Experimental Study On Treatment Of Coal Pyrolysis Of Phenol-containing Wastewater By Pitch Based Activated Carbon Adsorption

Coal pyrolysis wastewater contains a large amount of phenolic substances,and this wastewater is difficult to deal with because of its poor biodegradability.Phenols are often used as bactericides and have certain toxic effects on organisms.Untreated phenols in wastewater will damage the ecological environment and may directly harm human health.In this paper,activated carbon adsorption method was used to optimize the treatment process of phenol wastewater from coal pyrolysis,and coal tar pitch was used to prepare activated carbon with selective adsorption capacity for phenols,and the adsorption mechanism was studied.Pitch-based formed activated carbons were prepared,and the effects of activation temperature,activation time,and activator CO2 flux on the microstructure and phenol adsorption performance were analyzed.The phenol adsorption capacity of activated carbon prepared at 900 ?,1 h and CO2 flux of 20 mL/(min·g)is 112 mg/g(measurement followed national standard),and the saturation adsorption capacity of Langmuir is 175 mg/g.The compressive strength is 21 MPa.Adjustment of the activation conditions can continue to increase the phenol adsorption capacity,but the mechanical strength will decrease at the same time.The pore structure analyses of activated carbons show that the 1-10 nm pores are the main structure of phenol adsorption,and the pore distribution of activated carbons prepared by CO2 activation is mostly concentrated in this pore size.The activated carbon consists of a large number of graphite nanocrystals with diameter about 5 nm The stacking microstructure of these nanocrystals leads to the higher mechanical strength of the activated carbon,while the high-temperature heat treatment and hydroforming deformation lead to grain refinement and this microstructure.This stacking microstructure of nanocrystals makes it easier to create and enlarge pores through activation.The analyses of surface functional group indicate that the oxygen-containing functional group is not the activated site of phenol adsorption,and they are conversely harmful to phenol adsorption.Part of the oxygen-containing functional groups are removed by the reducing atmosphere during the CO2 activation process.At the same time,the electron donor-acceptor mechanism is denied,and the electrostatic interaction has little effect in the adsorption process.The ?-? interaction is the most likely adsorption mechanism.The adsorption isotherm is fitted best by Langmuir model,which shows that the activated carbon adsorbed monolayers and similar adsorption sites.Internal diffusion model gives the best fit of adsorption kinetics,indicating that the adsorption process is divided into two parts:external diffusion and internal diffusion.Thermodynamic studies show that phenol adsorption of activated carbon is a spontaneous,entropy-increasing and exothermic process,which is closer to physical adsorption,so it is conducive to regeneration,and the heat adsorption is also consistent with ?-?interaction mechanism.The phenomenon that the phenol adsorption capacity of activated carbons increases with the increase of temperature shows that the phenol adsorption is more affected by the diffusion resistance than the heat of adsorption.The thermal regeneration effect of activated carbon is not good,and it is influenced by the diffusion resistance of phenol in the complex pore structure of activated carbons,while the high temperature regeneration effect is better(carbonization temperature).A regeneration method of thermal regeneration with alcohol vapor purging was developed,and the regeneration efficiency is over 90%.The activated carbon shows adsorption selectivity in the actual wastewater adsorption experiments,and has good adsorption effect on phenols,while has little effect on adsorption of polar organic small molecules such as alcohols and ethers(easily biodegradable).At the same time,its catalytic degradation and catalyzed ring formation of long-chain ethers was found.A double fluidized bed with activated carbon adsorption and regeneration gas-liquid-solid circulation was designed,which can be used for activated carbon adsorption treatment of phenol-containing wastewater without interruption.The treatment process of phenolic wastewater from coal pyrolysis was improved,and it is expected to have the advantages of stable operation and safety,as well as better impact resistance.