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Membrane Degassing Technology O2 and CO2

3M Liqui-Cel Membrane Degassing Technology

Liqui-Cel Membrane Degassing Technology, efficiently removes (or adds) dissolved gases from (to) liquids. These membrane devices have displaced older technologies such as vacuum towers, forced draft deaerators, and oxygen scavengers in the last 25 years. Typical applications are O2 and CO2 removal from water.

Liqui-Cel Schematic
Cross section of a 3M Liqui-Cel Degassing Module

In addition Liqui-Cel membranes are also capable of adding or removing nitrogen, adding carbonation, humidifying gases, removing VOCs, debubbling inks, and controlling gases for improved ultrasonics.

Liqui-Cel membrane contactors can remove oxygen O2 down to 1 ppb or remove CO2 down to 0.5 ppm at the outlet with proper system design.

X40 membrane (tighter) is used for O2 removal. X50 membrane (looser) is used for CO2 removal.

How does Liqui-Cel Membrane Degassing work?

Henry’s Law for Gases and Liquids

3m Liqui-Cel membranes are hollow fiber, hydrophobic, and porous. A sweep gas or vacuum is applied in the lumen of the fibers, and fluid flows outside of the fiber. Henry’s Law (see diagram) defines the equilibrium between gases in contact with a liquid and the dissolved gas in the liquid. The gases permeate the membrane pores, but water does not.

For O2 removal, pure N2 (99.9999%) is combined with vacuum to drive the dissolved O2 (DO) out of the water, down to about 1 ppb.

For CO2 removal, filtered air (low CO2) is pulled through the fibers, and aqueous CO2 crosses the membrane and is swept away, down to about 1 ppm.

The devices (membrane contactors) efficiently allow contact between the liquid and gas/vacuum so that Henry’s Law can work properly to achieve an equilibrium.

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Technical: How to Optimize pH for best CO2 removal by GTM

CO2 exists in 3 different species in water depending on pH. It is CO2 at low pH, bicarbonate (HCO3-) at intermediate (neutral pH), and carbonate (CO3-2) at high pH.

CO2 Species vs pH

For effective CO2 removal using Liqui-Cel, the CO2 should all be the “Dissolved CO2” gas, so the pH should be under about 6.5.

For effective CO2 removal using RO, the CO2 should be all carbonate (CO3-2) or bicarbonate (HCO3-), so the pH should be above about 7.5. pH for 2-pass RO with interstage caustic: the 2nd stage should be ideally pH 8.4-8.7 for best results.

Application: Boiler feedwater DO removal and corrosion control

Liqui-Cel membranes control corrosion in boilers, piping, and system components. By removing dissolved oxygen (DO) oxidation is reduced thereby protecting against costly maintenance. In addition, these devices are chemical-free to operate, an advantage for operations, cost, and environmental impact.

For these reasons, Liqui-Cel membranes have become the technology of choice to control dissolved gas removal in many industries. These types of installations are particularly popular in the power generation, semiconductor, chemical, and other processing industries.

Application: Water degassing for microelectronics, semiconductor wafers, and flat panel displays

Liqui-Cels have become the degassing standard in the semiconductor and flat panel industries because they are clean, have very low extractables, and do not negatively impact the water quality. Since Liqui-Cel membrane devices are small, compact, and can easily remove dissolved oxygen down to 1 ppb and dissolved carbon dioxide down to 1 ppm, it is a match that makes perfect sense.

Ultrapure water rinses process materials off semiconductor wafers and flat panel displays in a multi-step rinse process. Gases present in the water can deposit on to the wafer surface and cause defects. Hence degassing using clean membrane technology is critical to quality.

Application: Degassing for Ultrapure Water (using EDI technology)

EDI (electrodeionization) is a common technology in the semiconductor and pharmaceutical industries. EDI technologies operate more efficiently when dissolved CO2 is removed from the water. CO2 cannot load the EDI resin, and the EDI operates more efficiently. This reduces the number of EDI stacks required because they operate more efficiently.

Ultrapure water also needs dissolved oxygen (DO) removal, done with Liqui-Cel X40 membranes.

Application: Pharmaceutical Water degassing

Purified (high-purity) water is an integral part of processing pharmaceuticals. Pharmaceutical plants require a continuous supply of USP compliant water with a conductivity of <1.3µS/cm. This level of purity has to be constant and maintained throughout processing. CO2 removal is the optimal means to achieve this level of purity.

Liqui-Cel membranes are an efficient, chemical-free means to accomplish carbon dioxide removal. Liqui-Cel systems have the benefit of being closed systems that do not introduce environmental contaminants into the water like an old forced draft deaerator does.

Chemical dosing with NaOH was also commonly used to control CO2 in plant water for many years. However, environmental pressures, safety concerns, and cost has pushed the industry away from chemicals.

As with the microelectronics industry, RO and GTM and EDI have become common technologies in the pharmaceutical industry. These technologies efficiently remove the dissolved CO2 from the water.