Volume 17, Issue 7 -

Ethylene is the most important olefin in the petrochemical context, since it is the main raw material for the production of many polymers. Traditional production of ethylene via thermal cracking and catalytic dehydrogenation consumes large amounts of energy; hence selective partial oxidation of ethane has been considered as an attractive alternative production path. Recently, development of a promising catalyst for selective partial oxidation of ethane, which consists of multi-metallic mixed oxides of Mo, Te, V, and Nb, has been published. It is also noteworthy that this catalytic system starts to be active at temperatures below 400 °C, substantially lower than the one required by commercial thermal processes, >800 °C. In this work, a kinetic mechanism based on Mars van Krevelen formalism is proposed for the selective partial oxidation of ethane, considering the surface itself as active protagonist of the reaction. RedOx steps on active sites are considered as the controlling ones, and the rest of transformations are considered as pseudo-steady steps. It is noticed that there are side reactions, which produces CO and CO 2 as combustion by-products. Additionally, there is competition for reduced sites on the catalytic surface, mainly between oxygen and water molecules, which adsorb strongly on these sites. Adjusted results by the mechanism proposed are in agreement with experimental observations of reaction rates diminishing proportionally to partial pressure of water, caused by competition of reduced sites on catalyst surface.

In this work, a previously reported unstructured kinetic model of Clostridium acetobutylicum ATCC 824, validated with experimental data under different culture conditions, was used to determine the optimal process conditions from an ABE fermentation system for biofuel production. The goal of this work was to simultaneously maximize two conflicting objectives: volumetric productivity and final concentration of butanol considering both Fed-Batch and single-stage CSTR operation regimes using either a free or immobilized cell reactor. The result of the after mentioned strategy was the construction of the Pareto Fronts and optimal trajectories for the inlet solution feeding rate and concentration using a Sequential Quadratic Programming methodology. The obtained results suggest that the maximum concentration and productivity of butanol are achieved in a semi-continuous system operating with immobilized cells, obtaining values of 19.1454 kg m -3 and 0.3655 kg m -3  h -1 , respectively, representing an increase of 48 % and 104 % compared to the most recent industrial process reported to date.

The selective synthesis of p-ethyl phenol in vapor phase alkylation of phenol with ethanol was investigated in a fixed bed flow reactor on cerium modified zeolite CeZSM5 at temperature 693 K. A series of cerium modified zeolite such as Ce 4 ZSM5 4 , Ce 6 ZSM5 6 , Ce 8 ZSM5 8 , Ce 10 ZSM5 were prepared by modifying with 4 %, 6 %, 8 % and 10 % ceric ammonium nitrate solution respectively. HZSM-5 zeolite exchanged with 10 % cerium nitrate solution was proved to be the best of all the catalyst used. The modified catalyst was further characterized by SEM, XRD and EDS. Phenol reacted with ethanol to form ethylphenyl ether by O-alkylation, and p-ethylphenol- and o-ethylphenol isomers by C-alkylation; secondary products were m-ethylphenol and dialkylated compounds. Reactions were carried out in the temperature 623 K–693 K, reactant mole ratio 0.2–0.5 over modified HZSM-5 zeolite. The optimum operating condition for maximum selectivity of p-ethyl phenol were EtOH to phenol mole ratio, 4:1; temperature, 623 K; space-time, 10.2 kg h/kmol and 1 atm pressure. A detailed kinetic study was carried out for the ethyl phenol synthesis reaction. From the product distribution pattern, a kinetic model for the reactions was proposed following the Langmuir–Hinshelwood approach. The kinetic and adsorption parameters of the rate equation were determined by non-linear regression analysis. From the kinetic analysis of the experimental data, the apparent activation energy for the reaction was determined as 43.27 kJ/mol.

Modelling and controlling of Continuous Stirred Tank Reactor (CSTR) is one of the significant problems in the process industry. Chemical reactions inside the CSTR depend on the reference value of the temperature. Design and implementation of suitable control device for such system is a challenge for researchers. This paper proposes the Model Reference Adaptive Control (MRAC) based control strategy as a solution to control problem of CSTR. An enhancement of Signal Synthesis MRAC scheme has been proposed in this study to improve the steady-state and transient-state performance of CSTR. Genetic Algorithm (GA) based controller parameter tuning method is employed to obtain the optimal performance of the controller. This paper presents the design and implementation of conventional Proportional–Integral–Derivative (PID) tuned with Ziegler–Nichols (ZN) tuning method, PID tuned with GA, MRAC, and GA-MRAC for CSTR. Detailed comparison based on simulation studies is also presented to show the improved transient and steady state response with GA-based improved MRAC scheme.

In this work, the modified Mn-based NH 3 -SCR (NH 3 low-temperature selective catalytic reduction) catalysts with excellent NO conversion and N 2 selectivity be designed. N 2 yield was hardly more than 75 % over MnO x /TiO 2 for NH 3 -SCR reaction, whereas the NH 3 -SCR performance has been significantly improved by using 50 wt.% HPW (H 3 PW 12 O 40 )-MnO x /TiO 2 . 100 % NO conversion and more than 95 % N 2 yield was obtained in wide operating temperature window (150–400°C), suggesting that the addition of HPW could effectively improve the NO reduction conversion. After that, the catalysts were further characterized by XRD, H 2 -TPR, XPS and in situ DRIFT. DRIFT analysis implied that the introduction of HPW significantly improve the capacity of NH 4 + species adsorbed on Brønsted acid sites accompanied with inhibiting the formation and consumption of nitrite species. It proved that the non-selective catalytic reduction reaction over HPW-MnO x /TiO 2 catalysts are restrained. HPW could accelerate the formation and consumption of NH 4 + species adsorbed on Brønsted acid sites with deactivation of nitrate species. In addition, NH 3 (ad) could be hardly oxidized to NH species and then reacted with nitrate species (L-H mechanism) and gaseous NO (E-R mechanism). More importantly, the oxidation of NH 3 was also suppressed, which plays a dominate role to form N 2 O above 300°C. Besides, the deactivation of potassium poisoning on the SCR activity significantly weakened for modified samples compared to parent catalyst.

In this work, a model for a trickle-bed reactor for catalytic hydrotreating (HDT) of oil fractions is developed and simulations are performed to investigate its behavior. The model considers dynamic, one-dimensional plug-flow to describe a heterogeneous, adiabatic trickle-bed reactor. It takes into consideration the main reactions present in the HDT process: hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodearomatization (HDA) with a reconstructed petroleum feedstock using a practical approach of generation of pseudo-components by dividing the boiling point curves of the feedstock. The model is solved using the method of lines with a finite difference scheme for discretization in the axial direction and simulations are performed for an industrial hydrotreating unit to evaluate the behavior of the system under different conditions and assumptions e. g. related to the linear gas velocity. A study of the dynamics is carried out to investigate the behavior of the system with a change in the sulfur compound concentration of the feed. In addition, a sensitivity analysis of the most relevant model parameters is performed.

A series of reactors including a sequencing batch reactor (SBR) and a sequencing batch biofilm reactor (SBBR) were used for nitrogen removal. The aim of this study was simultaneous removal of NH 4 + -N and NO x – -N from synthetic wastewater. In the novel proposed method, the effluent from SBR was sequentially introduced into SBBR, which contained 0.030 m 3 biofilm carriers, so the system operated under a paired sequence of aerobic-anoxic conditions. The effects of different carbon sources and aeration conditions were investigated. A low dissolved oxygen (DO) level in the biofilm depth of the fixed-bed process (SBBR) simulated the anoxic phase conditions. Accordingly, a portion of NH 4 + -N that was not converted to NO 3 – -N by the SBR process was converted to NO 3 – -N in the outer layer of the biofilm in the SBBR process. Further, simultaneous nitrification and denitrification (SND) was achieved in the SBBR where NO 2 – -N was converted to N 2 directly, before NO 3 – -N conversion (partial nitrification). The level of mixed liquid suspended solids (MLSS) was 2740 mg/l at the start of the experiments. The required carbon source (C: N ratio of 4) was provided by adding an internal carbon source (through step feeding) or ethanol. Firstly, as part of the system (SBR and SBBR), SBR operated at a DO level of 1 mg/l while SBBR operated at a DO concentration of 0.3 mg/l during Run-1. During Run-2, the system operated at the low DO concentration of 0.3 mg/l. When the source of carbon was ethanol, the nitrogen removal rate (R N ) was higher than the operation with an internal carbon source. When the reactors were operated at the same DO concentration of 0.3 mg/l, 99.1 % of the ammonium was removed. The NO 3 – -N produced during the aerobic SBR operation of the novel method was removed in SBBR reactor by 8.3 %. The concentrations of NO 3 - -N and NO 2 – -N in the SBBR effluent were reduced to 2.5 and 5.5 mg/l, respectively. Also, the total nitrogen (TN) removal efficiency was 97.5 % by adding ethanol at the DO level of 0.3 mg/l. When C:N adjustment was carried out SND efficiency at C:N ratio of 6.5 reached to 99 %. The increasing nitrogen loading rate (NLR) to 0.554 kg N/m 3 d decreased SND efficiency to 80.7 %.

Solid particle dispersion and chemical reactions in high-viscosity non-Newtonian fluid are commonly encountered in polymerization systems. In this study, an interphase mass transfer model and a finite-rate/eddy-dissipation formulation were integrated into a computational fluid dynamics model to simulate the dispersion behavior of particles and the mass transfer–reaction kinetics in a condensation polymerization-stirred tank reactor. Turbulence fields were obtained using the standard k – ε model and employed to calculate the mixing rate. Cross model was used to characterize the rheological property of the non-Newton fluid. The proposed model was first validated by experimental data in terms of input power. Then, several key operating variables (i.e. agitation speed, viscosity, and particle size) were investigated to evaluate the dispersive mixing performance of the stirred vessel. Simulation showed that a high agitation speed and a low fluid viscosity favored particle dispersions. This study provided useful guidelines for industrial-scale high-viscosity polymerization reactors.

In this work, a comparative study of Euler-Euler and Euler-Lagrange approaches for modeling gas-solid flows in the multiple-spouted bed has been carried out to investigate the hydrodynamics of gas-solid flows. The influence of inlet gas velocity on the hydrodynamics of gas-solid flows in the multiple-spouted bed is investigated as well. Hydrodynamic characteristics of gas-solid flows such as flow behaviors, solid volume fraction, particle velocity and particle trajectory are analyzed and discussed in detail, providing some basic mechanism analysis of the gas-solids in the multiple-spouted bed. It is found that the central spout gas jet is a little confined by the auxiliary gas jets, and the hole-to-hole synergy is quite obvious when the auxiliary spout gas velocity is higher than the central spout gas velocity. When central/auxiliary gas velocity is 10/20 m/s, the maximum vertical particle velocities predicted by Euler-Euler and Euler-Lagrange approaches are 452 mm/s and 721 mm/s at the height of 10 mm respectively. A typical cycle period of a single particle is about 1.25 s, and the residence time in the spout regions is about 0.14 s in one cycle period in auxiliary dominant pattern. The curves of bed expansion height versus time calculated by Euler-Lagrange approach rise and fall periodically, while the curves calculated by Euler-Euler approach keep steady with little change. It is much easier for particles to be blew in the multiple-spouted bed using the Euler-Lagrange approach. The simulation results obtained from two models can provide some guidance for modifying the multiple-spouted bed to optimize physical operations such as drying and coating in the multiple-spouted bed.

Pakistan is very rich in coal reserves specifically after exploration of Thar coal reserves. At the same time country is facing energy crises due to shortage or unavailability of sustainable fuel supply at a cheaper rate. One potential solution is coal gasification which gives clean synthetic gas usually called syngas for use as an alternative fuel source for electricity production at a cheaper rate as well as a source of recovering different chemicals used as basic raw materials in other industries. Numerical simulations have been performed in this work for the gasification process of indigenous coal on a 2D computational fluid dynamic (CFD) model of downdraft entrained-flow gasifier using commercial CFD software FLUENT®6.3.26. Navier-stokes equations along with transport equations for species have been solved using eddy-dissipation combustion model. The compositions of indigenous coals (Thar, Lakhra, and Sonda) were used in simulations as gasification feedstock. Rich oxidant conditions 95 % O 2 and 5 % N 2 were set for gasification. The gasification performance was studied by comparing efficiencies of gasification and quality of syngas produced for three types of coal feedings. The temperature and pressure profiles inside the gasifier were also studied. From simulation results, the great influence of coal composition was observed in the performance of gasification. Lakhra coal produced syngas with a maximum heating value of 20.55 MJ/kg whereas sonda coal produced syngas with a minimum heating value of 17.96 MJ/kg.