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1.
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
2.
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
3.
The pretreatment of softwood with sulfuric acid impregnation in the production of ethanol, based on enzymatic hydrolysis,
has been investigated. The parameters investigated were: H 2SO 4 concentration (0.5 – 4.4% w/w liquid), temperature (180 – 240°C), and residence time (1-20 minutes). The combined severity
(log Ro-pH) was used to combine the parameters into a single reaction ordinate. The highest yields of fermentable sugars,
i.e., glucose and mannose, were obtained at a combined severity of 3. At this severity, however, the fermentability declined
and the ethanol yield decreased. In a comparison with previous results, SO 2 impregnation was found to be preferable, since it resulted in approximately the same sugar yields, but better fermentability. 相似文献
4.
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
5.
In this study, corn stover with a dry matter content of 20% was impregnated with SO 2 and then steam pretreated for various times at various temperatures. The pretreatment was evaluated by enzymatic hydrolysis
of the solid material and analysis of the sugar content in the liquid. The maximum overall yield of glucose, 89% of the theoretical
based on the glucan in the raw material, was achieved when the corn stover was pretreated at 200°C for 10 min. The maximum
overall yield of xylose, 78%, was obtained with pretreatment at 190°C for 5 min. 相似文献
6.
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
8.
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
9.
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
10.
Theoretical and Experimental Chemistry - On the basis of analysis and thermodynamic calculations of the reaction paths of the catalytic conversion of ethanol a two-step process is proposed for the... 相似文献
11.
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
12.
纤维素酶是一种有效的纤维质类物质水解催化剂,工业应用时可通过固定化纤维素酶来降低其成本。本文将烟曲霉原变种JCF产生的纤维素酶固定在MnO2纳米颗粒上。 MnO2可提高纤维素酶的活性,并充当一个更好的载体。采用扫描电镜表征了所制MnO2纳米粒子及其负载纤维素酶的表面性质,以傅里叶变换红外光谱分析了固定在MnO2纳米粒子上纤维素酶的官能团性质。纤维素酶在MnO2纳米粒子上最大的固定化效率为75%。考察了固定化纤维素酶的活性、操作pH值、温度、热稳定性和重复使用性等性质。结果表明,所制固定化酶的稳定性比游离酶更高。固定于MnO2纳米粒子上的纤维素酶可用于纤维质类物质的水解反应,且能在较宽的温度和pH值范围内使用。表征结果证实了该催化剂具有非常高的催化纤维素类物质水解的活性。 相似文献
13.
The development of bioconversion technologies for production of fuels, chemicals, and power from renewable resources is currently a high priority for developed nations such as the United States, Canada, and the European Union as a way to improve national energy security and reduce greenhouse gas emissions. The widespread implementation of such technologies will require a sustainable supply of biomass from forestry and agriculture. Forests are a major source of feedstocks for biofuels production in Canada. Woody biomass includes residues from logging and forest thinning, and from wood processing and pulp production. More recently, damaged wood caused by beetle infestations has become available on a large scale in Western Canada. This study evaluates beetle-killed British Columbian hybrid spruce (HS) (Picea glauca x P. engelmannii) as a feedstock for the production of bioethanol. In the past 30 yr, attack by the beetle Dendroctonus rufipennis and associated fungi has resulted in estimated losses of more than three billion board feet in British Columbia alone. Here we describe the chemical and some physical characteristics of both healthy (HHS) and beetle-killed (BKHS) British Columbian HS and evaluate the technical feasibility of using these feedstocks as a source of biomass for bioethanol production. Untreated HHS and BKHS did not differ significantly in chemical composition except for the moisture content, which was significantly lower in BKHS (approx 10%) compared with HHS (approx 18%). However, the yields of carbohydrates in hydrolyzable and fermentable forms were higher at mild pretreatment conditions (H-Factor <1000) for BKHS compared with HHS. At medium (H-Factor 1000-2000) and severe (H-Factor >2000) pretreatment conditions HHS and BKHS behaved similarly. Organosolv pretreated HHS and BKHS demonstrated good ethanol theoretical yields, approx 70 and 80%, respectively. 相似文献
14.
Time-of-flight detection of neutral metastable fragments has been applied to the study of electron-impact dissociation of SO 2 molecules. The time-of-flight distributions indicate that a variety of processes are involved in the production of metastable fragments with a wide range of energies. Rydberg S and O atoms and SO molecules have been identified. Data for these processes have been measured up to 300 eV. The results presented are compared with other studies of fragmentation of SO 2. 相似文献
17.
In a recent study investigating the suitability of solvent extraction (SX) for the separation of Ta and Nb, it was shown that speciation data would be required to help explain the data obtained. As traditional speciation techniques cannot be readily applied for Ta and Nb, it was decided to determine the suitability of molecular modeling for this purpose. During the SX experiments the aqueous phase consisted of sulfuric acid (H 2SO 4), water, and metal species. In this study density functional theory (DFT) modeling was used to calculate the formation energy of five possible reactions of H 2SO 4 and H 2O. Different functional and basis set combinations were compared as well as the effect of infinite dilution by using the conductor-like screening model (COSMO), which simulates infinite dilution of solvents of varying polarity and includes the short-range interactions of the solute particles. The results obtained were used to determine whether it is possible to predict the reactions and mechanism when H 2SO 4 and H 2O interact during SX. According to the results, the deprotonation of H 2SO 4 was endothermic in a 1:1 acid–water ratio, while being both exothermic in the 1:5 and 1:10 acid–water ratio forming HSO 4− and SO 42− respectively. Furthermore, it was seen that the hydration and dehydration of H 2SO 4 in a bulk H 2O solution was a continuous process. From the energy calculations it was determined that although the H 2SO 4●H 2O, HSO 4−●H 2O, and H 2SO 4●2H 2O species could form, they would most likely react with H 2O molecules to form HSO 4−, H 3O +, and H 2O. © 2018 Wiley Periodicals, Inc. 相似文献
18.
The amount of corn stover and wheat straw that can be sustainably collected in North Carolina was estimated to be 0.64 and
0.16 million dry t/yr, respectively. More than 80% of these crop residues are located in the coastal area. The bioethanol
potential from corn stover and wheat straw was estimated to be about 238 million L (63 million gal/yr) in North Carolina.
The future location of ethanol plant in North Carolina was estimated based on feedstock demand and collection radius. It is
possible to have four ethanol plants with feedstock demand of 400, 450, 500, and 640 dry t/d. The collection radii for these
four ethanol plants are 46, 60, 42, and 67 km (28, 37, 26, and 42 miles), respectively. The best location for a bioethanol
plant includes four counties (Beaufort, Hyde, Tyrrell, and Washington) with feedstock demand of 500 t/d and collection radius
about 26 mile. 相似文献
19.
The hydrolysis of sulfonylamine (HNSO 2) results in the formation of sulfuric acid along with ammonia, and is of significant interest due to their negative impact on environment and life on Earth. The formation of H 2SO 4 through the reaction of HNSO 2 with (H 2O) 2-4 has been studied using high level electronic structure calculations. This hydrolysis reaction is a step-wise process, in the first step a H-atom from H 2O is transferred to the N-atom of HNSO 2 which results in the formation of NH 2, and in the next step, H 2SO 4, NH 3 and water molecule(s) are formed. The results show that the energy barrier associated with the formation of intermediates and product complexes is reduced by 7 to 10 kcal/mol when the number of water molecules is increased from 2 to 4. The rate constant was calculated using canonical variational transition state theory with small curvature tunneling correction over the temperature range of 200 to 1000 K. At 298 K, the calculated rate constant for the formation of intermediate in the first step is 2.24 × 10 −16, 1.03 × 10 −12, and 2.10 × 10 −11 cm 3 mol −1 s −1, respectively, for the reaction with water dimer, trimer and tetramer. The calculated enthalpy and free energy show that the reaction corresponding to the formation of H 2SO 4 is highly exothermic and exoergic in nature. 相似文献
20.
The interactions of Al 2O 3, CeO 2, Pt/Al 2O 3, and Pt/CeO 2 films with SO 2, SO 2 + H 2O, SO 2 + O 2, and SO 2 + O 2 + H 2O in the temperature range 300–673 K at the partial pressures of SO 2, O 2, and H 2O equal to 1.5 × 10 2, 1.5 × 10 2, and 3 × 10 2 Pa, respectively, were studied using X-ray photoelectron spectroscopy. The formation of surface sulfite at T 473 K (the S 2 p
3/2 binding energy ( E
b) is 167.5 eV) and surface sulfate at T 573 K ( E
b = 169.2 eV) was observed in the reactions of Al 2O 3 and CeO 2 with SO 2. The formation of sulfates on the surface of CeO 2 occurred much more effectively than in the case of Al 2O 3, and it was accompanied by the reduction of Ce(IV) to Ce(III). The formation of aluminum and cerium sulfates and sulfites on model Pt/Al 2O 3 and Pt/CeO 2 catalysts occurred simultaneously with the formation of surface platinum sulfides ( E
b of S 2 p
3/2 is 162.2 eV). The effects of oxygen and water vapor on the nature and yield of sulfur-containing products were studied. 相似文献
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