Metathesis Feed Pretreatment via Isobutene Dimerization
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Solution Overview
Problem
Current processes for converting olefinic C4 streams into more valuable products, such as propylene and octene, face challenges including the deactivation of metathesis catalysts, low-value byproduct formation, and high capital and operating costs, particularly due to the presence of isobutene and other undesirable compounds.
Innovation Solution
A process that separates an olefinic C4 stream to produce an isobutene-rich stream for dimerization to form octene, which can be used as a motor gasoline alkylate fuel, while combining distillation operations to reduce costs and improve metathesis feed pretreatment efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isobutene is removed from metathesis feed by reacting to form MTBE, ETBE or TBA, then isobutene conversion is greater than 99.9% with negligible butene conversion, but the phase out of MTBE as gasoline additive has reduced the economic advantage and new processes are needed to convert isobutene into more valuable products
Solution Approach 1:
The patent changes the reaction parameters and catalyst system to transform isobutene into high-value oligomers (C8-C12) rather than traditional low-value ethers. By using solid acid catalysts and controlling temperature, pressure, and residence time, the process achieves selective oligomerization that produces premium gasoline blending components, thereby increasing product value while maintaining high conversion efficiency
Solution Approach 2:
The patent converts the harmful effect of isobutene (which causes catalyst deactivation and low-value byproducts in traditional processes) into a beneficial outcome by using it as feedstock for high-value oligomer production. The isobutene that would otherwise be a problem becomes the primary feed for producing premium gasoline blendstocks, transforming a liability into an asset
2Reliability
If the entire C4 stream is subjected to polymerization conditions to remove isobutene, then isobutene is reacted away, but substantial conversion of normal butenes also occurs which reduces overall propylene yield
Solution Approach 1:
The patent applies local quality by creating different reaction zones with distinct catalyst properties. The process uses specific solid acid catalysts with controlled acidity and pore structure that selectively oligomerize isobutene while leaving normal butenes largely unaffected. This localized selectivity within the reaction system allows preferential conversion of isobutene to oligomers while preserving normal butenes for subsequent metathesis to propylene
3Reliability
If separation of isobutene from normal butenes is performed, then isobutene can be selectively processed, but separation is difficult as isobutene boils very close to butene-1
Solution Approach 1:
The patent extracts isobutene from the C4 stream through selective oligomerization rather than physical separation. By using solid acid catalysts that selectively convert isobutene to higher oligomers (C8-C12), the process effectively 'takes out' isobutene through chemical transformation. The resulting oligomers have significantly different boiling points and properties from the remaining C4 stream, making any subsequent separation straightforward and reducing overall process complexity
Solution Approach 2:
The patent uses solid acid catalysts as intermediaries to facilitate selective isobutene conversion. These catalysts act as mediators that selectively interact with isobutene molecules, promoting oligomerization while leaving normal butenes unchanged. This intermediary catalytic step enables effective isobutene removal without requiring complex physical separation equipment
4Adaptability or versatility
If butene-1 is fed to metathesis process, then it reacts with butene-2 to produce pentenes and with itself to produce hexenes, but these are low-value byproducts
Solution Approach 1:
The patent performs preliminary action by converting butene-1 to butene-2 through isomerization before the metathesis reaction. This pre-treatment step ensures that the metathesis feed is rich in butene-2, which produces high-value propylene when reacted with ethylene. By preparing the feedstock in advance through selective isomerization, the process prevents the formation of low-value pentene and hexene byproducts and maximizes propylene yield
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 enhances the overall performance of the metathesis feed pretreatment process, significantly reducing capital and operating costs while achieving high yields of propylene and octene, with the octene product being suitable for use in motor gasoline.
Implementation Method 1
A portion of the isobutene-rich liquid stream is reacted in a dimerization reactor to produce an olefinic stream rich in octene
Implementation Method 2
The dimerization reactor product is distilled to give an overhead stream and a bottoms stream
Data Source
AI summary
Disclosed is a process for integrating a butene dimerization process with a metathesis process to remove isobutene from the feed stream to the metathesis reactor. The isobutene is preferentially dimerized in the dimerization process to leave n-butenes for metathesis with ethylene. An upstream selective hydrogenation process also isomerizes 1-butenes to 2-butenes which is the preferred butene reagent in the metathesis process. A common fractionator column for the dimerization and hydrogenation processes is also described.