|
Activated carbon has rich porous shape structures. With characteristics of developed Internal pore structure, high specific surface and strong adsorption, they can absorb the materials which are low concentration in the water and hard to remove. They have been widely used in wastewater treatment, desulfurization, organic solution recycling, air purification, semiconductor and many other application fields.Supercritical technology has been widely studied and applied, as a new approach of straw resource-oriented utilization. However, during the process of straw pre-treatment with supercritical water, the solid residual are ignored by society as of no value or importance, having no reasonable disposal methods. The solid residual produced from rice straw pre-treatment with supercritical water were as materials in this paper, and activated carbon were made from them. It increased the use value of the straw and improved the energy efficiency of straw. Activated carbon was produced from straw saccharification residue as raw material with phosphoric acid and zinc chloride as activating agent. Factors, which affect activated carbon ullage, are analyzed. A series of batch experiments were carried out to study the adsorption behaviour and thermodynamics of BPA from aqueous solution by carbon derived from rice straw. The results show that, when phosphoric acid is activating agent, activation temperature 900℃, activation time 60 min, impregnation time 12 h and impregnation ratio 1:5, the corresponding yield of activated carbon, the number of iodine and methylene blue was 42.3%, 1011.7 mg/g and 116.5 mg/g, respectively. The adsorption capacity of the adsorbent that uses are higher than the general selling activated carbon, 12.4%; when zinc chloride is activating agent, activation temperature 900℃, activation time 60 min, impregnation time 12 h and impregnation ratio 1:5, the corresponding yield of activated carbon, the number of iodine and methylene blue was 46.3%, 1201.1 mg/g and 146.5 mg/g, respectively. The adsorption capacity of the adsorbent that uses is higher than the general selling activated carbon, 33.4%.Choose the optimum conditions to prepare activated carbon and use them to simulate adsorption of bisphenol A in the wastewater. Activated carbons by using the zine chloride activation have better adsorption performance than them by using the zine chloride activation method. Activated carbons from zine chloride activation have the maximum adsorption quantity of methylene blue 214.1 mg·g-1, and the maximum adsorption quantity of bisphenol A 123.2 mg·g-1. These two kinds of activated carbon have relatively similar kinetic and thermodynamic characteristics. The BPA adsorption equilibrium data of activated carbon by chemical activation both obey Langmuir model and the kinetic data are well described by the pseudo-second-order model. Langmuir model would demonstrate the single molecule layer absorption and the pseudo-second-order model could indicate the existence of chemical adsorption. Thermodynamics research shows that, H>0, explains for an endothermic process; G<0, explains that adsorption quality tend to the surface of the absorbent from in the solution, and the reaction process is spontaneous; S>0, explains methylene blue in the active carbon adsorption of entropy is process on promoting, motion of molecular on solid/liquid interface are more chaos.Through supercritical pretreatment of the rice straw and the use of residue, the results calculated show that 1 t rice straw can produce 210 kg sugar, and the residue obtained can produce 300 kg phosphoric acid activated carbon or 320 kg zinc activated carbon, the output value made is 1766.70 RMB and 1932.59 RMB, respectively.
|