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Papers by Heather Trajano

ABSTRACT Both fluidized sand baths and steam chambers have been used to heat laboratory reactors,... more ABSTRACT Both fluidized sand baths and steam chambers have been used to heat laboratory reactors, in particular for studies of biomass pretreatment. In this study, several aspects of the heating performance of these devices were compared: time to heat reactors to reaction temperature, the stability of reactor temperature, and the convection coefficient. The convection coefficient was determined using correlations and multiple analyses of empirical data. On the basis of the results presented in this study, the steam chamber can heat reactors to temperature in a tenth of the time sand baths can, can maintain a more stable temperature during pretreatment, and has a convection coefficient one to two magnitudes greater than that of the sand bath. Therefore if heat transfer is critical, a steam chamber is advantageous.

Wyman/Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals, 2013

ABSTRACT Production of fuels and chemicals from lignocellulosic biomass typically requires an ini... more ABSTRACT Production of fuels and chemicals from lignocellulosic biomass typically requires an initial treatment to produce reactive intermediates. For ethanol production via biological conversion of sugars, this step is referred to as pretreatment and produces a more digestible form of biomass for subsequent enzymatic hydrolysis. Additionally, new developments in catalytic production of hydrocarbons for use as drop-in fuels or chemicals has generated interest in the conversion of biomass to reactive intermediates in addition to sugars such as furfural and levulinic acid that result from sugar dehydration. All of these intermediates can be generated through acid hydrolysis of biomass. In this chapter, changes in cellulose, hemicellulose, lignin, ash, and ultrastructure following acid hydrolysis of biomass are described. Furthermore, the evolution of acid treatment objectives is outlined along with common acidifying agents, reaction temperatures and times, and reactor configurations. Kinetic models of these reactions are also reviewed.

PeerJ, 2014

The cost of enzymes makes enzymatic hydrolysis one of the most expensive steps in the production ... more The cost of enzymes makes enzymatic hydrolysis one of the most expensive steps in the production of lignocellulosic ethanol. Diverse studies have used commercial enzyme cocktails assuming that change in total protein concentration during hydrolysis was solely due to adsorption of endo- and exoglucanases onto the substrate. Given the sensitivity of enzymes and proteins to media conditions this assumption was tested by evaluating and modeling the protein concentration of commercial cocktails at hydrolysis conditions. In the absence of solid substrate, the total protein concentration of a mixture of Celluclast 1.5 L and Novozyme 188 decreased by as much as 45% at 50 °C after 4 days. The individual cocktails as well as a mixture of both were stable at 20 °C. At 50 °C, the protein concentration of Celluclast 1.5 was relatively constant but Novozyme 188 decreased by as much as 77%. It was hypothesized that Novozyme 188 proteins suffer a structural change at 50 °C which leads to protein aggregation and precipitation. Lyophilized β-glucosidase (P-β-glucosidase) at 50 °C exhibited an aggregation rate which was successfully modeled using first order kinetics (R (2) = 0.97). By incorporating the possible presence of chaperone proteins in Novozyme 188, the protein aggregation observed for this cocktail was successfully modeled (R (2) = 0.96). To accurately model the increasing protein stability observed at high cocktail loadings, the model was modified to include the presence of additives in the cocktail (R (2) = 0.98). By combining the measurement of total protein concentration with the proposed Novozyme 188 protein aggregation model, the endo- and exoglucanases concentration in the solid and liquid phases during hydrolysis can be more accurately determined. This methodology can be applied to various systems leading to optimization of enzyme loading by minimizing the excess of endo- and exoglucanases. In addition, the monitoring of endo- and exoglucanases concentrations can be used to build mass balances of enzyme recycling processes and to techno-economically evaluate the viability of enzyme recycling.

Biotechnology for Biofuels, 2013

Background: Effective enzymatic hydrolysis of lignocellulosic biomass benefits from lignin remova... more Background: Effective enzymatic hydrolysis of lignocellulosic biomass benefits from lignin removal, relocation, and/or modification during hydrothermal pretreatment. Phase transition, depolymerization/repolymerization, and solubility effects may all influence these lignin changes. To better understand how lignin is altered, Populus trichocarpa x P. deltoides wood samples and cellulolytic enzyme lignin (CEL) isolated from P. trichocarpa x P. deltoides were subjected to batch and flowthrough pretreatments. The residual solids and liquid hydrolysate were characterized by gel permeation chromatography, heteronuclear single quantum coherence NMR, compositional analysis, and gas chromatography-mass spectrometry. Results: Changes in the structure of the solids recovered after the pretreatment of CEL and the production of aromatic monomers point strongly to depolymerization and condensation being primary mechanisms for lignin extraction and redeposition. The differences in lignin removal and phenolic compound production from native P. trichocarpa x P. deltoides and CEL suggested that lignin-carbohydrate interactions increased lignin extraction and the extractability of syringyl groups relative to guaiacyl groups. Conclusions: These insights into delignification during hydrothermal pretreatment point to desirable pretreatment strategies and plant modifications. Because depolymerization followed by repolymerization appears to be the dominant mode of lignin modification, limiting the residence time of depolymerized lignin moieties in the bulk liquid phase should reduce lignin content in pretreated biomass. In addition, the increase in lignin removal in the presence of polysaccharides suggests that increasing lignin-carbohydrate cross-links in biomass would increase delignification during pretreatment.

Bioresource Technology, 2015

Previous studies defined easy and difficult to hydrolyze fractions of hemicellulose that may resu... more Previous studies defined easy and difficult to hydrolyze fractions of hemicellulose that may result from bonds among cellulose, hemicellulose, and lignin. To understand how such bonds affect hydrolysis, Populus trichocarpa × Populus deltoides, holocellulose isolated from P. trichocarpa × P. deltoides and birchwood xylan were subjected to hydrothermal flow-through pretreatment. Samples were characterized by glycome profiling, HPLC, and UPLC-MS. Glycome profiling revealed steady fragmentation and removal of glycans from solids during hydrolysis. The extent of polysaccharide fragmentation, hydrolysis rate, and total xylose yield were lowest for P. trichocarpa × P. deltoides and greatest for birchwood xylan. Comparison of results from P. trichocarpa × P. deltoides and holocellulose suggested that lignin-carbohydrate complexes reduce hydrolysis rates and limit release of large xylooligomers. Smaller differences between results with holocellulose and birchwood xylan suggest xylan-cellulose hydrogen bonds limited hydrolysis, but to a lesser extent. These findings imply cell wall structure strongly influences hydrolysis.

ABSTRACT Both fluidized sand baths and steam chambers have been used to heat laboratory reactors,... more ABSTRACT Both fluidized sand baths and steam chambers have been used to heat laboratory reactors, in particular for studies of biomass pretreatment. In this study, several aspects of the heating performance of these devices were compared: time to heat reactors to reaction temperature, the stability of reactor temperature, and the convection coefficient. The convection coefficient was determined using correlations and multiple analyses of empirical data. On the basis of the results presented in this study, the steam chamber can heat reactors to temperature in a tenth of the time sand baths can, can maintain a more stable temperature during pretreatment, and has a convection coefficient one to two magnitudes greater than that of the sand bath. Therefore if heat transfer is critical, a steam chamber is advantageous.

Wyman/Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals, 2013

ABSTRACT Production of fuels and chemicals from lignocellulosic biomass typically requires an ini... more ABSTRACT Production of fuels and chemicals from lignocellulosic biomass typically requires an initial treatment to produce reactive intermediates. For ethanol production via biological conversion of sugars, this step is referred to as pretreatment and produces a more digestible form of biomass for subsequent enzymatic hydrolysis. Additionally, new developments in catalytic production of hydrocarbons for use as drop-in fuels or chemicals has generated interest in the conversion of biomass to reactive intermediates in addition to sugars such as furfural and levulinic acid that result from sugar dehydration. All of these intermediates can be generated through acid hydrolysis of biomass. In this chapter, changes in cellulose, hemicellulose, lignin, ash, and ultrastructure following acid hydrolysis of biomass are described. Furthermore, the evolution of acid treatment objectives is outlined along with common acidifying agents, reaction temperatures and times, and reactor configurations. Kinetic models of these reactions are also reviewed.

PeerJ, 2014

The cost of enzymes makes enzymatic hydrolysis one of the most expensive steps in the production ... more The cost of enzymes makes enzymatic hydrolysis one of the most expensive steps in the production of lignocellulosic ethanol. Diverse studies have used commercial enzyme cocktails assuming that change in total protein concentration during hydrolysis was solely due to adsorption of endo- and exoglucanases onto the substrate. Given the sensitivity of enzymes and proteins to media conditions this assumption was tested by evaluating and modeling the protein concentration of commercial cocktails at hydrolysis conditions. In the absence of solid substrate, the total protein concentration of a mixture of Celluclast 1.5 L and Novozyme 188 decreased by as much as 45% at 50 °C after 4 days. The individual cocktails as well as a mixture of both were stable at 20 °C. At 50 °C, the protein concentration of Celluclast 1.5 was relatively constant but Novozyme 188 decreased by as much as 77%. It was hypothesized that Novozyme 188 proteins suffer a structural change at 50 °C which leads to protein aggregation and precipitation. Lyophilized β-glucosidase (P-β-glucosidase) at 50 °C exhibited an aggregation rate which was successfully modeled using first order kinetics (R (2) = 0.97). By incorporating the possible presence of chaperone proteins in Novozyme 188, the protein aggregation observed for this cocktail was successfully modeled (R (2) = 0.96). To accurately model the increasing protein stability observed at high cocktail loadings, the model was modified to include the presence of additives in the cocktail (R (2) = 0.98). By combining the measurement of total protein concentration with the proposed Novozyme 188 protein aggregation model, the endo- and exoglucanases concentration in the solid and liquid phases during hydrolysis can be more accurately determined. This methodology can be applied to various systems leading to optimization of enzyme loading by minimizing the excess of endo- and exoglucanases. In addition, the monitoring of endo- and exoglucanases concentrations can be used to build mass balances of enzyme recycling processes and to techno-economically evaluate the viability of enzyme recycling.

Biotechnology for Biofuels, 2013

Background: Effective enzymatic hydrolysis of lignocellulosic biomass benefits from lignin remova... more Background: Effective enzymatic hydrolysis of lignocellulosic biomass benefits from lignin removal, relocation, and/or modification during hydrothermal pretreatment. Phase transition, depolymerization/repolymerization, and solubility effects may all influence these lignin changes. To better understand how lignin is altered, Populus trichocarpa x P. deltoides wood samples and cellulolytic enzyme lignin (CEL) isolated from P. trichocarpa x P. deltoides were subjected to batch and flowthrough pretreatments. The residual solids and liquid hydrolysate were characterized by gel permeation chromatography, heteronuclear single quantum coherence NMR, compositional analysis, and gas chromatography-mass spectrometry. Results: Changes in the structure of the solids recovered after the pretreatment of CEL and the production of aromatic monomers point strongly to depolymerization and condensation being primary mechanisms for lignin extraction and redeposition. The differences in lignin removal and phenolic compound production from native P. trichocarpa x P. deltoides and CEL suggested that lignin-carbohydrate interactions increased lignin extraction and the extractability of syringyl groups relative to guaiacyl groups. Conclusions: These insights into delignification during hydrothermal pretreatment point to desirable pretreatment strategies and plant modifications. Because depolymerization followed by repolymerization appears to be the dominant mode of lignin modification, limiting the residence time of depolymerized lignin moieties in the bulk liquid phase should reduce lignin content in pretreated biomass. In addition, the increase in lignin removal in the presence of polysaccharides suggests that increasing lignin-carbohydrate cross-links in biomass would increase delignification during pretreatment.

Bioresource Technology, 2015

Previous studies defined easy and difficult to hydrolyze fractions of hemicellulose that may resu... more Previous studies defined easy and difficult to hydrolyze fractions of hemicellulose that may result from bonds among cellulose, hemicellulose, and lignin. To understand how such bonds affect hydrolysis, Populus trichocarpa × Populus deltoides, holocellulose isolated from P. trichocarpa × P. deltoides and birchwood xylan were subjected to hydrothermal flow-through pretreatment. Samples were characterized by glycome profiling, HPLC, and UPLC-MS. Glycome profiling revealed steady fragmentation and removal of glycans from solids during hydrolysis. The extent of polysaccharide fragmentation, hydrolysis rate, and total xylose yield were lowest for P. trichocarpa × P. deltoides and greatest for birchwood xylan. Comparison of results from P. trichocarpa × P. deltoides and holocellulose suggested that lignin-carbohydrate complexes reduce hydrolysis rates and limit release of large xylooligomers. Smaller differences between results with holocellulose and birchwood xylan suggest xylan-cellulose hydrogen bonds limited hydrolysis, but to a lesser extent. These findings imply cell wall structure strongly influences hydrolysis.