Factors influencing the thermal oxidation of polyethylene

The thermal stability of polyethylene containing conventional antioxidants is adversely affected by contact with copper, by certain pigments, and by the addition of a few percent of polypropylene as a processing aid. Polyethylene inhibited with 0.1% of phenolic antioxidants has approximately the same oxidative stability when in contact with a copper surface as the unprotected polymer. A mechanism is suggested to account for the loss of stability in the presence of copper. Pigments vary in the extent to which they adversely affect the oxidative stability of polyethylene. Since several factors may combine to decrease the stability of protected polyethylene compositions, as determined by accelerated tests, it is essential that their contribution under service conditions be determined. The predicted life at temperatures encountered in service is determined by extrapolating accelerated test data to that constant temperature which is calculated to cause the same degree of degradation as would occur during the daily and seasonal temperature cycles encountered in use.     

挥发性有机化合物催化氧化技术

基于环境友好,对使用催化氧化法去除挥发性有机化合物(VOCs)的原理、特点以及催化剂、工艺流程等研究进行综述。挥发性有机化合物完全催化氧化机理分为:Mars-van Krevelen(MVK)模型、Langmuir-Hinshelwood(L-H)模型和Eley-Rideal(E-R)模型。复合金属氧化物催化剂是研究的热点,去除VOCs的核心是使反应温度降低,即具有低温和高活性的催化剂。延长催化剂寿命、提高去除效率也可以带来良好的节能效果和降低投资成本。对于低浓度和大体积VOCs排放,可通过吸附+催化混合法先进技术实现去除,且成功应用于实践。     

含氯挥发性有机物的催化氧化研究进展

催化氧化是控制挥发性有机污染物排放的有效途径之一,但传统催化剂在氧化消除含氯挥发性有机物(CVOCs)时易中毒而失活,因此,研发新型、高效、稳定的催化剂对其工业应用具有重要意义。简要综述近年来稀土及过渡金属氧化物、分子筛和负载贵金属催化剂对CVOCs氧化的催化性能和催化反应机理,剖析CVOCs氧化反应副产物的形成和催化剂失活的原因,并展望CVOCs催化氧化技术的未来发展趋势。     

Identification of volatile flavor compounds in roasted coconut

Heating of coconut leads to browning and development of fine roasted flavor. Flavor studies were carried out with control and heated samples of conconut. Gas chromatography (GC) and GC/mass spectrometry analyses of the basic, neutral and acid fractions of flavor, isolated by hydrodistillation and selective extraction, showed the presence of pyrazines and other heterocyclic compounds in heated samples. These compounds contribute to the overall roasted flavor. Twenty pyrazines were identified in roasted coconut, which included pyrazine, methyl pyrazine, dimethyl pyrazines, ethyl methyl pyrazines, vinyl pyrazine and isopropyl pyrazine. Pyrazine content increased with temperature. In addition to these compounds,δ-lactones, esters, ketones and fatty acids were present in control and heated samples of coconut.     

Performance of a membrane-catalyst for photocatalytic oxidation of volatile organic compounds

The performance of a hybrid Sil-1/nanostructured anatase TiO₂ membrane-catalyst and a catalytic titanium silicalite-1 (TS-1) membrane was evaluated for gas-phase photocatalytic oxidation (PCO) of trichloroethylene. The membrane-catalyst outperformed the catalytic plate coated with a similar amount of nanostructured TiO₂ catalyst. However, the activity of the catalytic TS-membrane for PCO is low due to the insufficient number of active titanium sites in the TS-1 zeolite.     

Evaluation of H-type zeolites in the destructive oxidation of chlorinated volatile organic compounds

The deep oxidation of 1,2-dichloroethane (DCE) and trichloroethylene (TCE) over H-type zeolites (H-Y and H-ZSM-5) was evaluated. Experiments were performed at conditions of lean hydrocarbon concentration (around 1000 ppmv) in dry air, between 200 and 550°C in a conventional fixed-bed reactor. H-ZSM-5 zeolite resulted more active than H-Y zeolite in the decomposition of both chlorinated volatile organic compounds. It was established that Brønsted acidity plays an important role in controlling the catalytic behaviour of the H-type zeolites. DCE was completely decomposed at 400°C, whereas TCE required higher temperatures (550°C). Vinyl chloride was identified as an intermediate in the DCE oxidation in the range of 250–400°C. When vinyl chloride is destroyed at higher temperatures, both zeolite catalysts show a high selectivity (>90%) towards HCl formation. Trace amounts of tetrachloroethylene were detected in the TCE oxidation, which peaked at 500°C. CO was promoted in quantity in the destruction of both DCE and TCE reflecting the difficulty of carbon monoxide oxidation over H-type zeolites.     

Diffusion mechanism of byproducts resulting from the peroxide crosslinking of polyethylene

In this study, a polyethylene grade used for applications in the insulation of energy cables was crosslinked by the peroxide crosslinking route. The impact of dicumyl peroxide (DCP) crosslinking on the polymer microstructure was studied. The different byproducts formed during the crosslinking reaction [acetophenone, α‐cumyl alcohol, and α‐methyl styrene (aMS)] were identified and quantified. Another molecule, 2,4‐diphenyl‐4‐methyl‐1‐pentene, regarded as an aMS dimer, was detected for the first time. Some amounts of residual DCP were also detected. A detailed study of the diffusion mechanism of each byproduct under different desorption conditions (e.g., samples exposed to vacuum or atmospheric conditions) and temperatures was performed. The diffusion coefficient values were determined and are discussed as a function of the desorption conditions and byproduct characteristics. Through this study, essential diffusion parameters were provided as a first step for further modeling development to allow the definition of optimized desorption conditions for a large range of sample geometries and thicknesses. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44525.     

Influence of thermal oxidation on surface and thermo-mechanical properties of polyethylene

Blown low density polyethylene (LDPE) films added with oxo-biodegradable additive containing pro-oxidant were subjected to thermo-oxidation in an oven at 70 °C for varying time periods. The changes in mechanical and surface properties were studied using tensile strength, elongation at break, wettability, surface morphology using SEM, surface topology by AFM, functional groups by FTIR spectroscopy, absorbance spectra by UV-Vis spectroscopy. The thermally aged films with pro-oxidant additive added polyethylene (PE) exhibited a higher level of oxidation as revealed by increase in their carbonyl index than the pristine PE. In addition to it, the DSC melting behavior showed a slight increase in crystallinity (%C) and melting temperature (Tm) of the polymer containing oxo-biodegradable additive. The SEM micrograph reveals the increase in the size of cracks and grooves, according to the increase in the concentration of pro-oxidant additive. The surface roughness also supports the same through AFM image. The increase in the wettability and surface free energy of the thermally aged samples were attributed to the formation of hydrophilic groups on the polymer surface by thermo-oxidation. The pro-oxidant additive offers a new insight into the thermo-oxidation strategy for PE and can be widely used in packaging industry.     

负载贵金属催化剂在挥发性有机物氧化反应中的应用

挥发性有机物(VOCs)是大气污染的主要来源,危害人体健康。催化氧化法是消除挥发性有机物的有效手段,其核心是高效催化剂,新型、高活性、高稳定性催化剂的研发具有重要意义。简要综述近年来负载Au、Pd和Pt贵金属催化剂对VOCs氧化消除的催化性能,分析VOCs氧化在典型催化剂表面形成的活性物种及其对催化活性的影响,并展望VOCs催化氧化的未来发展趋势。     

Recovery of volatile compounds from butter oil

Three methods for the isolation of volatile compounds from oils and fats were compared using small concentrations (approximately 1 ppm) of added C_3-12 n-alkan-2-ones and C_2-10 n-alkan-1-ols in commercial butter oil. These were : high vacuum degassing, cold-finger molecular distillation and reduced pressure steam distillation. Several modifications were incorporated. The highest yields of all compounds were obtained by cold-finger molecular distillation but difficulties were encountered in subsequent analysis. It was more convenient to recover compounds boiling below 150C by either high vacuum degassing or reduced pressure steam distillation. The latter was more efficient for the higher boiling compounds. Extraction with organic solvents was not required in any of these techniques. The combination of high vacuum degassing and cold-finger molecular distillation was found to be the best method of analyzing the complete range of model compounds.     

Characterization of the nonvolatile compounds formed during the thermal oxidation of triolein

Triolein was subjected to thermal oxidation at 200 C for 24 hr with an air flow of 0.15 ml/min/gm. The oxidized material was saponified and converted to its corresponding methyl ester. Nonoxidized materials were separated from nonvolatile oxidation products using preparative thin layer chromatography. Further separation of these fractions was achieved using gas chromatography, gel filtration chromatography and solvent-solvent extraction. Several compounds were isolated in this manner and their structures determined with the aid of nuclear magnetic resonance and mass spectrometry, as well as by supplementary chemical methods and by comparison with known compounds. These compounds were: (1) 2-cyclohexyldodec-5-enoic acid and isomers; (2) a mixture of 2-, 8-, 9-, and 10-monohydroxystearic acid; (3) 9,10-dihydroxystearic acid; (4) 1-decyl-2-(dec-6-enyl)-cyclohexane; (5) a mixture of isomers corresponding to a cyclic monomer of oleic acid containing both exocyclic and endocyclic unsaturation. This work represents a portion of the Ph.D. thesis presented by J.R. Anfinsen to the University of Illinois at Urbana-Champaign.     

高温烟气蒸发垃圾渗滤液膜浓缩液的挥发性有机物

通过对比和分析不同温度、不同时间下垃圾填埋场中膜浓缩液蒸发的挥发特性和挥发性有机物的种类，研究了在其蒸发过程中的有机物挥发情况，并基于此设计了直接利用高温烟气先间壁换热再直接换热的一体化蒸发装置，通过对高温烟气温度、浸没深度、蒸发时间的优化，最终实现了烟气热能的高效利用和常压下的减压蒸发效果。结果表明：随着温度的升高，尾气中高沸点、长碳链的挥发性有机物的种类和挥发量增多。挥发性有机物主要为烷烃类，100℃以后，苯系物和醇酯类物质增加明显；温度为80℃，蒸发0.5h和1h，低分子量有机物大量释放，高沸点物质挥发较少；400℃、450℃、500℃、550℃温度下高温烟气蒸发时，液相蒸发温度在85℃左右，与尾气温差保持在5～6℃，传热传质快，且挥发性有机物的种类与直接蒸发结论基本一致，提高了在较低温蒸发状态下热能的高效利用。同时，该尾气经活性炭吸附处理后，剩余挥发性有机物少，效果明显。     

Support effect on complete oxidation of volatile organic compounds over Ru catalysts

Catalytic combustion of ethyl acetate, acetaldehyde, and toluene was investigated on various supported Ru catalysts prepared by the impregnation method, and the effect of reduction treatment on the activity was examined. Among the as-calcined catalysts tested, Ru/CeO₂ showed the highest activity for all tests regardless of the pre-treatment in hydrogen atmosphere. The catalytic activity of Ru/SnO₂ was significantly degraded by the reduction treatment, whereas the activity of Ru/ZrO₂ and Ru/γ-Al₂O₃ was enhanced. To reveal these phenomena, the as-calcined and reduced catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and BET surface area. The dispersion of ruthenium on the supports was evaluated by chemisorption methods of carbon monoxide. The catalytic activity was strongly related to ruthenium species easily oxidizable and reducible at low temperatures. Such ruthenium species were loaded on CeO₂ in a highly dispersed state, resulting in the highest activity.     

Catalytic oxidation of trichloroethylene in two-component mixtures with selected volatile organic compounds

The activity of two noble metal catalysts (Pt and Pd) on metallic monolithic support and one perovskite (La_0.5Ag_0.5MnO₃) on cordierite monolith was tested in the oxidation of selected volatile organic compounds (VOCs) and trichloroethylene (TCE), oxidized alone and in two-component mixtures of TCE with a non-halogenated compound. Only over the Pt catalyst each compound in the reaction mixtures strongly enhanced TCE oxidation. Over Pd, promoting effect on TCE oxidation was observed for toluene and ethanol only. Over perovskite, each non-chlorinated compound was found to inhibit TCE oxidation. The presence of TCE was found to inhibit the oxidation of each compound added over both noble metal catalysts, but it had no influence on the oxy-derivatives oxidation over the perovskite catalyst.     

Photosensitized oxidation of methyl linoleate: Secondary and volatile thermal decomposition products

Studies of photosensitized oxidation of methyl linoleate show that the greater relative concentration of 9- and 13-hydroperoxides than 10- and 12-hydroperoxides is characteristic of singlet oxygenation and not due to either simultaneous autoxidation or type 1 photosensitized oxidation. Cyclization of the internal 10- and 12-hydroperoxides accounts for their lower relative concentrations. Secondary products separated by silicic acid and high pressure liquid chromatography were characterized spectrally (IR, UV,¹H-NMR,¹³C-NMR, GC-MS). Major secondary products included diastereomeric pairs of 13-hydroperoxy-10,12-epidioxy-trans-8-octadecenote (I and III) and 9-hydroperoxy-10,12-epidioxy-trans-13-octadecenoate (II and IV); minor secondary products included hydroperoxy oxy genated and epoxy esters. Thermal decomposition of the hydroperoxy cyclic peroxides produced hexanal and methyl 10-oxo-8-decenoate as major volatiles from I and III and methyl 9-oxo-nonanoate and 2-heptenal from II and IV. Hydroperoxy cyclic peroxides may be important sources of volatile decomposition products of photooxidized fats. Presented at 72nd Annual Meeting of the American Oil Chemists Society, New Orleans, LA, May 1981.     

有机蒸气膜回收系统在PE装置上的应用

有机蒸气膜回收技术首次在气相法聚乙烯(PE)装置上应用,取得了良好效果,排放的尾气中1-丁烯体积分数由投用前的5％～6％下降到4％;冷剂的体积分数由1．5％下降到0．7％,而排放量基本保持不变。该回收系统投用后,共聚单体1-丁烯的消耗量可以降低1．0 kg/t。     

Kinetics of the thermal oxidation of poly(4-methyl-1-pentene) from volatile products using thermogravimetric analysis

The kinetics of the thermal oxidation of isotactic poly(4-methyl-1-pentane) were studied in the bulk phase using thermogravimetric analysis (t.g.a.) at temperatures from 155° to 185°C and oxygen concentration from 75 to 100% by volume. The kinetics derived from formation of volatile products using t.g.a. correspond to those from non-volatile carbonyl products obtained from infra-red spectrometry.