Compounds In Coal Tar Research Articles

Dealkylation of alkylphenols in phenol oil on acid zeolites

The majority of the phenolic compounds in coal tar are alkyl-substituted phenols. To overcome the difficulty of separation, zeolites catalyzed dealkylation of alkylphenols was studied in a slurry-bed reactor. ZSM-5 displayed higher catalytic performance than other zeolites within a group of acidic zeolites with various topologies (including SAPO-34, ZSM-23, MCM-22, USY, and Mordenite). The yield of phenol gradually increased together with the zeolite acidity, but the types and yields of byproducts also increased in step with it. The pore size of the zeolites was a significant influence at similar acidity. The micropore of ZSM-5 inhibited some bimolecular processes, decreasing disproportionation/transalkylation as a result of transition state shape selection. In this study, the reaction paths of alkylphenols were investigated, based on the composition of products catalyzed by different zeolites, the distribution of products under different conditions, and the reaction process of various alkylphenols. Reaction process of alkylphenols included dealkylation, isomerization, disproportionation, transalkylation, and C-C cracking. Dealkylation took the place of isomerization as the primary reaction when the reaction temperature exceeded 350 °C. Disproportionation, transalkylation, and C-C cracking were exacerbated by excessive temperature. In addition, excessive reaction time and pressure can exacerbate side reactions, alkylphenols yields and coke deposition.

Characterization of nitrogen-containing compounds in coal tar and its subfractions by comprehensive two-dimensional GC × GC-TOF and ESI FT-ICR mass spectrometry based on new separation method

The molecular composition and structure of heavy oil and the subfraction have always been one of the most controversial topics despite the continuous improvement of detection and analytical methods. In this contribution, the composition and structure of nitrogen-containing compounds (NCs) in middle and low temperature coal tar (MLCT) and the subfractions are studied by GC × GC-TOF MS and ESI FT-ICR MS coupled with collision-induced dissociation (CID) through isolating a narrow window of mass-defined ions based on the developed MLCT subfraction separation method. It is found that the new separation subfraction method combined with high resolution mass spectrometry is efficient to detect the characteristics of each fraction at the molecular level. Eighty nitrogen compounds, dominant of quinolines, carbazoles and pyridines are identified in MLCT. The distribution laws of compound classes, carbon numbers, DBE are obtained with reasonable representative molecules for aromatic, resin and asphaltene. The qualitative analysis shows the island and archipelago structural motifs coexist in MLCT and the island-type is the predominant structure in aromatic (94%), resin (86%) and asphaltene (80%). The archipelagic structures in large molecules are more abundant. Meanwhile, the heterolysis mode is the predominant bond cleavages path for MLCT molecules and the proton transfers reactions occur during CID process.

Interactive tools to assist convenient group-type identification and comparison of low-temperature coal tar using GC × GC–MS

Coal tar is considered a valuable product obtained from coal pyrolysis. An accurate and convenient analytical study on its composition would be of great significance for its further processing and utilization. This work focused on the group-type identification and comparison of low-temperature coal tar by using comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC–MS). In this work, three low-temperature coal tar samples, diluted in dichloromethane, were analyzed by GC × GC–MS. It was observed that aliphatic hydrocarbons, benzene series, phenolic compounds, benzenediol compounds, naphthol compounds, naphthalene series, anthracene series, indene series and other different types of compounds in coal tar exhibited zonal distribution in the two-dimensional contour plot. The classification of different groups can be achieved by construction of spatial polygons. The classification results showed good reliability confirmed by manually identifying each compound contained in each group. The application of computer language for identifying compounds (CLIC) based on mass fragment characteristics and retention time assisted greatly in the identification of different chemical groups. Five major chemical groups including aliphatics, aromatics, oxygen-containing compounds, nitrogen-containing compounds and sulfur-containing compounds were retrieved from the two-dimensional contour plot by automated pattern recognition using CLIC expressions. The relative content of different chemical groups between a series of contour plots can be conveniently compared by comprehensive implementation of CLIC expressions and an interactive feature template matching function.

Analysis of Organic Sulphur Compounds in Coal Tar by Using Comprehensive Two-Dimensional Gas Chromatography-High Resolution Time-of-Flight Mass Spectrometry

Coal tar is a complex mixture of organic compounds obtained from the thermal treatment of coal; it contains several different chemical classes of compounds, such as polycyclic aromatic hydrocarbons, phenols and different heterocyclic compounds including sulphur derivatives. In the present research, a target analysis was carried out for the characterisation of fourteen different classes of organic sulphur compounds in coal tar by using cryogenically-modulated (CM) comprehensive two-dimensional gas chromatography-high resolution time-of-flight mass spectrometry (GC×GC-HR ToFMS) with the support of target analyte finding, a specific software function. Furthermore, absolute quantification data were obtained by using eight pure standard sulphur compounds, and 1-fluoronaphthalene as internal standard. Several figures-of-merit of the proposed method were measured (linearity, intra-day precision, limits of detection and quantification). Finally, the overall analytical performance of CM GC×GC-HR ToFMS was evaluated, in relation to MS similarities, mass accuracies, second-dimension peak widths, peak capacity and tailing factors. The approach proved itself as being a powerful analytical platform, benefiting from the high sensitivity, selectivity and resolving power, of both the GC and MS sides.

Molecular reaction kinetics model for the hydrodeoxygenation of low boiling point phenolic compounds in coal tar with Ni–Ce/SiO2 catalysts

In this study, 27 groups of hydrogenation experiments were carried out in a single-tube fixed-bed reactor using 9 phenolic compounds extracted from coal tar (fraction before 240 °C) as raw materials. Based on the experimental results, a set of molecular reaction kinetics model which involve 21 compounds and 33 chemical reactions was established. In this paper, the Runge–Kutta method was used to solve the dynamic equations, and the BFGS algorithm (a quasi-Newton optimization algorithm) is used to optimize the parameters of the dynamic model. The whole calculation process was completed on MATLAB software. The experimental results show that the maximum error of the model for predicting phenolic, unsaturated hydrocarbon and saturated hydrocarbon content in products is less than 5%, while the maximum error for predicting single substance is less than 10%. It could be calculated that the optimum temperature for hydrodeoxygenation of phenolic compounds is 633 K, which aims to retain aromatic hydrocarbons.

Pyrolysis characteristics of Shendong coal by CH3OH-THF swelling coupled with in-situ loading of metal ions

The effects of demineralization, CH3OH-THF mixed solvent swelling, CH3OH-THF swelling coupled with in-situ loading of metal ions (Ca2+, Mn2+, Cu2+ and Co2+) on pyrolysis reactivity and kinetic characteristics of Shendong low rank coal were investigated. The structure of coal samples was characterized by solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C NMR) and Fourier transform infrared spectrometer (FTIR). The pyrolysis characteristics and distribution of pyrolysis products of coal were analyzed by thermogravimetric analyzer/Fourier transform infrared spectrometer (TG-FTIR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and the fixed bed reactor. The results show that solvent swelling coupled with in-situ loading of Ca2+, Mn2+, Cu2+ and Co2+ promotes coal pyrolysis, and their net weight losses increase by 2.14 wt%, 0.07 wt%, 6.31 wt% and 6.18 wt%, respectively. Py-GC/MS analysis shows that the treatment of solvent swelling coupled with in-situ loading of metal ions Ca2+, Mn2+, Cu2+, Co2+ can increase the content of aromatic hydrocarbons and decrease the content of acidic compounds in coal tar. The content of benzene increases under the action of solvent swelling coupled with in-situ loading of Cu2+ and Co2+ by 42.73 wt% and 40.98 wt%, respectively. The kinetic calculation shows that the activation energies of the first and second stages of coal pyrolysis are reduced and the reactivity of coal can be improved by swelling coupled with in-situ loading of metal ions.

Transformation of sulfur and nitrogen during Shenmu coal pyrolysis

Transformation of sulfur and nitrogen and properties of pyrolysates (semicoke, retorting gas, coal tar) during Shenmu coal pyrolysis were investigated using XPS, TG-FTIR-MS, GC–MS and GC-PFPD. The results showed that total sulfur content in the semicoke decreased gradually and turned to sulfate sulfur and thiophenic sulfur with increasing pyrolysis temperature. In Shenmu coal, predominant nitrogen species consisted of pyrrolic and pyridinic compounds. Total nitrogen content was decreased, resulting from mutual conversion of different nitrogen compounds. The composition of retorting gas from TG-FTIR indicated that H2S began to release at 400 °C and reached maximum at about 600 °C. This trend was consistent with the release of carbonyl sulfide (500–650 °C) and SO2. GC-PFPD analysis revealed that detected sulfur compounds in coal tar were benzothiophene, dibenzothiophene and thiophene with the contents of 0.141%, 0.110% and 0.0004%, respectively. In coal tar, 57 kinds of nitrogen-containing compounds were identified using GC–MS, in which basic nitrogen was 0.90% and non-basic nitrogen was 0.23%.

Characterization of phenolic compounds in coal tar by gas chromatography/negative-ion atmospheric pressure chemical ionization mass spectrometry.

Phenolic compounds are commonly found in fossel fuels and bio-oils, and have a detrimental effect on the chemical stability of the fuels. A selective analytical method is needed to characterize the phenolic compounds in complex hydrocarbon mixtures. Gas chromatography/atmospheric pressure chemical ionization mass spectrometry (GC/APCI-MS) was used to characterize the phenolic compounds in a low-temperature coal tar and its narrow distillate fractions. Negative-ion APCI selectively ionized phenolic compounds in the coal tar. The [M-H](-) and [M-H+O](-) ions were derived from monohydric phenols, while [M-H](-) , [M-2H](-) , and [M-2H+O](-) were from benzenediols. Monohydric phenolic compounds with 1-4 aromatic rings and some dihydric phenolic compounds were identified. The results from GC/APCI-MS were validated by those from negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FTICRMS). Negative-ion GC/APCI-MS was proposed and successfully used to characterize phenolic compounds in coal tar samples. This technique can potentially be used for the characterization of phenolic compounds in other complex hydrocarbon systems. Copyright © 2016 John Wiley & Sons, Ltd.

On-line combination of high performance liquid chromatography with comprehensive two-dimensional gas chromatography-triple quadrupole mass spectrometry: a proof of principle study.

The present contribution is focused on the on-line combination of high performance liquid chromatography (HPLC), cryogenically modulated comprehensive two-dimensional gas chromatography (GC × GC), and triple quadrupole mass spectrometry (QqQ MS), generating a very powerful unified separation-science tool. The instrument can be used in seven different combinations ranging from one-dimensional HPLC with a photodiode array detector to on-line LC × GC × GC/QqQ MS. The main focus of the present research is directed to the LC-GC × GC/QqQ MS configuration, with its analytical potential shown in a proof-of-principle study involving a very complex sample, namely, coal tar. Specifically, a normal-phase LC process enabled the separation of three classes of coal tar compounds: (1) nonaromatic hydrocarbons; (2) unsaturated compounds (with and without S); (3) oxygenated constituents. The HPLC fractions were transferred to the GC × GC instrument via a syringe-based interface mounted on an autosampler. Each fraction was subjected to a specific programmed temperature vaporizer GC × GC/QqQ MS untargeted or targeted analysis. For example, the coal tar S-containing compounds were pinpointed through multiple-reaction-monitoring analysis, while full-scan information was attained for the oxygenated constituents.

GC-MS Analyzing of Coal Tar of Lignite Briquette from Low Temperature Pyrolysis

Distillation and GC-MS were employed to analysis the coal tar of low-temperature pyrolysis of lignite briquette by contrasting with standards: the fraction below 340°C in the tar distillates of brown coal tar accounted for 83.30% and the other greater than 340°C is pitch accounted for 16.32%. 34.00% of coal tar are hydrocarbons which are mainly consisted of fat aliphatic hydrocarbon and include few alkene and cycloparaffins. The content of phenolic compounds in coal tar, mainly comes from the fraction below 210°C, is 11.68%. 16.86% of coal tar is aromatic compounds which are mainly composed of substitutive derivative of polyalkylbenzene distributing in all kinds of fractions; and a small amount of aromatic compounds which is concentrated in the fraction below 300°C. The content of oxygen-containing, nitrogen-containing and heterocyclic compounds is 4.47%, 0.57%, 2.11%, respectively.

Mild hydrotreatment of low temperature coal tar distillate: Product composition

The hydrogenation of low temperature coal tar was carried out over a MoNiWP/Al2O3 catalyst under mild conditions to produce clean liquid fuel. The effects of temperature, pressure and liquid hourly space velocity (LHSV) on product composition were determined by FT-IR and GC–MS analysis. The feedstock and products were classified into several groups according to saturation level to probe the reaction mechanisms of the main aromatic compounds in coal tar. At 375°C, 6MPa and LHSV of 0.4h−1, alkyl-phenols and alkyl-naphthalenes were transformed into cycloalkanes and phenyl cycloalkanes with the yield of 60.4% and 83.9%, respectively. The properties of feedstock were clearly upgraded after hydrotreatment. Methyl substitution on aromatic rings negatively influenced to the conversion of phenyl cycloalkanes to bicyclic alkanes by inhibiting hydrogenation of the aromatic ring. In contrast to previous research on model components, phenyl olefins appeared to be the final product of alkyl-naphthalenes hydrogenation. The transformation of bicyclic compounds to monocyclic compounds was insignificant. Based on these results, a reaction scheme of aromatic compounds in coal tar distillate was proposed.

Dissolution and transport of coal tar compounds in fractured clay-rich residuum

We investigated the dissolution and transport of organic contaminants from a crude coal tar mixture in a monolith of fractured clay-rich residuum. An electrolyte solution was eluted through the residuum monolith containing a small emplaced source of coal tar under biologically inhibited and mildly acidic conditions. Concentrations of 10 coal tar compounds, representing mono-, poly-, and heterocyclic aromatic hydrocarbons that constitute crude coal tar were monitored in the effluent over a period of 377 days. Most compounds appeared in the effluent within the first 0.1 pore volume eluted indicating the importance of rapid dissolution and transport through the fracture networks. The concentrations continued to rise but did not reach the corresponding effective solubility limit in most cases. Compounds that were less soluble and those that were more susceptible to sorption or matrix diffusion eluted at a much slower rate. Analysis of contaminant concentrations in microcore residuum samples indicated that all 10 compounds had spread throughout the entire monolith and had diffused into the fine-grained matrix between fractures. These data suggest that the predominantly fine pore structure did not appear to inhibit coal tar dissolution and subsequent transport, even though only a small portion of tar was in direct contact with fractures and macropores that control most flow.

Investigation of sulphur compounds in coal tar using monodimensional and comprehensive two-dimensional gas chromatography

Coal is a non renewable fossil fuel, used mainly as a source of electrical energy and in the production of coke. It is subjected to thermal treatment, pyrolysis, which produces coke as a main product, in addition to a condensed liquid by-product, called tar. Tar is a complex mixture of organic compounds which contains different chemical classes, presenting aromatic and sulphur heterocyclic compounds. In general, identification of these compounds requires steps of isolation and fractionation, mainly due to co-elution of these compounds with polyaromatic hydrocarbons (PAH). The objective of this work is to characterize the sulphur compounds present in the coal tar obtained via pyrolysis, using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry detector (GC × GC/TOFMS). Coal samples from the State of Paraná, Brazil were subjected to laboratorial scale pyrolysis. Several experimental conditions were tested, such as sample weight (5, 10 and 15 g), heating ramp (10, 25 and 100 °C/min) and final temperature (500, 700 and 900 °C). Samples were analyzed by one dimensional gas chromatography (1D-GC) coupled to a quadrupole mass spectrometry detector (GC/qMS) and two-dimensional gas chromatography with time-of-flight mass spectrometry detector (GC × GC/TOFMS). The higher amount of sulphur compounds was obtained at a final temperature of 700 °C and a heating ramp of 100 °C/min. The main classes observed in the color plot were thiophenes, benzothiophenes and alkylated dibenzothiophenes. GC × GC/TOFMS allowed the identification of the greater number of compounds and the separation of several sulphur compounds from one another. Moreover, separation of sulphur compounds from polyaromatic hydrocarbons and phenols was achieved, which was not possible by 1D-GC. Comparing GC × GC/TOFMS and 1D-GC (SIM mode) also showed that 1D-GC, one of the most employed quantification tools for sulphur compounds, can be misleading for detection, identification and quantification, as the number of isomers of sulphur compounds found was greater than theoretically possible.

Activation of group IVC phospholipase A2 by polycyclic aromatic hydrocarbons induces apoptosis of human coronary artery endothelial cells

Exposure to environmental pollutants, such as polycyclic aromatic hydrocarbons (PAHs) found in coal tar mixtures and tobacco sources, is considered a significant risk factor for the development of heart disease in humans. The goal of this study was to determine the influence of PAHs present at a Superfund site on human coronary artery endothelial cell (HCAEC) phospholipase A(2) (PLA(2)) activity and apoptosis. Extremely high levels of 12 out of 15 EPA high-priority PAHs were present in both the streambed and floodplain sediments at a site where an urban creek and its adjacent floodplain were extensively contaminated by PAHs and other coal tar compounds. Nine of the 12 compounds and a coal tar mixture (SRM 1597A) activated group IVC PLA(2) in HCAECs, and activation of this enzyme was associated with histone fragmentation and poly (ADP) ribose polymerase (PARP) cleavage. Genetic silencing of group IVC PLA(2) inhibited both (3)H-fatty acid release and histone fragmentation by PAHs and SRM 1597A, indicating that individual PAHs and a coal tar mixture induce apoptosis of HCAECs via a mechanism that involves group IVC PLA(2). Western blot analysis of aortas isolated from feral mice (Peromyscus leucopus) inhabiting the Superfund site showed increased PARP and caspase-3 cleavage when compared to reference mice. These data suggest that PAHs induce apoptosis of HCAECs via activation of group IVC PLA(2).

Isotope Analysis for Understanding the Tar Formation in the Integrated Process of Coal Pyrolysis with CO2 Reforming of Methane

In our previous studies, a higher tar yield can be obtained from a novel integrated process of coal pyrolysis with CO2 reforming of methane (CRMP) than the traditional coal pyrolysis process. However, the tar formation mechanism in the CRMP process was not yet clear. In this work, deuterated methane (CD4) was used to investigate the formation mechanism of coal tar in the integrated process through analyzing the chemical compounds of coal tar with gas chromatography and mass spectrometry (GC/MS) analysis. The results showed that deuterium was detected in the main compounds of tar with the existing form of [•D] and [•CD3]. Deuterium in CD4 took part in the formation of coal tar compounds, indicating that the atmosphere took an important role in the formation of coal tar. When the formation process of certain compounds was analyzed, it can be deduced that the higher coal tar yield in the CRMP process can be attributed to the interaction of free radicals formed from the CO2 reforming of methane and from the cracking of the coal chemical structure in pyrolysis.

Biodegradation of phenols in a sandstone aquifer under aerobic conditions and mixed nitrate and iron reducing conditions

Ammonia liquor with very high concentrations of phenol and alkylated phenols is known to have leaked into the subsurface at a former coal carbonization plant in the UK, giving high concentrations of ammonium in the groundwater. In spite of this, no significant concentrations of phenols were found in the groundwater. The potential for biodegradation of the phenols in the sandstone aquifer at the site has been investigated in laboratory microcosms under aerobic (oxygen amended) and mixed nitrate and iron reducing (nitrate enriched and unamended) anaerobic conditions, at a range of concentrations (low: ∼5 mg l −1, high: ∼60 mg l −1, and very high: ∼600 mg l −1) and in the presence of other organic coal–tar compounds (mono- and polyaromatic hydrocarbons (BTEXs and PAHs) and heterocyclic compounds (NSOs)) and ammonia liquor. Sandstone cores and groundwater for the microcosms were collected from within the anaerobic ammonium plume at the field site. Fast and complete degradation of phenol, o- and p-cresol, 2,5- and 3,4-xylenol with no or very short initial lag-phases was observed under aerobic conditions at low concentrations. 2,6- and 3,5-Xylenol were degraded more slowly and 3,5-xylenol degradation was only just complete after about 1 year. The maximum rates of total phenols degradation in duplicate aerobic microcosms were 1.06 and 1.76 mg l −1 day −1. The degradation of phenols in nitrate enriched and unamended anaerobic microcosms was similar. Fast and complete biodegradation of phenol, cresols, 3,4-xylenol and 3,5-xylenol was observed after short lag-phases in the anaerobic microcosms. 2,5-xylenol was partially degraded after a longer lag-phase and 2,6-xylenol persisted throughout the 3 month long experiments. The maximum rates of total phenols degradation in duplicate nitrate enriched and unamended anaerobic microcosms were 0.30–0.38 and 0.29–0.31 mg l −1 day −1, respectively. The highest phenols concentrations in the anaerobic microcosms apparently required very long adaptation periods or inhibited biodegradation of the phenols. For the intermediate concentration level, degradation occurred after comparable lag-phases and at comparable rates to those observed at low concentration. However, after a while degradation of phenols suddenly decreased drastically and then stopped. Dilution by addition of anaerobic groundwater resulted in continued but slow degradation of phenols in unamended microcosms. The effect of other organic coal–tar compounds (BTEXs, PAHs, NSOs) on the degradation of the phenols under unamended conditions was limited to slightly longer lag-phases for some of the phenols. Other constituents of the ammonia liquor did not appear to significantly affect the degradation of the phenols. Fast and complete degradation of 2,3- and 2,4-xylenol was indicated. These experiments were continued for a longer period of time and revealed complete degradation of 2,5-xylenol and, after an approximately 6-month-long lag-phase partial degradation of 2,6-xylenol. The potential for natural attenuation of phenols from process effluents from coal carbonization under aerobic conditions and mixed nitrate and iron reducing conditions appears promising.

Diffusion of heterocyclic compounds from a complex mixture of coal–tar compounds in natural clayey till

The diffusion of coal–tar compounds in natural clayey till was studied experimentally. Cores were exposed to a solution with near constant concentration of coal–tar compounds in a multi-component mixture for 5 months, the cores were subsequently sub-sampled and analyzed. Diffusion profile data strongly indicates highly non-linear sorption isotherms. For dibenzofuran, dibenzothiophene, 2-methylquinoline, carbazole, phenanthrene, and fluorene, the profiles indicated significantly stronger sorption at high solute concentrations than at low solute concentrations, and than expected based on linear sorption isotherms. This corresponds with observed dramatic increase in sorption of these compounds at high surface density. For benzofuran, benzothiophene, quinoline, phenols, naphthalenes, and BTEXs the profiles indicated significantly weaker sorption at high solute concentrations than at low solute concentrations and than expected based on linear or Freundlich isotherms. The observed diffusion profiles have important implications with respect to transport of dissolved coal–tar compounds in multi-component mixtures of high concentrations as expected near immiscible phase coal–tar sources. Breakthrough times and concentration levels are affected significantly.

Sorption of heterocyclic compounds from a complex mixture of coal-tar compounds on natural clayey till

The sorption and desorption of heterocyclic organic compounds in a complex multisolute system to a natural clayey till was investigated. The composition of the solutes reflect a simplified composition of an aqueous phase in contact with coal tar. Sorption was studied for two ratios (s:l) of clayey till (solid) to aqueous phase (liquid). The effect of the complex mixture of solutes on sorption of the four heterocyclic compounds: benzofuran, dibenzofuran, benzothiophene, and dibenzothiophene is evaluated by comparison with their sorption measured in single-solute systems. Sorption of the four compounds is affected by the complex mixture, with sorption decreases for all four compounds at high s:l ratio indicating competitive sorption. The effect on sorption of the individual compounds is not related to solubility or hydrophobicity of the compounds. Freundlich-type isotherms are observed for all compounds in the high s:l-ratio experiments, but for the most hydrophobic compounds isotherms are close to linear. The sorption of N-compounds and benzofuran is apparently influenced by cation exchange and dipole–dipole attraction to clay minerals. At high concentrations a dramatic increase in the sorption of the most strongly sorbing compounds is observed in the low s:l-ratio experiment. The dramatic increase in sorption appears to be a result of multimolecular layer sorption or condensation on surfaces in the clayey till at high surface density of organic compounds, and the data are fitted by BET (Brunauer, Emmet, and Teller) type 2 isotherms. The increase may or may not be induced by the presence of N-heterocyclic compounds sorbed by cation exchange and dipole–dipole attraction. The desorption of the compounds was studied for the low s:l ratio where multimolecular layer formation apparently had occurred. Partially irreversible sorption, hysteric Langmuir type desorption with isotherms of very high K l coefficient, or behaviour reflecting dissolution of a condensed phase is observed.

Groundwater contamination from a coal carbonization plant

Abstract The Rexco coal carbonization plant near Mansfield in the UK East Midlands produced coke by the process known as ‘Rexco’ in the 1950s to early 1960s. In the process gas and coal-tar were also produced. The gas was cooled with water whereby ammonia and coal-tar in the gas were dissolved/condensed. Ammonia liquor and coal-tar are known to have leaked into the subsurface from cracked tanks at the site. Based on this, a large plume of ammonium and coal-tar compounds was expected to be present in the aquifer. Effluent compositions have been determined, and an extensive reconnaissance study of the groundwater contamination in the sandstone aquifer has been carried out. The coal-tar contained phenols, naphthalenes and BTEXs, and low levels of PAHs. The ammonia liquor contained very high concentrations of phenols and ammonium. Extensive contamination with ammonium has been encountered, indicating the ammonia liquor as the primary source of contamination. No significant contamination with specific organic coal-tar compounds is present today in spite of the extensive leaks of coal-tar and ammonia liquor in the past. The organic coal-tar compounds released with the ammonia liquor have likely been degraded/transformed in the saturated part of the aquifer as well as in the vadose zone.

Sorption of three heterocyclic compounds and their hydrocarbon analogue from coal-tar contaminated water in a natural clayey till

Abstract The natural attenuation of contaminants in fractured media is controlled by biodegradation and by diffusion into the matrix. The effective rate of diffusion and the mass of contaminants thereby removed from the aqueous phase in the fracture depends on the sorption of the contaminants. The sorption of three heterocyclic compounds and their hydrocarbon analogue from an aqueous solution of a complex mixture of 25 organic coal-tar compounds including all major groups of organic coal-tar compounds in clayey till was studied in batch experiments for a large range of concentrations including concentrations approaching the effective solubility of the mixture and for two different solid:liquid (s:l) ratios. For the high s:l ratio sorption experiment the isotherms were close to linear and best fitted by Freundlich isotherms. Sorption of the four compounds was correlated with K ow , but an order of magnitude greater than predicted from a K ow - K ow relationship for aquifer materials. Sorption was primarily dominated by hydrophobic sorption. However, at high surface density carbazole sorption appeared to be influenced by dipole-dipole attraction. For the low s: 1 ratio experiment at higher concentrations a dramatic increase in sorption was observed for all four compounds. The dramatic increase is likely a result of multi-layer formation/condensation of organic compounds on mineral surfaces at high surface density of organic compounds possibly induced by the complexity of solutes. The steepness of the increase and sensitivity to total compound surface density appears to be related to compound hydrophobicity. The impact of these four compounds on groundwater quality from sources of coal-tar in fractured clayey till overburden may be significantly lower than predicted from general sorption relationships.