沥青质引发的蜡油体系结蜡层分层现象及分层规律

利用自主研发的Couette结蜡装置,对蜡含量相同的油样1(不含沥青质)和油样2[含0.75%(质量分数)沥青质]进行结蜡实验,并研究其结蜡层的分层现象和分层规律。通过对油样1和油样2结蜡表层和底层的宏观形貌、DSC放热、析蜡量、蜡晶微观形貌的分析发现:油样1结蜡层无明显分层现象,而油样2结蜡层分层现象明显,沥青质的加入导致了结蜡层的分层。与结蜡表层相比,油样2结蜡底层的析蜡点、蜡含量与沥青质含量显著升高,蜡晶形貌发展为致密的类球状大蜡晶。油样2结蜡表层沉积量随壁温的升高、油壁温差和转速的增大而减小;结蜡底层沉积量随壁温升高而减小,随油壁温差和转速的增大而增大;总的蜡沉积量随壁温的升高和转速的增大而减小,随油壁温差的增大先增大后减小。     

原油中石蜡沉积的热力学模型

1 INTRODUCTION Crude oils are mixture of light and heavy hydro-carbons. The components in crude oils can be classi-fied into paraffin, naphthene and aromatic compo-nents[1]. Though the non-n-alkane components in crude oils are minor, it is essential to consider the in-fluence of non-alkane components in the model since their properties, such as fusion temperature and fusion enthalpy, are much different from paraffin. The solu-bility of each component of crude oils depends on the temperatu…     

Deposition from waxy mixtures in a flow‐loop apparatus under turbulent conditions: Investigating the effect of suspended wax crystals in cold flow regime

The effect of suspended wax crystals in wax‐solvent mixtures on the solid deposition process in the cold flow regime was investigated experimentally and analyzed with a steady‐state heat transfer model. A bench‐scale flow‐loop apparatus, incorporating a concentric‐cylinder heat exchanger, was used to measure solid deposition, in the cold flow and hot flow regimes, from wax‐solvent mixtures under turbulent flow conditions. The deposition experiments were performed with two wax‐solvent mixtures, at two flow rates, with two coolant temperatures, at 8 wax‐solvent mixture temperatures, and for several deposition times. The role of wax crystals on the deposition process was investigated by repeating some of the deposition experiments with a pre‐filtered wax‐solvent mixture. In all experiments, the deposit was formed rapidly such that a thermal steady‐state was attained within 30 min. The deposit mass increased with decreasing the mixture temperature in the hot flow regime, reached a maximum as the mixture temperature became equal to the WAT, and then decreased linearly to zero in the cold flow regime as the mixture temperature approached the coolant temperature. Also, the deposit mass decreased with an increase in the Reynolds number and the coolant temperature. The data and predictions confirmed the solid deposition to be a thermally‐driven process. The experimental deposit mass results in the cold flow regime, supported by model predictions, were identical for the unfiltered and filtered mixtures, which showed that the suspended wax crystals do not affect the deposit mass or thickness.     

A generalized model for predicting non-Newtonian viscosity of waxy crudes as a function of temperature and precipitated wax

Precipitated wax, shear and thermal history have pronounced effects on viscosity and rheological behavior of waxy crudes. On the basis of mechanism of waxy crude rheology, a shear-rate-dependent viscosity model has been developed by applying theory of suspension rheology. This model is characterized by its capability to predict viscosities of crude oils with various thermal and shear history and beneficiated with pour-point-depressants (PPD). Once viscosities at only two temperatures above the wax appearance temperature and apparent viscosities at one temperature in the non-Newtonian regime are known, viscosities or apparent viscosities at any temperatures above the gel point can be predicted by using the model together with the concentration of precipitated wax at that specified temperature. Verification by using 3458 viscosity data points ranging from 5 to 2900 mPa s from 33 virgin crudes and 14 PPD-beneficiated crudes with various thermal and shear history shows that the model predicts viscosities with an absolute average deviation of 7.43%. Furthermore parameters of rheological models such as the consistency coefficient K and the flow behavior index n of the power law model may be obtained by regressing predicted viscosity data and corresponding shear-rates.     

Characterization of the wax precipitation in Mexican crude oils

This paper reports the rheological and thermodynamic characterization of the wax formation phenomenon in three Mexican crude oils where the effect of waxes and asphaltenes content on wax precipitation and rheological behavior of crude oils is evaluated and discussed. Wax appearance temperature is measured by using differential scanning calorimetry, rheometry and densitometry. The wax precipitation curves were obtained by fourier transform infrared spectroscopy. Pour point temperatures were evaluated according to the ASTM-D97 method, whereas gelation temperatures were determined by rheological experiments made with a controlled-stress rheometer. Waxes of the crude oils were separated and characterized by gas chromatography/mass spectrometry and differential scanning calorimetry. The methods used in this work for the wax appearance temperature determination showed to be sensitive to the crude oil composition. Results showed that the presence of asphaltenes impacts significantly the liquid–solid equilibrium and rheological behavior of the crude oils studied whereas the wax melting temperature was a key factor to evaluate the propensity of crude oils to present wax precipitation problems.     

Designing maleic anhydride-α-olifin copolymeric combs as wax crystal growth nucleators

Modification of the wax crystal habit is of great practical interest during transportation and processing of crude oil at low temperature. Various pour point depressant (PPD) additives can facilitate this modification by different mechanisms. Comb shaped polymer additives are known to depress the pour point of crude oil by providing different nucleation sites for the precipitation of wax. This paper describes performance based design, synthesis, characterization and evaluation of comb shaped polymeric diesters. Copolymers of maleic anhydride with different unsaturated C₂₂ esters were synthesized and copolymers then reacted with two unsaturated fatty alcohols. All products were characterized by Fourier Transform Infra Red (FTIR) spectroscopy and Gel Permeation Chromatography (GPC). Rheological properties of crude (with and without additive) were studied by Advance Rheometer AR-500. In this study the additive based on oleic acid was evaluated as good PPD and rheology modifier.     

An aging theory-based mathematic model for estimating the wax content of wax deposits using the Fick's second law

In this study, a mathematic model is proposed for estimating the wax content of wax deposits. The proposed model was built based on the diffusion of wax molecules and counter-diffusion of oil molecules and described using the Fick's second law, allowing for the stacking fraction and orientational order of precipitated wax crystals and the tortuosity of diffusion path of de-waxed oil molecules during the counter-diffusion. The calculated results were verified by comparing with the flow-loop wax deposition experimental results. Dependence of radial position, deposition duration, bulk temperature, and wall temperature were investigated. These factors significantly affected the wax content during wax deposition. Good agreements were observed between the predictions and experimental results. The variation trends of wax content affected by various aspects are consistent with the existing studies.     

A thermodynamic model for predicting n-paraffin crystallization in diesel fuels

Diesel fuels contain n-paraffins in the range from C₁₀ to C₂₅. At low temperatures, some of the heavier n-paraffins crystallize as wax crystals and plug fuel filters. A thermodynamic model has been developed to predict the cloud point and the amount and composition of wax formed at low temperatures in diesel fuels. In this model, the amounts of all n-paraffins in a diesel fuel are converted into equivalent amounts of a reference n-paraffin, and the fuel is then treated as a solution in which the only solute is the reference n-paraffin. Cloud point, wax content and composition of several diesel fuels were measured and compared with values predicted by the model. The agreement between the measured and predicted values was good.     

A thermodynamic model for wax deposition phenomena

Wax precipitation is a serious problem in the petroleum industry because it may cause obstruction in well bores, production facilities and transportation pipelines during oil/gas production. To avoid this problem it is necessary to predict the wax appearance temperature (WAT) accurately. Consequently, a reliable thermodynamic model for predicting WAT is crucial in the design of production and transportation facilities. In this work, a thermodynamic model, based on multi-solid phase theory, has been developed. In this model the vapor and liquid phase fugacities are calculated using the Modified Peng Robinson (MPR) equation of state. The solid phase fugacities of pure components are evaluated indirectly from equation of state by the fugacity ratio. Fraction properties are estimated by using PNA analysis, and a correlation is developed for evaluating enthalpy of fusion. The major aim for performing this research was to develop a thermodynamic-computerized model for predicting WAT and the amount of precipitated wax in petroleum mixtures. The model has been applied to calculate wax appearance temperature and the amount of precipitated wax for some North Sea and synthetic oils. The predicted results are in a very good agreement with experimental data.     

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.     

Influence of polymeric additives on paraffin wax crystallization in model oils

Wax deposition, precipitation, and gelation make the transport of crude oil in pipelines challenging. The effect of several ethylene copolymers, and small molecules with a long alkyl chain, on wax formation was investigated for n-C₃₂H₆₆ in decane and de-aromatized white oil. Addition of a small amount of EVA (ethylene-co-vinyl acetate) copolymers delayed nucleation by reducing the onset temperature and the wax appearance temperature. They modified the wax crystal-structure and morphology from large plates to tiny particles by adsorbing to the wax surfaces and inhibiting growth. Viscosity and the pour-point were improved by inhibiting the formation of large aggregates. It was demonstrated that the content of vinyl acetate groups in EVA copolymers affected wax crystallization. The small molecules, propylene copolymers, and ethylene copolymers with ethyl acrylate, maleic anhydride, and ethylene glycol showed a weak inhibiting effect. The effect of wax inhibitors was determined by the content and by the type of structure-disturbing groups in the copolymers.     

Study on wax precipitation characteristics of wax deposit in pipes

Wax deposit properties are a significant concern in pipeline pigging during waxy crude oil transportation. In the present work, the impacts of flow conditions and oil properties on the wax precipitation characteristics of wax deposits are investigated. A flow loop apparatus was developed to conduct wax deposition experiments using four crude oils collected from different field pipes. The differential scanning calorimetry (DSC) technique was employed to observe the wax precipitation characteristics of crude oil and wax deposit. The results show that the wax content and the wax appearance temperature (WAT) of the deposits increase with shear stress and radial temperature gradient, and decrease with radial wax molecule concentration gradient near the pipe wall. The DSC tests on the wax deposits revealed that the deposit wax content is strongly correlated to the oil wax content. Furthermore, an empirical correlation was developed to predict the wax content and the WAT of the wax deposit. Verification of the empirical correlation using the different oils indicated that the average relative error of the wax content prediction and average absolute error of WAT prediction were 13.2% and 3.6°C, respectively.     

Physikalisch-chemische Eigenschaften von Braunkohlenextrakten und abgetrennten Wachs- und Harzstoffen

Physico-chemical Properties of Brown-Coal Extracts and Separated Wax and Resin Substances The component composition and the physico-chemical properties of the raw montane wax Romonta as well as of three samples of the toluene extracts from the mine Turów, obtained at different extraction temperatures, were determined. The wax and resin substances were separated from the raw montane wax Romonta and from the toluene extract of brown-coal from the mine Turów, obtained at 100°C, and then characterized. The rheological properties of the extracts, the separated components and the four selected processing products of the raw montane waxes Romonta (means of hydrophobation Romonta 55, acid wax R, ester wax K-60, partly saponified ester wax REW II) were determined by the rotation viscosity metre Rheotest 2. The viscosity measurements were carried out at higher temperatures than the dropping point of the investigated substance, in case of extracts rich on resin also at lower temperatures. A significant influence of the sort of coal and the extraction temperature on the component composition of the obtained extracts as well as on the properties of the separated wax and resin substances was established. Furthermore a different rheological behaviour of the wax substances and wax containing extracts in comparison to the resin components of brown-coal bitumen was observed. Concerning the extracts of brown-coal from the mine Turów it was found out that the viscosity slowly increases in case of an increase of the resin content up to 50%, but at higher resin content it increases very quickly.     

Solubilities of Soybean Oil,Jojoba Oil and Cuticular Wax in Dense Carbon Dioxide

The solubility of jojoba oil in dense carbon dioxide has been investigated by a dynamic method between 100 and 2600 bar and at temperatures within the range 20 to 80° C. The solubility isotherms and isobars of jojoba oil are compared with those of soybean oil. The appearance of solubility maxima was demonstrated for both cases in the high pressure region. The results are discussed and their implications for preparative extraction pointed out. In order to optimize the precipitation conditions a study was made of the solubility of cuticular wax in the low pressure region as a function of temperature and this was compared with the behaviour of typical essential oil components. The available differences can be utilized for an effective preprecipitation of wax from essential oils.     

A Simplified Method for Fractionation and Analysis of Waxes and Oils from Sorghum (Sorghum bicolor (L.) Moench) Bran

In the United States, sorghum is primarily used for animal feed and ethanol production but has potential to provide value-added coproducts including waxes and oil. The surface of sorghum contains 0.1–0.4% wax; however, wax extraction from whole kernels before fermentation may not be economical. An alternative method for this extraction could be facilitated through decortication, abrasion of the surface to remove bran. Decortication increases the starch content of decorticated sorghum, potentially improving ethanol yields, while concentrating wax and oil to the bran. Typically, oil (triacylglycerols) and waxes are extracted from bran in one extraction and waxes are precipitated from oil using cold temperatures then filtration. This research compared traditional fractionation (simulated with a two-step, single-temperature extraction) to a two-step, dual-temperature extraction, whereby oil is first extracted at room temperature and then waxes at elevated temperature. Extractions were performed using an accelerated solvent extractor with hexane or ethanol as solvents. Ethanol extraction showed greater yields (~15% w/w) compared to those of hexane (~11% w/w) because polar materials were extracted. Using hexane, the two-step, dual-temperature fractionation separated waxes from oils via the temperature of extraction solvent with similar purity to the traditional method that fractionated via cold precipitation and filtration. For ethanol, the traditional single-step method fractionated with higher wax purity but lower oil purity compared to the two-step, dual-temperature fractionation.     

The effect of environmental temperature on sebum composition in tropical and temperate breeds of cattle

This study compared the effect of environmental temperature on sebum composition in 2 breeds of cattle, British (SH) and Brahman (GB), which differ in their abilities to tolerate heat. By long-term exposure of both breeds to environmental temperatures of 24 C and 32 C and the more heat-tolerant GB breed to 38 C, it was possible to make breed comparison at (a) different body temperatures, i.e, when all animals were exposed to the same environmental temperature, and (b), at the same body temperature, i.e., when the 2 breeds were exposed to different ambient temperatures. The composition of sebum excreted to saturation level on the skin surface was determined. At the same body temperatures, the amounts of fatty acids in each lipid class were higher in GB than in SH animals except during hyperthermia when the amounts of triglyceride fatty acids were similar in both breeds. The total amounts of individual fatty acids except 14∶1, 16∶1, 20∶0 and 14∶OH were higher in both breeds at 32 C than at 24 C. The GB cattle excreted more essential fatty acids (EFA) than the SH cattle at 24 C and at 32 C. There was a significant genotype by environment interaction in the amounts of EFA partitioned between triglycerides and wax esters; in GB cattle, the amount of EFA excreted in triglycerides decreased whereas the amount excreted in wax esters increased with rising body temperature.     

柴油降凝剂复配及降凝机理

柴油降凝剂复配是有效提高其在柴油中降凝效果的手段之一。本文主要考察了不同类型柴油降凝剂在0^#柴油中的降凝效果,筛选出其中效果较好的降凝剂进行复配,并考察了不同配比对其降凝效果的影响,最终采用低温原位X射线衍射、低温偏光显微镜和差示扫描量热法对比研究了柴油降凝剂加入前后对柴油蜡晶的生长规律和低温结晶热力学的影响。结果表明,聚甲基丙烯酸酯类降凝剂KT4与聚乙烯-乙酸乙烯酯类降凝剂AH-BSFH复配起到协同作用,具有更好的降凝效果,其最佳复配比例为1∶1。XRD、低温偏光显微镜的分析结果表明,KT4降凝剂主要是通过吸附理论来降凝,AH-BSFH降凝剂主要是通过共晶理论来降凝。DSC分析结果证明,KT4与AH-BSFH按1∶1复配后使蜡晶的固-液相变能下降得更多,提高了降凝剂与蜡的匹配性,从而起到了协同作用。     

The influence of paraffin wax addition on the isothermal crystallization of LLDPE

The influence of paraffin wax addition on the isothermal crystallization kinetics of linear low density polyethylene (LLDPE) was studied in a temperature range where the wax was always in the molten state and could be considered a solvent for LLDPE. The LLDPE/wax blends were prepared by melt mixing in the following compositions: 100/0, 95/5, 90/10, 80/20, 70/30, and 60/40. The results obtained show that the rate of isothermal crystallization is depressed by wax addition at constant crystallization temperatures. LLDPE needs a higher amount of supercooling to start crystallizing as the content of wax increases in the blends. The Flory–Huggins theory (FH) for polymer/diluent mixtures was applied employing equilibrium melting temperature values obtained by extrapolation with the Hoffman–Weeks method. The results of the FH analysis indicate that the interactions between wax and LLDPE are nonlinear and strongly depend on composition. This nonlinear composition dependence of wax/LLDPE interactions is reflected in the complex way in which the overall crystallization kinetics rate depends on both supercooling and composition. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44398.     

Preparation of Y-type Barium Hexaferrite by the Glass–Ceramic Method

Y-type Ba-hexaferrites (Ba₂Zn₂Fe₁₂O₂₂), which have been identified as electromagnetic wave absorbers, were prepared by the glass–ceramic method. Glasses with the composition 0.1ZnO·0.9( x B₂O₃· y BaO·(1− x − y )Fe₂O₃) were prepared, and the precipitation of Y-type Ba-hexaferrite from the glass matrix was investigated. Y-type Ba-hexaferrite were precipitated by heating glass specimens with roughly the composition 0.1ZnO·0.9(0.2B₂O₃·0.5BaO·0.3Fe₂O₃) at temperatures above about 1073 K. The lower temperature limit at which single-phase Y-type powder was obtained after leaching with a dilute HCl solution was about 1093 K. The low-temperature formation of Y-type Ba-hexaferrite was linked to the generation of a liquid phase. The shape of Y-type crystals depended strongly on the heating temperature and changed from a plate-like hexagon to a complex polyhedron with increasing heating temperature.     

不同加热温度和降温速率对含蜡原油析蜡点的影响

利用差示扫描量热法(DSC)对原油的析蜡特性进行分析,并得到了析蜡过程的热谱图和dh/d T-T曲线。以大庆原油为研究对象,对dh/d T-T曲线进行分析,探讨了加热理温度、温降速率对析蜡点的影响。结果表明:加热温度高于溶蜡点温度时,析蜡点随温变化小;加热温度低于溶蜡点温度,析蜡点随温度的降低先增大后减小。温降速率越大,析蜡点越低。