S. Wallace

Quantification of nitrogen functional groups in coal and coal derived products

Abstract The identification and quantification of the nitrogen functions in coal and coal-derived liquids is important for the development of coal liquid-fuel processing technologies. This paper reports a method that provides a self-consistent analysis of nitrogen functionality in both solid coal and coal liquids. It involves the use of X-ray photoelectron spectroscopy (XPS), combined with potentiometric titration and i.r. spectroscopy, to provide an analysis of pyrrole- and pyridine-type functionality. The study has led to a revised value for the extinction coefficient of the N-H stretching i.r. absorption for coal-derived asphaltenes.

The functionality of nitrogen in coal and derived liquids: An XPS study

Abstract High molecular mass fractions considerably enriched in nitrogen compounds were obtained from coal-derived asphaltenes by means of a chemical separation scheme. X-ray photoelectron spectroscopy was used to determine the nitrogen functionality of samples before and after processing. It was found that the nitrogen species are predominantly pyrrole and pyridine types, with evidence of bifunctionality. Comparison with XPS spectra of the original coal and with a pyrolysis tar before hydrotreatment suggests that there was no significant change in the distribution of nitrogen functional groups in high molecular mass fractions after processing.

Isolation of nitrogen bases from coal-derived asphaltenes and preasphaltenes

Abstract High molecular-mass basic fractions considerably enriched in nitrogen compounds are obtained from coal-derived asphaltenes and pre-asphaltenes by means of a new acid/base fractionation procedure using acid-modified silica. Ultimate analysis, F.T.-i.r., and gas- and size-exclusion chromatography were used to characterise the basic fractions, and to show that the new method affords considerable advantages over adduction with gaseous hydrogen chloride.

Characterization of petroleum feedstocks for coal-oil co-processing

Abstract Point-of-Ayr coal was co-processed with five different petroleum residues under a variety of conditions in tubing bombs. In addition, a number of petroleum sub-fractions and hydrotreated fractions were co-processed with the coal to assess the influence of the various structural types on extraction yield. Feedstocks and liquid products were subjected to chemical fractionation followed by ultimate analysis, size exclusion chromatography and 1H nuclear magnetic resonance. Detailed analysis of the hydrotreated fractions indicates that under low severity conditions the aliphatic side chains are removed from the aromatics, whilst at higher severities this is followed by condensation of the aromatic units. Reasonable extraction yields were only obtained with the three most aromatic petroleum feedstocks and the most severely hydrotreated feeds. Coal extraction was found to correlate with the amount of pentane-insoluble aromatics in the solvent. The high yields obtained from experiments using anthracene oil as a third component indicate that the petroleum feedstocks contain significant amounts of hydrogen donors.

Quantification of organic sulphur containing functional groups for coal conversion processes

Abstract An improved and automated temperature programmed reduction (TPR) apparatus has been applied to the study of sulphur functional groups in model compounds, coals and coal derived products. Experiments were performed in two independent laboratories and showed good reproducibility. A set of sulphur containing model compounds representing the types of functional groups believed to be present in coal were studied and were found to exhibit characteristic H 2 S evolution profiles. Quantitative conversion was observed for the model compounds. To gain a better understanding of the processes involved cysteine was the subject of a detailed kinetic study. Samples from a coal liquefaction process were investigated and the changes in sulphur functional group distributions rationalised in terms of the processing conditions.

Characterization of pitches by solid state nuclear magnetic resonance

Abstract Solid petroleum, ethylene-cracker, and coal tar pitches were characterized by 13 C cross-polarizationmagic-angle-spinning nuclear magnetic resonance spectroscopy (CP/MAS n.m.r.) and by dipolar dephasing. The relative numbers of carbon atoms were determined by peak synthesis of the dipolar dephased (DD) spectrum and of the difference spectrum between the CP/MAS and DD spectra. Spectra and derived structural information obtained in this way were in good agreement with high-resolution n.m.r. spectra of pitch in solution. Solid state n.m.r. is shown to be an attractive alternative to the recording of spectra of pitches in reactive solvents.

Coal conversion in co-processing with heavy petroleum residues

Abstract Point-of-Ayr coal was co-processed with a series of petroleum residues under both mild and severe reaction conditions. Hydrocracking conditions were chosen to optimise coal conversion, whilst the lower severity reactions were used to investigate the structural effects of processing. Under hydrocracking conditions, co-processing conversions varied with coal/oil ratio, with the optimum near 50/50. Bimetallic catalysts were found to enhance coal conversion. In a second series of experiments coal was co-processed with a petroleum enriched by the addition of petroleum asphaltenes: enhanced solubilisation was associated with increased asphaltene content. In the same series the fates of nitrogen and sulphur were also dependent on asphaltene loadings.

DETERMINATION OF COAL REACTIVITY DURING COPROCESSING USING STABLE ISOTOPE MASS-SPECTROMETRY

The C-13/C-12 ratios of fractions with different functionality (saturates, aromatics, polar aromatics and asphaltenes) separated during mild coal-oil coprocessing runs have been determined by stable isotope ratio mass spectrometry on the CO2 produced by quantitative combustion. The proportions of coal-derived carbon in the different fractions can be determined from the difference in natural abundance of C-13 between the coal and oil starting materials. The correction of the data for isotope-selective effects between different fractions (based on data from oil-only runs) is discussed. The corrected data support a complex model for the mechanism of coal dissolution, with interactions between the coal reactant and all of the fractions of the soluble run product, together with retrograde reactions incorporating oil-derived carbon into the insoluble coke product.

Thermal extraction of bituminous coal with petroleum-derived solvents

Abstract A U.K. bituminous coal (84.1 wt.% C; 5.2 wt.% H; 7.2 wt.% O) has been coprocessed with a set of five petroleum residues of varied composition. The aim of the work was to test the feasibility of replacing a coal-derived solvent with a petroleum-derived solvent in the first, extraction, stage. The petroleum solvents used consisted of two atmospheric and three vacuum residues with widely varying structural properties. The optimum reaction conditions for the solubilization of coal with these residues was determined. The coal/petroleum interaction was enhanced by a high carbon aromaticity in the petroleum residue, but no simple correlations between the solvent structure and extraction efficiency have as yet been identified.

Electrochemical identification of aromatic structures containing basic nitrogen in coal-derived liquids

Abstract Differential pulse voltammetry at the hanging mercury drop electrode is used to determine the reduction potentials, E 1 2 , of the aromatic structures containing a basic nitrogen substituent in the asphaltene fractions of coal derived liquids. In comparison with PAH, the substitution of a nitrogen atom alters E 1 2 so that reduction occurs at less negative potentials. Comparisons of the voltammograms obtained from nitrogen rich and total asphaltene fractions show that the basic fractions are nitrogen analogues of the hydrocarbon structures found in the original asphaltenes.