Sulfur analysis of Bolu-Mengen lignite before and after microbiological treatment using reductive pyrolysis and gas chromatography/mass spectrometry

Atmospheric pressure-temperature programmed reduction coupled with on-line mass spectrometry (AP-TPR/MS) is used for the first time on microbiologically treated coal samples as a technique to monitor the degree of desulfurization of the various sulfur functionalities. The experimental procedure enables the identification of both organic and inorganic sulfur species present in the coal matrix. A better insight in the degradation of the coal matrix and the accompanying processes during the AP-TPR experiment is obtained by a quantitative differentiation of the sulfur. The determination of the sulfur balance for the reductive pyrolysis gives an overview of the side reactions and their relative contribution in the total process. The volatile sulfur species are unambiguously identified using AP-TPR off-line coupled with gas chromatography/mass spectrometry (GC/MS). In this way, fundamental mechanisms and reactions that occur during the reductive pyrolysis could be quantified, explaining the differences in AP-TPR recoveries. Therefore, this study gives a clearer view on the possibilities and limitations of AP-TPR as a technique to monitor sulfur functionalities in coal

Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework

Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts, and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area, and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multivalent cross-linker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 ??C with record-high surface area (4073 m2 g-1), large pore volume (2.26 cm-3), and hierarchical pore architecture. Such carbons simultaneously exhibit electrical conductivity >3 times more than activated carbons, very high electrochemical activity at high mass loading, and high stability, as demonstrated by supercapacitors and lithium-sulfur batteries with excellent performance. Moreover, the synthesis can be readily tuned to make a broad range of graphitic carbons with desired structures and compositions for many applications.clos

Activation and Micropore Structure Determination of Carbon-Fiber Composite Molecular Sieves

The progress of research in the development of novel, rigid, monolithic adsorbent carbon fiber composites is described. Carbon fiber composites am produced at ORNL and activated at the CAER using steam or CO{sub 2} under different conditions, with the aims of producing a uniform degree of activation through the material, and of closely controlling pore structure and adsorptive properties. The principal focus of the work to date has been to produce materials with narrow porosity far use in gas separations. Carbon fiber composites are prepared at ORNL, usually in plate or tubular form, by vacuum molding from water slurries containing phenolic resin and chopped isotropic petroleum pitch fibers. The composites are activated at the CAER in steam or CO{sub 2} using samples of dimensions up to 1.5 x 4 x 12 cm that are cut from the original plates. One of the objectives is to produce uniformly activated composites, which is especially critical when attempting to active large monoliths. It has been found that there are appreciable variations in the density and permeability of the as-formed composites that must relate to the forming technique. These variations are expected to exert some influence on the rate and extent of reaction and surface area development. In attempting to uniformly activate the composites, two reactor configurations have been investigated. In the more successful arrangement, steam ''is introduced at several points along the length of the composite. A reduction in steam partial pressure from 95vol% to 44vol% significantly improved the uniformity of surface area distribution. Activation with CO{sub 2} was still better, which is attributed to the much slower reaction rate than with steam. Measurements of composite dimensions have shown that there is an overall shrinkage during activation. A direct correlation is found between dimensional shrinkage and burnoff, and is similar for a and steam activation. The causes of the shrinkage are not yet clear. At levels of burnoff above about 40%, the extent of contraction is sufficient to produce stresses that result in fracture. Activated composites have been evaluated for the separation of CH{sub 4}-CO{sub 2} mixtures, and an apparatus has been constructed specifically for this purpose. Samples activated to low burn-off (5-7% wt loss) with low surface areas (from 300-500m{sup 2}/g) give much better separation of CO{sub 2} and CH{sub 4}, than samples produced at higher burnoff, and there appears to be no benefit in producing composites at burnoffs higher than 10%. The greater separation efficiency obtained at low burnoff means that the most effective CFCMS can be produced at relatively low cost. Continuing work will attempt to define the parameters that influence this gas separation, and whether these are applicable to other gas mixtures. Five samples of CFCMS have been recently prepared for shipment to British Oxygen Corporation (BOC) for testing as molecular sieves. The samples were machined to specific dimensions at ORNL (approx. 2.5 cm diameter x 1.25 cm thick) and activated at CAER. The samples were produced to different burn-off, but all have relatively narrow pore size distributions with average pore diameters around 6A

Activation and Micropore Structure Determination of Activated Carbon-Fiber Composites

Previous work focused on the production of carbon fiber composites and subsequently activating them to induce adsorbent properties. One problem related to this approach is the difficulty of uniformly activating large composites. In order to overcome this problem, composites have been made from pre-activated fibers. The loss of surface area upon forming the composites after activation of the fibers was investigated. The electrical resistivity and strength of these composites were compared to those made by activation after forming. It was found that the surface area is reduced by about 35% by forming the composite from pre-activated fibers. However, the properties of the activated sample are very uniform: the variation in surface area is less than {+-}0.5%. So, although the surface area is somewhat reduced, it is believed that making composites from pre-activated fibers could be useful in applications where the BET surface area is not required to be very high. The strength of the composites produced from pre-activated fibers is lower than for composites activated after forming when the carbon burnoff is below 45%. For higher burnoffs, the strength of composites made with pre-activated fibers is as good or better. In both cases, there is a dramatic decrease in strength when the fiber:binder ratio is reduced below 4:1. The electrical resistivity is slightly higher for composites made from pre-activated fibers than for composites that are activated after forming, other parameters being constant (P-200 fibers, similar carbon burnoffs). For both types of composite the resistivity was also found to increase with carbon burnoff. This is attributed to breakage of the fiber causing shorter conductive paths. The electrical resistivity also increases when the binder content is lowered, which suggests that there are fewer solid contact points between the fibers

Modification of the porous structure along the preparation of activated carbon monoliths with H3PO4 and ZnCl2

Two series of activated carbon monoliths (discs) have been prepared by chemical activation of olive stones with phosphoric acid or zinc chloride, without the use of any binder. A conforming step was introduced between impregnation with the chemical and heat treatment. Two equivalent series of granular activated carbons were also prepared in order to analyse the effect of conforming pressure on the porosity of the final activated carbon. The evolution of microporosity and the micropore size distribution has been followed by gas adsorption (N2 at −196 °C and CO2 at 0 °C) and immersion calorimetry into three liquids with different molecular dimensions (dichloromethane, benzene and 2,2-dimethylbutane). The experimental results indicate that activation by both chemicals produces a large development of microporosity but the differences between the granular and monolithic forms are more noticeable when using phosphoric acid. Thus, there is mainly a reduction in the interparticle space and macroporosity during the formation of the discs prepared using zinc chloride whereas there is an additional reduction in the volume and dimension of the meso- and microporosity when using phosphoric acid. The different behaviour of the two chemicals has been related to their effect on the precursor along the impregnation step.Authors acknowledge the financial support from MEC (The project MAT2004-03480-C02-02)

Activation and micropore structure determination of activated carbon-fiber composites

Rigid, high surface area activated carbon fiber composites have been produced with high permeabilities for environmental applications in gas and water purification. These novel monolithic adsorbents can be produced in single pieces to a given size and shape. The project involves a collaboration between the Oak Ridge National Laboratory (ORNL) and the Center for Applied Energy Research (CAER), University of Kentucky. The carbon fiber composites are produced at the ORNL and activated at the CAER using different methods, with the aims of producing a uniform degree of activation, and of closely controlling pore structure and adsorptive properties. The main focus of the present work has been to find a satisfactory means to uniformly activate large samples of carbon fiber composites and produce controlled pore structures. Several environmental applications have been explored for the activated carbon fiber composites. One of these was to evaluate the activated composites for the separation of CH{sub 4}-CO{sub 2} mixtures, and an apparatus was constructed specifically for this purpose. The composites were further evaluated in the cyclic recovery of volatile organics. The activated carbon fiber composites have also been tested for possible water treatment applications by studying the adsorption of sodium pentachlorophenolate, PCP

Activation and micropore structure determination of carbon-fiber composite molecular sieves. Topical report, 30 March 1994--14 April 1995

Progress in developing novel, rigid, monolithic adsorbent carbon fiber composites is described. Carbon fiber composites are activated using steam or CO{sub 2}, in order to produce uniform activation through the material and to control the pore structure and adsorptive properties. There is an overall shrinkage during activation, which is directly correlated with burnoff; burnoff above 40% results in fracture. Burnoffs higher than 10% does not produce any benefit for separation of CH{sub 4}-CO{sub 2} mixtures. Five samples of CFCMS have been prepared for testing as molecular sieves; all have relatively narrow pore size distributions with average pore diameters around 6A