Acetic Acid Flash Separation Methyl Iodide Control
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Solution Overview
Problem
Current acetic acid production processes face challenges in achieving improved separation steps, increased production capacities, and lower operating costs, particularly in minimizing the concentration of methyl iodide and hydrogen iodide, which affect the efficiency and cost-effectiveness of the carbonylation process.
Innovation Solution
A process involving the separation of a reaction medium in a flash vessel to form a vapor product stream with specific compositions, including acetic acid, methyl iodide, methyl acetate, water, and hydrogen iodide, which is then distilled to produce an acetic acid product stream with reduced hydrogen iodide levels and an overhead stream comprising methyl iodide and water, while maintaining optimal methyl iodide concentrations to support increased production rates and reduce corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the reaction medium is flashed to separate acetic acid from the reaction mixture, then the production capacity is increased and distillation columns are debottlenecked, but methyl iodide concentrates with the acetic acid causing iodide impurities and byproduct formation
Solution Approach 1:
The patent changes the concentration parameter of methyl iodide in the reaction medium, maintaining it within a specific range (0.5-5 wt%) to optimize the flash separation process. This parameter control allows adequate methyl iodide for catalytic activity while preventing excessive concentration that would lead to impurity formation in the distillation column
Solution Approach 2:
The patent applies local quality by creating different methyl iodide concentration zones: the reaction medium maintains sufficient methyl iodide for catalysis, while the flash vapor stream controls methyl iodide concentration to prevent impurity formation. This spatial differentiation of concentration quality resolves the contradiction between production capacity and product purity
2Manufacturing precision
If more distillation operations are performed to remove methyl iodide and achieve high purity acetic acid, then the manufacturing precision is improved, but the device complexity and operating costs increase
Solution Approach 1:
The patent extracts methyl iodide from the reaction medium before distillation by controlling its concentration in the flash vapor stream. This pre-extraction approach removes the problematic component early in the process, eliminating the need for additional distillation columns and reducing overall process complexity while maintaining high product purity
3Productivity
If the flash vessel operates at higher temperatures to increase separation efficiency, then the productivity is improved, but the concentration of methyl iodide in the vapor stream increases leading to more iodide impurities
Solution Approach 1:
The patent optimizes the temperature parameter of the flash vessel to achieve the desired balance. By controlling the flash temperature, the process achieves adequate separation efficiency while preventing excessive methyl iodide concentration in the vapor stream, thereby minimizing iodide impurity formation
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 enhances production capacities, reduces operating costs by minimizing methyl iodide recovery needs, and maintains low hydrogen iodide concentrations to prevent corrosion, thereby improving the overall efficiency and stability of the acetic acid production process.
Implementation Method 1
heating the flash vessel while concurrently flashing the reaction mixture to produce a crude product vapor stream
Implementation Method 2
passing the liquid reaction medium through a flash zone to produce a vapor fraction
Implementation Method 3
distilling at least a portion of the vapor product stream in a first column to obtain an acetic acid product stream and an overhead stream
Data Source
Figure 1
AI summary
A process for producing acetic acid is disclosed in which the methyl iodide concentration is maintained in the vapor product stream formed in a flashing step. The methyl iodide concentration in the vapor product stream ranges from 24 to less than 36 wt.%, based on the weight of the vapor product stream. In addition, the acetaldehyde concentration is maintained within the range from 0.005 to 1 wt.% in the vapor product stream. The vapor product stream is distilled in a first column to obtain an acetic acid product stream comprising acetic acid and hydrogen iodide in an amount of less than or equal to 300 wppm and/or methyl iodide in an amount from 0.1 to 6 wt.%, and an overhead stream comprising methyl iodide, water and methyl acetate.