The Preparation Of Sludge-Based Activated Carbon And Adsorptive Properties Of Toluene

Activated carbon absorption method, which can adsorb Volatile OrganicCompounds of low concentration, is a low energy consumption, mature process, andhigh removal efficiency. Activated carbon is usually from all kinds of organic materials,Because of carbon-rich and organic compound, through the pyrolysis or chemicalactivation method sludge can be transformed into activated carbon, this transformationnot only reduces the sludge quantity for providing a way of environmental protection,but also receives the low-cost absorbents. Realizing the sludge utilization, meanwhileabsorbents successfully treat the toluene waste gas.Dewatered sludge from municipal wastewater plant was activated with ZnCl2.Theactivation method, ZnCl₂concentration, activation temperature and activation time wereconsidered to study influence on the performance of the adsorption, using theorthogonal experiment got the best preparation plan, Then sludge activated carbon wasapplied in toluene adsorption test. The results show that the best preparation conditionsis the ratio of activator to sludge5:5, activation temperature550℃,activation time40min. Influence degree is as follows: activation temperature> ZnCl₂concentration>activation time.Test for heavy metal content finds after the sludge in preparation process is lessthan before of that, the activation process will change soluble metal ions into metal saltsto achieve stability role. Cu, Zn, Fe content is higher, so the metals help activatedcarbon catalytic reaction, and promote chemical adsorption effect of the sludgeactivated carbon for organic waste gas.During the activation process, it was mixed with appropriately additive saw dust（SAC-W） or coconut powder（SAC-C）, The BET surface area of them are as high as 450.3m²/g and539.4m²/g, increasing by31.63%and57.67%, respectively. Usingdynamic adsorption experiments, adsorptive properties for toluene was compared withcommercial activated carbon（CAC）, The results indicate that the order of adsorptioncapacities is SAC-C>CAC>SAC-W at same initial concentration, SAC has strongadsorption for toluene. The physicochemical properties of SACs were carried out, itshows that mesoporous structure and surface chemistry of sludge activated carbon playkeys role on the removal of toluene. Langmuir equilibrium isotherm model fits betteradsorption data with R2=0.995.Sludge activated carbon was used as adsorbent for toluene in fixed bed. At thesame time, the effects of bed depth, initial concentration and gas linear velocity onremoval of toluene were studied, and mass transfer model for this process was establis-hed to calculate mass transfer zone and total mass transfer coefficient. Results show thatwith bed depth changing from3cm to5cm, mass transfer zone has no significantchange, while the total mass transfer coefficient increases by66.66%; mass transferzone increases by17.19%and total mass transfer coefficient reduces by22.05%with thetoluene concentration increasing by3.36times; In the operation of the gas linearvelocity range, with the gas linear velocity2times than that of the original, total masstransfer coefficient increases by65.27%, which indicates that this process belongs toexternal diffusion control.