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Title: Recovery of wheat straw soda lignin using flocculation by proteins, synthetic flocculants, and a metal coagulant

Author
item Piazza, George
item LORA, JAIRO H. - Green Value
item Garcia, Rafael

Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2015
Publication Date: 8/1/2015
Citation: Piazza, G.J., Lora, J., Garcia, R.A. 2015. Recovery of wheat straw soda lignin using flocculation by proteins, synthetic flocculants, and a metal coagulant. Journal of Biobased Materials and Bioenergy. 9(4):447-455. DOI: 10.1166/jbmb.2015.1542.

Interpretive Summary: The main components of biomass are cellulose, hemicellulose, and lignin. Lignin interferes with the conversion of cellulose and hemicellulose to fuel ethanol. Although several delignification technologies have been developed to remove lignin, the lignin must be recovered and converted to commercial products to make the production of fuel ethanol more economical. Compounds called flocculants can help with the recovery of lignin 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 filtered lignin. Removal of the lignin and other impurities will allow for the reuse of the process water. 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 several synthetic polymeric flocculants, biobased flocculants, and a metal salt were effective lignin flocculants. Two of the effective biobased flocculants were prepared from a byproduct of animal processing. The results of this research will aid in the conversion of biomass to fuel ethanol.

Technical Abstract: Non-sulfonated lignin, a byproduct of biomass conversion to fuel ethanol, is finding increasing applications and can be converted to chemical substances which replace those obtained from petrochemicals. To date, most studies of flocculant function on non-sulfonated lignin 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. The window of flocculant activity (WA) and lowest effective concentration was determined. Several synthetic flocculants, a metal salt, and biobased flocculants were able to remove lignin from colloidal suspensions. Synthetic polymeric cationic flocculants, poly(diallydimethylammonium chloride), polyquaternaryamine, and high molecular weight cationic polyacrylamide, were effective at 9, 13, and 11 mg/g lignin, respectively. Their WA values were 0.39, 0.39, and greater than or equal to 0.79, respectively. Neutral poly(ethylene oxide) was an effective flocculant at 10 mg/g lignin, and its WA greater than or equal to 1.8. Iron (III) sulfate was an effective flocculant at 115 mg/g lignin, and its WA greater than or equal to 1.2. Two proteins and protein rich blood were also found to have flocculant activity. Bovine hemoglobin (HEM), wheat gliadin, and porcine blood were effective at 86, 183, and 175 mg/g lignin, respectively. Their WA values were 0.45, greater than or equal to 0.92, and greater than or equal to 1.0, respectively. HEM flocculation was optimal at pH 4.8-6.0 and diminished at higher pH values, whilst gliadin flocculation was optima at pH 4.9-7.0 and diminished at higher pH values. Three tested substances had no flocculant activity with non-sulfonated lignin: anionic polyacrylamide mixed with calcium chloride to provide calcium ion for bridging, neutral polyacrylamide, and soybean protein. Zeta potential measurements were obtained for all tested flocculants, and these aided the interpretation of the mechanism of flocculation.