Acetic Acid Distillation Column with Extractive Solvent
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Solution Overview
Problem
Current processes for producing acetic acid through methanol carbonylation face challenges in efficiently separating permanganate reducing compounds (PRCs) like acetaldehyde and methyl iodide, leading to low-quality acetic acid due to high energy consumption and complex distillation requirements.
Innovation Solution
A process involving distillation in a column where water is added as an extractive solvent to create a concentration zone, allowing for efficient separation of methyl iodide and acetaldehyde by transferring acetaldehyde from the methyl iodide phase to the aqueous phase, reducing energy usage and distillation stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ordinary distillation means is used to separate acetaldehyde and methyl iodide, then separation is attempted, but the separation efficiency is low due to close boiling points
Solution Approach 1:
Water is introduced as an intermediary extractive solvent that selectively dissolves acetaldehyde from the mixture of acetaldehyde and methyl iodide. This mediator enables efficient separation by exploiting the differential solubility and distribution coefficients of the two components between aqueous and organic phases, overcoming the limitation of close boiling points that makes ordinary distillation ineffective.
2Manufacturing precision
If water extraction is used to separate methyl iodide from acetaldehyde, then acetaldehyde is extracted into aqueous phase, but methyl iodide is also undesirably extracted into aqueous phase causing loss of methyl iodide
Solution Approach 1:
The extraction process is optimized by controlling local conditions in different phases. The aqueous phase is designed to have high affinity for acetaldehyde while the organic phase retains methyl iodide. By adjusting parameters such as water-to-feed ratio, temperature, and phase separation conditions, the extraction selectively targets acetaldehyde in the aqueous phase while minimizing methyl iodide co-extraction, thus achieving high acetaldehyde removal efficiency with minimal methyl iodide loss.
3Manufacturing precision
If distillation of water is performed to separate acetaldehyde, then a large amount of energy is required due to large latent heat of evaporation of water
Solution Approach 1:
Instead of using energy-intensive distillation to separate acetaldehyde from water, the invention extracts acetaldehyde into the aqueous phase using water as an extractive solvent. This extraction process occurs at or near ambient temperatures, avoiding the need to vaporize large amounts of water. The acetaldehyde is removed from the organic phase through liquid-liquid extraction, eliminating the requirement for high-energy distillation operations while achieving the desired separation purity.
4Use of energy by moving object
If the number of distillation stages is increased to reduce energy consumption, then separation efficiency improves, but device complexity and capital cost increase
Solution Approach 1:
Water serves as an intermediary extractive solvent that enables separation in a single or few extraction stages rather than requiring multiple distillation stages. The extractive distillation or liquid-liquid extraction process using water as mediator achieves high separation efficiency in one pass by exploiting the selective distribution of acetaldehyde between phases, thereby reducing both the number of stages needed and the associated capital costs while maintaining low energy consumption.
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 enables the efficient separation of PRCs and methyl iodide with a compact apparatus, reducing energy consumption and the number of distillation stages, resulting in higher-quality acetic acid production.
Implementation Method 1
distilling the mixed composition in a distillation step to form an overhead stream, a side-cut stream, and a lower stream; in a distillation column of the distillation step, an extractant which can extract PRC's preferentially to methyl iodide is added to a concentration zone of PRC's and methyl iodide
Implementation Method 2
an extractant which can extract PRC's preferentially to methyl iodide is added to a concentration zone of PRC's and methyl iodide; transferring acetaldehyde from the methyl iodide phase to the aqueous phase
Data Source
AI summary
A process for producing acetic acid while efficiently separating permanganate reducing compounds (PRC's) and methyl iodide is provided. PRC's are separated or removed from a mixed composition (3A) containing PRC's and methyl iodide by distilling the mixed composition in a distillation step (5) to form an overhead stream (5A), a side-cut stream (5B), and a lower stream (5C). In a distillation column of the distillation step (5), an extractant (e.g., water) extracting PRC's preferentially to methyl iodide is added to a concentration zone in which PRC's and methyl iodide are concentrated, and an extraction mixture falling from the concentration zone is withdrawn as the side-cut stream (5B).