Experimental Study On Absorption Characteristics Of Ionic Liquids For Volatile Organic Compounds Removal

With the rapid development of China’s industrialization,the volatile organic pollutants(VOCs)from industrial emissions have increased year by year,causing great harm to the atmospheric environment and human health.Therefore,it has practical significance to develop practicable and efficient control technology of VOCs.Absorption method has been developed earlier for several advantages,such as high removal efficiency,widely application and maturity process.The key of absorption method is to develop an efficient and no secondary pollution absorbent.As a new kind of environmentally friendly solvent,ionic liquid(ILs)has the advantages of excellent solubility,extremely low volatility,high thermal stability.Using ILs to absorb VOCs can avoid solvent consumption and environmental pollution caused by solvent evaporation.Consequently,this paper employed imidazolium ILs as absorbent for the treatment of VOCs.To begin with,the dissolution equilibrium of four binary systems consisting of[Bmim][NTf2],[Bmim][PF6],toluene and acetone was studied.The absorption properties of ILs were evaluated through the response parameters such as intake concentration,absorption temperature and flow rate.And the best absorption condition was further optimized by orthogonal test.Finally,the regeneration characteristics and methods of ILs absorbent were explored,and thermal degradation characteristics of ILs were evaluated through thermogravimetric analysis.The results show that the solubility of toluene in[Bmim][NTf2]and[Bmim][PF6]at normal temperature and atmospheric pressure is 61.38%and 31.01%respectively,and the solubility of acetone in two ILs is 68.96%and 63.19%respectively.The high solubility of VOCs in the IL shows the strong affinity of the IL for toluene,indicating a high capacity of ILs to dissolve VOCs.With intake concentration of 300 ppm,absorption temperature of 20 ℃,flow rate of 50 mL/min,the absorptivity of[Bmim][NTf2]to toluene and acetone is 98.3%and 95.6%respectively,and the absorptivity of to toluene and acetone is 99.3%and 92.9%,respectively.To further explore main factors affecting the absorption experiment,the orthogonal test was used to optimize the test conditions.The results showed that intake concentration is the primary cause of absorptivity.In this study,the absorbent ILs was regenerated via thermal distillation and the absorptivity of the regenerated[Bmim][PF6]for toluene examined.The absorptivity of[Bmim][PF6]for toluene remained above 92%after five multiple reuse phases.The regenerated ILs and original ILs,as well as the recovered VOCs and fresh VOCs,were all characterized using FTIR and the spectra showed that the intensity,position and shape of the absorption peak were not obviously changed.Thermal degradation of[Bmim][NTf2]and[Bmim][PF6]was investigated through TGA.The thermogravimetric analysis showed that the thermal decomposition of[Bmim][NTf2]mainly occurs in the temperature range of 613.5-759.67K,while the temperature range of[Bmim][PF6]was 617.5-770.67K,and the TG curve showed a distinct single weightlessness stage.The activation energies of thermal degradation for[Bmim][NTf2]and[Bmim][PF6]was calculated through KAS method,FWO method and Starink method,which were 115.9-121.3 kJ/mol and 93.4-99.9 kJ/mol.Reaction order derived from Avrami theory was 1.33-1.39 for[Bmim][NTf2]and 1.29-1.55 for[Bmim][PF6].