Silica Removal Filter Using Charged and Asymmetric Membranes

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Solution Overview

Problem

Commercially available media for removing silica from ultra-pure water used in semiconductor manufacturing exhibit low flow rates and undesirable retention levels of colloidal and particulate silica, leading to defects in semiconductor devices.

Innovation Solution

A filter comprising a microporous cationically charged membrane and a porous asymmetric membrane with decreasing pore sizes, where the porous asymmetric membrane contacts the downstream surface of the microporous cationically charged membrane, effectively removing colloidal and particulate silica while maintaining desirable flow rates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If commercially available media are used to remove silica from ultra pure water, then silica removal is achieved, but flow rates are low and retention levels of colloidal and particulate silica are undesirable

Engineering Contradiction:

Improvesilica removal effectivenessVSAvoidflow rate

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The filter is divided into two distinct membrane layers: a microporous cationically charged membrane for removing dissolved and colloidal silica, and a porous asymmetric membrane for removing particulate silica. Each layer targets specific silica forms, enabling effective overall removal while maintaining higher flow rates through optimized pore structures in each segment.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite membrane structure combining two different membrane types with complementary properties. The cationically charged membrane provides chemical attraction for silica removal, while the asymmetric porous membrane provides physical filtration. This composite approach achieves superior silica removal across all forms (dissolved, colloidal, particulate) while maintaining desirable flow rates.

Inventive Principle:

Principle #40Composite materials

2Reliability

If commercially available media are used to remove silica from ultra pure water, then silica removal is achieved, but retention levels of colloidal and particulate silica are undesirable

Engineering Contradiction:

Improvesilica removal effectivenessVSAvoidretention level

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Each membrane layer is designed with specific local properties optimized for its function: the cationically charged membrane has positive charge sites localized to attract and retain colloidal silica through electrostatic interaction, while the asymmetric porous membrane has a specific pore size distribution localized to physically trap particulate silica. This local optimization of properties ensures high retention levels for each silica form.

Inventive Principle:

Principle #3Local quality

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 filter achieves a high colloidal silica log retention value of at least log 2 (99%) for particles between 10 nm to 12 nm, ensuring high purity of ultra-pure water and efficient removal of silica and hard particles.

Implementation Method 1

microporous cationically charged membrane

Methodology Applied

Scientific EffectElectrostatic attraction: Electrostatics

Implementation Method 2

microporous cationically charged membrane

Methodology Applied

Scientific EffectIon exchange: Ion Exchange

Implementation Method 3

porous asymmetric membrane having decreasing pore sizes

Methodology Applied

Scientific EffectPhysical filtration: Filter (physical)

Implementation Method 4

porous asymmetric membrane having decreasing pore sizes in a direction from the first surface and the upstream portion to the downstream portion and the second surface

Methodology Applied

Scientific EffectSize exclusion: Molecular Sieve

Data Source

PatentUS11241657B2Filter for removing silica from ultra pure water and method of use

Publication Date: 2022.02.08 PALL CORP

AI summary

A method for removing silica from ultra pure water (UPW) comprises passing UPW through a filter comprising a microporous cationically charged membrane having an upstream surface and a downstream surface; and a porous asymmetric membrane having a first surface and an upstream portion and a downstream portion and a second surface, and a bulk between the first surface and the second surface including the upstream portion and the downstream portion, the porous asymmetric membrane having decreasing pore sizes in a direction from the first surface and the upstream portion to the downstream portion and the second surface, the second surface comprising a skin having a nanoporous average pore size, wherein the first surface of the porous asymmetric membrane contacts the downstream surface of the microporous cationically charged membrane; the method including passing the UPW through the microporous cationically charged membrane before passing the UPW through the porous asymmetric membrane.