses high temperatures and pressures and allows for extraction to occur at up to an hour. Results obtained indicated that shorter extraction times provide a marginally higher quantity of terpenes in the extracts. Thus, selecting time as a variable parameter was applied in Section 4.3 and the results validated the extraction over shorter time periods, for extracting more value from the sawdust residue. In Section 4.3, the extracting solvent and the particle size was also investigated. After various experiments, the optimised extraction conditions were determined as being: a 2-hour extraction time, 3:1 cyclohexane-ethanol (v/v) as the extracting solvent and 375-micron particle size. The temperature of the solvent was investigated in Section 4.5, the kinetic study. It is required that the temperature be close to the boiling point of the solvent, as when the temperature is lower, a slightly lower terpene content is noticed. On the other hand, when the temperature is greater than the boiling point, the terpenes are decomposed. 3:1 Cyclohexane-ethanol (v/v) as an extracting solvent, requires a maximum temperature of 80℃ after which components of the extract begin to decompose. The kinetic study enabled the development of a model equation that could determine concentrations at any time. The effect of storage time was investigated during the seasoning study. This however, was seen to have no significant impact on the overall extraction results. Based on the various experiments conducted, the maximised terpene yield can be extracted at a 2-hour extraction, using 3:1 cyclohexane-ethanol (v/v) as the extracting solvent and grinding the sawdust residues to a 375-micron particle size.