Methanol-to-Propylene Process with Extractive Distillation
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Solution Overview
Problem
The existing MTP process for producing propylene requires very pure oxygenates, leading to high energy costs due to expensive purification methods, and using less pure oxygenates results in lower propylene yield and complex downstream purification.
Innovation Solution
A process involving heterogeneously catalyzed conversion of methanol followed by distillation to separate C3- and C4+ fractions, with extractive distillation to maximize separation efficiency and reduce methanol pre-purification needs, allowing the use of methanol with lower purity without reducing propylene yield and improving energy balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If very pure oxygenates are used as starting substances in the MTP process, then the propylene yield is maintained, but the energy costs and purification expenses increase significantly
Solution Approach 1:
The patent extracts and removes higher olefins (C5+) from the reaction product stream using a dedicated separation column. By extracting these higher olefins as a separate stream, the system prevents them from interfering with the propylene purification process, allowing for energy-efficient separation of propylene from the remaining stream without requiring extensive purification of the feed methanol
Solution Approach 2:
The patent segments the product separation into distinct stages: first separating C5+ higher olefins in one column, then separating propylene (C3) in another column. This segmentation allows each column to be optimized for its specific separation task, reducing the overall energy requirement compared to a single comprehensive separation column that would need to handle all components simultaneously
2Use of energy by stationary object
If less pure oxygenates are used to reduce pre-purification costs, then energy balance improves, but the propylene yield decreases and downstream purification becomes more complex
Solution Approach 1:
The patent introduces a first separation column as an intermediary step between the reactor and the propylene separation column. This intermediate column removes higher olefins (C5+) from the product stream, acting as a mediator that protects the downstream propylene separation system from complex mixtures. This allows the system to tolerate less pure feedstock while maintaining efficient propylene recovery
Solution Approach 2:
The patent performs preliminary separation of higher olefins (C5+) in the first column before the main propylene separation occurs. This preliminary action simplifies the composition entering the second column, enabling efficient propylene separation even when the feed methanol contains impurities, thus maintaining propylene yield without requiring high feed purity
3Manufacturing precision
If three distillation columns are used for methanol pre-purification, then the required purity specification (AA) is achieved, but the equipment complexity and investment costs increase
Solution Approach 1:
Instead of purifying methanol before the reactor (conventional approach), the patent inverts the strategy by tolerating less pure methanol feed and performing separation after the reactor. The reaction process itself and the subsequent product separation columns achieve the necessary purification, eliminating the need for three pre-purification distillation columns
Solution Approach 2:
The system uses the reaction process and product separation to achieve the purification function that would otherwise require dedicated pre-purification equipment. The separation columns process the reaction product stream to recover pure propylene, and the system self-regulates to maintain product quality without requiring highly purified feed methanol
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 enables the use of methanol with lower purity, reducing energy consumption and eliminating the need for expensive pre-purification, while maintaining propylene yield and product spectrum integrity.
Implementation Method 1
By a heterogeneously catalyzed reaction in at least one reactor, the educt mixture is converted to a reaction mixture comprising low-molecular olefins and gasoline hydrocarbons
Implementation Method 2
distillation for separating the C 3- fraction from a bottom product
Implementation Method 3
distillation for separating a stream containing the C 4+ fraction and dimethyl ether from a stream containing water and methanol
Implementation Method 4
distillation for separating the C 3- fraction (process step (ii)) is carried out as extractive distillation, as the separation efficiency of the column thus is maximized
Data Source
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AI summary
The present invention relates to a process for the production of olefins from oxygenates, comprising the following steps: (i) heterogeneously catalyzed conversion of methanol to a product stream containing a C3- and a C4+ fraction, (ii) distillation of the product stream for separating the C3- fraction from a bottom product, and (iii) distillation of the bottom product for separating a stream containing the C4+ fraction and dimethyl ether from a stream containing water and methanol. Furthermore, the invention also comprises a plant for carrying out this process.