Inhibition of wax crystallization and asphaltene agglomeration by core-shell polymer@SiO_(2) hybride nano-particles

The gelation of crude oil with high wax and asphaltene content at low temperatures often results in the block of transportation pipeline in Africa. In recent years, it was reported that surface hydrophobicmodified nanoparticles have important applications in crude oil flow modification. In this work, four kinds of core-shell hybride nanoparticles by grafting poly(octadecyl, docosyl acrylate) and poly(acrylate-α-olefin) onto the surface of nano-sized SiO_(2) were synthesized by grafting polymerization method.The chemical structure of nanoparticles was analyzed by Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM) and thermogravimetric analysis(TGA). The rheological behaviors of crude oil and precipitation of asphaltenes in the presence of nanoparticles were studied by measuring the viscose-temperature relationship curve, the cumulative wax precipitation amount, and morphology of waxes and asphaltenes. The results indicate that the docosyl polyacrylate@SiO_(2) nanoparticle(PDA@SiO_(2)) can reduce the cumulative wax precipitation amount of crude oil by 72.8%, decline the viscosity of crude oil by 85.6% at 20℃, reduce the average size of wax crystals by 89.7%, and inhibit the agglomeration of asphaltene by 74.8%. Therefore, the nanoparticles not only adjust the crystalline behaviors of waxes, but also inhibit the agglomeration of asphaltenes. Apparently, core-shell hybride nanoparticles provides more heterogeneous nucleation sites for the crystallization of wax molecules,thus inhibiting the formation of three-dimensional network structure. The core-shell polymer@SiO_(2) hybride nanoparticles are one of promising additives for inhibiting crystallization of waxes and agglomeration of asphaltenes in crude oil.

The effect of ethylene-vinyl acetate copolymer on the formation process of wax crystals and hydrates

Ethylene-vinyl acetate copolymer(EVA) as a kind of effective polymeric pour point depressant has been extensively used in the pipeline transportation of crude oil to inhibit wax deposition and improve the low temperature fluidity of crude oil. In this work, molecular dynamics simulations were performed to investigate the effect of EVA on wax-hydrate coexistence system to evaluate the application potentiality of EVA to the flow assurance of deep-sea oil-gas-water multiphase flow system. Our simulation results reveal that wax molecules gradually stretched and stacked from random coiling to a directional and ordered crystalline state during the process of wax solidification. The strong affinity of polar vinyl acetate side chains of EVA to neighboring water molecules made the EVA molecule prefer being in a curly state,which disrupted the ordered crystallization of surrounding wax molecules and delayed the solidification rate of wax cluster. In addition, it is found that EVA cocrystallized with wax molecules to form eutectic when the wax was fully solidified. The simulation results of hydrate nucleation and growth show that the EVA molecule displayed a two-sided effect on gas adsorption of wax crystals, which was the key factor that affected the nucleation and growth of hydrates in the methane-water system. The nonpolar hydrocarbon backbone of EVA increased the diffusion rate of methane and water, allowing more methane to diffuse to the surface of wax crystals, reducing the methane concentration in aqueous solutions and inhibiting the hydrate formation. On the other hand, the nonpolar vinyl acetate chains had a repulsive effect on methane, which reduced the adsorption area of methane on the eutectic surface and decreased the adsorption threshold value of the wax crystal. The excluded methane molecules would continue dissociating in the aqueous phase and participating in the nucleation and growth process of hydrates.Therefore, the probability of hydrate formation would be increased. It was worth noting that the inhibition performance of EVA on hydrate formation mainly played a significant role in the system with small wax crystal, while its hydrate promotion effect played a dominant role in the system with lager wax crystal. In summary, EVA could significantly inhibit both of the wax and hydrate deposition for the waxgas-water multiphase system with low wax content. When the wax content in the system was high, the role of EVA was mainly played in the alleviation of wax crystallization rather than the gas hydrates. The results of the present work can contribute to a better understanding of EVA on wax deposition and hydrate formation, and provide theoretical support of the potential industrial applications of EVA.

Study on the effect of CH_(4) dissolution on the microstructure of wax crystal in waxy crude oil

In this work, the influence of the dissolution of methane(CH_(4)) gas on the wax crystal of waxy crude oil and the effect on the rheology of crude oil by dissolved CH_(4) were studied comprehensively. A self-deign high-pressure micro visualization device was developed to analyze wax crystals before and after gas dissolution. The crude oil from Shengli and Nanyang was tested by the device under various gas pressures. Results showed that the viscosity, maximum shear stress and equilibrium shear stress of Shengli crude oil decreased with the increasing pressure of the dissolved CH_(4). Due to the supersaturation of dissolved gas, the viscosity, maximum shear stress and equilibrium shear stress of Nanyang crude oil decreased initially and increased with the increasing pressure of dissolved CH_(4). The change in rheology of the dissolved gas crude oil can be a combined influence of gas pressure and dissolution mechanisms caused by CH_(4). Additionally, the wax precipitation point of Shengli crude oil decreased at the saturated dissolution of CH_(4), while Nanyang crude oil showed an increasing wax precipitation temperature.Notably, the wax precipitation area, number of wax particles, and average diameter of wax crystal in both crude oils gradually decreased with dissolution. However, a saturation of CH_(4) caused a small amount of precipitation of wax crystals in Nanyang crude oil, and the small wax crystals were aggregated to form the large wax crystals. The dissolution of CH_(4) gas can affect the wax crystallization process, crystallization ability, and morphology of wax crystals that resulted in significant variation in the rheology of crude oil.

Fine mapping of a novel wax crystal-sparse leaf3 gene in rice

Cuticular wax plays an important role in protecting plants against water loss and pathogen infection and in the adaptations to environmental stresses. The genetic mechanism of the biosynthesis and accumulation of epicuticular wax in rice remains largely unknown. Here, we show a spontaneous mutant displaying wax crystal-sparse leaves and decreased content of epicuticular wax that was derived from the cytoplasmic male sterility （CMS） restorer line Zhenhui 714. Compared with the wild type Zhenhui 714, the mutant exhibited hydrophilic features on leaf surface and more sensitivity to drought stress. The mutation also caused lower grain number per panicle and thousand grain weight, leading to the decline of yield. Genetic analysis indicates that the mutation is controlled by a single recessive gene, named wax crystal-sparse leaf3 （wsl3）. Using segregation populations derived from crosses of mutant/Zhendao 88 and mutant/Wuyujing 3, respectively, the wsl3 gene was fine-mapped to a 110-kb region between markers c3-16 and c3-22 on chromosome 3. According to the rice reference genome and gene analysis, we conclude that a novel gene/mechanism involved in regulation of rice cuticular wax formation.

Relationship between waxy crude viscosities and wax crystal microstructure

It is important and profound to quantitatively study the relation between rheology and microstructure for development of the microstructural mechanism of crude oil rheology and even for the waxy crude oil pipelining.However,due to the high complexity and irregularity of wax crystal morphology,quantitative characterization is hard to achieve.This has hampered further study on the rheology-microstructure relationship.A new approach combined the fractal geometry and the stereology theory is presented for quantifying the intricate wax crystal morphology and structure.Based on the characterization,the effects of microstructures and oil composition on the waxy crude viscosities are analyzed quantitatively.It further validates the previous qualitative research and enriches understanding into the microstructural mechanism of waxy crude oil rheology.

Slippery Surface of Nepenthes alata Pitcher： The Role of Lunate Cell and Wax Crystal in Restricting Attachment Ability of Ant Camponotus japonicus Mayr

This study attempts to investigate how the slippery surface of Nepenthes alata pitchers restricts the attachment ability of ant Camponotus japonicus Mayr, via climbing behavior observation and friction force measurement. Ants exhibited ineffective climbing behaviors and rather small friction forces when attached to upward-oriented slippery surfaces, but opposite phenomena were shown when on inverted surfaces. Friction forces of intact, claw tip-removed and pad-destroyed ants were measured on intact and de-waxed slippery surfaces, exploring the roles of wax crystals and lunate cells in restricting ant＇s attachment. On downward-directed slippery surfaces, greater forces were exhibited by intact and pad-destroyed ants; on the two slippery sur- faces, pad-destroyed ants presented slightly smaller forces and clawless ants generated considerably smaller forces. Somewhat different force was provided by clawless ants on upward and downward oriented slippery surfaces, and slightly higher force was shown when ants climbed on wax-removed surface. Results indicate that the lunate cells contribute greatly to decrease the friction force, whereas the wax crystals perform a supplementary role. Mechanical analysis suggests that the directionally growing lunate cells possess a sloped structure that effectively prevents the claw＇s mechanical interlock, reducing the ant＇s attachment ability considerably. Our conclusion supports a further interpretation of slippery surface＇s anti-attachment mecha- nism, also provides theoretical reference to develop biomimetic slippery plate to trap agricultural insect.

石油沥青质结构及其对蜡分子结晶和沉积行为影响研究进展

深水油气资源将是21世纪全球油气资源开发的战略性接替区域。高沥青质含量作为深水油气资源的一个重要特征,对油气开采、储存运输和炼化过程都具有重要影响,尤其是沥青质与蜡在深水油气开发过程中的相互作用至关重要。以深水油气资源开采为契机,从沥青质结构角度,对沥青质结构表征、沥青质在油水界面的分布、沥青质对蜡结晶和原油胶凝及沉积过程影响等进行了系统论述。结果表明:沥青质结构特征可以采用原子力显微镜等进行表征,且多以多环芳烃为核心,直链或支烃基作为其支链;沥青质结构中表面官能团(亚砜基官能团、吡啶官能团等)对油水界面的稳定性影响不一;沥青质对蜡分子结晶和沉积行为影响,目前研究多集中在定性层面,微观机理分析有待深入。但分析沥青质与蜡的作用关系、作用过程及机理,将是未来主要的研究方向,能够为深水油气资源开采与输送提供理论参考和技术支持。

含蜡及表面活性剂环戊烷水合物浆液生成及黏度特性

随着油气资源开采不断向深水领域发展,在深水管道多相混输过程中,低温高压的输送环境极易导致水合物和蜡等固相沉积堵塞管道的问题产生,尤其当蜡和水合物同时存在时,集输管道将面临更高的堵管风险。为此,使用流变仪研究了含蜡和表面活性剂(Span 80)的油水体系中环戊烷水合物的生成规律及水合物浆液流变性,明确了含蜡量(质量分数,下同)、Span 80浓度(质量分数,下同)等因素对蜡-水合物共存体系临界时间及浆液剪切稀释性的影响规律。结果表明,Span 80浓度为1.0%时,含蜡量由0.00%增大至1.00%,水合物生成临界时间由25.8 min延长至49.8 min,增幅约93%。在Span 80浓度为1.5%、2.0%及3.0%时,水合物生成临界时间同样随含蜡量增大而延长,增幅分别为113%、93%及241%。对中低含蜡量体系(≤0.75%),水合物生成临界时间随Span 80浓度的增大而缩短;对高含蜡量体系(≥1.00%),水合物生成临界时间则随着Span 80浓度的增大呈现波动变化。此外,随着水合物的生成,含蜡与不含蜡体系水合物浆液的黏度均先快速增大再逐渐减小并趋于稳定,含蜡体系水合物浆液的黏度峰值与最终平衡黏度均显著大于不含蜡体系的对应值。通过比较稠度系数和流动特性指数,发现含蜡体系水合物浆液的流动特性指数随着含蜡量、Span 80浓度的增大而增大,含蜡油水乳状液、水合物浆液及含蜡水合物浆液均具有剪切稀释性,含蜡水合物浆液则具有更强的剪切稀释性。

含蜡油气水合物生成特性及其浆液黏度影响因素

蜡、水合物及其耦合沉积是海洋油气多相混输工艺潜在风险问题。以天然气、去离子水、3#工业白油和石蜡为实验介质,依托可视化高压反应釜,基于正交实验设计的方法,分别选用L9(34)和L16(45)正交表设计并开展了无蜡和含蜡2种体系下天然气水合物生成实验;以流体当量黏度为评价指标,分析了含蜡量、搅拌速率、流体平衡温度、含水率、起始压力对水合物浆液当量黏度的影响显著程度。实验结果表明:黏度值恒定并不能判断反应釜中水合物生成是否结束,因为在剪切稳定阶段,脱离搅拌中心区域的水合物与搅拌区域新生成的水合物存在一种“动态平衡”状态;含蜡量越高,水合物生长诱导期越长;在含蜡量2%与3%水合物的快速生长阶段,扭矩与转速会发生2次突变,第1次突变原因是蜡晶的大量析出导致搅拌中心区域油相胶凝结构增强,第2次突变原因是水合物大量生成并与析出的蜡晶相互吸附形成了蜡-水合物聚集体,在离心作用下脱离了搅拌中心区域;各因素对于无蜡和含蜡体系水合物浆液当量黏度的影响显著程度相似,搅拌速率均为主要影响因素。研究结果对深水油气管道的安全运行具有重要的理论意义和实用价值。

EVA/PMMA杂化改性降凝剂对长庆含蜡原油流变性的影响机理

基于聚甲基丙烯酸甲酯(PMMA)微球良好的有机相容性,通过熔融共混法将PMMA微球与乙烯-醋酸乙烯酯共聚物(EVA28)降凝剂复合制备了EVA/PMMA杂化改性降凝剂;以长庆含蜡原油为研究对象,通过流变实验评价了EVA/PMMA杂化改性降凝剂对原油流变性的改善效果,利用差示扫描量热法和偏光显微镜法考察了添加降凝剂前后原油的结晶特性和蜡晶形貌变化。结果表明:与纯EVA28降凝剂相比,加入质量分数20 mg/kg EVA/PMMA杂化改性降凝剂使长庆含蜡原油的凝点从8℃降低到5℃,5℃时的黏度从40.96 mPa·s减小到35.56 mPa·s,屈服值从0.527 Pa减小到0.224 Pa。EVA/PMMA杂化改性降凝剂可以进一步降低长庆含蜡原油的析蜡点,增溶石蜡的正向作用更加显著,利于改善原油的流变性。

蜡基温拌剂对沥青微观特性的影响分析

【目的】探讨蜡基温拌剂对沥青微观特性及蜡析出过程的影响。【方法】选择两种常用的商业蜡基温拌剂——Sasobit和Asphaltan作为研究对象,通过红外光谱试验定性分析温拌剂与沥青的混合机理,通过变温偏光显微镜试验定量分析蜡析出过程中蜡晶体的变化规律,从而深入探讨温拌剂在沥青中的作用机理及其对沥青中蜡析出过程的影响。【结果】相比于Sasobit,Asphaltan温拌剂还具有碳氧双键。蜡基温拌剂与沥青之间未发生复杂的化学反应,仅发生物理共溶。随着温度的降低,沥青的析蜡速率逐渐减小并最终趋于稳定。同时,蜡晶体的数量、平均粒径和面积分数均随着温度降低而增大。在晶体生长过程中,蜡晶体相互连接形成网络结构。此外,温拌沥青蜡析出过程受温度和降温速率的影响,较小的降温速率有助于形成更为完整、有序的蜡晶体。【结论】蜡基温拌剂在沥青中主要通过物理共溶作用影响蜡晶体的析出过程。通过优化降温速率,可以显著改善蜡晶体的结构和性能,从而提高温拌沥青的整体性能。

热处理温度对含蜡原油触变过程微观蜡晶的影响

热力条件是影响含蜡原油低温流变特性的主要因素。通过微观实验研究热处理温度对触变过程中含蜡原油蜡晶微观结构的影响,以探究热力条件对含蜡原油胶凝体系流变特性的影响规律。结果表明:不同加热温度下的蜡晶微观参数统计学量随剪切时间的变化趋势一致,且热处理温度越高,相同时刻微观蜡晶的面积均值、粒度均值及周长均值越大,而蜡晶的长径比均值越小;经剪切破坏后,在动态平衡阶段,热处理温度越高的蜡晶重新聚集形成的Delaunay三角形越小越密集;剪切结束后的恒温静置恢复阶段,加热温度较高的含蜡原油恢复效果较好。

基于差示扫描量热法的费托蜡非等温结晶动力学

以滴熔点为113、104、92、83、78和73℃的6种窄馏分费托蜡为研究对象,采用差示扫描量热法(DSC)研究其在不同冷却速率下的非等温结晶过程,应用Jeziorny法和莫志深法对结晶动力学参数进行理论预测,通过Kissinger方程计算非等温结晶活化能。结果表明:不同蜡样品的非等温结晶过程相似,并且结晶过程依赖于冷却速率;所采用的动力学模型与试验数据吻合良好,Avrami指数n平均值在1~2之间,说明结晶过程为二次成核,成核后生长形成棒状或纤维状晶体;蜡样品的非等温结晶活化能越小或冷却速率越快,越容易发生结晶。

基于DFSS方法优化52^(#)费托蜡的制备工艺

以煤间接液化的加氢精制减三线油为原料,采用溶剂萃取-结晶的方法制备52^(#)费托蜡,并通过六西格玛设计对制备工艺进行开发。利用响应曲面设计中的中心复合设计建立响应值含油量、收率、熔点与剂油比、溶剂比、结晶时间、降温速率、结晶温度之间的数学模型,深入分析了各考察因素及其间的交互作用对响应值的影响。通过优化实验结果,验证模型,得到最佳的制备工艺参数组合以及较优的操作窗口,指导100kg/h中试试验顺利进行。研究结果表明:当剂油比为5、溶剂比为2、结晶时间6min、结晶温度5℃、降温速率为5.3℃/min时,实验室小试和中试试验产品蜡的熔点在52~54℃,含油量为0.2%~0.8%(质量分数),收率均大于25%(质量分数),产品符合国标GB/T446—2010《全精炼石蜡》的要求;实验值和模型预测值较为接近,模型的拟合效果好,预测精度高,质量可靠。

多孔二氧化钛强化的相变材料储热机理研究

相变材料在热能存储技术中的应用往往受到形状不稳定、低导热等限制。基于钛酸四丁酯的水解反应,通过一步法原位合成了基于二氧化钛的新型定型相变材料。相变材料的定型过程无须任何固化剂和有机溶剂,且无任何污染排放。此外,定型相变材料表现出理想的形状稳定性和防泄漏性能,并具有较高潜热(115 J/g)。进一步研究发现未完全干燥的样品(SP)出现异常的双峰相变行为。以干燥时间为变量,通过对SP进行质量损失测试、组分分析等研究后发现,SP中残留的非石蜡液相物质和二氧化钛的协同效应促进了(110+111)晶体结构的生长,从而增大了结晶过程中石蜡的平均晶面间距,进一步导致被封装的石蜡结晶过程中(110+111)晶面与020晶面比例失衡,最终在差示扫描量热法(DSC)曲线中出现异常的双峰相变现象。

基于蜡酯型乳化剂的液晶结构乳状液的制备研究及应用性能表征

研究了制备工艺和配方组成(油脂、多元醇、流变调节剂和离子性成分)对蜡酯型乳化剂液晶结构形成的影响,并对其液晶结构乳状液进行了相关的应用性能测试。实验结果表明,一罐法制备乳液更有利于该乳化剂配方体系液晶结构的形成。该乳化剂与植物油脂相溶性较好,乳化能力较佳,对于植物来源酯类油脂,遵循油水界面张力越小,乳化效果越佳,越有利于液晶结构形成的规律;甘油的添加能使体系保持最初优异的液晶结构及其稳定性,但1,3-丁二醇会由于其氢键与水形成的水合基团扰乱界面膜分子排列,从而使体系的液晶结构完整性及稳定性有所降低;离子性成分的添加可通过增加乳化剂紧密排列来明显增强体系的液晶结构;天然流变调节剂的加入,如AX和Tara,可以增强体系液晶结构的高温稳定性,而卡波类可增强其低温稳定性。同时,通过对液晶结构乳状液应用性能的研究发现,使用蜡酯型乳化剂制备得到的液晶结构乳状液保湿性能明显优于普通结构乳状液,且具有一定的缓释作用。

改性防护蜡对轮胎胎侧胶性能的影响及蜡膜表征

研究不同类型防护蜡在半钢子午线轮胎胎侧胶中的应用性能以及蜡膜的表征方法。结果表明:添加不同类型防护蜡的胶料硫化特性及物理性能差异较小,选用不同类型防护蜡对轮胎的使用性能基本无影响;通过表面喷霜以及蜡膜分析得出,改性防护蜡在橡胶表面形成的蜡膜薄而致密、结晶尺寸小,对橡胶的防护效果极佳,有效提升了轮胎的外观质量。

蜡晶形态、结构与含蜡原油流变性的关系

叙述了蜡晶的显微观察特征,讨论了添加降凝剂前后以及施加剪切作用前后蜡晶大小和形态与原油流变性的关系。利用基于数学形态学的蜡晶图像特征提取软件,分析对比了不同试验条件下获得的蜡晶显微图像,实现了蜡晶大小及其分布特征的量化描述,描述结果与已知的定性认识相一致。

高凝原油降凝剂的制备及其降凝机理

以丙烯酸十八酯、马来酸酐和醋酸乙烯酯三元共聚物的胺解改性物(MAVA)和乙烯-醋酸乙烯酯的共聚物(EVA)为原料,通过复配制备了1种高凝原油降凝剂(PPD),并对其降凝效果和降凝机理进行了研究。结果表明,所制备的高凝原油降凝剂对凝点为43℃的胜利原油具有明显的降凝效果,在加剂质量分数为400μg/g时,原油的凝点降低了11℃;由原油中的沥青质和胶质所形成的聚集体结构是原油的蜡晶成核剂,降凝剂可以同原油中的沥青质和胶质结合形成新的沥青质-降凝剂-胶质聚集体结构,该聚集体结构作为加剂原油的蜡晶成核剂,可以改变蜡的结晶方式,延缓蜡晶的析出速率,大幅地降低了原油的凝点。