M.A. Olivella

A study of sulfur functionalities in fossil fuels using destructive- (ASTM and Py-GC/MS) and non-destructive- (SEM-EDX, XANES and XPS) techniques

Abstract A set of Spanish coals and oil shales were studied using destructive and non-destructive techniques to identify the functionalities of the sulfur compounds. The selected samples included organic-sulfur-rich Spanish lignites mined in the Mequinenza, Utrillas and Calaf basins; calcareous source-rocks from Organya and sulfur-rich oil shales from Ribesalbes. Using analytical pyrolysis coupled to gas chromatography–mass spectrometry, we estimated the ratio Sorg/C in these coals and oil shales, and compared them with those obtained by the ASTM method D2492. Also, a scanning electron microscope (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX) allowed the direct determination of organic sulfur content in coals. Two major non-destructive techniques, XANES and XPS, were used to investigate sulfur functionalities, such as pyritic, sulfidic, thiophenic, sulfoxide, sulfone, sulfonate and sulfate forms. The study shows that sulfur characterization in coal is not without difficulties and no method is exempt from problems and the introduction of possible artifacts.

The use of cork waste as a biosorbent for persistent organic pollutants–Study of adsorption/desorption of polycyclic aromatic hydrocarbons

The aim of this study is to determine the sorption-desorption behavior of a mixture of thirteen aqueous PAHs on cork waste at a particle of size 0.25–0.42 mm obtained from the remains of cork strips. The final purpose is to use this natural adsorbent as an alternative to activated carbon in an innovative approach for the removal of this class of toxic compounds, and significantly reduce the regeneration costs of the process. The chemical composition of the selected cork revealed that suberin (38.5 %) and lignin (31.6 %) were the main structural components of the cell wall. The high efficiency of cork as a biosorbent of PAHs is shown by the fact that just over 80 % of adsorption occurred during the first two minutes of contact time. Both Freundlichs and Langmuirs isotherms gave good fits to the sorption process. The highest adsorption affinities were exhibited for pyrene, anthracene, and phenanthrene. Desorption studies indicate a high degree of irreversibility for all PAHs, and especially so in the case of high molecular PAHs. The correlation with KF and low molecular weight PAHs was the most significant. The quantity of cork required to reduce water pollution was estimated to be between 3 and 15 times less than the quantities required in the case of other materials (i.e. aspen wood and leonardite). This study demonstrates for the first time that cork is a potential biosorbent for PAHs and may have relevance in the future treatment of PAH-contaminated waters.

Characterization of humic acid from leonardite coal: an integrated study of PY-GC-MS, XPS and XANES techniques

Abstract We studied the humic-acid fraction isolated from a Spanish leonardite coal (Torrelapaja, Cretaceous basin belonging to the Utrillas facies) using a suite of chromatographic and spectroscopic techniques to characterize the structure of the carbon skeleton and the nature of the sulfur-containing compounds. In particular, analytical pyrolysis coupled to gas chromatography-mass spectrometry was used to gain detailed molecular information on the organic structures. Pyrolysis in the presence of a methylating agent (tetramethyl-ammonium hydroxide, TMAH) was used to characterize polar moieties. We employed non-destructive techniques, XANES and XPS, to investigate the composition of the sulfur functionalities (such as sulfide, polysulfide, thiophene, sulfoxide, sulfonate and sulfate). The combination of these different approaches allows a more complete understanding of the organic sulfur structures in the leonardite coal. In agreement with previous studies, our results show that oxidized sulfur functionalities, such as sulfonate and sulfate, represent the major forms of sulfur in leonardite coal.

An integrated approach to understanding the sorption mechanism of phenanthrene by cork

Previous studies have shown the high sorption affinity of polycyclic aromatic hydrocarbons by cork. The aim of the present work is to go further by investigating the sorption mechanism of polycyclic aromatic hydrocarbons (exemplified by phenanthrene) on cork and the availability of the chemical components (i.e. lignin, suberin, holocellulose and extractives) to retain phenanthrene. Two approaches were integrated to reach this objective: (1) statistical multivariate analysis to obtain correlations between the sorption capacity, measured as K(oc), and the sorbent properties (i.e. polarity, acidic functional groups, %dichloromethane extractives, %ethanol and water extractives, %suberin, %lignin and %holocellulose) and (2) modeling calculations to obtain information on interaction at the molecular level. The statistical multivariate analysis demonstrated a strong and positive correlation between K(oc) and the lignin content as well as negative correlations between K(oc) and the phenolic groups and %dichloromethane extractives contents. The modeling study showed that the lignin-phenanthrene interaction is mostly hydrophobic in nature being largely determined by the π-stacking interaction between the aromatic groups of the interacting partners. This result justifies the observed correlations as dichloromethane extractives, being hydrophobic, compete with phenanthrene adsorption, whereas phenolic groups, as well as negatively charged groups, enhance the hydrophilic character of the sorbent surface, thus hindering the adsorption of phenanthrene.

Fungal biodegradation of anthracene-polluted cork: A comparative study

ABSTRACT The efficiency of cork waste in adsorbing aqueous polycyclic aromatic hydrocarbons (PAHs) has been previously reported. Biodegradation of contaminated cork using filamentous fungi could be a good alternative for detoxifying cork to facilitate its final processing. For this purpose, the degradation efficiency of anthracene by three ligninolytic white-rot fungi (Phanerochaete chrysosporium, Irpex lacteus and Pleurotus ostreatus) and three non-ligninolytic fungi which are found in the cork itself (Aspergillus niger, Penicillium simplicissimum and Mucor racemosus) are compared. Anthracene degradation by all fungi was examined in solid-phase cultures after 0, 16, 30 and 61 days. The degradation products of anthracene by P. simplicissimum and I. lacteus were also identified by GC-MS and a metabolic pathway was proposed for P. simplicissimum. Results show that all the fungi tested degraded anthracene. After 61 days of incubation, approximately 86%, 40%, and 38% of the initial concentration of anthracene (i.e., 100 µM) was degraded by P. simplicissimum, P. chrysosporium and I. lacteus, respectively. The rest of the fungi degraded anthracene to a lesser extent (<30%). As a final remark, the results obtained in this study indicate that P. simplicissimum, a non-ligninolytic fungi characteristic of cork itself, could be used as an efficient degrader of PAH-contaminated cork.

New insights into the interactions between cork chemical components and pesticides. The contribution of π-π interactions, hydrogen bonding and hydrophobic effect

The role of chemical components of cork in the sorption of several pesticides has been investigated. For this purpose raw cork and three cork extracted fractions (i.e. cork free of aliphatic extractives, cork free of all extractives and cork free of all extractives and suberin) were used as sorbent of three ionic pesticides (propazine, 2,4-dichlorophenoxy acetic acid (2,4-D) and alachlor) and five non-ionic pesticides (chlorpyrifos, isoproturon, metamitron, methomyl and oxamyl) with a logKow within the range -0.47 to 4.92. The effect of cations on the ionic pesticides, propazine and 2,4-D sorption was also analyzed. Results indicated that the highest yields were obtained for chlorpyrifos and alachlor sorption onto raw cork (>55%). After removal of aliphatic extractives sorption of all pesticides increased that ranged from 3% for propazine to 31% for alachlor. In contrast, removal of phenolic extractives caused a sorption decrease. Low sorption yields were obtained for hydrophobic pesticides such as metamitron, oxamyl and methomyl (<11%) by using all cork fractions and extremely low when using raw cork (<1%). FTIR analysis was useful to indicate that lignin moieties were the main components involved on the sorption process. Modelling calculations evidenced that π-stacking interactions with the aromatic groups of lignin play a major role in determining the adsorption properties of cork toward aromatic pesticides. Results presented in this paper gain insights into the cork affinities for pesticides and the interactions involved in the sorption process and also enables to envisage sorption affinity of cork for other organic pollutants.

Binding interactions between suberin monomer components and pesticides

Understanding the role of biomacromolecules and their interactions with pollutants is a key for elucidating the sorption mechanisms and making an accurate assessment of the environmental fate of pollutants. The knowledge of the sorption properties of the different constituents of these biomacromolecules may furnish a significant contribution to this purpose. Suberin is a very abundant biopolymer in higher plants. In this study, suberin monomers isolated from cork were analyzed by thermally-assisted methylation with tetramethylammonium hydroxide (TMAH) in a pyrolysis unit coupled to gas chromatography-mass spectrometry (GC/MS). The isolated monomer mixture was used to study the sorption of three pesticides (isoproturon, methomyl and oxamyl). The modes of pesticide-sorbent interactions were analyzed by means of two modeling calculations, the first one representing only the mixture of suberin monomers used in the sorption study, and the second one including glycerol to the mixture of suberin monomers, as a building block of the suberin molecule. The results indicated that the highest sorption capacity exhibited by the sorbent was for isoproturon (33%) being methomyl and oxamyl sorbed by the main suberin components to a lesser extent (3% and<1%, respectively). In addition to van der Waals interactions with the apolar region of sorbent and isoproturon, modeling calculations evidenced the formation of a hydrogen bond between the isoproturon NH group and a carboxylic oxygen atom of a suberin monomer. In the case of methomyl and oxamyl only weak van der Waals interactions stabilize the pesticide-sorbent adducts. The presence of glycerol in the model provoked significant changes in the interactions with isoproturon and methomyl.