Synthetic Sorbents Research Articles

CO2 capture performance of calcium-based synthetic sorbent with hollow core-shell structure under calcium looping conditions

A novel calcium-based synthetic CO2 sorbent with hollow core-shell structure was prepared by a carbon microsphere template route where carbide slag, alumina cement and glucose were employed as the low-cost calcium precursor, support and carbon source, respectively. The effects of the alumina cement addition, the pre-calcination temperature during the preparation process, the carbon template addition and calcination conditions on CO2 capture performances of the calcium-based synthetic sorbents were studied during calcium looping cycles. The synthetic sorbent containing 5 wt.% alumina cement possesses the highest CO2 capture capacity during calcium looping cycles, which is mainly composed of CaO and Ca12Al14O33. The CO2 capture capacities of the synthetic sorbent under mild and severe calcination conditions can retain 0.37 and 0.29 g/g after 20 cycles, which are 57% and 99% higher than those of carbide slag under the same conditions, respectively. The synthetic sorbent possesses a hollow micro-sphere morphology with a nano-structured shell and meso-porous structure, which decreases the diffusion resistance of CO2. Periodic density functional theory (DFT) calculations are used to explain why Ca12Al14O33 can effectively retard both agglomeration and sintering of the synthetic sorbent. The hollow core-shell model is proposed to explain the CO2 capture mechanism of the synthetic sorbent. For the same CO2 capture efficiency, the energy consumption in the calciner using the synthetic sorbent is much lower than those using carbide slag and natural limestone. This work designs a good method to prepare the hollow sphere-structured synthetic sorbents with high CO2 capture capacity and provides a promising way to integrate efficient CO2 capture with the utilization of industrial waste.

Evaluation of the effect of inert support on the carbonation reaction of synthetic CaO-based CO2 sorbents

Calcium oxide has been proved to be a suitable sorbent for high temperature CO2 capture processes based on the cyclic carbonation-calcination reaction. In this work several synthetic sorbents have been prepared with CaO contents between 40 and 95% wt. on to two different inert supports MgO and Ca12Al14O33. The effect of CaO content and inert nature on materials CO2 carrying capacity and reactivity towards carbonation reaction has been assessed. The materials have been texturally characterised. A complete kinetic study has been performed and the Random Pore Model has been applied to determine the intrinsic rate parameters for the carbonation reaction. Suitable particles for operation in fixed bed reactor have been produced from some selected powdered materials, and a complete particle reaction model that incorporate the intrinsic kinetic data has been developed and validated.

The effects of water vapor and coal ash on the carbonation behavior of CaO-sorbent supported by γ-Al2O3 for CO2 capture

Coal ash and water vapor are usually present in the flue gas derived from coal combustion, which inevitably impact the performance of calcium sorbents in a Calcium-Looping process for CO2 capture. This study investigated the influence of high-temperature water vapor and coal ash on the carbonation behavior of γ-Al2O3-supported calcium sorbent in a fluidized-bed reactor and a TGA apparatus. It was found that the presence of water vapor during carbonation induced the extensive formation of large voids on the sorbent surface and the decomposition of inert mayenite (Ca12Al14O33) into CaO and Al2O3. As a result, the reactivity and carrying capacity of the synthetic sorbent were significantly increased. During the significant exothermic carbonation reaction, the enhanced cooling effects of sorbent particles by water vapor in flue gas may provide a better equilibrium condition for higher carbonation rate and capture capacity. Coal ash impurities caused severe decay of the sorbent surface, but high-temperature water vapor exerted a very strong activation function to the ash-contaminated synthetic sorbents for better carbonation.

Development and investigations of kapok fiber based needle punched nonwoven as eco-friendly oil sorbent

ABSTRACTIn this work an attempt has been made to produce kapok/polypropylene (80/20) needle punched nonwoven for oil spill clean-up process. The difficulties involved in structuring kapok fiber through needle punching process and hence to develop a nonwoven are discussed. As an outcome, hydrophobic-oleophilic kapok fiber nonwoven has been produced and characterized for its oil sorption and retention. The maximum oil sorption was found to be 40.80 g/g and 29.0 g/g for high density oil (HD) and diesel oil respectively which is higher than the commercial polypropylene based oil sorbent pad. An interesting observation found was its retention value ranging from 0.88 to 1.00 which makes it an alternative for synthetic sorbents. The burning test of the oil sorbed samples ended up with only less amount of ash residue confirming its suitability and eco-friendly nature.

A study on the CO2 capture and attrition performance of construction and demolition waste

CaO-based sorbent deactivation is one of challenges to develop CaO-based chemical looping technology. The replacement of non-renewable natural or expensive synthetic CaO-based sorbents with cheap and environmental CaO-based waste sorbents is an effective way to overcome this challenge. As high CaO content, construction and demolition waste (CDW) has ability to capture CO2. Due to the rapid development of cities, a great deal of CDW is produced every year. According to the characteristics of CDW, six components were selected in this paper. From the initial CO2 carrying capacity, hydrated limestone had the highest initial CO2 carrying capacity, about 0.592 g CO2/g sorbent in TGA and 0.414 g CO2/g sorbent in fluidized bed system, followed by limestone, cement-based limestone, hydrated cement, cement-based sand, cement raw and sand. For multiple carbonation-calcination cycles, cement played a positive role in maintaining high cyclic CO2 carrying capture. Hydration degree and free lime content increased with the increase of hydration time, which improved the CO2 capture performance of CDW. For cement-based sorbents, evidence from this study suggested that extending hydration time played a positive role in improving the attrition resistance and maintaining the initial specific surface area in fluidized bed system.

Determination of the viability of chicken feather as oil spill clean-up sorbent for crude oil and its lower fractions

In this study a comparative assessment was conducted between chicken feather and a conventional synthetic sorbent mat used in the oil industry to clean-up oil spill. The result of the study shows that chicken feather has higher oil sorption capacity and sorbed oil recoverability than the standard (synthetic sorbent mat), and competes well with the standard in terms of sorbed oil retainability. Chicken feather sorbed per unit mass 13.10±0.67g/g of crude oil, 11.15±0.84g/g of diesel and 9.70g/g±0.91 of kerosene while the standard sorbed per unit mass 11.50±0.54g/g of crude oil, 10.35±0.77g/g of diesel and 8.20±0.93g/g of kerosene. Sorbed oil recovered from a unit mass of chicken feather and standard are 12.25±0.38g/g of crude oil, 10.30±0.91g/g of diesel, 8.50±0.27g/g of kerosene and 9.67±0.36 g/g of crude oil, 8.40±0.95 g/g of diesel and 6.50±0.49 g/g of kerosene respectively. Langmuir adsorption model and pseudo second order models fitted the process more precisely. Chicken feather competed favourably with the standard and both can be applied on land and aqueous environment in oil spill cleanup. It is an effective and viable sorbent for oil spill clean-up. Keywords : Chicken feather, crude oil, diesel, adsorption kinetics, oil sorption capacity.

Production of Zeolite Sorbents from Burning and Co-burning Biomass with Coal

The limited resources of natural zeolites make it necessary to search for and use synthetic products. This paper presents a method of producing zeolite sorbents resulting from hydrothermal synthesis in an autoclave. The raw materials used in the syntheses were fluidized-bed fly ashes derived from the burning of forest biomass and sunflower hulls and two fly ashes derived from biomass combustion. The raw materials and zeolite sorbents were characterised using the analysis methods of phase composition and textural properties of the samples. The sorptive capacity of the raw materials and zeolite sorbents was determined by means of cation and anion exchange capacity. The analyses and research have shown that as a result of the synthesis process it is possible to obtain the following zeolite phases: sodalite, faujasite, chabazite. The determined value of the cation and anion exchange capacity for synthetic zeolite sorbents are greater than those which characterise natural zeolites.

A critical assessment of the testing conditions of CaO-based CO2 sorbents

Calcium (or carbonate) looping (CaL) is a high-temperature process to capture CO2 from industrial installation using CaO-based materials as the sorbent. A large number of natural and synthetic CaO-based sorbents for CO2 capture have been developed and investigated in the laboratory by cycling the material between a low-temperature carbonation stage and a high-temperature calcination stage. We demonstrate the importance of the exact experimental protocol chosen to transition from the carbonation to the calcination step by varying the CO2 concentration and the heating rate while keeping the conditions during the actual carbonation (650 °C, 15 vol.% CO2) and calcination (950 °C, 80 vol.% CO2) stages constant. The experiments were performed in a thermogravimetric analyser, the equipment most frequently used in investigations of the cyclic CO2 uptake, using a natural limestone as the sorbent. Our results show that the reaction conditions under which the CaCO3 is decomposed to CaO determines the cyclic performance of the sorbent, whereas the effect of the CO2 concentration during the set calcination stage (which usually begins after most of the CaCO3 has been converted to CaO) appears to be insignificant. Higher heating rates facilitate a higher cyclic CO2 uptake because the carbonate phase, known to be prone to sintering, is exposed to higher temperatures for a shorter time. The reaction conditions during the transition period crucially affect the CO2 uptake determined in laboratory tests and hence need to be reported in full detail, yet this is currently hardly the case. Otherwise it is unclear whether differences in the CO2 uptake of different CO2 sorbents are due to modifications of the material or variations in the testing protocol.

Sorption of cations of heavy metals and radionuclides from the aqueous media by new synthetic zeolite-like sorbent

Expensive conventional sorption materials are applied for implementing control and treatment of water media of nuclear atomic plants. New synthetic alumosilicate zeolite-like adsorbent capable to efficiently purify aqueous media both of NPPs and of other facilities of the nuclear industry objects is suggested. Such sorbent properties as thermal, radiation and chemical resistance allowing performing purification of hot aqueous media without their prior cooling down at NPPs are of particular importance. The sorbent is synthesized from inexpensive raw materials produced by the domestic industry using energy-efficient production methods within single technological process. The product thus obtained has high specific surface ∼1000 m2/g, high thermal and chemical resistance and withstands temperatures up to 650 °С with maintaining its physics-chemical and sorption properties, it is resistant to aggressive media, radiation doses from 5 to 10 MGy produce no effect on its structure and sorption capacity. The sorbent demonstrates high ability for sorption of cations of heavy metals and radionuclides. Sorption capacity amounts for Ni2+ to 140 mg/g, for Cu2+ to 160 mg/g, for Fe3+ to 560 mg/g, for Cr3+ to 110 mg/g, for Cs+ to 2000 mg/g and for Sr2+ to 226 mg/g. Purification factor for 137Сs from solutions of liquid radioactive waste (LRW) is equal to 2.6. Possible mechanism for spent sorbent utilization is to expose it during 2–3 h to temperatures from 700 to 800 °C. After that this material is highly compacted changing the bulk densities of from 0.2 g/cm3 to 2.5 g/cm3 and is vitrified with closure of pores.It is assumed that the new sorbent can be applied by all facilities within lifecycles of which complex water purification process is used.

In-depth evaluation of a ZrO2 promoted CaO-based CO2 sorbent in fluidized bed reactor tests

Carbonate looping, based on the reversible gas–solid reaction of CaO with CO2, is considered as a promising alternative to amine scrubbing for post-combustion CO2 capture. Solid sorbents suffer however from degradation, mainly due to thermal sintering and elutriation of fine particles due to enhanced attrition rates in fluidized-bed reactors. In this work, a previously developed synthetic Zr-promoted CaO-based CO2 sorbent was tested in a fluidized bed reactor unit to determine its performance in cyclic CO2 capture over various operating conditions, relevant to industrial application. The material exhibited very high carbonation conversion (60–85%) during pre-breakthrough under all investigated conditions, with more than 75% CO2 removal. The addition of steam in both the carbonation and calcination steps resulted, not only in higher conversions, but also in significantly enhanced cyclic stability. Deactivation was less than 16% after 20 consecutive cycles. The performance of the sorbent was further tested under lower temperature difference between carbonation (680 °C) and calcination (750 °C), a scheme more favourable for utilizing the heat generated by the highly exothermic carbonation reaction for the thermal demands of the calciner in the actual process. The material displayed similar carbonation conversion, but inferior performance in terms of stability. Advanced post-reaction characterization with in-situ XRD revealed that even though the sintering effect was more limited due to the lower calcination temperature, calcination of CaCO3 was incomplete, rendering a small fraction of the sorbent inactive for CO2 capture. Under severe calcination conditions (920 °C and 80 vol% CO2 concentration) the sorbent maintained more than 70% of its initial sorption capacity (7.1 mol of CO2/kg of sorbent after 20 cycles), a value more than 5 times higher compared to natural limestone.

Study of the Sorption Properties of Synthetic Sorbents Produced Based on Alumino-Phenylsiloxane

The paper has demonstrated that modification of alumino-phenylsiloxane alkaline solution at different molar ratio of sodium hydroxide to alumino-phenylsiloxane in a heterogeneous system of toluene-water produces synthetic sorbents. The compounds were characterized by the methods of elemental analysis, FTIR and XRD spectroscopy. The study of specific surface area and pore size distribution showed that the sorbents have more extended surface as compared to the original alumino-phenylsiloxane. The determination of sorption activity of the products by methylene blue has showed that their sorption activity exceeds that of natural zeolite.

Development of High-performance CaO-based CO2 Sorbents Stabilized with Al2O3 or MgO

Two organic templating methods, viz., a Pechini and a resorcinol/formaldehyde (RF) carbon-gel approach were employed to prepare CaO-based, Al2O3- and MgO-stabilized CO2 sorbents. Scanning electron microscopy confirmed the formation of micro- and nanostructured morphologies in the synthetic sorbents. The cyclic CO2 uptake performance of the sorbents was assessed in a thermo-gravimetric analyzer and compared to the reference limestone. It was found that as little as 10 mol% Al3+ was required to obtain cyclically stable CO2 sorbents independent of the synthesis method used. However, a sintering-induced capacity decay of MgO-supported CaO could only be overcome via RF carbon-gel templating approach using at least 20 mol% of Mg2+ for stabilization. X-ray diffraction revealed the formation of mayenite, whereas MgO did not form a solid solution with CaO. The CO2 uptake of the best synthetic sorbent exceeded limestone by more than 300% (after 10 carbonation/calcination cycles).

Development of Synthetic Ca-based CO2 Sorbents for Sorption Enhanced Reforming Coupled to Ca/Cu Chemical Loop

Sorption Enhanced Reforming (SER) is a very promising option that allows H2 production coupled with capturing CO2 by sorption. The present research work focus in the sorbent point of view and several synthetic materials with a high CO2 absorption capacity and chemically and mechanically stable during multi-cyclic operation (at least 40 calcination-carbonation cycles and 100 cycles in some cases) under the typical SER process conditions have been developed. Two different synthesis routes (co-precipitation and mechanical mixing) have been followed trying to evaluate the effect of two different inert supports (magnesium oxide and mayenite) on the evolution of the CO2 carrying capacity of the materials. Also, sorbents have been synthesized with different morphologies (powder and particles) and sizes (from 100 microns up to 2mm) in order to test their reactivity and mechanical suitability for large scale reactor system operation. Synthetic dolomite with a molar CaO/MgO ratio of 2:1 synthesized by co-precipitation method exhibited very stable performance for 100 consecutive carbonation/calcination cycles and a residual CO2 carrying capacity of 0.29 grCO2/grcalcinedsorbent. Also a very promising result has been obtained for this sorbent mixed with a commercial catalyst in a preliminary SER experiment that yield a H2 production of 92% vol. (d.b.).

CO2 capture performance of a novel synthetic CaO/sepiolite sorbent at calcium looping conditions

A novel synthetic sorbent was fabricated from CaO and sepiolite by the hydration and its CO2 capture performance was investigated during the calcium looping cycles. The effects of the sorbent preparation conditions including preparation method, hydration temperature, hydration duration and sepiolite content on CO2 capture by synthetic CaO/sepiolite sorbent were examined in a dual fixed-bed reactor. The results showed that CaO/sepiolite possesses higher CO2 capture capacity than original CaO. CO2 capture capacity of CaO/sepiolite after 10 cycles is 39% and 56% higher than those of hydrated CaO and original CaO, respectively. The hydration temperature has an important effect on CO2 capture by CaO/sepiolite during the preparation. When the hydration temperature is 95°C, the obtained CaO/sepiolite exhibits the highest cyclic CO2 capture capacity, because the good supports such as MgO and Ca2SiO4 are formed in the calcined CaO/sepiolite at 95°C, which can improve the sintering resistance of CaO during the cycles. However, these supports are not found in the calcined CaO/sepiolite at the other hydration temperatures. In addition, CaO/sepiolite possesses more porous structure, larger surface area and pore volume, compared to hydrated CaO and original CaO. After the 1st calcination, the volume of pores in 10–100nm in diameter of CaO/sepiolite is much higher than those of hydrated CaO and original CaO, respectively, which facilitates CO2 capture of the sorbent. CaO/sepiolite appears promising as an effective and low-cost CO2 sorbent at calcium looping conditions.

CO2 Capture Performance of Mesoporous Synthetic Sorbent Fabricated Using Carbide Slag under Realistic Calcium Looping Conditions

Calcium looping is techno-economically feasible for industrial CO2 reduction. Carbide slag as a waste from the PVC (polyvinyl chloride) industry is a good candidate for low-cost calcium-based CO2 sorbents. A novel synthetic sorbent with rich mesopores was fabricated from high alumina cement, carbide slag, and byproduct of biodiesel, in order to overcome the loss in CO2 capture capacity of calcium-based sorbents with the number of carbonation/calcination cycles. The CO2 capture capacities of synthetic sorbents were examined under the severe calcination condition of high CO2 concentration and high temperature, which is close to the actual atmosphere for industrial applications. The effects of high alumina cement addition, byproduct of biodiesel addition, calcination condition, and steam addition in carbonation atmosphere on CO2 capture by the synthetic sorbents were also discussed. Results show that the synthetic sorbent with 90 wt % CaO achieves the highest CO2 capture capacity of about 0.27 g/g after 30 c...

Development of Synthetic Sorbents Based on Ca Oxide for CO2 Capture in Fluidized Bed Reactors

Development of Synthetic Sorbents Based on Ca Oxide for CO₂ Capture in Fluidized Bed Reactors

Effects of steam on CO2 absorption ability of calcium-based sorbent modified by peanut husk ash

The CO2 absorption ability of synthetic calcium-based sorbent modified by peanut husk ash (PHA) was tested by Thermal Gravimetric Analyzer (TGA), and the effects of steam and calcination temperature were investigated. The PHA composition was analyzed by X-Ray Fluorescence (XRF), the apparent morphology was characterized by scanning electron microscope (SEM), and the phases of the sorbent before and after calcination were examined by X-ray diffraction (XRD). The addition of PHA effectively improved the cyclic stability of the calcium-based sorbent. The optimal molar ratio of SiO2 in PHA to CaO was around 0.07. Steam had positive effect on keeping porosity of the sorbent at the chemical reaction stage, and improved its CO2 absorption ability. Steam also reduced the diffusion resistance of the product layer, and depressed the influence of high temperature calcination. It was also found that the steam hydration after calcination was an effective way to recover the absorption ability of the sorbent, while the hydration duration of 10 min was enough.

Effectiveness of CO2 Capture by Calcium Looping with Regenerated Calcium Sorbents – Last Step Calcination

The Ca looping process offers many advantages over the other CO2 capture technologies, such as a relatively small decrease in power plant efficiency and a potential for is further reduction. However, calcium sorbents in the consecutive cycles of adsorption and regeneration by calcination undergo deactivation, which is a considerable drawback of this technology. The depletion of sorbent reactivity is due to sintering, which causes changes in the sorbent's porous and crystal structure, whereby its reacting surface area decreases.The approaches to reducing sorbent deactivation (sorption capacity loss) include thermal preactivation, reactivation by hydration and/or the production of synthetic sorbents and doping.This paper studies three methods of regenerating deactivated sorbents. The sorbents underwent deactivation after working in the calcium looping of 10 calcination/carbonation cycles at respectively 900°C and 650°C. The first regeneration method consisted in hydration with water in controlled time and temperature conditions. The second regeneration method consisted in hydration with steam in controlled time and temperature conditions. The third method – 2-stage regeneration – besides water or steam hydration, included a second stage consisting in the controlled exposition of the sorbent to a CO2 enriched atmosphere. In all the methods the regeneration of the spent sorbent was conducted after the final calcination process. After regeneration the sorbent was subjected to 24 calcination/carbonation cycles in similar conditions as before regeneration.This study compares the three methods of regeneration in terms of the CO2 capture efficiency of the regenerated sorbent. The sorbents collected after the looping tests and after each regeneration step were analysed by mercury porosimetry, X-ray diffraction and scanning electron microscopy to determine the interdependences between the sorbents’ physicochemical properties and their CO2 capture capacity.The investigations showed that: 1) an improvement in CO2 capture capacity in the calcium looping process was achieved by applying both water/steam hydration and 2-stage regeneration after 10 calcination/carbonation cycles), 2) the size of CaO crystallites increased during looping cycles and decreased as a result of the 2-stage regeneration, 3) the sorbent's pore and particle structure showed significant changes after the reactivation, which may explain the increase in its CO2 capture capacity.The regeneration and CO2 sorption capacity of deactivated sorbent can be effected by radically changing the process temperature and simultaneously feeding saturated steam and then washing the sorbent with a gas with a high CO2 content. The novelty of this idea consists in the fact that the desired regeneration effects can be achieved by changing the regeneration parameters and only slight modifying the structure of the regenerators.

Developing a Novel CaO-Based Sorbent for Promoted CO2 Capture and Tar Reduction

Biomass gasification based on calcium looping sorption enhanced reforming (CLSER) has the advantages of generating syngas with high purity hydrogen and simultaneously capturing CO2 in process. This study first aims to develop a novel synthetic CaO-based sorbent, addressing its tar reduction potential and mechanical strength along with cyclic carbonation reactivity. The novel sorbent was synthesized by integrating CaO with iron catalyst and an inert support based on a two-step sol–gel method. Comprehensive properties of the novel sorbent including chemical components, effects on biomass pyrolysis and tar reduction, cyclic CO2 capture reactivity, morphology, and mechanical strength were examined by using various methods and facilities. The characterized chemical and physical properties were also compared with pure CaO and two referenced synthetic sorbents. Results showed that a novel sorbent (Ca–Fe–Al) consisting of CaO, iron oxide (Fe2O3), and mayenite (Ca12Al14O33) was successfully synthesized. Evolutions...

Сорбция катионов тяжелых металлов и радионуклидов из водных сред новым синтетическим цеолитоподобным сорбентом

Сорбция катионов тяжелых металлов и радионуклидов из водных сред новым синтетическим цеолитоподобным сорбентом