Butene Hydroisomerization Side Draw Recycle
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Solution Overview
Problem
Existing methods for double bond hydroisomerization of C4 olefins, such as those used in the production of 2-butene for ethylenolysis to propylene, face inefficiencies due to high hydrogenation of 1-butene to butane and the presence of isobutylene, which reduces propylene selectivity and requires large catalyst quantities and high utility costs.
Innovation Solution
A process involving a fixed bed hydroisomerization reactor with a side draw from a deisobutylenizer tower to recycle 1-butene back to the reactor, combined with multiple hydrogen streams and optional carbon monoxide injection to inhibit hydrogenation reactions, enhances the conversion of 1-butene to 2-butene while minimizing butane production and reducing butadiene content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional fixed bed hydroisomerization is used to convert 1-butene to 2-butene, then some 2-butene is produced, but excessive hydrogenation to butane occurs and large catalyst quantities are required
Solution Approach 1:
The patent applies preliminary action by removing isobutylene from the feed stream before it enters the hydroisomerization reactor. This prevents isobutylene from competing for catalyst sites and causing unwanted hydrogenation reactions. The side draw tower selectively removes isobutylene overhead, ensuring that only purified C4 olefins (1-butene and 2-butene) contact the catalyst, thereby minimizing undesired hydrogenation to butane while maintaining high 2-butene production rates
Solution Approach 2:
The patent implements local quality by creating a specialized zone within the distillation tower where hydroisomerization catalyst is placed in the lower section. This localized catalyst placement ensures that hydroisomerization occurs only in the liquid phase at specific conditions (temperature, pressure, composition) within that zone, while the upper section handles separation. This spatial differentiation of functions optimizes both isobutylene removal and 1-butene to 2-butene conversion while minimizing side reactions
2Adaptability or versatility
If isobutylene is present in the feed stream, then the process can handle broader feed composition, but it reduces propylene selectivity in downstream metathesis and increases utility costs
Solution Approach 1:
The patent applies the extraction principle by using a side draw tower to selectively remove isobutylene from the feed stream before hydroisomerization. The tower exploits the volatility differences among C4 components, with isobutylene being the most volatile and exiting overhead. This extraction of the problematic component (isobutylene) ensures that the hydroisomerization reactor receives a purified feed containing primarily 1-butene and 2-butene, thereby maximizing propylene selectivity in downstream metathesis operations while still allowing the process to accommodate various feed compositions upstream
3Manufacturing precision
If sulfur is added to reduce hydrogenation tendency, then hydroisomerization selectivity improves, but catalyst deactivation and process complexity increase
Solution Approach 1:
The patent uses an intermediary approach by introducing a side draw tower as a mediating unit between the feed stream and the hydroisomerization reactor. Instead of modifying the catalyst with sulfur (which would cause deactivation and complexity), the tower acts as an intermediary that selectively removes isobutylene through physical separation based on volatility differences. This intermediary device protects the catalyst from deactivation while maintaining high hydroisomerization selectivity, avoiding the need for sulfur promotion and its associated drawbacks
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 the yield of 2-butene, reduces catalyst requirements, and minimizes fouling of downstream metathesis catalysts, leading to improved propylene production and reduced utility costs.
Implementation Method 1
double bond hydroisomerization of C4 olefins
Implementation Method 2
contacting the stream with a noble metal catalyst
Implementation Method 3
passing the hydroisomerization effluent through a fractionation column to form a top stream comprising isobutane and isobutylene and a bottoms stream comprising 2-butene
Implementation Method 4
mixing the C4 stream with a first hydrogen stream to form a feed stream, hydroisomerizing the feed stream in the presence of a first hydroisomerization catalyst
Data Source
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AI summary
A process is disclosed for the preferential conversion to 2-butene of a stream containing C4 compounds including 1-butene and 2-butene. The process involves mixing the C4 stream with a first hydrogen stream to form a feed stream, hydroisomerizing the feed stream in the presence of a first hydroisomerization catalyst in order to convert at least a portion of the 1-butene to 2-butene, thereby producing a hydroisomerization effluent, passing the hydroisomerization effluent through a fractionation column to form a top stream comprising isobutane and isobutylene and a bottoms stream comprising 2-butene, withdrawing a recycle stream from said fractionation column at a location above the feed point at which the weight ratio of 1-butene to 2-butene is high, and combining the recycle stream with at least one of the C4 stream and the feed stream upstream from the hydroisomerization catalyst. A corresponding apparatus also is disclosed.