Structural characterization of FCC feeds from Indian refineries by NMR spectroscopy

Fluid catalytic cracking (FCC) feeds from four Indian refineries are structurally characterized by ¹H, gated-decoupled ¹³C, distortionless enhancement by polarization transfer (DEPT) and 2D ¹H–¹³C HETeronuclear CORrelation (HETCOR) and other 2D nuclear magnetic resonance (NMR) methods. Detailed structural analyses are completely supported by a range of NMR information including chemical shifts of ¹H and ¹³C, CH_n type distributions and ¹H –¹³C connectivities. The average structural parameters like branching sites, average number of branching per molecule, average length of side chains, percentage of saturates, aromatics and naphthenes are obtained from these NMR data. A novel approach based on “multipoint spline base line correction” is employed for estimation of naphthenes and n-paraffins that gives better quantitative estimation than the conventional methods. In this paper, importance is given to the study of those structural parameters that plays a key role in cracking chemistry as well as coke forming tendency of the feedstock. To the best of our knowledge, this is the first attempt to characterize and quantitatively estimate compositions of the high boiling fractions of petroleum feed by NMR methods and especially the complex structure of vacuum gas oil (VGO) fractions used in Indian refineries. The importance of this paper is to help in optimizing the product slate of Indian refineries through proper feedstock blending using few hundreds of million metric tons (MMT) of crude oil consisting of blends of light crudes with different heavy crudes and bottom of the barrel due to escalating cost of crudes.     

Combustion characteristics of droplets composed of light cycle oil and diesel light oil in a hot-air chamber☆

Development of gas turbines fueled with light cycle oil (LCO) and oil mixture of LCO and diesel light oil (LO) requires an understanding of the droplet burning and vaporization characteristics of those oils. The present study is devoted to comparing the burning characteristics of isolated fuel droplets composed of an LCO and an LO. The tests were conducted in an atmospheric hot-air chamber preset at 1173 K, and the examined LCO had a lower cetane number but higher volatility and aromatics content compared to LO. It was demonstrated that the burning of the LCO droplet was sootier, while that of the LO droplet was more disruptive. At the tested temperature, coke formation was indistinct for both the oils, whereas slightly higher ignition delay time was shown for the LO droplet. The microexplosive burning more or less complicated the time-series droplet size d, an explicit burning rate constant, however, was still definable according to the d²-law to show the overall regression speed of the droplet surface area d² with burning time t. The rate constant exhibited little difference for smaller LCO and LO droplets but was greater for LO when the droplet was larger. The rate constant also gradually increased with increasing the initial droplet diameter d₀, which caused the relative size d/d₀ to be unified (normalized) into a single curve by a burning time t/d₀ⁿ (1.0<n<2.0). Analysis revealed that this unification resulted from the respective overlaps of the unsteady and quasi-steady burning phases for differently sized droplets. Further, it was clarified that the unification and analysis are generally valid to isolated liquid fuel droplet burning in hot ambiences.     

Structural characterization of Saudi Arabian medium crude oil by n.m.r. spectroscopy

Saudi Arabian medium crude oil has been characterized by ¹H and ¹³C n.m.r. spectroscopy. Several structural parameters such as the percentage of aliphatic carbons, aromatic carbons, n-alkanes, naphthenes, branched alkanes and chain length of paraffinic chains were calculated. The aromatic carbons were further classified as those attached to a hydrogen, methyl or alkyl group, or bridgehead carbons.     

Effects of hydroprocessing on structure and properties of base oils using NMR

The hydroprocessing technologies such as hydrocracking, hydrofinishing provide an opportunity to modify the chemistry of hydrocarbons to improve the properties of petroleum base oils. Quantitative ¹H and ¹³C NMR data has been used to generate average structural profile for a variety of base oil samples and aromatic fractions. The average structural parameters were used to study the effect of hydroprocessing on structure and properties of paraffinic neutral base oils. In addition, the effect of severity of hydrogenation on structure and properties has been investigated on three aromatic extract fractions obtained from different degree of hydrogenation of catalytic cycle stock. A linear relationship was found between average structural parameters and properties such as viscosity index, volatility and refractive index. Thermo-oxidative stability of samples was measured using differential scanning calorimetry and thin film micro oxidation tests. Variation in oxidative stability of various samples was explained using structural parameters. The NMR data was found useful in explaining property changes as a result of hydroprocessing. The results suggest that deepest knowledge of chemical structure could help in selecting base oils to meet future product specifications.     

A modified Flory-Huggins model for prediction of asphaltenes precipitation in crude oil

The Flory-Huggins model has been modified to predict the phase behavior of asphaltene precipitation process by adding solvents such as n-C5, n-C6 and n-C7 to an oil sample. The adjustable parameters of this model are calculated by optimization of an objective function and experimental data of asphaltene precipitation. The amount of asphaltene precipitation has been calculated based on the modified Flory-Huggins model compared with the Flory-Huggins model and the experimental data of references. It is shown that the modified Flory-Huggins model can accurate predict the asphaltene precipitation. Also, the differential solubility parameters of asphaltene and oil at different proportions of solvent have been calculated. The results show that the values of this parameter increases when solvent ratio enhancement.     

Liquefaction reaction of coal: 2. Structural correlation between coal and its liquefaction products

The structural correlation between coal and its liquefaction products has been examined using cross-polarization, magic angle spinning (CP/MAS) ¹³C n.m.r. and field ionization mass spectrometry (f.i.m.s.). The CH₂/aromatic carbon ratios of all solid products (asphaltene, preasphaltene and residue) were close to the corrected +CH₂/aromatic carbon ratio for the coal. This suggests that the ring structure of the structural unit of each solid product is essentially similar to that of the parent coal, except for a difference in the degree of polymerization of the structural units. The CH₂/aromatic carbon ratios of aromatic ring-type oil fractions also correlated with the corrected ratio for the coal, although they were larger. The z series distribution obtained from the f.i.m.s. of oil fractions revealed that coal with a higher CH₂/aromatic carbon ratio produced an oil rich in naphthenic structures.     

Separation and characterization of bitumen from Athabasca oil sand

Separation and chemical analysis was investigated using bitumen samples from Athabasca oil sand in Alberta. Fractionation according to solubility and polarity has been used to separate bitumen into its fractions. The solvent de-asphaltening was performed by n-pentane solvent (solubility fractionation), and the polarity fractionation using Fuller’s earth allows maltene to separate into SARA components (saturates, aromatics, resins and asphaltenes). The SARA components are analyzed comprehensively using elemental analysis (EA), Fourier-transformed infrared (FTIR), ultraviolet-visible spectroscopy (UV-vis), high performance chromatography (HPLC) and thermogravimetric analysis (TGA). EA (C, H, N, S), heavy metals (Ni, V) concentrations, FT-IR and UV-vis tests provided the explanation of chemical composition. From IR spectra, maltene and saturates/aromatics (sat/aro) contained more aliphatic compounds than resin or asphaltene. Also, IR spectrum of sat/aro was similar to crude oil and VGO (vacuum gas oil). Different UV signal data clearly indicates the contribution of aromatic constituents in the fractions. Using optimized analysis conditions of HPLC, we successfully separated the peaks for bitumen and its fractions. The characteristic peak pattern of SARA (saturates, aromatics, resins, asphaltenes) fractions was observed, and also the peak pattern of sat/aro was similar to that of crude oil and VGO. However, TGA results revealed that thermal behavior for sat/aro was similar to that of crude oil but different from that of VGO. Also, from the comparison between decomposition temperature of TGA and boiling point, their correspondence was found.     

In-situ synthesis and catalytic activity of ZSM-5 zeolite

ZSM-5 zeolite has been hydrothermally synthesized in-situ on the external surface of calcined kaolinite in the presence of n-butylamine. This supported zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and N₂ adsorption. Several synthesis variables were systematically investigated, including SiO₂ to Al₂O₃ ratio, pH, crystallization time, and crystallization temperature. After mixing the ZSM-5 with a Fluid Catalytic Cracking (FCC) catalyst, catalytic performance was evaluated by cracking vacuum gas oil (VGO) in a micro-fixed bed reactor. ZSM-5 addition was favorable for the production of light olefins by catalytic cracking of VGO.     

Assisted electrochemical conversion of nitrogen heterocompounds using active hydrogen passing through a Pd membrane. A non conventional diesel and VGO hydrotreating option

The conversion of pyridine (PY), quinoline (QUI) and meso-tetraphenylporphyrin (TPP) using active hydrogen passing through a Pd membrane under mild conditions (25 °C and ambient pressure) by applying −1.92 mA cm⁻² is reported. Moreover, some results regarding VGO and diesel hydrotreating, under similar conditions, are shown. Relative kinetic conversion constants (k′), calculated for each tested molecules, support the following reactivity order: PY (k′ = 87 × 10⁻⁴ min⁻¹) > QUI (k′ = 5 × 10⁻⁴ min⁻¹) > TPP (k′ = 1 × 10⁻⁴ min⁻¹). Based on the reduction and increasing factors found for aromatic and saturated fractions respectively, it can be established that diesel is easier to transform than VGO. Nevertheless, hydrodenitrogenation seems to be more notable for VGO than for diesel.     

Structure of Green River oil shale kerogen: Determination using solid state 13C n.m.r. spectroscopy

A sample of kerogen isolated from a Green River oil shale has been examined using high resolution solid state ¹³C n.m.r. spectroscopy. The relative concentrations of carbon types have been determined using a novel peak-synthesis technique applied to the ¹³C spectra. This technique has been successfully applied in determining the amount and type of individual carbon atoms in a sample of Green River oil shale kerogen, with sufficient resolution to enable an average structure to be proposed. The kerogen is highly aliphatic and appears to contain substantial quantities of both saturated polycondensed ring structures, and long chain n-alkanes or n-alkyl substituents.     

Grain boundary engineered,multilayer graphene incorporated LaCoO3 composites with enhanced thermoelectric properties

Enhancement of thermoelectric properties by virtue of decreased electrical resistance through grain boundary engineering is realised in this study. A robust strategy of optimisation of the transport properties by tuning the energy filtering effects at the interfaces by decreasing the interfacial electrical resistance is achieved in LaCoO₃ (LCO). This is accomplished by the incorporation of multilayer graphene within the parent LCO matrix containing multi-scale nano/micro grains. The present work has attained a substantial increment in electrical conductivity from a value of 96 Scm^-1 for bare LCO to ～5300 Scm^-1 at 750 K by incorporating 0.08 wt% multilayer graphene in LCO. No significant change in thermal conductivity is observed due to the presence of multilayer graphene in LCO. A zT of 0.33 at 550 K for 0.08 wt% multi-layer graphene incorporated LCO composite is achieved which is the highest thermoelectric figure of merit value for undoped LCO reported until now.     

Crystallization kinetics and morphology of polymer blends of poly(tetramethyl-p-silphenylene siloxane) fractions

The crystallization behaviour of polymer blends or mixtures of the same system has been studied over a wide range of molecular weight and crystallization temperatures. Blends were made by mixing fractionated polymer samples. The spherulitic growth in these mixtures is dependent upon the number-average molecular weight of the system at the shorter chain lengths, but then becomes insensitive to molecular weight values when about 10⁵ to 10⁶ are reached. The growth rate kinetics of mixtures can be described by a kinetic model used for fractionated poly(tetramethyl-p-silphenylene siloxane) (TMPS) polymers. The crystal surface energies deduced from these rate data are molecular weight dependent as are the pre-exponential and transport factors in the rate equation. These parameters are explained in terms of the crystallite morphology. Mixtures (as well as fractions themselves) of all polymer fractions ranging from the monomer to the highest molecular weight (10⁶ approximately) have similar morphological features and form negatively birefringent spherulites. Although molecular weight segregation appears to play an important role in crystallization at comparatively small undercoolings, its influence seems to be minimal at large undercoolings (close to or below the growth rate maxima). Very low molecular weight additives significantly affect the overall crystallization kinetics. Compared to the undiluted sample, mixtures so formed have lower observed melting points and glass transition temperatures. Rates of crystallization are generally facilitated by the diluent with the peak in the growth rate being displaced to lower temperatures. The growth rates for diluted over the undiluted polymer at similar undercoolings are usually larger. At high molecular weights the log of the spherulitic growth rate varies as $\text{M}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}{}_{\mathrm{n}}$, over a considerable range, but at low molecular weight values the rate depends more strongly on M_n approaching a limit of M^?1.2_n as the monomeric state is approached.     

Semiquantitative analysis of thiophenic compounds in light cycle oil (LCO) using C NMR spectroscopy

S-methyltetrafluoroborate salts of the thiophenic compounds (CH₃-S⁺:BF₄⁻) present in LCO petroleum fractions were obtained and analyzed by ¹H and ¹³C NMR spectroscopy. The methylation of the samples was carried out using 99.5% ¹³C enriched methyl iodine, to improve the sensitivity of the technique. The amount of the methylated derivatives was determined by the internal standard method; using dioxane as a reference, 37 sulphur compounds were detected. Among them, benzo[b]thiophene, dibenzo[b,d]thiophene, and several isomers of methyl, dimethyl and trimethyl[b]benzothiophenes were the most abundant. With this research, it was demonstrated that NMR spectroscopy can be used to analyze thiophenic compounds from petroleum medium fractions.     

Charge states of atoms in ceramic superconductors HgBa2Ca n − 1Cu n O2n + 2, Tl2Ba2Ca n − 1Cu n O2n + 4, and Bi2Sr2Ca n − 1Cu n O2n + 4 (n = 1–3)

The parameters of the electric-field-gradient tensor for copper sites in the HgBa₂Ca _{n ? 1}Cu _n O_{2n + 2}, Tl₂Ba₂Ca _{n ? 1}Cu _n O_{2n + 4}, and Bi₂Sr₂Ca _{n ? 1}Cu _n O_{2n + 4} (n = 1–3) lattices have been determined using ⁶⁷Cu(⁶⁷Zn) Mössbauer emission spectroscopy and calculated in the framework of the point-charge approximation. The agreement between the experimental and calculated parameters has been achieved under the assumption that the holes formed as a result of the decrease in the oxidation state of a part of the mercury, thallium, or bismuth atoms are distributed over the oxygen sites in the Cu-O or adjacent planes. It has been demonstrated that the oxidation state of cations can be controlled in high-temperature superconducting ceramic materials.     

29Si nuclear magnetic resonance studies of oligomeric and polymeric siloxanes: 4. Chemical shift effects of end-groups

²⁹Si n.m.r. spectra have been obtained for mixtures of polysiloxane oligomers in four cases, viz. MD_nM, M^HD_nM^H, M^OHD_nM^OH and MD^H_nM. Spectral dispersion is best (under the conditions studied) for the M^OHD_nM^OH series, where signals due to oligomers up to n = 9 have been separately detected. The spectra have been fully assigned, and shift effects due to the end-groups (equivalent to shifts expected in long chain polymers) have been derived. The significance of the data is discussed.     

A study of the mechanism of gas absorption into oil-water emulsions

The mechanism of oxygen and argon transfer into aqueous emulsions of n-alkans and of oleic acid was studied both theoretically and experimentally. An apparatus allowing to measure the coefficient of mass transfer from individual bubbles into the turbulent medium of either a single- or multi-phase liquid has been designed and constructed. The effect of the oil phase on the bubble-to-emulsion mass transfer coefficient was investigated. In o/w type emulsions (oil as the dispersed and water as the continuous phase) of n-alkans (the system with negative spreading coefficient) the mass transfer coefficient k_L^w is not affected by the content of the oil phase, and is equal to the coefficient of mass transfer into a pure aqueous phase. In the w/o type emulsion the k_L^w value increases proportionately to the volume fraction of n-alkans. In the oleic acid-in-water emulsion (the system with positive spreading coefficient) k_L^w initially decreases and then increases proportionately to the oil fraction. The initial decrease of k_L^w is attributed to surface activity effects of oleic acid. The data suggest that the mechanism of gas transfer to the emulsions is as follows: No direct contact between the oil and the gas phase exists in o/w type emulsions with negative spreading coefficient, and the transfer path is gas-water-oil. In w/o type emulsions (both with negative and positive spreading coefficient), however, there is a direct contact between the gas and both the continuous oil phase and the dispersed aqueous phase; there is a parallel transfer of gas to both the phases.     

Unsaturated polyesters based on terephthalic acid: 3. Characterization of poly(propylene terephthalate) prepolymer by gel permeation chromatography

Oligomers in prepolymers prepared by the polyesterification of terephthalic acid (T) with excess 1,2-propylene glycol (P) have been separated by gel permeation chromatography (g.p.c.). The assignment of chromatogram peaks to oligomers according to the structure P (TP)_n where n is the number of 1,2-propylene terephthalate repeating units has been confirmed by a g.p.c. examination of bis(2-hyroxypropyl) terephthalate and by a ¹H nuclear magnetic resonance (n.m.r.) spectroscopic study of fractions isolated from a preparative separation. The infrared g.p.c. detector response has been interpreted quantitatively in order to deduce the concentration of each oligomer from the area of its chromatogram peak. Mol fraction distributions as a function of n have been determined for the prepolymer samples. Number average molecular weights have been calculated for the terephthalate-based components of the prepolymer and for all components including excess propylene glycol. These g.p.c. molecular weights are in excellent agreement with values previously reported in a study of prepolymers by ¹H n.m.r. spectroscopy. G.p.c. studies on prepolymers after reactions with a carbodiimide and diazomethane suggest a very minor quantity of carboxyl terminated species in the prepolymer samples.     

Effect of aromatics and iso-alkanes on the pour point of different types of lube oils

In this work, we have studied the quantitative composition of seven lube oils obtained from different refineries by Nuclear Magnetic Resonance (NMR) spectroscopy and Gas Chromatography (GC) methods. A trend of low temperature flow behavior of these lube oils has been correlated with the composition, i.e. n-alkane, iso-alkanes and aromatics. The pour point of these lube oils does not depend only on distribution of n-alkanes, rather with quantity and types of other molecules like iso-alkanes and aromatics. Two alkylacrylate co-polymers with different mole fractions of co-monomers synthesized by free radical mechanism are used as pour point depressant (PPD) additives. Effectiveness of additive is dependent on polar aromatic type molecules along with iso-alkane type molecules in lube oil.     

Generation of highly uniform droplets using asymmetric microchannels fabricated on a single crystal silicon plate: Effect of emulsifier and oil types

Uniform droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a mean diameter of 26-29 μm have been generated using a silicon 24 × 24 mm microchip consisting of 23,489 asymmetric microchannels fabricated by photolitography and deep-reactive ion etching. Each microchannel consisted of a circular 10-μm diameter straight hole with a length of 70 μm and a 50 × 10 μm rectangular microslot with a depth of 30 μm. At the constant oil flux of 10 L m^− 2 h^− 1, the percent of active channels increased with increasing the oil viscosity and ranged from 4% for n-tetradecane to 48% for soybean oil. The size distribution span for SDS (sodium dodecyl sulphate)- and Tween 20 (polyoxyethylene (20) sorbitan monolaurate)-stabilized soybean and MCT oil droplets was 0.21-022. The ability of asymmetric microchannels to generate monodisperse soybean oil droplets at the very low SDS concentration of 0.01 wt.% has been demonstrated. At the SDS concentration below the CMC, the generated droplets tend to attach to the plate surface, whereas at the higher SDS concentration they detach from the plate as soon as they are formed. The agreement between the experimental and CFD (Computational Fluid Dynamics) simulation results was excellent for soybean oil and the poorest for n-tetradecane.