Study On Structure Regulation And Electrochemical Performance Of Porous Carbon Prepared From Phenol/Ammonia Components Of Semi-Coking Wastewater

Semi-coking wastewater is a challenging of wastewater due to its high chemical oxygen demand（COD）,high levels of ammonia nitrogen（NH₃-N）,and the presence of phenolic and amine substances that are difficult to degrade.Direct discharge of this wastewater not only leads to environmental pollution but also hinders the full utilization of its valuable chemical components.This study aims to transform semi-coking wastewater from"treatment"to"conversion"and fully utilize the many phenolic and ammonia nitrogen components in semi-coking wastewater to prepare porous carbon materials with natural advantages using mixed phenolic-formaldehyde resins.Semi-coking wastewater is prepared into phenolic-formaldehyde resins and used as a precursor for carbon material.KOH,Na₂CO₃,and other activators are used to activate the resins,and then porous carbon-super capacitor electrode materials are prepared.The study explores the operating conditions and mechanisms of the preparation process,with the goal of realizing the pretreatment and resource utilization of semi-coking wastewater,expanding the production chain of semi-coking enterprises,and providing theoretical guidance for environmental protection,corporate image-building,energy conservation,emission reduction,and other improvements.The main work accomplished includes:（1）The pollutants in the semi-coking wastewater were analyzed by GC-MS,ion chromatography and XRD,which found that the main pollutants in the wastewater were phenolic compounds and ammonia-nitrogen compounds.In this study,semi-coking wastewater was used as the research object,and the phenolic and ammonia and nitrogen substances in it were reacted with formaldehyde to produce phenol-formaldehyde resin and curing agent urea.The effects of wastewater pH value,reaction time,reaction temperature,and formaldehyde addition amount on the quality of the phenol-formaldehyde resin were investigated,and the preparation conditions were optimized using response surface methodology.The experimental results showed that the optimal conditions were the reaction temperature was 95°C,the pH of wastewater was 9.59,the reaction time of 2.0 h,and amount of formaldehyde added was 1.20 m L,and the resulting phenol-formaldehyde resin quality was 2.1811 g.The COD removal rate of the treated wastewater was 44.46%,the ammonia nitrogen removal rate was 60.10%,the free phenol removal rate was 99.19%,and the residual free aldehyde was 0.87 mg/L.The solid content,residual carbon rate,gel time,viscosity,free phenol,and free aldehyde of the prepared phenol-formaldehyde resin were measured,and its characterization was carried out using in-situ infrared spectroscopy,field emission scanning electron microscopy,and differential thermal analysis.Additionally,the phenolic and ammonia substances in the semi-coking wastewater were separately reacted with formaldehyde,and it was found that the phenol-formaldehyde resins and HMTA formed by the various phenolic and ammonia substances in the semi-coking wastewater had different thermal decomposition rates,providing a natural advantage for preparing hierarchical porous carbon from phenol-formaldehyde.This study demonstrates that the reaction of semi-coking wastewater with formaldehyde can not only allow for the utilization of pollutants in the wastewater but also reduce the content of phenolic and ammonia nitrogen substances,achieving the effect of pretreating semi-coking wastewater.The resulting phenol-formaldehyde resin can also be used as a precursor to produce phenol-formaldehyde porous carbon for comprehensive utilization.（2）Activated carbon from semi-coking wastewater-based phenolic resin was prepared by using KOH as an activating agent.The effects of the KOH/resin ratio,carbonization-activation temperature,and carbonization-activation time on the iodine adsorption and specific capacitance of the resulting porous carbon were investigated,and the operating conditions were optimized using response surface methodology.The prepared porous carbon exhibited an iodine adsorption value of 1461.83 mg/g and a specific capacitance of 291.50 F/g.Characterization of the phenolic resin-based porous carbon was performed using scanning electron microscopy,transmission electron microscopy,X-ray diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy,BET surface area analysis,and Fourier transform infrared spectroscopy,which revealed a high specific surface area of 2522.9 m²g^-1,a total pore volume of1.29 cm³/g,and low contents of surface heteroatoms such as N,O,and S.The electrochemical performance of the prepared porous carbon was characterized by its excellent conductivity and reliable rechargeability.The assembled supercapacitor exhibited a stable cycle life of 10000 cycles,with a capacity retention rate of 100%and a Coulombic efficiency of 97%during cycling,indicating a significant charge transfer and ion diffusion rate.Furthermore,KOH activation of the five main phenolic compounds and two main ammonia compounds in the semi-coking wastewater separately or in combination to prepare phenolic resin-based porous carbon and HMTA revealed that mixed phenol ammonium resulted in a thermosetting phenolic resin that reacted with HMTA,which was difficult to activate with KOH.（3）Weak alkaline activating agents such as sodium carbonate,sodium bicarbonate,sodium acetate,and sodium citrate with low corrosion were used to activate and pore-form phenol-formaldehyde resin.The effects of the type and proportion of activating agents,carbonization-activation temperature,carbonization-activation time on the iodine adsorption and specific capacitance of phenolic porous carbon were investigated,and the operating conditions were optimized using the response surface method.The results showed that the iodine adsorption value of porous carbon material activated by Na₂CO₃was 1046.36 mg/g,the specific capacitance was 315.32 F/g,the specific surface area was 717.51 m²g^-1,and the total pore volume was 0.31 cm³g^-1.The N,O,and S doping amounts were significantly increased compared with KOH activation.The electrochemical performance of phenolic porous carbon activated by Na₂CO₃had excellent cyclic stability.After 10000 stable cycles of assembling a supercapacitor,the capacity retention rate was 99.83%and the Coulomb efficiency was 100%.The activation of phenolic porous carbon and HMTA using Na₂CO₃as the activating agent in a mixture of phenol,ammonia,phenol-formaldehyde resin confirmed the dual role of Na₂CO₃as a hard template and an activating agent.