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Thoeretical Study Of The Pyrolysis Mechanism Of Oil Shale Kerogen Molecule In The First Step

Posted on:2019-01-02Degree:MasterType:Thesis
Country:ChinaCandidate:Y F WangFull Text:PDF
GTID:2321330545492087Subject:Chemical Engineering and Technology
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Oil shale is one of the most important alternative energy resources of oil,and kerogen is the main organic substance in oil shale to produce oil.When the pyrolysis temperature reached475?during the first stage of oil shale pyrolysis,the output amount of hydrogen sulfide gas reached the highest value,which proved that sulfur elements from inorganic sulfate,elemental sulfur and aliphatic sulfur were involved in the first stage of pyrolysis reaction process.A great nunmber of thiol radicals attacked H atoms in the kerogen and formed hydrogen sulfide gas.This thesis used density functional theory?DFT?of quantum chemistry calculation methods,calculated level in B3LYP/6-311+g?d?,explored the breaking reaction activation energy and bonding properties of C-H bonds under the attack of thiol group,and calculated the activation energy and reaction step of the breaking reaction of C-H bond under the attack of thiol on the small molecule model of kerogen.This thesis has studied the radical reactions induced by thiol during the first step of pyrolysis of kerogen,and perfected the raction mechanism of the first step of kerogen pyrolysis.The conclusions obtained are summarized as follows:?1?In this paper,91 small molecule models with C-H bonds in different chemical environments were extracted from the 2D model of the six different kinds of kerogen average molecules that have been proposed.The effects on the reaction site activity aroused by the branching degree of the carbon skeleton,the type of functional group and the functional group substitution position in the pyrolysis of kerogen were studied.The results showed that:in the carbon skeleton structure of kerogen,the higher branching degree leaded to the lower activation energy of the bond breaking reaction,because the electropositive property was more dispersed after the removal of H.Among the various functional groups obtained by characterization of kerogen structure,the activity of the C-H bond connected to the nitrogen containing functional group such as amino and imino groups was most obviously increased,however,the sulfinyl group,carboxyl group and ester group would reduce the reactivity of C-H bond.The electrons of the substituted hydrocarbon on the aromatic ring were affected by the aromatic ring conjugation,and the C-H bond was more easily attacked by the thiol group.In the heterocyclic structure,the change of the activation energy of the substituted hydrocarbon in the ortho position,meta position and para position of the heteroatom was different,and the reaction activity was the highest when it was attached in the ortho position.When two functional groups are simultaneously attached to the C-H bond,the activation energy of the bond breaking reactions was significantly reduced.?2?To investigate the influence of grid structure and unsubstituted functional groups on the C-H bond of active sites in kerogen macromolecules,11 small models of C-H bonds of which the breaking reaction activation energy is below 9 kcal/mol were reconstituted in the chemical environment of kerogen.The results of the density functional calculation study of reconstructed C16-C400 kerogen model showed that:the space ring structure composed of carbon skeleton and functional groups didn't affect the activity of C-H bond.When there were other functional groups such as carbonyl group,aromatic ring connected with the functional groups which could reduce the breaking reaction activation energy of the C-H bond,the activation energy of the breaking reaction increased due to the weakening effect to the functional group linked with C-H bond.In the carbon skeleton,when the functional group was attached to a position where the distance to C-H bond was more than three chemical bonds,the effect on the activity of the C-H bond was negligible.During the first step of kerogen pyrolysis,the highly reactive C-H bond was attacked by the thiol group at first and losed the H atom,then the kerogen macromolecules formed multiple unstable intermediates,and the consequent electron recombination caused a chain reaction to split kerogen macromolecules into C16-C400 hydrocarbons.The results of this study has improved the mechanism of the first step pyrolysis reaction by taking the participation of free radicals into account.
Keywords/Search Tags:density functional theoretical, oil shale, kerogen pyrolysis, reaction activation energy barrier
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