Circulating Fluidized Bed Reactor for Polyolefin Production
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Solution Overview
Problem
Traditional gas-phase fluidized-bed reactors face challenges in producing bimodal and multimodal polyolefin products with broad molecular weight distributions due to their well-mixed nature, requiring specialized catalysts or multiple reactors, and struggle with agglomeration and temperature control in the down-flowing moving bed section.
Innovation Solution
A continuous gas-phase circulating bed reactor with a riser and downer section, each operating under fast-fluidization or dilute-phase pneumatic conveying regimes, allows for independent control of gas compositions and recirculation of catalyst and polymer, enabling the production of a diverse range of polyolefin products without specialized catalysts or multiple reactors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a traditional gas-phase fluidized-bed reactor with well-mixed CSTR nature is used, then the reactor structure is simple and cost-competitive, but it cannot produce bimodal and multimodal products or products with broad molecular weight distributions
Solution Approach 1:
The reactor is divided into multiple zones (e.g., riser section, down-flowing section, fluidized bed section) that operate under different flow regimes and conditions. Each zone can independently produce polymer with different molecular weight characteristics, enabling bimodal and multimodal product distributions without requiring multiple separate reactors.
Solution Approach 2:
Different zones within the reactor are assigned different local conditions (gas velocity, residence time, catalyst concentration) optimized for specific polymerization functions. The riser section operates in dilute-phase regime for one type of polymerization, while the down-flowing section operates in dense-phase regime for another, allowing simultaneous production of polymers with different properties in a single reactor system.
2Adaptability or versatility
If a down-flowing dense-phase moving bed section is used to achieve product differentiation, then product diversity is improved, but agglomeration problems and temperature control difficulties occur
Solution Approach 1:
The reactor operates with dynamic gas-solid flow patterns where particles continuously circulate between different zones. The gas velocity and flow regime are dynamically adjusted in each section to maintain optimal conditions - dilute-phase in the riser to prevent agglomeration, and controlled dense-phase in the down-flowing section for product differentiation while managing temperature through enhanced gas-solids contact.
Solution Approach 2:
Pneumatic conveying principles are applied to maintain particles in suspension and control their movement through the reactor. Gas flow rates and distributions are carefully controlled to provide adequate fluidization in the riser section, preventing particle agglomeration while enabling continuous circulation and heat transfer throughout the system.
3Adaptability or versatility
If multiple reactors in series or specialized catalysts are used to produce bimodal and multimodal products, then product complexity is improved, but the process becomes more complex and costly
Solution Approach 1:
A single reactor system is designed to perform multiple polymerization functions simultaneously - producing different molecular weight polymers, different copolymer compositions, and different particle morphologies within one vessel. This multi-functional approach eliminates the need for multiple specialized reactors while achieving the same product diversity.
Solution Approach 2:
Instead of adding more reactors in series (one-dimensional approach), the invention adds spatial and operational dimensions within a single reactor by creating multiple zones with different flow regimes, gas compositions, and residence times. This allows simultaneous production of multiple polymer types in parallel within the same physical space.
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 configuration allows for the production of unimodal, bimodal, and multimodal polymers with controlled molecular weight distributions, reducing agglomeration and temperature uniformity issues, and enhancing catalyst productivity and product uniformity by segregating larger polymer particles.
Implementation Method 1
a riser for contacting a catalyst and a first gas composition including an olefin as a fast-fluidized bed to form a polyolefin
Implementation Method 2
operating in a dilute-phase fast fluidization regime
Implementation Method 3
the fluidization of the polymeric solids is provided by a circulating mixture of gases including one or more monomers
Implementation Method 4
vapor phase polymerization is a common process, widely used for the production of polyolefins
Implementation Method 5
contacting a catalyst and a first gas composition including an olefin to form a polyolefin
Data Source
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AI summary
A continuous gas phase circulating bed reactor, including: a riser for contacting a catalyst and a first gas composition comprising an olefin to form a polyolefin under fast-fluidization regime or a dilute-phase pneumatic conveying regime conditions; a downer for contacting the catalyst and a second gas composition comprising an olefin to form additional polyolefin under fast fluidization regime or a dilute-phase pneumatic conveying regime conditions; and a transport section for conveying at least a portion of the catalyst, polyolefin, and additional polyolefin from the downer to the riser. Also disclosed is a polymerization process using such a circulating bed reactor.