J. Vela

Application of Thin-layer Chromatography with Fluorescence Scanning Densitometry for Analysing Saturates in Heavy Liquids Derived from Co-pyrolysis of Biomass and Plastics

SummaryTwo alternative methods, based on Thin-Layer Chromatography (TLC) with Fluorescence Scanning Densitometry have been developed for characterization of heavy liquids from copyrolysis of different kinds of biomass and plastics in autoclaves under inert atmosphere.A conventional TLC system, which includes a vertical developing tank, and a High Performance TLC (HPTLC) system, with a horizontal developing chamber and the use of HPTLC plates, have been used. The analytical method involves in both cases the measurement of two chromatograms per sample: the first, on a silica gel berberine-impregnated plate, for detection of saturates using the phenomenon of berberine-induced fluorescence; and the second, on a silica gel plate, for detection of aromatic-polars and polars, by native fluorescence.Although the HPTLC system is more sensitive and faster, both techniques represent an improvement with regard to current methods for analyzing these kinds of products. However their application depends on the particular solubility of each sample and on its slope of the fluorescent response-sample load regression.

Coal-tar pitch characterization by thin-layer chromatography with flame ionization detection

SummaryA rapid and quantitative method for compound class characterization of coal-tar pitches without previous fractionation, using an improved TLC method with an FID system, has been developed. Results show adequate accuracy and precision, including the sampling step.A fast calibration method, based on a variation of the internal normalization procedure, can be used for up to 18 μg of whole sample application, avoiding the usually tedious absolute calibration in such analyses. This range is more than sufficient in view of the small amounts usually spotted in this technique.Speed of sample application by autospotter influences the shape of the peak nearest the point of application. For the coal tar pitch studied (9 wt.% non-eluted), slow application (0.5 μL min−1) gives a non-eluted Gaussianintegratable peak. A faster speed (10 μL min−1) is usable for analysing fossil products with lower non-eluted content. Total analysis time is less than 2 h, a considerably improvement on current methods.

Structural modifications of petroleum asphaltenes by reductive alkylation investigated by TLC-FID

Abstract The reductive alkylation of a French petroleum asphaltene (Lagrave) was studied with potassium in THF, in absence of an electron transfer reagent. From the number of butyl and benzyl groups added to the starting asphaltene, the difference of reactivity of the alkyl reagents, butyl iodide and benzyl bromide, was pointed out. Special attention was focused on the cleavage of C–S and C–O linkages in relation to the structural modifications. From the number of hydrogen atoms added during the reduction step, it was concluded that the sulphide linkages are mainly of aryl-S-aryl, aryl-S-alkyl or alkyl-S-alkyl types. The TLC-FID (Iatroscan) analysis was found to be very suitable to follow the “depolymerization” process of the asphaltene, qualitatively as well as quantitatively, by the application of quantitative hydrocarbon group type analysis.

Planar chromatography for the hydrocarbon group type analysis of petroleum middle distillates and coal-derived products

Abstract Different methodologies, based on planar chromatography/detection with densitometry, have been used to analyse compound classes (also known as hydrocarbon group type (HGT)) in samples coming from petroleum and coal conversion. The main problem encountered to analyse these samples is the choice of standard: because of the high variability of the signal that is dependent of molecular structure, one pure hydrocarbon does not reflect the response of a mixture. However, a step based on thin layer chromatography at preparative scale has allowed the fractionation of sample to obtain its derived standards. After this, alkanes have been quantified by fluorescence in presence of berberine sulfate and aromatic compounds have been detected by UV after separation by high performance thin layer chromatography (HPTLC) at analytical scale. The feasibility of the planar chromatography has been tested. The quantitative results obtained for different samples are in agreement with those provided using well-established techniques in the petrochemical industry and the coal-derived product (CDP) analysis.

Evaluation of hydroconverted residues. Rationalization of analytical data through hydrogen transfer balance

Abstract Analytical evaluation of petroleum based materials and processed feeds is a complex task relying on a compromise between tedious in-depth characterizations and fast responding tools for process control. In the present paper, a large number of hydroprocessed vacuum residues, obtained either under catalytic or thermal conditions, have been submitted to the following analytical techniques: Simulated distillation, coupled Simdist/MS, UV spectroscopy, 13 C NMR, quantitative thin-layer chromatography/FID, vapor phase osmometry. A confrontation of analytical data in the light of correlations with hydrogen transfer evaluation is proposed, which accounts for observed variations in aromatic content. Conradson carbon residue largely influences the results obtained with some of the examined techniques. Apparent discrepancies are rationalized and a strategy for a comprehensive analytical evaluation of hydroprocessed feeds is proposed.

FULLERENES: LIQUID CHROMATOGRAPHY

The contribution of Liquid Chromatography to the separation of fullerenes and fullerene-derivatives, treated from the aspects of parent fullerenes isolation from production techniques, the organic and organometallic chemistry of fullerenes, and their determination in environmental and biological samples, has been reviewed. Special emphasis has been paid to the influence of stationary and mobile phases on the selectivity of separations, as well as to the possibility of carrying out preparative separations.

PETROLEUM PRODUCTS | Liquid Chromatography

Liquid Chromatography remains a fundamental tool to analyze petroleum and petroleum-derived products. Classical fractionation methods and separation techniques have evolved to provide an effective set of tools ranging from petroleum group analysis to fraction characterization. Many Liquid Chromatography techniques play an important role, either as reference, as routine analytical techniques, or as base for new improvements. Petroleum analysis is still far from completion. We try to trace a general perspective including future evolution lines.