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1.
Applied Biochemistry and Biotechnology - A reverse-flow, two-temperature dilute-acid prehydrolysis process of commercial yellow poplar sawdust using two percolation reactors was designed to... 相似文献
2.
Applied Biochemistry and Biotechnology - The Microtox assay represents a rapid, accurate, and reproducible method for determining general microbial toxicity. This assay was used to evaluate the... 相似文献
3.
The use of stalks instead of tubers as a source of carbohydrates for ethanol production has been investigated. The inulin
present in the stalks of Jerusalem artichoke was extracted with water and the effect of solid-liquid ratio, temperature, and
acid addition was studied and optimized in order to attain a high-fructose fermentable extract. The maximum extraction efficiency
(corresponding to 35 g/L) of soluble sugars was obtained at 1/6 solidliquid ratio.
Fermentations of hydrolyzed extracts by baker's yeast and direct fermentation by an inulinease activity yeast were also performed
and the potential to use this feedstock for bioethanol production assessed. The results show that the carbohydrates derived
from Jerusalem artichoke stalks can be converted efficiently to ethanol by acidic hydrolysis followed by fermentation with
Saccharomyces cerevisiae or by direct fermentation of inulin using Kluyveromyces marxianus strains. In this last case about 30 h to complete fermentation was required in comparison with 8–9 h obtained in experiments
with S. cerevisiae growth on acid extracted juices. 相似文献
4.
The advantages of the use of SO 2 in steam pretreatment are described. Two different large scale continuous reactors, the Stake and the Wenger, have been used
for this purpose. Pine, aspen and corn stover were prehydrolysed by SO 2 in these reactors and hydrolysed by enzymes. The solution of hexoses and pentoses so obtained were fermented by Pichia stipitis R, yielding 372, 346 and 388 L ethanol/tonne for the 3 feedstocks, respectively. When a mixed culture of P. stipitis R, which is an excellent pentose fermenter, and Brettanomyces clausenii which is an excellent cellobiose fermenter, was used in a simultaneous saccharification-fermentation made with SO 2-prehydrolysed aspen, the yield rose to 384 L/tonne. These are higher yields than have been reported in the literature to
date. 相似文献
5.
Opportunities for matching chemical and physical properties of woody feedstocks to ethanol production process requirements via genetic improvement have long been recognized. Exploitation is now feasible owing to advances in trait measurement, breeding, and gene transfer technologies. Poplar genetic parameters are favorable largely for reducing lignin and increasing cellulose contents and specific gravity. Transgenic poplars with decreased lignin and increased cellulose contents, but otherwise normal growth and development, have been produced via genetic transformation. The long-standing debate on feasibility has thus become one of when, not if, designer varieties will become available. 相似文献
6.
Applied Biochemistry and Biotechnology - Inclusion of coal inSaccharomyces cerevisiae cultures enhanced ethanol and biomass production (from dextrose) similarly to yeast extract. Coal-induced... 相似文献
7.
Hybrid poplar (Populus nigra x P. maximowiczii) chips were pretreated using an organosolv ethanol process. The effect of pretreatment conditions (temperature, time, catalyst, and ethanol concentration) on the substrate characteristics, including fiber size, crystallinity, and degree of polymerization of cellulose, was investigated using an experimental matrix designed with response surface methodology. The conditions ranged 155-205 degrees C, 26-94 min, 0.83-1.67% catalyst (H(2)SO(4)) on oven-dry wood chip (w/w), and 25-75% ethanol concentration (v/v). The results indicated that the substrate characteristics are controllable and predictable. Desirable substrates can be prepared by fine-tuning the processing parameters. The regression models developed, allowed the quantitative prediction of the substrate characteristics from the pretreatment conditions used. 相似文献
8.
In this work, the effect of the addition of different concentrations of Tween-80 and three different zeolite-like products
on enzymatic hydrolysis, ethanol fermentation, and simultaneous saccharification and fermentation (SSF) process has been investigated.
The ability of these products to enhance the effectiveness of the SSF process to ethanol of steam-exploded poplar biomass
using the thermotolerant strain Kluyveromyces marxianus EMS-26 has been tested.
Tween-80 (0.4 g/L) increased enzymatic hydrolysis yield by 20% when compared to results obtained in hydrolysis in absence
of the additive. Zeolite-like products (ZESEP-56 and ZECER-56) (2.5 g/L) improved rates of conversion and ethanol yields in
the fermentation of liquid fraction recovered from steam-exploded poplar. The periods required for the completion of fermentation
were approx 10 h in the presence of zeolite-like products and 24 h in the absence of additives. The probable mode of action
is through lowered levels of inhibitory substances because of adsorption by the additive. 相似文献
9.
In the Escherichia coli cell-free system, the modification of cell extract can be achieved by preparation of the strains carrying additional property
or those being induced with a certain gene expression prior to harvesting. In this study, we analyzed the cell-free system
with S30 extract containing T7 RNA polymerases (S30 extract-T7pol) prepared from E. coli BL21(DE3) strain, which includes T7 RNA polymerase from extrinsic genes by IPTG induction, as a model for the improvement
of the cell-free system. The fact that a significant degree of mRNA degradation was observed in the cell-free system with
S30 extract-T7pol indicates the increase of ribonuclease activity was an unfavorable influence derived from the cell-extract
modification process. We also showed that this influence was settled by the addition of an effective ribonuclease inhibitor,
such as copper (II) ion, to the reaction mixture. 相似文献
10.
A series of pilot plant experiments have been conducted to compare the performance of a system utilizing two percolation reactors in series to a single reactor system. Although theoretically capable of producing higher glucose yields or concentrations, the two-reactor system concentrations were approximately the same and the yields were considerably lower than those from the single reactor study. An associated kinetics study found the glucose degradation kinetics to be accelerated by chromium ions, but this effect was greatly reduced in the presence of wood. The presence of metal surfaces also increased the rate of degradation even without large ion concentrations. The poor performance of the reactor system is proposed to be caused by intraparticle glucose diffusion effects and the catalytic effect on glucose degradation reactions of chromium ions from the corrosion of stainless steel by the acid. Strategies for reducing the effects of these phenomena on PBR performance are presented. 相似文献
11.
The application of Fenton’s reaction to enhance the fermentability of prehydrolysates obtained from steam explosion pretreatment
of poplar biomass was studied. Reaction conditions of temperature and H 2O 2 and Fe(II) concentrations were studied. The fermentability of prehydrolysate treated by Fenton’s reaction was tested by using
different inoculum sizes of thermotolerant strain Kluyveromyces marxianus CECT 10875. The highest percentages of toxic compound degradation (ranging from 71 to 93% removal) were obtained at the highest
H 2O 2 concentration tested (50 m M). However, a negative effect on fermentability was observed at this H 2O 2 concentration at the lower inoculum loading. An increase in inoculum size to 0.6 g/L resulted in an enhanced ethanol fermentation
yield of 95% relative to control. 相似文献
12.
Prehydrolysis with dilute acid and steam explosion constitute the most promising methods for improving enzymatic digestibility of biomass for ethanol production. Despite world wide acceptance, these methods of pretreatment are quite expensive considering costs for the reactor, energy, and fractionation. Using peracetic acid is a lignin-oxidation pretreatment with low-energy input by which biomass can be treated in a silo-type system without need for expensive capitalization. Experimentally, ground hybrid poplar and sugar cane bagasse are placed in plastic bags and a peracetic acid solution is added to the biomass in different concentrations based on ovendried biomass. The ratio of solution to biomass is 6∶1 and a 7-d storage period at ambient temperature (20°C) has been used. As an auxiliary method, a series of pre-pretreatments using stoichiometri camounts of sodium hydroxide and ammonium hydroxide based on 4-methyl-glucuronic acid and acetyl content in the biomass are performed before addition of peracetic acid. The basic solutions are added to the biomass in a ratio of 14∶1 solution to biomass, and mixed for 24 h at the same ambient temperature. Biomass is filtered and washed to a neutral pH before peracetic acid addition. The aforementioned procedures give high xylan content substrates as a function of the selectivity of peracetic acid for lignin oxidation and the mild conditions of the process. Consequently, xylanase/β-glucosidase combinations were more effective than cellulase preparations in hydrolyzing these materials. The pretreatment efficiency was evaluated through enzymatic hydrolysis and simultaneous saccharification and cofermentation (SSCF) tests. Peracetic ac treatment improves enzymatic digestibility of hybrid poplar and sugar cane bagasse with no need of high temperatures. Alkaline treatments are helpful in reducing peracetic acid requirements in the pretreatment. 相似文献
13.
Applied Biochemistry and Biotechnology - The need for chemical pretreatment of biomass for the enzyme-catalyzed production of ethanol from lignocellulosic feedstocks has been established. Past... 相似文献
14.
The performances of rice straw (RS) degradation and biogas production were examined at different pretreatment temperatures from 90℃ to 130℃ to improve biogas fermentation efficiency and net energy production in whole slurry. Test at 100℃ pretreatment, which achieved 12.8% higher net energy production from RS than that observed in the control, could be considered as the optimal choice. 相似文献
15.
Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification
and fermentation (SSF) system comprised of Trichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation by Saccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised of Clostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H 2SO 4) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H 2SO 4). The short residence time pretreatment resulted in a somewhat (10–20%) more reactive substrate, with the reactivity difference
particularly notable at low enzyme loadings and/or low agitation. Based on a preliminary screening, inhibition of SSF by byproducts
of short residence time pretreatment was measurable, but minor. Both SSF and DMC were carried out successfully in well-mixed
continuous systems, with steady-state data obtained at residence times of 0.58–3 d for SSF as well as 0.5 and 0.75 d for DMC.
The SSF system achieved substrate conversions varying from 31% at a 0.58-d residence time to 86% at a 2-d residence time.
At comparable substrate concentrations (4–5 g/l) and residence times (0.5–0.58 d), substrate conversion in the DMC system
(77%) was significantly higher than that in the SSF system (31%). Our results suggest that the substrate conversion in SSF
carried out in CSTR is relatively insensitive to enzyme loading in the range 7–25 U/g cellulose and to substrate concentration
in the range of 5–60 g/L cellulose in the feed. 相似文献
16.
The potential of dilute-acid prehydrolysis as a pretreatment method for sugarcane bagasse, rice hulls, peanut shells, and cassava stalks was investigated. The prehydrolysis was performed at 122 degrees C during 20, 40, or 60 min using 2% H(2)SO(4) at a solid-to-liquid ratio of 1:10. Sugar formation increased with increasing reaction time. Xylose, glucose, arabinose, and galactose were detected in all of the prehydrolysates, whereas mannose was found only in the prehydrolysates of peanut shells and cassava stalks. The hemicelluloses of bagasse were hydrolyzed to a high-extent yielding concentrations of xylose and arabinose of 19.1 and 2.2 g/L, respectively, and a xylan conversion of more than 80%. High-glucose concentrations (26-33.5 g/L) were found in the prehydrolysates of rice hulls, probably because of hydrolysis of starch of grain remains in the hulls. Peanut shells and cassava stalks rendered low amounts of sugars on prehydrolysis, indicating that the conditions were not severe enough to hydrolyze the hemicelluloses in these materials quantitatively. All prehydrolysates were readily fermentable by Saccharomyces cerevisiae. The dilute-acid prehydrolysis resulted in a 2.7- to 3.7-fold increase of the enzymatic convertibility of bagasse, but was not efficient for improving the enzymatic hydrolysis of peanut shells, cassava stalks, or rice hulls. 相似文献
17.
Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production.
Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment
the material is impregnated with a catalyst, for example, H 2SO 4, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study,
soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose
and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and
monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked
barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration
(0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H 2SO 4. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw.
Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that
were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt%
H 2SO 4 and 220°C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment
with 0.2wt% H 2SO 4 at 190°C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material. 相似文献
18.
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
19.
Thermodynamic data indicate that the oxidation of oxygenated organic species originating from biomass instead of water at the anode of an electrolysis cell should allow decreasing the cell voltage below 1.23 V. Biosourced alcohols, polyols, sugars, lignocellulosic compounds, and their derivatives are then electroreformed to produce clean hydrogen at the cathode and compounds at the anode of electrolysis cells. The reported studies highlight the main challenges to make electroreforming a future industrial process: higher reaction kinetics and hydrogen evolution rate; better selectivity of anode catalysts toward the formation of CO 2 or added-value compounds; and utilization of nonstrategical metals. An attractive solution to decrease hydrogen production costs and to make bankable other economic activities consists in directly valuing wastes from agriculture/forestry (lignocellulosic raw materials) and/or wastes from biofuel industries. 相似文献
20.
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 SO 2 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% SO 2. Sequential SO 2-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
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