共查询到20条相似文献,搜索用时 31 毫秒
1.
Abolghasem Shahbazi Yebo Li Michele R. Mims 《Applied biochemistry and biotechnology》2005,124(1-3):973-987
The FIRST (Feedstock Impregnation and Rapid Steam Treatment) approach was used in this study to isolate extractives, hemicellulose,
lignin, fibers, and cellulosic fines of softwood. With hydrolysis and fermentation of the hemicellulose and cellulosic fines
fractions, this approach produces four co-products: extractives, cellulose, lignin, and ethanol. The first unit operation
uses aqueous/alcohol to remove and recover the extractive rich fraction. The second unit operation uses steam treatment to
destructure the matrix and solubilize a large fraction of the hemicelluloses. The third unit operation uses alkaline delignification
to dissolve a lignin fraction. The fourth unit operation uses the refining process to separate fibers from cellulosic fines.
The fibers are bleached. The yields of lignin and bleached cellulose were about 20.0 kg and 38.3 kg out of 100 kg initial
dry pine, respectively. The recovered hemicelluloses were 23.3 kg (containing 16.1 kg hexoses and 5.0 kg pentoses) and the
cellulose fines derived hexoses amounted to 3.4 kg out of 100 kg initial dry pine. When the two liquors containing the hemicellulose
sugars and the cellulose fines-derived hexoses were fermented for ethanol production, an ethanol yield of 6.8 kg was obtained. 相似文献
2.
Michael M. Wu Kevin Chang David J. Gregg Abdel Boussaid Rodger P. Beatson John N. Saddler 《Applied biochemistry and biotechnology》1999,77(1-3):47-54
A combination of Douglas fir heartwood and sapwood chips were steam pretreated under three conditions as measured by the Severity
Factor (log Ro), which incorporated the time, temperature/pressure of pretreatment. By adjusting the steam pretreatment conditions, it was
hoped to recover the majority of the hemicellulose component as monomers in the water-soluble stream, while providing a cellulosic-rich,
water-insoluble fraction that could be readily hydrolyzed by cellulases. These three conditions were chosen to represent either
high hemicellulose sugar recovery (low severity [L], log Ro=3.08), high-enzyme hydrolyzability of the cellulosic component (high severity [H], log Ro=4.21), and a compromise between the two conditions (medium severity [M], log Ro=3.45). The medium-severity pretreatment conditions (195°C, 4.5 min, 4.5% SO2 logRo=3.45) gave the best compromise in terms of relatively high hemicellulose recovery after stream pretreatment and the subsequent
efficiency of enzymatic hydrolysis of the water-insoluble cellulosic fraction. The percent recovery of the original hemicellulose
in the water-soluble fraction dropped significantly when the severity was increased (L-76.8%, M-64.7%, and H-37.5%). However,
the ease of enzymatic hydrolysis of the cellulose-rich, water-insoluble fraction increased with increasing severity (L-24%,
M-86.6%, and H-97.9%). Although more severe pretreatment conditions provided optimum hydrolysis of the cellulosic component,
less severe conditions resulted in better recovery of the combined hemicellulose and cellulosic components. 相似文献
3.
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
4.
5.
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
6.
Bura Renata Mansfield Shawn D. Saddler John N. Bothast Rodney J. 《Applied biochemistry and biotechnology》2002,98(1-9):59-72
Corn fiber, a by-product of the corn wet-milling industry, represents a renewable resource that is readily available in significant
quantities and could potentially serve as a low-cost feedstock for the production of fuel-grade alcohol. In this study, we
used a batch reactor to steam explode corn fiber at various degrees of severity to evaluate the potential of using this feedstock
in the bioconversion process. The results indicated that maximum sugar yields (soluble and following enzymatic hydrolysis)
were recovered from corn fiber that was pretreated at 190°C for 5 min with 6% SO2. Sequential SO2-catalyzed steam explosion and enzymatic hydrolysis resulted in very high conversion (81%) of all polysaccharides in the corn
fiber to monomeric sugars. Subsequently, Saccharomyces cerevisiae was able to convert the resultant corn fiber hydrolysates to ethanol very efficiently, yielding 90–96% of theoretical conversion
during the fermentation process. 相似文献
7.
Beatriz Palmarola-Adrados Mats Galbe Guido Zacchi 《Applied biochemistry and biotechnology》2004,115(1-3):989-1002
Steam treatment of an industrial process stream, denoted starch-free wheat fiber, was investigated to improve the formation
of monomeric sugars in subsequent enzymatic hydrolysis for further bioconversion into ethanol. The solid fraction in the process
stream, derived from a combined starch and ethanol factory, was rich in arabinose (21.1%), xylose (30.1%), and glucose (18.6%),
in the form of polysaccharides. Various conditions of steam pretreatment (170–220°C for 5–30 min) were evaluated, and their
effect was assessed by enzymatic hydrolysis with 2 g of Celluclast + Ultraflo mixture/ 100 g of starch-free fiber (SFF) slurry
at 5% dry matter (DM). The highest overall sugar yield for the combined steam pretreatment and enzymatic hydrolysis, 52g/100
g of DM of SFF, corresponding to 74% of the theoretical, was achieved with pretreatment at 190°C for 10 min followed by enzymatic
hydrolysis. 相似文献
8.
Palonen H Thomsen AB Tenkanen M Schmidt AS Viikari L 《Applied biochemistry and biotechnology》2004,117(1):1-17
The wet oxidation pretreatment (water, oxygen, elevated temperature, and pressure) of softwood (Picea abies) was investigated for enhancing enzymatic hydrolysis. The pretreatment was preliminarily optimized. Six different combinations
of reaction time, temperature, and pH were applied, and the compositions of solid and liquid fractions were analyzed. The
solid fraction after wet oxidation contained 58–64% cellulose, 2–16% hemicellulose, and 24–30% lignin. The pretreatment series
gave information about the roles of lignin and hemicellulose in the enzymatic hydrolysis. The temperature of the pretreatment,
the residual hemicellulose content of the substrate, and the type of the commercial cellulase preparation used were the most
important factors affecting the enzymatic hydrolysis. The highest sugar yield in a 72-h hydrolysis, 79% of theoretical, was
obtained using a pretreatment of 200°C for 10 min at neutral pH. 相似文献
9.
Renata Bura Rodney J. Bothast Shawn D. Mansfield John N. Saddler 《Applied biochemistry and biotechnology》2003,106(1-3):319-335
A batch reactor was employed to steam explode corn fiber at various degrees of severity to evaluate the potential of using
this feedstock as part of an enzymatically mediated cellulose-to-ethanol process. Severity was controlled by altering temperature
(150–230°C), residence time (1–9 min), and SO2 concentration (0–6% [w/w] dry matter). The effects of varying the different parameters were assessed by response surface
modeling. The results indicated that maximum sugar yields (hemicellulose-derived water soluble, and cellulose-derived following
enzymatic hydrolysis) were recovered from corn fiber pretreated at 190°C for 5 minutes after exposure to 3% SO2. Sequential SO2-catalyzed steam explosion and enzymatic hydrolysis resulted in a conversion efficiency of 81% of the combined original hemicellulose
and cellulose in the corn fiber to monomeric sugars. An additional posthydrolysis step performed on water soluble hemicellulose
stream increased the concentration of sugars available for fermentation by 10%, resulting in the high conversion efficiency
of 91%. Saccharomyces cerevisiae was able to ferment the resultant corn fiber hydrolysates, perhydrolysate, and liquid fraction from the posthydrolysis steps
to 89, 94, and 85% of theoretical ethanol conversion, respectively. It was apparent that all of the parameters investigated
during the steam explosion pretreatment had a significant effect on sugar recovery, inhibitory formation, enzymatic conversion
efficiency, and fermentation capacity of the yeast. 相似文献
10.
Ma Prado García-Aparicio Ignacio Ballesteros Alberto González José Miguel Oliva Mercedes Ballesteros Ma José Negro 《Applied biochemistry and biotechnology》2006,129(1-3):278-288
The influence of the liquid fraction (prehydrolysate) generated during steam-explosion pretreatment (210°C, 15 min) of barley
straw on the enzymatic hydrolysis was determined. Prehydrolysate was analyzed for degradation compounds and sugars' content
and used as a medium for enzymatic hydrolysis tests after pH adjusting to 4.8. Our results show that the presence of the compounds
contained in the prehydrolysate strongly affects the hydrolysis step (a 25% decrease in cellulose conversion compared with
control). Sugars are shown to be more potent inhibitors of enzymatic hydrolysis than degradation products. 相似文献
11.
Kim Sung Bae Um Byung Hwan Park Soon Chul 《Applied biochemistry and biotechnology》2001,91(1-9):81-94
The effect of pretreatment reagent and hydrogen peroxide on enzymatic digestibility of oak was investigated to compare pretreatment
performance. Pretreatment reagents used were ammonia, sulfuric acid, and water. These solutions were used without or in combination
with hydrogen peroxide in the percolation reactor. The reaction was carried out at 170°C for the predetermined reaction time.
Ammonia treatment showed the highest delignification but the lowest digestibility and hemicellulose removal among the three
treatments. Acid treatment proved to be a very effective method in terms of hemicellulose recovery and cellulose digestibility.
Hemicellulose recovery was 65–90% and digestibilities were >90% in the range of 0.01–0.2% acid concentration. In both treatments,
hydrogen peroxide had some effect on digestibility but decomposed soluble sugars produced during pretreatment. Unlike ammonia
and acid treatments, hydrogen peroxide in water treatment has a certain effect on hemicellulose recovery as well as delignification.
At 1.6% hydrogen peroxide concentration, both hemicellulose recovery and digestibility were about 90%, which were almost the
same as those of 0.2% sulfuric acid treatment. Also, digestibility was investigated as a function of hemicellulose removal
or delignification. It was found that digestibility was more directly related to hemicellulose removal rather than delignification. 相似文献
12.
Francesco Zimbardi Donato Viggiano Francesco Nanna Mario Demichele Daniela Cuna Giovanni Cardinale 《Applied biochemistry and biotechnology》1999,77(1-3):117-125
The effects of the steam-explosion treatment on aqueous fractionation and bioconversion of wheat straw have been investigated.
The treatments have been carried out in batch and continuous reactors with capacity of 0.5 Kg/cycle and 150 Kg/h, respectively.
The exploded materials have been sequentially extracted with water at 65°C and sodium hydroxide 1.5%. Analytical determinations
of liquid fractions and solid residues haveled to the fractionation pattern of the carbohydrates as, monomers, oligomers,
and polymers. Evaluations of total acidity, ash content, and lignin recovery have improved understanding of the process. This
part of the work has allowed us to derive: the empiric relationship between the batch and the continuous reactors and the
yield and availability of pentoses and hexoses in various phases. Selected samples have been tested in enzymatic-hydrolysis
experiments, pointing out the effect of treatment severity and reactor used on the saccharification yield. 相似文献
13.
Aspen wood was treated with steam at different time-temperature severity factors. Analysis of the amounts of acids released
revealed a relationship between the acidity and the formation of furfural and hydroxymethyl furfural as degradation products
from carbohydrates. It is suggested that two concurrent or consecutive mechanisms are responsible for the observed results:
a homolytic cleavage and an acid hydrolysis of glucosidic linkages in the polysaccharides. By preimpregnating the wood with
alkali, hydrolysis can be eliminated, resulting in a much cleaner depolymerization of the polysaccharides without any further
acid-catalyzed degradation. The enzymatic digestibility of the steam-treated wood material for the formation of glucose was
compared with that of steam-exploded wood. A more efficient route for glucose production from steam-exploded wood was found
as long as the biomass-pretreated material was homogeneous and without shives. 相似文献
14.
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
15.
Söderström Johanna Pilcher Linda Galbe Mats Zacchi Guido 《Applied biochemistry and biotechnology》2002,98(1-9):5-21
Two-step steam pretreatment of softwood was investigated with the aim of improving the enzymatic digestibility for ethanol
production. In the first step, softwood was impregnated with SO2 and steam pretreated at different severities. The first step was performed at low severity to hydrolyze the hemicellulose
and release the sugars into the solution. The combination of time and temperature that yielded the highest amount of hemicellulosic
sugars in the solution was determined. In the second step, the washed solid material from the optimized first step was impregnated
once more with SO2 and steam pretreated under more severe conditions to enhance the enzymatic digestibility. The investigated temperature range
was between 180 and 220°C, and the residence times were 2, 5 and 10 min. The effectiveness of pretreatment was assessed by
both enzymatic hydrolysis of the solids and simultaneous saccharification and fermentation (SSF) of the whole slurry after
the second pretreatment step, in the presence of antibiotics. For each pretreatment combination, the liquid fraction was fermented
to determine any inhibiting effects. At low severity in the second pretreatment step, a high conversion of cellulose was obtained
in the enzymatic hydrolysis step, and at a high severity a high conversion of cellulose was obtained in the second pretreatment
step. This resulted in an overall yield of sugars that was nearly constant over a wide range of severity. Compared with the
one-step steam pretreatment, the two-step steam pretreatment resulted in a higher yield of sugar and in a slightly higher
yield of ethanol. The overall sugar yield, when assessed by enzymatic hydrolysis, reached 80%. In the SSF configuration, an
overall ethanol yield of 69% was attained. 相似文献
16.
Enhancing the enzymatic hydrolysis of cellulosic materials using simultaneous ball milling 总被引:1,自引:0,他引:1
Mais Ursula Esteghlalian Ali R. Saddler John N. Mansfield Shawn D. 《Applied biochemistry and biotechnology》2002,98(1-9):815-832
One of the limiting factors restricting the effective and efficient bioconversion of softwood-derived lignocellulosic residues
is the recalcitrance of the substrate following pretreatment. Consequently, the ensuing enzymatic process requires relatively
high enzyme loadings to produce monomeric carbohydrates that are readily fermentable by ethanologenic microorganisms. In an
attempt to circumvent the need for larger enzyme loadings, a simultaneous physical and enzymatic hydrolysis treatment was
evaluated. A ball-mill reactor was used as the digestion vessel, and the extent and rate of hydrolysis were monitored. Concurrently,
enzyme adsorption profiles and the rate of conversion during the course of hydrolysis were monitored. α-Cellulose, employed
as a model substrate, and SO2-impregnated steam-exploded Douglas-fir wood chips were assessed as the cellulosic substrates. The softwood-derived substrate
was further posttreated with water and hot alkaline hydrogen peroxide to remove >90% of the original lignin. Experiments at
different reaction conditions were evaluated, including substrate concentration, enzyme loading, reaction volumes, and number
of ball beads employed during mechanical milling. It was apparent that the best conditions for the enzymatic hydrolysis of
α-cellulose were attained using a higher number of beads, while the presence of air-liquid interface did not seem to affect
the rate of saccharification. Similarly, when employing the lignocellulosic substrate, up to 100% hydrolysis could be achieved
with a minimum enzyme loading (10 filter paper units/g of cellulose), at lower substrate concentrations and with a greater
number of reaction beads during milling. It was apparent that the combined strategy of simultaneous ball milling and enzymatic
hydrolysis could improve the rate of saccharification and/or reduce the enzyme loading required to attain total hydrolysis
of the carbohydrate moieties. 相似文献
17.
Pretreatment of softwood by acid-catalyzed steam explosion followed by alkali extraction 总被引:2,自引:0,他引:2
Schell Daniel Nguyen Quang Tucker Melvin Boynton Brian 《Applied biochemistry and biotechnology》1998,(1):17-24
A process for converting lignocellulosic biomass to ethanol hydrolyzes the hemicellulosic fraction to soluble sugars (i.e.,
pretreatment), followed by acid- or enzyme-catalyzed hydrolysis of the cellulosic fraction. Enzymatic hydrolysis may be improved
by using an alkali to extract a fraction of the lignin from the pretreated material. The removal of the lignin may increase
the accessibility of the cellulose to enzymatic attack, and thus improve overall economics of the process, if the alkali-treated
material can still be effectively converted to ethanol.
Pretreated Douglas fir produced by a sulfuric-acid-catalyzed steam explosion was treated with NaOH, NH4OH, and lime to extract some of the lignin. The treated material, along with an untreated control sample, was tested by an
enzymatic-digestion procedure, and converted to ethanol by simultaneous saccharification and fermentation using a glucose-fermenting
yeast. NaOH was most effective at removing lignin (removed 29%), followed by NH4OH and lime. However, the susceptibility of
the treated material to enzymatic digestion was lower than the control and decreased with increasing lignin removal. Ethanol
production was similar for the control and NaOH-treated material, and lower for NH4OH- and lime-treated material. 相似文献
18.
Johanna Söderström Linda Pilcher Mats Galbe Guido Zacchi 《Applied biochemistry and biotechnology》2003,105(1-3):127-140
Fuel ethanol can be produced from softwood through hydrolysis in an enzymatic process. Prior to enzymatic hydrolysis of the
softwood, pretreatment is necessary. In this study, two-step steam pretreatment employing dilute H2SO4 impregnation in the first step and SO2 impregnation in the second step, to improve the overall sugar and ethanol yield, was investigated. The first pretreatment
step was performed under conditions of low severity (180°C, 10 min, 0.5% H2SO4) to optimize the amount of hydrolyzed hemicellulose. In the second step, the washed solid material from the first pretreatment
step was impregnated with SO2 and pretreated under conditions of higher severity to make the cellulose more accessible to enzymatic attack, as well as
to hydrolyze a portion of the cellulose. A wide range of conditions was used in the second step to determine the most favorable
combination. The temperatures investigated were between 190 and 230°C, the residence times were 2, 5, and 10 min; and the
SO2 concentration was 3%. The effect of pretreatment was assessed by both enzymatic hydrolysis of the solids and by simultaneous
saccharification and fermentation (SSF) of the whole slurry, after the second pretreatment step. For each set of pretreatment
conditions, the liquid fraction was also fermented to determine any inhibitory effects. Ethanol yield using the SSF configuration
reached 66% of the theoretical value for pretreatment conditions in the second step of 210°C and 5 min. The sugar yield using
the separate hydrolysis and fermentation configuration reached 71% for pretreatment conditions of 220°C and 5 min. 相似文献
19.
Effect of crystallite size on the catalysis of alumina-supported cobalt catalyst for steam reforming of ethanol 总被引:2,自引:0,他引:2
F. Haga T. Nakajima K. Yamashita S. Mishima 《Reaction Kinetics and Catalysis Letters》1998,63(2):253-259
The selectivity for steam reforming of ethanol on alumina-supported cobalt catalysts is closely related to the crystallite
size of cobalt, which varies the strength of ethanol adsorption. 相似文献
20.
Xuejun Pan Dan Xie Neil Gilkes David J. Gregg Jack N. Saddler 《Applied biochemistry and biotechnology》2005,124(1-3):1069-1079
Pretreatment of Douglas-fir by steam explosion produces a substrate containing approx 43% lignin. Two strategies were investigated
for reducing the effect of this residual lignin on enzymatic hydrolysis of cellulose: mild alkali extraction and protein addition.
Extraction with cold 1% NaOH reduced the lignin content by only approx 7%, but cellulose to glucose conversion was enhanced
by about 30%. Before alkali extraction, addition of exogenous protein resulted in a significant improvement in cellulose hydrolysis,
but this protein effect was substantially diminished after alkali treatment. Lignin appears to reduce cellulose hydrolysis
by two distinct mechanisms: by forming a physical barrier that prevents enzyme access and by non-productively binding cellulolytic
enzymes. Cold alkali appears to selectively remove a fraction of lignin from steam-exploded Douglas-fir with high affinity
for protein. Corresponding data for mixed softwood pretreated by organosolv extraction indicates that the relative importance
of the two mechanisms by which residual lignin affects hydrolysis is different according to the pre- and post-treatment method
used. 相似文献