Preparation Of Phenolic Porous Carbon Derived From Semi-coking Wastewater And Study On Its Electrical And Thermal Storage Properties

Semi-coking wastewater is a type of high concentration phenol ammonia wastewater,phenols can prepare high value-added phenolic porous carbon,ammonia nitrogen impurities can provide N,O,S self-doping.Based on this,this paper selects semi-coking wastewater as raw material,adds formaldehyde to prepare phenolic resin and uses it as carbon precursor,and uses KOH and Na₂CO₃ as activators to prepare porous carbon（PC）,to explore the influence of different activators on the pore structure and electricity and thermal storage properties of PC.The research content includes the following three parts.（1）In order to effectively utilize phenol and ammonia in semi-coking wastewater,phenolic resin was obtained by polycondensation of formaldehyde and phenols in semi-coking wastewater and mixed with KOH.N,O and S self-doping porous carbon（NOSPC）was obtained by one-step carbonization activation method.The results showed that the activated NOSPC had a large specific surface area（SSA,2523 m²/g）,excellent pore volume（V_t,1.30 cm³/g）and reasonable pore structure.At the same time,the impurity atoms in the wastewater were doped into NOSPC,and the contents of NOSPC impurity atoms were N（0.71 at.%）,O（8.53 at.%）and S（0.32 at.%）,respectively.The symmetric capacitor（S-NOSPC）made of NOSPC exhibits an energy density of 9.1 Wh/kg at an operating voltage of1.2 V（at an energy density is 150 W/kg）.After 10,000 charge and discharge cycles at 20 A/g,the capacitance retention rate remains at 99%.（2）In order to fully retain the content of N,O and S atoms in phenolic resin（SWPR）,NOSPC was prepared by using less corrosive Na₂CO₃.The effects of activator ratio and temperature on pore structure and capacitance performance were investigated.The results showed that the SSA and V_t of NOSPC-700 were 718 m²/g and 0.31 cm³/g,respectively,when the activator ratio was 2.5:1 and the activation temperature was 700℃.The content of heteroatoms（2.54 at.%N,15.86 at.%O and 0.48 at.%S）in porous carbon activated by Na₂CO₃ were higher than those in porous carbon activated by KOH,indicating that Na₂CO₃activation could better retain the heteroatom content in SWPR.In addition,symmetrical supercapacitors composed of NOSPC-700 provide a high energy density of 5.92 Wh/kg at a power density of 124.9 W/kg.At 20 A/g,the Coulomb efficiency was 100%and the capacity retention rate was 99.4%for 10000 cycles.The results show that NOSPC-700 has good practical performance.（3）In order to effectively utilize phenolic porous carbon activated by KOH and solve the leakage problems of organic PCM,the phenolic porous carbon activated by KOH was used as the skeleton,and the PCM composite（PCC）was obtained by loading PW.The results show that the prepared PCC have excellent thermal properties,shape stability and cycle stability.In addition,PCC has a melting enthalpy of 80.25 J/g even after 500 heating/cooling cycles.The solar thermal conversion efficiency of PCC is up to 95%.