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Synthesis of DOTP from PET and octanol

Created on 12.19
Synthesis of DOTP from PET and octanol
The core of synthesizing dioctyl terephthalate (DOTP) using polyethylene terephthalate (PET) and octanol is to achieve the depolymerization of PET and the combination with octanol through transesterification. The following is a specific method based on industrial practice and scientific research results:
  1. Reaction principle
The ester bond in the PET molecular chain is broken under the action of octanol and catalyst, and ethylene glycol is replaced by octanol, generating DOTP and by-product ethylene glycol:
This process involves breaking down the polymer structure of PET through alcoholysis, followed by functional group substitution through transesterification.
II. Key steps
  1. Raw material pretreatment
PET processing: Remove impurities from waste PET and crush it into 2-4mm particles.
Octanol selection: Use industrial-grade isooctanol (2-ethylhexanol) with a purity of ≥99%, and add excess to drive the reaction in the forward direction.
2. Continuous production process
Equipment configuration: A continuous feeding alcoholysis reactor is employed, equipped with a distillation tower, a multi-stage ethylene glycol absorption tank, and an octanol refining device.
Process design:
Alcoholysis stage: PET, octanol, and catalyst are stirred at high temperature in a reaction kettle, and the generated ethylene glycol and octanol vapor enter the distillation column.
Separation stage: After condensation, the steam enters the secondary absorption tank, where ethylene glycol is absorbed by water. The octanol is removed of water through a drying tower and then recycled for use.
Purification stage: The reaction mixture is subjected to vacuum distillation to separate the remaining octanol, and then impurities are removed through activated carbon adsorption and water washing, ultimately yielding DOTP.
III. Separation and purification
Crude product processing: After cooling the reaction mixture, filter it with suction to remove unreacted PET residue.
Distillation recovery:
Vacuum distillation: Separate unreacted octanol (recovery rate > 90%) and DOTP.
Vacuum distillation: purify ethylene glycol to meet the standard of superior quality (purity > 99.5%).
Deep refining: Use activated carbon for adsorption and decolorization (with a dosage of 5% of the product mass), stir at 80°C for 1 hour, and filter to obtain colorless and transparent DOTP.
IV. Safety and Economy
Risk control: High-temperature reactions should be conducted in an inert atmosphere (such as nitrogen) to avoid the oxidation of octanol; catalysts (such as tetrabutyl titanate) should be stored in sealed conditions to prevent hydrolysis.
Cost advantage:
Utilizing waste PET can reduce raw material costs by 40%-60%, while also reducing waste disposal expenses.
The investment in equipment for continuous processes can be recovered within 2-3 years through raw material savings and increased production capacity.
Through the aforementioned methods, efficient resource utilization of PET can be achieved, while simultaneously obtaining the environmentally friendly plasticizer DOTP with excellent performance, thus yielding both economic and environmental benefits.
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