Membrane gas absorption processes

Jansen AE, Klaassen R, Feron PHM, Hanemaaijer JA, and ter Meulen BPh. Membrane gas absorption processes in environmental applications. In Crespo JG and Boddekar KW, Eds. Membrane Processes in Separation and Purification. Dordrecht Kluwer Academic, 1994 pp. 343-356. 

Membrane Processes in Separation and Purification published in 1993, contains chapters on pervaporation, facilitated transport membrane processes, membrane gas absorption processes, hollow fiber contactors, membrane reactors, and the preparation and application of inorganic membranes. In addition to an introductory chapter by the editors. Polymeric... 

In the present study, we fabricated hollow fiber membrane modules and performed experiments at several conditions. The energy consumption of this process is compared to those of conventional gas absorption processes and membrane gas separation processes. 

Klaassen R and Jansen AE. Achieving fine gas desulphurization with membrane gas absorption. Filtration Separation 2003 40 26. Mavroudi M, Kaldis SP, and Sakellaropoulos GP. Reduction of CO2 emissions by a membrane contacting process. Fuel 2003 82 2153. Sengupta A and Sirkar KK. Analysis and design of membrane permeators for gas separation. In Noble RD and Stem SA, eds. Membrane Separation Technology. Principles and Applications, Amsterdam Elsevier Science, 1995, p. 498. 

Qi and Cussler [26] investigated the removal of ammonia by H2SO4. H2SO4 being a strong acid, the mass resistance offered by the membrane controlled the process. An industrial membrane gas absorption unit for ammonia recovery from an ammonia containing off-gas stream produced in a dyes intermediates production plant has been installed by TNO. The membrane plant is able to remove 99.9% of ammonia and produces aqueous solutions of 27% ammonia that can be reused in the dyes process [38]. 

Membrane gas absorption (MGA) is a gas-liquid contacting operation [1,2,24,25]. The key element in the process is a microporous hydrophobic HFM. The process is illustrated in Figure 4.3 for removal of component X from a gas stream. The gas stream is fed along one side of the membrane where an absorption liquid is flowing at the other side of the membrane. The hydrophobic membrane wall keeps gas phase and absorption liquid separated from each other. The absorption liquid is chosen in such a way that it has a high affinity for component X. Component X will now diffuse through the gas-filled pores of the membrane to the other side of the membrane where it is absorbed in a liquid phase. Absorption in the liquid phase takes place either by physical absorption or by a chemical reaction. This determines the selectivity of the process. The membrane used... 

Figure 1. Principe of membrane gas absorption (MGA) and Membrane Gas Desorption (MGD) process for CO2 removal.

Membrane gas separation processes can be improved by using multistage separation as depicted in Figure 3.3.68 for natural gas treatment with a two-stage membrane for the separation of CO2. Traditionally, amine absorption is used to separate CO2 from natural gas. Membrane plants require less operator attention and smaller units may even operate unattended. Hence, membrane separations are favored in remote locations like offshore platforms. 

We have been studying the novel process for CO2 separation named membrane/absorption hybrid method. The advantages of this process are that high gas permeance and selectivity were obtained. The concept of this process is shown in Fig. 1. Both feed gas and absorbent solution are supplied to the inside of hollow fibers. While Ae liquid flows upward inside the hollow fibers, absorbent solution absorbs CO2 selectively and it becomes a rich solution. Most of rich solution permeates the membrane to the permeate side maintained at reduced pressure, where it liberated CO2 to become a lean solution. Compared to a conventional gas absorption... 

The great advantage of the absorption process over the synthesis of a by-product was its direct recovery of chlorine. Such a process or one that uses chlorine in another on-site process with steady demand is the ideal. More vigorous liquefaction is one approach to reducing the amount of chlorine value to be disposed of, and it has usually been chosen as the substitute for absorption. In this chapter, we discuss the use of gas-separation membranes as an alternative. 

Besides absorption processes, adsorption processes, cryogenic separation or membrane separation can be applied. Adsorption processes are based on the physical attachment and bonding of components from the gas mixture on the surface of solid sorbents. As with absorption a distinction can be made between physical and chemical adsorption the first one is referred to as pressure-swing adsorption (PSA), where... 

Another type of gas exchange process, developed to the pilot plant stage, is separation of gaseous olefin/paraffin mixtures by absorption of the olefin into silver nitrate solution. This process is related to the separation of olefin/paraffin mixtures by facilitated transport membranes described in Chapter 11. A membrane contactor provides a gas-liquid interface for gas absorption to take place a flow schematic of the process is shown in Figure 13.11 [28,29], The olefin/paraffin gas mixture is circulated on the outside of a hollow fiber membrane contactor, while a 1-5 M silver nitrate solution is circulated countercurrently down the fiber bores. Hydrophilic hollow fiber membranes, which are wetted by the aqueous silver nitrate solution, are used. 

In particular, liquid-liquid extractions, wastewater treatments, gas absorption and stripping, membrane, and osmotic distillation, are the processes more studied. For example, the VOCs removal, the extraction of aroma compounds and metal ions, the concentration of aqueous solutions, the acid-gases removal, the bubble-free oxygenation/ozonation, have been successfully carried out by using membrane contactors [1, 2]. 

Process Descriptions Selectively permeable membranes have an increasingly wide range of uses and configurations as the need for more advanced pollution control systems are required. There are four major types of membrane systems (1) pervaporation (2) reverse osmosis (RO) (3) gas absorption and (4) gas adsorption. Only membrane pervaporation is currently commercialized. 

The membrane in a contactor acts as a passive barrier and as a means of bringing two immiscible fluid phases (such as gas and hquid, or an aqueous hquid and an organic hquid, etc.) in contact with each other without dispersion. The phase interface is immobilized at the membrane pore surface, with the pore volume occupied by one of the two fluid phases that are in contact. Since it enables the phases to come in direct contact, the membrane contactor functions as a continuous-contact mass transfer device, such as a packed tower. However, there is no need to physically disperse one phase into the other, or to separate the phases after separation is completed. Several conventional chemical engineering separation processes that are based on mass exchange between phases (e.g., gas absorption, gas stripping, hquid-hquid extraction, etc.) can therefore be carried out in membrane contactors. 

Mass transfer plays an important role in many industrial processes. A group of operations for separating the components of mixtures is based on the transfer of material from one homogeneous phase to another. These methods—covered by the term mass-transfer operations—include such techniques as distillation, gas absorption, humidification, liquid extraction, adsorption, membrane separations, and others. The driving force for transfer in these operations is a concentration gradient, much as a temperature gradient provides the driving force for heat transfer. 

Rate processes, on the other hand, are limited by the rate of mass transfer of individual components from one phase into another under the influence of physical shmuli. Concentrahon gradients are the most common stimuli, but temperature, pressure, or external force fields can also cause mass transfer. One mass-transfer-based process is gas absorption, a process by which a vapor is removed from its mixture with an inert gas by means of a liquid in which it is soluble. Desorption, or stripping, on the other hand, is the removal of a volatile gas from a Hquid by means of a gas in which it is soluble. Adsorption consists of the removal of a species from a fluid stream by means of a solid adsorbent with which it has a higher affinity. Ion exchange is similar to adsorption, except that the species removed from solution is replaced with a species from the solid resin matrix so that electroneutrality is maintained. Lastly, membrane separations are based upon differences in permeability (transport through the membrane) due to size and chemical selectivity for the membrane material between components of a feed stream. 

Reversible complexatlon reactions have long been used to improve the speed and selectivity of separation processes, especially those Involving the separation or purification of dilute solutes (j ). Such reactions are the basis of a multitude of separation unit operations Including gas absorption, solvent extraction, and extractive distillation. When a reversible complexatlon reaction (carrier) Is Incorporated into a membrane, the performance of the membrane can be improved through a process known as facilitated transport. In this process, shown schematically In Figure 1, there are two pathways available for the transport of the solute through the membrane. The solute can permeate through the membrane by a solution-diffusion mechanism and by the diffusion of the solute-carrier complex. Other solutes are not bound by the carrier due to the specificity of the complexatlon reaction this Increases the selectivity of the process. 

Zhang HY, Wang R, Liang DT, Tay JH. Theoretical and experimental studies of membrane wetting in the membrane gas-liquid contacting process for CO absorption. J Membr Sci 2008 308 162-170. 

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