The production of formaldehyde and hydroxyacetone in methacrolein photooxidation: New insights into mechanism and effects of water vapor (2023)

Methacrolein is a typical α, β-unsaturated aldehyde in the combustion of various hydrocarbons and oxygenated biofuels. The oxidation behavior of fuels that contain resonant C=C and CHO groups in the molecular structure has not been well established in the literature. Understanding the effects of these functional groups on oxidation chemistry is also significant in developing a comprehensive core mechanism. In this work, the oxidation of methacrolein is studied in a jet-stirred reactor at atmospheric pressure at temperatures ranging from 475 to 875K, employing synchrotron vacuum ultraviolet photoionization mass spectrometry technology to identify and quantify the intermediates. A kinetic model is developed following our previous works on trans-crotonaldehyde and examined against the present experimental datasets. Based on experimental observations and modeling analyses, the crucial pathways governing the oxidation reactivities are illustrated. A new pathway is proposed to interpret theformation of ketene during the oxidation process of methacrolein and trans-crotonaldehyde. Furthermore, the effects of molecular structures on the oxidation reactivities are discussed for methacrolein, trans-crotonaldehyde, n-butanal, and isobutanal. Hydrogen abstractions from the -CHO group dominate the initial fuel consumption for the four fuels producing R-CO radicals. The different R radicals produced from R-CO radicals’ dissociation subsequently influence the oxidation reactivities.

A compilation of new advances made in the research field of laboratory reaction kinetics in China's Key Development Project for Air Pollution Formation Mechanism and Control Technologies was presented. These advances are grouped into six broad, interrelated categories, including volatile organic compound (VOC) oxidation, secondary organic aerosol (SOA) formation, new particle formation (NPF) and gas-particle partitioning, ozone chemistry, model parameters, and secondary inorganic aerosol (SIA) formation, highlighting the laboratory work done by Chinese researchers. For smog chamber applications, the current knowledge gained from laboratory studies is reviewed, with emphasis on summarizing the oxidation mechanisms of long-chain alkanes, aromatics, alkenes, aldehydes/ketones in the atmosphere, SOA formation from anthropogenic emission sources, and oxidation of aromatics, isoprene, and limonene, as well as SIA formation. For flow tube applications, atmospheric oxidation mechanisms of toluene and methacrolein, SOA formation from limonene oxidation by ozone, gas-particle partitioning of peroxides, and sulfuric acid-water (H₂SO₄-H₂O) binary nucleation, methanesulfonic acid-water (MSA-H₂O) binary nucleation, and sulfuric acid-ammonia-water (H₂SO₄-NH₃-H₂O) ternary nucleation are discussed.

Journal of Environmental Sciences, Volume 66, 2018, pp. 310-317

Natural organic matter (NOM), present in natural waters and wastewater, decreases adsorption of micropollutants, increasing treatment costs. This research investigated mechanisms of competition for non-imprinted polymers (NIPs) and activated carbon with humic acid and wastewater. Three different types of activated carbons (Norit PAC 200, Darco KB-M, and Darco S-51) were used for comparison with the NIP. The lower surface area and micropore to mesopore ratio of the NIP led to decreased adsorption capacity in comparison to the activated carbons. In addition, experiments were conducted for single-solute adsorption of Methylene Blue (MB) dye, simultaneous adsorption with humic acid and wastewater, and pre-loading with humic acid and wastewater followed by adsorption of MB dye using NIP and Norit PAC 200. Both the NIP and PAC 200 showed significant decreases of 27% for NIP (p=0.087) and 29% for PAC 200 (p=0.096) during simultaneous exposure to humic acid and MB dye. There was no corresponding decrease for NIP or PAC 200 pre-loaded with humic acid and then exposed to MB. In fact, for PAC 200, the adsorption capacity of the activated carbon increased when it was pre-loaded with humic acid by 39% (p=0.0005). For wastewater, the NIP showed no significant increase or decrease in adsorption capacity during either simultaneous exposure or pre-loading. The adsorption capacity of PAC 200 increased by 40% (p=0.001) for simultaneous exposure to wastewater and MB. Pre-loading with wastewater had no effect on MB adsorption by PAC 200.

Journal of Environmental Sciences, Volume 66, 2018, pp. 328-337

Advanced oxidation technologies are a friendly environmental approach for the remediation of industrial wastewaters. Here, one pot synthesis of mesoporous WO₃ and WO₃-graphene oxide (GO) nanocomposites has been performed through the sol–gel method. Then, platinum (Pt) nanoparticles were deposited onto the WO₃ and WO₃-GO nanocomposite through photochemical reduction to produce mesoporous Pt/WO₃ and Pt/WO₃-GO nanocomposites. X-ray diffraction (XRD) findings exhibit a formation of monoclinic and triclinic WO₃ phases. Transmission Electron Microscope (TEM) images of Pt/WO₃-GO nanocomposites exhibited that WO₃ nanoparticles are obviously agglomerated and the particle sizes of Pt and WO₃ are ~10nm and 20–50nm, respectively. The mesoporous Pt/WO₃ and Pt/WO₃-GO nanocomposites were assessed for photocatalytic degradation of Methylene Blue (MB) as a probe molecule under visible light illumination. The findings showed that mesoporous Pt/WO₃, WO₃-GO and Pt/WO₃-GO nanocomposites exhibited much higher photocatalytic efficiencies than the pure WO₃. The photodegradation rates by mesoporous Pt/WO₃-GO nanocomposites are 3, 2 and 1.15 times greater than those by mesoporous WO₃, WO₃-GO, and Pt/WO₃, respectively. The key factors of the enhanced photocatalytic performance of Pt/WO₃-GO nanocomposites could be explained by the highly freedom electron transfer through the synergetic effect between WO₃ and GO sheets, in addition to the Pt nanoparticles that act as active sites for O₂ reduction, which suppresses the electron hole pair recombination in the Pt/WO₃-GO nanocomposites.

Science of The Total Environment, Volume 751, 2021, Article 141620

With the development of the economy, anthropogenic emissions in the atmospheric environment increases, and air pollution has caused wide public concern. Vehicle exhaust is an important emission source in the atmosphere, and alkanes are the representative components in it. In this study, the optical properties of secondary organic aerosol (SOA) derived from several C₁₂ alkanes (2-methylundecane, hexylcyclohexane, and cyclododecane) in the absence of NO_X were determined. Absorption (imaginary part of the refractive index (RI), k) at 532nm was negligible for all the derived SOA, and the scattering (real part of RI, n) of the SOA at 532nm followed the order of cyclododecane SOA<hexylcyclohexane SOA<2-methylundecane SOA, at both room- (25°C) and low- (5°C) temperature. The chemical compositions of the SOA formed were analyzed with an electrospray ionization time-of-flight mass spectrometer (ESI-TOF-MS). The mass spectra showed that the oligomers were generated in the reactions. It was shown that the different reaction pathways (due to various alkane structures) leaded to the difference in SOA chemical composition, which changed the RI values. The low-temperature condition promoted the progress of the oligomerization reaction so that the final RI values also changed. This work suggested that when estimating the radiative forcing of SOA using regional or global models, the structure of the precursors and reaction conditions should be taken into account.

Bioresource Technology, Volume 149, 2013, pp. 238-243

Escherichia coli Lin43 is a strain which has some mutations in glycerol kinase (GlpK) and the repressor for the glycerol 3-phosphate regulon (GlpR). When exposed to glycerol, it quickly accumulates lethal levels of methylglyoxal, which is a precursor of acetol; acetol is important for the manufacture of polyols, acrolein, dyes, and skin tanning agents. This work reports the engineering of E. coli Lin 43 for the conversion of glycerol into acetol. First, the glyoxalase system was interrupted by deleting the gloA gene, which increased the acetol yield by 32%. In addition, the aldehyde reductase YqhD was overexpressed which led to an increase of acetol production by 11.4-fold. Acetol production was optimized by varying the cell density, glycerol concentration, supplemental carbon source, pH and temperature. Under the optimal conditions (OD₆₀₀=20, 20g/L glycerol, 2g/L succinate, pH 7.0, and 28°C), we obtained 5.4g/L acetol in 21h.

Atmospheric Environment, Volume 82, 2014, pp. 250-257

The gas phase photolysis of two α-diketones, 2,3-pentanedione (PTD) and 2,3-hexanedione (HEX), has been studied in a Teflon simulation chamber using UV lamps in the 330–480nm wavelength range. Photolysis rates have been determined at room temperature and atmospheric pressure. Using NO₂ actinometry allows estimating the lifetime of PTD and HEX in the atmosphere to be about 2.5h, assessing the dominance of the photolysis loss process over the OH reaction for such α-dicarbonyl compounds. Effective quantum yields for PTD and HEX have also been calculated over the whole wavelength range: Φ_PTD=0.20±0.02 and Φ_HEx=0.18±0.03, consistent with literature values on α-dicarbonyls. Various end-products from the photolysis of PTD and HEX have been identified and quantified. For PTD, CH₂O and CH₃CHO have been detected with molar yields of (48±0.5)% and (41±0.7)%, respectively. For HEX, CH₂O and C₂H₅CHO have been detected with molar yields of (45±1.1)% and (37±0.8)%, respectively. Small amounts of CO have also been observed, with yields of about 2%, as well as organic acids. Experiments performed in the absence of OH-radical scavengers showed significantly faster photolysis rates and higher CO yields (∼7%), indicating clear formation of OH radicals in the chemical systems. A reaction mechanism was developed for PTD and HEX photolysis based on the product observations, which allowed simulating the reactant and product time profiles with very good agreement. The present work represents the first study of 2,3-pentanedione and 2,3-hexanedione photolysis, to our knowledge, and may contribute to a better understanding of the photolysis of the α-diketones in the troposphere.

Journal of Environmental Sciences, Volume 66, 2018, pp. 368-378

Road salts are frequently used for deicing of roads in the Nordic countries. During snow-melt, the road run-off containing high concentrations of road salt and various metals such as Cu remobilized from sand, silt and dust may negatively influence organisms in downstream receiving water bodies. The present work focuses on the impact of road salt (NaCl) and Cu, separately and in mixtures on Atlantic salmon alevins from hatching till swim-up. The results showed that high road salt concentrations could induce a series of negative effects in alevins such as reduced growth, deformities, delayed swim-up and mortality. For alevins exposed to all tested road salt concentrations (100–1000mg/L), mortality was significantly higher compared to control. In exposure to Cu solutions (5–20μgCu/L), no effects on growth, morphology, swim-up or mortality of alevins compared to control were observed. In mixture solutions (road salt and Cu), ultrafiltration of the exposure water demonstrated that only 20%–40% of Cu was present as positively charged low molecular mass (LMM) Cu species assumed to be bioavailable. When exposed to road salt and Cu mixtures, negative effects in alevins such as reduced growth, deformities, delayed swim-up and mortality were observed. The overall results indicated that the road salt application could seriously affect sensitive life stages of Atlantic salmon, and application of road salt should be avoided during the late winter–early spring period.