Comparison of Hemicellulose Extracts from Two Pulping Woodchips with Green Liquor Followed by Scale-Up Pre-Hemicellulose Extraction

Acetic Acid Removal from Pre-Pulping Wood Extract with Recovery and Recycling of Extraction Solvents

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 hemicelluloses and acetic acid (HAc) for recovery as bioprocessing feedstock or chemical products. The HAc that is present in the wood extraction is inhibitory to microorganisms and can hinder fermentation. HAc is also a commodity chemical that may provide sufficient value to justify recovery and purification. In this study, a liquid-liquid extraction (LLE) method is applied to extract HAc from a green liquor pre-pulping hardwood extract (GLE). The HAc removal is carried out after acid hydrolysis and prior to fermentation. Two organic solutions: trioctylphosphine oxide (TOPO) diluted in undecane and trioctylamine (TOA) diluted in octanol were tested for their abilities to extract HAc from GLE and to be recycled back through the process. GLE was contacted with the organic solvents, phase separated by centrifugation, and the organic phase was then distilled to recover the acetic acid. The solvent was then recycled back for a subsequent extraction of fresh GLE. It was found that TOA was a superior extractant, but failed to easily release its HAc through distillation. It also quickly became contaminated with other compounds in the wood extracts and lost its extraction efficiency after only a few recycles. The TOPO solvent did release its HAc through distillation but also lost extraction capacity with recycling. Back extraction of the TOPO solvent with sodium hydroxide solution restored the performance of the TOPO solvent.

Dilute sulfuric acid fractionation of Korean food waste for ethanol and lactic acid production by yeast

Fermentation of food waste biomass can be used to produce biochemicals such as lactic acid and ethanol in a cost-effective manner. Korean food waste (KFW) dewatered by a screw press contains 23.1% glucan on a dry basis and is a potential raw material for the production of ethanol and lactic acid through fermentation. This study was conducted to optimize the dilute acid fractionation conditions for KFW fermentation with respect to the H₂SO₄ concentration (0-0.8% w/v), temperature (130-190 °C), and residence time (1-128 min) using response surface methodology. Dilute sulfuric acid fractionation was carried out using a 30-mL stainless steel reactor under conditions, and then the dilute acid fractionation was scaled-up in 1-L and 7-L stainless steel reactors under the optimal conditions. The hydrolysate was concentrated, liquid-liquid extracted and neutralized for lactic acid and ethanol production. The highest concentration of glucose obtained from the KFW was 26.4 g/L using fractionation with 0.37% w/v H₂SO₄ at 156 °C for 123.6 min. Using recombinant Saccharomyces cerevisiae containing a codon-optimized lactate dehydrogenase, the yield of lactic acid and ethanol was 77% of the theoretical yield for 17.4 g/L of fermentable sugar at pH 5.5. Additionally, the yield of ethanol produced by Issatchenkia orientalis was 89% of the theoretical yield for 25 g/L of fermentable sugar at pH 3.