Aromatic Carboxylic Acid Solvent Recovery via Fractionating Zone
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Solution Overview
Problem
Current processes for manufacturing aromatic carboxylic acids face challenges in efficiently separating and recovering oxidation reaction solvents, water, and by-products from high temperature and pressure off-gases, leading to material losses and energy inefficiencies, particularly due to the corrosive nature and complex separation of components like acetic acid and methyl bromide.
Innovation Solution
A process and apparatus that selectively separates solvent monocarboxylic acid and water from high pressure vapor phases using a fractionating zone with countercurrent flow, allowing for the apportionment of by-products into liquid and gas phases, thereby reducing impurities and facilitating the reuse of recovered materials and energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If high temperature and pressure off-gas from liquid phase oxidation is directly condensed, then water and acetic acid can be recovered, but the corrosive nature and complex separation of components like methyl bromide make the process inefficient and cause material losses
Solution Approach 1:
The separation process is divided into multiple stages: first condensing water and acetic acid together, then separately separating acetic acid from the condensate, and finally treating the remaining stream to remove methyl bromide. This segmentation allows each separation task to be optimized independently, reducing overall complexity while improving recovery efficiency.
Solution Approach 2:
A caustic wash stage is introduced as an intermediary step between acetic acid separation and final product recovery. This intermediate treatment removes corrosive methyl bromide and neutralizes acids, creating a less corrosive environment for subsequent equipment and simplifying material selection.
2Loss of energy
If conventional condensation and separation methods are used for off-gas, then some water and solvent can be recovered, but energy inefficiencies and material losses occur due to lack of selective separation
Solution Approach 1:
The off-gas is pre-heated and pre-condensed in a controlled manner before final separation, maximizing heat recovery from the hot vapor stream. This preliminary action captures energy that would otherwise be lost, reducing the energy required for subsequent separation steps while improving solvent recovery.
Solution Approach 2:
The process utilizes temperature and pressure parameter changes throughout the separation sequence. By carefully controlling condensation temperature and pressure conditions at each stage, the process optimizes both energy efficiency and separation effectiveness, recovering solvents at different points in the temperature-pressure profile.
3Adaptability or versatility
If impurities from off-gas are not separated, then process simplicity is maintained, but re-use of recovered streams is prevented due to adverse effects on product quality
Solution Approach 1:
Impurities including methyl bromide, carbon oxides, and other contaminants are systematically extracted and removed at dedicated stages. The caustic wash extracts acidic and halogenated impurities, while final polishing stages remove remaining contaminants, ensuring recovered streams meet purity requirements for reuse in oxidation reactions.
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 enables the recovery of solvent monocarboxylic acid, water, and energy with reduced impurities, balancing water usage, and minimizing material losses, thus improving process efficiency and product purity.
Implementation Method 1
separating solvent monocarboxylic acid and water from high pressure vapor phases
Implementation Method 2
apportionment of by-products into liquid and gas phases
Implementation Method 3
oxidizing aromatic feed material to an impure aromatic carboxylic acid product in a liquid phase oxidation reaction mixture
Implementation Method 4
The oxidation is exothermic and yields aromatic carboxylic acid together with by-products
Implementation Method 5
a vapor phase formed as a result of the exothermic oxidation is evaporated from the liquid phase and removed from the reactor to control reaction temperature
Data Source
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AI summary
A process and apparatus for manufacture of aromatic carboxylic acids comprises a liquid phase oxidation of aromatic hydrocarbon feed materials and treatment of a high pressure off-gas from the liquid phase oxidation to separate water and reaction solvent and preferentially apportion liquid phase oxidation by-product species between gas and liquid phases resulting from separation. Processes for making pure forms of aromatic carboxylic acid also are included.