Akiho and Kobayashi (Fuel, 2019) demonstrated a regenerable copper-based sorbent in honeycomb form ('A-CBS') for removing gaseous elemental mercury (Hg0\mathrm{Hg}^0) from the pressurized, reducing syngas of an oxy-fuel integrated gasification combined cycle (IGCC) power plant: after pre-sulfidation, the honeycomb cut Hg0\mathrm{Hg}^0 from roughly 75–250 µg/m³N to below 1.0 µg/m³N at 140 °C and near 1 MPa, and regeneration by heating in dilute O2\mathrm{O_2} released the captured mercury — over exactly three laboratory cycles on simulated syngas, leading the authors to describe A-CBS as a 'potential candidate' for the dry mercury removal process. The qualification items beyond that demonstration (cyclic behavior beyond three cycles, unquantified mechanical durability, untested effects of real-syngas contaminants, integration of the Hg0\mathrm{Hg}^0/SO2\mathrm{SO_2} regeneration off-gas with downstream concentrating sorbents, and module scale-up) are the facets on which qualification turns, and it is to be established whether any later work extends the A-CBS honeycomb, or an equivalent regenerable honeycomb (a fixed-bed honeycomb mercury sorbent operated at IGCC pressure on reducing syngas and regenerated by heating in dilute O2\mathrm{O_2}), to long-term operation on pressurized contaminant-loaded syngas, while the regenerable-sorbent field has continued on powder metal oxides at laboratory scale under atmospheric simulated syngas. The question is therefore whether the qualification gap can be closed: to establish, by extended cyclic testing under representative pressurized oxy-fuel IGCC syngas, whether a regenerable honeycomb mercury sorbent sustains capture capacity, mercury mass balance, mechanical integrity, and off-gas compatibility at engineering scale, or whether a documented failure mode establishes that it does not.

Background

In an integrated gasification combined cycle (IGCC) plant, coal is gasified into synthesis gas (syngas, a CO- and H2\mathrm{H_2}-rich fuel gas) that is burned in a gas turbine; in the oxy-fuel variant the gasifier is blown with O2\mathrm{O_2} together with recycled CO2\mathrm{CO_2} instead of air, so the plant delivers a concentrated CO2\mathrm{CO_2} stream for capture at a low efficiency penalty — a concept estimated to reach about 44% thermal efficiency (lower-heating-value basis) with a roughly 93 vol% CO2\mathrm{CO_2} product (Kobayashi and Akiho, Journal of Environmental Management, 2017, DOI 10.1016/j.jenvman.2017.05.067). To preserve that efficiency, the fuel gas should be cleaned dry, meaning by regenerable fixed-bed sorbents at elevated temperature and pressure, rather than by wet scrubbing, which cools the gas and produces wastewater. A long-running program at Japan's Central Research Institute of Electric Power Industry (CRIEPI) developed this dry syngas purification train: a halide-removal stage and a desulfurization stage using a honeycomb of zinc ferrite (a mixed zinc–iron oxide that binds H2S\mathrm{H_2S} as solid sulfide) (Kobayashi and Akiho, Fuel, 2017, DOI 10.1016/j.fuel.2017.02.087), which were verified at bench scale on syngas from a real O2\mathrm{O_2}/CO2\mathrm{CO_2}-blown gasifier over five sulfidation–regeneration cycles (Kobayashi, Akiho, Ozawa and Nakajima, Fuel, 2019, DOI 10.1016/j.fuel.2019.03.136).

Mercury is the remaining trace contaminant without a qualified dry stage. During gasification, mercury in coal partitions almost entirely to the gas phase, predominantly as gaseous elemental mercury (Hg0\mathrm{Hg}^0), in a hot (at least about 100 °C), pressurized (near 1 MPa), strongly reducing gas. The conventional control — activated carbon (AC), usually sulfur-impregnated — works by physical adsorption mainly at low temperature and chiefly for oxidized mercury (Hg2+\mathrm{Hg}^{2+}), and is a once-through consumable rather than a regenerable upstream process. Akiho and Kobayashi (Fuel, 2019, DOI 10.1016/j.fuel.2019.05.075) therefore developed copper-based sorbents (CBS) in a honeycomb form they call A-CBS: copper oxide (CuO) impregnated into a silica honeycomb support (2.8 wt% Cu, calcined at 600 °C). The honeycomb geometry gives low pressure drop and better mechanical integrity than the earlier extruded CBS honeycombs, which cracked and lost most of their surface area (from 94 to 40 m²/g) upon sulfidation. In operation the sorbent is first pre-sulfidized — exposed to 1000 ppm H2S\mathrm{H_2S} in N2\mathrm{N_2} at 120 °C until H2S\mathrm{H_2S} breakthrough (breakthrough being the point at which an impurity first appears in the outlet of a fixed bed) — which converts CuO to copper sulfide (CuxSy\mathrm{Cu_xS_y}). The sulfided copper chemically binds Hg0\mathrm{Hg}^0 as mercuric sulfide (HgS): CuxSy+z Hg0→z HgS+CuxSy−z\mathrm{Cu_xS_y} + z\,\mathrm{Hg}^0 \rightarrow z\,\mathrm{HgS} + \mathrm{Cu_xS_{y-z}} The spent sorbent is regenerated by heating to 280 °C in 1–2 vol% O2\mathrm{O_2} in N2\mathrm{N_2}, which oxidizes the HgS and releases the mercury back to the gas phase as Hg0\mathrm{Hg}^0 while producing SO2\mathrm{SO_2}: z HgS+z O2→z Hg0+z SO2z\,\mathrm{HgS} + z\,\mathrm{O_2} \rightarrow z\,\mathrm{Hg}^0 + z\,\mathrm{SO_2} In three sequential laboratory cycles of pre-sulfidation, capture, and regeneration at 140 °C and near 1 MPa (0.9–0.98 MPa reported) with simulated syngas (CO\mathrm{CO} 66.4 vol%, H2\mathrm{H_2} 18.8 vol%, CO2\mathrm{CO_2} 8.6 vol%, CH4\mathrm{CH_4} 1.5 vol%, H2O\mathrm{H_2O} 3.2 vol%, N2\mathrm{N_2} 1.5 vol%; inlet Hg0\mathrm{Hg}^0 75–250 µg/m³N), the pre-sulfidized A-CBS honeycomb held more than 99% capture with outlet Hg0\mathrm{Hg}^0 below 1.0 µg/m³N; the mercury sorbed in each capture step matched the mercury released in the following regeneration; and the specific surface area (about 96–98 m²/g) and pore structure were preserved. The authors proposed that the released Hg0\mathrm{Hg}^0 be concentrated at low temperature on a downstream sorbent such as impregnated AC, closing the loop of a reusable mercury stage. What the demonstration did not establish — long-term cycling, mechanical lifetime, real-syngas chemistry, off-gas integration, and scale — defines the question below.

Problem Statement

Can the reusable copper-based honeycomb mercury sorbent be qualified as the upstream mercury-removal stage of the dry syngas purification train of an oxy-fuel IGCC power plant — that is, does the demonstrated three-cycle laboratory performance on simulated syngas extend to long-term, realistic, engineering-scale operation? Five linked questions remain open, all serving this single qualification objective. (1) Long-term cyclic behavior: over many more than the demonstrated three pre-sulfidation–capture–regeneration cycles, does the sorbent reach a stable capacity, or does mercury accumulate irreversibly or capacity fade (the three-cycle data showed sorption still increasing with cycle number, and textural properties were tracked only through the first cycle)? (2) Mechanical durability: what is the quantified strength and crack resistance of the honeycomb under prolonged thermal cycling between roughly 120 and 280 °C, pressure cycling near 1 MPa, and full-scale flow and handling loads — the current claim rests only on the absence of cracking in three laboratory cycles? (3) Real-syngas performance: how do capture, pre-sulfidation dynamics, mercury speciation, and regeneration chemistry respond to the full compositional variability of actual oxy-fuel IGCC syngas — variable H2S carryover, HCl and other halides, NH3, particulates, and trace species — at IGCC pressure, noting that regeneration behavior at IGCC pressure has not been reported? (4) Off-gas integration: can the regeneration off-gas, containing the released Hg0\mathrm{Hg}^0 together with the SO2\mathrm{SO_2} formed by HgS oxidation, be captured and concentrated reliably on a downstream low-temperature sorbent such as impregnated activated carbon, in a form compatible with plant environmental control systems? (5) Scale-up: what pressure drop, reactor engineering, and economics result for a full-size fixed-bed honeycomb module? The qualification gap is closed if a regenerable honeycomb mercury sorbent is shown to sustain capture capacity, mercury mass balance, mechanical integrity, and off-gas compatibility over extended cyclic operation on representative pressurized oxy-fuel IGCC syngas at engineering scale (facets (1)-(4)), and is shown not to extend if a documented failure mode — such as capacity fade, irreversible mercury accumulation, mechanical failure, or failure of regeneration or off-gas handling under extended or pressurized operation — arises in any one facet; facet (5), scale-up, concerns the pressure drop, reactor engineering, and economics reported for a full-size fixed-bed honeycomb module; and the qualification gap remains open for any facet that the available evidence leaves undetermined.

References

  1. Hiroyuki Akiho and Makoto Kobayashi, 'Development of reusable mercury sorbents for an oxy-fuel IGCC power generation system', Fuel, 2019. DOI: 10.1016/j.fuel.2019.05.075, https://doi.org/10.1016/j.fuel.2019.05.075
  2. Makoto Kobayashi and Hiroyuki Akiho, 'Dry syngas purification process for coal gas produced in oxy-fuel type integrated gasification combined cycle power generation with carbon dioxide capturing feature', Journal of Environmental Management, 2017. DOI: 10.1016/j.jenvman.2017.05.067, https://doi.org/10.1016/j.jenvman.2017.05.067
  3. Makoto Kobayashi, Hiroyuki Akiho, Yasushi Ozawa, and Akira Nakajima, 'Evaluation of dry acid gas removal process on bench scale test facility coupled with syngas produced by O2/CO2-blown gasifier', Fuel, 2019. DOI: 10.1016/j.fuel.2019.03.136, https://doi.org/10.1016/j.fuel.2019.03.136
  4. Makoto Kobayashi and Hiroyuki Akiho, 'Performance evaluation of honeycomb shaped sorbent for sulfur removal in advanced oxy-fuel IGCC power generation plant', Fuel, 2017. DOI: 10.1016/j.fuel.2017.02.087, https://doi.org/10.1016/j.fuel.2017.02.087
  5. Makoto Kobayashi, 'Development of sorbents used in dry syngas purification', in Dry Syngas Purification Processes for Coal Gasification Systems, Elsevier, 2021. DOI: 10.1016/b978-0-12-818866-8.00004-5, https://doi.org/10.1016/b978-0-12-818866-8.00004-5
  6. Makoto Kobayashi, 'Measurement of impurities in syngas', in Dry Syngas Purification Processes for Coal Gasification Systems, Elsevier, 2021. DOI: 10.1016/b978-0-12-818866-8.00003-3, https://doi.org/10.1016/b978-0-12-818866-8.00003-3
  7. Zhen Wang, Jing Liu, Yingju Yang, Yingni Yu, Xuchen Yan, and Zhen Zhang, 'AMn2O4 (A = Cu, Ni and Zn) sorbents coupling high adsorption and regeneration performance for elemental mercury removal from syngas', Journal of Hazardous Materials, 2020 (volume 388, published online November 2019). DOI: 10.1016/j.jhazmat.2019.121738, https://doi.org/10.1016/j.jhazmat.2019.121738
  8. Zhen Wang, Jing Liu, Yingju Yang, Yingni Yu, Xuchen Yan, and Zhen Zhang, 'Regenerable CoxMn3−xO4 spinel sorbents for elemental mercury removal from syngas: Experimental and DFT studies', Fuel, 2020. DOI: 10.1016/j.fuel.2020.117105, https://doi.org/10.1016/j.fuel.2020.117105
  9. Zhuang Liu, Jinsong Zhou, Liang Jin, Qixin Zhou, Lingtao Zhou, Yang Lu, and Bohao Li, 'Mercury removal from syngas by metal oxides based adsorbent: A review', Fuel, 2022. DOI: 10.1016/j.fuel.2022.125057, https://doi.org/10.1016/j.fuel.2022.125057
  10. Guopei Zhang, Cong Wang, Xiaoyang Zhang, Yong Dong, Zhaomin Li, and Leteng Lin, 'Syngas mercury removal using LaMeOx/ZSM-5 sorbents: Mechanistic insights and performance tests under industrial conditions', Chemical Engineering Journal, 2025. DOI: 10.1016/j.cej.2025.159801, https://doi.org/10.1016/j.cej.2025.159801
  11. Takeharu Hasegawa, 'Numerical Study of Ammonia/O2-Fired Semiclosed Cycle Gas Turbine for Oxy-Fuel IGCC Power Generation With CO2 Capture', Journal of Engineering for Gas Turbines and Power, 2021. DOI: 10.1115/1.4050064, https://doi.org/10.1115/1.4050064
  12. Dunyu Liu, Chaoran Wang, Yunpei Fan, Qiuqi Liu, Xudong Wang, Kailong Xu, Jing Jin, Jingjing Ma, and Jinchen Ma, 'Mercury transformation and removal in chemical looping combustion of coal: A review', Fuel, 2023. DOI: 10.1016/j.fuel.2023.128440, https://doi.org/10.1016/j.fuel.2023.128440
  13. Yiming Wang, Bo Zhao, Weiwei Shan, Linbo Qin, Xi Sun, Qiang Zhang, Wangsheng Chen, Xiaowei Liu, and Jun Han, 'Effect of Tungsten on Hg0^0 Removal by W–Mn–Mo/CNT During Oxy-Fuel Combustion Simulated Flue Gas', Industrial & Engineering Chemistry Research, 2023. DOI: 10.1021/acs.iecr.3c01164, https://doi.org/10.1021/acs.iecr.3c01164
  14. Vineet Singh Sikarwar, Michael Pohorely, Arun Krishna Vuppaladadiyam, Christian Frilund, Marek Staf, Christoph Pfeifer, Frederik Ronsse, Pekka Simell, Ajay Kumar Kaviti, and Michal Jeremias, 'Progress in deep cleaning and upgrading of biomass- and waste-derived syngas for production of renewable fuels, chemicals and power', Resources, Chemicals and Materials, 2026. DOI: 10.1016/j.recm.2026.100172, https://doi.org/10.1016/j.recm.2026.100172
  15. Makoto Kobayashi, 'Scaling-up strategies', in Dry Syngas Purification Processes for Coal Gasification Systems, Elsevier, 2021. DOI: 10.1016/b978-0-12-818866-8.00007-0, https://doi.org/10.1016/b978-0-12-818866-8.00007-0