Search

Search Results

• 1. [Article] The role of manganese peroxidase in biomass conversion technologies

  Currently, the technologies used to separate lignocellulosic biomass into its component parts (cellulose, hemicellulose, and lignin) and enzymatically hydrolyze the cellulose to glucose for conversion ...

  Citation × Citation Citation Abstract Copy Title: The role of manganese peroxidase in biomass conversion technologies Author: Yee, Kelsey L. Currently, the technologies used to separate lignocellulosic biomass into its component parts (cellulose, hemicellulose, and lignin) and enzymatically hydrolyze the cellulose to glucose for conversion to ethanol could be improved economically and in terms of efficiency. A major impediment to utilizing the biomass is the presence of residual lignin. The residual lignin "poisons" the cellulase enzymes and as a result, a lower glucose yield is obtained. A higher titer of cellulases could be used to increase the yield of glucose, but cellulases are expensive. A possibility to reduce the cost of cellulase enzymes and improve the efficiency, economics, extent and/or rate of hydrolysis is to use lignin-degrading fungal heme peroxidase such as manganese peroxidases. An efficient and economical glucose assay was developed to monitor the rate and extent of enzymatic hydrolysis of cellulose. The glucose assay is based on the glucose oxidase horseradish peroxidase enzymatic method, but uses bulk enzymes making it more economical than commercial kits. The glucose assay also has a higher throughput rate and is more economical than HPLC. In order to evaluate possible synergistic effects between cellulases and manganese peroxidase (MnP), rMnP was produced in high cell density fed-batch cultivations by the genetically engineered yeast, P. pastoris. In addition, a mathematic model was developed to describe the temperature dependant growth of P. pastoris and consumption of glucose and the production and temperature dependent degradation of rMnP in the bioreactor broth. The model successfully predicted the cell growth, substrate consumption, and rMnP production for the base case and also for cultivations with varying fed-batch air flow rates (k[subscript L]a) and temperatures. The production of rMnP requires cultures amended with exogenous heme and there are several sources of heme. Through shake flask experiments and bioreactor cultivations it was determined that 0.1 g/L of heme was necessary for producing high titers of rMnP (4,500 U/L). It was also determined that not all types of heme will yield the same rMnP titer. The water soluble fraction post pretreatment of lignocellulosic biomass contains inhibitors to fermentation such as 5-hydroxymethyl furfural (HMF) and furfural. rMnP was shown to degrade HMF (1 g/L) and furfural (1 g/L) and detoxify medium containing these inhibitors. The rMnP reduced furfural and HMF, measured by absorbance at 276 and 286 nm respectively and the degree of absorbance decrease was dependent on rMnP concentration. Furfural was more readily degraded by rMnP than HMF. Growth assays using S. cerevisiae indicated rMnP treatment detoxified medium containing furfural and HMF. The optimal conditions (temperature, pH, and buffer) for enzyme activity were determined for both AccelleraseTM 1000 (commercially available combination of cellulases) and rMnP using filter paper as a substrate. Woody biomass and corn stover were pretreated and then exposed to simultaneous or sequential treatment with rMnP and AccelleraseTM 1000. The results for the sequential treatment of Ponderosa pine and corn stover with rMnP and AccelleraseTM 1000 was inconclusive as to whether or not rMnP effected the production of glucose due to the high variability between replicates. Finally, part of my doctoral program was significant mentoring and facilitation of undergraduate research. A significant portion of my time was dedicated toward senior laboratory teaching assistance, serving as a mentor for high school students, and participating in research mentoring with 24 undergraduate students over five years, 19 of whom were women. Title: The role of manganese peroxidase in biomass conversion technologies Author: Yee, Kelsey L. Currently, the technologies used to separate lignocellulosic biomass into its component parts (cellulose, hemicellulose, and lignin) and enzymatically hydrolyze the cellulose to glucose for conversion to ethanol could be improved economically and in terms of efficiency. A major impediment to utilizing the biomass is the presence of residual lignin. The residual lignin "poisons" the cellulase enzymes and as a result, a lower glucose yield is obtained. A higher titer of cellulases could be used to increase the yield of glucose, but cellulases are expensive. A possibility to reduce the cost of cellulase enzymes and improve the efficiency, economics, extent and/or rate of hydrolysis is to use lignin-degrading fungal heme peroxidase such as manganese peroxidases. An efficient and economical glucose assay was developed to monitor the rate and extent of enzymatic hydrolysis of cellulose. The glucose assay is based on the glucose oxidase horseradish peroxidase enzymatic method, but uses bulk enzymes making it more economical than commercial kits. The glucose assay also has a higher throughput rate and is more economical than HPLC. In order to evaluate possible synergistic effects between cellulases and manganese peroxidase (MnP), rMnP was produced in high cell density fed-batch cultivations by the genetically engineered yeast, P. pastoris. In addition, a mathematic model was developed to describe the temperature dependant growth of P. pastoris and consumption of glucose and the production and temperature dependent degradation of rMnP in the bioreactor broth. The model successfully predicted the cell growth, substrate consumption, and rMnP production for the base case and also for cultivations with varying fed-batch air flow rates (k[subscript L]a) and temperatures. The production of rMnP requires cultures amended with exogenous heme and there are several sources of heme. Through shake flask experiments and bioreactor cultivations it was determined that 0.1 g/L of heme was necessary for producing high titers of rMnP (4,500 U/L). It was also determined that not all types of heme will yield the same rMnP titer. The water soluble fraction post pretreatment of lignocellulosic biomass contains inhibitors to fermentation such as 5-hydroxymethyl furfural (HMF) and furfural. rMnP was shown to degrade HMF (1 g/L) and furfural (1 g/L) and detoxify medium containing these inhibitors. The rMnP reduced furfural and HMF, measured by absorbance at 276 and 286 nm respectively and the degree of absorbance decrease was dependent on rMnP concentration. Furfural was more readily degraded by rMnP than HMF. Growth assays using S. cerevisiae indicated rMnP treatment detoxified medium containing furfural and HMF. The optimal conditions (temperature, pH, and buffer) for enzyme activity were determined for both AccelleraseTM 1000 (commercially available combination of cellulases) and rMnP using filter paper as a substrate. Woody biomass and corn stover were pretreated and then exposed to simultaneous or sequential treatment with rMnP and AccelleraseTM 1000. The results for the sequential treatment of Ponderosa pine and corn stover with rMnP and AccelleraseTM 1000 was inconclusive as to whether or not rMnP effected the production of glucose due to the high variability between replicates. Finally, part of my doctoral program was significant mentoring and facilitation of undergraduate research. A significant portion of my time was dedicated toward senior laboratory teaching assistance, serving as a mentor for high school students, and participating in research mentoring with 24 undergraduate students over five years, 19 of whom were women. Close

• 2. [Article] Conversion of biomass constituents to hydrogen-rich gas by supercritical water in a microchannel reactor

  Microreactors offer high rates of heat transfer able to intensify highly endothermic biomass reforming reactions in supercritical water. In this study, two continuous flow microreactor configurations were ...

  Citation × Citation Citation Abstract Copy Title: Conversion of biomass constituents to hydrogen-rich gas by supercritical water in a microchannel reactor Author: Goodwin, Aaron K. Microreactors offer high rates of heat transfer able to intensify highly endothermic biomass reforming reactions in supercritical water. In this study, two continuous flow microreactor configurations were used to gasify biomass constituents in supercritical water. The first reactor configuration was a micro diameter stainless steel or Hastelloy tube (508 µm – 762 µm) imbedded into a reactor block. The reactor provided high rates of heat transfer to the reacting fluid to sustain an isothermal reaction temperature and was used to elucidate interactions between phenol, a lignin model compound, and xylose, a hemicellulose model compound, during co-gasification. In addition, a reaction mechanism and kinetics for phenol and xylose gasification by supercritical were estimated. The second microreactor configuration studied was a parallel channel Hastelloy microreactor. The reactor consisted of 14 parallel rectangular microchannels (1000 µm by 127 µm) integrated into a single contiguous reactor block by diffusion bonding a series of shims between two header plates. Fabrication of the reactor from Hastelloy C-276, a high nickel content alloy, substantially intensified biomass gasification reactions and promoted the water gas shift and methanation reactions due to its high catalytic activity and the large surface area to volume ratio in the microchannel. The dispersion and channel flow distribution in the microchannel reactor was characterized experimentally and modeled using computational fluid dynamics by a tracer pulse study. Furthermore, computational fluid dynamics were used to investigate the effect of endothermic biomass reforming reactions and the average fluid Reynolds number on the reaction temperature. Lastly, xylose was completely gasified to hydrogen and carbon dioxide in the parallel channel microreactor at 650°C and 250 bar within a 1.4 second residence time. Title: Conversion of biomass constituents to hydrogen-rich gas by supercritical water in a microchannel reactor Author: Goodwin, Aaron K. Microreactors offer high rates of heat transfer able to intensify highly endothermic biomass reforming reactions in supercritical water. In this study, two continuous flow microreactor configurations were used to gasify biomass constituents in supercritical water. The first reactor configuration was a micro diameter stainless steel or Hastelloy tube (508 µm – 762 µm) imbedded into a reactor block. The reactor provided high rates of heat transfer to the reacting fluid to sustain an isothermal reaction temperature and was used to elucidate interactions between phenol, a lignin model compound, and xylose, a hemicellulose model compound, during co-gasification. In addition, a reaction mechanism and kinetics for phenol and xylose gasification by supercritical were estimated. The second microreactor configuration studied was a parallel channel Hastelloy microreactor. The reactor consisted of 14 parallel rectangular microchannels (1000 µm by 127 µm) integrated into a single contiguous reactor block by diffusion bonding a series of shims between two header plates. Fabrication of the reactor from Hastelloy C-276, a high nickel content alloy, substantially intensified biomass gasification reactions and promoted the water gas shift and methanation reactions due to its high catalytic activity and the large surface area to volume ratio in the microchannel. The dispersion and channel flow distribution in the microchannel reactor was characterized experimentally and modeled using computational fluid dynamics by a tracer pulse study. Furthermore, computational fluid dynamics were used to investigate the effect of endothermic biomass reforming reactions and the average fluid Reynolds number on the reaction temperature. Lastly, xylose was completely gasified to hydrogen and carbon dioxide in the parallel channel microreactor at 650°C and 250 bar within a 1.4 second residence time. Close