Extrusion processing for ammonia fiber explosion (AFEX)

The ammonia fiber explosion (AFEX) process, previously run only in a batch reactor, has been adapted to run on a twin-screw extruder. The sugar yield of AFEX material after enzymatic hydrolysis has been increased up to 3.5 times over that of completely untreated material. The ruminant digestibility of corn fodder has been increased up to 32% (from 54–71%) over completely untreated material, and 23% (from 63–77%) over material extruded with no ammonia. Extrusion-treated material proved more digestible by the ruminant at 48 h than material treated in the batch reactor.     

Ethanol production from AFEX-treated forages and agricultural residues

Lignocellulosic materials derived from forages, namely timothy grass, alfalfa, reed canary grass, and agricultural residues, such as corn stalks and barley straw, were pretreated using ammonia fiber explosion (AFEX) process. The pretreated materials were directly saccharified by cellulolytic enzymes. Sixty to 80% of theoretical yield of sugars were obtained from the pretreated biomasses. Subsequent ethanolic fermentation of the hydrolysates byPachysolen tannophilus ATCC 32691 resulted in 40-60% of theoretical yield after 24 h, based on the sugars present in the hydrolysates. The uptake of sugars was not complete, indicating a possible inhibitory effect onP. tannophilus during the fermentation of these substrates.     

Pretreatment processes for lignocellulosic biomass conversion to biofuels and bioproducts

Lignocellulosic materials, such as forestry, agricultural and agroindustrial residues, are among the most important sources of biomass for the production of fuels, chemicals and materials. However there are physical and chemical barriers in the lignin–carbohydrate supramolecular structure that render most plant cell wall components almost completely unavailable for conversion into commercial products. Thus successful conversion strategies must lead to the disruption of this structure and result in partial or total separation of the lignocellulosic components, increasing the accessibility of cellulose, hemicelluloses and lignins. It must also minimize the formation of by-products. Each pretreatment technology has its own characteristics and is usually applied to a specific source of carbohydrates and lignins. A general overview of the most important pretreatment methods for the production of platform chemicals and fermentable sugars are given in this paper.     

Predicting digestibility of ammonia fiber explosion (AFEX)-treated rice straw

The enzymatic digestibility of ammonia fiber explosion (AFEX)-treated rice straw was modeled by statistically correlating the variability of samples to differences in treatment using several different analytical techniques. Lignin content and crystallinity index of cellulose affect enzymatic hydrolysis the most. X-ray diffraction was used to measure the crystallinity index (CrI), while fluorescence and diffuse reflectance infrared (DRIFT) spectroscopy measured the lignin content of the samples. Multivariate analysis was applied to correlate the enzymatic hydrolysis results of the various samples with X-ray diffraction and spectroscopic data. Principal component analysis (PCA) and multilinear regression (MLR) techniques did not accurately predict the digestibility of the rice straw samples. The best correlation (R value of 0.775) was found between the treatment conditions of the AFEX process and the concentration of xylose at 24 h after enzymatic hydrolysis.     

Pretreatment of switchgrass by ammonia fiber explosion (AFEX)

The effects of ammonia fiber explosion (AFEX) pretreatment of switch grass using its major process variables are reported. The optimal pretreatment conditions for switchgrass were found to be near 100°C reactor temperature, and ammonia loading of 1:1 kg of ammonia: kg of dry matter with 80% moisture content (dry weight basis [dwb]) at 5 min residence time. Hydrolysis results of AFEX-treated and untreated samples showed 93% vs 16% glucan conversion, respectively. The ethanol yield of optimized AFEX-treated switchgrass was measured to be about 0.2 g ethanol/g dry biomass, which is 2.5 times more than that of the untreated sample.     

Extraction of Proteins from Switchgrass Using Aqueous Ammonia within an Integrated Biorefinery

Switchgrass (Panicum vergatum) is a potential feedstock for future cellulosic biorefineries. Such a feedstock may also provide protein, most likely for use as an animal feed. In this paper, we present a potential scheme for integrating fiber processing with extractions to obtain both sugar and protein products from switchgrass pretreated using Ammonia Fiber Expansion (AFEX). Solutions of 3% aqueous ammonia at pH 10.5 provided optimal extraction of proteins. Addition of the nonionic surfactant Tween-80 improved protein recovery for AFEX-treated materials. It was determined that an extraction following AFEX solubilized approximately 40% of the protein, while a subsequent hydrolysis solubilized much of the remaining protein while producing 325 g sugar per kg biomass. The remaining insoluble residue contained very little protein or ash, making it ideal for heat and power production. In contrast, an extraction following hydrolysis solubilized only 68% of the original protein in the biomass, while obtaining slightly higher sugar yields.     

Understanding factors that limit enzymatic hydrolysis of biomass

Spectroscopic characterization of both untreated and treated material is being performed in order to determine changes in the biomass and the effects of pretreatment on crystallinity, lignin content, selected chemical bonds, and depolymerization of hemicellulose and lignin. The methods used are X-ray diffraction for determination of cellulose crystallinity (CrI); diffusive reflectance infrared (DRIFT) for changes in C-C and C-O bonds; and fluorescence to determine lignin content. Changes in spectral characteristics and crystallinity are statistically correlated with enzymatic hydrolysis results to identify and better understand the fundamental features of biomass that govern its enzymatic conversion to monomeric sugars. Models of the hydrolysis initial rate and 72 h extent of conversion were developed and evaluated. Results show that the hydrolysis initial rate is most influenced by the cellulose crystallinity, while lignin content most influences the extent of hydrolysis at 72 h. However, it should be noted that in this study only crystallinity, lignin, and selected chemical bonds were used as inputs to the models. The incorporation of additional parameters that affect the hydrolysis, like pore volume and size and surface area accessibility, would improve the predictive capability of the models.