Effect of polyethylene pipe on wax deposition under different temperature and flow rate conditions

Wax deposition is an important but troublesome boulder in petroleum industry that has always plagued pipeline engineering operators. In this study, wax deposition in the polyethylene pipes has different behaviors comparing wax deposition in stainless steel pipes such as smaller weight of wax deposits and lower wax content. After wax deposition experiments, some important parameters, including diffusivity and temperature gradient, were measured and calculated to explore the differences between two material pipes. Moreover, those factors can make a significant impact on radial mass flux. A series of results in polyethylene pipes suggests that higher diffusivity enhances diffusion flux of wax in the radial direction. But it was found that radial concentration gradient accounted for a larger proportion. These factors are the relationship of competition and cooperation and the combination of them results in different performances of wax deposition between polyethylene and stainless steel pipes.     

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.     

Investigation of inhibitors efficacy in wax deposition mitigation using a laboratory scale flow loop

Statistically reliable wax inhibition experimental data was obtained by utilizing the newly built laboratory scale flow loop. The comb‐shaped inhibitors are found more effective in decreasing the thickness compared to the linear inhibitor under the same conditions. Moreover, this becomes more predominant as the chain length of inhibitors increases. Interestingly, even though all the inhibitors decreased the deposit thickness, the wax content increased significantly. Besides, the longer chain length (PI‐B) of the inhibitor results in a higher wax content. Since the combination of growth and aging influenced by the presence of inhibitor significantly, paraffin inhibition efficiency (PIE) based on the wax mass was proposed to quantitatively assess the inhibitors. Based on the PIE, PI‐B, and PI‐C have more inhibition efficiency than PI‐A. Therefore, when selecting wax inhibitor, one should be aware about the strength of the deposit gel in addition to the reduction of the deposit mass. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4131–4139, 2016     

蜡沉积厚度随时间变化规律的模型研究

在分析蜡沉积过程的基础上, 基于一定的假设条件, 建立了蜡沉积厚度随时间变化的模型。通过提取蜡沉积厚度随时间变化曲线的数据, 拟合了模型中的待求常数, 并对模型计算值和实验值的吻合程度进行了分析。结果表明:对数模型、指数模型及动平衡模型均能反映蜡沉积厚度随时间的变化趋势, 对数模型与实验值的吻合程度最好;指数模型和动平衡模型所得的结果与实验结果的吻合程度相当, 在沉积初期, 指数模型的吻合程度高于动平衡模型, 但当沉积时间接近实验规定时间时, 动平衡模型的吻合程度高于指数模型;所建立的模型简单实用, 能够反映沉积厚度随时间变化的增长快慢趋势, 不同实验数据应用时仍需对各模型的计算精度进一步验证, 从而使得选用模型能更好地符合实际。     

聚乙烯蜡的生产及应用前景

概述了聚乙烯蜡的生产方法及其改性研究进展,介绍了聚乙烯蜡在涂料、色母粒、油墨以及塑料加工等领域的应用情况,指出了其今后的发展前景。     

Chemical binding of jojoba liquid wax to polyethylene

Jojoba wax was chemically bonded to polyethylene—in film or hollow fiber form—via a stable sulfonamide bond. The jojoba-bonded polyethylene was obtained by binding allyl amino jojoba derivatives to chlorosulfonated polyethylene. The amount of jojoba added to the polymer ranged from 9 to 98% (w/w), depending onthe reaction conditions. Swelling of the polymer in the reaction solvent was the major factor affecting the efficacy of the chemical binding of the jojoba amino groups to the chlorosulfonyl entities of the polymer. The double-bond regions in the bound jojoba wax were preserved, i.e., they were shown to be reactive in a bromination reaction. These modified membranes can find application in separation processes, such as metal ion separation and pervaporation.     

Rheological characterization of linear low-density polyethylene–Fischer–Tropsch wax blends

The thermal and rheological behavior of blends of a Fischer–Tropsch (F-T) wax with linear low-density polyethylene (LLDPE) were investigated by differential scanning calorimetry and cone-and-plate rheometry. F-T wax is used as a possible low-cost processing aid alternative for LLDPE masterbatch applications. The melting- and crystallization thermograms indicated a two-phase solid-state morphology and full compatibility in the fully molten material. Both the high-melting and low-melting phase contained co-crystalized wax and polymer. Rheological data of F-T wax-LLDPE blends over the full composition range was also obtained. The zero-shear viscosity data was adequately predicted by the Friedman and Porter mixing rule: $\mathrm{\eta }={\left(w_p{\mathrm{\eta }}_p^{1/\mathrm{\alpha }}+{w_w\mathrm{\eta }}_w^{1/\mathrm{\alpha }}\right)}^{\mathrm{\alpha }}$ with α = 3.4. This implies that the melt viscosity is dominated by the effects of polymer chain entanglement and that the main consequence of adding the wax is to reduce the concentration of the polymer present. The complex viscosity also fitted this model albeit with α = 4.81. All Han plots, that is, plots of the logarithm of the storage modulus (G') against the logarithm of the loss modulus (G"), were linear. Within the experimental uncertainty, they were essentially unaffected by variations in blend composition, temperature and the applied angular frequency. Additionally, Cole–Cole plots were also in agreement that wax-LLDPE blends are miscible at melt state. This supports full miscibility of the F-T wax-LLDPE blend system down to temperatures as low as 120°C.     

Investigation of wax deposit ‘sloughing’ from paraffinic mixtures in pipe flow

Deposit ‘sloughing’ from ‘waxy’ crude oils has been described in the literature as a possible mechanism, leading to partial or complete dislodging of the deposit from the pipe wall due to changes in flow parameters. A bench‐scale flow loop apparatus was used to investigate ‘sloughing’ with prepared single‐phase ‘waxy’ mixtures of a multicomponent paraffinic wax dissolved in a multicomponent solvent. Experiments were performed to study the changes in the deposit‐layer thickness due to step increments in the ‘waxy’ mixture flow rate, the mixture temperature, and the coolant temperature. It was observed that the deposit‐layer thickness decreased with an increase in each of the three parameters; however, a complete or sudden dislodging of the deposit‐layer did not occur in any of the experiments. A steady‐state heat‐transfer model was used to predict the variation in the deposit mass or thickness due to changes in the selected parameters. In each case, the step‐wise decrease in the deposit thickness, as observed experimentally, was predicted to be caused by changes in the thermal resistance and/or thermal driving force.     

氧化聚乙烯蜡乳液的组成研究

在常压下制备氧化聚乙烯蜡乳液,研究乳化剂的用量、水蜡质量比以及助乳化剂种类、含量等因素对氧化聚乙烯蜡乳液粒径的影响。研究助乳化剂碱性添加物和短链异构醇对氧化聚乙烯蜡乳液粒径的影响。结果表明,氧化聚乙烯蜡乳液的最佳组成为：m[乳化剂（平平加O＋Span-60）]∶m（氧化聚乙烯蜡）=25∶100,m（水）∶m（氧化聚乙烯蜡）=2∶1;乳化剂最佳组成：m（平平加O）∶m（Span-60）=4∶1;助乳化剂的比例：m（三乙醇胺）∶m（氧化聚乙烯蜡）=5∶100,m（异辛醇）∶m（氧化聚乙烯蜡）=3∶100,所得乳液平均粒径为0.341μm。     

聚乙烯蜡氧化及接枝改性研究

高密度聚乙烯生产过程中副产聚乙烯蜡,采用空气催化氧化法和马来酸酐接枝法均可在聚合物分子链上生成羧基或马来酸酐极性基团,可大大提高聚乙烯蜡的应用价值。采用空气催化氧化法,氧化温度为145~155℃,空气流速为5~6 m/s,复配催化剂(M1∶M2=1∶1)量0.4%~0.5%,连续氧化6 h,可获得微黄色酸值为24.0~27.0 mg KOH/g的氧化聚乙烯蜡;采用马来酸酐接枝法最佳条件:反应温度155℃、反应时间5 h、引发剂加入量2.0%、MAH加入量5%,可获得酸值为48.30 mg KOH/g的接枝聚乙烯蜡。挤出接枝法采用自动化连续生产方法,在挤出温度80~90℃,转速30 r/min,扭矩0~4 N.m,引发剂和MAH加入量分别为2.0%和15%条件下,可得到酸值为17.6 mg KOH/g的接枝产品。     

乙烯聚合法制备聚乙烯蜡的研究进展

介绍了乙烯聚合法生产聚乙烯蜡常用的催化剂和工艺.高压自由基聚合法得到的产品结晶度低,熔点低,对颜料和填料的润湿性好,但相对分子质量分布较宽,难以控制产品质量.采用齐格勒-纳塔催化剂可以调节产物的相对分子质量和结晶度,制备的产品性能优良.使用茂金属催化剂制备聚乙烯蜡的优点是支链含量少,密度可调,相对分子质量分布窄,产品熔...     

Thermal fractionation and properties of different polyethylene/wax blends

The influence of paraffin‐wax type and content on the properties of its blends with HDPE, LDPE, and LLDPE was investigated. Melt‐mixing of HDPE with wax gave rise to completely miscible blends for both 10 and 20% wax contents. A wax content of 30% gave rise to a partially miscible blend. These observations were supported by the thermal fractionation (stepwise cooling) results. Melt‐mixing of LDPE with hard paraffin wax gave rise to a partially miscible blend for all wax contents investigated, while complete miscibility was observed for the 10% oxidized hard paraffin wax containing blend. Complete miscibility was observed for all the LLDPE/A1 wax blends, with A1 wax as an oxidized hard paraffin wax. This indicates possible cocrystallization of this wax with LLDPE, which was also evident from the thermal fractionation curves. LLDPE blends with hard paraffin wax were, however, partially miscible for all wax contents. All the observations were supported by the surface free energy results. It is further clear from the thermal fractionation results that the presence of wax changed the crystallization behavior of LDPE and LLDPE. Changes in the tensile properties are explained in terms of the miscibility and proposed morphologies of the blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2225–2236, 2007     

影响沥青蜡含量准确分析的因素

简单介绍了石油沥青蜡含量的测定方法,对影响蜡含量准确分析的因素进行了剖析。结果表明：裂解蒸馏速度、馏出油取样量、乙醇纯度、温度、冷洗剂加入量、抽滤过程、砂芯漏斗的孔径是影响测定结果的显著因素。     

聚乙烯微粉蜡在精细化工行业中的应用

本文介绍了聚乙烯微粉蜡乳液在涂料度水性油墨中的应用，阐述了微粉蜡的应用机理和在加工中所使用的工艺，列举了聚乙烯微粉蜡乳液在使用过程中应注意的问题以度其行业发展前景。     

油水两相流蜡沉积研究进展

蜡沉积研究中,油水两相蜡沉积的研究已成为研究重点,但对此领域的研究还处于起步阶段。本文系统阐述了国内外蜡沉积研究的发展现况,对近些年蜡沉积机理研究的新进展--剪切剥离以及老化机理作了分析。介绍了冷板、冷指实验装置和环道实验装置,对国内外学者进行的蜡沉积实验情况作了概述。介绍了国内外单相原油与油水两相蜡沉积动力学模型的研究现状,在单相模型基础上对Couto油水两相模型和Bruno改进模型进行了描述。今后的研究应以蜡沉积机理与预测模型为重点,分析油水两相流蜡沉积的影响因素,这对于缓解输油管道蜡沉积问题,增强管道输送能力具有现实意义。     

Liquid-phase degradation of polyethylene wax over mordenite catalysts with different Si/Al molar ratios

The catalytic liquid-phase degradation of polyethylene wax into fuel oil was studied using mordenite catalysts with various Si/Al molar ratios prepared by dealumination. The total yield of gas and liquid products showed a volcano plot along the Si/Al molar ratio of mordenite. No significant change was observed in the composition of the liquid product for all catalysts used in this study. Fast deactivation was anticipated on the mordenite catalysts with low Si/Al molar ratios such as 5 and 10, due to pore blocking by the carbon deposited on the external surface of the zeolite. A high activity and a long catalyst life were obtained on the mordenite catalyst with a Si/Al molar ratio of 12.     

PEW包覆型稳定性高铁酸钾制备及性能研究

采用熔融搅拌分散冷凝法制备了聚乙烯蜡包覆型稳定性高铁酸钾,考察物料配比、搅拌速度和搅拌时间对包覆率的影响,用SEM和IR对包覆的高铁酸钾进行表征。结果表明:高铁酸钾可被聚乙烯蜡较好地包覆,在m(聚乙烯蜡)∶m(K_2Fe O_4)为5∶1、搅拌速度为600 r/min、搅拌时间为40 min的最佳制备条件下,包覆率可达90%以上;m(聚乙烯蜡)∶m(K_2Fe O_4)为3∶1~8∶1包覆品的10 d吸水率在0.67%~4%之间(25℃、湿度75%),远低于未包覆K_2Fe O_4的吸水率(39%)。K_2FeO_4在水中的释放规律符合η=ktn动力学模型(R20.97)。     

Mechanical properties of uncrosslinked and crosslinked linear low‐density polyethylene/wax blends

The mechanical properties of uncrosslinked and crosslinked linear low‐density polyethylene (LLDPE)/wax blends were investigated, using differential scanning calorimetry (DSC), tensile testing, and melt flow indexing. A decrease in the degree of crystallinity, as determined from the DSC melting enthalpies, was observed with an increase in the dicumyl peroxide (DCP) concentration. The Young's modulus increased with increased wax portions, and there was a higher increase for crosslinked blends. The yield stress generally decreased with increased peroxide content. Crosslinking caused an increase in elongation at yield, but increased wax content caused a decrease in elongation at yield. The stress at break generally increased with increasing peroxide content, but it decreased with increased wax content. The elongation at break decreased with an increase in the DCP concentration. Melt flow rate measurements indicated a mutual miscibility in LLDPE/wax blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 973–980, 2001     

Phase‐separation phenomena in the polymerization of styrene in the presence of polyethylene wax

The demixing processes that occur during the polymerization of styrene in the presence of a low molar mass polyethylene wax were investigated. Quantitative information on the phase behavior of such a three‐component system was obtained through the investigation of the temperature‐induced phase separation and the observation of the phase separation during polymerization. Both techniques allow the construction of the same ternary phase diagram. Such phase behavior can be understood through the discussion of the interference of a liquid–liquid phase‐separation process and crystallization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2234–2243, 2004     

甲醇合成结蜡原因和处理方法

甲醇合成生产普遍以铜基催化剂为主,此催化剂下生产甲醇的同时伴有高碳链的碳氢化合物和石蜡生产。当正常生产过程中石蜡过多时会造成甲醇气液分离器、水冷器、阀门管道、甚至合成塔出口的堵塞,严重时会造成停车清蜡。因此研究石蜡产生的机理以及如何避免和减少石蜡的产生是很有必要的。