Low-temperature Oxidation Stage Research Articles

New view on the oxidation mechanisms of crude oil through combined thermal analysis methods

In the previous study, the oxidation behavior of four Chinese crude oils (Oil 1 to 4) in the presence and absence of rock cuttings was investigated by thermogravimetry/derivative thermogravimetry (TG/DTG) techniques and oxidation tube experiments. The present work investigates the thermal behavior of these oils by combining DTG–DTA method. First, we conducted comparative analysis about mass loss rate from DTG curves and endothermic/exothermic phenomenon from DTA curves attempting to clarify the endothermic or exothermic mechanism in crude oil low-temperature oxidation. Finally, we combined the thermal analysis method with low-temperature oil oxidation tube experiment in porous media to ascertain, whether the two methods are consistent in the aspect of low-temperature oxidation mechanism of crude oil by O2 consumption rate and CO2 generating rate (carbon bond stripping reaction rate). Results show that crude oils undergo an endothermic oxidation behavior during low-temperature oxidation stage, suggesting the decomposition of hydrocarbon components. Clay can play a catalytic effect on low-temperature oil oxidation. The results of DTG–DTA tests can also better reflect oil oxidation mechanism under real conditions.

A New Method to Quantitatively Partition "Three Zones" of Coal Spontaneous Combustion Based on Key Parameters

the paper determines and calculates the parameter of coal temperature distribution rule and oxidation thermal intensity in the stage of low temperature oxidation of radiating heating, builds the mathematic model with 5 key parameters which affect the coal spontaneous combustion, newly defines a probability function to descript the coal spontaneous combustion dangerous degree, then puts forward a quantitative evaluating parameters: the different value of the indicator represents different dangerous area, a fully extinguished zone, a base extinguished zone, a heat dissipation zone and a oxidation of radiating heating zone. The results have a good accordance with the actual observations value.

Initial stage in the low-temperature oxidation of coal in air

The main chemical reactions during the initial stage of low-temperature coal oxidation in air are discussed. The contribution of these reactions to the overall oxidative process is determined by the coal structure. Water molecules may accelerate coal oxidation by the formation of aldehyde fragments that react with molecular oxygen by a radical-chain reaction, to produce acidic structures. However, they may also slow the reaction of oxygen with coal by screening the active centers.

Study on Coal Spontaneous Combustion Characteristic Structures Affected by Ionic Liquids

According to modern coal chemical structure theory, the active chemical structure categories in coal spontaneous combustion process were summed up, which show that the coal spontaneous combustion characteristic structures are dynamic, such as methyl, methylene, hydroxyl, carbonyl and others in coal bridge bonds and side chains. The amount and activity of these structures play an important role in coal low temperature oxidation stage. Based on this, the article analyzed the effect of ionic liquids to coal spontaneous combustion characteristic structures, which indicates that the structure amount of coal affected by ionic liquids decreases obviously compared with raw coal.

Thermal transformation of penwithite

Thermal transformation of penwithite in air has been studied minutely in the temperature range up to 1200°C, using the differential thermal, thermogravimetric, chemical, and X-ray analyses. A correlation of thermal and chemical data with phase determinations shows that the chemical reactions caused thermally are dehydration, oxidation of a part of Mn2+ to Mn4+, and reduction of Mn4+ formed at the former stage to Mn2+, in order of increasing temperature, and penwithite transforms, in general, into braunite at the low-temperature oxidation stage and into rhodonite at the high-temperature reduction stage. The braunite formed at the low-temperature oxidation stage contains a greater amount of SiO2 in its structure than naturally occuring braunite. At the high-temperature reduction stage, Fe3+, if it is present remarkably, combines with manganese oxides and forms jacobsite, and then excess SiO2 is released as silica minerals.