Hydrocarbon Matrix Research Articles

Reciprocal influence of crystallization and vitrification processes in complex hydrocarbon systems

The reciprocal influence of crystallization and vitrification processes in complex hydrocarbon systems was analyzed. These systems consist of a high-molecular-weight amorphous matrix in which easily crystallized components of different molecular weight and composition are dissolved. It was shown that the invariability of the position of the glass transition line indicates that the hydrocarbon matrix of the system does not change when waxes, asphaltenes, and resins are extracted. The presence and composition of the crystalline clusters in the hydrocarbon matrix do not affect the glass transition process. Calorimetric studies of the model system at atmospheric pressure in the 130-370 K temperature range were conducted. The measurements confirmed the existence of the crystallization process in a narrow temperature range and the absence of the glass transition process. The results also show that the appearance of crystallization does not affect the glass transition process.

Influence of deposition parameters on the structure and mechanical properties of nanocomposite coatings

Nanocomposite coatings based on TiC nanoparticles embedded in an amorphous hydrocarbon (a-C:H) matrix are deposited via reactive closed field unbalanced magnetron sputtering, employing Ti targets and acetylene gas as material precursors. The composition of the coatings is varied by changing the acetylene gas flow during the depositions. Different values of substrate bias are employed. Electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) monitor the variation of composition and the formation of TiC. Nanoindentations with a Berkovich indenter measure the coatings hardness ( H) and effective Young's modulus ( E*), and a cube corner indenter is employed to probe the coatings toughness. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) investigations confirm the formation of TiC nanoparticles and are employed to determine the particle size and size distribution, respectively, both as a function of the applied substrate bias and of the composition. The TiC volume fractions ( V F) and interparticle distances are calculated based on the compositional analysis and the measured particle sizes. As a consequence of the different nanostructures, the coatings exhibit different toughness. The highest toughness is observed for low TiC volume fractions (0.2) and particle size (≈ 2 nm). The evolution of the H/ E and H 3/ E* 2 parameters as a function of the nanostructure is investigated, and opportunities for their optimization are described.

Production of nanodiamond composites in a low-pressure microwave gas-discharge plasma

Kinetically favorable regions are determined for the production of film carbon materials of different allotropic modifications in the microwave plasma of the low-pressure ethanol vapor. Self-organization effects and polymorphic transformations caused by kinetic factors are detected. These phenomena are used to design a low-temperature technology of diamond-graphite and diamond-hydrocarbon nanocomposite materials with controlled surface concentrations and sizes of vertically bonded nanodiamond clusters from 4–5 to 100 nm in size located in a heterogeneous matrix. The influence of the technological parameters of the production of diamond-graphite nanocomposite film materials on their field-emission properties is determined. The emission properties are improved due to a change in the electrophysical properties of the material that is induced by an increase in the role of surface states on the strongly developed surface and by a decrease in the diamond micro-crystallite size in the heterogeneous hydrocarbon matrix.

Specific Nitrogen Boiling Point Profiles of Vacuum Gasoils

Vacuum gasoils are heavy petroleum cuts that are hydrotreated prior to being transformed into valuable fuels by hydrocracking. Hydrotreatment is a refining process carried out to reduce the content of heteroatomic molecules in petroleum cuts to meet the stringent fuel specifications and to prevent catalyst poisoning in downstream conversion processes. Kinetic modeling of hydrotreatment reactions requires information about the distribution of nitrogen compounds in vacuum gasoils and in their hydrotreated effluents. Analysis of heavy distillates is a challenge since nitrogen molecules are present in small amounts in the hydrocarbon matrix. Moreover, a large number of isomers are distributed over a large boiling point range (350−650 °C). This paper presents a GC-NCD method developed to determine the nitrogen distribution in vacuum gasoils. To validate the GC-NCD results, vacuum gasoils, narrow cuts as well as hydrotreated vacuum gasoils, have been analyzed. Quantitative data were compared to the total nitrog...

Ferromagnetism in Colloidal Mn2+-Doped ZnO Nanocrystals

High-temperature hydrolysis of Zn(II) and Mn(II) alkoxides in a high boiling point solvent in the presence of surfactants was used to prepare surfactant-coated Zn(1-x)Mn(x)O nanocrystals with average size of 5.5 nm and x = 0.04 +/- 0.03. The magnetic properties of the nanocrystals were measured both for isolated particles diluted in a hydrocarbon matrix and for a nanocrystal powder. Nanocrystals of manganese oxide and ZnO coated with manganese oxide were prepared for comparison to the Zn(1-x)Mn(x)O nanocrystals. We find that the manganese ions primarily substitute zinc ions in the hexagonal ZnO lattice, and part of them are ferromagnetically coupled up to room temperature even in isolated noninteracting nanocrystals. The rest of the ions are magnetically disordered or uncoupled. Surprisingly, these small Zn(1-x)Mn(x)O nanocrystals poses relatively large low-temperature magnetic coercivity and relatively high blocking temperature in the isolated form, which indicate large magnetic anisotropy. In the nanocrystal powder the coercive field decreased significantly. This study highlights the advantages of working with noninteracting single domain particles of these intriguing materials.

Varied performance of PLS calibration using different overtone and combination bands in a near-infrared region

In quantitative analysis, the importance of selecting bands out of several overtone and combination bands in a near-infrared (NIR) region has been studied with the aid of a simple hydrocarbon matrix. In an NIR region (10,000 to 4000 cm − 1 ), there are four major hydrocarbon absorption bands that can be used for multivariate analysis. The four bands cannot be used simultaneously because the molar absorptivity of each band differs greatly. Two different analytes ( n-hexane and toluene) and n-heptane were selected as a solvent to study variations in the performance of calibrations based on the difference in molecular structure. Models of calibration that rely on the partial least squares for both n-hexane and toluene were developed in which the four spectral bands were used separately. In addition, the performance of the calibration varied for both analytes under degradation of the signal-to-noise ratio that naturally occurs when a spectrometer is used over a period. Selecting the appropriate NIR band for quantitative analysis is important, particularly when there is a need to resolve minor spectral variation such as that of n-hexane in n-heptane.

Nanostructure and properties of TiC/a-C:H composite coatings

TiC/a-C:H nanocomposite coatings, deposited with closed-field unbalanced magnetron sputtering, have been scrutinized with atomic force, scanning and high-resolution transmission electron microscopy, nanoindentation and tribo-tests. These coatings consist of 2–5nm TiC nanocrystallites embedded in an amorphous hydrocarbon (a-C:H) matrix. A transition from a columnar to a glassy microstructure has been observed in the nanocomposite coatings with increasing substrate bias or carbon content. Microcracks induced by nanoindentation or sliding wear readily propagate through the column boundaries whereas the coatings without a columnar microstructure exhibit substantial toughness. The toughening of the nanocomposite coatings has been achieved effectively on two different scales, namely by restraining the formation of columns on a microscale and by manipulating the nanostructure on a nanoscale. The hardness (H) and elastic modulus (E) of the coatings are found to increase monotonically with increasing substrate bias, whereas the ratio of the hardness to the elastic modulus (H/E) remains approximately constant. In contrast, H/E increases with C content. Ball-on-disc tribo-tests confirm that the nanocomposite coatings possess superior wear resistance and strong self-lubrication effects with a coefficient of friction as low as 0.05 in ambient air and below 0.02 in dry air, under dry sliding against uncoated bearing steel balls. Physical arguments are presented to explain the toughening mechanism and the ultra-low friction.

Advanced TiC/a-C:H nanocomposite coatings deposited by magnetron sputtering

TiC/a-C:H nanocomposite coatings have been deposited by magnetron sputtering. They consist of 2–5 nm TiC nanocrystallites embedded in the amorphous hydrocarbon (a-C:H) matrix. A transition from a columnar to a glassy microstructure has been observed in the nanocomposite coatings with increasing substrate bias or carbon content. Micro-cracks induced by nanoindentation or wear tests readily propagate through the column boundaries whereas the coatings without a columnar microstructure exhibit substantial toughness. The nanocomposite coatings exhibit hardness of 5–20 GPa, superior wear resistance and strong self-lubrication effects with a friction coefficient of 0.05 in air and 0.01 in nitrogen, under dry sliding against uncoated bearing steel balls. Especially, reversible transitions from low to ultra-low friction are observed if the atmosphere is cycled between ambient air and nitrogen. The lowest wear rate is obtained at high humidity.

DP-SCD and LTMGC for Determination of Low Sulfur Levels in Hydrocarbons

Abstract A novel measurement technique has been developed for the rapid determination of low levels of sulfur in hydrocarbon matrices. The technique employs low thermal mass gas chromatography (LTMGC) and a dual plasma sulfur chemiluminescence detector (DP-SCD). Highly sensitive total volatile sulfur measurement can be made in less than 30 s with detection limits in the 20–30 parts per billion range. Response is linear over at least three orders of magnitude sulfur with excellent repeatability. By taking advantage of LTMGC's rapid temperature programming and cool down time, it is also possible to measure individual sulfur species, analogous to ASTM D 5623. Conditions have also been developed using the same analytical apparatus to detect the major elemental sulfur allotropes (S2, S3, S6, S7, and S8) in gasoline at levels that can cause silver corrosion.

Quantitative Analysis of Conjugated Dienes in Hydrocarbon Feeds and Products

We report a new method for the detailed speciation and quantification of low levels of conjugated dienes (diolefins) in complex hydrocarbon matrixes, such as steam-cracked naphthas, catalytically cracked naphthas, and heavy coker naphthas. Conjugated dienes are responsible for hydrocarbon polymerization (fouling) in various refinery processes. Until now, complete analysis of conjugated dienes, particularly C6+ conjugated dienes, was almost impossible, because of their low concentrations and severe matrix interference. Here, we show that selective derivatization of conjugated dienes with MTAD, in combination with gas chromatography−chemical ionization mass spectrometry (GC/CIMS) and gas chromatography−nitrogen chemiluminescence detection (GC/NCD) can be used to analyze the total conjugated dienes (up to C10) in various hydrocarbon matrixes quantitatively.

Formation of calcium crystallites in dry natural rubber particles

In this paper, the effects of drying and aging of natural rubber particles of Hevea brasiliensis are studied. The evolutions of the particle morphology and of the elemental distribution are investigated using electron-energy-loss spectroscopy imaging in a low-energy transmission electron microscope (ESI-TEM). It is found that when the sample is aged, calcium salt crystallites are formed around the particles. Fusion of these crystallites with time to form larger crystals shows evidence of ion mobility in the dry rubber matrix. Electron diffraction patterns and elemental mapping analysis indicate the crystals to be calcium sulfate. These crystallites are closely associated with membrane materials of the rubber particle and are surprisingly compatible with the hydrocarbon matrix of the rubber particle. It is proposed that polar sites on the membrane materials provide nucleation sites for the crystallization of calcium and sulfate ions from the latex serum.

Determination of sulphur in liquids obtained by thermal cracking of waste polymers and commercial fuels with different analytical methods

Low sulphur concentration in hydrocarbon products as fuels or lubricants is an important requirement for the high quality standards of refineries. A non-polarised energy dispersive X-ray fluorescence spectroscopy (EDXRFS) and sample combustion technique (ASTM D6428-99) was compared. A new application of energy dispersive X-ray spectrometry as analytical method for the determination of sulphur in fuels and fuel-like fractions was investigated. Low sulphur containing fuels and hydrocarbon mixtures obtained by thermal cracking of waste polymers were measured and the influence of C/H ratio on accuracy was studied. The concentration of sulphur in samples was measured with calibration graphs of different hydrocarbon matrices (commercial gasoline, diesel oil and white oil were used). Good correlation was observed between the different methods, but the correlation was depending on the characteristics of the matrices. Detection limits of 1.0 ppm, 1.1 ppm and 0.9 ppm were obtained for S in gasoline, diesel oil and white oil, respectively.

Cesium Removal from Savannah River Site Radioactive Waste using the Caustic-Side Solvent Extraction (CSSX) Process

:Researchers at the Savannah River National Laboratory successfully demonstrated the Caustic-Side Solvent Extraction (CSSX) process flow sheet using a 33-stage, 2-cm centrifugal contactor apparatus in two 24 h tests using actual high-level waste. The CSSX process for removal of cesium from alkaline solutions is the reference process for decontamination of high-level waste (HLW) at the Savannah River Site (SRS). The solvent consists of a calix[4]arene-crown-6 extractant, an alkyl-phenoxy alcohol modifier, and trioctylamine dissolved in an inert hydrocarbon matrix. Previously, we demonstrated the solvent extraction process with actual SRS HLW supernatant solution using a nonoptimized solvent formulation. Following that test, the solvent system was optimized to enhance extractant solubility in the diluent by increasing the modifier concentration. We now report results of two tests with the new and optimized solvent. The first test used a composite of supernatant solutions from two waste tanks, and the second test used a solution derived from dissolved salt cake. Test results showed that the CSSX process using the optimized solvent reduces 137Cs in HLW supernatant solutions to concentrations below the waste acceptance criterion of 45nCi/g for disposal as low-level waste (called “saltstone”). Waste decontamination factors as high as three million were achieved during testing. Test durations exceeded 24 h of uninterrupted operation and demonstrated hydraulic stability of the contactor array while operating with the optimized solvent. Carryover of organic solvent in aqueous streams (and aqueous in organic streams) was found to be less Ilian 1 %. The concentration factor (i.e., the ratio of the cesium concentration in the strip raftinate to the concentration in the waste) averaged approximately 13 during both tests, slightly below the process requirement of 15. Uncertainties in process flow-rate measurement and control prevented the test from achieving the target of 15.

Deposition and microstructure of Ti-containing diamond-like carbon nanocomposite films

Ti-containing diamond-like carbon (DLC) films were deposited by plasma decomposition of CH 4/Ar gas mixtures with an introduction of tetrakis(dimethylamino)titanium (TDMAT, Ti[(CH 3) 2N] 4), which was used as a precursor of titanium. The films deposited were found to be nanocomposite coatings consisting of TiN nanocrystalline clusters and amorphous hydrocarbon (a-C:H), indicating that the nanocrystalline clusters were embedded in the DLC matrix. The crystallinity of TiN clusters, as well as the Ti atomic concentrations in the films, increased with an increase of substrate temperature. The substrate temperature applied to form a crystalline phase in the DLC matrix induced a graphitization of amorphous hydrocarbon matrix. The increase of volume fraction of TiN nanocrystalline clusters in the DLC matrix enhanced the mechanical properties of nanostructured coatings, although the graphite-like structural transition of DLC matrix happened due to the applied heating.

The Characterization of Basic Petroleum Extracts by High-Resolution Mass Spectrometry and Simultaneous Orthogonal Acceleration Time-of-Flight−Magnet Scanning Tandem Mass Spectrometry

A hybrid double-focusing high-resolution magnetic sector−orthogonal acceleration time-of-flight (oa-TOF) tandem mass spectrometer has been used for the characterization of the basic compounds in a whole crude oil and its 400−414 °C distillation cut. Detailed compositional characterization is obtained from high-resolution experiments. Structural information is obtained from automated magnet scanning mass spectroscopy (MS/MS) experiments that are conducted by continuous oa-TOF data acquisition and simultaneous scanning of the magnet. Solid-phase weak cation exchange is used to remove the basic compounds from the hydrocarbon matrix. Samples are introduced into the mass spectrometer via a dynamic batch inlet system. Molecular ions are produced by charge exchange chemical ionization. The most-abundant compounds in the two basic extracts are due to the CnH2n+zN and CnH2n+zNS compound classes. Other compound classes of lower concentration are also detected (−NO, −SON, −NO2, −O, −SO, −O2, −SO2). The contour plot of the MS/MS data for the 400−414 °C extract has revealed two characteristic peak patterns: (i) a series of peaks parallel to the precursor ion series, containing information about the degree of alkyl substitution, and (ii) a series of peaks parallel to the MS-1 axis containing information about the aromatic nuclei. Despite the complexity of the data, a substantial structural similarity between the various basic nitrogen compounds is indicated by the two peak patterns. The important capability of the simultaneous MS/MS method to provide structural information about isobaric peak components is demonstrated. The chemical formulas of selected isobaric precursor ions are validated, and structures consistent with their product ion spectra are proposed.

Analysis of chemical warfare agents: I. Use of aliphatic thiols in the trace level determination of Lewisite compounds in complex matrices

A series of normal aliphatic thiols have been used to derivatise the chemical warfare agents Lewisites I and II (LI and LII) in hydrocarbon matrices. Varying the chain length of the thiol allowed adjustment of derivative t R by 5.9 min for Lewisite I and 5.3 min for Lewisite II. Linear regression analysis of the chain length of the thiol derivatives of the Lewisite species, and that of a series of normal alkanes against t R, allowed regression models to be developed for each set of compounds. Application of the models allowed thiol reagents to be chosen to give derivatives of Lewisites I and II that eluted before and after the major hydrocarbon contaminant. Limits of detection were comparable for all thiol derivatives analysed by GC–MS in the selection ion monitoring mode (all below 1 μg ml −1). The robustness of this approach was illustrated by successful identification of Lewisite I in samples from the Sixth Proficiency Test (organised by the Organisation for the Prohibition of Chemical Weapons, OPCW) in a matrix of 1 mg ml −1 diesel oil.

Investigation of the sulfur speciation in petroleum products by capillary gas chromatography with ICP-collision cell-MS detection

Recent regulations concerning the low-sulfur gasoline require analytical methods able to provide specific information on sulfur containing compounds present in petroleum products at the ng g−1 range. The on-line coupling of capillary GC with ICP-collision cell-MS was proposed for the speciation of sulfur in hydrocarbon matrices. The technique showed an absolute detection limit 0.5 pg for a 1 µL sample injected in the splitless mode which is about two orders of magnitude lower than the currently used techniques.

Fine structure of carbon films deposited from a microwave low-pressure gas discharge

We have studied the conditions of synthesis and the fine structure of carbon films of various structural modifications possessing preset electrical properties. The phase diagram of polymorphous transformations is constructed for carbon films grown from the plasma of microwave discharge in low-pressure ethanol vapor. Technological factors influencing the efficiency of extracting diamondlike microcrystals from a hydrocarbon matrix have been studied. Depending on the extraction regime and initial layer thickness, the size of extracted microcrystals can vary from 10–12 to 100–120 nm, while their surface concentration may reach 1.4×107 cm−2.

Effect of Palladium on Thermal Degradation of Fiban K-1 Fibrous Sulfonic Cation Exchanger. Study by Thermal Analysis, Epr Spectroscopy, and Mass Spectrometry

Thermal degradation of palladium-containing samples of Fiban K-1 fibrous sulfonic cation exchanger in the H form fabricated by ion exchange and reduced with hydrazine hydrate was investigated by methods of DTA, x-ray phase analysis, mass spectrometry, and EPR spectroscopy. It was found that palladium in the reduced state added to the cation exchanger in relatively small amounts, 1.5-2.5 wt. %, stabilizes the hydrocarbon matrix (increases the temperature of the onset of desulfurization of the sulfonic cation exchanger and thermal degradation of the hydrocarbon matrix). With a higher content (14%), palladium significantly changes these characteristics, manifested by a decrease in the temperature of the onset of desulfurization of the ion exchanger and thermal degradation of the hydrocarbon matrix.

Demonstration Of The Caustic-side Solvent Extraction Process For The Removal Of 137Cs From Savannah River Site High Level Waste#

This article describes a demonstration of a solvent extraction process for removal of 137Cs from alkaline high-level radioactive waste (HLW) solutions from the Savannah River Site (SRS) tank farm. The process employed a calix[4]arene-crown-6 extractant dissolved in an inert hydrocarbon matrix, along with an alkylphenoxy alcohol modifier and an additional additive, trioctylamine, to improve stripping performance and mitigate the effects of organic anions present in the feed stream. Testing included washing and recycle of the solvent. Tests conducted with two nonradioactive simulants of SRS tank waste verified proper hydraulic operation prior to the radioactive experiments. An additional 12-hour demonstration used simulated SRS tank waste spiked with 137Cs to confirm proper hydraulic operation, decontamination, and volume reduction factors following installation of the equipment in a shielded cell facility. Finally, a 48-hour demonstration was performed employing a composite waste from SRS tank farms. Approximately 106 L of waste (1.5E+09 d/min/mL 137Cs activity) was processed through the test unit. Average 137Cs decontamination factors for the decontaminated waste streams in all tests exceeded the target value of 40,000. Concentration factors in the strip section agreed to within 5% of the target value of 15. #The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE-AC09-96SR18500. Accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.