The Research On Adsorptive Performance Of Aniline By Wheat Straw

To make wheat straw residue recyclable and remove aniline from water and wastewater,wheat straw was used to adsorb aniline in water as a kind of an adsorbent.First of all,its adsorption capacity for aniline was systematically examined through batch experiments; the equilibrium, thermodynamics and kinetic studies on the adsorption of aniline by wheat straw were evaluated,the isotherm parameters were estimated by non-linear regression analysis.Secondly, the adsorption of aniline onto wheat straw was investigated using fixed-bed adsorption.The effects of inlet aniline concentration, feed flow rate, solution pH and wheat straw bed height on the breakthrough characteristics of the adsorption system were determined; at the same time,the BDST and Thomas models were applied to simulate fixed-bed adsorption data and to gain the characteristic parameters of the two models using linear regression.Finally, the original weat sraw was made into carbonized materials. The adsorption kineticses of aniline adsorpted by wheat sraw on different carbonization temperature were inspected, and the effects of initial pH of solution,initial concentration of solution and different carbonization temperature on the adsorption of aniline by wheat straw were evaluated.The Langmuir and Freundlich models were applied to simulate adsorption data to estimate the isotherm parameters.The results of experiments indicated that wheat straw could adsorb aniline effectively.The capacity of adsorption of aniline on wheat straw reached 0.4mg?g-1 when the adsorption time is 15 min and the best adsorption capacity was 0.66 mg?g-1 when the initial pH of aniline was 4.0.The removal rates of aniline in water was from 23% to 69.57% while the range of solid-to-lipuid ratio on adsorption of aniline was 8～80g?L-1.The initial concentration of aniline and the temperature increasing resulted a improve of the adsorption capacity,while the effect of temperature was not remarkable. Wheat straw saturated can be regenerated by HCl of 0.9M under 60℃,and the second capacity of adsorption of aniline on wheat straw increased sharply.The equilibrium process was described well by the Freundlich isotherm model. The maximum wheat straw adsorption capacity was found to be 6.0mg?g-1 at 323℃.The results of thermodynamics showed that the isosteric adsorption enthalpy change (ΔH ) is in the range of 13.58～22.34 kJ?mol-1 when the isosteric adsorption capacity is increased from 0.2 to 2.5mg?g-1,and Gibbs free energy change (ΔG ) is negative while entropy change (ΔS ) is positive.The kinetics of aniline adsorption on wheat straw followed the Lagergren's pseudo-second-order model well and the overall rate of aniline uptake was found to be controlled by boundary-layer diffusion at the beginning of adsorption, while pore diffusion controlled the overall rate of adsorption at a later stage.The adsorption of aniline onto wheat straw was investigated using fixed-bed adsorption.The effects of inlet aniline concentration, feed flow rate, solution pH and wheat straw bed height on the breakthrough characteristics of the adsorption system were determined. At the same time,the BDST and Thomas models were applied to simulate fixed-bed adsorption data and to gain the characteristic parameters of the two models using linear regression.The results showed that wheat straw as an adsorbent to remove aniline from aqueous solution is efficient.The filler height increasing result in a extension of breakthrough time,while the increase of the flow rate, solution pH and the initial concentration of aniline lead a sharp decrease of breakthrough time.The breakthrough time at different flow rates and initial concentrations is forecasted accurately by the BDST model (error<5%).Thomas model is found suitable for describing the kinetics of fixed-bed adsorption,and the balance adsorption capacities from the Thomas model are close to the values of the experiments.Desorption of saturated wheat straw could use hydrochloric acid whose concentrition was 0.6M.The adsorption of aniline by wheat straw carbonized more than 500℃can reach an equilibrium in 100min,and the removal rate of aniline rapidly increase with the increase of carbonization temperature.The removal rate of aniline are in all above 90%, when the initial pH of aniline is 4.0.The isothermal adsorption curves are corresponded with the Freundlich isotherm model,the nonlinear levels of which gradually increase with the carbonization temperature up. That means the materials were gradually transformed from "soft carbon"into"hard carbon".