Application Progress of Pour Point Depressant in Pipeline Transportation of Waxy Crude Oil|News|UNPChemicals

March 11, 2026

Application Progress of Pour Point Depressant in Pipeline Transportation of Waxy Crude Oil

What is a pour point depressant?

A pour point depressant is a chemical additive that lowers the freezing point and improves the low-temperature fluidity of crude oil or oil products. It mainly changes the crystal shape of wax and prevents wax crystals from forming a network structure, so that crude oil can still flow smoothly at low temperatures, avoiding pipeline blockage caused by solidification and wax deposition during pipeline transportation. It is widely used in waxy crude oil transportation, diesel oil, lubricating oil and other fields, and is an important additive to ensure safe low-temperature transportation and save energy.

Abstract

During pipeline transportation, waxy crude oil faces issues such as reduced fluidity and wax deposition on pipe walls, which increase power costs for pipeline transportation, shorten pigging cycles, and even pose risks of pipeline blockage in severe cases. Adding a certain dosage of pour point depressant (PPD) to waxy crude oil can appropriately improve its fluidity, reduce frictional resistance along the pipeline, and help lower operational risks and investment. This paper summarizes the current status of the application and research of adding PPD to crude oil in pipeline engineering, briefly describes the main types and mechanisms of waxy crude oil PPDs, discusses the application effects of PPDs in engineering cases, compares the combined operation schemes of PPD addition with heating and crude oil blending, points out existing problems such as insufficient stability of PPDs and weak sensitivity of crude oil to additives, and finally proposes that PPDs should develop toward new materials and universal applicability, while pipeline transportation application schemes need to transform from single to comprehensive.

Waxes in crude oil are hydrocarbon mixtures with more than 16 carbon atoms, mainly normal alkanes, with a small amount of isoparaffins and cycloparaffins. They have complex structures and strong cohesive and aggregating properties. Once precipitated in crystalline form, they easily combine and aggregate with other wax crystals, asphaltenes, and resins to form solid-phase sediments that hinder crude oil flow. During the flow of waxy crude oil in pipelines, as the ambient temperature decreases, the crude oil temperature gradually drops to below the pour point under the drive of temperature difference, meeting the conditions for wax precipitation. Wax crystals then continuously precipitate from the crude oil and form a three-dimensional network structure through intermolecular interactions, reducing the fluidity of the crude oil. Coupled with factors such as temperature gradients and flow rates in the pipeline environment, the precipitated wax crystals gradually deposit on the pipe wall, forming wax deposits that reduce the inner diameter of the pipe, further affecting the pigging cycle of the pipeline and ultimately impeding the normal operation of crude oil pipelines.

Wax precipitation depends on temperature conditions, while the aggregation and sedimentation of precipitated wax crystals are affected by microscopic molecular structures and complex flow environments. Currently, to address the massive precipitation, aggregation, and sedimentation of wax crystals, physical heating, emulsified transportation, dilution transportation, and PPD addition are commonly used to transport waxy crude oil, aiming to increase the solubility and dispersion of wax crystals in crude oil and improve the fluidity of waxy crude oil. Among these methods, adding a small dosage of PPD to waxy crude oil involves chemically treating the crude oil to lower its pour point and improve fluidity, thereby enhancing pipeline transportation efficiency. Compared with physical heating, emulsified transportation, and dilution transportation, chemical PPD addition has advantages such as reduced equipment investment, lower heat loss, and shortened post-treatment processes, with strong economic and environmental benefits.

Different waxy crude oils have different physical properties and varying sensitivities and adaptabilities to PPDs, making it difficult for conventional PPDs to meet production demands to a certain extent. Moreover, the complex environment along the pipeline during crude oil transportation raises an important question: how to efficiently apply PPDs in crude oil pipeline engineering. Therefore, it is necessary to review and summarize the current application of PPD addition in pipeline transportation of waxy crude oil, analyze the application effects and existing problems in actual engineering, point out directions for the future development and application of PPDs, and provide a reference for research in this field.

1 Types and Mechanisms of Pour Point Depressants

1.1 Types of Pour Point Depressants

Currently, commonly used PPDs are mainly divided into three types: surfactant-type, polymer-type, and compound-type. Surfactant-type PPDs are based on the principle of molecular surface adsorption, which can form mechanical isolation between crystals, reduce the surface tension of the solution, decrease the contact angle between liquid and solid phases, thereby reducing the chance of forming three-dimensional network structure crystals and achieving the purpose of pour point depression. Polyoxyethylene alkylamine-based PPDs are commonly used in this category.

Polymer-type PPDs are mostly composed of long-chain alkyl groups and polar groups. The former acts through nucleation and adsorption, while the latter disperses wax crystals and inhibits their growth to change crystallization properties, thereby improving the fluidity of crude oil. This type of PPD mainly includes polyacrylates, polyesters, polyolefins, and long-chain alkyl naphthalenes. It has been pointed out that the self-developed poly-α-olefin PPD in China has excellent performance and low price, and can be widely used in various oil products compared with polyester-type PPDs. With the development of new PPDs, researchers have attempted to prepare nano-composite PPDs and applied them in pipeline crude oil pour point depression research, achieving certain results.

Compound-type PPDs are formed by compounding two or more single-type PPDs, or by compounding surfactants, cosolvents, etc., with PPDs to achieve synergistic effects. Aiming at the high-pour-point crude oil in the Weibei block of Shengli Oilfield, a compound-type PPD AMVES was prepared, and its effect was evaluated. The results showed that when the dosage was 1000 mg/L, the pour point of Weibei crude oil decreased from 48 °C to 37 °C, and the wax appearance temperature decreased by 2 °C, with significant effects.

1.2 Mechanisms of Pour Point Depressants

There is no unified theory regarding the pour point depression mechanism of crude oil PPDs, but scholars have reached a consensus: PPDs can only change the morphology and structure of wax crystals and hinder the formation of stable three-dimensional network structures, but cannot prevent wax crystals from precipitating from crude oil. Currently, the pour point depression mechanisms widely accepted by scholars mainly include nucleation, adsorption, co-crystallization, and solubilization.

Nucleation refers to the fact that PPDs form crystal nuclei before wax crystals precipitate, and the subsequently precipitated wax crystals attach to the surface of these nuclei, blocking the aggregation of wax crystals. Adsorption means that PPD molecules adhere to the precipitated wax crystals to form a coating layer, blocking the bonding between wax crystal molecules. Co-crystallization involves the long-chain alkyl groups (non-polar groups) in PPD molecules co-crystallizing with the precipitated wax crystals, while the polar groups repel the wax crystals. The alkyl chains in PPDs are more than the carbon chains in wax (Figure 1). Solubilization means that after PPDs are added to waxy crude oil, the supersaturation of the solution decreases, increasing the solubility and dispersion of wax in the crude oil sample, reducing the formation of three-dimensional network structures and ensuring the fluidity of waxy crude oil.

In addition to the above four mechanisms, some scholars have proposed other mechanisms, such as co-crystallization-adsorption, anti-gelation, and self-pour point depression. Some scholars have also put forward the viewpoint of synergistic action of multiple mechanisms. It is believed that the pour point depression effect of PPDs does not depend on a single mechanism, but on the synergistic action of multiple mechanisms, with one mechanism dominating at different stages. However, current research on the synergistic action of multiple mechanisms is limited.

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Figure 1 Schematic diagram of co-crystallization effect

2 Application of Waxy Crude Oil Pour Point Depressants

Currently, researchers from multiple scientific research units have made certain progress in the research of adding PPDs to pipeline transportation of waxy crude oil, and this process has been successfully applied to multiple crude oil pipelines, including foreign lines such as the Rotterdam-Rhine Pipeline, Indonesia's Handil Pipeline, Sudan's Black Greenberg-Sudan Pipeline, and Kazakhstan's Akshabulak Pipeline, as well as domestic lines such as the Heshishi Pipeline, Pulin Line, and Ma Huining Line, achieving good pour point depression effects. However, due to the different physical properties of crude oil and pipeline conditions, not all pipeline applications are ideal, and there are certain problems. Scholars have conducted active research and exploration targeting different pipeline transportation processes and additive schemes.

2.1 Engineering Case Applications

Different crude oils have different adaptabilities to various PPDs. With the development of oilfields and the reconstruction or expansion of pipelines, the physical properties of crude oil in existing pipelines change, and new crude oil in new pipelines requires additional research on adding PPDs. In recent years, there have been many targeted studies on the modification effect of adding PPDs on crude oil, and various pipeline application cases have emerged continuously.

Nanomaterials were used as PPDs in the pipeline transportation test of waxy crude oil, studying the low-temperature fluidity of crude oil in the pilot pipelines of Qian'an-Baodi Industrial Pipeline and Baodi-Baodi on the Qinhuangdao-Beijing Line. The results showed that compared with untreated crude oil, adding nanomaterial modifiers reduced the pour point of crude oil by 16 °C, the yield point temperature by 14 °C, the wax appearance temperature by approximately 6 °C, and the apparent viscosity (at a shear rate of 50 s⁻¹) at 25 °C by 86.7%, significantly improving the low-temperature fluidity of crude oil with good application effects.

In the application of adding PPDs to the Karamay-Dushanzi crude oil pipeline, KD-1 type PPD was added to the three pipelines of the Karamay-Dushanzi Pipeline at a total station dosage of 30 mg/kg. The pipeline saved approximately 2×10⁶ yuan/a in costs by adding PPDs, bringing good economic benefits. However, the application effect in Pipeline 377 of the Karamay-Dushanzi Pipeline was poor, failing to meet the heat demand after some pipeline sections stopped heating.

Nanometer PPDs were applied to the Shikong-Lanzhou and Renqiu-Beijing crude oil pipelines. The results showed that the pour point of crude oil in the Shikong-Lanzhou Pipeline decreased from 19 °C to -3 °C, and the viscosity at 10 °C decreased to below 40 mPa·s; the pour point of crude oil in the Renqiu-Beijing Pipeline decreased from 30 °C to 18~20 °C, and the viscosity at 30 °C decreased to below 50 mPa·s.

Research was conducted on the application of PPDs in the Tianjin Port-North China Petrochemical crude oil pipeline project (Jinhuaxian Line). Aiming at the characteristics of high waxy content and high pour point of the transported crude oil, field tests were carried out on the Gaoshangbao-Qian'an Pipeline before commissioning the Jinhuaxian Line. JD# PPDs with mass fractions of 1.0×10⁻⁴ and 5.0×10⁻⁵ and nanometer PPDs with a mass fraction of 1.0×10⁻⁴ were added respectively, reducing the pour point of crude oil from 22 °C to 11~13 °C. In the Jinhuaxian Line, the measured pour point of crude oil at the initial station was 11 °C, at the intermediate station 13 °C, and at the terminal station 16 °C, which was basically consistent with the laboratory and Gaoshangbao-Qian'an Pipeline field test results, achieving good actual effects.

Aiming at the winter operation of the Shixi-Karamay and Karamay-Dushanzi crude oil pipelines, LS-1 and KD-31 type PPDs were selected as two oil types of PPDs based on laboratory experiments. In the field test, different dosages of PPDs were added according to different operation stages. The results showed that the pour point of crude oil in the Shixi-Karamay Pipeline decreased by 12~15 °C, the viscosity reduction rate was higher than 80%, and the pour point of crude oil in the Karamay-Dushanzi Pipeline decreased by 12~20 °C, with a viscosity reduction rate higher than 69%, saving 1036.20 t/a of crude oil, reducing carbon emissions by 5677.02 t/a, and saving production and operation costs of more than 7.846×10⁵ yuan/a.

Aiming at the poor sensitivity of Xifei ZD crude oil to conventional PPDs, a four-component (acrylate, vinyl acetate, styrene, maleic anhydride) polymer PPD was prepared and compared with two conventional PPDs (EVA, T801) and two foreign PPDs (P4, P5). The results showed that this polymer PPD could reduce the pour point of ZD crude oil by 8 °C, refine wax crystals, and had a more significant pour point depression effect than the other four PPDs, making it suitable for the pipeline transportation of Xifei ZD crude oil.

In summary, the process of adding PPDs to pipeline transportation of waxy crude oil has been successfully applied to multiple engineering cases, with significant pour point depression effects, improving the low-temperature fluidity of crude oil, having certain rationality and feasibility, reducing heat and labor costs, and thus saving production and operation costs, with certain application value and economic benefits.

2.2 Research on Pipeline Transportation Operation Schemes for Waxy Crude Oil

During pipeline transportation of waxy crude oil, a single PPD addition scheme cannot meet the production and operation of all crude oil pipelines, especially for easily gelled high-viscosity crude oil with low throughput in harsh transportation environments, which has poor fluidity during winter operation and is prone to accidents such as pipe clogging and blockage. Therefore, it is necessary to consider introducing other feasible improvement schemes.

Aiming at the problem of normal temperature transportation of high-wax and high-pour-point crude oil in Sudan's Neem Oilfield, KS-10-21 type PPD was prepared using ethylene-vinyl acetate ester and high-carbon alkyl acrylate polymers as raw materials, combined with a heating treatment scheme. At a heat treatment temperature of 80 °C and an optimal dosage of 350 mg/L, the field application was carried out in a certain block of the oilfield. The results showed that the pour point of crude oil after treatment decreased from 31~33 °C to 23~24 °C, with good effects, providing a guarantee for the safe operation of Sudan's 124 District Pipeline.

In the optimization study of the operation scheme of the Shikong-Lanzhou crude oil pipeline, three schemes of normal temperature, heating, and heating with PPD addition were adopted according to different operation periods, with the heating treatment scheme as the indicator: the initial heating treatment temperature of the station was 75~85 °C, and the oil temperature after heat exchange was not lower than 60 °C; the PPD dosage was not lower than 25 g/t from January to February, and not lower than 12.5 g/t in other months. Under the winter throughput of 5.0×10⁶ t/a, the costs of heating and heating with PPD addition transportation schemes were compared, and it was found that the heating with PPD addition treatment scheme had better economic efficiency. Similarly, in the research on the winter and autumn operation conditions of the Hui'an-Baichuan crude oil pipeline, the two transportation schemes of heating and heating with PPD addition were comprehensively compared. The results showed that under the winter throughput of 3.2×10⁸ t/a, adding 25 g/t of PPD to crude oil and heat treatment to 65 °C at the outlet could save (2.66~6.01)×10⁴ yuan/d compared with heating transportation, with good economic efficiency; during autumn operation, the heat treatment temperature was the same as in winter, but the PPD dosage was reduced by half, resulting in better economic efficiency; moreover, the heating with PPD addition treatment scheme could extend the shutdown time of the pipeline under two working conditions, with better adaptability and safety.

Nanometer PPDs were added to the Renqiu-Beijing crude oil pipeline, realizing the hot oil startup of the power station at the Gaolidian Station, one of the intermediate stations, under the heat treatment temperature of 57~60 °C for waxy crude oil; at a heat treatment temperature of 60 °C and a dosage of 100 g/t, the transportation volume could be reduced to 250 m³/h, significantly reducing the energy consumption of pipeline operation. At the same time, this heating with PPD addition treatment scheme could make the pipeline start smoothly 26 h after shutdown, extending the safe shutdown time and providing a safety guarantee for pipeline operation.

According to the sensitivity of different crude oils to PPDs, DPD8861 type PPD was selected, and the research was carried out with a high pour point oil to low pour point oil ratio of 5:5 and a PPD mass concentration of 30 mg/L in the mixed oil, studying the fluidity of mixed crude oil under three mixed oil comprehensive additive modification methods. The results showed that the method of mixing high pour point oil and low pour point oil first and then modifying with additives had the most significant improvement in crude oil fluidity, while the direct mixing of high pour point oil with high temperature modification and low pour point oil with normal temperature modification, and the equal temperature mixing of high pour point oil after dynamic cooling and low pour point oil had poor effects. This research provided a theoretical guidance for the collaborative mixed oil transportation scheme of adding PPDs to pipeline waxy crude oil.

Aiming at the problem of a large rebound in pour point in the later stage of adding PPDs to the Shixi-Karamay crude oil pipeline, a research scheme of adding PPDs and blending with other crude oils was carried out on the crude oil of the Shixi-Karamay Pipeline and Shinan 21# Line. Based on laboratory and field experiments, when the blending ratio of the two crude oils to the blended crude oil was 1:1 and the PPD mass concentration was 30 mg/L, the pour point of the mixed crude oil decreased to -10 °C, and when the blending ratio was 8:2 and the PPD mass concentration was 20 mg/L, it could meet the normal transportation requirements of the Shixi-Karamay Pipeline and Shinan 21# Line in winter. Moreover, this scheme could inhibit the deterioration of crude oil fluidity caused by small temperature rebound and low shear rate, improving the utilization rate of the pipeline with certain application value.

2.3 Existing Problems

Although multiple pipeline engineering cases have been successfully applied, some problems are inevitable. After analyzing the changes in crude oil physical properties and dosing effects of a certain pipeline, it was found that during normal pipeline operation, adding PPDs to a certain pipe section resulted in unstable pour point depression effects: the pour point of the dosed crude oil at the starting point of the pipe section was 19~21 °C, while at the end point of the pipe section it rose to 24~27 °C, indicating poor stability of the PPD. In the research on the technology of adding PPDs to the Yaodian-Ganquan crude oil pipeline, it was found that the PPD addition scheme could only reduce the transportation cost of the pipeline under the minimum throughput transportation condition, while at the maximum throughput and average throughput, the pour point depression effect was poor due to the lower outlet oil temperature than the optimal PPD dosage and temperature, making it difficult to save costs. In the research on the modification transportation process of the Da Luochao Pipeline, aiming at the characteristics of crude oil viscosity, pour point, and wax content increasing in the external transportation pipeline of Santanghu Oilfield, the pour point depression test was carried out. The results showed that the crude oil of this pipeline had weak sensitivity to PPDs, and the transportation technology of blending with other crude oils could reduce the pour point and viscosity of the crude oil, lower the minimum pipeline throughput, and extend the safe shutdown time. This indicates that the effect of PPDs is not applicable to any crude oil, and specific formulation and test research need to be carried out for crude oils with different physical properties.

Based on the current engineering case applications and scheme research of pipeline transportation, the following problems exist in adding PPDs to crude oil pipeline transportation:

For the long-distance transportation of easily gelled high-viscosity crude oil and heavy viscous crude oil, the single PPD addition method is difficult to meet pipeline transportation requirements, and it is necessary to consider introducing other parallel processes.
Some crude oils have weak sensitivity to PPDs, and the pour point depression effect after adding PPDs is not obvious, such as the crude oil of Santanghu Oilfield.
For complex pipeline conditions and changing crude oil physical properties, the stability of PPDs will decrease or fail.

3 Conclusions and Prospects

At present, domestic research on adding PPDs to pipeline transportation of waxy crude oil has made certain progress, but there are still certain deficiencies in field tests and production applications, and there is room for further improvement in PPD formulation, experimental research, and pipeline application.

Existing PPDs are greatly affected by factors such as crude oil composition and pipeline conditions. It is necessary to develop universal PPDs with a wider range of applications and stronger adaptability. Emerging nanometer PPDs and compound-type PPDs have good application prospects and can be combined with technologies from other fields to guide the development of new PPDs in the future.
General PPDs are difficult to meet the requirements of long-distance transportation of easily gelled high-viscosity crude oil and heavy viscous crude oil in pipelines, and there are problems such as weak sensitivity of some crude oils to PPDs and insufficient stability. It is necessary to screen or formulate specific PPDs according to specific pipeline transportation processes to better meet pipeline applicability.
Pipeline transportation application schemes are gradually transforming from single to comprehensive, from a single PPD addition scheme to comprehensive schemes such as heating with PPD addition, and PPD addition with crude oil blending. The future development direction needs to consider the combination of adding PPDs and other parallel schemes that can improve pipeline transportation efficiency.