Thermal behavior of corn fibers and corn fiber gums prepared in fiber processing to ethanol

In this work, a thorough study of all solid products obtained in corn fiber processing to ethanol has been carried out with thermogravimetry/mass spectrometry (TG/MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The thermal behavior of corn fiber, destarched corn fiber, various alkali pretreated fibers and corn fiber gums were compared.It has been established that no significant changes occur in the thermal behavior of the feedstock material as a result of treatment with amylolytic enzymes. On one hand only the concentration of the alkali (NaOH or KOH) seems to be important in determining the chemical composition of the pretreated corn fiber samples. On the other hand, the composition of the corn fiber gums depends on the type and not the concentration of the alkali used in the pretreatment step. The presence of H₂O₂ degrades the structure and alters the composition of the corn fiber to a larger extent. The polymeric hemicellulose which is precipitated after pretreatment with NaOH + H₂O₂ contains less impurities than the corn fiber gum prepared in the absence of hydrogen peroxide.The results indicate that the applied analytical methods are suitable for studying changes in the composition of the variously treated corn fibers. The observed effects of the treatments are in good agreement with data determined with conventional analytical techniques.     

Textile grade long natural cellulose fibers from bark of cotton stalks using steam explosion as a pretreatment

Textile grade long natural cellulose fibers with fineness of 27 dtex have been extracted from bark of cotton stalks by a combination of steam explosion, potassium hydroxide and peroxide treatments (explosion–KOH–H₂O₂). It was reported that natural cellulose fibers from bark of cotton stalks had significantly better mechanical properties than those from other lignocellulosic agricultural byproducts such as rice and wheat straws. Fibers from bark of cotton stalks were used to reinforce thermoplastic composites but could not be spun into yarns for textile applications due to their high fineness value (around 50 dtex) and/or low aspect ratio (around 660). In this research, barks of cotton stalks were treated using three methods, including steam explosion, a combination of steam explosion and potassium hydroxide treatments (explosion–KOH) and explosion–KOH–H₂O₂. The morphology, composition, carding yield, crystalline structures and tensile properties of three different cotton stalk fibers were analyzed. Results showed that cotton stalk fibers extracted by explosion–KOH–H₂O₂ had the lowest fineness value of 27 dtex and moderate aspect ratio of 1,150 in three kinds of fibers. The fibers also had most clean and smooth surfaces, highest carding yield of 68.6 %, and highest cellulose content of 82.1 wt% due to effective removal of non-cellulose impurities. Moreover, the fibers had tensile properties close to cotton fibers. Overall, the cotton stalk fibers presented a better potential to be used as textile fibers than those reported by previous researches. explosion–KOH–H₂O₂ could be an efficient method for exploring textile applications of bark of cotton stalks.     

Application of fentonś reaction to steam explosion prehydrolysates from poplar biomass

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 H₂O₂ 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 H₂O₂ concentration tested (50 mM). However, a negative effect on fermentability was observed at this H₂O₂ 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.     

Fire and explosion hazard evaluation for the acetone aqueous solutions

The prevention of fire and explosion is recognized as an imperative necessity that is a first priority in all operating management details of the chemical process industries. Based on significant research and original emphasis on loss control and disaster prevention, this study investigated the flammability characteristics, comprising the lower/upper explosion limit (LEL and UEL), maximum explosion overpressure (P _max), maximum rate of explosion pressure rise [(dP dt ⁻¹)_max], gas or vapor deflagration index (K _g), and explosion class (St class) of four acetone aqueous solutions [water vapor (steam)/acetone: 75/25, 50/50, 25/75, and 0/100 vol.%], and discussed the effect of inert steam (H₂O_(g)) on them. Interactive influences of various loading fuel concentrations and initial testing conditions of 150, 200 °C, and 101, 202 kPa on flammability characteristics were revealed via a 20-L-apparatus. Weighting analysis of the above influence factors was explored by employing the GM(h,N) grey system theory for rating their fire and explosion hazard degrees both specifically and quantitatively. The results indicated that the most important influence factor was the initial pressure that the manager or engineer in such a steam/acetone mixing system should consider to be well-controlled first. The second influence factor in GM(1,N) and GM(0,N) model was the initial temperature and steam/acetone mixing concentration, but the third influence factor was individual contrariwise. This study established a complete flammability hazard evaluation approach that is combined with an experimentally and theoretically feasible way for fire/explosion prevention and protection. The outcomes would be useful for positive decisions for safety assessment for the relevant practical plants or processes.     

Ozonation of deciduous wood in the presence of hydrogen peroxide

The kinetic curves of the dependence of ozone specific absorption (Q _{r, sp} ) upon aspen wood ozonation in the presence and absence of hydrogen peroxide are obtained. It is established that the rate of ozone and Q _{r, sp} absorption increase in the O₃/H₂O₂ system. It is demonstrated by ESR, IR, and UV spectroscopy of diffuse reflection that wood ozonation in the O₃/H₂O₂ system results in the destruction of lignin aromatic and quinoid structures. The ozonation process in the presence of H₂O₂ is accompanied by destruction of the carbohydrate component of the lignocarbohydrate complex. We conclude that O₃/H₂O₂ can be used in the deep delignification of wood. It is shown that the presence of hydrogen peroxide upon ozonation increases the efficiency of the process, allowing its duration and total ozone consumption to be reduced.     

The kinetics and the mechanism of the oxidation of carbon monoxide in the presence of hydrogen

The kinetics of the slow oxidation of CO in the presence of H₂ have been studied above the second explosion limit for the mixture 2CO + O₂ + X% H₂ at the temperature range of 530–570°C, pressures from 300 to 530 torr, and hydrogen contents of 1.1, 2.8, and 5.7%. The second explosion limit has been experimentally determined for the mixture of 2CO + O₂ containing 1.0, 3.0, and 5.7% H₂. On the basis of the oxidation scheme of CO in the presence of H₂, which includes the accepted mechanism of oxidation of hydrogen supplemented by the reactions in which CO takes part, the second explosion limit and the profiles of the slow reaction are calculated by computer methods. The agreement found between experimental and calculated values allows one to conclude that the scheme under consideration rather completely described the slow reaction above the second limit and the occurrence of the second explosion limit in the mixture CO–O₂–H₂. The rate constant for the reaction HO₂ + CO → OH + CO₂ was calculated from the experimental data and was found to agree with previous determinations.     

Fullerene C60 Bound to Insoluble Hydrophilic Polymer: Synthesis,Photophysical Behavior,and Generation of Singlet Oxygen in Water Suspensions

Fullerene C₆₀ has been covalently bound to an insoluble hydrophilic polymeric matrix: Sephadex ^® G‐200. The new polymeric equivalent of C₆₀ swells in H₂O to form gel‐like suspensions. The transient photochemical behavior of this polymeric fullerene has been studied in dry and H₂O‐suspended samples. Both samples show a transient absorption similar to the absorption of the parent C₆₀ solution. There is a lack of triplet‐triplet annihilation and of a O₂‐quenching process in the dry sample. On the contrary, the O₂‐quenching process is very efficient in the H₂O‐suspended samples (k_q(O₂)=(1.9±0.5)×10⁸ dm³ mol⁻¹ s⁻¹) and results in the formation of singlet oxygen, which is detected by its emission at 1270 nm. These results point to this hydrophilic polymeric equivalent of C₆₀ as a good candidate for use as a singlet‐oxygen solid sensitizer in H₂O suspensions.     

Flammability studies of 3-methyl pyridine/water system

In industrial processes, information on the safety property of chemicals is essentially crucial for safe handling during unit operations. Ensuring the safe use of combustible or flammable substances in processes is unlikely without detailed investigations of their flammability characteristics and related hazards. We studied 3-methyl pyridine (3-picoline), e.g., flammability limits (LFL/UFL), maximum explosion pressure (P _max), maximum explosion pressure rise (dP/dt)_max, minimum oxygen concentration (MOC), vapor deflagration index (K _g), and characterized the influence of inert steam (H₂O) on critical parameters for 3-picoline/water mixtures at 270°C, 1 atm, various oxygen concentrations, and vapor mixing ratios (100/0, 30/70, 10/90 and 5/95 vol.%) with a 20-L-Apparatus in simulated conditions, respectively. The results showed that the flammability characteristics of 3-picoline_(aq) all increased with the oxygen concentration. However, as the composition of inert steam increased, the flammability parameters and the degree of fire and explosion hazards were significantly reduced, instead. This study elucidated the flammability properties of 3-picoline mixed with inert steam. The conclusions could be applied to proactively prevent the relevant processes from incurring fire and explosion accidents.     

Pretreatment of wastepaper and pulp mill sludge by aqueous ammonia and hydrogen peroxide

Pretreatment of two different softwood-based lignocellulosic wastes (newsprint and Kraft pulp mill sludge) was investigated. Pretreatment was done by aqueous ammonia and hydrogen peroxide (H₂O₂), two delignifying reagents that are environmentally benign. Three different treatment schemes were employed: aqueous ammonia alone (ammonia recycled percolation [ARP]), mixed stream of aqueous ammonia and H₂O₂ and successive treatment with H₂O₂ and aqueous ammonia. In all cases there was a substantial degree of delignification ranging from 30 to 50%. About half of the hemicellulose sugars were dissolved into the process effluent. Retention of cellulose after pretreatment varied from 85 to 100% for newspaper feedstock and from 77 to 85% for the pulp mill sludge. After treatment with aqueous ammonia alone (ARP), the digestibility of newspaper and the pulp mill sludge was improved only by 5% (from 40 to 45% for the former and from 68 to 73% for the latter), despite a substantial degree of delignification occurring after the ARP process. The lign in content thus did not correlate with the digestibility for these substrates. Simultaneous treatment with H₂O₂ and aqueous ammonia did not bring about any significant improvement in the digestibility over that of the ARP. A succcessive treatment by H₂O₂ and ARP showed the most promise because it improved the digestibility of the newspaper from 41 to 75%, a level comparable to that of α-cellulose.     

SYNTHESIS AND CRYSTAL STRUCTURE OF A POLYMERIC 1,2,4,5-BENZENETETRACARBOXYLATO COMPLEX OF Cu(II) WITH IMIDAZOLE,Cu2(C10H2O8)(C3H4N2)6(H2O)4 · 4H2O

Abstract

The title complex, Cu₂(C₁₀H₂O₈)(C₃H₄O₂)₆(H₂O)₄ · 4H₂O, consists of polymeric copper(II) complex anions and discrete copper(II) complex cations. Benzenetetracarboxyl anions bridge copper(II) atoms coordinated to water and imidazole groups to form the anionic polymeric chains along the a axis, while discrete copper(II) complex cations involving four imidazole and two water ligands are packed between parallel polymeric anionic chains, an extensive H-bonding network linking complex cations and anions.     

Catalytic Activity of Alkali Metal Cations for the Chemical Oxygen Reduction Reaction in a Biphasic Liquid System Probed by Scanning Electrochemical Microscopy

Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane-based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H₂O₂ detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H₂O₂, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase.     

The oxidative stream reforming of methane to syngas in a thin tubular mixed-conducting membrane reactor

The oxidative stream reforming of methane (OSRM) to syngas, involving coupling of exothermic partial oxidation of methane (POM) and endothermic steam reforming of methane (SRM) processes, was studied in a thin tubular Al₂O₃-doped SrCo_0.8Fe_0.2O_3−δ membrane reactor packed with a Ni/γ-Al₂O₃ catalyst. The influences of the temperature and feed concentration on the membrane reaction performances were investigated in detail. The methane and steam conversions increased with increasing the temperature and high conversions were obtained in 850–900 °C. Different from the POM reaction, in the OSRM reaction the temperature and H₂O/CH₄ profoundly influenced the CO selectivity, H₂/CO and heat of the reaction. The CO selectivity increased with increasing the temperature or decreasing the H₂O/CH₄ ratio in the feed owing to the water gas shift reaction (H₂O + CO → CO₂ + H₂). And the H₂ selectivity based on methane conversion was always 100% because the net steam conversion was greater than zero. The H₂/CO in product could be tuned from 1.9 to 2.8 by adjusting the reaction temperature or H₂O/CH₄. Depending on the temperature or H₂O/CH₄, furthermore, the OSRM process could be performed auto-thermally with idealized reaction condition.     

Sorption-enhanced steam methane reforming over Ni/Al2O3/KNaTiO3 bifunctional material

The performance of a new lab-made bifunctional material Ni/Al₂O₃/KNaTiO₃ for producing high purity H₂ via sorption-enhanced steam methane reforming (SESMR) was investigated. A series of bifunctional materials with 10 wt% Ni loading but different wt% ratios of KNaTiO₃ and Al₂O₃ was prepared by wetness impregnation method. All the materials were calcined at 700 °C for 3 hours and screened for their catalytic activity in a continuous flow fixed-bed reactor. The material containing 50 wt% each of KNaTiO₃ and Al₂O₃ (designated as HM) was found to be the best choice. The optimum process parameters for the production of high purity H₂ were determined: temperature = 700 °C, steam to carbon (S/C) molar ratio = 6 and gas-hourly space velocity (GHSV) = 2000 cm³ g^-1 h^-1. The values of CH₄ conversion, H₂ yield and H₂ purity were 87, 87 and 90%, respectively, at the optimum reaction conditions. The adsorption capacity of HM was found to be 14.7 wt%. With a breakthrough time of 10 min, the material was stable for 8 adsorption-desorption cycles. The regeneration of HM was achieved with N₂ gas at the same reaction temperature. Overall, the activity of this material for SESMR was very promising.     

Heteroatom Dopants Promote Two-Electron O2 Reduction for Photocatalytic Production of H2O2 on Polymeric Carbon Nitride

Polymeric carbon nitride modified with selected heteroatom dopants was prepared and used as a model photocatalyst to identify and understand the key mechanisms required for efficient photoproduction of H₂O₂ via selective oxygen reduction reaction (ORR). The photochemical production of H₂O₂ was achieved at a millimolar level per hour under visible-light irradiation along with 100 % apparent quantum yield (in 360–450 nm region) and 96 % selectivity in an electrochemical system (0.1 V vs. RHE). Spectroscopic analysis in spatiotemporal resolution and theoretical calculations revealed that the synergistic association of alkali and sulfur dopants in the polymeric matrix promoted the interlayer charge separation and polarization of trapped electrons for preferable oxygen capture and reduction in ORR kinetics. This work highlights the key features that are responsible for controlling the photocatalytic activity and selectivity toward the two-electron ORR, which should be the basis of further development of solar H₂O₂ production.     

Heteroatom Dopants Promote Two‐Electron O2 Reduction for Photocatalytic Production of H2O2 on Polymeric Carbon Nitride

Polymeric carbon nitride modified with selected heteroatom dopants was prepared and used as a model photocatalyst to identify and understand the key mechanisms required for efficient photoproduction of H₂O₂ via selective oxygen reduction reaction (ORR). The photochemical production of H₂O₂ was achieved at a millimolar level per hour under visible‐light irradiation along with 100 % apparent quantum yield (in 360–450 nm region) and 96 % selectivity in an electrochemical system (0.1 V vs. RHE). Spectroscopic analysis in spatiotemporal resolution and theoretical calculations revealed that the synergistic association of alkali and sulfur dopants in the polymeric matrix promoted the interlayer charge separation and polarization of trapped electrons for preferable oxygen capture and reduction in ORR kinetics. This work highlights the key features that are responsible for controlling the photocatalytic activity and selectivity toward the two‐electron ORR, which should be the basis of further development of solar H₂O₂ production.     

Magnesium,calcium and strontium salts of phenylacetic acid

Three alkaline earth metal salts of phenylacetic acid were examined and all were found to have similar structural types to analogous salts of benzoic and halobenzoic acids. Thus, a synchrotron study shows that the cations in catena‐poly[[[tetraaquamagnesium(II)]‐μ‐phenylacetato‐κ²O:O′] phenylacetate], {[Mg(C₈H₇O₂)(H₂O)₄](C₈H₇O₂)}_n, form a one‐dimensional coordination polymer that propagates through Mg—O—C—O—Mg interactions involving both crystallographically independent Mg centres (Z′ = 2) and through translation along the a axis. The polymeric chains pack to give alternate inorganic layers and organic bilayers. The Ca and Sr species catena‐poly[[[diaqua(phenylacetato‐κ²O,O′)calcium(II)]‐μ₃‐phenylacetato‐1′:1:1′′κ⁴O:O,O′:O′] monohydrate], {[Ca(C₈H₇O₂)₂(H₂O)₂]·H₂O}_n, and catena‐poly[[[diaqua(phenylacetato‐κ²O,O′)strontium(II)]‐μ₃‐phenylacetato‐1′:1:1′′κ⁴O:O,O′:O′] monohydrate], {[Sr(C₈H₇O₂)₂(H₂O)₂]·H₂O}_n, are essentially isostructural. Both form one‐dimensional coordination polymers through a carboxylate group that forms four M—O bonds. The polymeric chains propagate via 2₁ screw axes parallel to the b axis and are further linked in the bc plane by hydrogen bonding involving the non‐metal‐bound water molecule. Similarly to the Mg salt, both have inorganic layers that alternate with organic bilayers.     

Triaqua­benzoatocalcium(II) monobenzoate: coordination polymer chains linked into a two‐dimensional framework by hydrogen bonds

In the title complex, catena‐poly[[[diaqua­calcium(I)]‐μ₂‐aqua‐μ₃‐benzoato‐κ⁴O:O,O′:O′] benzoate], {[Ca(C₇H₅O₂)(H₂O)₃](C₇H₅O₂)}_n, obtained by the reaction of CaCl₂ and potassium benzoate in water, the Ca atom is eight‐coordinated by four carboxyl­ate O atoms and four water mol­ecules. The structure consists of polymeric {[Ca(C₆H₅COO)(H₂O)₃]⁺}_∞ chains alternating with layers of uncoordinated C₆H₅COO⁻ anions. The nearly planar anions are linked to the chain by short hydrogen bonds to form a two‐dimensional network.     

Optimization of SO2-catalyzed steam pretreatment of corn fiber for ethanol production

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 SO₂ 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% SO₂. Sequential SO₂-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.     

Construction of a PbII coordination polymer from a semi-rigid ditopic 2,2-biimidazole derivative: synthesis,crystal structure and characterization

<!?tlsb=-0.04pt>A new Pb^II coordination polymer, poly[0.75(aqua)[μ₃-4,4′-(1H,1′H-[2,2′-biimidazole]-1,1′-diyl)dibenzoato-κ⁵O,O′;N;O′′,O′′′]]lead(II)] 1.25-hydrate], {[Pb(C₂₀H₁₂N₄O₄)(H₂O)_0.75]·1.25H₂O}_n or {[Pb(L)(H₂O)_0.75]·1.25H₂O}_n ( 1 ) [H₂L = 4,4′-(1H,1′H-[2,2′-biimidazole]-1,1′-diyl)dibenzoic acid], was synthesized under solvothermal reaction conditions and characterized using microanalysis, IR spectroscopy and thermogravimetric analysis. Single-crystal structure analysis reveals that a two-dimensional corrugated layer structure is formed in 1 and that neighbouring layers are further extended into a three-dimensional structure by hydrogen-bonding interactions. In addition, a fluorescence sensing experiment towards Cu²⁺ based on the polymeric Pb^II complex was carried out.     

New Mixed Ligand Copper(II) Complexes: Syntheses and Crystal Structures of Cu(Imid)2(H2O)L with Imid = Imidazole,L = Succinic and Fumaric Anions

Reactions of freshly prepared Cu(OH)_2—2x(CO₃)_x · yH₂O and imidazole (Imid) with succinic acid and fumaric acid, respectively, in CH₃OH/H₂O yields Cu(Imid)₂(H₂O)L with L = (C₄H₄O₄)^2— ( 1 ) and (C₄H₂O₄)^2— ( 2 ). Both isostructural complexes consist of 1D [Cu(Imid)₂(H₂O)L_2/2] polymeric chains, in which the T‐shaped [Cu(Imid)₂(H₂O)]²⁺ moieties are bridged by bis‐monodentate dicarboxylato ligands. Through the interchain hydrogen bonds between the coordinating H₂O molecule and the non‐coordinating carboxylate O atom, the polymeric chains are assembled into 2D layers, which are further assembled via interlayer N—H···O hydrogen bonds between imidazole N atom and the coordinating carboxylato O atom. Thermal analyses of 1 under N₂ stream showed that dehydration is immediately followed by decomposition of the anhydrous “Cu(Imid)₂(C₄H₄O₄)” intermediate into imidazole and “Cu(C₄H₄O₄)”. Upon further heating, sublimation of imidazole is followed by dissociation of the resulting “Cu(C₄H₄O₄)” into CO, CO₂, C₂H₄ in gaseous phase and solid CuO as residue. Crystal data: ( 1 ) C2/c (no. 15), a = 13.712(2), b = 5.589(1), c = 17.517(2)Å, β = 105.76(1)°, U = 1292.0(3)ų, Z = 4; ( 2 ) C2/c (no. 15), a = 13.758(2), b = 5.501(1), c = 17.464(2)Å, β = 106.05(2)°, U = 1270.2(3)ų, Z = 4.