Carboxyl group in coal

Correlation of percent oxygen in carboxyl groups in coal, Blom et al (20) (O) this study (7) (4-) this study corrected for decomposition of carbonates ( ) Campbell and Stevens (21) (A) Loison and Chauvin (22) (D) Fitzgerald and Van Krevelen (23) (V) Juutgen and Van Heek (24) after Hanbaba et al. (25). 

Further reference to Fig. 6 shows that the latter tar yield now plots with the bituminous coals with reference to the effect of the atomic H/C ratio. Similarly a second brown coal sample (Loy Yang) which, as recovered from the seam, has a very low ash yield (0.4% dry ash-free basis), and most of the carboxyl groups in the acid form, plots with the bituminous coals in Fig. 6 however, when the sodium-salt is produced from this coal before flash pyrolysis the tar yield is almost complete supressed. 

It is worth noting that XANES and EXAFS spectra obtained from a severely weathered bituminous coal were nearly identical to those obtained from lignite samples. This indicates that in the weathered coal calcium is also present in a dispersed form in which it is bonded to carboxyl groups in the macerals. A more detailed report of this work is given elsewhere (17). 

Examination of the data on C02 and pyrolytic water evolution may provide some insight into the thermal decomposition behavior of specific organic and inorganic structures in the parent coals. Some C02 may arise from the decomposition of inorganic matter within the coal. It also has been suggested (16) that decomposition of carboxyl groups in the... 

The NMR data confirm and amplify the IR data hydrogen-bonded protons are presented from phenolic and carboxylic groups in the coal and phenol groups added with the chemically combined phenol. The monoaromatic content (of fractions A and B especially) is high, also because of added phenol, but two-ring aromatic material also is present in all fractions (even triaromatic in C), which must have come from the original coal. The aliphatic material observed in the IR spectra of A, B, and C now is seen to consist principally of methylene bridges and short, branched aliphatic chains (a- and P-methyl predominate). 

It has been shown that fairly quantitative solid-state spectra can be obtained for coals. With other polymers our experience indicates the same behaviour. Only in the case of highly polar groups, e.g. carbonyl and carboxyl groups, may difficulties be noted. 

Figure 8. Percent oxygen converted vs. rank (2-5 min) (%), percent oxygen lost as CO or C02 (X), percent oxygen in coal as carboxyl or carboxyl groups.

Question 4. Why is the preliquefied insoluble product so easily liquefied The most probable answer. The preliquefaction product with the reduced carboxyl groups content is more easily liquefied than the parent coal. Based on the product distribution, solvent swelling data and the model simulation, this improvement results from a reduction in the CO2 associated crosslinks and from the bond breaking which produces the chloroform solubles. Both effects reduce the total number of bonds linking the network so that the coal can become fluid. If the chloroform soluble fraction is removed after preliquefaction and the residue liquefied, the drastic improvement in the liquefaction is not observed. The model simulation confirms that the residue alone will liquefy slightly better than the parent coal, but not nearly as well as the mixture. 

There is ample evidence in the literature for conversion of reactive hydrocarbons to carbonyl compounds by autoxidation. In coals, the final products of autoxidation under the conditions used in the present study could be a mixture of carbonyl and carboxylic acid surface groups. Under mild oxidation conditions, a different set of functional groups such as ethers as proposed by Liotta et al. or epoxides as suggested in Scheme V could be formed. There are numerous examples of alkoxy radicals rearranging to epoxides . Choi and Stock have shown that ethers can be produced from benzhydrol structures, which are invoked as intermediates in Scheme IV. At higher temperatures, the epoxides and ethers are unstable and may rearrange to carbonyl compounds. 

The distribution of carbon in the form of aromatic, hydroaromatic, and methyl carbon (as assessed in the present work) is presented in Table VIII. The sum of the three forms of carbon accounts for about 97.5-98.09f of the total carbon in lower rank bituminous coal (C < 86% carbon, dmf basis) and about 99.4% of the total carbon in case of the highest rank bituminous coal (C = 90.4%) studied. Small proportions of carboxyl groups are present in lower rank bituminous coal, and if this carbon is taken into account, it may bring the total up to 98% at the maximum. 

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