May-2025

Solid-state adsorbent technology for carbon capture

A pathway to low-cost carbon capture from a wide range of sources using an energy-efficient process.

Nigel Campbell and Shane Telfer
Captivate Technology

Article Summary

Carbon capture adoption is recognised by the United Nations Intergovernmental Panel on Climate Change (IPCC) as vital for mitigating harmful carbon dioxide (CO₂) and other greenhouse gas emissions to achieve net-zero goals, particularly in sectors like power generation, cement, steel, and biogas upgrading. Capturing CO₂ not only eliminates emissions from these processes; it also reduces the need for fossil fuel extraction, with fuels and products increasingly being manufactured from CO₂ as a raw material.

Despite the growth of renewable energy, hydrocarbons will continue to be used for the foreseeable future. Hydrocarbons remain necessary for our daily lives and the growing needs of developing countries. Carbon capture plays a key role in mitigating the damaging effects of hydrocarbon combustion and can reduce the need for fossil-sourced hydrocarbons. Increasingly, refineries and petrochemical plants are able to secure carbon feedstock from non-fossil sources.

CO₂ separation is a necessary part of many hydrocarbon processes but has historically had high capital and operating costs. Methods using chemical absorption of CO₂ with solvents have been used for more than a century and involve significant chemical process equipment (such as large processing towers) and massive amounts of heat (commonly fuelled by further fossil fuel combustion and emissions) for CO₂ recovery from the solvent. Naturally occurring CO₂ in fossil gas and CO₂ produced in hydrogen manufacture must be separated, and costs flow through to be included the price of the product.

With the fairly recent adoption of CO₂ separation to reduce the emissions in power generation or product manufacture, chemical absorption methods using solvents have proven to be costly in both economic and environmental terms. This is due to the nature of working with solvents. They are prone to side reactions, are volatile, are difficult to handle, and have environmental concerns. In response, and driven by industry and government commitments to net zero, there is a surge of interest, technology development, and investment in lower-cost methods for CO₂ separation.

One such method used by Captivate Technology employs a solid-state adsorbent that provides a low-cost process for CO₂ separation. Adsorption of CO₂ in Captivate’s process occurs at ambient temperature and pressure, eliminating the need to use energy to compress the entire emissions stream at the start of the process. The emissions stream may only contain in the order of 10% CO₂, depending on the source. In the adsorption process used by Captivate, energy use is significantly less than solvent absorption because energy is only used for the CO₂ fraction of the emissions stream and thermal energy is not used to regenerate the adsorbent.

Such low-cost methods are not just achieving emission reductions; they are spurring a completely new CO₂ feedstock utilisation opportunity as low-cost CO₂ is produced at scale. From being a harmful waste greenhouse gas, new opportunities for harnessing CO₂ are rapidly emerging, and as a consequence an emerging market for CO₂ use is also rapidly growing, for example, in the manufacture of liquid fuels or polymers.

Captivate is an integral part of the emerging circular economy for carbon that obviates the need for the introduction of extra carbon into the biosphere from fossil fuel extraction. CO₂ is captured in waste emission streams and transformed into useful products using established and emerging process technologies, for example, with the addition of hydrogen produced from renewable electricity. As shown in Figure 1, once combusted or used, the CO₂ is captured and transformed again into a useful product, allowing the circular use of CO₂.

Captivate Technology has built a carbon capture capability by developing a porous, solid-state material that is a sponge for CO₂. This novel material, a type of metal-organic framework (MOF), selectively sieves CO₂ from gas streams. The process is continuous and recyclable, generating a steady stream of gaseous CO₂ to be stored or used. The company is rapidly moving to demonstration scale in collaboration with industrial partners and end users.

MOFs are porous, crystalline materials built using metal ions and organic ligands. Certain MOFs have other advantageous properties for carbon capture applications, including high thermal and chemical stabilities, tuneable selectivity, low energy of desorption, and recyclability. MOF-based carbon capture has the potential to deliver significant advantages over incumbent technologies, including increased energy efficiency, lower process complexity, and smaller operating footprints.

Figure 2 shows MUF-16 (MUF = Massey University Framework), a MOF discovered at Massey University, New Zealand, in 2018. The conclusions from de-risking work and a survey of the commercial landscape indicated that the adsorbent is at the forefront of CO₂ capture from various gas emission streams. Captivate Technology was subsequently launched as a start-up in 2023.

MUF-16 is made inexpensively and easily in large quantities using a straightforward process and readily available raw materials. It is then pelletised and deployed in adsorbent columns. Industrial flue gases or biogas are separated into CO₂-rich and CO₂-light streams using vacuum pressure swing adsorption (VPSA).

Its network of pores traps CO₂ via weak interactions, and CO₂ is easily removed once the MUF-16 bed reaches saturation capacity. This regenerates MUF-16 for another round of carbon capture, a process that can be repeated many thousands of times. The rate of CO₂ adsorption is high for the adsorbent which means there are no kinetic limitations on its performance.

Captivate Technology has developed the use of MUF-16 for separating CO₂, determining its performance in real-world scenarios, and scaling up to pilot demonstration at industrial sites across New Zealand. De-risking showed that the combination of selectivity, capacity, tolerance to water and impurities, ease of manufacture, and cost make it an ideal adsorbent for CO₂ capture from flue gas streams. The US Department of Energy targets for purity (95%) and recovery (90%) can be exceeded using a simple step VPSA process, with high productivity and low energy consumption.

Solid-state adsorbent technology for carbon capture requires one-quarter to one-third of the energy needed to capture one tonne of CO₂ using chemical absorption, the incumbent process employed to separate CO₂ from a mixture of gases (Hong, 2022). The combination of MUF-16 in a VPSA process provides very low Capex and Opex costs for industrial users, as demonstrated by the commercial costs of analogous modular carbon capture systems. This opens up carbon capture beyond large-scale applications that require economies of scale, significant Capex, and government support. Captivate Technology provides a pathway for modular carbon capture that can be applied economically on a small or large scale.

In addition, the adsorbent has a low affinity for nitrogen, methane, and other gases, which translates into a high purity for the captured CO₂. Its durability and longevity stem from its tolerance of impurities, such as water vapour, steam, H₂S, NOx, and SOx. It is compatible with well-established engineering processes, such as pressure swing adsorption (PSA).