Pretreatment dilute-acid

The Purdue concepts have been applied to several different agricultural products, such as corn stalks, alfalfa, orchard grass, tall fescue, and sugarcane bagasse. No experiments have been reported on either hardwoods or softwoods. The processes have been explored in two major modes. In the first, the entire agricultural residue is treated with solvent in the second, a dilute acid pretreatment to remove hemicellulose precedes solvent treatment. The first process is especially desirable for making furfural or fermentation products from hemicellulose as a separate activity. Then, the hemicellulose-free raw material can be converted to substantially pure glucose. 

The oils present in the QF differ from those found in the germ (corn oil) and in particular are enriched for phytosterols, which are cholesterol-lowering agents (5-9). A prior study with corn fiber demonstrated that the oils withstood dilute-acid) pretreatment and became enriched in the pretreated solids (22). Therefore, it was of interest to determine whether dilute-acid-pretreated QF solids might also serve as a source for these valuable nutraceutical chemicals. Following SSF, the solids residue was recovered and analyzed for the presence of oils. It was determined that only 1.12% oils was present in the residual solids (post-SSF, Table 3), which is comparable with that found in untreated QF (1.24-3.49% oil as noted in ref. 2). 

Many favor dilute sulfuric acid pretreatment because both high hemicellulose recovery and good cellulose digestibility can be achieved (6-8). Moreover, most of the soluble sugars from dilute-acid pretreatment are released as monomers that can be readily fermented to ethanol by recombinant organisms (9,10). Pretreatment with just hot water or steam, termed uncatalyzed hydrolysis or autohydrolysis, eliminates chemical additives, lowers the cost of materials of construction, and generates less waste, but hemicellulose and cellulose yields from batch systems are limited. 

Conversion of Distiller s Grain into Fuel Alcohol and a Higher-Value Animal Feed by Dilute-Acid Pretreatment... 

Pretreating wet DG with S02 (experiment 2) resulted in higher solubilization of residual carbohydrates than uncatalyzed steam explosion (experiment 1), however, higher yields and conversions are possible if homogeneous absorption of the acid gas can be accomplished. Careful examination of the S02-pretreated residue indicated nonhomogeneous pretreatment because the S02 appears to have been absorbed only at the surface of the particles and did not penetrate far into the interior. However, less expensive pretreatment reactors are possible if S02 is used as the catalyst, as opposed to dilute-acid pretreatment, because exotic alloys may not be needed. 

Karimi, K., Emitiazi, G., and Taherzadeh, M. J. 2006. Ethanol production from dilute-acid pretreated rice straw by simultaneous saccharification and fermentation with Mucor indicus, Rhizopus oryzae, and Saccharomyces cerevisiae. Enz Microbial Technol., 40,138-144. 

Grohmann, K., Torget, R., and Himmel, M., Optimization of dilute acid pretreatment of biomass. Biotechnol Bioeng Symp 1985, 15, 59-80. 

Torget, R., Walter, P., Himmel, M., and Grohmann, K., Dilute-acid pretreatment of com residues and short-rotation woody crops. Appl Biochem Biotechnol 1991, 28-9, 75-86. 

Keywords. Dilute acid. Pretreatment, Hydrolysis, Kinetics, Reactor design... 

The effectiveness of dilute acid hydrolysis as a pretreatment has been verified experimentally. Researchers at NREL have characterized the susceptibility of a variety of short rotation woody and herbaceous crops and agricultural residues upon dilute acid pretreatment [17,38-41]. What is more interesting is that the maximum digestibility usually coincides with complete hemicellulose removal. The dilute acid treatment of biomass aimed at hemicellulose hydrolysis has since become a widely accepted pretreatment method for enzymatic hydrolysis [16,42-44]. 

Chen and Lee [24] studied lactic acid production from dilute acid pretreated a-cellulose and switchgrass by L. delbruckii NRRL-B445 in the presence of a fungal cellulase in a fermentor extractor employing a microporous hollow fiber membrane (MHF). This reactor system was operated in a fed-batch mode with continuous removal of lactic acid by in situ extraction. A tertiary amine (alamine... 

Dien, B. S., Jung, H. J. G., Vogel, K. P., Casler, M. D., Lamb, J. F. S Iten, L et al. (2006). Chemical composition and response to dilute-acid pretreatment and enzymatic saccharification of alfalfa, reed canarygrass, and switchgrass. Biomass Bioenergy, 30, 880-891. 

Process Design and Economics for Biochemical Conversion ofLignocel-lulosic Biomass to Ethanol Dilute-Acid Pretreatment and Enzymatic Hydrolysis of Corn Stover, National Renewable Energy Laboratory, Golden, CO. 

Data and kinetic models of dilute acid pretreatment ate vital to provide a foundation for undostanding hemicellulose hydrolysis and the cause of enhanced performance by flow system systems. Initial hemicellulose hydrolysis models were adapted from Saeman s first-order homogeneous kinetic model of cellulose hydrolysis in a dilute acid batch system (30) and later modified to include two different fractions of hemicellulose, one of which is more easily... 

Xylan removal increased with flow rate and temperature for both water-only and very dilute acid pretreatment, as illustirated by Figure 1. As can be seen from this figure, flowthrough pretreatment of com stover with hot water at a flow rate of 10 mL/min removes more xylan at the same temperature and time than... 

Samuel R, Pu YQ, Raman B, Ragauskas AJ (2010) Structural characterization and comparison of switchgrass ball-milled lignin before and after dilute acid pretreatment. Appl Biochem Biotechnol 162 62... 

Humbird DA, Davis R, Tao L, Kinchin C, Hsu D, Aden A, Schoen P, Lukas J, Olthof B, Worley M, Sexton D, Dudgeon D. (2011). Process design and economics for biochemical conversion of lignocellulosic biomass to ethanol-dilute-acid pretreatment and enzymatic hydrolysis of corn stover. National Renewable Energy Laboratory, Golden, CO. NREL/TP-5100-47764. 

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