Determining the wax content of crude oils by using differential scanning calorimetry

By the use of differential scanning calorimetry (DSC), a new method to measure the wax content of crude oil has been developed. In this paper, the wax content of a crude oil is proposed and proved to be the Q (total thermal effect of wax precipitation in sample) ratio of the crude oil and its corresponding wax obtained by using standard acetone method, i.e. Q_oil/Q_wax. For the 14 studied crude oils with the wax content ranging from 1 to 27 wt.%, the wax contents determined by the presented method are in good agreement with those determined by standard acetone method, with an absolute average deviation of only 0.82 wt.%. This method has an advantage over reported DSC methods in which the exact dissolution or precipitation enthalpy of wax is a must. It is also found that the wax contents determined by either of the two methods show good linear relationship with the total thermal effect Q_oil, with the correlation coefficients over 0.96. According to the empirical correlations, the wax content of a crude oil can be easily determined by using the DSC total thermal effect Q_oil. In addition and more significantly, the new method can be applied to improve the accuracy in determining the amount of precipitated wax in a waxy crude oil at different temperatures.     

Thermal behavior and solid fraction dependent gel strength model of waxy oils

Thermal behavior of waxy oils is investigated using the techniques of thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Model waxy oils and real waxy crude oils are utilized. Decomposition temperatures of waxy oils are obtained using TG analysis. The effects of thermal history, wax content, and additive on the gelation process of waxy oils are investigated using DSC. The DSC method provides a measure of wax solubility as well as solid fraction. An integration method and a computation method are utilized to predict solid fraction. In addition, wax crystallization onset points are obtained at the cooling rates ranging from 1 to 20 °C min^?1. Similarly, wax dissolution endset points are obtained at heating rates ranging from 1 to 20 °C min^?1. Extrapolated onset and endset points yield wax precipitation temperature and wax dissolution temperature, respectively. Subsequently, wax solubility curves are obtained using thermodynamic computations. A wax precipitation temperature method and a wax dissolution temperature method combine thermodynamic phase behavior with onset/endset points to predict solid fraction. Both the wax precipitation temperature method and the wax dissolution temperature method can predict solid fraction of waxy oil samples. The wax precipitation temperature method and the wax dissolution temperature method are accurate when the temperature is close to the wax appearance temperature. A heat-integration method provides accurate values of the solid fraction at temperatures significantly below the wax appearance temperature. Therefore, integration method and wax precipitation temperature/wax dissolution temperature method are combined to predict solid fraction. The effect of solid fraction on yield stress is also investigated using differential scanning calorimetry and rheometry. Finally, a new solid fraction dependent gel strength model is obtained for shut in and restart of waxy crude oil pipelines.     

Thermal characteristics of crude oils treated with rheology modifiers

Thermal characteristics of eight crude oils and their treatment with additives were studied by differential scanning calorimetry (DSC), thermomicroscopy, viscometer and pour point tester. Different additives were found as more effective for different type of crude oils depending on the wax content. Crude oils showed a reduced pour point after treatment with additives. Effects of different additives were also discussed by analysing the DSC curves and thermomicroscopy result.     

Experimental measurement and modeling study for estimation of wax disappearance temperature

Wax deposition is a frequent problem in oil pipelines and down-stream industries. Correct prediction of wax formation conditions is required to prevent this phenomenon. In this study, wax appearance temperature (WAT) of 12 Iranian oil and condensate samples were measured using viscometry data and differential scanning Calorimetry (DSC) analysis. Also, a new empirical correlation and intelligent artificial neural network (ANN) model were developed to estimate wax disappearance temperature (WDT) of crude oils. Specific gravity, pressure, and molecular weight of oil sample were used as input variables for these models. The ANN model was trained using different hidden neurons and training algorithms. Experimental measurements studies were used for validation of the new correlation. Comparing the results indicated that the ANN model has 0.27% error while most thermodynamic models have an average error of 0.35% to 2.19%. Also, the proposed correlation can predict WDT with good accuracy and minimum input data. Results show that this correlation has a maximum error of 1.16% for 310 published experimental data and 1.19% for 9 Iranian samples.     

Study on the Inherent Factors Affecting the Modification Effect of EVA on Waxy Crude Oils and the Mechanism of Pour Point Depression

The Ar-Sai waxy crude oils were taken as the research objects, and the viscosity reduction rates and the condensation point reduction rates were regarded as the evaluation indexes, the impacts of components content of the crude oils and carbon number distribution of waxes on the modification effect of EVA-type pour point depressant (PPD) were analyzed by using gray correlation analysis method. The oil wax was acquired by applying the extraction and separation techniques initially, then the structures and the lattice parameters of wax crystals before and after adding the PPD were studied by polarized light microscopy observation and x-ray diffraction techniques, the mechanism of pour point depression was discussed at last. The results indicate that wax content and the low carbon number wax have significant influences on the modification effect of PPD, while the impact of high carbon number wax is relatively small. Co-crystallization is the main mechanism of pour point depression, nevertheless, the impacts of the asphaltenes, resins, solid particles, and light components of the crude oils on the modification effect of the PPD cannot be ignored.     

Thermodynamic phase equilibria of wax precipitation in crude oils

Economic loss due to wax precipitation in oil exploitation and transportation has reached several billion dollars a year recently. Development of a model for better understanding of the process of wax precipitation is therefore very important to reduce the loss. In this paper, a new thermodynamic model for predicting phase equilibriums of crude oils is proposed. The modified SRK EOS and the UNIQUAC equations are used to describe the vapor, liquid phase and the wax, respectively. New correlations have been introduced to calculate the volume parameter, c, in SRK EOS and the heat of vaporization in UNIQUAC equation. The model can be used to describe the systems which contain paraffin, naphthene and aromatic fractions. New correlations for the enthalpies, temperatures of solid–solid transitions and fusion enthalpies of paraffins are established in this paper based on data obtained from open literature. By using the proposed modified model, the wax precipitation in hydrocarbon fluids has been predicted for three crude oil systems. The calculation results have been compared with experimental observations and those results obtained using regular solution models. It is found that wax precipitation in complex systems can be better predicted by using this new model.     

贯叶连翘挥发油成分的分析

报道了当前全球研究开发的热点抗抑郁植物药贯叶连翘原药材和商品浸膏粉中挥发油成分的分析。贯叶连翘原药材粗粉中挥发油得率0．4％(mL/l00g)，从中鉴定了41种化合物；从浸膏粉的挥发油中鉴定了14种化合物。结果表明：因原料产地、药用部位的不同，以贯叶连翘挥发油为主要成分的油类制剂药效将有所不同。     

Characterization of petroleum products by DSC analysis

Some petroleum products, as paraffin waxes, microcrystalline waxes, lube oils, fuel oils, bitumens, were studied using DSC. DSC makes it possible to determine the wax content of various petroleum fractions, to study the effects of additives, to determine the glass transitions of bitumens; it is a useful technique both for research and for product analysis.     

Copyrolysis of naphtha with polyalkene cracking products; the influence of polyalkene mixtures composition on product distribution

The steam cracking (copyrolysis) of naphtha with oils/waxes from thermal decomposition of polyalkenes has been investigated as a process for chemical recycling of plastic wastes. High-density polyethylene (HDPE), two-component mixture (LDPE/PP) and three-component mixture (HDPE/LDPE/PP) were thermally decomposed in a batch reactor at 450 °C, thus forming oil/wax products. Subsequently, these products were dissolved in heavy naphtha in the amount of 10 mass% to obtain steam cracking feedstock. The composition of gaseous and liquid products during copyrolysis was studied at 780 °C and 820 °C in dependence on residence time from 0.08 s to 0.51 s. The obtained results were compared with the product composition from steam cracking of naphtha at identical experimental conditions. The decomposition of polyalkene oils/waxes during copyrolysis was confirmed on the basis of analysis of liquid products. It was shown that more ethene and propene was formed during copyrolysis of oil/wax from HDPE in comparison with naphtha and both mixtures and so oil/wax from HDPE seems to be favourable component of steam cracking feedstock. There were slight differences between product compositions from copyrolysis of two- and three-component mixtures. The presence of HDPE in three-component mixture supported formation of gas and ethene. The presence of oil/wax form PP enhanced formation of propene and branched alkenes. For both type of polyalkenic mixtures the yields of desired low molecular alkenes and alkanes were higher or approximately the same as from naphtha. The results confirm suitability of oils/waxes from polyalkenes as a co-feed for steam cracking units.     

原油加剂降凝的研究

采用高温气相色谱分析了越南、阿曼和大庆原油中蜡的碳数及分布组成,采用偏光显微镜观察了不同蜡含量原油的蜡晶形态变化时,分析了蜡结晶过程中的结构、分布状态和生长规律与不同原油组成的关系,得出了蜡结晶过程与原油组成之间的变化规律。结合采用X射线衍射仪和DSC差示扫描量热仪对自制聚合物(MOA)的结晶度和热性能的分析测试,表明原油中蜡晶结构与聚合物的结晶度密切相关,结晶度变化时,蜡晶分散效果有所区别,两者匹配状态时分散效果最佳,体系的粘温特性研究也证明了这一点。同时,降凝剂使得系统的热性能——溶解焓和溶解熵均发生了改变,原油中石蜡的熔程变长,相变能变大。     

Choice of paraffin inhibitors for crude oils by principal component analysis

Accumulation of paraffin wax in the equipment for petroleum production causes large financial losses. The most effective and most economic means of avoiding deposition is often to add chemical additives to the crude oil, but it is not easy to find the most suitable additive for a particular situation because the phenomena involved are too complex for traditional approaches. Principal component analysis is used for data reduction of parameters to represent chemical additives and crude oils. On the basis of physicochemical properties (including spectral parameters) and the activity of additives on the crystallisation temperature of the paraffin wax, crude oils are classified into two families and chemical inhibitors into three families. A model for predicting the activity of additives is discussed.     

Pyrolysis Analysis and Kinetics of Crude Oils

This research presents the results of an experimental study on the determination of pyrolysis behaviour and kinetics of six crude oils by differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). Crude oil pyrolysis indicated two main temperature ranges where loss of mass was observed. The first region between ambient to 400°C was distillation. The second region between 400 and 600°C was visbreaking and thermal cracking. Arrhenius-type kinetic model is used to determine the kinetic parameters of crude oils studied. It was observed that as crude oils gets heavier (°API decreases) cracking activation energy increases. Activation energy of cracking also show a general trend with asphaltene content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Inorganic Solids,Wax to Asphaltene Ratio,and Water Cut on the Stability of Water-in-Crude Oil Emulsions

The formation of stable water-in-crude oil emulsions during petroleum production and refinery may create sever and costly separation problems. It is very important to understand the mechanism and factors contributing to the formation and stabilization of such emulsions for both great economic and environmental development. This article investigates some of the factors controlling the stability of water-in-crude oil emulsions formed in Burgan oil field in Kuwait. Water-in-crude oil emulsion samples collected from Burgan oil filed have been used to separate asphaltenes, resins, waxes, and crude oil fractions. These fractions were used to prepare emulsion samples to study the effect of solid particles (Fe₃O₄) on the stability of emulsions samples. Results indicate that high solid content lead to higher degree of emulsion stability. Stability of emulsion samples under various waxes to asphaltenes (W/A) ratios have also been tested. These tests showed that at low W/A content, the emulsions were very stable. While at a wax to asphaltene ratio above 1 to 1, the addition of wax reduced emulsion stability. Stability of emulsion samples with varying amount of water cut has also been investigated. Results indicated that stability and hence viscosity of emulsion increases as a function of increasing the water cut until it reaches the inversion point where a sharp decline in viscosity takes place. This inversion point was found to be approximately at 50% water cut for the crude oils considered in this study.     

倍半硅氧烷/改性乙烯-乙酸乙烯酯共聚物复配降凝剂对蜡油倾点的影响

乙烯-乙酸乙烯酯共聚物(EVA)是原油常用的降凝剂(PPDs),但其分子结构相对比较单一,对部分油品降凝效果不佳。 为了提高EVA的降凝效果,使用硬脂酰氯与羟基化的EVA直接反应的方法制备烷基长链接枝改性EVA,并与带有烷基长链的倍半硅氧烷(SS)纳米粒子进行复配。 研究了改性EVA和SS复配降凝剂对蜡油的降凝效果和降凝机理。 结果表明:复配降凝剂为蜡提供晶核,使蜡晶变小并降低蜡的沉淀量,导致蜡油中形成的蜡晶难以搭接在一起,形成了松散的结构,当复配质量比m(EVA-g)∶m(SS-L)=1∶2时,在蜡油中的质量分数为0.1%时,蜡油倾点降低了25 ℃。     

Analysis of Crude Oils by Frequency Domain Spectroscopy—Effect of Composition and Physical Properties on Conductivity and Dielectric Response

The dielectric properties and the composition of fourteen light to heavy crude oils have been analyzed. Frequency domain spectroscopy (FDS) has been used in order to determine their dielectric response in the frequency range 0.01 to 1000 Hz. For all the crude oils, over the whole frequency range under study, dielectric loss, ?″, shows a linear dependence of frequency indicating a pure direct current (DC) conductivity. As temperature is gradually increased, the dielectric loss, ?″, increases as well, showing a strong temperature dependence. The storage modulus, ?′, shows an explicit behaviour at low frequency that could be due to adsorption of oil components onto the electrodes. We tried to correlate some physical and chemical properties (density, viscosity, SARA, TAN, water content) of the studied crude oils with their conductivity measured at various temperatures. No correlation was found and different hypothesis are suggested by the authors to explain this phenomenon.     

Combustion characteristics and kinetic analysis of Turkish crude oils and their SARA fractions by DSC

In this study, two Turkish crude oils from southeastern part of Turkey and their saturate, aromatic, resin fractions were analyzed by differential scanning calorimetry (DSC). The experiments were performed at three different heating rates (5, 10, 15 °C min^?1) under air atmosphere. Two different reaction regions were observed from DSC curves due to the oxidative degradation of crude oil components. In the first reaction region, it was deduced that the free moisture, volatile hydrocarbons were evaporated from the crude oils, light hydrocarbons were burned, and fuel was formed. The second reaction region was the main combustion region where the fuel was burned. From DSC curves, it was observed that as the sample got heavier, the heat of the reaction increased. Saturates gave minimum heat of reaction. As the heating rate increased, shift of peak temperatures to high values and extended reaction region intervals were observed. The kinetic analysis of the crude oils and their fractions were also performed using ASTM E-698 and Borchardt and Daniels methods, respectively. Activation energy values of the crude oil samples and the fractions’ high-temperature oxidation region were close to each other and varied between 67 and 133 kJ mol^?1 in ASTM and 35 and 154 kJ mol^?1 in Borchardt and Daniels methods, respectively.     

Wax deposition rate model for heat and mass coupling of piped waxy crude oil based on non-equilibrium thermodynamics

In this paper, wax deposition in waxy crude oil transportation process was regarded as an irreversible process. Based on the entropy production rate equations, the linear phenomenological equations for the diffusion of wax molecules were derived by using the theory and method of non-equilibrium thermodynamics and heat-mass transfer. Combined with the mass and energy conservation laws, the differential equations of heat and mass transfer in the process of pipeline transportation were established, and the molecular diffusion rate of dissolved wax was solved. On the basis of this, the mathematical model of actual wax deposition rate was established by considering the attachment process and scouring process of the wax molecules. Taking an oil pipeline in Daqing as an example, the change law and influencing factors of the wax molecular diffusion coefficient, the wax deposition rate, and the net wax deposition rate were studied by numerical simulation. The wax deposition rate test results of the laboratory loop test were compared with the theoretical calculation results in order to analyze the accuracy and the adaptability of heat and mass coupling mechanism and to provide a theoretical basis for further study of wax deposition in the process of waxy oil pipeline transportation.     

Effect of graphene nanoplatelets as nanofiller in plasticized poly(lactic acid) nanocomposites

Plasticized PLA-based nanocomposites were prepared by melt blending of the matrix with 5 mass% of epoxidized palm oils (EPO) and different amount of graphene nanoplatelets (xGnP). Plasticized PLA (p-PLA) reinforced with 0.3 mass% xGnP resulted in an increase of up to 26.5 and 60.6 % in the tensile strength and elongation at break of the nanocomposites, respectively. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were performed to study the thermal behavior of the prepared nanocomposites. p-PLA reinforced with xGnP shows that increasing the xGnP content triggers a substantial increase in thermal stability. Crystallinity of the nanocomposites as well as cold crystallization and melting temperature did not show any significant changes upon addition of xGnP. However, there is a significant decrease of glass transition temperature up to 0.3 mass% of xGnP incorporation.     

Effect of modified nano-silica/EVA on flow behavior and wax crystallization of model oils with different wax contents

The nano-hybrid pour-point depressant (PPD) was prepared with organically modified nano-silica covering in EVA. The effects of modified nano-silica/EVA on the flow behavior and wax crystallization of model oils with different wax contents were evaluated. Compared with pure EVA and nano-silica/EVA, modified nano-silica/EVA exhibited a better effect, when doped with 500?ppm, the pour point of the model oil containing 20?wt% wax was reduced from 33°C to 0°C. However, it is noteworthy that pour point cannot accurately reflect the effect of YSiO2/EVA as cold flow improver for a high wax content. The crystal morphology and crystallization behavior of the model oils at low temperature were also observed using polarizing optical microscopy (POM). The results indicated that modified nano-silica/EVA can reduce the size of the wax crystals and disperse the wax crystals by heterogeneous nucleation.     

A new quick method of determining the group hydrocarbon composition of crude oils and oil heavy residues based on their oxidative distillation (cracking) as monitored by differential scanning calorimetry and thermogravimetry

A calorimetric-thermogravimetric method is described of determining mass percent contents of distillate fractions, paraffins, base oils, resins, asphaltenes and carbines in various crude oils. The method is based on recording DSC curves of a 10–15 mg sample heated in air in a calorimetric-cell at a rate of 40–50 °C/min. Additionally, weight loss of sample is found at temperatures before and after the reaction. At temperatures from 220 °C or higher distillation of the hydrocarbon mixture starts to be accompanied by its exothermic oxidation, thereby making possible monitoring the distillation (oxidation) of consecutive HC fractions by simple calorimetric-techniques. Differential scanning calorimeter “Thermodat” of high-calorimetric-resolution and sensitivity equipped with dedicated software was used for conducting the experiments and performing all the calculations. Percent contents of the main constituents in a number of heavy and light crude oils were determined and formulas for establishing paraffinic, base oil and coke-forming potentials of crude oils and oil residues derived. One full analysis of a sample takes no longer than 1.0–1.5 h. The method can be used for on-line quality control of various petroleum products, such as atmospheric and vacuum oil residues, cracking residues, lubricants, ceresins and paraffins.