Integrated direct air capture and CO₂ utilization of gas fertilizer based on moisture swing adsorption

A new concept of low-cost direct air capture technology integrated with a fertilization system is proposed, as an alternative to the application of air derived CO₂. A moisture swing sorbent can elevate the CO₂ concentration from 400 parts per million (ppm) to several thousand ppm, and this can be used to cultivate plants. Desorption isotherms were determined and are described well by a Langmuir model. The adsorption rate constant and the desorption rate constant were gained at 25 °C, 35 °C, and 45 °C under 1000 ppm concentration of CO₂. In accelerated cultivation experiments, the effects of CO₂ concentration, light intensity, and spectrum on the CO₂ uptake rate of the plants were investigated. A multi-bed desorption system which is capable of providing a continuous and stable CO₂ supply for a greenhouse is demonstrated based on the desorption characteristic and CO₂ uptake feature of plants. An energy and cost assessment for the integrated system was performed and the results indicated that minimum energy requirements and cost estimate of CO₂ are 35.67 kJ/mol and 34.68 USD/t, respectively. This makes direct air capture a competitive and sustainable carbon source for agriculture.