Carbonaceous precursors

The parent materials differ from each other in many aspects the differences are being related both to their origin (coal or pitch) and heat treatment temperature. Clearly, coal should be classified as a polymeric type precursor while the others, such as carbonaceous precursors of relatively low, except for AC, carbonization degree. Specific of pitch-derived materials is distinctly lower mineral matter and heteroatoms content. Anisotropic appearance with predominating flow type texture proves the superior extent of structural ordering in pitch-derived materials. 

In templating method, many polymeric precursors including resorcinol-formaldehyde gel,38,40,42,69,70,73"76 furfuryl alcohol,41,49,53, 55 7677 phenolic resin,49 72 74 melamine-formaldehyde resin,69,72 and mesophase pitch,17,45,46,54 etc. are generally used as carbonaceous precursors. The porous carbons are prepared by templating method according to the following procedures ... 

Among the inorganic templates, zeolite produces more regulated pores as compared to the silica template. If nano-channels in zeolite are completely filled with carbonaceous precursor and then the carbon materials are extracted from the zeolite framework, one can obtain the porous carbon of which structure reflects the porosity of the original zeolite template. The ordered mesoporous silica templates, e.g., MCM-4 838,39,47 and SBA-1547 have been employed to prepare the ordered porous carbons by the procedures involving the pore filling of the silica template with carbonaceous precursor followed by carbonization and silica dissolution. The resulting pore sizes of the ordered mesoporous carbons are smaller than about 10 nm. 

An important goal is to be able to produce a carbon material with well-defined properties from a given carbonaceous precursor. Based on carbonization mechanisms, some concepts concerning the control of anisotropic development from a given starting material can be developed. There are two principal approaches ... 

Activated carbons are the most widely used adsorbents in gas and liquid adsorption processes. They are manufactured from carbonaceous precursors by a chain of chemical and thermal activation processes. The temperature for carbonization and activation reaches up to 1100°C in thermal processes. Activated carbons develop a large surface area, between 500 and 2000m2g 1, and micropores with an average pore diameter <2nm. Mesoporosity and macroporosity is generated by secondary procedures such as agglomeration. The products are shaped as granules, powders and pellets depending on their application. 

Solid-state C NMR has been used to examine the crystalline quahty of cubic diamond produced either via firing of explosive compositions, or through compression of mixtures containing carbonaceous precursors with metallic matrix. In particular, the MAS technique has been used to estimate spVsp phase ratios for the obtained condensed carbon, whereas functionality of surface carbon atoms has been studied using the CPMAS method. 

As an alternative way, carbon has been loaded on Ti02 particles. This can be put in practice through the introduction of carbonaceous precursors on the Ti02 particles formed, and subsequent carbonization to produce Ti02-carbon composites. The carbon materials, derived from various carbonaceous precursors, have been practically introduced by means of thermal treatment in n-hexane, ethanol, or cyclohexane vapor [145-147,182-185] and carbonization of a mixture of Ti02 with poly(vinyl alcohol), poly(ethylene terephthalate), cellulose, sucrose, or citric acid [87,132-144,148,149,151]. A chemical vapor deposition method was also used to prepare MWCNTs deposited on Ti02 [198]. 

Carriazo D, Gutierrez MC, Ferrer ML, del Monte F (2010) Resorcinol-based deep eutectic solvents as both carbonaceous precursors and templating agents in the synthesis of hierarchical porous carbon monolith. Schem Mater 22 6146-6152... 

Commercial carbon fibers are obtained from solid organic precursor fibers such as polyacrylonitrile fibers, or from solid carbonaceous precursor fibers derived from pitch or mesopitch, the semisolid residue of oil refineries. 

Physical activation has traditionally included a controlled gasification of the carbonaceous material that has previously been carbonized, although occasionally the activation of the precursor can be done directly. Many different carbonaceous precursors have been employed for physical activation lignocellulosic materials, coals, woods, and materials of polymeric origin. The samples are typically treated to 800-1100°C with an oxidant gas, mainly CO2 or steam, so that carbon atoms are removed selectively. Although this process obviously involves a chemical reaction (and is not merely a physical process), it is known as physical activation. 

We begin by emphasizing that only carbon precursors will be analyzed (and not carbonaceous precursors) and reiterate that the selection of the precursor is crucial for the final porous texture of the AC. In this sense. Figure 1.4 presents the... 

The importance of the size of precursor and activating agent for porosity development of samples prepared by physical mixing has been analyzed. The decrease in the carbonaceous precursor particle size produces some inCTease in the final porosity. As an example, the decrease in the particle size from 2 to 0.6 mm leads to an ino-ease in porosity that could be up to 10% for a bituminous coal. Regarding the activating agent size, comparison between an anthracite activated with hydroxide lentils or powder hydroxide shows no meaningful porosity difference. 

As discussed in Section I, in this chapter we strive to simplify the study of reactions occurring during chemical activation with alkaline hydroxides by limiting our analysis to the activation of carbon materials. In other words, carbonaceous precursors that are not carbons are excluded. To identify the reaction products, to understand the types of reactions occurring, and to propose a main global reaction for hydroxide activation, a combination of different techniques has been used FTIR, in situ XRD, analysis of activation products followed by mass spectrometry, as well as thermodynamic data [99-101]. 

Some of the results discussed previously show that KOH and NaOH present similar activation behavior. However, there are some differences, as discussed in Section II.B. The relative effectiveness of the hydroxides depends on the nature of the precursor, especially on its structural order [100,101] NaOH is apparently better for carbons without structural order, whereas KOH seems better for those having some structural order. These intriguing results could be related to the different behaviors of Na and K as intercalates in the graphene layers of the carbonaceous precursors (or the carbon products) such influence of metal insertion has been recently reported [98,101]. 

This section focuses on the importance of structural order of the carbonaceous precursor. With this purpose, different MWCNTs have been prepared at different temperatures and thus have different structural order [101]. 

As mentioned above, only the minerals diamond and natural graphite are found in nature. All other carbon products are man-made and derive from carbonaceous precursors. These synthetic products eu e manufactured by a number of processes summarized inTable 1.2. Each process will be reviewed in the relevant chapters. 

Similar problems are encountered when isothermal phase systems are investigated in ambient atmospheres at temperatures lower than the thermodynamic firing temperatures from carbonaceous precursors. Below some 700 to 800°C the difficulties are so severe that the phase diagrams are rather constructed by calculation from measured thermodynamic data. Unfortunately, unavailable structural and compositional definitions for some of... 

The YBaiCus u(C03) 06 + w-3(t/2 oxide carbonate would appear as an intermediate phase upon an increased synthesis temperature of the 123 oxide from carbonaceous precursors (Karen and Kjekshus 1991, Gotor et al. 1995, Karen et al. 1990a, Karen and Kjekshus 1994a, Gotor et al. 1993). In O2 atmosphere, the oxide carbonate would... 

The volume of micropores and their size distributions in activated carbons, are a function of (a) the activation equipment (b) bum-off (c) the starting carbonaceous precursor (d) the activating gas (e) rate of gasification (a function of temperature) (f) rate of diffusion of activating gas(es) into and product gas(es) out of the carbon (g) extent of product inhibition of rate (h) amount and nature of inorganic impurities in char and (i) amounts of oxygen surface complexes present. 

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