Methanol-to-Olefin Process with Naphthene Recirculation
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Solution Overview
Problem
The existing Methanol-to-Olefin (MTO) process has a propylene yield of about 65%, which is not economically optimal due to the lower market value of by-products and undesired alkylation reactions that decrease propylene yield upon recirculation of aromatics.
Innovation Solution
A process involving the heterogeneously catalyzed conversion of oxygenates to a stream containing propylene, aromatics, and cyclic olefins, followed by hydrogenation of aromatics and cyclic olefins to naphthenes, which are then recirculated to prevent alkylation and enhance propylene yield through olefin interconversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If aromatics are recirculated into the MTP reactor to increase propylene yield, then propylene production is enhanced, but undesired alkylation reactions occur consuming methanol and decreasing overall propylene yield
Solution Approach 1:
The harmful aromatics are extracted and removed from the recirculation stream by subjecting the MTP gasoline to hydroprocessing. This eliminates the alkylation reactions that would otherwise occur when aromatics are recirculated into the MTP reactor, while still allowing the recirculated stream to contribute to propylene production through olefin interconversion reactions.
Solution Approach 2:
A hydroprocessing unit is introduced as an intermediary between the MTP reactor and the recirculation stream. This intermediary unit performs selective hydrogenation of aromatics to remove the harmful components while preserving the olefins needed for propylene production, thus mediating between the conflicting requirements of maximizing propylene yield and preventing harmful alkylation reactions.
2Productivity
If MTP gasoline is subjected to post-processing olefin interconversion to increase propylene yield, then propylene production is enhanced, but the total yield still lies below 70 mol-% due to process limitations
Solution Approach 1:
The recirculation of MTP gasoline and the olefin interconversion processes are merged into a single integrated system. The hydroprocessed recirculation stream is combined with the MTP reactor feed, allowing olefin interconversion to occur within the reactor itself. This integration achieves higher propylene yields while simplifying the overall process structure by eliminating separate post-processing units.
3Ease of operation
If the MTP process operates with standard conditions to maintain simplicity, then process operation is straightforward, but propylene yield is limited to about 65% with significant by-product formation
Solution Approach 1:
The operating parameters of the MTP process are optimized and adjusted to enhance propylene selectivity. By modifying reaction conditions such as temperature, pressure, and catalyst composition, the process achieves propylene yields exceeding 70 mol-% while maintaining operational simplicity. The hydroprocessing unit operates under mild conditions that do not significantly complicate the overall process.
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 yield by converting aromatics and cyclic olefins to naphthenes, which are then recirculated to produce additional propylene without alkylation, resulting in a higher overall propylene yield and improved process economics.
Implementation Method 1
heterogeneously catalyzed conversion of at least one oxygenate to a stream containing propylene, aromatics and cyclic olefins
Implementation Method 2
at least partial hydrogenation of the aromatics and cyclic olefins to naphthenes
Data Source
AI summary
A process for producing olefins from oxygenates includes the following steps:(i) heterogeneously catalyzed conversion of at least one oxygenate to a stream containing propylene, aromatics and cyclic olefins,(ii) at least partial hydrogenation of the aromatics and cyclic olefins to naphthenes, and(iii) at least partial recirculation of the naphthenes into the heterogeneously catalyzed conversion.