Coal dissolution, mechanism

A most striking result from the work described above is that the composition of the bottoms product and residues from the dissolution reaction did not depend on the chemical structure of the original coal material only their relative quantities differed. This supports the view of a mechanism involving the stabilisation of reactive fragments rather than an asphaltene-intermediate mechanism. The formation of a carbon-rich condensed material as a residue of the reaction and the fact that hydrogen transfer occurred largely to specific parts of the coal further supports this view. 

Mechanism of Microbial Desulfurization. The microbial dissolution of pyritic sulfur in coal by acidophilic bacteria has been thoroughly investigated (17,18,29). The pyrite is readily oxidized by oxygen or ferric ion, resulting in the ferrous state as follows ... 

The reaction of phenol and the ensuing dissolution of coal in the phenol catalyst mixture appears to follow no simple rate mechanism. Ouchi, al. were able to fit their data to a simple first order rate equation which upon integration is of the form ... 

Figure 3. Dissolution of Montour coal in accordance with a second-order rate mechanism...

The results from the IGC experiment on Upper Freeport Coal (APCS No. 1) are presented in Figure 3. There are three retention mechanisms likely to affect the IGC results. These mechanisms include molecular sieving, surface adsorption, and the dissolution of the probe in the stationary phase. The observed retention behavior results from the combination of the effects operating under the given conditions. The specific retention volume, Vg, is given by the sum of the retention terms in Equation 1 ... 

The mechanism of oxydesulfurization of coal has been extensively investigated by Vracar et al. (1970), Friedman and Warzinski (1977), Vetter (1967), and Joshi et al. (1982). The dissolution of sulfide minerals can be interpreted as an electrochemical surface reaction similar to the corrosion of metals. Oxygen is reduced at cathodic areas, and sulfides are dissolved liberating electrons to... 

In contrast to SCC of carbon and low-alloy steels in chloride, sulfide, and sulfuric acid environments by hydrogen-embrittlement mechanisms, cracking in several environments is attributed to passive-film cracking and/or active-corrosion-path anodic-dissolution penetration mechanisms (Ref 124). These environments include nitrates, hydroxides, ammonia, carbon-dioxide/carbonate solutions, and aqueous car-bon-monoxide/carbon-dioxide. Nitrate-bearing solutions are encountered in coal distillation and fertilizer plants hydroxide solutions in the production of NaOH and in crevices of steam boilers and ammonia cracking has occurred in tanks and distribution systems for agricultural ammonia applications. 

TRCS with the dissolution-induced cell detachment character is reported by Rollason et al. (Rollason et al., 1993) after Okano s and Takezawa s reports (Takezawa et al., 1990 Yamada et al., 1990). Recently, a few reports point out more convenient fabrication of cell sheet from the coated polymer dissolution-based TRCS (Mukundan et al., 2011 Nash et al., 2011 Varghese, Raj, Sreenivasan, Kumary, 2010). Nash et al. have showed that various ceU lines are able to be harvested from PIPAAm homopolymer-coated Thermonox disk surfaces. Cell adhesive character on a PIPAAm homopolymer-coaled disk surface is independent from coated polymer layer thickness. CeU detachment mechanism described in these reports is speculated to be due to the dissolution of coated polymers, as mentioned previously, by Rollason et al. (1993). 

Data for the kinetics of coal liquefaction have been published in the literature (1-11). A review of the reported studies has recently been given by Oblad (12). The reported data were mostly obtained in bench-scale reactors. Guin et al. (7) studied the mechanism of coal particle dissolution, whereas Neavel (7), Kang et al. (8), and Gleim (10) examined the role of solvent on coal liquefaction. Tarrer et al. (9) examined the effects of coal minerals on reaction rates during coal liquefaction, whereas Whitehurst and Mitchell (11) studied the short contact time coal liquefaction process. It is believed that hydrogen donor solvent plays an important role in the coal liquefaction process. The reaction paths in a donor solvent coal liquefaction process have been reviewed by Squires (6). The reported studies examined both thermal and catalytic liquefaction processes. So far, however, very little effort has been made to present a detailed kinetic model for the intrinsic kinetics of coal liquefaction. 

Murayama et al. [3] have explained the mechanism of zeolite synthesis from coal fly ash by its hydrothermal reaction with alkali. They have observed that alkaline medium type (viz., NaOH, Na2C03 and KOH) affects the mechanism of crystallization of zeolites. The authors have employed synthesis matrix bearing a specific solid/slurry ratio (i.e., 100 g/400 cm ), with the slurry being an aqueous mixmre of two different alkalis (viz., NaOH and Na2C03, NaOH and KOH and Na2C03 and KOH) to investigate the effect of the presence of different cations and/or anions on the alkali activation of fly ash. It has been reported that zeohtes, P and Chabazite, are the main crystals present in the synthesized product. The OH in the alkali solution remarkably contributes to the dissolution of Si" and Al " from coal fly ash, whereas Na" makes a contribution to the crystaUization of zeolite P, which has the tendency to capture K" in the cation exchange process. 

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