RESUMEN
Switchgrass is a North American grass that is considered to be a highly promising herbaceous bioenergy feedstock. Differences in processing conditions and yields specifically related to switchgrass cultivar or cytotype (upland or lowland) can be confounded by differences in harvest date or region of growth. For this research, AFEX™ pretreatment conditions and hydrolysis enzyme mixtures were statistically optimized for Alamo (lowland) and Shawnee (upland) switchgrass that had been harvested in December in Oklahoma. Optimal pretreatment conditions and enzyme mixtures were almost identical for both varieties and gave similar mass sugar yields. Inclusion of hemicellulases in the enzyme mixture maintained total sugar yields with 50% reduction in enzyme loading. Regardless of variety, the biorefinery should be able to obtain high sugar yields using the same pretreatment and hydrolysis conditions to process switchgrass grown under the same environmental conditions, in the same location, and harvested at the same time of the year.
Asunto(s)
Carbohidratos/síntesis química , Glicósido Hidrolasas/química , Modelos Químicos , Simulación por Computador , PanicumRESUMEN
Six biomass pretreatment processes to convert switchgrass to fermentable sugars and ultimately to cellulosic ethanol are compared on a consistent basis in this technoeconomic analysis. The six pretreatment processes are ammonia fiber expansion (AFEX), dilute acid (DA), lime, liquid hot water (LHW), soaking in aqueous ammonia (SAA), and sulfur dioxide-impregnated steam explosion (SO(2)). Each pretreatment process is modeled in the framework of an existing biochemical design model so that systematic variations of process-related changes are consistently captured. The pretreatment area process design and simulation are based on the research data generated within the Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI) 3 project. Overall ethanol production, total capital investment, and minimum ethanol selling price (MESP) are reported along with selected sensitivity analysis. The results show limited differentiation between the projected economic performances of the pretreatment options, except for processes that exhibit significantly lower monomer sugar and resulting ethanol yields.
Asunto(s)
Biotecnología/economía , Biotecnología/métodos , Etanol/economía , Etanol/metabolismo , Lignina/metabolismo , Panicum/metabolismo , Amoníaco/farmacología , Compuestos de Calcio/farmacología , Carbohidratos/análisis , Calor , Óxidos/farmacología , Panicum/efectos de los fármacos , Dióxido de Azufre/farmacología , Ácidos Sulfúricos/farmacología , Agua/farmacologíaRESUMEN
Accellerase 1000 cellulase, Spezyme CP cellulase, ß-glucosidase, Multifect xylanase, and beta-xylosidase were evaluated for hydrolysis of pure cellulose, pure xylan, and switchgrass solids from leading pretreatments of dilute sulfuric acid, sulfur dioxide, liquid hot water, lime, soaking in aqueous ammonia, and ammonia fiber expansion. Distinctive sugar release patterns were observed from Avicel, phosphoric acid swollen cellulose (PASC), xylan, and pretreated switchgrass solids, with accumulation of significant amounts of xylooligomers during xylan hydrolysis. The strong inhibition of cellulose hydrolysis by xylooligomers could be partially attributed to the negative impact of xylooligomers on cellulase adsorption. The digestibility of pretreated switchgrass varied with pretreatment but could not be consistently correlated to xylan, lignin, or acetyl removal. Initial hydrolysis rates did correlate well with cellulase adsorption capacities for all pretreatments except lime, but more investigation is needed to relate this behavior to physical and compositional properties of pretreated switchgrass.
Asunto(s)
Biotecnología/métodos , Celulasa/metabolismo , Celulosa/metabolismo , Glicósido Hidrolasas/metabolismo , Panicum/metabolismo , Xilanos/metabolismo , Adsorción , Glucosa/análisis , Hidrólisis , Cinética , Ácidos Fosfóricos/química , Xilosa/metabolismoRESUMEN
The US Department of Energy-funded Biomass Refining CAFI (Consortium for Applied Fundamentals and Innovation) project has developed leading pretreatment technologies for application to switchgrass and has evaluated their effectiveness in recovering sugars from the coupled operations of pretreatment and enzymatic hydrolysis. Key chemical and physical characteristics have been determined for pretreated switchgrass samples. Several analytical microscopy approaches utilizing instruments in the Biomass Surface Characterization Laboratory (BSCL) at the National Renewable Energy Laboratory (NREL) have been applied to untreated and CAFI-pretreated switchgrass samples. The results of this work have shown that each of the CAFI pretreatment approaches on switchgrass result in different structural impacts at the plant tissue, cellular, and cell wall levels. Some of these structural changes can be related to changes in chemical composition upon pretreatment. There are also apparently different structural mechanisms that are responsible for achieving the highest enzymatic hydrolysis sugar yields.
Asunto(s)
Biotecnología/métodos , Panicum/ultraestructura , Agricultura , Amoníaco/metabolismo , Pared Celular/metabolismo , Pared Celular/ultraestructura , Color , Ecotipo , Hidrólisis , Microfibrillas/ultraestructura , Panicum/citología , Porosidad , Propiedades de SuperficieRESUMEN
The objective of this work is to investigate the effects of cellulase loading and ß-glucosidase supplementation on enzymatic hydrolysis of pretreated Dacotah switchgrass. To assess the difference among various pretreatment methods, the profiles of sugars and intermediates were determined for differently treated substrates. For all pretreatments, 72 h glucan/xylan digestibilities increased sharply with enzyme loading up to 25mg protein/g-glucan, after which the response varied depending on the pretreatment method. For a fixed level of enzyme loading, dilute sulfuric acid (DA), SO(2), and Lime pretreatments exhibited higher digestibility than the soaking in aqueous ammonia (SAA) and ammonia fiber expansion (AFEX). Supplementation of Novozyme-188 to Spezyme-CP improved the 72 h glucan digestibility only for the SAA treated samples. The effect of ß-glucosidase supplementation was discernible only at the early phase of hydrolysis where accumulation of cellobiose and oligomers is significant. Addition of ß-glucosidase increased the xylan digestibility of alkaline treated samples due to the ß-xylosidase activity present in Novozyme-188.
Asunto(s)
Biotecnología/métodos , Panicum/metabolismo , beta-Glucosidasa/metabolismo , Celobiosa/metabolismo , Glucanos/metabolismo , Glucosa/metabolismo , Hidrólisis , Panicum/efectos de los fármacosRESUMEN
For this project, six chemical pretreatments were compared for the Consortium for Applied Fundamentals and Innovation (CAFI): ammonia fiber expansion (AFEX), dilute sulfuric acid (DA), lime, liquid hot water (LHW), soaking in aqueous ammonia (SAA), and sulfur dioxide (SO(2)). For each pretreatment, a material balance was analyzed around the pretreatment, optional post-washing step, and enzymatic hydrolysis of Dacotah switchgrass. All pretreatments+enzymatic hydrolysis solubilized over two-thirds of the available glucan and xylan. Lime, post-washed LHW, and SO(2) achieved >83% total glucose yields. Lime, post-washed AFEX, and DA achieved >83% total xylose yields. Alkaline pretreatments, except AFEX, solubilized the most lignin and a portion of the xylan as xylo-oligomers. As pretreatment pH decreased, total solubilized xylan and released monomeric xylose increased. Low temperature-long time or high temperature-short time pretreatments are necessary for high glucose release from late-harvest Dacotah switchgrass but high temperatures may cause xylose degradation.
Asunto(s)
Biotecnología/métodos , Metabolismo de los Hidratos de Carbono , Panicum/metabolismo , Polímeros/metabolismo , Biomasa , Pared Celular/metabolismo , Glucosa/análisis , Hidrólisis , Solubilidad , Xilosa/análisisRESUMEN
BACKGROUND: Corn stover composition changes considerably throughout the growing season and also varies between the various fractions of the plant. These differences can impact optimal pretreatment conditions, enzymatic digestibility and maximum achievable sugar yields in the process of converting lignocellulosics to ethanol. The goal of this project was to determine which combination of corn stover fractions provides the most benefit to the biorefinery in terms of sugar yields and to determine the preferential order in which fractions should be harvested. Ammonia fiber expansion (AFEX) pretreatment, followed by enzymatic hydrolysis, was performed on early and late harvest corn stover fractions (stem, leaf, husk and cob). Sugar yields were used to optimize scenarios for the selective harvest of corn stover assuming 70% or 30% collection of the total available stover. RESULTS: The optimal AFEX conditions for all stover fractions, regardless of harvest period, were: 1.5 (g NH3 g-1 biomass); 60% moisture content (dry-weight basis; dwb), 90 degrees C and 5 min residence time. Enzymatic hydrolysis was conducted using cellulase, beta-glucosidase, and xylanase at 31.3, 41.3, and 3.1 mg g-1 glucan, respectively. The optimal harvest order for selectively harvested corn stover (SHCS) was husk > leaf > stem > cob. This harvest scenario, combined with optimal AFEX pretreatment conditions, gave a theoretical ethanol yield of 2051 L ha-1 and 912 L ha-1 for 70% and 30% corn stover collection, respectively. CONCLUSION: Changing the proportion of stover fractions collected had a smaller impact on theoretical ethanol yields (29 - 141 L ha-1) compared to the effect of altering pretreatment and enzymatic hydrolysis conditions (150 - 462 L ha-1) or harvesting less stover (852 - 1139 L ha-1). Resources may be more effectively spent on improving sustainable harvesting, thereby increasing potential ethanol yields per hectare harvested, and optimizing biomass processing rather than focusing on the selective harvest of specific corn stover fractions.