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Series: De Gruyter STEM
Series: De Gruyter STEM
Case Studies with Solved Examples
Series: De Gruyter STEM

Abstract

The oxidative coupling of methane (OCM) is a potential option for conversion of excess natural gas to higher value products or useful feedstocks. The preferred or ideal OCM stoichiometry is: 2CH4 + O2 → C2H4 + 2H2O, but real OCM produces a variety of species. Using a detailed mechanism from the literature for OCM over a La2O3/CeO2 catalyst that combines coupled elementary gas phase and surface reactions, a reactor engineering study has been done. Adiabatic packed bed reactor (PBR, modeled as plug flow) and continuous stirred tank reactor (CSTR, perfect mixing) simulations using this mechanism are presented. Each reactor simulation used the same total number of catalyst sites. Process variables included CH4/O2 feed ratio (7, 11), feed temperature (843–1243 K), and feed rate. All runs were conducted at 1.01E5 Pa pressure. The results show the CSTR produces high conversions at much lower feed temperatures than those required by the PBR. Once full PBR “light off” occurs, however, its CH4 conversions exceed CSTR. The simulations reveal OCM over this catalyst at these conditions gives a mixture of synthesis gas (CO, H2) and C2Hx (primarily C2H4 plus small quantities of C2H6 and C2H2). The CSTR favors the production of synthesis gas, while the PBR favors C2Hx. Within the suite of CSTR cases, C2Hx is favored at the lowest feed temperature and highest CH4/O2 feed ratio.

Abstract

White-light emitting lanthanide(iii) metal-organic coordination polymers (LMOCPs) were prepared via a green synthesis method performed in pure aqueous solution at room temperature without using toxic solvent and reagents. This kind of LMOCP, denoted as adenosine monophosphate (AMP)/Ln-CIP, was composed of Ln3+ {Ln = Tb (1), Eu (2), and Gd (3)}, hydrosoluble biomolecule of AMP, and nonpoisonous antenna ligand of CIP (ciprofloxacin). The complex of Tb(1), Eu(2), and Gd(3) in AMP/Ln-CIP emits strong green, red, and blue light, respectively. With careful adjustment of the doping mole ratio of the three lanthanide ions {Ln = Tb:Eu:Gd = 0.1:0.9:99.0} in one framework, white light-emission can indeed be achieved. AMP/Ln-CIP is network-structural and amorphous by transmission electron microscope and X-ray diffraction analysis. The fluorescence lifetime and quantum yield of AMP/Ln-CIP are 4.36 ms and 36.5%, respectively.

Abstract

The separation and recovery of copper and indium from a solution arising from the reductive leaching of a zinc leaching residue was studied. Copper was enriched into a copper precipitate produced by iron powder precipitation; indium was hydrolyzed and enriched into a gypsum indium precipitate produced by limestone adjustment of pH. Separation and recovery of both copper and indium were achieved. The results showed that precipitation of copper(II) and arsenic(III) as Cu2O and Cu3As is thermodynamically feasible by adding iron powder to the reductive leach of a zinc leaching residue. Increasing the iron powder addition and reaction temperature promoted the formation of Cu2O and Cu3As. In the process of neutralizing and precipitating indium by adjusting the pH using limestone, indium was mainly concentrated in the precipitate by hydrolytic precipitation. The pH of the neutralization endpoint plays a decisive role in this hydrolytic enrichment. The extent of indium precipitation exceeded 98%, and the indium content of the precipitate reached 3.6 kg/t. Addition of limestone balances the acid across the entire production process. The main phase in the gypsum indium precipitate was CaSO4·2H2O, the stable properties of which create favorable conditions for the recovery of indium in subsequent steps.

Abstract

The paper industry is an essential but energy-intensive economic sector. This study aims to propose an appropriate inventory method to first determine the GHG emission factor in the life cycle of paper products of Vietnam. The approach overcomes the limitations of the ISO 14067 method by including the environmental burdens from the paper mill’s processes. In 2018, the amount of GHG emitted from cradle to gate when producing a ton of carton box, writing paper, and tissue products (EFCO2eq) was 1,366 kg CO2eq, 1,224 kg CO2eq, and 751 kg CO2eq, respectively. High energy intensity is identified as the main reason that causes high life cycle analysis (LCA) GHG emission factors and virgin paper-based products often emit higher LCA GHG amounts than recycled paper-based products. To reduce the emission, the Vietnamese paper mills should increase the use of recycled paper and replace fossil fuels with environmentally friendly energy resources.

Abstract

Batch and packed bed adsorption of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was performed using bagasse fly ash (BFA) as an adsorbent. In batch process, characteristics of adsorbent, and the influence of adsorbent dosage, initial herbicide concentration, time, pH, particle size of adsorbent and temperature on adsorption were studied. Results disclose higher removal of MCPA on bigger particles of BFA owing to higher specific surface area because of greater carbon and lesser silica percentage in bigger particles. Application of isotherm models in present study indicates the best fitting of Langmuir and Temkin isotherms whereas the kinetic models suggest the suitability of pseudo second order and Elovich models. Thermodynamic study specifies the temperature preferred adsorption process. In packed bed technique, the effect of influent concentration, flow rate and bed height were investigated. The deactivation kinetic model which was previously considered only for studies in gas-solid adsorption is applied in this study to solid-liquid adsorption along with conventional packed bed models. In packed bed study, Bohart-Adams and Wolborska models are appropriate to explain the experimental data upto 60% saturation of the column. The deactivation kinetic model is found the best to elucidate the nature of breakthrough curves till the complete saturation of column. Batch capacity and packed bed capacity per m2 specific surface area of BFA is found about two and three times greater than the previously used adsorbents for MCPA respectively.

Abstract

Fluidization characteristics of wide-size-distribution particles in the gas-solid fluidized bed reactor are investigated by applying experiment and computational fluid dynamics (CFD) methods. In this study, three types of narrow-cut particles and two sets of wide-size-distribution particles are used. A model considering particle size distribution is developed in the Eulerian frame, and good agreement between numerical results and experimental data is observed. The particle size distribution has an important effect on the average bed voidage. The axial particle diameter profiles along bed height have a “S” type feature. Minimum fluidization velocity is determined from the standard deviation of pressure fluctuations and bubble dynamics are analyzed based on power spectra. Results indicate that fine particle composition can reduce the minimum fluidization velocity of wide-size-distribution particle system and the bubble diameter in the fluidized bed.