Acetic Acid Carbonylation Pre-Flash Vessel Catalyst Stability
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Solution Overview
Problem
Catalyst deactivation and vent losses, particularly carbon monoxide losses, remain inefficiencies in methanol carbonylation systems, and there is a need to reduce capital and operating expenses associated with vent scrubbing and product purification in traditional methanol carbonylation processes.
Innovation Solution
A carbonylation system with staged reaction and pre-flash removal of light ends, where the reaction mixture is processed in a pre-flasher/post reactor vessel at a reduced pressure, consuming methyl acetate and enriching the acetic acid while diminishing methyl iodide and methyl acetate levels, thereby reducing the load on subsequent purification columns and enhancing catalyst stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If traditional methanol carbonylation processes are used with high pressure absorbers and multiple purification columns, then product purification is achieved, but capital and operating expenses increase and carbon monoxide losses occur
Solution Approach 1:
The patent applies preliminary action by introducing a pre-flash vessel before the main purification train that removes light ends (methyl iodide and methyl acetate) in advance. This preliminary removal of impurities before the main purification process reduces the load on subsequent columns and minimizes carbon monoxide losses that would otherwise occur during extensive purification operations.
Solution Approach 2:
The patent extracts and removes light ends (methyl iodide and methyl acetate) from the reaction mixture in the pre-flash vessel before the mixture enters the main purification train. This extraction of harmful components early in the process prevents them from interfering with subsequent purification steps and reduces carbon monoxide losses.
2Ease of manufacture
If acetic acid is used as scrubber solvent in high pressure and low pressure absorbers, then vent streams are scrubbed, but the acid must be stripped of light ends in additional purification columns increasing capital and operating expenses
Solution Approach 1:
The pre-flash vessel performs preliminary removal of light ends from vent streams before they enter the acetic acid scrubber. By removing methyl iodide and methyl acetate in advance, the scrubber solvent requires less intensive stripping operations, eliminating or reducing the need for additional high-pressure absorbers and purification columns.
Solution Approach 2:
The patent converts the potentially harmful light ends (methyl iodide and methyl acetate) into a benefit by using them as indicators for the pre-flash removal process. Their removal in the pre-flash vessel protects the acetic acid scrubber from becoming saturated with these components, thereby reducing the need for extensive stripping operations and additional equipment.
3Ease of manufacture
If methanol is used as scrubber solvent, then noncondensibles are scrubbed, but the scrubber solvent residual stream requires additional processing and mixing with pure methanol
Solution Approach 1:
The pre-flash vessel performs preliminary removal of light ends from the vent streams before they reach the methanol scrubber. This preliminary action reduces the contamination load on the methanol solvent, minimizing the amount of residual stream that requires additional processing and mixing with fresh methanol.
4Productivity
If catalyst is exposed to carbon monoxide depleted or low pressure environments in the flasher, then flashing removes crude product, but catalyst deactivation occurs
Solution Approach 1:
The pre-flash vessel performs preliminary removal of light ends and methyl acetate before the reaction mixture enters the low-pressure flasher. By removing these components in advance at higher pressure, the catalyst is less exposed to carbon monoxide-depleted environments during the main flashing operation, thereby reducing catalyst deactivation while maintaining effective product separation.
Solution Approach 2:
The pre-flash vessel acts as a cushioning stage that protects the catalyst from the harsh low-pressure, carbon monoxide-depleted environment of the main flasher. By performing partial flashing and light end removal in advance at higher pressure, the catalyst experiences a more gradual transition to low pressure, reducing deactivation while still achieving effective product separation.
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 increases productivity, de-bottlenecks the light ends column, and improves carbon monoxide efficiency, reducing operating costs by minimizing the need for high-pressure absorbers and optimizing catalyst stability.
Implementation Method 1
catalytically reacting methanol or a reactive derivative thereof with carbon monoxide in the presence of a homogeneous Group VIII metal catalyst and a methyl iodide promoter
Implementation Method 2
venting light ends in the pre-flasher vessel and concurrently consuming methyl acetate in the pre-flasher/post reactor vessel
Implementation Method 3
flashed a crude acetic acid stream from the reaction mixture. The flash vessel is operated at a pressure below the pressure of the pre-flasher/post reactor vessel
Data Source
AI summary
A method of making acetic acid includes: (a) catalytically reacting methanol or a reactive derivative thereof with carbon monoxide in the presence of a homogeneous Group VIII metal catalyst and a methyl iodide promoter in a reactor vessel in a liquid reaction mixture including acetic acid, water, methyl acetate, methyl iodide and homogeneous catalyst, the reactor vessel being operated at a reactor pressure; (b) withdrawing reaction mixture from the reaction vessel and feeding the withdrawn reaction mixture along with additional carbon monoxide to a pre-flasher/post reactor vessel operated at a pressure below the reactor vessel pressure; (c) venting light ends in the pre-flasher vessel and concurrently consuming methyl acetate in the pre-flasher/post reactor vessel. Reaction conditions, residence time and composition are controlled in the pre-flasher/post reactor vessel such that a pre-flash mixture is enriched in acetic acid and diminished in methyl iodide and methyl acetate in the pre-flasher/post reactor vessel. From the pre-flasher/post reaction vessel the acetic acid enriched mixture is (d) withdrawn and fed to a flash vessel.