Low-temperature oxidation

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

At low temperatures, oxidation with chromic acid gives propynal [624-67-9] C2H2O (14), or propynoic acid [471-25-0] C2H2O2 (15), which can also be prepared in high yields by anodic oxidation (16). 

Perfluoroepoxides have also been prepared by anodic oxidation of fluoroalkenes (39), the low temperature oxidation of fluoroalkenes with potassium permanganate (40), by addition of difluorocarbene to perfluoroacetyl fluoride (41) or hexafluoroacetone (42), epoxidation of fluoroalkenes with oxygen difluoride (43) or peracids (44), the photolysis of substituted l,3-dioxolan-4-ones (45), and the thermal rearrangement of perfluorodioxoles (46). 

Propane. The VPO of propane [74-98-6] is the classic case (66,89,131—137). The low temperature oxidation (beginning at ca 300°C) readily produces oxygenated products. A prominent NTC region is encountered on raising the temperature (see Fig. 4) and cool flames and oscillations are extensively reported as compHcated functions of composition, pressure, and temperature (see Fig. 6) (96,128,138—140). There can be a marked induction period. Product distributions for propane oxidation are given in Table 1. 

Free radicals are initially generated whenever polymer chains are broken and carbon radicals are formed. These effects occur during manufacture and in service life. Many elastomers are observed to oxidize at relatively low temperature (about 60°C), where carbon-hydrogen and carbon-carbon bond cleavages are highly unlikely. It has been demonstrated [52] that traces of peroxides impurities in the rubber cause low-temperature oxidation of rubber. These initiating peroxides are present in even the most carefully prepared raw rubber polymer [53]. 

Pathway temperatures must be strictly controlled (especially in single-phase systems) to create a balance between low-temperature oxide dissolution and high-temperature mass transfer limitations. 

Low-temperature oxidation of sulphilimines with potassium permanganate in dioxane... 

S. Tsubota, D.A.H. Cunningham, Y. Bando, and M. Haruta, Preparation of nanometer gold strongly interacted with Ti02 and the structure sensitivity in low-temperature oxidation of CO, in Preparation of catalysts VI, G. Ponchelet, ed. (1995), pp. 227-235. 

The low-temperature oxidation of hydrogen as in the cap of a lead-acid storage battery is an example of heterogeneous catalysis. It is proposed to model this reaction as if it were homogeneous ... 

TS-1 is a material that perfectly fits the definition of single-site catalyst discussed in the previous Section. It is an active and selective catalyst in a number of low-temperature oxidation reactions with aqueous H2O2 as the oxidant. Such reactions include phenol hydroxylation [9,17], olefin epoxida-tion [9,10,14,17,40], alkane oxidation [11,17,20], oxidation of ammonia to hydroxylamine [14,17,18], cyclohexanone ammoximation [8,17,18,41], conversion of secondary amines to dialkylhydroxylamines [8,17], and conversion of secondary alcohols to ketones [9,17], (see Fig. 1). Few oxidation reactions with ozone and oxygen as oxidants have been investigated. 

Air as a steam additive results in an increased rate at which oil is recovered because of low-temperature oxidation reactions [894]. 

Cap Gas. Both crude and asphaltene-free oil were used to determine the consequences of low-temperature oxidation. It was found that the oxygen content in an artificial gas cap was completely consumed by chemical reactions (i.e., oxidation, condensation, and water formation) before the asphaltene content had reached equilibrium. 

Haruta M, Tsubota S, Kobayashi T, et al. 1993. Low-temperature oxidation of CO over gold supported on Ti02, a-Ee203, and C03O4. J Catal 144 175-192. 

In the laboratory of Professor R.G. Moore at the University of Calgary, kinetic data were obtained using bitumen samples of the North Bodo and Athabasca oil sands of northern Alberta. Low temperature oxidation data were taken at 50, 75, 100, 125 and 150"C whereas the high temperature thermal cracking data at 360, 397 and 420"C. 

The two-component models are "too simple" to be able to describe the complex reactions taking place. Only model D was found to describe early coke (COK) production adequately. For Low Temperature Oxidation (LTO) conditions the model was adequate only up to 45 h and for cracking conditions up to 25 h. 

Figures 18.13, through 18.17 show the experimental data and the calculations based on model I for the low temperature oxidation at 50, 75, 100, 125 and 150TZ of a North Bodo oil sands bitumen with a 5% oxygen gas. As seen, there is generally good agreement between the experimental data and the results obtained by the simple three pseudo-component model at all temperatures except the run at 125 TT. The only drawback of the model is that it cannot calculate the HO/LO split. The estimated parameter values for model I and N are shown in Table 18.2. The observed large standard deviations in the parameter estimates is rather typical for Arrhenius type expressions.

Figure 18.13 Experimental and calculated concentrations of Coke (COK) "A , Asphaltene (ASP) o" and Heavy Oil + Light Oil (HO+LO) "a" at 50 °C for the low temperature oxidation of North Bodo oil sands bitumen using model l.

Table 18.2 Estimated Parameter Values for Models I and Nfor the Low Temperature Oxidation of North Bodo Oil Sands Bitumen...

Hanson, K. and N. Kalogerakis, "Kinetic Reaction Models for Low Temperature Oxidation and High Temperature Cracking of Athabasca and North Bodo Oil Sands Bitumen", NSERC Report, University of Calgary, AB, Canada, 1984. 

The cracking and the low-temperature oxidation of crude oils have been studied previously in order to simulate the thermal transformations of oil to gas and coke during enhanced oil recovery (1-6). Other authors characterize the thermal modifications of oil in the presence of a vapor phase (7)-... 

Aromatics Resins — Asphaltenes — coke where the resin + asphaltene content remains constant and asphaltenes are the main precursors of coke. The same observations have been made in low-temperature oxidation experiments (6). 

Table I. Values of Kinetic Parameters for Low Temperature Oxidation of Athabasca Bitumen...

Toshio, S. and Y. Hiroyuki, Hydrogen as an ignition-controlling agent for HCCI combustion engine by suppressing the low-temperature oxidation, 32(14), 3066-3072,2007. 

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