[en] Highlights: • Two-train elevated temperature pressure swing adsorption for H₂ purification. • Optimal process achieves 99.9994% hydrogen purity and 97.51% hydrogen recovery ratio. • Total steam consumption is significantly reduced with reflux structures. The trade-off between hydrogen recovery ratio (HRR) and hydrogen purity (HP) is one of the main drawbacks in normal temperature pressure swing adsorption (NT-PSA) for producing high-purity hydrogen from shifted gas. In this paper, a two-train elevated-temperature pressure swing adsorption (ET-PSA) process that achieved 99.999% HP and over 95% HRR is proposed, which has wide application potentials in fuel cells and chemical industries. Potassium-promoted layered double oxide (K-LDO), which shows reasonable working capacity and fast adsorption/desorption kinetics at elevated temperatures (200–450 °C), is adopted as the CO₂ adsorbent. CO in the shifted gas is co-purified by high-temperature water gas shift (WGS) catalysts added to the columns. The first-train ET-PSA adopted an eight-column thirteen-step configuration with shorter step time to remove most of the CO/CO₂ in the shifted gas, and the second-train ET-PSA adopted a double-column seven-step configuration with longer step time to purify the residual gas impurities. The introduction of co-current high-pressure steam rinse and counter-current low-pressure steam purge is the key to achieve both high HRR and HP. The high-temperature steam is the main energy consumption of ET-PSA rather than low HRR in NT-PSA, and the total steam consumption is reduced by adopting the tail gas from second-train ET-PSA as the purge gas for first-train ET-PSA. The optimal results achieved 97.51% HRR and 99.9994% HP with only 0.188 rinse-to-feed ratio and 0.263 purge-to-feed ratio, which are the highest values reported for PSAs producing high-purity hydrogen from carbon-based fuels.

[en] Hydrogen from coal-based syngas is usually purified by deep desulfurization and decarbonization scrubbing technologies. Such electricity consuming processes cost a large number of heat exchangers and compressors. In this study, a two-stage demonstration unit had been constructed and demonstrated to purify hydrogen (including useful nitrogen for ammonia synthesis) from on-site sideline shift gas mixture at Yangmei Fengxi ammonia plant. For the first stage, an 8-column hydrogen purification process by novel elevated temperature pressure swing adsorption (ET-PSA, operated at 180 to 220 °C) was developed and demonstrated to capture H₂S and CO₂ simultaneously by hydrophobic activated carbon (AC) to reduce the impurities compared to that of room temperature PSA. Working condition at elevated temperature was proved to be appropriate and stable for reversible H₂S removal by AC. The second stage was a temperature swing adsorption for deep purification of CO to 0.2 ppm by commercial CuCl monolayer dispersed zeolites (PU-1 synthesized by Beijing Peking University Pioneer Technology Co., Ltd.). In order to examine the standard of trace impurities such CO and H₂S in product H₂, the purified H₂ was offered to a 3 kW proton exchange membrane fuel cell (PEMFC) stack to prove that all carbon and sulfur impurities met the demand not only for ammonia synthesis, but for PEMFC as well. Besides, two novel PSA steps: high pressure steam rinse and low pressure nitrogen purge were adopted to improve H₂ recovery to above 93%. To demonstrate its stability, over 2500 h of operation had been carried out on the small-scale demonstration rigs by far.

[en] Highlights: • Flower-like structure of AMO-LDHs with dense elevated temperature CO₂ active sites. • CO₂ working capacity was 63.4% higher than that of commercial LDOs. • Exfoliated LDH layers provided increased promoters for surface modification. -- Abstract: Layered double oxides (LDOs), which derives from the calcination of layered double hydroxides (LDHs), are a type of elevated temperature CO₂ adsorbents for pre-combustion carbon capture. Due to its highly aggregated stone-like structure, the CO₂ capture capacity of commercial MgAl-CO₃ LDO is relatively low. A novel method, the aqueous miscible organic solvent treatment (AMOST), was proposed to synthesize LDH precursors with increased surface area. In this work, three types of LDHs and LDOs with different Mg/Al ratios were synthesized using the conventional and AMOST methods. The aqueous miscible organic (AMO) solvent-treated Mg₂Al-CO₃ presented the highest CO₂ working capacity of 0.506 mmol/g at 400 °C of all the LDOs, which was 63.4% higher than that of commercial MG63. By removing the interlayered water using AMO solvent washing, the LDH was exfoliated into nanosheets and formed flower-like structures. The exposed internal surfaces increased the density of effective active sites after calcination. The AMO solvent-treated LDH also provided more alkali ion promoters for surface modification and led to better dispersion. After impregnation with 20 wt.% K₂CO₃, the CO₂ working capacity of the AMO solvent-treated K-Mg₃Al-CO₃ could reach a stable value of 1.069 mmol/g at 400 °C, which was 22.9% higher than that of commercial K-MG70.