Adeniyi Lawal

Nonisothermal model of single screw extrusion of generalized Newtonian fluids

Abstract A nonisothermal model of Ike single screw extrusion processing of generalized Newtonian fluids is presented. Various temperature dependent forms of a generalized Newtonian fluid constitutive equation representing the Herschel-Bulkley fluid and its simplifications, including Bingham plastic, power law of Ostwald-de Waele, and Newtonian fluids, are applicable. The model includes the generally ignored transverse convection terms of the equation of energy. The importance of keeping the transverse convection terms in the analysis is demonstrated by applying the model and comparing findings to experimental results involving the transverse flow temperature distributions in single screw extruders, available in the literature. The numerical instabilities, arising principally from the convection terms, generally encountered in high-Peclet-number extrusion flows, could be eliminated by the use of the streamline upwind / Petrov-Galerkin formulation. The model is sufficiently general to accommodate Naviers w...

Hydrodeoxygenation of microalgae oil to green diesel over Pt, Rh and presulfided NiMo catalysts

The catalytic characteristics, activity and selectivity of 1% Pt/Al2O3, 0.5% Rh/Al2O3 and presulfided NiMo/Al2O3 catalysts have been investigated in the hydrodeoxygenation of microalgae (Nannochloropsis salina) oil to produce green diesel in a microreactor. Coke accumulation decreased in the order NiMo > Pt > Rh. The amount of formed coke over NiMo increased with reaction duration, while no on-stream time dependence was found over Pt and Rh. Rhodium was found to be very active for CH4 production via hydrocracking at its freshly reduced state. The activity and selectivity of all three investigated catalysts were positively affected by increased reaction pressure, temperature, H2/oil ratio and residence time. The selectivity of NiMo for the hydrodehydration (DHYD) route was changed to a hydrodecarbonylation/hydrodecarboxylation (DCO/DCO2) route at a reduced H2/oil ratio and residence time, while the selectivity of Pt and Rh for the DCO/DCO2 route was not affected by the reaction conditions. The highest hydrocarbon yield, 76.5%, was obtained over 1% Pt (310 °C, 500 psig, 1000 SmL mL−1 gas/oil ratio, 1.5 s residence time), which is 13.8% higher than that over NiMo (360 °C, 500 psig, 1000 SmL mL−1 gas/oil ratio, 1 s residence time). The 50 °C decrease in the reaction temperature for Pt indicates possible energy saving via heat supply.

EXTRUSION AND LUBRICATION FLOWS OF VISCOPLASTIC FLUIDS WITH WALL SLIP

Abstract The simplest model flow which approximates the extrusion (shallow screw channels) and lubrication flow is the steady, laminar flow occurring between two infinitely long parallel plates i.e., the generalized plane Couette flow. Here we develop an analytical model of the generalized plane Couette flow of viscoplastic fluids. The deformation and flow behavior of viscoplastic fluids can be realistically represented with the Herschel-Bulkley constitutive equation, which we have utilized as the basis for the development of our analytical model. Furthermore, as also demonstrated here, the deformation behavior of viscoplastic fluids is generally complicated by the presence of wall slip at solid walls, which occurs as a function of the wall shear stress. The wall slip versus the wall shear stress behavior of viscoplastic fluids can be experimentally characterized using viscomelric flows, including steady torsional and capillary flows. Thus determined Naviers wall slip coefficient can then be utilized in ...

The Catalytic Hydrogenation of Aromatic Nitro Ketone in a Microreactor: Reactor Performance and Kinetic Studies

Catalytic hydrogenation of nitro aromatics is an important class of reactions in the pharmaceutical and fine chemical industries. These reactions are extremely fast and highly exothermic in nature; hence, mass and heat transfer limitations play an important role when these reactions are conducted in conventional batch reactors. The use of a micro-channel reactor for such reactions provides improved mass transfer rates which may ensure that the reaction operates close to intrinsic kinetics. In the present study, the hydrogenation of a model aromatic nitro ketone was conducted in a packed-bed microreactor. The effects of different processing conditions were studied using 5%Pd/Alumina catalyst, viz.: hydrogen pressure, substrate concentration, temperature, and residence time on the conversion of substrate, Space Time Yield (STY), and selectivity of product. Internal and external mass and heat transfer limitations in the microreactor were examined. The kinetic study was undertaken in a differential reactor mode, keeping the conversion of the reactant at less than 10%. The overall reaction was treated as comprising two separate reactions: first, the reduction of the nitro compound to hydroxylamine and then, the reduction of the hydroxylamine to amine. Two rate equations for the two consecutive reactions assuming the Langmuir-Hinshelwood mechanism provided the best fit to the experimental data. These two rate equations predicted the experimental rates satisfactorily and the differences were within 10% error. Experiments were also carried out in an integral reactor, and the reactor performance data were found to be in agreement with the predictions of the theoretical models.

Cycloaddition of Isoamylene and ?-Methylstyrene in a Microreactor using Filtrol-24 catalyst: Microreactor Performance Study and Comparison with Semi-Batch Reactor Performance

The cycloaddition reaction between isoamylene and ?-methylstyrene yields indane compounds 1,1,2,3,3,-pentamethylindane and 3-ethyl-1,1,3-trimethylindane, which are intermediate cyclic products used in the synthesis of musk fragrances. This exothermic reaction is conventionally carried out industrially in large semi-batch reactors, which have high heat and mass transfer resistances, are difficult to optimize, and scale-up. Aqueous sulfuric acid is conventionally used as the catalyst for the cycloaddition reaction, but solid catalysts offer many advantages over the corrosive aqueous sulfuric acid catalyst including the elimination of expensive separation and purification steps, and the need to use corrosion resistant materials of construction. A microreactor, which has enhanced heat and mass transfer characteristics, high surface to volume ratio, and improved fluid mixing, was used for the reaction using an acidic solid catalyst, Filtrol-24. A parametric study to obtain the dependence of product yield, reactant conversion and space-time yield on process variables such as catalyst particle size, residence time, velocity, temperature, pressure and the molar ratio of the reactants in the feed, was conducted. Through this study the optimum reaction conditions were obtained. The cycloaddition reaction was also performed in the semi-batch reactor using Filtrol-24 catalyst in order to compare its performance to that of the microreactor. Higher product yields were obtained in the microreactor compared to the semi-batch reactor, and the space-time yield in the microreactor was 4.8 times larger than that obtained in the semi-batch reactor at optimum reaction conditions in both reactors.

Isothermal Pseudo-2D Analysis of Reactive Extrusion in Single-Screw Extruders

Reactive extrusion involves the continuous synthesis and modification of polymers in a screw extruder. Over the years, it has received a lot of attention both in academic research and industrial applications. It remains a potential source for further development of new products and processes. The present analysis is focused on power-law fluids undergoing isothermal homogeneous and heterogeneous reactions simulating reactive extrusion in a single-screw extruder. The assumption of shallow screw geometry enables the flow to be modeled as that occurring between infinitely long parallel plates, the analytical solutions of which are available in the literature. For the concentration problem, the reaction is taken to be first order, and the equation of conservation of component species is transformed into an eigenvalue problem. The eigenvalues and eigenfunctions are determined using the Runge–Kutta method. Analytical solutions are developed for the concentration distribution in the extruder and expressions for the conversion of the reactant, and Sherwood number are presented. The accuracy of the solutions is established and the concentration profiles at different axial locations in the extruder are presented for various values of power-law index, flow rate, and the homogeneous and heterogeneous reaction rate parameters. The effects of these parameters on the Sherwood number, reactant conversion and, bulk and wall concentration are also investigated.

Mathematical Modeling of Three-Dimensional Die Flows of Viscoplastic Fluids with Wall Slip

The mathematical modeling of the continuous processing of filled polymers, and concentrated suspensions in screw extruders and dies of complex shapes is undertaken. The simulation of the flow of such filled systems in complex geometries is rendered complicated by the occurrence of wall slip at fluid/solid boundaries. The incorporation of wall slip in the analysis of three-dimensional flows including flows through dies, single/twin-screw extruders and other processing geometries is currently lacking. Here we present an analysis of three-dimensional flows with wall slip, and demonstrate the procedure using the flow of a Herschel-Bulkley fluid in a tapered die.

CFD Simulations of Gas and Liquid Slugs for Taylor Flow in a Microchannel

The rapid development of microfabrication techniques creates new opportunities for applications of microchannel reactor technology in chemical reaction engineering. The extremely large volume-to-surface ratio and the short transport path in microchannels enhance heat and mass transfer dramatically and hence provide many potential opportunities in chemical process development and intensification. Multiphase reactions involving gas/liquid reactants with a solid as a catalyst are ubiquitous in the chemical and pharmaceutical industries, and the hydrodynamics play a prominent role in reactor design and performance. For gas/liquid two-phase flow in a microchannel, the Taylor slug flow regime is the most commonly encountered flow pattern, therefore the present study deals with the numerical simulation of gas and liquid slugs in a microchannel. A T-junction microchannel (empty or packed) with varying cross-sectional width (0.25, 0.5, 0.75, 1, 2 and 3 mm) served as the model micro-reactor, and a finite volume based commercial CFD package, FLUENT, was adopted for the numerical simulation. The gas and liquid slug lengths at various operating conditions were obtained and found to be in good agreement with the literature data.© 2005 ASME