Primary Microcalorimetry Study Of Typicle Phase Transition Process

Microcalorimetry can get more details from chemical processes.This article uses microcalorimetry,together with other measure methods on structure and component,to study typical phase transition process and its reaction mechanism in geological process.This article studies 3 types of phase transition processes as combination reaction(A+B?C)of hydration and ion complexation on kaolinite,constant transition process(A?B?C)of the thermal evolution process of Schwertmannite,and decomposition reaction(A?B+C)of hydrocarbon generation from kerogen.I have mastered how to study phase transition process by microcalorimetry and have learned some of the reaction mechanism in this 3 processes:(1)Hydration and cation adsorption on kaolinite is influenced by the types of metal cations and the temperature.Alkali metal cations with larger radius have stronger interaction with kaolinite surface,and are more likely to form inner-sphere complexation on kaolinite surface.It follows the sequence of Cs+ > K+ > Na+.Higher temperature benefit the inner-sphere complexation on kaolinite with a higher heat release of kaolinite mixed with salt solution,and meanwhile the increase of innersphere complexation cause the decrease of outer-sphere.The heat-time curve of kaolinite mixed with salt solution shows that hydration and cation adsorption on kaolinite occur rapidly and reach the maximum heat release in about 5 minutes.But the whole adsorption reaction process lasts about 0.5 hours.The reaction duration of higher concentration is slightly longer,and that of higher higher temperature is shorter.The reaction duration of different cation solutions is in the order of Cs+ > K+ > Na+.(2)Schwertmannite decomposes and transforms into hydronium jarosite and hematite as temperature rising.Schwertmannite successively undergo several processes during temperature increase as desorption of adsorption water,transformation of sulfate configuration,decomposition of schwertmannite with the loss of structural water,recrystallization forming hydronium jarosite,recrystallization forming hematite nanocrystal,recrystallization from hematite nanocrystal to larger crystal,decomposition of hydronium jarosite and decomposition of hematite.We observe 6 discrete endothermal peaks in the heat-temperature curve at a very slow heating rate.They belong to the first 5 processes because the desorption of adsorption water is divided into 2 conditions of high energy adsorption and low energy adsorption corresponding to 2 endothermal peaks.The sulfate radical in schwertmannite has similar property with the oxyanions of heavy metal elements,leading to the replacement of sulfate radical by oxyanions of heavy metal elements and the adsorption of heavy metal elements in schwertmannite.We have observed that S from sulfate radical in schwertmannite in the dry environment can only migrate in 3 processes of decomposition of schwertmannite with the loss of structural water,recrystallization forming hydronium jarosite and decomposition of hydronium jarosite.Heavy metal elements react similar with S from sulfate radical.So there will be the spread of heavy metal elements in dry soil environment during these 3 processes.We can predict the beginning temperature and the peak temperature of these 3 processes in any geological condition by the calculation of activation energy of the 6 peaks observed in the heattemperature curve.(3)Sulfur groups make great contribution to the hydrocarbon generation processes of kerogen.2 exothermal peaks with low activation energy is found in heat-temperature curve of microcalorimetry experiment,and is proved belonging to hydrocarbon generation of sulfur group cracking in kerogen by thermogravimetry-mass spectrometry experiments.These 2 peaks are respectively corresponding to the completely cracking reaction of R3-C-S-R' groups producing heavy oil and partly cracking reaction of R-(C=S)-R' groups forming R-(C?S)+ cation groups with heavy oil.The sulfur groups in kerogen can reduce the activation energy of the hydrocarbon generation reaction,so that the hydrocarbon generation reaction can occur at a lower temperature.The oil from hydrocarbon generation of sulfur group cracking has more carbon and is mainly heavy oil,while the oil from hydrocarbon generation of C-C group cracking has less carbon and is mainly light oil.The sulfur group can also join in the gas generation process of kerogen with main product of wet gas.In addition,the C=S group can also produce a large amount of ethylene and propylene by complete cracking at a temperature slightly higher than the temperature of gas generation process.