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.     

A new approach for modeling adsorption kinetics and transport of methane and carbon dioxide in shale

In this article, a new approach is proposed to investigate adsorption kinetics and transport of gases in shale. Due to co-existence of pores with different size in the shale, a set of adsorption processes happened in pores of different sizes are considered. A first-order multi-process model is developed, which can perfectly fit the adsorption kinetic data of CH₄ and CO₂ obtained at different temperatures. The modeling and pore characterization results indicate that an adsorption process happens in micropores/mesopores (<50 nm) and another adsorption process happens in macropores (>50 nm) in the Wufeng shale. Gas diffusion mechanism is dominant in micropores/mesopores, and gas seepage mechanism is dominant in macropores. The effective diffusivity of CO₂ is smaller than that of CH₄, because the adsorption of large amount of CO₂ in the pores hinders its diffusion. The coefficients related to the diffusion and seepage have no obvious trend with temperature.     

氢氧化钾活化烟杆制造活性炭及表征

以烟杆为原料,氢氧化钾为活化剂,采用一步炭化法制备了活性炭。采用正交实验研究了对活性炭得率和吸附性能的影响的主要因素,得到了最佳工艺条件,所制活性炭碘吸附值为1198.27 mg/g,亚甲基蓝吸附值为国家一级品标准的3倍。还测定了该活性炭的氮吸附等温线,通过H-K方程和密度函数理论表征了活性炭的孔结构,其结果与电子探针和透射电镜分析的活性炭微观结构相一致。     

微波辐射烟杆CO2活化制取活性炭及孔结构表征

以烟杆为原料,CO2为活化剂,采用微波辐射法制备了活性炭。采用正交实验研究了CO2流量、活化时间和微波功率对活性炭得率和吸附性能的影响,得到了最佳工艺条件。该工艺将常规加热方法的炭化和活化简化为一个过程,产品的碘吸附值超过了国家一级品标准,所需要加热时间仅为传统法的1/10,同时测定了该活性炭的氮吸附等温线,并通过BET、H-K方程和密度函数理论表征了活性炭的孔结构,结果表明该活性炭为微孔孔型,最后采用电子探针和透射电镜分析了活性炭的微观结构,结果与氮吸附测定的较为一致。     

Pore structure of activated carbons prepared by carbon dioxide and steam activation at different temperatures from extracted rockrose

The influence of the activation temperature on the pore structure of granular activated carbons prepared from rockrose (Cistus ladaniferus L.), extracted previously into petroleum ether, is comparatively studied. The preparation was carried out by pyrolysis of a char in nitrogen and its subsequent activation by carbon dioxide and steam (flow of water controlled to generate the same mol number per minute of water as well as carbon dioxide/nitrogen) at 700-950°C to 40% burn-off. The techniques applied to study the pore structure were: pycnometry (mercury, helium), adsorption (carbon dioxide, 298 K; nitrogen, 77 K), mercury porosimetry and scanning electron microscopy. The preparation by steam activation, especially at 700°C, yields activated carbons showing a total pore volume larger than those prepared by carbon dioxide activation. The pore structures present the greatest differences when the activations are carried out between 700 and 850°C and closer at higher temperatures. At high temperatures, the decrease of differences in pore development caused by carbon dioxide or steam is attributed to an external burn-off. The micropore structure of each activated carbon is mainly formed by wide micropores. At the lowest activation temperatures, especially at 700°C, steam develops the mesoporosity much more than carbon dioxide. At 950°C, a similar reduction of pore volume in the macropore range occurs.     

活性炭孔径分布对CH4/N2体系分离的影响

采用变压吸附分离的方法分离CH4/N2体系时,活性炭作为一种主要的吸附剂受到广泛研究.本文采用10-4-3模型计算得出,孔径为0.7～2.0nm的活性炭微孔对CH4/N2体系分离的效果最好;同时利用扩展Langmuir方程通过拟合4种活性炭对CH4/N2的吸附等温线,计算得出分离系数;最后讨论样品的孔径分布与分离系数的关系,进一步证明了10-4-3模型的计算结果.     

微波辐射-KOH活化兰炭粉制备活性炭

研究了以兰炭粉为原料,KOH为活化剂,采用微波辐射法制备活性炭的可行性。探讨了微波功率、碱炭质量比和活化时间对活性炭吸附性能的影响。同时采用美国ASAP-2020吸附仪测定了所制备活性炭的N2吸附脱附等温线和孔径分布,采用红外光谱分析了样品的表面官能团。结果表明:微波功率为700 W,碱炭质量比为3,活化时间为15 min工艺条件下制得的活性炭碘吸附值为694.5 mg/g,比表面积为513.62 m2/g,总孔容为0.510 3 cm3/g,平均孔径为3.973 8 nm,该活性炭为中孔型。以兰炭粉为原料,传统加热和微波加热制备的活性炭红外光谱图其峰形基本一致,只是峰强不同。     

Preparation of microporous activated carbon from Aegle marmelos fruit shell by KOH activation

Activated carbon (AC) is well‐known for its unique properties; hence, the search for new precursors and the investigation of new methods for the preparation of AC is still drawing attention of many researchers. In the present work, microporous AC was prepared from Aegle marmelos fruit shell (AMFS) by potassium hydroxide (KOH) activation. The effect of process parameters such as impregnation ratio, carbonisation temperature and holding time on porous characteristics was investigated. The porous characteristics of prepared AC samples were analysed by N₂ adsorption–desorption isotherms, and it was found that the isotherms obtained resemble typical microporous solids (Type‐I). The Langmuir surface area and total pore volume of the sample prepared at optimum conditions were found to be 937 m²/g and 0.33 cm³/g, respectively. The contribution of micropores to the porous characteristics of the prepared AC is very much appreciable, and about 97% of the total surface area and pore volume is attained by micropores. Pore size distribution (PSD) by Dubinin–Astakhov (DA) and micro‐pore (MP) methods confirmed the presence of micropores to a great extent with insignificant mesoporosity. © 2013 Canadian Society for Chemical Engineering     

金属壁与催化层一体化汽车尾气净化催化剂

开发了用于汽车尾气净化的金属壁与催化层一体化催化剂。该催化剂由金属表面氧化层载体和催化组分所组成。比较了孔径分布、比表面积、催化组分负载量对催化性能的影响 ,并讨论了空速对催化性能的影响。     

微波辐射-水蒸气法制备烟杆基颗粒活性炭

研究了以烟杆废弃物为原料,炭化过程中所产生的木焦油为主的复合粘结剂,采用微波辐射-水蒸气法制备颗粒活性炭的可行性。探讨了微波功率、活化时间以及水蒸气质量流量对颗粒活性炭吸附性能和得率的影响。得到了微波辐射-水蒸气法制备颗粒活性炭的最佳工艺:微波功率700 W,活化时间40 m in,水蒸气质量流量1.70 g/m in。此工艺条件制得的颗粒活性炭,碘吸附值1 060.81 mg/g,亚甲基蓝吸附值175 mL/g,得率30.83%。同时,测定了该颗粒活性炭氮吸附,通过BET法计算了活性炭的比表面积,并通过DFT表征了活性炭的孔结构。结果表明:该活性炭为微孔型,BET比表面积为1 109.22 m2/g,总孔容为0.613 1 mL/g。     

Extraction and purification of paeonol from Moutan Cortex by a combined method of steam distillation and antisolvent recrystallization to reduce energy consumption and carbon dioxide emissions

This study aimed to obtain paeonol with high purity by using the combination of steam distillation and antisolvent recrystallization (ASR) and to reduce the energy consumption and CO₂ emission in the preparation process. First, different experimental parameters were optimized by response surface methodology (RSM). Under the optimal conditions, the purity and yield of the as-obtained paeonol were about 98% and 56.97%, respectively. The physicochemical properties of purified paeonol were tested, showing consistency with those of standard paeonol. The energy consumption and CO₂ emission of the preparation process of ASR and single-solvent recrystallization were also investigated. Results showed that the energy consumption and CO₂ emission of ASR were about 4.41 J/mg and 0.006 kg/mg, respectively, which were 6.89 J/mg and 0.0095 kg/mg lower than those of ethanol recrystallization, respectively, and 50.22 J/mg and 0.0144 kg/mg lower than methanol those of recrystallization, respectively. The above results showed that ASR could obtain paeonol with high purity in a high-efficiency, low-energy, and environmentally protective manner.     

Supercritical carbon dioxide extraction,purification, and characterization of wax from sorghum and sorghum by-products as an alternative natural wax

The objective of this work was to obtain high purity natural wax from sorghum and by-products of sorghum processing (sorghum dried distillers grains with solubles [DDGS] and sorghum bran) using a green process based on supercritical carbon dioxide (SC-CO₂). SC-CO₂ extractions were carried out at varying temperatures (50, 70°C) and pressures (30, 40 MPa) at a CO₂ flow rate 1 L/min for 120 min. Significantly higher wax yield (4.9%) from DDGS was obtained by SC-CO₂ at 40 MPa/70°C compared with whole kernel (0.6%) and bran (3.3%) (p < 0.05). The yield of the extracts obtained by SC-CO₂ extraction was higher than that of the conventional hexane extraction for all three sorghum sources. The highest fraction of wax in the SC-CO₂ extracts was obtained from whole kernel extracts (89%), whereas it was 53.3% from the DDGS and 26.8% from the bran at the same extraction conditions. SC-CO₂ and hexane extracts from sorghum whole kernel shared a similar melting peak temperature of 76.3–77.9 and 79.7°C, respectively, while DDGS and bran extracts by SC-CO₂ showed a much lower melting temperature in the range of 50.7–61.9°C, indicating the presence of lower melting point components such as triacylglycerols. However, the melting points of the DDGS and bran extracts after ethanol purification were significantly increased with the observed peak temperature of 80.8 and 82.0°C, respectively. While the wax yield from DDGS and bran was higher than that of whole kernel, the sorghum whole kernel feedstock was found to be a more feasible feedstock to obtain higher purity wax.     

Hydrogenation of carbon dioxide by hybrid catalysts,direct synthesis of aromatics from carbon dioxide and hydrogen

Direct synthesis of aromatics from carbon dioxide hydrogenation was investigated in a single stage reactor using hybrid catalysts composed of iron catalysts and HZSM-5 zeolite. Carbon dioxide was first converted to CO by the reverse water gas shift reaction, followed by the hydrogenation of CO to hydrocarbons on iron catalyst, and finally the hydrocarbons were converted to aromatics in HZSM-5. Under the operating conditions of 350°C, 2100 kPa, and CO₂/H₅ = 1/2, the maximum aromatic selectivity obtained was 22% with a CO₂ conversion of 38% using fused iron catalyst combined with the zeolite. Together with the kinetic studies, thermodynamic analysis of the CO₂ hydrogenation was also conducted. It was found that unlike Fischer Tropsch synthesis, the formation of hydrocarbons from CO₂ may not be thermodynamically favored at higher temperatures.     

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO₂. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO₂/CH₄ molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO₂ molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO₂ concentration in the aqueous phase may not result in faster growth of CO₂ hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO₂, the growth for carbon dioxide hydrate was very slow in the beginning.     

Efficient synthesis of ethanol and acetic acid from methane and carbon dioxide with a continuous,stepwise reactor

The synthesis of C₂‐oxygenates such as ethanol and acetic acid accomplished by CH₄ dissociation and subsequent CO₂ insertion onto methyl radicals, named the stepwise reaction technology, has been demonstrated to be both feasible and efficient through initial experiments conducted in microreactor units. This article describes the development of this technology, highlighting the aforementioned stepwise technology using a dual‐reactor system, which can ensure that two raw gases enter the reactor uninterruptedly and are not mixed after reaction. The system productivity for acetic acid and ethanol displayed efficiencies greater than 5–10 times that of previous microreactor units. The investigation of mechanism indicates that acetic acid arises from insertion of CO₂ into M? CH_x, while ethanol is formed either by hydrogenation of acetic acid or by hydration of C₂H₄, which results from homo‐coupling of CH₄. The latter route is the preferred of the two. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

微波加热核桃壳制取活性炭及孔结构表征

以核桃壳为原料,采用微波加热-水蒸汽活化法制备了活性炭。研究了微波功率、活化时间和水蒸汽流量等因素对吸附性能的影响。最佳工艺条件为：微波功率600 W、活化时间7 min、水蒸汽流量5 mL/min,活性炭产品的碘吸附值1076．57 mg/g,亚甲基蓝吸附值195 mg/g,得率25．11%。该工艺将常规加热方法的炭化和活化简化为一个过程,所需加热时间仅为传统方法的1/21,产品活性炭的亚甲基蓝吸附值为国家一级品标准的1．44倍。同时测定了该活性炭的氮吸附等温线,通过BET计算了活性炭的比表面积,并通过H—K方程和密度函数理论表征了活性炭的孔结构。结果表明,该活性炭为微孔型,BET 比表面积1 154．91 m~2/g,总孔体积0．564 9 mL/g,微孔占总孔体积(体积分数,下同) 79．86%,中孔体积分数19．97%,大孔占0．17%。     

Pulsed plasma deposition from 1,1,2,2‐tetrafluoroethane by electron cyclotron resonance and conventional plasma enhanced chemical vapor deposition

Pulsed electron cyclotron resonance (ECR) plasmas from 1,1,2,2‐C₂H₂F₄ are used to deposit fluorocarbon films. The deposited films have a F : C ratio of 1, with only slight variations in % CF_x as the deposition pressure is decreased. The optical emission (OES) spectra of the pulsed C₂H₂F₄ plasmas show high intensity peaks for H, C₂, and C₃, with lower intensity CF₂ and F peaks. The dominant OES peak shifts from H_α to C₂ when the pressure is reduced, most likely a result of the increased electron temperature at the lower pressure. Gas‐phase recombination reactions may be occurring between the OES sampling region and the deposition substrate (～ 8‐in. distance), producing fluorocarbon molecular deposition species, thus accounting for the high degree of fluorination in the deposited films. Parallel plate plasma deposited films from C₂H₂F₄ show less fluorination than their ECR counterparts, as well as vastly different OES spectra, with CF₂ peaks dominating the spectra versus H and C₂. The presence of ion bombardment in the parallel plate system tends to defluorinate the depositing films, and thus can account for the less fluorinated films deposited in the parallel plate versus ECR systems. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2084–2092, 2001     

Growth and optical properties of cerium dioxide nanocrystallites prepared by coprecipitation routes

Nanosized cerium dioxide (CeO₂) powders have been synthesized using coprecipitation methods and cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) as the starting material. The growth and optical properties of nanosized CeO₂ powders were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano-beam electron diffraction (NBED), high resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) absorption spectrophotometry. The XRD result shows that the dried CeO₂ precursor powders (both before and after calcination at various temperatures and times) contained a single crystalline phase of CeO₂. In the dried precursor powders, the crystallites of CeO₂ measured 10.4 nm and 66.8 nm before and after calcination at 1273 K for 240 min, respectively. The indirect band gap energy (_Ei$E_i$) of CeO₂ decreased from 3.03 eV to 2.68 eV as the crystallite size increased from 10.4 nm to 66.8 nm, whereas the direct band gap energy (_Ed$E_d$) of CeO₂ also decreased from 3.79 eV to 3.38 eV.     

Review on photocatalytic conversion of carbon dioxide to value-added compounds and renewable fuels by graphitic carbon nitride-based photocatalysts

Photocatalytic reduction of CO₂ is known as one of the most promising methods to produce valuable fuels and value-added compounds. To overcome selectivity and efficiency downsides, various photocatalysts have been designed and developed. This review discusses the state-of-the-art in photo-conversion of CO₂ over graphitic carbon nitride (g-C₃N₄)-based composites. The modification strategies to improve photocatalytic activity of g-C₃N₄ were classified into different categories and discussed as structural modifications, elemental doping, copolymerization, fabricating heterojunctions between g-C₃N₄ and other semiconductors, Z-scheme heterojunctions, noble metal/g-C₃N₄ photocatalysts, and design of ternary nanocomposites based on g-C₃N₄. Finally, perspectives and future research works in this field were also outlined.     

甲基咪唑盐酸盐/草酸型低共熔溶剂的制备及其在模拟油中氧化脱硫中的应用

通过简单加热并搅拌甲基咪唑盐酸盐和草酸的混合物合成了甲基咪唑盐酸盐/草酸（[HMIM]Cl/H₂C₂O₄）型酸性低共熔溶剂,以[HMIM]Cl/H₂C₂O₄为萃取剂和催化剂、H₂O₂为氧化剂催化氧化法脱除模拟油中的二苯并噻吩,考察不同的脱硫体系、反应温度、催化剂加入量、氧硫比、模拟油中含硫化合物类型对脱硫率的影响。实验表明,在反应温度为40℃、模拟油量为5 ml、[HMIM]Cl/H₂C₂O₄加入量为1.25 ml、O/S 12、反应时间为140 min的最佳反应条件下二苯并噻吩的脱除率可以达到92.2%。动力学分析表明,该氧化脱硫体系符合一级反应动力学方程。循环使用7次后催化剂的活性没有明显降低。