APPLICATION FOR SEPARATION MEMBRANE CONTACTOR CO2 Global warming (global warming) is an environmental issue that has a lot of serious attention at this time. The consequences of global warming include increasing the earth's average temperature and sea levels, prolonged droughts, spreading deserts, the heat wave, split up of ecosystems, and reduced agricultural activity. CO2 gas has the greatest contribution to the greenhouse effect, Based on observations made laboratory Mauna Loa, Hawaii, the amount of carbon dioxide in the air is increasing rapidly, from 310 ppmv in 1958 to 370 ppmv in 2001. Increasing the amount of carbon dioxide is mainly caused by the use of fossil fuels, which produce around 24 billion tonnes of CO2 per year, and only half of that can be absorbed by natural processes. CO2 is needed in small amounts for the carbon cycle in nature, as we know plants need CO2 for photosynthesis. However, large amounts of CO2 is also used in the chemical industry. Some applications such as CO2 gas: 1. carbonated Drinks 2. The process of making urea 3. production of ethanol 4. Fire extinguisher 5. dry ice 6. Supercritical carbon dioxide CO2 gas in large quantities can be found in the flue gas generated from industrial equipment such as steam generators, furnaces, blast furnaces in the iron and steel industry, the rotary kiln in cement, and so forth. In principle, the various ways it can be used for the separation of CO2. Selection of suitable method depends on several parameters, such as the concentration of CO2 in the feed stream, the nature of the feed components, pressure and temperature. Selection of CO2 separation process can be seen in Figure-1 below. Based on the diagram, the most widely used process for CO2 separation is absorption of fluid. Absorbent used must have a great capacity for CO2 and must be regenerated. Membrane Contactors for CO2 Separation Membrane Contactors Contactors versus Gas / Liquid In general, the absorption process carried out using gas-liquid contactor. Mass transfer of gas-liquid contactor obtained by direct contact and dispersion of one phase into another phase. Industrial contactors are classified into three categories depending on the phase terdispersinya. 1. Contactor which the liquid flows as a thin film (eg, packed column, disc contactors, etc.). 2. Contactors where the gas is dispersed into the liquid phase (eg, plate column, bubble column, Mechanically Agitated contactors, etc.). 3. Contactors where the liquid is dispersed into the gas phase (eg, spray column, venturi scrubbers, etc.). Unfortunately, conventional contactor has some shortcomings, such as: large energy consumption, difficult to operate due to emerging problems such as frequent flooding, foaming, channeling and entrainment. Limitations of this technology led process becomes less efficient and expensive. picture: Hollow Fiber Membrane Appropriate alternative technology to replace the conventional contactors are hollow fiber membrane contactor. Now the question is, why is that? To answer that, let us review some of the advantages the membrane contactor compared to conventional contactors, among others: 1. Contacts are non-dispersive so not possible flooding and entrainment 2. Gas and liquid flow rate is lower than conventional contactors and can vary freely 3. Contact surface area is very large, the M2/M3 500-1500. This broad is much larger than the surface area of conventional contactors 100-250 M2/M3 4. Hold up low solvent, solvent is very attractive for high 5. Scale-up can be done easily The advantages offered by the size of the membrane contactor contactor has to be much smaller than conventional contactors. picture-3: Non-dispersive contact the Membrane Contactors Hollow Fiber Membrane Contactors This membrane applications using hollow fiber modules. Is it actually hollow fiber? Hollow fiber membranes can be defined as consisting of the capillary tube and shell, just like the heat exchanger. In the membrane contactor, absorbent flows inside the tube while the gas flow will flow in the shell or can be otherwise. Type of membrane that used to be a porous membrane or non-porous membrane. In the non-porous membrane, the membrane serves as a boundary between the gas phase and liquid phase. While in the porous membrane, a process of selective and controlled movement of particles from the gas phase to a liquid phase. However, the porous membrane causes the transfer of mass transfer from gas to liquid to be small due to resistance of the membrane. Thus, preferably porous membrane membrane contactor applications. Dijelakan As above, it contacts the membrane contactor non-dispersive, which means no direct contact occurs between the absorbent and gas. Surface (interface) fluid / fluid formed at the mouth of the pore membrane, and mass transfer will occur by diffusion on the surface of the fluid in the membrane pores. Unlike other types of reverse osmosis or nanofiltration membranes using pressure as the driving force for the membrane contactor thrust used is the difference in concentration. CO2 will move from gas that has a high concentration of CO2 into liquid absorbent that has low CO2 concentrations. Modelling the mass displacement and Membrane Contactors Gas / Liquid Mass transfer of a component from the gas phase into the liquid flowing through the hollow fiber membrane consists of three phases, namely the diffusion of solutes from the bulk gas phase to the surface of the membrane, diffusion through the pores of the membrane to the surface of the liquid, and the diffusion of the liquid surface to the bulk liquid phase . Overall mass transfer coefficient mass transfer resistance depends on the individual, for the gas phase (1/kg), membrane (1/km), liquid phase (1/mkLE) by the following equation [Kreulen et al]: E is the enhancement factor that showed an increase in the rate of absorption due to chemical reactions and m is the physical solubility of the gas components in the liquid absorbent. While the mass transfer coefficient g is related to hydrodynamic. Target in the process of membrane contactors is the large mass transfer from the gas stream into the liquid absorbent. The main issues that emerged at the membrane absorber is wetting. picture-4: (a) Membrane Contactors gas / liquid non-wetted, (b) Membrane Contactors gas / liquid wetted Wetting event caused by the entry of fluid into the absorbent membrane pores that cause an increase in the resistance movement in the event of CO2 into the liquid absorbent so that the mass transfer coefficient decreased significantly. For porous membranes, the minimum pressure required by the fluid to penetrate into the pore. This pressure is called the breakthrough pressure and to avoid wetting, liquid pressure must be under pressure breakthrough. In addition, there are other factors to consider such as the membrane pore size, and material properties of the membrane picture-5: SEM. Hollow Fiber in Detail. OD = 0.6 mm Commercial Applications Membrane Contactors Some companies are already using membrane contactors gas / liquid separation of commercial CO2: • Kvaerner Oil & Gas and W.L. Gore & Associates GmbH developed a membrane gas absorption for separation of acid gases from natural gas and exhaust gas from the gas turbine offshore. In this process, the PTFE hollow fiber membranes are used with a physical solvent (Morphysorb) and chemical (alkanolamine) • TNO Environment Energy and Process Innovation (Netherlands) has developed a process MGA for the separation of CO2 from flue gas using hollow fiber membrane PP. The solvent used is called CORAL which is a mixture of salt and amino acids. Currently, the membrane contactor technology moving towards the use of dual hollow fiber membrane for absorption and desorption processes simultaneously. Currently, the use of membrane contactors used only in the absorption process, while the regeneration process is done by using a high temperature to remove CO2 from the liquid absorbent. In terms of energy, it is very inefficient. Therefore, the desorption process was also developed through the membrane. picture-6: Dual Hollow Fiber Membrane for CO2 Separation Such is one of the many functions that are useful for membrane complement and enhance perfomansi CO2 separation technologies that already exist.
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