Mass balance on green liquor pre-pulping extraction of northeast mixed hardwood

Abstract

A forest biorefinery configuration employing a hemicellulose pre-pulping extraction is being investigated that will retain pulp yields, reduce the organic and inorganic load for liquor recovery, and create a hemicellulose feed stream for the generation of biofuels and biomaterials. Current efforts are focused on developing extract production and conditioning processes that will result in fermentable sugars suitable for conversion to fuel alcohols or organic acid chemical products. As efforts move the process closer to commercial demonstration, it is apparent that a high level of confidence is needed in the analysis of the partitioning of fresh wood into its extracted wood and liquid extract fractions. Of particular interest is the partitioning of the carbohydrates, as these constitute the feedstock for bioconversion to fuels and chemicals.The extraction method employed utilizes green liquor derived from the kraft pulping process for pretreatment of the woodchips. To enable analysis, green liquor extraction was followed by 4% sulfuric acid hydrolysis to complete hydrolysis of the oligomers that were still present. High performance anion-exchange chromatography (HPAEC-PAD) and high performance liquid chromatography (HPLC) methods were used to analyze the carbohydrates in northern hardwood and its extract fractions. The Bio-Rad Aminex HPX-87H column did not separate mannose, xylose, and galactose, but the area of the collective peak corresponds well to the sum of these components as measured by HPAEC. In addition to sugars, standard methods were employed for quantification of the individual components (e.g., lignin, ash, nitrogen, carbon, extractives, uronic and acetic acid). The analytical mass balance closure was 102.2% and 103.6% for raw wood, 99.3% and 102.3% for extracted wood, and 94.7% and 95.6% for hemicellulose extract from the HPAEC and HPLC, respectively. The extraction mass balance was 96.9% and 98.2% for HPAEC and HPLC, respectively. The data generated by this analysis are important to further design work in commercializing the pulp and biorefinery processes.