Sorbent Precursors Research Articles

CO2 Sorption on Ti-, Zr-, and [Ti,Zr]-Pillared Montmorillonites.

Montmorillonite is a layered clay mineral whose modification by pillaring, i.e., insertion of oxide nanoclusters between the layers, yields porous materials of great potential in sorption and catalysis. In the present study, an unrefined industrial bentonite from Kopernica (Slovakia), containing ca. 70% of montmorillonite, was used for the preparation of Ti-, Zr-, and mixed [Ti,Zr]-pillared clay sorbents. The pillared samples were characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and N2 adsorption at -196 °C and tested for the capacity of CO2 sorption at 0 °C and 1 bar pressure. The experiments revealed that pillared samples sorbed at least four times more CO2 than the parent bentonite. Of the materials tested, the sample pillared with mixed [Ti,Zr] oxide props showed the best performance, which was attributed to its superior microporosity. The results of CO2 adsorption demonstrated that the cost-effective use of crude industrial bentonite as the sorbent precursor is a viable synthesis option. In another experiment, all pillared montmorillonites were subjected to 24 h exposure at room temperature to a flow of dry CO2 and then tested using simultaneous thermal analysis (STA) and the mass spectrometry (MS) analysis of the evolving gases (STA/QMS). It was found that interaction with dry CO2 reduces the amount of bound carbon dioxide and affects the processes of dehydration, dehydroxylation, and the mode of CO2 binding in the pillared structure.

Cu-Zn interaction regulating via heat treatment and the ultra-deep desulfurization for thiophene over Cu/ZnO sorbent

The ultra-deep removal of thiophene is a necessary process for the coke oven gas (COG) to methane technology via methanation. It is usually carried out using copper-zinc (Cu-Zn) based sorbent, which was reported to has excellent desulfurization performance, however the effect of Cu-Zn interaction on the desulfurization activity of the sorbent is still need to be further understood. Here, the sorbent precursor was prepared via co-precipitation method, and it was treated at different temperatures to obtain a series of sorbents with different Cu-Zn interaction. The fixed bed reactor was used to evaluate the desulfurization performance, the XPS and H2-TPR was carried out to determine the Cu-Zn interaction in sorbents, and the N2 adsorption, XRD, N2O adsorption, FT-IR were used to characterize the physical and chemical properties of samples. The results show that the Cu-Zn interaction could be effectively controlled by heat treatment temperature. At 300 °C, the sorbent precursor would be easily transformed into Cu-Zn solid solution, where the Cu-Zn interaction is strong, and the dispersion of Cu on the sorbent surface is maximized (16.0 %). Those greatly increase the desulfurization activity, and the breakthrough adsorption capacity for thiophene could reach up to 25.1 mg/g. At 250 °C, the temperature is not enough for the transforming of sorbent precursor into Cu-Zn solid solution, so that the breakthrough adsorption capacity for thiophene is only 12.4 mg/g. Whereas, when the temperature is higher than 350 °C, the Cu-Zn solid solution would be further transformed into CuO and ZnO, which significantly decreases the desulfurization activity. In addition, the density functional theory (DFT) calculation results provide further evidence that strong Cu-Zn interaction is beneficial to the desulfurization behavior of sorbent. This work provides both theoretical guidance for promoting the desulfurization performance of copper-based sorbents.

Blending Wastes of Marble Powder and Dolomite Sorbents for Calcium-Looping CO2 Capture under Realistic Industrial Calcination Conditions.

The use of wastes of marble powder (WMP) and dolomite as sorbents for CO2 capture is extremely promising to make the Ca-looping (CaL) process a more sustainable and eco-friendly technology. For the downstream utilization of CO2, it is more realistic to produce a concentrated CO2 stream in the calcination step of the CaL process, so more severe conditions are required in the calciner, such as an atmosphere with high concentration of CO2 (>70%), which implies higher calcination temperatures (>900 °C). In this work, experimental CaL tests were carried out in a fixed bed reactor using natural CaO-based sorbent precursors, such as WMP, dolomite and their blend, under mild (800 °C, N2) and realistic (930 °C, 80% CO2) calcination conditions, and the sorbents CO2 carrying capacity along the cycles was compared. A blend of WMP with dolomite was tested as an approach to improve the CO2 carrying capacity of WMP. As regards the realistic calcination under high CO2 concentration at high temperature, there is a strong synergetic effect of inert MgO grains of calcined dolomite in the blended WMP + dolomite sorbent that leads to an improved stability along the cycles when compared with WMP used separately. Hence, it is a promising approach to tailor cheap waste-based blended sorbents with improved carrying capacity and stability along the cycles under realistic calcination conditions.

Modeling the deactivation of CaO-based sorbents during multiple Ca-looping cycles for CO2 post-combustion capture

A novel model is presented for the estimation of natural CaO-based sorbents carbonation reactivity decay during Calcium Looping carbonation-calcination cycles. The model consists of a cyclic framework of two sub-models, the Overlapping Grain Model and the novel proposed modified Rate Theory for the Pore Size Distribution model. The model was implemented in gPROMS ModelBuilder® and parameter estimation was used for model validation using experimental data from three CaO-based sorbent precursors. The carbonation profile for the three sorbents was simulated with average deviations under 5%. The calcination sub-model predicted the evolution of total porous volume and total surface area for the calcination and sintering of dolomite, with an error of 3%. The cyclic framework successfully predicted the carbonation behavior of dolomite for 20 carbonation-calcination cycles. The model can be used for other CaO-based sorbents and the flexible modular structure allows the integration of other modules or approaches.

High-Efficiency CaO-Based Sorbent Modified by Aluminate Cement and Organic Fiber Through Wet Mixing Method

CaO-based sorbents are usually used for high-temperature postcombustion CO2 capture through cyclic carbonation–calcination reactions. However, the rapid decay of sorbent reactivity limits their application. In this study, three types of CO2 sorbent precursors, namely Ca(CH3COO)2, Ca(OH)2, and CaCO3, are used to produce initial CaO-based sorbents. Then, the initial sorbents are mixed with aluminate cement and organic fibers at an appropriate ratio to synthesize high-efficiency sorbents. Our results show that the cyclic performance of the sorbent that decomposed from Ca(CH3COO)2 is better than that decomposed from Ca(OH)2 and CaCO3. It is mainly because the sorbent pore structure becomes much developed after Ca(CH3COO)2 decomposition. Furthermore, when mixed with aluminate cement, the CaO-based sorbent achieves a good performance for CO2 capture because of the formation of the sorbent skeleton Ca12Al14O33. For example, when the mass ratio of Ca(OH)2 to aluminate cement is set as 1:1, CaO conversion achieves...

Characterization of a Marl-Type Cement Raw Meal as CO2 Sorbent for Calcium Looping.

The use of cement raw meals as sorbent precursors for CO2 capture can reinforce the synergies between the cement production process and calcium looping CO2 capture technology. In this work, we measure the CO2-carrying capacity of different calcined samples of a particular marl, which were obtained under very different calcination conditions and setups (a thermogravimetric analyzer, a drop tube furnace, and an industrial calciner). We find that the reactivity toward CO2 of these calcined materials displays a strong sensitivity to the calcination conditions, in particular to calcination time. A pronounced competition between the belite (Ca2SiO4) formation reaction and the formation of free CaO needed for CO2 capture is detected. As the calcination of the raw meal approaches flash conditions (i.e., >90% calcination conversion in less than 10 s), the belite formation is shown to be minimized, leading to sorbents with CO2-carrying capacities of approximately 0.4 mol CO2/mol CaO.

Influence of CaO precursor on CO2 capture performance and sorption-enhanced steam ethanol reforming

This work presents the effect of calcium and carbonate precursors on properties of CaCO3. The synthetic CaCO3 samples were transformed into CaO and tested their application to high-temperature CO2 capture. Four different sorbent precursors were investigated in this work, including calcium chloride (CaCl2) and calcium acetate (CaAc2) as calcium precursor, and sodium carbonate (Na2CO3) and urea (CO(NH2)2) as carbonate precursor. The results show that both calcium and carbonate precursors affect morphologies of CaCO3; CaCO3,Cl-Urea, and CaCO3,Cl-Na have calcite phase, whereas mixed-phases of calcite (30%) and vaterite (70%) are observed with CaCO3,Ac-Na, and aragonite is found with CaCO3,Ac-Urea. CaCO3,Cl-Na exhibits small cubic (rhombohedral) particle, CaCO3,Cl-Urea possesses spherical particle with rough surface, CaCO3,Ac-Na has spherical-like morphology with smooth surface, and CaCO3,Ac-Urea possesses aggregated form of CaCO3 particles. For application to CO2 capture, CaO derived from CaCO3,Ac-Urea provides the highest CaO conversion of 80% at 700 °C. The synthetic CaO-based sorbents were further incorporated with nickel oxide to form one-body bi-functional catalysts for H2 production from sorption-enhanced steam ethanol reforming. The results show that 87%H2 purity could be obtained with pre-breakthrough period of 60 min. Sorbent reactivity can be maintained the production of H2 for at least 10 consecutive cycle tests.

Ordered mesoporous Zn-based supported sorbent synthesized by a new method for high-efficiency desulfurization of hot coal gas

A new approach (microwave-hydrothermal plus oxidation) was proposed for the preparation of the Zn-based sorbents supported on the ordered mesoporous Si-based material. The hydrothermal synthesis and oxidation conditions of the sorbent precursor (ZnS/MCM41 mesophase) with Zn(AC)2 and thioacetamide (TAA) as the Zn and S sources, respectively, were optimized. The sorbents were evaluated in a fixed bed using the simulate gas of 2000 ppm H2S, 39% H2, 27% CO, 12% CO2, and N2 as balance gas. The structure of the sorbents was characterized by means of XRD, N2 adsoprtion, SEM, EDX, and TEM analysis. The results indicate that the optimal microwave-hydrothermal conditions are 400 W, 2.5 h, and 1:3 (the mole ratio of the Zn(AC)2 to TAA). The oxidation of ZnS in the sorbent precursor to ZnO is invalid at 550 °C due to unfavorable reaction kinetics. Both the fresh and used sorbents show ordered hexagonal mesoporous structure. It is confirmed that Zn2SiO4 present in the fresh and regenerated sorbents could be consumed during the desulfurization process via the reaction (Zn2SiO4 + 2H2S → 2ZnS + SiO2 + 2H2O), giving a positive effect on the desulfurization of the sorbents. The optimized Zn-based mesoporous sorbent (actual Zn content: 20.3%) exhibits superior (high breakthrough sulfur capacity: 5.4–5.7%) and stable desulfurization ability during five sulfidation/regeneration cycles. In addition, sulifidation reaction only leads to low-degree plugging of the pore structure of the regenerated sorbents, and the regeneration reaction could restore (at least mostly) the aforementioned changes in the pore properties.

Measuring attrition properties of calcium looping materials in a 30 kW pilot plant

The attrition of CaO-based solids operating in calcium looping (CaL) post-combustion CO2 capture systems is an important factor to consider when limestones are selected as sorbent precursors. In this work, four commercial natural limestones with similar chemical compositions but with very different mechanical properties were tested in a 30kWth calcium looping pilot plant. The main attrition mechanisms that act upon the limestones (i.e. fragmentation, decrepitation and abrasion) were identified on the basis of the evolution of their particle size distributions during the start-up and the first calcination of each batch. Great differences in the performance of the selected limestones were observed, which confirms the suitability of the experimental procedure employed for sorbent screening purposes in these high-velocity, high-temperature pilot plants. Several attrition indexes reported in the literature were tested to conclude that the Total Particle Generated Index (TPGI) and the Maximum Diameter of Particles Generated (MDPG) indexes are the most useful for quantifying attrition phenomena and rank limestones.

Separation of dissolved oil from aqueous solution by sorption onto acetylated lignocellulosic biomass—equilibrium, kinetics and mechanism studies

The potential use of lignocellulosic biomass as oil sorbents was demonstrated through acetylation of mercerized pineapple leaves (M-PAL) using acetic anhydride with catalysts (N-bromosuccinimide and pyridine) in order to enhance its surface hydrophobicity and thus oil sorption capacity for treatment of dissolved oil contaminated wastewaters. The raw and acetylated PAL sorbents, before and after oil sorption, were characterized by a scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The oil sorption experiment was evaluated in batch sorption mode using dissolved o/w solution prepared by mixing crude oil and double-distilled water. It was found that the M-NBS-PAL sorbent yielded better oil sorption performance than R-PAL sorbent due to the replacement of hydroxyl group which has more hydrophobic acetyl group on the PAL surfaces, with strong affinity towards oil. The batch equilibrium data were fitted well by Langmuir isotherm model with the maximum sorption capacity (qm) of 37.45 and 90.91mg/g for the R-PAL and M-NBS-PAL sorbents, respectively. The oil sorption process was thermodynamically feasible and exothermic, while the nature of interaction could be described via the physisorption mechanism. The kinetic sorption data were found to be fitted well into the pseudo-second order kinetic model. The sorption–desorption cycle was repeated four times whereby isopropanol was used as a desorbing agent and the results were comparable with freshly prepared sorbent. Finally, the present findings indicate that the lignocellulosic biomass could be a potential alternative as sorbent precursors for oil removal from oil contaminated wastewaters.

Ca-looping for postcombustion CO2 capture: A comparative analysis on the performances of dolomite and limestone

The low cost and wide availability of natural limestone (CaCO3) is at the basis of the industrial competitiveness of the Ca-looping (CaL) technology for postcombustion CO2 capture as already demonstrated by ∼1Mwt scale pilot projects. A major focus of studies oriented towards further improving the efficiency of the CaL technology is how to prevent the gradual loss of capture capacity of limestone derived CaO as the number of carbonation/calcination cycles is increased. Natural dolomite (MgCa(CO3)2) has been proposed as an alternative sorbent precursor to limestone. Yet, carbonation of MgO is not thermodynamically favorable at CaL conditions, which may hinder the capture performance of dolomite. In the work described in this paper we carried out a thermogravimetric analysis on the multicyclic capture performance of natural dolomite under realistic regeneration conditions necessarily implying high calcination temperature, high CO2 concentration and fast transitions between the carbonation and calcination stages. Our study demonstrates that the sorbent derived from dolomite has a greater capture capacity as compared to limestone. SEM analysis shows that MgO grains in the decomposed dolomite are resistant to sintering under severe calcination conditions and segregate from CaO acting as a thermally stable support which mitigates the multicyclic loss of CaO conversion. Moreover, full decomposition of dolomite is achieved at significantly lower calcination temperatures as compared to limestone, which would help improving further the industrial competitiveness of the technology.

Use of one-pot wet gel or precursor preparation and supercritical drying procedure for development of a high-performance CO2sorbent

The objective of this research was to develop a new high-performance CO2 sorbent with a simple method. A new CO2 aerogel sorbent was synthesized by using one-pot wet gel or sorbent precursor preparation, and supercritical drying (SCD). The performance of the aerogel sorbent prepared with SCD, A-SCD, is much better than that prepared with ambient pressure drying (APD). The highest CO2 sorption capacity achieved with the new sorbent in 1% CO2 flow stream within 20 min is 4.51 mmol g−1, much higher than its state-of-art counterparts even with a 10% CO2 gas mixture which is favorable to increase in CO2 sorption capacity of any given sorbent. According to XPS data, the theoretical equilibrium CO2 sorption capacity of the A-SCD is 7.99 mmol g−1. The characterization results of N2 adsorption/desorption, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and zeta potential measurements used for the first time in CO2 research demonstrate that the pore structure and surface N concentration of the sorbent are significantly improved because of the use of SCD. The sorbent preparation method is inspiring and its resulting sorbent is exceptional in capacity and regenerability.

Flow properties of CO2 sorbent powders modified with nanosilica

In this work, the flow behavior of a CO2 sorbent precursor (natural limestone) and a modified sorbent precursor, obtained by dry mixing the natural limestone and a silica nanostructured powder, is investigated. After dry mixing, small silica nanoparticle aggregates are seen to coat the limestone particle surface, which serves to decrease interparticle adhesion thus improving powder flowability. The tensile strength of the modified material subjected to small consolidation stresses has been tested before and after calcination. In addition, laser diffraction particle size analysis has been performed to test the mechanical strength of the aggregates as they are pre-dispersed in-situ by high energy processes such as high velocity air jets or ultrasonication in a liquid. The results also indicate that calcination leads to an increase of the average size of the limestone/nanosilica composite aggregates whose mechanical strength is enhanced as compared to that of calcined limestone aggregates.

Influence of the operation conditions on CO2 capture by CaO-derived sorbents prepared from synthetic CaCO3

In this work, a statistical experimental design is performed in order to prepare CaCO3 materials for use as CaO-based CO2 sorbent precursors. The influence of different operational parameters such as synthesis temperature (ST), stirring rate (SR) and surfactant percent (SP) on CO2 capture is studied by applying Response Surface Methodology (RSM). The samples were characterized using different analytical techniques including X-ray diffraction, N2 adsorption isotherm analysis and Scanning Electron Microscopy–X-ray Energy Dispersive Spectroscopy (SEM-EDX). CO2 capture capacity was determined by means of a thermogravimetric analyzer which recorded the mass uptake of the samples when these were exposed to a gas stream containing diluted (15%) CO2. The statistical approach used in this work provides a rapid way of predicting and optimizing the main preparation variables of CaO-derived sorbents for CO2 sorption. The results obtained clearly indicate that four parameters statistically influence CO2 uptake: SR, the square of SR, its interaction with SP and the square of SP.

Calcium enhanced hydrogen production with CO2 capture

Abstract The addition of a calcium-based sorbent to a standard methane reforming catalyst alters the equilibrium and permits both the reforming and water-gas shift reactions to approach completion in a single step at a temperature approximately 200 K lower than currently used. Depending on reaction conditions greater than 95% CO 2 capture is possible and the product may contain 98+% H 2 (dry basis) and only ppm levels of CO and CO 2 . The requirements for final H 2 purification are thereby minimized for some applications and eliminated for others. While dolomite and limestone sorbent precursors have received the majority of attention because of their widespread availability and low cost, some researchers have studied synthetic calcium-based materials in an effort to improve sorbent durability. Regardless of the source, process economics requires that the sorbent be regenerable and used in many reaction-regeneration cycles. Regeneration is accomplished using temperature swing in an atmosphere of pure CO 2 or a mixture of CO 2 and steam from which pure CO 2 can be produced by condensing the H 2 O. Circulating fluidized-bed reactors are appropriate for large-scale operations while dual fixed-bed reactors with alternating reaction-regeneration functions may be appropriate for small-scale operations. No supplemental energy is required in the H 2 production reactor as the combined reforming, shift, and carbonation reactions are essentially thermally neutral. Supplemental energy is required in the regeneration step but overall energy reduction of 20–25% has been estimated. Other advantages of sorption-enhanced H 2 production include a reduction in capital cost due to process simplification, replacement of high temperature, high alloy steels in the reformer with less expensive materials of construction due to the lower operating temperature, total elimination of the shift reactor(s) and shift catalyst(s), and reduction of carbon deposition in the reformer. The concept is equally applicable to H 2 production from syngas from coal or biomass, with the added advantage that the need for reforming catalyst is eliminated.

Possibility of obtaining hydrogen from coal/waste–tyre mixture

Technically applicable gas with a high hydrogen content (ca 78%) was obtained through a two-stage pyrolysis of the mixture of Lazy bituminous coal with 15% waste tyre-rubber. The experiments were carried out in a laboratory pyrolysis unit with a 100 g charge. The incorporation of a thermal-degradation module in the stream of steam–gas mixture at the output of the pyrolysis reactor induced the decomposition of volatile products and significantly increased the yield of hydrogen. The influence of temperature of the cracking module (in the range between 900 and 1200 °C) on the amount of hydrogen in the pyrolysis gas was monitored. The solid by-product (carbonaceous residue) may be used as smokeless fuel or a sorbent precursor.

Immobilization of Heavy Metals in Combustion Systems by Injecting Sorbent Precursors

Immobilization of Heavy Metals in Combustion Systems by Injecting Sorbent Precursors

Comparison of Hg0 capture efficiencies of three in situ generated sorbents

AbstractThree different sorbent materials (Ti‐, Si‐, and Ca‐based) were compared for their mercury (Hg0) capture efficiencies in an entrained flow reactor. Agglomerated particles with a high specific surface area were generated in situ by injecting gas‐phase sorbent precursors into a high‐temperature furnace reactor. Titania particles in the presence of UV irradiation were most effective at mercury capture (>98%). In situ generated CaO particles had a capture efficiency of 33% (without any UV irradiation), while SiO2 was completely ineffective at Hg0 capture. The efficiency of elemental Hg capture of both CaO and TiO2 particles decreased with increasing SO2 concentration. The increase in the feed rate of the Ti sorbent resulted in the recovery of the higher Hg0 capture efficiency due to the availability of more active sites. The in situ generated titania sorbents were also effective at Hg0 capture (>87%) at elevated temperatures (160°C).

In Situ Processing of Ferroelectric Materials from Lead Waste Streams by Injection of Gas Phase Titanium Precursors: Laser Induced Fluorescence and X-ray Diffraction Measurements

Several industrial process exhaust gas streams contain enriched toxic metal species such as lead and cadmium. Gas phase sorbent precursor techniques have been developed to effectively capture these toxic metal species. This methodology is further extended to not only capture the toxic metal species, but produce useful materials. Injection of gas phase titanium precursors to reactively capture the lead species is proposed for the processing of ferroelectric lead titanatematerials in enriched lead exhaust streams. Conditions to produce lead titanate in high temperature systems are established. Diagnostic techniques such as X-ray diffraction and laser induced fluorescence spectroscopy are used to determine optimal conditions to not only capture the lead species but also produce perovskite structured lead titanate. Such approaches can be extended to real combustor exhaust streams with high toxic metal concentrations such as lead smelters for effective environmental control and production of novel materials.

Capture of Mercury in Combustion Systems by In Situ–Generated Titania Particles with UV Irradiation

ABSTRACT In situ–generated sorbent titania particles with ultraviolet (UV) irradiation have been shown to be effective in capture of mercury in combustor exhausts. Results of experiments conducted with the (1) sorbent precursor only, (2) mercury only, (3) mercury and UV irradiation, and (4) mercury, titania, and UV irradiation are presented to elucidate the mechanisms of the capture process. Capture efficiencies (percentage of Hg captured on the filter) as high as 96% were measured for mercury by titania with UV irradiation. A very high surface area titania sorbent was first formed, with mercury vapors condensing onto this surface, followed by photocatalytic oxidation and binding with the sorbent particles. The process has significant potential as a low-cost methodology for mercury control in practical combustion systems. Minimal retrofitting may be necessary as conventional particulate control devices such as electrostatic precipitators have coronas with UV radiation present. Key words: Mercury; sorbents...