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...
Carboxylic acids are traditionally produced from fossil fuels and have significant applications i... more Carboxylic acids are traditionally produced from fossil fuels and have significant applications in the chemical, pharmaceutical, food, and fuel industries. Significant progress has been made in replacing such fossil fuel sources used for production of carboxylic acids with sustainable and renewable biomass resources. However, the merits and demerits of each carboxylic acid processing platform are dependent on the application of the final product in the industry. There are a number of studies that indicate that separation processes account for over 30% of the total processing costs in such processes. This review focuses on the sustainable processing of biomass resources to produce carboxylic acids. The primary focus of the review will be on a discussion of and comparison between existing biochemical processes for producing lower-chain fatty acids such as acetic-, propionic-, butyric-, and lactic acids. The significance of these acids stems from the recent progress in catalytic upgrading to produce biofuels apart from the current applications of the carboxylic acids in the food, pharmaceutical, and plastics sectors. A significant part of the review will discuss current state-of-art of techniques for separation and purification of these acids from fermentation broths for further downstream processing to produce high-value products.
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.
Biorefinery lignin stream obtained after wet explosion pretreatment of forest residues were furth... more Biorefinery lignin stream obtained after wet explosion pretreatment of forest residues were further degraded using wet oxidation to produce high-value biochemicals. The biorefinery lignin stream was characterized to understand efficiency of oxidative degradation process.
Experiments on the aqueous-based carbonated water hydrolysis of switch grass have shown the poten... more Experiments on the aqueous-based carbonated water hydrolysis of switch grass have shown the potential of producing carbochemicals derived from the rearrangement of sugars at temperatures between 150-200°C. In this study, both pure and carbonated water have been used to treat switch grass at higher temperatures (220-310°C) and commensurate higher pressure (68 bars) in a semi-continuous batch flow system designed with the provisions for sample dilution after reactions as well as continuous in-situ carbon dioxide addition to the flowing water stream. Using small reaction cells containing comminuted switch grass, the rate of production of furfural, 5-hydroxymethylfurfural (HMF), formic acid and acetic acid were determined by taking samples of the aqueous reaction over a 60 minutes time periods. Integral accumulation curves for these four carbochemicals derived from sugars intermittently hydrolyzed from switch grass showed varying behavior. Furfural was rapidly produced at all temperatures within 10 min at 310°C. Formic acid and acetic acids could be produced at levels of 3-6 g/100g switch grass between temperatures of 220-310°C. The resultant pH of the flowing water solution along with an estimate of precipitated biomass material allowed further overall assessment on the applicability of the experimental system to yield information on using high temperature water to convert biomass-derived sugars to target carbochemicals.
Process engineering operations in food and nutraceutical industries pertaining to the design of e... more Process engineering operations in food and nutraceutical industries pertaining to the design of extraction of value-added products from biomass using pressurized liquids involve a careful selection of the solvent and optimal temperature conditions to achieve maximum yield. Complex molecular structure and limited physical property data in the literature of biological solutes extracted from biomass compounds have necessitated the process modeling of such operations. In this study, we have applied the Hansen 3-dimensional solubility parameter concept to optimize the extraction of molecularly complex solutes using subcritical fluid solvents. Hansen solubility spheres characterized by the relative energy differences (RED) have been used to characterize and quantify the solute-subcritical solvent interactions as a function of temperature. The solvent power of subcritical water and compressed hydroethanolic mixtures above their boiling points has been characterized using the above-mentioned method. The use of group contribution methods in collaboration with computerized algorithms to plot the Hansen spheres provides a quantitative prediction tool for optimizing the design of extraction conditions. The method can be used to estimate conditions for solute-solvent miscibility, an optimum temperature range for conducting extractions under pressurized conditions, and approximate extraction conditions of solutes from natural matrices.
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...
Background: In biorefineries, various pretreatments traditionally employ hazardous chemicals (amm... more Background: In biorefineries, various pretreatments traditionally employ hazardous chemicals (ammonia, sulfuric acid, sulfite, etc.) for opening the softwood structure and to facilitate easy accessibility of the cellulose for further downstream processing. The resultant lignin (known as technical lignin) after extraction of the carbohydrate fraction as sugars has been either burned as fuel or used in biochemical or biofuel production. It has been observed that the technical lignin after such biomass pretreatments is often more condensed and, hence, cannot be easily used to produce fine chemicals of high value. In this study, we examine lignin after wet explosion pretreatment where the biomass in subjected to oxygen to understand how these interactions will affect lignin utilization for biochemical production.
Supercritical fluids and their liquefied analogues have been traditionally used in single unit op... more Supercritical fluids and their liquefied analogues have been traditionally used in single unit operations, i.e. extraction, fractionation, using neat supercritical carbon dioxide (SC-CO 2 ) or with appropriate modifiers. Many of the supercritical fluid extraction processes have been devoted to extraction of food and natural products. Beginning in the mid-1980s, columnar and chromatographic techniques followed by reactions in supercritical fluids were developed to facilitate supercritical fluid derived extracts or products, thereby extending the application of a critical fluids processing platform beyond SFE. These newer developments were investigated in part due to the complexity of many natural product matrices and the desire to concentrate specific target components for food and other industrial uses. In this chapter the advantages of coupling processing options using critical fluids are discussed and pertinent examples provided. Hence by combining different unit processes and sequencing them with the use of multiple fluids utilized at different temperatures and pressures, one can obtain multiple products and optimize the extraction or reaction process. Several specific options are illustrated for the cases of processing lipid-based materials such as concentrates of tocopherols, sterols, and phospholipids. Sequential isolation of both non-polar and polar ingredients is documented using a combination of fluids and/or unit processes. Finally the merits and difficulties in integrating critical fluid technology into the concept of a "bio-refinery" are provided.
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...
Carboxylic acids are traditionally produced from fossil fuels and have significant applications i... more Carboxylic acids are traditionally produced from fossil fuels and have significant applications in the chemical, pharmaceutical, food, and fuel industries. Significant progress has been made in replacing such fossil fuel sources used for production of carboxylic acids with sustainable and renewable biomass resources. However, the merits and demerits of each carboxylic acid processing platform are dependent on the application of the final product in the industry. There are a number of studies that indicate that separation processes account for over 30% of the total processing costs in such processes. This review focuses on the sustainable processing of biomass resources to produce carboxylic acids. The primary focus of the review will be on a discussion of and comparison between existing biochemical processes for producing lower-chain fatty acids such as acetic-, propionic-, butyric-, and lactic acids. The significance of these acids stems from the recent progress in catalytic upgrading to produce biofuels apart from the current applications of the carboxylic acids in the food, pharmaceutical, and plastics sectors. A significant part of the review will discuss current state-of-art of techniques for separation and purification of these acids from fermentation broths for further downstream processing to produce high-value products.
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.
Biorefinery lignin stream obtained after wet explosion pretreatment of forest residues were furth... more Biorefinery lignin stream obtained after wet explosion pretreatment of forest residues were further degraded using wet oxidation to produce high-value biochemicals. The biorefinery lignin stream was characterized to understand efficiency of oxidative degradation process.
Experiments on the aqueous-based carbonated water hydrolysis of switch grass have shown the poten... more Experiments on the aqueous-based carbonated water hydrolysis of switch grass have shown the potential of producing carbochemicals derived from the rearrangement of sugars at temperatures between 150-200°C. In this study, both pure and carbonated water have been used to treat switch grass at higher temperatures (220-310°C) and commensurate higher pressure (68 bars) in a semi-continuous batch flow system designed with the provisions for sample dilution after reactions as well as continuous in-situ carbon dioxide addition to the flowing water stream. Using small reaction cells containing comminuted switch grass, the rate of production of furfural, 5-hydroxymethylfurfural (HMF), formic acid and acetic acid were determined by taking samples of the aqueous reaction over a 60 minutes time periods. Integral accumulation curves for these four carbochemicals derived from sugars intermittently hydrolyzed from switch grass showed varying behavior. Furfural was rapidly produced at all temperatures within 10 min at 310°C. Formic acid and acetic acids could be produced at levels of 3-6 g/100g switch grass between temperatures of 220-310°C. The resultant pH of the flowing water solution along with an estimate of precipitated biomass material allowed further overall assessment on the applicability of the experimental system to yield information on using high temperature water to convert biomass-derived sugars to target carbochemicals.
Process engineering operations in food and nutraceutical industries pertaining to the design of e... more Process engineering operations in food and nutraceutical industries pertaining to the design of extraction of value-added products from biomass using pressurized liquids involve a careful selection of the solvent and optimal temperature conditions to achieve maximum yield. Complex molecular structure and limited physical property data in the literature of biological solutes extracted from biomass compounds have necessitated the process modeling of such operations. In this study, we have applied the Hansen 3-dimensional solubility parameter concept to optimize the extraction of molecularly complex solutes using subcritical fluid solvents. Hansen solubility spheres characterized by the relative energy differences (RED) have been used to characterize and quantify the solute-subcritical solvent interactions as a function of temperature. The solvent power of subcritical water and compressed hydroethanolic mixtures above their boiling points has been characterized using the above-mentioned method. The use of group contribution methods in collaboration with computerized algorithms to plot the Hansen spheres provides a quantitative prediction tool for optimizing the design of extraction conditions. The method can be used to estimate conditions for solute-solvent miscibility, an optimum temperature range for conducting extractions under pressurized conditions, and approximate extraction conditions of solutes from natural matrices.
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...
Background: In biorefineries, various pretreatments traditionally employ hazardous chemicals (amm... more Background: In biorefineries, various pretreatments traditionally employ hazardous chemicals (ammonia, sulfuric acid, sulfite, etc.) for opening the softwood structure and to facilitate easy accessibility of the cellulose for further downstream processing. The resultant lignin (known as technical lignin) after extraction of the carbohydrate fraction as sugars has been either burned as fuel or used in biochemical or biofuel production. It has been observed that the technical lignin after such biomass pretreatments is often more condensed and, hence, cannot be easily used to produce fine chemicals of high value. In this study, we examine lignin after wet explosion pretreatment where the biomass in subjected to oxygen to understand how these interactions will affect lignin utilization for biochemical production.
Supercritical fluids and their liquefied analogues have been traditionally used in single unit op... more Supercritical fluids and their liquefied analogues have been traditionally used in single unit operations, i.e. extraction, fractionation, using neat supercritical carbon dioxide (SC-CO 2 ) or with appropriate modifiers. Many of the supercritical fluid extraction processes have been devoted to extraction of food and natural products. Beginning in the mid-1980s, columnar and chromatographic techniques followed by reactions in supercritical fluids were developed to facilitate supercritical fluid derived extracts or products, thereby extending the application of a critical fluids processing platform beyond SFE. These newer developments were investigated in part due to the complexity of many natural product matrices and the desire to concentrate specific target components for food and other industrial uses. In this chapter the advantages of coupling processing options using critical fluids are discussed and pertinent examples provided. Hence by combining different unit processes and sequencing them with the use of multiple fluids utilized at different temperatures and pressures, one can obtain multiple products and optimize the extraction or reaction process. Several specific options are illustrated for the cases of processing lipid-based materials such as concentrates of tocopherols, sterols, and phospholipids. Sequential isolation of both non-polar and polar ingredients is documented using a combination of fluids and/or unit processes. Finally the merits and difficulties in integrating critical fluid technology into the concept of a "bio-refinery" are provided.
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Papers by Keerthi Srinivas