Propylene Copolymer Recovery Process via Stream Segmentation

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Solution Overview

Problem

Existing processes for producing propylene copolymers face challenges in efficiently recovering unreacted propylene monomer, particularly when high concentrations of ethylene comonomer are present, leading to operational troubles and increased costs.

Innovation Solution

The process involves splitting a specific stream from the recovery system into three distinct streams, where one stream is passed to a stripping column, one to the last reaction stage, and one is recycled back into the distillation column, thereby improving the recovery efficiency of propylene without affecting process stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If unreacted propylene monomer is recycled to the reaction stage, then productivity is improved, but ethylene comonomer accumulates causing operational troubles

Engineering Contradiction:

Improverecovery efficiency of propyleneVSAvoidprocess stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The recycling stream is divided into multiple separate recycling streams, each directed to different reaction stages. This segmentation prevents ethylene accumulation in any single stage while maintaining overall propylene recovery efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the recycling stream are directed to different reaction stages based on their local requirements. The first portion is recycled to the first reaction stage while the second portion is recycled to the second reaction stage, optimizing the composition for each specific stage.

Inventive Principle:

Principle #3Local quality

2Reliability

If ethylene comonomer is removed from the recycling stream, then process stability is improved, but additional process steps increase operational costs

Engineering Contradiction:

Improveprocess stabilityVSAvoidnumber of process steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of removing ethylene from the recycling stream through additional separation steps, the solution extracts only the necessary propylene portions and directs them to appropriate reaction stages. This avoids the need for ethylene removal while maintaining process stability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The reaction stages themselves handle the ethylene composition management by receiving controlled portions of the recycling stream. The system uses the inherent reactivity of the reaction stages to consume ethylene at appropriate rates, eliminating the need for external ethylene removal processes.

Inventive Principle:

Principle #25Self-service

3Reliability

If stripping column is used to remove ethylene, then process stability is improved, but energy consumption increases

Engineering Contradiction:

Improveprocess stabilityVSAvoidenergy consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The solution extracts and directs portions of the recycling stream to different reaction stages without using energy-intensive stripping columns. This achieves ethylene management through process integration rather than separate separation operations.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention changes the operational parameters by directing different flows to different stages rather than using thermal separation. This avoids the high energy consumption associated with stripping columns while maintaining process stability.

Inventive Principle:

Principle #35Parameter changes

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 enhances the recovery efficiency of unreacted propylene monomer while reducing operational and installation costs, without requiring additional process steps for ethylene removal.

Implementation Method 1

the distillation column, wherein the condensed overhead stream is fed into the distillation column

Methodology Applied

Scientific EffectDistillation: Distillation

Implementation Method 2

the overhead stream from the distillation column is condensed, thereby producing the condensed overhead stream

Methodology Applied

Scientific EffectCondensation: Condensation

Data Source

PatentUS12291594B2Process for preparing polypropylene with improved recovery

Publication Date: 2025.05.06 BOREALIS AG

AI summary

Described herein is a process for producing a propylene copolymer in at least a pre-polymerization stage, a first and a second reaction stage connected in series with improved monomer recovery, wherein a product stream, comprising a propylene polymer mixture, unreacted propylene, unreacted ethylene and hydrogen, if present, is separated in a separation unit into a first overhead stream and a first bottom product stream, wherein the desired propylene polymer mixture is recovered from the first bottom product stream. The first overhead stream is at least partially condensed, passed to a distillation column and separated into a second overhead stream and a second bottom product stream. The second overhead stream is at least partially condensed and split into three distinct streams, wherein a distillation reflux stream is returned into the distillation column, a first recycle stream is passed to the second reaction stage and a second recycle stream is passed to a stripping column from where a third bottom product stream is withdrawn and at least a part of it is passed to a propylene feed vessel, to the pre-polymerisation stage, to the first reaction stage, or to a combination thereof. Further disclosed is a polymerization unit, particularly suitable for carrying out the inventive process.