| Activated carbon is widely used in the field of environmental pollution control due to its outstanding adsorption ability,however,the grade,the price and the supply of the activated carbon materials restrict its mass production.According to previous studies,The waste biomass such as cheap plant straw,coconut shell,cocoa shell,walnut shell,bagasse,sawdust,pulping black liquor can be activated to produce high performance activated carbon.As one of the biomass,coffee grounds have been generated worldwide?in the order of 9,600,000 tons/year?,most of the coffee grounds are burned as a waste,which results in production of carbon dioxide,the green house gas.It isnecessary to develop new technologies enabling to reuse coffee grounds for useful purposes and converting this waste into a new resource material.Activated carbons were prepared from biomass renewable coffee grounds was using H3PO4 as activator.First,the Conventional one-step preparation conditions were optimized by using the response surface methodology,and effects of various activation conditions?Activation temperature,Activation time and Impregnation ratio?on the performance of the coffee grounds activated carbon were considered.Then,a novel process of preparing activated carbon by two-step activation method was put forward,activated carbon was made from coffee grounds impregnated by phosphoric acid through vacuum pyrolysis self-activation,effects of various activation conditions?Activation temperature,Pyrolysis pressure,Heating rate,Activation time and Impregnation ratio?on the performance of the coffee grounds activated carbon were considered.Analysis methods such as scanning electron microscopy?SEM?,BET specific surface area analyzer,Fourier transformed infrared?FT-IR?were used to characterize the surface morphology,BET specific surface area,pore size and surface functional group of activated carbon.Finally,through single factor experiment,the effects of various factors such as different dosage,adsorption time,solution p H and adsorption temperature on the two kinds of optimal activated carbon in simulated wastewater by Cr???adsorption were considered.Conventional one-step experimental results show that the best absorption performance of the activated carbon under the activation temperature was 498.1?,1.04 h of activation time and impregnation ratio set as 1.72wt%.Under these conditions,the yield of activated carbon was 30.4%,the adsorption of iodine gets up to 799±16mg·g-1,the relative surface area can reach 1004 m2·g-1,the total pore volume was 0.777 cm3·g-1,the t-Plot micropore volume was 0.051 cm3·g-1 and the average pore size was 3.088 nm.Additionally,the optimal preparation conditions of coffee grounds activated carbon was applied for 100 mg·L-1 Cr???absorption tests.Results show that the maximum adsorption capacity of heavy metal Cr???was 80% at adsorption temperature of 15? under the activated carbon dosage of 8g·L-1,adsorption time 60 min,and pH 3.0.Two-step experimental results show that the best absorption performance of the activated carbon under the optimum conditions of vacuum pyrolysis self-activation at operating temperature was 450 ?,activation temperature was 600 ?,-0.02 MPa of pyrolysis pressure,20 ?·min-1 of heating rate,30 min of activation time and impregnation ratio set as 1.6.Under these conditions,the yield of activated carbon was 27.1%,the iodine adsorption efficiencies of activated carbon increased up to 1398.4 mg·g-1,respectively,and then,relative surface area of activated carbon reached to 1420 m2·g-1,the total pore volume was 0.747cm3·g-1,the t-Plot micropore volume was 0.428 cm3·g-1 and the average pore size was 2.104 nm,Additionally,the optimal preparation conditions of coffee grounds activated carbon was applied for 100 mg·L-1 Cr???absorption tests.Results show that the maximum adsorption capacity of heavy metal Cr???was 87% at adsorption temperature of 15 ? under the activated carbon dosage of 7 g·L-1,adsorption time 80 min,and p H 3.0.Correlation study indicates that the optimal activated carbon?Two-step preparation?surface acidic oxygen functional group content is less,but the surface structure is complex,corrosion pits are more,the specific surface area is larger,the microporous are more,the adsorption performance is better.In this paper,the preparation of activated carbon from coffee grounds by one-step activation method was optimized,and a new process of preparing activated carbon from coffee grounds by two-step activation was put forward.Two-step activation process is the recovery of coffee residue pyrolysis oil,also prepared iodine value higher than the national standard(Iodine adsorption value 1100 mg·g-1)of activated carbon,the the commodity and the high value of its resources,and has a certain enviro nment,economic and social benefits. |
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