| Coal-tar pitch(CTP),a residual substance after distillation of coal tar,which has good adhesion,permeability,thermoplasticity and coking ability,is widely used in the production and processing in the field of building sealants,road materials,various new carbon materials and so on.CTP is rich in polycyclic aromatic hydrocarbons(PAHs),and most of them have carcinogenicity,teratogenicity and gene mutagenicity.The practical application of coal tar-pitch containing abundant PAHs has adverse effects on human health,and also causes pollution to the ecological environment,so those PAHs must be removed or controlled.Different with published chemical modification methods of coal-tar pitch,this paper adopts Friedel-Crafts alkylation reaction to reduce the content of PAHs.At first,anthracene,a model compound,was ultilized to optimize the alkylation reaction conditions.With the help of GC-MS and FTIR characterization,the reaction kinetic rate equation was caculated,and also the mechanism of chemical reaction had been deduced.After that,the reaction activtity of four model compounds were made a comparison under the same condition.Some methods to improve the conversion rate of anthracene,like modifying molecular sieves,raplacing alkylating agents,screening new catalysts,were tried.Finally,the optimized reaction conditions,according to the alkylation reaction of anthracene,were applied to the test of reducing toxic and mofication in coal-tar pitch,and modified coal-tar pitch was evaluated by removal rate of toxicity.The conclusions of this article are as follows:(1)Anthracene and 1-hendecene went on alkylation reaction in a high-presssure autoclave(250 mL),where the reaction was catalyzed by HY molecular sieve with cyclohexane as solvent.The optimized process conditions were as follows:reaction temperature of 180?,reaction pressure of 2 MPa,reaction time of 2 h,molar ratio of anthracene to olefin as 1:1,mass fraction of catalyst of 8%.The alkylation reaction of anthracene with 1-hendecene conforms to the mechanism of electrophilic substitution reaction of carbocation,accompanied by many side reactions such as polyalkylation,isomerization,cyclization,polymerization,cracking reaction and so on.(2)The kinetic rate equation of anthracene alkylation was estimated by the control variable method,and the overall reaction order was 2.26.The change curves of conversion of anthracene(X_A)with time(T)were stimulated by Origin software,and the mathematical relationship between the reaction rate constant and the reciprocal of temperature was used to futher calculate the activation energy.Exp Dec equation to simulate the first-order reaction process figured out the activation energy value of 16.14 kJ/mol,and logistic equation was used to model the second-order reaction process,whose activation energy value was116.46 kJ/mol.(3)5 kinds of catalysts,such as HY molecular sieve,H?molecular sieve,phosphotungtic acid,p-toluenesulfonic acid and anhydrous aluminum chloride,were separately used in the alkylation reaction of anthracene,where the other raction conditions were the same.Compared with the other three model compounds,like fluoranthene and pyrene and benzo[a]pyrene,a conclusion could be made that with the increase in the number of polycyclic aromatic ring,the activity of alkylation reaction had a trend of early increase and then decrease,which indicated that the activity of alkylaton is not only related with electron number of benzene ring,and also the minimum activation energy.(4)Eight kinds of metal ions consisting of iron,chrome,manganese,plumbum,calcium,copper,cobalt,aluminum,were loaded in HY zeolite and H?zeolite,and the experiment results show that modified H?zeolite can improve the catalytic activity of anthracene alkylation,while the catalytic activity of modified HY molecular sieve is opposite,and that the selectivity to target product of two modified molecular sieves is enhanced to same extent.(5)The above optimized technology of anthracene alkylation in atmospheric reaction device,namely 1-hexadecene as modification reagent,phosphotungtic acid as catalyst,the reaction temperature of 170?,the reaction time of two hour,was applied to the detoxification and modification test of coal-tar pitch.when the mass ratio of mixed solvent at?(1-hexadecene):?(cyclohexane)=4:1,the concentration of toxic materials in modified CTP dropped maximum to 67.63g/Kg,and the total reduction rate was 41.24%,and Benzo[a]pyrene equivalent(BaPeq)reduction rate in the modified CTP was 45.97%.When the mass ratio of mixed solvent at?(1-hexadecene):?(toluene)=4:1,the concentration of toxic substances in CTP declined maximum to 71.5 g/kg,and the total reduction rate decreased 34.32%,and BaPeq reduction rate in the modified CTP was 33.99%.TG and IR showed that there were polyalky substituted polycyclic aromatic hydrocarbons in the modified filtrate of CTP,while the total amount of PAHs in the modified residue decreased,and its thermal stability increased as well as the coking rate. |
PDF Full Text Request