Acetic Acid Purification Heavy Phase Reflux
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Solution Overview
Problem
In acetic acid production via carbonylation processes, the reflux of the light phase to the light ends column increases water content in the product stream, leading to higher dehydration column loading and reduced acetic acid concentration, due to restrictive vapor-liquid equilibrium between acetic acid and water.
Innovation Solution
Refluxing the heavy phase instead of the light phase from the LE OH decanter to the LE column, which predominantly contains methyl iodide, reduces acetic acid concentration and allows for efficient recycling of the light phase to the reactor without loss of reflux rate, thereby reducing water content in the dehydration column.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If light phase is refluxed to the light ends column, then reflux rate is maintained, but water content in product stream increases and acetic acid concentration decreases
Solution Approach 1:
The invention extracts and separates the heavy phase (containing water and acetic acid) from the light phase (containing methyl iodide) in a decanter, and selectively refluxes only the light phase to the light ends column. This extraction separates the harmful water-carrying heavy phase from the useful light phase, allowing high reflux rates while preventing water contamination in the product stream.
Solution Approach 2:
Conventionally, the light phase is refluxed to maintain reflux rate while the heavy phase is discarded. The invention inverts this approach by refluxing the heavy phase (which has favorable VLE properties) and discarding or recycling the light phase. This inversion resolves the contradiction because the heavy phase's VLE characteristics prevent water from being forced into the product stream, maintaining both high reflux rates and high acetic acid concentration.
2Duration of action of stationary object
If light phase is refluxed to the light ends column, then reflux operation continues, but dehydration column loading increases
Solution Approach 1:
The decanter extracts the heavy phase containing the majority of water before the reflux stream enters the light ends column. By removing this water-rich heavy phase and preventing it from entering the reflux loop, the system can maintain continuous reflux operation without accumulating excess water that would otherwise increase dehydration column loading.
Solution Approach 2:
The invention changes the composition parameter of the reflux stream by selecting only the light phase (low water content) rather than the conventional light phase mixture. This parameter change in reflux composition allows continuous operation while keeping water content in the product stream low, thereby reducing the burden on the dehydration column.
3Manufacturing precision
If heavy phase is refluxed to the light ends column, then acetic acid concentration is maintained, but light phase recycling efficiency is reduced
Solution Approach 1:
The decanter acts as an intermediary device that separates the mixture into light and heavy phases. This intermediary separation allows the system to selectively route the light phase (suitable for recycling) to the reactor while routing the heavy phase (suitable for reflux) to the light ends column, thereby resolving the contradiction between maintaining acetic acid concentration and preserving recycling efficiency.
Solution Approach 2:
The invention segments the reflux stream into two distinct phases based on density and composition. The light phase segment is recycled to the reactor for productivity, while the heavy phase segment is refluxed to the light ends column for maintaining acetic acid concentration. This segmentation allows both objectives to be achieved simultaneously without compromise.
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 decreases the acetic acid content in the light phase, alleviates VLE restrictions in the drying column, and allows for a reduction in dehydration column reflux rate, enabling higher capacities and improved acetic acid profile management.
Implementation Method 1
the overhead vapor is condensed in a condenser and decanted into a heavy phase and a light phase
Implementation Method 2
decanted into a heavy phase and a light phase in a decanter
Implementation Method 3
purification train includes a light ends column which removes 'light' or low boiling components as overhead
Data Source
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AI summary
An improved method of producing acetic acid includes condensing overhead vapor from a light ends column and decanting the condensed vapor to a light phase and a heavy phase. The heavy phase consists predominantly of methyl iodide and at least a portion of the decanted heavy phase is refluxed to the light ends column. Acetic acid content of the light ends column overhead stream and water content of the light ends column product (sidedravv) stream are both decreased, improving purification efficiency.