Recycling and reuse of waste agricultural plastics with hydrothermal pretreatment and low-temperature pyrolysis method.

Recycling and reuse of agricultural plastics is an urgent worldwide issue. In this work, it is shown that low-density polyethylene (PE) typically used in mulch films can be converted into high-capacity P and N adsorbents through a two-step method that uses hydrothermal pretreatment (180 °C, 24 h) followed by pyrolysis at 500 °C with Ca(OH)2 additive. CaPE@HC500 materials prepared with the proposed two-step method were found to have high adsorption capacities for phosphate (263.6 mg/g) and nitrogen (200.7 mg/g) over wide ranges of pH (3-11). Dynamic adsorption of phosphate by CaPE@HC500 material in a packed-bed had a half-time breakthrough of 210 min indicating the feasibility of continuous systems. Material stability, cost, environmental-friendliness, and recyclability of the CaPE@HC500 material were determined to be superior to literature-proposed Ca-containing adsorbents. The two-step method for converting waste agricultural plastic mulch films into adsorbents is robust and highly-applicable to industrial settings.

Siloxane-modified MnOx catalyst for oxidation of coal-related o-xylene in presence of water vapor.

In coal-combustion energy production, presence of water vapor in flue gas causes catalyst deactivation and leads to the release of large quantities of volatile organic compounds (VOCs). In this study, design of a low-temperature, hydrophobic catalyst for flue gas purification was achieved by modifying support material with inorganic siloxane. Introduction of 5% water vapor into simulated flue gas at 300 °C reduced oxidation efficiency for o-xylene removal by 26% with unmodified MnOx/γ-Al2O3 catalyst, whereas with modified catalyst MnOx-Si0.9/γ-Al2O3 oxidation efficiency was reduced by only 5%. MnOx-Si0.9/γ-Al2O3 exhibited stable catalytic efficiency for o-xylene gas oxidation containing water vapor for over 200 min. Water-resistance of the catalyst was effective for removal of multi-coal combustion pollutants (Hg0 and NO) and moreover, hydrophobicity of the catalyst led to a reduction in surface sulfate deposition, thereby lowering toxicity of SO2 from simulated flue gas. DRIFTS analysis showed that the hydrophobic catalyst surface not only reduces water adsorption, but also promotes water volatilization. Based on molecular adsorption energies, catalyst support modification with siloxane inhibits water adsorption and promotes organic adsorption and thus provides a new strategy for preparing water-resistant catalysts for flue gas purification.

Additive-free hydrothermal leaching method with low environmental burden for screening of strontium in soil.

In this work, hydrothermal leaching was applied to simulated soils (clay minerals vermiculite, montmorillonite, and kaolinite) and actual soils (Terunuma, Japan) to generate organic acids with the objective to develop an additive-free screening method for determination of Sr in soil. Stable strontium (SrCl2) was adsorbed onto soils for the study, and ten organic acids (citric, L(+)-tartaric, succinic, oxalic, pyruvic, formic, glycolic, lactic, acetic, and propionic) were evaluated for leaching Sr from simulated soils under hydrothermal conditions (120 °C to 200 °C) at concentrations up to 0.3 M. For strontium-adsorbed vermiculite (Sr-V), 0.1 M citric acid was found to be effective for leaching Sr at 150 °C and 1 h treatment time. Based on these results, the formation of organic acids from organic matter in Terunuma soil was studied. Hydrothermal treatment of Terunuma soil produced a maximum amount of organic acids at 200 °C and 0.5 h reaction time. To confirm the possibility for leaching of Sr from Terunuma soil, strontium-adsorbed Terunuma soil (Sr-S) was studied. For Sr-S, hydrothermal treatment at 200 °C for 0.5 h reaction time allowed 40% of the Sr to be leached at room temperature, thus demonstrating an additive-free method for screening of Sr in soil. The additive-free hydrothermal leaching method avoids calcination of solids in the first step of chemical analysis and has application to both routine monitoring of metals in soils and to emergency situations.

Supercritical water pretreatment method for analysis of strontium and uranium in soil (Andosols).

Hydrothermal pretreatment of soils (Andosols) from Ibaraki prefecture (Japan) was used to improve methods for monitoring radioactive Sr and U. Calcined samples were pretreated with subcritical or supercritical water (SCW) followed by extraction with 0.5 M HNO3 solutions. With SCW pretreatment, recoveries of Sr and U were 70% and 40%, respectively. Experimental recoveries obtained can be described by a linear relationship in water density. The proposed method is robust and can lower environmental burden of routine analytical protocols.

Role of impurity components and pollutant removal processes in catalytic oxidation of o-xylene from simulated coal-fired flue gas.

Volatile organic compounds (VOCs) emitted from coal-fired flue gas of thermal power plants have reached unprecedented levels due to lack of understanding of reaction mechanisms under industrial settings. Herein, inhibition mechanisms for catalytic oxidation of o-xylene in simulated coal-fired flue gas are elucidated with in-situ and ex-situ spectroscopic techniques considering the presence of impurity components (NO, NH3, SO2, H2O). MnCe oxide catalysts prepared at Mn: Ce mass ratios of 6:4 are demonstrated to promote 87% o-xylene oxidation at 250 °C under gas hourly space velocities of 60,000 h-1. Reaction intermediates on the catalyst surface are revealed to be o-benzoquinones, benzoates, and formate and they were stably formed under O2/N2 atmospheres. When either NO or NH3 was introduced into the simulated flue gas, the formed species shifted toward formate in minutes, which indicated that changes in catalyst surface chemistry are directly related to impurity components. Presence of NH3 in the simulated flue gas inhibited o-xylene oxidation by reducing Mn and lowering Brønsted acidity of the catalyst. Impurity components associated with pollutant removal processes (Hg0 oxidation and selective catalytic reduction of NO) lowered o-xylene removal efficiency. Presence of o-xylene in the flue gas had little effect on the efficiency of pollutant removal processes. Layered catalytic beds located downstream from Hg0/NO pollutant removal processes are proposed to lower VOC emissions from coal-fired flue gases of thermal power plants in industrial settings.

Complete dechlorination of lindane over N-doped porous carbon supported Pd catalyst at room temperature and atmospheric pressure.

Transfer hydrogenation is highly effective for dechlorinating priority organic pollutants in wastewater. Lindane could be completely dechlorinated at room temperature and atmospheric pressure via transfer hydrogenation, in which Pd (3.1 wt%) supported on chitosan-derived porous carbon (3.1Pd@A600) and formic acid (FA) were used as catalyst and hydrogen source, respectively. Favorable catalytic activity of 3.1Pd@A600 is attributed to pyridinic N of the support that allowed Pd nanoparticles to be well-dispersed in the solid and to pyridinic N-Pd interactions that enhanced FA decomposition over that observed for commercial carbon supported Pd catalyst (5Pd@AC). In the reaction system containing 3.1Pd@A600 and FA, 99.7% lindane conversion and 100% dechlorination efficiency could be achieved at 25 °C and atmospheric pressure within 60 min. Benzene and cyclohexane were identified as end-products of lindane dechlorination. The transfer hydrogenation strategy developed in this study has wide application to chlorinated organic pollutants contained in actual waste streams.

N-formyl-stabilizing quasi-catalytic species afford rapid and selective solvent-free amination of biomass-derived feedstocks.

Nitrogen-containing compounds, especially primary amines, are vital building blocks in nature and industry. Herein, a protocol is developed that shows in situ formed N-formyl quasi-catalytic species afford highly selective synthesis of formamides or amines with controllable levels from a variety of aldehyde- and ketone-derived platform chemical substrates under solvent-free conditions. Up to 99% yields of mono-substituted formamides are obtained in 3 min. The C-N bond formation and N-formyl species are prevalent in the cascade reaction sequence. Kinetic and isotope labeling experiments explicitly demonstrate that the C-N bond is activated for subsequent hydrogenation, in which formic acid acts as acid catalyst, hydrogen donor and as N-formyl species source that stabilize amine intermediates elucidated with density functional theory. The protocol provides access to imides from aldehydes, ketones, carboxylic acids, and mixed-substrates, requires no special catalysts, solvents or techniques and provides new avenues for amination chemistry.

Correspondence between Spectral-Derived and Viscosity-Derived Local Composition in Binary Liquid Mixtures Having Specific Interactions with Preferential Solvation Theory.

Local interactions between unlike molecules (1-2) in solution are commonly measured with spectroscopy and used to estimate local composition. Herein, a viscosity model based on preferential solvation (PS) theory is developed for aqueous and nonaqueous binary liquid mixtures containing a dipolar aprotic solvent that provides local composition considering the hydration or solvation shell around complex (1-2) molecules. Spectral-derived and viscosity-derived local composition distributions showed similar trends with bulk composition, and their correspondence is attributed to characteristics of the hydration or solvation shell. Viscosity-derived local compositions were consistent with literature molecular simulations, whereas spectral-derived local composition distributions contained artifacts. The PS viscosity model is also applicable to nonpolar-polar mixtures for which self-association occurs, and it can be used to estimate solvent mixture dipolarity/polarizability. Since the PS viscosity model only requires bulk viscosity, it may provide a means to estimate microviscosity or the solvent environment around biomolecules.

Does Synergism in Microscopic Polarity Correlate with Extrema in Macroscopic Properties for Aqueous Mixtures of Dipolar Aprotic Solvents?

Aqueous mixtures of dipolar aprotic solvents (acetonitrile, γ-valerolactone, γ-butyrolactone, tetrahydrofuran, 1,4-dioxane, acetone, pyridine, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide) show synergism in microscopic polarity and extrema in macroscopic viscosity (η) and molar excess enthalpy (HE) in water-rich compositions that correlate with solvent functional group electrostatic basicity (ß2H). Microscopic polarities of aqueous solvent mixtures were estimated by measuring the spectral shift (λmax) of 4-nitroaniline with UV-vis spectroscopy at 25 °C. Dynamic viscosities (η) and densities were measured for eight aqueous dipolar aprotic mixtures over the full range of compositions at (25 to 45) °C. The λmax, η, and HE values of the aqueous mixtures showed a linear trend with increasing electrostatic basicity of the solvent functional groups that is attributed to the size and strength of the hydration shell of water. Density functional theory (DFT) calculations were performed for 1:3 complexes (solvent: (H2O)3) and it was found that aqueous mixtures with high basicity have high binding energies and short hydrogen bonding distances implying that the size and strength of the hydration shell of water is proportional to functional group basicity. Consideration of functional group basicity of dipolar aprotic solvents allows one to relate synergism in microscopic polarity to extrema in macroscopic properties for a wide range of aqueous dipolar aprotic solvent mixtures.

Analysis of the Cybotactic Region of Two Renewable Lactone-Water Mixed-Solvent Systems that Exhibit Synergistic Kamlet-Taft Basicity.

Kamlet-Taft solvatochromic parameters (polarity, basicity, acidity) of hydrogen bond donor (HBD)/acceptor (HBA) mixed-solvent systems, water (H2O)-γ-valerolactone (GVL), methanol (MeOH)-GVL, ethanol (EtOH)-GVL, H2O-γ-butyrolactone (GBL), MeOH-GBL, and EtOH-GBL, were measured over their entire composition region at 25 °C using UV-vis spectroscopy. Basicity of H2O-GVL and H2O-GBL systems exhibited positive deviation from ideality and synergism in the Kamlet-Taft basicity values. The cybotactic region around each indicator in the mixed-solvent systems was analyzed with the preferential solvation model. Both H2O-GVL and H2O-GBL mixed-solvent systems were found to be completely saturated with mutual complex molecules and to have higher basicity than pure water because water prefers to interact with GVL or GBL molecules rather than with itself. Formation of H2O-GVL and H2O-GBL complex molecules via specific hydrogen bond donor-acceptor interactions were confirmed by infrared spectroscopy. In MeOH-GVL or MeOH-GBL mixed-solvent systems, MeOH molecules prefer self-interaction over that with GVL or GBL so that synergistic basicity was not observed. Synergistic basicity and basicity increase for various functional groups of ten mixed-solvent (water-HBA solvent) systems can be quantitatively explained by considering electrostatic basicity and a ratio of the partial excess HBA solvent basicity with the HBA solvent molar volume that correlate linearly with the preferential solvation model complex molecular parameter (f12/1). Analysis of the cybotactic region of indicators in aqueous mixtures with the preferential solvation model allows one to estimate the trends of mixed-solvent basicity.

Spectroscopic Analysis of Binary Mixed-Solvent-Polyimide Precursor Systems with the Preferential Solvation Model for Determining Solute-Centric Kamlet-Taft Solvatochromic Parameters.

Hydrogen bond donor/acceptor mixed-solvent systems for solutes that exhibit strong specific interactions are not readily characterized with methods that depend on solvatochromic parameters. In this work, the reaction of two monomers, 4,4'-oxidianiline (ODA) and pyromellitic dianhydride (PMDA), to form the common engineering plastic precursor, poly(amic acid) (PAA), are studied for the tetrahydrofuran (THF) mixed-solvent systems (THF-methanol, THF-ethanol, THF-water) with spectroscopy. Solute-centric (SC) Kamlet­Taft solvatochromic (K-T) parameters for the solvent environment around the monomer are determined using a proposed model that incorporates spectroscopically determined local composition (X(L)) around the ODA monomer and the preferential solvation model. For the example reaction to occur under homogeneous conditions, mixed-solvent conditions need have HBA-rich local compositions (0.30 < X(HBA)(L) < 0.83), high solute-centric basicity (ß(SC) > 0.60), high solute-centric polarity, (π(SC)* > 0.63), and low solute-centric acidity (α(SC) < 0.63). The method developed allows characterization of mixed-solvent effects and can be readily extended to other systems that have strong specific interactions.

Effects of light intensity and temperature on photoautotrophic growth of a green microalga, Chlorococcum littorale.

A highly CO2-tolerant green alga, Chlorococcum littorale, was investigated at temperatures ranging from 8 to 28 °C, light intensities from 30 to 170 µmol m-2 s-1, a constant CO2 concentration of 5% (v/v) and atmospheric pressure. The experimental results showed that a specific growth rate µ, defined in terms of cell growth rate under a logarithmic growth phase, increased with temperature up to the maximum value (ca. 22 °C), while the µ decreased at higher temperatures. These promotion and inhibition of the cell growth rate were expressed by both a multiple linear regression and a mathematical model taking account of the Arrhenius activation/deactivation energies. Light intensity affected on the cell growth was independently treated in the mathematical model. The proposed growth model agreed well with the experimental data to within 6.6 %, which provides good correlation for both temperature and light intensity effects on the microalgal cell growth.

Carotenoid production from Chlorococcum littorale in photoautotrophic cultures with downstream supercritical fluid processing.

Carotenoid production from highly CO(2 )tolerant microalga Chlorococcum littorale in photoautotrophic cultures with downstream supercritical fluid processing was studied. Increasing temperature, increasing light intensity and decreasing CO(2) and O(2) gas concentrations enhanced growth rate under nitrate-rich conditions. Carotenoid content was insensitive to nitrate concentration, temperature and gas composition, but was greatly promoted by light intensity. Growth rate and carotenoid content had an optimum light intensity of ca. 120 micromol-photon * m(-2)s(-1). Separation of two sample cultures was studied by applying supercritical fluid extraction with CO(2 )and 10 mol% ethanol co-solvent. Extraction yield of carotenoids was 90% with 10 mol% ethanol at 333 K and 30 MPa. Selectivity of a sample with less lipid content (12.9 wt%) was five-fold higher than that with higher lipid content (29.4 w%).