Quantum Chemistry Study On Alkylation Reaction Of 16 Polycyclic Aromatic Hydrocarbons In Coal Tar Pitch

Under the catalysis of HF,the alkylation reaction of 16 PAHs in coal tar with olefin was studied based on the density functional theory by using Gaussian 09 package.In the process of the above reseach,the 6-31G(d)basis set and b3 lyp method were used.The alkylation reaction mechanism of PAHs with olefins catalyzed by HF was revealed in this paper,which could provide theoretical help for the selection of catalysts.The difficulty level of reactions of 16 PAHs with ethylene was achieved based on the calculated activation energies,which could provid guidance to select model compounds for the modification of CTP.The alkylation reaction of Benzo [a] pyrene which was as the model compound with linear olefins was studied and the rules of alkylation of PAHs with olefins were obtained,which could provide gudience to selecting the proper modifier for the modification of the coal tar pitch.The main conclusions are obtained in this paper as follows:1.Based on the analysis of the properties of the single and double bonds of carbon-carbon bonds of 16 PAHs,it was found that from the view of the bond energy fluorine has the most uniform bond energy distribution.So fluorene was the least active substance in these 16 PAHs.The distribution of the bond energy of the carbon-carbon bonds of the remaining 15 PAHs was quite different,so the reaction sites could be divided into active sites and inactive sites.2.The reaction enthalpy of the alkylation 16 PAHs with ethylene was approximately between 10 kcal/mol~25 kcal/mol.Among 16 PAHs,there was little difference in thermodynamic stability of the all kinds products which were achieved by the alkylation of naphthalene,acenaphthylene,acenaphthene,fluorene,anthracene,pyrene,fluoranthene,benzo[k]fluoranthene and indeno[1,2,3-cd]pyree respectively with ethylene,and the enthalpy of reaction was about between 20 kcal/mol~25 kcal/mol;however,the thermodynamic stability of the products which were obtained by the alkylation of phenanthrene,benzo[a]anthracene,chrysene,benzo[a]pyrene,benzo[b]fluoranthene,dibenz[a,h]anthrace and benzo[g,h,i]perylene respectively with ethylene was quite different,and the enthalpy of reaction was about between 10 kcal/mol~25 kcal/mol.The difference between the maximum reaction enthalpy and the minimum enthalpy was about 15 kcal/mol.3.The alkylation reaction mechanism of 16 PAHs with ethylene was discussed according to the adsorption enthalpy and the activation energy.The reactants could go through three processes to form the six-membered-ring transition state.In any reaction process,ethylene molecules were activated by HF and the fluorine atom helped to remove hydrogen from the aromatic rings.Acenaphthylene,chrysene,benzo[a]pyrene and benzo[g,h,i]perylene were selected from 16 PAHs as objects of study,and the activation energy of alkylation reaction of the four substances were calculated.The calculated activation energy located in two discontinuous ranges.The lower energies were between 35 and 41 kJ/mol and higher energies were between 58 and 59 kJ/mol.An obvious feature of the inactive sites with higher activation energies was that the carbon was linked by two carbon atoms which had one C-H bond respectively.The activation energies of active sites of the rest 12 PAHs were calculated in the following calculations.The difficulty level of reactions of 16 PAHs with ethylene was achieved based on the calculated activation energies.Among the 16 PAHs,the substance with lowest activation energy was benzo[a]anthracene and the substance with highest activation energy was fluorine.This paper provided guidance to select model compounds for the modification of CTP.4.The activation energy of alkylation reaction of linear alkenes and benzo[a]pyrene was about between 36 kcal/mol~48 kcal/mol.With the increase of the carbon chain,the activation energy of the alkylation reaction of benzene[a]pyrene with olefin decreased gradually,which indicated that the longer linear olefin was easier to react with PAHs.The double bond of the linear olefin moved into the middle carbon atoms,which formed different isomers of olefin.The activation energy of the alkylation of benzo[a]pyrene with these isomers of olefin increased,which indicated that the olefin with the double bond at its ends was easier to react with PAHs,but the olefin with the double bond at its middle was not easy to react with PAHs.