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1.
A pretreatment method using aqueous ammonia was investigated with the intent of minimizing the liquid throughput. This process
uses a flow-through packed column reactor (or percolation reactor). In comparison to the ammonia recycle percolation (ARP)
process developed previously in our laboratory, this process significantly reduces the liquid throughput to one reactor void
volume in packed bed (2.0–4.7 mL of liquid/g of corn stover) and, thus, is termed low-liquid ARP (LLARP). In addition to attaining
short residence time and reduced energy input, this process achieves 59–70% of lignin removal and 48–57% of xylan retention.
With optimum operation of the LLARP to corn stover, enzymatic digestibilities of 95, 90 and 86% were achieved with 60, 15,
and 7.5 filter paper units/g of glucan, respectively. In the simultaneous saccharification and fermentation test of the LLARP
samples using Saccharomyces cerevisiae (NREL-D5A), an ethanol yield of 84% of the theoretical maximum was achieved with 6% (w/v) glucan loading. In the simultaneous saccharification
and cofermentation (SSCF) test using recombinant Escherichia coli (KO11), both the glucan and xylan in the solid were effectively utilized, giving an overall ethanol yield of 109% of the
theoretical maximum based on glucan, a clear indication that the xylan content was converted into ethanol. The xylooligomers
existing in the LLARP effluent were not effectively hydrolyzed by cellulase enzyme, achieving only 60% of digestibility. SSCF
of the treated corn stover was severely hampered when the substrate was supplemented with the LLARP effluent, giving only
56% the overall yield of ethanol. The effluent appears to significantly inhibit cellulase and microbial activities. 相似文献
2.
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
3.
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
4.
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
5.
Pretreatment of switchgrass by ammonia fiber explosion (AFEX) 总被引:3,自引:0,他引:3
Hasan Alizadeh Farzaneh Teymouri Thomas I. Gilbert Bruce E. Dale 《Applied biochemistry and biotechnology》2005,124(1-3):1133-1141
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. 相似文献
6.
Pretreatment and enzymatic saccharification of corn fiber 总被引:14,自引:0,他引:14
Corn fiber consists of about 20% starch, 14% cellulose, and 35% hemicellulose, and has the potential to serve as a low-cost
feedstock for production of fuel ethanol. Several pretreatments (hot water, alkali, and dilute, acid) and enzymatic saccharification
procedures were evaluated for the conversion of corn fiber starch, cellulose, and hemicellulose to monomeric sugars. Hot water
pretreatment (121°C, 1 h) facilitated the enzymatic sacch arification of starch and cellulose but not hemicellulose. Hydrolysis
of corn fiber pretreated with alkali un dersimilar conditions by enzymatic means gave similar results. Hemicellulose and starch
components were converted to monomeric sugars by dilute H2SO4 pretreatment (0.5–1.0%, v/v) at 121°C. Based on these findings, a method for pretreatment and enzymatic saccharification
of corn fiber is presented. It in volves the pretreatment of corn fiber (15% solid, w/v) with dilute acid (0.5% H2SO4, v/v) at 121°C for 1 h, neutralization to pH 5.0, then saccharification of the pretreated corn fiber material with commercial
cellulase and β-glucosidase preparations The yield of monomeric sugars from corn fiber was typically 85–100% of the theoretical
yield.
Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard
of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also
be suitable. 相似文献
7.
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
8.
Isci A Himmelsbach JN Pometto AL Raman DR Anex RP 《Applied biochemistry and biotechnology》2008,144(1):69-77
Simultaneous saccharification and fermentation (SSF) of switchgrass was performed following aqueous ammonia pretreatment.
Switchgrass was soaked in aqueous ammonium hydroxide (30%) with different liquid–solid ratios (5 and 10 ml/g) for either 5
or 10 days. The pretreatment was carried out at atmospheric conditions without agitation. A 40–50% delignification (Klason
lignin basis) was achieved, whereas cellulose content remained unchanged and hemicellulose content decreased by approximately
50%. The Sacccharomyces cerevisiae (D5A)-mediated SSF of ammonia-treated switchgrass was investigated at two glucan loadings (3 and 6%) and three enzyme loadings
(26, 38.5, and 77 FPU/g cellulose), using Spezyme CP. The percentage of maximum theoretical ethanol yield achieved was 72.
Liquid–solid ratio and steeping time affected lignin removal slightly, but did not cause a significant change in overall ethanol
conversion yields at sufficiently high enzyme loadings. These results suggest that ammonia steeping may be an effective method
of pretreatment for lignocellulosic feedstocks. 相似文献
9.
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
10.
Bagasse, corn husk, and switchgrass were pretreated with ammonia water to enhance enzymatic hydrolysis. The sample (2 g) was
mixed with 1–6 mL ammonia water (25–28% ammonia) and autoclaved at 120°C for 20 min. After treatment, the product was vacuum-dried
to remove ammonia gas. The dried solid could be used immediately in the enzymatic hydrolysis without washing. The enzymatic
hydrolysis was effectively improved with more than 0.5 and 1 mL ammonia water/g for corn husk and bagasse, respectively. In
bagasse, glucose, xylose, and xylobiose were the main products. The adsorption of CMCase and xylanase was related to the initial
rate of enzymatic hydrolysis. In corn husks, arabinoxylan extracted by pretreatment was substantially unhydrolyzed because
of the high ratio of arabinose to xylose (0.6). The carbohydrate yields from cellulose and hemicellulose were 72.9% and 82.4%
in bagasse, and 86.2% and 91.9% in corn husk, respectively. The ammonia/water pretreatment also benefited from switchgrass
(Miscanthus sinensis and Solidago altissima L.) hydrolysis. 相似文献
11.
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
12.
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
13.
Philippe Savoie Kevin J. Shinners Benjamin N. Binversie 《Applied biochemistry and biotechnology》2004,113(1-3):41-54
Mixing fresh silage in water resulted in partial segregation of grain from stover. Grain concentration was 75% in the sunk
material when silage was relatively dry (64% moisture content [MC]) and 41% when silage was relatively wet (74% MC). Partial
drying to remove 20 percentage units of moisture prior to water separation increased grain concentration to 92%, and complete
drying increased grain concentration to 99%. Sieving without drying followed by water separation resulted in a grain concentration
of 79%. A byproduct of water separation is a large amount of soluble and deposited fine particles in the effluent: 18% of
original dry matter after one separation, and between 21 and 26% after eight separations. In an industrial setting, hydrodynamic
separation of silage with minimal pretreatment could provide a feedstock with a high concentration of grain (75–80%). In a
laboratory setting, hydrodynamic separation with prior oven drying could provide a method to separate grain from stover in
corn silage by reaching a grain concentration higher than 99%.
Contribution number 761, Soils and Crops Research and Development Centre, AAFC. 相似文献
14.
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
15.
Isci A Himmelsbach JN Strohl J Pometto AL Raman DR Anex RP 《Applied biochemistry and biotechnology》2009,157(3):453-462
Aqueous-ammonia-steeped switchgrass was subject to simultaneous saccharification and fermentation (SSF) in two pilot-scale
bioreactors (50- and 350-L working volume). Switchgrass was pretreated by soaking in ammonium hydroxide (30%) with solid to
liquid ratio of 5 L ammonium hydroxide per kilogram dry switchgrass for 5 days in 75-L steeping vessels without agitation
at ambient temperatures (15 to 33 °C). SSF of the pretreated biomass was carried out using Saccharomyces cerevisiae (D5A) at approximately 2% glucan and 77 filter paper units per gram cellulose enzyme loading (Spezyme CP). The 50-L fermentation
was carried out aseptically, whereas the 350-L fermentation was semiaseptic. The percentage of maximum theoretical ethanol
yields achieved was 73% in the 50-L reactor and 52–74% in the 350-L reactor due to the difference in asepsis. The 350-L fermentation
was contaminated by acid-producing bacteria (lactic and acetic acid concentrations approaching 10 g/L), and this resulted
in lower ethanol production. Despite this problem, the pilot-scale SSF of aqueous-ammonia-pretreated switchgrass has shown
promising results similar to laboratory-scale experiments. This work demonstrates challenges in pilot-scale fermentations
with material handling, aseptic conditions, and bacterial contamination for cellulosic fermentations to biofuels. 相似文献
16.
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
17.
Measurement of rheological properties of corn stover suspensions 总被引:1,自引:0,他引:1
Corn stover is currently being evaluated as a feedstock for ethanol production. The corn stover suspensions fed to reactors
typically range between 10 and 40% solids. To simulate and design bioreactors for processing highly loaded corn stover suspensions,
the rheologic properties of the suspension must be measured. In systems with suspended solids, rheologic measurements are
difficult to perform owing to settling in the measurement devices. In this study, viscosities of corn stover suspensions were
measured using a helical ribbon impeller viscometer. A calibration procedure is required for the impeller method in order
to obtain the shear rate constant, k, which is dependent on the geometry of the measurement system. The corn stover suspensions are described using a power law
flow model. 相似文献
18.
Exposure to anhydrous ammonia has been suggested as a pretreatment for corn milling. Batches of corn were exposed to ammonia
under controlled conditions. The amounts of ammonia absorbed and reacted with the corn were measured. The amounts were not
more than are needed as nutritional supplement for yeast fermentation to ethanol. Loosening of the hull was observed qualitatively,
and subsequent shearing in a disk mill followed by steeping for 2, 4, 6, or 8h showed that germ could be recovered at higher
yield and after a shorter steeping time compared to untreated control batches. Quality of oil was not affected by treatment
with ammonia.
Mention of brand or firm name does not constitute an endorsement by the U.S. Department of Agriculture above others of a similar
nature not mentioned. 相似文献
19.
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
20.
Corn stover, a well-known example of lignocellulosic biomass, is a potential renewable feed for bioethanol production. Dilute
sulfuric acid pretreatment removes hemicellulose and makes the cellulose more susceptible to bacterial digestion. The rheologic
properties of corn stover pretreated in such a manner were studied. The Power Law parameters were sensitive to corn stover
suspension concentration becoming more non-Newtonian with slope n, ranging from 0.92 to 0.05 between 5 and 30% solids. The Casson and the Power Law models described the experimental data
with correlation coefficients ranging from 0.90 to 0.99 and 0.85 to 0.99, respectively. The yield stress predicted by direct
data extrapolation and by the Herschel-Bulkley model was similar for each concentration of corn stover tested. 相似文献