Porosity Development in Carbons Derived from Olive Oil Mill Residue Under Steam Pyrolysis

Activated carbons were obtained from olive oil mill wastes (OMW) by a single-step steam pyrolysis process, under different conditions of heat treatment temperature (HTT = 873–1073 K) and duration of reaction (15–120 min). Porosity characteristics were determined from N₂ adsorption isotherms and subsequent analysis by the BET-and _s -methods. Development in the texture parameters was found to depend on both experimental variables. A two-step rate process of reaction is proposed to govern carbon activation: a slow external steam-carbon reaction (under mild conditions) removing disorganized material and is associated with considerable weight loss but with low generation of porosity. A second bulk gasification process dominates at high temperature, and/or prolonged duration, and leads to considerable evolution of porosity with minor change in burn-off. Pyrolysis/carbonization under the flow of steam is suggested to enhance removal of low molecular volatiles, retards decomposition of high molecular products, initiates controlled gasification at lower temperatures, and prevents shrinkage of the produced carbon skeleton. OMW seems to need severe conditions of temperature and duration to obtain good adsorbing carbons, or requires pretreatment to remove skin, flesh and seed contaminants.     

Activated Carbon from Some Agricultural Wastes Under Action of One-Step Steam Pyrolysis

A one-step steam pyrolysis scheme was applied, in the range 600–700°C, for the production of activated carbons from five lignocellulosic materials. The products were characterized by N₂/77 K adsorption for evaluating their surface area and pore volume. Simple carbonization at 700 C resulted in poor adsorbing carbons whereas porosity was remarkably enhanced under action of steam. Carbon precursors derived from date palm wastes (branches, leaves and date pits) proved feasible raw materials that produced good adsorbing carbons. Rice husks and barbecue charcoal developed porosity to a lower extent, due to the inherent ash content. All obtained carbons were essentially microporous due to the limited gasification. Steam is suggested to play a double role: it promotes both the release of volatiles with partial devolatalization, and enhances carbon formation.     

Control of pore development during CO2 and steam activation of olive stones

Several series of activated carbons were prepared from olive stones by means of carbonization followed by activation with carbon dioxide, water steam and a mixture of them, under different experimental conditions. The changes in porosity of the original char during activation were studied by adsorption of N₂ at 77 K, CO₂ at 273 K and Hg porosimetry. The study was carried out covering a wide range of burn-off (19–83%) using activation times of 20–120 min, and temperatures between 650 and 950 °C. It is shown quantitatively how the individual factors influence the development of microporosity. It was found that in general terms, increasing activation produces a continuous increase in the volume of micropores and mesopores. However, this development occurs in a different proportion whether CO₂ or steam are used: while CO₂ produces narrow micropores on the carbons and widens them as time is increased, steam yields pores of all the sizes from the early stages of the process. The simultaneous use of these two activating agents resulted positive at times higher than 1 h, since it yielded carbons with higher volumes of pores.     

Feasibility of bamboo-based activated carbons for an electrochemical supercapacitor electrode

This study focused on the preparation and electrochemical properties of bamboo-based activated carbons (ACs) through carbonization and subsequent activation with steam and non-aqueous electrolyte solutions. The specific surface areas and the capacitances of samples ranged from 445 to 1,025 m²/g and from 5 to 60 F/g, respectively, depending on the activation conditions. The sample activated at 900 ‡C for 60 min under our experimental conditions exhibited the highest capacitance and the largest specific surface area.     

Influence of HNO3 oxidation on the structure and adsorptive properties of corncob-based activated carbon

An investigation of the impact of strong oxidation with HNO₃ on the porosity and adsorption characteristics of char and activated carbons, derived from corncobs, is presented. Texture parameters, as obtained from N₂ adsorption at 77 K, showed a considerable decrease in surface area of the activated carbons with enhanced pore widening. The extent of porosity modification was found to depend on the scheme of activation of the precursor, simple carbonization, steam pyrolysis, steam gasification of the char, or chemical activation with H₃PO₄. Surface-chemical changes were detected by FTIR spectroscopy, where absorption bands assigned to carboxyl, carboxylate, carbonyl, and phenolic groups were observed. A SEM study demonstrated the erosive effect of HNO₃, detected by the presence of disintegration of the carbon grains, with the porous structure probably containing very large macropores. As a consequence of the oxidation process, elemental analysis showed high contents of O, H and N, and TG confirmed that the weight loss distribution in the thermogram becomes slower at higher temperatures. The removal of phenol decreased as a result of the formation of oxygen functionalities. Mono-nitrophenols were adsorbed in smaller amounts than phenol, and p-nitrophenol showed a relatively higher uptake than the other two mono-nitrophenols, whereas the uptake of Methylene Blue was improved. Removal of Pb²⁺ from aqueous non-buffered solution was considerably enhanced by chemical oxidation, which may be related to pore widening, increased cation-exchange capacity by oxygen groups, and the promoted hydrophilicity of the carbon surface.     

A study of the characteristics of activated carbons produced by steam and carbon dioxide activation of waste tyre rubber

This paper presents a study into the effect of different activation conditions on the porosity and adsorption characteristics of carbon adsorbents produced from waste tyre rubber. For the purpose of this work, three carbon series were produced using different activation temperatures (between 925 and 1100 °C) and oxidising agents (steam or carbon dioxide). Carbons produced to different degrees of burn off were characterised using gas (nitrogen) and liquid phase (phenol, methylene blue and Procion Red H-E2B) adsorption. Total micropore volumes and BET surface areas increased almost linearly with the degree of activation to 0.554 ml/g and 1070 m²/g, respectively, while the development of external surface area was particularly rapid at degrees of activation above 50 wt% burn off. Steam was observed to generate a narrower but more extensive microporosity than carbon dioxide. However, carbon dioxide produced carbons of slightly larger external surface areas. Activation at higher temperatures resulted in pores of slightly larger dimensions, although this was only evident in highly activated samples. Porosity characteristics were reflected in the capacity of the carbons to adsorb species of different molecular size from solution. In this respect, steam-activated carbons presented greater capacities for the adsorption of smaller molecular size compounds (phenol), while carbon dioxide-activated carbons adsorbed larger textile dyes more effectively.     

Steam and KOH activation of biochar: Experimental and modeling studies

Biochar was used as a precursor of activated carbon using physical (steam) and chemical (potassium hydroxide) activation processes. The effects of operating conditions for each activation method on the BET surface area of the product and reaction yield were investigated using central composite design (CCD). For both activation processes, quadratic models were developed, by Design-Expert software, for BET surface area and reaction yield. The optimum operating conditions were calculated by the models to produce physically and chemically activated carbons with large surface area and product yield. The optimum BET surface area and product yield of physical activation are, respectively, 643 m²/g and 56.9 wt%, and of chemically activated carbon are, respectively, 783 m²/g and 75.3 wt%, which showed good agreement with the experimental values. Average pore diameters of physically and chemically activated carbons were in the ranges of 13–26 Å and 13–15 Å, respectively.     

Gas adsorption on activated carbons from PET mixtures with a metal salt

Activated carbons were prepared from carbonized PET by steam activation via pretreatment by mixing PET with a metal salt [Ca(NO₃)₂·4H₂O, Ca(OH)₂, CaCO₃, ZnO, and AlNH₄(SO₄)₂·12H₂O], and with acid treatment after carbonization. The porous properties of the activated carbons were determined by the nitrogen adsorption method. The adsorption isotherms of CO₂, C₂H₆, nC₄H₁₀ and iC₄H₁₀ at 298 K on the prepared activated carbons were measured to determine practical applications and to obtain a better understanding of the porous structure of the prepared carbons. Steam-activated carbons via pretreatment have a larger mesoporosity than carbons with no pretreatment. The metal salt used in the pretreatment for steam activation has no influence on the microporous structure, but it does influence the mesoporous structure of the prepared carbons. Activated carbons prepared via pretreatment show a large adsorption capacity for nC₄H₁₀ and iC₄H₁₀. These carbons are suitable as adsorbents for canisters, etc. Application of the potential theory to adsorption data for the prepared carbons suggests that the pretreatment contributes to the formation of pores larger than 0.50 nm at high burnoff.     

水蒸汽活化工艺对石油焦基活性炭性能的影响

石油焦是易石墨化炭，孔隙率低，因此用水蒸汽法直接活化，吸附性能很差，其碘吸附值小于350mg/g。通过成型法得到了合格的活性炭，并考察了烧失率、活化温度、活化时间、水流量、水炭比等对活性炭吸附性能的影响，以独山子石油焦为原料制得活性炭的碘吸附值与亚甲蓝吸附值分别达871.58，100.67mg/g。     

Removal of Cu (II) from water pollutant with Tunisian activated lignin prepared by phosphoric acid activation

Activated lignin with a relative high BET surface area and a well-developed porosity has been prepared from Tunisian deposit lignin, by H₃PO₄ activation at various process conditions. Physical and chemical properties of activated carbons produced, implying BET surface area, Boehm titration, Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA), were investigated. It was found that the maximum surface area reached at the carbonization temperature of 500 °C in H₃PO₄ activation, and that the activated lignin prepared from lignin acidic activation, showed a surface area of 463 m²/g. The potential application of these carbons for the removal of heavy metal contaminant, has been investigated by measuring their adsorption capacities for Cu (II) as representative of main local toxic contaminant found in industrial wastewaters. The results obtained compare well and even favourably with those reported in literature for other unconventional materials.     

The development of porosity in heat-treated polymer carbons upon activation by carbon dioxide

A series of microporous carbons was prepared from cellulose triacetate by heat-treatment in the range 1230–2275°K and a parallel series of carbons was prepared by activation of members of the heat-treated series to 30% burn-off by reaction with carbon dioxide. The changes in porosity with heat-treatment temperature (HTT) were investigated by adsorption of carbon dioxide in the range 195–248°K and by measurement of mercury densities. By comparing porosity in unactivated and activated carbons the extents to which closed porosity can be recovered and open porosity developed by activation were investigated as a function of HTT. The predominant effect of heat-treatment was found to be conversion of open micropores to closed micropores with little change in total pore volume. Activation of 1230 and 1475°K carbons is confined almost entirely to development of micropores. With increasing HTT (meso- + macro-) pore development increases on activation while development of open micropores and opening of closed micropores become less significant.     

Characterization and application of activated carbon produced by H3PO4 and water vapor activation

Activated carbons have been prepared from woody biomass birch by using various activation procedures: a) treatment with phosphoric acid and pyrolysis at 600 °C in inert atmosphere, b) the same as in (a) followed by steam activation at the same temperature and c) treatment with phosphoric acid and direct pyrolysis in a stream of water vapor at 700 °C. The surface area and the porosity of the activated carbons were strongly dependent on the treatment after impregnation with H₃PO₄ (pyrolysis in inert atmosphere, steam pyrolysis or combination of both).Activated carbon, prepared by impregnation with phosphoric acid followed by steam pyrolysis (steam activation) had highly developed porous structure and the largest surface area among all prepared carbons (iodine number 1280 mg/g and BET surface area 1360 m²/g). The adsorption capacity of this sample for Hg(II) from aqueous solution was studied in varying treatment conditions: contact time, metal ion concentration and pH. The adsorption followed Langmuir isotherms and the adsorption capacity for Hg(II) at 293 K was 160 mg/g.     

Preparation of microporous sorbents from cedar nutshells and hydrolytic lignin

Carbon nutshells and hydrolytic lignin were used as starting materials for the preparation of microporous active carbons. Optimum parameters for cedar nutshell carbonization have been selected (temperature of carbonization 700-800 °C, rate of heating less than 3 °C/min) for the preparation of microporous carbons (average pore width 0.56 nm). The textural characteristics of microporous carbons made from nutshell are similar to those of a ‘Coconut’ carbon molecular sieve, but the latter has both a higher CO₂ adsorption capacity and a higher coefficient of N₂/O₂ separation. The influence of carbonization and steam-activation parameters on the microtexture and molecular-sieve properties of granular carbons made from hydrolytic lignin was also investigated. A low rate of heating (less 3 °C/min) promotes the formation of micropores with average sizes around 0.56-0.58 nm at carbonization temperature 700 °C. At the same carbonization temperature the average sizes of micropores were 0.7-0.78 nm at rates of heating more than 3 °C/min. The activation of lignin-char with steam at 800 °C resulted in the formation of active carbons with more developed micropore volume (0.3-0.35 cm³ g⁻¹) and with micropores of widths around 0.6-0.66 nm which are able to separate He from a He-CH₄ mixture. The size of the micropores was varied as a function of burn off value.     

糠醛废渣制备活性炭的研究

研究利用糠醛渣制取颗粒活性炭的工艺实验表明采用水蒸气活化法制备活性炭,最佳工艺条件为炭化温度400℃,活化温度800℃,活化时间1h;按本方法制得的活性炭强度可达93%,比表面积为45m2/g、碘值814mg/g、亚甲基兰吸咐值198mg/g、苯吸附值(质量百分数)为22.4%。这些指标与煤质活性炭的同类产品质量标准相当,能耗较低,投资少,具有良好的社会效益和经济效益。     

Transport and sorption of water vapour in activated carbons

The adsorption of water vapour on microporous carbons derived from the carbonization of coconut shell has been studied. The adsorption and desorption characteristics of water vapour on the activated carbons were investigated over the pressure range p/p₀ 0–0.95 in a static water vapour system. In these experiments the process of water adsorption/desorption was investigated by both kinetic and equilibrium experimental data. Activated carbons differing by the degree of burn-off have shown the importance of the microstructure. A carbon enriched with nitrogen functions underlined the influence of the surface chemistry.     

Steam-pyrolysis activation of wood char for superior odorant removal

A pre-charred, wood-based carbonaceous precursor was activated using a two-step process (steam-pyrolysis activation) to investigate the potential for optimizing an activation protocol for the production of powdered activated carbon (PAC) tailored to effectively remove the taste- and odor-causing compound 2-methylisoborneol (MIB). Activation temperature, activation time, and steam-to-carbon ratio were the activation parameters modified to find the best operating conditions. The success of the tailored PACs was judged on performance in batch experiments, which were designed to simulate actual water treatment plant conditions and used natural water spiked with ¹⁴C-MIB. Activation temperature had the greatest impact on PAC performance, with 1123 K providing the best operating point. The pore size distribution data revealed a strong correlation between an increase in mesoporosity and MIB removal in the raw waters. In addition, the tailored PAC with the optimized activation protocol outperformed existing commercially available PAC, indicating the plausibility of tailoring activation protocols for superior MIB removal from natural waters.     

KOH预处理除尘灰制备颗粒活性炭的实验研究

用除尘灰分离炭粉为原料，采用KOH预处理，水蒸汽活化的方法制备颗粒活性炭。实验证明，KOH预处理制备的活性炭有较高的比表面积，并且KOH预处理对活性炭的微晶结构和表面形貌产生影响。当KOH含量为10％时，所制备的活性炭比表面积和收率较高，灰分较低。同时本文对KOH影响机理进行了探讨，在炭化阶段KOH有利于促进生成难石墨化的炭素前驱体；在活化阶段，KOH对碳的气化有催化作用。     

Significance of the carbonization of volatile pyrolytic products on the properties of activated carbons from phosphoric acid activation of lignocellulosic material

Two series of activated carbons derived from China fir (Cunninghamia lanceolata) wood impregnated with phosphoric acid were prepared in a cylindrical container that was kept in a closed state covered with a lid (the covered case) or in an open state. The effects of the carbonization of volatile pyrolytic products of starting materials on the properties of activated carbon were investigated in the process of phosphoric acid activation. Elemental analysis and SEM observation showed that both activating in the covered case and increasing the mass of starting material used favored the carbonization of volatile pyrolytic products. An investigation of N₂ adsorption isotherms revealed that the carbonization of volatile pyrolytic products significantly enhanced mesopore development in the final carbons, especially pores with a size range from 2.5 to 30 nm, with little influence on micropores, and therefore produced a large increase in the adsorption capacity to Vitamin B12 (with a molecular size of 2.09 nm). Activated carbons with highly developed mesopores could be obtained in the covered case. The carbonization mechanism of volatiles was discussed and two different carbonization pathways (in solid and gas phases) were proposed during phosphoric acid activation.     

Effect of preparation conditions on the properties of a coal-derived activated carbon honeycomb monolith

Activated carbon honeycomb (ACH) monoliths were prepared by extruding of a mixture of bituminous coal and organic additives and subsequent carbonization and steam activation. Preparation parameters that were varied were carbonization temperature and activation time. The carbonization conditions were 500, 650 and 800 °C for 1 h and the steam activation conditions were 850 °C for 2, 4 and 6 h. The monoliths at various states were characterized by SEM, XRD, nitrogen adsorption and compression test. It was found that carbonization temperature has significant effects on pore size distribution and mechanical strength of ACH monoliths. The ACH monoliths prepared from high carbonization temperatures exhibited lower values of the BET surface area and total pore volume and higher value of the mechanical strength than those of the ACH monoliths prepared from low carbonization temperatures. This was attributed to the effect of high temperature carbonization that results in the formation of relatively less defective structures.     

Carbonization and CO<Subscript>2</Subscript> activation of scrap tires: Optimization of specific surface area by the Taguchi method

This research demonstrates the production of activated carbon from scrap tires via physical activation with carbon dioxide. A newly constructed apparatus was utilized for uninterrupted carbonization and activation processes. Taguchi experimental design (L16) was applied to conduct the experiments at different levels by altering six operating parameters. Carbonization temperature (550–700 °C), activation temperature (800–950 °C), process duration (30–120 min), CO₂ flow rate (400 and 600 cc/min) and heating rate (5 and 10 °C/min) were the variables examined in this study. The effect of parameters on the specific surface area (SSA) of activated carbon was studied, and the influential parameters were identified employing analysis of variance (ANOVA). The optimum conditions for maximum SSA were: carbonization temperature=650 °C, carbonization time=60 min, heating rate=5 °C/min, activation temperature= 900 °C, activation time=60 min and CO₂ flow rate=400 cc/min. The most effective parameter was activation temperature with an estimated impact of 49%. The activated carbon produced under optimum conditions was characterized by pore and surface structure analysis, iodine adsorption test, ash content, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The process yield for optimized activated carbon was 13.2% with the following properties: specific surface area=437 m²/g, total pore volume=0.353 cc/g, iodine number=404.7 mg/g and ash content=13.9% along with an amorphous structure and a lot of oxygen functional groups. These properties are comparable to those of commercial activated carbons.