Progress in the Application of Pour Point Depressants for Transporting Waxy Crude Oil via Pipelines-
What are Paraffin inhibitors？
Paraffin inhibitors are chemical additives widely used in the petroleum industry to prevent or mitigate the formation and deposition of paraffin waxes in crude oil and refined products such as diesel. By altering the crystallization process of wax molecules at low temperatures, these inhibitors disrupt the growth of large, interconnected wax networks that cause solidification. Instead, they promote the formation of smaller, isolated crystals, thereby reducing the pour point (temperature at which the fluid ceases to flow) and the cold filter plugging point (critical for diesel operability in cold climates). This improves the efficiency of pipeline transportation and ensures reliable performance of diesel engines in low-temperature environments.
Wax in diesel fuel gradually precipitates at low temperatures and interconnects to form a three-dimensional network structure, trapping low-pour-point components such as colloids, oil, and water, resulting in a gelatinous substance that causes the diesel to lose fluidity. Adding diesel cold flow improvers (also known as pour point depressants) significantly enhances the low-temperature fluidity of diesel, enabling its pour point and cold filter plugging point to meet specification standards. This method is a simple and effective way to improve refinery flexibility and economic efficiency.
1. Development of Diesel Pour Point Depressants Domestically and Internationally
1.1 International Developments
The earliest research on diesel pour point depressants began in the 1930s when Davis discovered that condensates of chlorinated paraffin and naphthalene were effective pour point depressants. This was followed by the emergence of condensates of chlorinated paraffin and phenol, as well as polymethyl methacrylate. In the 1940s, polyacrylamide and alkyl polystyrene depressants were developed. The 1950s saw the introduction of maleate-long-chain alkyl methacrylate copolymers, and in the 1960s, Esso produced EVA-based depressants (ethylene-vinyl acetate copolymers).
With the rise in global crude oil prices in the 1970s, refineries began adding heavy petroleum components to diesel, which reduced its low-temperature performance. This led to rapid advancements in pour point depressant research, with a focus on combinations and derivatives of various polymers. Today, international depressant products have become serialized, diversified, and highly targeted, with mature and well-established production processes.
1.2 Domestic Developments
China began researching pour point depressants in the 1960s. Lanzhou Refinery developed poly-α-olefin depressants (code T803) in the 1970s. By 1986, Beijing Organic Chemical Plant had an annual production capacity of 700 tons of EVA depressants (T-1804). In 1987, Sinopec Shanghai Petrochemical Complex invested in a continuous production facility with an annual capacity of 1,000 tons of diesel pour point depressants. Currently, domestically developed cold flow improvers are limited in variety, primarily consisting of ethylene-based polymers, EVA and its modifications, acrylate polymers, and maleic anhydride copolymers, with most developments being imitations of existing products.
2. Mechanisms of Diesel Pour Point Depressants
2.1 Nucleation Theory
Pour point depressant molecules precipitate at temperatures above the oil’s cloud point, acting as crystal nuclei, active centers, or crystallization centers. This increases the number of small wax crystals in the oil, effectively reducing the pour point or cold filter plugging point.
2.2 Co-crystallization Theory
Wax crystals in diesel grow two-dimensionally. The polar parts of depressant molecules hinder growth along the X and Y axes while accelerating growth along the Z axis, transforming crystal shapes from irregular blocks to tetrahedral or prismatic forms. This reduces surface area and energy, making it difficult for crystals to aggregate into a three-dimensional network.
2.3 Adsorption Theory
Below the oil’s cloud point, depressants crystallize and precipitate. Their polar groups alter the surface characteristics of wax crystals, hindering crystal growth or modifying growth habits. This increases the dispersion of wax crystals, preventing them from forming networks and thereby reducing the pour point.
2.4 Solubility Improvement Theory
Depressants enhance the solubility and dispersion of wax in oil, leveraging surface charge repulsion to prevent the formation of three-dimensional networks, thus lowering the pour point.
3. Current Market Status and Research Progress of Domestic Diesel Pour Point Depressants
3.1 Ethylene-Vinyl Acetate (EVA) Copolymers
Domestically developed diesel pour point depressants are limited in variety. EVA copolymers are widely used and effective cold flow improvers, capable of reducing the diesel pour point by approximately 5–10°C. They are extensively used in -10#, -20#, and -35# diesel processed from various domestic crude oils. The Petroleum Exploration and Development Research Institute primarily produces EVA-based depressants or EVA ternary copolymers. Products like Dodiflow 4744 (Dagang Petrochemical), T-1804 (Beijing Organic Chemical Plant), and T-1805 (Fushun Petrochemical) belong to this category, offering significant reductions in pour point and cold filter plugging point.
3.2 Acrylate Polymers
Acrylate polymers represent a diverse category of depressants. Their effectiveness depends on the composition of esters in the polymer and the average carbon number of ester side chains. The best results are achieved when the alkyl acrylate composition matches the normal paraffin composition in diesel. T602 depressants (Shengli Oilfield Design Institute and Shanghai Gaoqiao Petrochemical) and OEAM (Jiangsu Petrochemical College) are examples of acrylate-based depressants.
Domestic research has focused on acrylate polymers, leading to the development of various binary, ternary, and quaternary copolymers. For instance, You Mingming synthesized methacrylate-high carbon alcohol esters, which were polymerized with vinyl acetate to create copolymers. Adding 0.65% of this depressant to Liaohe crude oil reduced the pour point by 7°C.
Feng Lijuan et al. synthesized ternary copolymers of alkyl acrylate-vinyl acetate-styrene with varying alkyl chain lengths. AVS-16 reduced the diesel pour point by 12°C, while AVS-18 lowered the cold filter plugging point by 4°C. The discrepancy between pour point and cold filter plugging point reduction highlights that preventing three-dimensional network formation may reduce the pour point but not necessarily the cold filter plugging point.
Liu Dan et al. synthesized hexadecyl methacrylate-vinyl acetate copolymers, which reduced the cold filter plugging point of diesel by 11°C.
3.3 Polar Nitrogen-Containing Compounds
These compounds, such as amine salts of anhydrides or ricinoleic acid amides, contain 30–300 carbon atoms. When combined with other polymers, they effectively reduce the cold filter plugging point of diesel.
Yang Zhiyong et al. prepared monoamide monoammonium salts of phthalic acid and diamide polar nitrogen compounds. When combined with EVA or EVAP depressants, they achieved significant results.
Xue Wei et al. blended octadecyl ammonium salt depressants (POSA) with T-1805 and JKT-1010, studying their effects on market diesel and atmospheric diesel. Blending the three depressants in varying ratios yielded optimal results.
3.4 Vinyl Acetate-Fumarate Copolymers
These compounds have broad market applications, exemplified by Exxon's Paradyne series. Domestic researchers have also achieved promising results. Wang Jingjing et al. synthesized binary copolymers of dialkyl fumarate and vinyl acetate, reducing the cold filter plugging point of Tuha -10# and 0# diesel by 10°C and 7°C, respectively.
An Hong et al. synthesized PFA depressants from C8–18 fumarate higher alcohol esters and vinyl acetate. Blending PFA-12, PFA-14, PFA-16, and PFA-18 in a 16:2:2:2 mass ratio reduced the diesel pour point by 22°C and the cold filter plugging point by 8°C.
3.5 Maleic Anhydride Polymers
The EJ-6 series from the Changchun Institute of Applied Chemistry is a graft-modified product of EVA copolymers and maleic anhydride. Liao Kejian et al. developed PSM depressants by polycondensing pentaerythritol stearate esters with maleic anhydride, which showed effective pour point reduction in diesel from Daqing, Liaohe, Shengli, and Fuyu crude oils.
Lan Da et al. synthesized ternary copolymers of C12–C18 acrylate-styrene-maleic anhydride, reducing the pour point of three diesel component oils by 10°C, 5°C, and 7°C at a 0.1% dosage.
Zhi Lele et al. synthesized quaternary copolymers of methacrylate-maleic anhydride-styrene-vinyl acetate, optimizing synthesis conditions. Adding 0.5% of this depressant to 0# diesel reduced the condensation point by 13°C and the cold filter plugging point by 5°C.
3.6 Other Types
Zhejiang University has developed ethylene-propylene random copolymer depressants. Zhang Yuwei modified C5 petroleum resin by grafting maleic anhydride, followed by copolymerization with styrene and vinyl acetate, and alcoholysis with higher alcohols. This depressant reduced the cold filter plugging point of Fushun Petrochemical’s 0# diesel fraction by 5°C.
4. Current International Research on Pour Point Depressants
Pour point depressants first emerged internationally, evolving through condensation polymerization, homopolymerization, and copolymerization stages. Current research focuses on blended formulations, particularly combinations of EVA or long-chain acrylate esters with nitrogen-containing polymers. Recent international literature reports novel polymers as depressants, often binary or ternary copolymers with modified side-chain structures through grafting, branching, or backbone alterations. These depressants typically have specific molecular weights and comb-like or linear structures.
5. Summary
5.1 Existing Issues
Domestically developed depressants are limited in variety and functionality. While they significantly reduce the pour point, they often have minimal effects on the cold filter plugging point. Their performance is highly dependent on diesel composition, and they are particularly ineffective for high-wax diesel. Additionally, domestic research primarily focuses on synthesis, with limited studies on formulation composition and solvent diversity.
Analysis of 10 domestic and international diesel pour point depressants using infrared and superconducting NMR spectroscopy revealed that international products often have higher molecular weights, vinyl acetate polymer mass fractions exceeding 30%, complex solvent compositions, and added nitrogen-based dispersants, resulting in better performance.
5.2 Development Directions
(1) Develop depressants that effectively reduce both pour point and cold filter plugging point. Ideal depressants should prevent the formation of three-dimensional networks and inhibit the growth or aggregation of large wax crystals.
(2) Focus on improving the responsiveness of high-wax, narrow-cut diesel by developing multi-component blended depressants that leverage synergistic effects to enhance low-temperature fluidity.
Paraffin inhibitors manufacturer
UNPChemicals' PCMET series is a specialized line of high-performance paraffin inhibitors engineered to address wax deposition challenges in crude oil production and transportation. Formulated with advanced polymer-based chemistry, these inhibitors effectively modify wax crystallization behavior by adsorbing onto nascent wax crystals, disrupting their growth and preventing the formation of large, interlocking networks. This action significantly reduces the pour point and improves the cold flow properties of waxy crude oils, ensuring uninterrupted flow through pipelines and reducing the risk of blockages. The PCMET series is designed for versatility, offering solutions tailored to diverse crude compositions and operational conditions, including deepwater and cold climate applications. Its effectiveness in minimizing wax-related downtime and maintenance costs makes it a critical tool for enhancing production efficiency and asset integrity in upstream and midstream operations.