Application: Modifications to the traditional process for manufacturing dimethyl terephthalate (DMT) can significantly improve results including capacity increase, yield improvements, reduced energy consumption and upgrade of byproduct quality for increased commercial value. The technology is flexible and may be implemented in increments. GTC can optimize the design or configuration to maximize use of existing equipment.
Description: The common method for the production of DMT from paraxylene (PX) and methanol consists of four major steps: oxidation, esterification, distillation and crystallization. A mixture of PX and PT-ester is oxidized with air in the presence of a heavy metal catalyst. All useful organics are recovered from the offgas and recycled to the system. The acid mixture resulting from the oxidation is esterified with methanol (MeOH) to produce a mixture of esters. The crude ester mixture is distilled to remove all the heavy boilers and residue produced; the lighter esters are recycled to the oxidation section. The raw DMT is then sent to the crystallization section to remove DMT isomers, residual acids and aromatic aldehydes. This purification produces DMT that meets worldmarket specifications and is preferred in some polyester applications. Byproducts are recovered for sale or burned for fuel value and usable intermediate materials are recycled.
The GTC process improvements enhance the traditional process in each of the four sections through changes in process configurations and operating conditions, alteration of separation schemes, revision of recovery arrangements, increase in the value of byproducts and reduction in the total recycles in the plant. The upgrade options may be implemented individually, combined or through a series of revamps over a period of time.
Process advantages:
• Reduction in use of raw materials (p-xylene and methanol)
• Higher specific throughput
• Lower energy consumption/ton DMT produced
• Flexible application for revamp projects
• Accumulated technical expertise available through engineering packages and follow-up services
Oxidation section
• Improved oxidation reduces side reactions and more effectively uses reaction volume, resulting in lower PX consumption.
• New and more efficient scheme for the catalyst recovery in the plant helps reduce residue formation.
• Improved recovery of PX and removal of methyl benzoate: Product is upgraded to food or perfume grade.
• Carboxylic acid recovery: Recovery of formic and acetic acid as byproducts, upgrading value and reducing load in biotreatment unit.
Distillation section
• Improved distillation scheme increases purity of DMT to crystallization and reduces plant recycles.
• Improved residue treatment can increase the yields of the plant by recovering valuable materials.
Crystallization
• Typical double-crystallization scheme is simplified to increase throughputs and minimize equipment.
• New single-stage crystallization offers a low-cost alternative in revamps.
• Improved methanol recovery and handling system reduces plant losses.
• Improved isomer removal system helps reduce DMT losses.
Esterification
• Improved reactor design gives higher throughputs and improved methanol usage.
Licensor: GTC Technology.
