Acid-resistant zeolite RHO for deep dehydration

Abstract

The identification of dehydration materials with hydrophilic properties that are also acid-resistant is highly significant. In this study, we evaluated the performance of zeolite NaCs-RHO (Si/Al = 3) for deep dehydration in comparison to conventional adsorbents zeolite LTA (Si/Al = 1). Water isotherms were measured over the pressure range of 1 × 10−5 to 0.025 bar and temperatures ranging from 30 to 200 °C. The obtained isotherms were described well by a triple-site Langmuir model. Despite exhibiting lower water capacities than LTA, RHO surprisingly maintains comparable working capacities for pressure swing adsorption (PSA), which may be attributed to the unique phase changes occurring during the hydration. Additionally, RHO allows for lower regeneration temperatures compared to LTA. Process simulation further demonstrated that zeolite RHO can meet stringent specifications for deep dehydration in natural gas to cryogenic processing standards, achieving a water content of 0.008 ppm with a regeneration temperature as low as 130 °C. In contrast, 4A failed to achieve the target, resulting in a high water content of 9.2 ppm under the same conditions. Remarkably, RHO displays superior stability in removing water from acidic gases, experiencing only a 5% water capacity loss after 1000 temperature cycles swung between 35 and 400 °C. In comparsion,3A and 4A showed much higher capacity losses of approximately 20 and 50%, respectively, under the identical conditions. 5A performed even worse, losing 30% of its water capacity within 400 cycles. These findings highlight that zeolite RHO is capable of deep dehydration for acidic gases, providing enhanced stability and reducing operating costs. This is particularly advantageous for rapid cycle operations that require numerous cycles.