Effects of micropore development on the physicochemical properties of KOH-activated carbons

Effects of micropore development through varying the KOH/char ratio on the porous, electrochemical, electronic, and adsorptive properties for corncob-derived activated carbons (ACs) prepared by means of the KOH activation method were systematically compared. The pore properties of ACs, including BET surface area, total pore volume, micropore volume ratio, bulk density, and product yield based on the raw material were investigated to gain an understanding for the influence of KOH dosage on the pore development. Element analysis and temperature-programming desorption (TPD) were used to obtain the information of chemical composition and surface oxygen functional groups on ACs in order to propose the reaction mechanism of KOH activation. Based on the pore development, KOH-activated carbons can be classified into two groups: a combination of physical activation and chemical KOH etching at low KOH/char ratios (0.5-2) as well as chemically uniform etching at high KOH/char ratios (≥3.0). From the adsorption study for five organics with molecular weights varying from 129 to 466 g/mol, the specific adsorption capacity of ACs for organics is independent of their specific surface area. The specific capacitance of ACs reached a maximum as the KOH/char ratio was equal to 3, attributed to a compromise between the specific surface area and electronic resistance of ACs.     

油茶壳微孔活性炭的制备及表征

以油茶壳为原料,经炭化、KOH活化,制备微孔活性炭。考查了活化温度、活化时间和碱炭比对微孔活性炭碘吸附值和产率的影响,并采用正交试验优化了制备条件。研究结果表明：活化温度800℃、活化时间180 min、碱炭质量比3.5：1时,活性炭的碘吸附值达3 221 mg/g,产率51.2%。采用比表面积孔隙分析仪测定了氮气吸附/脱附等温线,计算得BET比表面积为1 755.72 m²/g,平均孔径为2.15 nm,总孔容为0.328 cm³/g,微孔孔容占总孔容的55.8%;SEM分析可见活性炭表面具有大量孔隙结构;FT-IR分析表明活化促进了—CH₃、—OH热解,活性炭中仍保存含氧官能团。     

葡萄糖基多孔碳材料对CO2/CH4的分离性能

以淀粉糖（主要成分为葡萄糖）为碳前体,制备了一系列多孔碳材料（C-GLCs-800）,对其进行孔隙结构分析,并应用FT-IR、SEM、TGA对其进行了表征,测定了材料在288、298和308 K下的CO₂和CH₄吸附等温线,根据IAST理论预测了材料对CO₂/CH₄二元体系的吸附选择性。实验结果显示,活化条件对材料的孔隙结构有明显影响,随着KOH/C质量比的增加,所制备的C-GLCs-800比表面积和总孔容先增加后降低。其中C-GLC-800-4的BET比表面积高达3153 m²·g^-1,总孔容为2.056 cm³·g^-1。C-GLC-800-2的窄微孔（V_d<1 nm,孔容0.3538 cm³·g^-1）含量最高,为30.63%。C-GLC-800-2在298 K和10⁵ Pa下对CO₂吸附量高达3.96 mmol·g^-1,明显高于许多传统吸附材料和MOFs材料在相同条件下对CO₂的吸附容量。应用Clausiuse-Clapeyron方程计算了CO₂和CH₄在材料上的吸附热,应用IAST理论计算了CO₂/CH₄的吸附选择性,结果显示C-GLC-800-2对CO₂/CH₄的吸附选择性为8.35。     

Adsorption of phenol onto activated carbons having different textural and surface properties

Adsorption of phenol in aqueous phase onto activated carbons (ACs) having different textural and surface properties has been considered. Six types of ACs were used: three were commercial, and three were obtained from Kraft lignin chemically activated with sodium hydroxide, potassium hydroxide or ortho-phosphoric acid. The apparent surface areas of the commercial ACs varied from 620 to 1320 m²/g, while ACs made from lignin presented surface areas as high as 1300 m²/g and 2900 m²/g when prepared with H₃PO₄ and alkaline hydroxides, respectively; moreover, the highest proportion of microporosity was found for ACs derived from lignin. A kinetic study was carried out, showing that the phenol adsorption data may be correctly adjusted, for all the ACs tested, by an equation corresponding to a pseudo second-order chemical reaction. Freundlich, Langmuir and Tempkin equations were tested for modelling the adsorption isotherms at equilibrium, and it was concluded that Langmuir model fitted adequately the experimental data. However, Tempkin model fitted even better the adsorption data obtained with ACs derived from lignin activated with alkaline hydroxides, which are characterized by the highest number of surface groups. Remarkably high phenol adsorption capacities were found for the ACs prepared by activation of Kraft lignin with NaOH and KOH: 238 and 213 mg/g of AC, respectively. Finally, the adsorption of phenol was found to depend not only on the micropore volume, but also on the total amount of carbonyl and basic groups and on the ratio of acid to basic groups.     

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.     

复合活化剂制备稻壳活性炭影响因素及特性

以稻壳为原料,ZnCl₂-CuCl₂为复合活化剂,制备稻壳活性炭,并以BET比表面积和吸附性能为指标,通过正交试验对制备的工艺条件进行优化,并对制得的稻壳活性炭采用氮气吸附等温线、X射线衍射仪(XRD)表征。结果表明,稻壳可以被制得大比表面积活性炭。影响活性炭比表面积和吸附性能最重要的因素是氯化锌浓度和活化温度,最佳制备工艺条件是氯化锌浓度5 mol/L,氯化铜浓度 0.4 mol/L,活化温度500 ℃,活化时间2 h。该条件下制得的稻壳活性炭比表面积为1 924 m²/g,碘吸附值为1 041 mg/g,亚甲基蓝吸附值为 188 mg/g。     

采用KOH与NaOH活化剂所制活性炭表面化学性质及孔结构的比较

采用沥青焦为原料,以KOH和NaOH活化剂制备出不同碱炭质量比（R）系列活性炭。利用X射线衍射（XRD）和X射线光电子能谱（XPS）表征出所制活性炭的石墨层结构和表面化学性质,并用氮气吸附和脱附等温线计算出BET比表面积、DFT孔径分布及孔容。实验结果表明,与NaOH活化剂相比,KOH活化剂所制活性炭石墨层破坏更明显,表面含氧官能团也明显增加。当R=5时,KOH活化剂所制样品BET比表面积高达2939m^2／g,孔容为1．43cm^2／g;而NaOH活化剂所制样品BET比表面积和孔容分别只有1098m^2／g、0．53cm^2／g。     

Activated carbon from solid wastes using a pilot-scale batch flaming pyrolyser

Activated carbon has been prepared from solid wastes carbonised in a pilot-scale batch flaming pyrolyser. Wood furniture waste (chipboard and plywood), scrap tyres, urban sewage, and straw were selected as pollutant solid wastes for this study. Burn-off levels, porosity, and BET surface were determined. From furniture waste derived char, a highly microporous solid was obtained at 850°C with a BET surface area of 855 m²/g. A medium surface area (431 m²/g) activated solid was obtained from tyre derived char at 1000°C. An FT-IR spectroscopic study of activated tyre and furniture derived chars showed different chemical structures and a higher water adsorption capacity for furniture derived solids than for those derived from tyres. The low cost flaming pyrolyser can produce, at pilot scale, chars suitable for activation from furniture wastes and tyres.     

水蒸气活化法制备椰壳活性炭的孔结构特征

以农林废弃物椰壳在600℃炭化2h后的炭化料为原料,以水蒸气为活化剂,研究了活化温度、活化时间、水蒸气用量对活性炭的比表面积、微孔容积和收率等的影响。结果表明：椰壳炭化料的比表面积仅为185m^2／g,且以中孔为主。在活化过程中,通过提高活化温度和水蒸气用量缩短了活化时间,扩宽了孔径;当水蒸气用量和活化温度较为适宜时,延长活化时间,有利于微孔的形成。活性炭的比表面积、总孔容积、微孔容积可达：1465m^2／g,0．9703cm^3/g,0．7519cm^2／g。并通过非定域密度函数理论（NLDFT）对活性炭的孔径分布进行了表征。     

油茶壳残渣制备活性炭的工艺

以油茶壳醇浸取后残渣为原料,以磷酸活化法制备活性炭,考察了浸渍比、磷酸质量分数和活化温度等对活性炭吸附性能及其得率的影响;活性炭的吸附性能由碘吸附值、亚甲基蓝吸附值表征。结果表明,在酸/炭浸渍比为3:1、磷酸质量分数70%、活化温度500℃时,活性炭的吸附性能最佳,其碘、亚甲基蓝吸附值和得率分别为1043.29mg/g、148.5mg/g和38.77%。采用物理吸附仪在77K下测定其N₂吸附脱附等温线,利用BET法和BJH法计算比表面积和孔径分布,其比表面积为1626.45m²/g,平均孔径为4.7nm,总孔容为1.94cm³/g。同时采用FTIR和XRD分析了活性炭的表面官能团和微观结构。     

Preparation and Phosphine Adsorption of Activated Carbon Prepared from Walnut Shells by KOH Chemical Activation

Walnut-shell activated carbons (WSACs) with high surface area and predominant micropore development were prepared by KOH chemical activation. The effects of carbonization temperature, activation temperature, and ratio of KOH to chars on the pore development of WSACs and PH₃ adsorption performance of the modified walnut-shell activated carbons (MWSACs) were studied. Criteria for determining the optimum preparation conditions were pore development of WSACs and PH₃ breakthrough adsorption capacity of MWSAC adsorbents. The result shows that the optimum preparation conditions are a carbonization temperature of 700°C, an activation temperature of 700°C, and a mass ratio of 3. The BET surface area and the micropore volume of the optimal WASC are 1636m²/g and 0.641cm³/g, respectively. The micropore volume percentage of WSAC plays an important role in PH₃ adsorption when there is a slight difference in BET surface areas. High-surface-area WSACs with predominant micropores are suitable for PH₃ adsorption removal. The MWSAC adsorbent owns the biggest PH₃ breakthrough adsorption capacity (284.12mg/g) due to the biggest specific surface area, total pore volume, and micropore volume percentage. The MWSAC adsorbent will be a potential adsorbent for PH₃ adsorption removal from yellow phosphorus tail gas.     

淀粉基多孔碳材料的制备及其吸附CO2/CH4性能

以淀粉为原料,使用水热法将其碳化后用活化剂KOH对其活化,制备了淀粉基多孔碳材料,并对其进行结构表征和CO₂/CH₄的吸附性能测试,计算吸附热以及材料对CO₂/CH₄的吸附选择性,讨论了碳材料结构对其吸附性能的影响。结果表明：在制备过程中,随着活化剂KOH用量比例的增大,所制得的材料其比表面积和孔容增大,其孔径分布也就越宽。所制得的碳材料其比表面积可达2972 m²·g^-1。这些淀粉基多孔碳材料对水蒸气的吸附等温线呈现出Ⅳ类等温线。所制备材料对CO₂吸附容量主要取决于其孔径小于0.8 nm的累积孔容（Vd < 0.8 nm）。材料的超微孔的孔容越大,其对CO₂吸附容量也越大。所制备的C-KOH-1材料在101325 Pa和298 K条件下,对CO₂的吸附量达到4.2 mmol·g^-1,其对CO₂的吸附热明显高于其对CH₄吸附热,其对CO₂/CH₄吸附选择性为3.7～4.26,同时本文通过对材料的水蒸气吸附等温线进行测试,结果表明所得材料主要表现为中等憎水性,这对材料在实际工况的应用奠定了基础。     

Effect of textural property of coconut shell-based activated carbon on desorption activation energy of benzothiophene

In this work, the effect of the textural property of activated carbons on desorption activation energy and adsorption capacity for benzothiophene (BT) was investigated. BET surface areas and the textural parameters of three kinds of the activated carbons, namely SY-6, SY-13 and SY-19, were measured with an ASAP 2010 instrument. The desorption activation energies of BT on the activated carbons were determined by temperature-programmed desorption (TPD). Static adsorption experiments were carried out to determine the isotherms of BT on the activated carbons. The influence of the textural property of the activated carbons on desorption activation energy and the adsorption capacity for BT was discussed. Results showed that the BET surface areas of the activated carbons, SY-6, SY-13 and SY-19 were 1106, 1070 and 689 m²g^-1, respectively, and their average pore diameters were 1.96, 2.58 and 2.16 nm, respectively. The TPD results indicated that the desorption activation energy of BT on the activated carbons, SY-6, SY-19 and SY-13 were 58.84, 53.02 and 42.57 KJ/mol, respectively. The isotherms showed that the amount of BT adsorbed on the activated carbons followed the order of SY-6 > SY-19 > SY-13. The smaller the average pore diameter of the activated carbon, the stronger its adsorption for BT and the higher the activation energy required for BT desorption on its surface. The Freundlich adsorption isotherm model can be properly used to formulate the adsorption behavior of BT on the activated carbons.     

KOH activation of ordered mesoporous carbons prepared by a soft-templating method and their enhanced electrochemical properties

Ordered mesoporous carbon (COU-2) was synthesized by a soft-templating method. The COU-2 mesoporous carbon was activated by using KOH to improve its porosity. The mesopore size of COU-2 was 5.5 nm and did not change by the KOH activation. But, the BET surface area of COU-2 largely increased from 694 to 1685 m²/g and total pore volume was increased from 0.54 to 0.94 cm³/g after the KOH activation. The large increase of micropore volume is due to the increase of the surface area. Electrochemical cyclic voltammetry measurements were conducted in aqueous (1 M sulfuric acid) and organic (1 M tetraethyl ammonium tetrafluoroborate/polypropylene carbonate) electrolyte solutions. The KOH-activated COU-2 carbon shows superior capacitances over the COU-2 carbon and a commercial microporous carbon both in aqueous and organic electrolyte solutions. These results suggest that the carbons having regularly-interconnected uniform mesopores and micropores in thin pore walls are desirable for the electrodes in electrochemical double-layer capacitors.     

Porous properties of activated carbon produced from Eucalyptus and Wattle wood by carbon dioxide activation

This work focused on the preparation of activated carbon from eucalyptus and wattle wood by physical activation with CO₂. The preparation process consisted of carbonization of the wood samples under the flow of N₂ at 400°C and 60 min followed by activating the derived chars with CO₂. The activation temperature was varied from 600 to 900°C and activation time from 60 to 300 min, giving char burn-off in the range of 20/2-83%. The effect of CO₂ concentration during activation was also studied. The porous properties of the resultant activated carbons were characterized based on the analysis of N2 adsorption isotherms at −196°C. Experimental results showed that surface area, micropore volume and total pore volume of the activated carbon increased with the increase in activation time and temperature with temperature exerting the larger effect. The activated carbons produced from eucalyptus and wattle wood had the BET surface area ranging from 460 to 1,490 m²/g and 430 to 1,030 m²/g, respectively. The optimum activation conditions that gave the maximum in surface area and total pore volume occurred at 900°C and 60 min for eucalyptus and 800°C and 300 min for wattle wood. Under the conditions tested, the obtained activated carbons were dominated with micropore structure (∼80% of total pore volume).     

Synthesis of activated carbons by chemical activation of new anthracene oil-based pitches and their optimization by response surface methodology

This paper deals with the synthesis of new anthracene oil-based activated carbons by chemical activation with KOH. It focuses on the optimization of the processing conditions involved by means of surface response methodology. A factorial design (2³+3) in one block with four degrees of freedom was used to optimize the process, based on the responses BET surface area, total pore volume, mesopore volume, micropore volume and mol ratio CO:CO₂. The variables measured include KOH to pitch ratio (1:1, 3:1 and 5:1), activation temperature (700 up to 1000 °C) and pitch characteristics. The activation of anthracene oil-based pitch led to activated carbons with BET surface area values of 2880 m² g⁻¹. The factorial design expresses every response factor as a mathematical equation using the experimental variables. The most critical factor for each experiment design response has been identified from the analysis of variance (ANOVA). These mathematical models were also used to obtain the optimum processing conditions for the production of activated carbon with controlled properties. The experimental processing of the optimized activated carbons gave rise to a sample with BET, total pore volume, mesopore volume, micropore volume values which were in good agreement with those predicted by statistical analysis.     

Study on synthesis of low surface area activated carbons using multi-step activation for use in electric double layer capacitor

Low surface area activated carbon derived from compact mesocarbon microbeads (MCMB2010) was synthesized using a lower amount of KOH (1:1 weight ratio of KOH to MCMB) than normally used followed by electrochemical activation. The specific capacitance of the activated carbon heat treated at between 650 and 900 °C was increased up to ca. 118 F/cc (half cell base, 750 °C-heat treated sample) after electrochemical activation, even with a low surface area carbon (<50 m²/g). The morphology of low surface area activated MCMB determined by FE-SEM showed a smooth carbon surface without pores. The charge/discharge profiles were similar to those of conventional activated carbon. The specific capacitance of the activated samples increased with increasing heat treatment up to 850 °C after electrochemical activation. However, it was lower for the sample heat treated at 900 °C.     

煤-生物质基活性炭成孔机制及其吸附乙酸乙酯的性能

以CO₂为活化气氛,通过一步快速热解活化法从黑山煤粉与生物质混合物中制取活性炭。讨论了不同质量比率、活化温度和CO₂浓度对活性炭比表面积的影响。通过N₂吸附（BET）、扫描电镜（SEM）、拉曼光谱（Raman）和红外光谱（FTIR）对活性炭的性能进行了表征。确定了制备活性炭的最佳条件为活化温度900℃、质量比1、CO₂体积分数30%、活化时间120min时,活性炭的比表面积和孔容最大,分别为901m²/g和0.39cm³/g。最后,用乙酸乙酯吸附量验证了其吸附性能,最大累积吸附量为766.51mg/g。     

高比表面积煤质活性炭的制备与活化机理

以煤为原料,采用KOH活化法制备了高比表面积活性炭,分别考察了活化温度、浸渍比和活化时间等工艺参数对活性炭吸附性能的影响;测试了高比表面积活性炭在-196℃对N₂的吸附等温线、比表面积和孔径分布。结果表明,当活化工艺参数为活化温度900℃,浸渍比4,活化时间1.5 h的条件下可以制得较好的高比表面积活性炭产品,其比表面积为3135 m²·g^-1,孔容为1.72 cm³·g^-1,碘吸附值为2657 mg·g^-1;采用扫描电子显微镜观察了高比表面积活性炭的微观结构,采用气体分析仪检测了活化过程中的尾气成分,提出了高比表面积活性炭的活化机理。     

炭化温度对活性炭孔结构及电化学性能的影响

以海南椰壳（HN）及石油焦（BS）为原料,在不同预处理炭化温度下制备出HN系列和BS系列炭化样品,使用TG和XRD检测考察炭化温度对炭化样品反应活性和结构的影响,使用KOH化学活化法制备HN系列和BS系列活性炭样品,所制样品用氮气吸附和脱附等温线计算出BET比表面积、DFT孔径分布及孔容,并且通过直流循环充放电和循环伏安方法表征研究系列样品的电化学性能。实验结果表明,随着炭化温度的升高,HN及BS系列活性炭样品的微孔含量均有明显增加。椰壳炭所制活性炭适合无机电解液体系,其最高比电容达317F／g;而石油焦所制活性炭适合有机电解液体系,其比电容可达162F／g。