Study On Preparation Of Air-modification Combined Sulfurization Activated Carbon And Its Adsorption Of Furfural

Biomass activated carbon not only has the advantages of low price,wide source of raw materials,good renewability,high environmental adaptability and strong adsorption capacity,but also regulated pore structure and surface groups according to the demand of adsorption application.In addition to monosaccharide,oligosaccharide and other effective components,the dilute acid hydrolysate of lignocellulosic materials usually contains hydrolysis by-products such as furfural and heavy metals,so it needs to be purified first.In order to improve the adsorption efficiency of furfural and purify dilute acid hydrolysate on a large scale and at low cost,it is an inevitable choice to use cheap modifier and convenient modification process in the process of activated carbon modification.In this paper,the preparation of air synchronous modified activated carbon and its adsorption of furfural were studied.(1)Using commercial coconut shell activated carbon as the raw material,using CO₂ to activate and enhance the surface area and then carrying out sulfurization modification,or using ammonium persulfate solution to increase the oxygen-containing groups on the surface and then carrying out sulfurization modification,and comparing the pore structure,surface groups and microcrystalline structure of two kinds of sulfurized composite modified activated carbon products.The results show that the surface area and pore volume of activated carbon activated and sulfurized by CO₂ are increased up to 1750 m²/g and 0.815 cm³/g.The highest 30.29%of amorphous sulfur can be introduced into CO₂ activated sulfurization,which exists in the form of various sulfur elemental molecules and sulfur oxidizing groups.Compared with the direct sulfurization products,the surface area and pore integral of the wet oxidation vulcanization product of ammonium persulfate solution are 1080 m²/g and 0.451 cm³/g,respectively.The sulfur content of activated carbon oxidized with ammonium persulfate solution was up to24.38%,which is higher than 19.14%of the direct vulcanization product.The proportion of C-O structure type in vulcanized activated carbon is 10%-33%,and the proportion of C=O structure type is 1%-11%.(2)Air modifier was used to modify activated carbon synchronously by synchronous activation and oxidation,and was used as adsorbent for furfural aqueous solution.The effects of air modification on activated carbon structure and furfural adsorption characteristics at different temperatures were compared.The results show that the air modification of activated carbon has dual functions of activation and oxidation.The surface area and pore volume of air-modified activated carbon can reach 1465 m²/g and 0.548 cm³/g,respectively,and the average pore diameter is less than 1.60 nm.With the increase of air modification temperature from350°C to 650°C,the proportion of C-O carbon atoms and C=O carbon atoms decrease from18.72%to 13.07%and 12.84%to 2.80%respectively.Due to the increase of micropore volume,the furfural adsorption removal rate of air modified activated carbon is 96.74%,which is higher than that of reference activated carbon(89.52%).The adsorption of furfural by air modified activated carbon is an adsorption process dominated by the diffusion rate in the particles,and is affected by the factors of solution p H value,salt content,adsorption temperature and adsorbent dosage.(3)Activated carbon is sulfurized with elemental sulfur,and the effect of sulfur-carbon ratio,sulfurization temperature,sulfurization time and sulfurization modification times on the structure and properties of sulfurized activated carbon were compared and analyzed.The results show that as the ratio of sulfur to carbon increases from 0.1:3 to 9.0:3,the sulfur content of activated carbon increased to 37.89%,but the surface area decreased to 7.91 m²/g.With the increase of curing temperature from 240°C to 480°C,the surface area of activated carbon prepared by sulfur co-thermal method increased from 13.9 m²/g to 1223 m²/g,but the sulfur content decreased from 46.22%to 3.56%,and the proportion of C-O type carbon atom gradually decreased from 48%to 14%.With the sulfurization time extended from 1 h to 4 h,the surface area of the sulfurized product increased from 47 m²/g to 649 m²/g,the sulfur content decreased from 25.28%to 19.12%.In addition,the sulfur content of activated carbon prepared by multiple sulfur co-thermal method is not related to the number of sulfurization repeats.The process of the filling of sulfur vapor in multi-stage pores is mainly related to temperature,so the sulfurization modification can be simplified to the regulation of sulfurization temperature in the following study.(4)Activated carbon is modified by air modification,pretreatment,co-heating sulfurization and composite modification process.The structural changes of activated carbon in the process of composite modification and the synergistic effect of composite modification conditions and adsorption conditions on furfural adsorption were analyzed.The research results show that the sulfurized activated carbon(SAC550)was prepared under the air modification at550°C and sulfurization at 600°C.The total surface area and total pore volume of SAC550 are increased by 46%(925 m²/g)and 56%(0.396 cm³/g),respectively.The adsorption removal rate of furfural by air modified sulfurized activated carbon SACO450 loaded with 9.22%sulfur content can reach 96.33%,and the adsorption capacity is 87.43 mg/g,which is higher than that of direct sulfurized product SAC.According to the analysis of Langmuir model,Freundlich model and Temkin model,the adsorption of furfural by sulfurized activated carbon has some monolayer adsorption characteristics,specific chemical adsorption characteristics and spontaneous characteristics of adsorption process.The rate limiting step in the adsorption process of furfural on sulfurized activated carbon mainly comes from the diffusion process of furfural molecules in sulfurized activated carbon particles.(5)Comparing the typical operating conditions of initial furfural concentration,flow rate,fixed bed length and fixed bed diameter,and adjusting these four operating parameters in turn on the breakthrough point of breakthrough curve.The results show that,the breakthrough curves of large granular activated carbon increase rapidly at first and then decrease gradually,while the breakthrough curves of medium granular activated carbon and small granular activated carbon show the trend of"S"shape and"inflection point"respectively.The cumulative flow and adsorption capacity of large granular activated carbon at breakthrough point Can be increased to 35.41 L and 88.94 mg/g after reducing the initial concentration of furfural solution,respectively.After reducing the initial flow rate of furfural solution,the breakthrough curve of activated carbon showed the initial breakthrough stage of low concentration effluent,and then increased linearly until the breakthrough point.When the diameter of the fixed bed was increased,the breakthrough curve of the activated carbon showed an obvious"S"shape,but when the length of the fixed bed was increased,the breakthrough curve of the air synchronous modified activated carbon showed the initial breakthrough stage of the low concentration effluent,and then changed linearly to the breakthrough point.S600ACO650 is prepared by air modification at 650°C and sulfurization at 600°C.S600ACO650 packed fixed bed is used to treat 1000 mg/L furfural solution.Under optimum operating conditions,S600ACO650 has a maximum cumulative flow of 56.99 L and an adsorption capacity of 234.25 mg/g at breakthrough point.The cumulative flow of activated carbon breakthrough curve is significantly affected by fixed bed length,fixed bed diameter and particle size,and the adsorption capacity of activated carbon is significantly affected by fixed bed length similarly.