Andrzej Krztoń

A study of carbonaceous char oxidation in air by semi-quantitative FTIR spectroscopy

Abstract The aim of this study was to describe the methodology of semi-quantitative characterization of carbonaceous material oxidized under mild thermal conditions. Infrared spectroscopic analysis was applied to the determination of chemical changes induced by oxidation. A curve fitting model has thus been developed to evidence the evolution of specific chemical groups during treatment. The possibility to follow mechanisms and kinetics of carbonaceous char oxidation through data obtained by this model has been demonstrated.

The characterization of coal macerals by diffuse reflectance infrared spectroscopy

Abstract Diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy was applied to study the structure of vitrinites, liptinites and fusinites isolated from different rank coals (77.0–91.5%C) using a centrifugal float–sink procedure. Among the macerals separated from a given coal, liptinites are characterized by the highest proportion of aliphatic CH groups, occurring principally as CH 2 , and fusinites by the most aromatic structure. Macerals separated from the low rank coals show comparable content of hydroxyl groups that occur as free OH or form similar types of hydrogen bonds. Carbonyl groups appear not only as conjugated ketones and quinones in vitrinites, but also as carboxylic groups in liptinites and low rank fusinites. CH ar /CH al ratio does not vary with carbon content in liptinites, but increases in vitrinites and fusinites. In the case of liptinites and vitrinites, a linear relationship between CH ar /CH al and reflectance is observed up to vitrinite R 0 value of 1.80%. For all macerals, the ratio CH ar /CC increases with reflectance, but at different rates. Structural parameters CH ar /CH al and CH ar /CC calculated from DRIFT spectra are very helpful in monitoring the differences among macerals of given coal and following structural rearrangement occurring with rank.

Application of Fourier self-deconvolution to the FT-i.r. characterization of coals and their N-methyl 2-pyrrolidinone extraction products

Abstract Analysis by Fourier transform infrared (FT-i.r.) spectroscopy of coals and their extraction products, i.e. extracts and residues, gives an insight into the chemical structure of the initial material and changes due to the separation procedure. High quality spectra are obtained for solids by diffuse reflectance FT-i.r. spectroscopy. They also provide rather broad overlapping bands which have to be manipulated to supply useful information. It is shown that Fourier self-deconvolution improves the qualitative and semi quantitative analysis of FT-i.r. spectra of the coals and their N -methyl 2-pyrrolidinone (NMP) extraction products. Several samples of coals (rank ranging from C (wt%, daf) 85.6 to 92.4) were studied. Four spectral regions were selected for discussion: 3100-2800 cm −1 ν(CH ar ), ν(CH ali ); 1750-1600 cm −1 ν(CO), ν(CC ar ); 1260-1034 cm −1 ν(CO); 900-650 cm −1 γ(CH ar ). Several ratios were calculated, including: [ν(CH ar )/ν(CH 2 ,CH 3 )], [ν(CO)/ν(CC)], [ν(CO)/ν(CC)], [γ(CH)(1H)/Σγ(CH)], [γ(CH)(2,3H)/Σγ(CH)] and [γ(CH)(4H)/Σγ(CH)]. These data led to a comparison of the structural characteristics of the coals and of their extraction products. In each case the results are discussed in relation to the various trends observed in the samples, the possible relations with Gieseler fluidity of coals and the sizes of molecular orientations in the relevant cokes obtained by pyrolysis at 1000°C.

A physicochemical study of carbonization phases. Part I. Tars migration and coking pressure

During the coking process, the production of volatile matters, in the plastic phase of the coking charge, leads to the development of dangerous internal pressures if hindrance is encountered in the gas release. By withdrawing and quenching coking coal charges at a given temperature in the course of heating, several phases of carbonization were isolated and submitted to physicochemical analyses: diffuse reflectance infrared spectroscopy (DRIFT), proximate and ultimate analysis, N-methyl-2-pyrrolidinone (NMP) extraction and hydrogen transfer (HT). By these means, two distinct ways of migration of volatile matters through coking material were evidenced. For ‘dangerous coals’ (including excessive coking pressure) the volatile materials migrate mainly from the plastic layer to the cold side of the oven, giving rise to impregnation of the remaining coal. On the contrary, a large part of volatile components of ‘safe’ coals migrate towards the hot side of the oven through semi-coke and coke. These results are in agreement with our preliminary study on the variations of the permeability of the different phases of carbonization.

Study of Residual Oxygen Species over Molybdenum Carbide Prepared During In Situ DRIFTS Experiments

In situ diffuse reflectance infrared Fourier transform spectroscopy was applied to monitor the temperature-programmed carburization of molybdenum trioxide. This technique indicated the existence of surface residual oxygen species on Mo2C synthesized even up to 973 K, indicating incomplete carburization. The presence of residual oxygen species on the carbide was deduced from the IR band at 790 cm-1. It was observed that the Mo2C sample, prepared with a final temperature of 1023 K, presented a higher density of sites titrated by carbon monoxide and a higher activity in benzene hydrogenation than the samples prepared at 923 or 973 K. This higher density of sites and activity were interpreted in terms of improved degrees of carburization at the surface of the carbide. The temperature-programmed desorption of benzene over those three Mo2C samples showed that the higher the activity in benzene hydrogenation, the lower the maximum desorption temperature: the tendency also observed going from Mo to Ru. This desorption temperature evolution could be explained in terms of an increased degree of carburization, which conferred to Mo2C a reactivity toward benzene closer to that of Ru.

Structure and properties of humic acids obtained from thermo-oxidised brown coal

Abstract The opportunity to isolate a considerable number of humic acids from the brown coal thermooxidative treatment products in the presence of small portions of oxygen and water has been shown. Variations in the functional content, thermal stability and biological activity of the prepared humic acids depending on the conditions of coal thermal processing have been revealed. It has been found that under the conditions of mild thermooxidative destruction a semicoke may yield up to 37.4% of the so-called ‘high-temperature’ humates and residual coal whose methylene-blue activity is 207.5 mg/g which is equal to that of the good activated carbon.

DRIFT spectroscopic characterization of coal samples modified by chemical treatments

The modifications afforded by several chemical treatments to the main functional groups of a bituminous coal were characterized by diffuse reflectance infrared spectroscopy. The starting materials were the polyanions and potassium coal adducts obtained from the parent coal, treated with potassium according to the Sternberg and Lazarov reactions. The results show the differences in the reactive sites involved in these reactions and in the behaviour of these sites during protonation or alkylation. Some of the typical functional groups introduced (or modified) can be active acceptor sites during hydrogen transfer from tetralin at low temperature (315°C) in conditions avoiding thermal bond cleavage. Taking into account the semiquantitative results of the i.r. analysis, the participation of several active sites in the total hydrogen transfer was estimated, indicating the role of quinonic, aromatic and alkyl groups.

The effect of water on the yield and structure of the products of brown coal pyrolysis and hydrogenation

The influence of various methods of Kansko-Achinsk brown coals humidification on their behaviour during pyrolysis and hydrogenation is investigated. Variations of derivatographic data, X-ray and DRIFT features of solid pyrolysis residues are presented. The hydrogenation liquid and gas products are studied by gas chromatography, gas chromatography-mass spectrometry and 1NMR spectroscopy. It was shown that part of the moisture is irreversible bound with coal, which participates in thermal hydrolysis reactions and produces the change in the polycyclic aromatic skeleton which is accompanied by a greater change in the yield of pyrolysis and hydrogenation products.

Reactivity and structural modification of coals in HNO3–Ac2O system

Abstract The interaction of different rank coals with equimolar HNO 3 –Ac 2 O mixture has been studied. This process, proceeding fast at 15–30 °C for several hours, results in changes of spatial and chemical structures because of nitration of coal arenes, formation of oxygen functional groups and partial cleavage of C–C cross-links. As a result, structurally modified coals (SMCs) are obtained as new coal-derived substances. Properties of SMCs were investigated by X-ray diffraction method, DRIFT spectroscopy and thermogravimetry. The main reactions responsible for structural modification have been proposed.

Thermodestruction of brown coals of different genetic types

The influence of brown coal genetic type and method of chemical pre-treatment on its behavior in pyrolysis processes has been shown. An important role of brown coal reductivity in coal thermal decomposition has been ascertained. It has been found that chemical pre-treatment permits variation of the rate of pyrolysis, the yields of pyrolysis products and structure of semi-cokes.