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1.
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% SO 2. Sequential SO 2-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
2.
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 H 2SO 4 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% H 2SO 4, 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
3.
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 SO 2 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 SO 2 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
4.
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
5.
Wheat straw was pretreated by wet explosion using three different oxidizing agents (H 2O 2, O 2, and air). The effect of the pretreatment was evaluated based on glucose and xylose liberated during enzymatic hydrolysis.
The results showed that pretreatment with the use of O 2 as oxidizing agent was the most efficient in enhancing overall convertibility of the raw material to sugars and minimizing
generation of furfural as a by-product. For scale-up of the process, high dry matter (DM) concentrations of 15–20% will be
necessary. However, high DM hydrolysis and fermentation are limited by high viscosity of the material, higher inhibition of
the enzymes, and fermenting microorganism. The wet-explosion pretreatment method enabled relatively high yields from both
enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) to be obtained when performed on unwashed slurry
with 14% DM and a low enzyme loading of 10 FPU/g cellulose in an industrial acceptable time frame of 96 h. Cellulose and hemicellulose
conversion from enzymatic hydrolysis were 70 and 68%, respectively, and an overall ethanol yield from SSF was 68%. 相似文献
6.
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
7.
Whole treechips obtained from softwood forest thinnings were pretreated via single-and two-stage dilute-sulfuric acid pretreatment.
Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage
pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried
out at low severity tomaximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate
by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute
sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and
to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated
samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid
pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification
and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement. 相似文献
8.
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
9.
A process was developed to fractionate and isolate the hemicellulose B component of corn fiber generated by corn wet milling.
The process consisted of pretreatment by soaking in aqueous ammonia followed by enzymatic cellulose hydrolysis, during which
the hemicellulose B was solubilized by cleavage into xylo-oligosaccharides and subsequently recovered by precipitation with
ethanol. The pretreatment step resulted in high retention of major sugars and improvement of subsequent enzymatic hydrolysis.
The recovered hemicellulose B was hydrolyzed by a cocktail of enzymes that consisted of β-glucosidase, pectinase, xylanase,
and ferulic acid esterase (FAE). Xylanase alone was ineffective, demonstrating yields of less than 2% of xylose and arabinose.
The greatest xylose and arabinose yields, 44% and 53%, respectively, were obtained by the combination of pectinase and FAE.
A mass balance accounted for 87% of the initially present glucan, 91% of the xylan, and 90% of the arabinan. The developed
process offered a means for production of corn fiber gum as a value-added co-product and C5 sugars, which could be converted
to other valuable co-products through fermentation in a corn wet-milling biorefinery. 相似文献
10.
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 H 2SO 4 impregnation in the first step and SO 2 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% H 2SO 4) to optimize the amount of hydrolyzed hemicellulose. In the second step, the washed solid material from the first pretreatment
step was impregnated with SO 2 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
SO 2 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
11.
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 H 2SO 4, HCl, and NaOH separately as well as consecutively under relative mild conditions (120°C, 1h). Pretreatment with 5% H 2SO 4 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
12.
Trimming vine shoot samples were treated with water under selected operational conditions (autohydrolysis reaction) to obtain
a liquid phase containing hemicellulose-decomposition products. In a further acid-catalyzed step (posthydrolysis reaction),
xylooligosaccharides were converted into single sugars for the biotechnological production of lactic acid using Lactobacillus
pentosus. A wide range of temperatures, reaction times, and acid concentrations were tested during the autohydrolysis–posthydrolysis
process to investigate their influence on hemicellulose solubilization and reaction products. The maximum concentration of
hemicellulosic sugars was achieved using autohydrolysis at 210 °C followed by posthydrolysis with 1% H 2SO 4 during 2 h. Data from autohydrolysis–posthydrolysis were compared with the results obtained at the optima conditions assayed
for prehydrolysis (3% H 2SO 4 at 130 °C during 15 min) based on previous works. Prehydrolysis extracted more hemicellulosic sugars from trimming vine shoots;
however, the protein content in the hydrolysates from autohydrolysis–posthydrolysis was higher. The harsher conditions assayed
during the autohydrolysis process and the higher content of protein after this treatment could induce Maillard reactions decreasing
consequently the concentration of hemicellulosic sugars in the hydrolysates. Therefore, despite the several advantages of
autohydrolysis (less equipment caused by the absence of mineral acid, less generation of neutralized sludges, and low cost
of reagents) the poor results obtained in this work with no detoxified hydrolysates ( Q
P = 0.36 g/L h, Q
S = 0.79 g/L h, Y
P/S = 0.45 g/g, Y
P/Sth = 61.5 %) or charcoal-treated hydrolysates ( Q
P = 0.76 g/L h, Q
S = 1.47 g/L h, Y
P/S = 0.52 g/g, Y
P/Sth = 71.5 %) suggest that prehydrolysis of trimming vine shoots with diluted H 2SO 4 is more attractive than autohydrolysis-posthydrolysis for obtaining lactic acid through fermentation of hemicellulosic sugars
with L. pentosus. Besides the higher hemicellulosic sugars concentration achieved when using the prehydrolysis technology, no detoxification
steps are required to produce efficiently lactic acid ( Q
P = 1.14 g/L h; Q
S = 1.64 g/L h; Y
P/S = 0.70 g/g; Y
P/Sth = 92.6 %), even when vinification lees are used as nutrients ( Q
P = 0.89 g/L h; Q
S = 1.54 g/L h; Y
P/S = 0.58 g/g; Y
P/Sth = 76.1 %). 相似文献
13.
Douglas-fir sapwood and heartwood were impregnated with SO2 and steam exploded at three severity levels, and the cellulose-rich, water-insoluble component was enzymatically hydrolyzed. The high-severity conditions resulted in near complete solubilization and some degradation of hemicelluloses and a significant improvement in the efficiency of enzymatic digestibility of the cell ulose component. At lower severity, some of the hemicellulose remained un hydrolyzed, and the cellulose present in the pretreated solids was not readily hydrolyzed. The medium-severity pretreatment conditions proved to be a good compromise because they improved the enzymatic hydrolyzability of the solids and resulted in the recovery of the majority of hemicellulose in a monomeric form within the water-soluble stream. Sapwood-derived wood chips exhibited a higher susceptibility to both pretreatment and hydrolysis and, on steam explosion, formed smaller particles as compared to heartwood-derived wood chips. 相似文献
14.
A combination of Douglas fir heartwood and sapwood chips were steam pretreated under three conditions as measured by the Severity
Factor (log R o), 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 R o=3.08), high-enzyme hydrolyzability of the cellulosic component (high severity [H], log R o=4.21), and a compromise between the two conditions (medium severity [M], log R o=3.45). The medium-severity pretreatment conditions (195°C, 4.5 min, 4.5% SO 2 logR o=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
15.
Ethanol can be produced from lignocellulosic biomass with the usage of ball milling pretreatment followed by enzymatic hydrolysis
and fermentation. The sugar yields from lignocellulosic feed stocks are critical parameters for ethanol production process.
The research results from this paper indicated that the yields of glucose and xylose were improved by adding any of the following
dilute chemical reagents: H 2SO 4, HCl, HNO 3, CH 3COOH, HCOOH, H 3PO 4, and NaOH, KOH, Ca(OH) 2, NH 3·H 2O in the ball milling pretreatment of corn stover. The optimal enzymatic hydrolysis efficiencies were obtained under the conditions
of ball milling in the alkali medium that was due to delignification. The data also demonstrated that ball milling pretreatment
was a robust process. From the microscope image of ball milling-pretreated corn stover, it could be observed that the particle
size of material was decreased and the fiber structure was more loosely organized. Meanwhile, the results indicate that the
treatment effect of wet milling is better than that of dry milling. The optimum parameters for the milling process were ball
speed of 350 r/min, solid/liquid ratio of 1:10, raw material particle size with 0.5 mm, and number of balls of 20 (steel ball,
Φ = 10 mm), grinding for 30 min. In comparison with water milling process, alkaline milling treatment could increase the enzymatic
hydrolysis efficiency of corn stover by 110%; and through the digestion process with the combination of xylanase and cellulase
mixture, the hydrolysis efficiency could increase by 160%. 相似文献
16.
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
17.
Iogen (Canada) is a major manufacturer of industrial cellulase and hemicellulase enzymes for the textile, pulp and paper, and poultry feed industries. Iogen has recently constructed a 40 t/d biomass-to-ethanol demonstration plant adjacent to its enzyme production facility. The integration of enzyme and ethanol plants results in significant reduction in production costs and offers an alternative use for the sugars generated during biomass conversion. Iogen has partnered with the University of Toronto to test the fermentation performance characteristics of metabolically engineered Zymomonas mobilis created at the National Renewable Energy Laboratory. This study focused on strain AX101, a xylose- and arabinose-fermenting stable genomic integrant that lacks the selection marker gene for antibiotic resistance. The “Iogen Process” for biomass depolymerization consists of a dilute-sulpfuric acid-catalyzed steam explosion, followed by enzymatic hydrolysis. This work examined two process design options for fermentation, first, continuous cofermentation of C 5 and C 6 sugars by Zm AX101, and second, separate continuous fermentations of prehydrolysate by Zm AX101 and cellulose hydrolysate by either wildtype Z. mobilis ZM4 or an industrial yeast commonly used in the production of fuel ethanol from corn. Iogen uses a proprietary process for conditioning the prehydrolysate to reduce the level of inhibitory acetic acid to at least 2.5 g/L. The pH was controlled at 5.5 and 5.0 for Zymomonas and yeast fermentations, respectively. Neither 2.5 g/L of acetic acid nor the presence of pentose sugars (C 6:C 5 = 2:1) appreciably affected the high-performance glucose fermentation of wild-type Z. mobilis ZM4. By contrast, 2.5 g/L of acetic acid significantly reduced the rate of pentose fermentation by strain AX101. For single-stage continuous fermentation of pure sugar synthetic cellulose hydrolysate (60 g/L of glucose), wild-type Zymomonas exhibited a four-fold higher volumetric productivity compared with industrial yeast. Low levels of acetic acid stimulated yeast ethanol productivity. The glucose-to-ethanol conversion efficiency for Zm and yeast was 96 and 84%, respectively. 相似文献
18.
Whole tree chips obtained from softwood forest thinnings were converted to ethanol via a two-stage dilute acid hydrolysis followed by yeast fermentation. The chips were first impregnated with dilute sulfuric acid, then pretreated in a steam explosion reactor to hydrolyze, more than 90% of the hemicellulose and approx 10% of the cellulose. The hydrolysate was filtered and washed with water to recover the sugars. The washed fibers were then subjected to a second acid im pregnation and hydrolysis to hydrolyze as much as 45% of the reamining cellulose. The liquors from both hydrolysates were combined and fermented to ethanol by a Saccharomyces cerevisiae yeast that had been adapted to the inhibitors. Based on available hexose sugars, ethanol yields varied from 74 to 89% of theoretical. Oligosaccharide contents higher than about 10% of the total available sugar appear to have a negative impact on ethanol yield. 相似文献
19.
This article presents the advanced technology that has been developed by BioEnergy International of Gainesville, Florida,
utilizing novel recombinant strains of bacteria developed by Lonnie Ingram of the University of Florida. The first commercial
applications of these unique fermenting organisms convert 5-carbon sugars, as well as 6-carbon sugars, and oligomers of cellulose
(e.g., cellobiose and cellotriose) directly to ethanol. The proposed systems that will be utilized for conversion of agricultural
wastes, mixed waste papers, and pulp and paper mill waste in forthcoming commercial installations are now under design. This
involves the extensive experience of Raphael Katzen Associates International, Inc. in acid hydrolysis, enzyme production,
enzymatic hydrolysis, large-scale fermentation engineering, and distillation/dehydration.
Specific examples of this advanced technology will be presented in different applications, namely:
1. |
Conversion of the hemicellulose content of sugar cane bagasse to 5-carbon sugars by mild-acid prehydrolysis, followed by fermentation
of the 5-carbon sugar extract with recombinantEscherichia coli in a commercial installation soon to be under construction in Brazil. This unique process utilizes the surplus hemicellulose
fraction of bagasse not required for steam and power generation to produce ethanol, additional to that from the original cane
juice, which has been converted by conventional sucrose fermentation to ethanol. The process also recovers and converts to
ethanol the majority of sucrose normally lost with the bagasse fibers. Resultant beer is enriched in an innovative process
to eliminate the need for incremental rectification capacity.
|
2. |
Application of this technology to mixed waste paper in Florida, with a moderate loading of newsprint (85% mechanical wood
fiber), will involve a mild-acid prehydrolysis, the partial extraction of the 5-carbon sugars produced from hemicellulose
as a feedstock for propagation of the recombinantKlebsiella oxytoca bacterium. Included is a facility providing for in-house production of cellulase enzyme, as an active whole broth for direct
use in simultaneous saccharification and fermentation (SSF) of the remaining cellulose and residual 5-carbon sugars to ethanol.
This is followed by distillation and dehydration in the advanced commercially available low-energy recovery system.
|
3. |
Another potential application of this unique technology involves utilization of a variety of wastes from several pulp and
paper mills in close proximity, permitting collection of these wastes at low cost and reducing the considerable cost encountered
in disposing of such low-energy wet waste. Based on pilot plant experiences with converting such waste by simultaneous enzymatic
hydrolysis and fermentation, the same techniques will be applied as in the second case, with use of acid prehydrolysis only
if the hemicellulose-derived sugars can be economically recovered. If not, acid hydrolysis will be eliminated and only the
simultaneous saccharification and fermentation will be carried out, utilizing in-house-produced enzyme broth and recombinantKlebsiella oxytoca.
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相似文献
20.
Agricultural residues were pretreated by steam explosion and the cellulosic component of these substrates were converted to
ethanol using a combined enzymatic hydrolysis and fermentation (CHF) process. The enzymatic hydrolysis was carried out using
culture filtrates of Trichoderma harzianum E58 while the liberated sugars were fermented to ethanol by S. cerevisiae.
Initially, pretreatment conditions were optimized to ensure that the substrates were readily hydrolyzed and fermented. The
agricultural residues were steamed for various times between 30 and 120 s at approximately 240‡C prior to rapid decompression
(explosion) in a small masonite-type gun. The various substrates were selectively extracted by water and alkali to see whether
the enzymatic hydrolysis and fermentability of the substrates were enhanced. A comparison between the overall conversion of
wheat and barley straw was made since these are the two most readily available agricultural residues in Canada.
Steam explosion did not affect the hexosan content of the residues, although the pentosan content of the substrates decreased
with increasing duration of steaming. The hexosan (cellulose) content of wheat straw was 50.7% of the total substrate while
a slightly higher 52.9% cellulose content was detected in the barley straw. Wheat straw was more efficiently hydrolyzed after
it had been steamed for 90 s while optimum hydrolysis of the barley straw was detected after 60 s.
Steam exploded wheat and barley straw that was subsequently extracted with water was readily hydrolyzed to their component
sugars. S. cerevisiae could almost quantitatively convert these sugars to ethanol. This indicated that water washing not only enhanced the enzymatic
hydrolysis of the steam exploded substrates, it also removed inhibitory material that restricted the growth of S. cerevisiae.
Maximum hydrolysis (78.5%) and ethanol yields (10 mg/mL) were obtained when wheat straw was steamed for 90 s. Slightly lower
hydrolysis (76.0%) and ethanol yields (9.5 mg/mL) were obtained with barley straw that had been steamed for 120 s. 相似文献
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