Band 14, Heft 5 -

In the present work, the catalytic conversion of ethanol to 1,3-butadiene (1,3-BD) was studied over monometallic of Cu and Ag, and bimetallic Cu-Ag supported on MgO-SiO 2 (with MgO/SiO 2 ratio of 2.0) under the temperature range from 250 to 325  ° C. All catalysts were prepared by 4 different techniques including (i) conventional impregnation, (ii) microwave-assisted method, (iii) polyvinyl alcohol/sodium borohydride (PVA/NaBH 4 ) assisted method, and (iv) benzoxaxine-assisted method to elucidate the effect of catalyst preparation method on their catalytic performance. All fresh and spent catalysts were also characterized by X-ray diffraction (XRD), N 2 adsorption and Temperature-programmed reduction (TPR) techniques to understand the relation between their physical/chemical properties and catalytic performance. From the reaction test, it was found that 5 %Ag/MgO-SiO 2 showed greater activity towards 1,3-BD production than 5 %Cu/MgO-SiO 2 ; nevertheless, higher deactivation after 6 h of operation was observed from 5 %Ag/MgO-SiO 2 . Importantly, this study revealed that bimetallic 2.5 %Cu-2.5 %Ag/MgO-SiO 2 enhanced significantly higher activity and stability towards the reaction than monometallic catalysts. In addition, 2.5 %Cu-2.5 %Ag/MgO-SiO 2 prepared by benzoxaxine-assisted method enhanced significantly higher reaction activity and stability than other preparation techniques, from which 1,3-BD yield of 46.40 % after 6 h of operation can be achieved. From the characterization, the good activity of this catalyst is mainly due to the dispersion improvement of metal over MgO-SiO 2 support.

Temperature control in bubble columns is of great importance, since chemical reactions in many of the chemical, pharmaceutical, fertilizer, etc. industries are usually accompanied by heat supply or heat removal operations. In the present research work, the heat transfer coefficient of a two-phase co-current vertical downflow bubble column (i.d. 0.05 m×1.6 m height) was evaluated. Experimental studies were carried out to calculate the heat transfer coefficient for operating temperature ranges from 60 °C to 90 °C. The effects of the superficial gas velocity (4.25×10 –3 to 9.58×10 –3 m/s), liquid velocity (8.50×10 –2 to 16.98×10 –2 m/s), gas holdup, and axial position were investigated. Empirical correlation was developed, based on a multiple regression analysis to calculate a heat transfer coefficient as a function of dimensionless numbers, including the Reynolds number, the Prandtl number, and the Froude number.

Spray Tower Loop Reactors is one of the most advanced ethoxylation reactors in the world. The special pressure swirl nozzles are the core component and important for production efficiency and product quality. A test rig was established, which was divided into four parts: spray system, laser measurement system, photographic system and flux distribution test system. An experimental study on the atomizing performances was conducted, including discharge coefficient, spray cone angle, spray flux distribution, Sauter mean droplets size and droplets size distribution. According to the measurement data, the correlation of volume flow rate, discharge coefficient, spray cone angle and Sauter mean droplets size versus pressure drop were respectively gained. The spray flow distributions of all measured nozzles are classified as a unimodal、bimodal and trimodal distribution due to the different structure. And the experimental Probability Density Function (PDF) of the droplets size was gained by a split-type spray laser droplets size analyzer and compared with five empirical distributions. The log-hyperbolic distribution has a most agreement with the measured PDF. At same time, reaction performance of the special nozzles was measured in the industrial STLR ethoxylation reactor. It is indicated that Sauter mean diameter determines the number of EO and the width of droplets size distribution determines the width of the molecular weight distributions. The present paper exhibits the measurement way and outcomes of spray characteristics of the nozzles in ethoxylation reaction and it is instructive for the optimization design of SPLT ethoxylation reaction.

Bubble columns are widely used for contacting gas–liquid and gas–liquid–solid mass transfer/chemical reactions. Gas distributor is the most important accessory because it decides the bubble size/rise velocity and gas distribution. In this study, the effect of distributor design on hydrodynamics and mass transfer coefficient are studied at different operating conditions of height to diameter ratio, solid loading, and superficial gas velocity The overall gas holdup, is studied experimentally using a rectangular slurry bubble column operating at ambient temperature and pressure, using liquid paraffin (C 9 –C 11 ), three heights to diameter ratios (6, 7.5 and 10) and silica as a solid phase (0 %, 9 % and 25 %) with oxygen as gas phase. Two types of distributor were used, perforated plate and ring type. The results showed that the overall gas holdup increased by increasing gas velocity and decreased by increasing height to diameter ratio and solid loading. Also, it is found that the perforated plate distributor gave a higher gas hold up than ring distributor at gas velocity higher than 0.03 m/sec. The following correlations are obtained: Plate distributor at presence of silica particles: εg=1.343Ug0.0612−0.00891εs−0.374−0.702LD0.0414.904−0.0251$$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} =& {\left({1.343{\rm{U}}_{\rm{g}}^{0.0612} - 0.00891{\rm{\varepsilon}}_{\rm{s}}^{- 0.374} - 0.702{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.041}}} \right)^{4.904}}\cr& - 0.0251}$$ Ring distributor at presence and absence of silica particles: εg=0.216Ug0.297−0.354εs1.4671−0.127LD0.1471.1206+0.058$$\eqalign{{{\rm{\varepsilon}}_{\rm{g}}} = &{\left({0.216{\rm{U}}_{\rm{g}}^{0.297} - 0.354{\rm{\varepsilon}}_{\rm{s}}^{1.4671} - 0.127{{\left({{{\rm{L}} \over {\rm{D}}}} \right)}^{0.147}}} \right)^{1.1206}} \cr&+ 0.058}$$ There is a good agreement between experimental and predicted values with a percent of error less than 2 %. It has been found that the mass transfer coefficient is higher for ring distributor than the perforated plate and growing higher for heterogeneous flow regime and higher solid loading.

The present work reveals the preparation and optimization of sea mango based activated carbon (SMAC) by microwave induced KOH activation for the adsorptive removal of organic and inorganic contaminants from the mature anaerobic landfill leachate using response surface methodology (RSM) technique. Chemical oxygen demand (COD) and ammoniacal nitrogen (NH 3 -N) are the main indicators for organic and inorganic compounds often found in aged landfill leachate. Hence, the treatment of this stabilized landfill leachate is considered to be an essential step prior to its discharge. The leachate sample was collected from Sahom Landfill site in Perak, Malaysia and the initial concentrations of COD and NH 3 -N were measured as 550 mg/L and 3,330 mg/L, respectively. The feasibility of converting Sea mango to activated carbon process to remove the COD and NH 3 -N pollutants from landfill leachate was investigated. The preparation conditions such as microwave heating at power range (350–600 W), impregnation of AC with KOH (0.5–3.0) and retention time (6–10 min) were evaluated, analyzed and optimized using response surface methodology (RSM). From the analysis of variance (ANOVA), the optimum conditions for preparation of SMAC was at 560 W of activation power, 8.4 min of activation time and 2.10 of impregnation ratios with higher adsorptive removal of COD (72.50 %), and NH 3 -N (79.77 %), respectively. The physical and chemical properties of SMAC were evaluated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and surface area. The findings exemplified the applicability of SMAC as an effective precursor for the simultaneous removal of organic and inorganic pollutants from mature landfill leachate.

Flame temperature and structure are a useful tool for describing flame dynamics and flame stability, especially at the micro-scale. The objective of this study is to examine the effect of different kinetic models (that have been proven to accurately predict the macro-combustion behavior of hydrocarbons) on the combustion characteristics and the flame stability in microreactors, and to explore the applicability of these kinetic models at the micro-scale. Computational fluid dynamics (CFD) simulations of lean premixed methane-air flame in micro-channel reactors were carried out to examine the effect of different reaction mechanisms (Mantel, Duterque and Fernández-Tarrazo model) on the reaction rate and the flame structure and temperature. The time-scales with regard to homogeneous reaction and heat transfer were analyzed. The CFD results indicate that kinetic models strongly affect flame stability. Large transverse gradients in temperature and species are observed in all kinetic models, despite the small scales of the microreactor. Preheating, combustion, and post-combustion regions can be distinguished only in Duterque and Mantel model. Duterque model causes a stable elongated homogeneous flame with a considerable ignition delay as well as a dead region with cold feed accumulation near the entrance, and is inappropriate for micro-combustion studies because of the seriously overestimated flame temperature. Fernández-Tarrazo model causes a rapid extinction and a flashback risk, and is also inappropriate for micro-combustion studies due to the significantly underestimated reaction rate, without taking all kinetic factors into account. Mantel model can accurately predict the micro-flame behavior and consequently can be used for describing micro-combustion.

A comparative study on the treatment of thermomechanical pulping (TMP) pressate between thermophilic (55 °C) and mesophilic (30 °C) membrane aerated biofilm reactors (MABRs) was conducted under different cycle lengths (CLs) for over 114 days. The performance of the MABRs was evaluated in terms of soluble chemical oxygen demand (COD) removal and biofilm detachment. With a total influent COD of 3,700–4,100 mg/L, the soluble COD removal efficiency of thermophilic MABR (40–65 %) was slightly lower than that of mesophilic MABR (50–80 %) under different CLs. The level of effluent suspended solids (ESS) in treated effluent of the thermophilic MABR was generally higher than that of the mesophilic MABR, suggesting a more significant biofilm detachment from membrane surfaces in the thermophilic MABR. The performance of COD removal improved at the time five to ten days after each significant biofilm detachment. The results suggest that MABR is a promising technology for TMP pressate treatment and biofilm thickness control is important for achieving better performance.

The 3D flow fields and power consumption within a cylindrical vessel stirred by a rotating turbine are numerically studied. Simulations are performed to determine the impact of changes in operating parameters on the mixing characteristics. Investigations are focused on effects of the impeller blade curvature, shaft speed and impeller rotational direction. The fluid simulated has a shear thinning behavior. Designing the blade in retreat shape seems very promising in term of power consumption since a reduction of Np is obtained with increasing blade curvature. In the positive rotational direction, the retreat bladed impeller yields highly radial flows with less power consumption than the straight bladed impeller. The 45° retreat blade gave an increase in the radial velocity by 39 %, compared with the straight blade. But, a better axial circulation is obtained with the straight blade. The comparison between the positive rotational direction (+ w ) and the negative rotational direction (– w ) cases revealed that, a reduced mixing time can be obtained with a retreat bladed impeller operating in the negative rotational direction (– w ), but with further power consumption.

The selective hydrogenation of acetylene to ethylene in acetylene/ethylene mixture over Pd-Ag/α-Al 2 O 3 catalysts prepared by sequential impregnation method was studied. The α-Al 2 O 3 support was prepared by thermal treatment of γ-Al 2 O 3 in temperature range of 1,090–1,100 °C. The samples were characterized for their structural properties and coke deposition. They showed egg-shell structure with penetration depth increasing with sintering temperature of the support. A kinetic model based on 1st order in acetylene and 0.5th order in hydrogen for the main reaction and 2nd order independent decay law for catalyst deactivation was used to fit the conversion-time data and to obtain quantitative assessment of catalyst performances. Fair fits were observed from which the reaction and deactivation rate constants were evaluated. The highest selectivity to ethylene, and therefore best performance, was obtained for the highest calcination temperature which was attributed to its lower acidity and larger pore diameters.

The effects of templating agent [i. e., tetraethyl ammonium hydroxide (TEAOH), triethylamine (TEA) and morpholine (MOR)] and molar ratio of SiO 2 /Al 2 O 3 and H 2 O/Al 2 O 3 over SAPO-34 catalysts in methanol to olefin (MTO) reaction were studied systematically. The exact effect of main factors and their interaction were studied by response surface methodology (RSM) applying central composite design (CCD). Two empirical models for two systems, based on these preparation variables for the yield of ethylene and propylene were constructed in two CCD studies and ultimately these models showed as counter and three-dimensional (3D) diagrams. Analysis of Variance (ANOVA) applied for investigating the significance of the variables indicated that TEA and SiO 2 /Al 2 O 3 content were the most significant variables in the case (1) and case (2), respectively. The maximum predicted ethylene and propylene yield was 58.57 wt. % and 30.22 wt. %, for catalyst with TEA = 0.2, TEAOH = 0.38 in case (1). For case (2), catalyst with SiO 2 /Al 2 O 3 = 0.17, H 2 O/Al 2 O 3 = 101.18 showed the maximum ethylene and propylene yield of 49.87 wt. % and 20.58 wt. %, respectively.

Platinum supported silica nanocatalyst was synthesized for hydrogen production by steam reforming of glycerol (SRG). The catalyst was prepared by the sol-gel method and characterized using BET, SEM, and XRD techniques. The performance of the catalyst was evaluated in terms of glycerol conversion, hydrogen yield and exit gas selectivity in reaction temperature range 300–400 °C in a plate-type microchannel reactor at atmospheric pressure. According to the experimental results, Pt/SiO 2 nanocatalyst was successfully synthesized by sol-gel method. The optimum conditions were obtained with inlet feed flow rate of 3 mL/h and temperature of 400 °C, leading to a low CO selectivity and high H 2 yield. The results showed that the Pt nanocatalyst supported on SiO 2 had a good performance on the gaseous products and yield of H 2 .

In this contribution, the effects of ceria loading, Si/Al ratio, and reaction temperature on the catalytic performance of HZSM-5 catalysts for production of ethylene and propylene from light naphtha were investigated. The elaborated catalysts were characterized by XRD, FTIR, SEM, and BET specific surface area. The acquired results demonstrated that HZSM-5 structure was preserved after ceria addition. XRD patterns exhibited a crystallinity degradation of HZSM-5 samples by aluminum addition. Box-Behnken experimental design was utilized with central composite design for investigation of parameters such as reaction temperature (600–700 °C), cerium loading (2–14 wt%), and Si/Al ratio (25–125) in ethylene and propylene production. Analysis of variance (ANOVA) indicated the significance of the studied parameters and the corresponding interactions. The results exhibited that the highest ethylene yield was at the highest reaction temperature, the highest cerium loading, and the lowest Si/Al ratio. The superior propylene yield was attained at the highest Si/Al ratio whereas an optimum can be found for reaction temperature and cerium loading.

The cocurrent downflow contacting reactor (CDCR) has a high oxygen transfer rate by providing the effective the gas-liquid contact. This property is an advantage for enzyme production. In this study, the CDCR was used for the production of α-amylase by Bacillus amyloliquefaciens for different starch concentrations in the range of 7.5–17.5 g l –1 at constant air and liquid flow rates. The values of the volumetric oxygen transfer coefficient ( k L a ) and specific oxygen uptake rate (qO2${{\rm{q}}_{{{\rm{O}}_2}}}$) were determined during enzyme production. It has been found that the starch concentration has great effect on the enzyme activity. Maximum enzyme activity (1,000 IU ml –1 ) was obtained in the fermentation broth containing of 15 g l –1 starch concentration at 37 °C and pH 7 for 28 h. The k L a and qO2${{\rm{q}}_{{{\rm{O}}_2}}}$ values were determined to be 175.83 h –1 and 47.5 mg O 2 g –1 cell h –1 , respectively.

The increased generation of renewable electricity (wind, solar), due to its fluctuating characteristic, leads to an increasing storage demand. A potential storage technology is the conversion of electrical energy into chemical energy (e.g. in form of gaseous hydrocarbons), which can be easily stored and distributed in an existing natural gas grid. CO 2 is the C-source of choice, from biogas plants or industrial processes, making possible the production and use of C-based fuels without increasing the CO 2 emissions into the atmosphere. The combination of Fischer–Tropsch synthesis and CO 2 shift reaction, using iron-based catalyst, offers the possibility to produce substitute natural gas (SNG) components from CO 2 . Due to the fluctuating nature of hydrogen production from renewable electrical energy, advantages can be identified if the chemical reactor is operated under variable load conditions. The aim of the present study is to evaluate the flexibility of a catalytic synthesis reactor as a potential component in a future energy system with a high contribution of renewable energy. The hydrogenation of CO 2 to gaseous components is studied in a fixed-bed lab-scale reactor to determine kinetic parameters and hydrocarbon product distribution. Results from the experimental work are implemented in the mathematical model and are the basis for the conceptual design of the catalytic fixed-bed reactor able to operate under variable load conditions.

In this article, we have considered an incompressible nanofluids flow and studied the effects of variable viscosity in the form of a well-known Reynold’s model of viscosity in an asymmetric channel. The fluid viscosity is assumed to vary as an exponential function of temperature. The governing fundamental equations are approximated under the assumption of long wavelength and low Reynold , s number. The governing momentum and energy and nanoparticle equations are solved using shooting technique to obtain the expressions for stream functions, pressure rise temperature and nanoparticle concentration field. Trapping phenomena are also discussed at the end of the article to see the behaviour of different parameters on streamlines. It is analyzed that the pressure rise and amount of flow rate are charitable conflicting consequences. It is analyzed that the temperature profile increases with the increase in Prandtl parameter P r , the Brownian motion parameter Nb${N_b}$ and the thermophoresis parameter Nt${N_t}$.