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Paul Gemperline has been active in many areas of data analysis in chemistry. In this contribution, we build on his developments in advanced process analysis. The most prominent aspect is data fusion, the combined analysis of measurements taken on different instruments, using different measurement techniques, and different chemical conditions. We have successfully applied these principles to the investigation of the chemistry of CO2 in aqueous amine solutions. There are two fields of chemometrics analyses, those which attempt at analysing the data without prior knowledge and those which based the analysis on as much chemical knowledge as possible. Paul Gemperline has been active in both. In this contribution, we concentrate on the chemistry‐based analysis ideas that have been developed by Paul: hard modelling and the globalisation of the analysis of several data sets. This contribution applies both above ideas for the investigation of the aqueous chemistry of CO2. [ABSTRACT FROM AUTHOR]

Abstract In many equilibrium systems, it is customary to use a simplified, apparent equilibrium reaction instead of the complete reaction model. The resulting apparent equilibrium constants are altered or controlled by changes of the chemical system, usually modifying the total concentration of auxiliary reagents, but the variation of other parameters such the intensity of light in photo-controlled reactions, types and concentration of solvents or composition of mixed solvents, the ionic strength of the chemical media, etc. is also possible. The main goal of this work is to propose a chemical equilibrium modelling based strategy to control the conditions governing equilibrium systems in order to tune the apparent constants. Indeed, by extracting the analytic relationship between the parameters of the complete model and apparent model, the magnitude of the apparent constant(s) can be predicted. At first, a basic strategy for calculating the tunable range of apparent constants of chemical equilibria is proposed. Next, three case studies for tuning the apparent constants are investigated in detail: inclusion complexes with cyclodextrin, aqueous micellar solutions for investigating the solvent effects and the boric acid/Mannitol system that allows the tuning of the apparent protonation constant. In all examples tuning the apparent constant is possible by regulating the chemical composition. Graphical abstract Image 1 Highlights • For many equilibrium systems it is customary to use a simplified apparent, instead of a complete complex equilibrium system. • By the thermodynamic laws and equilibrium models, the exact analytic relationship between complete and apparent models of equilibrium systems can be extracted. • The extracted relationship formula determine the external parameter (s) for controlling the apparent models of equilibrium systems. • By controlling the conditions, the apparent constant of equilibrium systems could be tuned in the desired value. [ABSTRACT FROM AUTHOR]

Abstract: Taurate has potential as an absorbent for CO2 capture and is also an effective rate promoter in aqueous NH3‐based absorbents. However, the detailed mechanism involved in the reaction of CO2(aq) with taurate in aqueous solution is not available and the reaction rate and equilibrium constants for some reactions in the mechanism have not yet been determined. This limits our understanding of the role of taurate in the capture process using an NH3/taurate mixture and hinders rigorous rate‐based process simulation. In this work, we studied the reaction of taurate with CO2 in aqueous solution with added acid‐base indicators at 288.0, 298.0, 308.0, and 318.0 K. Stopped‐flow spectrophotometry was used to record absorbance of the solutions, which reflects pH changes via colored acid‐base indicators as a function of time and over the wavelength range from 400.0–700.0 nm. Through global analysis of the kinetic data from the stopped flow reactor, we determined the temperature dependence of the rate and equilibrium constants using a detailed reaction scheme including all reactions in the taurate–CO2–H2O system. We then used stopped‐flow spectrophotometry to investigate the effect of taurate on the reaction of CO2 in the mixed taurate−NH3−CO2−H2O system at 298.0 K. The mechanism for the reaction of the taurate and NH3 mixture with CO2(aq) was found to be a simple combination of two individual systems. Taurate in the mixture can significantly enhance the CO2 absorption rate and NH3 can work as a proton sink making more taurate available for CO2 and the potential reduction of NH3 loss. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The kinetic instability of iron(III) thiocyanate complexes in aqueous solution, evidenced by the loss of solution colour with time, has made it difficult to determine reliable equilibrium data. A technique, which measures the absorbance of these solutions as a function of time within milliseconds of mixing Fe 3+ with SCN − and which extrapolates to an initial spectrum at time zero, has been designed to overcome these difficulties and is described in this paper. Two complexes, Fe(SCN) 2+ and Fe(SCN) 2 + , have been identified upon analysing the absorbance data for thiocyanate concentrations up to 0.25 M at 25 °C and an ionic strength of 0.5 M. Equilibrium constants, K 1 = ( 98 ± 1 ) / M - 1 and K 2 = ( 7 ± 1 ) / M - 1 have been determined and comparisons made with the literature. [ABSTRACT FROM AUTHOR]

A promising option to improve post combustion capture (PCC) is to use inorganic catalysts to accelerate the absorption process of CO 2 , in particular the reaction between CO 2 and water to form carbonic acid. In this study, the efficiency of sulfate and vanadate on enhancing the hydration reaction of CO 2 to form H 2 CO 3 for PCC has been studied at 25 °C by stopped-flow spectrophotometry. The catalytic rate constants were determined to be 14.2(2) and 277(6) M −1 s −1 for sulfate and vanadate, respectively. Their application to PCC was further investigated by simulating the effect of these catalysts on the absorption process under PCC operating conditions. Vanadate was confirmed to have a greater efficiency toward CO 2 hydration than sulfate and also a series of other inorganic catalysts reported earlier. [ABSTRACT FROM AUTHOR]

To reduce CO2 emission into the atmosphere, particularly from coal-fired power stations, post combustion capture (PCC) using amine-based solvents to chemically absorb CO2 has been extensively developed. From an infrastructure viewpoint, the faster the absorption of CO2, the smaller the absorber required. The use of catalysts for this process has been broadly studied. In this manuscript, a study of the catalytic efficiencies of inorganic oxoanions such as arsenite, arsenate, phosphite, phosphate, and borate is described. The kinetics of the accelerated CO2 absorption at 25 °C was investigated using stopped-flow spectrophotometry. The catalytic rate constants of these anions for the reaction of CO2 with H2O were determined to be 137.7(3), 30.3(7), 69(2), 32.7(9), and 13.66(7) M-1s-1, respectively. A new mechanism for the catalytic reaction of oxoanions with CO2 has also been proposed. The applicability of these catalysts to PCC was further studied by simulation of the absorption process under PCC conditions using their experimental catalytic rate constants. Arsenite and phosphite were confirmed to be the best catalysts for CO2 capture. However, considering the toxicological effect of arsenic and the oxidative instability of phosphite, phosphate would be the most promising inorganic catalyst for PCC process from the series of inorganic oxoanions studied. [ABSTRACT FROM AUTHOR]

In the current work ultraviolet spectrophotometric titrations at different S(IV) concentrations have been globally analysed using the entire spectral dataset to determine the complete speciation of S(IV) in aqueous solution over a large pH range (from 9.6 to 1). As a result, the dimerisation constant for the formation of disulfite from hydrogen sulfite has been accurately determined. Further, protonated disulfite has been identified and quantified for the first time. In addition, the molar absorptivities of all S(IV) species are also reported over the studied wavelength range. [ABSTRACT FROM AUTHOR]

pH indicators can be used both fast responsive as well as long-term stable sensors. They have been extensively used for monitoring pH changes in fast kinetic reactions as well as slowly changing pH in oceanic waters. If the pH range that needs to be covered is narrow it is possible to use only one indicator of appropriate protonation constant; otherwise, mixtures of two or more indicators are used for monitoring pH values covering a broad range of pH. In this paper we presented a new methodology for determining pH of solutions using mixtures of pH indicators. The pH calculation is based on the strict application of the basic laws of mass action and mass conservation. The proposed method was evaluated by the successful determination of the pH values of solutions containing three indicators (neutral red, phenol red (two different protonation constants), and methyl orange) covering a wide range of pH values from 0.5 to 9. The method was also applied for rapid monitoring of pH changes in stopped-flow measurements, investigating the reactions of CO 2 in aqueous amine solutions. Image 1 • Accurate pH from measured absorption spectra. • Multiple indicators allow pH determination over wide pH range. • Analysis based on adherence to law of mass conservation and to low of mass action. • Following fast-changing pH. [ABSTRACT FROM AUTHOR]

The Henry’s Coefficient of CO 2 is a fundamental property, it quantifies the equilibrium between the partial pressure of CO 2 in the gas phase and the concentration of dissolved free CO 2 in the liquid phase. This value is critical for simulation and may lead to improvements in the process of post combustion capture of CO 2 . However, because of its reactive nature, CO 2 reacts in amine solutions and forms multiple carbon-containing species, so that the free CO 2 concentration is very small and difficult to determine. The “N 2 O analogy” has been used to estimate the physical solubility of CO 2 based on the assumption that the two gases behave similarly in water and amine solutions. In the current study, a direct way is proposed for the determination of the Henry’s Coefficient of CO 2 in MEA solutions. The method only requires vapor-liquid equilibrium (VLE) measurements of the MEA-CO 2 -H 2 O system; and all equilibrium/protonation constants for all solution reactions are sourced from the open literature while activity coefficients for all ionic species were estimated using the Davis equation. The free CO 2 concentration in solution can be computed using the total MEA concentration, total CO 2 concentration and temperature, which allows the determination of the Henry’s Coefficient from the CO 2 partial pressure. A 10-parameter polynomial is used to approximate the Henry’s Coefficient as a function of the total MEA concentration, total CO 2 concentration and temperature. VLE calculations were performed using the liquid-phase equilibrium calculations and the polynomial function calculating the Henry’s Coefficient, and the results show the VLE calculations are adequate to describe the VLE data. [ABSTRACT FROM AUTHOR]

Globalefforts to reduce carbon dioxide emissions stemming fromthe combustion of fossil fuels have acknowledged and focused on theimplementation of post combustion capture (PCC) technologies utilizingaqueous amine solvents to fulfill this role. The cyclic diamine solventpiperazine has received significant attention for application as aCO2capture solvent, predominantly for its rapid reactivitywith CO2. A thorough investigation of alternative but simplercyclic amines incorporating a single amine group into the cyclic structuremay reveal further insight into the superior kinetic performance ofpiperazine and the wider applicability of such cyclic solvents forPCC processes. One such example is the cyclic monoamine 3-piperidinemethanol(3-PM). To facilitate the evaluation of 3-PM as a capture solventrequires knowledge of the fundamental chemical parameters describingthe kinetic and equilibrium of the reactions occurring in solutionscontaining CO2and 3-PM. Additionally, in parallel withthe preceding, experimental measurements of CO2absorptioninto 3-PM solutions, including mass transfer and vapor–liquidequilibrium measurements, can be used to validate the CO2absorption performance in 3-PM solutions and compared to that ofmonoethanolamine (MEA) under similar conditions. The present studyis focused in two parts on (a) determination of fundamental kineticand equilibrium constants via the analysis of stopped-flow kineticand quantitative equilibrium measurements via 1H/13C nuclear magnetic resonance (NMR) spectroscopy and (b) experimentalmeasurements of CO2absorption into 3-PM solutions viawetted wall column kinetic measurements, vapor–liquid equilibriummeasurements, and corresponding physical property data including densitiesand viscosities of the amine solutions over a range of concentrationsand CO2loadings. Fundamental kinetic rate constants describingthe reaction of CO2with 3-PM are significantly fasterthan MEA at similar temperatures (3-PM = 32 × 103M–1s–1, extrapolated to 40 °Cfrom kinetic data between 15.0 and 35.0 °C; MEA = 13 × 103M–1s–1, 40 °C).Conversely, the equilibrium constants describing the reaction betweenbicarbonate and amine, often termed carbamate stability constants,are significantly lower for 3-PM than MEA at similar temperatures.Overall CO2absorption rates in 3.0 M solutions of 3-PMand MEA, assessed in overall CO2mass transfer coefficients,are lower in the former case over the entire range of CO2loadings from 0.0 to 0.4 mol of CO2per mol of amine.The reduced absorption rates in the 3-PM solutions can be attributedto higher solution viscosities and thus corresponding reductions inCO2diffusion. CO2absorption and cyclic capacitiesin 3.0 M solutions of 3-PM and MEA were found to be significantlyhigher in the case of 3-PM. The larger CO2capacities areattributed to the lower stability 3-PM carbamate and the formationof larger amounts of bicarbonate compared to MEA. Overall, the largerCO2absorption capacity, cyclic capacity, and rapid kineticswith CO2position 3-PM as an attractive CO2capturesolvent. [ABSTRACT FROM AUTHOR]

Promoted aqueous ammonia is a potentialsolvent for CO2separation processes. In this work, weinvestigated the effect of temperature, sarcosinate concentration,and CO2loading on the mass transfer coefficients of CO2absorption in a sarcosinate-promoted aqueous ammonia solutionon a wetted-wall column. We further investigated the kinetics of thereaction between CO2and a blended NH3/sarcosinateabsorbent using stopped-flow spectrophotometric techniques, followingthe pH changes via coupling to pH indicators. Our study revealed thatthe mass transfer coefficient for CO2absorption in a 3M ammonia + 1.5 M sarcosinate blended solution at 288 K is close tothat in 5 M monoethanolamine absorbent at 313 K. We did not observeany synergistic or catalytic effects between NH3and sarcosinatein the blended solution; the mechanism of the reaction of CO2with the NH3/sarcosinate mixture is the simple combinationof the individual reactions of NH3and sarcosinate withCO2. [ABSTRACT FROM AUTHOR]

In an effort to advance the understanding of multiamine based C02 capture process absorbents, we report here the determination of the kinetic and equilibrium constants for a simple linear diamine N,N-dimethylethylenedi- amine (DMEDA) via stopped-flow spectrophotometric kinetic measurements and 'H/l3C NMR titrations at 25.0 °C. From the kinetic data, the formation of monocarbamic acid (DMEDACOOH) from the reaction of DMEDA with C02(aq) is the dominant reaction at high pH > 9.0 (k? = 6.99 X 103 M-,-s-1). Below this pH, the formation of protonated monocarbamic acid (DMEDACOOH2) via the pathway involving DMEDAH+ and C02(aq) becomes active and contributes to the kinetics despite the 107-fold decrease in the rate constant between the two pathways. 'H and l3C NMR spectra as a function of decreasing pH (increasing HCl concentration) at 25.0 °C have been evaluated here to confirm the protonation events in DMEDA. Calculations of the respective DMEDA nitrogen partial charges have also been undertaken to support the NMR protonation study. A comparison of the DMEDA kinetic constants with the corresponding data for piperazine (PZ) reveals that despite the larger basicity of DMEDA, the enhanced and superior kinetic performance of PZ with C02(aq) above its predicted Bronsted reactivity is not observed in DMEDA [ABSTRACT FROM AUTHOR]

Piperazine (PZ) is widely recognized as a promising solventforpostcombustion capture (PCC) of carbon dioxide (CO2). Inview of the highly conflicting data describing the kinetic reactionsof CO2(aq) in piperazine solutions, the present study focuseson the identification of the chemical mechanism, specifically thekinetic pathways for CO2(aq) in piperazine solutions thatform the mono- and dicarbamates, using the analysis of stopped-flowspectrophotometric kinetic measurements and 1H NMR spectroscopicdata at 25.0 °C. The complete set of rate and equilibrium constantsfor the kinetic pathways, including estimations for the protonationconstants of the suite of piperazine carbamates/carbamic acids, isreported here using an extended kinetic model which incorporates allpossible reactions for CO2(aq) in piperazine solutions.From the kinetic data determined in the present study, the reactionof CO2(aq) with free PZ was found to be the dominant reactivepathway. The superior reactivity of piperazine is confirmed in thekinetic rate constant determined for the formation of piperazine monocarbamicacid (k7= 2.43(3) × 104M–1s–1), which is within thewide range of published values, making it one of the faster reactingamines. The corresponding equilibrium constant for the formation ofthe monocarbamic acid, K7, markedly exceedsthat of other monoamines. Kinetic and equilibrium constants for theremaining pathways indicate a minor contribution to the overall kineticsat high pH; however, these pathways may become more significant athigher CO2loadings and lower pH values where the concentrationsof the reactive species are correspondingly higher. [ABSTRACT FROM AUTHOR]

Aqueous sarcosine salts are fast carbon dioxide (CO2) absorbents suitable for use in postcombustion CO2capturein coal-fired power plants. We have developed a detailed reactionscheme including all the reactions in the sarcosine–CO2–water system. All unknown rate and equilibrium constantswere obtained by global data fitting. We investigated the temperature-dependentrate and equilibrium constants of the reaction between aqueous CO2and sarcosine using stopped-flow spectrophotometry, by followingthe pH changes over the wavelength range 400–700 nm via couplingto pH indicators. The corresponding rate and equilibrium constantsranged from 15.0 to 45.0 °C and were analyzed in terms of Arrhenius,Eyring, and van’t Hoff relationships. The rate constant forthe reaction between CO2and sarcosine to form the carbamateat 25.0 °C is 18.6(6) × 103M–1s–1, which is very high for an acyclic amine;its activation enthalpy is 59(1) kJ mol–1and theentropy is 33(4) J mol–1K–1.In addition, we investigated the slow reaction between bicarbonateand sarcosine using 1H nuclear magnetic resonance spectroscopyand report the corresponding rate and equilibrium constants at 25.0°C. This rate constant is 5.9 × 10–3M–1s–1. [ABSTRACT FROM AUTHOR]

The kinetics of the fast reversible carbamate formation reaction of CO2(aq) with a series of substituted cyclic secondary amines as well as the noncyclic secondary amine diethanolamine (DEA) has been investigated using the stopped-flow spectrophotometric technique at 25.0 °C. The kinetics of the slow parallel reversible reaction between HCO3- and amine has also been determined for a number of the amines by 1H NMR spectroscopy at 25.0 °C. The rate of the reversible reactions and the equilibrium constants for the formation of carbamic acid/carbamate from the reactions of CO2 and HCO3- with the amines are reported. In terms of the forward reaction of CO2(aq) with amine, the order with increasing rate constants is as follows: diethanolamine (DEA) < morpholine (MORP) thiomorpholine (TMORP) < N-methylpiperazine (N-MPIPZ) < 4-piperidinemethanol (4-PIPDM) piperidine (PIPD) < pyrrolidine (PYR). Both 2-piperidinemethanol (2-PIPDM) and 2-piperidineethanol (2-PIPDE) do not form carbamates. For the carbamate forming amines a Brønsted correlation relating the protonation constant of the amine to the carbamic acid formation rate and equilibrium constants at 25.0 °C has been established. The overall suitability of an amine for PCC in terms of kinetics and energy is discussed. [ABSTRACT FROM AUTHOR]