RESUMEN
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
Dilute sulfuric acid (DA), sulfur dioxide (SO(2)), liquid hot water (LHW), soaking in aqueous ammonia (SAA), ammonia fiber expansion (AFEX), and lime pretreatments were applied to Alamo, Dacotah, and Shawnee switchgrass. Application of the same analytical methods and material balance approaches facilitated meaningful comparisons of glucose and xylose yields from combined pretreatment and enzymatic hydrolysis. Use of a common supply of cellulase, beta-glucosidase, and xylanase also eased comparisons. All pretreatments enhanced sugar recovery from pretreatment and subsequent enzymatic hydrolysis substantially compared to untreated switchgrass. Adding beta-glucosidase was effective early in enzymatic hydrolysis while cellobiose levels were high but had limited effect on longer term yields at the enzyme loadings applied. Adding xylanase improved yields most for higher pH pretreatments where more xylan was left in the solids. Harvest time had more impact on performance than switchgrass variety, and microscopy showed changes in different features could impact performance by different pretreatments.
Asunto(s)
Biotecnología/métodos , Carbohidratos/biosíntesis , Enzimas/metabolismo , Panicum/metabolismo , Amoníaco/metabolismo , Carbohidratos/análisis , Carbohidratos/aislamiento & purificación , Celulasa/metabolismo , Ecotipo , Endo-1,4-beta Xilanasas/metabolismo , Glucosa/análisis , Hidrólisis , Panicum/citología , Panicum/ultraestructura , Estaciones del Año , Xilosa/análisis , beta-Glucosidasa/metabolismoRESUMEN
Feedstock quality of switchgrass for biofuel production depends on many factors such as morphological types, geographic origins, maturity, environmental and cultivation parameters, and storage. We report variability in compositions and enzymatic digestion efficiencies for three cultivars of switchgrass (Alamo, Dacotah and Shawnee), grown and harvested at different locations and seasons. Saccharification yields of switchgrass processed by different pretreatment technologies (AFEX, dilute sulfuric acid, liquid hot water, lime, and soaking in aqueous ammonia) are compared in regards to switchgrass genotypes and harvest seasons. Despite its higher cellulose content per dry mass, Dacotah switchgrass harvested after wintering consistently gave a lower saccharification yield than the other two varieties harvested in the fall. The recalcitrance of upland cultivars and over-wintered switchgrass may require more severe pretreatment conditions. We discuss the key features of different pretreatment technologies and differences in switchgrass cultivars and harvest seasons on hydrolysis performance for the applied pretreatment methods.
Asunto(s)
Agricultura , Biotecnología/métodos , Ecotipo , Enzimas/metabolismo , Panicum/metabolismo , Hidrólisis , Estaciones del AñoRESUMEN
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RESUMEN
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
This work studied the benefits of adding different enzyme cocktails (cellulase, xylanase, ß-glucosidase) to pretreated switchgrass. Pretreatment methods included ammonia fiber expansion (AFEX), dilute-acid (DA), liquid hot water (LHW), lime, lime+ball-milling, soaking in aqueous ammonia (SAA), and sulfur dioxide (SO(2)). The compositions of the pretreated materials were analyzed and showed a strong correlation between initial xylan composition and the benefits of xylanase addition. Adding xylanase dramatically improved xylan yields for SAA (+8.4%) and AFEX (+6.3%), and showed negligible improvement (0-2%) for the pretreatments with low xylan content (dilute-acid, SO(2)). Xylanase addition also improved overall yields with lime+ball-milling and SO(2) achieving the highest overall yields from pretreated biomass (98.3% and 93.2%, respectively). Lime+ball-milling obtained an enzymatic yield of 92.3kg of sugar digested/kg of protein loaded.