Franciszek Czechowski

Physicochemical structural characterization of ambers from deposits in Poland

Abstract The physical and chemical properties of 8 samples of amber from different localities in Poland (Baltic Coast, Belchatow Tertiary brown coal, and Jaroszow clay mine) were investigated by N 2 sorption at 77 K, positron annihilation spectroscopy for chemical analysis (PASCA) and by organic geochemical methods (FT-IR, 1 H and 13 C NMR, GC, and GC-MS). The porosity of the ambers as determined by PASCA consists of narrow micropores with diameters ranging from 0.8 to 0.9 nm and a volume 0.025 cm 3 g −1 . In the external eroded part of the amber samples (rind) the concentration of pores where positronium atoms can form is lower and consists of approximately12 the concentration as in their interior. Values of pore parameters determined from sorption of N 2 are comparable with those found by the PASCA method. The average diameter of pores ranges from 2 to 12 nm, while their volume varies from 0.018 to 0.048 cm 3 g −1 .. The chemical character of the ambers is similar based on FT-IR spectroscopy. However, noticeable differences in concentrations of ester and hydroxyl groups are observed in both exterior and interior regions, where the abundances of the ester groups are lower in the exterior rind. The proportion of organic material extractable with chloroform-methanol (1:1, v/v) ranges from 15 to 50% and correlates inversely to the average reflectances (R r ) of polished amber surfaces which range from 1.7 to 0.1 %. These variations are attributed to differing concentrations of oxygenated groups in the respective amber samples. The FT-IR spectra of the non-polar fractions (NP) from the extracts resemble the spectra of the source ambers. However, the intensities of the absorbance for the hdroxyl group are much lower, while absorbances for exomethylene groups are not present. The 1 H and 13 C NMR data of NP fractions showed a complex diversity of components in mixtures with different relative concentrations but predominantly aliphatic in character for the respective samples. GC and GC-MS analyses of these fractions revealed that they are comprised of a mixture of compounds typical for Baltic amber but with variable relative concentrations. Two groups of compounds are found to be common to all NP fractions. The first is a minor concentration of homologous n -alkanes with a characteristic Gaussian distribution in the range from C 22 to C 32 and maximizing at C 26 –C 27 . In addition C 22 is characteristically slightly higher in concentration compared to C 23 . The second group of compounds is comprised of succinates with methyl, fenchyl, bomyl and isobornyl alcohols. The composition of these diesters revealed the same equilibrium ratio between compounds with fenchyl, bornyl and isobornyl alcohols in all NP fractions. We suggest an early enzymatically controlled (bacterial) process in the formation of succinates during resin diagenesis from the biotic precursors, yielding the same characteristic ratio of the respective succinates in these ambers. These results show that all the ambers analyzed here fall into a common class of fossil resin, succinite (class Ia) independent of the sample location in Poland.

Formation of porous structures in activated brown-coal chars using O2, CO2 and H2O as activating agents

Two brown coals, xylitic and earthy, carbonized at 1173 K were activated with water vapour, carbon dioxide and oxygen, each producing a different distribution of porosity. In the xylitic coke, activated in the range of burn-offs from 1 to 70%, the action of water vapour results in the development of pores of all dimensions. At the highest burn-off the product has an effective surface area of 920 m2 g−1 and a total sorptive pore volume of 0.83 cm3 g−1, 33% of which is in micropores. Carbon dioxide creates, from the xylitic coke at the burn-off of 70%, a highly microporous adsorbent with about the same surface area (890 m2 g−1) as the corresponding water-vapour activated product. The pore volume of the carbon dioxide sample is lower (0.49 cm3 g−1) but these contain 63% of micropores, which amounts to a contribution of 92% of these pores to the effective total surface area. The activation of the xylitic coke with oxygen leads to a high development of porosity at low burn-offs, but becomes ineffective on continuation of the process to medium and high burn-offs. This is thought to be due to a blocking of the entrances of the micropores by surface oxygen complexes formed on the surface of the coke. Oxygen gives, at a high burn-off, a product with the lowest total adsorptive volume (0.45 cm3 g−1) and surface area (650 m2 g−1). All the activated products obtained from the xylitic coke can be regarded, when effective surface areas are considered, as microporous adsorbents. With the earthy coke a total adsorptive pore volume (consisting mainly of wide mesopores) is developed which is higher than with the corresponding xylitic coke, but this result is difficult to reproduce, because the earthy coke samples are easily influenced by temperature in the process of activation, especially that by oxygen.

Phenylnaphthalenes and polyphenyls in Palaeozoic source rocks of the Holy Cross Mountains, Poland

Source rocks from a marine depositional setting from Palaeozoic formations in the Holy Cross Mountains region (Midlands, Poland) were analysed for aromatics using capillary gas chromatography–mass spectrometry (GC–MS). The occurrence of two novel series of aromatic hydrocarbons in these sediments, namely phenyl derivatives of fused ring polycyclic aromatic hydrocarbons (PhPAH) and polyphenyls (PPh), was established. Furthermore, the methyl derivatives of these compounds were also present. The chromatographic behaviour of the triaromatic members of the series, i.e. two isomers of phenylnaphthalene (1-PhN and 2-PhN) and three isomers of terphenyl (o-TrP, m-TrP and p-TrP) was evaluated using authentic standards. The isomeric composition of the phenylnaphthalenes (PhNs) and terphenyls (TrPs) was found to depend on thermal maturity. In the lower maturity samples abundances of 1-PhN and o-TrP are higher. Increase in sample maturity is indicated by an increase in the relative abundance of 2-PhN as well as m-TrP and p-TrP. Three thermal maturity parameters of the organic matter based on the relative abundances of the PhN and TrP isomers are proposed: PhNR=2-PhN/1PhN, TrP1=p-TrP/o-TrP, and TrP2=(m-TrP+p-TrP)/o-TrP. In general their values positively correlate with the vitrinite reflectance (Ro) and MDR, while correlation of the other biomarker maturity parameters such as the Ts/Tm ratio are less apparent. The compounds above are believed to be geochemical products from unknown precursors. A potential geochemical process of formation for the o-TrP is proposed, and involves initial preservation of carbohydrates in sediments through sulfur incorporation, further dehydration, cyclisation and aromatisation to respective furan and/or thiophene derivatives, and finally reductive elimination of oxygen and sulfur in the furan and thiophene products, respectively.

EPR investigations of structure of humic acids from compost, soil, peat and soft brown coal upon oxidation and metal uptake

Free radical concentration and theirg-values in humic acids (HA) isolated from various sources were studied by quantitative EPR technique. EPR data for HA formed during composting and natural humification processes occurring in soil, peat and brown coal are given. In more detail the EPR data were analyzed for brown coal HA under carbonization, air oxidation (150°C) as well as metal uptake (Ca(II), Zn(II), Cd(II), Hg(II), Co(II), Ni(II) and Cu(II)) and NO2 reaction. Two groups of metal complexes were distinguished on the basis of their interaction with free radicals in HA. Ca(II), Zn(II), Cd(II) and Hg(II) ions increase free radical concentration, while Co(II), Ni(II) and Cu(II) ions quench the radicals compared to the raw HA. This phenomenon can be explained either by the strong interaction of the metal ions with active centres responsible for the quinone-hydroquinone-semiquinone equilibria, and/or by the antiferromagnetic interaction between radical spins and metal d orbitals. Gaseous ammonia was found to be a very useful base easily penetrating the solid matrix of HA and strongly influencing the equilibria. β-Diketone groups present in HA react with NO2 yielding iminoxy radicals. In the HA-metal complexes these structural units are engaged in metal coordination which lowers effectiveness of the iminoxyl synthesis.

Influence of metal ions binding on free radical concentration in humic acids. A quantitative electron paramagnetic resonance study

Abstract The influence of metal ions, e.g. Co(II), Cu(II), Mn(II), Ni(II), Fe(II), on free radical concentration in humic acids isolated from soil, peat and compost was investigated by electron paramagnetic resonance (EPR). The results show that metal ions with unfilled d-shell exhibit antiferromagnetic interactions with semiquinone radicals. Moreover, coordinated metals shift the quinone–semiquinone–hydroquinone equilibrium in the macromolecular matrix of humic acids. A strong decrease of semiquinone radical concentration in humic acid–metal complexes is observed. This effect is caused by interactions of metal ions with oxygen-containing stable radicals occurring in the aromatic systems of humic acids. Furthermore, the effect of metal coordination on free radical concentration in humic acids–metal complexes depends on the humic acid origin. FTIR spectroscopy was also used as an additional tool for studies of the metal ions interactions with carboxylic groups.

Activation of brown-coal chars with oxygen

Abstract Semicokes and cokes prepared respectively at 773 and 1173 K from brown-coals, xylitic and earthy, from Polish coal seams, were activated with gaseous oxygen (10% oxygen and 90% argon) in a thermogravimetric apparatus to different burn-offs. With increasing temperature of oxygen activation a constant decrease of the sum of micropores and mesopores is observed, but probably as a result of chemisorption of oxygen the micropore volume passes through a maximum at 663 K. There is a strong influence of the temperature of carbonization of the char on the formation of porosity in the products of oxygen activation: activated cokes have better adsorptive properties than activated semicokes. The highest value of surface areas (benzene adsorption) are, for semicokes and cokes respectively, 520 and 700 m2 g−1. These differences can be attributed to the uniform microporosity in the non-activated coke as distinct from the wide range of the micropore diameters in the non-activated semicoke, and also to the lack of ultramicropores in the former sample. The earthy type of brown coal yields products with a less developed porosity than the corresponding products from the xylitic coal. For the xylitic semicoke as well as for the coke, after continuing the process of activation to burn-offs higher than 50%, a lowering of adsorptive properties is observed.

Reactivity and susceptibility to porosity development of coal maceral chars on steam and carbon dioxide gasification

Abstract Chars obtained at 1173 K from macerals of low rank Janina bituminous coal, i.e. exinite, vitrinite and fusinite, were gasified in steam and carbon dioxide to 50% d.a.f. burn-off (BO). The morphological changes of chars upon gasification, examined using optical and scanning electron microscopy, revealed characteristic external zonal BO of exinite and vitrinite char grains gradually diminishing from the outer to the inner part. The extent of external BO evaluated from mercury density data of chars and gasification products showed that the reaction of steam proceeds preferentially at the internal surface of the char pore structure (70% d.a.f. of total BO), while the reaction of carbon dioxide proceeds more readily at the external char surface (60% d.a.f. of total BO). Porosity parameters of investigated chars and gasification products evaluated from sorption data of CO2 and C6H6 at 298 K showed that vitrinite is the most susceptible coal constituent for the preparation of porous carbon. Its char exhibits the highest reactivity towards the studied gasification agents as well as gives gasification products with the highest pore structure parameters. On the contrary, the values of the corresponding parameters for exinite char are the lowest. The influence of petrographic constituent mineral substances on the reactivity and porosity development of their chars has been assessed from their behaviour in the reactions of model composite chars (obtained from brown coal humic acids (HA) doped with the macerals low temperature ash (LTA)). It was shown that the reactivity of composite chars proceeds in parallel to the sum concentration of elements, strongly enhancing the rates of reaction for steam and carbon dioxide. Catalytic LTA enhancement of composite char reaction rate resulted in gasification products of higher mesoporosity and lower microporosity development.

Porphyrin analysis and coal rank—Porphyrin index of Coalification for bituminous coals

Abstract Methods are described for the isolation of gallium, iron and (in a few cases) metal-free porphyrin concentrates from a range of bituminous coals from the United Kingdom and from Poland. The weighted mean molecular mass of the metalloporphyrin homologues in each concentrate is determined, and this, converted to the metal-free value, comprises the Porphyrin Index . This is suggested as an independent scientifically based measure of the degree of coalification of the coal. Different methods of metalloporphyrin analysis suited to this purpose are examined. For gallium porphyrins, reverse phase high-pressure liquid chromatography was the most convenient: for iron porphyrins electron impact mass spectrometry has been used. Where comparisons have been made, there is reasonable agreement between the methods, although differences do exist. Thus hplc was found to be more sensitive to small amounts of more highly degraded systems and tended to give lower values of the Porphyrin Index. The Porphyrin Index in the series studied ranges from about 460 to 410, and decreases as coalification increases. For some Polish bituminous coals, the Porphyrin Index has been tested both laterally and vertically. Thus five different samples from the same seam but at different locations show only a small spread of the index (432–436), whereas samples taken from different depths at a single site (Mikolow 2) show a decreasing index with increasing depth. The lowest index value (413) was found for a highly matured sample from about 1138 m below the surface. As the depth of the sample source increased, the amount of porphyrin concentrate which could be extracted decreased and ultimately became so small that analysis was not feasible. Thus, the highest ranks of bituminous coals, including anthracites, are not amenable to study by way of the Porphyrin Index. The borehole study also revealed a change in co-ordinated metal with depth. At modest depths (174–374 m), iron porphyrins predominated, but below this gallium porphyrins became the more important (but only up to 0.1 ppm). The higher reactivity of iron porphyrins may account for this. Comparisons are made between the Porphyrin Index and mean vitrinite reflectance. This shows a scatter of points when all analytical methods are considered together, but the trend is clear. When the preferred analytical method (hplc of gallium complexes) is used throughout, the plot of mean vitrinite reflectance against Porphyrin Index has a slope of −0.012(5)%; the corresponding slope for electron impact mass spectrometric analysis of iron porphyrins is not significantly different at −0.010(7)%. It is concluded that the Porphyrin Index is a useful and independent indicator of coalification, and its usefulness appears likely to extend into the lignitic range.

Structural identification of paramagnetic iron porphyrins from Colorado coal with the use of 1D and 2D 1H NMR spectroscopy: geochemical implications on their origin from heme

Abstract A fraction of iron porphyrins from Colorado coal constituting one major and one minor C28 isomer was analysed with the use of 1D and 2D 1 H nuclear magnetic resonance spectroscopy. 2D 1 H COSY and NOESY experiments in a low viscosity solvent (CD 3 OD) led to the structrural identification of the major component. Assignment of the hyperfine shifted resonances, of all the peripheral substituents on the porphyrin macrocycle, resulted in an unambiguous identification of iron(III) 2,7,12,18-tetramethyl-13,17-diethyl porphyrin. Reliability of the 2D 1 H NMR method used was confirmed by analyzing a related structure, i.e. deuteroheme-IX in the same way. The minor constituent of the analysed fraction was identified by reproducing the 1 H NMR spectrum with its synthetic counterpart: low-spin iron(III) 2,7,12,18-tetramethyl-3,8-diethyl porphyrin. Both identified coal iron porphyrins represent products derived from a common protoheme-IX related precursor, selectively degraded via different routes during coal diagenesis.

Multi-stage activation of brown-coal chars with oxygen

Activation of xylitic brown-coal coke XBC 900 with water vapour and carbon dioxide, when modified by partial replacement of the basic activating agent with 10% oxygen at a lower temperature, results in products with an increased microporosity. Thus, oxygen as activating agent for xylitic coke develops, preferentially, micropores, and this property is more strongly pronounced for oxygen than for the carbon dioxide and water vapour. A drawback to the process of activation with oxygen, i.e. blockage of initially formed micropores by chemisorbed oxygen, can be eliminated by removal of the chemisorbed oxygen by heat treatment in argon (multi-stage oxygen activation). This increases the micropore volume of the xylitic brown-coal coke XBC 900 activated with oxygen to 70% total burnoff, from about 0.2 cm3 g−1 to almost 0.5 cm3 g−1. The increase of the total adsorptive volume (micropores and mesopores) of these samples is from 0.45 cm3 g−1 to over 0.6 cm3 g−1 and the surface area SBET in benzene increases from 650 m2 g−1 to over 1200 m2 g−1. These last values are close to the limiting conditions for 70% activation obtainable for this material. Temperature of carbonization of the brown-coal char has a strong effect on the possibility of pore development through further activation. Multi-stage oxygen activation of xylitic brown-coal semicoke XBC 500 produces a material with a smaller micropore volume and a lower surface area than that of xylitic brown-coal coke XBC 900 similarly activated.