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Adsorption of 2-Butyl-2-ethyl-1,3-propanediol from Aqueous Solutions on Activated Carbon: Salt-Out Effect on Equilibrium, Kinetics, and Dynamics

Chang, Ganggang, Bao, Zongbi, Zhang, Zhiguo, Xing, Huabin, Su, Baogen, Yang, Yiwen, Ren, Qilong
Industrial & Engineering Chemistry Research 2014 v.53 no.20 pp. 8592-8598
activated carbon, adsorption, aqueous solutions, boron, brine solutions, calcium chloride, commercialization, cost effectiveness, equations, kinetics, magnesium chloride, models, process design, saline water, solvents, sorption isotherms, temperature
In recent decades, 2-butyl-2-ethyl-1,3-propanediol (BEPD) has been extensively evaluated as an efficient extractant for the recovery of boron from brine solutions commonly present in magnesium chloride. The BEPD leaked into the raffinate must be recovered in order to make the process of solvent extraction cost-efficient. The present study examined the feasibility of a commercialized coal-based activated carbon to recover BEPD from brine solutions. The salt-out effect on adsorption isotherms and kinetics of BEPD from brine solutions with salt concentrations up to 100 g/L were reported at different temperatures (20 °C, 30 °C, 40 °C, and 50 °C). It was found that the saturated adsorption capacities were significantly enhanced from 192 mg/g in the deionized water to 238 mg/g in the brine solution with an MgCl₂ concentration of 100 g/L at 30 °C. Kinetic analysis indicated that the adsorption kinetics of BEPD followed the pseudo-second-order equation, and the pseudo-second rate constant (k₂) affected by the varied salt concentrations complied with the following order: MgCl₂ (100g/L) > MgCl₂ (25g/L) ≈ CaCl₂ (20g/L) > deionized water. Also, the benefit from the salt-out effect was also verified by the extended dynamic breakthrough volume as well as the amount adsorbed. The dynamic adsorption capacity was much higher in a saline water, i.e., 235 versus 191 mg/g in the deionized water. The Thomas model was further applied to predict the experimental breakthrough data, and the obtained model parameters could be useful for future process design. The activated carbon has the potential for practical adsorption applications for BEPD recovery from aqueous solutions.