Homogeneous Phase Reaction Research Articles

Numerical simulation for investigating crevice corrosion of carbon steel in neutral/alkaline concrete construction

PurposeThis study aims to investigate the crevice corrosion behavior of carbon steel in neutral/alkaline environments utilizing a transient multi-physics field model.Design/methodology/approachThe crevice corrosion of carbon steel with different solution pH and crevice width was modeled, incorporating mass transfer, homogeneous phase and localized electrochemical reactions. The extent of crevice corrosion was evaluated by the geometric deformation of the model mesh. The hydro-chemical state inside the crevice was discussed through the Cl− concentration and potential distribution of the solution.FindingsResults revealed that the formation of pitting corrosion near the crevice mouth was accelerated in a neutral solution. When pH = 8 and pH = 9, the carbon steel matrix was dissolved and the Cl− content within the solution was significantly reduced due to the higher concentration of hydroxide ions (OH−).Originality/valueThe crevice corrosion behavior of carbon steel in neutral/alkaline environments is closely associated with solution pH rather than the crevice width. The inhibition of crevice corrosion in alkaline environments was proved by finite element simulation. These findings provide valuable insights that can be applied in engineering applications to prevent and mitigate crevice corrosion in neutral/alkaline environments.

Effect of Hyperthermal Hybrid Gas Composition on the Interfacial Oxidation and Nitridation Mechanisms of Graphene Sheet.

Graphene is one of the most promising thermal protection materials for high-speed aircraft due to its lightweight and excellent thermophysical properties. At high Mach numbers, the extremely high postshock temperature would dissociate the surrounding air into a mixture of atomic and molecular components in a highly thermochemical nonequilibrium state, which greatly affects the subsequent thermal chemical reactions of the graphene interface. Through establishing a reactive gas-solid interface model, the reactive molecular dynamics method is employed in this study to reveal the influences of the thermochemical nonequilibrium gas mixture on the thermal oxidation and nitridation mechanisms of graphene sheet. The results show that three distinctive stages can be recognized during bombardment of various nonequilibrium gas components toward the graphene sheet: (i) collision and surface adsorption stage, (ii) gas-solid heterogeneous reaction stage, and (iii) gas phase homogeneous reaction stage. The surface catalysis effect is found to be dominant during the first two stages, which can influence the following ablation behavior of graphene significantly at high-temperature conditions. Moreover, surface catalysis, oxidation, nitridation, and ablation mechanisms between nonequilibrium gas and graphene interface are revealed, which is of high relevance for future interfacial design and application of graphene as a thermal protection material.

Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization of o- and p-aminophenols under simulated aerosol and cloud conditions (pH 1–7, and ionic strength 0.01–1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4–0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products of o- and p-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions.

A Model for Radiolysis in a Flowing-Water Target during High-Intensity Proton Irradiation.

At the Facility for Rare Isotope Beams (FRIB), interactions between heavy-ion beams and beam-dump water will create a wide variety of radionuclides which can be accessed by a technique known as “isotope harvesting”. However, irradiation of water is always accompanied by the creation of numerous radical, ionic, and molecular radiolysis products. Some of the radiolysis products have sufficiently long lifetimes to accumulate in the irradiated water and affect the harvesting chemistry. Here we investigate the formation of hydrogen peroxide, molecular hydrogen, and molecular oxygen during a high-intensity proton irradiation of a flowing-water isotope-harvesting target and compare the experimental results to simulations. The simulations kinetically model the chemical reactions occurring in the homogeneous phase of radiolysis in flowing water and establish an “effective yield”. In both the experiment and simulations, the bulk quantities of H2, H2O2, and O2 are considerably lower than predicted by primary radiolysis yields (escape yields), meaning that in the high beam intensity regime the homogeneous phase reactions have a considerable impact on the overall chemical composition of the water. Further, it could be shown that for radiation which is characterized by a limited linear energy transfer, such as the here applied protons, the bulk outcome of the microscopic kinetic modeling could be estimated by a simplified steady-state model.

Study of Influence Factors in the Evaluation of the Performance of a Photocatalytic Fibre Reactor (TiO2/SiO2) for the Removal of Organic Pollutants from Water

The performance of a photocatalytic fibre reactor (UBE Chemical Europe), made of cartridges of fine particles of TiO2 dispersed within silicon fibres and irradiated by ultraviolet light, for the removal of organic pollutants from synthetic waters was evaluated. In the sensitivity analysis carried out, the factors catalytic surface area, fibre state, temperature and initial substrate concentration were studied using 4-chlorophenol as a test compound. The percentage of titanium in the fibre remained practically invariable after a series of experiments and cleaning procedures. Furthermore, the kinetics of removal of pyrene, phenol, 4-chlorophenol and bisphenol A (BPA) from water were evaluated by means of HPLC, UV-absorption and fluorescence techniques. Kinetic operational parameters were determined from a mathematical model proposed by Langmuir–Hinshelwood. Results show that catalytic surface, initial substrate concentration and temperature directly affect the degradation rate of organic compounds, whereas fibre state does not have a significant effect on that. It is proposed that removal of organic compounds from water mainly depends on the adsorption of the specific pollutant on the photocatalytic fibre and on the physical diffusion of the substrate towards the photocatalytic TiO2 active sites on the fibre, with the heterogeneous phase reaction prevailing over the homogeneous phase reaction.

Strategic way for valorization of manure into chemicals and fuels

Animal manure contains a variety of organic materials that can be used for synthesis of value-added biofuels and chemicals. To maximize the carbon recovery from animal manure waste, this study focused on consecutive valorization of horse manure into furfural and syngas (H2 and CO). Acid hydrolysis/dehydration of horse manure was employed to extract furfural, and the residue after furfural extraction was valorized into syngas and bio-oil through CO2-assisted pyrolysis. In acid treatment process, the levulinic acid and furfural were produced from horse manure, and the maximum yield (3.68 wt%) of furfural was achieved at 0.5 M H2SO4 (40 wt% based on hemicellulose content). Horse manure residue was further converted into bio-oil and syngas under N2/CO2 environments. Under CO2 atmosphere, gas phase homogeneous reactions were occurred, which simultaneously reduced CO2 and oxidized bio-oil showing enhanced CO formation (18 times higher comparing to pyrolysis under N2). The homogeneous reaction also resulted in decrease of aromaticity in bio-oil. To enhance the reaction kinetics of the homogeneous reaction and thermal cracking of bio-oil under CO2, catalytic pyrolysis was performed in the presence of Ni/SiO2 catalysts. The catalytic pyrolysis improved syngas (H2 and CO) production more than one order of magnitude higher, comparing to pyrolysis without Ni catalyst. All the experimental findings suggested that horse manure and CO2 could be used as raw materials for production of value-added chemicals and syngas.

Carbon black-polydopamine-ruthenium composite as a recyclable boomerang catalyst for the oxidative cleavage of oleic acid

A new composite heterogeneous catalytic system is proposed for the transformation of cheap unsaturated fatty acids into value-added molecules through their oxidative cleavage. The valorization of oleic acid to azelaic and pelargonic ones (which are demanded in pharmacology) is specifically studied. The reaction is efficiently performed with a novel composite catalyst inspired from metal recovery technology, namely Ru species supported on a carbon black that was previously oxidized and then functionalized with polydopamine. Being a polymer with hydroxyl and amine groups polydopamine provides moieties acting as tweezers able to complex Ru species. A representation of this novel composite catalyst is built from its characterization by FTIR, TGA, N2 physisorption TEM and XPS. Using NaIO4 as oxidizing agent in a biphasic system at room temperature the conversion of oleic acid, and selectivity towards pelargonic and azelaic acids, reached around 95% after 3 h. The reaction mechanism is explored by UV–Vis spectrophotometry, ICP elementary analysis and NMR spectroscopy, together with recyclability and hot centrifugation tests. The occurrence of a boomerang mechanism is demonstrated. The solid catalyst is indeed recyclable at least 5 times without activity loss, but at the same time Ru species are shown performing the reaction in homogeneous phase namely in a dissolved state. Actually, polydopamine is confirmed to recover Ru species once the reaction ends, guarantying the recyclability of the catalyst. The composite catalyst therefore combines the advantages of homogeneous and heterogeneous catalysis in the investigated reaction.

Polysaccharides on gelatin-based hydrogels differently affect chondrogenic differentiation of human mesenchymal stromal cells

Selection of feasible hybrid-hydrogels for best chondrogenic differentiation of human mesenchymal stromal cells (hMSCs) represents an important challenge in cartilage regeneration. In this study, three-dimensional hybrid hydrogels obtained by chemical crosslinking of poly (ethylene glycol) diglycidyl ether (PEGDGE), gelatin (G) without or with chitosan (Ch) or dextran (Dx) polysaccharides were developed. The hydrogels, namely G-PEG, G-PEG-Ch and G-PEG-Dx, were prepared with an innovative, versatile and cell-friendly technique that involves two preparation steps specifically chosen to increase the degree of crosslinking and the physical-mechanical stability of the product: a first homogeneous phase reaction followed by directional freezing, freeze-drying and post-curing. Chondrogenic differentiation of human bone marrow mesenchymal stromal cells (hBM-MSC) was tested on these hydrogels to ascertain whether the presence of different polysaccharides could favor the formation of the native cartilage structure. We demonstrated that the hydrogels exhibited an open pore porous morphology with high interconnectivity and the incorporation of Ch and Dx into the G-PEG common backbone determined a slightly reduced stiffness compared to that of G-PEG hydrogels. We demonstrated that G-PEG-Dx showed a significant increase of its anisotropic characteristic and G-PEG-Ch exhibited higher and faster stress relaxation behavior than the other hydrogels. These characteristics were associated to absence of chondrogenic differentiation on G-PEG-Dx scaffold and good chondrogenic differentiation on G-PEG and G-PEG-Ch. Furthermore, G-PEG-Ch induced the minor collagen proteins and the formation of collagen fibrils with a diameter like native cartilage.This study demonstrated that both anisotropic and stress relaxation characteristics of the hybrid hydrogels were important features directly influencing the chondrogenic differentiation potentiality of hBM-MSC.

Strategic disposal of flood debris via CO2-assisted catalytic pyrolysis

Recent abnormal climate changes resulted in the dramatic alternation of rainfall and flood patterns in many countries. The massive generation of flood debris, a mixture of soil (sediment), biomass, plastic, metal, and various hazardous materials, poses various environmental and public health problems. This study suggests a sustainable technical platform to convert the hazardous materials into value-added products. CO2-assisted pyrolysis was used to thermally convert flood debris into syngas (H2 and CO). CO2 enhanced the syngas production due to gas phase homogeneous reactions (HRs) between CO2 and volatile hydrocarbons evolved from pyrolysis of flood debris. For improvement of HRs in line with enhancement of syngas production, additional thermal energy and earth abundant catalyst were used. In particular, Ni/SiO2 catalyst increased more than one order of magnitude higher syngas production, comparing to non-catalytic pyrolysis. Synergistic effect of CO2 and Ni catalyst showed nearly 50% more production of syngas in reference to catalytic pyrolysis under N2. During flood debris pyrolysis, compositional matrix of flood debris was also determined by detecting index chemicals of waste materials that cannot be identified by naked eyes. Thus, this study confirmed that CO2-assisted pyrolysis is a useful tool for conversion of flood debris into value-added chemicals.

Offering a new option to valorize hen manure by CO2-assisted catalytic pyrolysis over biochar and metal catalysts

• Hen manure (HM) was valorized into biochar catalyst and syngas. • Catalytic pyrolysis of HM using HM-derived biochar signified syngas formation. • CO 2 -assisted pyrolysis expedited CO production via gas phase reactions. • HM biochar was catalytically active with almost half performance of Ni catalyst. The huge generation of animal manures from livestock industries has resulted in detrimental environmental effects such as soil and stream contaminations in line with emissions of greenhouse gases ( i.e., CH 4 and CO 2 ). To alleviate the environmental problems from the animal manure waste, this study proposed a new option for disposal of hen manure waste and its valorization as energy and catalyst. To make this platform more environmentally sound, CO 2 was used as a feedstock to control the pyrogenic products (biochar, syngas, and biocrude) from HM. CO 2 contributed to more thermal cracking of volatile matters (VMs) evolved from HM pyrolysis into syngas in reference to pyrolysis in N 2 . In detail, enhanced CO production from gas phase homogeneous reactions (HRs) between CO 2 with VMs was observed. To improve the reaction kinetics for syngas formations, HM biochar was used as a catalyst. HM biochar substantially expedited the syngas formation due to presence of alkaline species. The catalytic capability of HM biochar was nearly the half of Ni catalyst, though the price of HM is a few orders of magnitude lower. This offers that CO 2 -assisted pyrolysis with HM biochar could be considered an environmentally and economically viable way for syngas formation from biomass waste.

Exploiting starfish in pyrolysis for the enhanced generation of syngas and CO2-looping agent

Starfish (Asterina pectinifera) has been considered a major invasive species with no natural predators in the marine ecosystem. They can destroy the natural marine system when the population growth is too high, suggesting the development of a sustainable way to dispose of starfish. Therefore, this study offers a sustainable thermo-chemical platform for the direct conversion of starfish waste into value-added syngas (CO and H2) and biochar. Major gaseous products from the starfish pyrolysis under both the N2 and CO2 conditions were H2, CH4 and CO. H2 and CH4 were likely ascribed to dehydrogenation and C–C bond scission of starfish, while CO formation was from homogeneous reaction of CO2 with volatile organic matters from starfish pyrolysis. Under the N2 environment, CO2 liberated from the thermolysis of CaCO3, a major constituent of starfish, contributed to formation of CO. Such the mechanistic effectiveness of CO2 was confirmed by starfish pyrolysis under the CO2 environment. However, the effectiveness of CO2 on gas phase homogeneous reaction with volatile compounds was not fully activated during thermolysis in one-stage pyrolysis due to source depletion at high temperature. To improve the effectiveness of CO2, additional thermal energy was applied through two-stage pyrolysis (isothermal running at 600 °C). The homogeneous reaction of CO2 with volatile compounds liberated from starfish pyrolysis with additional thermal energy highly contributed to enhanced formation of CO. In line with the substantial generation of CO in the presence of CO2, high concentration of CO2 also contributed to more pore creation. These observations indicate that the construction of CO2-looping system from starfish pyrolysis would become a sustainable way to produce syngas and porous biochar.

In Situ Monitoring of the Seeding and Growth of Silver Metal-Organic Nanotubes by Liquid-Cell Transmission Electron Microscopy.

Metal-organic nanotubes (MONTs) are highly ordered one-dimensional crystalline porous frameworks. Despite being nanomaterials, virtually all studies of MONTs rely on characterization of the bulk crystalline material (micron-sized) by single-crystal X-ray diffraction. For MONTs to achieve their raison d'être as tunable one-dimensional nanomaterials, individual tubes or small finite bundles of tubes must be synthesized and characterized. Therefore, to directly observe their formation under a variety of reaction conditions in solution, we employ liquid-cell transmission electron microscopy (LCTEM), which allows the early stages of MONT assembly to be monitored in real time. Notably, changing the metal-to-ligand ratio alters the local concentrations of reactant monomers, resulting in multiple nucleation and growth pathways and diverse morphologies at the nanoscale. These various initial seeds grow to form the same nanocrystalline needle phase. This approach of employing LCTEM to study these nanomaterials is analogous to monitoring typical homogeneous solution phase reactions by NMR for controlled nanomaterial formation.

CO2-Mediated catalytic pyrolysis of rice straw for syngas production and power generation

As emissions of anthropogenic CO2 from the use of fossil fuels become more severe, the renewable energy production has received considerable interests. In this study, CO2 was used as a raw material to produce energy as a form of syngas (H2/CO) as a precautious measure for mitigating the atmospheric CO2 levels. Rice straw pyrolysis was conducted under various N2/CO2 purge gas environments. The present study experimentally proved that CO2 expedited gas phase homogeneous reactions between volatile organic compounds (VOCs), evolved from rice straw pyrolysis. These CO2 functionalities led to the conversion CO2/rice straw into CO at ≥ 480°C. To accelerate reaction kinetics of syngas formation, additional thermal energy (500 or 700°C) was applied through multi-stage pyrolysis setups. In addition, SiO2 supported Co (Co/SiO2) catalyst was further accelerate reaction kinetics of CO (3 times) and H2 (6 times) in reference to non-catalytic pyrolysis at 500°C. The synergistic effects of Co/SiO2 catalyst and CO2 feedstock resulted in substantial formations of H2 and CO at ≤ 480°C. To analyze the potential capability of rice straw fuels, their power generation performances were evaluated through a simple gas turbine cycle. When the constant amount of air was assumed to be supplied to a combustion chamber, different amounts of fuel feedstocks were required for their complete combustions. In this condition, the resulting power generations of rice straw fuels (maximum 138 MJ s−1 from catalytic pyrolysis under 100% CO2) were up to 1.9 times higher than the power generations from natural gas references (74 and 82 MJ s−1). These results suggest that a renewable power generation platform could be constructed with a valorization of greenhouse gas (CO2) and biomass waste (rice straw) through pyrolysis process at mild temperature.

Guar gum cinnamate ouzo nanoparticles for bacterial contact killing in water environment

Herein we report the synthesis of newer guar gum cinnamate esters (GGC) following a Hofmeister cation guided homogeneous phase reaction. High degree of substitution (DS) guar gum cinnamate was obtained using, cinnamic acid halide reactant at a 1:3 M ratio. The biopolymer was fully characterized in FT-IR,13C NMR, XRD and thermal analysis. Nanoparticles were further developed in a facile ouzo solvent diffusion technique. SEM studies confirmed quasi spherical shape of the nanoparticles (GGCN) with an average size of 200 nm. Nanoparticles GGCN, expressed antibacterial activity against water borne gram negative and gram positive bacteria. The MIC was recorded at 300 μg mL−1against Escherichia coli and 500 μg mL−1against Staphylococcus aureus. Bacterial contact killing was confirmed from the bacterial morphology studies in SEM. Thus, nanoparticles from GGC may be employed for bacterial killing and water decontamination.

CO2 to fuel via pyrolysis of banana peel

Abstract Considering the global production of banana, a large amount of banana peel (BP) waste is being generated world widely. Thus, pyrolysis of BP was investigated to develop a technically reliable platform for the simultaneous waste management and energy recovery. To synergistically increase the sustainability of BP pyrolysis, this study adopted carbon dioxide (CO2) as a raw material and examined the production of syngas as a function of temperature in reference to the N2 environment. CO2-cofeed pyrolysis expedited the thermal cracking of volatile pyrolysates from BP, resulting in the gas phase homogeneous reaction between CO2 and the pyrolysates at ≥420 °C. This promoted CO formation in the temperature region, and more than 20 times of CO formation was shown in comparison with pyrolysis in the N2 environment. These genuine mechanistic roles of CO2 offer a new mean for converting CO2 into CO. Also, CO2-cofeed pyrolysis of BP increased the aromaticity of biocrude (pyrolytic oil), expediting dehydrogenation of liquid pyrolysates without using any catalysts. Moreover, modification of biochar surface morphology under the CO2 condition was observed. Conclusively, this study informed a key clue for maximizing the carbon exploitation in the carbonaceous waste, which directly leads to the environmental benefits due to the use of CO2 as a reactant. CO2-cofeed pyrolysis can be an innovative and strategic thermo-chemical process to valorize food wastes.

Change in Characteristics of Pollution Gas and Water-soluble Ions at Different Development Stages of Haze

To explore the variation in characteristics of atmospheric pollutants at different stages of haze, the monitor for aerosols and gases in ambient air (MARGA) was used to observe the concentrations of precursor pollutants (NH3, HNO3, and SO2) and eight water-soluble ions in a regional haze in the Yangtze River Delta region from November 18 to December 07, 2018. Combined with environmental data (PM2.5, NO2, CO, and O3) and meteorological data, the causes of regional haze formation, diurnal variation characteristics of air pollutants, and distribution characteristics of air pollutants in different stages of haze were analyzed. The results showed that the Yangtze River Delta region was mainly controlled by a ridge of high pressure during the haze process and the weather situation was stable, which was conducive to the accumulation of air pollutants. On hazy days, the concentrations of PM2.5, NO2, NO3-, SO42-, NH4+, Cl-, and Na+ were (118.91±39.23), (61.62±26.34), (45.64±16.01), (18.80±8.02), (20.82±7.16), (3.02±2.25), and (0.23±0.22) μg·m-3, respectively, and these were 2.73, 1.63, 2.64, 1.94, 2.50, 2.05, and 2.56 times the levels found on clean days, respectively. The concentration of CO was (1.34±0.39) mg·m-3 on hazy days, which was 1.86 times that found on clean days. Diurnal variation characteristics of different air pollutants were different, as were the distribution characteristics of air pollutants at different haze stages. The concentrations of SO2 was the highest in the haze occurrence stage. The concentrations of PM2.5, NO2, NH3, CO, and SNA were highest in the haze development stage, and the concentrations of O3, Cl-, Na+, and K+ were highest in the haze dissipation stage. The relative contributions of SNA to PM2.5 in different stages of haze could reach 94%-96%, and their growth rate was largest in the development stage. The order of growth rate was NO3- > NH4+ > SO42-. SNA mainly existed in the form of NH4NO3 on clean days and in the occurrence and development stages, and (NH4)2SO4 in the dissipation stage. This haze process was mainly caused by the growth of NO3-, which was mainly generated by gas-phase homogeneous phase reaction, and NO3-contributes 51.06%, 51.85%, and 48.22%, respectively, to PM2.5 in the occurrence, development, and dissipation stages of haze.

Homogeneous phase synthesis of chitosan silica hybrid materials in ionic liquid medium and adsorption of Fe(III) from aqueous solutions

Two chitosan silica hybrid materials were prepared by a two-step process in 78–84% yields using the homogeneous phase reaction of 3-(triethoxysilyl)propyl isocyanate with chitosan dissolved in 1-n-butyl-3-methylimidazolium chloride ionic liquid (∼10% w/w), which was followed by NH4OH catalyzed hydrolysis of triethoxysilyl groups and then sol-gel process. These new hybrid materials were shown to adsorb up to about 95% of Fe3+ from 5 × 10−4 M aqueous solution at room temperature in 24 h.

Production of syngas from steam gasification of three different ranks of coals and related reaction kinetics

The steam gasification properties of three different ranks of coals, Shengli lignite (SL), Shenhua subbituminous coal (SH), and Tavan Tolgoi anthracite (TT), were investigated using a lab-scale fixed-bed reactor, and the thermodynamic equilibrium constant and kinetics of the reaction were analyzed. The results showed that the aromaticity and condensation of aromatic structures in SL, SH, and TT became higher, and the maturity of organic substance became lower. The steam gasification reaction showed that the syngas from low-rank SL had a high H2/CO molar ratio, while the syngas from high-rank TT had relatively high CO content. The direct carbon gasification reactions for these three different ranks of coals were far from in equilibrium; the water gas shift reaction of SL was near equilibrium, and the degree of reaction for SL was higher than that of SH and TT. We studied a random pore model (RPM), shrinking core model (SCM), and hybrid model (HM), and the hybrid model was found to be the most suitable model of the three for fitting the steam gasification reactions of the three types of coal. It had high fitting correlation coefficient R2 values (ranging from 0.9939 to 0.9990) and small average error θ values (ranging from 0.009 to 0.016). The apparent activation energy E values of SL, SH, and TT fitted by HM were 179.10, 48.14, and 63.06 kJ/mol, respectively, and the corresponding pre-exponential factor k0 values were 3.14 × 107, 1.01, and 1.22 min−1, respectively. This study finds that the steam gasification of SL, SH, and TT coal samples consists of homogeneous phase reaction and shrinking core reaction.

Differences in Formation and Oxidation of Colombian Coal Chars in Air and Oxy-fuel Atmospheres

The increasing interest towards more efficient and clean technologies, specially paying attention to CO2 neutral processes is encouraging the investigation of coal thermochemical conversion under oxy-fuel atmospheres (i.e. without N2). The process offers many advantages such as easy separation of the CO2 produced and low NOX/SOX emissions. While coal conversion in air is already well understood, full understanding of the influences of CO2-rich atmospheres is still required. A series of experiments in thermogravimetric analyser, drop-tube reactor and flat-flame burner were performed using a mid-range bituminous coal (Colombian coal) to understand the differences in the chars obtained after the pyrolysis step. Comparing the pyrolysis in N2 and CO2 atmospheres, significant differences were observed in the resulting chemical (composition) and physical properties of the chars, whereas mass loss was very similar for short residence times (< 130 ms). Afterwards, the chars obtained were submitted to oxidation and gasification, under several different operating conditions, in order to evaluate the difference in reactivity of these chars. Chars obtained under CO2 atmospheres revealed a lower reactivity, despite their higher surface area. These aspects cannot be explained and captured by a model which does not focus on some important details. In this paper, the results obtained in these experiments are summarized and discussed on the point of view of the POLIMI modelling approach for thermochemical conversion of solids. This model offers several advantages, such as being flexible to improvements, requiring simple experimental data of the fuel and offers an all-in-one solution for describing the kinetics of the whole process. The developments accounted for a wide range of experimental data, which allowed its calibration for several fuels, mostly in air combustion. It was first developed to describe the pyrolysis step, and later char oxidation/gasification was included in a simplified approach. The detailed mechanism of homogeneous gas phase reactions of the volatiles is also coupled. In order to extend the predictive capabilities of the model for oxy-fuel conditions, dedicated experiments must be considered for future improvements. In this work these missing effects are discussed, identifying the main necessary improvements, allowing this model to be extended and applied also for the designing of reactors that use oxy-fuel technologies.

NMR spectroscopic method for studying homogenous liquid phase reaction kinetics in systems used in reactive gas absorption and application to monoethanolamine–water–carbon dioxide

An NMR spectroscopic method for measuring homogenous liquid phase reaction kinetics in systems that are used in reactive gas absorption processes is presented. In the kinetic experiment, carbon dioxide loaded and unloaded aqueous amine solutions are mixed such that no gas phase is involved. This procedure enables studying liquid phase reaction kinetics without the influence of the kinetics of the physical absorption process. A rapid-mixing NMR flow cell is used for the measurements, which are carried out in stopped-flow mode. 1H NMR spectra are taken at short intervals to monitor the kinetic process. The cell is liquid thermostatted and pressure resistant, such that a wide range of conditions can be studied. The new method was used for studying reaction kinetics in the system monoethanolamine (MEA)–water (H2O)–carbon dioxide (CO2) at temperatures between 293 and 333 K. From the data, information on the kinetics of the reaction of MEA with bicarbonate (HCO3-) to form MEA carbamate was obtained. That reaction was investigated for the first time in the present work without using bicarbonate salts. An Arrhenius model was fitted to the new data. The formation of MEA carbamate from MEA and HCO3- is often neglected in models for describing the reactive absorption of CO2 with aqueous MEA solutions. A process simulation study carried out in the present work reveals that it should be taken into account in predictions of reactive absorption processes that are operated under elevated pressure with a high mole fraction of CO2 in the gaseous phase.