Experimental procedure of ICCU-DRM

Fixed-bed reaction systems are normally used for ICCU-DRM. Although TGA can also be used to demonstrate the stability of DFMs. However, the feeding gas composition could be different, in addition to temperature, materials and gas analytical equipment. Gas analysis can be done using GC-TCD and on-line gas analyser. The following section provides ICCU-DRM experimental procedures reported in the literature:

DOI: 10.1126/sciadv.aav507

“The proposed CaL methane reforming process was tested using the prepared CaO-Ni bifunctional sorbent-catalysts in a ChemBET PULSAR TPR/TPD chemisorption analyzer. Approximately 0.1 g of the sorbent-catalyst was placed in a quartz U-tube and heated to 1073 K at a rate of 25 K min−1 under a N2 flow of 8 ml min−1. Then, the temperature was held for 60 min with the introduction of H2 (2 ml min−1) to reduce the sample. After that, the temperature was decreased to 873 K, followed by the introduction of a CO2 flow of 2 ml min−1 instead of the H2 flow to carbonate the sample for 6 min (the CO2 capture step). Then, the temperature was increased to 1073 K at a rate of 40 K min−1, followed by the introduction of a CH4 flow of 2 ml min−1 instead of the CO2 flow to calcine the sample for 6 min (the CO2 conversion and CH4 reforming step). Subsequently, the temperature was decreased to 873 K, and then a new CaL CH4 reforming cycle was started by the introduction of a CO2 flow. Ten CaL CH4 reforming cycles were investigated in this study, and a blank run was performed to correct for the effects of temperature and gas flow switches. During the whole experiment, concentrations of CO2, CH4, and H2 in the outlet gas from the reaction tube were monitored every 1.2 min using a micro-gas chromatograph (GC; 490-GC, Varian), while the concentration of CO in the outlet gas was monitored every 1.2 min using another GC (7890B, Agilent). Both the Varian micro-GC and the Agilent GC were equipped with a molecular sieve 5A column and a thermal conductivity detector (TCD).”

“The isothermal alternated cyclic performance of Ni-Ba catalyst in the CO2 storage and regeneration process was evaluated, feeding CO2-He and CH4-He pulses (10,000 ppm each one and GHSV = 21,220 h−1) with an intermediate purge of He, using Ar as a tracer at 600, 650, and 700 °C as three different temperatures were used at ordinary pressure. The catalyst was previously reduced in situ at 600 °C under hydrogen atmosphere. In Fig. 3, the concentration profiles of CO2, CH4, CO, H2 and Ar at the reactor outlet at 280 min (7 cycles) are represented (Fig. 3a). The steady-state is reached after the third operation cycle and the initial disturbance of the signals at the beginning of each cycle is due to the valve-shift. During the CO2-storage step, for this feed, the saturation is reached within 3 min. In the regeneration step using methane (as a reducing and regenerating agent) both, CO2 desorbed and H2 formed are detected, although CO is also detected in less extension. In the next cycle during the CO2-storage step an increased formation of CO was also evidenced. In Fig. 3b, a magnification of the first and second cycles of operation is displayed. As can be seen, in the first cycle and during the CO2-acumulation period, CO2 signal presents a shorter breakthrough time in the saturation curve. Once the CO2 storage-step was finished the reactor was purged with He and the CO2 desorption mass-signal progressively decreased until it reaches zero. For the same cycle, the regeneration period starts by feeding 10,000 ppm of CH4 and contemporaneously, joint to CO2 desorption and with a delay time of 2.5 s, H2 and CO appeared as main products. ”

“The schematic diagram of a fixed-bed reactor facility is shown in Figure 2. A stainless steel reactor tube (i.e., 10 mm inner diameter and 700 mm length) is equipped with an N-type thermocouple and an external heating unit to measure the reaction temperature and to provide the heat supply for the reaction, respectively. The flow rates for all feeding gases were controlled and that of the outlet gas was detected by the mass flowmeter. The as-prepared samples together with quartz wool were placed on a stainless steel strut in the constant temperature zone of the reactor tube. Prior to each test, the desired amount of sample was first placed in the reactor tube and 100 mL min–1 N2 (99.999%) was then introduced and functioned as: a purge gas to blow away the residual air in the tube to avoid the occurrence of unwanted reactions, a standard gas to calibrate the CO2 sensor for reducing the instrument error, and a flowing gas to detect the reactor air tightness for ensuring the accuracy of the experiment.”


“Figure 2. Schematic diagram of the fixed-bed reactor facility.”

“For integrated CO2 capture and conversion experiment, 1 g of solid materials (i.e., a mixture of 40 wt % Fe2O3/Al2O3 and CaCO3 in a mole ratio of 0.80:0.15 (17)) was loaded into the fixed-bed reactor. During the reforming process, the reactor was first heated up to 900 °C in 10 min and then 100 mL min–1 CH4 (4.5% balanced with N2) was introduced into the reactor for 30 min. For the oxidation and carbonation reactions, air and CO2 (99.99%, 100 mL min–1) were respectively introduced into the reactor at 600 °C for 2 h in sequence. A gasbag was used to collect the total product gas and a gas chromatograph (GC) with a TDX-01 column was applied to detect the transient product gas composition. Because GC detection for one gas sample needed 20 min, the product gas component was collected per 1 or 2 min, stored, and then analyzed later. In addition, to identify the interaction between the oxygen storage material and CO2 sorbent during the reforming reaction, two single methane-reforming experiments based on CaCO3 and Fe2O3/Al2O3 were adopted as the reference cases.
The cyclic performance for this novel Ca–Fe chemical looping process was also evaluated in the fixed-bed reactor facility. The reforming reaction of 1 g of solid materials was first took place in 4.5% CH4 balanced with N2 (100mL min–1) at 900 °C for 30 min. Subsequently, the reaction temperature was ramped down and maintained at 600 °C. Then, oxidation and carbonation reactions were successively conducted in air and CO2 (100 mL min–1) for 2 h. Finally, the reaction temperature was ramped up and kept at 900 °C before methane was introduced to begin the next cycle. Five cycles for integrated CO2 capture and conversion were performed to allow assessment of the thermal stability and deactivation of the solid materials.”

“The decarbonation and carbonation temperatures were determined by respectively performing temperature-programmed calcination (in 50 N mL min−1 of He flow) and temperature-programmed carbonation (in 50 N mL min−1 of CO2 flow) for the as-prepared and reduced materials in the thermogravimetric analyzer (Shimadzu DTG-60). After purging with the corresponding gas at room temperature for 1 h, the sample (approximately 10–20 mg) was heated from 30 °C to 950 °C with a ramping rate of 10 °C min−1. Then, the stability of cyclic CO2 uptake of the as-prepared materials was tested by CO2 capture and release cycling experiemnts at 720 °C. Approximately 10–20 mg of the as-prepared material was loaded into the analyzer chamber, followed by purging with He for 30 min at room temperature. Afterwards, the material was precalcined at 720 °C (with a ramping rate of 10 °C min−1) for 5 min in He flow. Subsequently, the material carbonation (i.e. CO2 capture) was performed at 720 °C for 15 min in pure CO2 flow (50 N mL min−1) followed by the material regeneration (i.e. CO2 release) at same temperature for 45 min in pure He flow (50 N mL min−1). Totally 10 cycles of CO2 capture and release were performed for each material. The changes in sample weight as a function of time were monitored online, shown as the variation of TGA curve. The exothermic and endothermic properties of the reactions were respectively indicated by the positive and negative peaks in the DTA profile.”

“The activity and stability of the as-prepared materials during DRM reaction were examined by steady-state experiments conducted in a quartz tube microreactor (inner diameter: 4 mm) at 720 °C and 1 bar. The reactor was heated by a wire wound tube furnace with an inner diameter of 15 mm and a body length of 150 mm, equipped with K-type thermocouples (Carbolite, MTF 10/15/130). Typically, 50 mg of material without diluent was packed into the reactor between quartz wool plugs, positioned in the middle of the furnace within a length of 30 mm, where the heating is most uniform, with maximum temporal temperature fluctuations in the catalyst bed around 5 °C. The flow rate of feed gas was controlled by means of Brooks mass flow controllers calibrated with the corresponding gases. After passing through a water trap, the composition of the outlet gas was analyzed online using gas chromatography (GC) (Agilent, HP 6890) equipped with a TCD, while the gas flow rate was measured by an Agilent ADM digital flow meter. The concentration (vol%) of each product in the outlet gas was calculated by the corresponding conversion factor determined from the calibration curve of concentration versus GC peak area. Prior to the DRM reaction, the material was reduced at 750 °C (with a ramping rate of 10 °C min−1) under 10 vol% H2/He (50 N mL min−1) for 30 min, then the temperature was decreased to 720 °C (at a rate of 10 °C min−1) in He flow and stabilization for 20 min. Subsequently, the DRM reaction started by feeding 50 N mL min−1 of 10 vol% CH4 + 10 vol% CO2 + 80 vol% He mixture gas. After 10 min, GC online analysis started and sampling was taken every 1 h. The H2/CO ratio of syngas was determined by the ratio between H2 and CO concentrations in the outlet product. “

“The tests of ICCU-DRM were performed in a fixed bed with a quart pipe reactor (inner diameter of 20 mm and 400 mm in length) heating by a furnace and the schema of the experimental test system is presented in Fig. S1. Accurate mass flow controllers were used to adjust the feeding of CH4, CO2, and N2. Meanwhile, the concentrations of CH4, CO2, CO and H2 in the exhaust gas were detected continuously by an online gas analyzer (NOVA-975PA) equipped with non-dispersive infrared detectors and thermal conductivity detector. In a typical experiment, the blended sample containing 2 g K-Li4SiO4 sorbent and 2 g catalyst were added in quart pipe reactor and preliminarily the reduction of 2 g catalyst was performed at 650 °C for 1 h under 10 vol% H2/N2 (500 mL min−1). Subsequently, the atmosphere was switched into 15 vol% CO2/N2 for simulate flue gas (500 mL min−1) and CO2 capture was performed at 600 °C, 625 °C or 650 °C for 0.5 h. After CO2 capture, the gas was changed into N2 (500 mL min−1) for 2 min so as to purge the reactor under the same temperature of carbon capture, and then the gas was varied into mixture of CH4 and N2 with specified volume concentration (1.7 vol% CH4 for 600 °C, 2.1 vol% CH4 for 625 °C, and 2.4 vol% CH4 for 650 °C) under the same flow velocity for CO2 desorption and conversion.”

“Figure S1. Schematic of the experimental test system. (”

“Integrated CO2 capture and CH4 reforming was conducted with both residual O2-containing flue gas and O2-free CO2 gas. The experiments were conducted in a U-tube with 0.5 g material in each test. While conducting SLDRM with residual O2-containing flue gas, the sample was periodically exposed to 25 vol% flue gas (3 vol% O2, 15 vol% CO2 and 82 vol% Ar) in Ar during the carbonation stage and 10 vol% CH4 in Ar during the reforming stage. The flow rate in the carbonation stage is flue gas/Ar = 10/30 sccm. And the flow rate in the reforming stage is CH4/Ar = 3.3/30 sccm. 2 min Ar of 30 sccm was used for purging between each stage. While conducting SLDRM with O2-free CO2 gas, the sample was first reduced by 25% H2 in Ar at 850 °C for 2 h before the experiment. The sample was periodically exposed to 25 vol% CO2 in Ar (10 sccm CO2 and 30 sccm Ar) during the carbonation stage and 10 vol% CH4 in Ar (3.33 sccm CH4 and 30 sccm Ar) during the reforming stage. 2 min Ar of 30 sccm was used for purging between each stage. The composition of product gas was online analyzed with a Cirrus 2 mass spectrometer.”

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