Linear Pentene Metathesis for Propylene Production
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Solution Overview
Problem
Conventional metathesis reactors inefficiently convert isopentenes to propylene due to non-productive reactions and the difficulty in separating linear pentenes from isopentenes, resulting in lower propylene productivity compared to linear pentene metathesis.
Innovation Solution
A process involving an etherification reactor to convert isopentenes to tertiary amyl alkyl ether, a decomposition reactor to recover isopentenes, a skeletal isomerization reactor to convert isopentenes to linear pentenes, and a metathesis reactor to convert linear pentenes with ethylene to propylene, enhancing separation and conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If isopentenes are fed to a conventional metathesis reactor, then metathesis reaction occurs, but propylene productivity is low (only one mole of propylene per mole of isopentene)
Solution Approach 1:
The patent extracts isopentenes from the mixed C5 stream before metathesis by converting them to TAME (tertiary amyl methyl ether) through etherification with methanol. This separation removes the low-productivity isopentenes from the feed to the metathesis reactor, allowing only linear pentenes to undergo metathesis and produce propylene at high productivity (three moles per mole of linear pentene).
Solution Approach 2:
The patent performs preliminary conversion of isopentenes to TAME before the metathesis step. This preliminary action prevents isopentenes from entering the metathesis reactor and undergoing non-productive reactions, thereby preparing the feed stream to maximize propylene productivity in the subsequent metathesis step.
2Ease of manufacture
If simple distillation is used to separate linear pentenes from isopentenes, then separation is attempted, but separation is not easily achievable due to staggered boiling points
Solution Approach 1:
The patent changes the chemical parameter of isopentenes by converting them into a different compound (TAME) with significantly different physical properties, specifically boiling point. TAME boils at 83°C while linear pentenes boil at 30-37°C, creating a large boiling point difference that enables easy and precise separation by distillation, overcoming the limitation of the original staggered boiling points.
3Productivity
If mixed pentenes (isopentenes and linear pentenes) are directly processed by metathesis, then the process is simple, but propylene production is limited by the high isopentene content (40-60 wt%)
Solution Approach 1:
The patent segments the mixed C5 feed stream into two separate streams: one containing linear pentenes (sent directly to metathesis) and another containing isopentenes (converted to TAME, separated, then decomposed). This segmentation allows each stream to be processed optimally - linear pentenes for high-productivity metathesis and isopentenes through a separate conversion-decomposition pathway - thereby maximizing overall propylene production despite the added process steps.
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 process increases propylene production by up to 36% to 67% compared to traditional metathesis of mixed pentenes, effectively utilizing linear pentenes for propylene production while minimizing carbon loss to side products.
Implementation Method 1
reacting the alcohol and isopentenes in the etherification reactor to convert at least a portion of the isopentenes to tertiary amyl alkyl ether
Implementation Method 2
reacting the tertiary amyl alkyl ether in the decomposition reactor to convert at least a portion of the tertiary amyl alkyl ether to alcohol and isopentenes
Implementation Method 3
feeding the isopentene fraction to a skeletal isomerization reactor to convert at least a portion of the isopentenes to linear pentenes
Implementation Method 4
feeding ethylene and the linear pentene fraction to a metathesis reactor to convert at least a portion of the linear pentenes and ethylene to propylene
Implementation Method 5
separating the linear pentenes from the tertiary amyl alkyl ether to recover a linear pentene fraction and a tertiary amyl alkyl ether fraction
Data Source
AI summary
Mixed pentenes may be converted to propylene by feeding an alcohol, linear pentenes, and isopentenes to an etherification reactor. The alcohol and isopentenes may be reacted in the etherification reactor to convert isopentenes to tertiary amyl alkyl ether, which may be separated from the linear pentenes, recovered as a linear pentene fraction. The tertiary amyl alkyl ether may be fed to a decomposition reactor to convert at least a portion of the tertiary amyl alkyl ether to alcohol and isopentenes. The alcohol and isopentenes may then be separated to recover an isopentene fraction and an alcohol fraction. The isopentene fraction is then fed to a skeletal isomerization reactor to convert at least a portion of the isopentenes to linear pentenes, the effluent from which may be recycled to the etherification reactor. Ethylene and the linear pentene fraction may then be fed to a metathesis reactor to produce propylene.