Terephthalic Acid Purification via Ionic Liquid Solvent
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Solution Overview
Problem
Current processes for producing terephthalic acid from para-xylene are costly and time-consuming, requiring multiple purification steps and often involve catalytic hydrogenation, while also producing terephthalic acid compositions with varying contaminant ratios that are difficult to purify.
Innovation Solution
A process involving the oxidation of para-xylene with a mixture of a carboxylic acid solvent, a dialkyl imidazolium ionic liquid, and a catalyst such as cobalt or manganese, which produces solid terephthalic acid compositions with controlled contaminant levels, specifically reducing 4-carboxybenzaldehyde and para-toluic acid content, and eliminates the need for catalytic hydrogenation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional oxidation processes are used to produce terephthalic acid, then the oxidation reaction can proceed, but multiple purification steps and catalytic hydrogenation are required, increasing process complexity and cost
Solution Approach 1:
The patent extracts and removes the problematic intermediate oxidation products (4-CBA and para-toluic acid) from the reaction mixture by designing a solvent system that selectively dissolves these impurities while leaving terephthalic acid as a solid precipitate. This extraction approach eliminates the need for complex purification steps including catalytic hydrogenation, achieving polymer-grade purity through simple filtration and washing operations.
2Productivity
If conventional oxidation processes are used, then terephthalic acid can be produced, but the contaminant ratios vary and are difficult to purify, increasing time and cost
Solution Approach 1:
The patent changes the physical-chemical parameters of the reaction medium by employing a specific solvent system comprising a carboxylic acid and an ionic liquid. This parameter change in solvent composition selectively controls the solubility of different oxidation products, causing terephthalic acid to precipitate while keeping intermediates (4-CBA and para-toluic acid) in solution. The result is consistent, controlled contaminant levels that are easily separated, reducing both purification time and cost while achieving polymer-grade purity.
3Productivity
If halogen-containing promoters are used in oxidation, then conversion can be improved, but severe corrosion problems occur requiring special corrosion-resistant materials
Solution Approach 1:
The patent introduces an ionic liquid as an intermediary substance that mediates the oxidation reaction. The ionic liquid serves as both a solvent and a catalyst promoter, replacing the traditional halogen-containing promoters (such as HBr or Br2). This intermediary provides the necessary catalytic activity to achieve high conversion rates while being non-corrosive to standard equipment materials, thereby eliminating the need for expensive corrosion-resistant liners or special materials.
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 process results in terephthalic acid compositions that are less costly and time-consuming to purify, achieving high purity without hydrogenation steps and allowing for the production of polymer-grade terephthalic acid with controlled contaminant levels.
Implementation Method 1
the oxidation of para-xylene in the presence of a solvent comprising a carboxylic acid and an ionic liquid
Implementation Method 2
US 2009/0326265 A1 discloses a process for preparing an aromatic polycarboxylic acid by liquid phase oxidation of a di- or tri-substituted benzene or naphtalene compound, the process comprising a step of contacting the aromatic compound with an oxidant in the presence of a carboxylic acid solvent, a metal catalyst and a promoter in a reaction zone, wherein the promoter is an ionic liquid
Implementation Method 3
a solvent comprising a carboxylic acid and an ionic liquid
Implementation Method 4
produce solid terephthalic acid compositions with controlled contaminant levels
Data Source
AI summary
A solid terephthalic acid composition and a process for producing terephthalic acid from para-xylene. The process comprises forming a mixture comprising the para-xylene, a solvent, a bromine source, and a catalyst; and oxidizing the para-xylene by contacting the mixture with an oxidizing agent at oxidizing conditions to produce a solid oxidation product comprising terephthalic acid, para-toluic acid, 4-carboxybenzaldehyde. The solvent comprises a carboxylic acid having from 1 to 7 carbon atoms and an dialkyl imidazolium ionic liquid; and the catalyst comprises at least one of cobalt, titanium, manganese, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium, and zirconium. The solid terephthalic acid composition comprises, less than about 4,000 ppm-wt 4-carboxybenzaldehyde content, and more than about 2,000 ppm-wt a para-toluic acid.