Process Intensification in Gas–Liquid Mass Transfer by Modification of Reactor Design: A Review

Abstract

Increasing greenhouse gas (GHG) emissions is a major issue facing the global environment and the public. This increase is due to accelerating industrial development and rising emissions of gases, including carbon dioxide (CO 2 ), methane (CH 4 ), and nitrogen oxides (NO x ). These gases are believed to be the source of global warming. [1] According to the Intergovernmental Panel on Climate Change (IPCC), total GHGs need to be reduced by 50-80% by 2050 to avoid extreme consequences. [2] Therefore, gas removal needs to be improved. In the late 1970s, a new method was developed, namely, carbon capture and storage (CCS), as an effective way to avoid CO 2 emissions into the atmosphere. In addition, H 2 absorption is required for microbial conversion to CH 4 . H 2 -liquid mass transfer limits the rate of biomethanation reactions due to the low H 2 distribution in solution that limits its solubility and, thus, its availability to methanogens. The development of biomethanation technology needs to focus on H 2 -liquid mass transfer to develop large biomethanation capacity. Therefore, an in-depth understanding of process design and operating conditions that affect H 2liquid mass transfer is necessary. In addition to, methane is the main component of natural gas and shale gas, accounting for 90% of the total abundance. [3,4] Thus, as one of the most widely used high-energy resources on earth, methane is considered as the next generation of carbon feedstock. Nevertheless, methane is a nonpolar gas, and its low solubility in solution hinders efficient mass transfer. Therefore, it is necessary to overcome these limitations to achieve high methane conversion. [5][6][7] To the best of our knowledge, as low-cost green oxidant, oxygen is widely used in microbial growth and product synthesis. [8] However, oxygen is less soluble in aqueous solution. At 294.15 K and 1 bar, the dissolved oxygen content of pure water is only 9.2 mg L À1 . [9] Therefore, it is a great challenge for reactor engineering to improve the oxygen transfer capacity of the equipment to meet the needs of the reaction.Ozonation is one of the most widely used advanced oxidation processes (AOPs), which has been applied to treat various types of organic wastewater. However, the equilibrium concentration and mass transfer efficiency of ozone in water are limited, leading to the poor ozone utilization. [10] Therefore, it is necessary to find effective methods to enhance ozone-liquid mass transfer.As deduced in the above finding, new approaches are needed to deal with the pointed out these limitations.Process reinforcement is an important part of the varied aspects of chemical science and engineering. [11] It allows for resource maximization and does more with less. [12] As shown in Table 1, the more and the less were summarized. [13] Mass transfer between gas and liquid is widely used in chemical engineering. It is closely correlated with reaction engineering, separation engineering, and many branches of chemical engineering. The rate and efficiency of mass transfer de...