Leveraging the phase change of water for energy efficient direct air capture

The deployment of Direct air capture (DAC) remains constrained by high thermal energy requirements during desorption. Conventional solid-sorbent DAC cycles reject the thermal energy invested to heat the contactor mass during cooling. To avoid this energy loss, this work proposes the Latent Heat–Temperature Vacuum Swing Adsorption (LH-TVSA) cycle, which exploits the phase-change enthalpy of H 2 O to heat and cool the contactor. The cycle utilizes steam as a direct heating agent and employs vacuum-induced water desorption for cooling. A key operational challenge of direct steam heating is the bulk liquid accumulation. Introducing a detailed condensation model, this study identifies a clear operational threshold, below which the system is self-regulating and the process can be operated leveraging water adsorption rather than condensation. The process performance is quantified using a first-principles, one-dimensional dynamic column model. An integrated heat-recovery scheme is introduced that extends mechanical vapor recompression (MVR) to the cooling step and utilizes a recovery boiler to capture latent heat from steam breakthrough. The proposed heat recovery configuration effectively reduces the specific exergy demand to 50% across a wide operating window. Such a drastic lowering of the energy penalty highlights the capacity of this cycle to recover and repurpose thermal energy that would otherwise be wasted.