胶凝含蜡原油的连续剪切实验研究

胶凝含蜡原油由于其蜡晶的三维网状空间结构,具有复杂的流变性。胶凝原油的流变性质一直是研究的重点和热点。很多学者对胶凝原油的性质做了详细而又深入的研究,但这些研究一般集中在恒定剪切速率上,对胶凝原油的连续剪切的研究较少。通过控制不同的降温速率和胶凝温度,来研究胶凝原油连续剪切的变化规律。实验结果表明,当降温速率越大时,初始的粘度越小,但剪切一段时间后,不同降温速率下的粘度无多大差别;当胶凝温度越低是,其初始的结构强度越大,并且在结构破坏以后,在同一剪切速率下,其粘度也越大,但不同温度下的差距在减小;当从高到低的剪切情况下,其粘度随着剪切速率的减小,呈增大的趋势,并且这趋势越来越明显,相对于从低到高的剪切情况下,在同一剪切速率下,从低到高情况下的粘度比从高到低的粘度要大。     

Dynamic rheological study of paraffin wax and its organoclay nanocomposites

Dynamic rheological data for paraffin wax and its organoclay nanocomposites are reported. Dynamic mechanical analysis of paraffin wax for temperatures ranging from ?40 to 55°C showed a decrease of several orders of magnitude in the dynamic moduli and a significant shift toward viscous behavior, which resulted from the occurrence of two solid–solid phase transitions. In both the crystalline and mesophase regions, the dispersion of organoclay platelets in paraffin wax via ultrasonication increased the storage modulus, whereas the effect on the loss modulus was temperature‐dependent. The melt rheology data of the wax–clay nanocomposites at 70°C showed that the complex viscosities increased monotonically with clay addition and demonstrated shear‐thinning behavior for frequencies between 0.1 and 100 rad/s. The complex viscosity versus angular frequency data were well fit by a power‐law function for which the shear‐thinning exponent provides a gauge for the extent of clay exfoliation. The nanocomposites exhibited low‐frequency solid behavior, which indicated good exfoliation of the organoclay in the wax matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of polymeric pour point depressants for Nada crude oil (Gujarat,India) and its impact on oil rheology

Five flow improvers have been synthesized to study rheological properties of Nada crude oil (Gujarat, India). Anhydride copolymers were prepared making use of the copolymerization of acrylates of different alkyls with maleic anhydride and the Poly (n-alkyl acrylates-co-N-hexadecylmaleimide) were prepared by the reaction of copolymer with hexadecylamine. The additives were purified and characterized by FTIR, GPC. The prepared polymeric additives shows dual function both as wax dispersants and flow improvers and all of them acts as good pour point depressants. Yield stress and the viscosity of the crude oil at different temperatures and concentrations of additives were evaluated by zero friction advanced rheometer AR-500 of TA instrument. Comparison of morphologies and structures of wax crystals or aggregates in waxy crude oils beneficiated with and without a PPD was also done by micro photographic studies which show the modification in wax crystal morphology due to additives.     

温度及剪切速率对延长原油粘度的影响规律研究

延长原油为高含蜡原油,原油中石蜡在输送过程中受温度及剪切力的影响较大。因此,采用流变学测试与分析方法对温度及剪切速率对粘度的影响规律进行了研究。研究结果表明：延长原油的凝点为26℃,粘度在温度由28℃降至23℃时由96mPa·s激增至192mPa·s,提高剪切速率可较大幅度的降低原油粘度但增加到100S^-1后对粘度的影响趋于稳定。     

BEM/PMSQ杂化降凝剂对青海含蜡原油作用效果及其机理

基于聚甲基硅倍半氧烷（PMSQ）微球良好的有机相容性与规则的微观球形形貌,将PMSQ微球与BEM降凝剂通过熔融共混制备了BEM/PMSQ杂化降凝剂。以青海含蜡原油为研究对象,通过流变实验评价了BEM/PMSQ杂化降凝剂对原油的凝点、黏弹性、黏度与屈服值的影响,利用偏光显微镜观察了加剂前后原油蜡晶形貌的变化,并与单独添加BEM降凝剂的油样进行了对比。结果表明：不加剂原油凝点27.0℃;在相同的降凝剂加量下（100 μg·g^-1）,降凝效果最好的是BEM/PMSQ 2%杂化降凝剂,可降低原油凝点19.0℃,相较于添加BEM降凝剂,进一步降凝6.0℃,降低胶凝点4.3℃,10℃时平均降黏率39.0%,G'值降低了62.0%。PMSQ微球与BEM/PMSQ杂化降凝剂在十二烷中的分散状态照片表明PMSQ微球表面吸附了BEM降凝剂,从而在原油中作为蜡晶的成核模版存在,使所形成的蜡晶结构更为紧凑,包覆更少的液态油,从而改善原油的宏观流变性。     

Mixture temperature prediction of waxy oil–water two-phase system flowing near wax appearance temperature

Temperature sensitivity of waxy crude oils makes it difficult to study their flow behaviour in the presence of water especially near their wax appearance temperature(WAT). In this study a method was proposed and implemented to mitigate such difficulties which was applied in predicting mixture temperatures(Tm) of a typical Malaysian waxy crude oil and water flow in a horizontal pipe. To this end, two analytical models were derived firstly from calorimetry equation which based on developed two correlations for defining crude oil heat capacity actualized from the existed specific heat capacities of crude oils. The models were then applied for a set of experiments to reach the defined three predetermined Tm(26 °C, 28 °C and 30 °C). The comparison between the predicted mixture temperatures(Tm,1and Tm,2) from the two models and the experimental results displayed acceptable absolute average errors(0.80%, 0.62%, 0.53% for model 1; 0.74%, 0.54%, 0.52% for model 2). Moreover,the average errors for both models are in the range of standard error limits(±0.75%) according to ASTM E230.Conclusively, the proposed model showed the ease of obtaining mixture temperatures close to WAT as predetermined with accuracy of ± 0.5 °C approximately for over 84% of the examined cases. The method is seen as a practical reference point to further study the flow behaviour of waxy crudes in oil–water two-phase flow system near sensitive temperatures.     

Viscosity profile prediction of a heavy crude oil during lifting in two deep artesian wells

It has been known that the productivity of artesian wells is strongly dependent on the rheological properties of crude oils.This work targets two deep artesian wells (＞5000 m) that are producing heavy crude oil.The impacts of well conditions including temperature,pressure and shear rate,on the crude oil rheology were comprehensively investigated and correlated using several empirical rheological models.The experimental data indicate that this heavy oil is very sensitive to temperature as result of microstructure change caused by hydrogen bonding.The rheological behavior of the heavy oil is also significantly impacted by the imposed pressure,i.e.,the viscosity flow activation energy (Eμ) gently increases with the increasing pressure.The viscosity-shear rate data are well fitted to the power law model at low temperature.However,due to the transition of fluid feature at high temperature (Newtonian fluid),the measured viscosity was found to slightly deviate from the fitting data.Combining the evaluated correlations,the viscosity profile of the heavy crude oil in these two deep artesian wells as a function of well depth was predicted using the oilfield producing data.     

Temperature shifting of convergent flow measured effective elongational viscosity

The effective elongational viscosity data on a series of polyolefins as a function of temperature are shifted to a reference temperature using the approach for shifting shearing viscosity data. The temperature shift factors are obtained from complex and capillary shear rheology, and these are the same factors used for shifting the shear rheology. A Carreau rheological model was used to determine the zero shear rate viscosity at different temperatures, and an Arrhenius expression was used to determine the temperature shift factors. The same shift factors are shown to produce separate master curves for shear and elongational rheology at reference temperatures. The commercial grades of polyolefins studied include an extrusion grade of polypropylene and metallocene and conventionally catalyzed low and high density polyethylene materials. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1387–1396, 2003     

Effect of wax inhibitors on pour point and rheological properties of Iranian waxy crude oil

A variety of techniques have been employed in order to reduce problems caused by the crystallization of paraffin during the production and/or transportation of waxy crude oil. Flow improvers are used extensively to increase the mobility of crude oil. In this study, the influence of the ethylene-vinyl acetate copolymer (EVA), as flow improver, with different ranges of molecular weight on the viscosity and pour point of five Iranian waxy crude oils was evaluated. Five types of Iranian waxy crude oil were selected based on their similar wax (> 10%) but different asphaltene contents. Also, the effect of asphaltene content on the performance of this flow improver was studied. The rheological behavior of these crude oils, with middle range API gravity, in the absence/presence of flow improver was studied. The rheological data cover the temperature range of 5 to 40 °C. The results indicated that the performance of flow improver was dependent on the molecular weight and the asphaltene content. For crude oil with low asphaltene, higher molecular weight flow improvers are the best additive and lower molecular weight flow improvers showed good efficiency for crude oil with high asphaltene content. Addition of small quantities of asphaltene solvents such as xylene (1 wt.%), alone or in combination with flow improver, can improve viscosity of crude oil with high asphaltene content.     

剪切速率和温度对低水胶比水泥浆流变性能的影响

水泥浆体的流变性能不仅与材料本身有关,还受环境及外部作用影响。本文针对水泥基材料实际工程中存在的主要外部影响因素,即剪切作用与环境温度,研究了两者对低水胶比水泥浆流变性能的耦合作用。结果表明:水泥浆体在剪切过程中的流变行为与所施加的预剪切有关,水泥浆体的屈服应力随预剪切速率的增大而减小,剪切增稠的程度随预剪切速率的增大而增大;温度升高,水泥颗粒对减水剂的吸附量增加,浆体在不同剪切速率下的平衡表观黏度减小;温度和剪切速率对水泥浆平衡表观黏度的影响具有耦合效应,剪切速率越高,温度的影响越小,反之亦然,并建立了不同温度和剪切速率下平衡表观黏度的数学关系。     

热历史作用对含蜡原油流变性的影响

管输过程中热处理作用对含蜡原油的流变性具有很大的影响。本文对经历不同热处理作用后的原油进行了对比实验,分析了热历史作用对含蜡原油流变性能影响的作用机理。研究表明,热历史作用能使蜡晶的形状、大小以及结构等发生变化从而影响原油的流变性能,而且热历史作用对含蜡原油流变性能的影响是有规律的。     

Physico-chemical properties of heavy crude oil-in-water emulsions stabilized by mixtures of ionic and non-ionic ethoxylated nonylphenol surfactants and medium chain alcohols

This work describes the formulation and evaluation of concentrated, heavy oil-in-water emulsions stabilized by mixtures of ethoxylated surfactants and normal alcohols. The rheology, stability and droplet size of these emulsions were investigated as functions of the emulsification process parameters. The parameters investigated for this study include emulsifier agent composition, presence of additives, pH and salinity of the continuous aqueous phase, emulsification temperature, oil content and emulsion aging. The produced emulsions had viscosities ranging from 30 to 150 mPa s and represent a 30-fold reduction of the crude oil viscosity. Sauter mean diameters of the droplets ranged from 10 to 50 μm. The emulsions were produced by mixing the oil with an aqueous solution containing medium normal-chain alcohols and small quantities of a mixture of ethoxylated nonylphenol and ethoxylated amine surfactants. The presence of these alcohols led to a sharp decrease in the droplet size of the emulsion. This size decrease had a direct impact on the emulsions’ stability and apparent viscosity. The rheological parameters of the aged emulsions were also essentially constant over a 42-day period.     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

热历史和剪切历史对原油触变性的影响研究

剪切历史和热历史是影响原油触变性的关键因素。以大庆含蜡原油为例,测试了不同剪切历史和热历史处理后的原油滞回环曲线。研究表明,含蜡原油的触变性与测试温度、回升温度、剪切历史等因素有关,当回升温度为非牛顿温度时,原油的流动性得到改善;剪切历史使原油触变性变弱,且恒温剪切较降温剪切对原油的流动性改善效果好。     

制备条件对聚酰胺蜡触流变剂性能的影响

研究了聚酰胺蜡粉末的粒径和活化试剂的种类对聚酰胺蜡触流变剂改善涂料流变性能的影响。在环氧树脂体系中,与未研磨的聚酰胺蜡相比较,研磨后的聚酰胺蜡使体系具有更好的流变性能。考察了活化剂正丁醇、异丙醇、乙醇和甲醇的加入对聚酰胺蜡流变性能的影响,发现将乙醇与异丙醇按质量比5∶7复配后活化的聚酰胺蜡浆,能使环氧树脂体系具有更高低剪切黏度和更低高剪切黏度的触流变性能。     

Rheological Behaviors of Polyacrylonitrile/1-Butyl-3-Methylimidazolium Chloride Concentrated Solutions

One of the room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) was chosen to prepare the concentrated solutions of Polyacrylonitrile (PAN). The rheological behaviors of the solutions were measured with rotational rheometry under different conditions, including temperatures, concentration, and molecular weight of PAN. The solutions exhibited shear-thinning behaviors, similar to that of PAN/DMF solutions. The viscosities decreased with the increasing of shear rates. However, the viscosity decreased sharply at high shear rates when the concentration was up to 16wt%. The dependence of the viscosity on temperature was analyzed through the determination of the apparent activation energy. Unusually, the viscosity of solutions of higher concentration is lower than that of lower concentration. Similarly, the viscosity of low molecular weight PAN was higher than high molecular weight PAN at high shear rates. The dynamic rheological measurement indicates the loss modulus is much higher than storage modulus. The trend of complex viscosity is similar with the result of static rheological measurement. The interaction between PAN and ionic liquid [BMIM]Cl was discussed.     

Thermal,viscoelastic and adhesion properties of EVA (ethylene-co-vinyl acetate) hot melts containing polypropylene waxes of different nature

Wax determines the compatibility of tackifier and polymer in hot melt adhesives. Although the influence of the addition of microcrystalline and Fischer-Tropsch waxes on the properties of ethylene-co-vinyl acetate (EVA) hot melts has been studied, the addition of polypropylene wax has not been considered yet. In this study, different polypropylene waxes (polypropylene wax – PP, – maleic anhydride grafted polypropylene wax – PPMA – copolymer of polypropylene and 10.9?wt.% polyethylene wax – PP-E) were added to EVA hot melts and they were characterized by Brookfield viscosity, softening point measurement, differential scanning calorimetry, thermal gravimetric analysis, dynamic mechanical thermal analysis, plate–plate rheology, tack, and single-lap shear adhesion. The viscosities of EVA hot melts containing polypropylene waxes were relatively high, the highest viscosity corresponded to the formulation containing PP-E wax which also showed pseudoplasticity. The change in viscoelastic properties (i.e., from dominantly viscous to dominantly elastic) was produced at lower temperature in EVA hot melt containing PP-E wax, this adhesive exhibited the highest tack. On the other hand, the addition of acrylic PPMA wax increased the adhesion of EVA hot melt but lower tack was obtained. Finally, the PP-E wax was more compatible with EVA copolymer than the other polypropylene waxes.     

Rheological behavior of low molecular weight polystyrene composites containing monodisperse crosslinked polystyrene beads

Steady shear viscosities and dynamic moduli of polymer composites, consisting of crosslinked polystyrene beads and low molecular weight polystyrene matrix, were measured in a cone-and-plate rheometer at different temperatures. Viscosities and dynamic moduli were found to be very sensitive to filler loading and measurement temperature. Steady shear viscosities of 30% and 40% loaded low molecular polystyrene composites showed a power-law behavior over the entire range of shear rates. Storage and loss moduli were initially linear with frequency on double logarithmic plots, with limiting slopes of 0.3 and 0.1. At high concentration of filler particles, they showed a flat plateau at low frequencies, indicating that these systems exhibit a yield behavior. A 20% PS composite loaded with beads of high crosslink densities resulted in poor dispersion of beads as a result of poor dispersion of particles. PS beads 1.16 μm in diameter showed a higher viscosity. It is due to the apparent increase in loading resulting from broken particles. At low measurement temperature, filler effects were suppressed by high viscosity matrix and showed a similar rheological behavior to high molecular weight by PS matrix. We suggest that rheological behavior reflects the state of dispersion of beads in the matrix.     

Effects of pore fractal structures of ultrafine coal water slurries on rheological behaviors and combustion dynamics

The ultrafine coal water slurry (CWS) with the particle size of 1-10 μm, ash content of 1-2%, solid concentration of 50% is a promising substitute fuel for diesel oil. The effects of pore fractal structures of three ultrafine CWSs on their rheological behaviors and combustion dynamics were studied in this paper. When the pore fractal dimensions of Yanzhou, Huainan and Shenhua ultrafine CWSs increase, their apparent viscosities all increase and the increase extents gradually enlarge with decreasing shear rates, while their ignition temperatures and apparent activation energies all decrease. For example, when the pore fractal dimension of Yanzhou coal increases from 2.31 to 2.43, the CWS apparent viscosity at a low shear rate of 12 s⁻¹ increases from 75 mPa s to 2400 mPa s, and that at a high shear rate of 100 s⁻¹ increases from 80 mPa s to 820 mPa s. Meanwhile, the ignition temperature of Yanzhou CWS decreases from 445 °C to 417 °C at a heating rate of 12.5 °C/min, and the apparent activation energy decreases from 104 kJ/mol to 32 kJ/mol.     

Melt rheology of poly(lactic acid): Consequences of blending chain architectures

The rheology of blends of linear and branched poly(lactic acid) (PLA) architectures is comprehensively investigated. Measurement of the melt rheological properties of PLA is complicated by degradation effects but the addition of 0.35 wt% tris(nonylphenyl) phosphite (TNPP) provides excellent stabilization over a range of temperatures. Master curves of dynamic viscosity constructed using time‐temperature superposition show significant dispersion for unstabilized samples; this behavior is accompanied by a loss of molecular weight. TNPP stabilized samples show excellent superposition throughout the entire frequency range and minimal loss in molecular weight. For the linear architecture, the Cox‐Merz rule is valid for a large range of shear rates and frequencies. The branched architecture deviates from the Cox‐Merz equality and blends show intermediate behavior. Both the zero shear viscosity and the elasticity (as measured by the recoverable shear compliance) Increase with increasing branched content. The viscosities of both the unstabilized samples and the TNPP stabilized samples roughly obey a log additivity mixing rule. The recoverable shear compliance is monotonic in blend composition and a mixing rule for this property is also presented. For the linear chain, the compliance is independent of temperature but this behavior is apparently lost for the branched and blended materials. Tensile and thermal properties of the blends are also measured and found to be roughly equal within the statistical error of the experiments. The results suggest that excellent control over rheological behavior of PLA is possible through blending chain architectures without compromising mechanical properties.