(365c) Acetic Acid Removal From Pre-Pulping Wood Extract

Pre-pulping extraction is a means of deriving a hemicellulose-rich process stream from the front end of a kraft pulp mill. When the extraction is carried out using green liquor, pulp quality and quantity can be retained while still releasing hemicellulose and acetic acid for recovery as bioprocessing feedstock or chemical products. The acetic acid that is present in the wood extraction is inhibitory to microorganisms and can inhibit fermentation. It is also a commodity chemical that may provide sufficient value to justify recovery and purification.

In this study, a liquid-liquid extraction method is applied to extract acetic acid from a green liquor pre-pulping hardwood extract. The acetic acid removal process takes place as an initial step prior to the fermentation process. A solution of trioctylphosphine oxide (TOPO) and un-decane is prepared and mixed with wood extract. TOPO has strong hydrogen bonding acceptor properties that induce the carboxylic acid to transfer to the extract phase. Next the extract phase is centrifuged in order to separate the aqueous and organic phases. The aqueous phase is sent on to fermentation. Distillation is used to separate acetic acid from the organic phase. The acetic acid is recovered and the organic solvents are recycled back to the extraction. Results present the extraction and recovery efficiencies. Preliminary comparisons are made with other potential separation technologies.