C4 Hydrocarbon Purification by Aqueous Extraction for Catalyst Protection
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Solution Overview
Problem
Existing plants for reactive separation of isobutene from C4-hydrocarbon mixtures face challenges due to catalyst deactivation, necessitating frequent reactor shutdowns and additional costs, as they are not robust against catalyst deactivation over time.
Innovation Solution
A process involving pre-treatment of the raw C4-hydrocarbon mixture by countercurrent extraction with an aqueous stream to reduce catalyst deactivators like amines, ammonia, and dimethylformamide to at most 1 ppm, followed by etherification, ether cleavage, and distillation to obtain high-purity isobutene.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the raw C4-hydrocarbon mixture is directly fed to the etherification reactor without pre-treatment, then the process is simpler and requires fewer equipment, but the catalyst deactivates quickly due to polar nitrogen compounds, requiring frequent shutdowns and replacement
Solution Approach 1:
The patent applies preliminary action by implementing a pre-treatment step before the etherification reactor. An extraction column is used to remove polar nitrogen compounds (catalyst deactivators) from the C4-hydrocarbon mixture before it enters the etherification reactor. This preliminary removal action prevents catalyst deactivation, extending catalyst lifetime and reducing shutdowns, while adding only one extraction unit to the process.
2Productivity
If the catalyst activity is monitored continuously and the reactor is shut down when activity falls below a limit, then the catalyst performance is maintained, but the productivity decreases due to frequent shutdowns and catalyst replacement
Solution Approach 1:
The extraction column performs preliminary removal of catalyst deactivators before the mixture enters the etherification reactor. This preliminary action ensures that the catalyst operates in a clean environment, maintaining stable catalyst activity over extended periods and enabling continuous operation without frequent shutdowns for catalyst replacement.
Solution Approach 2:
The patent applies the extraction principle by using an extraction column to separate and remove polar nitrogen compounds (catalyst deactivators) from the C4-hydrocarbon mixture. This extraction action takes out the harmful components that cause catalyst deactivation, allowing the catalyst to maintain its activity stability and enabling prolonged continuous operation.
3Adaptability or versatility
If the feed contains higher and variable amounts of catalyst deactivators, then the process can handle more challenging feeds, but the catalyst deactivates faster, requiring more frequent shutdowns
Solution Approach 1:
The extraction column continuously removes polar nitrogen compounds from the C4-hydrocarbon feed stream, regardless of their concentration or variability. This extraction action isolates the catalyst from deactivators, allowing the process to handle feeds with higher and variable amounts of catalyst deactivators without compromising catalyst lifetime or requiring frequent shutdowns.
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 significantly increases catalyst lifetime, allowing for more flexible operation with feeds containing higher and variable catalyst deactivators, reducing shutdowns and costs while maintaining high isobutene purity.
Implementation Method 1
contacting the raw C4-hydrocarbon mixture in countercurrent flow with an aqueous stream in an extraction unit yielding an intermediate C4-hydrocarbon mixture
Implementation Method 2
reacting the mixture with a primary alcohol in the presence of an acidic ion exchange resin to form an alkyl tert-butyl ether
Implementation Method 3
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 4
feeding the bottom product to an ether cleavage unit to decompose the alkyl tert-butyl ether to obtain isobutene and primary alcohol
Implementation Method 5
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 purifying a raw C4-hydrocarbon mixture comprising at least 2% by weight of isobutene, at least 23% by weight of butenes other than isobutene, less than 3% by weight of butadienes, at least 1.5 ppm by weight of a catalyst deactivator selected from the group of polar nitrogen containing compounds and mixtures thereof, wherein the sum of all components in the C4-hydrocarbon mixture is 100% by weight, the process comprising the steps of (d) contacting the raw C4-hydrocarbon mixture in countercurrent flow with an aqueous stream in an extraction unit yielding an intermediate C4-hydrocarbon mixture, (e) withdrawing at least part of the intermediate C4-hydrocarbon mixture from the extraction unit, and (f) dewatering the withdrawn intermediate C4-hydrocarbon mixture to obtain a purified C4-hydrocarbon mixture having a content of the catalyst deactivator of at most 1 ppm by weight. The invention further relates to a process for obtaining isobutene from an isobutene containing C4-hydrocarbon mixture in a plant comprising an etherification unit, a first distillation unit, an ether cleavage unit and a second distillation unit.