Preparation and characterization of activated carbon from rubber-seed shell by physical activation with steam

The use of rubber-seed shell as a raw material for the production of activated carbon with physical activation was investigated. The produced activated carbons were characterized by Nitrogen adsorption isotherms, Scanning electron microscope, Thermo-gravimetric and Differential scanning calorimetric in order to understand the rubber-seed shell activated carbon. The results showed that rubber-seed shell is a good precursor for activated carbon. The optimal activation condition is: temperature 880 °C, steam flow 6 kg h^?1, residence time 60 min. Characteristics of activated carbon with a high yield (30.5%) are: specific surface area (S_BET) 948 m² g^?1, total volume 0.988 m³ kg^?1, iodine number of adsorbent (q_iodine) 1.326 g g^?1, amount of methylene blue adsorption of adsorbent (q_mb) 265 mg g^?1, hardness 94.7%. It is demonstrated that rubber-seed shell is an attractive source of raw material for producing high capacity activated carbon by physical activation with steam.     

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.     

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.     

Production of bioethanol and associated by-products from potato starch residue stream by Saccharomyces cerevisiae

Potato starch residue stream produced during chips manufacturing was used as an economical source for biomass and bioethanol production by Saccharomyces cerevisiae. Results demonstrated that 1% H₂SO₄ at 100 °C for 1 h was enough to hydrolyze all starch contained in the residue stream. Two strains of S. cerevisiae (y-1646 and commercial one) were able to utilize and ferment the acid-treated residue stream under both aerobic and semi-anaerobic conditions. The maximum yield of ethanol (5.52 g L^?1) was achieved at 35 °C by S. cerevisiae y-1646 after 36 h when ZnCl₂ (0.4 g L^?1) was added. Addition of NH₄NO₃ as a source of nitrogen did not significantly affect either growth or ethanol production by S. cerevisiae y-1646. Some secondary by-products including alcohol derivatives and medical active compound were found to be associated with the ethanol production process.     

Assessment of nitrogen fertilization for the CO2 balance during the production of poplar and rye

This study was designed to consider all nitrogen fertilizer-related effects on crop production and emission of greenhouse gases on loamy sandy soils in Germany over a period of nine years (1999–2007). In order to set up a CO₂ balance for the production of energy crops, different nitrogen pathways were investigated, such as direct N₂O emissions from the soil and indirect emissions related to NO₃ leaching and fertilizer production. Fluxes of N₂O were measured in an experimental field using closed chambers. Poplar (Populus maximowiczii × P. nigra) and rye (Secale cereale L.) as one perennial and one annual crop were fertilized at rates of 0 kg N ha^?1 yr^?1, 75 kg N ha^?1 yr^?1 and 150 kg N ha^?1 yr^?1. The mean N₂O emissions from the soil ranged between 0.5 kg N ha^?1 yr^?1 and 2.5 kg N ha^?1 yr^?1 depending on fertilization rate, crop variety and year. The CO₂ fixed in the biomass of energy crops is reduced by up to 16% if direct N₂O emissions from soil and indirect N₂O emissions from NO₃ leaching and fertilizer production are included. Taking into account the main greenhouse gas emissions, which derive from the production and the use of N fertilizer, the growth of poplar and rye may replace the global warming potential of fossil fuels by up to 17.7 t CO₂ ha^?1 yr^?1 and 12.1 t CO₂ ha^?1 yr^?1, respectively.     

Dry matter partitioning and quality of Miscanthus,Panicum, and Saccharum genotypes in Arkansas,USA

The partitioning and quality of aboveground biomass have important ramifications for crop management and biomass conversion. In preliminary studies, Saccharum sp. × Miscanthus sp. hybrids exhibited stubble cold tolerance in west-central Arkansas, unlike Saccharum sp. × Saccharum spontaneum hybrids. The objective was to examine foliar and stem quality of the C₄ grasses Miscanthus sinensis (‘Gracillimus’), Miscanthus x giganteus (Q42641, proprietary), Panicum virgatum (‘Alamo’), and two F₁ hybrids of Saccharum sp. × Miscanthus sp. (US84-1028 and US84-1058) in a field study during 2004 (plant cane) and 2005 (first stubble) near Booneville, AR. Switchgrass produced more stems m^?2 than the other entries both years, and there was little difference in stem number among other entries. Clone US84-1028 yielded more dry mass m^?2 than other entries in plant cane, while switchgrass, US84-1028, and M. x giganteus did not differ in first stubble. Clone US84-1028 also had more stem dry mass and leaf dry mass than other entries both yr. Tissue N concentrations were low for these entries, but leaves contained about twice the N of stems (≤15.2 and 7.8 g kg^?1, respectively). Leaves represented as much as one-third of total biomass, and had large cellulose (≤482 g kg^?1) and lignin (167 g kg^?1) concentrations. The competitively high biomass yield of this small sample of sugarcane alleles should encourage the expansion of the crop beyond its current production regions. Sugarcane and M. x giganteus should be examined in higher-input temperate systems because of their bioenergy potential.     

Suitability of pineapple,Aloe vera,molasses, glycerol,and office paper as substrates in the MixAlco process?

The MixAlco? process biologically converts biomass to carboxylate salts that may be chemically converted to a wide variety of chemicals and fuels. This study looked at the viability of the following substrates: office paper, pineapple residue, Aloe vera rinds, wood molasses, sugar molasses, and glycerol. All agricultural substrates were initially tested to determine their carbohydrate and lignin content because lignin reduces substrate digestibility. Only pineapple residue had a high enough lignin content (18.3%) to necessitate pretreatment. Pineapple residue was treated with excess lime (300 g kg^?1 Ca(OH)₂ on dry biomass, t = 1 h) and then neutralized with CO₂, which reduced the lignin content to 4.89%. All substrates were anaerobically fermented in batch culture with marine microorganisms for 24 days. The acid concentrations (g mixed acid L^?1) were Aloe vera (25.5), office paper (24.0), glycerol (22.6), pineapple residue (17.2), wood molasses (19.4) and sugar molasses (18.9). The conversions (g volatile solids digested g^?1 volatile solids fed) were Aloe vera (0.59), office paper (0.50), glycerol (0.62), pineapple residue (0.52), wood molasses (0.42) and sugar molasses (0.82). The selectivities (g acetic acid equivalents g^?1 VS digested) were Aloe vera (0.64), office paper (0.62), glycerol (0.51), pineapple residue (0.39), wood molasses (0.61) and sugar molasses (0.33).     

Life cycle assessment of a Brassica carinata bioenergy cropping system in southern Europe

The energetic and environmental performance of production and distribution of the Brassica carinata biomass crop in Soria (Spain) is analysed using life cycle assessment (LCA) methodology in order to demonstrate the major potential that the crop has in southern Europe as a lignocellulosic fuel for use as a renewable energy source.The Life Cycle Impact Assessment (LCIA) including midpoint impact analysis that was performed shows that the use of fertilizers is the action with the highest impact in six of the 10 environmental categories considered, representing between 51% and 68% of the impact in these categories.The second most important impact is produced when the diesel is used in tractors and transport vehicles which represents between 48% and 77%. The contribution of the B. carinata cropping system to the global warming category is 12.7 g CO₂ eq. MJ⁻¹ biomass produced. Assuming a preliminary estimation of the B. carinata capacity of translocated CO₂ (631 kg CO₂ ha⁻¹) from below-ground biomass into the soil, the emissions are reduced by up to 5.2 g CO₂ eq. MJ⁻¹.The production and transport are as far as a thermoelectric plant of the B. carinata biomass used as a solid fuel consumes 0.12 MJ of primary energy per 1 MJ of biomass energy stored. In comparison with other fossil fuels such as natural gas, it reduces primary energy consumption by 33.2% and greenhouse gas emission from 33.1% to 71.2% depending on whether the capacity of translocated CO₂ is considered or not.The results of the analysis support the assertion that B. carinata crops are viable from an energy balance and environmental perspective for producing lignocellulosic solid fuel destined for the production of energy in southern Europe. Furthermore, the performance of the crop could be improved, thus increasing the energy and environmental benefits.     

Photocatalytic oxidation of cyanide in aqueous titanium dioxide suspensions: Effect of ethylenediaminetetraacetate

The kinetics of the photocatalytic oxidation of cyanide in aqueous TiO₂ suspensions was investigated as a function of catalyst loading (0.1–5.0 g l^?1), air-flow rate (0.2–1.1 l min^?1), and the concentration of ethylenediaminetetraacetate, EDTA (0.4–40 mM) at pH 13.0. The cyanide oxidation rate did not vary with the TiO₂ loading while a slight increase in the degradation rate with an increase in the air-flow rate was found. Cyanate (NCO^?) was the only product of the cyanide decomposition. The effect of EDTA on the photocatalytic oxidation of cyanide was examined at different molar ratios of EDTA to cyanide (0.1–10.5) by keeping the initial cyanide concentration at 3.85 mM. EDTA retarded the photocatalytic oxidation of cyanide and the decrease in the oxidation rate was not proportional to the molar ratio of EDTA to cyanide. The first-order rate constant, k (min^?1) for the oxidation of cyanide in the presence of EDTA may be expressed as k = 3.38 × 10^?3 × ([EDTA]/[CN^?])^?0.23. A mechanism of the oxidation of cyanide by a photocatalytic process in absence and presence of EDTA is presented.     

Isolation and characterization of two soil derived yeasts for bioethanol production on Cassava starch

Two ethanol-producing yeast strains, CHY1011 and CHFY0901 were isolated from soil in South Korea using an enrichment technique in a yeast peptone dextrose medium supplemented with 5% (w v^?1) ethanol at 30 °C. The phenotypic and physiological characteristics, as well as molecular phylogenetic analysis based on the D1/D2 domains of the large subunit (26S) rRNA gene and the internally transcribed spacer (ITS) 1 + 2 regions suggested that they were novel strains of Saccharomyces cerevisiae. During shaking flask cultivation, the highest ethanol productivity and theoretical yield of S. cerevisiae CHY1011 in YPD media containing 9.5% total sugars was 1.06 ± 0.02 g l^?1 h^?1 and 95.5 ± 1.2%, respectively, while those for S. cerevisiae CHFY0901 were 0.97 ± 0.03 g l^?1 h^?1 and 91.81 ± 2.2%, respectively. Simultaneous saccharification and fermentation for ethanol production was carried out using liquefied cassava (Manihot esculenta) starch in a 5 l lab-scale jar fermenter at 32 °C for 66 h with an agitation speed of 2 Hz. Under these conditions, S. cerevisiae CHY1011 and CHFY0901 yielded a final ethanol concentration of 89.1 ± 0.87 g l^?1 and 83.8 ± 1.11 g l^?1, a maximum ethanol productivity of 2.10 ± 0.02 g l^?1 h^?1 and 1.88 ± 0.01 g l^?1 h^?1, and a theoretical yield of 93.5 ± 1.4% and 91.3 ± 1.1%, respectively. These results suggest that S. cerevisiae CHY1011 and CHFY0901 have potential use in industrial bioethanol fermentation processes.     

Economics of switchgrass and miscanthus relative to coal as feedstock for generating electricity

Switchgrass (Panicum virgatum) serves as a model dedicated energy crop in the U.S.A. Miscanthus (Miscanthus x giganteus) has served a similar role in Europe. This study was conducted to determine the most economical species, harvest frequency, and carbon tax required for either of the two candidate feedstocks to be an economically viable alternative for cofiring with coal for electricity generation. Biomass yield and energy content data were obtained from a field experiment conducted near Stillwater, Oklahoma, U.S.A., in which both grasses were established in 2002. Plots were split to enable two harvest treatments (once and twice yr^?1). The switchgrass variety ‘Alamo’, with a single annual post-senescence harvest, produced more biomass (15.87 Mg ha^?1 yr^?1) than miscanthus (12.39 Mg ha^?1 yr^?1) and more energy (249.6 million kJ ha^?1 yr^?1 versus 199.7 million kJ ha^?1 yr^?1 for miscanthus). For the average yields obtained, the estimated cost to produce and deliver biomass an average distance of 50 km was $43.9 Mg^?1 for switchgrass and $51.7 Mg^?1 for miscanthus. Given a delivered coal price of $39.76 Mg^?1 and average energy content, a carbon tax of $7 Mg^?1 CO₂ would be required for switchgrass to be economically competitive. For the location and the environmental conditions that prevailed during the experiment, switchgrass with one harvest per year produced greater yields at a lower cost than miscanthus. In the absence of government intervention such as requiring biomass use or instituting a carbon tax, biomass is not an economically competitive feedstock for electricity generation in the region studied.     

Photofermentative hydrogen production using purple non-sulfur bacteria Rhodobacter sphaeroides O.U.001 in an annular photobioreactor: A case study

For meeting the increasing demand of energy, biohydrogen production is to be considered in higher yield. Biohydrogen can be produced both by dark and photofermentative process. In this study, the photofermentative pathway is followed by using dl malic acid (IUPAC name: 2-hydroxybutanedioic acid, molecular weight: 134.08744 g mol^?1, molecular formula: C₄H₆O₅) as carbon source. Pure strain of purple non-sulfur (PNS) bacteria: Rhodobacter sphaeroides strain O.U.001 was studied to produce biohydrogen using the photobioreactor. The photobioreactor was constructed aiming the uniform light distribution. The objective of this study was to investigate the performance of 1 L annular photobioreactor operating in indoor conditions. The highest rate of hydrogen production was obtained at 92 h. In the designed photobioreactor, using Rhodobacter sphaeroides strain O.U.001 (initial dl malic acid concentration of 2.01 g L^?1) at an initial pH of 6.8 ± 0.2, temperature 32 ± 2 °C, inoculum volume 10% (v/v), inoculum age of 48 h, 250 rpm (rotation per minute) stirring and light intensity of 15 ± 1.1 W m^?2, the average H₂ production rate was about 6.5 ± 0.1 mL H₂ h^?1 L^?1 media and yield 4.5 ± 0.05 mol of H₂ mol^?1 of dl malic acid. Luedeking–Piret model was applied for the data fitting to determine the relationship between the cell growth and photofermentative hydrogen production. The photofermentative hydrogen production by this PNS bacterium was found to be microbial mixed growth associated function.     

Synthesis and characterization of spinel Li4Ti5O12 anode material by oxalic acid-assisted sol–gel method

Anode material Li₄Ti₅O₁₂ for lithium-ion batteries has been prepared by a novel sol–gel method with oxalic acid as a chelating agent and Li₂CO₃ and tetrabutyl titanate [Ti(OC₄H₉)₄] as starting materials. Various initial conditions were studied in order to find the optimal conditions for the synthesis of Li₄Ti₅O₁₂. Oxalic acid used in this method functioned as a fuel, decomposed the metal complexes at low temperature and yielded the free impurity Li₄Ti₅O₁₂ compounds. Thermal analyses (TG–DTA) and XRD data show that powders grown with a spinel structure (Fd3m space group) have been obtained at 800 °C for 16 h. SEM analyses indicated that the prepared Li₄Ti₅O₁₂ powders had a uniform cubic morphology with average particle size of 200 nm. The influence of synthesis conditions on the electrochemical properties was investigated and discussed. The discharge capacity of Li₄Ti₅O₁₂ synthesized with an oxalic acid to titanium ratio R = 1.0 was 171 mAh g⁻¹ in the first cycle and 150 mAh g⁻¹ after 35 cycles under an optimal synthesis condition at 800 °C for 20 h. The very flat discharge and charge curves indicated that the electrochemical reaction based on Ti⁴⁺/Ti³⁺redox couple was a typical two-phase reaction.     

Simultaneous saccharification and fermentation (SSF) of very high gravity (VHG) potato mash for the production of ethanol

Simultaneous saccharification and fermentation (SSF) of very high gravity (VHG) potato mash, containing 304 g L^?1 of dissolved carbohydrates, was carried out for ethanol production. Potato tubers were ground into a mash, which was highly viscous. Mash viscosity was reduced by the pretreatment with mixed enzyme preparations of pectinase, cellulase and hemicellulase. The enzymatic pretreatment established the use of VHG mash with a suitable viscosity. Starch in the pretreated mash was liquefied to maltodextrins by the action of thermo-stable α-amylase at 85 °C. SSF of liquefied mash was performed at 30 °C with the simultaneous addition of glucoamylase, yeast (Saccharomyces cerevisiae) and ammonium sulfate as a nitrogen source for the yeast. The optimal glucoamylase loading, ammonium sulfate concentration and fermentation time were 1.65 AGU g^?1, 30.2 mM and 61.5 h, respectively, obtained using the response surface methodology (RSM). Ammonium sulfate supplementation was necessary to avoid stuck fermentation under VHG condition. Using the optimized condition, ethanol yield of 16.61% (v/v) was achieved, which was equivalent to 89.7% of the theoretical yield.     

LiMn2O4 cathode materials synthesized by the cellulose–citric acid method for lithium ion batteries

A new technique was employed to synthesize spinel LiMn₂O₄ cathode materials by adding cellulose and citric acid to an aqueous solution of lithium and manganese salts. Various synthesis conditions such as the calcination temperature and the citric acid-to-metal ion molar ratio (R) were investigated to determine the ideal conditions for preparing LiMn₂O₄ with the best electrochemical characteristics. The optimal synthesis conditions were found to be R = 1/3 and a calcination temperature of 800 °C. The initial discharge capacity of the material synthesized using the optimal conditions was 134 mAh g⁻¹, and the discharge capacity after 40 cycles was 125 mAh g⁻¹, at a current density of 0.15 mA cm⁻² between 3.0 and 4.35 V. Details of how the initial synthesis conditions affected the capacity and cycling performance of LiMn₂O₄ are discussed.     

Bioethanol production by a flocculent hybrid,CHFY0321 obtained by protoplast fusion between Saccharomyces cerevisiae and Saccharomyces bayanus

Fusion hybrid yeast, CHFY0321, was obtained by protoplast fusion between non-flocculent-high ethanol fermentative Saccharomyces cerevisiae CHY1011 and flocculent-low ethanol fermentative Saccharomyces bayanus KCCM12633. The hybrid yeast was used together with the parental strains to examine ethanol production in batch fermentation. Under the conditions tested, the fusion hybrid CHFY0321 flocculated to the highest degree and had the capacity to ferment well at pH 4.5 and 32 °C. Simultaneous saccharification and fermentation for ethanol production was carried out using a cassava (Manihot esculenta) powder hydrolysate medium containing 19.5% (w v^?1) total sugar in a 5 l lab scale jar fermenter at 32 °C for 65 h with an agitation speed of 2 Hz. Under these conditions, CHFY0321 showed the highest flocculating ability and the best fermentation efficiency for ethanol production compared with those of the wild-type parent strains. CHFY0321 gave a final ethanol concentration of 89.8 ± 0.13 g l^?1, a volumetric ethanol productivity of 1.38 ± 0.13 g l^?1 h^?1, and a theoretical yield of 94.2 ± 1.58%. These results suggest that CHFY0321 exhibited the fermentation characteristics of S. cerevisiae CHY1011 and the flocculent ability of S. bayanus KCCM12633. Therefore, the strong highly flocculent ethanol fermentative CHFY0321 has potential for improving biotechnological ethanol fermentation processes.     

Effects of ball-milling on lithium insertion into multi-walled carbon nanotubes synthesized by thermal chemical vapour deposition

The effects of ball-milling on Li insertion into multi-walled carbon nanotubes (MWNTs) are presented. The MWNTs are synthesized on supported catalysts by thermal chemical vapour deposition, purified, and mechanically ball-milled by the high energy ball-milling. The purified MWNTs and the ball-milled MWNTs were electrochemically inserted with Li. Structural and chemical modifications in the ball-milled MWNTs change the insertion–extraction properties of Li ions into/from the ball-milled MWNTs. The reversible capacity (C_rev) increases with increasing ball-milling time, namely, from 351 mAh g⁻¹ (Li_0.9C₆) for the purified MWNTs to 641 mAh g⁻¹ (Li_1.7C₆) for the ball-milled MWNTs. The undesirable irreversible capacity (C_irr) decreases continuously with increase in the ball-milling time, namely, from 1012 mAh g⁻¹ (Li_2.7C₆) for the purified MWNTs to 518 mAh g⁻¹ (Li_1.4C₆) for the ball-milled MWNTs. The decrease in C_irr of the ball-milled samples results in an increase in the coulombic efficiency from 25% for the purified samples to 50% for the ball-milled samples. In addition, the ball-milled samples maintain a more stable capacity than the purified samples during charge–discharge cycling.     

The influence of CO2 mitigation incentives on profitability of eucalyptus production on clay settling areas in Florida

Fast growing, short-rotation tree crops provide unique opportunities to sequester carbon on phosphate-mined lands in central Florida and, if used as a biofuel, can reduce CO₂ emissions associated with electricity generation. Base case land expectation values (LEVs) of phosphate-mined land under Eucalyptus amplifolia (EA) forestry range from 762 to 6507 $ ha^?1 assuming real discount rates of 10% and 4%, respectively. Assuming 5 $ Mg^?1 C, these LEVs increase from 3% to 24% with incentives for in situ carbon sequestration benefits, or 21% to 73% given in situ carbon sequestration with additional incentives for reducing CO₂ emissions through the use of EA as an energy feedstock. Potential benefits from below-ground C sequestration and mine land reclamation are estimated to be worth an additional 5642–11,056 $ ha^?1.     

Cynara cardunculus L. genotypes as a crop for energy purposes in a Mediterranean environment

Previous studies indicate biomass and grain production for energy purposes as potential utilizations of the three Cynara cardunculus botanical varieties (globe artichoke, cultivated cardoon, and wild cardoon). In this work, the results of C. cardunculus biomass and grain yield under Sicilian (south Italy) low input conditions are shown. Over a 3 year period on the plain of Catania (South Italy) six genotypes of C. cardunculus, including 1 cultivated cardoon cultivar, 1 globe artichoke line, 1 wild cardoon ecotype, 3 F₁ progenies: “globe artichoke × wild cardoon”, “globe artichoke × cultivated cardoon” and “cultivated cardoon × wild cardoon”, were evaluated for lignocellulosic biomass production, energy yield and grain yield. On a 3 year average, the dry aboveground biomass and grain yield resulted, respectively, about 2000 g plant^?1 and 100 g plant^?1 in “globe artichoke × wild cardoon”, 1720 and 126 g plant^?1 in cultivated cardoon, 1570 and 90 g plant^?1 in “globe artichoke × cultivated cardoon”, 1480 and 109 g plant^?1 in “cultivated cardoon × wild cardoon”, 1116 and 75 g plant^?1 in wild cardoon and 990 and 60 g plant^?1 in globe artichoke. The results showed that genotypes deriving from the cross of globe artichoke with cultivated and wild cardoon improved the performance both of globe artichoke and wild cardoon separately. It is reasonable to expect further improvements for biomass and grain yield in C. cardunculus in the future by breeding work.     

Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2–CO mixtures at atmospheric condition

The objective of this investigation was to study the effect of dilution with CO₂ on the laminar burning velocity and flame stability of syngas fuel (50% H₂–50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched burning velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ? = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H₂–CO–CO₂–O₂–N₂ mixtures, the peak burning velocity shifts from ? = 2.0 for 0% CO₂ in fuel to ? = 1.6 for 30% CO₂ in fuel. For H₂–CO–O₂–CO₂ mixtures, the peak burning velocity occurred at ? = 1.0 unaffected by proportion of CO₂ in the mixture. If the mole fraction of combustibles in H₂–CO–O₂–CO₂ mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar burning velocities of H₂–CO–O₂–CO₂ and H₂–CO–O₂–N₂ mixtures suggested that CO₂ has a stronger inhibiting effect on the laminar burning velocity than nitrogen. The enhanced dilution effect of CO₂ could be due to the active participation of CO₂ in the chemical reactions through the following intermediate reaction CO + OH ? CO₂ + H.