Key Aspects of Catalyst Design for the Selective Oxidation of Paraffins

This review examines some aspects in the development of heterogenous catalysts for the oxyfunctionalization of light paraffins. Particular attention is devoted to the raction of paraffin oxydehydrogenation to olefins and of n-butane oxidation to maleic anhydride. Most catalyst compositions are based on vanadium oxide as the main component, and the peculiar properties of this element with respect to the catalytic performance are discussed. These properties are also examined in ligh of the stability of the product of partial oxidation towards consecutive unselective oxidation reactions, and with respect to the mechanism of paraffin activation.     

新型无催化剂石蜡氧化改性研究

分别以硬脂酸和H2O2为引发剂进行了石蜡氧化改性研究,考察了空气流量、氧化引发剂的质量分数、反应温度和反应时间对石蜡氧化过程的影响,以及反应条件对氧化石蜡性质的影响,并确定了最佳的氧化工艺条件:其中氧化温度为145~150℃,氧化时间为6~8 h。并对两种引发剂的反应效果进行了比较,其中硬脂酸效果更佳。结果表明,采用上述两种引发剂,在不添加任何催化剂的前提下,选取适当的反应条件,可以制备出酸值高、颜色浅、气味轻的氧化蜡。制得的氧化石蜡性质与天然蜂蜡相近,而且能替代天然蜂蜡制成稳定的乳化蜡。     

石蜡无催化剂氧化工艺研究

研究了石蜡在一种氧化引发剂作用下的氧化反应工艺,考察了反应温度、空气量、反应时间、引发剂的用量、引发温度、引发时间等对石蜡氧化的影响。结果表明,石蜡氧化的最佳工艺条件是:反应温度140℃左右,反应时间6.5～7 h,引发剂用量2.0%,引发温度160℃,引发时间30 min,空气量0.5～0.75 m3/(h.kg)。在此条件下,制备出了具有良好性能、符合产品性能指标的氧化石蜡。     

石蜡氧化研制特种蜡工艺条件的研究

通过对20世纪石蜡氧化技术发展的回顾,总结了三年来石蜡氧化试验成果和相关美国专利。从石蜡氧化生产特种蜡的角度出发,并结合石蜡氧化合成脂肪酸生产工艺,对石蜡氧化生产特种蜡工艺中的反应温度、含氧气体通入量、反应时间、催化剂和反应器选型五个方面进行了讨论。所得出的结论不但很好地指导了氧化法研制特种蜡的试验,而且所证实的规律具有普适性,可以直接应用到特种蜡工业生产。该研究的目的是通过加快石蜡深加工和特种蜡产业化的步伐,改变我国特种蜡大量进口的现状。     

Liquid-phase oxidation of p-cresol and Substituted p-Cresols by Air

The liquid-phase oxidation of p-cresol and substituted p-cresols by air under alkaline conditions using cobaltous chloride as a catalyst and methanol as solvent, has been investigated with a view to obtain the corresponding aldehydes with sufficiently high selectivities. In the case of p-cresol, the effects of various process parameters on the reaction rate and selectivity with respect to the aldehyde have been investigated. The results obtained are likely to be useful for the development of processes for the production of industrially relevant products such as 4-hydroxybenzaldehyde, vanillin and syringaldehyde by using p-cresol as the starting material. Various alternative process schemes have been proposed and evaluated.     

Oil for polypropylene and polyester fibres

An analysis of the basic characteristics of samples of the new product Avivazh NTP with a different liquid paraffin content and a comparison with the properties of Hansa oil, highly recommended in synthetic fibre production, showed that Avivazh NTP No. 4 (6% liquid paraffin content) and NTP No. 5 (10% liquid paraffin content) is superior to the imported product with respect to its properties. Translated from Khimicheskie Volokna, No. 2, pp. 37-40, March-April, 2009.     

Substituted thiobisphenols as antioxidants: Correlation between antioxidant activities and13C chemical shifts

The antioxidant activities of ten thiobisphenols were evaluated by an oxygen-absorption method at 60°C in tetralin and determination of peroxide values at 160°C in paraffin. For the 4,4′-thiobisphenols, alkyl groupsortho to the phenolic hydroxyl groups increased the induction period compared to that of other thiobisphenols for both oxidation of tetralin and paraffin. The data on electrochemical oxidation potentials that were determined by linear-sweep voltammetry and the¹³C nuclear magnetic resonance chemical shifts (δ) of these compounds were associated with antioxidant activities. In particular, the activities exhibited during the induction period closely correlated with the¹³C chemical shifts of ipso-carbon of the OH substituent.     

Reactivity of t-butyl chromate resins with substituted α-phenylethanols: A kinetic study

Polystyrene and polyacenaphthylene supports were functionalized to generate a t-butyl chromate function and the resulting polymer-supported reagents were used for the oxidation of alcohols. They were found to oxidize primary and secondary alcohols to the corresponding carbonyl compounds in quantitative yields. Oxidation of differently substituted α-phenylethanols was attempted for this purpose and the kinetics of oxidation reactions was studied. The reaction was found to be first order with respect to the substrate, the reaction being carried out with an excess of the t-butyl chromate reagent. The rate of oxidation was also found to be dependent on the nature of the substrate, concentration of the reagent function, and the nature and concentration of the acid catalyst used. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 799–804, 1998     

Catalytic dense membranes of doped Bi4V2O11 (BIMEVOX) for selective partial oxidation: chemistry of defects versus catalysis

A catalytic dense membrane reactor (CDMR) is used to physically separate the reaction step from the reoxidation of the catalyst. By decoupling the redox mechanism prevailing in mild oxidation of hydrocarbons, the operating conditions may be optimized resulting in an increase of selectivity. The membranes are made up of BIMEVOX oxides, obtained by partial substitution of V in γ-Bi₄V₂O₁₁ by ME (Co, Cu, Ta). Experiments performed on BIMEVOX dense membranes using propene and propane are described in terms of, (i) active sites on polished or unpolished surfaces, (ii) operating conditions (T, pO₂ in the high oxygen partial pressure compartment), which determine the selectivity, either to mild oxidation products (acrolein, hexadiene, CO), or to partial oxidation products (CO, H₂), and, (iii) nature of ME cations and relative properties. The discussion deals with the respective role of electronic versus oxide ion conductivities which depend on defects in the structure as well as on the redox properties of cations.     

Oxidation of p-methoxyphenol on SnO2–Sb2O5 electrodes: Effects of electrode potential and concentration on the mineralization efficiency

The oxidation of p-methoxyphenol in aqueous solution on antimony-doped tin oxide has been studied, and the effects of applied potential and initial PMP concentration upon the oxidation rate have been identified. The concentration decay of PMP during its electrooxidation follows first-order reaction kinetics. Analysis solution during electrolysis using UV–Vis spectroscopy revealed that under some experimental conditions partial oxidation of PMP occurs. The principal products were p-benzoquinone and aliphatic (maleic and oxalic) acids. The Faradaic efficiencies for oxidation at different applied potentials were determined from the UV–Vis spectra obtained. It is shown that production of CO₂ was very low at potentials below 2.3 V with respect to the saturated calomel electrode, and that at more positive potentials mineralization to CO₂ decreased as the concentration of PMP in solution increased.     

Some aspects that affect the selective oxidation of paraffins

This paper examines the most important factors that affect the functionalization of light alkanes by means of selective oxidation. The state-of-the-art in paraffin oxidation and the main features that affect the choice of the reactor and the process configuration are discussed.     

Selection of Natural Extracts for their Antioxidant Capacity by Using a Combination of In Vitro Assays

Numerous different in vitro assays, labeled as “antioxidant assays,” are used intensively to predict the antioxidant capacity of phenolic compounds. Most of these methods give valuable information in terms of chemical reactivities but also present some weaknesses. It may be difficult to use them to predict antioxidant capacity in real conditions. Indeed, lipid oxidation is a complex reaction, with numerous paths and components, and antioxidant action can occur via a multitude of mechanisms, especially when different phases coexist in the lipid-based formulation. Yet, correctly combining selected in vitro methods to extract complementary information with respect to antioxidant behaviors would be much better and will help reducing the gap between prediction and efficacy in the finished product. Thus, we hereby propose a methodology to evaluate the antioxidant properties of 12 selected natural polyphenolic extracts based on the appropriate combination of in vitro assays. The scores obtained with the DPPH test, the measure of the chelation capacity, the evaluation of antioxidants efficiency in emulsions (CAT and VESICAT assays), or in bulk oils were submitted to a statistical treatment. This analysis allowed a ranking on their global antioxidant capacities and the creation of clusters depending on their mechanisms of action and the type of media where the tests were performed.     

Properties and performance of Pd based catalysts for catalytic oxidation of volatile organic compounds

Catalytic oxidations of volatile organic compounds (VOCs) (benzene, toluene and o-xylene) over 1 wt% Pd/γ-Al₂O₃ catalyst were carried out to assess the properties and performance of the Pd based catalyst. The properties of the prepared catalysts were characterized by the Brunauer Emmett Teller (BET) surface area, H₂ chemisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The experimental results revealed a significant increase in VOCs conversion with the lapse of the reaction time at certain reaction temperatures. On the other hand, the hydrogen pretreated 1 wt% Pd/γ-Al₂O₃ catalyst, whose shape of conversion curve is similar to the non pretreated catalyst, led the conversion curves for the total oxidation of VOCs to be shifted to lower temperature. It was also found that such increases in VOCs conversion were highly dependent on the oxidation state of Pd and the growth of Pd particles in the catalyst. In addition, in the case of the catalyst consisting of the same oxidation state (PdO/Pd²⁺ or Pd⁰), the particle sizes possibly play a more important role in the catalytic activity. The activity order of 1 wt% Pd/γ-Al₂O₃ catalyst with respect to the VOC molecule was o-xylene > toluene > benzene.     

The efficient liquid‐phase oxidation of aromatic hydrocarbons by molecular oxygen in the presence of MnCO3

BACKGROUND: The liquid‐phase catalytic oxidation of aromatic hydrocarbons by molecular oxygen is a commercially important process. We consider the MnCO₃‐promoted oxidation of toluene to produce benzaldehyde and benzoic acid. In this investigation, toluene was oxidized with 25.0% conversion and 80.8% selectivity with respect to benzoic acid in the presence of MnCO₃ under 1.0 MPa of oxygen at 190 °C for 2 h. RESULTS: Moreover, the oxidation of other aromatic hydrocarbons, such as ethylbenzene, p‐xylene, m‐xylene, o‐xylene, and p‐chlorotoluene, were also efficiently promoted by MnCO₃. CONCLUSION: It is concluded that an efficient oxidation of aromatic hydrocarbons can be achieved in the presence of MnCO₃ under solvent‐free conditions. The catalytically active species are high‐valence Mn generated via the action of MnCO₃ with oxygen. Copyright © 2007 Society of Chemical Industry     

Formation of fine magnetite particles by oxidation of aqueous suspensions of ferrous hydroxide

Fine magnetite particles were prepared by oxidation of aqueous ferrous hydroxide suspensions in a bubble column equipped with an internal concentric draft tube. The oxidation reaction rate could be expressed apparently as zero-order with respect to the concentration of total ferrous species and first-order with respect to the concentration of dissolved oxygen. The final particle size generally decreased with increasing reaction rate. The geometric Standard deviation of size-distribution ranged from 1.20 to 1.35 under the present experimental conditions, and increased with an increase in reaction rate.     

Effect of carbon content on the oxidation resistance and kinetics of MgO-C refractory with the addition of Al powder

The effect of carbon content of MgO-C refractory was studied with respect to the physical properties, oxidation resistance and kinetics. The oxidation mechanism was investigated by calculating the relevant parameters of oxidation and analyzing the evolutions of phases and microstructures. The oxidation resistance of MgO-C refractory was influenced by the indirect oxidation of carbon through the formation of the MgO constituent layer. The effect of indirect oxidation resulted in the MgO-C refractory with 3 wt% carbon content having a lower oxidation rate and weight loss rate when fired at 1600 °C than when fired at 1400 °C. The oxidation kinetics results based on shrinking core model showed that the effective diffusion coefficient and full oxidation time increased with the increasing of carbon content. This seemingly paradoxical result was mainly due to the effect of the molar density of carbon prevailing over that of the effective diffusion coefficient in the oxidation process.     

Photocatalyzed oxidation of crude oil residue by beach sand

Crude-oil residue in contact with beach sand and air was observed to undergo photocatalytic oxidation on exposure to light from a high pressure mercury vapor lamp. The kinetics of the heterogeneous reaction were of zero order in the mass of organic material present. Carbon dioxide was the oxidation product. No dark reaction occurred. The beach sand used contained magnetite and ilmenite as minor constituents. These materials are known to have catalytic properties for hydrocarbon oxidation. The results point to a self-cleaning process provided by the natural environment for the photocatalytic removal of crude-oil contamination from sandy beaches.     

Oxidation and adsorption of arsenic species by means of hybrid polymer containing manganese oxides

The aim of this work was a comprehensive study of the oxidative and sorptive properties of a hybrid polymer containing manganese oxide toward As(III) and As(V). A poly(styrene‐divinylbenzene) copolymer containing oxidative functional groups (? SO₂NBrNa) was used as the supporting material for MnO₂. The inorganic component was deposited as a result of the oxidation reaction of Mn(II) with oxidative groups of the host polymer. The surface of the polymer matrix was evenly covered with a thin layer of manganese oxide. The obtained product (R/S/Mn) exhibited high oxidative capacity over a wide pH range (2–12); however, under acidic and neutral conditions, the reaction ran significantly faster. The studied material shows some sorption properties but its sorption capacity is much lower than its oxidation capacity. The treatment, in a column regime, of the arsenic solution containing 1 mg As(III) dm^?3 and coexisting ions in concentrations similar to those in natural waters, confirmed the excellent oxidation capacity of the obtained product. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39489.     

高碳醇的合成

首次选用石蜡、硼酸为原料,通过液相氧化反应合成硼酸酯,再与氢氧化钠发生水解反应制得高碳醇。应用红外定量分析原理对其含量进行分析。得到制备高碳醇的较优工艺条件：n（石蜡）∶n（硼酸）=1∶4,氧化时间为6 h,氧化温度为170℃,水解温度为80℃,水解时间为1 h。产物收率约为12.7%。     

Quality changes in edible oils at high temperature. Kinetic analysis

In our paper we present the results of the analysis of three oil types which have been heated to 140°C: soybean, sunflower, and rapeseed. As a result of the oxidation reaction the reaction products caused a reduction of oil quality. Existence of fat decomposition products is reflected for example in the increase of peroxide number and decrease of savoriness. In our experimental analysis, we applied kinetic functions of rate and slowness, whose basic parameters are the process order n and the rate constant w_n. In our paper we have specified a method for determining the increase of the peroxide number rate and the decrease of the savoriness rate with respect to the oils under consideration; in addition the methods for comparing the rates for changing quality parameters have been studied.