Hydroxylamine decomposition in the presence of iron studied by calorimetry, online mid-IR and UV-vis spectroscopy

Recent explosions at two chemical plants, one in the United States and one in Japan, involving hydroxylamine manufacture underline the lack of mechanistic understanding about this industrially relevant compound. The basic chemical properties of hydroxylamine have been known for decades but its tendency to decompose in the presence of transition metals, in particular Fe(II)/Fe(III), still remains a mystery. Recent studies [1, 2] have not been successful in identifying without controversy the mechanism, products and intermediates of decomposition. In this context we are undertaking a research project to investigate the decomposition of hydroxylamine in aqueous solution in the presence of 3d transition metals. The final aim is to obtain a satisfactory description of the reaction mechanism. A concentration, pH and temperature dependence mechanistic study will be completed using a new pressure-proof small volume reactor [3] that combines calorimetry with online mid-infrared and UV-visible spectroscopy. Chemical models will be fitted to the measured data to determine the reaction mechanism and associated kinetic and thermodynamic parameters [4]. Since there is significant gas production during the decomposition process, the pressure increase inside the reactor will be used as a forth signal. Validation of the online measurements and determination of the chemical species present in the liquid and gas phases will be done by offline GC/MS analysis. Preliminary results for the decomposition of hydroxylamine in the presence of Fe(II)/Fe(III) will be presented including measurements from all the online instrumentation. [1] Cisneros, L. O.; Wu, X. et al. Process Safety and Environmental Protection 2003 81(B2), 121. [2] Wei, C. Y.; Saraf, S. R. et al. Thermochimica Acta 2004, 421(1-2), 1. [3] Visentin, F.; Gianoli, S. I. et al. Organic Process Research & Development 2004, 8(5), 725. [4] Puxty, G.; Maeder, M. et al. Journal of Chemometrics 2005, in print

CO2 absorption into aqueous amine blended solutions containing monoethanolamine (MEA), N,N-dimethylethanolamine (DMEA), N,N-diethylethanolamine (DEEA) and 2-amino-2-methyl-1-propanol (AMP) for post-combustion capture processes

Presently monoethanolamine (MEA) remains the industrial standard solvent for CO2 capture processes. Operating issues relating to corrosion and degradation of MEA at high temperatures and concentrations, and in the presence of oxygen, in a traditional PCC process, have introduced the requisite for higher quality and costly stainless steels in the construction of capture equipment and the use of oxygen scavengers and corrosion inhibitors. While capture processes employing MEA have improved significantly in recent times there is a continued attraction towards alternative solvents systems which offer even more improvements. This movement includes aqueous amine blends which are gaining momentum as new generation solvents for CO2 capture processes. Given the exhaustive array of amines available to date endless opportunities exist to tune and tailor a solvent to deliver specific performance and physical properties in line with a desired capture process. The current work is focussed on the rationalisation of CO2 absorption behaviour in a series of aqueous amine blends incorporating monoethanolamine, N,N-dimethylethanolamine (DMEA), N,N-diethylethanolamine (DEEA) and 2-amino-2-methyl-1-propanol (AMP) as solvent components. Mass transfer/kinetic measurements have been performed using a wetted wall column (WWC) contactor at 40°C for a series of blends in which the blend properties including amine concentration, blend ratio, and CO2 loadings from 0.0-0.4 (moles CO2/total moles amine) were systematically varied and assessed. Equilibrium CO2 solubility in each of the blends has been estimated using a software tool developed in Matlab for the prediction of vapour liquid equilibrium using a combination of the known chemical equilibrium reactions and constants for the individual amine components which have been combined into a blend.From the CO2 mass transfer data the largest absorption rates were observed in blends containing 3M MEA/3M Am2 while the selection of the Am2 component had only a marginal impact on mass transfer rates. Overall, CO2 mass transfer in the fastest blends containing 3M MEA/3M Am2 was found to be only slightly lower than a 5M MEA solution at similar temperatures and CO2 loadings. In terms of equilibrium behaviour a slight decrease in the absorption capacity (moles CO2/mole amine) with increasing Am2 concentration in the blends with MEA was observed while cyclic capacity followed the opposite trend. Significant increases in cyclic capacity (26-111%) were observed in all blends when compared to MEA solutions at similar temperatures and total amine concentrations. In view of the reasonable compromise between CO2 absorption rate and capacity a blend containing 3M MEA and 3M AMP as blend components would represent a reasonable alternative in replacement of 5M MEA as a standalone solvent

Real-time kinetic hard-modelling for the optimisation of reaction conditions and the detection of process upset in semi-batch reactors

Process Analytical Technology (PAT) has greatly evolved in the last decades due to the development of multivariate online sensors that are able to monitor the properties of industrial processes in real time [1, 2]. The online monitoring of product quality and the detection of process upsets are important for the pharmaceutical and fine chemical industry in order to maintain their product specifications and their commitments regarding safety, health and environment. Most frequent sources of deviations from normal operating conditions in semi-batch processes are due to slightly imprecise initial conditions or impurities in the initial reactants causing unexpected side reactions [3]. Online monitoring of industrial processes usually relies on calibration methods, such Principal Component Regression (PCR), Partial Least Squares (PLS) or Black Box models (e.g. Neural Networks) [4, 5]. A drawback of these calibration methods is their poor behaviour regarding extrapolation, requiring a constant effort for the operator to maintain the calibration conditions. Kinetic modelling techniques [6] do not suffer from this drawback as they are based on first principal models and can also be adapted for the monitoring of highly fluctuating processes, e.g. semi-batch processes. In this contribution, we propose a method for the online monitoring of semi-batch processes based on kinetic hard-modelling. The proposed method assumes that the kinetic model and the associated rate constants have already been determined at an earlier stage in R&D. In a first phase, the algorithm corrects estimates for the initial concentrations from dosing a small amount of reagent and fitting the kinetic model to the measured signals, e.g. mid-IR, UV-vis or released/consumed heat. In a second phase, if no process upset is detected, the corrected initial concentrations are fed back into the kinetic model and the algorithm optimises the dosing rate of the reagent or the operating temperature by maximising a property of the process, e.g. yield, selectivity or conversion. When optimum operating conditions are found, the algorithm forces the reactor to work under these improved conditions and the process is continuously re-optimised to detect possible process upsets. The method will be discussed based on simulated and experimental data taken from our high performance small scale reaction calorimeter coupled to in-situ mid-IR and UV-vis ATR-spectroscopy [7]. [1] P. Gemperline, G. Puxty, M. Maeder, D. Walker, F. Tarczynski, M. Bosserman, Analytical Chemistry 76 (2004) 2575-2582. [2] J. Workman, M. Koch, D. Veltkamp, Analytical Chemistry 77 (2005) 3789-3806. [3] E.N.M. van Sprang, H.J. Ramaker, H.F.M. Boelens, J.A. Westerhuis, D. Whiteman, D. Baines, I. Weaver, Analyst 128 (2003) 98-102. [4] M. Spear, Chemical Processing 70 (2007) 20-26. [5] T.J. Thurston, R.G. Brereton, D.J. Foord, R.E.A. Escott, Journal of Chemometrics 17 (2003) 313-322. [6] M. Maeder, Y.M. Neuhold, Practical Data Analysis in Chemistry, Elsevier, Amsterdam NL, 2007. [7] F. Visentin, S.I. Gianoli, A. Zogg, O.M. Kut, K. Hungerbühler, Organic Process Research & Development 8 (2004) 725-737

Simulating combined SO2 and CO2 capture from combustion flue gas

The requirement to pre‐treat flue gas prior to the CO2 capture step is an economic challenge when using aqueous amine absorbents for capturing CO2 from coal‐fired power station flue gases. A potentially lower cost alternative is to combine the capture of both CO2 and SO2 from the flue gas into a single process, removing the requirement for the desulfurization pre‐treatment step. The CSIRO's CS‐Cap process uses a single aqueous amine absorbent to capture both of these acid gases from flue gas streams. This paper covers the initial simulation of this process applied to both brown and black coal flue gases. Removal of absorbed SO2 is achieved via reactive crystallization. This is simulated here using a ‘black box’ process, resulting in a K2SO4 product. Different operating conditions have been evaluated that increase the sulfate concentration of the absorbent in the SO2 capture section of the process, which is expected to increase the efficiency of the reactive crystallization step. This paper provides information on the absorption of SO2 into the amine solution, and heat and mass balances for the wider process. This information will be required for further detailed simulation of the reactive crystallization step, and economic evaluation of the CS‐Cap process. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

Protonation Constants and Thermodynamic Properties of Amino Acid Salts for CO2 Capture at High Temperatures

Amino acid salts have greater potential for CO2 capture at high temperatures than typical amine-based absorbents because of their low volatility, high absorption rate, and high oxidative stability. The protonation constant (pKa) of an amino acid salt is crucial for CO2 capture, as it decreases with increasing absorption temperature. However, published pKa values of amino acid salts have usually been determined at ambient temperatures. In this study, the pKa values of 11 amino acid salts were determined in the temperature range of 298–353 K using a potentiometric titration method. The standard-state molar enthalpies (ΔHm0) and entropies (ΔSm0) of the protonation reactions were also determined by the van’t Hoff equation. It was found that sarcosine can maintain a higher pKa than the other amino acids studied at high temperatures. We also found that the CO2 solubilities and overall mass-transfer coefficients of 5 m′ sarcosinate (moles of sarcosine per kilogram of solution) at 333–353 K are higher than those of 30% MEA at 313–353 K. These results show that some possible benefits can be produced from the use of sarcosine as a fast solvent for CO2 absorption at high temperatures. However, the pronotation reaction of sarcosine is the least exothermic among those of all amino acids studied. This could lead to a high regeneration energy consumption in the sarcosinate-based CO2 capture proces

Uncertainties and error propagation in kinetic hard-modelling of spectroscopic data

A novel method is presented for the rigorous propagation of uncertainties in initial concentrations and in dosing rates into the errors in the rate constants fitted by multivariate kinetic hard-modelling of spectroscopic data using the Newton–Gauss–Levenberg/Marquardt optimisation algorithm. The method was successfully validated by Monte-Carlo sampling. The impact of the uncertainties in initial concentrations and in the dosing rate was quantified for simulated spectroscopic data based on a second and a formal third order rate law under batch and semi-batch conditions respectively. An important consequence of this study regarding optimum experimental design is the fact that the propagated error in a second order rate constant is minimal under exact stoichiometric conditions or when the reactant with the lowest associated uncertainty in its initial concentration is in a reasonable excess (pseudo first order conditions). As an experimental example, the reaction of benzophenone with phenylhydrazine in THF was investigated repeatedly (17 individual experiments) by UV–vis and mid-IR spectroscopy under the same semi-batch conditions, dosing the catalyst acetic acid. For all experiments and spectroscopic signals, reproducible formal third order rate constants were determined. Applying the proposed method of error propagation to any single experiment, it was possible to predict 80% (UV–vis) and 40% (mid-IR) of the observed standard deviation in the rate constants obtained from all experiments. The largest contribution to this predicted error in the rate constant could be assigned to the dosing rate. The proposed method of error propagation is flexible and can straightforwardly be extended to propagate other possible sources of error

Measurement and modelling of semi-batch reactions using small-scale reaction calorimetry, in-situ spectroscopy and gas consumption/production

The rapid and complete characterization of chemical reaction mechanisms is of the utmost importance in terms of chemical understanding, safety and efficiency. In this presentation a new small volume reaction calorimeter (25-45mL) is described. With this reactor it is possible to make in-situ UV-vis and IR measurements, calibration free calorimetry measurements and gas production/consumption measurements. Firstly, the operating principle of the reactor is outlined. Following this, its application to the three-phase hydrogenation of nitrobenzene and ethyl-4-nitrobenzoate is shown along with the type of qualitative interpretation that can rapidly be made from the multiple in-situ signals. The fitting of chemical models to data collected with the reactor is complex and involves the evaluation of the model parameters against multiple objective functions that do not always share the same optimal parameter values. A multiobjective function genetic algorithm has been developed for this task and its application to calorimetric and spectroscopic data measured during the epoxidation of 2,5-di-tert-butyl-1,4-benzoquinone will be shown

Editorial: The Role of Carbon Capture and Storage (CCS) Technologies in a Net-Zero Carbon Future

The authors would like to acknowledge funding from the Research Councils UK under grants EP/N024567/1 (CCS from Industrial clusters and their Supply chains), NE/P019900/1 (Comparative assessment and region-specific optimisation of GGR) and EP/T033940/1 (Multiphysics and multiscale modelling for safe and feasible CO2 capture and storage)

Experimental evaluation of methods for reclaiming sulfur loaded amine absorbents

Sulfur dioxide (SO2) is a major flue gas contaminant that has a direct effect on the performance of amine-based carbon dioxide capture units operating on power plant flue gases. In many countries, flue gas desulfurisation (FGD) is an essential upstream requirement to CO2 capture systems, thereby increasing the overall operational and capital cost of the capture system. In Australia, the efficacy of CO2 capture may be compromised by the accumulation of SO2 in the absorption solvent. CSIRO’s CS-Cap process is designed to capture of both these acidic gases in one absorption column, thereby eliminating the need for a separate FGD unit which could potentially save millions of dollars. Previous research at CSIRO’s post-combustion capture pilot plant at Loy Yang power station has shown that mono-ethanolamine (MEA) solvent absorbs both CO2 and SO2, resulting in a spent amine absorbent rich in sulfates. Further development of the CS-Cap concept requires a deeper understanding of the properties of the sulfate-rich absorbent and the conditions under which it can be effectively regenerated. In the present study, thermal reclamation and reactive crystallisation processes were investigated, allowing the parameters affecting the regeneration of sulfate-loaded amine to be identified. It was found that amine losses were considerably higher in thermal reclamation than in reactive precipitation. During thermal reclamation, vacuum conditions were more effective than atmospheric, and pH of the initial solution played a significant role in recovery of MEA from the sulfate-rich absorbent. Reactive crystallisation could be effectively accomplished with the addition of KOH. An advantage of this process was that high purity K2SO4 crystals (~99%) were formed, despite the presence of degradation products in the solvent

Small-scale reactor for data oriented process development

During the early stages of research and development chemical industry needs flexible and versatile tools to investigate chemical reaction systems. An important part of the optimisation of a process considering economic factors, risk analysis and environmental impacts is the determination of a reaction mechanism and its associated parameters (i.e. activation energies, rates and heat of reactions). We present here a new fully automated small-scale reaction calorimeter combining a power-compensation heater and a thermoelectrically regulated metal surrounding. This dual temperature control makes the reactor highly suitable for fast and exothermic reactions and eliminates the need for time-consuming calibration of heat transfer coefficients. With a working volume from 25 to 45ml the device is particularly suited for the fine and pharmaceutical chemical industries where only small amounts of test substances are available. An integrated ATR-IR probe coupled to an FT-IR spectrometer allows the investigation of complex reaction mechanisms. Moreover, the new reactor design allows the simultaneous use of various additional in-situ analytics such as UV-Vis, gas intake/uptake and particle size analysis. The performance of the new reaction calorimeter has already been successfully demonstrated based on several reactions [1, 2, 3]. Different analytical techniques may point to different optimum reaction parameters. Algorithms and mathematical tools, such as multi-objective multivariate kinetic modelling, become an important research area in data oriented process development. Only a short introduction into these methods will be given here. [1] Zogg, A., Fischer, U., & Hungerbühler, K. (2003). A new small-scale reaction calorimeter that combines the principles of power compensation and heat balance. Industrial & Engineering Chemistry Research, 42, 767-776. [2] Visentin, F., Gianoli, S. I., Zogg, A., Kut, O. M., & Hungerbühler, K. (2004). Pressure-resistant smallscale reaction calorimeter that combines the principles of power compensation and heat balance (CRC.v4). Organic Process Research & Development, 8(5), 725-737. [3] Visentin, F., Puxty, G., Kut, O. M., & Hungerbühler, K. (2006). Study of the hydrogenation of selected nitro compounds by simultaneous measurements of calorimetric, FT-IR, and gas-uptake signals. Industrial & Engineering Chemistry Research, 45(13), 4544-4553