共查询到20条相似文献,搜索用时 15 毫秒
1.
Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility 总被引:3,自引:0,他引:3
Melvin P. Tucker Kyoung H. Kim Mildred M. Newman Quang A. Nguyen 《Applied biochemistry and biotechnology》2003,105(1-3):165-177
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 H2SO4 pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H2SO4, and 70-s to 840-s residence times. The combined severity (Log10 [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
2.
Impact of fluid velocity on hot water only pretreatment of corn stover in a flowthrough reactor 总被引:1,自引:0,他引:1
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
3.
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
4.
Corn stover, the most abundant agricultural residue in Hungary, is a potential raw material for the production of fuel ethanol
as a result of its high content of carbohydrates, but a pretreatment is required for its efficient hydrolysis. In this article,
we describe the results using various chemicals such as dilute H2SO4, HCl, and NaOH separately as well as consecutively under relative mild conditions (120°C, 1h). Pretreatment with 5% H2SO4 or 5% HCl solubilized 85% of the hemicellulose fraction, but the enzymatic conversion of pretreated materials increased only
two times compared to the untreated corn stover. Applying acidic pretreatment following a 1-d soaking in base achieved enzymatic
conversion that was nearly the theoretical maximum (95.7%). Pretreatment with 10% NaOH decreased the lignin fraction >95%,
increased the enzymatic conversion more than four times, and gave a 79.4% enzymatic conversion. However, by increasing the
reaction time, the enzymatic degradability could also be increased significantly, using a less concentrated base. When the
time of pretreatment was increased three times (0.5% NaOH at 120°C), the amount of total released sugars was 47.9 g from 100
g (dry matter) of untreated corn stover. 相似文献
5.
Yongming Zhu Tae Hyun Kim Y. Y. Lee Rongfu Chen Richard T. Elander 《Applied biochemistry and biotechnology》2006,130(1-3):586-598
A novel method of producing food-grade xylooligosaccharides from corn stover and corn cobs was investigated. The process starts
with pretreatment of feedstock in aqueous ammonia, which results delignified and xylan-rich substrate. The pretreated substrates
are subjected to enzymatic hydrolysis of xylan using endoxylanase for production of xylooligosaccharides. The conventional
enzyme-based method involves extraction of xylan with a strong alkaline solution to form a liquid intermediate containing
soluble xylan. This intermediate is heavily contaminated with various extraneous components. A costly purification step is
therefore required before enzymatic hydrolysis. In the present method, xylan is obtained in solid form after pretreatment.
Water-washing is all that is required for enzymatic hydrolysis of this material. The complex step of purifying soluble xylan
from contaminant is essentially eliminated.
Refining of xylooligosaccharides to food-grade is accomplished by charcoal adsorption followed by ethanol elution. Xylanlytic
hydrolysis of the pretreated corn stover yielded glucan-rich residue that is easily digestible by cellulase enzyme. The digestibility
of the residue reached 86% with enzyme loading of 10 filter paper units/g-glucan. As a feedstock for xylooligosaccharides
production, corn cobs are superior to corn stover because of high xylan content and high packing density. The high packing
density of corn cobs reduces water input and eventually raises the product concentration. 相似文献
6.
Optimization of dilute-acid pretreatment of corn stover using a high-solids percolation reactor 总被引:1,自引:0,他引:1
Yongming Zhu Y. Y. Lee Richard T. Elander 《Applied biochemistry and biotechnology》2005,124(1-3):1045-1054
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
7.
Ammonia fiber explosion treatment of corn stover 总被引:1,自引:0,他引:1
Farzaneh Teymouri Lizbeth Laureano-Pérez Hasan Alizadeh Bruce E. Dale 《Applied biochemistry and biotechnology》2004,115(1-3):951-963
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
8.
R. Torget M. Himmel J. D. Wright K. Grohmann 《Applied biochemistry and biotechnology》1988,17(1-3):89-104
A preliminary process design for dilute sulfuric acid pretreatment of aspen wood chips in order to obtain fermentable sugars
has been prepared and subjected to an economic evaluation. The process design was prepared according to experimental data
on the kinetics of dilute sulfuric acid prehydrolysis and particle size effects obtained in this study and our previous work.
The initial economic evaluation shows woodchips are 56% of the cost of production, whereas the reactor is only 4%, and the
comminution operation is just under 10%, indicating that the process economics are extremely vulnerable to feedstock costs
and are thus yield-sensitive. Although chances for major cost improvements by modification of the reactor design and finding
alternatives to dry milling of aspen chips to small (20–80 mesh) particles needed for acid penetration and enzymatic saccharification
are not great, design improvements of the process will necessitate development of a cheaper acid resistant pretreatment reactor
and a less energy intensive comminution system. Experimental results on effects of particle size on the dilute acid pretreatment
design are presented. 相似文献
9.
Karin Öhgren Mats Galbe Guido Zacchi 《Applied biochemistry and biotechnology》2005,124(1-3):1055-1067
In this study, corn stover with a dry matter content of 20% was impregnated with SO2 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
10.
R. Eric Berson John S. Young Sarah N. Kamer Thomas R. Hanley 《Applied biochemistry and biotechnology》2005,124(1-3):923-934
A technique for the removal of acetic acid from an actual pretreated corn stover hydrolysate was investigated. A powdered
form of activated carbon previously shown to be effective in the removal of acetic acid from a synthetic hydrolysate was utilized.
The method proved to be effective at lowering acetic acid levels while exhibiting minimal adsorption of the desired sugars
from the hydrolysate, although at a lower efficiency in the actual hydrolysate than in the synthetic hydrolysate. Results
are obtained for temperatures between 25 and 35°C and agitation rates between 150 and 350 rpm in shake flasks. Adsorption
isotherm and kinetic rate date are presented. Temperature differences over this range did not have an effect on adsorption
characteristics. Five stages of detoxification were necessary to lower acetic acid concentration to the maximum 2 g/L desired
for fermentation. 相似文献
11.
Optimization of steam pretreatment of corn stover to enhance enzymatic digestibility 总被引:5,自引:0,他引:5
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% H2SO4) 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
12.
Biomechanics of wheat/barley straw and corn stover 总被引:3,自引:0,他引:3
Christopher T. Wright Peter A. Pryfogle Nathan A. Stevens Eric D. Steffler J. Richard Hess Thomas H. Ulrich 《Applied biochemistry and biotechnology》2005,121(1-3):5-19
The lack of understanding the mechanical characteristics of cellulosic feedstocks is a limiting factor in economically collecting
and processing crop residues, primarily wheat and barley stems and corn stover. Several testing methods—compression, tension,
and bend—were investigated to increase the understanding of the biomechanical behavior of cellulosic feedstocks. Biomechanical
data from these tests can provide required input to numerical models and help advance harvesting, handling, and processing
techniques. In addition, integrating the models with the complete data set from this study can identify potential tools for
manipulating the biomechanical properties of plant varieties in such a manner as to optimize their physical characteristics
to produce higher-value biomass and more energy-efficient harvesting practices. 相似文献
13.
Pretreatment of corn stover using wet oxidation to enhance enzymatic digestibility 总被引:17,自引:0,他引:17
Corn stover is an abundant, promising raw material for fuel ethanol production. Although it has a high cellulose content,
without pretreatment it resists enzymatic hydrolysis, like most lignocellulosic materials. Wet oxidation (water, oxygen, mild
alkali or acid, elevated temperature and pressure) was investigated to enhance the enzymatic digestibility of corn stover.
Six different combinations of reaction temperature, time, and pH were applied. The best conditions (60g/L of corn stover,
195°C, 15 min, 12 bar O2, 2 g/L of Na2CO3) increased the enzymatic conversion of corn stover four times, compared to untreated material. Under these conditions 60%
of hemicellulose and 30% of lignin were solubilized, whereas 90% of cellulose remained in the solid fraction. After 24-h hydrolysis
at 50°C using 25 filter paper units (FPU)/g of dry matter (DM) biomass, the achieved conversion of cellulose to glucose was
about 85%. Decreasing the hydrolysis temperature to 40°C increased hydrolysis time from 24 to 72 h. Decreasing the enzyme
loading to 5 FPU/g of DM biomass slightly decreased the enzymatic conversion from 83.4 to 71%. Thus, enzyme loading can be
reduced without significantly affecting the efficiency of hydrolysis, an important economical aspect. 相似文献
14.
Fred A. Keller Jenny E. Hamilton Quang A. Nguyen 《Applied biochemistry and biotechnology》2003,105(1-3):27-41
Typical pretreatment requires high-energy (steam and electricity) and corrosion-resistant, high-pressure reactors. A review
of the literature suggests that fungal pretreatment could potentially lower the severity requirements of acid, temperature
and time. These reductions in severity are also expected to result in less biomass degradation and consequently lower inhibitor
concentrations compared to conventional thermochemical pretreatment. Furthermore, potential advantages of fungal pretreatment
of agricultural residues, such as corn stover, are suggested by its effectiveness in improving the cellulose digestibility
of many types of forage fiber and agricultural wastes. Our preliminary tests show a three- to five-fold improvement in enzymatic
cellulose digestibility of corn stover after pretreatment with Cyathus stercoreus; and a ten- to 100-fold reduction in shear force needed to obtain the same shear rate of 3.2 to 7 rev/s, respectively, after
pretreatment with Phanerochaete chrysosporium. 相似文献
15.
研究了AlCl3 催化剂作用下, 水热体系中玉米秸秆中半纤维素组分在温和条件下的选择性转化. 详细考察了反应温度、反应时间和AlCl3用量对半纤维素选择性转化的影响. 原料及反应后的固体残渣分别采用化学滴定、X射线衍射和扫描电镜进行表征. 结果表明, 140 ℃下反应1 h可转化玉米秸秆中的大部分半纤维素, 转化率为85.1%;而玉米秸秆中的绝大部分纤维素和木质素组分仍保留在固体残渣中, 此时纤维素和木质素的转化率分别为10.7%和23.9%. 半纤维素转化的主要液体产物为木糖, 同时含有一些乙酸和糠醛. 升高温度, 将滤液进行进一步反应可促进木糖的转化. 在水/四氢呋喃反应体系中, 滤液的进一步反应有利于乙酰丙酸、甲酸和糠醛的生成. 固体酸催化剂γ-Al2O3/SO42-的加入可进一步提高糠醛的收率. 相似文献
16.
R. Eric Berson John S. Young Thomas R. Hanley 《Applied biochemistry and biotechnology》2006,130(1-3):612-620
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
17.
Michael J. Selig William S. Adney Michael E. Himmel Stephen R. Decker 《Cellulose (London, England)》2009,16(4):711-722
Analysis of variously pretreated corn stover samples showed neutral to mildly acidic pretreatments were more effective at
removing xylan from corn stover and more likely to maintain the acetyl to xylopyranosyl ratios present in untreated material
than were alkaline treatments. Retention of acetyl groups in the residual solids resulted in greater resistance to hydrolysis
by endoxylanase alone, although the synergistic combination of endoxylanase and acetyl xylan esterase enzymes permitted higher
xylan conversions to be observed. Acetyl xylan esterase alone did little to improve hydrolysis by cellulolytic enzymes, although
a direct relationship was observed between the enzymatic removal of acetyl groups and improvements in the enzymatic conversion
of xylan present in substrates. In all cases, effective xylan conversions were found to significantly improve glucan conversions
achievable by cellulolytic enzymes. Additionally, acetyl and xylan removal not only enhanced the respective initial rates
of xylan and glucan conversion, but also the overall extents of conversion. This work emphasizes the necessity for xylanolytic
enzymes during saccharification processes and specifically for the optimization of acetyl esterase and xylanase synergies
when biomass processes include milder pretreatments, such as hot water or sulfite steam explosion. 相似文献
18.
Extraction and characterization of native heteroxylans from delignified corn stover and aspen 总被引:1,自引:0,他引:1
Radnaa Naran Stuart Black Stephen R. Decker Parastoo Azadi 《Cellulose (London, England)》2009,16(4):661-675
Dimethylsulfoxide-solubilized polysaccharides from delignified corn stover and aspen were characterized. The biomass was delignified
by two different techniques; a standard acid chlorite and a pulp and paper QPD technique comprising chelation (Q), peroxide
(P), and acid-chlorite (D). Major polysaccharides in all fractions were diversely substituted xylan. Xylan acetylation was
intact after chlorite delignification and, as expected, xylan from QPD-delignified fraction was de-acetylated by the alkaline
peroxide step. The study of DMSO-extractable xylans from chlorite-delignified biomass revealed major differences in native
acetylation patterns between corn stover and aspen xylan. Xylan from cell walls of corn stover contains 2-O- and 3-O-mono-acetylated xylan and [MeGlcA-α-(1 → 2)][3-OAc]-xylp units. In addition, aspen xylan also contains 2,3-di-O-acetylated xylose. 1,4-β-d-xylp residues substituted with MeGlcA at O-2 position are absent in chlorite-delignified aspen xylan. Sugar composition in accord with NMR-spectroscopic data indicated
that corn stover xylan is arabinosylated while aspen xylan is not. We have shown that corn stover xylan has similar structure
with xylans from other plants of Poales order. No evidence was found to indicate the presence of 1,4-β-d-[MeGlcA-α-(1 → 2)][Ara-α-(1 → 3)]-xylp in corn stover xylan fractions. 相似文献
19.
Enzyme recovery and recycling following hydrolysis of ammonia fiber explosion-treated corn stover 总被引:1,自引:0,他引:1
Bernie Steele Srini Raj John Nghiem Mark Stowers 《Applied biochemistry and biotechnology》2005,124(1-3):901-910
Both cellulase and cellobiase can be effectively recovered from hydrolyzed biomass using an ultrafiltration recovery method.
Recovery of cellulase ranged from 60 to 66.6% and for cellobiase from 76.4 to 88%. Economic analysis shows that cost savings
gained by enzyme recycling are sensitive to enzyme pricing and loading. At the demonstrated recovery of 60% and current loading
of 15 Filter paper units of cellulase/g of glucan, enzyme recycling is expected to generate a cost savings of approx 15%.
If recovery efficiency can be improved to 70%, the savings will increase to >25%, and at 90% recovery the savings will be
50%. 相似文献
20.
Summary of findings from the Biomass Refining Consortium for Applied Fundamentals and Innovation (CAFI): corn stover pretreatment 总被引:1,自引:0,他引:1
Richard T. Elander Bruce E. Dale Mark Holtzapple Michael R. Ladisch Y. Y. Lee Colin Mitchinson John N. Saddler Charles E. Wyman 《Cellulose (London, England)》2009,16(4):649-659
The Biomass Refining Consortium for Applied Fundamentals and Innovation, with members from Auburn University, Dartmouth College,
Michigan State University, the National Renewable Energy Laboratory, Purdue University, Texas A&M University, the University
of British Columbia, and the University of California at Riverside, has developed comparative data on the conversion of corn
stover to sugars by several leading pretreatment technologies. These technologies include ammonia fiber expansion pretreatment,
ammonia recycle percolation pretreatment, dilute sulfuric acid pretreatment, flowthrough pretreatment (hot water or dilute
acid), lime pretreatment, controlled pH hot water pretreatment, and sulfur dioxide steam explosion pretreatment. Over the
course of two separate USDA- and DOE-funded projects, these pretreatment technologies were applied to two different corn stover
batches, followed by enzymatic hydrolysis of the remaining solids from each pretreatment technology using identical enzyme
preparations, enzyme loadings, and enzymatic hydrolysis assays. Identical analytical methods and a consistent material balance
methodology were employed to develop comparative sugar yield data for each pretreatment and subsequent enzymatic hydrolysis.
Although there were differences in the profiles of sugar release, with the more acidic pretreatments releasing more xylose
directly in the pretreatment step than the alkaline pretreatments, the overall glucose and xylose yields (monomers + oligomers)
from combined pretreatment and enzymatic hydrolysis process steps were very similar for all of these leading pretreatment
technologies. Some of the water-only and alkaline pretreatment technologies resulted in significant amounts of residual xylose
oligomers still remaining after enzymatic hydrolysis that may require specialized enzyme preparations to fully convert xylose
oligomers to monomers. 相似文献