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1.
Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification
and fermentation (SSF) system comprised ofTrichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation bySaccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised ofClostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H2SO4) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H2SO4). The short residence time pretreatment resulted in a somewhat (10–20%) more reactive substrate, with the reactivity difference
particularly notable at low enzyme loadings and/or low agitation. Based on a preliminary screening, inhibition of SSF by byproducts
of short residence time pretreatment was measurable, but minor. Both SSF and DMC were carried out successfully in well-mixed
continuous systems, with steady-state data obtained at residence times of 0.58–3 d for SSF as well as 0.5 and 0.75 d for DMC.
The SSF system achieved substrate conversions varying from 31% at a 0.58-d residence time to 86% at a 2-d residence time.
At comparable substrate concentrations (4–5 g/l) and residence times (0.5–0.58 d), substrate conversion in the DMC system
(77%) was significantly higher than that in the SSF system (31%). Our results suggest that the substrate conversion in SSF
carried out in CSTR is relatively insensitive to enzyme loading in the range 7–25 U/g cellulose and to substrate concentration
in the range of 5–60 g/L cellulose in the feed. 相似文献
2.
Applied Biochemistry and Biotechnology - 相似文献
3.
Grohmann K. Mitchell D. J. Himmel M. E. Dale B. E. Schroeder H. A. 《Applied biochemistry and biotechnology》1989,(1):45-61
Xylan backbones in native plant cell walls are extensively acety-lated. Previously, no direct investigations as to their role
in cellulolytic enzyme resistance have been done, though indirect results point to their importance. An in vitro deesterification
of aspen wood and wheat straw has been completed using hydroxylamine solutions. Yields of 90% acetyl ester removal for both
materials have been accomplished, with little disruption of other fractions (i.e., lignin). Apparently, as the xylan becomes
increasingly deacetylated, it becomes 5–7 times more digestible. This renders the cellulose fraction more accessible, and
2–3 times more digestible. This effect levels off near an acetyl removal of 75%, where other resistances become limiting. 相似文献
4.
Nguyen Q. A. Tucker M. P. Boynton B. L. Keller F. A. Schell D. J. 《Applied biochemistry and biotechnology》1998,(1):77-87
Selective thinning of forests in the western United States will generate a large, sustainable quantity of softwood residues
that can be an attractive feedstock for fuel ethanol production. The major species available from thinning of forests in northern
California and the eastern Rocky Mountains include white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii), and Ponderosa pine (Pinus ponderosa). Douglas fir chips were soaked in 0.4% sulfuric acid solution, then pretreated with steam at 200 – 230°C for 1 – 5 min.
After pretreatment, 90 – 95% of the hemicellulose and as much as 20% of the cellulose was solubilized in water, and 90% of
the remaining cellulose can be hydrolyzed to glucose by cellulase enzyme. The prehydrolysates, at as high as 10% total solid
concentration, can be readily fermented by the unadapted yeastSaccharomyces cerevisiae D5A. 相似文献
5.
Stenberg Kerstin Tengborg Charlotte Galbe Mats Zacchi Guido Palmqvist Eva Hahn-Hägerdal Bärbel 《Applied biochemistry and biotechnology》1998,(1):697-708
In ethanol production from lignocellulose by enzymatic hydrolysis and fermentation, it is desirable to minimize addition of
fresh-water and waste-water streams, which leads to an accumulation of substances in the process. This study shows that the
amount of fresh water used and the amount of waste water thereby produced in the production of fuel ethanol from softwood,
can be reduced to a large extent by recycling of either the stillage stream or part of the liquid stream from the fermenter.
A reduction in fresh-water demand of more than 50%, from 3 kg/kg dry raw material to 1.5 kg/kg dry raw material was obtained
without any negative effects on either hydrolysis or fermentation. A further decrease in the amount of fresh water, to one-fourth
of what was used without recycling of process streams, resulted in a considerable decrease in the ethanol productivity and
a slight decrease in the ethanol yield 相似文献
6.
Tucker M. P. Farmer J. D. Keller F. A. Schell D. J. Nguyan Q. A. 《Applied biochemistry and biotechnology》1998,(1):25-35
Single-stage cocurrent dilute acid pretreatments were carried out on yellow poplar (Liriodendron tulipifera) sawdust using an as-installed and short residence time modified pilot-scale Sunds hydrolyzer and a 4-L bench-scale NREL
digester (steam explosion reactor). Pretreatment conditions for the Sunds hydrolyzer, installed in the NREL process development
unit (PDU), which operates at 1 t/d (bone-dry t) feed rate, spanned the temperature range of 160 – 210°C, 0.1 – 1.0% (w/w)
sulfuric acid, and 4-10-min residence times. The batch pretreatments of yellow poplar sawdust in the bench-scale digester
were carried out at 210 and 230°C, 0.26% (w/w) sulfuric acid, and 1-, 3-, and 4-min residence times. The dilute acid prehydrolysis
solubilized more than 90% of the hemicellulose, and increased the enzymatic digestibility of the cellulose that remained in
the solids. Compositional analysis of the pretreated solids and liquors and mass balance data show that the two pretreatment
devices had similar pretreatment performance. 相似文献
7.
8.
Lactic acid production from cellulosic biomass by cellulase andLactobacillus delbrueckii was studied in a fermenter-extractor employing a microporous hollow fiber membrane (MHF). This bioreactor system was operated
under a fed-batch mode with continuous removal of lactic acid by anin situ extraction. A tertiary amine (Alamine 336) was used as an extractant for lactic acid. The extraction capacity of Alamine
336 is greatly enhanced by addition of alcohol. Long-chain alcohols serve well for this purpose since they are less toxic
to micro-organism. Addition of kerosene, a diluent, was necessary to reduce the solvent viscosity. A solvent mixture of 20%
Alamine 336, 40% oleyl alcohol, and 40% kerosene was found to be most effective in the extraction of lactic acid. Progressive
change of pH from an initial value of 5.0 down to 4.3 has significantly improved the overall performance of the simultaneous
saccharification and extractive fermentation over that of constant pH operation. The change of pH was applied to promote cell
growth in the early phase, and extraction in the latter phase. 相似文献
9.
Comparison of the model with experimental data is currently in progress. It appears that more detailed studies of the adsorption
dynamics, not just adsorption equilibrium, are needed. 相似文献
10.
Torres José L. Grethlein Hans E. Lynd Lee R. 《Applied biochemistry and biotechnology》1989,(1):621-633
High energy costs are associated with the recovery of ethanol from fermentation broths. This paper discusses a computer simulation
of the Dartmouth Process, which aims to reduce these costs by the use of IHOSR distillation, extensive heat integration, and
extractive distillation using a salt.
To resolve the uncertainty in modeling alcohol-water-salt vapor-liquid equilibrium, a new and more accurate activity coefficient
model was used. An Aspen™ model was used to generate capital and energy costs for a range of ethanol concentrations in the
feed. Simulation results show that the Dartmouth Process offers substantial economic advantages over benzene azeotropic distillation,
particularly at low feed concentrations. 相似文献
11.
12.
Based on this preliminary study, a metric ton of dry southern red oak chips subjected to a first-stage dilute sulfuric acid
hydrolysis would yield 132 kg of xylose and 40 kg of glucose and mannose. A second-stage dilute sulfuric acid hydrolysis on
the first-stage residue would yield only 128 kg of additional glucose, but a second-stage cellulytic enzyme hydrolysis on
the first-stage residue would yield an additional 265 kg of glucose. Fermentation of these hydrolyzates would show that the
hybrid process would yield over 50% more ethanol. Results on other biomass are also included. 相似文献
13.
Converse A. O. Kwarteng I. K. Grethlein H. E. Ooshima H. 《Applied biochemistry and biotechnology》1989,(1):63-78
The results of an experimental study of the acid hydrolysis of hardwood are presented in the form of values for the three
parameters, activation energy, power on the acid concentration, and pre-exponen-tial factor, of the first order kinetic constants
for each of the following reaction participants: xylan remaining, glucan remaining, xylose formed, and xylose decomposed.
These are used as a base for a quantitative theory to predict the temperature, time, and acid concentrations needed for effective
pretreatment of the substrate for subsequent enzymatic hydrolysis of the glucan. This theory is based on the assumption that
successful pretreatment requires >90% removal of the xylan, <10% removal of the glucan, and >80% xylose yield. This theory
is compared with selected published data. 相似文献
14.
Goldstein Irving S. Bayat-Makooi Fred Sabharwal H. S. Singh T. M. 《Applied biochemistry and biotechnology》1989,(1):95-106
Satisfactory separation of either hydrochloric or sulfuric acid from sugars in wood hydrolyzates by application of membrane
technology is technically feasible. The permeability of disaccharides is less than 1% that of the acids. Acid flux in diffusion
dialysis is only 6% of acid flux at optimum current density in electrodialysis. Critical parameters for economic feasibility
are acid to wood ratio in hydrolysis, current efficiency, and membrane service life. Best case estimates project total costs
for sulfuric acid recovery and loss of about $0.02 per pound of glucose produced. 相似文献
15.
Soni Bhupendra K. Kelley Robert L. Srivastava Vipul J. 《Applied biochemistry and biotechnology》1998,(1):651-659
A two-stage process for the manufacture of propylene oxide is described. The preliminary economics based on use of methanol
as a regeneration factor has resulted in a production cost of $12.10/lb of propylene oxide based on propylene oxide production
rate of 40 mg/g-cell/h in conventional reactor. Increasing the propylene oxide production from 40 to 500 mg/g-cell/h resulted
in a cost reduction from $12.10 to 5.8/lb of propylene oxide. The granular-activated, carbon-fluidized bed reactor (GAC-FBR)
absorbs the propylene oxide and when saturated is eluted with ethyl acetate, and the bed is regenerated by steam to drive
off the residual solvents. The estimated manufacturing costs are approx 59% lower (from $12.10/lb in conventional reactors
to $5.00/lb for GAC-FBRs) for products that are highly inhibitory such as epoxides. In the GAC-FBR reactor, enhancing the
propylene oxide production rate from 120 to 1500 mg/g-cell/h has resulted in the cost reduction to $2.00/lb. Enhancing the
production capacity from 1 million lb to 10 million lb/yr has further reduced the cost of production to $1.00/lb. 相似文献
16.
Vavilin Vasily A. Rytov Sergei V. Lokshina Ljudmila Ya. 《Applied biochemistry and biotechnology》1997,(1):45-57
The various equations of hydrolysis kinetics included into the generalized simulation model (METHANE) were tested on the anaerobic
digestion of cellulose, sludge, and cattle manure. The good agreement between the model simulation results and experimental
data was obtained. The Contois equation, taking into account a hydrolytic biomass, and the firstorder equation with respect
to the particulate substrate only, were shown to be the approximations of two-phase hydrolysis kinetics. 相似文献
17.
The potential market for lactic acid as the feedstock for biodegradable polymers, oxygenated chemicals, and specialty chemicals
is significant. L-lactic acid is often the desired enantiomer for such applications. However, stereospecific lactobacilli
do not metabolize starch efficiently. In this work, Argonne researchers have developed a process to convert starchy feedstocks
into L-lactic acid. The processing steps include starch recovery, continuous liquefaction, and simultaneous saccharification
and fermentation. Over 100 g/L of lactic acid was produced in less than 48 h. The optical purity of the product was greater
than 95%. This process has potential economical advantages over the conventional process. 相似文献
18.
Ethanol is being considered as an attractive alternative transportation fuel for the future. One method of producing ethanol
from lignocellulose involves reducing the size of biomass to smaller particles, and using acid or enzyme treatments to hydrolyze
the biomass to sugars. The size-reduction step is necessary to eliminate mass- and heat-transfer limitations during the hydrolysis
reactions. However, milling to small size consumes large amounts of energy, and reducing the energy usage is critical to the
overall process economics. In this study, the energy requirements and size distribution for milling wood were measured for
various pilot-scale size-reduction equipment. Hammer milling used less energy than disk milling, but produced particles with
a larger-size distribution. Additionally, energy requirements were measured for shredding paper and switchgrass. 相似文献
19.
Weil Joseph Brewer Mark Hendrickson Richard Sarikaya Ayda Ladisch Michael R. 《Applied biochemistry and biotechnology》1998,(1):99-111
Yellow poplar wood sawdust consists of 41% cellulose and 19% hemicellulose. The goal of pressure cooking this material in
water is to hydrate the more chemically resistive regions of cellulose in order to enhance enzymatic conversion to glucose.
Pretreatment can generate organic acids through acid-catalyzed degradation of monosaccharides formed because of acids released
from the biomass material or the inherent acidity of the water at temperatures above 160°C. The resulting acids will further
promote the acid-catalyzed degradation of monomers that cause both a reduction in the yield and the formation of fermentation
inhibitors such as hydroxymethyl furfural and furfural. A continuous pH-monitoring system was developed to help characterize
the trends in pH during pretreatment and to assist in the development of a base (2.0 M KOH) addition profile to help keep
the pH within a specified range in order to reduce any catalytic degradation and the formation of any monosac-charide degradation
products during pretreatment. The results of this work are discussed. 相似文献
20.
Chynoweth D. P. Bosch G. Earle J. F. K. Legrand Robert Liu Kexin 《Applied biochemistry and biotechnology》1991,(1):421-432
A novel process has been developed and evaluated in a pilotscale program for conversion of the biodegradable fraction of municipal
solid waste (MSW) to methane via anaerobic composting. The sequential batch anaerobic composting (SEBAC) process employs leachate
management to provide organisms, moisture, and nutrients required for rapid conversion of MSW and removal of inhibitory fermentation
products during start-up. The biodegradable organic materials are converted to methane and carbon dioxide in 21–42 d, rather
than the years required in landfills. 相似文献