To understand the innovativeness of Wet-TSA adsorption and concentration technology, it's necessary to understand the conventional TSA (Thermal Swing Adsorption) method. The TSA method involves adsorbing gaseous substances onto an adsorbent, then heating and desorbing/recovering the concentrated gaseous substance.

For example:

1. A desiccant dehumidifier produces dry air by adsorbing and removing water vapor from the air using a desiccant (a desiccant). The principle is that the adsorbed water vapor is regenerated by heating and desorbing, allowing for continuous dehumidification.

2. A VOC (Volatile Organic Compound) concentration device removes VOCs evaporated during processes such as painting and printing by adsorbing them onto a VOC adsorbent before exhaust, purifying the air before discharge. The adsorbed VOCs can be desorbed and recovered at, for example, a 10-fold increase in concentration by heating, enabling combustion and detoxification with 10 times the efficiency.

Previously, activated carbon was used, but since the invention of high-silica hydrophobic zeolite, which does not easily adsorb water vapor, it has become possible to supply non-flammable types with different properties, and hydrophobic zeolite is now the mainstream.

However, even with hydrophobic zeolite, the VOC concentration performance decreases when the relative humidity is high because it begins to adsorb water vapor.

　Water vapor exists everywhere on Earth. In the case of dehumidifiers, water vapor is adsorbed and removed, so it's not a problem. However, adsorbing and removing other gaseous substances presents a troublesome issue. When adsorbing other gaseous substances, water vapor is also adsorbed, hindering the adsorption of the other gaseous substances. During desorption, energy is wasted to desorb the adsorbed water vapor, significantly reducing performance. Therefore, researchers have focused their efforts on developing hydrophobic (water vapor-repellent) adsorbents and techniques to remove water vapor beforehand.

Another drawback of the TSA method that I focused on is the heat of adsorption generated when adsorbing gaseous substances. The heat of adsorption of gaseous substances corresponds to the latent heat of evaporation from a liquid and is thermodynamically inevitable. This heat of adsorption raises the temperature of the adsorbent and the gas being treated, significantly reducing the adsorption capacity. This is unavoidable in the TSA method, which utilizes a temperature difference for adsorption and desorption.

When using air as the desorption gas, high-concentration recovery is impossible.

 The superheated steam regeneration method (a method of desorption by heating steam to over 100°C) has been used for some time. VOC recovery methods using activated carbon adsorbents are also known. This method includes a step of cooling the mixed gas desorbed by superheated steam to condense the water vapor, and then separating and recovering the VOCs and condensed water. Since air is not used as the desorption gas, it has the advantage of avoiding ignition of the activated carbon and oxidative decomposition of VOCs. However, if water vapor condenses on the activated carbon, it becomes unusable due to blockage by the condensed water. As a countermeasure, it is necessary to either increase the superheating temperature to prevent condensation or to include a cooling and drying process after desorption.

The wet TSA method has significant differences and advantages. This is because it uses saturated steam at approximately 100°C for desorption. In other words, condensation heat is generated the moment the saturated steam comes into contact with the adsorbent, and CO2 is desorbed. The amount of condensed water is approximately equal to the amount of desorbed CO2 and its latent heat (condensation/evaporation or adsorption/desorption). Therefore, adsorption sites with high desorption rates generate large amounts of condensed water, while sites with low desorption rates generate small amounts. Consequently, flooding due to excessive condensation does not occur.

The superheated steam regeneration method is classified as a general TSA method. This method uses superheated steam instead of air, and condensation does not occur. In the superheated steam regeneration method, water vapor in the adsorbed gas is adsorbed along with CO2, generating heat of adsorption and inhibiting CO2 adsorption. During desorption, water vapor also needs to be desorbed, resulting in a loss of heat of desorption. Condensation is an even more serious problem. Capillary condensation occurs in the gaps of the adsorbent, obstructing the flow of superheated steam and causing desorption failure. In the adsorption zone, condensation obstructs the gas flow, leading to adsorption failure. To avoid these problems, the superheated steam regeneration method incorporates a drying process between the desorption and adsorption processes, resulting in energy loss.