Process Operability Analysis of Membrane-Based Direct Air Capture for Low-Purity CO₂ Production

Area of Science:

• Environmental Science
• Chemical Engineering
• Materials Science

Background:

• Anthropogenic CO2 emissions are a primary driver of climate change.
• Developing negative emission technologies is crucial for achieving net-zero targets.
• Direct air capture (DAC) technologies are needed to remove existing CO2 from the atmosphere.

Purpose of the Study:

• To investigate the feasibility of membrane-based direct air capture (m-DAC) for producing low-purity CO2.
• To model and analyze a two-stage hollow fiber membrane module process for CO2 capture.
• To determine the operability and potential applications of low-purity CO2 streams from m-DAC.

Main Methods:

• A two-stage hollow fiber membrane module process was designed and modeled using AVEVA Process Simulation.
• Operability analysis was conducted by varying membrane surface area and performance metrics.
• A facilitated transport membrane with high CO2/N2 separation performance was used as the base case.

Main Results:

• The m-DAC process can produce a low-purity (≈5%) CO2 permeate stream suitable for applications like algae growth and enhanced oil recovery.
• Membrane intrinsic performances significantly impact CO2 purity, recovery, and energy consumption.
• The first module's area is dominant; increasing the second module's area negatively impacts energy consumption without purity gains.
• The m-DAC process is suitable for small-capacity systems (0.1-1 Mt/year).

Conclusions:

• Membrane-based DAC is a viable technology for specific applications and scales.
• The energy source for the DAC process is critical; renewable energy is required for it to qualify as a negative emission technology.
• Further analysis of CO2 capture capacity is important for large-scale implementation.