Industrial Adsorption Research Articles

Analysis of porous alkali activated materials using bauxite residue as principal precursor

Bauxite residue is a red-hued and mineral-rich material that is released from the production of alumina during the Bayer process. There are large areas of land across the world dedicated to the storage of this underutilized material. The growing nature of the alumina-producing industry implies that the production of bauxite residue will increase, which necessitates solutions for valorizing bauxite residue. One area of research involves using bauxite residue as a precursor in preparation of porous alkali activated materials and the novelty of the study is to make porous alkali-activated material with bauxite residue. Porous AAMs have applications as industrial adsorbents and as insulating materials. This study focused on the pore analysis of AAMs prepared with a high proportion of bauxite residue and fly ash addition, using varying percentages of hydrogen peroxide and added water to form the pore structure, with hydrogen peroxide and water acting as a “green reagent”. The sample containing the highest percentage of added water displayed the highest open porosity, with the sample consisting of large millipores and the widest distribution of pore sizes out of all the samples. The samples containing only hydrogen peroxide displayed a uniform distribution of smaller pores as measured by nitrogen adsorption. The study describes a process to create highly porous AAMs in low temperatures using a limited number of constituents. Furthermore, it optimizes the variation of hydrogen peroxide and added water to tailor the pore character depending on the desired application of the material, with only as much as 3 % hydrogen peroxide needed for porosity. The porous alkali-activated bauxite residue has the potential to be used as insulating material in the building.

Adsorption of Heavy Metal Ions on Alginate-Based Magnetic Nanocomposite Adsorbent Beads.

Graphene oxide and its magnetic nanoparticle-based composites are a well-known tool to remove heavy metals from wastewater. Unfortunately, one of the major issues in handling such small particles consists of their difficult removal from treated wastewater (even when their magnetic properties are exploited), due to their very small diameter. One possible way to overcome this problem is to embed them in a macroscopic biopolymer matrix, such as alginate or chitosan beads. In this way, the adsorbent becomes easier to handle and can be used to build, for example, a packed column, as in a traditional industrial adsorber. In this work, the removal performances of two different embedded magnetic nanocomposite adsorbents (MNAs) are discussed. The first type of MNA is based on ferrite magnetic nanoparticles (MNPs) generated by coprecipitation using iron(II/III) salts and ammonium hydroxide, while the second is based on a 2D material composed of MNP-decorated graphene oxide. Both MNAs were embedded in cross-linked alginate beads and used to treat artificial water contaminated with chromium(III), nickel(II), and copper(II) in different concentrations. The yield of removal and differences between MNAs and non-embedded magnetic nanomaterials are also discussed. From the results, it was found that the time to reach the adsorption equilibrium is higher when compared to that of the nanomaterials only, due to the lower surface/volume ratio of the beads, but the adsorption capacity is higher, due to the additional interaction with alginate.

Study of carbon materials using X-ray diffraction method, qualitative and quantitative analysis of adsorption

Active carbons are porous industrial adsorbents and carbonaceous materials derived from various organic raw materials and used to treat drinking and waste water. This study aimed to X-ray analyzes the structure of the sorbent based on coal and the efficiency of ion extraction from solutions by this sorbent. The diffraction patterns of the sorbents were obtained on a powder diffractometer. The qualitative and quantitative composition of the sorbents was determined by X-ray fluorescence method. The sorbent surface was imaged using scanning electron microscopy. It was found that the isotherms of the studied systems are satisfactorily described by the Langmuir and Freundlich models. The constants of the Freundlich equation were 0.31, 0.004, and 0.029 for adsorption of iron ions, manganese ions, and nitritions, respectively. The maximum adsorption of Langmuir iron ions was 3.61 mg/g, manganese ions 2.49 mg/g, and nitrite ions 0.33 mg/g. The Gibbs energy during adsorption of iron ions, manganese ions and nitrite ions were −17.93 kJ/mol, −30.5 kJ/mol and −20.5 kJ/mol, respectively. It is shown that effective extraction of ions can occur due to ion exchange and complexation processes for metal ions with active centers on the sorbent surface. Development of the technology of treatment of open-pit and surface wastewater of coal mining enterprises using sorbents based on coal will allow to solve environmental problems of resource-oriented regions and will contribute to the restoration and ecological rehabilitation of water bodies.

Temperature Evolution of Sorbonorit-4 Methane-Induced Deformation through the Eyes of Classical Density Functional Theory.

Activated carbons are widely used industrial adsorbents due to their attractive sorption properties. Although extensive research on activated carbon has been carried out for several centuries, some aspects of the adsorption-induced deformation of activated carbon remain unclear. The puzzling temperature dependence of the methane-induced deformation of activated carbon is investigated in the present work. Several experimental studies have shown that an increase in temperature leads to a reversal of the sign of adsorption strain at low pressures, i.e., the contraction turns into an expansion. Here we suggest a possible explanation for this effect by applying classical density functional theory to the adsorption isotherms of nitrogen, carbon dioxide, and methane as well as to methane-induced deformation isotherms. Our calculations show that the adsorption stress generated in the smallest pores predominates at higher temperatures and leads to material swelling. Lowering the temperature, on the other hand, leads to a predominance of larger pores and compression of the activated carbon material. We also investigated the possibility of determining the pore size distribution from methane-induced deformation and adsorption data and the predictive capabilities of our theoretical approach.

Analysis of the adsorption characteristics of SF6 and its decomposition products in ZIF-67: based on GCMC and DFT

Given the superior performance of SF6 in arc extinguishing and its wide application in high voltage fields, the search for new adsorbent materials for SF6 and its main decomposition products holds significant importance in mitigating greenhouse gas potential and its implications for the environment and energy sectors. We chose ZIF-67, an organic framework with a high specific surface area and distinctive pore size structure, to address this important issue. Using the grand canonical Monte Carlo simulation approach, we investigated the adsorption of SF6 and its main decomposer gases by ZIF-67 at GPa. The interaction of ZIF-67 with SF6 and its main breakdown products was then examined at the level of atomic orbital interactions, with the adsorption energy and density of states estimated using density functional theory. The findings reveal that ZIF-67 has the best ability to capture H2S, with a saturation capacity of 3.2 mmol g−1 at room temperature. Its adsorption capacity for SOF2 and SO2F2 is about five to seven times higher than that of industrial adsorbents kdhF-03, and the working conditions are milder. The molecule radius and adsorption capacity are tightly correlated. An innovative method for the widespread recovery and treatment of SF6 and its byproducts is presented in this research. This paper aims to provide new insights and solutions to promote sustainable development in the power industry.

Enhanced moisture adsorption of activated carbon through surface modification

Activated carbons are widely used as adsorbents in industries for various applications. The mechanism of moisture interaction with the industrial adsorbents is complex and yet to be clearly elucidated. The adsorption mechanism heavily depends on several parameters that include the pore size and distribution, surface chemistry, and treatment conditions. Various surface functional groups on the carbonaceous materials play a significant role in water adsorption, mainly the oxygen-containing functional groups (OFGs). A commercial mesoporous steam-activated carbon was subjected to surface modification on treatment with strong oxidizing agents and subjected to the adsorption of moisture. The isotherms were generated covering a temperature range of 30–50 °C. The adsorption capacity was observed to significantly improve post-treatment with oxidizing agents, while the effect was observed to be profound at lower partial pressures. A sharp increase in the moisture uptake indicates that the oxidized carbons have a higher affinity to moisture even at low concentrations and this could have a significant influence on the targeted molecules, since the moisture as a contaminant is expected to be present at low partial pressures. On the other hand, such a trend is highly favorable if carbon is to serve as a sorbent for the removal of moisture, as several-fold improvements in adsorption capacity were noticed as compared to virgin AC. Additionally, the adsorption capacity was also found to be significantly higher as compared to popular moisture adsorbents, such as silica gel and zeolites, especially at low partial pressures.

C-S cleavage of dibenzothiophenes with or without steric hindrance by the interface between PtSx and ZnO

Desulfurization plays a critical role in refining crude oil to produce fuel and the manufacture of fine chemicals. However, its low efficiency becomes a great challenge for the present desulfurization if only the C-S cleavage is considered a promising approach to reducing hydrogen consumption under atmospheric pressure. Accordingly, we investigate the critical factors necessary to achieve high C-S cleavage of dibenzothiophenes under mild conditions of 0.1 MPa and H2/oil = 100. The mechanism of reactive adsorption desulfurization of dibenzothiophenes with or without steric hindrance at atmospheric pressure on Pt/ZnO is proposed by studying the adsorption model of active metal sites, the Pt efficiency in C-S cleavage influenced by the steric hindrance and the structural evolution of Pt active centers in the presence of sulfur adsorption/deposition. Based on both experimental and DFT results, we report C-S cleavage of dibenzothiophenes with (TOF = 15 h−1) or without steric hindrance (TOF = 128 h−1) that can be highly efficiently fractured (99.9%) by the interface between PtSx and ZnO. This work has great practical significance for developing atmospheric industrial adsorbents for ultra-deep reactive adsorption desulfurization.

Chitin/deacetylated chitin nanocomposite film for effective adsorption of organic pollutant from aqueous solution

Cross-linked chitin/deacetylated chitin nanocomposite films can be considered as a potential industrial adsorbent for the removal of organic pollutants for water purification. Chitin (C) and deacetylated chitin (dC) nanofibers were extracted from raw chitin and characterized using FTIR, XRD and TGA techniques. The TEM image confirmed the formation of chitin nanofibers with a diameter range of 10–45 nm. The deacetylated chitin nanofibers (DDA-46 %) having 30 nm diameter was evidenced using FESEM. Further, the C/dC nanofibers were prepared at different ratios (80/20, 70/30, 60/40 & 50/50 ratios) and cross-linked. The highest tensile strength of 40 MPa and Young's modulus of 3872 MPa was exhibited by 50/50C/dC. The DMA studies revealed that the storage modulus enhanced by 86 % for 50/50C/dC (9.06 GPa) in comparison to 80/20C/dC nanocomposite. Further, the 50/50C/dC exhibited a maximum adsorption capacity of 30.8 mg/g at pH = 4 in 30 mg/L of Methyl Orange (MO) dye within 120 min. The experimental data agreed with pseudo-second-order model indicating chemisorption process. The adsorption isotherm data was best described by Freundlich model. The nanocomposite film is an effective adsorbent that can be regenerated and recycled for five adsorption-desorption cycle.

A potential remediation of chromium (VI) containing aqueous media onto surface-treated clinoptilolite vs. brief evaluation of other natural materials

A broad range of various natural and commercial adsorption materials and waste products was examined in order to verify the removal of commonly occurring cationic, anionic and some organic pollutants and briefly to compare each other. The inland natural zeolites of clinoptilolite type and its surface-treated modifications were used too. Actually, untreated clinoptilolite can compete with other natural materials or even waste products, occurring in the markets of many countries at very low prices. Industrial adsorbents are usually characterized with a high surface area, mechanical stability and uniformly accessible and interlinked pores. Abundantly occurring clinoptilolite tuffs, the Slovak one used in this research, possess the necessary interparticle mesoporosity. Moreover it is a natural cost-effective resource. The most extensive uptake of the studied chromate oxyanions at laboratory measure was observed by montmorillonite (142.86 mg/g), probably based on the large interplanar dimensions of this microcrystallite. The octadecyl ammonium hydrophobized i.e. ODA-clinoptilolite approached the second highest adsorption capacity to chromate (64.93 mg/g), while the MnOx-zeolite (clinoptilolite) proved the lowest adsorption ability (12.99 mg/g). Almost for all the systems studied, the Langmuir isotherm fitted better for mathematical description of the above adsorption process. From the breakthrough curves recorded, the Pb – and ODA – clinoptilolite packed column quantitatively removed chromate anion from the solution, apparently more efficiently using the lower flow rate.

Design of frontal chromatography separation of 1-phenylethanol and acetophenone using a hydrophobic resin

Adsorption and chromatographic processes havegood potential in the purification of natural aromas produced via biocatalytic routes. This work deals with the recovery of 1-phenylethanol (PE) from mixtures containing different amounts of acetophenone (AP). Amberlite FPX68, an industrial adsorbent with high selectivity with respect to acetophenone, was chosen for the separation of PE and AP by frontal chromatography. Small-scale experiments were performed for two different feed compositions and various flow rates and bed lengths. Using the target purity of 99 %, promising yields close to 90 % were obtained. The breakthrough curves were fitted with the equilibrium dispersive model, which provided HETP values under the different conditions. The obtained dependences of HETP on flow velocity complied with the Van Deemter equation. The contributions of individual phenomena responsible for adsorption zone broadening were analyzed. The experimental and modelling results obtained for the small-scale column became the basis for the scale-up of frontal chromatography separation of PE with an annual capacity up to 500 kg.

Efficient nitrous oxide capture by cationic forms of FAU and CHA zeolites

Nitrous oxide is a strong greenhouse gas contributing over 300 times global warming potential higher than carbon dioxide. The capture of nitrous oxide from industrial emission source represents an efficient and promising strategy for its further treatment or recycling, which receives less attention in the past decades. Herein, a comprehensive study on nitrous oxide capture by alkali and alkaline-earth metal ions (Li, Na, K, Mg, Ca and Ba) exchanged FAU and CHA zeolites was conducted, with focuses on the underlying adsorption mechanism and the structure-performance relationship. Under ambient conditions, Ba-FAU and Na-CHA show remarkable nitrous oxide dynamic uptakes of 2.25 and 2.41 mmol/g, respectively, at high concentration of 50000 ppm, and Ba-FAU shows good dynamic uptake of 0.35 mmol/g at extremely low concentration of 1000 ppm. The dynamic nitrous oxide uptakes by zeolites at high concentrations are related to the surface area and the adsorption strength controlled by local electrostatic field, while the diffusion resistance shows serious negative impacts at low concentrations. The intrinsic stability of zeolite and the perfect recyclability make Ba-FAU an eligible industrial adsorbent for nitrous oxide capture. In situ Fourier transform infrared spectroscopy and Grand Canonical Monte Carlo simulations reveal that nitrous oxide molecules prefer to anchor to extraframework cations via terminal-oxygen atoms and meanwhile stabilized by framework oxygen through electrostatic interaction via central nitrogen atoms. The explicit structure-performance relationship and the underlying mechanism are very important for the understanding of nitrous oxide capture by zeolites and most helpful for the rational design of robust adsorbents.

The application of wasteLeucaena leucocephalaseed pods as a bio-based adsorbent for decolourization of solution

AbstractThe adsorption method is widely used in water and wastewater treatment; however, most industrial adsorbents are expensive, limiting the use of the adsorption method in developing countries. Therefore, this study aims at developing a biosorbent from waste Leucaena leucocephala seed pods (LLSP) and apply it (as a cost-effective bio-adsorbent) to remove Janus Green B dye (JGBD) from solutions at different values of pH, agitation time, LLSP dose and JGBD concentration. Different techniques were used to characterize LLSP before and after JGBD removal, including pore size distribution, surface area (SBET) analysis, FTIR, SEM, SPM and the point of zero charges (pHpzc) of the LLSP surface. The results proved that LLSP could remove up to 95% of JGBD at pH, LLSP dose, JGBD concentration and agitation time of 9, 0.08 g/100 ml, 50 mg/l and 30 min, respectively. Langmuir and Freundlich analyses were applied to fit the data for equilibrium biosorption, and it was noticed that the Langmuir isotherm model fits the data, and the full monolayer biosorption ability for JGBD was 142.85 mg/g.

Design of bionic amphoteric adsorbent based on reed root loaded with amino-functionalized magnetic nanoparticles for heavy metal ions removal

Renewable and cheap reed roots are rich in polysaccharide and lignin and naturally possesses wastewater purification ability. However, if applied as industrial adsorbent, the active sites of reed roots need further enhancement to fit realistic amphoteric ion adsorption requirement and its recovery also request for optimization to avert secondary pollution caused by adsorbent residues. Under this background, a novel adsorbent based on reed root loaded with magnetic amino-functionalized nanoparticles (RrH@Fe3O4 @SiO2-NH2) with a bionic dendritic structure and a pleated surface was designed. The reed roots were firstly pretreated with hydrogen peroxide solution with strong oxidizing properties under UV light irradiation to expose more oxygen-containing functional groups, which then condensed with the amino groups on the surface of Fe3O4 @SiO2-NH2 nanoparticles, leading to the formation of the final adsorbent. The carboxyl, hydroxyl and methoxy and amino groups on the surface of the adsorbent synergistically contribute to the adsorption of both anions and cations. The maximum adsorption capacity for Pb (II) and Cr (VI) ions per unit mass of reed root in RrH@Fe3O4 @SiO2-NH2 reached 99.1 and 106.5 mg g− 1, much higher than those obtained with raw reed roots (24.8 and 30.6 mg g−1). The superior adsorption performance was ascribed to its physicochemical properties as characterized by a series of characterization methods. The adsorption process followed pseudo-second-order kinetic and Freundlich isotherm model, indicating a chemical multi-layer endothermic adsorption process. The addition of magnetic Fe3O4 endows the easy recovery of the adsorbent by applying a magnetic field, and after five cycles, the adsorption capacity can still reach 82% of that of the first time. In summary, the desirable adsorption performance, easy recovery, and low cost make the bionic RrH@Fe3O4 @SiO2-NH2 a promising amphoteric adsorbent for eliminating heavy metal ions from wastewater.

Double-edged role of interlayer water on Li+ extraction from ultrahigh Mg2+/Li+ ratio brines using Li/Al-LDHs

Lithium-aluminum layered double hydroxides (Li/Al-LDHs) are the only industrial adsorbents for Li+ extraction from Mg2+/Li+ ratio brines dependent on the special neutral desorption without dissolution damage. In this work, Li/Al-LDHs with different interlayer water contents were designed for the investigation of correlation between interlayer water and Li+ adsorption performances in high Mg2+/Li+ ratio brines. On the one hand, the Li+ adsorption capacity of Li/Al-LDHs in the Qarham Salt Lake old brine with a Mg2+/Li+ ratio exceeding 300 presented a positive correlative relation with the interlayer water content, rising from 1.05 mg/g to 7.89 mg/g as the interlayer water content increased from 5.52% to 18.18%. On the other hand, the interlayer water content would not affect the structure stability of Li/Al-LDHs, while the interlayer spacing was lessened with less interlayer water resulting in an uptrend to the adsorption selectivity on account of the depressed confinement effect. The density functional theory (DFT) calculation further indicated that LiCl was easier to enter the structure of Li/Al-LDHs with more interlayer water in view of the greater interaction energy.

High-Performance Selective CO2 Capture on a Stable and Flexible Metal-Organic Framework via Discriminatory Gate-Opening Effect.

Selective CO2 capture is of great significance for environmental protection and industrial demand. Here, we report a stable and flexible metal-organic framework (MOF) with excellent water/moisture stability, namely, ZnDatzBdc, that enables high-performance selective CO2 capture from N2 and CH4 via a discriminatory gate-opening effect. ZnDatzBdc shows reversible structural transformation between the open-phase (OP) state and the close-phase (CP) state, owing to the synergistic effect of breakage/re-formation of intraframework hydrogen bonds and the rotation of the phenyl rings. Significantly, ZnDatzBdc exhibits S-shaped isotherms toward CO2, resulting in a large CO2 theoretical working capacity of 94.9 cm3/cm3 under typical pressure vacuum swing adsorption (PVSA) operations, which outperforms other flexible MOFs showing the CO2 selective gate-opening effect except for the miosture-sensitive ELM-11. In addition, CO2 uptake of ZnDatzBdc is well maintained upon multiple water/moisture exposure, indicating its excellent stability. Moreover, ZnDatzBdc establishes remarkable CO2 selectivity with ultrahigh uptake ratios of CO2/N2 (107 at 273 K and 129 at 298 K) and CO2/CH4 (35 at 273 K and 44 at 298 K) at 100 kPa. The in situ gas sorption PXRD experiment verifies that the gate-opening effect takes place in the atmospheric environment of CO2 but not for N2 or CH4. Molecular simulation suggests the selective gate-opening of CO2 comes from its strong electrostatic interactions with the amino groups. Furthermore, effective breakthrough performance and easy regeneration are further confirmed. Hence, combined with excellent separation performance and remarkable stability, ZnDatzBdc can serve as a potential industrial adsorbent for selective CO2 capture.

Immobilization of gaseous elemental mercury by Ag nanoparticles: A combined DFT and experimental study

Silver nanoparticles (AgNPs) have attracted considerable attention as promising industrial adsorbents of gaseous mercury. The underlying mechanism of immobilization of Hg0 on different AgNP surfaces was investigated in theoretical and experimental approaches. The crystallographic properties of AgNPs obtained by X-ray diffraction and selected area electron diffraction were incorporated into comparative DFT calculations to evaluate the adsorption energy on AgNP surfaces such as low-index and edge planes. In addition, the energy pathway of oxidation of adsorbed Hg to HgO on AgNP surfaces was analysed by an ab-initio method, which suggested chemisorption rather than catalytic oxidation to be the main mechanism of mercury removal by AgNPs in the low-to-middle temperature range (≤326 °C). Mercury adsorption and desorption tests were conducted in a fixed-bed reactor with Ag nanoparticles and microparticles as adsorbent, where AgNPs were more efficient than microparticles in mercury removal, and the removal efficiency remained stable after four rounds of regeneration. Furthermore, temperature-programmed desorption analysis suggested a second-order desorption of Hg from AgNPs with an activation energy of 0.84 eV. X-ray photoelectron spectroscopy showed that the chemical characteristics of AgNPs remained stable while adsorbing Hg0 and that the adsorbed Hg was not in an oxidation state, validating the DFT results. By providing an integrated understanding of mercury adsorption on AgNPs, these computational and experimental results will help to guide the design and optimisation of Ag-based mercury adsorbents for industrial applications.

An Overview of Modified Chitosan Adsorbents for the Removal of Precious Metals Species from Aqueous Media.

This mini-review provides coverage of chitosan-based adsorbents and their modified forms as sustainable solid-phase extraction (SPE) materials for precious metal ions, such as gold species, and their complexes in aqueous media. Modified forms of chitosan-based adsorbents range from surface-functionalized systems to biomaterial composites that contain inorganic or other nanomaterial components. An overview of the SPE conditions such as pH, temperature, contact time, and adsorbent dosage was carried out to outline how these factors affect the efficiency of the sorption process, with an emphasis on gold species. This review provides insight into the structure-property relationships for chitinaceous adsorbents and their metal-ion removal mechanism in aqueous media. Cross-linked chitosan sorbents showed a maximum for Au(III) uptake capacity (600 mg/g), while S-containing cross-linked chitosan display favourable selectivity and uptake capacity with Au(III) species. Compared to industrial adsorbents such as activated carbon, modified chitosan sorbents display favourable uptake of Au(III) species, especially in aqueous media at low pH. In turn, this contribution is intended to catalyze further research directed at the rational design of tailored SPE materials that employ biopolymer scaffolds to yield improved uptake properties of precious metal species in aqueous systems. The controlled removal of gold and precious metal species from aqueous media is highly relevant to sustainable industrial processes and environmental remediation.

Mathematical Tool Based on Breakthrough Curves to Evaluate the Economic Advantages of Chemical Regeneration of Activated Carbon in Power Plants: A Comparative Study

A mathematical tool has been developed to evaluate the economic advantages of in-situ chemical regeneration of fixed-bed industrial adsorbers of granular activated carbon for cooling water treatment systems in Cuban power plants. Two scenarios of activated carbon (AC) management in a power plant were compared by applying the proposed model. The economic profit by implementing the regeneration strategy as a function of the number of regeneration cycles was determined and optimized. Breakthrough curves were obtained to assess the adsorption performance of the AC after progressive saturation–chemical regeneration cycles using synthetic water and hydrochloric acid, respectively. For the first saturation cycle, the breakthrough time was 272 min and after 10 cycles, it was reduced to 58 min, indicating a decrease of the adsorption capacity of 21%. The AC adsorption performance in terms of saturation time as a function of the number of regeneration cycles was considered one of the tool parameters. The proposed tool allows to determine the optimal number of regeneration cycles for a maximum economic profit in the regeneration strategy. It was demonstrated, using the proposed tool, that after an optimum of seven regeneration cycles, the power plant expends only 26% of the total investment. The simplicity of the tool permits a rapid way to find the most profitable number of regeneration cycles by combining economic, technical and adsorption efficiency parameters in one function, thus improving the AC management strategy at an industrial scale with corresponding environmental and economic advantages, including sustainability.

Self-sulfidation adsorbent for reactive adsorption desulfurization

The Ni/ZnO-Al2O3-SiO2 adsorbent is a widely used industrial adsorbent for reactive adsorption desulfurization (RADS) process. Metallic Ni and NiO are assumed as the main RADS active sites, and NiSx is the intermediate phase to transfer sulfur to ZnO. However, NiSx could also be the active center for RADS process. In this work, to conduct the desulfurization activity of NiSx, a novel NiSO4/ZnO-Al2O3-SiO2 adsorbent was prepared and examined through a serious experimental and theoretical study over the conventional adsorbents. Results showed that NiSO4 based adsorbents could first self-sulfide to NiSx phases, and then NiSx plays as main active sites for RADS. The NiSO4 phases improved the direct desulfurization selectivity of dibenzothiophene (DBT). By adjusting the content of nickel, the sulfur removal rate of adsorbent with 3 wt% Ni from NiSO4 could achieve the same level of adsorbent prepared with 18 wt% Ni from NiO. Moreover, NiSO4 based adsorbent performs excellent desulfurization activity, and its breakthrough sulfur capacity achieves 122.0 mgS/g. The evolution of Ni species on NiSO4 adsorbent has been studied, and a desulfurization mechanism that takes both NiO and NiSx as active phases has been carried out. NiO phase mainly promotes the hydrodesulfurization pathway, while NiSx phase prefers the direct desulfurization pathway. Finally, the mechanism of RADS on NiSx and the reaction pathways of DBT are also presented.

Process analysis of SO3 removal by Ca(OH)2 particles from flue gas

SO3 in coal-fired flue gas will cause equipment corrosion and the emission of sulfuric acid mist. The performance of injecting the alkaline adsorbent into the flue gas to remove SO3 is affected by the adsorption of SO2 in the flue gas. Taking Ca(OH)2 as a typical alkaline adsorbent, a model describing the adsorption of SO3 and SO2 by Ca(OH)2 particles was established, based on the combination of the product-island-growth model and the grain model. The parameters in the model were determined by the experimental data of adsorption in the fixed-bed reactor. The adsorption process of a single Ca(OH)2 particle was studied by numerical simulation. The adsorption of SO3 and SO2 was found to involve two stages: (1) In the early stage when there existed unreacted grain surface in the particle, SO3 and SO2 mainly reacted with the left fresh grain surface. The SO3 adsorption was controlled by internal pore diffusion and surface reaction, in which internal pore diffusion played a major role. The SO3 adsorption showed a shrinking core mode. The SO2 adsorption was controlled by internal pore diffusion and surface reaction and occurred throughout the entire particle. The SO3 adsorption selectivity at the outer surface of the particle was the highest, and decreased with a decreasing dimensionless particle radius R/R0. (2) In the later stage when the grain surface was completely reacted, the SO3 adsorption was controlled by internal pore diffusion and product-layer diffusion, in which product-layer diffusion played a major role. The SO2 adsorption was controlled by product-layer diffusion. The product-layer diffusion coefficient in the SO3 adsorption process was significantly higher than that of the SO2 adsorption, so SO3 was still significantly adsorbed in the later stage. The adsorption process of Ca(OH)2 under different particle structure parameters showed that decreasing the particle radius and increasing the particle porosity and specific surface area increased the SO3 removal efficiency as well as the total conversion of Ca(OH)2. Decreasing the particle radius and the specific surface area and increasing the particle porosity increased the SO3 adsorption selectivity by Ca(OH)2. When preparing industrial adsorbents, the optimization of the particle porous structure should be given attention.