Roberto García

Regenerable sorbents for mercury capture in simulated coal combustion flue gas.

This work demonstrates that regenerable sorbents containing nano-particles of gold dispersed on an activated carbon are efficient and long-life materials for capturing mercury species from coal combustion flue gases. These sorbents can be used in such a way that the high investment entailed in their preparation will be compensated for by the recovery of all valuable materials. The characteristics of the support and dispersion of gold in the carbon surface influence the efficiency and lifetime of the sorbents. The main factor that determines the retention of mercury and the regeneration of the sorbent is the presence of reactive gases that enhance mercury retention capacity. The capture of mercury is a consequence of two mechanisms: (i) the retention of elemental mercury by amalgamation with gold and (ii) the retention of oxidized mercury on the activated carbon support. These sorbents were specifically designed for retaining the mercury remaining in gas phase after the desulfurization units in coal power plants.

Improved capillary electrophoresis method for measuring rare-earth elements in synthetic geochemical standards

An improved capillary electrophoresis (CE) method for quantifying rare-earth elements (REEs) in synthetic geochemical standards was developed. Synthetic standard solutions were obtained from high purity metal oxides. The separation of REE total group (lanthanum to lutetium) was defined as a primary objective. Special attention was also focused on the optimized separation of europium (Eu) and gadolinium (Gd) because in earlier applications they presented overlapping problems. Their separation and quantitative determinations are essential for geological applications. For the rapid separation of REEs in synthetic geochemical standards, the temperature of the separation device was optimized. An analysis temperature of 15 degrees C enabled both the rapid separation of REEs within 2 min and the overlapping problem of Eu-Gd to be resolved. The detection limits (<0.1 ng) and precision estimates (generally better than 5%) were found to be satisfactory for most geological applications.

Thermal behaviour of extrographic fractions of coal tar and petroleum pitches

Two coal tar pitches and a petroleum pitch were fractionated by extrography on a preparative scale. The chemical composition of the fractions was determined by elemental analysis, FT-i.r., 1H n.m.r. and solid-state 13C n.m.r. spectroscopies and number-average molecular weight, Mn, and their thermal behaviour was studied using thermal analysis techniques (t.g., d.t.g. and d.t.a.). The fractions were also carbonized in a horizontal furnace, and the resulting cokes were characterized by optical microscopy. Exo- and endothermic effects shown by the d.t.a. curves of extrographic fractions of the pitches were associated with the physicochemical phenomena expected to occur during the pyrolysis of their respective constituents. It was found that the composition of a pitch and the reactivity of its constituents are reflected in the degree of overlap between the endothermic effect of volatilization and the exothermicity of polymerization. The study of the optical texture of the cokes in relation to the chemical and structural composition of the pyrolysed samples provided new evidence on the relations between composition, reactivity and thermal behaviour of pitches.

Characterisation of pitch by HPLC

SummaryA new high performance liquid chromatography method for the characterisation of toluene-soluble fractions of pitches has been developed. Although a chromatographic system typical of size exclusion chromatography was used, results indicate that, for these structurally complex samples, separation does not follow the usual discrimination by molecular size. A differentiation between several classes of polyaromatic hydrocarbons is achieved instead. Data are reported on the analysis of individual standard polyaromatic hydrocarbons, showing that four different elution ranges can be observed: three ofcata-condensed compounds (Cata1, Cata2 and Cata3) and one ofperi-condensed compounds (Peri). Results are reported proving the capacity of this high performance liquid chromatography method to distinguish between pitches of different origin and nature. It is also effective for the study of the chemical reactions occurring during heat treatment.

Metasedimentary xenoliths in the lavas of the Timanfaya eruption (1730- 1736, Lanzarote , Canary Islands ): metamorphism and contamination processes

We report on the investigation of contact metamorphism provoked by the emplacement of a shallow magma chamber during the Timanfaya eruption of Lanzarote from 1730 to 1736 AD. The study was carried out on metamorphic xenoliths from basaltic Timanfaya lavas, and shows how the primary basanitic magma was contaminated by sedimentary and metamorphic rocks. Mineralogical and chemical studies allowed the definition of several xenolith types. Silica xenoliths (quartz, tridymite, cristobalite or a mixture of these, constituting more than 50 % of the xenolith) and cale-silicate xenoliths (wollastonite, sometimes the 2M type, diopside, forsterite or mixture of these, constituting more than 50 % of the xenolith) are the most frequent. Other minerals recognized were calcite, dolomite, augite, enstatite, hypersthene, spinel and scapolite. The mineralogy and some textures of the metamorphic forsteritic xenoliths are identical to those found in ultrabasic xenoliths (dunites) and point to a possible metamorphic origin for some of them. Major and trace elements showed a diversity of composition, controlled by the mineralogy. The REE composition of the metamorphic xenoliths is high, compared with the sedimentary xenoliths not affected by metamorphism. The mineral assemblages define metamorphic facies of low, medium and high grade, depending on the distance of the sedimentary rocks from the magma chamber border. The IGPETWIN-MIXING program was used to verify the contamination process, taking the xenoliths as representative of the sedimentary/metamorphic rocks that were melted. The results indicated that sedimentary/metamorphic rock contamination of a basanitic magma can produce tholeiitic compositions.

ATR-FTIR spectroscopy for the determination of Na4EDTA in detergent aqueous solutions.

Fourier transform infrared spectroscopy in the attenuated total reflectance mode (ATR-FTIR) combined with partial last square (PLS) algorithms was used to design calibration and prediction models for a wide range of tetrasodium ethylenediaminetetraacetate (Na4EDTA) concentrations (0.1 to 28% w/w) in aqueous solutions. The spectra obtained using air and water as a background medium were tested for the best fit. The PLS models designed afforded a sufficient level of precision and accuracy to allow even very small amounts of Na4EDTA to be determined. A root mean square error of nearly 0.37 for the validation set was obtained. Over a concentration range below 5% w/w, the values estimated from a combination of ATR-FTIR spectroscopy and a PLS algorithm model were similar to those obtained from an HPLC analysis of NaFeEDTA complexes and subsequent detection by UV absorbance. However, the lowest detection limit for Na4EDTA concentrations afforded by this spectroscopic/chemometric method was 0.3% w/w. The PLS model was successfully used as a rapid and simple method to quantify Na4EDTA in aqueous solutions of industrial detergents as an alternative to HPLC-UV analysis which involves time-consuming dilution and complexation processes.

Capillary electrophoretic analysis of inorganic anions in atmospheric hailstone samples.

A new application of capillary electrophoresis (CE) for measuring inorganic anions in hailstones was carried out. Five hailstone specimens were collected from large blocks of ice that fell in January 2000 in some provinces of Spain. Sample handling and preparation procedures were performed with care. CE analysis of anions was carried out using indirect UV detection at 254 nm with a negative power supply (-15 kV) and hydrostatic injection (10 cm for 30 s) at 35 degrees C. Anion separation was completed in less than 4 min. The working electrolyte consisted of 4.7 mM sodium chromate, 4.0 mM OFM-OH (tetradecyltrimethylammonium hydroxide), 10 mM CHES [2-(N-cyclohexylamino)ethanesulfonic acid], and 0.1 mM calcium gluconate (pH 9.1). Good repeatability of migration times after eight injections (<0.7% RSD), adequate linearity responses (r2>0.9) as well as satisfactory detection limits (<0.35 ppm) were achieved. The analytical results provided by CE were compared with those obtained by traditional wet-chemical (WCH) methods. Most of the results obtained by CE were consistent with those of WCH, except for one sample.

A spectroscopic study of structural changes occurring in supercritical gas extraction of a Spanish lignite with alcohols

Abstract Supercritical gas (SCG) extraction of a Spanish lignite was conducted with methanol and ethanol in a semicontinuous mode at temperatures between 250 and 350 °C and pressures up to 15.2 MPa. The resultant extracts and residues were characterized principally by FT-i.r. spectroscopy and n.m.r. to specifically provide information on the mode and extent of solvent incorporation via secondary reactions. FT-i.r. and n.m.r. revealed that alkylation and esterification reactions both occur to a significant extent. The extent of alkylation increases with increasing temperature and SCG extractions with 13C-labelled methanol demonstrated that the incorporated methyl groups are mainly bound to C atoms but also to O, S and N atoms. The extent of esterification is incomplete, as indicated by the presence of free carboxylic acids in both the chars and extracts, and decreases with increasing temperature due to the competing effect of decarboxylation reactions.

Coal tar: a by-product in cokemaking and an essential raw material in carbochemistry

Abstract The carbonization of coal to produce metallurgical coke in slot-type recovery ovens is the main source of coal tar production. But tar is not a prime process target, and its composition and properties are subordinated to the primary aim of producing metallurgical coke. Nevertheless, coal tar has long been recognized as a valuable source of aromatic chemicals and pitch for various applications. There is a close relationship between the composition and thermal behavior of tar and pitches and the history of tar production. This chapter offers an overview of the composition and properties of coal tars and the pitches derived from them. It also includes a description of the traditional and modern analytical techniques used to describe the main features of tar and pitches with special emphasis on the combination of chromatographic techniques, GC-FID-MS, and high-performance liquid chromatography as an effective way to separate, identify, and quantify individual and/or classes of polycyclic aromatic compounds present in tars and pitches. Furthermore, the chapter analyzes the basic principles underlying the formation of aromatic compounds during the coking process and gives a brief outline of the effects of operational coking conditions on the distribution of the main aromatic hydrocarbons in tars.

Determination of Organic Sulphur Forms in Type I/II Kerogens by High Pressure Temperature Programmed Reduction (TPR)

The temperature programmed reduction (TPR) technique has been extended to two kerogens: Goynuk oil shale, a type I kerogen, and Kimmeridge (Dorset-Cuddle), a type II kerogen. In each case thiophenic sulphur was confirmed as the dominant organic sulphur form with sulphides accounting for ≈40–50% of Goynuk and ≈35% in Kimmeridge. From the hydrogen sulphide (H2S) profiles obtained from TPR, the position of the Tmax gives a good indication of the average ring size of the thiophenic structures, suggesting that the type I kerogen contains mainly single ring thiophenes, whilst the higher Tmax, displayed by the type II kerogen implies a prevalence of 2–3 ring thiophenes, consistent with the recognised structural differences between the two kerogen types. Additionally, for Goynuk oil shale, the proportion of H2S evolving from non-thiophenic forms below 250°C indicates the probable presence of polysulphides.