Lithium Acetate Control in Acetic Acid Flashing
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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 methyl iodide concentrations to avoid costly losses and reduce iodide impurities.
Innovation Solution
A process involving carbonylation of a reactant feed stream with water, rhodium catalyst, iodide salt, and methyl iodide, where a lithium compound is introduced to maintain lithium acetate concentrations in the reaction medium, allowing for controlled methyl iodide levels in the vapor product stream, thereby optimizing separation and reducing hydrogen iodide concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional carbonylation processes are used without lithium compound addition, then the process is simpler to operate, but methyl iodide concentrations are higher causing costly losses and iodide impurities
Solution Approach 1:
Lithium acetate is introduced as an intermediary substance that mediates between methyl iodide and the reaction medium. It controls methyl iodide concentration by forming lithium iodide and acetic acid, thereby reducing methyl iodide losses and iodide impurities without requiring fundamental changes to the carbonylation process equipment or operation procedures.
2Productivity
If higher production capacities are pursued, then output increases, but separation steps become more difficult and operating costs increase
Solution Approach 1:
The addition of lithium compound changes the chemical parameters of the reaction medium, specifically controlling methyl iodide concentration and forming lithium iodide. This parameter change facilitates easier separation of product streams and reduces the complexity of purification steps, allowing higher production capacities to be achieved without proportionally increasing separation difficulty or operating costs.
3Loss of substance
If methyl iodide concentrations are reduced to minimize losses, then substance loss decreases, but catalyst promoter availability may be insufficient
Solution Approach 1:
Lithium acetate serves as a mediator that releases iodide ions in a controlled manner through reaction with methyl iodide. This intermediary mechanism ensures sufficient catalyst promoter availability by maintaining appropriate iodide concentrations in the reaction medium while simultaneously reducing overall methyl iodide losses through the formation of lithium iodide.
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 debottlenecks distillation columns, increases production capacities, and lowers operating costs by maintaining methyl iodide within specific ranges, minimizing corrosion and facilitating the recovery of valuable catalyst promoters.
Implementation Method 1
maintaining a concentration of lithium acetate in the reaction medium in an amount from 0.3 to 0.7 wt. %
Implementation Method 2
separating the reaction medium in a flash vessel to form a liquid recycle stream and a vapor product stream
Implementation Method 3
the vapor product stream comprises acetic acid in an amount from 45 to 75 wt. %, methyl iodide in an amount from 24 to less than 36 wt. %
Implementation Method 4
distilling at least a portion of the vapor product stream 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
Data Source
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 process includes introducing a lithium compound into the reactor and maintaining a concentration of lithium acetate in the reaction medium is in an amount from 0.3 to 0.7 wt. %. The reaction medium is fed forward to the 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. 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. %.