Study on the synchronous removal mechanisms of typical refractory hydrophilic and hydrophobic organics in the biochemical effluent of coal gasification by semicoke-PSAFS

Abstract

To study the synchronous removal mechanisms of hydrophilic organics 2,4-di-tert-butylphenol and 2-palmitoyl-rac-glycerol and the hydrophobic organics n-octadecane and 2-stearoyl-rac-glycerol coexisting in the biochemical effluent of coal gasification processes treated by a semicoke-polysilicate aluminum ferric sulfate (PSAFS) process, the fitting results of the D-R adsorption isotherm model show that the maximum equilibrium adsorption qe for hydrophobic organics was 3.2–7.8 times that of hydrophilic organics. Based on the contrast with 8 kJ/mol of the average adsorption free energy, physical adsorption occurred in the hydrophobic organics, and chemical adsorption occurred in the hydrophilic organics. Adsorption kinetics analysis showed that the adsorption rates of three typical organics except for 2-palmitoyl-rac-glycerol increased by more than 40.0% in semicoke-PSAFS compared with the semicoke adsorption. To analyze the adsorption driving forces, a linear solvation energy relationship (LSER) model was selected and showed that the hydrogen-bond acid effect contributed by PSAFS had the largest regression coefficients among the five adsorption forces. The typical hydrophilic organics had lower zeta potentials than hydrophobic organics, which suggests that hydrophilic organics that were easily ionized at neutral pH were electrostatically neutralized with the Fe and Al cations in PSAFS. The floc in hydrophilic organic solutions had larger D50 and Df than those in hydrophobic organic solutions, which indicates that the hydrophilic organics had polar functional groups that combined with the silicon, iron and aluminum polymers in PSAFS through a hydrogen-bonded acid effect to form larger and denser floc structures. Hydrophobic organics were adsorbed in the pores of semicoke; then, in combination with semicoke, they were captured by the iron and aluminum polymers in PSAFS.