Absorption Column Scrubbing for Methyl Iodide Without Acetic Acid Freezing
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Solution Overview
Problem
Existing acetic acid production processes face challenges in efficiently scrubbing off-gas streams, particularly during non-steady state conditions, due to the limitations of using methanol as a scrubbing solvent, which can lead to freezing issues with acetic acid and reduced scrubbing efficiency.
Innovation Solution
The process involves scrubbing off-gas streams in an absorption column using methanol at temperatures above the freezing point of acetic acid, allowing for efficient methyl iodide removal, and transitioning between methanol and acetic acid scrubbing solvents by maintaining specific temperature and flow rate ratios to maintain efficient scrubbing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If methanol is used as scrubbing solvent at low temperature, then scrubbing efficiency is improved, but freezing issues occur with acetic acid
Solution Approach 1:
The invention changes the temperature parameter of the methanol scrubbing solvent from conventional low temperatures (e.g., 5°C) to higher temperatures (at least 18°C, preferably at least 20°C). This parameter change resolves the contradiction by maintaining scrubbing efficiency while eliminating freezing issues with acetic acid, which occurs at temperatures below its freezing point of 16.7°C.
2Reliability
If methanol is used as scrubbing solvent, then methyl iodide removal is improved, but acetic acid freezing occurs
Solution Approach 1:
The invention applies parameter changes by raising the methanol temperature to at least 18°C (preferably at least 20°C), which maintains the solvent's ability to absorb methyl iodide while preventing acetic acid from freezing. This resolves the contradiction between effective methyl iodide removal and avoiding acetic acid freezing.
3Adaptability or versatility
If acetic acid is used as scrubbing solvent during start-up and shut down, then operational flexibility is improved, but freezing issues occur at low temperatures
Solution Approach 1:
The invention changes the operating temperature parameter to at least 18°C (preferably at least 20°C) when using acetic acid as scrubbing solvent during start-up and shut down operations. This parameter change maintains operational flexibility while preventing acetic acid freezing, which occurs below 16.7°C.
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 methyl iodide levels in the off-gas to below 500 ppmv, ensuring continuous and efficient scrubbing operations without freezing issues, even during transitions between solvents.
Implementation Method 1
contacting the off-gas stream with the methanol stream; withdrawing a first liquid effluent from the absorption column, the first liquid effluent comprising methanol and methyl iodide
Data Source
AI summary
The present disclosure relates generally to processes for scrubbing an off-gas stream of an acetic acid production unit. In one aspect, a process includes introducing the off-gas stream to the absorption column; introducing to the absorption column, a methanol stream at a first flow rate, the methanol stream having a first temperature at the liquid inlet, the first temperature being at least 18° C. (e.g., at least 20° C., or at least 22° C.); in the absorption column, contacting the off-gas stream with the methanol stream; through a liquid outlet of the one or more liquid outlets, withdrawing a first liquid effluent from the absorption column, the first liquid effluent comprising methanol and methyl iodide; and through the vapour outlet, withdrawing a vapour effluent from the absorption column.