Hydrocarbon Removal from Acetic Acid via Liquid-Liquid Extraction
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Solution Overview
Problem
Current methods for producing acetic acid through methanol carbonylation face challenges such as high water consumption, corrosive hydrogen iodide issues, stress crack corrosion, and the presence of hydrocarbon impurities like alkanes and aromatics, which are difficult to remove effectively.
Innovation Solution
A method involving a carbonylation catalyst, catalyst stabilizer, methyl iodide, water, and methyl acetate is used to produce an acetic acid stream, which is then flashed and separated into vapor and liquid streams. The vapor stream is distilled to separate acetic acid from hydrocarbon impurities, and the resulting organic phase is extracted with an aqueous solution to remove the majority of hydrocarbon impurities, recycling the aqueous phase back to the reactor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water concentration is lowered in the methanol carbonylation process, then catalyst stability is improved and water removal cost is reduced, but hydrocarbon impurity formation increases
Solution Approach 1:
The patent extracts hydrocarbon impurities from the acetic acid product stream through a dedicated extraction unit. The extraction system uses a selective solvent to separate hydrocarbon impurities from the main product, allowing the process to operate with lower water concentrations while maintaining product purity by removing the harmful byproducts that would otherwise accumulate.
Solution Approach 2:
The patent converts the harmful effect of hydrocarbon impurity formation into a manageable separation challenge. By accepting that hydrocarbons will form under low-water conditions but using this as a driving force for enhanced separation unit design, the system achieves both low-water operation and high product purity. The extracted hydrocarbons can be recycled or disposed of, turning a waste problem into a controlled process parameter.
2Object-generated harmful factors
If traditional alkane distillation methods are used to remove hydrocarbon impurities, then some alkanes are removed, but low boiling alkanes build up in the reaction system due to overhead recycling
Solution Approach 1:
The patent introduces an intermediary extraction solvent that selectively transfers hydrocarbon impurities from the acetic acid stream to a separate phase. This intermediary medium allows for the removal of both light and heavy hydrocarbons without requiring high-temperature distillation that would cause low boiling alkanes to co-vaporize and recycle back into the reactor, thus preventing buildup while effectively cleaning the product.
3Reliability
If lithium iodide salt is added to increase catalyst stability, then water concentration can be reduced, but stress crack corrosion of reactor vessels increases
Solution Approach 1:
The patent replaces the problematic lithium iodide salt with an alternative catalyst stabilizer system that does not cause stress crack corrosion. The new system uses a different chemical approach to maintain catalyst stability without introducing the corrosive effects of high浓度的碘盐, effectively substituting a harmful long-term stabilizer with a safer alternative.
4Loss of substance
If high bottoms temperature is used in alkane distillation to minimize methyl iodide loss, then methyl iodide is retained, but low boiling alkanes are removed with the overhead stream
Solution Approach 1:
The patent uses an extraction solvent as an intermediary to separate hydrocarbon impurities at lower temperatures. The solvent selectively dissolves hydrocarbons from the acetic acid-methyl iodide mixture, allowing separation without the high temperatures needed for traditional distillation. This prevents low boiling alkanes from vaporizing and being lost with the overhead, while still effectively removing hydrocarbon impurities through the extraction phase.
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 method effectively reduces hydrocarbon impurities in the acetic acid production process, minimizing waste and reducing the need for costly water and corrosive substances, while maintaining high acetic acid yield and catalyst stability.
Implementation Method 1
At least a portion of the acetic acid stream is flashed into a vapor stream comprising acetic acid, water, methanol, methyl acetate, methyl iodide and the hydrocarbon impurity, and a liquid stream comprising the catalyst and the catalyst stabilizer
Implementation Method 2
The vapor stream is separated by distillation into a product stream comprising acetic acid and a minor amount of water and heavy impurities such as propionic acid, and an overhead stream comprising methyl iodide, water, methyl acetate, acetic acid and the hydrocarbon impurity
Implementation Method 3
The overhead stream is condensed and separated into a light, aqueous phase comprising water, acetic acid, and methyl acetate, and a heavy, organic phase comprising methyl iodide, acetic acid, methyl acetate, and the hydrocarbon impurity
Implementation Method 4
The bottom stream is extracted with water, or an acetic acid aqueous solution, or with a methanol aqueous solution to form an organic phase comprising the majority of the hydrocarbon impurity (over 50% of the hydrocarbon impurity from the bottoms stream) and an aqueous phase comprising the majority of methyl iodide (over 50% of the methyl iodide from the bottoms stream)
Data Source
AI summary
A method for removing hydrocarbon impurities from an acetic acid production process is disclosed. The method comprises distilling at least a portion of the heavy organic phase from the decanter of the acetic acid production process into a vapor stream comprising the majority of methyl iodide (i.e., over 50% of the methyl iodide from the heavy organic phase) and a bottoms stream comprising the majority of acetic acid, methyl acetate, methyl iodide and the hydrocarbon impurity (i.e., over 50% of each of the components from the heavy organic phase); extracting the bottoms stream with water, an acetic acid aqueous solution, or with a methanol aqueous solution to form an organic phase comprising the majority of the hydrocarbon impurity (over 50% of the hydrocarbon impurity from the bottom stream) and an aqueous phase comprising the majority of methyl iodide (over 50% of the methyl iodide from the bottoms stream); and recycling the aqueous phase to the carbonylation reaction.