Study On Coking Mechanism Of Pyridine-based Nitrogen Compounds In Coal Chemical Concentrated Brine Evaporation

The problems of water use and drainage in coal chemical production have become the bottlenecks restricting the development of coal chemical industry.For this reason,new coal chemical enterprises have concentrated concentrated brine through multi-stage reverse osmosis to recover fresh water,and the produced high brine is evaporated to crystallize to produce salt.However,the residual biodegradable organic matter in the high salt water makes the steam heating pipeline of the evaporation and crystallization device often suffer from coking and blockage problems,which has caused serious safety hazards to coal chemical companies.Based on this engineering background,this study focused on the characteristic pollutants in coal chemical wastewater,pyridine nitrogen compounds,to study the mechanism and pathway of coking in concentrated brine,and the coking inhibitory effect of UV/H₂O₂ advanced oxidation pretreatment on pyridine nitrogen-containing compounds was discussed.Coking conditions,influencing factors,and mechanism studies of pyridine and pyridine derivatives show that phenols and aldehydes contribute significantly to the coking of pyridine-based substances,and the presence of both can increase the coking rate of pyridine-based nitrogen-containing heterocyclic compounds by 3.3%the above.The coking rate of the four nitrogen-containing compounds is2,6-dichloropyridine>pyridine-N-oxide>2-methylpyridine>pyridine.When quinoline and indole nitrogen-containing compounds are present in wastewater,the coking rate of pyridine-based compounds can be increased.Characterization and analysis of SEM,GPC,ATR and GC-MS of typical tar samples show that the pyridine nitrogen-containing heterocyclic compounds undergo dehydrogenation and condensation reactions during thermal evaporation,and the carbon number distribution of the tar component finally formed is 8¹6,the main molecular weight distribution is 258⁴57,and the structure may be that the pyridine skeleton is connected to the aromatic ring through a carbonyl group and an ether bond.UV/H₂O₂ advanced oxidation pretreatment experiments show that as the amount of H₂O₂ increases,the degradation efficiency of 2,6-DCLPY also gradually increases,but excess H₂O₂ will compete with 2,6-DCLPY for·OH.The ratio is 37:1,and the highest degradation rate is 77.3%when the pH of the wastewater is 7.2.HCO₃^-and NO₃^-in wastewater have a significant inhibitory effect on the degradation of2,6-DCLPY.At a concentration of 5 g/L,the degradation rate of 2,6-DCLPY is reduced to 27.5%;while the relative effects of Cl^-and SO₄^2-Smaller,the degradation rate of 2,6-DCLPY was reduced to 46.9%only at the concentration of 50 g/L.Finally,the changes in coking rate,solubility,morphological characteristics and molecular weight distribution of pyridine-based tar samples obtained from2,6-DCLPY thermal evaporation before and after pretreatment were analyzed.Experiments show that the maximum difference in coking rate of tar samples produced by evaporation at pH 8.0 after pretreatment is 3.64%.The temperature and concentration multiples reduce the average coking rate of tar produced by evaporation by less than 3%,and reduce the gum content in tar samples.The changes of SEM and GPC before and after further indicate that the pretreated pyridine nitrogen-containing compound reacts violently during the evaporation and coking process,the degree of ring condensation is greatly reduced,and the molecular weight of the main body also changes from 457 to 259.