Desulfurization Sorbents Research Articles

Addition of Caco3 in the Incineration of Wastewater Sludge at 900º C. Preparation of Desulfurant Sorbents with the Incinerated Sludge

Addition of Caco3 in the Incineration of Wastewater Sludge at 900º C. Preparation of Desulfurant Sorbents with the Incinerated Sludge

Study on the Characterization of Zinc Ferrite High-Temperature Coal Gas Desulfurization Agent

Using ferric nitrate, zinc nitrate, ammonia liquor and binder as main raw materials, five kinds of zinc ferrite sorbents were prepared by the co-precipitation method. The effects of the different binders on the structure and texture of zinc ferrite sorbents were investigated. The morphology, composite structure, pore properties, and mechanical strength were studied by using modern several physicochemical techniques such as powder X-ray diffraction (XRD), scanning electronic microscopy (SEM), strength tester and gas absorption meter. It is showed that spinel structure ZnFe2O4 is not affected by different binders，and its particle diameter is in micron leve1. The spinel structures are present in the sorbents that have been calcined at 750 0C.. The sorbent employed kaolinite as binder is the best one of the five types of sorbents for desulfurization, while the one employed diatomite is the worst.Different binders modify the textural properties, modifying consequently the sorbent reactivity. Furthermore, the reactivity and sulfur capacity of sorbents are increasing with an increase in the pore volume.

Regeneration of Fe2O3-based high-temperature coal gas desulfurization sorbent in atmosphere with sulfur dioxide

Regeneration of a high-temperature coal gas desulfurization sorbent is a key technology in its industrial applications. A Fe2O3-based high-temperature coal gas desulfurizer was prepared using red mud from steel factory. The influences of regeneration temperature, space velocity and regeneration gas concentration in SO2 atmosphere on regeneration performances of the desulfurization sorbent were tested in a fixed bed reactor. The changes of phase and the composition of the Fe2O3-based high-temperature coal gas desulfurization sorbent before and after regeneration were examined by X-ray diffraction (XRD) and X-ray Photoelectron spectroscopy(XPS), and the changes of pore structure were characterized by the mercury intrusion method. The results show that the major products are Fe3O4 and elemental sulfur; the influences of regeneration temperature, space velocity and SO2 concentration in inlet on regeneration performances and the changes of pore structure of the desulfurization sorbent before and after regeneration are visible. The desulfurization sorbent cannot be regenerated at 500°C in SO2 atmosphere. Within the range of 600°C–800°C, the time of regeneration becomes shorter, and the regeneration conversion increases as the temperature rises. The time of regeneration also becomes shorter, and the elemental sulfur content of tail gas increases as the SO2 concentration in inlet is increased. The increase in space velocity enhances the reactive course; the best VSP is 6000 h−1 for regeneration conversion. At 800°C, 20 vol-% SO2 and 6000 h−1, the regeneration conversion can reach nearly to 90%.

Review of Experimental Characterization of Active Sites and Determination of Molecular Mechanisms of Adsorption, Desorption and Regeneration of the Deep and Ultradeep Desulfurization Sorbents for Liquid Fuels

This review analyzes the recent literature on the direct experimental determination of molecular and atomic-level nature of adsorption sites, mechanisms of adsorption under the mild (close to ambient) conditions, desorption of sulfur-aromatic compounds, and surface chemical reactions upon regeneration of the “spent” sorbents for desulfurization of the liquid fuels. Supported noble, transition metals and metal oxides, binary, and ternary metal oxides, activated carbons, zeolites, supported polymers, pervaporation membranes and other advanced adsorptive desulfurization materials are discussed. The recent trends in developing the deep and ultradeep desulfurization sorbents are discussed, and challenges of the direct determination of molecular mechanisms are described.

Hollow Fiber Sorbents for Desulfurization of Natural Gas

Pipeline natural gas is the primary fuel of choice for distributed fuel cell-based applications due to its well-developed infrastructure. The concentration of sulfur in odorized pipeline natural gas is about 30 ppm, with the acceptable level being <1 ppm for catalyst stability in such applications. Packed bed technology for desulfurization suffers from several disadvantages including high pressure drop and slow regeneration rates that require large unit sizes. This paper describes a new sorption platform utilizing hollow fibers with polymer “binder”, impregnated with high loadings of sulfur selective zeolite sorbent “fillers”. Temperature Swing Adsorption (TSA) can be utilized to thermally cycle the sorbents between sorption and regeneration cycles. A simplified flow pattern minimizes pressure drop, while a porous core morphology maximizes sorption efficiencies and high surface area to volume ratio structures can enable smaller bed sizes. This new technology represents a fusion of membrane science and adsorption technology.

Study on Deactivation of Zinc-Based Sorbents for Hot Gas Desulfurization

The possible reasons that were associated with the reduction of zinc oxide and the deposition of elemental Zn on the zinc-based sorbent surfaces were proposed in this study and examined by monitoring chemical reactivity and physical/chemical properties of the sorbents during the multicyclic tests with the aid of various diagnostics in order to investigate the deactivation of the sorbents that was observed in previous works. The reactivity of the sorbents was investigated using a temperature programmed technique (TPT) with a thermal gravimetric analyzer (TGA). From our experiments, the undesirable features due to the reduction of ZnO that was caused by the reducing components in the gasified coal gas were observed in the chemical reactivity and sorbent properties. In the investigation of the migration of elemental Zn onto the sorbent surface, elemental Zn accumulated on the surface of the sorbents rather than the zinc vaporization. It might have caused the deactivation of the zinc-based sorbents.

Use of Ash from Sewage Sludge in the Preparation of Desulfurant Sorbents

This work aims to develop new uses for sewage sludge, which is a byproduct of municipal wastewater treatment plants, by examining the calcination of this waste, the characterization of ashes is obtained, and its use to prepare desulfurant sorbents. Samples of sewage sludge were obtained from a local municipal wastewater treatment plant. This plant applies a pre-treatment followed by a biological treatment, where anaerobic digestion and centrifugation reduces the sludge. Three samples were characterized (in humidity, volatile and fixed solids content), dried, and ignited at two temperatures, 550 and 750°C. The composition of the ash obtained at both ignition temperatures was studied by x-ray fluorescent spectroscopy and the BET specific surface area of the two ashes and of the prepared sorbents was measured. Ash composition was similar for the two temperatures tested, where the components were Si, Ca, Al, Fe, P, S, Mg, K, Cl, Zn and Ti. BET specific surface area values indicate that the lower temperature of calcination produces ash with the highest SSA values (18 m2/g against near 10 m2/g). Preparation of desulfurant sorbents was carried out by mixing the ash with CaO or Ca(OH)2 at room temperature and different experimental conditions. The BET SSA of the prepared desulfurant sorbents showed higher values for the sorbents prepared with the ashes obtained at the lowest temperature. The behaviour of the ash and the prepared sorbents was tested in a fixed bed reactor at 58°C with a flue gas containing 5000 ppm of SO2 with a relative humidity of 55%. Results in the desulfurization process show that the calcium from the sludge seems more efficient than the calcium added as CaO or Ca(OH)2 to prepare the sorbents.

Reduction Behavior of Iron Oxide Sorbent and Its Effect on Sulfidation

The study of reduction of metal oxide sorbents for desulfurization at high temperatures has been attractive for many years. To investigate the reduction behaviors of iron oxide sorbent prepared from red mud and different additives and to evaluate the effects of reduction on the subsequent sulfidation kinetics, temperature-programmed reduction (TPR) tests and isothermal experiments were carried out using a thermogravimetric technique in a gaseous mixture consisting of30% H 2 in nitrogen and a simulated coal-derived gas, respectively. It was found that the sorbents prepared from different clay additives had different reduction behaviors, and the compensation effect existed in the reduction of iron oxide sorbents. In a strong reducing atmosphere, such as a coal-derived gas from a Texaco gasifier, iron oxide was converted to lower oxidation states and the degree of reduction differed as the temperature changed. There was no evidence of reduction bellow 400 °C, whereas iron oxide was reduced quite rapidly and even to a very deep reduction state of metallic iron at 600 °C. The low oxidation states of iron, such as those in Fe 3 O 4 and FeO, are active for sulfidation.

Effect of binder on the properties of iron oxide sorbent for hot gas desulfurization

The most difficult problem in hot gas desulfurization in Integrated Coal Gasification Combined Cycle (IGCC) is the pulverization of sulfur removal sorbents. Appropriate binders for hot gas sulfur removal sorbents can solve the pulverization problem. In this paper, six sorbents with binders of different argillaceous minerals were prepared by mechanical mixing method. Desulfurization behavior for hot gas desulfurization sorbents was investigated in a fixed-bed reactor. Result showed that sorbent NTKW2 with binder of clay had a better sulfidation performance. NTKW2 had a more stable performance than other sorbents in the continuous sulfidation-regeneration cycles. Sulfur capacity of sorbent remained the same in each cycle. The desulfurization efficiency and mechanical strength of NTKW2 were the best among the tested sorbents. The behavior of NTKW2 at different temperatures showed different performances, and the best reaction temperature was 550 °C. Higher heat stability, sulfur capacity and desulfurization efficiency were found on NTKW2 in six continuous sulfidation-regeneration cycles.

Study of the Surface Chemical Reactions of Thiophene with Ag/Titania by the Complementary Temperature-Programmed Electron Spin Resonance, Temperature-Programmed Desorption, and X-ray Photoelectron Spectroscopy: Adsorption, Desorption, and Sorbent Regeneration Mechanisms

Reaction of thiophene with the ultradeep desulfurization sorbent Ag/titania under ambient conditions was studied by the multiple complementary temperature-programmed techniques: electron spin reson...

Mercury Emission from Co-combustion of Coal and Sludge in a Circulating Fluidized-Bed Incinerator†

Co-combustion of coal and sewage sludge is known as one of the most effective thermal treatments for sludge use and disposal. However, multiple pollutants emitted from this process, especially heavy metal mercury emission, have become a worldwide concern on the environment and public health. An experimental study on mercury emission and its speciation from co-combustion of sludge and coal was conducted in a circulating fluidized-bed incinerator with a fluidized-bed cross-section of 0.23 x 0.23 m and a total height of 7 m. Mercury speciation in flue gas and mercury contents in fly and bottom ashes were measured on the basis of the Ontario Hydro method. The mercury mass balance of the co-combustion process was calculated. Effects of some major factors, such as Ca/S molar ratio, desulfurization sorbent categories, excess air coefficient, and SO 2 and NO x concentrations, on the distribution of mercury speciation were investigated. Results showed that most of the mercury from the mixed fuel of the coal and sludge went into the flue gas, in which elemental mercury was the major species. A small amount of mercury remained in the fly ash, and none of the mercury was detected in the bottom ash. As desulfurization sorbents, both CaO and CaCO 3 can remove Hg 2+ in flue gas effectively, but CaO had a bigger capacity than CaCO 3 . The percentage of Hg 2+ in flue gas was found added with an increase of SO 2 and NO x concentrations. It can be concluded that an excess air coefficient exerted dominant influences on the distribution of mercury species among flue gas, fly ash, and bottom ash.

Desulfurization mechanism of FCC gasoline: A review

This paper reviews the most important developments on the desulfurization mechanism of Fluid Catalytic Cracking (FCC) gasoline. First, the origin of sulfur compounds in FCC gasoline and the current developed desulfurization approaches and technologies are briefly introduced, and then the researches on desulfurization mechanism are summarized from experimental and theoretical perspectives. Further researches on the desulfurization mechanism will lay a foundation for optimizing desulfurization sorbents and technologies.

Review of Mid- to High-Temperature Sulfur Sorbents for Desulfurization of Biomass- and Coal-derived Syngas

This review examines state-of-the-art mid- and high-temperature sulfur sorbents that remove hydrogen sulfide (H2S) from syngas generated from coal gasification and may be applicable for use with biomass-derived syngas. Biomass feedstocks contain low percentages of protein-derived sulfur that is converted primarily to H2S, as well as small amounts of carbonyl sulfide (COS) and organosulfur compounds during pyrolysis and gasification. These sulfur species must be removed from the raw syngas before it is used for downstream fuel synthesis or power generation. Several types of sorbents based on zinc, copper, iron, calcium, manganese, and ceria have been developed over the last two decades that are capable of removing H2S from dry coal-derived syngas at mid- to high-temperature ranges. Further improvement is necessary to develop materials more suitable for desulfurization of biomass-derived syngas because of its hydrocarbon, tar, and potentially high steam content, which presents different challenges as compared to desulfurization of coal-derived syngas.

Glass-Based Processing of Mixed-Oxide Desulfurization Sorbents

The favorable thermodynamics of the reaction between H2S and oxides of iron, nickel, and zinc make these materials suitable for the sorption of sulfur from coal-derived synthesis gas. As an alternative to traditional solid-state processing, the suitability for coal gas desulfurization of glass-ceramics based on transition metal oxides has been evaluated. Glass-ceramics based on NiAl2O4 and ZnFe2O4 have similar sorption properties and a high resistance to agglomeration, but the inexpensive raw materials and moderate processing temperature of the ZnFe2O4-based glass makes it more suitable for a commercial application. The overall performance is highly dependent on the particle size of the sorbent, but these materials can be formed with relatively high surface areas by using fiber-based processing. This material is a potential alternative to mixed oxide sorbents prepared by solid-state processing, as it offers comparable performance combined with the ability to process the glass by existing glass-processing ...

High performance sorbents for diesel oil desulfurization

Sorbents with different Ni loading supported on silica–alumina (SiAl) and activated carbon (AC) were synthesized and tested for removal of sulfur compounds from a model diesel oil, containing nearly 250 ppmw S as benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). A state-of-art Commercial Ni-based sorbent and two Norit activated carbons were also tested for comparison. Moreover, the influence on sorbents uptake capacity of the presence of aromatics in amounts representative of real diesel oils was studied. Both commercial and home-made materials performed worse in presence of aromatic compounds. Probably, the latter competed with the refractory sulfur compounds (DBT and 4,6-DMDBT) in the adsorption on active sites. As a first important result of the investigation the sorbents carrying 45% and 30% of Ni on SiAl showed a breakthrough uptake capacity of nearly, respectively, 2 and 2.6 times higher than Commercial sorbent as a consequence of their higher Ni dispersion and surface area. Moreover, activated carbons and the sample with 28%Ni on AC showed an even higher breakthrough uptake capacities. In particular, the deposition of nickel on activated carbon is an innovative approach which takes advantage of the selectivity of Ni towards S-species and the high adsorptive capacity of AC support.

Desulfurization matching with coal poly-generation system based on dual gas resources

The coal poly-generation system for the production of alcohol and ether fuels as well as power is one of advanced coal utilization techniques. The team leaded by Professor Xie Kechang is carrying out the research on the poly-generation system to produce the syngas from the combination of gasified and pyrolyzed coal gas (dual gas resources) for the alcohol ether synthesis. Gas desulfurization is one of the key technologies for this system. The desulfurization matching with dual gas resources based poly-generation system for the production of alcohol and ether fuels as well as power is presented according to gas components, sulfur content, sulfur species and desulfurization accuracy in this technology. This matching desulfurization is classified into hot gas desulfurization, normal gas desulfurization, warm gas desulfurization and organic sulfur catalytic conversion. The preparation of H 2S removal sorbents, organic sulfur hydrolysis catalyst and the evaluation of their activities involved in the system were investigated. The H 2S removal efficiencies of the crude and fine desulfurization sorbents prepared for hot gas desulfurization are 90% and 99% at 500 °C in simulating coal gas, and their sulfur capacities are 21.85 wt.% and 24.91 wt.%, respectively. The organic sulfur catalyst shows the high hydrolysis activity, and the hydrolysis conversion of COS is more than that of CS 2 on the same catalyst. The research will provide necessary information for the matching desulfurization technology in the demonstration project on dual gas resources coal poly-generation system.

Desulfurization using ZnO nanostructure prepared by matrix assisted method

A ZnO nanostructure having a high surface area was developed for use as a desulfurization sorbent. The ZnO nanostructure was prepared by using zinc acetate and activated carbon by the matrix-assisted method. Activated carbon was the matrix in the matrix-assisted method and zinc acetate was the precursor. The desulfurization tests of the ZnO nanostructure were carried out in a packed bed desulfurization system in the temperature range of 300–500 °C. The ZnO nanostructures before and after the sulfidation process were characterized by BET, XRD and SEM. The formulated ZnO nanostructure consisted of ZnO nanoparticles with a size of 10–20 nm and its surface area was very high. Therefore, the sulfur capture efficiency of the ZnO nanostructure was 3 times higher than that of commercial ZnO. However, a reduction of some of the ZnO occurred because of the reducibility of the coal-derived gas, and the surface area of the ZnO nanostructure was slightly reduced due to the sintering of ZnO. It was also confirmed that the silica and alumina containing activated carbon used as the matrix prevent the thermal sintering of ZnO in the sulfidation process at high temperature.

Comparison of reduction behavior of Fe 2O 3, ZnO and ZnFe 2O 4 by TPR technique

Advanced integrated gasification combined cycle (IGCC) power generation systems require the development of high-temperature, regenerable, desulfurization sorbents capable of removing hydrogen sulfide from coal gasifier gas to very low levels. As a sort of effective desufurizer, such as Fe 2O 3, ZnO and ZnFe 2O 4, it will endure strong reducing atmosphere in desulfurization process. The reduced degree of desufurizer can have an effect on its desulfurization reactivity. In this paper, Fe 2O 3, ZnO and ZnFe 2O 4 were synthesized by precipitation or co-precipitation at constant pH. After aging, washing and drying, the solids were calcined at 800 °C. The reduction behaviors of sample were characterized by temperature-programmed reduction (TPR). It is found that there are two reduction peaks for Fe 2O 3 in TPR, and whereas no reduction peaks for ZnO are found. The reduction process of ZnFe 2O 4 prepared by co-precipitation is different from that of Fe 2O 3. ZnFe 2O 4 is easier to be reduced than Fe 2O 3. The activation energy of reduction process for Fe 2O 3 and ZnFe 2O 4 is obtained at different reduction periods.

Study on the Stability of Sorbents Removing H2S from Hot Coal Gas

Mixed metal oxide containing iron with the high-sulfur capacity and reactivity is considered as one of the most favorable sorbents for desulfurization in hot gas. The stability and life of iron-based sorbents are the main challenges for the hot gas cleanup techniques. Not only the effect of gas atmosphere but also the effect of ZnO and MgO on the stability of iron-based sorbent was studied in this work. The mechanism and factors influencing sorbent stability are discussed. The results showed that the coexistence of CO and H2 result in the instability of the zinc−iron-based sorbents. The reaction of carbon deposit is the crucial step affecting the stability of sorbent for hot gas desulfurization. ZnO in the sorbent is adverse to the physical stability of the iron-based sorbents. MgO in the sorbent hardly affects the physical stability of the iron-based sorbents but improves the capacity of removing the hydrogen sulfide from hot coal gas at 773 K.

Desulfurization Characteristics of Waste Cement Particles as a Sorbent in Dry Desulfurization

Dry desulfurization characteristics of waste cement particles were examined with laboratory-scale experimental apparatus based on the weight change of the sample exposed to a gas flow containing SO2. The waste cement particles, a byproduct of recycling aggregates from waste concrete, are fine particles with diameters ranging from 10 to 200 μm and an average diameter of 105 μm. The effects of the operation parameters, i.e., the reaction temperature (650−950 °C), SO2 concentration (61−1543 ppm), oxygen concentration (0−10%), NO2 concentration (0−500 ppm), absolute humidity (0−15000 ppm), and particle size (10−200 μm), on the desulfurization performance were investigated. The desulfurization rates were found to depend on the 1.26th order of the SO2 concentration and to slightly depend on the absolute humidity and the particle size, but they were almost independent of the concentrations of oxygen and NO2 in the gas flow. Arrhenius type temperature dependence was observed up to 850 °C with activation energy of 12 kJ/mol. The observed dry desulfurization rates of the waste cement particle were almost equivalent to those of the conventional sorbents such as limestone and calcium hydroxide. Therefore, it is confirmed that the waste cement particles could be applicable in dry desulfurization as an inexpensive sorbent derived from wastes.