Membrane Separation for Permanent Gas Recovery from Polymerization Offgas

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Solution Overview

Problem

The existing methods for recovering C2+ hydrocarbons using pressure swing adsorption often result in a high-pressure mixture of permanent gas components that is primarily utilized thermally for combustion, limiting the use spectrum of the high-gas product.

Innovation Solution

The method involves a membrane separation of the stream of matter after C2+ fraction removal, enriching the retentate with a substance that permeates less efficiently and the permeate with a substance that permeates more efficiently, allowing for recycling of the retentate at the same pressure level and utilization of the permeate for thermal purposes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If pressure swing adsorption is used to remove C2+ fraction from the stream, then the C2+ fraction is effectively removed, but the high-pressure product is limited to thermal utilization only

Engineering Contradiction:

Improveuse spectrum of high-gas productVSAvoidcomplexity of separation system

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent divides the gas mixture into two separate streams using membrane separation: a retentate stream enriched in nitrogen and a permeate stream enriched in hydrogen. This segmentation allows each stream to be directed to appropriate utilization pathways, extending the use spectrum from单一 thermal combustion to multiple applications including process gas recycling and hydrogen recovery.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The high-pressure gas product from pressure swing adsorption is processed through membrane separation to produce two valuable streams with different functions: nitrogen-rich retentate for process gas replacement and hydrogen-rich permeate for energy production or chemical synthesis. This multi-functionality transforms a single-purpose thermal fuel into multiple valuable products.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If membrane separation is added after pressure swing adsorption, then the use spectrum of gas products is extended, but the device complexity increases

Engineering Contradiction:

Improveuse spectrum of high-gas productVSAvoidcomplexity of separation system

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent combines pressure swing adsorption and membrane separation into an integrated two-stage process. The pressure swing adsorption unit removes C2+ hydrocarbons while the membrane separation unit simultaneously separates permanent gases into nitrogen-rich and hydrogen-rich streams. This merging of functions in series achieves multiple separation objectives without requiring parallel independent systems.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

Instead of discarding or merely combusting the nitrogen-rich gas stream, the patent recovers and redirects it for useful applications such as replacing process gases in polymerization reactors. The hydrogen-rich stream is similarly recovered for energy production or chemical synthesis, transforming waste streams into valuable resources.

Inventive Principle:

Principle #34Discarding and recovering

3Loss of substance

If the retentate is recycled into the polymerization process, then fresh nitrogen consumption is reduced, but pressure maintenance requires additional energy input

Engineering Contradiction:

Improvefresh nitrogen consumptionVSAvoidenergy for pressure compensation

Core Design Contradiction:

Loss of substanceVSUse of energy by moving object

Solution Approach 1:

The retentate stream is recycled back into the polymerization process at high pressure, where it serves as a process gas replacement. The system uses the existing high pressure from the pressure swing adsorption unit to minimize compression requirements, and only compensates for pressure drops in recirculation lines using small fans rather than large compressors.

Inventive Principle:

Principle #25Self-service

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 extends the use spectrum of the high-gas product by enabling the recycling of nitrogen-rich retentate into polymerization processes and thermal utilization of hydrogen-rich permeate, reducing the need for fresh nitrogen and minimizing flared gas, while maintaining the pressure level of the cleaned stream.

Implementation Method 1

the stream of matter, after removal of the C2+ fraction, is separated by means of a membrane into a retentate and a permeate, the retentate being rich in the first substance, and the permeate by contrast being rich in the second substance

Methodology Applied

Scientific EffectPermeation: Permeation

Implementation Method 2

the stream of matter is subjected to a pressure swing adsorption to remove the C2+ fraction

Methodology Applied

Scientific EffectAdsorption: Adsorption

Data Source

PatentUS10092876B2Recovery of gases, especially permanent gases, from streams of matter, especially from offgas streams from polymerizations

Publication Date: 2018.10.09 LINDE AG

AI summary

A method of cleaning a stream of matter that includes a C2+ fraction and a first gaseous substance and a second gaseous substance. The stream of matter is subjected to a pressure swing adsorption to remove the C2+ fraction by means of a membrane to obtain a retentate and a permeate. The first substance is enriched in retentate and depleted in permeate and the second substance is depleted in retentate and enriched in permeate.