Thokozile A. Kathyola, Elizabeth A. Willneff, Colin J. Willis, Peter J. Dowding, Sven L. M. Schroeder
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Combined <i>ex situ</i> mid-IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray absorption spectroscopy and scanning electron microscopy examination of the reaction product formed in the presence of CO<sub>2</sub> reveals the formation of calcium dimethylcarbonate (Ca(OCOOCH<sub>3</sub>)<sub>2</sub>). This strongly suggests that carbonation takes place by reaction with the Ca(OCH<sub>3</sub>)<sub>2</sub> formed from a Ca(OH)<sub>2</sub> and CH<sub>3</sub>OH reaction. Time-resolved XRD indicates that in the presence of H<sub>2</sub>O the Ca(OCOOCH<sub>3</sub>)<sub>2</sub> ester releases CH<sub>3</sub>OH and CO<sub>2</sub>, forming ACC, which subsequently transforms into vaterite and then calcite. TGA reveals that thermal decomposition of Ca(OCOOCH<sub>3</sub>)<sub>2</sub> in the absence of H<sub>2</sub>O mainly leads to the reformation of Ca(OCH<sub>3</sub>)<sub>2</sub>, but this is accompanied by a significant parallel reaction that releases dimethylether (CH<sub>3</sub>OCH<sub>3</sub>) and CO<sub>2</sub>. CaCO<sub>3</sub> is the final product in both decomposition pathways. For CH<sub>3</sub>OH/H<sub>2</sub>O mixtures containing more than 50 mol % H<sub>2</sub>O, direct formation of calcite from Ca(OH)<sub>2</sub> becomes the dominant pathway, although the formation of some Ca(OCOOCH<sub>3</sub>)<sub>2</sub> was still evident in the <i>in situ</i> mid-IR spectra of 20 and 40 mol % CH<sub>3</sub>OH systems. In the presence of ≤20 mol % H<sub>2</sub>O, hydrolysis of the ester led to the formation of an ACC sol–gel. In both the 90 and 100 mol % CH<sub>3</sub>OH systems, diffusion-limited ACC → vaterite → calcite transformations were observed. Traces of aragonite were also detected. We believe that this is the first time that these reaction pathways during the carbonation of Ca(OH)<sub>2</sub> in a methanolic phase have been systematically and experimentally characterized.","PeriodicalId":29796,"journal":{"name":"ACS Physical Chemistry Au","volume":"1 1","pages":""},"PeriodicalIF":3.7000,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Reactive CaCO3 Formation from CO2 and Methanolic Ca(OH)2 Dispersions: Transient Methoxide Salts, Carbonate Esters and Sol–Gels\",\"authors\":\"Thokozile A. Kathyola, Elizabeth A. Willneff, Colin J. Willis, Peter J. Dowding, Sven L. M. Schroeder\",\"doi\":\"10.1021/acsphyschemau.4c00041\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"A combination of <i>ex situ</i> and <i>in situ</i> characterization techniques was used to determine the mechanism of calcium carbonate (CaCO<sub>3</sub>) formation from calcium hydroxide (Ca(OH)<sub>2</sub>) dispersions in methanol/water (CH<sub>3</sub>OH/H<sub>2</sub>O) systems. Mid-infrared (mid-IR) analysis shows that in the absence of carbon dioxide (CO<sub>2</sub>) Ca(OH)<sub>2</sub> establishes a reaction equilibrium with CH<sub>3</sub>OH, forming calcium hydroxide methoxide (Ca(OH)(OCH<sub>3</sub>)) and calcium methoxide (Ca(OCH<sub>3</sub>)<sub>2</sub>). Combined <i>ex situ</i> mid-IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray absorption spectroscopy and scanning electron microscopy examination of the reaction product formed in the presence of CO<sub>2</sub> reveals the formation of calcium dimethylcarbonate (Ca(OCOOCH<sub>3</sub>)<sub>2</sub>). This strongly suggests that carbonation takes place by reaction with the Ca(OCH<sub>3</sub>)<sub>2</sub> formed from a Ca(OH)<sub>2</sub> and CH<sub>3</sub>OH reaction. Time-resolved XRD indicates that in the presence of H<sub>2</sub>O the Ca(OCOOCH<sub>3</sub>)<sub>2</sub> ester releases CH<sub>3</sub>OH and CO<sub>2</sub>, forming ACC, which subsequently transforms into vaterite and then calcite. TGA reveals that thermal decomposition of Ca(OCOOCH<sub>3</sub>)<sub>2</sub> in the absence of H<sub>2</sub>O mainly leads to the reformation of Ca(OCH<sub>3</sub>)<sub>2</sub>, but this is accompanied by a significant parallel reaction that releases dimethylether (CH<sub>3</sub>OCH<sub>3</sub>) and CO<sub>2</sub>. CaCO<sub>3</sub> is the final product in both decomposition pathways. For CH<sub>3</sub>OH/H<sub>2</sub>O mixtures containing more than 50 mol % H<sub>2</sub>O, direct formation of calcite from Ca(OH)<sub>2</sub> becomes the dominant pathway, although the formation of some Ca(OCOOCH<sub>3</sub>)<sub>2</sub> was still evident in the <i>in situ</i> mid-IR spectra of 20 and 40 mol % CH<sub>3</sub>OH systems. In the presence of ≤20 mol % H<sub>2</sub>O, hydrolysis of the ester led to the formation of an ACC sol–gel. In both the 90 and 100 mol % CH<sub>3</sub>OH systems, diffusion-limited ACC → vaterite → calcite transformations were observed. Traces of aragonite were also detected. We believe that this is the first time that these reaction pathways during the carbonation of Ca(OH)<sub>2</sub> in a methanolic phase have been systematically and experimentally characterized.\",\"PeriodicalId\":29796,\"journal\":{\"name\":\"ACS Physical Chemistry Au\",\"volume\":\"1 1\",\"pages\":\"\"},\"PeriodicalIF\":3.7000,\"publicationDate\":\"2024-07-23\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"ACS Physical Chemistry Au\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.1021/acsphyschemau.4c00041\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"CHEMISTRY, PHYSICAL\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Physical Chemistry Au","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1021/acsphyschemau.4c00041","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
Reactive CaCO3 Formation from CO2 and Methanolic Ca(OH)2 Dispersions: Transient Methoxide Salts, Carbonate Esters and Sol–Gels
A combination of ex situ and in situ characterization techniques was used to determine the mechanism of calcium carbonate (CaCO3) formation from calcium hydroxide (Ca(OH)2) dispersions in methanol/water (CH3OH/H2O) systems. Mid-infrared (mid-IR) analysis shows that in the absence of carbon dioxide (CO2) Ca(OH)2 establishes a reaction equilibrium with CH3OH, forming calcium hydroxide methoxide (Ca(OH)(OCH3)) and calcium methoxide (Ca(OCH3)2). Combined ex situ mid-IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray absorption spectroscopy and scanning electron microscopy examination of the reaction product formed in the presence of CO2 reveals the formation of calcium dimethylcarbonate (Ca(OCOOCH3)2). This strongly suggests that carbonation takes place by reaction with the Ca(OCH3)2 formed from a Ca(OH)2 and CH3OH reaction. Time-resolved XRD indicates that in the presence of H2O the Ca(OCOOCH3)2 ester releases CH3OH and CO2, forming ACC, which subsequently transforms into vaterite and then calcite. TGA reveals that thermal decomposition of Ca(OCOOCH3)2 in the absence of H2O mainly leads to the reformation of Ca(OCH3)2, but this is accompanied by a significant parallel reaction that releases dimethylether (CH3OCH3) and CO2. CaCO3 is the final product in both decomposition pathways. For CH3OH/H2O mixtures containing more than 50 mol % H2O, direct formation of calcite from Ca(OH)2 becomes the dominant pathway, although the formation of some Ca(OCOOCH3)2 was still evident in the in situ mid-IR spectra of 20 and 40 mol % CH3OH systems. In the presence of ≤20 mol % H2O, hydrolysis of the ester led to the formation of an ACC sol–gel. In both the 90 and 100 mol % CH3OH systems, diffusion-limited ACC → vaterite → calcite transformations were observed. Traces of aragonite were also detected. We believe that this is the first time that these reaction pathways during the carbonation of Ca(OH)2 in a methanolic phase have been systematically and experimentally characterized.
期刊介绍：
ACS Physical Chemistry Au is an open access journal which publishes original fundamental and applied research on all aspects of physical chemistry. The journal publishes new and original experimental computational and theoretical research of interest to physical chemists biophysical chemists chemical physicists physicists material scientists and engineers. An essential criterion for acceptance is that the manuscript provides new physical insight or develops new tools and methods of general interest. Some major topical areas include:Molecules Clusters and Aerosols; Biophysics Biomaterials Liquids and Soft Matter; Energy Materials and Catalysis
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