Prepared Carbon-based Metal-free Catalyst From Adsorbing Dyeing Wastewater For Acetylene Hydrochlorination

Dyeing wastewater discharged from the printing and dyeing industry is one of the main sources of water pollution.The usual treatment of the adsorbent after the adsorption method might cause the waste of resources and secondary source of pollution to some extent.The recovering utilization of the used adsorbent is the key to the sustainable development of adsorption technology for dyeing wastewater treatment.The mercury pollution caused by the polyvinyl chloride(PVC)production process is also an environmental problem brought about by industrial process and the development of mercury-free catalysts is imperative.Compared with metal catalysts,metal-free catalysts have the advantages of low cost and insensitivity to impurities in industrial raw materials.Therefore,it is necessary to develop reasonable and efficient metal-free catalysts for acetylene hydrochlorination.Firstly,the coconut activated carbon(CAC)was screen out as the optimal adsorbent by static adsorption experiments.Two isotherm adsorption models were used to fit the neutral red(NR)solution adsorption process.Langmuir model was more consistent with the experimental data and could depict the adsorption process better.The adsorption of NR was a spontaneous endothermic process,which was dominated by monolayer adsorption.For the adsorption kinetics study,the adsorption process was coincident with the pseudo-second-order model and could be divided into three stages,as instantaneous external surface adsorption,intra-particle diffusion and adsorption equilibrium.Then,the dynamic adsorption experiments under different operating conditions were explored.It was found that the adsorption capacity of the CAC column increased with the increasing of the bed depths and decreased with the increasing of the feed flow rates.The Thomas model and the Yoon-Nelson model were used to fit the breakthrough curve and both had better prediction results.Then,the CAC after adsorbing NR was synthesized to the N-doped metal-free catalyst for acetylene hydrochlorination via a simple calcination.The optimal3NR/4CAC catalyst exhibited the highest acetylene conversion of 97.9%and maintained at 96.2%during the 48 h reaction under the conditions of 220 ^oC,GHSV(C₂H₂)=30 h^-1,V_HCl/V_C2H2=1.2.The N₂ adsorption/desorption experiments combined with Reax FF molecular dynamic simulation reveal that a porous carbon material generated on the surface of CAC which significantly improved the mesoporosity of the catalyst.TEM and Raman analysis showed that the graphitization degree of CAC changed and the defect structure increased after nitrogen doping.The Reax FF molecular dynamic simulation reveals pyridinic nitrogen was preferentially formed and in the leading position for the quantity,corresponding with the XPS results.In the formation of pyridinic nitrogen,amino N in NR is more facile to dope in than the others and a typical amino N doping pathway has been exhibited for further understanding the doping mechanism.The catalytic mechanism study via density functional theory(DFT)calculations demonstrate that the pyridinic nitrogen and pyrrolic nitrogen are the active sites for acetylene hydrochlorination and the pyridinic nitrogen which has the lowest reaction energy barrier is the most active site.