CERES :: Browsing by Author "Gu, Sai"

Browsing by Author "Gu, Sai"

Now showing 1 - 20 of 33

Open Access
Adaptive mesh refinement of gas-liquid flow on an inclined plane
(Elsevier, 2013-10-03) Cooke, J. J.; Armstrong, L-M.; Luo, K. H.; Gu, Sai
Carbon Capture & Storage (CCS) is one of the various methods that can be used to reduce the carbon footprint of the energy sector. The efficiency with which CO2 is absorbed from flue gas using packed columns is highly dependent on the structure of the liquid films that form on the packing materials. This work examines the hydrodynamics of these liquid films using the CFD solver, OpenFOAM to solve two-phase, isothermal, non-reacting flow using the volume-of-fluid (VOF) method. Local adaptive mesh refinement (AMR) is used to ensure improved resolution of the geometrical grids at the gas–liquid interface. Comparisons are made between the solutions obtained using AMR and those obtained using highly refined static meshes. It was observed that local AMR produced results with much better correlation to experimental data.
Open Access
An agent-based model schema to understand how shocks to the household a ect energy consumption behaviour
(Cranfield University, 2014-12) Wood, Katherine; Gu, Sai; Varga, Liz
There are many factors which are understood to a ect domestic energy consumption, including: occupant demographics such as age, income and family type, occupant attitudes, peer networks and occupant-building interactions such as window opening, heating and lighting patterns. Both top-down and bottom-up modelling approaches have been used previously to represent these behavioural factors and other domestic energy usage variables such as dwelling construction. Top-down models were found to lack the granularity and exibility to accurately portray the UK domestic energy sector from the perspective of individual households. Conversely, bottom-up models were found to be more applicable to behavioural factors due to their ability to model individual entities and interactions. However, it was also identi ed that most current models only consider building construction or occupant behaviour, with few combining the two. This project aims to combine occupant behaviour and dwelling construction variables by suggesting an agent-based model implementation schema to provide insight into the domestic energy consumption system, with special interest in the e ects of life-stage changes on the household and the e ect of peer networks on the adoption of energy e ciency measures. Five `shock' groups are considered, namely, households a ected by a recent: retirement, unemployment, new child, house move or reduction in household size. A pilot survey was conducted in order to obtain results to inform model design decisions and the results are discussed.
Open Access
Application of a high density ratio lattice-Boltzmann model for the droplet impingement on flat and spherical surfaces
(Elsevier, 2014-06-06) Zhang, Duo; Papadikis, Konstantinos; Gu, Sai
In the current study, a 3-dimensional lattice Boltzmann model which can tolerate high density ratios is employed to simulate the impingement of a liquid droplet onto a flat and a spherical target. The four phases of droplet impact on a flat surface, namely, the kinematic, spreading, relaxation and equilibrium phase, have been obtained for a range of Weber and Reynolds numbers. The predicted maximum spread factor is in good agreement with experimental data published in the literature. For the impact of the liquid droplet onto a spherical target, the temporal variation of the film thickness on the target surface is investigated. The three different temporal phases of the film dynamics, namely, the initial drop deformation phase, the inertia dominated phase and the viscosity dominated phase are reproduced and studied. The effect of the droplet Reynolds number and the target-to-drop size ratio on the film flow dynamics is investigated.
Open Access
CFD modelling of particle shrinkage in a fluidized bed for biomass fast pyrolysis with quadrature method of moment
(Elsevier, 2017-05-08) Liu, Bo; Papadikis, Konstantinos; Gu, Sai; Fidalgo, Beatriz; Longhurst, Philip J.; Li, Zhongyuan; Kolios, Athanasios
An Eulerian-Eulerian multi-phase CFD model was set up to simulate a lab-scale fluidized bed reactor for the fast pyrolysis of biomass. Biomass particles and the bed material (sand) were considered to be particulate phases and modelled using the kinetic theory of granular flow. A global, multi-stage chemical kinetic mechanism was integrated into the main framework of the CFD model and employed to account for the process of biomass devolatilization. A 3-parameter shrinkage model was used to describe the variation in particle size due to biomass decomposition. This particle shrinkage model was then used in combination with a quadrature method of moment (QMOM) to solve the particle population balance equation (PBE). The evolution of biomass particle size in the fluidized bed was obtained for several different patterns of particle shrinkage, which were represented by different values of shrinkage factors. In addition, pore formation inside the biomass particle was simulated for these shrinkage patterns, and thus, the density variation of biomass particles is taken into account.
Open Access
CFD modelling of post-combustion carbon capture with amine solutions in structured packing columns
(Cranfield University, 2016-06) Sebastia-Saez, J. Daniel; Gu, Sai; Fidalgo, Beatriz
The scope of the present thesis is the development of a Computational Fluid Dynamics model to describe the multiphase flow inside a structured packing absorber for postcombustion carbon capture. The work focuses mainly on two flow characteristics: the interface tracking and the reactive mass transfer between the gas and the liquid. The interface tracking brings the possibility of studying the liquid maldistribution phenomenon, which strongly affects the mass transfer performance. The development of a user-defined function to account for the reactive mass transfer between phases constitutes the second major concept considered in this thesis. Numerical models found in the literature are divided into three scales due to the current computational capacity: small-, meso- and large-scale. Small-scale has usually dealt with interface tracking in 2D computational domains. Meso-scale has usually been considered to assess the dry pressure drop performance of the packing (considering only the gas phase). Large-scale studies the liquid distribution over the whole column assuming that the structured packing behaves as a porous medium. This thesis focuses on small- and meso-scale. The novelty of this work lies in expanding the capabilities of the aforementioned scales. At small-scale, the interfacial tracking is implemented in a 3D domain, instead of 2D. The user-defined function that describes the reactive mass transfer of CO2 into the aqueous MEA solution is also included to assess the influence of the liquid maldistribution on the mass transfer performance. At the meso-scale, the Volume of Fluid method for interface tracking is included (instead of only the gas phase) to describe flow characteristics such as the liquid hold-up, the interfacial area and the mass transfer. At the theoretical level, this model presents the particularity of including both a mass and a momentum source term in the conservation equations. A comprehensive mathematical development shows the influence of the mass source terms on the momentum equation.
Open Access
CFD simulations on the effect of catalysts on the hydrodeoxygenation of bio-oil
(Royal Society of Chemistry, 2015-04-16) Gollakota, Anjani R. K.; Subramanyam, Malladi D.; Kishore, Nanda; Gu, Sai
Bio-oil derived from lignocellulose biomass is an emerging alternative resource to conventional fossil fuel. However, the as-obtained unprocessed bio oil is oxy-rich, has low pH and contains high moisture, which suppresses the heating value; thus, its mixing with conventional fuel is not compatible. Therefore, studies on the upgradation of bio oil using catalytic hydrodeoxygenation (HDO) have become prominent in recent years. This study presents computational fluid dynamics (CFD) based simulation results on the effect of catalysts (Pt/Al2O3, Ni–Mo/Al2O3, Co–Mo/Al2O3) on the upgradation of bio oil using a hydrodeoxygenation process in an ebullated bed reactor. These numerical simulations are performed using an Eulerian multiphase flow module that is available in a commercial CFD based solver, ANSYS Fluent 14.5. Prior to obtaining the new results, the present numerical solution methodology is validated by reproducing some of the experimental results on the upgradation of bio oil available in the literature. Furthermore, the influence of weight hourly space velocities (WHSVs), operating temperature, and pressure inside the reactor for the different catalysts on the performance of HDO for bio oil upgradation in an ebullated bed reactor are delineated. It is observed that the gaseous stream products are higher in the presence of Pt/Al2O3 catalyst; phenols are higher when Ni–Mo/Al2O3 is used, and higher aromatics are obtained with the Co–Mo/Al2O3 catalyst. Finally, a comparison among the mass fraction of the individual species of three phases with respect to different catalysts for various combinations of WHSV, temperature and pressure values are presented.
Open Access
Comparative evaluation of GHG emissions from the use of Miscanthus for bio-hydrocarbon production via fast pyrolysis and bio-oil upgrading
(Elsevier, 2016-05-13) Shemfe, Mobolaji B.; Whittaker, Carly; Gu, Sai; Fidalgo Fernandez, Beatriz
This study examines the GHG emissions associated with producing bio-hydrocarbons via fast pyrolysis of Miscanthus. The feedstock is then upgraded to bio-oil products via hydroprocessing and zeolite cracking. Inventory data for this study were obtained from current commercial cultivation practices of Miscanthus in the UK and state-of-the-art process models developed in Aspen Plus®. The system boundary considered spans from the cultivation of Miscanthus to conversion of the pyrolysis-derived bio-oil into bio-hydrocarbons up to the refinery gate. The Miscanthus cultivation subsystem considers three scenarios for soil organic carbon (SOC) sequestration rates. These were assumed as follows: (i) excluding (SOC), (ii) low SOC and (iii) high (SOC) for best and worst cases. Overall, Miscanthus cultivation contributed moderate to negative values to GHG emissions, from analysis of excluding SOC to high SOC scenarios. Furthermore, the rate of SOC in the Miscanthus cultivation subsystem has significant effects on total GHG emissions. Where SOC is excluded, the fast pyrolysis subsystem shows the highest positive contribution to GHG emissions, while the credit for exported electricity was the main ‘negative’ GHG emission contributor for both upgrading pathways. Comparison between the bio-hydrocarbons produced from the two upgrading routes and fossil fuels indicates GHG emission savings between 68% and 87%. Sensitivity analysis reveals that bio-hydrocarbon yield and nitrogen gas feed to the fast pyrolysis reactor are the main parameters that influence the total GHG emissions for both pathways.
Open Access
Computational modelling of thermal spraying processes
(Cranfield University, 2016-03) Mahrukh, Mahrukh; Gu, Sai; Sher, Ilai
The main aim of this project is to model the effects of varied injection parameters on the gas dynamics and droplet dynamics of the HVSFS and SP- HVOFS processes for improving the droplet breakup and evaporation to enhance the nanoparticles heating and deposition efficiency. Thermal spraying processes are widely used to generate thermal-, corrosion-, and wear-resistant layers over the machine parts, to increase the durability of the equipment under severe environmental conditions. The liquid feedstock is used to achieve nanostructured coatings. It is used either in the form of a suspension or a solution precursor. The suspension is a mixture of solid nanoparticles suspended in a liquid medium consisting, for instance, of water, ethanol, or isopropanol. This dispersion mechanism in a liquid carrier provides adequate flowability to the nanoparticles, which cannot be handled by conventional gas- based feeding systems, whereas the solution precursor is mixed at the molecular level; hence, more uniform phase composition and properties are expected in the sprayed coatings as compared to the suspension and conventional powder spraying. Firstly, experiments are conducted to analyse the effects of different precursor concentrations, solvent types and injection nozzles on the size and morphology of synthesized nanoparticles. The results indicate that the particle size increased with increasing precursor concentration due to the variations in the physical properties of the mixture solution. The higher precursor concentrations had an adverse effect on the droplet atomization and evaporation process that led to bigger size particle formation. The use of aqueous solvent has some limits and with higher precursor concentration the surface tension increases that resulted in the reduction of droplets’ disintegration, and thus bigger size precursor droplets generate larger nanoparticles. A mixture of aqueous-organic solvents and pure organic precursors are preferred to improve the process efficiency of the nanoparticles size and morphology. Furthermore, the nanoparticles size can be controlled by using liquid feedstock atomization before injecting into the HVOF torch. A new effervescent injection nozzle is designed and compared to different types of existing injection nozzles, to see the variations in the droplet disintegration, and its effects on the performance of the HVOF torch processes. It is detected that the atomization would result in smaller size particles with homogeneous morphology. In a numerical study, different droplet injection types are analysed to see their effects on the gas and droplet dynamics inside the HVOF torch. The group-type injection (GTI) and effervescent-type atomization (ETI) are used effectively to overcome the heat losses and delays in the droplet evaporation. These approaches reduce the thermal and kinetic energy losses in the suspension-fed-HVOF torch, thereby improving the coating formation. The effects of using multicomponent water-ethanol mixture injection in the HVOF torch are also modelled, and its impact on the droplet breakup and evaporation are studied. The organic solvents have a low heat of vaporization and surface tension, and can effectively be used in the HVOF spraying process over the water-based solvents. Furthermore, nanoparticles are suspended in the liquid feedstock and injected into the HVOF torch. The effect of increasing nanoparticles’ concentration in the feedstock and its consequence on the gas dynamics, droplet breakup and evaporation are analysed. The augmentation in the nanoparticles loading in the suspension droplets can decrease the droplet breakup and evaporation rate because the required heat of vaporization increases significantly. Moreover, the size of injection droplet affects the droplet fragmentation process; bigger sized droplets observed a delay in their evaporation that resulted in coating porosity. The results suggest that smaller droplet sizes are preferred in coating applications involving a higher concentration of nanoparticles with high melting point. Further, the gas flow rates (GFRs) are regulated to control the droplet dispersion, atomization and evaporation inside the solution precursor fed-HVOF torch. The size of the droplet diameter is decreased by an increment in the GFR, as higher combustion rates increase the combustion flame enthalpy and kinetic energy. Moreover, the increase in the oxygen/fuel flow rates dilutes the injected precursor. It reduces ZrO2 concentration in the process and decreases the rate of particle collision; as a result, non-agglomerated nanoparticles can be obtained.
Open Access
Deoxygenation in anisole decomposition over bimetallic catalysts supported on HZSM-5
(Elsevier, 2018-10-29) Zhang, Jiajun; Fidalgo, Beatriz; Wagland, Stuart; Shen, Dekui; Zhang, Xiaolei; Gu, Sai
This work investigated the deoxygenation reaction in anisole decomposition over HZSM-5 (HZ(25)) zeolite supported bimetallic catalysts to produce benzene, toluene and xylene (BTX). Experiments were performed in order to evaluate the synergistic effect between the two active metals with the focus on the effect of temperature, metal type, and metal loading ratio. Experimental results showed that 1%Ni-1%Mo/HZ(25) led to both the highest BTX yield (i.e. 30.0 wt%) and selectivity (i.e. 83.7%). On the contrary, bimetallic catalysts containing Fe were less effective in promoting the BTX production. It was identified that the optimum temperature for BTX production over 1%Ni-1%Mo/HZ(25) catalysts was 500 °C. Characterization of fresh and spent catalysts showed microcrystal particles of bi-metal loadings highly dispersed on the zeolite surface, and some agglomeration of metallic particles were also observed. Large amount of carbonaceous deposit was observed on the spent catalysts mainly in the form of amorphous. Density Functional Theory (DFT) modelling was carried out in order to study the adsorption energy of anisole and phenol molecules onto Ni-Mo, Ni-Fe and Mo-Fe surfaces; and the interactions between phenol molecule and bimetal surfaces were further analysed. All the analysed bimetal surfaces exhibited strong interactions with the adsorbed molecule. Ni-Mo surface declined electrons energy levels mainly around 1.5 eV in the adsorbate molecule and released the highest adsorption energy; while Ni-Fe and Mo-Fe surface led to more electrons exchange with the adsorbate during the adsorption. The modelling results agreed well with experiments by revealing that the strong binding between phenolic compounds (Phs) and the Ni-Mo based catalysts bimetal surface would lead to a higher BTX production in the deoxygenation reaction in the decomposition of anisole.
Open Access
Double emulsion production in glass capillary microfluidic device: parametric investigation of droplet generation behaviour
(Elsevier, 2015-03-20) Nabavi, Seyed Ali; Vladisavljević, G. T.; Gu, Sai; Ekanem, E. E.
A three-phase axisymmetric numerical model based on Volume of Fluid–Continuum Surface Force (VOF–CSF) model was developed to perform parametric analysis of compound droplet production in three-phase glass capillary devices that combine co-flow and countercurrent flow focusing. The model predicted successfully generation of core–shell and multi-cored double emulsion droplets in dripping and jetting (narrowing and widening) regime and was used to investigate the effects of phase flow rates, fluid properties, and geometry on the size, morphology, and production rate of droplets. As the outer fluid flow rate increased, the size of compound droplets was reduced until a dripping-to-jetting transition occurred. By increasing the middle fluid flow rate, the size of compound droplets increased, which led to a widening jetting regime. The jetting was supressed by increasing the orifice size in the collection capillary or increasing the interfacial tension at the outer interface up to 0.06 N/m. The experimental and simulation results can be used to encapsulate CO2 solvents within gas-permeable microcapsules.
Open Access
Dynamics of double emulsion break-up in three phase glass capillary microfluidic devices
(Elsevier, 2015-03-13) Nabavi, Seyed Ali; Gu, Sai; Vladisavljević, G. T.; Ekanem, E. E.
Pinch-off of a compound jet in 3D glass capillary microfluidic device, which combines co-flowing and countercurrent flow focusing geometries, was investigated using an incompressible three-phase axisymmetric Volume of Fluid–Continuum Surface Force (VOF–CSF) numerical model. The model showed good agreement with the experimental drop generation and was capable of predicting formation of core/shell droplets in dripping, narrowing jetting and widening jetting regimes. In dripping and widening jetting regimes, the presence of a vortex flow around the upstream end of the necking thread facilitates the jet break-up. No vortex flow was observed in narrowing jetting regime and pinch-off occurred due to higher velocity at the downstream end of the coaxial thread compared to that at the upstream end. In all regimes, the inner jet ruptured before the outer jet, preventing a leakage of the inner drop into the outer fluid. The necking region moves at the maximum speed in the narrowing jetting regime, due to the highest level of shear at the outer surface of the thread. However, in widening jetting regime, the neck travels the longest distance downstream before it breaks.
Open Access
Effects of angular injection, and effervescent atomization on high-velocity suspension flame spray process
(Elsevier, 2016-06-11) Mahrukh, Mahrukh; Kumar, Arvind; Gu, Sai
This work presents the nanostructured coating formation using suspension thermal spraying through the HVOF torch. The nanostructured coating formation requires nanosize powder particles to be injected inside a thermal spray torch using liquid feedstock. The liquid feedstock needs to be atomized when injected into the high-velocity oxygen fuel (HVOF) torch. This paper presents the effects of angular injection and effervescent atomization of the liquid feedstock on gas and droplet dynamics, vaporization rate, and secondary breakup in the high-velocity suspension flame spray (HVSFS) process. Different angular injections are tested to obtain the optimum value of the angle of injection. Moreover, effervescent atomization technique based on twin-fluid injection has been studied to increase the efficiency of the HVSFS process. Different solid nanoparticle concentrations in suspension droplets are considered. In angular injection the droplets are injected into the core of the combustion zone; this immediately evaporates the droplets, and evaporation is completed within the torch. The value of 10°–15° is selected as the optimal angle of injection to improve the gas and droplet dynamics inside the torch, and to avoid the collision with the torch's wall. The efficiency of the effervescent atomization can be enhanced by using high gas-to-liquid mass flow rate ratio, to increase the spray cone angle for injecting the suspension liquid directly into the combustion flame. It is also found that the increment in the nanoparticle concentration has no considerable effects on the droplet disintegration process. However, the location of evaporation is significantly different for homogeneous and non-homogeneous droplets.
Open Access
Hydrodynamic experiments on a small-scale circulating fluidised bed reactor at elevated operating pressure, and under An O2/Co2 environment
(VINCA Institute of Nuclear Sciences, 2017-03-01) Sarbassov, Yerbol; Zayoud, Azd; Mahanta, Pinakeswar; Gu, Sai; Ranganathan, Panneerselvam; Saha, Ujjwal
Pressurised circulating fluidised bed (CFB) technology is a potentially promising development for clean coal technologies. The current work explores the hydrodynamics of a small-scale circulating fluidised bed at elevated operating pressures ranging from 0.10 to 0.25 MPa. The initial experiments were performed at atmospheric pressure with air and O/CO environments as the fluidisation gas to simulate the hydrodynamics in a CFB. A comparison between the effects of air and O/CO mixtures on the hydrodynamics was outlined in this paper for particles of 160 μm diameter. A small but distinct effect on axial voidage was observed due to the change in gas density in the dense zone of the bed at lower gas velocity, while only minimal differences were noticed at higher gas velocities. The hydrodynamic parameters such as pressure drop and axial voidage profile along the height were reported at two different bed inventories (0.5 and 0.75 kg) for three mean particle sizes of 160, 302 and 427 μm and three superficial gas velocities. It was observed that the operating pressure had a significant effect on the hydrodynamic parameters of bed pressure drop and axial bed voidage profiles. The effect of solids loading resulted in an exponential change in pressure drop profile at atmospheric pressure as well as at elevated pressure. The experimental results on hydrodynamic parameters are in reasonable agreement with published observations in the literature.
Open Access
Linking energy behaviour, attitude and habits, and social practices with environmental predisposition and knowledge:what are the factors with influence on environmental behaviour?
(Cranfield University, 2015-01) Pothitou, Mary; Gu, Sai; Varga, Liz
This research aims to understand which factors influence environmental behaviour in order to contribute to the existing theory and practice which is focused on individuals' energy consuming behaviour. As a first step, this thesis reviews existing up-to-date literature related to individual household energy consumption. The how and why individual behaviour affects the energy use are discussed, together with the principles and perspectives which have so far been considered in order to explain the habitual consuming behaviour. The research gaps, which are revealed from previous studies in terms of the limitations or assumptions of the methodology with respect to altering individuals’ energy usage, give insights for a conceptual framework to define a comprehensive approach which attempts to contribute to existing theory. The proposed framework suggests that the individual energy perception gaps are affected by psychological, habitual, structural and cultural variables in a wider-contextual (i.e. national scale), meso-societal and micro-individual spectrum. All these factors need to be considered in order for a variety of combined intervention methods, which are discussed and recommended, to introduce a more effective shift of the conventional energy consuming behaviour, advancing insights for successful energy policies. Furthermore, this thesis presents and discusses the findings of an empirical study which compares individuals’ environmental predisposition and knowledge with their: (a) energy behaviour, attitude and habits; and (b) social practices related to the use and ownership of appliances. This study also attempts to correlate education level and household income with the above variables. The investigation is based on a survey of 68 employees of an educational institution, corresponding to a medium-sized enterprise, which was selected as the first phase of research aiming to compare energy saving behaviour at home and in the workplace. The current study relates only to the domestic aspects of this work attempting to contribute to existing practice by presenting a detailed evaluation of pro-environmental behaviour which can be applied to similar studies while considering different demographics. In particular, the sample of this study is composed of a relatively highly educated and professional population. The statistical analysis reveals significant correlations between environmental value and knowledge and elements of individuals’ energy attitudes, habits and behaviour. The respondents’ predisposition and attitudes is further correlated with social practices associated with domestic appliances. No significant correlations were established to demonstrate that education level may influence environmental predisposition and knowledge, energy saving attitudes, habits and behaviours however, given the nature of the population sample, this is not surprising. An unanticipated outcome from the Principal Component Analysis (PCA) was that household income, and to a lesser extent gender, are associated with energy saving habits and behaviours. On further investigation, household income was found to be correlated with knowledge of greenhouse gas emissions and the number of laptops and electric showers owned per household. Conversely, a relationship between individuals’ energy habits and household consumption practices was not indicated by significant correlations.
Open Access
Mechanism of deoxygenation in anisole decomposition over single-metal loaded HZSM-5: Experimental study
(Elsevier, 2017-11-20) Zhang, Jiajun; Fidalgo, Beatriz; Kolios, Athanasios; Shen, Dekui; Gu, Sai
This work investigates the deoxygenation reaction during the decomposition of anisole (methoxy-rich model compound of lignin) over bi-functional catalyst. The bi-functional catalyst consisted of a single metal loaded on an acid support; the active metals, i.e. Ni, Co, Mo and Cu, were loaded at various rates, and the acid support was HZSM-5 zeolite with a Si/Al ratio of 25 (HZ(25)). Experiments were conducted in a bench-scale fluidised bed reactor within the temperature range from 400°C to 600°C. Experimental results revealed that the increase in temperature and metal loading promoted the selectivity of BTX fraction. Nevertheless, a simultaneous increase in the yield of carbonaceous deposits was also observed at the expense of liquid fraction, both phenolics compounds (Phs) and aromatic hydrocarbons (AHs). 500°C was the preferred temperature for BTX production. Ni-loaded HZ(25) catalyst could dramatically facilitate the conversion of Phs to monoaromatics and increase the selectivity of BTX fraction by 43.4%; Mo-loaded HZ(25) catalyst exhibited the best catalytic activity towards the total production of AHs and promoted the BTX yield by 27.1%. It was also found that 1 wt.% was the optimum loading ratio for both Ni and Mo on HZ(25) to obtain the highest BTX yield and selectivity. Characterization of fresh bi-functional catalysts showed that micro polycrystalline metal sites, in the range of 4 -10 nm, existed on the fresh catalyst and exhibited strong interaction with the HZ(25) support. For the spent catalysts, large amount of amorphous carbonaceous deposit was observed, ascribed to the polycondensation of aromatic compounds during the reaction. Three reaction pathways were proposed for the catalytic deoxygenation of anisole, with the hydrogen being available in-situ as product of the polycondensation reactions
Open Access
Mechanism of transmethylation in anisole decomposition over HZSM-5: Experimental study
(Elsevier, 2016-09-15) Zhang, Jiajun; Fidalgo Fernandez, Beatriz; Shen, Dekui; Xiao, Rui; Gu, Sai
This work investigated the decomposition of anisole (methoxyl-based lignin model compound) in a fluidized bed reactor over no catalysts and a series of HZSM-5 zeolite catalysts with different Si/Al atomic ratios. Transmethylation reaction was identified as the initial step of the thermal decomposition of anisole, leading to the prominent production of phenolic compounds. Methyl phenols were identified as the main products, with the yield of o-cresol being higher than that of p-cresol at the temperatures below 600° C. The transmethylation reaction over HZSM-5 zeolite catalyst was found to occur at temperatures 150° C lower than those for non-catalytic reaction, with the yield of the phenolic compounds being promoted by 2.5 times. Production of the main phenolic compounds during the catalytic decomposition of anisole was enhanced to different extents depending on the Si/Al ratio. The highest selectivity of 79 wt.% was achieved over the zeolite catalyst with a Si/Al ratio of 80. The Brønsted acid sites of the catalyst played a significant role in both the preferential formation of phenolic compounds and preservation of the methyl group.
Open Access
Mechanism of transmethylation in anisole decompostion over Brønsted acid sites: Density Functional Theory (DFT) study
(Royal Society of Chemistry, 2017-08-15) Zhang, Jiajun; Fidalgo, Beatriz; Kolios, Athanasios; Shen, Dekui; Gu, Sai
In this work, the mechanism and intrinsic reaction energy barriers of transmethylation, as the initial stage of the catalytic and non-catalytic anisole decomposition, were investigated by Density Functional Theory (DFT). Molecule analyses indicated that methyl free radical transfer happened in the absence of catalyst, and the catalytic transmethylation over Brønsted acid sites was considered based on the dual electrophilic attack mechanism with protonation and carbocation substitution respectively. Reactions modelling for the formation of methyl-contained compounds in both non-catalytic and catalytic anisole decomposition indicated that the energy barriers were significantly decreased in the presence of catalyst by 60 kcal/mol at the most in the case of o-cresol. The results also revealed that the intrinsic transmethylation orientation preferred the ortho- and para-positions on the acceptor compounds contained oxygen-rich substituents due to its large electronegativity, and the lowest energy barrier was observed in the case of transmethylation towards the para-position of the cresol molecule (54.1 kcal/mol).
Open Access
Micro-scale CFD modeling of reactive mass transfer in falling liquid films within structured packing materials
(Elsevier, 2015-02) Sebastia-Saez, Daniel; Gu, Sai; Ranganathan, Panneerselvam; Papadikis, Konstantinos
Post-combustion carbon capture in structured packing columns is considered as a promising technology to reduce greenhouse gas (GHG) emissions because of its maturity and the possibility of being retrofitted to existing power plants. CFD plays an important role in the optimization of this technology. However, due to the current computational capacity limitations, the simulations need to be divided into three scales (i.e. micro-, meso- and macro-scale) depending on the flow characteristics to be analyzed. This study presents a 3D micro-scale approach to describe the hydrodynamics and reactive mass transfer of the CO2-MEA chemical system within structured packing materials. Higbie's penetration theory is used to describe the mass transfer characteristics whereas enhancement factors are implemented to represent the gain in the absorption rate attributable to the chemical reaction. The results show a detrimental effect of the liquid load on the absorption rate via a decrease in the enhancement factor. The evolution of the wetted area for MEA solutions is compared to the case of pure water highlighting the differences in the transient behavior. The CO2 concentration profiles are examined showing the capability of the model to reproduce the depletion of the solute within the bulk liquid ascribed to the high value of the Hatta number. Also, several approaches on the reaction mechanism such as reversibility and instantaneous behavior are assessed. The results from micro-scale are to be used in meso-scale analysis in future studies to optimize the reactive absorption characteristics of structured packing materials.
Open Access
Micro-scale CFD study about the influence of operative parameters on physical mass transfer within structured packing elements
(Elsevier Science B.V., Amsterdam, 2014-09-01T00:00:00Z) Sebastia-Saez, Daniel; Gu, Sai; Ranganathan, Panneerselvam; Papadikis, Konstantinos
In this work a VOF-based 3D numerical model is developed to study the influence of several operative parameters on the gas absorption into falling liquid films. The parameters studied are liquid phase viscosity, gas phase pressure and inlet configuration, liquid-solid contact angle and plate texture. This study aims to optimize the post-combustion CO2 capture process within structured packed columns. Liquid phase viscosity is modified via MEA (i.e. monoethanolamine) concentration. The results show that an increase in liquid viscosity reduces the diffusivity of oxygen within the liquid film thus hindering the efficiency of the process. Higher pressure carries an absorption improvement that can be attractive to be applied in industry. The simulations show that enhanced oxygen absorption rates can be achieved depending on the velocity of the gas phase and the flow configuration (i.e. co- and counter-current). Also, the importance of wetting liquid-solid contact angles (i.e. less than 90°) is highlighted. Poor liquid-solid adhesion has similar effects as surface tension in terms of diminishing the spreading of the liquid phase over the metallic plate. Finally the influence of a certain geometrical pattern in the metallic surface is also assessed.
Open Access
Modeling the effects of concentration of solid nanoparticles in liquid feedstock injection on high-velocity suspension flame spray process
(American Chemical Society, 2016-02-03) Mahrukh, Mahrukh; Kumar, Arvind; Gu, Sai; Kamnis, S.; Gozali, E.
This paper presents the eﬀects of the concentration of solid nanoparticles in the liquid feedstock injection on the high-velocity suspension ﬂame spray (HVSFS) process. Four diﬀerent concentrations of solid nanoparticles in suspension droplets with various droplet diameters are used to study gas dynamics, vaporization rate, and secondary breakup. Two types of injections, viz. surface and group, are used. The group-type injection increases the eﬃciency of droplet disintegration and the evaporation process and reduces the gas cooling. The initiation of the fragmentation process is diﬃcult for small droplets carrying a high concentration of nanoparticles. Also, smaller droplets undergo rapid vaporization, leaving clogs of nanoparticles in the middle of the barrel. For larger droplets, severe fragmentation occurs inside the combustion chamber. For a higher concentration of nanoparticles, droplets exit the gun without complete evaporation. The results suggest that, in coating applications involving a higher concentration of nanoparticles, smaller droplet sizes are preferred.