Acetic Acid Purification via Alkylimidazolium Iodide Flash Separation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The production of acetic acid through methanol carbonylation faces challenges with high water content leading to excessive hydrogen iodide formation, which is corrosive and results in the formation of hard-to-separate long-chain alkyl iodide by-products, causing equipment corrosion and purification complications.
Innovation Solution
Introducing an alkylimidazolium iodide into the flash zone to interact with the reaction mixture, either as an extraneous compound or formed in situ, reduces hydrogen iodide entrainment and volatilization, facilitating its separation and reducing water vaporization, thereby alleviating corrosion and by-product issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water is used to stabilize the catalyst and produce hydrogen via water-gas shift reaction, then catalyst stability and hydrogen production are improved, but hydrogen iodide formation increases causing corrosion and by-product issues
Solution Approach 1:
Lithium iodide is introduced as an intermediary substance that mediates between water and hydrogen iodide. It facilitates hydrogen production through the reaction LiI + H2O → LiOH + HI, but then captures the generated hydrogen iodide through complex formation, effectively controlling its harmful effects while maintaining catalyst stability.
2Reliability
If large amounts of water are present in the reaction mixture, then catalyst regeneration is improved, but separation of water from acetic acid becomes more difficult and costly
Solution Approach 1:
The process utilizes parameter changes in the form of temperature-dependent solubility and vapor pressure differences. By controlling the temperature during separation operations, water can be selectively removed from the acetic acid mixture, facilitating easier separation while maintaining catalyst regeneration efficiency.
3Productivity
If hydrogen iodide is present in high concentrations, then carbonylation reaction proceeds efficiently, but equipment corrosion and formation of long-chain alkyl iodide by-products increase
Solution Approach 1:
Lithium iodide serves as a mediator that allows the carbonylation reaction to proceed with sufficient hydrogen iodide concentration while simultaneously capturing excess hydrogen iodide through complex formation, thereby preventing equipment corrosion and unwanted side reactions that form long-chain alkyl iodides.
4Quantity of substance
If lithium iodide is added to reduce water content, then water vaporization is reduced, but hydrogen iodide problems persist
Solution Approach 1:
The addition of lithium iodide changes the physical-chemical parameters of the system, specifically reducing water activity and vapor pressure. This allows for reduced water content and suppressed water vaporization while the lithium iodide simultaneously manages hydrogen iodide concentrations through complex formation, addressing both issues together.
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 effectively reduces hydrogen iodide in the vapor phase, simplifies its separation, minimizes the formation of unwanted alkyl iodides, and decreases water vaporization, enhancing the acetic acid purification process and reducing equipment corrosion.
Implementation Method 1
the alkylimidazolium iodide interacts with hydrogen iodide and thus reduces the tendency of hydrogen iodide to become entrained in the vapor stream (BV)
Implementation Method 2
the alkylimidazolium iodide has been found to reduce the volatilization of water thereby further facilitating the purification of acetic acid
Implementation Method 3
the withdrawn part of the reaction mixture (A) is introduced into a flash zone where it is brought into contact with an alkylimidazolium iodide to form a secondary mixture (B), and where the secondary mixture (B) is separated to obtain a vapor stream (BV)
Data Source
AI summary
The disclosure relates to a process in which methanol is carbonylated in a reaction zone in the presence of a catalyst to obtain a reaction mixture (A) comprising acetic acid, hydrogen iodide, methyl iodide, water and the catalyst. At least a part of the reaction mixture (A) is withdrawn from the reaction zone. The withdrawn part of the reaction mixture (A) is introduced into a flash zone where it is brought into contact with an alkylimidazolium iodide to form a secondary mixture (B), and where the secondary mixture (B) is separated to obtain a vapor stream (BV) which comprises the acetic acid, water and methyl iodide, and a liquid stream (BL) which comprises the catalyst, the alkylimidazolium iodide and hydrogen iodide. The vapor stream (BV) is processed to purify the acetic acid, and the liquid stream (BL) is recycled to the reaction zone. The reaction mixture (A) is brought into contact with the alkylimidazolium iodide in the flash zone1) by introducing to the flash zone separately from the withdrawn part of the reaction mixture (A) an extraneous alkylimidazolium iodide; or2) by introducing to the flash zone separately from the withdrawn part of the reaction mixture (A) an alkylimidazole and forming the alkylimidazolium iodide in situ by reacting the alkylimidazole with the hydrogen iodide or the methyl iodide.