Flocculation of wheat straw soda lignin by hemoglobin and chicken blood: Effects of cationic polymer or calcium chloride

Authors: Piazza, George; LORA, J.H. - Green Value; Garcia, Rafael

Submitted to: Journal of Chemical Technology & Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2016
Publication Date: 8/24/2016
Publication URL: http://handle.nal.usda.gov/10113/5717659
Citation: Piazza, G.J., Lora, J., Garcia, R.A. 2016. Flocculation of wheat straw soda lignin by hemoglobin and chicken blood: Effects of cationic polymer or calcium chloride. Journal of Chemical Technology & Biotechnology. doi: 10.1002/jctb.5061.

Interpretive Summary: Biomass is composed mostly of cellulose, hemicellulose, and lignin. The lignin must be separated from the celluloses which are used to prepare biobased fuel. Compounds called flocculants can help with lignin separation by flocculating or precipitating the lignin. Additionally, flocculants can remove small particles of lignin which are found in the water used to wash impurities from lignin. To date most studies of flocculant function have used mixtures of lignin, cellulose, and hemicellulose, and it has not been possible to determine how cellulose and hemicellulose affect flocculant function. To determine the best flocculants for lignin isolation, flocculants were tested on a fine suspension of highly purified lignin. It was found that the addition of calcium chloride greatly increased the lignin flocculant activity of a biobased flocculant obtained from a byproduct of animal processing. It was found that the activity of this biobased flocculant was also increased by the addition of a highly charged polymer. The results of this research will aid in the conversion of biomass to fuel ethanol and will provide a lignin byproduct which can be converted to useful chemical materials.

Technical Abstract: Flocculation can be used to separate non-sulfonated lignin from base hydrolyzed biomass. In the industrial process, the lignin is isolated by filtration and washed with water. Some of the lignin is lost in the wash water, and flocculation can be used to recover this lignin. Several ways of enhancing the action of bio-based flocculant on suspensions of high purity lignin were investigated, and two methods were found to be effective: the addition of CaCl2 to lignin-hemoglobin (HEM) mixtures and the addition of poly(diallydimethylammonium chloride) (pDADMAC) to lignin-HEM and lignin-chicken blood (CB). Zeta potential readings were increased by the addition of CaCl2 to lignin-HEM mixtures. However, optimal lignin flocculation occurs at negative Zeta potential suggesting that in addition to charge neutralization, another factor is contributing to improved flocculation by CaCl2. CaCl2 does not change the pH of water, but the pH of aqueous lignin suspensions decreased as CaCl2 was added, demonstrating the release of hydrogen ion from lignin. By measuring the loss of supernatant calcium, it was shown that a small fraction of added calcium was tightly absorbed by lignin. Infrared spectrometric analysis of the solid formed from mixtures of lignin, HEM, and CaCl2 showed that the intensity HEM amide I band increased substantially as CaCl2 was added, providing additional evidence for an interaction of CaCl2 with lignin-HEM. The addition of the cationic polymer, poly(diallydimethylammonium chloride) (pDADMAC), to lignin promoted lignin flocculation at relatively low levels of HEM or CB. In addition to the benefit of needing less HEM or CB for lignin flocculation, chemical oxygen demand of the supernatant was reduced when pDADMAC was used.