Recent Solutions for Efficient Carbonyl Sulfide Hydrolysis: A Review

Carbonyl sulfide (molecular formula COS) is the most abundant organic sulfur compound present in the atmosphere, and its removal to satisfy the worldwide limitations on emissions of injurious substances is one of the challenging issues in the desulfurization technologies scenario. The hydrolysis of carbonyl sulfide can be addressed as a new frontier in the removal of sulfur compounds. The interest toward this process arose significantly in the past 20 years, mainly because of the new regulations on harmful gases emissions and because of the exploitation of fossil fuels with higher sulfur content. According to the current literature, COS hydrolysis can be performed as low-temperature and high-temperature processes, giving rise to the establishment of different mechanisms and phenomena. Through a detailed analysis of the recent advances in the field, low-temperature hydrolysis was identified as the most promising alternative for the industrial scenario. To overcome the kinetic limitations, the modification of alumina-based catalysts having enhanced porous structures with electron-donating substituents (such as alkaline and alkaline-earth metals) was found particularly effective, since hydrolysis has been identified as a base-catalyzed reaction. In addition, in this process, hydrotalcite and hydrotalcite-like materials find a satisfactory application. Due to the strongly limited kinetics, the adsorption of the components of the reaction mixtures is controlling, and therefore, the most credited reaction mechanism is described through a Langmuir–Hinshelwood model. Despite the strong appeal of the process, industrial applications still involve mainly high-temperature hydrolysis; indeed, most of the recent patents report operating temperatures in the range of 100–300 °C.