Dimethyl Terephthalate Yield via Diol Extraction

Solution Overview

Problem

The existing methanolysis depolymerization process for polyesters, such as PET, faces challenges with low yield and high energy consumption due to the reversible nature of the reaction, requiring a significant stoichiometric excess of methanol, which increases operational costs and energy usage.

Innovation Solution

A method involving treating polyester with methanol in a depolymerization reaction system to form dimethyl terephthalate and a diol, followed by converting the diol to a compound that is substantially non-reactive with dimethyl terephthalate, using a cyclic carbonate-forming reactant to enhance yield and reduce methanol requirements, and producing cyclic carbonates as valuable by-products.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a large stoichiometric excess of methanol is used to drive the reversible methanolysis reaction forward, then the yield of dimethyl terephthalate is improved, but the energy consumption and operational costs increase significantly

Engineering Contradiction:

Improveyield of dimethyl terephthalateVSAvoidenergy consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The invention extracts and removes the diol byproduct from the reaction system as it forms. By continuously removing one of the products (diol) from the equilibrium system, the reaction is driven forward to produce more dimethyl terephthalate without requiring a large excess of methanol, thus reducing energy consumption associated with heating and condensing excess methanol.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention changes the parameters of the reaction system by converting the diol to a different chemical form (compound substantially non-reactive with dimethyl terephthalate). This parameter change removes the diol from the equilibrium mixture, shifting the reaction equilibrium toward the desired product and reducing the need for excess methanol.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If a large stoichiometric excess of methanol is used to achieve high yield, then the yield of dimethyl terephthalate is improved, but the operational costs and material usage increase

Engineering Contradiction:

Improveyield of dimethyl terephthalateVSAvoidmethanol consumption

Core Design Contradiction:

ProductivityVSLoss of substance

Solution Approach 1:

The invention extracts and removes the diol byproduct from the reaction system as it forms. By continuously removing one of the products (diol) from the equilibrium system, the reaction is driven forward to produce more dimethyl terephthalate without requiring a large excess of methanol, thus reducing material usage and operational costs.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention changes the parameters of the reaction system by converting the diol to a different chemical form (compound substantially non-reactive with dimethyl terephthalate). This parameter change removes the diol from the equilibrium mixture, shifting the reaction equilibrium toward the desired product and reducing the need for excess methanol.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If superheated methanol vapor is used to evaporate the DMT and EG products, then the separation process is simplified, but the energy usage and equipment costs increase

Engineering Contradiction:

Improveseparation process simplicityVSAvoidenergy usage

Core Design Contradiction:

Ease of manufactureVSUse of energy by stationary object

Solution Approach 1:

The invention performs preliminary action by converting the diol to a non-reactive compound during the reaction process itself, before the separation stage. This preliminary conversion simplifies the subsequent separation process by eliminating the need to separate diol from the product mixture, and reduces energy usage by avoiding the need to superheat methanol vapor for evaporation.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach increases the yield of dimethyl terephthalate and reduces methanol consumption, thereby lowering operational costs and energy usage, while generating valuable chemical compounds like cyclic carbonates.

Implementation Method 1

In methanolysis, the polyester is reacted with methanol to produce a depolymerized polyester mixture comprising polyester oligomers, dimethyl terephthalate ("DMT"), and ethylene glycol ("EG").

Methodology Applied

Scientific EffectMethanolysis: Chemical Bonding

Implementation Method 2

converting the diol to a compound that is substantially non-reactive with dimethyl terephthalate, using a cyclic carbonate-forming reactant to enhance yield and reduce methanol requirements, and producing cyclic carbonates as valuable by-products.

Methodology Applied

Scientific EffectChemical reaction: Chemical Bonding

Data Source

PatentEP4077267B1Method for producing dimethyl terephthalate from polyester methanolysis depolymerization systems

Publication Date: 2024.11.27 EASTMAN CHEM CO

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AI summary

Disclosed is a method for depolymerization of polyester. The method includes (a) treating said polyester with methanol under conditions sufficient to depolymerize at least some of said polyester and form a reaction product that includes dimethyl terephthalate and at least one diol; and (b) converting the diol to a compound substantially non-reactive with said with dimethyl terephthalate and the polyester. A method for producing a cyclic carbonate is also described.