Crosslinked Siloxane Membranes for C3+/CH4 Separation

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Solution Overview

Problem

Conventional polydimethylsiloxane (PDMS)-based membranes exhibit low selectivities for C3+ hydrocarbons to methane due to high degrees of swelling under hydrocarbon-rich natural gas feed streams, necessitating more efficient membranes with higher C3+/CH4 selectivity for enhanced C3+ hydrocarbon recovery.

Innovation Solution

Crosslinked siloxane composite membranes with rigid or bulky substituent groups, such as phenyl or trifluoropropyl groups, are used to enhance the selectivity and permeability of C3+ hydrocarbons over methane, prepared via chemical crosslinking with silanol functional polymers on a polyacrylonitrile support.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If conventional PDMS membranes with flexible dimethylsiloxane chains are used, then high permeability is achieved, but C3+/CH4 selectivity is low due to high degrees of swelling under hydrocarbon-rich natural gas feed streams

Engineering Contradiction:

ImprovepermeabilityVSAvoidC3+/CH4 selectivity

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent modifies the siloxane membrane by changing the chemical structure parameters - replacing some methyl groups with rigid aromatic groups (phenyl, naphthyl) or bulky alkyl groups. This structural parameter change reduces the membrane's swelling degree under hydrocarbon feed streams while maintaining high permeability, thereby improving C3+/CH4 selectivity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates composite siloxane membranes by combining flexible dimethylsiloxane segments with rigid aromatic segments (such as diphenylsiloxane, dinaphthylsiloxane) or bulky alkyl segments in a copolymer structure. This composite approach maintains the high permeability of flexible chains while the rigid/bulky segments reduce swelling and enhance selectivity

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If rigid or bulky substituent groups are introduced to increase C3+/CH4 selectivity, then separation performance is improved, but membrane permeability may be reduced

Engineering Contradiction:

ImproveC3+/CH4 selectivityVSAvoidpermeability

Core Design Contradiction:

Manufacturing precisionVSQuantity of substance

Solution Approach 1:

The patent applies local quality by introducing rigid aromatic groups or bulky alkyl groups at specific positions within the siloxane chain structure, rather than uniformly throughout. The repeat unit structure allows strategic placement of these groups to optimize the balance between selectivity enhancement and permeability maintenance

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent optimizes the concentration parameters of rigid/bulky groups by controlling the molar ratios in the copolymerization process. By adjusting the feed ratios of different siloxane monomers and controlling polymerization conditions, the patent achieves optimal group concentration that maximizes selectivity while preserving sufficient permeability

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

The crosslinked siloxane membranes demonstrate improved C3+/CH4 selectivity and reduced swelling, achieving enhanced C3+ hydrocarbon recovery from natural gas under industrially relevant conditions, reducing capital and operating expenditures.

Implementation Method 1

The high permeability of PDMS allows for the simultaneous rejection of N2 and for the concentration of C3+ hydrocarbons in membrane permeate streams

Methodology Applied

Scientific EffectPermeation: Permeation

Implementation Method 2

conventional PDMS membranes with flexible dimethylsiloxane (Me2SiO)x chains exhibit low selectivities of C3+ to methane (for example, C3+/CH4 selectivity) due to high degrees of swelling under hydrocarbon-rich natural gas feed streams

Methodology Applied

Scientific EffectSwelling:

Data Source

PatentUS12516192B2Modified siloxane rubbery composite membranes for C<sub>3+</sub> heavy hydrocarbon separation

Publication Date: 2026.01.06 SAUDI ARABIAN OIL CO

AI summary

This disclosure relates to siloxane membrane materials and polymeric membranes containing the siloxane membrane materials. The siloxane membrane materials are crosslinked with silanol polymers having backbones functionalized with bulky or rigid substituents. This disclosure also relates to methods of using the membranes for natural gas liquid recovery, such as removal and recovery of C3+ hydrocarbons from natural gas.