Decarbonisation Technology August 2022 issue

systems alone, this specification is unattainable and requires the addition of an adsorbent guard bed. This raises the question: can adsorption alone be applied for CO₂ dehydration, eliminating the many complexities of TEG systems? Adsorption dehydration options Solid adsorption-based systems are another proven dehydration technology. These materials include activated alumina, molecular sieves, and silica gels. This article will closely compare activated alumina to amorphous aluminosilicate gel, two products in the BASF portfolio sold as F200 and Sorbead, respectively. BASF has decades of experience designing temperature swing adsorption units with these materials, so it is well positioned to offer the optimum solution for each project. The adsorption options available share some common benefits, including no maintenance between turnaround, quick start-up times (0-5 hours), and easily achieved pipeline glycol specifications. Also, the solid nature of these adsorbents eliminates the safety and storage concerns associated with the liquid chemical nature of TEG systems. While adsorption in general has many benefits, each of these materials has unique properties, making some better suited for CO₂ dehydration than others. Molecular sieves have traditionally been employed in the dehydration of natural gas for liquefied natural gas (LNG) production. BASF supplies molecular sieves into numerous natural gas dehydration applications annually, but as much as these materials are well suited for the dehydration of natural gas, they are unsuited for that of CO₂. Molecular sieves are very unstable in acidic environments, like wet CO₂. To account for molecular sieve degradation in acidic conditions, much larger bed sizes are required, along with more difficult and frequent bed changeouts. Additionally, when compared to the other adsorbent solutions available, they have some of the highest regeneration temperatures (≥250°C depending on the specific material chosen) and thus the highest energy requirement. For these reasons, molecular sieves are not recommended for CCS applications. Activated alumina maintains many of the same pitfalls as molecular sieves, although to a lesser degree. They are not acid resistant, leading to shorter bed lifetimes, larger bed sizes, and the corresponding higher Capex

and Opex costs. They also require a higher heat of regeneration. While these pitfalls exist, in some instances activated alumina may still be a good option for CCS dehydration applications. BASF is a leading supplier of aluminosilicate gels, having served natural gas and CO₂ treatment applications with the Sorbead portfolio for over 60 years. While other standard silica gel options with cheaper initial material costs are available on the market, these materials do not exhibit all the same benefits, robustness, and lifetime cost savings. Sorbead aluminosilicate gel is made using a specialised production process that imparts increased durability and adsorbent surface area, resulting in an overall higher-performing material. There is a clear benefit to using an advanced aluminosilicate for CO 2 dehydration (see Table 1 ), as these provide the best combination of material properties for CO 2 dehydration. Sorbead aluminosilicate – the best adsorbent for CO₂ dehydration The acidic chemistry of an aluminosilicate makes it the only adsorbent stable to the acidic conditions in CO₂ dehydration. This stability ensures long lifetimes of 5-10 years and bed sizes up to 75% smaller than activated alumina. This further results in lower Capex costs (smaller bed sizes) and lower Opex costs (fewer bed changeouts, lower heat duty, less regeneration gas). While the acidic nature of Figure 1 Sorbead is the ideal adsorbent for CO₂ dehydration