Propylene Rectification Tower for DME Removal in Polypropylene Production
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Solution Overview
Problem
Current methods for producing polypropylene from oxygenate-to-olefins processes face challenges in maximizing propylene yield while minimizing investment and operating costs, as increasing propylene yield often results in higher dimethyl ether (DME) production, making it difficult to produce propylene suitable for polymerization at a reasonable cost without introducing DME to the polymerization reactor.
Innovation Solution
A method involving contacting an oxygenate stream with a molecular sieve to form an olefin stream, followed by rectification in a propylene rectification tower with fewer than 200 theoretical stages to separate DME, propane, and propylene, and then processing the streams through a condenser and splitter to produce a propylene-rich stream for polymerization, while recirculating DME to maintain low oxygenate levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the yield of propylene product is increased in the OTO process, then the productivity is improved, but the amount of DME as a side product increases, making it difficult to produce propylene suitable for polymerization
Solution Approach 1:
The patent extracts and removes DME from the propylene product stream through a dedicated DME removal unit positioned between the OTO reactor and the propylene separation train. This extraction approach allows high propylene yield to be maintained while selectively removing the harmful DME component that would otherwise contaminate the polymerization feed
Solution Approach 2:
The patent introduces an intermediary DME removal unit that acts as a mediator between the OTO reactor and the propylene separation system. This intermediary unit processes the crude propylene stream to eliminate DME before the propylene is sent to polymerization, thereby decoupling the propylene production rate from the DME contamination level
2Object-generated harmful factors
If conventional methods are used to isolate DME from olefins streams, then the DME can be removed, but the investment and operating costs increase
Solution Approach 1:
The patent employs parameter changes in the form of temperature-swing adsorption or membrane separation technology to remove DME from the propylene stream. These methods operate under optimized temperature and pressure conditions that selectively capture DME while allowing propylene to pass through, achieving effective DME removal with simpler and more cost-effective equipment compared to conventional distillation trains
3Ease of manufacture
If a simple combination of known elements is used, then the process is easier to implement, but it is not sufficient to produce propylene suitable for polymerization at a reasonable cost with low DME levels
Solution Approach 1:
The patent segments the propylene purification process into distinct functional units: (1) DME removal unit to eliminate oxygenates, (2) propylene separation train to isolate propylene from other olefins, and (3) optional DME recycle unit. This segmentation allows each unit to be optimized for its specific function while maintaining overall process simplicity and achieving the required propylene purity for polymerization
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 allows for the production of intermediate-grade propylene suitable for polypropylene production with reduced investment costs and minimal DME presence, optimizing the separation efficiency and reducing the overall cost of the process.
Implementation Method 1
contacting an oxygenate stream with a molecular sieve to form an olefin stream
Implementation Method 2
introducing the olefin stream into a propylene rectification tower possessing from less than 200 theoretical stages; withdrawing (i) from the propylene rectification bottoms a DME stream, (ii) from a propylene rectification sidestream a propane stream, and (iii) from the propylene rectification overhead a gas stream comprising propane and propylene
Implementation Method 3
introducing the gas stream to a condenser to accumulate a propylene-rich stream
Data Source
Figure 1~2
AI summary
Provided is a method of producing polypropylene comprising contacting an oxygenate stream with a molecular sieve to form an olefin stream comprising propane, propylene and dimethylether; introducing the olefin stream into a propylene rectification tower possessing from less than 200 theoretical stages; withdrawing from the propylene rectification tower a bottom stream comprising dimethylether, a sidestream comprising propane, and an overhead stream comprising propane and propylene; introducing the overhead to a condenser to accumulate a propylene-rich stream; passing the propylene-rich stream to a splitter to produce (i) a first propylene stream that is introduced into a polypropylene reactor to contact a polyolefin catalyst, and (ii) a second propylene stream that is re-introduced into the rectification tower, the first and second propylene streams introduced at a desirable ratio; and recirculating the dimethylether stream to contact the molecular sieve.