Adsorption Behavior Of Anionic Surfactants By Ion Exchange Resins

Three polystyrene weakly basic anion exchange resins (SZ-1, SZ-2 and SZ-3) were prepared in current work using dicyclohexylamine, piperidine and piperazine respectively. The physicochemical structures of the resulting resins were characterized using Fourier Transform Infrared Spectroscopy and pore size distribution analysis. Static and dynamic adsorption behaviors of these three resins to three kinds of anionic surfactants were studied, and the common commercial weakly basic anion exchanger D301 was also employed for comparison purpose. The optimal desorption agent was screened out, and the static and dynamic desorption experiments were studied. This work also conducted experiments on adsorption behaviors coexisting with two kinds of inorganic salts and evaluated the selectivity of these resins. Experimental results showed that:(1) Adsorption isotherms of all reactions were found to be well represented by the Langmuir model (R2?0.99). The order of adsorption amount for BA was SZ-2>D301>SZ-3>SZ-1. For SDS, the order was SZ-2>D301>SZ-1?SZ-3. The order of adsorption amount for SDBS was D301>SZ-2>SZ-l>SZ-3 at 288K and 303K, and the order changed to SZ-2>D301>SZ-3>SZ-1 at 318K. Ion exchange interaction was the predominant adsorption mechanism for adsorption of BA, the adsorption of SDS and SDBS were led by both hydrophobic interaction and ion exchange interaction.(2) Adsorption processes were spontaneous under experimental conditions. Adsorption of BA on all resins was an exothermic process, and lower temperature was beneficial to adsorption. But for SDS as well as SDBS, adsorption was endothermic, and higher temperature was beneficial to adsorption. The values of adsorption entropy (AS) were all positive, which meant chaos of reaction system increased.(3) Adsorption capacities of all the resins for BA were decreased when NaCl or Na2SO4 was introduced into the system. The effect of NaCl on adsorption of SZ-1, SZ-2 and SZ-3 was more significant than Na2SO4, while the effects of NaCl and Na2SO4 on that of D301 were both obvious. With the increase of inorganic salts concentration in the system, the adsorption of SDBS on D301 decreased constantly. But for SZ-1, SZ-2 and SZ-3, the adsorption amounts were decreased and then increased.(4) Adsorption kinetics fitted well with the pseudo-second-order model (R2>0.98), and the adsorption rate was determined by particle diffusion process.(5) The optimal desorption agents for BA and SDBS were 3% NaCl aqueous solution and 3% NaCl ethanol/water (50/50) solution, respectively. For desorption kinetics experiments of BA, SZ-2 and D301 reached desorption equilibrium in about 80 minutes, while the other two resins need about 300 minutes. D301 reached desorption equilibrium within about 25 minutes, while the other three resins need 250-300 minutes for desorption of SDBS, and the ultimate desorption rate could all reach about 80%.(6) The dynamic adsorption effects of BA on SZ-1 and SDBS on SZ-2 were both better than those on D301. The dynamic desorption rate of SZ-1 was comparable with that of D301, while the rate of SZ-2 was higher than that of D301.