Coal-derived Syngas Research Articles

Insights into the Adsorption, Alloy Formation, and Poisoning Effects of Hg on Monometallic and Bimetallic Adsorbents.

The removal of elemental mercury (Hg0) from coal-derived syngas at high temperatures is desired to improve the thermal efficiency of the coal-to-chemical processes. First-principles density functional theory (DFT) calculations for Hg0 adsorption are performed using different exchange correlation functionals (PBE, optPBE-vdW, and optB88-vdW). Gibbs free energy (ΔG) calculations are further performed to evaluate the feasibility of Hg0 adsorption on various exposed planes of metal nanoparticles and to obtain bimetallic compositions for Hg0 removal at various temperatures. Pd and Pt are shown to be suitable for Hg0 adsorption at high temperatures (473 K), whereas Rh and Ru are effective only until 373 K. The bimetallic adsorbents comprising Ag or Au along with Rh, Ru, Pd, or Pt are identified for Hg0 removal at high temperatures (473 K). The increase in Hg0 adsorption strength on various bimetallic surfaces is correlated to the upward shift in the d-band center. Further, calculations predict the tendency of Hg to segregate toward the surface of amalgams and disturb the perfect planar geometry of the Pd, Pt, Rh, Ru, Ir, Cu, Ag, and Au surfaces to form a noncrystalline Hg-rich amalgam surface. An analysis of the binding of various adsorbates (H, O, N, and S) shows that the adsorption becomes significantly weaker on various sites in close proximity to pre-adsorbed Hg. Moreover, for specific combinations of the adsorbate, surface composition, and the site location, the adsorption does not take place on the proximal sites. These results are complemented by the partial density of states calculations, which show changes in the electronic properties of the amalgam surface, thus explaining the poisoning effect of Hg on metallic catalysts.

Simultaneous Removal of Hg0 and H2S over a Regenerable Fe2O3/AC Catalyst

Simultaneous removal of Hg0 and H2S over a regenerable activated coke supported Fe2O3 catalyst (Fe2O3/AC) was studied in simulated coal-derived syngas. It was found that the Fe2O3/AC catalyst exhibited high capability for Hg0 and H2S removal, which was attributed to the catalytic oxidation activity of Fe2O3. Its capability for Hg0 and H2S removal increased with an increase of Fe2O3 loading amount, and the highest was at 150 °C for Hg0 removal. CO and H2 showed no obvious effect on Hg0 removal by Fe2O3/AC, while H2S had a promotion effect, which was due to S and FeSx produced by the H2S reaction on Fe2O3/AC. The results of SEM-EDX and the temperature programmed desorption experiment (TPD) revealed that Fe2O3 played a critical role in Hg0 oxidation, and HgS was generated upon the reaction of Hg0 with H2S on Fe2O3/AC. The used Fe2O3/AC catalyst after Hg0 and H2S removal could be effectively regenerated and still had high capability for Hg0 and H2S removal.

Conceptual design of syngas production by the integration of gasification and dry-reforming technologies with CO2 capture and utilization

Syngas is an important intermediate feedstock to produce various downstream chemicals and clean fuels. In this study, two standalone process models are first developed to produce syngas from coal gasification and natural gas dry reforming which provide the results for benchmarking the conceptual design. Two process models are then developed by integrating the gasification and dry-reforming models in the parallel and series configuration to improve the process performance. All the models are developed in Aspen Plus for producing the syngas at the rate of 10,000 kmol/h with H2/CO ratio of 2. The heat integration is also developed in a way to utilize the heat energy from the coal-derived syngas into the dry-reformer without any energy penalties. The performance of the proposed designs is compared to the standalone processes in terms of the energy, emissions and economics. The energy analysis reveals that the integrated design requires 62% less energy input compared to the standalone dry reforming process. The results also show that combining the synergies of the two technologies reduce the CO2 emission by 53.5% compared to the standalone gasification process. In addition to improved process efficiency and reduced emissions, the integrated design offers the lowest syngas production cost of $ 0.99/kmol among all the designs. The proposed integrated designs can enable the utilization of fossil fuels in an environment friendly, technically feasible and an economical way.

Facilitated transport membranes for H2 purification from coal-derived syngas: A techno-economic analysis

A single-stage membrane process has been designed for using facilitated transport membranes (FTMs) to decarbonize the coal-derived syngas from an integrated gasification combined cycle (IGCC) power plant. The necessary process model and costing method have also been developed to assess the technical feasibility and process economics. In order to account for the carrier saturation phenomenon associated with FTMs, a homogeneous reactive diffusion model is integrated into the process model. The techno-economic study reveals that the mitigated carrier saturation upon bulk CO2 removal can lead to appreciable increases in the CO2 permeance and CO2/H2 selectivity, which can be utilized to achieve 95% CO2 purity and 95% H2 recovery with a CO2/H2 selectivity of 50 at the complete carrier saturation. FTMs with different facilitated transport characteristics can also be arranged in a hybrid membrane configuration to render a H2 recovery of 99% and a cost of electricity of $118.5/MWh, which is 12.5% lower than that of the benchmark Selexol process.

Performance analysis of a 550MWe solid oxide fuel cell and air turbine hybrid system powered by coal-derived syngas

We here present and analyze a novel conceptual design of 550 MW-level, syngas-fueled intermediate-temperature solid oxide fuel cell (SOFC)/Air Turbine (AT) hybrid system with an oxy-fuel combustion. To decouple the operation of SOFC and AT and allow independent operation of each, an intermediate heat exchanger is implemented between SOFC and AT cycles to transfer only heat from SOFC to AT. To facilitate CO2 separation and capture, the gas streams from both electrodes are separately operated and pure O2 is used in the afterburner for combustion. A total of four scenarios has been analyzed to cover the effects of current density, pressure and staged SOFC design. The results show that by elevating the pressure to 10 atm and using two-stage SOFC design, the system can achieve an overall efficiency of 64% at a nominal power output. The work provides important engineering insights in SOFC staged design and operating conditions for the next-generation SOFC/turbine hybrid systems.

CO Hydrogenation to C2 Oxygenates over SiO2 Supported Rh-Based Catalyst: The Effect of pH Value of Impregnation Solution

The synthesis of C2 oxygenates including ethanol directly from coal-derived syngas is significant from both academic and practical points of view and SiO2 supported Rh-based catalysts are very effective for this conversion. However, the high price of Rh requires the improvement of its dispersion to maximize Rh efficiency. The adjustment of impregnation solution pH value can modify effectively the metal dispersion over the support. Herein, we reported the pH effect on catalytic performance of Rh-Mn-Li/SiO2 for CO hydrogenation to C2 oxygenates for the first time. A series of catalysts were prepared from different pH values of impregnation solutions, and were characterized by various techniques. With the increasing of solution pH value above zero point of charge (ZPC) of silica, Rh particle sizes increased with much wider size distribution and reduction of Rh species was restrained over the prepared catalysts owing to the stronger interaction between Rh and support. As a result, the active sites for CO insertion, especially for CO or H2 dissociation was lowered, leading to the depletion of the activity for the formation of C2 oxygenates from CO hydrogenation, and larger Rh particle size with wider size distribution favors the production of long chain hydrocarbons. On the contrary, when the catalyst was prepared using solution with pH below ZPC of silica, the dispersion and the reduction of Rh were promoted due to suitable Rh-support interaction, and in the CO hydrogenation reaction, the space time yield and selectivity of C2 oxygenates reached 679.4 g/kg-cat/h and 73.3%, respectively. The pH value of impregnating solution regulate the metal-support interaction and thus Rh particle sizes and its reduction, which effects strongly CO hydrogenation activity and selectivity.

Interaction mechanism among CO, H2S and CuO oxygen carrier in chemical looping combustion: A density functional theory calculation study

When using coal-derived syngas or coal as fuel in chemical looping combustion (CLC), CO as a representative pyrolysis/gasification product and H2S as the main sulfurous gas coexist in fuel reactor. Either CO or H2S can absorb on the surface of CuO (the active component of Cu-based oxygen carriers), and reactions will occur among them. In this study, density functional theory (DFT) calculations are conducted to investigate the interaction among H2S, CO, and CuO, including: the reaction between CO and H2S over CuO particle, the influence of CO on the H2S dissociation and further reaction process, and the impact of H2S dissociation products on CO oxidation. Firstly, the co-adsorption results suggest that H2S might directly react with CO to produce COS via the Eley–Rideal mechanism, while CO prefers to react with HS* or S* via the Langmuir–Hinshelwood mechanism. This means that the reaction mechanisms between CO and H2S will change as the H2S dissociation proceeds, which has already been forecasted by the co-adsorption energies and verified by all of potential Eley–Rideal and Langmuir–Hinshelwood reaction pathways. Then, the influence of CO on the H2S dissociation process is examined, and it is noted that the presence of CO greatly limits the dissociation of H2S due to the increased energy barrier of the rate-determining dehydrogenation step. Furthermore, the impact of H2S dissociation products on CO oxidation by CuO is also investigated. The presence of H2S and S* significantly supresses the CO oxidation activity, while the presence of HS* slightly promotes the CO oxidation activity. Finally, the complete interaction mechanisms among H2S, CO, and CuO are concluded. It should be noted that COS will be inevitably produced via the Langmuir–Hinshelwood reaction between surface S* and CO*, which is prior to H2O generation and subsequent sulfidation reaction.

Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions

A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas.

Experimental and Theoretical Insights into the Effect of Syngas Components on Hg0 Removal over CoMn2O4 Sorbent

CoMn2O4 spinel sorbent was applied to remove Hg0 in coal-derived syngas. The impacts of syngas components, including H2S, H2, CO, HCl, and H2O, on Hg0 abatement were examined. Moreover, the Hg0 rem...

Experimental and DFT studies of the role of H2S in Hg0 removal from syngas over CuMn2O4 sorbent

Abstract Elemental mercury (Hg0) and hydrogen sulfide (H2S) are two typical toxic pollutants in coal-derived syngas. The specific role of H2S in Hg0 elimination over CuMn2O4 sorbent and the involved reaction mechanism were systematically studied by experimental and theoretical methods. The synthesized CuMn2O4 sorbent was tested for Hg0 removal under simulated syngas and exhibited superior Hg0 capture performance (up to 95.6% at 200 °C). In the absence of H2S, both H2 and CO inhibited Hg0 removal over CuMn2O4, but the Hg0 removal efficiency was greatly improved after the introduction of 400 ppm H2S. H2S played a key role in Hg0 elimination in syngas by generating reactive sulfur species upon CuMn2O4. Density functional theory (DFT) calculations indicated that Hg0 and HgS were strongly chemisorbed upon CuMn2O4 surface with the adsorption energies of −129.84 and −220.21 kJ/mol, respectively. H2S was dissociatively adsorbed on CuMn2O4 and generated active sulfur species. Both H2S-pretreatment experiments and DFT calculations demonstrated that Hg0 reaction with H2S over CuMn2O4 occurred via a Langmuir–Hinshlwood mechanism, where chemisorbed Hg0 reacted with active sulfur species to form surface-bonded HgS. Furthermore, XPS and TPD analyses certified that the formation of active sulfur species and HgS upon the spent CuMn2O4 sorbents.

Multi-scale membrane reactor (MR) modeling and simulation for the water gas shift reaction

This work focuses on the multi-scale modeling of a high-pressure membrane reactor (MR) carrying out the water gas shift reaction (WGSR). The work assesses the MR’s effectiveness in transforming coal-derived syngas into two streams, one rich in hydrogen and the other rich in carbon dioxide. The model employs Reynolds Transport Theorem derived constitutive equations at the reactor and the catalyst pellet scales. Convection/conduction/reaction/diffusion phenomena are accounted for, using the Ergun, Chapman-Enskog, Stefan-Maxwell, and Dusty-Gas models, respectively. The model’s power and flexibility are demonstrated by carrying out numerical simulations for both the MR and packed-bed reactors (PBR) for various operating conditions and design parameters. It is shown that significant variation of the catalyst pellet effectiveness factor occurs along the reactors’ axial direction, and that catalyst pellets of the same diameter exhibit different effectiveness factors within the PBR and MR environments. The effect of the catalyst solid’s thermal conductivity on the temperature gradients within the catalytic pellet, and the effect of the sweeping gas’ pressure/temperature on the MR’s behavior are both quantified. Adiabatic and wall-isothermal operations are examined and are shown to exhibit significant differences from each other for both reactors.

250 kWth high pressure pilot demonstration of the syngas chemical looping system for high purity H2 production with CO2 capture

Chemical looping combustion (CLC) is an advanced technology for converting fossil fuel while achieving in-situ CO2 capture. The high purity CO generated in the combustion product stream is sequestration/utilization ready, which makes chemical looping one of the most attractive carbon emission control technology. In this paper, the authors present the design, simulation and experimental operation results of the 250 kWth high pressure syngas chemical looping (SCL) pilot plant. The pilot plant’s unique countercurrent moving bed design allows near-full conversion of coal-derived syngas with simultaneous production of high purity, carbon-free H2. Critical aspects of the design efforts, including heat and material balances, reactor sizing approach and solid flow control and measurement devices are presented. An ASPEN Plus® model is constructed to predict the gas and solid conversions of the SCL process the gas and solid conversions of the SCL process under different experimental conditions. The highest syngas conversion achieved was 97.95% with 16.03% oxygen carrier conversion, which were close to the thermodynamic limits for both the gas and solid phases in the reducer. Differences between the experimental results and predicted conversion values were more significant under conditions with lower oxygen carrier to fuel ratio. Greater than 99% purity H2 was produced from the moving bed oxidizer, and the scalability and feasibility of SCL process were successfully demonstrated.

Hydrogen production from coal-derived syngas undergoing high-temperature water gas shift reaction in a membrane reactor

In this study, a numerical model to predict the hydrogen production from water-gas shift reaction using coal-derived syngas as a feedstock was presented. The reaction was carried out in a palladium (Pd)-based membrane reactor operated at 900°C for yielding carbon monoxide (CO) conversion higher than the thermodynamic equilibrium limit. The sweep gas flow, membrane permeance, and steam-to-carbon ratio effects on the reactor performance were examined. Based on the obtained results, it was found that high CO conversion and hydrogen (H2) recovery were obtained when the reactor was operated in counter-flow mode and with high sweep gas flow rate, steam-to-carbon ratio, and membrane permeance. However, the H2S-to-H2 ratio in the reactor was found to increase with the CO conversion and can be higher than the thermodynamic limit for Pd sulfidization. Optimum operation parameters should be sought for obtaining high CO conversion and H2 recovery while preventing membrane failure due to Pd sulfidization.

Promoting the ambient-condition stability of Zr-doped barium cerate: Toward robust solid oxide fuel cells and hydrogen separation in syngas

Increasing the stability of perovskite proton conductor against atmospheric CO2 and moisture attack at ambient conditions might be equally important as that at the elevated service temperatures. It can ease the transportation and storage of materials, potentially reducing the maintenance cost of the integral devices. In this work, we initially examined the surface degradation behaviors of various Zr-doped barium cerates (BaCe0.7Zr0.1Y0.1Me0.1O3) using XRD, SEM, STEM and electron energy loss spectroscopy. Though that the typical lanthanide (Y, Yb and Gd) and In incorporated Zr-doped cerates well resisted CO2-induced carbonation in air at elevated temperatures, they were unfortunately vulnerable at ambient conditions, suffering slow decompositions at the surface. Conversely, Sn doped samples (BCZYSn) were robust at both conditions yet showed high protonic conductivity. Thanks to that, the anode supported solid oxide fuel cells equipped with BCZYSn electrolyte delivered a maximum power density of 387 mW cm−2 at 600 °C in simulated coal-derived syngas. In the hydrogen permeation test using BCZYSn based membrane, the H2 flux reached 0.11 mL cm−2 min−1 at 850 °C when syngas was the feedstock. Both devices demonstrated excellent stability in the presence of CO2 in the syngas.

Thermodynamic equilibrium analysis of water-gas shift reaction using syngases-effect of CO2 and H2S contents

Abstract Thermodynamic equilibrium of water-gas shift reaction (WGSR) under various temperatures, pressures and steam-to-CO (S/C) ratios was analyzed by Gibbs free energy minimization method. Coal-derived syngases with various CO2 and H2S contents were used as the feedstock. Based on the obtained results, it was found that CH4 and carbon formations were enhanced when syngas CO2 content increases. Carbon-free WGSR can be resulted using high S/C ratio. However, CH4-free WGSR cannot be resulted even with low S/C ratios. From the H2O conversion and H2 yield variations, the temperature at which reverse WGSR occurs can be identified and found to decrease with the increase in S/C ratio. Solid CaO sorbent was employed for both CO2 and H2S removals in WGSR when sour syngas was used as the feedstock. It was found that WGSR performance was enhanced due to the CO2 and H2S removals by CaO. The H2S concentration can be decreased with decreased S/C ratio while increasing the reaction pressure was not favourable for H2 production and H2S removal in WGSR with CaO. Because WGSR performance enhancement due to CO2 and H2S removals occurred at high temperature, catalysts can be eliminated in sorption-enhanced WGSR.

No.22 固体酸化物型燃料電池アノード発電能および微細焼結構造に対する石炭ガス化ガス中微量成分の影響調査(灰・微量元素(2))

No.22 固体酸化物型燃料電池アノード発電能および微細焼結構造に対する石炭ガス化ガス中微量成分の影響調査(灰・微量元素(2))

1-1-3 石炭ガス化ガス中微量不純物による固体酸化物型燃料電池燃料極の性能劣化に関する基礎的研究(1-1 選炭、微量元素、燃料電池,Session 1 石炭・重質油等)

1-1-3 石炭ガス化ガス中微量不純物による固体酸化物型燃料電池燃料極の性能劣化に関する基礎的研究(1-1 選炭、微量元素、燃料電池,Session 1 石炭・重質油等)

Warm Cleanup of Coal-Derived Syngas: Multicontaminant Removal Process Demonstration

Warm (250–450 °C) cleanup of coal- or biomass-derived syngas requires sorbents and catalysts to protect downstream conversions. We report first a sequential ZnO bed operation in which the capacity is optimized for bulk desulfurization at 450 °C, while subsequent removal of sulfur to parts-per-billion levels can be accomplished at a lower temperature of approximately 300 °C. At this temperature, gaseous sulfur (H2S and COS) could be adsorbed equally well using ZnO, both with and without the presence of H2O in the feed, suggesting direct absorption of COS can occur. Following five sulfidation and regeneration cycles, the bulk desulfurization bed lost about a third of its initial sulfur capacity; however, sorbent capacity stabilized. A bench-scale process consisting of five unit operations is described for the cleanup of a several contaminants in addition to sulfur. Syngas cleanup was demonstrated through successful long-term performance of a poison-sensitive Cu-based water-gas shift catalyst placed downstre...

Performance of a pilot-scale multitube membrane module under coal-derived syngas for hydrogen production and separation

Pilot-scale tests generate information about the performance of energy systems and thus help in the deployment of new technologies. This work aims at demonstrating the pilot-scale application of palladium-based membrane technology for the purification of H2. A multitube membrane module with a total permeable area of 1050cm2 was tested under actual coal-derived syngas. The module was composed of seven membranes with a Pd/Au/Pd layered structure supported on PSS tubes. The membranes were arranged with one membrane at the center and six equally distributed around it. The membranes had a composition of 7µmPd and 0.4µm Au and a cumulative He leak of <0.01cm3/min/bar before testing. The module was operated at 450°C, 12.6bar and 10lb/h of desulfurized syngas provided by a gasification unit and enriched with H2 to 34%. The module showed a stable H2 permeance of 16.2 Nm3m−2h−1bar−0.5 throughout 840h. The produced H2 purity was in the range of 99.87–98%. An H2 production of 6lb/day and recovery of 64% were achieved, representing a significant development in the field. The scalability and industrial applicability of this technology was successfully demonstrated. Furthermore, a CFD model illustrated different physical phenomena associated with this multitube configuration.

Novel Sorption-Enhanced Methanation with Simultaneous CO2 Removal for the Production of Synthetic Natural Gas

With increasing consumption of natural gas as a clean energy source and demand for efficient use of cheap and abundant coal, the production of synthetic natural gas from coal has been receiving considerable interest. In this study, the methanation reaction of coal-derived syngas for the production of synthetic natural gas was investigated using numerical simulations. In particular, the concept of a sorption-enhanced reaction, in which CO2 removal by sorption is carried out simultaneously with the reaction, was newly applied to the methanation reaction. Effects of the operating parameters such as the fraction of catalyst and sorbent, temperature, pressure, and feed ratio (H2/CO, H2O/CO, and CO2/CO) on CO conversion and purity, selectivity, and productivity of CH4 were evaluated by computational studies. It was found that the performance of the sorption-enhanced methanation reaction is controlled by both thermodynamic equilibrium and reaction kinetics. Therefore, the reaction would require an optimal cataly...