| Volatile organic compounds（VOCs）are one of the important precursors for the formation of ozone（O3）and fine particulate matter(PM2.5)pollution,and their effective control is an important safeguard for the ecological environment and human health.The adsorption method has the advantages of being efficient,economical and recyclable,and is currently one of the main control technologies for the effective purification of VOCs.The key to adsorption is the adsorbent material,and porous carbon is widely used as an adsorbent for VOCs due to its wide source,high specific surface area and excellent performance.However,in practice,porous carbon faces the challenge of competing with water vapour for adsorption in engineering applications,especially in high humidity environments or operating conditions,which can lead to a dramatic reduction in the adsorption capacity of porous carbon for VOCs,or even failure.Therefore,the modification of porous carbon materials with high hydrophobic properties can be used as an efficient VOCs adsorbent,which is expected to overcome the shortcomings of existing porous carbon materials such as low adsorption capacity in high humidity environment and poor adsorption performance in competition with water vapor,and has a good application prospect.In this study,the natural organic acid myristic acid was used to construct the hydrophobic structure on the surface of biomass-based porous carbon by ethanol deposition method with mild and simple operating conditions,so as to explore its modification and preparation,and to develop hydrophobic porous carbon materials with high selective adsorption performance for VOCs in high humidity（80RH%）environment.The main findings of this thesis are as follows.The main contents and conclusions of this thesis are as follows.（1）The modification conditions of myristic acid-modified porous carbon were screened and optimized by response surface methodology combined with orthogonal tests,and the best modification conditions were determined as follows:a carbon to acid mass ratio of 0.52:1,a reaction temperature of 65℃and a reaction time of 18 h.Among the above conditions,reaction temperature has the greatest influence.The toluene adsorption capacity of the myristic acid modified porous carbon prepared under these conditions was 488 mg/g at 80RH%,which was close to the maximum predicted theoretical value of 493 mg/g,while the adsorption capacity of the unmodified porous carbon was only 151 mg/g.To verify the universality of the method,commercial porous carbon was modified by this method,and it was found that the adsorption capacity of toluene at 80RH%increased by 66-83%.In addition,the raw material for the preparation of the adsorbent was recycled six times with a reuse rate of 95%,again showing good recycling stability.Therefore,the modification method has high practical application potential,and can provide an effective solution for the adsorption of porous carbon in the high humidity environment.（2）In this study,the physical and chemical structures of porous carbon（AC and AC-MA）before and after myristic acid modification were analyzed.It was found that they were similar in morphology and structure,but after modification,the specific surface area and pore size distribution parameters were reduced to different degrees,and the water contact Angle showed that the hydrophilic was changed to hydrophobic.FTIR and XPS confirmed that alkyl only appeared on the surface of AC-MA,and AC-MA had higher O-C=O and C-C content than AC.Toluene-tpd results show that AC-MA has larger area and higher temperature toluene desorption peak than AC.As the thermogravimetric temperature increased,the myristic acid grafted onto the porous carbon surface was desorbed,while AC-MA had a larger area and higher temperature toluene desorption peak than AC.All of the above characterisations demonstrate that myristic acid has been successfully grafted onto the porous carbon surface and exhibits hydrophobicity.As the amount of grafting increased,the alkyl（C-C）and ester（O-C=O）signals were found to increase,and the thermogravimetric results indicated that the amount of myristic acid desorbed increased,as did the amount of toluene adsorbed at 80 RH%.（3）The adsorption capacity of modified porous carbon（AC）for VOCs was investigated under different influencing factors such as humidity,temperature and the characteristics of VOCs exhaust gas.As the relative humidity continued to increase,the toluene adsorption capacity of ACs decreased,but AC-MA always showed higher toluene diffusion rate and adsorption capacity than AC.The Langmuir and Freundlich adsorption isotherm models were able to predict the adsorption of toluene and water before and after modification of the porous carbon material.The Yoon-Nelson model for ACs at different initial concentrations was applied to the dynamic adsorption profiles of toluene on porous carbon materials,and AC-MA consistently showed higher toluene adsorption and stability than AC.In addition,AC-MA exhibited better toluene adsorption performance and cycling stability than AC,with toluene adsorption amount reaching 96%of the original amount after 5 sorption/desorptions.（4）The adsorption mechanism of toluene on the modified porous carbon surface under high humidity was investigated by IAST and molecular simulations.Toluene adsorption selectivity of AC-MA was 150,which was significantly higher than that of AC by 11,indicating that AC-MA has good toluene/water adsorption selectivity.The toluene adsorption energy of AC-MA（-0.90 e V）was higher than that of AC（-0.18 e V）,and the toluene adsorption amount on AC-MA was higher than that of AC when the pressure was between 0and 2 k Pa.This is attributed to the high binding capacity between the non-polar alkyl groups introduced by AC-MA and non-polar toluene molecules.The toluene adsorption mechanism of modified porous carbon under humid conditions was summarized by the previous experiments combined with molecular simulations,including:1)hydrophobic effect,2)“similar solubility”principle,and 3)donor-acceptor electron complex. |
PDF Full Text Request