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BACKGROUND The kaolin flocculant activities of bovine blood (BB) and hemoglobin (HEM) at different salt and pH values were determined. Lower limit concentration (LLC), window of application (WA), and degrees of clarification (DC) values for BB and HEM were determined and compared with those of the synthetic polymeric flocculants poly(diallydimethylammonium chloride) (PDADMAC), cationic polyacrylamide (PAM), and anionic PAM. BB flocculation of lignin, a bioproduct of biomass conversion to bioethanol, was demonstrated. RESULTS Flocculation of kaolin by BB and HEM increased at acidic pH and in the presence of NaCl. LLC values of HEM and BB were similar to LLC values of cationic and anionic PAM. LLC values of HEM and BB were 18–20-fold higher than that of PDDMAC. WA values of BB and HEM were similar to those of PDADMAC, cationic PAM, and anionic PAM. For lignin flocculation, the ratio of LLC for BB/PDADMAC was 20–38, but the ratio of WA for BB/PDADMAC was > 3.6. For kaolin and lignin flocculation, DC values were similar for all flocculants. CONCLUSIONS The renewable flocculants BB and HEM rapidly settle kaolin and lignin suspensions; BB and HEM could be used in the process to separate lignin from other biomass components. Published 2014. This article is a U.S. Government work and is in the public domain in the USA

The reactions between aspen milled wood lignin (MWL) and 2-naphthol, resorcinol, and p-hydroxybenzoic acid were studied under simulated autohydrolysis conditions. The material after the reaction was separated into a dioxane-insoluble fraction (DI), a dioxane-soluble but ether-insoluble fraction (DSEI), and an ether-soluble fraction (ES). In the absence of additive, the lignin first depolymerized and remained solvent soluble, then repolymerized to become insoluble. With 2-naphthol as additive, the amount of DI lignin decreased proportionally to the amount of additive present. When more than 0.1 mole of 2-naphthol/C-9 unit was present, no DI lignin was formed, that is, all the lignin was soluble. Gel permeation chromatography studies indicated that the additive was acting effectively as a blocking agent, preventing lignin repolymerization. Small amounts of resorcinol acted as a repolymerizing agent since two or more fragments of lignin could readily condense with a molecule of the very active additive. As a result of this bridging effect, the amount of DI lignin increased. As the amount of resorcinol was increased, it behaved more like a blocking agent and a reduction in the amount of DI lignin was observed. The presence of a large excess of resorcinol resulted in the formation of soluble lignin only. The molecular weight distributions supported the proposed dual role of resorcinol as a bridging or blocking agent. The use of an excess of p-hydroxybenzoic acid prevented the formation of DI material and resulted in low molecular weight soluble lignin.

In a previous article the authors have described changes in molecular weight which occur when aspen milled wood lignin is subjecte to autocatalyzed hydrolysis (autohydrolysis) in the presence of three aromatic additives: 2-naphthol, resorcinol, and p-hydroxybenzoic acid. In the present work, the reactions of these additives have been studied from the viewpoint of their effect on the structure of the lignin. The use of milled wood lignin instead of aspen wood served to distinguish those reactions between the additives and the lignin, without involving the other wood components. The reaction products have been charactrized by elemental analysis and UV and IR spectroscopy. It was concluded that keto groups, generated on the lignin side-chain during autohydrolysis, condense with the additives, which become incorporated into the lignin. This occurs most probably through an aromatic eletrophilic substitution reaction. While 2-naphthol condensed primarily with the β-keto carbonyl groups, resorcinol attacked also the α-keto carbonyl groups. When p-hydroxybenzoic acid was the additive, its incorporation was accompanied by an increase in lignin carboxylic acid groups.

In order to obtain further understanding of the nature of lignin reactions during autocatalysed hydrolysis (autohydrolysis) of wood, milled wood lignin (MWL) was isolated from aspen (Populus tremuloides) and treated under autohydrolysis conditions. By this means reactions of the lignin itself could be distinguished from those taking place between lignin and the carbohydrate or other components of the wood. The material after the reaction was separated into a dioxane insoluble fraction (DI), a dioxane soluble but ether insoluble fraction (DSEI), and an ether soluble fraction (ES). Studies were carried out on the DI and DSEI fractions; no direct study was made of the small ES fraction.The formation of DI material increased linearly during the first 7.5 min at 170 °C and then levelled off. At the same time DSEI decreased and then levelled off. Gel permeation chromatography of the DSEI fraction suggested that during autohydrolysis there is an initial generation of low molecular weight fragments which recombine to form first a high molecular weight soluble fraction and from this the insoluble product. The DSEI fraction contained increased conjugated and unconjugated keto groups. Carboxylic acids were also detected; they have been attributed to the reincorporation of low molecular weight aromatic acids generated by the hydrolysis of the corresponding esters. The dioxane insoluble (DI) fraction had fewer unconjugated keto groups than the DSEI fraction, indicating that these groups participated in the condensation reactions leading to the formation of insoluble material. These probably involve position 6 of the aromatic ring.