Facile and Versatile Sol-Gel Strategy for the Preparation of a High-Loaded ZnO/SiO2 Adsorbent for Room-Temperature H2S Removal.

Preparation of well-dispersed ZnO nanograins is necessary to improve their reactivity toward room-temperature H2S removal. However, the challenge to design such a ZnO-based adsorbent with high ZnO loading is yet to be fulfilled. Herein, a facile sol-gel strategy is reported for the preparation of ZnO/SiO2 adsorbents for efficient H2S removal, by innovating a gel-drying method and simultaneously controlling ZnO grain formation through optimizing the molar ratio of ethylene glycol (EG)/nitrates in its precursors. The fabricated adsorbent embedded well-dispersed ZnO nanograins, of approximately 10-15 nm, into a SiO2 matrix (57 wt % ZnO loading) and thus yielded a high H2S removal capacity of 108.9 mg S/g sorbent. Therein, EG was used as a modifier for inhibiting the formation of a denser SiO2 network during the gel drying process and was used as a fuel for promoting the decomposition of nitrates and increasing the surface area of the composites in the subsequent calcination. Modulating the molar ratio of EG/nitrates ≤ 2 in precursors or traditional drying of the gel in an oven should be avoided because these would lead to the oxidation of EG by metallic nitrates and form carboxylate complexes during the gel-drying process. Although the produced ZnO grains had a very small size of less than 5 nm, a layer of monodentate ZnCO3 impurity was formed on the ZnO surface, which will drastically decrease the reactivity of ZnO toward H2S. According to the encouraging results from CuO and Co3O4, this strategy has proved to be versatile for the preparation of other metal oxide/SiO2 adsorbents.

Three-dimensionally ordered macroporous iron oxide for removal of H2S at medium temperatures.

A series of iron oxide sorbents with novel structures of three-dimensionally ordered macropores (3DOM), ranging in size from 60 to 550 nm, were fabricated and creatively used as sorbents for the removal of H2S at medium temperatures of 300-350 °C. Evaluation tests using thermogravimetric analysis (TGA) and a fixed-bed reactor showed that, in comparison to the iron oxide sorbent prepared by a conventional mixing method, the fabricated iron oxide sorbent with a 3DOM structure exhibited much higher reactivity and efficiency, as well as high sorbent utilization with low regeneration temperature. The excellent performance of 3DOM iron oxide as a sulfur sorbent is attributed to its special texture, i.e., the open and interconnected macroporous, large surface area, and nanoparticles of iron oxide, which are revealed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption techniques. The investigation results of the pore effect on the performance of the sorbent show that sorbents with pores size around 150 nm in diameter revealed the best performance. The reason is that pores of this size are large enough to allow gas to pass through even if the channel is partially blocked during the reaction process while remaining a large surface area that can provide more active sites for the reaction.

Synergistic effect of bimetal in isoreticular Zn-Cu-1,3,5-benzenetricarboxylate on room temperature gaseous sulfides removal.

Isoreticular bimetal M-Cu-BTC has considerable potential in improving the sulfides removal performance of Cu-BTC. Herein, three transition metals, namely, Zn2+, Ni2+ and Co2+, were assessed to fabricate M-Cu-BTC, a desirable isoreticular bimetal. Results demonstrated the feasibility of using Zn2+ to fabricate an isoreticular bimetallic Zn-Cu-BTC. The Zn2+ doping content of Zn-Cu-BTC was varied to investigate its influence on the hydrogen sulfide (H2S) and methyl sulfide (CH3SCH3) removal performance of Cu-BTC. The experimental results indicated that the sulfides removal performance of Zn-Cu-BTC increased and then decreased with increasing Zn doping content. The highest H2S and CH3SCH3 removal capacities of 84.3 and 93.9 mg S/g, respectively, were obtained when the Zn2+ doping content was 17%. The hybridisation of Zn and Cu in Zn-Cu-BTC induced a strong interaction between them. This interaction increased the binding energies of H2S and CH3SCH3 towards the Cu and Zn adsorption sites while weakening the bond order between Zn and Cu. The weakened bond order made the Zn-Cu bonds easier to form metal sulfides during desulfurization process, thereby synergistically enhancing sulphide removal.

New Strategy toward Household Coal Combustion by Remarkably Reducing SO2 Emission.

A large amount of sulfur dioxide (SO2) will be released during rural household coal combustion, causing serious environmental pollution. Therefore, it is very urgent to develop a clean and efficient fuel to substitute rural household coal controlling SO2 emission. In this paper, a new strategy toward scattered coal combustion with remarkably reducing SO2 emission was proposed. Coal and compound additive of Al2O3 and CaCO3 were blended and then copyrolysis at 1050 °C was performed to produce clean coke. First, the sulfur content of clean coke was reduced, meanwhile, generating sulfur fixation precursor during pyrolysis. Then, clean coke is used for efficient sulfur fixation during the subsequent combustion process to reduce SO2 emissions. The effects of combustion temperature, Al/S molar ratio, and the mechanism of sulfur retention during clean coke combustion were studied in the tube furnace and muffle furnace. The mechanism can be attributed the following reason: (a) CaS produced during pyrolysis and CaO decomposed by complex additives were oxidized during combustion, and CaO captured the SO2 released from clean coke combustion, which formed CaSO4. (b) CaSO4 reacts with Al2O3 to produce calcium sulfoaluminate at high temperatures, which improves the sulfur fixation efficiency of clean coke combustion at high temperatures. In a word, this new strategy can greatly reduce the emission of SO2, thus helping to solve rural household coal pollution problems.

Tuning the ZnO-activated carbon interaction through nitrogen modification for enhancing the H2S removal capacity.

Herein, an unusual strategy is reported to enhance the H2S uptake capacity by varying the ZnO-support interaction and controlling the acid-basic environment of the pore channel; this is in place of the generally reported method of decreasing ZnO nanoparticle size and optimizing their porosity. With this regard, coal based activated carbon (AC) is selected as the support and the interaction with ZnO is tuned by introducing N species on AC surface through a soft nitriding strategy. Our strategy is confirmed to be prospective based on the fact that the N-modifying AC supported ZnO adsorbent show a maximum breakthrough sulfur capacity (BSC) of 62.5 mg S/g sorbent, two times larger than that without N-modification (30.5 mg S/g sorbent). The enhanced BSC is attributed to the introduced N species, which not only increases the basicity of the water film condensed in the pores, promoting the dissociation of H2S and H2O, but also influences the electronic structure of ZnO, accelerating the rate of lattice diffusion during in sulfidation process. It is also found that the high BSC of sorbent with N modification is related to the doped N concentrations, ZnO dispersion and the material porosity. This paper provides a new insight for designing supported ZnO based adsorbents.

Mechanistic and Kinetic Analysis of Na2SO4-Modified Laterite Decomposition by Thermogravimetry Coupled with Mass Spectrometry.

Nickel laterites cannot be effectively used in physical methods because of their poor crystallinity and fine grain size. Na2SO4 is the most efficient additive for grade enrichment and Ni recovery. However, how Na2SO4 affects the selective reduction of laterite ores has not been clearly investigated. This study investigated the decomposition of laterite with and without the addition of Na2SO4 in an argon atmosphere using thermogravimetry coupled with mass spectrometry (TG-MS). Approximately 25 mg of samples with 20 wt% Na2SO4 was pyrolyzed under a 100 ml/min Ar flow at a heating rate of 10°C/min from room temperature to 1300°C. The kinetic study was based on derivative thermogravimetric (DTG) curves. The evolution of the pyrolysis gas composition was detected by mass spectrometry, and the decomposition products were analyzed by X-ray diffraction (XRD). The decomposition behavior of laterite with the addition of Na2SO4 was similar to that of pure laterite below 800°C during the first three stages. However, in the fourth stage, the dolomite decomposed at 897°C, which is approximately 200°C lower than the decomposition of pure laterite. In the last stage, the laterite decomposed and emitted SO2 in the presence of Na2SO4 with an activation energy of 91.37 kJ/mol. The decomposition of laterite with and without the addition of Na2SO4 can be described by one first-order reaction. Moreover, the use of Na2SO4 as the modification agent can reduce the activation energy of laterite decomposition; thus, the reaction rate can be accelerated, and the reaction temperature can be markedly reduced.

Investigation on activated semi-coke desulfurization.

An activated semi-coke with industrial-scale size was prepared by high-pressure hydrothermal chemistry activation, HNO3 oxidation and calcination activation in proper order from Inner Mongolia Zhalainuoer semi-coke, which is rich in resource and cheap in sale. SO2 adsorption capacity on this activated semi-coke was assessed in the fixed bed in the temperature range of 60-170 degrees C, space velocity range of 500-1300 h(-1), SO2 concentration of 1000-3000 ppmv, and N2 as balance. The surface area, elemental and proximate analysis for both raw semi-coke and activated semi-cokes were measured. The experimental results showed that the activated semi-coke has a high adsorption capacity for sulfur dioxide than the untreated semi-coke. This may be the result of increase of surface area on activated semi-coke and surface oxygen functional groups with basicity characteristics. Comparison to result of FTIR, it is known that group of -C-O-C- may be active center of SO2 catalytic adsorption on activated semi-coke.

Design of a sorbent to enhance reactive adsorption of hydrogen sulfide.

A series of novel zinc oxide-silica composites with three-dimensionally ordered macropores (3DOM) structure were synthesized via colloidal crystal template method and used as sorbents for hydrogen sulfide (H2S) removal at room temperature for the first time. The performances of the prepared sorbents were evaluated by dynamic breakthrough testing. The materials were characterized before and after adsorption using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the composite with 3DOM structure exhibited remarkable desulfurization performance at room temperature and the enhancement of reactive adsorption of hydrogen sulfide was attributed to the unique structure features of 3DOM composites; high surface areas, nanocrystalline ZnO and the well-ordered interconnected macroporous with abundant mesopores. The introduction of silica could be conducive to support the 3DOM structure and the high dispersion of zinc oxide. Moisture in the H2S stream plays a crucial role in the removal process. The effects of Zn/Si ratio and the calcination temperature of 3DOM composites on H2S removal were studied. It demonstrated that the highest content of ZnO could reach up to 73 wt % and the optimum calcination temperature was 500 °C. The multiple adsorption/regeneration cycles showed that the 3DOM ZnO-SiO2 sorbent is stable and the sulfur capacity can still reach 67.4% of that of the fresh sorbent at the fifth cycle. These results indicate that 3DOM ZnO-SiO2 composites will be a promising sorbent for H2S removal at room temperature.