HCl Reaction Research Articles

Interaction between radio-oxidized polypropylene and gaseous HCl. Part 2. Kinetics and reaction mechanisms

In Part 1 of this article, evidence of cross-infection effects of polyolefins and halogenated polymers present in the long-lived intermediate-level waste (LL-ILW) packages was shown. We choose to study the interaction between polypropylene and one of the main degradation products of PVC, i.e. HCl. Polyolefins and chlorinated polymers were chosen because they are the two most abundant classes of polymer types found in the LL-ILW packages. We showed that the interaction between HCl and pristine or radio-oxidized PP results in HCl consumption and in CO2, H2O and CO formation. The object of the present article is to further study the reaction mechanisms. Using derivative methods at room temperature, the reaction of HCl with hydroperoxide was documented while alcohols seem stable. A model taking into account HCl diffusion, sorption in PP and reaction with hydroperoxide is insufficient to explain the observed HCl consumption kinetics. We concluded that HCl consumption is not only due to physical sorption and to chemical reaction with a unique oxidized compound, but multiple reactions with different oxidation products should be considered as well.

Synthesis of nano-calcium carbonate from waste cement and techno-economic and environmental evaluation

Mineral carbonation stands out not only as an effective method for reducing CO2 emissions but also as a strategic approach to upcycling industrial waste. This study introduces a novel procedure for generating high-purity nano-calcium carbonate (nCaCO3) from waste cement powder, deploying hydrochloric acid (HCl), and sodium hydroxide (NaOH), both obtained through the electrolysis of sodium chloride (NaCl). Our approach, aimed at both environmental preservation and techno-economic feasibility, encompasses optimizing calcium extraction conditions through rigorous analysis of variables such as HCl concentration, solid-to-liquid ratio, and reaction temperature, subsequently proposing a rate law for the extraction process. Furthermore, the method emphasizes the production of high-purity CaCO3 by meticulously removing metallic impurities from the extracted solution with 1.0 M NaOH, culminating in pure calcium hydroxide and the generation of nCaCO3 particles with superior purity (>99 %) and a uniform particle size (80–140 nm). An exhaustive environmental and economic assessment indicates that our process, while consuming varying energy levels based on operational potentials, anticipates a significant reduction in CO2 emissions by 46.1 %, alongside a competitive production cost (335 USD/ton of nCaCO3), thereby demonstrating substantial advantages over traditional methods in terms of sustainability, efficiency, and cost-effectiveness.

Molecular mechanisms and atmospheric implications of the simplest criegee intermediate and hydrochloric acid chemistry in the gas phase and at the aqueous interfaces

The atmospheric chemistry of Criegee Intermediates has become a frontier research point in environmental pollution in recent years. In this work, quantum chemical calculations and Born-Oppenheimer Molecular Dynamics (BOMD) simulations were employed to explore the gas phase and aqueous interface behavior of the simplest Criegee Intermediate (sCI, CH2OO) and hydrochloric acid (HCl) reaction. Quantum chemical calculations have revealed that the product of ClCH2OOH (CMHP) formation from the CH2OO + HCl reaction without and with water molecule undergoes a barrierless or near barrierless process in the gas phase. The results of the rate coefficients calculated by the master equation indicate that the gas-phase CMHP formation from the reaction of CH2OO + HCl could compete with the hydrolysis of CH2OO with (H2O)2 at the altitude of 15 km. BOMD simulations at the aqueous interfaces show that the CH2OO + HCl reaction occurs through stepwise mechanisms that are distinct from those in the gas phase. Three different interfacial reaction channels were identified: i) CMHP direct formation, ii) water-mediated CMHP formation, and iii) HCl-mediated hydroxymethyl hydroperoxide (HMHP) formation, and completed in picosecond time scales. Considering the harsh reaction conditions between CH2OO and HCl at the interface (i.e., the two molecules must be sufficiently close to form the CH2OO-HCl complex), the route of HMHP formation via the hydrolysis of CH2OO remains the main atmospheric loss pathway of CH2OO at the aqueous interfaces. Interestingly, molecular dynamic simulations in nanosecond time scales reveal that the formed CMHP in the gas phase has a tendency to aggregate with sulfuric acids, ammonia, and water molecules to form stable clusters within 213–278 K. The present results for the CMHP and HMHP formations from the sCI-HCl chemistry in the atmosphere will enhance our comprehension of the atmospheric behavior of Criegee intermediates in urban and marine pollution areas.

Recovery of Cerium Salts from Sewage Sludge Resulting from the Coagulation of Brewery Wastewater with Recycled Cerium Coagulant.

Due to the high cost and limited sources of cerium coagulants, it is extremely important to take measures to recycle this raw material. This paper presents the new possibility of recovering cerium(III) chloride, cerium(III) sulphate, cerium(IV) sulphate, and potentially phosphate from sewage sludge (101.5 g/kg Ce and 22.2 g/kg total P) through a brewery wastewater treatment process using recycled CeCl3 as a coagulant. In order to recover the Ce and P, the sludge was subjected to extraction using an HCl solution. Optimal process conditions were determined by means of central composite design and response surface methodology (CCD/RSM) for three input parameters (HCl mass, reaction time, and extractant volume). Under optimal conditions (0.35 g HCl per 1 g of sludge, 40 min reaction time, extractant volume of 25 mL per 1 g of sludge), the highest efficiency obtained was 99.6% and 97.5% for Ce and P, respectively. Cerium(III) oxalate as Ce2(C2O4)3∙10H2O was precipitated from the obtained solution using H2C2O4 (99.97%) and decomposed into CeO2 (at 350 °C), which was afterwards subjected to a reaction with HCl (30%, m/m) and H2O2 (30%, m/m), which led to the crystallisation of CeCl3∙7H2O with a purity of 98.6% and a yield of 97.0%. The obtained CeO2 was also subjected to a reaction with H2SO4 (96%, m/m) and H2O2 (30%, m/m), which produced Ce2(SO4)3 with a yield of 97.4%. The CeO2 was also subjected to a reaction with only H2SO4 (96%, m/m), which produced Ce(SO4)2 with a yield of 98.3%. The filtrate obtained after filtering the Ce2(C2O4)3∙10H2O contained 570 mg/L of P, which enabled its use as a source of phosphorus compounds. The presented processes of Ce and potentially P recovery from sewage sludge originating from brewery wastewater contribute to the idea of a circular economy.

Bio-versus Chemical Approaches to Produce Maltodextrin (de 9 – 12) for Potential Applications in Functional Foods and Pharmaceuticals

Maltodextrin is recognized as a food and pharmaceutical additive that is safe for direct human consumption. The physical and chemical properties of maltodextrin strongly depend on its DE (dextrose equivalent) index. Maltodextrin is a hydrolyzed product derived from starch that has gained numerous industrial applications since the last few decades. Currently, there is an increasing demand for modified starch products. Unfortunately, the relevant production process remains inefficient, leading to relatively low product quality and performance. This paper reports the results of parameterized production processes of maltodextrin with DE values ranging from 9 to 12, achieved by hydrolyzing cassava starch. Two approaches were conducted in this work, including hydrolysis with the catalysis of α-amylase enzyme and HCl acid. In the α-amylase enzyme method, various factors were investigated, such as starch content, hydrolysis time, enzyme concentration, and hydrolysis temperature. In the HCl acid method, process parameters were studied, including starch content, HCl acid concentration, reaction time, and temperature. For both approaches, the DE index of maltodextrin was selected as the objective function, and it was found to be influenced by several process conditions. Utilizing a full Design of Experiment (DoE) plan, a regression equation was developed to illustrate the influence of these factors. From the regression equation, the optimal conditions for the production of desired maltodextrin were derived and compared between the two hydrolysis methods.

Effect of CO2 on HCl removal from syngas using normal and modified Ca-based hydrotalcites: A comparative study

MSW pyrolysis and gasification technologies have been recognized as effective means to enhance the resource utilization of MSW and promote a circular economy. However, the presence of HCl gas can significantly impact the quality and application of syngas. To maximize syngas resource utilization, develop highly efficient HCl adsorbent, this study investigates the performance and mechanism of HCl removal from syngas using a conventional hydrotalcite (Mg-Al-CO3) and modified Ca-based hydrotalcite (Ca-Mg-Al-CO3). The impact of CO2, a component naturally presents in syngas, on the performance of both materials, were also investigated. Characterization techniques, including XRD, TGA, SEM, and analysis of pore properties and specific surface area, were employed to understand the underlying reaction mechanism. The results demonstrated that the performance of Ca-Mg-Al-CO3 was significantly superior to that of conventional Mg-Al-CO3 sorbents, particularly in the presence of CO2 However, the presence of CO2 had a detrimental impact on the performance of Ca-Mg-Al-CO3 in HCl removal, and this effect became increasingly pronounced with higher concentrations of CO2. TGA results revealed a competitive relationship between HCl and CO2 during the adsorption process. Additionally, the fitting results of adsorption kinetics suggested that the adsorption reaction of HCl and CO2 by Ca-Mg-Al-CO3 followed multiple rate-controlling mechanisms.

A single-step upcycling of PVC-containing municipal solid waste compositions for greener chemicals and clean solids as fuel or oil absorbent

Polyvinyl chloride (PVC) containing municipal solid waste (MSW) streams are difficult to recycle and mostly landfilled due to various detrimental effects PVC causes to waste recycling. In this work, a single-step upcycling of PVC-containing commingled wastes in tetrahydrofuran was investigated using cellulose, PVC, polyethylene (PE), polypropylene (PP), and polystyrene (PS) to model the wastes. During the co-conversion, in-situ produced HCl derived from PVC decomposition acted as an acid catalyst to selectively decompose cellulose into liquid mainly containing levoglucosan (LGA) and furfural. It was also found that the presence of PE, PP, and PS in the mixture synergistically enhanced the cellulose-derived monomer productions and increased the reaction rate for producing the monomers by suppressing secondary reactions of HCl in the solvent. The maximum LGA yield from co-conversion of cellulose, PVC, and PS was 35.4% after a 5 min reaction compared to the 31.7% obtained without PS in the mixture. In addition to converting cellulose to chemicals, PVC-derived polyaromatics and partly decomposed PE, PP, and PS were recovered as solids. The dechlorinated solids had higher heating values up to 46.11 MJ/kg, achieved by co-converting cellulose, PVC, and PP. When used as oil absorbents in water, the solid recovered from converting cellulose, PVC, and PE mixture showed the highest absorption capability. Overall, the presented approach offers a promising way for upcycling PVC-containing wastes in which PVC properties and its molecular structure are leveraged to enhance the conversion.

Li + HF and Li + HCl Reactions Revisited I: QCT Calculations and Simulation of Experimental Results.

The Li + HF and Li + HCl reactions share some common features. They have the same kinematics, relatively small barrier heights, bent transition states, and are both exothermic when the zero point energy is considered. Nevertheless, the pioneering crossed beam experiments by Lee and co-workers in the 80s (Becker et al., J. Chem. Phys. 1980, 73, 2833) revealed that the dynamics of the two reactions differ significantly, especially at low collision energies. In this work, we present theoretical simulations of their results in the laboratory frame (LAB), based on quasiclassical trajectories and obtained using accurate potential energy surfaces. The calculated LAB angular distributions and time-of-flight spectra agree well with the raw experimental data, although our simulations do not reproduce the experimentally derived center-of-mass (CM) differential cross section and velocity distributions. The latter were derived by forward convolution fitting under the questionable assumption that the CM recoil velocity and scattering angle distribution were uncoupled, while our results show that the coupling between them is relevant. Some important insights into the reaction mechanism discussed in the article by Becker et al. had not been contrasted with those that can be extracted from the theoretical results. Among them, the correlation between the angular momenta involved in the reactions has also been examined. Given the kinematics of both systems, the reagent orbital angular momentum, , is almost completely transformed into the rotation of the product diatom, j'. However, contrary to the coplanar mechanism proposed in the original paper, we find that the initial and final relative orbital angular momenta are not necessarily parallel. Both reactions are found to be essentially direct, although about 15% of the LiFH complexes live longer than 200 fs.

Intrinsic reaction selectivity between gaseous HCl and SO2 over ethanol-hydrated CaO adsorbent in coal-fired flue gas dechlorination

The reaction selectivity between HCl and SO2 on Ca-based adsorbents has attracted increasing concern for coal-fired flue gas HCl removal, while previous studies have not reached a convincing consensus. To address this knowledge gap, the reaction selectivity of HCl and SO2 over a newly-developed ethanol-hydrated CaO adsorbent was studied under series of experimental conditions. Essential factors of temperature, SO2 concentration, and products layers on the HCl reaction selectivity were revealed and the reaction pathways, thermodynamic and kinetic characteristics and turnover frequency were elucidated using DFT calculations. The results show that HCl has superior priority over SO2 to active sites. Though the opponent SO2 has thermodynamic advantage in terms of Gibbs free energy and adsorption ratios in equilibrium state, the reaction selectivity highly depends on the kinetics, where the dechlorination reaction shows larger chemical reaction rate than desulfurization reactions. The in-situ FTIR spectra indicates that HCl reacts with the desulfurized products, which exhibits the cleaning effect of sulfide product layers and benefits the high selectivity of the dechlorination reaction. The findings of competitive reaction mechanism of HCl and SO2 on Ca-based adsorbents provide a good foundation for flue gas dechlorination in commercial applications.

Ab initio molecular dynamics benchmarking study of machine-learned potential energy surfaces for the HBr+ + HCl reaction

Ab initio molecular dynamics benchmarking study of machine-learned potential energy surfaces for the HBr+ + HCl reaction

Cooper Basin REM gas shales after CO2 storage or acid reactions: Metal mobilisation and methane accessible pore changes

Shale - water - CO2 reactions may occur during CO2 geological storage, enhanced gas recovery, enhanced oil recovery, or supercritical CO2 fracturing. Shale-acid reactions occur during fracturing or acid stimulation. The mobilisation of metals from these processes can be an environmental concern if production water leaks or is released at surface. In addition, reactions may cause changes at the pore scale and affect gas or fluid flow. Three gas shales from the Australian Cooper Basin REM sequence were characterised for metals in minerals by synchrotron X-ray fluorescence microscopy. Metals including Zn, As, Ni, Cr were hosted in sphalerite associated with organic matter, Pb was in pyrite cement, and Mn was hosted in siderite. The shales were separately reacted with brine and supercritical CO2, with CO2-SO2, with dilute HCl, or with N2 at 100 °C and 20 MPa in batch reactors. The solution pH decreased during mineral reactions releasing metals to solution with the general concentrations from reaction with HCl > CO2-SO2 > CO2 > N2 and brine. Of the total available Pb, As, Li, and Zn in the shales, from 0 to 17%, 0.3 to 23%, 3 to 13%, and 0.4 to 28% was released to solution respectively. Corrosion of siderite and ankerite was observed after the CO2 reactions, with precipitation of Fe-oxides. After CO2-SO2 reaction siderite and ankerite were dissolved with pyrite, barite, and Fe-rich precipitates. HCl reactions resulted in complete dissolution of carbonates, with dissolution pits and no mineral precipitation observed. The changes to the fractions of gas accessible mesopores were characterised by small angle neutron scattering (SANS). The Epsilon Formation had the greatest fraction of open accessible pores in the SANS range of 10 to 150 nm, followed by the Murteree and Roseneath shale samples. After CO2 or CO2-SO2 reactions a small decrease in pore accessibility was more pronounced in the Murteree and Roseneath shales, consistent with mineral precipitation. HCl reaction resulted in opening of pores at 150 nm and closing of the smallest measured pores at 10 nm. Metals were mobilised from siderite, ankerite and sulphide minerals mainly, and were dependent on the mineral and metal content but also on the injected gas stream or fluid composition. CO2 based fluids may result in cleaner flow back water, than HCl based fluids. Geochemical reactions during CO2 storage or acid treatment in reactive shales cause pore changes that can affect gas migration. Mineral precipitation during CO2 and CO2-SO2 reactions can result in favourable self-sealing.

Comparative study of the gas phase reaction of SiCl4, SiHCl3, SiH2Cl2, and SiH3Cl by thermodynamic analysis

Thermodynamic analyses based on first-principles calculations were performed for SiHxCl4−x (x = 0 ∼ 3) to compare the characteristics of these chlorosilanes. In the range of 600 °C–1100 °C, SiCl4 almost does not decompose, while SiHCl3, SiH2Cl2, and SiH3Cl decompose and generate SiCl2 as the main radical species. SiHCl3 and SiH2Cl2 have 3.8 and 4.5 times higher SiCl2 equilibrium partial pressure than SiH3Cl at 600 °C, respectively. SiH3Cl has a lower equilibrium partial pressure of HCl than SiHCl3 and SiH2Cl2 by order level. Thus, it is expected that CVD using SiH3Cl gas is less affected by the HCl reaction.

Synergetic analysis between polyvinyl chloride (PVC) and coal in chemical looping combustion (CLC)

This effort is to investigate three different Cu-based oxygen carriers (OCs) with polyvinyl chloride (PVC) and coal in chemical-looping combustion (CLC). The combustion process and synergetic analysis of PVC with coal were evaluated. There were four stages in the reaction of OCs with PVC, which HCl released from PVC could react with OCs at about 200–400 °C. CuO and CuO modified by limestone showed better immobilization of chlorine while CuO modified by iron ore and chrysolite inhibited the reaction of HCl with CuO. PVC char combustion temperature started at about 500 °C which were lower than that of coal char. The combustion efficiency of PVC CLC was all above 92%, except using Cu-Fe as OC which was about 88%. The presence of ZD in PVC showed positive effect on every stage. The addition of coal inhibited the reaction of HCl with CuO. The presence of PVC in ZD reduced the temperature of coal char and the addition of ZD in PVC increased the reaction rate. The synergistic effect was obvious between the PVC and coal blends which is beneficial for the complete combustion in solid fuel CLC

Significant influence of water molecules on the SO3 + HCl reaction in the gas phase and at the air-water interface.

The products resulting from the reactions between atmospheric acids and SO3 have a catalytic effect on the formation of new particles in aerosols. However, the SO3 + HCl reaction in the gas-phase and at the air-water interface has not been considered. Herein, this reaction was explored exhaustively by using high-level quantum chemical calculations and Born Oppenheimer molecular dynamics (BOMD) simulations. The quantum calculations show that the gas-phase reaction of SO3 + HCl is highly unlikely to occur under atmospheric conditions with a high energy barrier of 22.6 kcal mol-1. H2O and (H2O)2 play obvious catalytic roles in reducing the energy barrier of the SO3 + HCl reaction by over 18.2 kcal mol-1. The atmospheric lifetimes of SO3 show that the (H2O)2-assisted reaction dominates over the H2O-assisted reaction within the altitude range of 0-5 km, whereas the H2O-assisted reaction is more favorable within an altitude range of 10-50 km. BOMD simulations show that H2O-induced formation of the ClSO3-⋯H3O+ ion pair and HCl-assisted formation of the HSO4-⋯H3O+ ion pair were identified at the air-water interface. These routes followed a stepwise reaction mechanism and proceeded at a picosecond time scale. Interestingly, the formed ClSO3H in the gas phase has a tendency to aggregate with sulfuric acids, ammonias, and water molecules to form stable clusters within 40 ns simulation time, while the interfacial ClSO3- and H3O+ can attract H2SO4, NH3, and HNO3 for particle formation from the gas phase to the water surface. Thus, this work will not only help in understanding the SO3 + HCl reaction driven by water molecules in the gas-phase and at the air-water interface, but it will also provide some potential routes of aerosol formation from the reaction between SO3 and inorganic acids.

Atmospheric chemistry of methoxyflurane: Reaction with Cl atoms and further degradation

AbstractA dual‐level direct dynamics technique is used to explore the kinetic properties of the reaction of Cl atoms with methoxyflurane (CH3OCF2CHCl2). The energy profiles of two reaction channels of the two conformers are refined with the interpolated single‐point energies (ISPE) method at the CCSD(T)/M06‐2X level. The canonical variational transition state theory (CVT) with a small‐curvature tunneling (SCT) correction is used to assess the rate coefficients over a wide temperature range (250–500 K) in order to get accurate results. At a temperature of 296 K, the calculated CVT/SCT rate coefficient kCl = 2.71 × 10−13 cm3 molecule−1 s−1 is found to be in reasonably good agreement with the experimental result. Our calculations demonstrate that CH3OCF2CHCl2 + Cl → CH2OCF2CHCl2 + HCl (R1) reaction is the key pathway and a prominent conduit for CH3OCF2CHCl2 degradation in the troposphere. The atmospheric loss of C•H2OCF2CHCl2 and CH3OCF2C•Cl2 radicals are discussed. The rate coefficient value of the oxidation of the primary product HC(O)OCF2CHCl2 with the Cl atoms is 1.8 × 10−14 cm3 molecule−1 s−1, and for the first time, the rate coefficient of HC(O)OCF2CHCl2 + OH reaction has also been reported here.

Dynamical and Mechanical Insights into the Li(2 S)+ HCl( ) Reaction: A Detailed Quantum Wavepacket Study.

Quantum wave packet dynamics of the Li(2 S)+HCl( ) reaction in its electronic ground state is studied. The initial state-selected and energy-resolved dynamical attributes such as reaction probability, integral cross section, and thermal rate constant for the Cl-abstraction and H-abstraction pathways are reported. All partial wave contributions of J up to 120 were found to be necessary for the title reaction up to the collision energy of ∼1.0 eV. The dynamical results reveal that the Cl-abstraction is more favored over the H-abstraction for the different rovibrational (v, j) excitations. Due to the existence of an early barrier in the potential energy surface, the cross sections increase with increasing collision energy. The rate constants also monotonously increase with temperature for both channels. Resonances are identified and characterized in terms of eigenfunctions and lifetimes. Nearly 120 well-resolved eigenstates are reported for the LiHCl complex, and they are categorized as van der Waals (vdW), barrier and product states according to the nodal progressions along (R, r, γ). The vdW resonances reveal a local-mode behavior of quasibound type at low energies and extended progressions at high energies. Further, the single-quantized periodic orbit type is also observed in the barrier region, which decays very fast. Finally, the lifetime analysis reveals that the vdW resonances can survive as long as ∼2.2 ps, which is much longer than the lifetime of the resonances in the barrier region.

Hierarchically Porous Graphene Aerogels with Abundant Oxygenated Groups for High-Energy-Density Surpercapacitors

A hierarchically porous graphene aerogel (HP-GA) with abundant oxygenated groups and hand-tearing bread-like macromorphology is achieved by a sacrificial MnO2 template approach. Oxygenated groups on graphene sheets improve the wettability of HP-GA to an aqueous electrolyte and contribute to pseudocapacitance. The chlorine (Cl2) gas as a result of the reaction of MnO2 and HCl is responsible for the formation of the hierarchically porous microstructure and hand-tearing bread-like macromorphology, ensuring a large electrolyte accessible surface area within the electrodes. When used as the active electrode material in supercapacitors, HP-GA exhibits a large specific capacitance of 284 F g–1 at 1 A g–1 and ultrahigh energy density of 10 Wh kg–1 at 250 W kg–1 in an aqueous electrolyte. This work provides a versitile, simple, and easy to control way to alter the microstructure and macromorphology of graphene-based areogels that have promising applications in many areas, including adsorption, energy storage, heat insulation, acoustical insulation, and intelligent sensing system.

Adsorption of Co(II) from simulated low acid leaching solution of spent lithium-ion batteries by AG®50W-X4 resin

ABSTRACT To find a novel resin to remove Co(II), the adsorption behaviour of Co(II) from the simulated acid leaching solution was investigated by ion exchange with AG®50W-X4 resin. Parameters such as reaction time, HCl concentration, and resin concentration affected the loading efficiency of Co(II) by AG®50W-X4 resin were tested. The adsorption behaviour of Co(II) strongly depended on HCl and resin concentration while reaction time was little effect on the loading percentage of Co. The loading behaviour of Co(II) into the resin fitted well with the Langmuir adsorption isotherm and the loading capacity for Co(II) was found at 29.8 mg/g. Moderate HCl solution was effective in eluting Co(II) from the loaded AG®50W-X4 resin. The obtained results investigated that AG®50W-X4 resin was a promising resin to absorb Co(II) from the low acid leaching solution of the spent lithium-ion mobile phone batteries.

A kinetic study on mercury oxidation by HCl over typical Mn-based SCR catalysts

A kinetic approach was adopted to analyze the reaction mechanism of elemental mercury (Hg0) oxidation by HCl over three Mn-based low-temperature SCR catalysts, MnOx/TiO2, Fe-MnOx/TiO2 and CeMnO3. Experimental results validated that Hg0 oxidation efficiencies of the catalysts were promoted by HCl at different temperatures. The kinetic models for the heterogeneous Hg0 oxidation were established and verified based on the experimental data. The verification results demonstrated that Hg0 oxidation over the Mn-based catalysts follows Langmuir-Hinshelwood mechanism. The kinetic parameters of reaction rate constant and HCl adsorptionconstant were calculated from the model fitting equations. The reaction rate constant was raised with the increase of temperature, while the HCl adsorptionconstant presented the opposite trend. The Mn-based catalysts with the reaction rate constant of 84.17–335.77 s−1 showed the advantage over some other catalysts such as commercial V2O5-(WO3)/TiO2 and CeO2/TiO2. The kinetic parameters were further improved in the presence of O2. The apparent activation energy for Hg0 oxidation over the catalysts that was derived from the kinetic parameters was 4.13–12.53 kJ/mol, which was much lower than that of the other approaches. The advantageous kinetic parameters and apparent activation energy were favorable for the Mn-based catalysts to act as low-temperature SCR catalyst for synergistic Hg0 removal. The kinetic study results were of fundamental significance for designing the reactor according to the known flue gas conditions, used catalyst and required Hg0 oxidation efficiency.

Photodecomposition of Urea in the Presence of Titanium Dioxide

Urea is used as a fertilizer, food supplement, and also as raw ingredient for the production of polymers and pharmaceuticals. If urea is not adequately processed, it can accumulate in the environment and pollute groundwater and surface water. Although urea is biodegradable, it has negative impacts on aquatic creatures in the long run. It courses eutrophication and algal blooms in waters. Therefore, as a feasible solution, the development of efficient photocatalysts for the breakdown of urea is essential. In this study, titanium dioxide (Merck 21 nm anatase) was used as a catalyst by applying a thin layer of TiO2 onto glass sheets (1 cm×1 cm), the active surface. Such coated glass sheets were placed in prepared 400 nm urea solution exposed to UV light for 120 minutes. The concentration of urea was detected 15 minutes time intervals for the kinetic analysis. Urea concentration with the UV exposure time was determined by the spectrophotometric method. This approach determines the amount of water soluble urea in the medium via fast, accurate, and low-cost manner. The urea was determined based on its ability to inhibit the reaction between bromate ion with HCl reaction. The reaction was monitored spectrophotometrically at 505 nm by decolorization of methyl orange dye with bromine and chlorine produced by the reaction products. Results indicate that urea decomposition in UV irradiated solutions were faster than in the dark under the same conditions. Approx. 22 wt.% of urea was degraded within 120 minutes of UV irradiation when compared to 3.9 wt.% decomposition with the dark condition experiment. In addition, titanium dioxide plated glass sheets proved to be stable in repeated urea degradation cycles.
 Keywords: Photocatalysis, Urea degradation, Titanium dioxide