Oxidative Combustion And Microscopic Mechanism Of Coal-Based Activated Carbon Adsorbing VOCs

Coal-based activated carbon is widely used in various industries as a valuable tool for the treatment of volatile organic solvents(VOCs)in industrial production.However,studies have shown that when coal-based activated carbon is used in the industry to adsorb organic solvents,explosion accidents often occur.Therefore,indepth exploration of the oxidative combustion performance of coal-based activated carbon before and after adsorption of VOCs is of great significance for finding measures to curb the occurrence of accidents.Based on coal-based activated carbon samples commonly used in industrial production,acetone,cyclohexane,and butyl acetate were used as organic solvents to prepare three coal-based activated carbon samples after adsorption of coal VOCs.Through the simultaneous thermal analysis experiment and the flammability test of the substance,the oxidation process and combustion process of the four samples were studied in detail,and the macromolecular model before and after the adsorption of coal-based activated carbon was constructed.The reaction molecular dynamics(Reax FF-MD)method to analyze its combustion mechanism under different oxygen concentration conditions,to find the direct cause of activated carbon combustion at the molecular level.The article firstly conducts experimental analysis on the structural characteristics of activated carbon.The appearance,morphology,element composition,functional group types and structural skeleton of coal-based activated carbon were analyzed and studied by various experimental methods such as SEM scanning electron microscope test,elemental analysis test,infrared analysis,and high-resolution transmission electron microscope analysis.The experimental results show that the adsorption sites of coal-based activated carbon to organic solvents are mainly concentrated around the voids;the content of C element is the main element of coal-based activated carbon,and contains a small proportion of N element;the main functional groups in coalbased activated carbon are It is hydroxyl(-OH),ether bond(C-O-C)and carbonyl(-C=O);the C atom skeleton in the graphite microcrystalline layer structure is mainly a six-membered ring structure.Secondly,the coal-based activated carbon sample(ROW),the coal-based activated carbon sample after acetone adsorption(BT),the coal-based activated carbon sample after cyclohexane adsorption(HJW),and the coal-based activated carbon sample after butyl acetate adsorption(YSDZ)Four samples were analyzed by TG-DSC at different air flow rates,and TG-FTIR combined experiments were performed on the oxidation process of the samples for specific air flow rates.The experimental results show that the adsorption of organic solvents has a significant impact on the characteristic temperature of coal-based activated carbon during the oxidation process,resulting in the decrease of the critical temperature and thermal decomposition temperature of low-temperature oxidation,the difficulty of oxidation reaction is reduced,and the sample is more likely to react.Through the phased analysis of coal based active oxidation process before and after adsorption of VOCs,there is abnormal heat release in the desorption stage of organic solvent.Combined with thermal red cross analysis,it is found that the organic solvent may burn in the desorption process,resulting in the increase of heat in the system.In the thermal decomposition stage,the heat absorption of the sample after adsorption of VOCs is less than that before adsorption,which is more prone to oxidation reaction.At the same time,the ISO5660 cone calorimeter was used to study and analyze the combustion characteristics of coal-based activated carbon before and after adsorption.The changes of ignition time,flame shape,heat release rate(HRR),effective heat of combustion(EHC)and total heat release(THR)of the four coalbased activated carbon samples of the same quality were quantitatively analyzed.Among them,the ignition time was shortened after coal-based activated carbon adsorbed organic solvent;the peak heat release rate and the time when it reached the peak were significantly moved forward;the effective combustion heat and total heat release increased.The results show that the combustion performance of coal-based activated carbon after adsorption of VOCs is significantly enhanced,and the danger becomes greater.Finally,with the help of reactive molecular dynamics simulation method,the coal-based activated carbon models before and after adsorption of acetone under different oxygen concentrations were calculated.The experimental results show that oxygen and acetone molecules significantly increase the content of free radicals in the system,resulting in an increase in the reaction activity of the system and a deepening of the decomposition of coal-based activated carbon molecules.In addition,comparing the changes of potential energy during the simulation process before and after adsorption,it can be found that the potential energy of the coal-based activated carbon molecules after adsorption of organic solvents has a greater decrease in potential energy during the simulation process,showing that the reaction is more severe.In this state,the number and types of organic small molecule products increase,and combustion occurs under sufficient oxygen conditions,thus promoting the oxidation and combustion reaction of activated carbon molecules.