Volume 16, Issue 4 -

The process of CO 2 hydrogenation into methanol has recently attracted more attention for reducing CO 2 , a main green-house gas in the atmosphere. In addition, methanol can be used as fuel or a basic chemical to satisfy the growing demand for energy in the world. In this study, the performance of NaA membrane reactor on the methanol yield and methanol selectivity obtained from the CO 2 hydrogenation process was evaluated at different reaction conditions by varying the temperature, pressure, gas hourly space velocity (GHSV) and H 2 /CO 2 ratio. The results show that the methanol yields and methanol selectivities obtained from the membrane reactor (MR) at all reaction conditions are higher than those from the traditional reactor (TR). The ratio of methanol yield in MR over methanol yield in TR are varied from 1.4 to 1.7 depending on the operating conditions. It is also observed that the use of membrane reactor is more efficient at low GHSV and the temperature in the range of 220–240°C.

In recent work, we investigated analytically low Reynolds number bubbly flows in pipes. We showed that the distribution of bubbles results from a balance between lift, dispersion and wall forces, and exhibited an analytical expression for this void fraction profile. We then performed a comparison of this analytical Bubble Force Balance Formula (BFBF) with an experiment from the literature. Antal’s model was used for the wall force. The objective of the present work is to compare and assess the three main wall force models in the literature: Antal’s, Tomiyama’s and Frank’s models. We begin by deriving two new BFBF, respectively with Tomiyama’s and Frank’s forces. We can see that the choice of the model impacts the velocity with which the analytical void fraction profile goes to zero at the wall. We then compare our three analytical profiles with experimental measurements and DNS simulations of laminar flows from the literature. We restrict ourselves to the near-wall region. The choice of Antal’s wall force model yields the best agreement. The data is also used to estimate the dispersion coefficient at the wall. Interestingly, we obtain the same order of magnitude with the three wall force models.

1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX) is one of the high explosives extensively used for various military and civil applications. RDX is predominantly used in warheads, the most advanced solid propellants for guns and rockets and in plastic bonded explosives for improving performance characteristics. Thus the increasing demand of RDX necessitates study on reaction engineering and reactor stability in view of enhancement of safety as well as productivity. In present study, Bachmann process has been studied in detail for understanding role of reagents, time and temperature on reaction yield. Reaction rates of RDX and side products have been evaluated at various temperatures using continuous flow technique. Second order reaction was found sensitive towards temperature and concentrations of nitric acid and acetic anhydride. Higher magnitude of activation energy was evaluated for side products (25.2 kcal/mol) than RDX (18.71 kcal/mol). Optimum temperature of reaction has been obtained on profiling its progression at various reaction rates and temperature. Further, reactor stability analysis has been carried out to identify the safe operation conditions for this highly exothermic reaction. Effect of coolant flow rate and temperature as well as feed temperature has been analyzed on heat removal rate to obtain the safe regime of reaction. The information related to maximization of RDX formation and safe design of continuous process has been presented in manuscript.

The photocatalytic activities of TiO 2 Degussa P25 and Millennium PCs (PC50, PC100, PC105 and PC500) were evaluated by the photocatalytic degradation of Bromothymol Blue (BTB). The relationship between the photocatalytic reaction and the adsorption of BTB on the TiO 2 catalysts at acidic, natural and basic mediums of pH was investigated. The crystalline phase, average crystalline size and surface area of the catalyst were found to have a significant influence on the adsorption and photocatalytic activity of the TiO 2 samples. The mixed phase of anatase/rutile (Degussa P25) was found to be the most efficient photocatalytical material than pure phase anatase (Millennium PCs) and faster degradation is observed for PC500 compared to other Millennium PCs, this was attributed to the high surface area of PC500. Within the PC50, PC100 and PC105 series, the photocatalytic efficiency increased with the decrease of the surface area. The COD and TOC removals increased slowly, however, the decolorization ratio of BTB increased rapidly at the same time. Thereafter, the efficiency of P25 and PC500 were compared in presence of H 2 O 2 , Cl − and HCO 3 − at different mediums of pH. H 2 O 2 was found to enhance strongly the BTB degradation in presence of P25 with an optimum at natural pH. In contrast, the reaction was inhibited in the presence of PC500, due to the inhibition of dye adsorption. At different pH, the BTB degradation has been significantly inhibited in the presence of the mixtures of HCO 3 − /H 2 O 2 . In contrast, the mixtures of Cl − /H 2 O 2 accelerate the BTB degradation at acidic pH.

The agglomeration of bed material is one of the most serious problems in combustion of biomass in fluidized-bed boilers, due to the presence of some inorganic alkali elements such as K and Na in the biomass ash, which form low-melting-point alkali compounds during the process. In this study, agglomeration behaviors of bed materials (silica sand particles) were investigated in a bench-scale bubbling fluidized-bed reactor operating at 800 °C using simulated biomass ash components: KCl, K 2 SO 4, and a mixture of KCl and K 2 SO 4 at eutectic composition (molar ratio K 2 SO 4 /(KCl+ K 2 SO 4 )=0.26). The signals of temperature and differential pressure across the bed were monitored while heating up the fluidized bed of silica sand particles premixed with various amounts of KCl, and the KCl-K 2 SO 4 mixture in bubbling bed regime. A sharp decrease in temperature and differential pressure was observed around 750 °C and 690 °C for 0.4–0.6 wt% loading of the low melting-point KCl and KCl-K 2 SO 4 mixture, respectively, suggesting the formation of bed material agglomeration and even de-fluidization of the bed. Moreover, this work demonstrated the effectiveness of kaolin and aluminum sulfate to minimize agglomeration. The results indicated that these additives could successfully prevent the formation of agglomerates by forming compounds with high melting points.

Chemical reaction aspect is utilized for heat mass transfer analysis of nano non-Newtonian liquid flow past a cone and a wedge. Flow is steady, laminar and two dimensional created due to a cone and a wedge. The Carreau liquid and Cattaneo-Christov heat flux models are utilized. The magneto-nano Carreau liquid material occupies the porous space. The relevant PDEs are rendered into coupled non-linear ODEs via appropriate transformations before treated them numerically through Runge-Kutta and Newton’s method. The computed results are plotted for employing the various values of physical constraints on the profiles of velocity, temperature and nanoparticle volume fraction. Moreover, vitiation of the friction factor, Nusselt number and Sherwood number against physical parameters are presented numerically. It is figured out that convective heating and Brownian motion effects are constructive for thermal boundary layer growth. Aspect of chemical reaction is significant to control the solute layer growth and mass transfer rate.

Residence time distribution (RTD) within vessels is a critical aspect for the design and operation of continuous flow technologies, such as hydrothermal synthesis of nanomaterials. RTD affects product characteristics, such as particle size distribution. Tracer techniques allow measurement of RTD, but often cannot be used on an individual vessel in multiple vessel systems due to unsuitable exit flow conditions. However, RTD can be measured indirectly by removal of this vessel from the system and deconvoluting the resulting detected tracer profile from the original trace of the entire system. This paper presents three models for deconvolution of RTD: BAY an application of the Lucy-Richardson iterative algorithm using Bayes’ Theorem, LSQ an adaptation of a least squares error approach and FFT a Fast Fourier Transform. These techniques do not require any assumption about the form of the RTD. The three models are all accurate in theoretical tests with no simulated measurement error. For scenarios with simulated measurement error in the convoluted distribution, the FFT and BAY models are both very accurate. The LSQ model is the least suitable and the output is very noisy; smoothing functions can produce smooth curves, but the resulting RTD is less accurate than the other models. In experimental tests the BAY and FFT models produce near identical results which are very accurate. Both models run quickly, but in real time control the runtime for BAY would have to be considered further. BAY does not require any filtering or smoothing here, and so potentially there are applications where it might be more useful than FFT.

A series of Mg doped LaNiO 3 nano particles by solids denoted as LaNi 1-x Mg x O 3-δ (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8 and 1) were prepared by the modified citrate sol-gel method and investigated as catalysts for combine reforming of methane (CRM).The resulting oxides were examined by using XRD, BET, ICP, SEM, EDS, TEM, TPR and TGA techniques, under the condition of as-synthesized and used samples. The results showed that highly homogeneous and crystalline oxides with particle sizes in the range of nanometers were obtained through this synthesis method. The XRD patterns of the prepared LaNi 1-x Mg x O 3-δ solids confirmed with increasing Mg amount not only perovskite structure could not form correctly but also the spinel (La 2 NiO 4 ) and oxide phases (MgO and NiO) are produced on the sample surface. Also according to BET results, the presence of these oxide phases lead to the increase in the surface area of samples .Although, increasing in surface area had not a significant effect in results of activity tests. TPR analysis revealed that the reduction of the prepared samples became more difficult by increasing the degree of substitution (x). The effects of the partial substitution of Ni by Mg and reaction temperatures (600–800 °C) were investigated in CRM process, after reduction of the samples under hydrogen. Although, all catalysts, except LaMgO 3 , were found to be highly active toward the syngas production during the CRM process but substitution of Ni by Mg could not improve the catalytic activity of the LaNi 1-x Mg x O 3- δ in this process. The catalytic activity in the steady state was found to decrease in the following order: $${\text{LaNi}}{{\text{O}}_{\text{3}}} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.4}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.6}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.6}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.4}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.9}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.1}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaN}}{{\text{i}}_{{\text{0}}{\text{.8}}}}{\text{M}}{{\text{g}}_{{\text{0}}{\text{.2}}}}{{\text{O}}_{{\text{3 - }}\delta }} \gt {\text{LaMgO3 - }}\delta$$LaNiO3 \gtLaNi0.4Mg0.6O3 - δ>LaNi0.6Mg0.4O3 - δ>LaNi0.9Mg0.1O3 - δ>LaNi0.8Mg0.2O3 - δ>LaMgO3 - δ Of course, according to the TPR and TGA results, the stability of the samples increased and the coke deposits on the catalyst surface decreased with increasing of x, respectively.

A series of vanadium oxide (VO x ) catalysts prepared using three different supports were tested for the partial oxidation of ethanol to acetaldehyde. Optical absorption spectroscopy and Temperature Programmed reductions experiments indicate that the reducibility and average domain size of the vanadia clusters anchored on the supports are very sensitive to vanadia loading. The catalytic activity results were modeled using a pseudo steady state approximation using the ethanol hydrogen abstraction step as rate limiting. The results obtained strongly suggest that catalytic activity can be correlated to both average vanadia cluster size and the ability of vanadia to uptake hydrogen during TPR experiments.

Calculation of simultaneous catalytic reaction rates represents a system of nonlinear differential equations with two boundaries; additionally, nonlinear algebraic equations are added if external mass and energy resistances are significant. For highly exothermic reactions and some reaction networks, numerical solution with typical shooting methods encounters difficulties to find good initial guesses since the equation system becomes very rigid. A Numerical Homotopy Continuation approach is proposed in which the particle size is progressively increased until the specified dimensions; shooting variables corresponding at the center of the particle are used as nearby solutions which allows to trace and update the initial guesses.