Extensive research has been done on examining the autotrophic growth of Acetobacterium woodii wit... more Extensive research has been done on examining the autotrophic growth of Acetobacterium woodii with gaseous substrates (hydrogen and carbon dioxide) to produce acetic acid. However, only limited work has been performed on the heterotrophic growth of A. woodii using pure sugars or lignocellulosic feedstocks-derived sugars as substrates. In this study, we examine the growth kinetics and acetic acid production of A. woodii on glucose and xylose. While good growth was observed with glucose as substrate, no significant growth was obtained on xylose. Kinetic studies were performed in batch culture using different concentrations of glucose, ranging from 5 g/L to 40 g/L. The highest acetate production of 6.919 g/L with a product yield of 0.76 g acetic acid/g glucose was observed with 10 g/L glucose as initial substrate concentration. When testing A. woodii on corn stover hydrolysate (CSH) and wheat straw hydrolysate (WSH) formed after pretreatment and enzymatic hydrolysis, we found that A. w...
Lignin, while economically and environmentally beneficial, has had limited success in use in rein... more Lignin, while economically and environmentally beneficial, has had limited success in use in reinforcing carbon fibers due to harmful chemicals used in biomass pretreatment along with the limited physical interactions between lignin and polyacrylonitrile (PAN) during the spinning process. The focus of this study is to use lignin obtained from chemical-free oxidative biomass pretreatment (WEx) for blending with PAN at melt spinning conditions to produce carbon fiber precursors. In this study, the dynamic rheology of blending PAN with biorefinery lignin obtained from the WEx process is investigated with the addition of 1-butyl-3-methylimidazolium chloride as a plasticizer to address the current barriers of developing PAN/lignin carbon fiber precursors in the melt-spinning process. Lignin was esterified using butyric anhydride to reduce its hydrophilicity and to enhance its interactions with PAN. The studies indicate that butyration of the lignin (BL) increased non-Newtonian behavior a...
The full use of biomass in future biorefineries has stimulated studies on utilization of lignin f... more The full use of biomass in future biorefineries has stimulated studies on utilization of lignin from agricultural crops, such as coffee husk, a major residue from coffee processing. This study focuses on characterizing the lignin obtained from coffee husk and its further wet oxidation products as a function of alkali loading, temperature and residence time. The lignin fraction after diluted acid and alkali pretreatments is composed primarily of p-hydroxylphenyl units (≥49%), with fewer guaiacyl and syringyl units. Linkages appear to be mainly β-O-4 ether linkages. Thermal degradation of pretreated lignin during wet oxidation occurred in two stages. Carboxylic acids were the main degradation product. Due to the condensed structure of this lignin, relatively low yields of aromatic aldehydes were achieved, except with temperatures over 210 °C, 5 min residence time and 11.7 wt% NaOH. Optimization of the pretreatment and oxidation parameters are important to maximizing yield of high-valu...
The wastewater stream from hydrothermal liquefaction (HTL) process used in biofuel production, co... more The wastewater stream from hydrothermal liquefaction (HTL) process used in biofuel production, contains a large amounts of organic compounds where several can be regarded as environmentally hazardous and requires significant treatment before disposal. In this study, semi-continuous anaerobic digestion is used to degrade the organic fraction of wastewater streams from HTL of the algae Tetraselmis (AgTet) and Chlorella (AgChlr). Results indicated high methane yields at 20-30% (v/v) HTL wastewater together with clarified manure, producing 327.2mL/gVS(or volatile solids in feed) for AgTet and 263.4mL/gVSfor AgChlr. There was a significant reduction in methane production at concentrations higher than 40% (v/v) HTL wastewater in the feed, possibly due to the accumulation of chloride salts or inhibitory compounds such as pyridines, piperidines and pyrrolidines. This was further confirmed by comparing COD, salt and the ammonia concentrations of the effluents after anaerobic digestion at different concentrations of wastewater in manure.
Flavonoids present in freeze-dried Sunbelt (Vitis labrusca L.) grape pomace were extracted at a p... more Flavonoids present in freeze-dried Sunbelt (Vitis labrusca L.) grape pomace were extracted at a pressure of 10.3 MPa and temperatures between 60 and 140C using pressurized hydroethanolic solvents (0, 40, 80% v/v ethanol in water) acidified with organic acids (formic, acetic, citric and tartaric acid at a pH of 2.5). Acetic acid had a significant effect in maximizing anthocyanin yield from grape pomace when using 80% aqueous ethanol as a solvent at 80C (1028.9 mg/100 g DW). However, organic acids did not have a significant effect on the extraction of flavonols from grape pomace. The maximum amount of flavonols extracted from grape pomace using 80% aqueous ethanol as the solvent at 120-140C was 9.65 mg/100 g DW. Surface response regression analysis of the experimental data indicated the optimum temperature for extraction of a maximum amount of anthocyanins from grape pomace was 85.4C and that for flavonols was 124C. These optimized conditions obtained from this study performed on an a...
Extensive research has been done on examining the autotrophic growth of Acetobacterium woodii wit... more Extensive research has been done on examining the autotrophic growth of Acetobacterium woodii with gaseous substrates (hydrogen and carbon dioxide) to produce acetic acid. However, only limited work has been performed on the heterotrophic growth of A. woodii using pure sugars or lignocellulosic feedstocks-derived sugars as substrates. In this study, we examine the growth kinetics and acetic acid production of A. woodii on glucose and xylose. While good growth was observed with glucose as substrate, no significant growth was obtained on xylose. Kinetic studies were performed in batch culture using different concentrations of glucose, ranging from 5 g/L to 40 g/L. The highest acetate production of 6.919 g/L with a product yield of 0.76 g acetic acid/g glucose was observed with 10 g/L glucose as initial substrate concentration. When testing A. woodii on corn stover hydrolysate (CSH) and wheat straw hydrolysate (WSH) formed after pretreatment and enzymatic hydrolysis, we found that A. w...
Lignin, while economically and environmentally beneficial, has had limited success in use in rein... more Lignin, while economically and environmentally beneficial, has had limited success in use in reinforcing carbon fibers due to harmful chemicals used in biomass pretreatment along with the limited physical interactions between lignin and polyacrylonitrile (PAN) during the spinning process. The focus of this study is to use lignin obtained from chemical-free oxidative biomass pretreatment (WEx) for blending with PAN at melt spinning conditions to produce carbon fiber precursors. In this study, the dynamic rheology of blending PAN with biorefinery lignin obtained from the WEx process is investigated with the addition of 1-butyl-3-methylimidazolium chloride as a plasticizer to address the current barriers of developing PAN/lignin carbon fiber precursors in the melt-spinning process. Lignin was esterified using butyric anhydride to reduce its hydrophilicity and to enhance its interactions with PAN. The studies indicate that butyration of the lignin (BL) increased non-Newtonian behavior a...
The full use of biomass in future biorefineries has stimulated studies on utilization of lignin f... more The full use of biomass in future biorefineries has stimulated studies on utilization of lignin from agricultural crops, such as coffee husk, a major residue from coffee processing. This study focuses on characterizing the lignin obtained from coffee husk and its further wet oxidation products as a function of alkali loading, temperature and residence time. The lignin fraction after diluted acid and alkali pretreatments is composed primarily of p-hydroxylphenyl units (≥49%), with fewer guaiacyl and syringyl units. Linkages appear to be mainly β-O-4 ether linkages. Thermal degradation of pretreated lignin during wet oxidation occurred in two stages. Carboxylic acids were the main degradation product. Due to the condensed structure of this lignin, relatively low yields of aromatic aldehydes were achieved, except with temperatures over 210 °C, 5 min residence time and 11.7 wt% NaOH. Optimization of the pretreatment and oxidation parameters are important to maximizing yield of high-valu...
The wastewater stream from hydrothermal liquefaction (HTL) process used in biofuel production, co... more The wastewater stream from hydrothermal liquefaction (HTL) process used in biofuel production, contains a large amounts of organic compounds where several can be regarded as environmentally hazardous and requires significant treatment before disposal. In this study, semi-continuous anaerobic digestion is used to degrade the organic fraction of wastewater streams from HTL of the algae Tetraselmis (AgTet) and Chlorella (AgChlr). Results indicated high methane yields at 20-30% (v/v) HTL wastewater together with clarified manure, producing 327.2mL/gVS(or volatile solids in feed) for AgTet and 263.4mL/gVSfor AgChlr. There was a significant reduction in methane production at concentrations higher than 40% (v/v) HTL wastewater in the feed, possibly due to the accumulation of chloride salts or inhibitory compounds such as pyridines, piperidines and pyrrolidines. This was further confirmed by comparing COD, salt and the ammonia concentrations of the effluents after anaerobic digestion at different concentrations of wastewater in manure.
Flavonoids present in freeze-dried Sunbelt (Vitis labrusca L.) grape pomace were extracted at a p... more Flavonoids present in freeze-dried Sunbelt (Vitis labrusca L.) grape pomace were extracted at a pressure of 10.3 MPa and temperatures between 60 and 140C using pressurized hydroethanolic solvents (0, 40, 80% v/v ethanol in water) acidified with organic acids (formic, acetic, citric and tartaric acid at a pH of 2.5). Acetic acid had a significant effect in maximizing anthocyanin yield from grape pomace when using 80% aqueous ethanol as a solvent at 80C (1028.9 mg/100 g DW). However, organic acids did not have a significant effect on the extraction of flavonols from grape pomace. The maximum amount of flavonols extracted from grape pomace using 80% aqueous ethanol as the solvent at 120-140C was 9.65 mg/100 g DW. Surface response regression analysis of the experimental data indicated the optimum temperature for extraction of a maximum amount of anthocyanins from grape pomace was 85.4C and that for flavonols was 124C. These optimized conditions obtained from this study performed on an a...
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Papers by Keerthi Srinivas