Sodium-based Sorbents Research Articles

A review of hydrogen chloride removal from calcium- and sodium-based sorbents.

With the steady progress of ultra-low emissions in various industries, the management of unconventional pollutants is gradually attracting attention. A such unconventional pollutant that negatively affects many different processes and pieces of equipment is hydrogen chloride (HCl). Although it has strong advantages and potential in the treatment of industrial waste gas and synthesis gas, the process technology of removing HCl by calcium- and sodium-based alkaline powder has not yet been thoroughly studied. The impact of reaction factors on the dechlorination of calcium- and sodium-based sorbents is reviewed, including temperature, particle size, and water form. The most recent developments in sodium- and calcium-based sorbents for capturing hydrogen chloride were presented, and the dechlorination capabilities of various sorbents were contrasted. In the low-temperature range, sodium-based sorbents had a stronger dechlorination impact than calcium-based sorbents. Surface chemical reactions and product layer diffusion between solid sorbents and gases are crucial mechanisms. Meanwhile, the effect of the competitive behavior of SO2 and CO2 with HCl on the dechlorination performance has been taken into account. The mechanism and necessity of selective hydrogen chloride removal are also provided and discussed, and future research directions are pointed out to provide the theoretical basis and technical reference for future industrial practical applications.

Extracting high-purity hydrogen via sodium looping-based formic acid dehydrogenation

Formic acid (FA) has been considered as a prospective hydrogen carrier for its potentials to realize hydrogen storage, transportation, and in-situ supply under mild conditions. However, the application of FA dehydrogenation is limited by its unsatisfactory hydrogen concentration and carbon monoxide selectivity. Herein, a sodium looping-based (Na 2 CO 3 ↔NaHCO 3 ) formic acid dehydrogenation (SLFAD) system is proposed for high-purity hydrogen production with ultra-low CO generation via the Na 2 CO 3 ↔NaHCO 3 looping. The SLFAD system consists of three parts, which are FA dehydrogenation reactor (FADR), sorption-enhanced carbon oxide removal reactor (CORR), and sodium-based sorbent regeneration reactor (SSRR). Experimental results proved that no sodium formate and sodium oxalate was formed under NaHCO 3 reduction by H 2 . A comprehensive assessment of the system was carried out to preliminary verify the feasibility and optimize the operation parameters of the SLFAD system. Results indicated that a maximum hydrogen concentration of 97.905 vol%, a minimum CO concentration of 11.97 ppm, and a high hydrogen production rate of 0.99989 kmol H 2 h −1 can be obtained under the conditions of atmospheric pressure, FADR temperature at 80 °C, H 2 O/HCOOH = 1.2, CORR temperature at 80 °C, and Na 2 CO 3 /HCOOH = 1.0. • A sodium looping based formic acid dehydrogenation (SLFAD) concept was proposed. • A high hydrogen concentration of 97.90 vol% can be obtained at low temperatures. • Carbon monoxide concentration can be restricted to be 11.97 ppm via SLFAD process. • Sodium-based absorbent can be regenerated with the achievement of CO 2 capture.

Investigation of a hybrid thermochemical Cu–Cl cycle, carbon capturing, and ammonia production process

In this paper, a new integrated system is proposed consisting of four subsystems, including a Cu–Cl cycle, a carbon capture cycle (sodium-based sorbent), an ammonia production unit, and a methanation unit. Carbon capturing cycle with sodium-based sorbent could adsorb 1.5 times more than other sorbents such as amine-based sorbent. Moreover, Cu–Cl cycle is one of the promising cycles in terms of economic and low temperature. Therefore, integrating these two cycles with ammonia and methane production unit is the novelty for this paper. Also, Aspen plus software was used to simulate the developed system to evaluate the process of the system. Moreover, sensitivity analysis and mass/energy balance are performed for the developed systems through the simulation. The energy required to capture carbon dioxide was found to be 6.313 MW per kg of CO2, and the overall efficiency of the system is equal to 19.6%.

Element doped sodium-based sorbents with high attrition resistance and CO2 capture capacity during CO2 sorption/desorption processes

The technology of removing CO2 from coal-fired power plants by sodium-based sorbents has received increasing attention. However, the researches on sodium-based sorbents both with high CO2 capture capacity and attrition resistance are still insufficient, which hindering the industrial applications of the sodium-based sorbent. This paper is devoted to solve this problem. Different elements, including Zr2+, Mg2+ and Ca2+, were separately doped in the sorbent and the corresponding CO2 sorption and attrition resistance performances were studied. Under the desired doping content (1–15 wt%), Zr2+, Mg2+ and Ca2+ improved the mechanical strength of the sorbent with the order of Zr2+ < Mg2+ < Ca2+, while the corresponding CO2 sorption capacity of the sorbent were improved with the order of Zr2+ < Ca2+ < Mg2+. NaAlMg15, with 15 wt% of Mg doping, performed good CO2 sorption and attrition resistance due to that doping 15 wt% of Mg increased the alkaline sites and changed the cellular structure, which enhanced the strength of the sorbent. Finally, extrusion-spheronization method was used to fabricate the spherical sorbent with NaAlMg15, which exhibited excellent attrition resistance and CO2 sorption performances.

Optimization of CO2 Capture Process Using Dry Sodium-Based Sorbents

Sodium carbonate (Na2CO3) supported by gamma-alumina (g-Al2O3) is one of the best sorbents for CO2 capture in economic terms because of its low raw material cost and excellent performance in low-temperature operation. The fundamental goal of this study is to optimize the operating conditions of CO2 adsorption by Na2CO3/Al2O3 sorbent in a fixed bed reactor. The sorbent characterization was studied using BET, SEM, XRF, and XRD analyses, and the sorbent structure was compared before and after the carbonation reaction. Moreover, the effects of side reactions on the adsorption process were investigated. The Response Surface Methodology (RSM) was used with Box-Behnken Design (BBD) to design the experiments. The optimum conditions are introduced at the point where initial CO2 capture capacity and deactivation rate constants are as high and as low as possible, respectively. The optimum values of the variables corresponding to the temperature of 50°C, vapor pretreatment time of 9 min, and H2O/CO2 mole ratio of 1. The amounts of initial CO2 capture capacity and deactivation rate constant in the optimum conditions were obtained to be 39.238 mgCO2/gsorbent and 0.416 min-1, respectively.

A study on the effects of textural properties of γ-Al2O3 support on CO2 capture capacity of Na2CO3

Na2CO3/γ-Al2O3 is one of the most promising sorbents to capture CO2 from industrial flue gas streams due to its high efficiency in low-temperature and low cost. The textural properties of the γ-Al2O3 support, such as specific surface area and pore volume play key roles in performance of the sorbent. Therefore, the aim of this study was to improve the sorbent performance, using several γ-Al2O3 supports, prepared through a modified sol-gel process in the presence of polyethylene glycol (PEG). N2 adsorption-desorption analysis showed that the pore volume and specific surface area of the sample with the PEG/Al(OPri)3 mole ratio of 0.05 were, respectively, about 340 % and 38 % higher than the sample synthesized in the absence of PEG. In addition, improving the specific surface area and pore volume of γ-Al2O3 enhanced the total CO2 capture capacity of a Na2CO3/γ-Al2O3 sorbent by 34 %. Moreover, the effect of Na2CO3 loading on the best γ-Al2O3 sample was investigated, and the optimum loading of Na2CO3 and the corresponding total CO2 capture capacity were observed to be 50 wt.% and 131.6 mg CO2/gsorbent, respectively. Finally, the regeneration conditions of the sodium-based sorbent were determined using chemical kinetic study and temperature programmed desorption (TPD) analysis.

A molding method of Na2CO3/Al2O3 sorbents with high sphericity and low roughness for enhanced attrition resistance in CO2 sorption/desorption process via extrusion-spheronization method

Using sodium-based sorbents for capturing CO2 is considered an effective and promising method for industry application. However, the attrition problem and how to improve the attrition resistance of sorbents are still unclear thus inhibiting the development of this technology. This paper was desired to address this problem. Multi-factors, including particle size, roughness, sphericity, fluidization number, temperature alternation and chemical reaction were supposed to result in the attrition of sorbents. Our results indicated that temperature alternation is a key factor affecting the attrition performance of sorbents. Moreover, microcrystalline cellulose was found to be an effective additive to produce the spherical sodium-based sorbents via extrusion-spheronization method. In summary, this work can benefit both the understanding and reduction of attrition of sodium-based sorbents and accelerate this technology into real industry.

Curtailing the generation of sulfur dioxide and nitrogen oxide emissions by blending and oxy-combustion of coals

This research examined the reduction of combustion-generated sulfur dioxide and nitrogen oxide emissions from a pulverized high-sulfur bituminous coal by co-firing it with a lignite coal and by substituting air with O2/CO2 gases, of compositions pertinent to dry once through oxy-fuel combustion conditions. Oxygen mole fractions were in the range of 21–30%. The neat bituminous and lignite coals as well as a 50–50wt% blend thereof were burned in a laboratory-scale electrically-heated drop-tube furnace under fuel-lean conditions. Coal particles were in the size range of 75–90μm and the furnace was operated at 1400K. Results showed that the SO2 emissions from the lignite coal were drastically lower than those from the bituminous coal, whereas the NOx emissions were only mildly lower. Co-firing the high-sulfur bituminous coal and the low-sulfur lignite coal reduced the SO2 emissions, under both air and oxy-combustion conditions, to values well-below those predicted by linear interpolation of the respective emissions of the two neat coals. This observation, in conjunction with ash analysis shows that the alkali-rich ashes of the lignite coal acted as sulfur sorbents for the copious SO2 emissions of the bituminous coal. This behavior was contrasted to SO2 sorption when the bituminous coal was co-injected with calcium- and sodium-based sorbents at analogous alkali to sulfur ratios. Co-firing of the coals reduced the NOx emissions only mildly, whereas the substitution of the background N2 gas with CO2 resulted in much more extensive NOx reductions.

Reduction of pulverized coal boiler's emissions through ReEngineered Feedstock™ co-combustion

This paper presents an experimental study of ReEF™ co-firing with coal in a pilot-scale PCB (pulverized coal boiler). ReEF™, or ReEngineered Feedstock™, is a novel fuel composed of both waste and alkaline sorbent, combining therefore the PCB emission control techniques of waste derived fuel co-firing and that of sorbent blending. The results show that ReEF™ co-firing resulted in a higher sorbent utilization and a higher sulfur emissions reduction than sorbent alone. Several combinations of calcium-based and sodium-based sorbents were tested at different stoichiometric ratios. Emissions of SO2, NOx and HCl at different feed compositions, furnace temperatures and air injection patterns were measured. SO2 emission reductions of up to 55% were observed during experiments at gas residence time 4 times lower than that of pulverized coal boiler. The slagging propensity of the ashes in the reactor was also studied. Finally, a model was developed that satisfactorily predicted the experimental SO2 emissions. It was further applied to conditions typical of existing PCB.

Na2CO3-based sorbents coated on metal foil: CO2 capture performance

The release of carbon dioxide from fossil fuel combustion into the atmosphere is one of the leading causes of global climate change. The existing technologies for the capture of CO2 suffer from various drawbacks creating an opportunity for the development of new technologies. In this investigation, sodium-based sorbents were prepared and evaluated for performance in CO2 sorption. A series of Na2CO3-based sorbents was coated onto metal foils. The loading of Na2CO3 was maintained in the range of 25–40wt.% on Al2O3. The performance of these sorbents was tested in a fixed-bed reactor at various absorption temperatures and at various water concentrations. To compare the performance of the sorbent coated metal foils, a series of Na2CO3/Al2O3 powder sorbents was also prepared by impregnation method with the same concentration of Na2CO3 as in the case of foil samples. In general, sorbent powders showed better performance compared to those of foil samples, but 35% Na2CO3/Al2O3 sorbent coated on foil showed highest performance (∼7.7mol of CO2/kg of Na2CO3). This sorbent was also investigated for 500 cycles to evaluate the stability of the sorbent.

Carbonation Characteristics of Dry Sodium-Based Sorbents for CO2 Capture

Carbonation Characteristics of Dry Sodium-Based Sorbents for CO₂ Capture

Carbonation Characteristics of Dry Sodium-Based Sorbents for CO2Capture

Na2CO3 is one potential capture medium with the potential to decrease CO2 emission. Carbonation characteristics of four sodium-based sorbents were studied using thermogravimetric analysis (TGA), X-ray diffraction, scanning electron microscopy, and nitrogen adsorption apparatuses. Results show that, in TGA tests (carbonation atmosphere of 15% CO2 + 15% H2O(g) + 70% N2 and carbonation temperature of 333 K), sorbent Na2CO3 [analytical reagent (AR)] is impervious, while sorbent Na2CO3 calcined from NaHCO3 (AR) reacts, mostly forming Na5H3(CO3)4 instead of NaHCO3, corresponding to 72.87% conversion of Na2CO3 in about 140 min. With regard to the TGA tests of sorbent Na2CO3/Al2O3 and sorbent Na2CO3/Al2O3 calcined from NaHCO3/Al2O3, only NaHCO3 is generated and the carbonation conversions are both above 85% in about 55 min. The microstructure changes were observed to analyze the reaction mechanisms and carbonation characteristics. It is confirmed that, by loading active components on Al2O3, the microscopic structures can be significantly improved, contributing to the great improvement of carbonation characteristics of the latter two sorbents. On the other hand, there is little improvement of carbonation characteristics using NaHCO3 as precursors for sorbents supported on Al2O3.

Novel Regenerable Sodium-Based Sorbents for CO2 Capture at Warm Gas Temperatures

A novel sorbent consisting of NaOH/CaO was developed for CO2 capture at 315 °C suitable for high-temperature CO2-capture applications, such as coal gasification systems. The sorbent is regenerable at 700 °C, and steam does not affect the sorbent performance. A multicycle test conducted in the atmospheric reactor at 315 °C indicated that the sorbent improved the performance with an increased number of cycles. The sorbent can also capture CO2 at a wide range of temperatures from ambient to 500 °C. However, the mechanism of CO2 capture is different at ambient temperature. The sorbent is unique because it has a high CO2-capture capacity of more than 3 mol/kg at 315 °C and is regenerable at 700 °C.

Halide compound removal from hot coal-derived gas with reusable sodium-based sorbent

The hydrogen chloride removal characteristics of molded sodium-based sorbents containing sodium aluminate (NaAlO 2) were examined in simulated hot coal-derived gas. The reaction rate and absorbing capacity of the molded sorbent were lower in comparison to the particle sorbent, and the ability to remove hydrogen chloride to below 1 ppm lasted only a short time. For improved reactivity of molded sorbent, γ-alumina powder was added as supporting material in the process of NaAlO 2 formation. This sorbent had a higher surface area, reaction rate and absorbing capacity, and the removal ability to below 1 ppm was improved. Reaction modeling of the sodium-based sorbents indicated that the cross-flow type reactor was suitable for continuous removal of hydrogen chloride in large-scale cleanup systems for coal-derived gas.

Carbon Dioxide Capture Using Dry Sodium-Based Sorbents

Electrobalance and fixed-bed reactors have been used to study the capture of CO2 from simulated flue gas using a regenerable Na2CO3 sorbent. CO2 capture was effective in the temperature range of 60−70 °C, while regeneration occurred in the range of 120−200 °C, depending on the partial pressure of CO2 in the regeneration gas. Equal molar quantities of CO2 and H2O are produced during sorbent regeneration, and pure CO2 suitable for use or sequestration is available after condensation of the H2O. Capture of as much as 90% of the CO2 was possible at appropriate reaction conditions, and little or no reduction in either carbonation rate or sorbent capacity was observed in limited multicycle tests. The concept is potentially applicable to the capture of CO2 from existing fossil fuel-fired power plants, where amine scrubbing is the only CO2 capture process currently available.

Control of Chromated Copper Arsenate Wood Incineration Air Emissions and Ash Leaching Using Sorbent Technology

Chromated copper arsenate (CCA) has been the predominant wood preservative used in North America in recent years. The emission of volatile metals and leaching from the combustion ash of CCA-treated wood pose serious concerns. In this work, mineral sorbents were evaluated for their capabilities to control both problems. Results of thermodynamic analyses suggested that alkali and alkaline earth metal-based sorbents can potentially react with the metals during combustion. Experiments were conducted by mixing and burning mineral sorbents including lime and soda ash with CCA-treated wood in a fixed bed. Calcium-based sorbents showed great increase in the retention of arsenic (from 60 to 85%) and chromium (from 55 to 80%) and reduction in the leaching of arsenic (from 200 down to 0.1 mg/L) and copper (from 100 down to 1 mg/L). Sodium-based sorbents successfully retained metals in the ash below 750°C, but the products were highly leachable (over 1000 mg/L). The speciation of the products plays a critical role in...

97/01837 Removal of hydrogen chloride from hot coal gas streams

During gasification, chloride species in coal are converted to HCl, a reactive, corrosive, and toxic gas that must be removed to meet environmental regulations, to protect power generation equipment, and to minimize deterioration of hot coal gas desulfurization sorbents. Thermochemical calculations indicated that sodium-based sorbents are capable of reducing HCl vapor to less than 1 ppm in coal gas streams up to a temperature of 650 C, but they are not easily regenerable. The mineral nahcolite (NaHCO{sub 3}) was used to make inexpensive sorbents suitable for fixed- and fluidized-bed reactors. Bench-scale tests confirmed that these sorbents have >50 wt% chloride capacity. The reaction of HCl with the sorbent was rapid and followed overall first-order kinetics.

A New Dry Process for Simultaneous Removal of SO2 and NO from Flue Gas by Powder-particle Fluidized Bed.

A new process, which is a combination of dry processes for flue gas desulfurization and selective catalytic reduction of NOx with NH3 for simultaneous removal of SOx and NOx from the flue gas, was developed using a powder-particle fluidized bed. In the process, SOx was removed by fine sorbent, and NOx was reduced to N2 with NH3 catalyzed by coarse DeNOx catalyst in a powder-particle fluidized bed reactor. The powder-particle fluidized bed was made of a stainless steel tube of 0.053m internal diameter and 1.0m in height above the distributor. Three kinds of fine sorbents, iron oxide dust (a by-product of steel production), sodium-based sorbents (sodium bicarbonate and sodium carbonate), and copper-based sorbents (CuO, CuO•V2O5/Al2O3, and CuO•V2O5•K2SO4/Al2O3), were evaluated in this study. Coarse particles of inactive silica sand and DeNOx catalysts of WO3/TiO2 and V2O5•WO3/TiO2 were used as fluidized medium particles. The effects of various operating conditions and properties of DeSOx sorbent and DeNOx catalyst on removal of SO2 and NO were investigated. The iron oxide dust appeared to be a potential low-cost sorbent for removal of SOx and also a catalyst for reduction of NOx. Both sodium-based and copper-based sorbents had sufficient reactivity for removal of SO2. The powder-particle fluidized bed reactor was effective for simultaneous removal of SOx and NOx from the flue gas. In the proposed process, the simultaneous removal of over 90% of SO2 and NO was achieved by proper combination of fine sorbent and coarse catalyst.