Polyester (such as PET chips and PBT) is one of the most widely used synthetic polymers in textiles, packaging, and engineering plastics. Its industrial production typically involves esterification/transesterification followed by polycondensation. Below is an overview of the mainstream polyester production processes, their advantages and disadvantages, and the future trends in sustainable polyester development.

1. Direct Esterification Process (PTA Method)

Raw Materials: Purified Terephthalic Acid (PTA) + Ethylene Glycol (EG)

This is the most common method in PET production, where PTA reacts directly with EG to form bis(2-hydroxyethyl) terephthalate (BHET), which is then polycondensed into polyester resin.

Advantages:

  • Shorter process, lower energy consumption.

  • Lower cost compared with the DMT method.

  • High product purity and a narrow molecular weight distribution – ideal for polyester fiber and PET bottle chips.

Disadvantages:

  • Requires high temperature (250–290 °C) and pressure.

  • Demands high-purity PTA to prevent side reactions.

👉 Application: Over 90% of global PET fiber and bottle chip production adopts the PTA method.

2. Transesterification Process (DMT Method)

Raw Materials: Dimethyl Terephthalate (DMT) + Ethylene Glycol (EG)

This method first converts DMT and EG into BHET through transesterification, followed by polycondensation.

Advantages:

  • Milder reaction conditions (180–220 °C, atmospheric pressure).

  • DMT is stable and easy to store.

Disadvantages:

  • Generates methanol as a by-product, increasing environmental costs.

  • A more complex process with higher energy consumption.

  • Broader molecular weight distribution, leading to lower product performance.

👉 Application: Mostly replaced by the PTA process, but still used in PBT resin and some specialty polyester products.

3. Polycondensation Types in Polyester Production

(1) Melt Polycondensation

  • Conducted at 270–300 °C in the molten state under vacuum.

  • Pros: Continuous production, efficient, controllable intrinsic viscosity.

  • Cons: Thermal degradation risk, IV usually ≤ 0.72, high energy demand.

  • Application: Mainstream for PET bottle resin and polyester fiber chips.

(2) Solid-State Polycondensation (SSP)

  • Conducted in a solid state at temperatures below the melting point.

  • Pros: Produces high IV polyester (≥ 0.85), ideal for bottle-grade PET and industrial yarns. We manufacture the following high IV and low Carboxyl Group (COOH Value) PET Chip through both batch and continuous SSP processes.

    PROPERTY UNIT STANDARD TEST RESULTS
    IV (60:40, phenol:TCE @25℃) dl/g 0.646-0.660 0.65 0.67 0.70 0.81 0.86
    End Carboxyl mol/t ≤12 10.21 7 7 13 9
    Color Value L ≥ 80.5 84.66 88.2 89.2 91.3 88.3
    b 5±1.5 4.24 6.5 6.5 5.8 6.8
    Irregular Chip w% ≤0.4 0.00 0.00 0.00 0.00 0.00
    hundred-grain Weight g/100 3±0.5 2.85 2.7 2.7 2.7 2.7
    Moisture Content w% ≤0.4 0.05 0.1 0.1 0.1 0.1
    TiO2 Content w% 0.295±0.03 0.28 0.32 0.32 0.31 0.30
    DEG Content w% ≤1.25 1.15 1.2 1.2 1.0 1.3
    Melting Point ℃ 260±2 259.8 260 261 259 259
    Agglomerate Particle pce/mg ≤1 0.00 0.00 0.00 0.00 0.00
    Powder Content mg/kg ≤100 16.00 15.00 15.00 0.0 0.00

  • Cons: Long processing time, high energy consumption, requires inert gas protection.

(3) Vacuum Polycondensation

  • Conducted under vacuum to accelerate small molecule removal.

  • Pros: Higher molecular weight, faster reaction.

  • Cons: More complex and costly equipment.

4. Emerging & Sustainable Polyester Technologies

Bio-Based Polyester Production

  • Uses biomass-based EG or PTA (e.g., corn-derived EG). Hubei Decon can supply bio-based PET based on biomass-based EG. For more information, please email info@polyestermfg.com.

  • Reduces reliance on petroleum and supports sustainability goals.

  • Higher costs and less mature technology continue to be challenges.

Copolyester Modification

  • Introduces third monomers (e.g., IPA, CHDM) to improve transparency, heat resistance, or toughness.

  • Expands applications such as optical films and hot-fill bottles.

5. Development Trends in the Polyester Industry

  1. Green & Low-Emission Processes – adoption of titanium-based catalysts instead of antimony-based.

  2. Circular Economy Solutions – Chemical recycling, such as glycolysis and depolymerization of PET waste.

  3. High-Performance Polyester Materials – enhanced properties via copolymerization and nanocomposites (e.g., flame-retardant PET, conductive polyester).

Conclusion

The PTA method, which involves melt and solid-state polycondensation, remains the mainstream choice for producing PET chips and polyester fibers. However, with a global emphasis on sustainability, bio-based polyester and recycled polyester production technologies are expected to become the future focus of the polyester industry.

By selecting the optimal production process, polyester manufacturers can strike a balance between cost, performance, and sustainability, thereby meeting both industrial demand and environmental regulations.