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1.
Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production
from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production
by a simultaneous saccharification and fermentation process were studied, using diluted acid [H 2SO 4 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures
(160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic
digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best
pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after
steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated
biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the
filtrate (300 g/kg wheat straw). 相似文献
2.
The olive pulp fraction contained in the residue generated in olive oil extraction by a two-step centrifugation process can
be upgraded by using the cellulose fraction to produce ethanol and recovering high value phenols (tyrosol and hydroxytyrosol).
Olive pulp was pretreated in a laboratory scale stirred autoclave at different temperatures (150–250°C). Pretreatment was
evaluated regarding cellulose recovery, enzymatic hydrolysis effectiveness ethanol production by a simultaneous saccharification
and fermentation process (SSF), and phenols recovery in the filtrate. The pretreatment of olive pulp using water at temperatures
between 200°C and 250°C enhanced enzymatic hydrolysis. Maximum ethanol production (11.9 g/L) was obtained after pretreating
pulp at 210°C in a SSF fed-batch procedure. Maximum hydroxytyrosol recovery was obtained in the liquid fraction when pretreated
at 230°C. 相似文献
3.
Previous shake flask and stirred tank evaluations of temperature tolerant (37–43°C) yeasts in simultaneous saccharification and fermentation (SSF) on Sigmacell-50 cellulose substrates to ethanol have identified several good microorganisms for further SSF studies (27). Of these, the glucose fermenting yeastCandida acidothermophilum, C. brassicae, Saccharomyces cerevisiae, S. uvarum, and a mixed culture of the cellobiose fermenting yeastBrettanomyces clausenii withS. cerevisiae as a control were chosen for shake flask SSF screening experiments with pretreated wheat straw. This study indicates that theSaccharomyces strainscerevisiae anduvarum, give very good performance at high cellulase loadings or when supplemented with Novo-188 β-glucosidase. In fact, with the higher enzyme loadings these yeast will give complete conversion of cellulose to ethanol. Yet at the lower, more economical enzyme loadings, the mixed culture ofBrettanomyces clausenii andS. cerevisiae performs better than any single yeast. 相似文献
4.
Ethanol production was studied in simultaneous saccharification and fermentation (SSF) of steam-pretreated spruce at 42°C,
using a thermotolerant yeast. Three yeast strains of Kluyveromyces marxianus were compared in test fermentations. SSF experiments were performed with the best of these on 5% (w/w) of substrate at a
cellulase loading of 37 filter paper units/g of cellulose, and a β-glucosidase loading of 38 IU/gof cellulose. The detoxification
of the substrate and the lack of pH control in the experiments increased the final ethanol concentration. The final ethanol
yield was 15% lower compared to SSF with Saccharomyces cerevisiae at 37°C, owing to the cessation of ethanol fermentation after the first 10 h. 相似文献
5.
Lignocellulosic materials pretreated using liquid hot water (LHW) (220°C, 5 MPa, 120 s) were fermented to ethanol by batch
simultaneous saccharification and fermentation (SSF) using Saccharomyces cerevisiae in the presence of Trichoderma reesei cellulase. SSF of sugarcane bagasse (as received), aspen chips (smallest dimension 3 mm), and mixed hardwood flour (−60 +70
mesh) resulted in 90% conversion to ethanol in 2–5 d at enzyme loadings of 15–30 FPU/g. In most cases, 90% of the final conversion
was achieved within 75 h of inoculation. Comminution of the pretreated substrates did not affect the conversion to ethanol.
The hydrolysate produced from the LHW pretreatment showed slight inhibition of batch growth of S. cerevisiae. Solids pretreated at a concentration of 100 g/L were as reactive as those pretreated at a lower concentration, provided
that the temperature was maintained at 220°C. 相似文献
6.
The present work presents an alternative approach to ethanol production from sweet sorghum: without detoxification, acid-impregnated
fresh sweet sorghum stem which contains soluble (glucose and sucrose) and insoluble carbohydrates (cellulose and hemicellulose)
was steam pretreated under mild temperature of 100 °C. Simultaneous saccharification and fermentation experiments were performed
on the pretreated slurries using Saccharomyces cerevisiae. Experimentally, ground fresh sweet sorghum stem was combined with H 2SO 3 at dosages of 0.25, 0.50, and 0.75 g/g dry matter (DM) and steam pretreated by varying the residence time (60, 120, or 240 min).
According to enzymatic hydrolysis results and ethanol yields, H 2SO 3 was a powerful and mild acid for improving enzymatic digestibility of sorghum stem. At a solid loading of 10% ( w/ v) and acid dosage of 0.25 g/g DM H 2SO 3 at 100 °C for 120 min, 44.5 g/L ethanol was obtained after 48 ± 4 h of simultaneous saccharification and fermentation. This
corresponded to an overall ethanol yield of 110% of the theoretical one, based on the soluble carbohydrates in the fresh sweet
sorghum stem. The concentrations of hydroxymethylfurfural and furfural of the sulfurous acid pretreated samples were below
0.4 g/L. Ethanol would not inhibit the cellulase activity, at least under the concentration of 34 g/L. 相似文献
7.
The cellulose reactivity of two lignocellulosic feedstocks, switchgrass and poplar, was evaluated under straight saccharification
(SS) and simultaneous saccharification and fermentation (SSF) conditions following dilute sulfuric acid pretreatments designed
for optimum xylose yields. The optimum pretreatment conditions, within the constraints of the experimental system (Parr batch
reactor), were 1.2% acid, 180°C, and 0.5 min for switchgrass and 1% acid, 180°C, and 0.56 min for poplar. The cellulase enzyme
preparation was from Trichoderma reesei and fermentations were done with Saccharomyces cerevisiae. Time courses for SS were monitored as the sum of glucose and cellobiose; those for SSF as the sum of glucose, cellobiose,
and ethanol. Percentage conversions under SS conditions were 79.1% and 91.4% for the pretreated poplar and switchgrass feedstocks,
respectively. Analogous values under SSF conditions were 73.0% and 90.3% for pretreated poplar and switchgrass, respectively. 相似文献
8.
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
9.
Thermophilic ethanol fermentation of wet-exploded wheat straw hydrolysate was investigated in a continuous immobilized reactor
system. The experiments were carried out in a lab-scale fluidized bed reactor (FBR) at 70°C. Undetoxified wheat straw hydrolysate
was used (3–12% dry matter), corresponding to sugar mixtures of glucose and xylose ranging from 12 to 41 g/l. The organism,
thermophilic anaerobic bacterium Thermoanaerobacter BG1L1, exhibited significant resistance to high levels of acetic acid (up to 10 g/l) and other metabolic inhibitors present
in the hydrolysate. Although the hydrolysate was not detoxified, ethanol yield in a range of 0.39–0.42 g/g was obtained. Overall,
sugar efficiency to ethanol was 68–76%. The reactor was operated continuously for approximately 143 days, and no contamination
was seen without the use of any agent for preventing bacterial infections. The tested microorganism has considerable potential
to be a novel candidate for lignocellulose bioconversion into ethanol. The work reported here also demonstrates that the use
of FBR configuration might be a viable approach for thermophilic anaerobic ethanol fermentation. 相似文献
10.
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
11.
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 (D 5A) 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
12.
In this paper, four nonionic surfactants with different hydrophilic–lipophilic balance (HLB) based on sorbitan monolaurate
were synthesized by introducing ethylene oxide gas ( n = 20, 40, 60, and 80 ethylene oxide units). The chemical structure of the prepared ethoxylated surfactants was confirmed
using Fourier transform-infrared and 1H NMR spectroscopes. The surface tension and thermodynamic properties of the prepared surfactants have been studied. The simultaneous
saccharification and fermentation (SSF) process for ethanol production from microwave/alkali pretreated wheat straw has been
assayed using nonionic surfactants have different ethylene oxide units. Ethanol yield was 82% and 61% for Kluyveromyces marxianus and Saccharomyces cerevisiae, respectively, with the addition of 2.5 g/l of the prepared nonionic surfactant (HLB = 18.2). Results show that the production
of ethanol from microwave/alkali pretreated wheat straw increased with increasing the (HLB) value of the nonionic surfactant. 相似文献
13.
Glucose yield from the enzymatic hydrolysis of cellulose was investigated as a function of cellulase enzyme loading (7–36
filter paper units [FPU]/g cellulose) and solids concentration (7–18% total solids) for up to 72 h on dilute sulfuric-acid
pretreated Douglas Fir. The saccharification was performed on whole hydrolysate with no separation or washing of the solids.
Enzyme loading had a significant effect on glucose yield; solids concentration had a much smaller effect even at higher glucose
concentrations. The data were used to generate an empirical model for glucose yield, and to fit parameters of a cellulose
hydrolysis kinetic model. Both models could be used for economic evaluation of a separate hydrolysis and fermentation process. 相似文献
14.
A mixed solids waste (MSW) feedstock, comprising construction lumber waste (35% oven-dry basis), alm ond treeprunings (20%),
wheat straw (20%), office waste paper (12.5%), and newsprint (12.5%), was converted to ethanol via dilute-acid pretreatment
followed by enzymatic hydrolysis and yeast fermentation. The MSW was pretreated with dilute sulfuricacid (0.4% w/w) at 210°C
for 3 min in a 4-L stea mexplosion reactor, then washed with water to recover the solubilized hemicellulose. The digestibility
of water-washed, pretreated MSW was 90% in batch enzymatic hydrolysis at 66 FPU/g cellulose. Using an enzyme-recycle bioreactor
system, greater than 90% cellulose hydrolysis was achieved at a net enzyme loading of about 10 FPU/g cellulose. Enzyme recycling
using mebrane filtration and a fed-batch fermentation technique is a promising option for significantly reducing the cost
of enzyme in cellulose hydrolysis. The hexosesugars were readily fermentable using a Saccharomyces cerevisiae yeast strain that was adapted to the hydrolysate. Solid residue after enzyme digestion was subjected to various furnace experiments
designed to assess the fouling and slagging characteristics. Results of these analyses suggest the residue to be of a low
to moderate slagging and fouling type if burned by itself. 相似文献
15.
The pretreatment of yellow poplar wood sawdust using liquid water at temperatures above 220°C enhances enzyme hydrolysis.
This paper reviews our prior research and describes the laboratory reactor system currently in use for cooking wood sawdust
at temperatures ranging from 220 to 260°C. The wood sawdust at a 6–6.6% solid/liquid slurry was treated in a 2 L, 304 SS,
Parr reactor with three turbine propeller agitators and a proportional integral derivative (PID) controller, which controlled
temperature within ±1°C. Heat-up times to the final temperatures of 220, 240, or 260°C were achieved in 60–70 min. Hold time
at the final temperature was less than 1 min. A serpentine cooling coil, through which tap water was circulated at the completion
of the run, cooled the reactor’s contents within 3 min after the maximum temperature was attained. A bottoms port, as well
as ports in the reactor’s head plate, facilitated sampling of the slurry and measuring the pH, which changes from an initial
value of 5 before cooking to a value of approx 3 after cooking. Enzyme hydrolysis gave 80–90% conversion of cellulose in the
pretreated wood to glucose. Simultaneous saccharification and fermentation of washed, pretreated lignocellulose gave an ethanol
yield that was 55% of theoretical. Untreated wood sawdust gave less than 5% hydrolysis under the same conditions. 相似文献
16.
Different treatments to improve the thermotolerance of fermenting yeasts for simultaneous ethanol saccharification and fermentation
process of cellulosic materials have been examined. Yeasts of the genera Saccharomyces and Kluyveromyces were tested for growth and fermentation at progressively higher temperatures in the range of 42–47°C. The best results were
obtained with K. marxianus LG, which was then submitted to different treatments in order to achieve thermotolerant clones. A total of 35 new clones
were obtained that dramatically improved the SSF of 10% Solka-floc substrate at 45°C when compared to the original strain,
some with ethanol concentrations as high as 33 g/L. 相似文献
17.
Barley straw was used to demonstrate an integrated process for production of fuel ethanol and astaxanthin as a value-added co-product. Barley straw was pretreated by soaking in aqueous ammonia using the previously determined optimum conditions, which included 77.6 °C treatment temperature, 12.1 h treatment time, 15 wt% ammonia concentration, and 1:8 solid-to-liquid ratio. In the newly developed process, the pretreated barley straw was first hydrolyzed with ACCELLERASE® XY (a commercial hemicellulase product) to generate a xylose-rich solution, which contained 3.8 g/l glucose, 22.9 g/l xylose, and 2.4 g/l arabinose, with 96 % of the original glucan being left intact. The xylose-rich solution was used for production of astaxanthin by the yeast Phaffia rhodozyma without further treatment. The resulting cellulose-enriched solid residue was used for ethanol production in a fed-batch simultaneous saccharification and fermentation using ACCELLERASE® 1500 (a commercial cellulase product) and the industrial yeast Saccharomyces cerevisiae. At the end of the fermentation, 70 g/l ethanol was obtained, which was equivalent to 63 % theoretical yield based on the glucan content of the solid substrate. 相似文献
18.
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 H 2SO 4 pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H 2SO 4, and 70-s to 840-s residence times. The combined severity (Log 10 [ 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
19.
To have all-year-round available feedstock, whole-crop maize is harvested premature, when it still contains enough moisture
for the anaerobic ensiling process. Silage preparation is a well-known procedure for preserving plant material. At first,
this method was applied to obtain high-quality animal feed. However, it was found that such ensiled crops are very suitable
for bioenergy production. Maize silage, which consists of hardly degradable lignocellulosic material, hemicellulosic material,
and starch, was evaluated for its potential as a feedstock in the production of bioethanol. It was pretreated at low severity
(185 °C, 15 min) giving very high glucan (∼100%) and hemicellulose recoveries (<80%)—as well as very high ethanol yield in
simultaneous saccharification and fermentation experiments (98% of the theoretical production based on available glucan in
the medium). The theoretical ethanol production of maize silage pretreated at 185 °C for 15 min without oxygen or catalyst
was 392 kg ethanol per ton of dry maize silage. 相似文献
20.
Ionic liquid (IL) 1-ethyl-3-methylimidazolium dimethylphosphate ([Emim]DMP) was chosen as an environment-friendly solvent
to enzymatically hydrolyze cellulose in situ. Under optimal reaction condition, 80.2 % of cellulose (10 mg mL −1) were converted to glucose in aqueous-IL-DMSO ( φ
r = 74: 25: 1) media at 55°C in 18 h. Finally, fermentability of the recovered hydrolyzates was evaluated using Saccharomyces cerevisiae which is able to ferment hydrolyzates efficiently, the ethanol production was 0.44 g g −1 of glucose within 24 h of the process. Such information is vital for the saccharification of more complex cellulose materials
and for the fermentation of hydrolyzates into biofuel. 相似文献
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