Optimization of ethanol production from sweet sorghum (Sorghum bicolor) juice using response surface methodology

Sweet sorghum juice was fermented into ethanol using Saccharomyces cerevisiae (ATCC 24858). Factorial experimental design, regression analysis and response surface method were used to analyze the effects of the process parameters including juice solid concentration from 6.5 to 26% (by mass), yeast load from 0.5 g L⁻¹ to 2 g L⁻¹ and fermentation temperature from 30 °C to 40 °C on the ethanol yield, final ethanol concentration and fermentation kinetics. The fermentation temperature, which had no significant effect on the ethanol yield and final ethanol concentration, could be set at 35 °C to achieve the maximum fermentation rate. The yeast load, which had no significant effect on the final ethanol concentration and fermentation rate, could be set at 1 g L⁻¹ to achieve the maximum ethanol yield. The juice solid concentration had significant inverse effects on the ethanol yield and final ethanol concentration but a slight effect on the fermentation rate. The raw juice at a solid concentration of 13% (by mass) could be directly used during fermentation. At the fermentation temperature of 35 °C, yeast solid concentration of 1 g L⁻¹ and juice solid concentration of 13%, the predicted ethanol yield was 101.1% and the predicted final ethanol concentration was 49.48 g L⁻¹ after 72 h fermentation. Under this fermentation condition, the modified Gompertz's equation could be used to predict the fermentation kinetics. The predicted maximum ethanol generation rate was 2.37 g L⁻¹ h⁻¹.     

Yield and composition of herbaceous biomass harvested from naturalized grassland in southern Iowa

Much of the land area in southern Iowa is used for perennial pastures that are dominated by cool-season grass species. These species are well adapted to the soils and climate and have become naturalized within the region. Biomass produced from these pastures might potentially be used as a feedstock for cofiring with coal to supplement supplies of dedicated energy crops such as switchgrass (Panicum virgatum L.). While much is known about the use of these pasture species for forage production, relatively little information is available on their use as a bioenergy feedstock. This research was conducted to assess the potential of harvesting cool-season pastures for cofiring with coal. Ten representative sites located in south central Iowa were evaluated. Across all sites, 26 plant species were identified, with individual sites having between 5 and 14 species. Biomass yield was determined at several sampling locations within each site. Yields ranged from 0.75 to 8.24 t ha⁻¹ over all sites. Mean yield across all sites was 4.20 t ha⁻¹. Fuel characteristics of the cool-season species were evaluated for burning qualities. Concentrations of ash, chlorine and sulfur are important for determining suitability in a biofuel. Ash content ranged from 58.5–118.1 g kg⁻¹ DM across all sites. Chlorine ranged from 0.8–7.6 g kg⁻¹ DM and sulfur content ranged from 0.7–3.4 g kg⁻¹ DM. Highest heating value (HHV) ranged from 17.69–19.46 MJ kg⁻¹. These results indicate that cool-season grassland in southern Iowa can produce biomass of sufficient yield and quality to supplement other sources for cofiring with coal to generate electricity.     

Hydrothermal catalytic gasification of fermentation residues from a biogas plant

Biogas plants, increasing in number, produce a stream of fermentation residue with high organic content, providing an energy source which is by now mostly unused. We tested this biomass as a potential feedstock for catalytic gasification in supercritical water (T ≥ 374 °C, p ≥ 22 MPa) for methane production using a batch reactor system. The coke formation tendency during the heat-up phase was evaluated as well as the cleavage of biomass-bound sulfur with respect to its removal from the process as a salt. We found that sulfur is not sufficiently released from the biomass during heating up to a temperature of 410 °C. Addition of alkali salts improved the liquefaction of fermentation residues with a low content of minerals, probably by buffering the pH. We found a deactivation of the carbon-supported ruthenium catalyst at low catalyst-to-biomass loadings, which we attribute to sulfur poisoning and fouling in accordance with the composition of the fermentation residue. A temperature of 400 °C was found to maximize the methane yield. A residence time dependent biomass to catalyst ratio of 0.45 g g⁻¹ h⁻¹ was found to result in nearly full conversion with the Ru/C catalyst. A Ru/ZrO₂ catalyst, tested under similar conditions, was less active.     

Formulation of a low-cost medium for mass production of Spirulina

A new medium was formulated for mass production of Spirulina sp. by incorporating selected nutrients of the standard Zarrouk's medium (SM) and other cost-effective alternative chemicals. This newly formulated medium (RM₆) contains single super phosphate (1.25 g l⁻¹), sodium nitrate (2.50 g l⁻¹), muriate of potash (0.98 g l⁻¹), sodium chloride (0.5 g l⁻¹), magnesium sulphate (0.15 g l⁻¹), calcium chloride (0.04 g l⁻¹), and sodium bicarbonate (commercial grade) 8 g l⁻¹. The alga was grown in an illuminated (50 μmol photons m⁻² s⁻¹ white light) growth room at 30±1 °C. Maximum growth rate in terms of dry biomass, chlorophyll and proteins in SM was recorded between 6 and 9 days of growth and values were 0.114, 0.003 and 0.068 as compared to 0.112, 0.003 and 0.069 mg ml⁻¹ d⁻¹ in RM₆,. No significant differences were observed in the protein profiles of Spirulina sp. grown in both the media. From the scale up point of view, the revised medium was found to be highly economical, since it is five times cheaper than Zarrouk's medium.     

The effects of different additives in electrolyte of AGM batteries on self-discharge

Hydrogen and oxygen evolution at the negative and positive electrodes in AGM batteries are the main reasons of self-discharging. The self-discharge of five AGM batteries was investigated by measuring different potential between two electrodes during 48 days. Five different battery electrolytes were used including 35% (w/w) H₂SO₄ without additives and the remaining contain 7.1, 9.94, and 21.3 g l⁻¹ sodium sulfate, 4 g l⁻¹ boric acid, 3 g l⁻¹ citric acid, and finally 0.7 and 1 g l⁻¹ stearic acid except one containing boric acid that the concentration of H₂SO₄ was 36% (w/w). The results revealed that the rate of self-discharge for battery without additive was 0.01 V day⁻¹. The battery with boric acid showed the lowest rate of self-discharge with 0.0025 V day⁻¹. It was also found that stearic and citric acids are comparatively appropriate additives for decreasing the self-discharge. They caused a decrease of the self-discharge rate to 0.005 and 0.0075 V day⁻¹ on appropriate concentration, respectively. In compared to other additives, sodium sulfate showed to be not an appropriate additive for decreasing battery self-discharging. The rate of 0.03 V day⁻¹ of self-discharging was obtained for the battery containing all selected concentration of sodium sulfate during first 4 days of measuring.     

Manganese oxide film electrodes prepared by electrostatic spray deposition for electrochemical capacitors from the KMnO4 solution

Manganese oxide film electrodes for electrochemical capacitors were deposited on the polished Pt foils by electrostatic spray deposition (ESD) from KMnO₄ precursor solution. The electrochemical properties of electrodes were systematically studied using cyclic voltammetry (CV), constant current charge–discharge tests, and electrochemical impedance spectroscopy (EIS). The specific capacitance (SC) of thick deposited film was 149 F g⁻¹ at the very high scan rate of 500 mV s⁻¹, in comparison with 209 F g⁻¹ at the low scan rate of 5 mV s⁻¹. The electrode shows good cyclic performance. The initial SC value was 163 F g⁻¹ and 103% of the initial SC can be retained after 10,000 cycles at the scan rate of 50 mV s⁻¹.     

Cracking causing cyclic instability of LiFePO4 cathode material

The capacity of pure LiFePO₄ faded gradually from initial 149 mAh g⁻¹–117 mAh g⁻¹ under current density of 30 mA g⁻¹ at room temperature after 60 cycles. Some obvious cracks are observed in LiFePO₄ particles after cycling. The formation of cracks would lead to poor electric contact and capacity fading. A possible mechanism is proposed for the appearance of the cracks.     

Properties of containing Sn nanoparticles activated carbon fiber for a negative electrode in lithium batteries

Activated carbon fiber (ACF) containing Sn nanoparticles were prepared by impregnation and were investigated as a negative electrode material in lithium batteries. The tin particle size was controlled by selecting an ACF with an adequate surface structure. This Sn/ACF composite cycled versus Li metal showed a first discharge capacity as high as 200 mAh g⁻¹ compared to the pristine ACF which showed only 87 mAh g⁻¹. Excellent cyclability with these composites was obtained with ACF BET SSA as large as 2000 m² g⁻¹ and 30 wt.% Sn.     

Nanoparticled Li(Ni1/3Co1/3Mn1/3)O2 as cathode material for high-rate lithium-ion batteries

Nanoparticle of Li(Ni_1/3Co_1/3Mn_1/3)O₂ with size smaller than 40 nm was obtained by non-aqueous system co-precipitation method. The particle morphology and crystal plane orientation were observed by TEM and HRTEM. Electrochemical properties of this nanostructued material were studied with experiment cells. The results show that the material has high capacity of 160 mAh g⁻¹ and excellent rate capability for charge and discharge. For the 50C and 100C rate, its capacity remains above 100 mAh g⁻¹ after tens of cycles.     

Influence of pore structure on electric double-layer capacitance of template mesoporous carbons

The behavior of two types of mesoporous carbons with different pore structures (i.e. unimodal and bimodal) as electrode material in an electrochemical double-layer capacitor has been analyzed. The carbon samples were prepared using mesostructured silica materials (MSM) as templating agents. The unimodal mesoporous carbon has a BET surface area of 1550 m² g⁻¹, and a pore volume of 1.03 cm³ g⁻¹; the porosity is mainly made up of structural mesopores of ca. 3 nm that exhibit a narrow pore size distribution (PSD). The bimodal carbon shows larger surface area (1730 m² g⁻¹) and larger pore volume (1.50 cm³ g⁻¹); the porosity is composed of two types of mesopores: structural (size around 3 nm) and complementary (size around 16 nm) mesopores. Both carbons show a disordered 3-D pore structure. Heat treatments at high temperatures (1000 °C) for long times (11 h) do not significantly change the pore structure with respect to the two synthesised carbons (800 °C). From the synthesized and heat-treated carbons, electrodes were processed as composites in which the carbons, polivinilidene fluoride (PVDF) and carbon black (CB) were the components. The effect of the heat treatment and relative CB content on specific capacitance, energy density and power density were studied. We found a specific capacitance of 200 F g⁻¹ for low current density (1 mA cm⁻²) and 110 F g⁻¹ for high current density (150 mA cm⁻²). Moreover, the curve of the specific capacitance versus current density shows three regimes, which are related to the three types of pore: micropores, structural mesopores and complementary mesopores. An energy density of 3 Wh kg⁻¹ at a power density of 300 W kg⁻¹ was obtained in some particular cases.     

Block sulfonated poly(ether ether ketone)s (SPEEK) ionomers with high ion-exchange capacities for proton exchange membranes

A series of block SPEEK copolymers with high ion-exchange capacities (IEC) consisting of hydrophobic and hydrophilic blocks were synthesized successfully. Membranes were cast from their DMF solutions, and characterized by determining the ion-exchange capacity, water uptake, water retention, proton conductivity and thermal properties. Membranes exhibited conductivities from 0.027 to 0.068 S cm⁻¹ at 30 °C and from 0.049 to 0.11 S cm⁻¹ at 80 °C; water uptake from 34% to 54% and IEC from 1.25 to 1.48 mequiv. g⁻¹. Block-3 membrane with IEC 1.38 mequiv. g⁻¹ showed relatively higher proton conductivity compared to that of a random SPEEK membrane with IEC 1.37 mequiv. g⁻¹. The SAXS profiles of block SPEEK copolymers exhibited a well-defined ionomer peak at low angles due to the phase separation between ionic domains and hydrophobic domains. It is believed that their microstructure features attribute to the enhanced proton conductivity of block SPEEK membranes.     

Novel organic–inorganic poly (3,4-ethylenedioxythiophene) based nanohybrid materials for rechargeable lithium batteries and supercapacitors

Synthesis and characterization of poly (3,4-ethylenedioxythiophene) (PEDOT) interleaved between the layers of crystalline oxides of V and Mo is discussed with special emphasis on their application potential as electrodes for rechargeable Li batteries and supercapacitors. The expansion of the interlayer spacing of crystalline oxides (for example, V₂O₅ causes expansion from 0.43 to 1.41 nm) is consistent with a random layer stacking structure. These hybrid nanocomposites when coupled with a large-area Li foil electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcarbonate (1:1, v/v), give enhanced discharge capacity compared to pristine oxides. For example a discharge capacity of ∼350 mAh g⁻¹, in the potential range 4.2–2.1 V (versus Li⁺/Li) is obtained for PEDOT–V₂O₅ hybrid which is significantly large compared to that for simple Li-intercalated V₂O_5. The improvement of electrochemical performance compared with that of pristine oxides is attributed to higher electric conductivity, enhanced bi-dimensionality and increased structural disorder. Although these conducting polymer-oxide hybrids delivered more than 300 mAh g⁻¹ in the potential range 1.3–4.3 V, their cycle life needs further improvements to realize their commercial potential. Similarly, the double layer capacitance of MoO₃ increases from ∼40 mF g⁻¹ to ∼300 F g⁻¹ after PEDOT incorporation in the interlayer gap of MoO₃ under similar experimental conditions and the nanocomposite displays intriguing effects with respect to electrochemical Li⁺ insertion. The PEDOT–MoO₃ nanocomposite appears to be a promising electrode material for non-aqueous type supercapacitors.     

Synthesis and electrochemical properties of lithium cobalt oxides prepared by molten-salt synthesis using the eutectic mixture of LiCl–Li2CO3

Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li₂CO₃ salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO₂ powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g⁻¹, and 100 mA h g⁻¹ after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO₂ on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated.     

Conductivity percolation in carbon–carbon supercapacitor electrodes

Composite electrodes which comprise a non-conductive activated carbon of large surface area (1420 m² g⁻¹) and a conductive carbon black (CB) of small surface area (220 m² g⁻¹) have been prepared and studied for their capacitive properties in aqueous KOH and Na₂SO₄ electrolytes. For either electrolyte, maximum capacitance exists at the composition believed to correspond to the percolation threshold for CB, the conductive phase. At a CB content less than the threshold, the capacitance is limited mainly by the electronic resistance on the electrode side. The interfacial surface area becomes the limiting factor as the threshold is exceeded. A maximum capacitance of 108 F g⁻¹ at a voltage sweep rate of 20 mV s⁻¹ is obtained in 1 M KOH aqueous electrolyte with a CB content of 25 wt.% (or ∼14 vol.%).     

Effects of pore structure and electrolyte on the capacitive characteristics of steam- and KOH-activated carbons for supercapacitors

Four kinds of activated carbons (denoted as ACs) with specific surface area of ca. 1050 m² g⁻¹ were fabricated from fir wood and pistachio shell by means of steam activation or chemical activation with KOH. Pore structures of ACs were characterized by a t-plot method based on N₂ adsorption isotherms. The amount of mesopores within KOH-activated carbons ranged from 9.2 to 15.3% while 33.3–49.5% of mesopores were obtained for the steam-activated carbons. The pore structure, surface functional groups, and raw materials of ACs, as well as pH and the supporting electrolyte were also found to be significant factors determining the capacitive characteristics of ACs. The excellent capacitive characteristics in both acidic and neutral media and the weak dependence of the specific capacitance on the scan rate of cyclic voltammetry (CV) for the ACs derived from the pistachio shell with steam activation (denoted as P-H₂O-AC) revealed their promising potential in the application of supercapacitors. The ACs derived from fir wood with KOH activation (denoted as F-KOH-AC), on the other hand, showed the best capacitive performance in H₂SO₄ due to excellent reversibility and high specific capacitance (180 F g⁻¹ measured at 10 mV s⁻¹), which is obviously larger than 100 F g⁻¹ (a typical value of activated carbons with specific surface areas equal to/above 1000 m² g⁻¹).     

Sonochemical synthesis of amorphous manganese oxide coated on carbon and application to high power battery

The nanocomposite material of amorphous manganese oxide and acetylene black (HSMO/AB), was synthesized by sonochemical method. The acetylene black particles were homogeneously coated with amorphous manganese oxide. In order to demonstrate that these characteristic structures were suitable for rapid discharge–charge, the composite material was tested under large current density. The result exhibited 185 mAh g⁻¹ in specific discharge capacity under 10 A g⁻¹ in current density. Assuming that an operating voltage of 2.5 V, this capacity corresponded 20 kW kg⁻¹ in power density and 90 Wh kg⁻¹ in energy density.     

Enhanced biohydrogen production from cornstalk wastes with acidification pretreatment by mixed anaerobic cultures

Biohydrogen production from the cornstalk wastes with acidification pretreatment was reported in this paper. Batch tests were carried out to analyze influences of several environmental factors on biohydrogen production from cornstalk wastes. Two predominant bacterial morphologies, namely spore-forming rod shape bacteria and micrococcus were screened, purified, and identified after enriched from a hydrogen-producing fermentor with cow dung composts. The maximum cumulative H₂ yield of 149.69 ml H₂ g⁻¹ TVS was obtained at initial pH 7.0 and substrate concentration 15 g l⁻¹, the value is about 46-fold as compared with that of raw cornstalk wastes. The maximum hydrogen production rate was 7.6 ml H2 h⁻¹. The hydrogen concentration in biogas was 45–56% (v/v) and there was no significant methane observed in the biogas throughout this study. In addition, biodegradation characteristics of the substrate by microorganisms were also discussed. During the conversion of cornstalk wastes into hydrogen, the acetate, propionate, butyrate, and the ethanol were main by-products in the metabolism of hydrogen fermentation. The test results showed that the acidification pretreatment of the substrate plays a crucial role in conversion of the cornstalk wastes into biohydrogen gas by the cow dung composts generating hydrogen.     

Synthesis and characterization of high tap-density layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ was prepared by mixing uniform co-precipitated spherical metal hydroxide (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with 7% excess LiOH followed by heat-treatment. The tap-density of the powder obtained was 2.38 g cm⁻³, and it was characterized using X-ray diffraction (XRD), particle size distribution measurement, scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and galvanostatic charge–discharge tests. The XRD studies showed that the material had a well-ordered layered structure with small amount of cation mixing. It can be seen from the EDS results that the transition metals (Ni, Co and Mn) in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are uniformly distributed. Initial charge and discharge capacity of 185.08 and 166.99 mAh g⁻¹ was obtained between 3 and 4.3 V at a current density of 16 mA g⁻¹, and the capacity of 154.14 mAh g⁻¹ was retained at the end of 30 charge–discharge cycles with the capacity retention of 93%.     

Effects of dark/light bacteria ratio on bio-hydrogen production by combined fed-batch fermentation of ground wheat starch

Bio-hydrogen production by combined dark and light fermentation of ground wheat starch was investigated using fed-batch operation. Serum bottles containing heat-treated anaerobic sludge and a mixture of Rhodobacter sp. was fed with a medium containing 20 g dm^?3 wheat powder (WP) at a constant flow rate. The system was operated at different initial dark/light biomass ratios (D/L). The optimum D/L ratio was 1/2 yielding the highest cumulative hydrogen (1548 cm³), yield (65.2 cm³ g^?1 starch), and specific hydrogen production rate (5.18 cm³ g^?1 h^?1). Light fermentation alone yielded higher hydrogen production than dark fermentation due to fermentation of volatile fatty acids (VFAs) to H₂ and CO₂. The lowest hydrogen formation was obtained with D/L ratio of 1/1 due to accumulation of VFAs in the medium.     

Nanocrystalline tin oxides and nickel oxide film anodes for Li-ion batteries

Tin oxides and nickel oxide thin film anodes have been fabricated for the first time by vacuum thermal evaporation of metallic tin or nickel, and subsequent thermal oxidation in air or oxygen ambient. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements showed that the prepared films are of nanocrystalline structure with the average particle size <100 nm. The electrochemical properties of these film electrodes were examined by galvanostatic cycling measurements and cyclic voltammetry. The composition and electrochemical properties of SnO_x (1<x<2) films strongly depend on the oxidation temperature. The reversible capacities of SnO and SnO₂ films electrodes reached 825 and 760 mAh g⁻¹, respectively, at the current density of 10 μA cm⁻² between 0.10 and 1.30 V. The SnO_x film fabricated at an oxidation temperature of 600 °C exhibited better electrochemical performance than SnO or SnO₂ film electrode. Nanocrystalline NiO thin film prepared at a temperature of 600 °C can deliver a reversible capacity of 680 mAh g⁻¹ at 10 μA cm⁻² in the voltage range 0.01–3.0 V and good cyclability up to 100 cycles.