Band 17, Heft 6 - Special Issue to Honour Professor Gülşen Doğu and Professor Timur Doğu

The acid activation of bentonite from Middle Anatolia, consisting of mostly montmorillonite, with a hot solution of H 2 SO 4 with different concentrations was carried out. SEM images, nitrogen sorption isotherms and FTIR spectra were used to examine structural changes of the bentonite with acid activation. Acid–base titration method was applied to determine surface acidities. SEM images, nitrogen sorption isotherms indicated that the acid activation caused considerable increases both in the surface area and pore volumes by changing the morphology and aluminum content. FTIR spectra showed the enhancement both in Lewis and Brønsted acidities, significant increases in H–bonding to the structure with acid concentration. Acid treatment gave good structural properties with high surface acidity. Stable structured acid activated bentonite with 2 M was tested in catalytic wet peroxide oxidation (CWPO) of phenol together with raw bentonite. Around 96 % phenol removal was achieved in 135 minutes at reaction temperature of 50 °C while the raw bentonite did not show good results. The data were in agreement with the first order dependency with respect to phenol.

This paper investigates the methane adsorption characteristics of activated carbons produced from coal by activation with KOH, NaOH and ZnCl 2 treatments at different agent to coal ratios (1:1–6:1) and temperatures (600–800 °C) under N 2 flow. CH 4 adsorption capacities and desorption behaviors of the activated carbons were examined at 0 °C and 25 °C. The relationship between CH 4 adsorption characteristics and surface properties of activated carbons, such as BET surface area determined by N 2 adsorption at −196 °C, and micropore volume determined by CO 2 adsorption at 0 °C were investigated. Optimal results for CH 4 adsorption at 0 °C and 25 °C were obtained for the activated carbon samples obtained with KOH treatment at 800 °C at 4:1 ratio, as 2.67 and 1.12 mmol/g, respectively. The results have shown that CH 4 adsorption increased proportionally with micropore volume of activated carbons, whereas BET surface area does not exhibit an exact consistency. CH 4 adsorption-desorption isotherms at 25 °C have shown that an increase in mesopore formation caused a decrease in adsorption; but allowed desorption to be reversible. Higher methane adsorption capacities were obtained from activated carbons produced from coal by various treatments in this study than most of the reported results in literature at the similar conditions, indicating the suitability of the evaluated materials for industrial applications of methane storage.

To meet the environmental regulations, volatile organic compounds (VOC) in waste streams of various industries are thermally oxidized before being released to the atmosphere. This thermal oxidation process requires use of additional fuel and energy, has high operational costs and requires frequent maintenance. As an alternative, these VOCs can be considered as fuels themselves. Even without considering the energy used for the supplemental fuel such as natural gas, the enthalpy of the VOCs incinerated is not negligible. Hydrogen, a valuable energy carrier, can be produced from VOCs by reforming them. In this study, a system that can reform VOCs in the exhaust stream of paint finishing operations and use it to produce hydrogen that can be used in a fuel cell for power generation was designed. Steam reforming experiments were conducted on different VOCs using a 10 % Co/CeO 2 catalyst. The effect of different functional groups and the chain length was examined. This study shows the potential of dilute VOCs in the waste stream of many industries if they can be recovered and used as a fuel effectively instead of being incinerated.

Microwave heated reactor which was loaded with carbon fiber supported iron and molybdenum incorporated monometallic catalysts was used to produce COx free hydrogen from ammonia. Impregnation procedure was applied to synthesize the catalysts at different metal loading (4–14 wt % according to ICP-OES) using iron nitrate or ammonium molybdate and reaction tests were carried out under the flow of pure ammonia (GHSV: 36,000 ml/hg cat ). Activities of molybdenum incorporated carbon fiber catalyts are found to be lower than that of the iron loaded ones in the conventional reaction system. The effect of metal loading was clealy seen in the activity of molybdenum incorporated catalyst, unlike iron incorporated catalyts, especially under high reaction temperature conditions. Catalysts showed greatly enhanced activities in microwave heated system in comparison to conventionally heated reactor system. Complete conversion of ammonia was achieved at 500 °C by using molybdenum incorporated catalysts and at 450 °C by using iron incorporated catalysts (with GHSV of 36,000 ml/hg cat ) in microwave heated reactor system. Transfer of energy directly to the active species and formation of carbide species, Fe 2 C or Mo 2 C, during the reaction under microwave application could be considered as the major factors leading to a better ammonia conversion. Structural properties of carbon support materials, such as the surface area, could be effective on the activity of the catalysts via the distribution of active species, however, this would be more pronounced effect in conventional system.

The ethylene hydrogenation reaction was investigated in a kinetic turbo reactor and a one-sided single-pellet reactor. An empirical kinetic expression was fitted to experimental results taken from the turbo reactor, and the gas compositions at the catalyst centers were measured for three different pore structures by means of the single-pellet reactor. A bimodal pore model was developed and applied to the computation of the gas composition profiles inside the three pore structures. The calculated results were compared to the measurements. A distinct influence of the pore structures on the gas fluxes and concentration profiles inside the pores could be detected which demonstrates that the proper choice of the pellet pore structure is of importance for a high conversion.

In this study, mesoporous alumina supported bi-metallic Ni-Co catalysts were synthesized and catalytic performances were investigated in hydrogen production through steam reforming of acetic acid reaction. Mesoporous alumina support was synthesized using a sol-gel method and metals were co-impregnated into the structure of the catalyst. The physicochemical properties of the synthesized materials were characterized by XRD, N 2 adsorption-desorption, SEM and TG-DT analysis. The activity test results showed that the bi-metallic 4Ni-1Co@SGA catalyst showed high and stable activity in steam reforming of acetic acid, giving a high H 2 selectivity at 750 °C. Bi-metallic Ni-Co catalysts showed higher performance than monometallic Co catalyst, yielding less methane production and coke deposition. Co incorporation decreased activity of Ni catalysts at high reaction temperature of 750 °C in terms of AcOH conversion; however, improved the activity of Ni catalysts at low reaction temperature of 550 °C in terms of AcOH conversion and H 2 Selectivity. Mg incorporation enhanced the coke resistance of the catalyst and further, among the bi- and tri-metallic catalysts, the lowest coke deposition was obtained over Mg incorporated 4Ni-1Co@SGA catalyst at 750 °C.

The ground water (GW) is a real sample of water which contains nitrates (81 mg/L), carbonates and sulphates. This sample was treated by catalytic reduction in a bubble column fixed-bed reactor. The reaction conditions were room temperature and atmospheric pressure, and hydrogen was used as reducing agent. A comparison between the catalytic activity of Pd,In/SiO 2 and Pd,In/Al 2 O 3 catalysts was performed, giving the latter the best results regarding the nitrate conversion and the former the selectivity to nitrogen. Synthetic water containing nitrates (SW) and the groundwater (GW) with high salinity (81 mg/L nitrates) and humic acid content were treated in these conditions using HCl and CO 2 as acidifiers. When the SW was acidified with CO 2 at an H 2 flow (2.17 mL/min), more than 50 % of conversion was obtained with an ammonia and nitrite concentrations of 0.44 and 0.92 ppm respectively. These results reached the level established by the WHO and the USEPA. However, both Pd,In/SiO 2 and Pd,In/Al 2 O 3 catalysts showed evidence of some deactivation process. This deactivation was higher in the GW sample, possibly due to the presence of Ca +2 and Mg +2 cations that precipitate on the active sites, and/or the presence of humic acids. The characterization studies indicated that, after the reaction, the composition of the metal phases was modified, specifically on their surface. As the catalyst activity is related to surface ratio Pd/In, a relative increase in the concentration of Pd decreases the activity and causes changes in the selectivity to N 2 . Some sintering of the metal particles was also observed to contribute to catalyst deactivation. Nevertheless, promising results were obtained since a high water volume could be treated with a relatively low amount of low metal loading catalysts.

In this work, 4,4ʹ-hexafluoroisopropiliden anhydride diftalic (6FDA) and 4,4ʹ-hexafluoropropiliden bis(p-phenilenoxi) dianiline (6FPA) polyimides were synthesized by two step polycondensation. The polyimides were utilized in the dense membrane formation by casting solution method. The membranes were cross–linked by immersion in a 1,5-pentadiamine in methanol solution prepared at different concentrations. The fraction of insoluble mass indicates the cross-linking degree, which varies from 0 to 1. In the other hand, the fractional free volume (FFV) calculated from Bondi theory decreases as the cross-linking degree increases in the membrane. The membranes were tested in the permeation of pure H 2 , CO 2 , N 2 and CH 4 gases. The results exhibited that permeability of the cross-linked membranes increases compared to the uncross-linked membrane. In the other hand, gas permselectivity data where located in the Robeson´s diagram being near to upper limit for the H 2 /CO 2 pair of gases. The membranes are good candidates to carry out the low molecular weight’s gas separation.

Lithium-ion batteries (LiBs) have gained a worldwide position as energy storage devices due to their high energy density, power density and cycle life. Nevertheless, these performance parameters are yet insufficient for current and future demands diversifying their range of applications, and competitiveness against other power sources. In line with the materials science, the optimization of LiBs, first, requires an in-depth characterization and understanding of their determining steps regarding transport phenomena and electrode kinetics occurring within these devices. Experimental and theoretical studies have identified the solid-state diffusion of Li + into the composite cathode material as one of the transport mechanisms limiting the performance of LiBs, in particular at high charge and discharge rates (C-rates). Nowadays, there is however ambivalence to characterize this mass transport mechanism using the diffusion coefficient calculated either by electrochemical techniques or ab initio quantum chemistry methods.  This contribution revisits conventional electrochemical methodologies employed in literature to estimate mass transport diffusivity of LiBs, in particular using LiFePO 4 in the cathode, and their suitability and reliability are comprehensively discussed. These experimental and theoretical methods include Galvanostatic and Potentiostatic Intermittent Titration Technique (GITT and PITT), Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and ab initio quantum chemistry methods. On the one hand, experimental methods seem not to isolate the diffusion mechanism in the solid phase; thus, obtaining an unreliable apparent diffusion coefficient (ranging from 10 –10 to 10 –16  cm 2  s −1 ), which only serves as a criterion to discard among a set of LiBs. On the other hand, atomistic approaches based on ab initio , density functional theory (DFT), cannot yet capture the complexity of the local environments involved at this scale; in consequence, these approaches have predicted inadequate diffusion coefficients for LiFePO 4 (ranging from 10 –6 to 10 –7  cm 2  s −1 ) which strongly differ from experimental values. This contribution, at long last, remarks the factors influencing diffusion mechanisms and addresses the uncertainties to characterize this transport mechanism in the cathode, stressing the needs to establish methods to determine the diffusion coefficient accurately, coupling electrochemical techniques, ab initio methods, and engineering approaches based on modeling.

Effect of non-ideal mixing on heat transfer phenomena is studied in an anchor agitated vessel processed with viscous Newtonian and non-Newtonian fluids. Influence of critical variables such as rotational speed and properties of the fluid on heat transfer coefficient and heat transfer area has been investigated. Based on the flow pattern generated by an anchor agitator, a multi parameter model for quantifying the extent of non-ideality is developed and the parameters of the model, fraction of well mixed zone and the exchange flow rate are evaluated on the basis of tracer response data. Heat transfer experiments are also conducted under unsteady state conditions using same agitated vessel under similar operating conditions using Castor oil, Castor oil methyl esters (CME) and carboxy methyl cellulose (CMC 0.5 %, 1 %), soap solution as process fluids. Based on the results obtained from this analysis, a commercial scale reactor of a capacity of 20 Kl for saponification of hydrogenated castor oil has been designed using different scaleup rules. Power per unit volume found to give desirable results as it gives acceptable values for heat transfer coefficient and power consumption. Equal power per unit volume gives good mixing and high heat transfer coefficient with slightly higher power consumption and the error involved in heat transfer area calculation is small giving optimum cost of the experimental unit.