Volume 17, Issue 5 - Special Issue to Honour Professor Gülşen Doğu and Professor Timur Doğu

Moment technique has been extensively used for the evaluation of the rate and equilibrium parameters in chemical reactors and also in adsorption vessels, for about five decades. Adsorption and reaction rate parameters, as well as axial dispersion constants, effective diffusivities within porous catalysts and heat and mass transfer coefficients were shown to be effectively evaluated by analyzing the moments of the response peaks, which could be obtained from pulse-response experiments performed in a reaction/adsorption vessel. A detailed review of chromatographic processes, involving moment analysis of adsorption equilibrium and rate constants in fixed beds, dynamic analysis of batch adsorbers, moment analysis of fluidized bed, slurry and trickle bed reactors are reported in this manuscript. Applications of the single-pellet moment technique, which was developed for the effective investigation of intrapellet rate and equilibrium processes, by eliminating the contributions of axial dispersion and external transport parameters, are comprehensively discussed. Recent studies for the analysis of reaction rate parameters using the TAP reactor approach, use of single pellet system for the investigation of catalytic and non-catalytic solid-gas reactions and extension of the moment technique to non-linear systems opened new pathways in reaction engineering research.

In this work, novel trimetallic catalysts based on transition metal sulphides (Ru, Mo and Ni) supported on SBA-15 were synthesized. Citric acid (CA) was used as chelating agent in order to enhance the dispersion of the active phase and minimize the metal-support interaction. Sulfided catalysts were evaluated in the reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT) at 320  ° C and 54.5 atm of total H 2 pressure. The effects of different Ru/(Ni + Mo) atomic ratios on the active phase were studied. The catalysts were characterized using Micro-Raman spectroscopy, DRIFTS, XRD, XPS, HR-TEM and SEM techniques. Results have shown that there was a better dispersion of the metallic phases, which improves the physicochemical properties of the catalysts, increasing the catalytic activity. The trimetallic Ru x MoNi catalyst with the lowest atomic ratio, have shown superior catalytic activity compared to their higher atomic ratio counterparts. The interaction of the chelating agent improved the catalytic activity, which was superior to that observed for NiMo based catalysts, considered one of the most active hydrotreating catalysts.

Activated carbons were produced from coal by activations applying physical and chemical (with KOH) treatments for adsorption of selected organic vapors. Physical activations were carried out at 400–900°C under N 2 /CO 2 flow. The effects of different variables such as carbonization temperature and flow rate on the final porous texture were investigated. Chemical activation gave more effective results in terms of both porosity development and adsorption capacity. Pore characterization of carbon samples was evaluated with the observation of N 2 adsorption-desorption isotherms at 77 K. The adsorption of isopropyl alcohol, acetone and ethyl alcohol on the coal derived activated carbons were determined by a volumetric technique at room temperature. The highest surface area was obtained as 1904 m 2 /g by KOH treatment at 800°C. The adsorption isotherm data of the selected organic vapors on carbon samples were compared with the BET, Langmuir, Freundlich, Dubinin-Radushkevich, Dubinin-Astakhov, Harkins-Jura, Henderson, Halsey and Smith adsorption models. Adsorption capacities of organic vapors for carbon samples were related with the development of surface area. Among the four chemically activated carbons produced K1_K_600, K1_K_700 and K1_K_800 showed better isopropyl alcohol and acetone adsorption than the commercial activated carbon. K1_K_700 and K1_K_800 samples showed better ethyl alcohol adsorption. Isopropyl alcohol, acetone and ethyl alcohol adsorption capacities of the obtained sample that had the maximum surface area were determined as 39.7, 44 and 43.5 %, respectively. Results indicate that activated carbons prepared with KOH at 600–800°C could be effectively used for the adsorption of organic vapors.

In this study, alumina supported Ti-Ce catalysts (10 % by weight and Ti/Ce molar ratio is 4:1) were prepared by using wet impregnation method and their catalytic activities were tested in H 2 S selective oxidation to elemental sulfur. The support alumina was synthesized by classical (SGC) and modified (SGM) sol-gel methods. The N 2 adsorption-desorption, XRD, XPS, EDS and FTIR techniques were used to characterize the synthesized catalysts. The N 2 adsorption-desorption isotherms showed that both catalysts have mesoporous structure. Only γ-Al 2 O 3 crystalline phase together with amorphous structure were observed in the XRD patterns. The pyridine adsorbed FTIR analyzes showed that 10 %Ti-Ce@SGC and 10 %Ti-Ce@SGM catalysts have the same Lewis acidity. The activity tests were carried out at 250 °C and with a stoichiometric feed ratio of O 2 to H 2 S being 0.5 for two different reaction times as 150 and 510 min. Complete conversion of H 2 S was obtained during 180 min. and 330 min. of reaction time over 10 %Ti-Ce@SGC and 10 %Ti-Ce@SGM, respectively. However, all catalysts showed very high sulfur selectivity. Sulfur deposition was detected over 10 %Ti-Ce@SGC catalyst both 150 and 510 min. of reaction time while it was observed after 510 min. of durability test over 10 %Ti-Ce@SGM catalyst. This can be the reason for the earlier loss of catalytic activity 10 %Ti-Ce@SGC than 10 %Ti-Ce@SGM.

Coupling of second and first order reactions in one pot fashion through a cascade process is an often encountered process. Consecutive reactions of this type are considered and selectivity analysis is performed demonstrating dependence of selectivity pattern on reaction parameters.

This study presents a novel analytical solution for the Population Balance Equation (PBE) involving particulate aggregation and breakage by making use of the appropriate solution(s) of the associated complementary equation of a nonlinear PBE via Fibonacci and Lucas Approximation Method (FLAM). In a previously related study, travelling wave solutions of the complementary equation of the PBE using Auxiliary Equation Method (AEM) with sixth order nonlinearity was taken to be analogous to the description of the dynamic behavior of the particulate processes. However, in this study, the class of auxiliary equations is extended to Fibonacci and Lucas type equations with given transformations to solve the PBE. As a proof-of-concept for the novel approach, the general case when the number of particles varies with respect to time is chosen. Three cases i. e. balanced aggregation and breakage and when either aggregation or breakage can dominate are selected and solved for their corresponding analytical solution and compared with the available analytical approaches. The solution obtained using FLAM is found to be closer to the exact solution and requiring lesser parameters compared to the AEM and thereby being a more robust and reliable framework.

Aluminum loaded silica aerogel based catalysts were synthesized by impregnation of aluminum into silica aerogel produced using sol-gel method in different aluminum loadings (2.5–15 wt%) to investigate their performances in degradation of polylactic acid (PLA). Synthesized catalysts showed Type IV isotherm with H1 hysteresis which indicates the mesoporosity of the materials. They have demonstrated favorable properties in terms of high surface area (743–510 m 2 /g), pore volume (1.79–0.69 cm 3 /g), and pore diameter (6.38–3.60 nm) depending on aluminum loading amounts. Thermogravimetric analysis demonstrated that metal loaded silica aerogel catalysts have an influence on degradation profile of PLA. A noticeable reduction in the activation energy for the PLA degradation was attained with an increase in aluminum loading. These findings show that silica aerogel catalysts are promising for the recycling processes of PLA with their pore characteristics and their acidity affect the degradation performance significantly.

Hydrodynamics and (catalytic & non-catalytic) reaction [high-pressure hydrodesulfurization; Fischer-Tropsch synthesis; CO 2 -monoethanolamine (MEA) absorption; simultaneous CO 2 and H 2 S absorption in MEA; CO 2 thermal desorption, enzymatic CO 2 hydration] performances of trickle-bed and packed-bed column reactors subjected to static inclination, rolling (symmetrical/asymmetrical externally-generated reactor oscillations) and heaving motions were analyzed via detailed dynamic 3-D models which couple the macroscopic volume-averaged momentum, mass, energy and species balance equations in the liquid/gas phases with diffusion/chemical reaction inside the catalyst particles, enzyme washcoat or liquid film near the gas-liquid interface. Axial symmetry breakdown once the packed bed systems become inclined inflicts noticeable reductions of the reactor (or scrubber) performances. Only the performance of Fischer-Tropsch synthesis in the presence of water-gas shift reaction increases slightly with the increase of trickle-bed reactor inclination because of facile uptake of reactants in the key reactions from the gas phase while a fraction of valuable CO can be forwarded in water gas-shift reaction. For most of the reactions examined, the reactor performance is negatively impacted in asymmetric oscillating multiphase reactors with Fischer-Tropsch synthesis as an exception owing to the presence of water-gas shift reaction the performance of which is slightly improved. This performance deterioration/enhancement is maximal for the reactor moving between vertical and an inclined position when the time-dependent performance waves develop around the steady-state solution of the mid-inclination angle. The oscillatory reactor performance moves towards the steady-state solution of the vertical state when the asymmetry between the two inclined positions dwindles. Symmetric oscillating and heaving trickle-bed and packed-bed column reactors generate an oscillatory performance around the steady-state solution of vertical state which is affected by the amplitude and period of the angular and heaving motions of the vessel.

A diffusion cell for the mass transfer investigation of the gases through the solid porous media is developed. The diffusion cell may be configured in two different ways. One configuration corresponds to the reflecting boundary condition, whereas another configuration satisfies the absorbing boundary. The mass balance equations for different cell configurations are provided. The mass balance equations are applicable for the calculations of the diffusate quantity decays. The latter are suitable for the mass transfer parameters estimation using the solutions of the transport equations, obtained for the boundary conditions that correspond to the diffusion cell configurations. Accounting for the impact of the apparatus function of the diffusion cell on the experimental data is also revisited. In addition, the practical use of the diffusion cell based on the installation of the cell into the gas chromatograph for the investigation of the methane transport through the porous silica pellet as an example is demonstrated.

The objective of the study was to prepare low-cost activated carbon from cornelian cherry stones (Cornus mas L.) and compare its adsorption capacities for CO 2 with that of commercial multiwalled carbon nanotubes, activated carbon, MCM-41 and four zeolites (silver exchanged, 13X, faujasite type and linde type A). BET, t-plot and DFT methods were used for the characterization of all adsorbent samples based on N 2 adsorption-desorption data obtained at 77 K. The produced activated carbon samples (KAC and NAC) were also characterized by scanning electron microscopy (SEM). The adsorption data were evaluated by several isotherm models such as Freundlich, Langmuir, Temkin, DR and Harkins-Jura isotherm models. Langmuir adsorption isotherms constants related to adsorption capacity, W m were found as 11.496, 6.175, 4.189, 3.986 and 3.50 mmol/g for NAC, KAC, faujasite type zeolit, MCM-41 and AC, respectively. The CO 2 adsorption capacities of the silver exchanged, 13X, faujasite type and linde type A zeolites were 10.814, 10.241, 14.608 and 13.343 wt%, respectively. Microporous zeolites showed higher CO 2 adsorption capacities than the mesoporous MCM-41 and MWCNT. The CO 2 adsorption capacity of commercial activated carbon (AC) was found to be 9.428 wt%, while the CO 2 adsorption capacities of activated carbons obtained using NaOH and KOH were found to be 13.685 and 15.057 wt%, respectively. The highest CO 2 adsorption capacity of 15.057 wt% was achieved with KAC. It could be confirmed that NaOH or KOH activation plays an important role to determine the porous structure and amount of CO 2 adsorbed. Results showed that activated carbon produced from cornelian cherry stones is suitable for the adsorption of CO 2 and could be used as a low cost effective adsorbent in the capture of CO 2 .