Catalytic characteristics of specialty carbon blacks in decomposition of methane for hydrogen production

Catalytic characteristics of specialty (color and conductive) carbon blacks (CBs) for methane decomposition were investigated and compared with those of rubber blacks. The catalytic characteristics of the color blacks were more similar to those of the rubber blacks, in such that both blacks exhibited very stable activity, a positive correlation of the activity with increasing specific surface area, and higher activation energies. However, the conductive blacks showed quasi-stable behavior, leveling-off of the activity at a somewhat higher value despite their specific surface areas being several times higher than the most active color black, and significantly lower activation energies. These differences were attributed to their morphology differences: the color and rubber blacks were nonporous, whereas the conductive blacks were highly porous. Particularly, the conductive blacks had many dented corners at the pore wall with a highly active armchair structure, resulting in the lower activation energies. Meanwhile, the reaction orders over all the specialty and rubber blacks lay between ca. 0.7 and 1, but no obvious trend in the reaction order was discernible with respect to the surface area or type of CBs.     

Surface energy distribution of carbon black measured by static gas adsorption

The energetic surface heterogeneity of various carbon blacks has been investigated by means of volumetric gas adsorption techniques. From the adsorption isotherms of ethene at a coverage of about 0.001 up to 1 monolayer the energy distribution functions of adsorption sites are evaluated. Four discrete species of energetic adsorption sites are identified on all carbon black surfaces irrespective of morphology. The fraction of the different adsorption sites is found to depend significantly on the microstructure and primary particle size and on manufacturing conditions as well.     

Hydrogen production by catalytic decomposition of methane over carbon black catalyst at high temperatures

Catalytic characteristics of carbon black for methane decomposition at high temperatures were investigated. A fixed bed reactor was made of carbon steel with 28 mm I.D and 450 mm height. The reaction was carried out under atmospheric pressure at temperature of 1,293–1,443 K. The objective was to investigate the catalytic activity of carbon black at high temperature, similar to the manufacturing process of carbon black. Almost 100% methane conversion was observed at 1,443 K, and the activation energy of the catalytic reaction over carbon black was 198 kJ/mol. The specific surface area decreased as the amount of deposited carbon increased. Since a large amount of the produced carbon was deposited on the surface, the increase of aggregates size and protrusions size of deposited carbon was larger than in the results of previous work.     

Hydrogen production by methane decomposition: Origin of the catalytic activity of carbon materials

A wide variety of carbon materials (ordered mesoporous carbons, carbon blacks, activated carbon, carbon nanotubes, coke and graphite) have been investigated as catalysts for hydrogen production by methane decomposition, with the aims of identifying the carbon properties which control in a greater extension the catalytic activity and determine the nature of the active sites involved in the reaction.The catalytic activity of the different carbon materials was determined and compared using temperature-programmed experiments in a thermobalance. The initial activity was followed through the threshold temperature, defined as the temperature at which hydrogen production starts being detected, whereas the average reaction rate was also calculated and compared. The lowest threshold temperature was observed with ordered mesoporous carbons (CMK materials), followed by activated carbon and carbon blacks. On the other hand, at long reaction times activated carbon was quickly deactivated yielding a relatively low average reaction rate. The deactivation process seems to be greatly linked to the presence of micropores while the long-term activity is retained in those materials with ordered mesoporosity (CMKs) or formed by nanoparticles (carbon blacks), which make them more resistant to deactivation by the formation of carbonaceous deposits.Whereas no clear dependence is observed between the threshold temperature and the surface area neither with the presence of polar groups in the carbon catalysts, characterization of these materials by XPS shows that a direct relationship exists with the amount of defects present on the graphene layers. This fact strongly supports that these defects are the main active sites for methane decomposition over carbon catalysts.     

Characterisation of Surface Activity of Carbon Black and its Relation to Polymer‐Filler Interaction

The surface activity of commercial and experimental carbon blacks varying in particle size and primary aggregate structure was investigated with regard to surface roughness and energetic surface structure of primary particles. The energetic surface structure was described by the site energy distribution function f(Q), which was determined mainly from the gas adsorption isotherms of ethene. It was found that the surface of carbon black was energetically very heterogeneous. It consisted of at least four different adsorption sites (I: Q ≈ 16 kJ · mol^?1; II: Q ≈ 20 kJ · mol^?1; III: Q ≈ 25 kJ · mol^?1; IV: Q ≈ 30 kJ · mol^?1). The fraction of the sites I–IV depended on the production process of the carbon black grades and the particle size. For the furnace blacks, the fraction of high‐energy sites decreased significantly with particle size and disappeared almost completely during graphitisation. This indicates that the reinforcing potential of carbon black is closely related to the amount of highly energetic sites that can be well quantified by the applied gas adsorption technique. The surface roughness was characterised by the surface fractal dimension, D_s, which was determined by two different techniques: the yardstick‐method and the extended Frenkel‐Halsey‐Hill‐theory (fractal FHH‐theory). It is found that the furnace blacks have an almost equal roughness with a surface fractal dimension of D_s ≈ 2.6 beyond a length scale z ≈ 6 nm. This result is shown to be in fair agreement with analytical models and computer simulations of surface growth of carbon black in a furnace reactor.

     

Carbon black used as a fluidization aid in gas phase elastomer polymerization: I. Carbon black-monomer interactions

The adsorption of butadiene on carbon black is a function of surface properties, high reinforcing, high surface area carbon black adsorbs more butadiene than low reinforcing big particle size carbon black. It is found that the functional groups on modified carbon blacks, oxidized or sulfur modified carbon blacks significantly reduces the butadiene concentration in headspace. Chemisorption of butadiene on the carbon black surface strongly holds butadiene on the surface, which prevents desorption of butadiene from the carbon black surface. These modified carbon blacks result in a very low concentration of butadiene in the headspace, usually 50-100 times lower than unmodified carbon black.     

废轮胎热解炭黑与工业炭黑的粒径及化学组成

用激光粒度分析仪测定了废轮胎热解炭黑的粒径分布,用扫描电子显微镜、X-射线衍射法及X-射线光电子能谱法分析了热解炭黑和工业炭黑的形态、表面化学组成以及表面碳元素的结合状况。结果表明,热解炭黑的粒径分布是添加在轮胎中各种型号工业炭黑粒径分布的叠加。热解炭黑表面形态和组成接近于工业炭黑N660;热解炭黑的表面附着更多的有机物以及ZnO、ZnS等无机物,且随着热解温度的升高,附着的有机物含量减小,无机物中ZnO含量减小,ZnS含量增多。     

不同炭黑对聚丙烯／炭黑复合材料导电性能的影响

研究了四种不同的导电炭黑与聚丙烯复合制得的复合材料的体积电阻率与炭黑含量的关系，确定了复合体系中炭黑的渗滤阈值。用扫描电镜(SEM)观察了不同炭黑含量的复合材料的断面形貌，用透射电镜(TEM)观察分析了四种炭黑的结构及粒径，并对其比表面积进行了测定。结果表明：炭黑不同，得到的复合材料的渗滤阈值有很大差别。炭黑结构性越高，比表面积越大，粒径越小，其导电性能越好，得到的渗滤阈值越低。特别是具有空壳结构的炭黑，其渗滤阈值明显低于其他三种炭黑。     

Variation in Catalytic Activity of Carbon Black during Methane Decomposition: Active Site Estimations from Surface Structural Characteristics

Abstract  

The variation in the catalytic activity of carbon black (CB) during methane decomposition was investigated by considering the number of active sites of CB. We demonstrated that the activity variation could be well estimated by assuming the edge length of graphitic sheets evolving from the CB surface. The results suggested that the activity variation originated from surface structural changes due to carbon deposition.     

炭黑对丁基橡胶硫化动力学的影响

本文主要研究了炭黑N330、N660和N990对丁基橡胶(IIR)硫化动力学的影响。研究表明,用三种不同炭黑填充的IIR其硫化反应均包含n=1级反应和n≠1级反应两个阶段。当n=1级反应时,反应速率常数K1均随着温度的升高而增大;当n≠1级反应时,反应速率常数K2则随着温度的升高而减小。同时,在硫化反应过程中活化能Ea随着炭黑粒径的增大而增大。     

Mixing of carbon black and polymer: Interaction and reinforcement

Interaction between carbon black and polymer starts during the mixing process; a primary agglomerate is formed, the composition of which is dependent upon the structure. The important carbon black properties are surface area, specific activity, structure (void, volume, anisometry), and porosity of the particles. On heat treatment of black at 3000°C., it loses its sites of high specific activity. Structure and specific activity determine incorporation time and further dispersion. During mixing, bound rubber is formed which is used as a measure of specific surface activity. In the final vulcanizate, the filler–polymer interaction is evident in reduced swelling in solvents (benzene, chloroform, cyclohexane,) etc. Below a certain critical degree of swelling, the percentage swelling is no longer dependent upon the amount of filler in the vulcanizate. Graphitized black vulcanizates exhibit in all solvents the same degree of swelling as the unfilled vulcanizate. This phenomenon is explained by the assumption of mobile adsorption of rubber chains on the carbon black surface. In untreated blacks the mobility on the surface is limited by sites of high energy of adsorption. In graphitized blacks such sites are no longer found, and swelling is unhindered by the presence of black. Reinforcement is explained by the more homegeneous distribution of tension between molecular chains due to slippage on the carbon surface.     

新一代炭黑——纳米结构炭黑的开发和应用

论及了纳米结构炭黑性能的表征方法，叙述了炭黑开发沿革和开发工作。纳米结构炭黑的性能可用反气相色谱法炭黑表面能分散分量来表征；纳米结构炭黑的改进向着限制炭黑聚集体尺寸分布中大尺寸的比例、进行干扰微品生成、增多微晶棱边、增加微晶缺陷的方向进展；不同粒径的炭黑可以通过沿反应炉轴线的不同位置注入原料油，使之在不同的温度场中反应获得。     

半焦炭催化甲烷裂解及动力学特性

在平推流反应器上,考察了非催化和半焦炭催化条件下甲烷裂解.利用气相色谱分析研究了甲烷裂解的规律.结果表明,半焦对甲烷裂解具有明显的催化作用,不同种类的炭催化剂表现出相似的催化活性.半焦炭催化剂条件下,甲烷裂解转化率同时受两方面的影响:一方面甲烷裂解产牛的积炭沉积在半焦表面及孔内,覆盖大部分的活性位,同时堵塞半焦内的孔道阻碍甲烷向半焦孔内扩散,使甲烷的裂解率降低;另一方面甲烷裂解生成的新物种反过来又对甲烷的裂解起催化作用,促进甲烷裂解.研究还表明,半焦中的灰分对甲烷裂解没有明显的作用,甲烷裂解主要受温度控制.采用简单的平推流模型对甲烷热分解动力学参数进行了计算,计算得到甲烷非催化和半焦催化裂解的表观活化能分别为154.02 kJ/mol和82.06 kJ/mol.     

Catalytic characteristics of carbon black for decomposition of ethane

The catalytic activities of rubber, color and conductive carbon black catalysts for decomposition of ethane were investigated in the temperature range from 973 to 1173 K. Significantly higher ethane conversion and lower ethylene selectivity were obtained in the presence of carbon black catalysts compared with non-catalytic decomposition, resulting in much higher hydrogen yields. This indicates that carbon black catalysts are effective catalysts for dehydrogenation of ethane to hydrogen and ethylene, as well as for the subsequent decomposition of ethylene to hydrogen and solid carbon. However, more methane was produced in the presence of carbon black catalysts than in non-catalytic decomposition. A reaction mechanism was proposed for the catalytic decomposition of ethane. The hydrogen yield increased with an increase in the specific surface area of the nonporous rubber and color carbon black catalysts with a surface area of up to approximately 100 m²/g. However, the hydrogen yield over the carbon black catalysts with higher surface areas, including the conductive carbon black catalysts with very high surface areas, did not increase significantly. The carbon black catalysts exhibited stable activity for ethane decomposition and hydrogen production for 36 h despite carbon deposition.     

炭黑化学镀铜及性能研究

以甲醛为还原剂,硫酸铜为主盐,采用还原法,在不同种炭黑表面化学镀铜。检测不同种镀铜炭黑的物理性能,包括电阻率、摩擦系数等;利用金相显微镜对各种镀铜炭黑进行金相分析,利用晶粒度评级软件分析镀铜炭黑的平均粒径。结果表明：控制合适的工艺条件,镀铜层能够比较完整地包覆在炭黑粒子及炭黑聚集体的表面,炭黑镀铜率可以高达70％;炭黑粒径越小,单位质量炭黑的比表面积越大,表面活化中心也越多,铜在炭黑表面的包覆效果越好;石墨化后炭黑的镀铜效果较石墨化前有所提高。     

Energy site distribution of carbon black surfaces by inverse gas chromatography at finite concentration conditions

Inverse gas chromatography (IGC) at finite concentration has been used to characterize the surface energy of a series of carbon blacks. It is known that there are many structural defects on carbon black surface and the surface energy is heterogeneously distributed. Using different molecular probes, IGC at finite concentration allows the determination of the surface energy sites distribution.     

Thermocatalytic decomposition of methane using palm shell based activated carbon: Kinetic and deactivation studies

Catalytic characteristics of activated carbon manufactured from palm shell (ACPS) for methane decomposition was studied using a thermobalance by measuring thee mass gain with time. A reaction order of 0.5 is obtained for methane decomposition over the activated carbon and the activation energy is 210 KJ mol^− 1. The activity of the activated carbon had decreased in almost a linear relationship with the amount of carbon deposited at 800 °C, which indicates that the carbon deposition occurred uniformly on to the carbon surface, while diffusion effect appeared to occur significantly at the last stage of the process at reaction temperatures up to 950 °C. The study of mass gain using different particle sizes indicates the existence of mass transfer effect and the pore mouth blocking which seem to take place particularly in large particles. Comparison between ACPS and commercial based activated carbon (AC) shows almost similar values with regard to change of mass gain with time, maximum amount of carbon deposited before deactivation and the deactivation time.     

Mesoporous carbon prepared from direct coal liquefaction residue for methane decomposition

Mesoporous carbons (MCs) were directly prepared from direct coal liquefaction residue (CLR) by KOH activation, and used as catalysts for methane decomposition. The results indicated that the prepared MCs were of a narrow pore size distribution centered at about 3.5 nm. The mineral matters in the CLR and their salts formed during KOH activation process served as templates for mesopore formation, through washing off the mineral matters and the salts occupied in the inner space of the carbon. The resultant MCs showed higher and more stable activity in methane decomposition reaction than commercial coal-based activated carbon and carbon black catalysts.     

压力对炭黑附聚体结构的影响研究

为了研究炭黑附聚体含量对橡胶补强的影响,本文在165MPa下将炭黑进行不同次数的压缩.采用SPM扫描了原样及压缩4次后的炭黑形貌;利用激光粒度分布仪测定了它们的粒径.讨论不同压缩次数下炭黑吸油值、吸碘值、CTAB及氮吸附值的变化规律.结果表明,从形貌图上看,压缩前后粒子的分布更加均匀.压缩后的颗粒粒径明显减小.随着压缩次数的增加,炭黑的吸油值都减小,且结构越高,减小值越大.炭黑的其余三个参数都随着压缩次数的增多而增大;其中,CTAB值和吸碘值的增幅较小,而氮吸附值增幅较大.     

Thermo-catalytic decomposition of waste lubricating oil over carbon catalyst

The thermo-catalytic decomposition of waste lubricating oil over a carbon catalyst was investigated in an I.D. of 14.5mm and length of 640mm quartz tube reactor. The carbon catalysts were activated carbon and rubber grade carbon blacks. The decomposition products of waste lubricating oil were hydrogen, methane, and ethylene in a gas phase, carbon in a solid phase and naphthalene in a liquid phase occurring within the temperature ranges of 700 °C-850 °C. The thermo-catalytic decomposition showed higher hydrogen yield and lower methane yield than that of a non-catalytic decomposition. The carbon black catalyst showed higher hydrogen yield than the activated carbon catalyst and maintained constant catalytic activity for hydrogen production, while activated carbon catalyst showed a deactivation in catalytic activity for hydrogen production. As the operating temperature increased from 700 °C to 800 °C, the hydrogen yield increased and was particularly higher with carbon black catalyst than activated carbon. As a result, carbon black catalyst was found to be an effective catalyst for the decomposition of waste lubricating oil into valuable chemicals such as hydrogen and methane.