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Membrane Gas Desorption for Natural Gas Treating
Mohammed J. Al-Marri and Fadwa El Jack (Editors), Proceedings of the 4th International Gas Processing Symposium, October 26–27, 2014 , Doha, Qatar. © 2015 Elsevier B.V. All rights reserved.
Membrane Gas Desorption for Natural Gas Treating Annemieke van de Runstraata, Earl L.V. Goetheera, Daphne E. Bakkera Alexey V. Volkovb, Abdelbaki Benamorc a
Department of Process and Instrument Development, Netherlands Organisation for Applied Scientific Research TNO, Delft, The Netherlands
b
A.V. Topchiev Institute of Petrochemical Synthesis, Moscow, Russian Federation.
c
Gas Processing Center, Qatar University, Doha, Qatar
Abstract Stable membrane gas desorption (MGD) using a thin-film composite membranes made of hydrophobic glassy polymer poly[1-(trimethylsylil)-1-propyne] on a flexible metal-ceramic microfilter was achieved based on MDEA as CO2-absorption liquid. MGD can be used as a novel methodology for desorption of amine solution for natural gas treatment. In particular, MGD can be useful for obtaining CO2 with methane pipeline specification. Keywords: Membrane contactor, СО2, Chemical solvent regeneration, acid gas removal 1. Introduction One of the most mature technologies for the removal of CO2 from natural gas is reactive absorption using alkanolamines. The CO2 loaded alkanolamine is typically thermally regenerated in a stripper. Such a stripper consists of a tower filled with random or structured packing. A reboiler is used to generate steam needed for regeneration. Absorber-stripper units represent a proven, well-accepted technology. However, major drawbacks of this process are the considerably high heat and energy penalties required for releasing the chemically bonded carbon dioxide as well as the capital expenditure. One of the potential routes for further development in this area is the introduction of gas-liquid membrane contactors, and in particular those directed at solvent regeneration. In that case, the solvent regeneration is based on a membrane flash. This means that the solvent is (partially) kept at high pressure and the CO2 is desorbed to lower pressure through the membrane due to a
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significant trans-membrane pressure (see Figure 1). This method is known as Membrane Gas Desorption (MGD). One of the advantages is that pumping energy is significantly reduced since the liquid phase is circulated at constant pressure.
Figure 1. Principle of MGD Despite a large number of publications on membrane contactors for CO2 removal, only a limited part of it is focusing on the use of membrane contactors during solvent regeneration. Moreover, in most of the reported research, trans-membrane pressures of 2 bar or lower were applied [1-4]. The main reason for that is the issue with pore wetting since the porous membranes are typically utilised for both absorption and desorption stage [1-6]. Pore wetting can cause a significant mass transfer resistance because of the stagnant liquid layer in the pores of the membrane. To eliminate the pore wetting, it was proposed to use membranes with a top non-porous layer. The authors of this paper have proposed the application of novel high performance membranes with the dense thin top-layer made of the glassy polymer PTMSP with the highest gas permeance among known polymers. It was already shown that PTMSP as a membrane material possesses long-term chemical and mechanical stability at typical MGD conditions – amine-based solvent, trans-membrane pressure up to 40 bar and temperature 100 °C [7]. Furthermore, PTMSP is a barrier material towards chemical solvents such as aqueous solutions of alkanolamines [7] and some physical solvents like water [8] and ionic liquid [9]. Details about the development of these membranes are described elsewhere [10]. In this paper, the focus is on experimental work on using these membranes in contactors and the implications for application in natural gas processing. 2. Experimental 2.1 General The membrane developed and used in this study is a thin-film composite membrane made of hydrophobic glassy polymer poly[1-(trimethylsylil)-1-propyne]
Membrane Gas Desorption for Natural Gas Treating
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on a flexible metal-ceramic microfilter. In the remainder of this paper abbreviated as PTMSP/MC TFC (thin film composite). Figure 2 shows a schematic drawing and a SEM picture of the membrane. Figure 3 shows a photo of the membrane on the bottom right. Details on this membrane can be found elsewhere [10].
Liquid + CO2 PTSMP-based selective layer
1.2 Pm
PTMSP
Metalceramic support
MC
CO2 (gas)
Figure 2. Schematic drawing of PTMSP/MC TFC (left) and SEM picture showing the top layer of the PTMSP/MC TFC membrane (right) [10] The solvent used for the absorption/desorption experiments is a 99% methyldiethanolamine (MDEA) from Sigma-Aldrich in a 50 wt% distilled water solution. 2.2 Pilot facility for MGD and conventional solvent regeneration testing
The pilot facility used for the experiments is THAHRA (TNO’s High pressure Absorption, Hybrid Regeneration Apparatus). A photo of the apparatus is shown in Figure 3 on the left.
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Figure 3. Photo of THAHRA (left), the membrane module (top right) and PTMSP/MC TFC membrane (bottom right) THAHRA is designed for the assessment of solvents for application in high pressure CO2 capture processes. Intercooling of the solvent in the absorber column is able to increase solvent capacity when using reactive solvents. Within the operating window of THAHRA, one is able to mimic the treatment of different feeds. These include shifted syngas for pre-combustion, typically 30 bar, 40%-60% CO2-H2, as well as natural gas for pipe line and LNG, typically 45 bar, 20%-80% CO2-CH4. The maximum feed flow is 5 Nm3/hr, with a liquid flow of up to 25 kg/hr. The solvent inventory is approximately 4.5 l. Due to the small liquid inventory, non-commercially available solvents can easily be tested. As a special feature, two alternative methods for the regeneration of the solvent can be selected: a conventional stripper or a Membrane Gas Desorption (MGD) module, hence the ‘Hybrid Regeneration’. The MGD module is shown in Figure 3 at the top right. Both the absorber and stripper are columns in which commercial high surface area structured packing material, currently Sulzer DX, is installed. The cold rich stream from the absorber and the hot lean solvent from the stripper or MGD module are heat exchanged. Temperature profiles along the absorber and stripper can be measured. In total 7 pressure, 19 temperature, 5 gas flow, 2 liquid flow and 2 sump sensors are installed and logged. Samples can be
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taken from the lean and rich stream for off-line analyses; the CO2 content of the gas leaving the absorber is continuously measured. A second on-line gas analysis channel is available for the analysis of the composition at either the exit of the stripper or the feed. For safety reasons, experiments described in this paper were all performed using CO2-N2 mixtures. Total pressure was 20 bar, gas feed flow rate 750 to 1500 Nl/h of which 20 to 40% CO2. Typical liquid flow rate was 10 l/h. 2.3 Concentration determination for the pilot samples
The concentration of CO2 in a loaded sample was measured using an analysis based on a reaction between the sample and hot phosphoric acid. The acid causes desorption of CO2 from the amine solvent; the total amount of desorbed CO2 is measured using a CO2 analyser. The method consists of heating phosphoric acid in a three-neck round flask, a liquid sample of known volume is then injected into the hot, vigorously boiling acid. The CO2 is released and carried off by a controlled flow of nitrogen. The CO2/N2 gas mixture is dried and then sent to the CO2 analyser. The total mass of CO2 in the sample is then calculated by integrating the CO2 concentration in the exhaust gas in time.
3. Results and Discussion 3.1 Results using the lab scale apparatus The results of membrane tests using a lab scale apparatus at TIPS RAS (Topchiev Institute of Petrochemical Synthesis) are presented in Figure 4. The temperature of regeneration was 100 °C, whereas the pressure of the MDEA solvent was up to 30 bar. Linear velocity was varied to identify the system performance at different conditions. The membrane was pressurized by CO2 loaded absorbent during 4 days, after and before membrane flux characterisation as shown in Figure 4. This figure shows that the membranes developed demonstrated stable performance during 100 hours of operation at 100 °С, 30 bar, рН≥11.
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Figure 4. Relationship between CO2 flux and 50% MDEA linear velocity during its regeneration using PTMSP TFC membranes on MC support from [10]. 3.2 Results from the pilot
Several PTMSP TFC membrane experiments at different settings were performed in the TNO pilot THAHRA for in total 20 hours at a pressure of 20 bar at temperatures above 80 °C. During this period, the CO2 flux decreased approximately 4%. The CO2 mass balance typically is closed within 10%. Figure 5 shows the CO2 flux measured as solvent temperature. This temperature is measured at the exit of the MGD module. Therefore, the actual average temperature of the module can be slightly higher. A clear increase in flux as a function of temperature is observed.
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Figure 5. CO2 flux as a function of the temperature of the solvent after the MGD module at a rich loading of 0.70 ± 0.05 mol/mol at the entrance of the module. A summary of the results of the tests are presented in Figure 6. To be able to compare the CO2 flux measured using different settings and different apparatus, all data points are expressed in terms of the driving force. This is done in the following way. First, the equilibrium CO2 pressure that corresponds to the rich loading measured by the phosphoric acid method at the desorption temperature is determined via data mentioned in reference [11]. The CO2 pressure at the permeate site is subtracted from this value leading to the driving force for CO2 desorption.
Figure 6. CO2 flux as a function of driving force for the TNO pilot experiments (blue diamonds) and TIPS-RAS lab-scale apparatus (red square; [10]).
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Figure 6 shows that the CO2 flux increases with driving force. However, it seems that there is a finite flux at zero driving force, which is actually not true. However, one should take into account that there is an estimated error of 10% in the measured flux and +/- 0.1 bar in the driving force. Figure 6 also shows that the order of magnitude of the measured fluxes in the pilot and laboratory facility are similar although the laboratory facility flux is slightly higher. This might be due to the difference in module configuration, which is more efficient in the laboratory facility. Another feature of the PTMSP TFC membrane is that it suppresses water evaporation. Figure 7 shows the water selectivity as function of temperature. It can be observed that the selectivity in the pilot increases with temperature and that it is higher at the THAHRA conditions as compared with the lab conditions. This is due to different CO2 loading between pilot plant and lab experiments. As a consequence different CO2 fluxes are obtained. Moreover, atlow CO2 fluxes the water selectivity (as expressed in Figure 7) decreases.
Figure 7. Water selectivity as a function of temperature for the TNO pilot experiments (blue diamonds) and TIPS-RAS lab-scale apparatus (red square; [10]).
3.3 Outlook to application of MGD in natural gas processing The flux data of Figure 6 were used to estimate the membrane area that is needed to regenerate the solvent from a natural gas treating plant. Aspen® rate based simulations were used to derive a typical MDEA flow and rich and lean loadings as well as water evaporation in case of conventional stripper
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regeneration. The case simulated was 1500 MMscfd with 5% CO2 gas feed at 80 bara. The methane leaving the absorber was at pipe line specifications, i.e. maximum 2% CO2. As a first step in the regeneration, the total solvent pressure was reduced to 40 bar. Thus a transmembrane pressure of 39 bar was applied. The CO2 flux at the log mean average feed concentration was used to calculate the average driving force for the PTMSP/MC TFC membranes at these conditions [13]. In this way, it was estimated that approximately 125000 m2 of membrane is needed. Typically, a packing density (surface area per m3) of more than 1000 m2/m3 can be achieved. This would lead to a column volume of 125 m3. A packed column for the same case would be 100000 m2 of surface area, with a standard structured packing with a surface area of 250 m2/m3. This would lead to a column with a volume of 400 m3. However, in these calculations the temperature in the module is kept constant. This is not completely true since the energy needed to overcome the heat of CO2 desorption and water evaporation will induce solvent cooling. Therefore, the same data were also used to estimate the temperature decrease of the solvent along the membrane modules. A heat of reaction of CO2 and MDEA of 50 kJ/mol was used [14]. A temperature loss of 5 °C was found, due to water evaporation and heat of reaction. One option to overcome the decrease in solvent temperature and thus desorption driving force is improved process design. As an example, the MGD section will consist of several modules in series and in parallel. Intermediate heating between the modules can be applied to retain driving force. Moreover, when the temperature of the solvent is increased along the flow direction, heat integration of the evaporated water from the next module can be applied to heat the solvent. In this way, even more energy, and, therefore, operational costs, can be saved. 4. Conclusions A novel way for the regeneration of a reactive solvent in natural gas treatment, Membrane Gas Desorption, is presented. Experimental and simulation work was performed to assess this technology. It was shown that it has potential for CO 2 capture from natural gas up to pipeline specifications. 5. Acknowledgements This work was partially funded in part by FP7 project “DECARBit” and was performed within the context of the CATO-2-program (www.co2-cato.org). This research cooperation is also part of the DutchRussian Centre of Excellence "Gas4S" (NWO-RFBR # 047.018.2006. 014/08-08-92890-CE).
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References (1) Simons, K., Nijmeijer, K., Wessling, M. J. Mem. Sci. 340 (2009) 214–220 (2) Scholes, C.A., Simioni, M., Qader, A., Stevens, G. W. , Kentish, S. E. Chem. Eng. J.
195–196 (2012) 188–197 (3) Dindore, V.Y., Brilman, D.W.F., Feron, P.H.M., Versteeg G.F. J. Mem. Sci. 235
(2004) 99–109 (4) Li, K, Teo, W.K. Chem. Eng. Res. Des., V. 74, (8) (1996) 856–862 (5) Pabby, A.K., Sastre, A.M J. Mem. Sci. 430 (2013) 263–303 (6) Simioni, M, Kentish, S.E., Stevens, G.W. J. Mem. Sci. 378 (2011) 18– 27 (7) Trusov A., Legkov S., van den Broeke L.J.P., Goetheer E., Khotimsky V., Volkov A, (8) (9) (10)
(11) (12) (13) (14)
J. Membr. Sci. 383 (2011) 241–249 Grekhov A., Belogorlov A., Yushkin A., Volkov A. J. Membr. Sci. 390-391 (2012) 160–163 Volkov A., Yushkin A., Grekhov A., Shutova A., Bazhenov S., Tsarkov S., Khotimsky V., Vlugt T.J.H., Volkov V. J. Membr. Sci. 440 (2013) 98-107 Dibrov, G.A., Volkov, V.V., Vasilevsky, V.P., Shutova, A.A., Bazhenov, S.D., Khotimsky, V.S., van de Runstraat, A. , Goetheer, E.L.V., Volkov, A.V. s J. of Membr. Sci. 470 (2014) 439–450 Jou, F.Y., Mather, A.E., Otto, F.D. Ind. Eng. Chem. Des. Dev., 21 (1982) 539-544 Wu, S.H., Caparanga, A.R., Leron, R.B., Li, M.-H. Exp. Therm. Fluid Sci. 48 (2013) 1–7 Mulder, M. Basic Principles of Membrane Technology, 1991 Zhang, Y. Chyun Chen, C.-C. Ind. Eng. Chem. Res., 50 (2011), 163–175
Membrane Gas Desorption for Natural Gas Treating Annemieke van de Runstraata, Earl L.V. Goetheera, Daphne E. Bakkera Alexey V. Volkovb, Abdelbaki Benamorc a
Department of Process and Instrument Development, Netherlands Organisation for Applied Scientific Research TNO, Delft, The Netherlands
b
A.V. Topchiev Institute of Petrochemical Synthesis, Moscow, Russian Federation.
c
Gas Processing Center, Qatar University, Doha, Qatar
Abstract Stable membrane gas desorption (MGD) using a thin-film composite membranes made of hydrophobic glassy polymer poly[1-(trimethylsylil)-1-propyne] on a flexible metal-ceramic microfilter was achieved based on MDEA as CO2-absorption liquid. MGD can be used as a novel methodology for desorption of amine solution for natural gas treatment. In particular, MGD can be useful for obtaining CO2 with methane pipeline specification. Keywords: Membrane contactor, СО2, Chemical solvent regeneration, acid gas removal 1. Introduction One of the most mature technologies for the removal of CO2 from natural gas is reactive absorption using alkanolamines. The CO2 loaded alkanolamine is typically thermally regenerated in a stripper. Such a stripper consists of a tower filled with random or structured packing. A reboiler is used to generate steam needed for regeneration. Absorber-stripper units represent a proven, well-accepted technology. However, major drawbacks of this process are the considerably high heat and energy penalties required for releasing the chemically bonded carbon dioxide as well as the capital expenditure. One of the potential routes for further development in this area is the introduction of gas-liquid membrane contactors, and in particular those directed at solvent regeneration. In that case, the solvent regeneration is based on a membrane flash. This means that the solvent is (partially) kept at high pressure and the CO2 is desorbed to lower pressure through the membrane due to a
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Runstraat et al.
significant trans-membrane pressure (see Figure 1). This method is known as Membrane Gas Desorption (MGD). One of the advantages is that pumping energy is significantly reduced since the liquid phase is circulated at constant pressure.
Figure 1. Principle of MGD Despite a large number of publications on membrane contactors for CO2 removal, only a limited part of it is focusing on the use of membrane contactors during solvent regeneration. Moreover, in most of the reported research, trans-membrane pressures of 2 bar or lower were applied [1-4]. The main reason for that is the issue with pore wetting since the porous membranes are typically utilised for both absorption and desorption stage [1-6]. Pore wetting can cause a significant mass transfer resistance because of the stagnant liquid layer in the pores of the membrane. To eliminate the pore wetting, it was proposed to use membranes with a top non-porous layer. The authors of this paper have proposed the application of novel high performance membranes with the dense thin top-layer made of the glassy polymer PTMSP with the highest gas permeance among known polymers. It was already shown that PTMSP as a membrane material possesses long-term chemical and mechanical stability at typical MGD conditions – amine-based solvent, trans-membrane pressure up to 40 bar and temperature 100 °C [7]. Furthermore, PTMSP is a barrier material towards chemical solvents such as aqueous solutions of alkanolamines [7] and some physical solvents like water [8] and ionic liquid [9]. Details about the development of these membranes are described elsewhere [10]. In this paper, the focus is on experimental work on using these membranes in contactors and the implications for application in natural gas processing. 2. Experimental 2.1 General The membrane developed and used in this study is a thin-film composite membrane made of hydrophobic glassy polymer poly[1-(trimethylsylil)-1-propyne]
Membrane Gas Desorption for Natural Gas Treating
235
on a flexible metal-ceramic microfilter. In the remainder of this paper abbreviated as PTMSP/MC TFC (thin film composite). Figure 2 shows a schematic drawing and a SEM picture of the membrane. Figure 3 shows a photo of the membrane on the bottom right. Details on this membrane can be found elsewhere [10].
Liquid + CO2 PTSMP-based selective layer
1.2 Pm
PTMSP
Metalceramic support
MC
CO2 (gas)
Figure 2. Schematic drawing of PTMSP/MC TFC (left) and SEM picture showing the top layer of the PTMSP/MC TFC membrane (right) [10] The solvent used for the absorption/desorption experiments is a 99% methyldiethanolamine (MDEA) from Sigma-Aldrich in a 50 wt% distilled water solution. 2.2 Pilot facility for MGD and conventional solvent regeneration testing
The pilot facility used for the experiments is THAHRA (TNO’s High pressure Absorption, Hybrid Regeneration Apparatus). A photo of the apparatus is shown in Figure 3 on the left.
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Figure 3. Photo of THAHRA (left), the membrane module (top right) and PTMSP/MC TFC membrane (bottom right) THAHRA is designed for the assessment of solvents for application in high pressure CO2 capture processes. Intercooling of the solvent in the absorber column is able to increase solvent capacity when using reactive solvents. Within the operating window of THAHRA, one is able to mimic the treatment of different feeds. These include shifted syngas for pre-combustion, typically 30 bar, 40%-60% CO2-H2, as well as natural gas for pipe line and LNG, typically 45 bar, 20%-80% CO2-CH4. The maximum feed flow is 5 Nm3/hr, with a liquid flow of up to 25 kg/hr. The solvent inventory is approximately 4.5 l. Due to the small liquid inventory, non-commercially available solvents can easily be tested. As a special feature, two alternative methods for the regeneration of the solvent can be selected: a conventional stripper or a Membrane Gas Desorption (MGD) module, hence the ‘Hybrid Regeneration’. The MGD module is shown in Figure 3 at the top right. Both the absorber and stripper are columns in which commercial high surface area structured packing material, currently Sulzer DX, is installed. The cold rich stream from the absorber and the hot lean solvent from the stripper or MGD module are heat exchanged. Temperature profiles along the absorber and stripper can be measured. In total 7 pressure, 19 temperature, 5 gas flow, 2 liquid flow and 2 sump sensors are installed and logged. Samples can be
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taken from the lean and rich stream for off-line analyses; the CO2 content of the gas leaving the absorber is continuously measured. A second on-line gas analysis channel is available for the analysis of the composition at either the exit of the stripper or the feed. For safety reasons, experiments described in this paper were all performed using CO2-N2 mixtures. Total pressure was 20 bar, gas feed flow rate 750 to 1500 Nl/h of which 20 to 40% CO2. Typical liquid flow rate was 10 l/h. 2.3 Concentration determination for the pilot samples
The concentration of CO2 in a loaded sample was measured using an analysis based on a reaction between the sample and hot phosphoric acid. The acid causes desorption of CO2 from the amine solvent; the total amount of desorbed CO2 is measured using a CO2 analyser. The method consists of heating phosphoric acid in a three-neck round flask, a liquid sample of known volume is then injected into the hot, vigorously boiling acid. The CO2 is released and carried off by a controlled flow of nitrogen. The CO2/N2 gas mixture is dried and then sent to the CO2 analyser. The total mass of CO2 in the sample is then calculated by integrating the CO2 concentration in the exhaust gas in time.
3. Results and Discussion 3.1 Results using the lab scale apparatus The results of membrane tests using a lab scale apparatus at TIPS RAS (Topchiev Institute of Petrochemical Synthesis) are presented in Figure 4. The temperature of regeneration was 100 °C, whereas the pressure of the MDEA solvent was up to 30 bar. Linear velocity was varied to identify the system performance at different conditions. The membrane was pressurized by CO2 loaded absorbent during 4 days, after and before membrane flux characterisation as shown in Figure 4. This figure shows that the membranes developed demonstrated stable performance during 100 hours of operation at 100 °С, 30 bar, рН≥11.
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Figure 4. Relationship between CO2 flux and 50% MDEA linear velocity during its regeneration using PTMSP TFC membranes on MC support from [10]. 3.2 Results from the pilot
Several PTMSP TFC membrane experiments at different settings were performed in the TNO pilot THAHRA for in total 20 hours at a pressure of 20 bar at temperatures above 80 °C. During this period, the CO2 flux decreased approximately 4%. The CO2 mass balance typically is closed within 10%. Figure 5 shows the CO2 flux measured as solvent temperature. This temperature is measured at the exit of the MGD module. Therefore, the actual average temperature of the module can be slightly higher. A clear increase in flux as a function of temperature is observed.
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Figure 5. CO2 flux as a function of the temperature of the solvent after the MGD module at a rich loading of 0.70 ± 0.05 mol/mol at the entrance of the module. A summary of the results of the tests are presented in Figure 6. To be able to compare the CO2 flux measured using different settings and different apparatus, all data points are expressed in terms of the driving force. This is done in the following way. First, the equilibrium CO2 pressure that corresponds to the rich loading measured by the phosphoric acid method at the desorption temperature is determined via data mentioned in reference [11]. The CO2 pressure at the permeate site is subtracted from this value leading to the driving force for CO2 desorption.
Figure 6. CO2 flux as a function of driving force for the TNO pilot experiments (blue diamonds) and TIPS-RAS lab-scale apparatus (red square; [10]).
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Figure 6 shows that the CO2 flux increases with driving force. However, it seems that there is a finite flux at zero driving force, which is actually not true. However, one should take into account that there is an estimated error of 10% in the measured flux and +/- 0.1 bar in the driving force. Figure 6 also shows that the order of magnitude of the measured fluxes in the pilot and laboratory facility are similar although the laboratory facility flux is slightly higher. This might be due to the difference in module configuration, which is more efficient in the laboratory facility. Another feature of the PTMSP TFC membrane is that it suppresses water evaporation. Figure 7 shows the water selectivity as function of temperature. It can be observed that the selectivity in the pilot increases with temperature and that it is higher at the THAHRA conditions as compared with the lab conditions. This is due to different CO2 loading between pilot plant and lab experiments. As a consequence different CO2 fluxes are obtained. Moreover, atlow CO2 fluxes the water selectivity (as expressed in Figure 7) decreases.
Figure 7. Water selectivity as a function of temperature for the TNO pilot experiments (blue diamonds) and TIPS-RAS lab-scale apparatus (red square; [10]).
3.3 Outlook to application of MGD in natural gas processing The flux data of Figure 6 were used to estimate the membrane area that is needed to regenerate the solvent from a natural gas treating plant. Aspen® rate based simulations were used to derive a typical MDEA flow and rich and lean loadings as well as water evaporation in case of conventional stripper
Membrane Gas Desorption for Natural Gas Treating
241
regeneration. The case simulated was 1500 MMscfd with 5% CO2 gas feed at 80 bara. The methane leaving the absorber was at pipe line specifications, i.e. maximum 2% CO2. As a first step in the regeneration, the total solvent pressure was reduced to 40 bar. Thus a transmembrane pressure of 39 bar was applied. The CO2 flux at the log mean average feed concentration was used to calculate the average driving force for the PTMSP/MC TFC membranes at these conditions [13]. In this way, it was estimated that approximately 125000 m2 of membrane is needed. Typically, a packing density (surface area per m3) of more than 1000 m2/m3 can be achieved. This would lead to a column volume of 125 m3. A packed column for the same case would be 100000 m2 of surface area, with a standard structured packing with a surface area of 250 m2/m3. This would lead to a column with a volume of 400 m3. However, in these calculations the temperature in the module is kept constant. This is not completely true since the energy needed to overcome the heat of CO2 desorption and water evaporation will induce solvent cooling. Therefore, the same data were also used to estimate the temperature decrease of the solvent along the membrane modules. A heat of reaction of CO2 and MDEA of 50 kJ/mol was used [14]. A temperature loss of 5 °C was found, due to water evaporation and heat of reaction. One option to overcome the decrease in solvent temperature and thus desorption driving force is improved process design. As an example, the MGD section will consist of several modules in series and in parallel. Intermediate heating between the modules can be applied to retain driving force. Moreover, when the temperature of the solvent is increased along the flow direction, heat integration of the evaporated water from the next module can be applied to heat the solvent. In this way, even more energy, and, therefore, operational costs, can be saved. 4. Conclusions A novel way for the regeneration of a reactive solvent in natural gas treatment, Membrane Gas Desorption, is presented. Experimental and simulation work was performed to assess this technology. It was shown that it has potential for CO 2 capture from natural gas up to pipeline specifications. 5. Acknowledgements This work was partially funded in part by FP7 project “DECARBit” and was performed within the context of the CATO-2-program (www.co2-cato.org). This research cooperation is also part of the DutchRussian Centre of Excellence "Gas4S" (NWO-RFBR # 047.018.2006. 014/08-08-92890-CE).
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References (1) Simons, K., Nijmeijer, K., Wessling, M. J. Mem. Sci. 340 (2009) 214–220 (2) Scholes, C.A., Simioni, M., Qader, A., Stevens, G. W. , Kentish, S. E. Chem. Eng. J.
195–196 (2012) 188–197 (3) Dindore, V.Y., Brilman, D.W.F., Feron, P.H.M., Versteeg G.F. J. Mem. Sci. 235
(2004) 99–109 (4) Li, K, Teo, W.K. Chem. Eng. Res. Des., V. 74, (8) (1996) 856–862 (5) Pabby, A.K., Sastre, A.M J. Mem. Sci. 430 (2013) 263–303 (6) Simioni, M, Kentish, S.E., Stevens, G.W. J. Mem. Sci. 378 (2011) 18– 27 (7) Trusov A., Legkov S., van den Broeke L.J.P., Goetheer E., Khotimsky V., Volkov A, (8) (9) (10)
(11) (12) (13) (14)
J. Membr. Sci. 383 (2011) 241–249 Grekhov A., Belogorlov A., Yushkin A., Volkov A. J. Membr. Sci. 390-391 (2012) 160–163 Volkov A., Yushkin A., Grekhov A., Shutova A., Bazhenov S., Tsarkov S., Khotimsky V., Vlugt T.J.H., Volkov V. J. Membr. Sci. 440 (2013) 98-107 Dibrov, G.A., Volkov, V.V., Vasilevsky, V.P., Shutova, A.A., Bazhenov, S.D., Khotimsky, V.S., van de Runstraat, A. , Goetheer, E.L.V., Volkov, A.V. s J. of Membr. Sci. 470 (2014) 439–450 Jou, F.Y., Mather, A.E., Otto, F.D. Ind. Eng. Chem. Des. Dev., 21 (1982) 539-544 Wu, S.H., Caparanga, A.R., Leron, R.B., Li, M.-H. Exp. Therm. Fluid Sci. 48 (2013) 1–7 Mulder, M. Basic Principles of Membrane Technology, 1991 Zhang, Y. Chyun Chen, C.-C. Ind. Eng. Chem. Res., 50 (2011), 163–175