Catalyst Mixing Device for MTO Process Uniformity
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Solution Overview
Problem
Existing methods for mixing particulate catalysts in the Methanol to Olefins (MTO) process face challenges in achieving quick and uniform mixing, leading to low selectivity of ethylene and propylene due to catalyst deactivation and carbon-based loss, particularly coking issues.
Innovation Solution
A mixing device comprising a riser and an outer casing vessel, where the first and second particulate catalysts are loaded and mixed within a mixing zone vessel, with specific structural and compositional differences, and a Peclet number and mean square error criteria to ensure uniform distribution, allowing for efficient mixing and regeneration of catalysts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional mixing methods are used for particulate catalysts, then the mixing process is simple, but the mixing speed is slow and uniformity is poor
Solution Approach 1:
The mixing device is segmented into multiple functional zones: a reaction zone where catalysts are generated and partially mixed, and a dedicated mixing zone where final uniform mixing occurs. This segmentation allows each zone to perform its specific function optimally, achieving fast and uniform mixing without requiring complex overall device design.
Solution Approach 2:
The riser is nested within the outer casing vessel, with both structures containing their respective catalysts and flowing into the mixing zone. This nested configuration allows compact arrangement of multiple catalyst delivery systems while maintaining their individual functionality, achieving efficient mixing without excessive device complexity.
2Reliability
If regenerated catalyst is not rapidly mixed with coked-deactivated catalyst, then catalyst regeneration is efficient, but selectivity to olefins decreases due to coking
Solution Approach 1:
Catalysts are pre-generated and pre-positioned in their respective risers before entering the mixing zone. The regenerated catalyst is prepared in advance in one riser while coked catalyst is prepared in another, allowing rapid mixing to occur immediately upon entering the mixing zone, minimizing the time loss between regeneration and reactivation.
Solution Approach 2:
Gas flow is used to transport both regenerated and coked catalysts through their respective risers and into the mixing zone. This pneumatic transport system enables continuous, rapid mixing of catalysts without mechanical intervention, maintaining catalyst activity while minimizing mixing time.
3Productivity
If methanol conversion is attempted in premixing area or initial contacting zone, then catalyst mixing occurs, but carbon-based loss increases and olefin selectivity decreases
Solution Approach 1:
Different zones are assigned different functions with appropriate local conditions: the reaction zone maintains conditions suitable for methanol conversion and olefin production, while the mixing zone is specifically designed for catalyst mixing without attempting methanol conversion. This local quality differentiation prevents carbon-based loss in the mixing zone while maintaining high olefin selectivity in the reaction zone.
Solution Approach 2:
The catalyst mixing function is extracted from the reaction zone and placed in a separate mixing zone. This separation ensures that methanol conversion and olefin production occur only in the reaction zone under optimal conditions, while catalyst mixing occurs in the mixing zone without competing reactions, eliminating carbon-based loss associated with premature conversion attempts.
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
The solution enables high selectivity and yield of ethylene and propylene, with a total yield of 90.4 wt% calculated as carbon, by ensuring uniform mixing and regeneration of catalysts, thereby overcoming the limitations of prior art.
Implementation Method 1
the bottom of the riser is provided with a riser feed inlet for a first lifting medium, which is used for delivering upwards the first particulate catalyst loaded in the riser
Implementation Method 2
at least a part of the upper portion of the riser and at least a part of the upper portion of the outer casing vessel both being located inside a mixing zone vessel
Data Source
AI summary
A mixing device for mixing at least two particulate materials has a first riser used for loading first particles and a second riser surrounding and being coaxial with the riser and used for loading second particles. The upper part of the first riser extending beyond the top of the second riser. At least a part of the upper part of the first riser and at least a part of the upper part of the second riser being located inside a mixing zone container, such that the first and second particles are delivered to the inside of the mixing zone container by means of the first and second risers respectively and mixed.