| Polyethylene naphthalate（PEN）possesses excellent chemical and physical properties and is widely used in electronic appliances,agriculture,national defense technology and other fields.As an important precursor for the synthesis of PEN,2,6-naphthalenedicarboxylic acid（2,6-NDA）is mainly obtained by direct oxidation of 2,6-disubstituted naphthalene.However,the synthesis cost of the existing naphthalene ring disubstituted compounds is relatively high and the process is relatively complicated.Therefore,how to prepare 2,6-disubstituted naphthalenes economically and efficiently is the current research focus.Compared with the process of synthesizing 2,6-dialkylnaphthalene by alkylation with lower selectivity and more difficult separation and purification,the preparation process of 2-methyl-6-acylnaphthalene by acylation with 2-methylnaphthalene（2-MN）has the advantages of more complete reaction and high selectivity.2-MN is an important component of tar,the main by-product of coal pyrolysis and coking process.Its refined utilization can increase the added value of tar and is conducive to promoting the efficient utilization of coal resources.In this thesis,2-MN was used as the raw material to optimize the acylation process,the recrystallization and purification process of the acylated product.The main research contents and conclusions are as follows:2,6-MAN and 2,6-MPN were synthesized from 2-MN with acetyl chloride（AC）and propionyl chloride（PC）as acylating agent and aluminum trichloride（Al Cl3）as catalyst in nitrobenzene solvent.The results from the analyses of GC-MS,FT-IR,1D-NMR and 2D-NMR showed that the main component of acylation products is 2,6-MAN containing C6-substituted acetyl and 2,6-MPN containing C6-substituted propionyl.The effects of different factors on the acetylation of 2-methylnaphthyl were investigated by orthogonal experiments.The ratio of reactants exerted the most influence on the product yield,followed by the addition temperature,the reaction time,and the reaction temperature.The reaction temperature exerted the most influence on the product purity,followed by the ratio of reactants,and the addition temperature,reaction time.The optimized conditions were obtained at the ratio of n（2-MN）/n（AC）/n（Al Cl3）being 1/1.20/1.45,the reaction temperature of 25℃,the reaction time of 4 h,and the addition temperature of-5 to-2℃.The products yield can reach 90.95%,along with the purity of 2,6-MAN being 76.32%.For the propionylation process,the optimized conditions were obtained at the ratio of n（2-MN）/n（AC）/n（Al Cl3）being 1/1.30/1.60,the reaction temperature of 25℃,the reaction time of 5 h.The products yield can reach 91.93%,along with the purity of 2,6-MPN being 88.03%.Compared with the acetylation process,the complex intermediate formed by propionyl with Al Cl3 has greater steric hindrance and shows higher product selectivity at the6-position.Nitrobenzene and waste water after the acetylation reaction were recovered.The recovered nitrobenzene contained part 2-MN,and the product yield were improved after the recovery was applied mechanically.The weight of Al（OH）3 precipitation obtained from the neutralization of wastewater by strong alkali solution and weak alkali solution was quite different.The optimal neutralization p H was 7 for Na OH,and the optimal neutralization p H was 9 for NH3·H2O.Due to low purity of the acylation products than requirements for the synthesis of 2,6-NDA by industrial oxidation,the acetylation products was purified by recrystallization.The effects of solvent amount,final crystallization temperature,cooling rate,addition of seed crystals and water content in solvent on the purity and yield of the target product were investigated.When methanol aqueous solution was chosen as solvent,it was found that the solvent amount had a significant effect on the purity and yield of the recrystallized product.As the mass ratio of solvent to acylation products increased from 2/1 to 6/1,the production purity increased from 87.31%to 94.07%,but the yield decreased gradually.Controlling the final crystallization temperature was beneficial to improve the purity of 2,6-MAN.DSC analysis showed that the increase of solvent amount made the precipitation temperature shift towards lower temperature.Slow cooling increased the residence time in the metastable zone,resulting in higher purity and yield of the obtained product than the medium and fast cooling.The purity and yield were 96.74%and 57.21%,respectively,at the mass ratio is 5/1.The addition of crystals seed promoted the formation of crystal nuclei,providing sites for crystal growth.The recrystallization process of slow cooling and adding crystals seed significantly improved the production purity.The increase of water content in solvent made the initial crystallization temperature shift toa higher temperature,the production purity showed a trend of first increase and then decrease,and the yield increased significantly.When the mass ratio of solvent to acylation products was 5/1,the product with purity over 98%can be obtained by slow cooling and the addition of crystal seed,which can meet the synthesis of 2,6-NDA by industrial oxidation. |
