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1.
Corn stover is a domestic feedstock that has potential to produce significant quantities of fuel ethanol and other bioenergy
and biobased products. However, comprehensive yield and carbon mass balance information and validated kinetic models for dilute-sulfuric
acid (H 2SO 4) pretreatment of corn stover have not been available. This has hindered the estimation of process economics and also limited
the ability to perform technoeconomic modeling to guide research. To better characterize pretreatment and assess its kinetics,
we pretreated corn stover in a continuous 1 t/d reactor. Corn stover was pretreated at 20% (w/w) solids concentration over
a range of conditions encompassing residence times of 3–12 min, temperatures of 165–195°C, and H 2SO 4 concentrations of 0.5–1.4% (w/w). Xylan conversion yield and carbon mass balance data were collected at each run condition.
Performance results were used to estimate kinetic model parameters assuming biphasic hemicellulose hydrolysis and a hydrolysis
mechanism incorporating formation of intermediate xylo-oligomers. In addition, some of the pretreated solids were tested in
a simultaneous saccharification and fermentation (SSF) process to measure the reactivity of their cellulose component to enzymatic
digestion by cellulase enzymes. Monomeric xylose yields of 69–71% and total xylose yields (monomers and oligomers) of 70–77%
were achieved with performance level depending on pretreatment severity. Cellulose conversion yields in SSF of 80–87% were
obtained for some of the most digestible pretreated solids. 相似文献
2.
The potential of dilute-acid prehydrolysis as a pretreatment method for sugarcane bagasse, rice hulls, peanut shells, and cassava stalks was investigated. The prehydrolysis was performed at 122 degrees C during 20, 40, or 60 min using 2% H(2)SO(4) at a solid-to-liquid ratio of 1:10. Sugar formation increased with increasing reaction time. Xylose, glucose, arabinose, and galactose were detected in all of the prehydrolysates, whereas mannose was found only in the prehydrolysates of peanut shells and cassava stalks. The hemicelluloses of bagasse were hydrolyzed to a high-extent yielding concentrations of xylose and arabinose of 19.1 and 2.2 g/L, respectively, and a xylan conversion of more than 80%. High-glucose concentrations (26-33.5 g/L) were found in the prehydrolysates of rice hulls, probably because of hydrolysis of starch of grain remains in the hulls. Peanut shells and cassava stalks rendered low amounts of sugars on prehydrolysis, indicating that the conditions were not severe enough to hydrolyze the hemicelluloses in these materials quantitatively. All prehydrolysates were readily fermentable by Saccharomyces cerevisiae. The dilute-acid prehydrolysis resulted in a 2.7- to 3.7-fold increase of the enzymatic convertibility of bagasse, but was not efficient for improving the enzymatic hydrolysis of peanut shells, cassava stalks, or rice hulls. 相似文献
3.
The pretreatment of corn stover with H 2SO 4 and H 3PO 4 was investigated. Pretreatments were carried out from 30 to 120 min in a batch reactor at 121°C, with acid concentrations
ranging from 0 to 2% (w/v) at a solid concentration of 5% (w/v). Pretreated corn stover was washed with distilled water until
the filtrate was adjusted to pH 7.0, followed by surfactant swelling of the cellulosic fraction in a 0–10% (w/v) solution
of Tween-80 at room temperature for 12 h. The dilute acid treatment proved to be a very effective method in terms of hemicellulose
recovery and cellulose digetibility. Hemicellulose recovery was 62–90%, and enzymatic digestibility of the cellulose that
remained in the solid was >80% with 2% (w/v) acid. In all cases studied, the performance of H 2SO 4 pretreatment (hemicellulose recovery and cellulose digestibility) was significantly better than obtained with H 3PO 4. Enzymatic hydrolysis was more effective using surfactant than without it, producing 10–20% more sugar. Furthermore, digestibility
was investigated as a function of hemicellulose removal. It was found that digestibility was more directly related to hemicellulose
removal than to delignification. 相似文献
4.
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 yeast Saccharomyces cerevisiae D 5A. 相似文献
5.
Pretreatment of corn stover by dilute sulfuric acid was investigated using a laboratory percolation (flowthrough) reactor
operated under high-solids conditions. The effects of reaction conditions and operating parameters on the performance of the
percolation reactor were investigated seeking the optimal range in which acceptable levels of yield and sugar concentration
could be attained. It was demonstrated that 70–75% recovery of xylose and 6 to 7% (w/w) xylose concentration were attainable.
The high sugar concentration was obtained as a result of dense packing of dry corn stover and the low liquid throughput. Xylose
was mostly unreacted, rather than decomposed. The cellulose and the unreacted xylan of treated corn stover were both effectively
hydrolyzed by a “cellulase” enzyme preparation that also exhibits some activity on xylan. The xylose yield was affected significantly
by the flow rate under the same reaction time and conditions. This behavior appears to be related to sugar decomposition,
mass transfer resistance, and the fact that acid is neutralized by the buffering components of the biomass. 相似文献
6.
Among the available agricultural byproducts, corn stover, with its yearly production of 10 million t (dry basis), is the most
abundant promising raw material for fuel ethanol production in Hungary. In the United States, more than 216 million to fcorn
stover is produced annually, of which a portion also could possibly be collected for conversion to ethanol. However, a network
of lignin and hemicellulose protects cellulose, which is the major source of fermentable sugars in corn stover (approx 40%
of the dry matter [DM]). Steam pretreatment removes the major part of the hemicellulose from the solid material and makes
the cellulose more susceptible to enzymatic digestion. We studied 12 different combinations of reaction temperature, time,
and pH during steam pretreatment. The best conditions (200°C, 5 min, 2% H 2SO 4) increased the enzymatic conversion (from cellulose to glucose) of corn stover more then four times, compared to untreated
material. However, steam pretreatment at 190°C for 5 min with 2% sulfuric acid resulted in the highest overall yield of sugars,
56.1 g from 100 g of untreated material (DM), corresponding to 73% of the theoretical. The liquor following steam explosion
was fermented using Saccharomyces cerevisiae to investigate the inhibitory effect of the pretreatment. The achieved ethanol yield was slightly higher than that obtained
with a reference sugar solution. This demonstrates that baker's yeast could adapt to the pretreated liquor and ferment the
glucose to ethanol efficiently. 相似文献
7.
Following detoxification of the liquid hydrolysate produced in a corn stover pretreatment process, inhibitor levels are seen
to increase with the re-addition of solids for the ensuing hydrolysis and fermentation processes. The solids that were separated
from the slurry before detoxification of the liquor contain approx 60% (w/w) moisture, and contamination occurs owing to the
diffusion of inhibitors from the moisture entrained in the porous structure of the corn stover solids into the bulk fluid.
This evidence suggests the need for additional separation and detoxification steps to purge residual inhibitors entrained
in the moisture in the solids. An overliming process to remove furans from the hydrolysate failed to reduce total organic
acids concentration, so acids were removed by treatment with an activated carbon powder. Smaller carbon doses proved more
efficient in removing organic acids in terms of grams of acid removed per gram of carbon powder. Sugar adsorption by the activated
carbon powder was minimal. 相似文献
8.
A series of pilot plant experiments have been conducted to compare the performance of a system utilizing two percolation reactors in series to a single reactor system. Although theoretically capable of producing higher glucose yields or concentrations, the two-reactor system concentrations were approximately the same and the yields were considerably lower than those from the single reactor study. An associated kinetics study found the glucose degradation kinetics to be accelerated by chromium ions, but this effect was greatly reduced in the presence of wood. The presence of metal surfaces also increased the rate of degradation even without large ion concentrations. The poor performance of the reactor system is proposed to be caused by intraparticle glucose diffusion effects and the catalytic effect on glucose degradation reactions of chromium ions from the corrosion of stainless steel by the acid. Strategies for reducing the effects of these phenomena on PBR performance are presented. 相似文献
9.
We have previously demonstrated that pretreatment of corn stover with dilute sulfuric acid can achieve high digestibility
and efficient recovery of hemicellulose sugars with high yield and concentration. Further improvement of this process was
sought in this work. A modification was made in the operation of the percolation reactor that the reactor is preheated under
atmospheric pressure to remove moisture that causes autohydrolysis. This eliminated sugar decomposition during the preheating
stage and led to a considerable improvement in overall sugar yield. In addition, liquid throughput was minimized to the extent
that only one reactor void volume of liquid was collected. This was done to attain a high xylose concentration in the hydrolyzate.
The optimum reaction and operating conditions were identified wherein near quantitative enzymatic digestibilities are obtained
with enzyme loading of 15 FPU/g glucan. With a reduced enzyme loading of 5 FPU/g glucan, the enzymatic digestibility was decreased,
but still reached a level of 92%. Decomposition of carbohydrates was extremely low as indicated by the measured glucan and
xylan mass closures (recovered sugar plus unreacted) which were 98% and 94%, respectively. The data obtained in this work
indicate that the digestibility is related to the extent of xylan removal. 相似文献
10.
Technoeconomic analysis has been used to guide the research and development of lignocellulosic biofuels production processes
for over two decades. Such analysis has served to identify the key technical barriers for these conversion processes so that
research can be targeted most effectively on the pertinent challenges. The tools and methodology used to develop conceptual
conversion processes and analyze their economics are presented here. In addition, the current process design and economic
results are described for dilute acid pretreatment followed by enzymatic hydrolysis and fermentation. Modeled ethanol costs
of $1.33/gallon (in consistent year 2007 dollars) are being targeted for this commercial scale corn stover conversion process
in 2012. State of technology models, which take actual research results and project them to commercial scale, estimate an
ethanol cost of $2.43/gallon at present. In order to further reduce costs, process improvements must be made in several areas,
including pretreatment, enzymatic hydrolysis, and fermentation. As the biomass industry develops, new fuels and new feedstocks
are being researched. Technoeconomic analysis will play a key role in process development and targeting of technical and economic
barriers for these new fuels and feedstocks.
相似文献
11.
The electrochemical process of anisole amination is studied in 1.5–9 M H 2SO 4 solutions containing acetonitrile or acetic acid. It is shown that the synthesis of aromatic monoamino compounds is better performed in moderately acidic media with high concentrations of organic solvents. Due to the chain mechanism of the electrochemical process, the current efficiency of amines can exceed 150% under these conditions. 相似文献
12.
Since cellulose accessibility has become more recognized as the major substrate characteristic limiting hydrolysis rates and glucan digestibilities, cellulose solvent-based lignocellulose pretreatments have gained attention. In this study, we employed cellulose solvent- and organic solvent-based lignocellulose fractionation using two cellulose solvents: concentrated phosphoric acid [~85?% (w/w) H 3PO 4] and an ionic liquid Butyl-3-methylimidazolium chloride ([BMIM]Cl). Enzymatic glucan digestibilities of concentrated phosphoric acid- and [BMIM]Cl-pretreated corn stover were 96 and 55?% after 72?h at five filter paper units of cellulase per gram of glucan, respectively. Regenerated amorphous cellulose by concentrated phosphoric acid and [BMIM]Cl had digestibilities of 100 and 92?%, respectively. Our results suggested that differences in enzymatic glucan digestibilities of concentrated phosphoric acid- and [BMIM]Cl-pretreated corn stover were attributed to combinatory factors. These results provide insights into mechanisms of cellulose solvent-based pretreatment and effects of residual cellulose solvents and lignin on enzymatic cellulose hydrolysis. 相似文献
13.
In this study, corn stover with a dry matter content of 20% was impregnated with SO 2 and then steam pretreated for various times at various temperatures. The pretreatment was evaluated by enzymatic hydrolysis
of the solid material and analysis of the sugar content in the liquid. The maximum overall yield of glucose, 89% of the theoretical
based on the glucan in the raw material, was achieved when the corn stover was pretreated at 200°C for 10 min. The maximum
overall yield of xylose, 78%, was obtained with pretreatment at 190°C for 5 min. 相似文献
14.
Applied Biochemistry and Biotechnology - Large-scale production of ethanol or other transportation fuels by biological conversion of lignocellulosic biomass will eventually require integration with... 相似文献
15.
Flowthrough pretreatment with hot water only offers many promising features for advanced pretreatment of biomass, and a better
understanding of the mechanisms responsible for flowthrough behavior could allow researchers to capitalize on key attributes
while overcoming limitations. In this study, the effect of fluid velocity on the fate of total mass, hemicellulose, and lignin
was evaluated for hot water only pretreatment of corn stover in tubular flow through reactors. Increasing fluid velocity significantly
accelerated solubilization of total mass, hemicellulose, and lignin at early times. For example, when fluid velocity was increased
from 2.8 to 10.7 cm/min, xylan removal increased from 60 to 82% for hot water only pretreatment of corn stover at 200°C after
8 min. At the same time, lignin removal increased from 30 to 46%. Dissolved hemicellulose was almost all in oligomeric form,
and solubilization of hemicellulose was always accompanied by lignin release. The increase in removal of xylan and lignin
with velocity, especially in the early reaction stage, suggests that chemical reaction is not the only factor controlling
hemicellulose hydrolysis and that mass transfer and other physical effects may also play an important trole in hemicellulose
and lignin degradation and removal. 相似文献
16.
The intrinsic viscosity [η] of dilute solutions of poly(1,4-phenylene terephthalamide) (PPPT) is found to depend strongly on sulfuric acid strength, exhibiting a maximum at about 100% H 2SO 4. This behavior instigated measurements of [η] and light scattering from dilute solutions of unfractionated PPPT in concentrated (≈96%) and 100% H 2SO 4. From [η] and weight-average molecular weight M w relationships, Mark-Houwink exponents a were determined to be 1.36 in 96.6% and 1.62 in 100.2 ± 0.2% H 2SO 4, indicating that the PPPT molecule can undergo considerable expansion in 100% H 2SO 4. For the case of 100% H 2SO 4, a noticeable polyelectrolyte effect is observed in the reduced viscosity versus concentration curves. This result suggests that the repulsive charges generated along the PPPT backbone may be responsible for the change in configuration of PPPT upon increasing the acid strength from 96.6% to 100% H 2SO 4. It is pointed out that there is considerable experimental difficulty in measuring consistent values of M w, and this may be the reason for the variation among published data. 相似文献
18.
Soaking in aqueous ammonia at moderate temperatures was investigated as a method of pretreatment for enzymatic hydrolysis as well as simultaneous saccharification and cofermentation (SSCF) of corn stover. The method involves batch treatment of the feedstock with aqueous ammonia (15-30 wt%) at 40-90 degrees C for 6-24 h. The optimum treatment conditions were found to be 15 wt% of NH(3), 60 degrees C, 1:6 of solid-to-liquid ratio, and 12 h of treatment time. The treated corn stover retained 100% glucan and 85% of xylan, but removed 62% of lignin. The enzymatic digestibility of the glucan content increased from 17 to 85% with 15 FPU/g-glucan enzyme loading, whereas the digestibility of the xylan content increased to 78%. The treated corn stover was also subjected to SSCF test using Spezyme-CP and recombinant Escherichia coli (KO11). The SSCF of the soaking in aqueous ammonia treated corn stover resulted in an ethanol concentration of 19.2 g/L from 3% (w/v) glucan loading, which corresponds to 77% of the maximum theoretical yield based on glucan and xylan. 相似文献
19.
Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment
of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility
of the remaining cellulose for fermentation into ethanol. In this study, dilute H 2SO 4 pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H 2SO 4, and 70-s to 840-s residence times. The combined severity (Log 10 [ R
o
] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose
yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180°C. However, yields >90% of theoretical
were found with dilute-acid pretreatments at 190°C. A narrower range of higher combined severities was required for pretreatment
to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to
63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190°C, using
an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol
yields were found using washed solid residues from 160 and 180°C pretreatments at similar combined severities but required
a higher enzyme loading of approx 25 FPU/g of cellulose. 相似文献
20.
Optimizing process conditions and parameters such as ammonia loading, moisture content of biomass, temperature, and residence
time is necessary for maximum effectiveness of the ammonia fiber explosion process. Approximate optimal pretreatment conditions
for corn stover were found to be temperature of 90°C, ammonia: dry corn stover mass ratio of 1∶1, moisture content of corn
stover of 60% (dry weight basis), and residence time (holding at target temperature), of 5 min. Approximately 98% of the theoretical
glucose yield was obtained during enzymatic hydrolysis of the optimal treated corn stover using 60 filter paper units (FPU)
of cellulase enzyme/g of glucan (equal to 22 FPU/g of dry corn stover). The ethanol yield from this sample was increased up
to 2.2 times over that of untreated sample. Lowering enzyme loading to 15 and 7.5 FPU/g of glucan did not significantly affect
the glucose yield compared with 60 FPU, and any differences between effects at different enzyme levels decreased as the treatment
temperature increased. 相似文献
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