I.D. Singh

Structural characterization of coke deposits on industrial spent paraffin dehydrogenation catalysts

Abstract Coke deposition on spent noble metal catalysts used in petroleum/petrochemical industries is of serious concern on account of its impact on the catalyst deactivation and consequent loss in the production yield. In order to counteract the effects of coke deposition, it is vital to know the location as well as the nature and composition coke deposited on the spent catalysts. In the present study, spent Pt-Sn/Al2O3 catalysts used in the industrial reactors for selective dehydrogenation of C10–C13 n-paraffins to mono-olefins at different coke loading (approximately 7–9%, w/w) were characterized. The characterization of coke deposits were analyzed by the combination of analytical techniques including HPLC, solid-state 13C CP/MAS NMR, and TGA. Average structural information has been obtained from the quantitative analysis of NMR data. The results indicate that the nature of coke present in the soluble coke extracts of spent catalysts is rich in alkylated mono- and diaromatics with low percentage of polyaromatics whereas the nature of insoluble coke is highly polyaromatic (aromaticity, fa>0.95). In addition, temperature programmed oxidation studies by TGA reveals that the coke is deposited on the dispersed metal as well as on the support.

Visbreaking studies on Aghajari long residue

Visbreaking studies on Aghajari long residue (370 °C+) have been conducted in a continuous bench-scale unit at different severity conditions. The effects of temperature and residence time on the yields and properties of the visbroken distillates and residues have been studied. The kinetics of cracking has been determined to be first order.

Characteristic changes of asphaltenes during visbreaking of North Gujarat short residue

The physico-chemical properties and structural parameters of asphaltenes separated from feed (short residue) and visbroken products (+ 500 °C) were estimated using various instrumental analytical techniques. Analysis of the variation of these properties and parameters with varying severity of operation (temperature and residence time in soaker visbreaking), provided information regarding the chemistry of visbreaking, and in particular the structural changes with respect to asphaltenes. The major reactions are dealkylation of aromatic clusters, and, at high severity, dehydrogenation and/or ring opening of naphthenic rings condensed with aromatic clusters. These reactions promote the condensation of aromatic clusters to yield more asphaltenes and coke.

Studies on the oxidative behavior of base oils and their chromatographic fractions

Abstract A modified IP 306 test procedure is used to study the high temperature liquid phase oxidation of five base oils and their hydrocarbon type subfractions. The base oils are selected so as to cover a wide range of physiochemical characteristics. Qualitative as well as quantitative analysis of the base oils and their fractions were done using chromatographic (column, HPLC) and spectroscopic (MS, NMR, FTIR) techniques to gain a better understanding of their compositional and structural details. Oxidized materials were also studied and structural changes identified as a result of thermal oxidation. Relative oxidative degradation of different base oils is discussed in terms of their NMR derived structural models. The results indicate that polyaromatic and naphthenoaromatic compounds undergo more oxidative degradation than saturated molecules. The oxygenated polar compounds and deposits formed are mainly derived from aromatic structures, which decreases as weight percent of the total base fluid as oxidation progresses. Alkyl substituted aromatic structures showed larger decrease in chain length than purely paraffin (n- and iso-) compounds during oxidation. Spectroscopic data also indicated that alkylation of aromatics is mainly through alkyl radicals generated from long chain alkyl aromatics.

Structural characterization of Bombay High crude oil fractions by nuclear magnetic resonance spectroscopy

Abstract Different fractions of Bombay High crude oil have been characterized using 13 C and 1 H n.m.r. spectrometry. The distribution of various types of hydrogens and carbons has been reported and several average structural parameters of the fractions have been compiled. Relative variation of structural parameters has been discussed. The data on light cycle oil (LCO) has also been presented and compared with the feed (vacuum gas oil, VGO) data. The study reveals that all the four samples/fractions are predominantly paraffinic, VGO being richest in n -paraffins. The comparison of LCO and VGO data indicates a slight reduction in the n -paraffinic chain during catalytic cracking.

Thermo-oxidative stability studies on some new generation API group II and III base oils

Abstract Due to the increasing demand for highly saturated (group II and III) base oils for use in specialty lubricant application, it is necessary to obtain a clear picture of the base oil molecular distribution. These oils are more stable to oxidation and exhibit superior performance-based characteristics as compared with group I type base oils. With the aromatic content reaching a minimum value, saturated molecules control most of the physical properties in these oils. Molecular structure based characterization developed for conventionally refined base oils will be inadequate to address all the structural diversities of these base fluids. In this study, results from thin film micro oxidation (TFMO) and pressure differential scanning calorimetry (PDSC) were discussed in terms of the quantitative 13 C NMR (inverse gated, CSE, GASPE) data. Correlations obtained with physical properties (e.g. viscosity), oxidation (evaporation, insoluble deposit) and structural data indicate the significance of base oils saturate hydrocarbon structures in influencing most of the performance properties.

Structural changes during visbreaking of light Arabian mix short residue: comparison of feed and product asphaltenes

Abstract Structural parameters and physicochemical properties of asphaltenes separated from light Arabian mix short residue and its visbroken products (500 °C) obtained from soaker visbreaking were determined by i.r., n.m.r., v.p.o. and other classical techniques. The variations of these parameters with severity of operation measured in terms of conversion (yield of material boiling

Storage stability of visbroken residual fuel oils: Compositional studies

Abstract Storage stability, at ambient conditions, of visbroken residues (150 °C + ) obtained at different severity conditions were studied in terms of sediment yield and viscosity. The effect of storage time, conversion levels (severities) and composition of residues on these parameters are reported. The reactions leading to formation of sediments are found to be more pronounced after about one year of storage of the visbroken residues (150 °C + ) obtained at the severities studied.

Compositional and structural studies of petroleum asphaltenes employing spectroscopic techniques

Abstract Petroleum asphaltenes of Bombay High (BH) and Gujrat Crude Mix (GCM) have been precipitated by extracting the respective residues (>500 °C) with normal heptane at room temperature. Ultimate compositions have been determined for deducing the average molecular formulae. Field ionization mass spectrometry (f.i.m.s.), 13 C and 1 H n.m.r. and i.r. techniques have been employed to generate the structural and compositional data. 13 C n.m.r. provided the percentage distribution of different types of carbons and some other structural parameters. I.r. allowed the identification and estimation of various polar functional groups.

Structural changes during hydrogenation of lube distillates: n.m.r. studies

13C and 1H n.m.r. spectra of raw and hydrogenated lube distillates of intermediate and heavy viscosity ranges along with their aromatic concentrates were recorded. Structural changes occurring during hydrogenation were derived and used to explain the reactions taking place. Besides hydrogenation of aromatics, hydrodesulphurization and hydrodenitrogenation are also seen under the conditions used. While some hydrocracking/dealkylation of aromatic structures is observed in the intermediate viscosity lube distillate, conversion of higher condensed aromatics into hydroaromatics is predominant in the heavy viscosity lube distillate.