The extension to long-chain alkanes and to high temperatures of the hydroperoxide chain mechanism of autoxidation

1969 ◽  
Vol 308 (1495) ◽  
pp. 547-568 ◽  
Keyword(s):  
Carbonyl Compounds ◽  
Oxidation Products ◽  
Antioxidant Compounds ◽  
Chain Mechanism ◽  
Chemical Methods ◽  
Alkyl Radicals ◽  
Phase Oxidation ◽  
Two Factors ◽  
Alkylperoxy Radicals ◽  
Long Chain

The liquid-phase oxidation of 2-methylhexadecane has been studied to determine how adequately the hydroperoxide chain mechanism describes the oxidation of high molecular weight alkanes and to elucidate the changes in this mechanism caused by increased temperature. The reaction between 2-methylhexadecane and molecular oxygen has been studied at temperatures of 145 to 230 °C and the oxidation products analysed by gas-chromatographic and chemical methods. Over 160 products including hydroperoxides, alkanes, alcohols, carbonyl compounds and acids have been identified and the dependence of their yields on time, temperature and oxygen concentration measured. The attack on 2-methylhexadecane at temperatures throughout this range is selective, indicating that chain propagation occurs predominantly by the reaction of alkylperoxy radicals with alkane molecules followed by the addition of oxygen to the alkyl radicals so formed. At low temperatures the former reaction is rate-determining. However, an increase in temperature increases the rate of this reaction and reduces the concentration of oxygen dissolved in the alkane; the combined effect of these two factors causes the addition of oxygen to alkyl radicals to become rate-determining at temperatures above ca . 210 °C. As a result of this change, the concentration of alkyl radicals relative to that of alkylperoxy radicals increases with temperature. Consequently, both the yield of alkanes, and the fraction of secondary alkyl radicals that react with 2-methylhexadecane molecules to form more stable tertiary radicals, increase. These results help to predict the necessary properties of a high temperature antioxidant; compounds that react specifically with alkyl radicals rather than with alkylperoxy radicals should function thus.

THE KINETICS OF THE OXIDATION OF GASEOUS ACETALDEHYDE

1932 ◽  
Vol 7 (2) ◽  
pp. 149-161 ◽  
Author(s):  
W. H. Hatcher ◽  
E. W. R. Steacie ◽  
Frances Howland
Keyword(s):  
Carbon Dioxide ◽  
Formic Acid ◽  
Induction Period ◽  
Reaction Vessel ◽  
Oxidation Products ◽  
Main Reaction ◽  
Chain Mechanism ◽  
Subsequent Reaction ◽  
A Chain ◽  
Kinetics Of

The kinetics of the oxidation of gaseous acetaldehyde have been investigated from 60° to 120 °C. by observing the rate of pressure decrease in a system at constant volume. A considerable induction period exists, during which the main products of the reaction are carbon dioxide, water, and formic acid. The main reaction in the subsequent stages involves the formation of peroxides and their oxidation products. The heat of activation of the reaction is 8700 calories per gram molecule. The indications are that the reactions occurring during the induction period are heterogeneous. The subsequent reaction occurs by a chain mechanism. The chains are initiated at the walls of the reaction vessel, and are also largely broken at the walls.

scholarly journals The formation of nitro-aromatic compounds under high NO<sub><i>x</i></sub> and anthropogenic VOC conditions in urban Beijing, China

2019 ◽  
Vol 19 (11) ◽  
pp. 7649-7665 ◽  
Author(s):  
Yujue Wang ◽  
Min Hu ◽  
Yuchen Wang ◽  
Jing Zheng ◽  
Dongjie Shang ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Aromatic Compounds ◽  
Total Concentration ◽  
Fine Particulate Matter ◽  
Oxidation Products ◽  
Urban Atmosphere ◽  
Formation Pathway ◽  
Relative Contribution ◽  
Phase Oxidation ◽  
Nitro Aromatic

Abstract. Nitro-aromatic compounds (NACs), as important contributors to the light absorption by brown carbon, have been widely observed in various ambient atmospheres; however, their formation in the urban atmosphere was little studied. In this work, we report an intensive field study of NACs in summer 2016 at an urban Beijing site, characterized by both high-NOx and anthropogenic VOC dominated conditions. We investigated the factors that influence NAC formation (e.g., NO2, VOC precursors, RH and photolysis) through quantification of eight NACs, along with major components in fine particulate matter, selected volatile organic compounds, and gases. The average total concentration of the quantified NACs was 6.63 ng m−3, higher than those reported in other summertime studies (0.14–6.44 ng m−3). 4-Nitrophenol (4NP, 32.4 %) and 4-nitrocatechol (4NC, 28.5 %) were the top two most abundant NACs, followed by methyl-nitrocatechol (MNC), methyl-nitrophenol (MNP), and dimethyl-nitrophenol (DMNP). The oxidation of toluene and benzene in the presence of NOx was found to be a more dominant source of NACs than primary biomass burning emissions. The NO2 concentration level was found to be an important factor influencing the secondary formation of NACs. A transition from low- to high-NOx regimes coincided with a shift from organic- to inorganic-dominated oxidation products. The transition thresholds were NO2 ∼ 20 ppb for daytime and NO2∼25 ppb for nighttime conditions. Under low-NOx conditions, NACs increased with NO2, while the NO3- concentrations and (NO3-)/NACs ratios were lower, implying organic-dominated products. Under high-NOx conditions, NAC concentrations did not further increase with NO2, while the NO3- concentrations and (NO3-)/NACs ratios showed increasing trends, signaling a shift from organic- to inorganic-dominated products. Nighttime enhancements were observed for 3M4NC and 4M5NC, while daytime enhancements were noted for 4NP, 2M4NP, and DMNP, indicating different formation pathways for these two groups of NACs. Our analysis suggested that the aqueous-phase oxidation was likely the major formation pathway of 4M5NC and 3M5NC, while photo-oxidation of toluene and benzene in the presence of NO2 could be more important for the formation of nitrophenol and its derivatives. Using the (3M4NC+4M5NC) ∕ 4NP ratios as an indicator of the relative contribution of aqueous-phase and gas-phase oxidation pathways to NAC formation, we observed that the relative contribution of aqueous-phase pathways increased at elevated ambient RH and remained constant at RH > 30 %. We also found that the concentrations of VOC precursors (e.g., toluene and benzene) and aerosol surface area acted as important factors in promoting NAC formation, and photolysis as an important loss pathway for nitrophenols.

Influence of Diene Content on the Photodegradation of Ethylene-Propylene-Diene (EPDM) Elastomers

2006 ◽  
Vol 514-516 ◽  
pp. 877-881 ◽  
Author(s):  
Gabriela Botelho ◽  
Arlete Queirós ◽  
Manuela A. Silva ◽  
Maria João Conceição
Keyword(s):  
Ftir Spectroscopy ◽  
Carbonyl Compounds ◽  
Oxidation Products ◽  
Ethylene Propylene ◽  
Photo Oxidation

The photodegradation of EPDM based on dicyclopentadiene was followed by FTIR spectroscopy and the main photo-oxidation products were identified by derivatization reactions. It could be found that the photodegradation is initiated at the diene with formation of α,β–unsaturated carbonyl compounds and is then propagated to the ethylene-propylene segments. The propagation reactions are accelerated and, hence, the rate of photodegradation increases with the diene content.

Probing aerosol formation by comprehensive measurements of gas phase oxidation products

2013 ◽  
Author(s):  
Mikael Ehn ◽  
Einhard Kleist ◽  
Heikki Junninen ◽  
Mikko Sipilä ◽  
Tuukka Petäjä ◽  
...  
Keyword(s):  
Gas Phase ◽  
Oxidation Products ◽  
Aerosol Formation ◽  
Phase Oxidation ◽  
Gas Phase Oxidation

Chloroform as an accelerator of propane oxidation

1963 ◽  
Vol 274 (1358) ◽  
pp. 413-426 ◽  
Keyword(s):  
Gas Phase ◽  
Maximum Rate ◽  
Isotopic Exchange ◽  
Pressure Change ◽  
Product Formation ◽  
Pressure Measurements ◽  
Chain Mechanism ◽  
Phase Oxidation ◽  
Gas Phase Oxidation ◽  
Simple Chain

Chloroform and the other chloromethanes, except carbon tetrachloride, accelerate the gas-phase oxidation of propane in the 'low-temperature' region. The relation of pressure change to reactant consumption and final product formation is not significantly modified in the catalyzed reaction, which can still be followed by pressure measurements. The value of the maximum rate in the presence of chloroform is given fairly closely by the expression (( ρ max .) [CHCL 3 ])/( ρ max .) 0 = 1 + constant x [CHCI 3 ]/[ R H]. The form of this suggests that, in the rate-determining steps, chloroform and paraffin are involved in analogous processes, and the key step is postulated to be R O 2 · + CHCI 3 → R OOH + CCl 3 · which re-inforces the reaction R O 2 · + R H → R OOH + R · in competing with those steps normally leading to degradation of R O 2 · radicals. Since little or no isotopic exchange occurs when CDCl 3 is used in place of CHCl 3 , the radical CCl 3 · does not regenerate chloroform, but initiates chains of the type CCl 3 ·→ ·CCl 2 · + Cl·, Cl· + R H → HCl + R · A slow consumption of chloroform (the oxidation of which is unimportant in the absence of propane) occurs, together with a slow build-up of hydrogen chloride. With certain approximations, a simple chain mechanism reproduces the experimental kinetic formula.

scholarly journals The composition and variability of atmospheric aerosol over Southeast Asia during 2008

2011 ◽  
Vol 11 (8) ◽  
pp. 22033-22073 ◽  
Author(s):  
W. Trivitayanurak ◽  
P. I. Palmer ◽  
M. P. Barkley ◽  
N. H. Robinson ◽  
H. Coe ◽  
...  
Keyword(s):  
Southeast Asia ◽  
Gas Phase ◽  
Organic Aerosol ◽  
Sea Salt ◽  
Dust Aerosol ◽  
Oxidation Products ◽  
Small Scale ◽  
Sulphate Aerosol ◽  
Modis Aod ◽  
Phase Oxidation

Abstract. We use a nested version of the GEOS-Chem global 3-D chemistry transport model to better understand the composition and variation of aerosol over Borneo and the broader Southeast Asian region in conjunction with aircraft and satellite observations. We particularly focus on July 2008 during when the UK BAe-146 research aircraft was deployed over northern Malaysian Borneo as part of the ACES/OP3 measurement campaign. During July 2008 we find using the model that Borneo (defined as Borneo Island and the surrounding Indonesian islands) was a net exporter of primary organic aerosol (42 kT) and black carbon aerosol (11 kT). We find only 13 % of volatile organic compound oxidation products partition to secondary organic aerosol (SOA), with Borneo being a net exporter of SOA (15 kT). SOA represents approximately 19 % of the total organic aerosol over the region. Sulphate is mainly from aqueous-phase oxidation (68 %), with smaller contributions from gas-phase oxidation (15 %) and advection into the regions (14 %). We find that there is a large source of sea salt, as expected, but this largely deposits within the region; we find that dust aerosol plays only a relatively small role in the aerosol burden. In contrast to coincident surface measurements over Northern Borneo that find a pristine environment with evidence for substantial biogenic SOA formation we find that the free troposphere is influenced by biomass burning aerosol transported from the northwest of the Island and further afield. We find several transport events during July 2008 over Borneo associated with elevated aerosol concentrations, none of which coincide with the aircraft flights. We use MODIS aerosol optical depth (AOD) data and the model to put the July campaign into a longer temporal perspective. We find that Borneo is where the model has the least skill at reproducing the data, reflecting the small-scale island-marine environment, with the model showing more skill at reproducing observed AOD over larger regions such as China and other parts of Southeast Asia. The model shows that AOD over Borneo is approximately evenly split between organic and sulphate aerosol with sea salt representing 10–20 % during May to September; there is a similar breakdown over continental Southeast Asia but with less sea salt aerosol and more dust aerosol. In contrast, East China AOD is determined mainly by sulphate aerosol and a seasonal source of dust aerosol, as expected. Realistic sensitivity runs designed to test our underlying assumptions about emissions and chemistry over Borneo constrained by MODIS AOD show that the model is most sensitive to isoprene emissions and organic gas-phase partitioning.

scholarly journals Bioactive compounds content of Snake Fruit Peel, Aloe Vera, and Stevia Extracts as Raw Material of Functional Drinks

2020 ◽  
Vol 1 (1) ◽  
pp. 34
Author(s):  
Amalya Nurul Khairi ◽  
Nurkhasanah Nurkhasanah
Keyword(s):  
Bioactive Compounds ◽  
Aloe Vera ◽  
Total Phenol ◽  
Raw Material ◽  
Antioxidant Compounds ◽  
Fruit Peel ◽  
Two Factors ◽  
Phenol Composition ◽  
Functional Drink ◽  
Peel Extract

The objective of the research is to analyze the content of the bioactive compounds of extracts made of snake fruit skin, Aloe vera, and Stevia as materials to make functional drinks. Salacca zalacca (Gaert.) Voss. cultivar has flavonoid, tannin, and a bit of alkaloid on its fruit peel. Aloe vera and Stevia also known to have antioxidant compounds. Aloe vera controls the metabolism of carbohydrates and maintaining homeostasis of glucose. The research methods are divided into steps: 1) the extraction of Snake fruit peel, Aloe vera, and Stevia; 2) the formulation of the functional drink; 3)the evaluation of antioxidant, total phenol, and tannin levels of the formulated extracts. The research used Randomized Group Design (RGD) of two factors, and each factor consists of 4 levels and 2 levels. Factor I=the ratio of snake fruit peel:Aloe vera extract (10:90 (v/v); 30:70 (v/v); 70:30 (v/v); 90:10 (v/v)) and factor II= addition of Stevia filtrate (2%; 4%) (v/v total). The best nutrient of the formulated functional drink is obtained by the composition of 90% snake fruit peel extract, 10% aloe vera, and 4% stevia. The snake fruit peel extract significantly affects the antioxidant activity and total phenol composition, aloe vera extract has an insignificant effect on active compounds, and stevia affects the tannin level of the functional drink.

Sign in / Sign up

Export Citation Format

Share Document