The present work establishes an analytical model for computing the temperature distribution, fin efficiency and optimum design parameters of a constructal T-shaped porous fin operating in fully wet condition. For more practical results, this study considers a cubic polynomial relationship between the humidity ratio of saturated air and the corresponding fin surface temperature. The temperature distribution has been determined by solving the highly non-linear governing equations using a semi-analytical transformation technique called Differential Transform Method. A comparison of the results with that of a numerical model shows that this transformation method is a very efficient and convenient tool for solution of non-linear problems. The effects of various geometric, thermo-physical and psychometric parameters on the temperature distribution, fin efficiency and optimum design condition have been investigated. Also, a comparison has been presented between solid and porous fins and the results point out that by selecting an appropriate value of porosity, the heat transfer rate can be increased than the corresponding solid fin.

In this article, we have considered the simultaneous influence of ohmic heating and chemical reaction on heat and mass transfer over a stretching sheet. The effects of applied magnetic field are also taken into consideration while the induced magnetic field is not considered due to very small magnetics Reynolds number. The governing flow problem comprises of momentum, continuity, thermal energy and concentration equation which are transformed into highly nonlinear coupled ordinary differential equations by means of similarity transforms, which are then, solved numerically with the help of Successive Linearization method (SLM) and Chebyshev Spectral collocation method. Numerical values of skin friction coefficient, local Nusselt number, and Sherwood number are also taken into account with the help of tables. The physical influence of the involved parameters of flow velocity, temperature and concentration distribution is discussed and demonstrated graphically. The numerical comparison is also presented with the existing published results and found that the present results are in excellent agreement which also confirms the validity of the present methodology.

This paper describes the application of ultrasound waves on hydrodynamics and mass transfer characteristics in the gas-liquid flow in a T-shape microreactor with a diameter of 800 μm. A 1.7 MHz piezoelectric transducer (PZT) was employed to induce the vibration in this microreactor. Liquid side volumetric mass transfer coefficients were measured by physical and chemical methods of CO₂ absorption into water and NaOH solution. The approach of absorption of CO₂ into a 1 mol·L^-1 NaOH solution was used for analysis of interfacial areas. With the help of a photography system, the fluid flow patterns inside the microreactor were analyzed. The effects of superficial liquid velocity, initial concentration of NaOH, superficial CO₂ gas velocity and length of microreactor on the mass transfer rate were investigated. The comparison between sonicated and plain microreactors (microreactor with and without ultrasound) shows that the ultrasound wave irradiation has a significant effect on k_La and interfacial area at various operational conditions. For the microreactor length of 12 cm, ultrasound waves improved k_La and interfacial area about 21% and 22%, respectively. From this study, it can be concluded that ultrasound wave irradiation in microreactor has a great effect on the mass transfer rate. This study suggests a new enhancement technique to establish high interfacial area and k_La in microreactors.

A three-dimensional (3D) fast fluidized bed with the riser of 3.0 m in height and 0.1 m in inner diameter was established to experimentally study the cluster behaviors of Geldart B particles. Five kinds of quartz sand particles (d_p=0.100, 0.139, 0.177, 0.250 and 0.375 mm and ρ_p=2480 kg·m^-3) were respectively investigated, with the total mass of the bed material kept as 10 kg. The superficial gas velocity in the riser ranges from 2.486 to 5.594 m·s^-1 and the solid mass flux alters from 30 to 70 kg·(m^-2·s)^-1. Cluster characteristics and evolutionary processes in the different positions of the riser were captured by the cluster visualization systems and analyzed by the self-developed binary image processing. The results found four typical cluster structures in the riser, i.e., the macro stripe-shaped cluster, saddle-shaped cluster, U-shaped cluster and the micro cluster. The increasing superficial gas velocity and particle sizes result in the increasing average cluster size and the decreasing cluster time fraction, while the solid mass flux in the riser have the reverse influences on the cluster size and time fraction. Additionally, clusters in the upper region of the riser often have the larger size and time fraction than that in the lower region. All these effects of operating conditions on clusters become less obvious when particle size is less than 0.100 mm.

Polymer-supported hydrous iron oxides (HFOs) are promising for heavy metals removal from aqueous systems. The ubiquitous inorganic ligands, e.g., sulfate, are expected to exert considerable impacts on pollutants removal by these hybrid sorbents. Herein, we obtained a hybrid sorbent HFO-PS by encapsulating nanosized HFO into macroporous polystyrene (PS) resin. Both batch and column sorption experiments of Cu(Ⅱ) by HFO-PS were carried out in the presence of sulfate. Obviously, the presence of sulfate is favorable for Cu(Ⅱ) sorption onto HFO-PS. The performances of column Cu(Ⅱ) removal were fitted and predicted with Adams-Bohart, Clark, Thomas and BDST models. Thomas model is suggested best-fit to predict the breakthrough curves. Besides, a linear correlation is observed between breakthrough time and column length based on BDST model, which might be useful for predicting the breakthrough time for Cu(Ⅱ) removal by HFO-PS.

The presence of Hg in the aqueous media is known to cause severe health issues in both humans and animals. Many technologies and especially adsorbents have been applied for its removal. In this study, a graphene oxide-carbon composite (GO-CC) as a new adsorbent was prepared by sol gel procedure and characterized using field emission scanning electron microscopy, BET and EDX. The effects of different variables including solution pH, contact time, adsorbent dose and GO ratio in adsorbent matrix on the removal capacity of Hg were studied. The isotherm data correlated well with the Langmuir isotherm model. Further analysis recommended that the Hg²⁺ adsorption process is governed by the intra-particle and external mass transfer, in which the film diffusion was the rate restrictive step. The presented composite has maximum absorption capacity, q_max of 68.8 mg·g^-1, which is comparable with carbon based adsorbent reported in the previous publications.

Bipolar membrane electrodialysis (BMED) has already been described for the preparation of quaternary ammonium hydroxide. However, compared to quaternary ammonium hydroxide, di-quaternary ammonium hydroxide has raised great interest due to its high thermal stability and good oriented performance. In order to synthesize N,N-hexamethylenebis(trimethyl ammonium hydroxide) (HM(OH)₂) by EDBM, experiments designed by response surface methodology were carried out on the basis of single-factor experiments. The factors include current density, feed concentration and flow ratio of each compartment (feed compartment:base compartment:acid compartment:buffer compartment). The relationship between current efficiency and the above-mentioned three factors was quantitatively described by a multivariate regression model. According to the results, the feed concentration was the most significant factor and the optimum conditions were as follows:the current efficiency was up to 76.2% (the hydroxide conversion was over 98.6%), with a current density of 13.15 mA·cm^-2, a feed concentration of 0.27 mol·L^-1 and a flow ratio of 20 L·h^-1:26 L·h^-1:20 L·h^-1:20 L·h^-1 for feed compartment, base compartment, acid compartment, and intermediate compartment, respectively. This study demonstrates the optimized parameters of manufacturing HM(OH)₂ by direct splitting its halide for industrial application.

A large number of surplus glycerol from the biodiesel production can be used as renewable feedstock to produce glycerol carbonate. In this paper, a series of guanidine-based ionic liquids were synthesized to catalyze the transesterification of glycerol and dimethyl carbonate. The tunable basicity and the anion-cation cooperative effect were responsible for the obtained results. The[TMG] [TFE] showed the best activity turnover frequency (TOF) of 1754.0 h^-1, glycerol (GL) conversion of 91.8%, glycerol carbonate (GC) selectivity of 95.5%) at 80℃ with 0.1 mol% catalyst for 30 min. The reaction mechanism of the transesterification was also proposed.

The acidity and acid distribution of hierarchical porous ZSM-5 were tailored via phosphate modification. The catalytic results showed that both benzene conversion and selectivity of toluene and xylene increased with the presence of appropriate amount of phosphorus. Meanwhile, side reactions such as methanol to olefins related with the formation of by-product ethylbenzene formation and isomerization of xylene to meta-xylene were suppressed efficiently. The acid strength and sites amount of Brönsted acid of the catalyst were crucial for improving benzene conversion and yield of xylene, whereas passivation of external surface acid sites played an important role in breaking thermodynamic equilibrium distribution of xylene isomers.

The alkylation of benzene with isopropanol over beta-zeolite is a more cost-effective solution to cumene production. During the benzene alkylation cycles, the cumene selectivity slowly increased, while the benzene conversion presented the sharp decrease due to catalyst deactivation. The deactivation mechanism of betazeolite catalyst was investigated by characterizing the fresh and used catalysts. The XRD, SEM and TEM results show that the crystalline and particle size of the beta-zeolite catalyst almost remained stable during the alkylation cycles. The drop in catalytic activity and benzene conversion could be explained by the TG, BET, NH₃-TPD and GC-MS results. The organic matters mainly consisted of ethylbenzene, p-xylene and 1-ethyl-3-(1-methyl) benzene produced in the benzene alkylation deposited in the catalyst, which strongly reduced the specific surface area of beta-zeolite catalyst. Moreover, during the reaction cycles, the amount of acidity also significantly decreased. As a result, the catalyst deactivation occurred. To maintain the catalytic performance, the catalyst regeneration was carried out by using ethanol rinse and calcination. The deactivated catalyst could be effectively regenerated by the calcination method and the good catalytic performance was obtained.

Metallic bismuth crystal is one important and interesting semimetal that has attracted great attention owing to its unique thermal and electrical properties. Herein, we report a facile, green, cost-effective and sustainable solvothermal process using ethanol, glycol, isopropanol, phenylcarbinol as solvent and commercial Bi₂O₃ as the starting material to produce high-purity metallic Bi with tunable morphologies on large scale. It is found that all alcohols are capable of reducing Bi₂O₃ to Bi and the reducibility of glycol is proved to be the strongest. The highest purity of the resultant Bi is calculated to be 99.74%. What's more, the morphology of final Bi particles is controllable by adding various types and concentrations of additives. As a consequence, our work lays the root for the large scale solvothermal production of high-purity Bi particles with various regular morphologies.

The solid acid SO₄^2-/TiO₂ was prepared by immersion method and applied for synthesis of propylene glycol methyl ether acetate (PMA) through esterification reaction of propylene glycol monomethyl ether (PM) and acetic acid (HAc). The optimal catalyst preparation condition was determined by orthogonal analysis of parameters in a five-factor and four-level test. The obtained solid acid catalysts were characterized in detail by means of X-ray powder diffraction, thermogravimetry, pyridine adsorbed IR analysis, scanning electron microscopy, and BET surface area method. Synthesis of PMA was studied in this paper through experimental investigation of reaction conditions such as temperature, molar ratio of reactants, catalyst dosage and agitation speed. Based on its possible reaction mechanism, a pseudo-homogeneous kinetic model was established and its activation energies E_a⁺ and E_a^-, 65.68×10³ J·mol^-1 and 57.78×10³ J·mol^-1, were estimated. To prepare shaped solid acid catalyst SO₄^2-/TiO₂, the shaping method of impregnation-shaping-impregnation was applied. The optimal molding formulation of solid acid catalyst, obtained from the orthogonal test, was found to be binder 7 wt%, reinforcing agent 20 wt%, pore forming material 2.5 wt%, and lubricant 4 wt%. The results of performance test of catalyst demonstrated that the shaped solid acid catalyst exhibited high activity and stability.

Mercuric chloride supported on activated carbon (HgCl₂/AC) is used as an industrial catalyst for the hydrochlorination of acetylene. Loss of HgCl₂ by sublimating from the surface of activated carbon causes the irreversible deactivation of mercury catalyst and environmental pollution. In this work, a ligand coordination approach based on the Principle of Hard and Soft Acids and Bases (HSAB) was employed to design more stable lowmercury catalyst. The low-mercury catalysts (4% HgCl₂ loading) were prepared by using HgCl₂ and potassium halides (KX, X=Cl, I) as precursors. The HgCl₂-4KI/AC catalyst showed best catalytic stability than HgCl₂/AC and HgCl₂-4KCl/AC in the hydrochloriantion of acetylene. HgCl₂ could form more stable complex with KI, K₂HgI₄ as the main active component of the HgCl₂-4KI/AC catalyst. The characterizations of XRD and EDX analysis illustrated that the active component of HgCl₂-4KI/AC was highly dispersed on the surface of activated carbon. The sublimation rates of HgCl₂ from the catalysts verified that the active component with larger stability constant had better thermal stability. Using Hg(Ⅱ) complexes with high stability constant as the active component may be the research direction of developing highly stable low-mercury catalyst for the hydrochlorination of acetylene.

The transesterification of palm oil and methanol catalyzed by Brønsted acidic ionic liquids was investigated. Four eco-friendly Brønsted acidic ionic liquids were prepared and their structures were characterized by NMR, FT-IR and TG-DTG. The results demonstrated that[CyN_1,1 PrSO₃H] [p-TSA] was more efficient than the other ionic liquids and chosen as catalyst for further research. The influences of various reaction parameters on the conversion of palm oil to biodiesel were performed, and the orthogonal test was investigated to seek the optimum reaction conditions, which were illustrated as follows:methanol to oil mole ratio of 24:1, catalyst dosage of 3.0 wt% of oil, reaction temperature of 120℃, reaction time of 150 min, and the biodiesel yield achieved 98.4%. In addition, kinetic study was established for the conversion process, with activation energy and preexponential factor of 122.93 kJ·mol^-1 and 1.83×10¹⁵, respectively. Meanwhile, seven-time recycling runs of ionic liquid were completed with ignorable loss of its catalyst activity. The refined biodiesel met the biodiesel standard EN 14214.

Feasibility analysis of soft constraints for input and output variables is critical for model predictive control (MPC). When encountering the infeasible situation, some way should be found to adjust the constraints to guarantee that the optimal control law exists. For MPC integrated with soft sensor, considering the soft constraints for critical variables additionally makes it more complicated and difficult for feasibility analysis and constraint adjustment. Therefore, the main contributions are that a linear programming approach is proposed for feasibility analysis, and the corresponding constraint adjustment method and procedure are given as well. The feasibility analysis gives considerations to the manipulated, secondary and critical variables, and the increment of manipulated variables as well. The feasibility analysis and the constraint adjustment are conducted in the entire control process and guarantee the existence of optimal control. In final, a simulation case confirms the contributions in this paper.

Hydrates always are considered as a threat to petroleum industry due to the operational problems it can cause. These problems could result in reducing production performance or even production stoppage for a long time. In this paper, we were intended to develop a LSSVM algorithm for prognosticating hydrate formation temperature (HFT) in a wide range of natural gas mixtures. A total number of 279 experimental data points were extracted from open literature to develop the LSSVM. The input parameters were chosen based on the hydrate structure that each gas species form. The modeling resulted in a robust algorithm with the squared correlation coefficients (R²) of 0.9918. Aside from the excellent statistical parameters of the model, comparing proposed LSSVM with some of conventional correlations showed its supremacy, particularly in the case of sour gases with high H₂S concentrations, where the model surpasses all correlations and existing thermodynamic models. For detection of the probable doubtful experimental data, and applicability of the model, the Leverage statistical approach was performed on the data sets. This algorithm showed that the proposed LSSVM model is statistically valid for HFT prediction and almost all the data points are in the applicability domain of the model.

The work presents density (ρ) and viscosity (η) data of binary system polyethylene glycol 600 (PEG) + dimethyl sulfoxide (DMSO) over the entire concentration range at T=(298.15, 303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. On the basis of density and viscosity values, the excess properties of PEG (1) + DMSO (2) mixtures, including excess molar volume (V_m^E), viscosity deviation (△η), excess free energies of activation (△G^*E), and isobaric thermal expansion coefficient (α_p), were calculated. At the same time, in order to conjecture the density viscosity under different conditions, the density and viscosity data were fitted with the corresponding formula. The calculated results of V_m^E, △η, and △G^*E were fitted with the Redlich-Kister equation to derive coefficients and estimate the standard deviations (σ) between the experimental and calculated values. Moreover, the intermolecular interaction of PEG with DMSO was discussed on the basis of FTIR and UV-Vis spectral results of PEG (1) + DMSO (2) mixtures. The results indicated that there were the hydrogen bonding and interactions of hydroxyl hydrogen atoms in PEG with oxygen atoms in DMSO.

The protection influence of 8-hydroxy-7-quinolinecarboxaldehyde derivatives against C-steel corrosion was studied in 2 mol·L^-1 HCl solutions at 30℃. Measurements were conducted under various experimental conditions using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. These studies have shown that 8-hydroxy-7-quinolinecarboxaldehyde derivatives are very good "green", mixed-type inhibitors. Corrosion rates obtained from both EFM and EIS methods are comparable with those recorded using Tafel extrapolation method, confirming validation of corrosion rates measured by the latter. The inhibitive action of these 8-hydroxy-7-quinolinecarboxaldehyde derivatives was discussed in terms of blocking the electrode surface by adsorption of the molecules through the active centers contained in their structures following Langmuir adsorption isotherm. Quantum chemical method was also employed to explore the relationship between the inhibitor molecular properties and its protection efficiency.

In the present study, new series of pyridinium carboxylate protic ionic liquids (PILs) were synthesized by pairing pyridinium cation with carboxylate anion from C₁-C₃ forming pyridinium formate ([C₅H₆N⁺] [HCOO^-]), pyridinium acetate ([C₅H₆N⁺] [CH₃COO^-]) and pyridinium propionate ([C₅H₆N⁺] [CH₃CH₂COO^-]) respectively. The physical properties namely, density, viscosity, surface tension (298.15-343.15) K, and refractive index (293.15-323.15) K were measured. Thermal properties namely, glass transition temperature, molar heat capacity, and thermal decomposition temperatures were also determined. The thermal expansivity was calculated using the experimental density data. The effect of increasing the alkyl chain length on the thermophysical properties of the pyridinium carboxylate PILs has been evaluated. As expected the physical properties i.e. density, viscosity, surface tension and refractive index of the investigated pyridinium carboxylates decreased with increasing temperature. In general pyridinium carboxylate PILs possessed low viscosity, high thermal stability and excellent hydrogen bonding capability, and these properties lead them to outperform conventional solvents employed for lignin dissolution.

In this work, some thermodynamic properties of nanofluids such as Sb₂O₅; SnO₂/(EG + H₂O), ZnO/(EG + H₂O), Al₂O₃/(EG + H₂O), ZnO/(PEG + H₂O), ZnO/PEG, and TiO₂/EG were estimated from the extended Tao-Mason equation of state, together with the Pak and Cho equation in various temperature, pressure, and volume fractions. The equations of state using minimum input data and density at room temperature as scaling constants, were developed to estimated densities of the above mentioned nanofluids. Furthermore, the artificial neural network plus principal component analysis (PCA) technique (with 20 neuron in hidden layer) was performed over the whole range of available conditions. The AADs of the calculated molar densities of all nanofluids using the EOS and ANN at various temperatures and volume fractions are 1.11% and 0.48%, respectively. In addition, the heat capacity and isentropic compressibility of the above mentioned nanofluids are predicted using obtained densities of EOS with the Pak and Cho equation.

Removal of dye from the industrial wastewater is one of the most important subjects in water pollution regulation. Successive adsorption/desorption cycles of a basic dye, methylene blue, on the internal almond shell, sheep manure waste and sawdust were investigated using fixed bed column experiments in order to study the adsorption capacity to remove MB and adsorbent regeneration efficiency. The adsorption breakthrough curves were predicted by the Thomas model, Yoon Nelson model, and Wolborska model and modified dose-response model using non-linear regression analysis. The results showed that the modified dose-response model was more suitable for the description of breakthrough curves for three adsorbents only in the first cycle. Although sheep manure waste presents the highest adsorption capacity, it is hard to regenerate and needs more time regeneration. Conversely, the internal almond shell presents lower adsorption capacity, but they are more readily regenerated.

Freezing processes of several liquids under static magnetic field (SMF) less than 50 mT were investigated. Central temperature of liquid samples held in glass test tubes immersed in a liquid bath was measured and collected. Nucleation temperature and phase transition time were obtained from freezing curves. Normality tests were performed for nucleation temperature of these liquids with/without magnetic field and normality distributions were justified. Analysis of variances was carried out for nucleation temperature of these liquids with magnetic field flux density as the influencing factor. Results showed that no significant difference was found for deionized water with or without SMF. However, differences exist in 0.9% NaCl solution and 5% ethylene glycol solution with and without SMF. Nucleation temperature of 0.9% NaCl with SMF is lower than that without SMF, while its phase transition time is shorter than that without SMF. Nucleation temperature of 5% ethylene glycol with SMF is higher than that without SMF, while its phase transition time is not modified with SMF.

Herein a novel aminopropyl-containing ionic liquid based organosilica (ILOS-NH₂) is prepared, characterized and applied as effective adsorbent for removal of crystal violet (CV) dye from wastewater. The ILOS-NH₂ material was synthesized by hydrolysis and co-condensation of 1,3-bis-(3-trimethoxysilylpropyl)-imidazolium chloride (BTMSPIC) under acidic conditions followed by treatment with 3-aminopropyl-trimethoxysilane in toluene under reflux conditions. This material was characterized using scanning electron microscopy (SEM), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), thermal gravimetric analysis (TGA) and energy dispersive X-ray analysis (EDAX). The material was effectively used in the removal of crystal violet at ambient temperature and showed high capacity and stability under applied conditions. The efficacy of pH, contact time, adsorbent dose, initial dye concentration, temperature, and isotherm studies and the applicability of pseudo-first, second order and Elovich kinetic models have also been investigated.

A new effective process to improve the utilization of industrial fluorosilicic acid of phosphate fertilizer by-product has been investigated to comprehensive application of the silicon and fluorine source. Two-step ammoniation was applied to recover high-quality silica. The recovered silica can be used to hydrothermal synthesize ZSM-5 zeolite without impurity phase contamination, which was confirmed by XRD, TG, SEM, BET and EDS characteristic techniques. It was found that with the increase of SiO₂/Al₂O₃ ratio and the extension of reaction time, the crystal type transform from the orthorhombic to the monoclinic phase. The impurity fluorine content of the recovered SiO₂ from H₂SiF₆ has great influence on the hydrothermal process for ZSM-5 crystal structure formation. Moreover, the increase of fluorine ions content in the hydrothermal process can control the crystal morphology and size of synthesized ZSM-5. Catalytic properties of synthesized HZSM-5 with different SiO₂/Al₂O₃ ratio in transalkylation of toluene and 1,2,4-trimethylbenzene show good and stable catalytic performance. The ZSM-5 synthesized with recovered silica source exhibits similar catalyst life as the performance of small particle size HZSM-5, because the ZSM-5 synthesized with the silica source from industrial hexafluorosilicic acid prefers a thin disk crystal along the b axis direction, which shortens the diffusion distance of generated products.

The aim of this paper is to analyze the change in the active structure of lignite during the process of lowtemperature oxidation by constructing a molecular structure model for lignite. Using quantum computation combined with experimental results of proximate analysis, ultimate analysis, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), a structural model for the large molecular structure was constructed. By analyzing the bond lengths in the model molecule, the evolution law for the active structure of lignite was predicted for the process of low-temperature oxidation. In low-temperature oxidation, alkanes and hydroxyls are the primary active structures observed in lignite, though ether may also react. These active functional groups react with oxygen to release heat, thereby speeding up the reaction between coal and oxygen. Finally, the content of various functional groups in the process of lignite low-temperature oxidation was analyzed by infrared analysis, and the accuracy of the model was verified.

A novel halogen-free phosphorus-nitrogen-silicon flame retardant monomer with reactive siloxy groups, N-(diphenylphosphino)-1,1-diphenyl-N-(3-(triethoxysilyl)propyl) phosphinamine (DPTA) has been synthesized and was applied to the fire-resistant finishing of cotton fabrics. The molecular structure of DPTA has been well characterized by elemental analysis, FTIR, ¹H NMR, and ³¹P NMR spectroscopies. The chemically-grafted cotton fabrics, which were treated with 25 wt% DPTA, were obtained and confirmed by attenuated total reflectance Fourier infrared spectroscopy (ATR-FTIR). The flame retardancy and thermal property of the treated samples were investigated by limited oxygen index (LOI), vertical flammability test (VFT), thermogravimetric analysis (TGA) and microscale combustion calorimeter (MCC). It is noted that in vertical flammability test, the treated samples extinguished immediately upon removing the ignition source, whereas the untreated one was completely burned out. Furthermore, TGA and MCC tests revealed that the treated samples produced a high char formation and a low heated release during combustion. The surface morphology of the untreated and treated samples and the char residues after LOI tests were observed by scanning electron microscopy (SEM). Therefore, all the results showed that the treated cotton fabrics with 25 wt% DPTA apparently improved the fireresistant and thermal performances.

In this work MgO/Al₂O₃ nanocomposites with weight ratios from 5% to 25% were synthesized by precipitationimpregnation method and their structural properties were characterized. In the next step, the capability of the nanocomposites in H₂S removal compared to Mg-Al spinel (MgAl₂O₄), synthesized through ion-pair complex precursor route and alumina samples, prepared via sol-gel precipitation methods, was investigated. The results indicated that among the studied sorbents Mg-Al spinel presents a distinctly higher H₂S removal. In addition, the MgO/Al₂O₃ nanocomposites compared to the alumina sorbents, exhibited much better performance in H₂S removal. Also CO₂-TPD analysis reveals higher amounts of basic sites for Mg-Al spinel compared to 25 wt% MgO/75 wt% Al₂O₃ nanocomposite.

Simulating the typical carbonation step in a mineral CO₂ sequestration, precipitated calcium carbonate (PCC) was prepared by bubbling CO₂ gas into a rich Ca solution. These carbonation reactions were conducted at three pH ranges, namely 10.0-9.0, 9.0-8.0, and 8.0-7.0, in which temperature and CO₂ flow rate are additional experimental variables. The PCC obtained in experiments was examined by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). It was found that supersaturation determined by pH value and flow rate of CO₂ has significant influence on polymorph of PCC. Vaterite was preferably formed at high supersaturation, while dissolution of metastable vaterite and crystallization of calcite occurred at low supersaturation. High temperature is a critical factor for the formation of aragonite. At 70℃, vaterite, calcite and aragonite were observed to coexist in PCC because transformation from vaterite to aragonite via calcite occurred at this temperature. Scanning electron microscopy (SEM) technology was performed on prepared PCC, and various morphologies consistent with polymorphs were observed.