High-temperature Gas Chromatography Research Articles

Liquid–Liquid Equilibrium Behavior of Ternary Systems Comprising Biodiesel + Glycerol and Triglyceride + Methanol: Experimental Data and Modeling

Having a comprehensive knowledge of phase equilibrium is advantageous for industrial simulation and design of chemical processes. For further acquisition of primary data to facilitate the separation and purification of waste oil biodiesel systems, a liquid–liquid equilibrium (LLE) tank is deployed for the ternary system of waste oil biodiesel + methanol + glycerin, thereby enhancing the precision and efficiency of the process. The phase equilibrium system was constructed under the influence of atmospheric pressure at precise temperatures of 303.15 K, 313.15 K, and 323.15 K. The equilibrium components of each substance were analyzed by employing high-temperature gas chromatography, a sophisticated analytical method that enables the identification and quantification of individual components of a sample. Moreover, the ternary liquid–liquid equilibrium data were correlated by implementing the NRTL and UNIQUAC activity coefficient models. Subsequently, the binary interaction parameters of the ternary system were derived by conducting regression analysis. The experimental data demonstrated that the presence of lower methanol content in the system resulted in nearly immiscible biodiesel and glycerol phases, which ultimately facilitated the separation of biodiesel and glycerol. Conversely, with the increase in methanol content, the mutual solubility of biodiesel and glycerol was observed to increase gradually. The results showed that the calculated values of the NRTL and UNIQUAC models aligned well with the experimental values. The root-mean-square deviations of the NRTL and UNIQUAC models at 313.15 K were 2.76% and 3.56%, respectively.

VARIABLE SELECTION METHODS APPLIED IN HTGC DATA TO DETERMINE PHYSICOCHEMICAL PROPERTIES OF CRUDE OILS

High-temperature gas chromatography (HTGC) is an analytical technique employed in the petroleum industry for component separation. By incorporating chemometrics, HTGC data can be effectively utilized to predict various properties of crude oil. However, HTGC chromatograms generate a substantial number of variables, some of which may lack pertinent chemical information. Consequently, employing variable selection methods becomes crucial to reduce the number of variables and enhance the predictive capability of calibration models. In this study, the interval partial least squares (iPLS), synergy interval partial least squares (siPLS), and ordered predictors selection (OPS) methods were applied for variable selection to construct linear regression models. The main objective was to investigate the potential of these methods in predicting eight properties of crude oil: American Petroleum Institute (API) gravity, standardized kinematic viscosity at 50 °C (VISp), flash point (FP), Reid vapor pressure (RVP), micro carbon residue (MCR), saturates (SAT), aromatics (ARO), and polar (POL) content. While all variable selection methods yielded satisfactory results, the OPS-PLS regression models consistently exhibited the best performance in estimating these properties, achieving root mean squared error of prediction (RMSEP) values of 1.244 for API, 0.029 for VISp, 15.356 °C for FP, 0.324 kPa for RVP, 0.629 wt% for MCR, 3.691 wt% for SAT, 2.939 wt% for ARO, and 3.374 wt% for POL. Variable selection demonstrated remarkable effectiveness, significantly improving the accuracy of the models, and allowing for the creation of concise models with a focused set of variables.

A systematic derivatization technique for characterization of ethoxylates by GC and GCMS

AbstractEthoxylation is one of the common industrial process in which ethylene oxide (EO) is added to compounds containing active hydrogen atom (OH, COOH, SH, NH, etc.) to form surfactants. Alcohol ethoxylates are a major class of non‐ionic surfactants composed of an alkyl chain combined with few EO units. They are widely used in homecare products, personal care products, textiles, oilfield, construction, lubricants, food, paper, leather. The analysis of these ethoxylates possess several challenges since they contain ‘n’ number of EO units (n > 1). With increase in “n,” the product becomes more and more viscous and the boiling point increases making it difficult to analyze by normal gas chromatography (GC) technique. This paper describes a method of derivatizing these ethoxylates so that they can be eluted on a high temperature GC. BSTFA (N, O‐bis (trimethylsilyl) trifluoroacetamide) is used as the derivatizing agent (silylating agent). The ethoxylate combines with BSTFA to form the corresponding trimethylsilylated (TMS) product, which have comparatively lower boiling point. Thus, we detect trimethyl silyl product, which is the resemblance for the ethoxylated product. In this paper, we present a quantitative GC method for the ethoxylates of a few simple alcohols (2‐ethyl hexanol, glycerin), and complex vegetable oils (castor oil). The products formed during the reaction have also been identified on a gas chromatograph coupled with mass spectrometer (GCMS). GCMS shows the mass corresponding to the TMS derivatized product. The derivatization technique not only helps in increasing the volatility of these compounds but also improves the chromatographic efficiency, selectivity, and enhances the detectability.

Characterization of chemical composition of high viscosity heavy oils: Macroscopic properties, and semi-quantitative analysis of molecular composition using high-resolution mass spectrometry

Heavy oil is an important resource in current petroleum exploitation, and the chemical composition information of heavy oil is crucial for revealing its viscosity-inducing mechanism and solving practical exploitation issues. In this study, the techniques of high-temperature gas chromatography and high-resolution mass spectrometry equipped with an electrospray ionization source were applied to reveal the chemical composition of typical heavy oils from western, central, and eastern China. The results indicate that these heavy oils display significant variations in their bulk properties, with initial boiling points all above 200 °C. Utilizing pre-treatment and ESI high-resolution mass spectrometry, an analysis of the molecular composition of saturated hydrocarbons, aromatic hydrocarbons, acidic oxygen compounds, sulfur compounds, basic nitrogen compounds, and neutral nitrogen compounds within the heavy oil was conducted. Ultimately, a semi-quantitative analysis of the molecular composition of the heavy oil was achieved by integrating the elemental content. The semi-quantitative analysis results of Shengli-J8 heavy oil and a conventional Shengli crude oil show that Shengli-J8 heavy oil lacks alkanes and low molecular weight aromatic hydrocarbons, which contributes to its high viscosity. Additionally, characteristic molecular sets for different heavy oils were identified based on the semi-quantitative analysis of molecular composition. The semi-quantitative analysis of molecular composition in heavy oils may provide valuable reference data for establishing theoretical models on the viscosity-inducing mechanism in heavy oils and designing viscosity-reducing agents for heavy oil exploitation.

Extraction of Coumarin Mixture from Tamanu Oil using Food-Grade

Indonesia’s flora and fauna are divided into four significant ecosystems: freshwater (rivers and lakes), marine, semi-terrestrial (mangrove and riparian), and terrestrial. Tamanu (Calophyllum inophyllum) is a member of the mangrove-associated plant species belonging to the mangosteen family. It is also known as Alexandrian laurel, bintangur (Malaysia), Borneo-mahogany, polanga (India), and nyamplung (Indonesia). The tamanu seed can produce oil with a 60-75% yield. It is applicable to treat various skin problems, including eczema, psoriasis, herpes, acne, haemorrhoids, and certain allergies. It is also beneficial as an antimicrobial, anticancer, anti-HIV, anti-inflammation, and anticoagulant agent. This is because tamanu oil contains bioactive compounds named coumarin. Previous works isolated coumarins with toxic solvents and using methods that are hard to scale up. Therefore, this study aims to know the best concentration of food-grade ethanol, the number of stages, and the solvent system to extract crude coumarin mixtures from tamanu oil by batchwise solvent extraction. The free fatty acid and triglyceride removal was also studied. The initial contents of free fatty acid, coumarin mixture, and triglyceride in tamanu oil were 25.87%, 11.96%, and 51.16%, respectively. Tamanu oil was extracted simultaneously with binary solvents (n-hexane and 70%/80%/90% aqueous food-grade ethanol) and a single solvent (96% food-grade ethanol). Each fraction was analysed by Thin Layer Chromatography (TLC) and High Temperature-Gas Chromatography (HT-GC). The best result was obtained using 80% aqueous food-grade ethanol, eight extraction stages, and a binary solvent system, which produced 48.64±6.57% purity and 88.68±1.38% recovery of coumarin mixture. Moreover, it was found that the method removed 64.15% of free fatty acid and 99.96% of triglyceride from the crude tamanu oil after eight stages of batchwise extraction.

Experimental study of the effects of a magnetic field/magnetic field-ferromagnetic nanocomposite pour point depressant on wax deposition.

A magnetic field and pour point depressant, as a new avenue for improving the submarine pipeline flow of waxy oils, has attracted increasing attention along with the development of efficient wax mitigation techniques. Although advances have been made recently in understanding the rheological behavior and crystallization properties of waxy oils, the effect of magnetic field and pour point depressants on wax deposition remains an open question. In this work, a ferromagnetic nanocomposite pour point depressant (FNPPD) was prepared. The variations in wax deposition mass and component under the effect of different magnetic treatments and magnetic field-FNPPDs were investigated using cold fingers and high-temperature gas chromatography. It was evident that both the high-intensity and high-frequency magnetic fields generated by the magnet and magnetic coil can effectively reduce the deposition mass and have a long-term magnetic history effect. The synergistic effect of magnetic fields and FNPPDs concurrently reduced the thickness/mass and wax content in the deposition layer, as compared to the individual use of magnetic fields or FNPPDs. The wax precipitation properties and wax crystal morphology of waxy oils under the action of the magnetic field were characterized by differential scanning calorimetry, focused beam reflectance measurement and polarizing microscopy experiments, and the mechanism of the magnetic field was elaborated from the perspective of crystallization kinetics by combining the fitting analysis of Avrami and size-independent growth model.

Morphology study of nickel and vanadium in asphaltenes via hydropyrolysis

The morphology of nickel and vanadium compounds in the asphaltenes were investigated via hydropyrolysis with the help of inductively coupled plasma mass spectrometer (ICP-MS), ultraviolet-visible (UV-Vis), high-temperature gas chromatography atomic emission detection (HT GC-AED), and positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (+ESI FT-ICR MS). The results showed that the toluene soluble yields of products decreased from 64% to 19% as the hydropyrolysis temperature increased from 330 to 410 °C, while the abundance of nickel and vanadium compounds detected by GC-AED increased significantly. The molecular composition distribution of nickel and vanadyl porphyrins showed rhythmic changes with different temperatures in the hydropyrolysis of asphaltenes.

Effects of solar radiations on stratum corneum hydration: Part I, protective role of skin surface lipids.

This study used Raman spectroscopy to develop a new approach to evaluate the effects of solar radiation on the stratum corneum (SC). The method measures the SC's hydration and dehydration kinetics by calculating the vOH/vCH ratio to monitor the relative water content during the drying process. The study also investigated the role of skin surface lipids (SSLs) in protecting the SC from solar radiation. The SSLs film is a complex mixture of free fatty acids, triglycerides, wax esters, squalene, free and esterified cholesterols, that play a crucial role in the skin's barrier function. The results showed that solar radiation alters the water content and balance within the SC, and SSLs provide protection by acting as an optical filter by absorbing some of the energy of the solar light. This is confirmed by high temperature gas chromatography coupled to mass spectrometry analyses by revealing a decrease in specific lipids after irradiating the SSLs .

Investigating the Chemical Composition of Lanolin Waste to Improve the Production of Sustainable Natural Fibre Materials

e Natural Fibre Company process raw wool into natural fibre materials utilising several processing steps. During the manufacturing, intermittent difficulties downstream of the scouring process of raw wool were encountered. Critically, the formation of an unknown paste- like grease deposit - which lead to downstream complications. To characterise the unknown by- product, the chemical composition of different raw wool lanolin extracts routinely employed in the manufacture of fibres were compared against a sample of the unknown grease deposit using high-temperature gas chromatography coupled with mass spectrometry. Major components of the unknown grease were putatively identified as psi-cholesterol, pentadecenol, palmitic and oleic acid, and a homologous series with mass spectra consistent with glycol ethers. The identification of chemicals predominantly with high interfacial properties was indicative of a potential issue with the surfactants used in the scouring process. the high inorganic content could indicate the presence of potassium salts derived from the suint, warranting further investigation of the inorganic fraction using inductively coupled plasma-optical emission spectroscopy or mass spectrometry.

High-Temperature Two-Dimensional Gas Chromatography with Flow Modulator for Analyzing Complex Objects of Catalytic Processing

High-Temperature Two-Dimensional Gas Chromatography with Flow Modulator for Analyzing Complex Objects of Catalytic Processing

Formation Damage Caused by Wax Deposition Results in Shale Production Decline

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 210414, “First Evidence for Shale Production Decline as a Result of Formation Damage Caused by C60+ Paraffin Wax Deposition: A Permian Case Study,” by Amir Mahmoudkhani, SPE, Locus Fermentation Solutions, and Jonathan Rogers and Martin Shumway, SPE, Locus Bio-Energy Solutions, et al. The paper has not been peer reviewed. _ Analysis of production decline curves revealed that three candidate wells in West Texas depleted faster than indicated by a type decline curve, indicating a potentially abnormal permeability-reduction mechanism. A biosurfactant-based squeeze program was recommended and applied in three horizontal wells. The biosurfactant treatment offers an alternative and economical method for remediation of formation damage caused by high‑molecular‑weight paraffin wax deposition in porous media that does not require costly intervention techniques to apply. Introduction The Bone Springs horizontal oil play in the Delaware Basin spans from southeast New Mexico into West Texas. Stacked, multipay reservoirs, each with diverse rock properties, possess upside but also complexity. The initial targets in the play were conventional sandstones. Wells then tapped into carbonate lenses and, ultimately, low-permeability sandstones. As a result of horizontal drilling technology combined with hydraulic fracturing, very thin sands and other facies are now being produced. Generally, reservoir quality of this unconventional hydrocarbon system is controlled by carbonate content, where increased carbonate content typically is associated with lower productivity. Experimental Methods All crude oils exhibited precipitation of organics at ambient laboratory temperatures. Even after storing crudes at the bottomhole temperature of 140°F, a small amount of wax remained insoluble in bulk liquid. Samples of formation drill cuttings were received for various depth intervals between 8,500 and 12,000 ft. X‑ray diffraction analyses of solids revealed quartz as the major mineral phase, with clays and carbonates account for remaining phases. Combined fractions with 160-micron size were used for microcolumn oil-recovery screening tests. Carbon distributions of oils and waxes were performed by high-temperature gas chromatography (HTGC). The Du Noüy ring method was used to measure static surface tensions of biosurfactant solutions at different concentrations and was applied to calculate critical micelle concentrations at ambient temperature. Interfacial tension (IFT) measurements were performed using a drop-shaped tensiometer using the pendant-drop method. Finally, the IFTs of oil in synthetic formation water and in biosurfactant solutions prepared in city tap water were determined. Contact-angle measurements also were performed. The wax-appearance temperature (WAT) of crude and wax samples was determined by the differential scanning calorimetry method. Spontaneous imbibition experiments were performed using the Amott-cell method at reservoir temperature. Berea sandstone core plugs (25×50 mm) with a permeability of 385 md and porosity of 18.4% were used. Core plugs were saturated with homogenized crude oil samples at 140°F for 7 days.

Effect of existence state of asphaltenes on the asphaltenes-wax interaction in wax deposition

Asphaltenes are the most elusive substances in waxy crude oil, especially the complex structures, which leads to significant precipitation and aggregation characteristics of asphaltenes, and affects the asphaltenes-wax interaction. In this study, the concept of the existence state of asphaltenes was introduced to semi-quantitatively investigate the precipitation and aggregation characteristics of asphaltenes. On this basis, the influence of the existence state of asphaltenes on wax deposition was studied by coldfinger device and high-temperature gas chromatography, and the composition and properties of the deposits were analyzed. Four main findings were made: (1) As the asphaltene concentration increases, the existence state of asphaltenes gradually transitions from dispersed state to aggregated state, and the asphaltene concentration of 0.30 wt% in this study is the starting point of the transition. (2) The existence state of asphaltenes in crude oil does affect the process of wax deposition, as shown in the fact that the dispersed asphaltenes promote the occurrence of wax deposition, while the aggregated asphaltenes can inhibit wax deposition. (3) In the presence of the aggregated asphaltenes, that is, when the asphaltene concentration is higher than 0.30 wt%, the shedding phenomenon of deposit layer was observed, and with the increase of aggregated asphaltenes, the deposit layer fell off earlier. (4) With the increase of the dispersed asphaltenes, the wax appearance temperature (WAT) and wax content of the deposits all showed an increasing trend, while with the appearance of the aggregated asphaltenes, the above situation was reversed. The findings of this study can help for better understanding of the interaction between the asphaltenes and wax in wax deposition.

Correlation analysis of modern analytical data - a chemometric dissection of spectral and chromatographic variables.

The Standard Practices for Infrared Multivariate Quantitative Analysis (ASTM E1655) provide a guide for determining physicochemical properties of materials using multivariate calibration techniques applied to chemical sources that have high multicollinearity and correlated information. Partial least squares (PLS) is the most widely used multivariate regression method due to its excellent prediction capabilities and easy optimization. Initially applied to chromatographic data, PLS has also shown great results in near-infrared (NIR) and mid-infrared (MIR) spectroscopies. However, complex chemical matrices with low correlation may not be efficiently modeled using PLS or other multivariate analyses limited by grouping similar information (such as latent variables or principal components). Therefore, this study aims to evaluate the multicollinearity of different analytical techniques, such as high-temperature gas chromatography (HTGC), NIR, MIR, hydrogen nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance (13C NMR), and Fourier transform ion cyclotron resonance mass spectrometry coupled to the electrospray source in positive and negative ionization modes (ESI(±)FT-ICR). Descriptive statistics (coefficient of determination, R2) and principal component analysis (PCA) were used to identify the distribution of correlated information. Results showed that NIR and MIR spectroscopies exhibited a higher percentage of correlated variables, while 13C NMR and ESI(±)FT-ICR MS had more discrete profiles. Therefore, PLS development may be more effectively applied to NIR, MIR, and 1H NMR data, while 13C NMR and mass spectra may require other algorithms or variable selection methods in combination with PLS.

Assessment of Aging Impact on Wax Crystallization in Selected Asphalt Binders.

For a better understanding of the changing trend in crystalline components of asphalt binders, asphalt binders originating from the SHRP Materials Reference Library with different oxidation degrees (unaged, 20 h PAV, and 60 h PAV) were prepared. The native asphalt binders and their oxidized residues were characterized by liquid-state nuclear magnetic resonance (NMR) spectroscopy and high-temperature gas chromatography (HTGC). The results showed that, compared with other carbon types, the content of internal methylene carbons of long paraffinic chains between different SHRP binders was quite different. The NMR average length of a long paraffinic internal methylene chain showed a good correlation with the wax content obtained at -20 °C using the methyl ethyl ketone (MEK) precipitation method and also the recently developed variable-temperature Fourier-transform infrared spectroscopy (VT-FTIR) method. In most cases, the average length of straight internal methylene carbons of a long paraffinic chain terminated by a methyl group increased with the oxidation of the asphalt binder. However, the difference caused by oxidation was significantly smaller than the difference caused by the source of the asphalt binder. In general, oxidation will make the n-alkanes distributed in asphalt binder fall within a narrower range. The carbon number of n-alkanes in the asphalt binder generally grew with oxidation.

Characterization of wellbore asphaltene deposition in well Gaotan-1 in Junggar Basin, China

Gaotan-1 is the first high-yield well explored in the southern margin of Junggar Basin, China, which is a major breakthrough in the oil exploration for Xinjiang Oilfield Company. The well produced high-quality light crude oil with very low sulfur content and total acid number. However, serious sedimentation occurred in the wellbore during production, which seriously affects production. In this paper, the sediments from Gaotan-1 were separated into organic soluble and inorganic solid fractions. The organic compounds were characterized by high resolution mass spectrometry and high temperature gas chromatography. It was found that the organic matter was rich in asphaltenes with very high molecular condensation. The high condensation compounds should be formed in the high temperature reservoir environment, which was extracted by the supercritical fluid formed by the light hydrocarbons under the ultra-high temperature and pressure. Due to its super-dissolving ability, the high-condensation hydrocarbons and asphaltenes are brought out of the reservoir, and deposit gradually mixed with silty sand on the wall of the wellbore as the temperature and pressure dropped in the process of oil exploitation.

Wax Precipitation in Crude Oil by Coutinho Model Based on Conventional Gas Chromatography Data

Wax precipitation in crude oils can produce problems in oil production and transportation operations. Prediction is the key of avoidance or remediation of the wax problem of flow assurance. Among the wax prediction thermodynamic model, Coutinho model can be run using limited laboratory data, but the result is comparably accurate. The model requires n-paraffin distribution, which commonly determined by high-temperature gas chromatography (HTGC) analysis. However, only few laboratories could perform the HTGC. Lemigas has abundant database of crude oil with conventional gas chromatography data. An extended n-paraffin distribution was calculated based on the conventional GC data by performing extrapolation and normalization to total wax content. The n-paraffin distribution was applied in Coutinho model to predict wax precipitation of a crude oil sample. The WAT obtained from the model deviated only 2°C from DSC data. The result was also valid to DSC data in term of precipitated wax amount along temperature range.

Analysis of low-volatility pesticides in cabbage by high temperature comprehensive two-dimensional gas chromatography.

High-temperature comprehensive two-dimensional gas chromatography (HTGC × GC) using a longitudinally modulated cryogenic system (LMCS) was developed for the analysis of low-volatility pesticides in cabbage. The method applied DB-17HT and DB-5HT as the first and second dimensional (1D and 2D) columns, respectively. Twelve pesticides, namely 6 organochlorines (4,4'-DDT, β-endosulfan, endosulfan sulfate, endrin, heptachlor, and dicofol), 4 carbamates (metolcarb, isoprocarb, methiocarb, and carbofuran), 1 organophosphate (chlorpyrifos), and 1 pyrethroid (permethrin), were spiked into cabbage samples and prepared using QuEChERS. The applied oven temperature was up to 340 °C, enabling the elution of all the target pesticides and the matrix. The effects of initial oven temperature program, temperature ramp rate, LMCS trap temperature, and modulation period (PM) on the separation results were investigated, leading to the suitable conditions of 80 °C, 15 °C min-1, 10 °C, and 12 s, respectively. The method detection limits, signal-to-noise ratio, and recoveries of the compounds were within the ranges of 0.01-0.09 mg kg-1, 4.26-32.7, and 78-104%, respectively. Good linearity ranges within the concentration range of 0.1-1 ppm with R2 > 0.9134 were also obtained with the intra and interday precisions of the peak areas of 0.4-9.8% and 1.0-10.2%, respectively.

Vanadium and nickel distributions in selective-separated n-heptane asphaltenes of heavy crude oils

Understanding vanadium and nickel distributions in asphaltene fractions have significant commercial importance throughout the petroleum value chain and the potential use of heavy feedstocks as a precursor of carbon-based materials, such as carbon fibers. This work extends our previous studies and aims to characterize volatile and non-volatile vanadium and nickel distributions by selective separation of n-heptane asphaltenes obtained from two Venezuelan heavy crude oils and the NIST Standard Reference Material (SRM) 8505. Asphaltenes were separated by extrography, i.e., adsorption on SiO2 and subsequent extraction with acetone, heptol (n-heptane/toluene 1:1 vol), and a mixture of toluene, THF, and methanol (TTM). The results suggest that their solubility and aggregation strongly correlate to a higher hydrogen deficiency and increased heteroatom levels. The qualitative analysis of the spent silica gel, containing irreversibly-adsorbed asphaltenes, by Light-Induced Breakdown Spectroscopy, suggests that regardless of the solvent power used during the extraction, strong chemisorbed Ni and V species remain on the SiO2, presumable associated with porphyrin molecules present on such feeds. High-Temperature Gas Chromatography coupled with Inductively Coupled Plasma Mass Spectrometry (HTGC-ICP-MS) showed that vanadium and nickel compounds have boiling points starting at 1050 °F. Quantification of the V-content below 1300 °F for the Venezuelan crude 1 indicated that the acetone fraction contains a large amount of distillable vanadium (∼62 %wt.). Interestingly, whole/unfractionated asphaltenes revealed only 47% of distillable vanadium, which suggests that the extrography method can obtain asphaltene fractions with “improved” properties (weaker aggregation, increased solubility, and lower boiling points). The characterization by atmospheric pressure photoionization Fourier Transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS) and HTGC-ICP-MS revealed that the acetone asphaltene fractions have a higher relative abundance of vanadyl porphyrins (with and without sulfur) than heptol and TTM.

Experimental Measurements of Wax Precipitation Using a Modified Method of Simultaneous Centrifugation and High-Temperature Gas Chromatography

Wax precipitation and deposition are serious flow assurance problems. Wax precipitation is investigated simultaneously using centrifugation and high-temperature gas chromatography (C-HTGC) to obtain the amount and component distribution of precipitated wax in artificial waxy oil and diesel at different temperatures. However, the conventional C-HTGC method gives upper measurements of the amount of precipitated wax, as it ignores wax dissolved in crude oil in the centrifugal cake. A modified C-HTGC method was developed to obtain the precipitated solid fraction of crude oil, based on the mass balances of the non-crystallized fraction of the centrifuged cake. The weight, percent and carbon number distribution of precipitated solid wax crystals at different temperatures of artificial oil and 0# diesel were obtained. It was found that wax precipitation characteristics are affected by many factors, including the carbon number distribution of the oil, the sensitivity of alkane crystallization to temperature and the temperature of the waxy oil solution. The average carbon number of alkanes in precipitated wax crystals decreases with the decrease in temperature. The distribution of alkanes in solid wax crystals is roughly the same as that in 0# diesel but slightly heavier than in diesel. Alkanes with high carbon numbers precipitate simultaneously with those with low carbon numbers.

Mapping Glyceride Species in Biodiesel by High-Temperature Gas Chromatography Combined with Chemical Ionization Mass Spectrometry.

Accurate and comprehensive identification of residual glycerides in biodiesel is an important part of fuel characterization due to the impact of glycerides on the fuel physicochemical properties. However, analysis of bound glycerol in biodiesel samples faces challenges due to lack of readily available standards of structurally complex glyceride species in nontraditional biodiesel feedstocks and a risk of misannotation in the presence of impurities in gas chromatographic separations. Here, we evaluate methane and isobutane chemical ionization-single quadrupole mass spectrometry combined with high-temperature gas chromatography separations for mapping monoacylglycerols, diacylglycerols, and triacylglycerols in biodiesel. Unlike electron impact ionization, which produces mostly in-source fragments, isobutane chemical ionization spectra of tetramethylsilyl-derivatized monoacylglycerols and diacylglycerols are dominated by molecular ions and M-SiO(CH3)3+ ions, which provide important diagnostic information. We demonstrate the utility of isobutane chemical ionization in identifying structurally complex glycerolipid standards as well as species in biodiesel samples from different plant and animal feedstocks.