Studies On The Catalytic Performance Of Modified Activated Carbon In The Regeneration Of Fe(Ⅱ)EDTA Solution

Nitric oxide can be absorbed to be removed by Fe(Ⅱ)EDTA aqueous solution effectively.However,the Fe(Ⅱ)EDTA is also easily oxidized to Fe(ⅢEDTA by oxygen contained in the flue gases,which loses the affinity to bind NO. Hence activated carbon is utilized to catalyze the reduction of Fe(Ⅲ)EDTA to Fe(Ⅱ)EDTA with sulfite to maintain the NO removal efficiency.In order to increase the catalytic performance,activated carbon is modified by various methods so that NO can be removed with a high efficiency for a long time.In this study,the modification methods using KOH and NH3·H2O solution have been investigated to meliorate the catalytic performance of coconut activated carbon in the regeneration of Fe(Ⅱ)EDTA solution.Experiments have been performed in a batch stirred cell to study the effects of midification conditions on the catalytic performance of activated carbon.Experimental results indicate that the catalytic capability of modified activated carbon is better than the raw one when it is treated with KOH or NH3·H2O solution.The optimal condition for the treatment of activated carbon by KOH and NH3·H2O solution is shown as follows:KOH concentration 6.0mol/L, impregnated time 9h,activation temperature 700℃,activation time 4h and NH3·H2O concentration 9.0mol/L, impregnated time 11h,activation temperature 700℃,activation time 4h,respectively.FTIR transmission spectra of the modified activated carbon samples show that no new peaks are found.It confirms that no new functional group appears on the surface of modified activated carbon.However,the strength of the peaks exist obvious difference that the peaks of phenolic hydroxyl and carboxyl become weaker.This indicates that the acidic functional groups of activated carbon decrease after modification.The physical structure and surface chemical properties of activated carbon is changed after treated with KOH and NH3·H2O solution.BET analysis manifests that the KOH and NH3·H2O modified activated carbon have smaller surface area and less micropores so that the adsorption ability of N2 decreases. Boehm titration and mass titration confirm that the acidic functional groups of modified activated carbon is less than that of raw one and the basic functional groups is more than that of raw activated carbon.The basic capability of activated carbon is enhanced after modification.And the change of surface chemical properties plays a key role in affecting the catalytic regeneration of Fe(Ⅱ)EDTA solution. The catalytic capability of the two midified activated carbon treated by KOH and NH3·H2O solution on the regeneration of Fe(Ⅱ)EDTA solution has been inveatigated in a stirred-cell reactor.The experimental results demonstrate that both the KOH and NH3·H2O modified activated carbon have almost equal catalytic efficiency in this process.The differences between them are that the KOH modified activated carbon has less acidic functional groups and the NH3·H2O modified activated carbon has more nitrogen functional groups.Continuous experiments are carried out in a fixed-bed reactor to test the catalytic performance of the modified activated carbon for the simultaneous absorption of NO and SO2 into the Fe(Ⅱ)EDTA and Na2SO3 solution.The experimental results demonstrate that the modification of activated carbon by KOH and NH3·H2O can improve its catalytic performance obviously. With the regeneration of Fe(Ⅱ)EDTA catalyzed by the modified activated carbon,a higher nitric oxide removal efficiency can be maintained for a long time.