Multimodal Polyolefin Process Vacuum Flash Drum Hydrogen Removal
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Solution Overview
Problem
Existing processes face challenges in producing multimodal polyolefin polymers with a large difference in molecular weights between the first and second polymerization reactors, often resulting in high wax content and inefficiencies due to the need for multiple flash drums.
Innovation Solution
A process involving a first polymerization reactor where polyolefin polymers are produced in the presence of hydrogen, followed by transferring the suspension to a flash drum operated at low pressure (<0.1 MPa) to vaporize and remove hydrogen, resulting in a hydrogen-depleted suspension fed to a second reactor, using a hydrocarbon mixture as a solvent and diluent to separate waxes and achieve a broader molecular weight distribution with a single flash drum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple flash drums are used to remove hydrogen from the first reactor suspension, then hydrogen removal efficiency is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple flash drum functions into a single flash drum by operating it at very low pressure (vacuum conditions, P≤0.1 MPa). This single drum performs the hydrogen removal function that would otherwise require multiple drums operating at different pressure stages, thereby reducing device complexity while maintaining hydrogen removal efficiency.
Solution Approach 2:
The patent changes the operating pressure parameter of the flash drum to extremely low values (vacuum conditions, P≤0.1 MPa). This parameter change enables a single flash drum to achieve the hydrogen removal effectiveness that would traditionally require multiple drums operating at progressively lower pressures, thus resolving the contradiction between removal efficiency and device complexity.
2Device complexity
If conventional flash drum pressure (0.1-1 MPa) is used, then process simplicity is maintained, but molecular weight difference between reactors is insufficient
Solution Approach 1:
The patent changes the pressure parameter from conventional ranges (0.1-1 MPa) to vacuum conditions (P≤0.1 MPa). This parameter change creates sufficiently different effective hydrogen concentrations between the two reactors, enabling proper molecular weight distribution control while maintaining process simplicity through a single flash drum.
3Productivity
If hydrogen concentration is not sufficiently reduced between reactors, then process simplicity is maintained, but molecular weight difference and multimodal distribution are insufficient
Solution Approach 1:
The patent utilizes the phase transition of hydrogen from dissolved state in the polymer suspension to gas phase by operating the flash drum at vacuum conditions. This phase transition enables efficient hydrogen removal and creates the necessary hydrogen concentration difference between reactors for proper multimodal molecular weight distribution.
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 a larger difference in molecular weights of polymers produced in the two reactors with reduced wax content and is cost-efficient by using a single flash drum, enhancing the production of multimodal polyolefin polymers.
Implementation Method 1
vaporizing a part of the suspension medium in the flash drum to obtain a hydrogen-depleted suspension
Implementation Method 2
the pressure of the flash drum is less than 0.1 MPa
Data Source
AI summary
The invention relates to a process for the preparation of a multimodal polyolefin polymer in a first polymerization reactor and a second polymerization reactor connected in series, wherein a first polyolefin polymer is prepared in the first polymerization reactor in suspension in the presence of hydrogen and a second polyolefin polymer is prepared in the second polymerization reactor in the presence of a lower concentration of hydrogen than in the first polymerization reactor, the process comprising: a) withdrawing a suspension of solid polyolefin particles in a suspension medium from the first polymerization reactor, wherein the suspension medium comprises hydrogen and a hydrocarbon mixture having an initial boiling point of at least 50° C. and a final boiling point of at most 120° C.; b) feeding the suspension to a flash drum having a pressure controlled by a vacuum pump, wherein the pressure of the flash drum is less than 0.1 MPa; c) vaporizing a part of the suspension medium in the flash drum to obtain a hydrogen-depleted suspension and d) withdrawing the hydrogen-depleted suspension from the flash drum and feeding it to the second polymerization reactor.