Structural Effects of HCl Adsorption on Mg–Fe Hydrotalcite-like Oxides at 350–650 °C in Flue Gas

Abstract

Calcined Mg–Fe hydrotalcite-like compounds (HTLs), hydrotalcite-like oxides (HTOs), have shown potential performance for removing hydrochloric acid (HCl) from flue gas at medium-high temperatures. The adsorption of HCl on Mg–Fe HTOs was studied from 350 to 650 °C. The average removal efficiency of HCl on Mg–Fe HTOs is affected primarily by temperature-dependent structural changes. Structural changes in pristine and calcined HTL samples were characterized using various analytical techniques. The pyrolysis kinetics of Mg–Fe HTLs were also studied using Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods at temperatures ranging from room temperature to 700 °C. The layered structure of HTLs was maintained at 255 °C, where the activation energy of decomposition was approximately 35–38 kJ·mol–1. At 350 °C, the removal efficiency of HCl adsorption on the HTOs was as high as 92.4%. Upon heating to 495 °C, the activation energy was 65–70 kJ·mol–1, and the HTL structure was destroyed by the decomposition of carbonate and hydroxyl functional groups, resulting in a slight decrease in HCl adsorption capacity but still exceeding 90%.

Contaminant removal by efficient separation of in situ formed layered double hydroxide compounds from mine wastewaters

“…Over the past two decades in particular, the unique physicochemical properties of layered double hydroxides (LDHs), often known more generically as hydrotalcites, have gained considerable attention in the research community, [1][2][3][4] and industry due to their application as sorbents or catalysts, [5][6][7][8][9][10][11][12] and for the treatment of mining or other wastewaters. [13][14][15][16] The utility of LDHs stems from their tuneable functional properties that may result from the substitution of a variety of cations into the metal double hydroxide layers and anions into the interlayer spaces.…”

Investigation on mechanochemically modified calcium‐based adsorbent for flue gas HCl removal

“…Many efforts have been devoted to developing superior adsorbents to remove HCl. Cao et al 14 prepared HCl antichlor of Ca‐Mg‐Al mixed oxides by using the coprecipitation method after being calcined at 350°C for 2 h, indicating that it has better performance than MgO, NaHCO 3 , and CaO. Wang et al 19 studied the synergistic removal effect of SO 2 , HCl, and other pollutants by viscose‐based activated carbon fibers in simulated incineration flue gas and found that the removal efficiency of HCl reached 100% during a long time 19 .…”

Synthesis, Characterization, and High-Temperature HCl Capture Capacity of Different Proportions of Potassium Fluoride-Doped CaMgAl Layered Double Hydroxides

“…28−30 Hydrotalcite-like composite is a good dechlorination adsorbent, especially in the water environment, but its dechlorination characteristics in a high-temperature gas environment are yet studied. In some literature studies, 31,32 the high-temperature dechlorination adsorbent for hydrotalcite-like materials was studied, including the preparation of the dechlorination adsorbent, adsorption test, cross-flow moving bed reactor, and numerical simulation. It was generally considered that the removal efficiency of HCl by a Ca–Mg–Al hydrothermal liquefaction (HTL) adsorbent at high temperature was significantly higher than that by CaO and NaHCO 3 adsorbents.…”

“…The compositions of LDHs have the general expression [M­(II) 1– x M­(III) x (OH) 2 ] x + (A n – ) x / n · m H 2 O, in which M­(II) and M­(III) are divalent and trivalent metallic cations located in the main layer, A n – is the interlayer anion, m is the number of interlayer water molecules, and x is the molar ratio of M 3+ /(M 2+ + M 3+ ). − The dechlorination performance and optimum ratio of hydrotalcite-like compounds have been previously studied. − Hydrotalcite-like composite is a good dechlorination adsorbent, especially in the water environment, but its dechlorination characteristics in a high-temperature gas environment are yet studied. In some literature studies, , the high-temperature dechlorination adsorbent for hydrotalcite-like materials was studied, including the preparation of the dechlorination adsorbent, adsorption test, cross-flow moving bed reactor, and numerical simulation. It was generally considered that the removal efficiency of HCl by a Ca–Mg–Al hydrothermal liquefaction (HTL) adsorbent at high temperature was significantly higher than that by CaO and NaHCO 3 adsorbents.…”