Methanol Carbonylation Purification via Water Extraction
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Solution Overview
Problem
Current processes for producing acetic acid through methanol carbonylation suffer from impurities such as permanganate reducing compounds and alkyl iodides, which affect the quality and catalyst stability, leading to increased costs and inefficiencies in purification, particularly at low water concentrations.
Innovation Solution
A process involving the separation of reaction products into volatile and less volatile phases, followed by distillation and multiple extractions with water to concentrate and remove permanganate reducing compounds and alkyl iodides, with dimethyl ether added to reduce methyl iodide solubility and minimize waste, allowing for recycling of valuable components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple extraction steps with water are used to remove permanganate reducing compounds, then purification quality improves, but process complexity and time increase
Solution Approach 1:
The purification process is divided into multiple sequential extraction steps, where each extraction stage targets specific impurities at different concentration levels. The first extraction removes bulk permanganate reducing compounds, while subsequent extractions remove residual impurities, achieving high purification quality through staged separation rather than a single complex operation.
Solution Approach 2:
The process employs periodic extraction cycles where the reaction mixture is sequentially contacted with fresh water portions in discrete stages. Each extraction cycle is performed separately, allowing complete phase separation between steps, which simplifies the equipment design compared to continuous multi-stage extraction systems while achieving equivalent purification results.
2Manufacturing precision
If extensive purification steps are implemented to remove all impurities, then acetic acid quality improves, but production time and energy consumption increase
Solution Approach 1:
The purification process targets specific locations and stages where impurities are most concentrated. The first extraction focuses on the volatile phase containing high concentrations of permanganate reducing compounds, while subsequent extractions address residual impurities in the acetic acid phase. This localized approach to purification removes critical impurities without subjecting the entire process to extended treatment times.
Solution Approach 2:
The process exploits changes in physical parameters during extraction, specifically the distribution coefficients of different impurities between organic and aqueous phases. By controlling extraction conditions and performing sequential extractions with fresh water, the process efficiently removes impurities that have different solubilities and partition behaviors, achieving high quality acetic acid without requiring all possible purification steps.
3Ease of manufacture
If conventional purification methods are used without phase separation, then process simplicity is maintained, but impurity removal efficiency decreases
Solution Approach 1:
The process separates the reaction products into two distinct phases: a volatile phase containing permanganate reducing compounds and an acetic acid phase. By physically extracting and removing the volatile phase before purification steps, the process eliminates a large portion of impurities upfront. This preliminary extraction simplifies subsequent purification steps while dramatically improving overall impurity removal efficiency compared to treating the homogeneous mixture.
Solution Approach 2:
Water serves as an intermediary extraction solvent that selectively transfers permanganate reducing compounds from the organic phase to the aqueous phase. This intermediary substance enables efficient separation of impurities from acetic acid through liquid-liquid extraction, achieving high purification efficiency while maintaining process simplicity through the use of a common, inexpensive solvent rather than complex specialized equipment.
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 permanganate reducing compounds and alkyl iodides by at least 50%, improving acetic acid quality and catalyst stability while minimizing the loss of costly methyl iodide, and allows for efficient recycling of materials.
Implementation Method 1
distilling the volatile product phase to yield a purified product and a first overhead that contains organic iodide, water, acetic acid, and unreacted methanol
Implementation Method 2
extracting the second overhead with water to provide a first aqueous extract and a first raffinate; and extracting the first raffinate with water to provide a second raffinate and a second aqueous extract containing concentrated PRC's
Implementation Method 3
with dimethyl ether added to reduce methyl iodide solubility and minimize waste
Data Source
AI summary
An improvement of the methanol carbonylation process for manufacturing acetic acid is disclosed. Specifically disclosed is a method for reducing the formation of alkyl iodides and C3-8 carboxylic acids by removing permanganate reducing compounds (“PRC's”) from the light phase of the condensed light ends overhead stream, including (a) distilling the light phase to yield a PRC enriched overhead stream; and (b) extracting the third overhead stream with water in at least two consecutive stages and separating therefrom one or more aqueous streams containing PRC″s.