Isobutene Recovery From C4 Mixtures With High-Boiling Purge
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Solution Overview
Problem
Existing plants for reactive separation of isobutene from C4-hydrocarbon mixtures face challenges in maintaining stable operation due to internal or external disturbances, such as impurity build-up and variations in feed composition, leading to potential shut-downs.
Innovation Solution
A process involving an etherification unit, a first distillation unit, an ether cleavage unit, and a second distillation unit, with a purge stream removing high-boiling components to prevent impurity accumulation and catalyst deactivation, using acidic catalysts to form and split alkyl tert-butyl ether, and recycling primary alcohol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a closed loop process is used for ether formation and back-splitting with alcohol recycling, then isobutene separation efficiency is improved, but impurity build-up occurs leading to operational instability
Solution Approach 1:
The patent introduces a purge stream that extracts high-boiling impurities from the process system. This purge stream is drawn from the bottom of the distillation column and removes accumulated impurities that would otherwise build up in the closed loop ether formation and cleavage process, thereby maintaining operational stability while preserving separation efficiency.
Solution Approach 2:
The patent modifies the operational parameters by introducing a purge flow rate parameter and adjusting the bottom product withdrawal rate. These parameter changes enable the system to maintain stable operation by controlling impurity accumulation, allowing the closed loop process to continue operating efficiently without shutdowns.
2Device complexity
If high-boiling components are not removed, then process simplicity is maintained, but catalyst deactivation occurs reducing process efficiency
Solution Approach 1:
The patent extracts high-boiling components from the process stream through a purge stream drawn from the bottom of the distillation column. This removes catalyst poisons and impurities that would accumulate and deactivate the acidic catalyst in the etherification unit, thereby maintaining process efficiency without requiring complex additional separation equipment.
Solution Approach 2:
The patent discards high-boiling impurities through the purge stream while recovering and recycling the primary alcohol from the bottom product to the etherification unit. This selective discarding of harmful components while recovering useful materials maintains catalyst activity and process efficiency.
3Ease of operation
If the operational window is narrow, then process control is easier, but frequent shut-downs are required due to disturbances
Solution Approach 1:
The patent implements a feedback mechanism through the purge stream that continuously removes accumulated impurities, preventing disturbances from building up to levels that would require shutdowns. This feedback loop maintains operational stability and extends the operational window between shut-downs.
Solution Approach 2:
The patent takes preliminary action by continuously removing high-boiling impurities through the purge stream before they can accumulate to harmful levels and cause catalyst deactivation or process disturbances. This preventive approach maintains operational stability and reduces the frequency of shut-downs.
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
The process enhances the operational stability and efficiency of isobutene separation by reducing the impact of disturbances and increasing the operational window, allowing for continuous operation and higher isobutene recovery.
Implementation Method 1
reacting the mixture with the primary alcohol in the presence of an acidic catalyst to form the corresponding alkyl tert-butyl ether
Implementation Method 2
distilling the reaction mixture to obtain an overhead product comprising the unconverted hydrocarbons, and a bottom product comprising the alkyl tert-butyl ether
Implementation Method 3
feeding the bottom product to an ether cleavage unit to decompose the alkyl tert-butyl ether to obtain isobutene and primary alcohol
Implementation Method 4
distilling the mixture of isobutene and primary alcohol produced in step (c) to obtain an overhead product comprising isobutene, and a bottom product comprising the primary alcohol
Data Source
AI summary
The invention relates to a process for obtaining isobutene from an isobutene containing C4-hydrocarbon mixture (1) in a plant comprising an etherification unit (3), a first distillation unit (5), an ether cleavage unit (10) and a second distillation unit (12), the process comprising: (a) contacting the C4-hydrocarbon mixture (1) with a primary alcohol (2) and reacting the mixture with the primary alcohol in the presence of an acidic catalyst to form the corresponding alkyl tert-butyl ether in the etherification unit (3); (b) distilling the reaction mixture (4) from the etherification unit (3) in the first distillation unit (5), a C4-hydrocarbon raffinate being withdrawn as the overhead product (6), and the alkyl tert-butyl ether being withdrawn as the bottom product (7); (c) vaporizing the bottom product from the first distillation unit (5) in an evaporator (8) obtaining a vapor stream (9); (d) reacting the vapor stream (9) of step (c) in the presence of an acidic catalyst obtaining isobutene and the primary alcohol as reaction products in the ether cleavage unit (10); (e) distilling the reaction mixture (11) from the ether cleavage unit (10) in the second distillation unit (12), isobutene being withdrawn as the overhead product (13), the primary alcohol and diisobutene being withdrawn as the bottom product (14) and being recycled to the etherification unit (3); wherein a purge stream (15) containing high boiling components with a normal boiling point higher than that of the alkyl tert-butyl ether is withdrawn from the evaporator (8) in step (c).