This document investigates using a regenerable buffer (tertiary amine) to control pH and enable the conversion of CO2 into magnesium carbonate minerals for carbon sequestration. Tertiary amines can complex with protons to raise the pH for magnesium carbonate precipitation at around 8.2. Increasing the temperature decreases the pH as the strength of the amine-proton bond decreases with higher temperatures. This approach provides both the low pH and high temperature needed for magnesium dissolution from minerals like serpentine, as well as the high pH for carbonate precipitation. The regenerable buffer concept was found to work, achieving 20-40% carbonate yields using triethylamine or tripropylamine at 18
A ruthenium-carbamato-complex derived from a siloxylated amine and carbon dio...Pawan Kumar
The rutheniumcarbamate complex derived from3-trimethoxysilyl-1-
propyl amine and carbon dioxidewas found to be a novel catalyst for
the oxidative cyanation of aromatic and cyclic tertiary amines to
corresponding a-amino nitriles in high to excellent yields by using
hydrogen peroxide and molecular oxygen as enviro-economic
oxidants. The developed protocol suggested an efficient alternative
for recycling carbon dioxide.
The Expander Gas and Ammonia Ratio Influence on the Calcium Cyanamide YieldYogeshIJTSRD
For the first time, thermodynamic calculations based on relatively new physicochemical constants clarified the onset temperature of thermal ammonia decomposition, as well as the side chemical reactions probability between ammonia and carbon dioxide. The influence of the main technological parameters on the calcium cyanamide synthesis is investigated. The exhaust gases composition from the reactor for the calcium cyanamide synthesis was studied depending on the temperature. Kinetic studies of the calcium cyanamide synthesis determined the chemical reaction orders with respect to ammonia and carbon dioxide, and it was proved that the limiting stage of calcium cyanamide synthesis is the initial gas components diffusion through the product layer. O. Kh. Panzhiev | A. Kh. Panzhiev | N. Umarov | O. Azimov "The Expander Gas and Ammonia Ratio Influence on the Calcium Cyanamide Yield" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Special Issue | International Research Development and Scientific Excellence in Academic Life , March 2021, URL: https://www.ijtsrd.com/papers/ijtsrd38440.pdf Paper Url: https://www.ijtsrd.com/engineering/other/38440/the-expander-gas-and-ammonia-ratio-influence-on-the-calcium-cyanamide-yield/o-kh-panzhiev
Bidentate Schiff base ligand 3-(3,4-Dihydroxy-phenyl)-2-[(4-dimethylamino-benzylidene)-amino]-2-methyl-propionic acid was prepared and characterized by spectroscopic techniques studies and elemental analysis. The Cd(II), Ni(II), Cu(II), Co(II), Cr(III),and Fe(III) of mixed-ligand complexes were structural explicate through moler conductance , [FT-IR, UV-Vis & AAS], chloride contents, , and magnetic susceptibility measurements. Octahedral geometries have been suggested for all complexes. The Schiff base and its complexes were tested against various bacterial species, two of {gram(G+) and gram(G-)} were shown weak to good activity against all bacteria.
A ruthenium-carbamato-complex derived from a siloxylated amine and carbon dio...Pawan Kumar
The rutheniumcarbamate complex derived from3-trimethoxysilyl-1-
propyl amine and carbon dioxidewas found to be a novel catalyst for
the oxidative cyanation of aromatic and cyclic tertiary amines to
corresponding a-amino nitriles in high to excellent yields by using
hydrogen peroxide and molecular oxygen as enviro-economic
oxidants. The developed protocol suggested an efficient alternative
for recycling carbon dioxide.
The Expander Gas and Ammonia Ratio Influence on the Calcium Cyanamide YieldYogeshIJTSRD
For the first time, thermodynamic calculations based on relatively new physicochemical constants clarified the onset temperature of thermal ammonia decomposition, as well as the side chemical reactions probability between ammonia and carbon dioxide. The influence of the main technological parameters on the calcium cyanamide synthesis is investigated. The exhaust gases composition from the reactor for the calcium cyanamide synthesis was studied depending on the temperature. Kinetic studies of the calcium cyanamide synthesis determined the chemical reaction orders with respect to ammonia and carbon dioxide, and it was proved that the limiting stage of calcium cyanamide synthesis is the initial gas components diffusion through the product layer. O. Kh. Panzhiev | A. Kh. Panzhiev | N. Umarov | O. Azimov "The Expander Gas and Ammonia Ratio Influence on the Calcium Cyanamide Yield" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Special Issue | International Research Development and Scientific Excellence in Academic Life , March 2021, URL: https://www.ijtsrd.com/papers/ijtsrd38440.pdf Paper Url: https://www.ijtsrd.com/engineering/other/38440/the-expander-gas-and-ammonia-ratio-influence-on-the-calcium-cyanamide-yield/o-kh-panzhiev
Bidentate Schiff base ligand 3-(3,4-Dihydroxy-phenyl)-2-[(4-dimethylamino-benzylidene)-amino]-2-methyl-propionic acid was prepared and characterized by spectroscopic techniques studies and elemental analysis. The Cd(II), Ni(II), Cu(II), Co(II), Cr(III),and Fe(III) of mixed-ligand complexes were structural explicate through moler conductance , [FT-IR, UV-Vis & AAS], chloride contents, , and magnetic susceptibility measurements. Octahedral geometries have been suggested for all complexes. The Schiff base and its complexes were tested against various bacterial species, two of {gram(G+) and gram(G-)} were shown weak to good activity against all bacteria.
Inhibitory Effect of Some Carbazides on Corrosion of Aluminium in Hydrochloric Acid and Sodium Hydroxide Solutions
The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of semicarbazide, thiosemicar- bazide and sym.dipheny1carbazide as corrosion inhibitors has been studied using thermometric, weight-loss and polarization methods. The three methods gave consistent results. The higher inhibition efficiency of these compounds in acidic than in alkaline madia may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive.The adsorption of these compounds were found to obey Frurnkin adsorption isotherm. Cathodic polarization measurements showed that these com- pounds are cathodic inhibitors and their adsorption in the double layer does not change the mechanism of the hydrogen evolution reaction. The results are analysed in terms of both molecular and cationic adsorption.
STUDY OF A CATALYST OF CITRIC ACID CROSSLINKING ON LOCUST BEAN GUMUniversitasGadjahMada
HCl, H2SO4, and potassium persulfate (PPS) were studied as catalysts of the process of citric acid (CA) crosslinking on
locust bean gum (LBG). The copolymer (CA-c-LBG) obtained was characterized by its viscosity, pH, FTIR, NMR and SEM.
It was found that the protonation of the hydroxyl groups at C6 atom of mannose and galactose in LBG and the hydrogen
atoms of CA carboxylic group was accelerated. The best catalytic effect was obtained in presence of HCl.
Mannich Synthesis Under Ionic Liquid [Et3NH][HSO4] CatalysisIOSRJAC
Ionic liquid [Et3NH][HSO4] was found to be a particularly efficient catalyst for the synthesis of β- amino carbonyl pyrimidines through the Mannich condensation reaction of substituted pyrimidin-2(1H)-ones, cyclohexanone and 4-fluro/chlorobenzaldehyde under ultrasonic irradiation at room temperature. The present methodology offers several advantages such as excellent yields, simple procedure and mild conditions.
Separation of calcium carbonate and barium sulphate from a mixed sludge prduc...Timothy Rukuni
South Africa is one of the first countries to implement full-scale mine water reclamation to drinking water quality. Reverse osmosis is already being used on full scale for desalination of mine water. However, with increased recycling of mine water, the result has been the increased generation of sludge. The Council for Scientific and Industrial Research (CSIR) has developed the Alkali-Barium-Carbonate (CSIR-ABC) process that can be used for neutralization and desalination of sulphate-rich effluents while recovering valuable by-products from the mixed sludges produced. A mixture of BaSO4 and CaCO3 sludge is produced as one of the by-products, which preferably needs to be separated into its components prior to thermal treatment. The aim of this study was to separate CaCO3 and BaSO4 from a CaCO3-BaSO4 mixed sludge through dissolution of CaCO3 as Ca(HCO3)2 in contact with CO2. Measured quantities of a simulated CaCO3-BaSO4 mixed sludge from the CSIR-ABC process were fed into a reactor vessel containing deionized water and pressurized CO2 was introduced. The effects of temperature and pressure with time were investigated while monitoring alkalinity, pH and calcium concentration. The findings of this study were: (1) The dissolution rate of CaCO3 was rapid i.e. from 0 to 2000mg/L in the first 20 minutes; (2) Ca(HCO3)2 had a high solubility of about 2 600 mg/L when in contact with CO2 at 1 atm., while BaSO4 was almost completely insoluble; (3) The solubility of Ca(HCO3)2 increased with decreasing temperature and increasing pressure; (4) CaCO3, after conversion to Ca(HCO3)2, was separated from BaSO4 in a CaCO3-BaSO4 mixed sludge; (5) Visual MINTEQ model is a powerful tool that can be used to predict the solubilities of CaCO3 and BaSO4 when contacted with CO2.
Multiple Equilibria and Chemical Distribution of Some Bio Metals With β-Amide...IOSR Journals
Abstract: Solution Chemistry of some bivalent metal ions (viz. CoII , NiII ,CuII ,ZnII ) with β-amide α-aminosuccinate (Asparagine)/ α-aminoisoverate( Valine ) (A) and 5-methyl 2,4- dioxopyrimidine ( Thymine ) (B)ligands have been analyzed. Formation constant of quaternary metal complexes and complexation equilibria at 30±1ºC and at constant ionic strength (I=0.1M NaNO3 ) have been explored potentiometrically. Formation of quaternary species in addition to hydroxyl, protonated, binary and ternary species have been reported. Overall formation constant have been evaluated using SCOGS computer program.Species distribution curves of complexes have been plotted as a function of pH to visualize the equlibria system and was refined using ORIGIN program.The metal ligand formation constant of MA,MB,MAB and M1M2AB type of complexes follow Irving William order. The order of stability constants of quaternary systems have been observed as: Cu – Ni > Cu –Zn > Cu–Co > Ni – Zn > Ni – Co > Co –Zn. Solution structures of metal complexes with said ligands have been compared and discussed.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Radiolysis of Transformer Oil in The Presence of Admixtures of Polychlorineb...IJMREMJournal
Dependence of concentration of CO2, H2O2, pH- indicator and IR-spectra of γ- irradiated transformer oil,
containing polychlorinebiphenyl (PCB) admixtures from adsorbed doses in the range of 4-136 kGy was studied.
It was established that radiation-chemical yields of CO2 and H2O2 are equal to 0.18 and 3.6 molec/100eV.
Irradiation leads to increasing of acidity, related with dechlorination of PCB molecules. A comparative study of
the radiolysis of used transformer oil and oil containing PCB under the influence of gamma radiation was carried
out. The pH-value dependence and concentration of hydrogen peroxide as a function of the absorbed dose was
studied. It found that during the radiolysis of transformer oil containing PCB in the presence of dissolved oxygen,
radiation-initiated oxidation of the oil takes place (formation of H2O2 and CO2, a decrease in the pH-value).
• Grossmann & Berger und Ellwanger & Geiger Privatbankiers gründen Netzwerk mit Standorten in den Top-7-Immobilienstädten
• Düsseldorfer Immobilienberater ANTEON ist gleichberechtigter Partner der Kooperation
• Fokus auf Investmentberatung und Gewerbevermietung
Digitale Objekte in digitalen Öffentlichkeiten: Die Rolle von Hashtags in po...Christian Katzenbach
Vortrag auf der DGPuK 2014, 29. Mai 2014, Passau
Digitale Öffentlichkeiten und ihre Rolle in der Politik stehen schon länger im Fokus der kommunikationswissenschaftlichen Internetforschung. Mit der breiten Etablierung sozialer Medien – auch als Forschungsobjekt – zeigt sich indes, dass Plattformen wie Facebook oder Twitter mehr als eine reine Vermittlerrolle in digitalen Öffentlichkeiten zukommt: Indem diese Plattformen die Kommunikation, die über sie stattfindet, konfigurieren, tragen sie maßgeblich zur Entstehung, Aufrechterhaltung und Auflösung digitaler Öffentlichkeiten bei – und präformieren diese auch in Struktur und Inhalt.
Unser Beitrag untersucht deshalb die Rolle von digitale Objekten in digitalen Öffentlichkeiten im Kontext der Mehr-Ebenen-Modelle von Öffentlichkeit von Gerhards/Neidhart und Klaus. Wir betrachten die plattformspezifischen Konfigurationen und hinterfragen dabei, wie digitale Öffentlichkeiten entstehen und wie sie sich stabilisieren. Anhand zweier jüngerer Fallbeispiele – #aufschrei und #bürgerforum – analysieren wir mit unterschiedlichen Methoden, welche Rolle Hashtags als „digital social objects” zukommt.
Inhibitory Effect of Some Carbazides on Corrosion of Aluminium in Hydrochloric Acid and Sodium Hydroxide Solutions
The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of semicarbazide, thiosemicar- bazide and sym.dipheny1carbazide as corrosion inhibitors has been studied using thermometric, weight-loss and polarization methods. The three methods gave consistent results. The higher inhibition efficiency of these compounds in acidic than in alkaline madia may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive.The adsorption of these compounds were found to obey Frurnkin adsorption isotherm. Cathodic polarization measurements showed that these com- pounds are cathodic inhibitors and their adsorption in the double layer does not change the mechanism of the hydrogen evolution reaction. The results are analysed in terms of both molecular and cationic adsorption.
STUDY OF A CATALYST OF CITRIC ACID CROSSLINKING ON LOCUST BEAN GUMUniversitasGadjahMada
HCl, H2SO4, and potassium persulfate (PPS) were studied as catalysts of the process of citric acid (CA) crosslinking on
locust bean gum (LBG). The copolymer (CA-c-LBG) obtained was characterized by its viscosity, pH, FTIR, NMR and SEM.
It was found that the protonation of the hydroxyl groups at C6 atom of mannose and galactose in LBG and the hydrogen
atoms of CA carboxylic group was accelerated. The best catalytic effect was obtained in presence of HCl.
Mannich Synthesis Under Ionic Liquid [Et3NH][HSO4] CatalysisIOSRJAC
Ionic liquid [Et3NH][HSO4] was found to be a particularly efficient catalyst for the synthesis of β- amino carbonyl pyrimidines through the Mannich condensation reaction of substituted pyrimidin-2(1H)-ones, cyclohexanone and 4-fluro/chlorobenzaldehyde under ultrasonic irradiation at room temperature. The present methodology offers several advantages such as excellent yields, simple procedure and mild conditions.
Separation of calcium carbonate and barium sulphate from a mixed sludge prduc...Timothy Rukuni
South Africa is one of the first countries to implement full-scale mine water reclamation to drinking water quality. Reverse osmosis is already being used on full scale for desalination of mine water. However, with increased recycling of mine water, the result has been the increased generation of sludge. The Council for Scientific and Industrial Research (CSIR) has developed the Alkali-Barium-Carbonate (CSIR-ABC) process that can be used for neutralization and desalination of sulphate-rich effluents while recovering valuable by-products from the mixed sludges produced. A mixture of BaSO4 and CaCO3 sludge is produced as one of the by-products, which preferably needs to be separated into its components prior to thermal treatment. The aim of this study was to separate CaCO3 and BaSO4 from a CaCO3-BaSO4 mixed sludge through dissolution of CaCO3 as Ca(HCO3)2 in contact with CO2. Measured quantities of a simulated CaCO3-BaSO4 mixed sludge from the CSIR-ABC process were fed into a reactor vessel containing deionized water and pressurized CO2 was introduced. The effects of temperature and pressure with time were investigated while monitoring alkalinity, pH and calcium concentration. The findings of this study were: (1) The dissolution rate of CaCO3 was rapid i.e. from 0 to 2000mg/L in the first 20 minutes; (2) Ca(HCO3)2 had a high solubility of about 2 600 mg/L when in contact with CO2 at 1 atm., while BaSO4 was almost completely insoluble; (3) The solubility of Ca(HCO3)2 increased with decreasing temperature and increasing pressure; (4) CaCO3, after conversion to Ca(HCO3)2, was separated from BaSO4 in a CaCO3-BaSO4 mixed sludge; (5) Visual MINTEQ model is a powerful tool that can be used to predict the solubilities of CaCO3 and BaSO4 when contacted with CO2.
Multiple Equilibria and Chemical Distribution of Some Bio Metals With β-Amide...IOSR Journals
Abstract: Solution Chemistry of some bivalent metal ions (viz. CoII , NiII ,CuII ,ZnII ) with β-amide α-aminosuccinate (Asparagine)/ α-aminoisoverate( Valine ) (A) and 5-methyl 2,4- dioxopyrimidine ( Thymine ) (B)ligands have been analyzed. Formation constant of quaternary metal complexes and complexation equilibria at 30±1ºC and at constant ionic strength (I=0.1M NaNO3 ) have been explored potentiometrically. Formation of quaternary species in addition to hydroxyl, protonated, binary and ternary species have been reported. Overall formation constant have been evaluated using SCOGS computer program.Species distribution curves of complexes have been plotted as a function of pH to visualize the equlibria system and was refined using ORIGIN program.The metal ligand formation constant of MA,MB,MAB and M1M2AB type of complexes follow Irving William order. The order of stability constants of quaternary systems have been observed as: Cu – Ni > Cu –Zn > Cu–Co > Ni – Zn > Ni – Co > Co –Zn. Solution structures of metal complexes with said ligands have been compared and discussed.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Radiolysis of Transformer Oil in The Presence of Admixtures of Polychlorineb...IJMREMJournal
Dependence of concentration of CO2, H2O2, pH- indicator and IR-spectra of γ- irradiated transformer oil,
containing polychlorinebiphenyl (PCB) admixtures from adsorbed doses in the range of 4-136 kGy was studied.
It was established that radiation-chemical yields of CO2 and H2O2 are equal to 0.18 and 3.6 molec/100eV.
Irradiation leads to increasing of acidity, related with dechlorination of PCB molecules. A comparative study of
the radiolysis of used transformer oil and oil containing PCB under the influence of gamma radiation was carried
out. The pH-value dependence and concentration of hydrogen peroxide as a function of the absorbed dose was
studied. It found that during the radiolysis of transformer oil containing PCB in the presence of dissolved oxygen,
radiation-initiated oxidation of the oil takes place (formation of H2O2 and CO2, a decrease in the pH-value).
• Grossmann & Berger und Ellwanger & Geiger Privatbankiers gründen Netzwerk mit Standorten in den Top-7-Immobilienstädten
• Düsseldorfer Immobilienberater ANTEON ist gleichberechtigter Partner der Kooperation
• Fokus auf Investmentberatung und Gewerbevermietung
Digitale Objekte in digitalen Öffentlichkeiten: Die Rolle von Hashtags in po...Christian Katzenbach
Vortrag auf der DGPuK 2014, 29. Mai 2014, Passau
Digitale Öffentlichkeiten und ihre Rolle in der Politik stehen schon länger im Fokus der kommunikationswissenschaftlichen Internetforschung. Mit der breiten Etablierung sozialer Medien – auch als Forschungsobjekt – zeigt sich indes, dass Plattformen wie Facebook oder Twitter mehr als eine reine Vermittlerrolle in digitalen Öffentlichkeiten zukommt: Indem diese Plattformen die Kommunikation, die über sie stattfindet, konfigurieren, tragen sie maßgeblich zur Entstehung, Aufrechterhaltung und Auflösung digitaler Öffentlichkeiten bei – und präformieren diese auch in Struktur und Inhalt.
Unser Beitrag untersucht deshalb die Rolle von digitale Objekten in digitalen Öffentlichkeiten im Kontext der Mehr-Ebenen-Modelle von Öffentlichkeit von Gerhards/Neidhart und Klaus. Wir betrachten die plattformspezifischen Konfigurationen und hinterfragen dabei, wie digitale Öffentlichkeiten entstehen und wie sie sich stabilisieren. Anhand zweier jüngerer Fallbeispiele – #aufschrei und #bürgerforum – analysieren wir mit unterschiedlichen Methoden, welche Rolle Hashtags als „digital social objects” zukommt.
Leer el Cine es una actividad de Alfabetización Audiovisual, es decir, enseñamos al público cómo se hacen y, sobre todo, por qué, las obras audiovisuales. Estamos ante un lenguaje (el audiovisual) que, por tanto, transmite un mensaje. Nosotros queremos enseñar su idioma para formar a espectadores críticos con lo que ven, especialmente los niños
Bopki es una comunidad dirigida exclusivamente a mujeres, basada en el concepto de word of mouth: dejar que los usuarios prueben el producto para que luego expresen libremente su opinión
Hoy nos conectamos 2.0 con Juan Pistone Director de Campañas de trnd.
Articulo sobre redes sociales en el sector asegurador en América Latina. Artículo publicado en la edición de julio agosto de la revista de Actualidad Aseguradora América Latina
Estudie el mensaje 'Andar enlutado' por el Pastor Alberto Solorzano. En este mensaje aprenda como uno puede matizar la vida de tinieblas, si no decide cambiar la actitud de enlutamiento. Y aprenda como cortar esta forma de opresión.
www.ccihonduras.org
Production of Renewable Fuels by the Photocatalytic Reduction of CO2 using Ma...Pawan Kumar
The photo-reductive performance of natural ilmenite was boosted and the production of renewable fuels from the reduction of CO2 was enhanced by doping the natural mineral with magnesium. The doping was achieved by high energy ball milling in the presence of MgO and Mg(NO3)2. The photo-reduction of CO2 in aqueous solution led to the evolution of H2, CH4, C2H4, and C2H6, and the insertion of Mg in the structure of ilmenite enabled increases of up to 1245% in the fuel production yield, reaching total production of 210.9 µmol h-1 gcat-1. Displacements of the conduction band to more negative potentials were evidenced for the samples doped with magnesium. Indirect effects such as increases in the valence band maximum, and the introduction of intermediate energy levels were also evidenced through the measurement of the crystallite size and the determination of the band structure of the materials. Mott-Schottky analyses of the samples showed the n-type nature of the semiconductor materials and enabled the estimation of the density of charge carriers, which strongly influenced the photocatalytic performance. The strong potential of the application of natural ilmenite in gas phase artificial photosynthesis was proved by the evaluation of CO2 reduction in gas conditions, which allowed the enhancement in the selectivity and significantly increased the production of CH4 as compared to aqueous solution, reaching an important yield of CH4 of 16.1 µmol h-1 gcat-1.
Presentation given by Greg Rau of UC Santa Cruz/LLNL on "Alternative Point-Source CO2 Mitigation: Spontaneous Conversion of CO2 to Ocean Alkalinity" at the Alternative CCS Pathways Workshop, Oxford Martin School, 26 June 2014
Graphene oxide immobilized copper phthalocyanine tetrasulphonamide: the first...Pawan Kumar
The first successful synthesis of DMC directly from methanol and carbon dioxide using a heterogenized
homogeneous graphene oxide immobilized copper phthalocyanine tetrasulphonamide catalyst in the
presence of N,N0-dicyclohexylcarbodiimide (DCC) as a dehydrating agent is described. The presence of a
dehydrating agent was found to be vital and in its absence the yield of DMC was found to be decreased
significantly. Under the optimized reaction conditions, the maximum yield of DMC reaches up to 13.3%.
Although the homogeneous copper phthalocyanine tetrasulphonamide catalyst provided a little higher
yield of DMC (14.2%), the facile recovery and recycling ability of the heterogeneous catalyst make the
developed method more attractive from environmental and economical viewpoints.
Visible light assisted photocatalytic reduction of CO2 using a graphene oxide...Pawan Kumar
A new heteroleptic ruthenium complex containing 2-thiophenyl benzimidazole ligands was synthesized
using a microwave technique and was immobilized to graphene oxide via covalent attachment. The synthesized
catalyst was used for the photoreduction of carbon dioxide under visible light irradiation without
using a sacrificial agent, which gave 2050 μmol g−1 cat methanol after 24 h of irradiation
Absorber Models for absorption of Carbon dioxide from sour natural gas byMeth...IJERA Editor
Mathematical models of the absorber for the absorption of carbon dioxide (CO2)from sour natural gas in Methyl-diethanol Amine (MDEA)solution were developed. The resulting ordinary differential model equations were solved numerically using theode45 solver of MATLAB 7.5. The accuracy of the models was ascertained using industrial plant data from the carbon dioxide absorber of the Obiafu/Obrikom Gas Treatment plant in Rivers State, Nigeria. The models predicted the CO2 concentration in the sweet gas, gas and solvent (MDEA) temperature progressions along the packed absorber. The results obtained from solutions to the models compared favorably with the plant outputs with a maximum deviation between models predictions and industrial plant outputs of 0.44%. The models were used to simulate the influence of sour gas flow rates and solvent (MDEA) concentration in solution on the performance (absorption rates of CO2) of the absorber.The results show that the absorption rate of CO2 increases with increasing gas flow rate and solvent concentration.
Paladio soportado sobre hidrotalcita como un catalizador para la reacción de ...52900339
Resumen
Se estudió la eficacia de diversas sales de paladio como catalizador en la reacción de acoplamiento cruzado de Suzuki, y la influencia de la base y de temperatura utilizados en su conversión, El uso de PdCl2 soportado sobre hidrotalcita como catalizador en presencia de carbonato de potasio como se encontró base para proporcionar los mejores resultados. Las temperaturas de reacción superiores a 90 °C garantizarse niveles de conversión a la par con los de muchos catalizadores homogéneos.
Balucan et al 2016_Acid induced mineral alteration on the permeability and co...
Steel et al 2013_Conversion of CO2 into mineral carbonates
1. Conversion of CO2 into mineral carbonates using a regenerable buffer
to control solution pH
Karen M. Steel ⇑
, Kimia Alizadehhesari, Reydick D. Balucan, Bruno Bašic´
School of Chemical Engineering, University of Queensland, St. Lucia, Queensland 4072, Australia
h i g h l i g h t s
Use of a regenerable buffer (tertiary amine) is studied to enable mineral carbonation.
Tertiary amines complex protons to give a pH of 8.2 which enables MgCO3 precipitation.
Increasing temperature from 18 to 85 °C decreases pH by 2.5 pH units.
Higher temperatures 85 °C might enable low pHs needed for Mg–silicate dissolution.
a r t i c l e i n f o
Article history:
Received 25 October 2012
Received in revised form 14 March 2013
Accepted 16 April 2013
Available online 30 April 2013
Keywords:
Mineral carbonation
CO2 sequestration
CO2 mineralisation
Regenerable buffer
a b s t r a c t
The barrier that is currently stalling the rapid conversion of magnesium silicate deposits into magnesium
carbonate as method for storing CO2 is considered to be the difference in pH needed for magnesium dis-
solution from the silicate and magnesium precipitation as the carbonate, whereby rapid dissolution
requires a low pH of around 1 while rapid precipitation requires a considerably higher pH of around 8.
This paper investigates a novel concept which is to use a tertiary amine to bind with protons and raise
the pH to around 8 and to then regenerate the amine through the use of heat due to the strength of
the amine–proton bond decreasing with increasing temperature. This approach provides the low pH
and high temperature that is needed for Mg dissolution and the high pH need for carbonate precipitation.
The amine can be thought of as a regenerable buffer.
Dissolution of Mg from serpentine has been found to be favourable with a solids to solution volume of
more than 50 g/L to enable a low pH, and with temperatures close to the boiling point of the solution. The
pH needed for magnesium carbonate precipitation was found to be approximately 8.2. Both triethyl-
amine and tripropylamine were found to be capable of achieving this at 18 °C. Yields of around 20–
40 wt.% carbonate were achieved using residence times of approximately 1 h. The pH swing for the ter-
tiary amines was found to be approximately 2.5 pH units between 5 and 85 °C, suggesting that an amine
capable of achieving a pH of 8.2 at low temperature generates a pH of 5.7 in solution when heated to
85 °C. Further work will examine whether the lower pH values needed for serpentine dissolution can
be achieved by heating the protonated amine to higher temperatures.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
This paper investigates a novel concept to enable the conversion
of CO2 into mineral carbonates using an aqueous route. The barrier
that is currently stalling conversion is pH control. The first part of
this introduction outlines why pH is critical, the second part out-
lines what work has been done in the field of converting CO2 into
mineral carbonates using an aqueous route, and the third part
introduces the novel concept behind this study.
1.1. Thermodynamic modelling of the carbonate system
In order for a mineral carbonate, such as MgCO3, to form the
concentrations of CO2À
3 and Mg2+
in solution must be high enough
for Eq. (1) to be satisfied [1].
½Mg2þ
Š½CO2À
3 Š 3:46 Â 10À8
ð1Þ
The solubility of CO2 in aqueous solution and the dissociation of
carbonic acid to form bicarbonate and carbonate anions can be de-
scribed by Eqs. (2)–(5) [1–4].
PPCO2
ðatmÞ ¼ 29:36½H2CO3Š ð2Þ
½HCOÀ
3 Š ¼ ½H2CO3Š=ð2:249 Â 106
½Hþ
ŠÞ ð3Þ
0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.fuel.2013.04.033
⇑ Corresponding author. Tel.: +61 733653977; fax: +61 733654199.
E-mail address: karen.steel@uq.edu.au (K.M. Steel).
Fuel 111 (2013) 40–47
Contents lists available at SciVerse ScienceDirect
Fuel
journal homepage: www.elsevier.com/locate/fuel
2. ½CO2À
3 Š ¼ ½HCOÀ
3 Š=ð2:133 Â 1010
½Hþ
ŠÞ ð4Þ
½Hþ
Š ¼ ½HCOÀ
3 Š þ 2½CO2À
3 Š ð5Þ
where 29.36 is the Henry’s law constant (dm3
atm molÀ1
) for CO2 in
water at 25 °C [2]. Here, [H2CO3] includes both dissolved molecular
CO2 and molecular H2CO3. Eqs. (3) and (4) shows that CO2À
3 ions
only start to become significant in solution when the pH is above
about 8 (see Fig. 1). It could be thought that if the partial pressure
of CO2 was raised the concentration of all species in solution
(H2CO3, HCOÀ
3 and CO2À
3 ) would increase, and therefore a raised con-
centration of CO2À
3 would result. However, solving Eqs. (2)–(5) for
various partial pressures of CO2 (PPCO2
) shows that the concentra-
tion of CO2À
3 in solution stays very low at around 5 Â 10À11
M de-
spite the partial pressure of CO2 rising to 50 atm (see Fig. 2). This
is due to the H+
ions, forming from the dissociation of H2CO3, always
suppressing the formation of CO2À
3 (see Eqs. (3) and (4)). Only the
concentration of HCOÀ
3 becomes appreciable at high CO2 partial
pressures.
Given the solubility limit of MgCl2 in solution (55 g/100 ml), the
maximum possible concentration of Mg2+
is approximately
6 M Mg2+
and the corresponding carbonate concentration required
to precipitate MgCO3 is 5 Â 10À9
M. Given that 6 M Mg2+
is difficult
to achieve as it is close to the solubility limit, a more realistic con-
centration of 0.6 M Mg2+
would require a CO2À
3 concentration of
5 Â 10À8
M CO2À
3 . Assuming a partial pressure of CO2 of 1 atm,
Eqs. (2)–(4) can be solved to establish a relationship between car-
bonate concentration and pH. Fig. 3 shows this relationship and
shows that when the carbonate concentration is 5 Â 10À8
M the
equilibrium pH is approximately 5.5. This means that in order to
precipitate MgCO3 the pH needs to exceed 5.5.
1.2. Work to date on converting CO2 into mineral carbonates using the
aqueous route
Bond and co-workers [5–7] looked at the potential of using an
enzyme, called carbonic anhydrase, to convert power station CO2
into CaCO3. Coral reefs use carbonic anhydrase to assist in the pro-
duction of CO2À
3 . The enzyme was found to catalyse the formation
of CO2À
3 , however, although the catalyst enables the rapid forma-
tion of CO2À
3 , there is also a simultaneous rapid drop in solution
pH to approximately 4, which prevents the precipitation of carbon-
ates. In the work of Bond et al. [5–7] and in recent work by Mirja-
fari et al. [8], Ozdemir [9] and Rayalu and co-workers [10,11],
precipitation of carbonates was only possible if a buffer was added
to the solution in order to complex H+
ions and keep the pH high.
The buffer used was tris(hydroxymethyl)aminomethane or ‘Tris’,
which is commonly used to maintain pH at around 8. This buffer
could not be continuously used in a large scale process, as it cannot
be regenerated, which presents a major obstacle to the further
development of this approach to sequestering CO2. Coral reefs have
the ocean as a giant buffer for the H+
that they generate. It is
worthwhile to note that Mirjafari et al. [8] found that calcium car-
bonate did not precipitate when they used carbonic anhydrase
with no buffer, but found precipitation to take place when they
used the buffer with no carbonic anhydrase.
Instead of converting salt solutions into carbonates, researchers
have also looked at converting Mg–silicate minerals into carbon-
ates in order to use the neutralising capacity of the mineral [12].
O’Connor and co-workers [13,14] found they could convert 34%
of serpentine (Mg3Si2O5(OH)4) to MgCO3 using aqueous CO2 at
115 atm, 185 °C and a residence time of 24 h. The pH generated
in solution would be around 3. The high temperature would be
assisting the kinetics of Mg dissolution. Presumably the pH in-
creases as dissolution proceeds and this aids precipitation of car-
bonate. However, as the pH increases the dissolution rate of Mg
would drop to negligible levels. The silica left behind and carbon-
ate forming would also hinder further Mg dissolution/carbonation.
O’Connor et al. found that artificially adding NaHCO3 to shift the
equilibria in favour of a higher CO2À
3 to H+
ratio aided carbonation.
pH
1 2 3 4 5 6 7 8 9 10 11 12 13 14
molfraction
0.0
0.2
0.4
0.6
0.8
1.0
H2 CO3
HCO3
-
CO3
2-
Fig. 1. Equilibrium distribution of H2CO3, HCOÀ
3 and CO2À
3 species in solution.
CO2
partial pressure (atm)
10
-11
10
-10
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
Concentration(M)
10
-12
10
-11
10
-10
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
H2 CO3
HCO3
-
CO3
2-
Fig. 2. Equilibrium concentration of H2CO3, HCOÀ
3 and CO2À
3 in water as a function
of CO2 partial pressure (derived from Eqs. (2)–(5)).
pH
1 2 3 4 5 6 7 8 9 10 11
CO3
2-
concentration(M)
10
-15
10
-14
10
-13
10
-12
10
-11
10
-10
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
0.1atm
1 atm
10 atm
100 atm
Fig. 3. Equilibrium concentration of CO2À
3 as a function of pH for CO2 partial
pressures of 0.1, 1, 10 and 100 atm.
K.M. Steel et al. / Fuel 111 (2013) 40–47 41
3. It follows that the best way to enable carbonation might be to
have a two stage process where the first stage is optimised for
Mg dissolution (high temperature and low pH) and the second is
optimised for Mg carbonation (high pH). This need has been recog-
nised as pH swing [15]. pH swing requires the removal of H+
ions
from solution, which is usually achieved with soluble oxides/
hydroxides, however, these come from the calcination of carbon-
ates which is obviously not possible.
1.3. Novel concept for converting CO2 into mineral carbonates using
the aqueous route
This paper investigates the use of weakly basic tertiary amines
for complexing H+
ions generated when CO2 is added to solution
and therefore enabling carbonate precipitation from a variety of
salt solutions. The acid dissociation constant for protonated ter-
tiary amines varies with temperature and so the approach is to
use ‘‘temperature swing’’ to regenerate the amine, whereby the
loaded amine is heated to strip the acid off. This concept has re-
cently been patented [16].
Conventional CO2 capture technologies involve absorbing CO2
into a mixture of primary and tertiary amines, including monoeth-
anolamine (MEA) and methyldiethanolamine (MDEA) respectively.
The reason for this is that while the primary amine forms a strong
carbamate bond and therefore enables a high CO2 loading due to
the strength of the bond considerable energy is needed to break
it and regenerate the MEA (approximately 3–5 MJ/kg CO2 [17]).
In order to reduce the energy load tertiary amines are blended. Ter-
tiary amines do not bond with CO2 but rather strip the solution of
H+
ions thus driving the formation of HCOÀ
3 and CO2À
3 ions in solu-
tion. The loading of CO2 in solution as these ions is much lower but
the energy needed to regenerate the MDEA is much less, such that
the total energy needed to regenerate the MEA/MDEA mixture is
around 1–3 MJ/kg CO2 [17]. The introduction of MDEA means that
taller towers are needed for a given separation efficiency and so a
balance between capital and operating (energy) cost must be
struck.
The idea put forward here is to use tertiary amines alone to con-
vert CO2 into mineral carbonates. It is thought that the loading of
CO2 can be higher than that for conventional CO2 capture using
MDEA because the CO2À
3 ions that form leave the solution as solid
carbonate, thus providing a stronger driving force for the capture of
CO2 into solution.
The advantage of this concept for CO2 sequestration is twofold.
Firstly, the energy needed for the process might be considerably
lower than that needed for conventional CO2 capture because less
energy is needed to regenerate the amine and compression of the
CO2 (needed for storage) is not necessary. Secondly, the CO2 would
be locked up in a mineral form that is known to be stable for mil-
lions of years, which is an important consideration given the scale
of CO2 that needs to be stored.
Fig. 4 shows a simplified diagram of the novel concept that is
being explored. In stage 1, acid loaded amine is heated to
$100 °C and contacted with a Mg silicate such as serpentine
((Mg, Fe)3Si2O5(OH)4). At the high temperature the acid (HCl) dis-
sociates from the amine, thereby providing a low pH capable of
dissolving Mg out of the serpentine. The Mg depleted serpentine
is separated by density and/or filtration and the solution, contain-
ing MgCl2 and regenerated amine, passes to stage 2. In stage 2, the
solution is cooled and the flue gas containing CO2 is sparged
through. At the low temperature acid generated by the dissociation
of H2CO3 plus excess acid generated in stage 1 are complexed by
the tertiary amine which causes the pH to rise and consequently
the CO2À
3 concentration to rise to a level that is sufficient to begin
interacting with Mg2+
and precipitating MgCO3. The MgCO3 is sep-
arated by density and/or filtration and the solution, containing acid
loaded amine is recycled to stage 1.
The overall reaction taking place in stage 1 is as follows:
Mg3Si2O5ðOHÞ4 þ 6R3NHCl ! 3MgCl2 þ 6R3N þ 5H2O
þ 2SiO2 ðR1Þ
And the overall reaction taking place in stage 2 is as follows:
MgCl2 þ CO2 þ H2O þ 2R3N ¡ MgCO3 þ 2R3NHCl ðR2Þ
The concept shown in Fig. 4 can be used in a variety of different
ways by a variety of different industries, and is not locked into one
industrial application.
The concept could be used for the treatment of magnesium sil-
icate deposits as described above. It is worthwhile to note that
many magnesium silicate deposits contain significant levels of
valuable heavy metals such as Ni, called Ni laterites, and the pro-
cess could therefore have the dual operation of Ni extraction com-
bined with CO2 sequestration. It is known that treating Ni laterites
with acid to dissolve the Mg enables a greater amount of Ni to be
extracted into solution.
Secondly, the concept could be used for salt mining operations.
Chloride and sulphate salt deposits are mined for KCl or K2SO4 to
be used as fertiliser. By using solution mining the salt comes up
hot and is cooled to separate the potassium salts. The refuse salt
represents a waste that is generally deposited back into the re-
serve. The salt solution could be processed using the sequestration
technology shown in Fig. 4 to form a mixture of carbonates and
bicarbonates that are deposited back into the reserve for longterm
CO2 storage. The heat that must be taken out of the solution as it
comes to the surface could be used to provide the heat needed
for stage 1. Using the concept for salt solutions means that a by-
product of the process is acid, either hydrochloric or sulphuric acid.
Therefore, the scale of the operation would need to be matched
with HCl or H2SO4 needs in the oil, chemical and mineral sectors.
This paper presents our work to date on this novel concept.
Fig. 4. Simplified block flow diagram of the proposed CO2 sequestration technology.
42 K.M. Steel et al. / Fuel 111 (2013) 40–47
4. 2. Experimental
2.1. Serpentine sample
The serpentinite sample (Mg3Si2O5(OH)4) used for this study
was obtained from a naturally occurring deposit in northern
Queensland, Australia. It was initially ground by hand in a pestle
and mortar and then in a laboratory attrition mill. The ground ser-
pentinite was sieved with ASTM standard sieves to obtain particles
with a diameter of 57 lm. Australian Laboratory Services (ALSs)
performed the elemental analysis via alkali fusion, acid digestion
and inductively coupled plasma-atomic emission spectroscopy
(ICP-AES) of the resulting solution. The loss on ignition at
1000 °C (LOI1000) was also performed using a TGA furnace. The re-
sults of ALS’s analysis based on their method ME-ICP85 (Silicates
by Fusion, ICP-AES) and ME-GRA05 (H2O/LOI by TGA Furnace)
are summarised in Table 1.
Mineral composition was first probed via X-ray diffraction anal-
ysis using a PANanalytical XPERT-PRO diffractometer with Cu Ka
target (k = 0.15406 nm) at room temperature. Measurements were
made in a step scan mode (0.1°/step) over the 2h range of 10–90°.
Phase matching of the X-ray powder diffraction (XRPD) pattern of
the serpentinite sample against the International Centre for Dif-
fraction Data (ICDD) database suggested antigorite to be the pri-
mary serpentine phase present. A calibrated TA Instrument
SDTQ600 Thermogravimetric analyser-differential scanning calo-
rimeter provided further mineral characterisation via thermogravi-
metry–derivative thermogravimetric analysis (TGA–DTG).
Replicate runs were obtained for 10 mg of the À53 lm samples
using alumina crucibles and heated from 30 °C to 1000 °C at a heat-
ing rate (b) of 10 °C minÀ1
. A 10-min isothermal stage was em-
ployed at 110 °C to determine the moisture content of the
material and was found to contain 1.0 wt.%. The total mass loss
of the dry sample (Dm105–850 °C) was determined as
11.5 ± 0.01 wt.%, which is in fair agreement with the analysis made
by ALS (11.7 wt.%).
Fig. 5 shows the TGA–DTG profile of the sample, where the
characteristic serpentine doublet comprising the DTG temperature
shoulder, Tsh, showing at 597 °C and the peak temperature, Tp, at
718 °C. Thermal analysis suggests that this particular serpentinite
sample is fully serpentinized and contains antigorite as well as
lizardite (antigorite + lizardite). The antigorite component displays
its DTG peak temperature, Tp1ATG at 718 °C and its diagnostic peak,
Tp2ATG at 747 °C. The shoulder at 701 °C is thought to indicate the
lizardite component, Tp1LIZ. Based on XRPD and TGA-DTG analysis,
we then refer to this sample as ‘‘serpentinite’’, rather than antigor-
ite as this specimen also contains lizardite.
2.2. Magnesium dissolution
Magnesium dissolution experiments were carried out using AR
grade HCl (37 wt.%) and Millipore water. 0.5 g of sample and acid
solution was mixed in a 250 ml spherical flat-bottom flask
mounted on a magnetic stirrer/hotplate and equipped with a cold
water condenser. The effects of temperature, concentration of HCl,
residence time and acid solution volume were investigated. At the
duration of the experiment, the residue was vacuum filtered, dried
overnight and weighed. The pH of the filtrate solutions was mea-
sured using a pH electrode. The solid remaining was analysed by
ALS using the procedure described above to determine the extent
of Mg dissolution.
2.3. Carbonate precipitation
Carbonate precipitation experiments were carried out using a
250 ml Erlenmeyer flask open to the atmosphere. Food grade CO2
was injected into the solution through a sparger containing five
holes of 2 mm diameter each. Pressure was regulated at 1.4 bar
and flow was set at approximately 1 L/min using a rotameter.
While sparging the solution with CO2, tertiary amine was added
dropwise via a burette while simultaneously measuring pH via a
pH electrode. The amines investigated were simple straight chain
trialkylamines with increasing chain length, i.e. triethylamine, tri-
propylamine, tributylamine, tripentylamine, trihexylamine. The
solution was observed for the onset of precipitation. If a precipitate
form, it was filtered through Whatman No. 1 filter paper, dried and
weighed. Precipitated solids were analysed by XRD and ICP-AES for
compound and elemental determinations, as described above.
2.4. Amine regeneration
The ability of the amines to be regenerated and liberate bound
acid was investigated via a series of titrations at various tempera-
tures whereby the amines were added to a standardised solution of
0.1 M HCl (10 ml). The HCl was placed in a 3-neck round bottom
flask which was immersed in a water bath to control temperature.
A condenser was fitted vertically to the middle neck and a ther-
mometer and pH electrode were inserted and sealed through each
of the side necks. Amine was added through the opening at the top
of the condenser using an automatic pipette. For experiments per-
formed at 5 °C ice was added to the water bath. The tertiary amines
studied were triethylamine, tripropylamine, tributylamine and
tripentylamine.
3. Results and discussion
3.1. Magnesium dissolution
The effect of HCl concentration on the dissolution of Mg from
serpentine is shown in Fig. 6. All percentages are weight percent-
ages. The residence time used was 3 h and the temperature was
the boiling temperature of the solution ($100 °C). The stoichiome-
tric amount of acid needed to dissolve all of the Mg according to R1
is approximately 0.12 M which gives approximately 40% extrac-
tion, while a plateau of approximately 65% extraction is reached
at around 0.5 M HCl. Fe and Al were also found to dissolve with
similar extraction levels to those of Mg, showing that the elements
do not appear to dissolve selectively with respect to HCl
concentration.
Because it is desirable to not have excess acid in solution to
minimise the energy needed for amine regeneration a compromise
between Mg extraction and solution pH must be struck. Fig. 6
shows the pH change as a function of HCl concentration. With
twice the stoichiometric amount needed, the pH of the spent solu-
tion is still $1.
The effect of residence time on dissolution of Mg in 0.25 M HCl
is shown in Fig. 7. Equilibrium is reached after approximately 3 h.
The effect of temperature on the dissolution of Mg in 0.25 M HCl is
shown in Fig. 8. For temperatures less than 50 °C only a small
amount of Mg dissolves. At temperatures higher than 50 °C a linear
Table 1
Chemical composition of the serpentinite sample.
wt.%, ±0.01
MgO*
SiO2
*
Fe2O3
*
Al2O3
*
CaO*
Ni*
MnO*
K2O*
LOI1000
**
39.3 44.1 7.38 1.03 0.35 0.24 0.10 0.04 11.7
*
Values obtained via inductively coupled plasma-atomic emission spectroscopy on
fused samples after acid digestion. Based on ALS’s ME-ICP85.
**
Value obtained by heating the moisture free sample to 1000 °C using TGA fur-
nace. Based on ALS’s ME-GRA05.
K.M. Steel et al. / Fuel 111 (2013) 40–47 43
5. increase in Mg dissolution with respect to temperature is obtained,
reaching approximately 65% at $100 °C and suggesting that at
temperatures above 100 °C higher extraction efficiencies might
be achieved. Extrapolation suggests that close to 100% extraction
might be achieved at 140 °C. Experiments using a pressurised ves-
sel to enable higher temperatures above 100 °C are recommended
to confirm the extrapolated trend shown.
As presented in the introduction, it is desirable to have a high
Mg2+
concentration in solution as this reduces the concentration
of CO2À
3 needed for MgCO3 precipitation. Experiments were per-
Fig. 5. The TGA–DTG profile of the serpentinite sample used in this study with the characteristic peaks indicated.
Fig. 6. Effect of HCl concentration on the dissolution of Mg and final pH (residence
time 3 h, $100 °C, 0.5 g, 100 ml).
Fig. 7. Effect of residence time on the dissolution of Mg (0.25 M HCl, solution and
$100 °C, 0.5 g, 100 ml).
Fig. 8. Effect of temperature on the dissolution of Mg (0.25 M HCl, residence time
3 h, 0.5 g, 100 ml).
Fig. 9. Effect of solution volume on the dissolution of Mg (0.025 mols HCl, residence
time 3 h, 0.5 g, $100 °C).
44 K.M. Steel et al. / Fuel 111 (2013) 40–47
6. formed keeping the amount of HCl the same and decreasing the
solution volume from 100 ml. Twice the stoichiometric amount
needed (0.024 mols) was chosen for the amount of HCl. Fig. 9
shows the effect of reducing the solution volume down to 10 ml.
The extraction increases as the solution volume decreases reaching
approximately 85% with only 10 ml of solution. The concentration
of Mg in solution is approximately 0.35 M.
This work has shown the importance of both acid concentration
and temperature on the dissolution of Mg. It is recommended to
operate with a solids to solution volume of more than 50 g/L for
the extraction stage, a temperature close to the boiling tempera-
ture of the solution or higher if using a pressurised vessel, a resi-
dence time of 3 h and concentration no more than twice the
stoichiometric amount needed for reaction. These conditions en-
able high extractions of Mg approaching 100%.
3.2. Carbonate precipitation
The extract solution from the experiment with 10 ml solution
volume shown in Fig. 9 was used for carbonation. Tripropylamine
was added dropwise. As the pH increased to approximately 5 a
light brown precipitate formed which was found from elemental
analysis to contain around 20.1 wt.% Fe, 10.8 wt.% Si and 5.5 wt.%
Al and only 0.2 wt.% Mg. This product comes from the hydrolysis
of Fe, Si and Al which dissolved during serpentine dissolution.
The leaching studies had shown that the elements dissolved simul-
taneously with Mg. After removing this precipitate further addi-
tions of TPA raised the pH to approximately 8 at which point a
white precipitate formed. This precipitate began forming within
a few minutes. After bubbling CO2 for 45 min, the precipitate was
recovered by filtration, dried and analysed. The weight was
0.20 g. XRD analysis indicated the formation of nesquehonite
(MgCO3Á3H2O). Elemental analysis showed that the purity was
high with a composition of 18.8 wt.% Mg, 0.2 wt.% Ca, 0.06 wt.%
Fe and 0.01 wt.% each of Al and Si. The yield was 29.1 wt.% (i.e.
29.1 wt.% of the Mg extracted into solution was converted to the
MgCO3 precipitate). The remaining Mg would be recycled to the
first stage of the process.
In order to study MgCO3 more precisely and the pH level needed
for carbonate precipitation without the hindrance of other dis-
solved elements model compound work was performed using
Mg(OH)2. 0.126 g of Mg(OH)2 was dissolved in 50 ml of 0.0965 M
HCl such that the acid was slightly in excess and gave a final pH
of 2.08 after the Mg(OH)2 had completely dissolved. To this solu-
tion 5 Â 10À4
mols of TPA was added, which is the amount needed
to neutralise the excess acid. The pH rose to 9.59. CO2 was then
bubbled through the solution and after 5 min the pH had decreased
and stabilised at 4.62 and no precipitate had formed. A further
addition of TPA was made (0.006 mols) and the pH stabilised at
approximately 8.27. This addition of TPA is 1.5 times that needed
for reaction 2. Over the next half an hour, CO2 was continually bub-
bled through the solution. It was found that TPA need to be contin-
ually added dropwise in order to maintain the pH at a level above
8. The total amount of TPA added (neglecting the initial 5 Â 10À4
-
mols) was 0.021 mols and the final pH was 8.43. The solution was
filtered and the solid recovered and air dried. The weight of the so-
lid was 0.051 g and as found above, analysis indicated nesqueho-
nite (MgCO3Á3H2O) to be the primary phase present. The yield
was approximately 17% and the amine used was 5 times in excess.
The above experiment was repeated with slower additions of
TPA. A total amount of 0.0085 mols (twice excess) was added over
a period of 1 h. The mass of solid recovered was 0.073 g (dried)
which is a yield of 24 wt.%.
The above experiment was repeated with triethylamine (TEA).
0.164 g of Mg(OH)2 was dissolved in 50 ml of 0.112 M HCl, which
is the stoichiometric amount needed for complete dissolution.
CO2 was bubbled which decreased the pH to 5.38. 0.0072 mols of
TEA was added and the pH increased to 10.16 and simultaneously
the solution became milky with precipitation. As CO2 addition con-
tinued the pH decreased to 7.27 even though the amount of TEA
added was 30% above that needed for reaction 2. A further addition
of 0.0036 mols of TEA increased the pH to 9.32 initially but then it
stabilised at 8.23. The solution was filtered to recover the solid,
which had a mass of 0.133 g and therefore a yield of 34 wt.%.
Tests with both tributylamine and tripentylamine did not yield
precipitates, which is thought to be due to the pH generated by the
amines not being high enough. It is possible that decreasing the
temperature would enable precipitation to take place with these
amines.
These experiments have shown that the pH needed for magne-
sium carbonate precipitation is approximately 8.2 and that trieth-
ylamine and tripropylamine are capable of achieving this. An
excess of amine has been found to be necessary to maintain the
pH of 8 while CO2 is bubbled through the solution. So far yields
of around 20–40 wt.% have been achieved. The reason why precip-
itation did not occur at lower pH levels, such as the pH level of 5.5
predicted from the theoretical modelling work reported in the
introduction, is thought to be due to the kinetics being too slow be-
low 8.2. It was found with TEA that precipitation was within sec-
onds when the pH was 10.
Further experiments will investigate the kinetics of carbonate
precipitation by sampling periodically, particularly during the
early stages.
3.3. Amine regeneration
Based on the serpentine dissolution work, to achieve dissolu-
tion of Mg under reasonable conditions of a residence time of less
than an hour and reaction time of 100–150 °C, the pH of the solu-
tion needs to be approximately less than 1. Based on the carbon-
ation work, the pH of the Mg rich solution needs to be raised to
approximately 8.2. To examine the ability of tertiary amines to
reversibly enable this change a series of titrations were performed.
The dissociation constant for triethylamine at various tempera-
tures has been published by Hamborg and Versteeg [18], whereby
the pKa is 10.89 at 18 °C and decreases to about 9.17 at 90 °C.
Fig. 10 shows these constants converted into a titration curve
whereby the amine is being added to 0.1 M HCl. Our own titration
points are also shown for comparison. The titration curve is ex-
pressed this way as it mimics the real system. Total amine essen-
Fig. 10. Titration curve for triethylamine against 0.1 M HCl at 18 °C and 90 °C
generated from pKa data obtained from literature and at 18 °C generated from
experiment.
K.M. Steel et al. / Fuel 111 (2013) 40–47 45
7. tially means the amount of amine added expressed as a concentra-
tion. At 20 °C the pH rises to approximately 11 while at 90 °C it
rises to approximately 9. While a pH of 11 would assist with the
precipitation of carbonates the pH of 9 at the higher temperature
will not assist with the dissolution of Mg from serpentine.
Figs. 11–13 shows our own titration curves for tripropylamine,
tributylamine and tripentylamine at various temperatures. For tri-
propylamine, the final pH is approximately 9.5 at 18 °C and 7.1 at
85 °C. For tributylamine, the final pH is approximately 8.6 at 5 °C
and 6.0 at 85 °C. For tripentylamine, the final pH is approximately
6.5 at 5 °C and 4.0 at 85 °C. It follows that with a temperature rise
from 5 to 85 °C, the change in final pH is approximately 2.5 pH
units. This work shows that at elevated temperatures an acid
loaded alkylamine with a long chain length behaves similarly to
a weak acid and therefore might have the ability to dissolve Mg
from serpentine.
The equivalence point (point of highest gradient) was found for
each titration curve from which pKa values were estimated. Table 2
shows results from this analysis and Fig. 14 shows the constants
for tributylamine and tripentylamine as a function of temperature.
Lines of best fit have been drawn through the data and extended to
135 °C. Fig. 14 also shows a line corresponding to the pKa values
reported by Hamborg and Versteeg [18] for triethylamine. The
lines obtained from this work appear to decrease more steeply
than those for triethylamine, which may be due to experimental
error associated with vapour losses from the system which could
concentrate the protons and give lower pH values.
Further experiments to obtain more accurate titration data
including data at higher temperatures and pressures (100–150 °C
and 1–5 bar) is planned for the future. The experiments at higher
temperature will also involve treating serpentine with the regener-
ated amine and acid mix to study the dissolution behaviour. These
experiments are akin to treating serpentine with weak organic
acids. There is currently a lack of studies on the behaviour of ser-
pentine with weak organic acids particularly at high temperatures
where the kinetics of dissolution is favourable. Teir et al. [19] have
reported the behaviour of carboxylic acids alongside stronger acids
however the studies were confined to 20 °C. Unlike strong acids
which provide a high initial concentration of protons which de-
creases as the mineral dissolves, weak acids provide a low concen-
tration that is maintained as the mineral dissolves, and protons are
consumed in the acid-base reaction thereby driving the dissocia-
tion of more protons from the weak acid.
Fig. 11. Titration curve for tripropylamine against 0.1 M HCl at 18 and 85 °C.
Fig. 12. Titration curve for tributylamine against 0.1 M HCl at 5, 18 and 85 °C.
Fig. 13. Titration curve for tripentylamine against 0.1 M HCl at 5, 18 and 85 °C.
Table 2
Calculated pKa values for tertiary amines at 5, 18 and 85 °C.
Amine pKa
5 °C 18 °C 85 °C
Tripropylamine nd 9.47 7.32
Tributylamine 9.84 8.44 6.32
Tripentylamine 6.81 5.80 3.98
nd: Not determined.
Fig. 14. Expected trend for pKa as a function of temperature for tributylamine and
tripentylamine with lines of best fit, and pKa line for triethylamine as derived from
Hamborg and Versteeg [18].
46 K.M. Steel et al. / Fuel 111 (2013) 40–47
8. If the regenerated amines enable high degrees of serpentine dis-
solution, experiments will move to examining the extent that the
amines can be continually recycled.
4. Conclusion
The best conditions for the dissolution of Mg from serpentine
have been found to be a solids to solution volume of more than
50 g/L to enable a high proton concentration. The amount of acid
should be no more than twice the stoichiometric amount needed
for reaction. Reaction temperature should be as high as possible,
close to the boiling temperature of the solution or higher (100–
150 °C) if using a pressurised vessel. These conditions combined
with a residence time of 3 h are able to dissolve approximately
85% of the Mg in serpentine.
These experiments have shown that the pH needed for magne-
sium carbonate precipitation is approximately 8.2 and that trieth-
ylamine and tripropylamine are capable of enabling this at 18 °C. It
appears that an excess of amine is needed to maintain the pH of 8
while CO2 is bubbled through the solution. So far yields of around
20–40 wt.% have been achieved for tripropylamine using residence
times of approximately 1 h. Precipitation occurred more rapidly for
triethylamine owing to the higher pH generated.
The association of tertiary amines with HCl has been found to
decrease with increasing temperature such that there is a differ-
ence of approximately 2.5 pH units between 5 and 85 °C. This
means that an amine capable of achieving a pH of 8.2 at low tem-
perature generates a pH of 5.7 in solution when heated to 85 °C.
While this is not low enough to provide a high rate of serpentine
dissolution it is thought that increasing the temperature beyond
85 °C may yield pH levels capable of dissolving high levels of Mg,
particularly given that high temperatures aid the kinetics of disso-
lution. Further work is required to study the dissolution behaviour
of serpentine with regenerated amine solutions at elevated tem-
peratures and pressures.
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