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Title: Annual Report: Fuels (30 September 2012)

Abstract

The thermochemical conversion of fossil fuels through gasification will likely be the cornerstone of future energy and chemical processes due to its flexibility to accommodate numerous feeds (coal, biomass, natural gas, municipal waste, etc.) and to produce a variety of products (heat, specialty chemicals, power, etc.), as well as the inherent nature of the process to facilitate near zero emissions. Currently, the National Energy Technology Laboratory (NETL) Fuels Program has two pathways for syngas utilization: The production of transportation fuels, chemicals, or chemical intermediates. The hydrogen production as an intermediate for power production via advanced combustion turbines or fuel cells. Work under this activity focuses on the production, separation, and utilization of hydrogen from syngas using novel separation materials and processes. Advanced integrated gasification combined cycle (IGCC) schemes require the production of clean hydrogen to fuel innovative combustion turbines and fuel cells. This research focuses on the development and assessment of membranes tailored for application in the severe environments associated with syngas conversion. The specific goals of this research include: Provide data needed to fully understand the impact of syngas environments and hydrogen removal on relevant hydrogen separation materials. Utilize the understanding of material stability to engineer a membrane tailoredmore » for operations in the severe environments associated with syngas conversion. Provide unbiased evaluation of hydrogen separation membranes being developed within the Fuels Program. Precious metals and alloys of historic interest (Pd, Cu, Ag, Au, Pt), as well as novel materials (carbides and phosphides) are candidates for evaluation of function as hydrogen separation membranes. The first step in the transport of hydrogen through dense metals is the adsorption and dissociation of hydrogen on the membrane surface. Observation shows that coal-based syngas contaminants can dramatically influence this process. Therefore, systems studies will determine the optimum location of a given membrane technology in the process, as well as the likely conditions that separation technologies will be exposed to at this location. Experiments are conducted to assess the effect of these conditions on the catalytic activity of the membrane surface in order to identify compositions which have promising combinations of acceptable flux and extended functionality in realistic environments. Efforts under this task were centered around the interpretation of test results and conclusions from previous work in preparation for various submissions to the scientific literature throughout fiscal year 2012 (FY12). The primary goal for efforts under these funds is to conduct limited amounts of experimental testing and/or computational work to complete the studies, followed by compilation and submission of technical manuscripts to peer-reviewed scientific journals. During the past year, work has continued on developing separation materials that are resistant to environments containing H{sub 2}S. Previous work on PdCu has indicated that over a range of PdCu compositions, PdCu is resistant to bulk corrosion by H{sub 2}S. In addition, at certain conditions, PdCu is also resistant to surface poisoning by H{sub 2}S. However, the temperature range at which PdCu is resistant to surface poisoning (> 600°C) is above those temperatures typically encountered in an IGCC flowsheet. Application of knowledge of the binary material will allow development of more complex alloys, as it is unlikely that a simple binary alloy will perform acceptably in all required dimensions, so efforts will focus on engineering ternary alloys that are more promising. Because ternary composition space is so large, high-throughput tools allow us to understand dissociation activity and response to H{sub 2}S across a complex composition space using composition spread alloy film (CSAF) tools. The high-throughput tools have been fully developed and have already provided insight into the fundamentals of surface segregation, dissociation, and H{sub 2}S response in Pd alloys for H{sub 2} separation. Sulfur uptake is a critical parameter in determining whether a membrane will corrode in the presence of H{sub 2}S. Testing of a ternary PdAuCu alloy found that the lowest S uptake was observed in the vicinity of Pd{sub 40}Au{sub 40}Cu{sub 20}, suggesting that compositions in this compositional region may display resistance to corrosion by H{sub 2}S for separation applications. Sulfur uptake also may indicate surface poisoning, which will hamper dissociation of hydrogen and essentially shut off transport through the membrane. Using the CSAF tool, H{sub 2}-D{sub 2} exchange kinetics were measured across the surface of a Cu{sub x}Pd{sub 1-x} composition spread library. The surface is most active for H{sub 2} dissociation at high Pd composition, where the alloy has face centered cubic (FCC) order. This result provides a fundamental basis for rational design of alloy membrane surfaces with high activity for H{sub 2} dissociation. Work continued on developing separation materials that are resistant to contaminated syngas environments. Previous work on binary materials has been expanded to more complex alloys, as it is unlikely that a simple binary alloy will perform acceptably in all required dimensions. Efforts focused on engineering ternary alloys that are more promising. Because ternary composition space is so large, high-throughput CSAF tools have been developed and continue to be used to provide insight into the fundamentals of surface segregation, dissociation, and H{sub 2}S response in Pd alloys for H{sub 2} separation. Efforts continued to characterize the dissociation and recombination activities of CuPd surfaces using the high-throughput CSAF sample libraries. H{sub 2}-D{sub 2} exchange kinetics were measured across the surface of a Cu{sub x}Pd{sub 1-x} CSAF, with activity being observed to increase with both temperature and Pd content in the alloy. A microkinetic model of the exchange reaction was developed to extract fundamental kinetic parameters from the raw reaction data. Preliminary results suggest that the kinetic parameter E{sub ads}, the energetic barrier to dissociative adsorption of H{sub 2} correlates with the details of the valence level electronic structure throughout composition space. This finding contributes to a fundamental understanding of H{sub 2} dissociation on alloy surfaces for separation applications. Exposure of PdCuX ternary alloys (X=Mg or Al) to H{sub 2}S (1000 ppm H{sub 2}S in H{sub 2}, 500°C, 16 hours) showed that the presence of Mg and Al led to more corrosion of the PdCu alloy. This indicates that minor components Mg and Al may not be good choices for inclusion in ternary alloys with Pd and Cu. Exposure tests for PdCuX ternary alloys (X=Mg, Al, or Y) to simulated syngas containing H{sub 2}S at levels including 0, 20, 100, 1,000, and 10,000 ppm H2S at 500°C for 120 hours showed that at H{sub 2}S levels below 100 ppm, the presence of Mg and Al led to minimal corrosion of the PdCuX alloy, while Y showed evidence of significantly more corrosion. At higher levels of H{sub 2}S (1,000 and 10,000 ppm), addition of Mg and Al had no significant effect on corrosion resistance, while the presence of Y showed a significant detrimental effect on corrosion resistance. Experiments also attempted to identify the mechanism of surface oxidation of the PdCuY alloy. Based on X-ray photoelectron spectroscopy (XPS) data, it appears that in the presence of oxygen, Y-oxides form at the top surface of the alloy. It does not appear that Y is a good choice for inclusion in ternary alloys with Pd and Cu for separation applications in syngas. Lab facility improvements were completed to allow membrane testing in both clean gaseous environments (H{sub 2}, CO{sub 2}, He, Ar, and N{sub 2}), as well as H{sub 2}S-contaminated environments. This improvement returned the capability for testing membranes in the presence of H{sub 2}S, which is a critical capability for the evaluation of membrane materials being developed at NETL. Membrane testing in both clean gaseous environments (pure H{sub 2}), as well as H{sub 2}S-contaminated environments (H{sub 2} with 1000 ppm H{sub 2}S) was conducted using the low pressure tubular reactor (LPTR) systems brought on-line this fiscal year. Overall, ten membrane tests were conducted during the quarter, with varying degrees of success. In one instance, a Pd-Cu membrane developed externally was tested in pure H{sub 2}, with the resulting performance being roughly 7% of that of pure Pd. In another instance, a PdCuMg membrane was tested in an initial feed of pure H{sub 2}, and then the feed was switched to 1,000 ppm H{sub 2}S in H{sub 2}. Exposure to H{sub 2}S caused the flux to fall to unmeasurable levels. In general, materials either provided very low H2 flux (at or near the measurable limit of the system) or failed mechanically. Efforts to determine failure mechanisms are on-going. Surface analysis of several alloys that have been exposed to real syngas at the National Carbon Capture Center (NCCC) experimental gasifier indicate that in addition to the expected sulfides, arsenide compounds were also found to have formed on membrane surface regions (up to several weight percent) and major surface restructuring occurred which can be linked to the growth of surface compounds such as sulfides and arsenides. These results show the importance of testing under real conditions by revealing the corrosion effects that even minor gas stream constituents such as As and Se can have on membrane materials. The results of experimental exposure tests were compared to those predicted by stability diagrams. The results of the exposure tests and the post-exposure characterization of the reaction surfaces agree well overall with the results predicted by the phase stability diagrams. The alloys that consist of part or all of the body-centered-cubic (bcc) phase (Cu{sub 50}Pd, Cu{sub 40}Pd, and Cu{sub 34}Pd) demonstrated significantly higher sulfidation resistance compared to the FCC phase (Cu{sub 70}Pd and pure Pd), indicating that alloying with copper significantly improves palladium's resistance to sulfidation. An assessment of the experiments and modeling work that was performed by Eltron, as well as the design of the proposed larger scale process development unit (PDU), was conducted and uncovered a potential issue in the substitution of a heat-exchanger tool as a surrogate for a mass-exchanger, which does not account for the fact that the mass flow in the two streams is changing through the system, which would then change the mass transfer coefficient. In addition, computational fluid dynamics (CFD) simulations performed by the group did not include an active membrane, only the flow around the tube and baffles. Exposure tests were conducted to provide the CFD modeling group with experimental data to aid in construction and validation of their CFD model. Parameters that were determined include leakage rates, effect of sweep rate on hydrogen flux, and effect of feed flow rate on hydrogen flux. It was determined that hydrogen flux increased with both sweep rate and with feed rate; however, at the higher end of the feed flow rate only small increases in flux were observed. A model using CFD to develop and design a membrane reactor was created and experimental data obtained in Task 6.0 was used to run five simulations of the model. The model predicted much higher H{sub 2} recovery than the experiment achieved. While the reasons behind the over-predictions continue to be investigated in conjunction with the experimental team, the goal remains to validate the computational approach so that larger scale designs can be modeled.« less

Authors:
 [1];  [1]
  1. NETL
Publication Date:
Research Org.:
National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). In-house Research
Sponsoring Org.:
USDOE Office of Fossil Energy (FE)
OSTI Identifier:
1098238
Report Number(s):
NETL-PUB-821
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN

Citation Formats

Link, Dirk, and Morreale, Bryan. Annual Report: Fuels (30 September 2012). United States: N. p., 2012. Web. doi:10.2172/1098238.
Link, Dirk, & Morreale, Bryan. Annual Report: Fuels (30 September 2012). United States. https://doi.org/10.2172/1098238
Link, Dirk, and Morreale, Bryan. Sun . "Annual Report: Fuels (30 September 2012)". United States. https://doi.org/10.2172/1098238. https://www.osti.gov/servlets/purl/1098238.
@article{osti_1098238,
title = {Annual Report: Fuels (30 September 2012)},
author = {Link, Dirk and Morreale, Bryan},
abstractNote = {The thermochemical conversion of fossil fuels through gasification will likely be the cornerstone of future energy and chemical processes due to its flexibility to accommodate numerous feeds (coal, biomass, natural gas, municipal waste, etc.) and to produce a variety of products (heat, specialty chemicals, power, etc.), as well as the inherent nature of the process to facilitate near zero emissions. Currently, the National Energy Technology Laboratory (NETL) Fuels Program has two pathways for syngas utilization: The production of transportation fuels, chemicals, or chemical intermediates. The hydrogen production as an intermediate for power production via advanced combustion turbines or fuel cells. Work under this activity focuses on the production, separation, and utilization of hydrogen from syngas using novel separation materials and processes. Advanced integrated gasification combined cycle (IGCC) schemes require the production of clean hydrogen to fuel innovative combustion turbines and fuel cells. This research focuses on the development and assessment of membranes tailored for application in the severe environments associated with syngas conversion. The specific goals of this research include: Provide data needed to fully understand the impact of syngas environments and hydrogen removal on relevant hydrogen separation materials. Utilize the understanding of material stability to engineer a membrane tailored for operations in the severe environments associated with syngas conversion. Provide unbiased evaluation of hydrogen separation membranes being developed within the Fuels Program. Precious metals and alloys of historic interest (Pd, Cu, Ag, Au, Pt), as well as novel materials (carbides and phosphides) are candidates for evaluation of function as hydrogen separation membranes. The first step in the transport of hydrogen through dense metals is the adsorption and dissociation of hydrogen on the membrane surface. Observation shows that coal-based syngas contaminants can dramatically influence this process. Therefore, systems studies will determine the optimum location of a given membrane technology in the process, as well as the likely conditions that separation technologies will be exposed to at this location. Experiments are conducted to assess the effect of these conditions on the catalytic activity of the membrane surface in order to identify compositions which have promising combinations of acceptable flux and extended functionality in realistic environments. Efforts under this task were centered around the interpretation of test results and conclusions from previous work in preparation for various submissions to the scientific literature throughout fiscal year 2012 (FY12). The primary goal for efforts under these funds is to conduct limited amounts of experimental testing and/or computational work to complete the studies, followed by compilation and submission of technical manuscripts to peer-reviewed scientific journals. During the past year, work has continued on developing separation materials that are resistant to environments containing H{sub 2}S. Previous work on PdCu has indicated that over a range of PdCu compositions, PdCu is resistant to bulk corrosion by H{sub 2}S. In addition, at certain conditions, PdCu is also resistant to surface poisoning by H{sub 2}S. However, the temperature range at which PdCu is resistant to surface poisoning (> 600°C) is above those temperatures typically encountered in an IGCC flowsheet. Application of knowledge of the binary material will allow development of more complex alloys, as it is unlikely that a simple binary alloy will perform acceptably in all required dimensions, so efforts will focus on engineering ternary alloys that are more promising. Because ternary composition space is so large, high-throughput tools allow us to understand dissociation activity and response to H{sub 2}S across a complex composition space using composition spread alloy film (CSAF) tools. The high-throughput tools have been fully developed and have already provided insight into the fundamentals of surface segregation, dissociation, and H{sub 2}S response in Pd alloys for H{sub 2} separation. Sulfur uptake is a critical parameter in determining whether a membrane will corrode in the presence of H{sub 2}S. Testing of a ternary PdAuCu alloy found that the lowest S uptake was observed in the vicinity of Pd{sub 40}Au{sub 40}Cu{sub 20}, suggesting that compositions in this compositional region may display resistance to corrosion by H{sub 2}S for separation applications. Sulfur uptake also may indicate surface poisoning, which will hamper dissociation of hydrogen and essentially shut off transport through the membrane. Using the CSAF tool, H{sub 2}-D{sub 2} exchange kinetics were measured across the surface of a Cu{sub x}Pd{sub 1-x} composition spread library. The surface is most active for H{sub 2} dissociation at high Pd composition, where the alloy has face centered cubic (FCC) order. This result provides a fundamental basis for rational design of alloy membrane surfaces with high activity for H{sub 2} dissociation. Work continued on developing separation materials that are resistant to contaminated syngas environments. Previous work on binary materials has been expanded to more complex alloys, as it is unlikely that a simple binary alloy will perform acceptably in all required dimensions. Efforts focused on engineering ternary alloys that are more promising. Because ternary composition space is so large, high-throughput CSAF tools have been developed and continue to be used to provide insight into the fundamentals of surface segregation, dissociation, and H{sub 2}S response in Pd alloys for H{sub 2} separation. Efforts continued to characterize the dissociation and recombination activities of CuPd surfaces using the high-throughput CSAF sample libraries. H{sub 2}-D{sub 2} exchange kinetics were measured across the surface of a Cu{sub x}Pd{sub 1-x} CSAF, with activity being observed to increase with both temperature and Pd content in the alloy. A microkinetic model of the exchange reaction was developed to extract fundamental kinetic parameters from the raw reaction data. Preliminary results suggest that the kinetic parameter E{sub ads}, the energetic barrier to dissociative adsorption of H{sub 2} correlates with the details of the valence level electronic structure throughout composition space. This finding contributes to a fundamental understanding of H{sub 2} dissociation on alloy surfaces for separation applications. Exposure of PdCuX ternary alloys (X=Mg or Al) to H{sub 2}S (1000 ppm H{sub 2}S in H{sub 2}, 500°C, 16 hours) showed that the presence of Mg and Al led to more corrosion of the PdCu alloy. This indicates that minor components Mg and Al may not be good choices for inclusion in ternary alloys with Pd and Cu. Exposure tests for PdCuX ternary alloys (X=Mg, Al, or Y) to simulated syngas containing H{sub 2}S at levels including 0, 20, 100, 1,000, and 10,000 ppm H2S at 500°C for 120 hours showed that at H{sub 2}S levels below 100 ppm, the presence of Mg and Al led to minimal corrosion of the PdCuX alloy, while Y showed evidence of significantly more corrosion. At higher levels of H{sub 2}S (1,000 and 10,000 ppm), addition of Mg and Al had no significant effect on corrosion resistance, while the presence of Y showed a significant detrimental effect on corrosion resistance. Experiments also attempted to identify the mechanism of surface oxidation of the PdCuY alloy. Based on X-ray photoelectron spectroscopy (XPS) data, it appears that in the presence of oxygen, Y-oxides form at the top surface of the alloy. It does not appear that Y is a good choice for inclusion in ternary alloys with Pd and Cu for separation applications in syngas. Lab facility improvements were completed to allow membrane testing in both clean gaseous environments (H{sub 2}, CO{sub 2}, He, Ar, and N{sub 2}), as well as H{sub 2}S-contaminated environments. This improvement returned the capability for testing membranes in the presence of H{sub 2}S, which is a critical capability for the evaluation of membrane materials being developed at NETL. Membrane testing in both clean gaseous environments (pure H{sub 2}), as well as H{sub 2}S-contaminated environments (H{sub 2} with 1000 ppm H{sub 2}S) was conducted using the low pressure tubular reactor (LPTR) systems brought on-line this fiscal year. Overall, ten membrane tests were conducted during the quarter, with varying degrees of success. In one instance, a Pd-Cu membrane developed externally was tested in pure H{sub 2}, with the resulting performance being roughly 7% of that of pure Pd. In another instance, a PdCuMg membrane was tested in an initial feed of pure H{sub 2}, and then the feed was switched to 1,000 ppm H{sub 2}S in H{sub 2}. Exposure to H{sub 2}S caused the flux to fall to unmeasurable levels. In general, materials either provided very low H2 flux (at or near the measurable limit of the system) or failed mechanically. Efforts to determine failure mechanisms are on-going. Surface analysis of several alloys that have been exposed to real syngas at the National Carbon Capture Center (NCCC) experimental gasifier indicate that in addition to the expected sulfides, arsenide compounds were also found to have formed on membrane surface regions (up to several weight percent) and major surface restructuring occurred which can be linked to the growth of surface compounds such as sulfides and arsenides. These results show the importance of testing under real conditions by revealing the corrosion effects that even minor gas stream constituents such as As and Se can have on membrane materials. The results of experimental exposure tests were compared to those predicted by stability diagrams. The results of the exposure tests and the post-exposure characterization of the reaction surfaces agree well overall with the results predicted by the phase stability diagrams. The alloys that consist of part or all of the body-centered-cubic (bcc) phase (Cu{sub 50}Pd, Cu{sub 40}Pd, and Cu{sub 34}Pd) demonstrated significantly higher sulfidation resistance compared to the FCC phase (Cu{sub 70}Pd and pure Pd), indicating that alloying with copper significantly improves palladium's resistance to sulfidation. An assessment of the experiments and modeling work that was performed by Eltron, as well as the design of the proposed larger scale process development unit (PDU), was conducted and uncovered a potential issue in the substitution of a heat-exchanger tool as a surrogate for a mass-exchanger, which does not account for the fact that the mass flow in the two streams is changing through the system, which would then change the mass transfer coefficient. In addition, computational fluid dynamics (CFD) simulations performed by the group did not include an active membrane, only the flow around the tube and baffles. Exposure tests were conducted to provide the CFD modeling group with experimental data to aid in construction and validation of their CFD model. Parameters that were determined include leakage rates, effect of sweep rate on hydrogen flux, and effect of feed flow rate on hydrogen flux. It was determined that hydrogen flux increased with both sweep rate and with feed rate; however, at the higher end of the feed flow rate only small increases in flux were observed. A model using CFD to develop and design a membrane reactor was created and experimental data obtained in Task 6.0 was used to run five simulations of the model. The model predicted much higher H{sub 2} recovery than the experiment achieved. While the reasons behind the over-predictions continue to be investigated in conjunction with the experimental team, the goal remains to validate the computational approach so that larger scale designs can be modeled.},
doi = {10.2172/1098238},
url = {https://www.osti.gov/biblio/1098238}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2012},
month = {9}
}