Petroleum Mixtures Research Articles

Using GC × GC-FID profiles to estimate the age of weathered gasoline samples

Predicting the amount of time that a petroleum mixture has been exposed to weathering effects has applications in areas of environmental and other forensic investigations, such as aiding in determining the cause and intent of a fire. Historically, research on the evaporation rates of hydrocarbon mixtures has focused on forensic oil spill identification and predicting if a fresh sample could be weathered to give an observed composition in an aged sample. Relatively little attention has focused on approaching the problem from the other direction: estimating exposure time based on the observed composition of a weathered sample at a given time and assuming a prior composition. Here, we build upon our previous research into the weathering of model mixtures by extending our work to gasoline. Samples of gasoline with varying octane ratings and from several vendors were weathered under controlled conditions and their composition monitored over time by two-dimensional gas chromatography (GC × GC). A variety of chemometric models were explored, including partial least squares (PLS), nonlinear PLS (PolyPLS) and locally weighted regression (LWR). A hierarchical application of multivariate techniques was able to predict the time for which a sample had been exposed to evaporative weathering. Partial least squares discriminant analysis could predict whether a sample was relatively fresh (<12 h exposure time) or highly weathered (>20 h exposure time). Subsequent regression models for these classes were evaluated for accuracy using the root mean square error of prediction. LWR was the most successful, whereby fresh and highly weathered samples were predicted to within 30 min and 5 h of exposure, respectively.

Study of alkyl phosphates in industrial petroleum mixtures by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Dialkyl phosphate esters used as gellants in some oil well fracturing processes for conventional oil production can result in contamination of the collected crude. Though the exact mechanism is unclear, such compounds form volatile phosphorus that compromises refinery processes. Our initial research involved producing a comprehensive two-dimensional gas chromatographic method (GC × GC) for the detection and quantification of alkyl phosphate esters in petroleum samples, which surpassed the current method employed in sensitivity and speciation capabilities. However, selective detection is required for such analytes in petroleum matrices. This article describes the application of GC × GC with time-of-flight mass spectrometry for selective detection to the analysis of di- and tri-alkyl phosphates in petroleum samples. Features in the electron impact mass spectra of alkyl phosphates are discussed along with the GC × GC retention characteristics of the compounds. Based on these discussions, a preliminary classification and quantification of alkyl phosphate contamination in a suite of industrial samples is then presented.

Estimation of the age of a weathered mixture of volatile organic compounds

The ability to predict the amount of time that a light petroleum mixture has been weathered could have many applications, such as aiding forensic investigators in determining the cause and intent of a fire. In our study, an evaporation chamber that permits control of airflow and temperature was constructed and used to weather a model nine-component hydrocarbon mixture. The composition of the mixture was monitored over time by gas chromatography and a variety of chemometric models were explored, including partial least squares (PLS), nonlinear PLS (PolyPLS) and locally weighted regression (LWR or loess). A hierarchical application of multivariate techniques was able to predict the time for which a sample had been exposed to evaporative weathering. A classification model based on partial least squares discriminant analysis (PLS-DA) could predict whether a sample was relatively fresh (< 12 h exposure time) or highly weathered (>20 h exposure time). Subsequent regression models for these individual classes were evaluated for accuracy using the root mean square error of prediction (RMSEP). Prior to regression model calculation, y-gradient generalized least squares weighting (GLSW) was used to preprocess the data by removing variance from the X-block, which was orthogonal to the Y-block. LWR was found to be the most successful regression method, whereby fresh samples could be predicted to within 40 min of exposure and highly weathered samples predicted to within 5.6 h. These results suggest that our hierarchical chemometric approach may also allow us to estimate the age of more complicated light petroleum mixtures, such as gasoline.

Partitioning tracer method for quantifying the residual saturation of refined petroleum products in saturated soil

The effective site assessment is crucial to the successful remediation of the subsurface contaminated with light nonaqueous phase liquids (LNAPLs). Recent studies showed that large spatial volumes of the subsurface contaminated with LNAPLs could be investigated with the partitioning tracer method. This study investigated the applicability of the partitioning tracer method for detecting and quantifying refined petroleum products in a saturated aquifer containing alluvial soil or weathered granite soil. In the batch-partitioning experiments, the partition coefficients of alcohol tracers between the petroleum mixture and water were measured, and they were found to be increased in proportion to the boiling points of the alcohol tracers when the molecular weights of the alcohol tracers were similar. The sorption isotherm experiments indicated that a considerable amount of 4-methyl-2-pentanol was sorbed into Jumunjin sand (JS) or weathered granite soil (WGS). In the column experiments, it was confirmed that the partitioning tracer method could be used as a method for detecting the presence of the petroleum mixture in saturated soil, and the residual saturation of the petroleum mixture in the soil column prepared by firstly contaminating with the petroleum mixture and secondly saturating with water was measured higher than that in the soil column prepared by firstly saturating and secondly contaminating. The highest accuracy of estimation using the partitioning tracer method was found for 2-ethyl-1-butanol and the lowest accuracy was found for 4-methyl-2-pentanol.

Analysis of ignition delay period of a dual fuel diesel engine with hydrogen and LPG as secondary fuels

In this study, experiments were performed on 4 cylinder turbocharged, intercooled with 62.5 kW gen-set diesel engine by using hydrogen, liquefied petroleum gas (LPG) and mixture of LPG and hydrogen as secondary fuels. The experiments were performed to measure ignition delay period at different load conditions and various diesel substitutions. The experimental results have been compared with ignition delay correlation laid down by other researchers for diesel and dual fuel diesel engine. It is found that ignition delay equation based on pressure, temperature and oxygen concentration for a dual fuel diesel engine run on diesel–biogas gives variation up to 6.56% and 14.6% from the present experimental results, while ignition delay equation for a pure diesel engine gives 7.55% and 33.3% variation at lower and higher gaseous fuel concentrations, respectively. It is observed that the ignition delay of dual fuel engine depends not only on the type of gaseous fuels and their concentrations but also on charge temperature, pressure and oxygen concentration.

Petrochemicals

This is a review on literature published in 2010 that covered issues related to the occurrence of petrochemicals in the environment, as well as methods and techniques used for the detection and chemical analysis of petroleum mixtures, together with the toxicity and impacts of various forms of petroleum spills. This review also included literature investigating petrochemicals in water and wastewater and their treatment options including biodegradation, advanced oxidation and modeling.

Predicting Vapor Pressure of Heavy Hydrocarbons from Molar Refraction and Its Applications to Petroleum Mixtures

In this paper a generalized relation based on the corresponding states approach and use of molar refraction is proposed for the estimation of vapor pressure of pure hydrocarbons from C1 to C100. The hydrocarbons are divided into three groups of n-alkanes, n-alkylcyclohexanes, and n-alkylbenzenes from the paraffinic, naphthenic, and aromatic families. The method is also extended to undefined petroleum mixtures using bulk measurable properties, and unified methods are proposed for the calculation of input parameters from measurable properties of the mixture. The AAD for the proposed method for pure hydrocarbons (C1−C100) and for temperature range of Tr = 0.4 to the critical point (ca. 91−968 K) for 1300 data points is 1.85% while from other available methods in the literature this error is about 24%. When evaluated against petroleum fractions the proposed method produces data slightly more accurate than the existing methods recommended specifically for petroleum mixtures. Application of the proposed method ...

Gasification characteristics of coke and mixture with coal in an entrained-flow gasifier

To enhance clean energy utilization and reduce greenhouse gases, various gasification technologies have been developed in the world. The gasification characteristics, such as syngas flow rate, compositions, cold gas efficiency and carbon conversion, of petroleum coke and mixture of petroleum coke and lignite were investigated in a 1 T/d entrained-flow gasifier (I.D. 0.2 m × height 1.7 m) with quencher as a syngas cooler. CO concentration was 31–42 vol% and H2 concentration was almost 22 vol% in the gasification experiments of petroleum coke. In the case of mixture of petroleum coke and lignite, CO concentration was 37–47 vol% and H2 concentration was almost 25 vol% due to synergy effect. The gasification of mixture resulted in higher syngas heating value and cold gas efficiency because of the higher H2 and CO composition in syngas.

Methodology for the derivatization and quantification of dialkyl phosphate esters in petroleum samples

Dialkyl phosphate esters are used as gellants in some oil well fracturing processes for conventional oil production. Residual amounts of these compounds that remain in the well represent a source of potential contamination of the crude oil produced from the well. This contamination results in fouling of refinery equipment. Current methodologies for the analysis of alkyl phosphates have a relatively poor detection limit (0.5 ± 1.0 µg mL−1) and provide no speciation information: only a total phosphorus concentration. Herein, we present an approach that permits speciation of individual alkyl phosphates and quantification of individual compounds with limits of detection and precision that represent an improvement on the existing methodology. The method that we present relies upon derivatization of dialkyl phosphates to their trimethylsilane (TMS) esters followed by a comprehensive two-dimensional gas chromatographic separation. Two dialkyl phosphate esters, dibutyl and bis(2-ethylhexyl) phosphate were used as model compounds. Recovery of spiked samples in pure solvent and a model petroleum mixture ranged from 92% to 120%. This approach represents a significant first step in the development of an analytical solution to the challenge of phosphorus contamination facing the oil industry.

Petrochemicals

This is a review on literature published in 2009 that covered issues related to the occurrence of petrochemicals in the environment, as well as methods and techniques used for the detection and chemical analysis of petroleum mixtures, together with the toxicity and impacts of various forms of petroleum spills. This review also included literature investigating petrochemicals in water and wastewater and their treatment options including biodegradation, advanced oxidation and modeling.

Calculation of isentropic compressibility and sound velocity in two-phase fluids

Derivative properties from equations of state (EoS) are well defined for homogeneous fluid systems. However, some of these properties, such as isothermal and isentropic (or adiabatic) compressibilities and sound velocity need to be calculated at conditions for which a homogeneous fluid splits into two (or more) phases, liquid or vapor. The isentropic compressibility and sound velocity of thermodynamically equilibrated fluids exhibit important discontinuities at phase boundaries, as noticed long ago by Landau and Lifschitz in the case of pure fluids. In this work, the two-phase isentropic compressibility (or inverse bulk modulus) is expressed in terms of the two-phase isothermal compressibility, two-phase thermal expansivity and an apparent heat capacity, defined as the partial derivative of total enthalpy with respect to temperature at constant pressure and composition. The proposed method is simple (simpler than previous approaches), easy to implement and versatile; it is not EoS-dependent and it requires only a flash routine and the expression of total enthalpy at given pressure, temperature and composition. Our approach is applied to a variety of fluid systems representative of reservoir applications and geophysical situations, including petroleum fluids (oil and gas condensate) and mixtures of water and gas (methane or CO 2). For low gas content in the two-phase fluid, i.e., near bubble point conditions, we obtain significantly lower bulk moduli and sound velocities than predicted within Wood's conventional approach, in which the liquid and gas phases are considered to be “frozen” at the passage of the acoustic wave.

Analysis of paraffin precipitation from petroleum mixtures by means of DSC: Iterative procedure considering solid–liquid equilibrium equations

Wax deposition is a well known flow assurance risk in crude oil production due to temperature decrease which depends mainly on the crude oil nature and the type and content of paraffin. The prevention of this problem requires a detailed characterization of the crude oil and the availability of reliable predictive models. The experimental determination and quantification of the precipitation process is quite complex and time consuming and simpler techniques are of interest to carry out such study. Among them, differential scanning calorimetry (DSC) technique is appropriate to develop routine essays and has been extensively applied to determine wax appearance temperature in crude oil and fractions because the simplicity and fast response of the technique. However, the determination of wax precipitation curve from a quantitative DSC interpretation is usually based on pure n-alkane properties and involves some difficulties. In this work, a new procedure has been developed including the effect of the fluid composition on the precipitation temperature and the melting heat. Solid–liquid equilibrium equations were introduced through a simplified thermodynamic model in the integration procedure resulting in an iterative method combining experimental and calculated values. The final method yields the wax appearance temperature (WAT), the full wax precipitation curve and the estimated wax composition. In order to validate the procedure, several crude oil fractions were used as standards due to the advantage of a narrow n-alkane distribution. Experimental characterization for the cloud point temperature, the n-alkane distribution (determined by gas chromatography with mass detector, GCMS) and DSC was carried out. The agreement between experimental results and those obtained from the DSC interpretation is a good check for the proposed procedure.

Biodegradation of diesel fuel by a microbial consortium in the presence of 1-alkoxymethyl-2-methyl-5-hydroxypyridinium chloride homologues

Fast development of ionic liquids as gaining more and more attention valuable chemicals will undoubtedly lead to environmental pollution. New formulations and application of ionic liquids may result in contamination in the presence of hydrophobic compounds, such as petroleum mixtures. We hypothesize that in the presence of diesel fuel low-water-soluble ionic liquids may become more toxic to hydrocarbon-degrading microorganisms. In this study the influence of 1-alkoxymethyl-2-methyl-5-hydroxypyridinium chloride homologues (side-chain length from C(3) to C(18)) on biodegradation of diesel fuel by a bacterial consortium was investigated. Whereas test performed for the consortium cultivated on disodium succinate showed that toxicity of the investigated ionic liquids decreased with increase in side-chain length, only higher homologues (C(8)-C(18)) caused a decrease in diesel fuel biodegradation. As a result of exposure to toxic compounds also modification in cell surface hydrophobicity was observed (MATH). Disulphine blue active substances method was employed to determine partitioning index of ionic liquids between water and diesel fuel phase, which varied from 1.1 to 51% for C(3) and C(18) homologues, respectively. We conclude that in the presence of hydrocarbons acting as a solvent, the increased bioavailability of hydrophobic homologues is responsible for the decrease in biodegradation efficiency of diesel fuel.

Petroleum-contaminated water treatment in a fluidized-bed bioreactor with immobilized Rhodococcus cells

Biotreatment of petroleum-contaminated water in a fluidized-bed bioreactor (FBB) is a relatively new and promising technology, which efficiency is strongly affected by the biocatalyst used. Our laboratory experiments involved biotreatment of the water contaminated with a synthetic petroleum mixture consisting of aliphatic and polyaromatic hydrocarbons (PAHs) using a continuous column bioreactor with recycle. Different type biocatalysts were tested, including Rhodococcus bacteria immobilized in hydrophobized carriers such as sawdust, poly(vinyl alcohol) cryogel (cryoPVA) and poly(acrylamide) cryogel (cryoPAAG). Biocatalyst abilities to oxidize petroleum hydrocarbons were evaluated using the Columbus Micro-Oxymax ® respirometer. The hydrophobized sawdust-supported biocatalyst demonstrated substantially higher metabolic activity than C 12-cryoPAAG-based biocatalyst due to larger number of immobilized Rhodococcus cells and, therefore, had benefits for application in FBBs. The obtained results showed that designed FBB process is successful, providing 70–100% removal of n-alkanes (C 10–C 19) and 66–70% removal of 2–3-ring PAHs from contaminated water after 2–3 weeks.

Polymer solution and lattice theory applications for modeling of asphaltene precipitation in petroleum mixtures

Here asphaltene precipitation in petroleum reservoirs during natural depletion and miscible gas injection is modeled via two distinct and new methods (polymer solution and lattice theories). The first model is based on the polymer solution theory, which is a combination of Miller's combinatorial term with a modified residual term of the original Flory-Huggins theory. The second one is the application of the well-known Sanchez-Lacombe equation of state (SL EOS) to describe the phase behavior of asphaltene compounds in crude oil. The results of both models show an acceptable and good agreement between the real data (field and experimental) and these two models. As it can be seen from the obtained results of these two models, it seems application of the lattice or polymer solution theories (based on The Miller's combinatorial term) could give the better and more close to real data.

Aqueous solubility calculation for petroleum mixtures in soil using comprehensive two-dimensional gas chromatography analysis data

An assessment of aqueous solubility (leaching potential) of soil contaminations with petroleum hydrocarbons (TPH) is important in the context of the evaluation of (migration) risks and soil/groundwater remediation. Field measurements using monitoring wells often overestimate real TPH concentrations in case of presence of pure oil in the screened interval of the well. This paper presents a method to calculate TPH equilibrium concentrations in groundwater using soil analysis by high-performance liquid chromatography followed by comprehensive two-dimensional gas chromatography (HPLC–GCXGC). The oil in the soil sample is divided into 79 defined hydrocarbon fractions on two GCXGC color plots. To each of these fractions a representative water solubility is assigned. Overall equilibrium water solubility of the non-aqueous phase liquid (NAPL) present in the sample and the water phase's chemical composition (in terms of the 79 fractions defined) are then calculated using Raoult's law. The calculation method was validated using soil spiked with 13 different TPH mixtures and 1 field-contaminated soil. Measured water solubilities using a column recirculation equilibration experiment agreed well to calculated equilibrium concentrations and water phase TPH composition.

Experimental Determination and Characterization of Wax Fractions Precipitated as a Function of Temperature

Wax precipitation at low temperatures in petroleum mixtures is one of the most important problems in flow assurance. Experimental quantification of such processes and the further characterization of the precipitated mixtures are very difficult and extremely time-consuming, and therefore, the available experimental information is scarce and usually not very confident. In this work, wax samples were precipitated from two crude oils at different temperatures and they were characterized by optical microscopy, elemental analysis, 1H NMR spectroscopy, differential scanning calorimetry (DSC), and mass spectroscopy. The obtained results show the presence of different compounds in such mixtures regarding the chemical nature of the crude oil. The well-known presence of soaked crude oils in the precipitated fractions was experimentally estimated from 1H NMR and mass spectroscopy, and the obtained results suggest a decrease in the soaked crude oil amount as the precipitation temperature becomes lower, in agreement with the qualitative paraffinic content determined by elemental analysis. These values were used to correct the amount of solid wax precipitated experimentally and the final comparison between such corrected values and the precipitation curve calculated from DSC results shows a good agreement within the high experimental uncertainties.

Concentration Dependence in the Spectra of Polycyclic Aromatic Hydrocarbon Mixtures by Front-Surface Fluorescence Analysis

Polycyclic aromatic hydrocarbons (PAHs) are a challenge for fluorescence analysis. Inner-filter quenching effects and energy transfers of PAHs in petroleum differ with concentration, leading to characteristically different fluorescence. At high concentrations of single PAH molecules and petroleum mixtures the classic rectangular quartz cell presents a particular challenge due to inner filter effects from right-angle illumination. While quite a few instrumental and mathematical corrections for these effects are reported throughout the literature, for researchers with standard instrumental sample compartments a triangular fluorometer cell can be used to emulate front-surface fluorescence analysis. This work presents concentration study results from the single PAH molecules fluoranthene and azulene dissolved in spectral-grade cyclohexane and also seeks to correct an aspect of our past work on the fluorescence of petroleum mixtures.

Petroleum mixtures: An efficient predictive method for surface tension estimations at reservoir conditions

The gradient theory of inhomogeneous fluid is for the first time used to study the fluid–fluid interfaces of real petroleum mixtures (gas condensate and oils) at reservoir conditions. The theory is combined with the volume-corrected Peng–Robinson equation of state which allows a good description of the vapour–liquid equilibria of these mixtures. First, it is demonstrated that a correlation that was derived previously to compute the influence parameters of pure hydrocarbons can be also used to obtain the influence parameters of cuts and pseudocompounds present in the petroleum fluids. It turns out that the gradient theory allows estimates of the surface tension in excellent agreement with the experimental data. In any case, it is found to be much more superior to the traditional parachor method that systematically underestimates the surface tension of these mixtures. Furthermore, unlike the parachor method, the gradient theory proves to be nearly insensitive to the compositional description of the fluid provided that the number of pseudocompounds is not too small (N > 5).

On the Construction of a Continuous Concentration−Reactivity Function for the Continuum Lumping Approach

Kinetic modeling based on continuum lumping is a powerful methodology for working with complex petroleum mixtures. The concentration of the lumped species in the reaction mixture, characterized by reactivity, is expressed as a continuous function. The continuous concentration−reactivity function can be constructed from the experimental data, which involves inverting an integral equation. A simple methodology based on a piecewise linear interpolation formulates the inversion problem as a constrained optimization problem. The proposed method is applied to two different vacuum gas oil feedstocks, and the weight fraction values calculated from the continuous concentration−reactivity function are compared with the actual weight fraction values from the true boiling point (TBP) curve.