Acetic Acid Purification via Acetaldehyde Control
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Solution Overview
Problem
The existing methods for producing acetic acid through the methanol carbonylation process face challenges in achieving high quality acetic acid with low impurity content and good potassium permanganate test values, due to the generation of by-products like crotonaldehyde, 2-ethyl crotonaldehyde, and hexyl iodide, which require expensive separation and removal apparatus, and lead to increased costs.
Innovation Solution
The method involves controlling the acetaldehyde concentration in the evaporator bottom fraction and adjusting the reflux ratio of the lower boiling point component removal column to increase the acetaldehyde distribution coefficient, allowing for efficient acetaldehyde removal and reduction of by-product generation, thereby eliminating the need for large-scale acetaldehyde removal apparatus and improving the potassium permanganate test value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If expensive separation and removal apparatus are used to remove acetaldehyde and crotonaldehyde, then the potassium permanganate test value of product acetic acid is improved, but the apparatus cost increases
Solution Approach 1:
The patent changes the concentration parameters of the reaction system by controlling acetaldehyde concentration in the evaporator bottom fraction and adjusting reflux ratio in the lower boiling point component removal column. These parameter changes optimize the distribution coefficient of acetaldehyde, enabling efficient removal without expensive additional apparatus.
Solution Approach 2:
The patent utilizes the existing purification apparatus to serve dual purposes: the lower boiling point component removal column is optimized to simultaneously remove both acetaldehyde and crotonaldehyde by controlling operational parameters, eliminating the need for separate dedicated removal apparatus.
2Object-generated harmful factors
If acetaldehyde is removed from the reaction system, then the generation of harmful by-products (crotonaldehyde, 2-ethyl crotonaldehyde, hexyl iodide) is suppressed, but the complexity of the purification process increases
Solution Approach 1:
The patent performs preliminary removal of acetaldehyde in the evaporator bottom fraction before it can react to form harmful by-products. By removing acetaldehyde early in the process, the subsequent formation of crotonaldehyde, 2-ethyl crotonaldehyde, and hexyl iodide is suppressed.
Solution Approach 2:
The lower boiling point component removal column is operated to simultaneously perform multiple functions: separating acetaldehyde from the reaction mixture and also removing crotonaldehyde and other harmful by-products, thereby simplifying the overall purification process.
3Manufacturing precision
If the acetaldehyde concentration in the reaction vessel is lowered, then the quality of product acetic acid is improved, but the efficiency of the reaction system may be affected
Solution Approach 1:
The patent implements a feedback control system where the acetaldehyde concentration in the evaporator bottom fraction is monitored and controlled within a specific range (0.01-5.0 wt%). This feedback mechanism maintains optimal acetaldehyde levels that ensure high product quality while preserving reaction system efficiency.
Solution Approach 2:
The patent dynamically adjusts the reflux ratio in the lower boiling point component removal column to optimize the distribution coefficient of acetaldehyde. By making the purification process dynamic and adaptable, the system maintains high efficiency while achieving superior product quality.
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 results in high-quality acetic acid with reduced impurity levels and lower production costs, as the acetaldehyde concentration in the reaction vessel is lowered, suppressing the generation of by-products like crotonaldehyde, 2-ethyl crotonaldehyde, and hexyl iodide, and enhancing the efficiency of the acetaldehyde separation process.
Implementation Method 1
heating the evaporator and simultaneously increasing the acetic acid concentration fed into a lower boiling point component removal column
Implementation Method 2
separating an overhead condensate in the lower boiling point component removal column into an aqueous phase and an organic phase
Implementation Method 3
control acetaldehyde distribution coefficient at the time of separating an overhead condensate in the lower boiling point component removal column into an aqueous phase and an organic phase
Data Source
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AI summary
There is provided a method allowing industrially efficient production of high quality acetic acid having a good potassium permanganate test value and a low impurity content without a large cost. The method for producing acetic acid according to the present invention has a carbonylation reaction step, an evaporation step and a lower boiling point component removal step, and wherein with heating of the evaporator, (i) an acetaldehyde concentration in the aqueous phase of an overhead condensate in a lower boiling point component removal column is controlled to not less than 2340 ppm by mass; and/or (ii) a methyl acetate concentration in the aqueous phase is controlled to less than 19.0% by mass and/or; (iii) a methyl acetate concentration in the organic phase of the overhead condensate in the lower boiling point component removal column is controlled to less than 38.0% by mass, and then at least a portion of the aqueous phase is treated in the acetaldehyde separation and removal step to recycle a residual liquid after the acetaldehyde separation and removal to the reaction vessel and/or the acetaldehyde separation and removal step and/or other processes.