The synthesis of dioctyl terephthalate (DOTP) from polyethylene terephthalate (PET) and octanol is an innovative recycling process that converts waste plastic into a high-value DOTP plasticizer. At Shandong Changxing Plastic Additives, we utilize advanced transesterification technology to achieve this transformation efficiently and economically.

Reaction Principle

The core of this process is a transesterification reaction. Under the action of a catalyst and heat, the ester bonds in the PET molecular chain break, and the MEG is replaced by octanol, generating DOTP and MEG as a by-product:

Key Process Steps

1. Raw Material Pretreatment

• PET processing: Waste PET is cleaned to remove impurities and crushed into 2-4 mm granules.
• Octanol selection: Industrial grade isooctanol (2-Octanol) with purity ≥99% is used in excess to drive the reaction forward.

2. Continuous Production Process

• Equipment configuration: Continuous feeding alcoholysis reactor, equipped with distillation tower, multi-stage MEG absorption tank, and octanol refining device.
• Alcoholysis stage: PET, octanol, and catalyst are stirred at high temperature in the reactor. Generated MEG and octanol vapor enter the distillation tower.
• Separation stage: Vapor is condensed and enters a secondary absorption tank. MEG is absorbed by water, while octanol is dehydrated in a drying tower and recycled.
• Refining stage: The reaction liquid is subjected to vacuum distillation to separate remaining octanol. Activated carbon adsorption and water washing remove impurities to obtain final DOTP.

Separation and Purification

• Crude product treatment: Reaction liquid is cooled and filtered to remove unreacted PET residue.
• Distillation recovery: Vacuum distillation separates unreacted octanol (recovery rate >90%). Negative pressure rectification purifies MEG to premium grade standard (purity >99.5%).
• Deep refining: Activated carbon adsorption for decolorization (dosage 5% of product mass), stirred at 80°C for 1 hour, then filtered to obtain colorless and transparent DOTP.

Safety and Economic Benefits

• Risk control: High-temperature reactions are carried out in an inert atmosphere (such as nitrogen) to prevent octanol oxidation. Catalysts (such as tetrabutyl titanate) must be stored sealed to prevent hydrolysis.
• Cost advantages: Using waste PET can reduce raw material costs by 40%-60%, while also reducing waste disposal fees. Continuous process equipment investment can be recovered within 2-3 years through raw material savings and capacity improvements.