In this paper,self-designed multi-hollow needle electrodes are used as a high-voltage electrode in a packed bed dielectric barrier discharge reactor to facilitate fast gas flow through the active discharge area and ac...In this paper,self-designed multi-hollow needle electrodes are used as a high-voltage electrode in a packed bed dielectric barrier discharge reactor to facilitate fast gas flow through the active discharge area and achieve large-volume stable discharge.The dynamic characteristics of the plasma,the generated active species,and the energy transfer mechanisms in both positive discharge(PD)and negative discharge(ND)are investigated by using fast-exposure intensified charge coupled device(ICCD)images and time-resolved optical emission spectra.The experimental results show that the discharge intensity,number of discharge channels,and discharge volume are obviously enhanced when the multi-needle electrode is replaced by a multihollow needle electrode.During a single voltage pulse period,PD mainly develops in a streamer mode,which results in a stronger discharge current,luminous intensity,and E/N compared with the diffuse mode observed in ND.In PD,as the gap between dielectric beads changes from 0 to250μm,the discharge between the dielectric bead gap changes from a partial discharge to a standing filamentary micro-discharge,which allows the plasma to leave the local area and is conducive to the propagation of surface streamers.In ND,the discharge only appears as a diffusionlike mode between the gap of dielectric beads,regardless of whether there is a discharge gap.Moreover,the generation of excited states N_(2)^(+)(B^(2)∑_(u)^(+))and N2(C^(3)Π_(u))is mainly observed in PD,which is attributed to the higher E/N in PD than that in ND.However,the generation of the OH(A^(2)∑^(+))radical in ND is higher than in PD.It is not directly dominated by E/N,but mainly by the resonant energy transfer process between metastable N_(2)(A^(3)∑_(u)^(+))and OH(X^(2)Π).Furthermore,both PD and ND demonstrate obvious energy relaxation processes of electron-to-vibration and vibration-to-vibration,and no vibration-to-rotation energy relaxation process is observed.展开更多
Selective hydrogenation plays an important role in chemical industries,yet its selectivity is usually limited by the mass transfer.In this work,the enhanced hydrogenation selectivity was achieved in a rotating packed ...Selective hydrogenation plays an important role in chemical industries,yet its selectivity is usually limited by the mass transfer.In this work,the enhanced hydrogenation selectivity was achieved in a rotating packed bed(RPB)reactor with excellent mass transfer efficiency.Aiming to be used under the centrifugal filed,a monolithic catalyst Pd/c-Al_(2)O_(3)/nickel foam suiting for the shape and size of the rotor of RPB reactor was prepared by the electrophoretic deposition method.The mechanical strength of the catalyst can meet the requirement of high centrifugal force in the RPB.The hydrogenation selectivity in the RPB reactor using the 3-methyl-1-pentyn-3-ol hydrogenation system was 3–8 times higher than that in a stirred tank reactor under similar conditions.This work proves the feasibility of intensifying the selectivity of hydrogenation process in the RPB reactor.展开更多
Rectangular wave current control of the electrochemical reduction of nitrobenzene im-proves the selectivity for p-aminophenol(PAP) compared to direct current(d.c.) control at thesame average current density in a flow-...Rectangular wave current control of the electrochemical reduction of nitrobenzene im-proves the selectivity for p-aminophenol(PAP) compared to direct current(d.c.) control at thesame average current density in a flow-by packed-bed reactor.Optimal increase in PAP selectivitycan be obtained at about a frequency of 50Hz and a duty cycle of 0.2.A mathematical model isset up to incorporate the effects of mass transfer,hydrogen evolution and double layer charging,and is solved using the Duhamel’s superposition principle and the modified Crank-Nicolson methodwith the upwind scheme.The conventional d.c.control cases are also calculated for comparison.Calculations can be applied to predict the reaction results under periodic current and d.c.control,but both display the same trends compared to experimental data.展开更多
A laboratory scale aerobic fixed film bioreactor packed with glass beads for biofilm growth was used to evaluate the removal efficiencies of COD and phenol for a carbohydrate—phenol mixture in wastewater. It was done...A laboratory scale aerobic fixed film bioreactor packed with glass beads for biofilm growth was used to evaluate the removal efficiencies of COD and phenol for a carbohydrate—phenol mixture in wastewater. It was done by an indigenous mixed culture inoculums developed after collecting sludge from a return line of an activated sludge plant. The test result on continuous flow in the above biofilm reactor indicated an optimum hydraulic loading range of 4-6.4 m3day-1m-2 for attainment of reasonable amount of COD removal in case of carbohydrate substrate only. The COD removal efficiency, however, gradually depleted from 100% to 54% by gradual increase in organic loading (OLR) from 0.72-4.32 kgday-1m-3, beyond which removal was not significant. For the identical loading conditions, in presence of phenol in the substrate along with carbohydrate, the COD removal was observed varying from 100-40% in the above organic loading range. The COD removal kinetics in presence of phenol also shows a decreasing trend compared to data obtained without the presence of phenol in wastewater that reveals biological inhibition. The experimental data were fitted in a simple plug flow model for evaluating the zero order, first order and Monod form of rate equations to evaluate the kinetics. It was found that Monod type rate equations combining a zero and first order rate expression is the best fit for the above hydraulic and organic loading that gives a best fit half velocity constant value of 35 mgL-1 (R2 = 0.9612).展开更多
Packed Bed biological Reactor (PBR) system has the potential to offer an effective and low-cost technology for upgrading the conventional wastewater treatment systems. The objective of this study was to evaluate the p...Packed Bed biological Reactor (PBR) system has the potential to offer an effective and low-cost technology for upgrading the conventional wastewater treatment systems. The objective of this study was to evaluate the performance of PBR in removing the organic matter and nutrient from different types of wastewater (primary treatment effluent and secondary treatment effluent (exit of biological unit)). The experiments were carried out in two laboratory-sized reactors with 4 L in volume made of Plexiglas. The reactor was filled with PET packing and the reactor was kept in a temperature-controlled water bath at 20°C. Wastewater samples used in this experiment were collected from Wadi Al-Arab wastewater treatment plant in Irbid, Jordan. The concentrations of COD, TN, and TP were 280 mg/l, 41.74 mg-N/l and 9 mg/l, respectively in the primary effluents. Also, the concentrations of COD, TN, and TP were 58 mg/l, 61.55 mg-N/l and 33 mg/l, respectively in the secondary effluents. The removal efficiencies of COD, TN, and TP were 52%, 52% and 79% respectively when using the primary effluent as an influent to the reactor. On the other hand, when using the secondary effluent as an influent to the reactor, the removal efficiencies of COD, TN, and TP were 30%, 77%, and 81%, respectively. Thus, this technique could be used as a posttreatment step for conventional biological wastewater treatment.展开更多
In this study, a simple and effective technique for establishing an external mass transfer model in a recirculated packed-bed batch reactor (RPBBR) with an immobilized lipase enzyme and Jatropha oil system is presente...In this study, a simple and effective technique for establishing an external mass transfer model in a recirculated packed-bed batch reactor (RPBBR) with an immobilized lipase enzyme and Jatropha oil system is presented. The external mass transfer effect can be represented with a model in the form of Colburn factor JD = K Re-(1–n). The value of K and n were derived from experimental data at different mass flow rates.The experiment shows an average increment of 1.51% FFA for calcium alginate and 1.62% FFA for carrageenan after the hydrolysis took place. Based on different biopolymer material used in immobilized beads, JD = 1.674 Re-0.4 for calcium alginate and JD = 1.881 Re-0.3 for k-carrageenan were found to be adequate to predict the experimental data for external mass transfer in the reactor in the Reynolds number range of 0.2 to 1.2. The purposed model can be used for the design of industrial bioreactor and scale up. Besides, the external mass transfer coefficients for the hydrolysis of Jatropha oil reaction and the entrapment efficiency for the two biopolymer materials used were also investigated.展开更多
A three-dimensional geometric model of the oxidative coupling of methane (OCM) packed-bed reactor loaded with Na2WO4-Mn/SiO2 partic- ulate catalyst was set up, and an improved Stansch kinetic model was established t...A three-dimensional geometric model of the oxidative coupling of methane (OCM) packed-bed reactor loaded with Na2WO4-Mn/SiO2 partic- ulate catalyst was set up, and an improved Stansch kinetic model was established to calculate the OCM reactions using the computational fluid dynamics method and Fluent software. The simulation conditions were completely the same with the experimental conditions that the volume velocity of the reactant was 80 mL/min under standard state, the ratio of CH4/O2 was 3, the temperature and pressure were 800 ℃ and 1 atm, respectively. The contour of the characteristics parameters in the catalyst bed was analyzed, such as the species mass fractions, temperature, the heat flux on side wall surface, pressure, fluid density and velocity. The results showed that the calculated values matched well with the experimental values on the conversion of CH4 and the selectivity to products (C2H6, C2H4, CO2, CO) in the reactor outlet with an error range of 4-2%. The mass fractions of CH4 and O2 decreased from 0.6 and 0.4 in the catalyst bed inlet to 0.436 and 0.142 in the outlet, where the mass fractions of C2H6, C2H4, CO and CO2 were 0.035, 0.061, 0.032 and 0.106, respectively. Due to the existence of laminar boundary layer, the contours of each component bent upwards in the vicinity of the boundary layer. This OCM reaction was volume increase reaction and the total moles of products were greater than those of reactants. The flow field in the catalyst bed maintained constant temperature and pressure. The fluid density decreased gradually from 2.28 kg/m3 in the inlet of the catalyst bed to 2.22 kg/m3 in the outlet of the catalyst bed, while the velocity increased from 0.108 m/s to 0.115 m/s.展开更多
Nowadays,the design of fixed packed bed reactors still relies on empirical correlations,which,especially for small tube to particle diameter ratios,are mostly too inaccurate because of the presence of wall effects.The...Nowadays,the design of fixed packed bed reactors still relies on empirical correlations,which,especially for small tube to particle diameter ratios,are mostly too inaccurate because of the presence of wall effects.Therefore,the simulation of fixed packed bed reactors plays an important role to predict and control the flow and process parameters in such,nowadays and in the future.Because of its straightforward applicability to non-uniform packings with particles of arbitrary shapes,the immersed boundary method(IBM)has advantages over other numerical methods and is used more and more frequently.This paper compares two approaches of IBMs for the simulation of fixed bed reactors with spherical shaped particles.The classic,smooth approach is compared to the straightforward to implement blocked-off method for velocity fields above the fixed bed for particle Reynolds numbers of 300 and 500.Results from experimental inline PIV-measurements of the reactor to be simulated serve as a basis for comparison.Very good agreement with the experiment is found for both simulation methodologies with higher resolutions,considering the more stable flow at a particle Reynolds number of 300.Differences in the different IBM approaches occurred for the more unsteady flow at a particle Reynolds number of 500.Compared to the blocked-off method,the smooth IBM reflects the formation of additional jets and recirculation zones better right above the bed,though increasing the fluid mesh resolution improves the accuracy of the blocked-off method.Overall,a more diffusive behaviour is found for the blocked-off simulations due to the stairstep representation,which is avoided by using interpolation stencils as in the smooth IBM.With higher mesh refinement in the blocked-off IBM this effect can be reduced,but this also increases the computational effort.展开更多
The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell(SUC)and body-centred cubic(BCC)configuration of particles in packed...The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell(SUC)and body-centred cubic(BCC)configuration of particles in packed beds.The experimental setup is built in such a way that suitable and simplified boundary conditions are imposed for the corresponding numerical framework,so the simulations can be done under very similar conditions as the experiments.Accordingly,a porous plate is used for the co-flow to achieve the uniform velocity and the fully developed flow is ensured for the jet flow.The SUC and BCC particle beds consist of 3D-printed spheres,and the non-isotropy near the walls is mostly eliminated by placing half-spheres at the channel walls.The flow velocities are analysed directly at the exit of the particle bed for both beds over 36 pores for the SUC configuration and 60 pores for the BCC configuration,for particle Reynolds numbers of 200,300,and 400.Stereo particle image velocimetry is experimentally arranged in such a way that the velocities over the entire region at the exit of the packed bed are obtained instantaneously.The numerical method consists of a state-of-the-art immersed boundary method with adaptive mesh refinement.The paper presents the pore jet structure and velocity field exiting from each pore for the SUC and BCC packed particle beds.The numerical and experimental studies show a good agreement for the SUC configuration for all flow velocities.For the BCC configuration,some differences can be observed in the pore jet flow structure between the simulations and the experiments,but the general flow velocity distribution shows a good overall agreement.The axial velocity is generally higher for the pores located near the centre of the packed bed than for the pores near the wall.In addition,the axial velocities are observed to increase near the peripheral pores of the packed bed.This behaviour is predominant for the BCC configuration as compared to the SUC configuration.The velocities near the peripheral pores can become even higher than those at the central pores for the BCC configuration.It is shown that both the experiments as well as the simulations can be used to study the complex fluid structures inside a packed bed reactor.展开更多
Recently, Fischer-Tropsch synthesis (FTS) has become an interesting technology because of its potential role in producing biofuels via Biomass- to-Liquids (BTL) processes. In Fischer-Tropsch (FT) section, biomas...Recently, Fischer-Tropsch synthesis (FTS) has become an interesting technology because of its potential role in producing biofuels via Biomass- to-Liquids (BTL) processes. In Fischer-Tropsch (FT) section, biomass-derived syngas, mainly composed of a mixture of carbon monoxide (CO) and hydrogen (H2), is converted into various forms of hydrocarbon products over a catalyst at specified temperature and pressure. Fixed-bed reactors are typically used for these processes as conventional FT reactors. The fixed-bed or packed-bed type reactor has its drawbacks, which are heat transfer limitation, i.e. a hot spot problem involved highly exothermic characteristics of FT reaction, and mass transfer limitation due to the condensation of liquid hydrocarbon products occurred on catalyst surface. This work is initiated to develop a new chemical reactor design in which a better distribution of gaseous reactants and hydrocarbon products could be achieved, and led to higher throughput and conversion. The main goal of the research is the enhancement of a fixed-bed reactor, focusing on the application of KenicsTM static mixer insertion in the tubular packed-bed reactor. Two FTS experiments were carried out using two reactors i.e., with and without static mixer insertion within catalytic beds. The modeled syngas used was a mixed gas composed of H2/CO in 2 : 1 molar ratio that was fed at the rate of 30 mL(STP)·min^- 1 (GHSV ≈ 136 mL·gcat^-1 ·h^-1) into the fixed Ru supported aluminum catalyst bed of weight 13.3 g. The reaction was carried out at 180 ℃ and atmospheric pressure continuously for 36 h for both experiments. Both transient and steady-state conversions (in terms of time on stream) were reported. The results revealed that the steady-state CO conversion for the case using the static mixer was approximately 3.5 times higher than that of the case without static mixer. In both cases, the values of chain growth probability of hydrocarbon products (α) for Fischer-Tropsch synthesis were 0.92 and 0.89 for the case with and without static mixer, respectively.展开更多
This paper brings the comparison of performances of CO_(2)conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field,organised in an open access online database.This t...This paper brings the comparison of performances of CO_(2)conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field,organised in an open access online database.This tool is open to all users to carry out their own analyses,but also to contributors who wish to add their data to the database in order to improve the relevance of the comparisons made,and ultimately to improve the efficiency of CO_(2)conversion by plasma-catalysis.The creation of this database and database user interface is motivated by the fact that plasma-catalysis is a fast-growing field for all CO_(2)conversion processes,be it methanation,dry reforming of methane,methanolisation,or others.As a result of this rapid increase,there is a need for a set of standard procedures to rigorously compare performances of different systems.However,this is currently not possible because the fundamental mechanisms of plasma-catalysis are still too poorly understood to define these standard procedures.Fortunately however,the accumulated data within the CO_(2)plasma-catalysis community has become large enough to warrant so-called“big data”studies more familiar in the fields of medicine and the social sciences.To enable comparisons between multiple data sets and make future research more effective,this work proposes the first database on CO_(2)conversion performances by plasma-catalysis open to the whole community.This database has been initiated in the framework of a H_(2)0_(2)0 European project and is called the“PIONEER Data Base”.The database gathers a large amount of CO_(2)conversion performance data such as conversion rate,energy efficiency,and selectivity for numerous plasma sources coupled with or without a catalyst.Each data set is associated with metadata describing the gas mixture,the plasma source,the nature of the catalyst,and the form of coupling with the plasma.Beyond the database itself,a data extraction tool with direct visualisation features or advanced filtering functionalities has been developed and is available online to the public.The simple and fast visualisation of the state of the art puts new results into context,identifies literal gaps in data,and consequently points towards promising research routes.More advanced data extraction illustrates the impact that the database can have in the understanding of plasma-catalyst coupling.Lessons learned from the review of a large amount of literature during the setup of the database lead to best practice advice to increase comparability between future CO_(2)plasma-catalytic studies.Finally,the community is strongly encouraged to contribute to the database not only to increase the visibility of their data but also the relevance of the comparisons allowed by this tool.展开更多
Fixed-bed reactors randomly packed with catalysts have many disadvantages that may adversely affect the desired chemical reaction.The increasingly used monolithic reactor,in contrast,has many operational advantages;ho...Fixed-bed reactors randomly packed with catalysts have many disadvantages that may adversely affect the desired chemical reaction.The increasingly used monolithic reactor,in contrast,has many operational advantages;however,for a kinetically-controlled reaction,it does not contain sufficient catalyst to sustain the reaction.To address the problems associated with both randomly packed-bed reactor and the monolithic reactor,a structured packed-bed reactor was proposed and mathematical models were built for randomly packed-bed reactor and structured packed-bed reactor.Their respective performances were compared when applied to the exothermic reaction of the isopropanol-acetone-hydrogen chemical heat pump system.The results showed that the structured packed-bed reactor performed better in terms of pressure drop and heat transfer capacity,and had a lower radial temperature gradient,indicating that this reactor had a higher effective heat conductivity.Isopropanol on the catalyst particle surfaces was more concentrated near the tube wall because a wall effect existed in the boundary layer around the particle-wall contact points.展开更多
The performance of heat transfer is a key issue for reactor design in petrochemical industry. Since the heat transfer in reactors is a complicated process and depends on multiple parameters, the evaluation of the heat...The performance of heat transfer is a key issue for reactor design in petrochemical industry. Since the heat transfer in reactors is a complicated process and depends on multiple parameters, the evaluation of the heat transfer performance is usually challenging, and few previous studies gave an overall view of heat exchange performance of different types of reactors. In this review, heat transfer coefficients of two types of petrochemical reactors, including the packed bed and the fluidized bed, were systematically analyzed and compared based on a number of reported correlations. The relationship between heat transfer coefficients and fluid flow velocity in different reactors has been well established, which clearly demonstrates the varying range of their heat transfer coefficients. Heat transfer coefficients of gas-phase packed bed can exceed 200 W/m^2·K, rather than the suggested values(17—89 W/m^2·K) mentioned in the literature. The fluidized bed shows better performance for both two-phase and three-phase beds as compared to the packed bed. Systems with liquid phase also show better heat transfer performance than other phases because of the larger heat capacity of liquid. Thus the industrial three-phase fluidized beds have the best heat transfer performance with an overall heat transfer coefficient of greater than 1 000 W/m^2·K. The heat transfer results provided by this review can afford not only new insights into the heat transfer in typical reactors, but also the basis and guidelines for reactor design and selection.展开更多
One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-s...One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-scale application is limited by their costly chemical synthesis methods.In this work,the niche feature of MXenes was capitalized in the packed-bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste.A simple NH4F solution was employed as the green electrolyte,which could be used repeatedly without any loss in its efficacy.Surprisingly,both fluoride and ammonium were found to play critical roles in the electrochemical etching,functionalization,and expansion of the layered parent materials(MAXs)through which the liberation of ammonia gas was observed.The electrochemically produced MXenes with excellent conductivity,applied as supercapacitor electrodes,could deliver an ultrahigh volumetric capacity(1408 F cm^(−3))and a volumetric energy density(75.8 Wh L^(−1)).This revolutionary green,energy-efficient,and scalable electrochemical route will not only pave the way for industrial-scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.展开更多
基金supported by National Natural Science Foundations of China(Nos.51977023 and 52077026)the Fundamental Research Funds for the Central Universities(No.DUT23YG227)。
文摘In this paper,self-designed multi-hollow needle electrodes are used as a high-voltage electrode in a packed bed dielectric barrier discharge reactor to facilitate fast gas flow through the active discharge area and achieve large-volume stable discharge.The dynamic characteristics of the plasma,the generated active species,and the energy transfer mechanisms in both positive discharge(PD)and negative discharge(ND)are investigated by using fast-exposure intensified charge coupled device(ICCD)images and time-resolved optical emission spectra.The experimental results show that the discharge intensity,number of discharge channels,and discharge volume are obviously enhanced when the multi-needle electrode is replaced by a multihollow needle electrode.During a single voltage pulse period,PD mainly develops in a streamer mode,which results in a stronger discharge current,luminous intensity,and E/N compared with the diffuse mode observed in ND.In PD,as the gap between dielectric beads changes from 0 to250μm,the discharge between the dielectric bead gap changes from a partial discharge to a standing filamentary micro-discharge,which allows the plasma to leave the local area and is conducive to the propagation of surface streamers.In ND,the discharge only appears as a diffusionlike mode between the gap of dielectric beads,regardless of whether there is a discharge gap.Moreover,the generation of excited states N_(2)^(+)(B^(2)∑_(u)^(+))and N2(C^(3)Π_(u))is mainly observed in PD,which is attributed to the higher E/N in PD than that in ND.However,the generation of the OH(A^(2)∑^(+))radical in ND is higher than in PD.It is not directly dominated by E/N,but mainly by the resonant energy transfer process between metastable N_(2)(A^(3)∑_(u)^(+))and OH(X^(2)Π).Furthermore,both PD and ND demonstrate obvious energy relaxation processes of electron-to-vibration and vibration-to-vibration,and no vibration-to-rotation energy relaxation process is observed.
基金supported by the National Natural Science Foundation of China(22022802 and 91934303).
文摘Selective hydrogenation plays an important role in chemical industries,yet its selectivity is usually limited by the mass transfer.In this work,the enhanced hydrogenation selectivity was achieved in a rotating packed bed(RPB)reactor with excellent mass transfer efficiency.Aiming to be used under the centrifugal filed,a monolithic catalyst Pd/c-Al_(2)O_(3)/nickel foam suiting for the shape and size of the rotor of RPB reactor was prepared by the electrophoretic deposition method.The mechanical strength of the catalyst can meet the requirement of high centrifugal force in the RPB.The hydrogenation selectivity in the RPB reactor using the 3-methyl-1-pentyn-3-ol hydrogenation system was 3–8 times higher than that in a stirred tank reactor under similar conditions.This work proves the feasibility of intensifying the selectivity of hydrogenation process in the RPB reactor.
基金Supported by the State Key Laboratory of Chemical Engineering,National Nature Science Foundation of China,and China Petrochemical Corporation.
文摘Rectangular wave current control of the electrochemical reduction of nitrobenzene im-proves the selectivity for p-aminophenol(PAP) compared to direct current(d.c.) control at thesame average current density in a flow-by packed-bed reactor.Optimal increase in PAP selectivitycan be obtained at about a frequency of 50Hz and a duty cycle of 0.2.A mathematical model isset up to incorporate the effects of mass transfer,hydrogen evolution and double layer charging,and is solved using the Duhamel’s superposition principle and the modified Crank-Nicolson methodwith the upwind scheme.The conventional d.c.control cases are also calculated for comparison.Calculations can be applied to predict the reaction results under periodic current and d.c.control,but both display the same trends compared to experimental data.
文摘A laboratory scale aerobic fixed film bioreactor packed with glass beads for biofilm growth was used to evaluate the removal efficiencies of COD and phenol for a carbohydrate—phenol mixture in wastewater. It was done by an indigenous mixed culture inoculums developed after collecting sludge from a return line of an activated sludge plant. The test result on continuous flow in the above biofilm reactor indicated an optimum hydraulic loading range of 4-6.4 m3day-1m-2 for attainment of reasonable amount of COD removal in case of carbohydrate substrate only. The COD removal efficiency, however, gradually depleted from 100% to 54% by gradual increase in organic loading (OLR) from 0.72-4.32 kgday-1m-3, beyond which removal was not significant. For the identical loading conditions, in presence of phenol in the substrate along with carbohydrate, the COD removal was observed varying from 100-40% in the above organic loading range. The COD removal kinetics in presence of phenol also shows a decreasing trend compared to data obtained without the presence of phenol in wastewater that reveals biological inhibition. The experimental data were fitted in a simple plug flow model for evaluating the zero order, first order and Monod form of rate equations to evaluate the kinetics. It was found that Monod type rate equations combining a zero and first order rate expression is the best fit for the above hydraulic and organic loading that gives a best fit half velocity constant value of 35 mgL-1 (R2 = 0.9612).
文摘Packed Bed biological Reactor (PBR) system has the potential to offer an effective and low-cost technology for upgrading the conventional wastewater treatment systems. The objective of this study was to evaluate the performance of PBR in removing the organic matter and nutrient from different types of wastewater (primary treatment effluent and secondary treatment effluent (exit of biological unit)). The experiments were carried out in two laboratory-sized reactors with 4 L in volume made of Plexiglas. The reactor was filled with PET packing and the reactor was kept in a temperature-controlled water bath at 20°C. Wastewater samples used in this experiment were collected from Wadi Al-Arab wastewater treatment plant in Irbid, Jordan. The concentrations of COD, TN, and TP were 280 mg/l, 41.74 mg-N/l and 9 mg/l, respectively in the primary effluents. Also, the concentrations of COD, TN, and TP were 58 mg/l, 61.55 mg-N/l and 33 mg/l, respectively in the secondary effluents. The removal efficiencies of COD, TN, and TP were 52%, 52% and 79% respectively when using the primary effluent as an influent to the reactor. On the other hand, when using the secondary effluent as an influent to the reactor, the removal efficiencies of COD, TN, and TP were 30%, 77%, and 81%, respectively. Thus, this technique could be used as a posttreatment step for conventional biological wastewater treatment.
文摘In this study, a simple and effective technique for establishing an external mass transfer model in a recirculated packed-bed batch reactor (RPBBR) with an immobilized lipase enzyme and Jatropha oil system is presented. The external mass transfer effect can be represented with a model in the form of Colburn factor JD = K Re-(1–n). The value of K and n were derived from experimental data at different mass flow rates.The experiment shows an average increment of 1.51% FFA for calcium alginate and 1.62% FFA for carrageenan after the hydrolysis took place. Based on different biopolymer material used in immobilized beads, JD = 1.674 Re-0.4 for calcium alginate and JD = 1.881 Re-0.3 for k-carrageenan were found to be adequate to predict the experimental data for external mass transfer in the reactor in the Reynolds number range of 0.2 to 1.2. The purposed model can be used for the design of industrial bioreactor and scale up. Besides, the external mass transfer coefficients for the hydrolysis of Jatropha oil reaction and the entrapment efficiency for the two biopolymer materials used were also investigated.
文摘A three-dimensional geometric model of the oxidative coupling of methane (OCM) packed-bed reactor loaded with Na2WO4-Mn/SiO2 partic- ulate catalyst was set up, and an improved Stansch kinetic model was established to calculate the OCM reactions using the computational fluid dynamics method and Fluent software. The simulation conditions were completely the same with the experimental conditions that the volume velocity of the reactant was 80 mL/min under standard state, the ratio of CH4/O2 was 3, the temperature and pressure were 800 ℃ and 1 atm, respectively. The contour of the characteristics parameters in the catalyst bed was analyzed, such as the species mass fractions, temperature, the heat flux on side wall surface, pressure, fluid density and velocity. The results showed that the calculated values matched well with the experimental values on the conversion of CH4 and the selectivity to products (C2H6, C2H4, CO2, CO) in the reactor outlet with an error range of 4-2%. The mass fractions of CH4 and O2 decreased from 0.6 and 0.4 in the catalyst bed inlet to 0.436 and 0.142 in the outlet, where the mass fractions of C2H6, C2H4, CO and CO2 were 0.035, 0.061, 0.032 and 0.106, respectively. Due to the existence of laminar boundary layer, the contours of each component bent upwards in the vicinity of the boundary layer. This OCM reaction was volume increase reaction and the total moles of products were greater than those of reactants. The flow field in the catalyst bed maintained constant temperature and pressure. The fluid density decreased gradually from 2.28 kg/m3 in the inlet of the catalyst bed to 2.22 kg/m3 in the outlet of the catalyst bed, while the velocity increased from 0.108 m/s to 0.115 m/s.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-Project-ID 422037413-TRR 287Gefordert durch die Deutsche Forschungsgemeinschaft(DFG)-Projektnummer 422037413-TRR 287.
文摘Nowadays,the design of fixed packed bed reactors still relies on empirical correlations,which,especially for small tube to particle diameter ratios,are mostly too inaccurate because of the presence of wall effects.Therefore,the simulation of fixed packed bed reactors plays an important role to predict and control the flow and process parameters in such,nowadays and in the future.Because of its straightforward applicability to non-uniform packings with particles of arbitrary shapes,the immersed boundary method(IBM)has advantages over other numerical methods and is used more and more frequently.This paper compares two approaches of IBMs for the simulation of fixed bed reactors with spherical shaped particles.The classic,smooth approach is compared to the straightforward to implement blocked-off method for velocity fields above the fixed bed for particle Reynolds numbers of 300 and 500.Results from experimental inline PIV-measurements of the reactor to be simulated serve as a basis for comparison.Very good agreement with the experiment is found for both simulation methodologies with higher resolutions,considering the more stable flow at a particle Reynolds number of 300.Differences in the different IBM approaches occurred for the more unsteady flow at a particle Reynolds number of 500.Compared to the blocked-off method,the smooth IBM reflects the formation of additional jets and recirculation zones better right above the bed,though increasing the fluid mesh resolution improves the accuracy of the blocked-off method.Overall,a more diffusive behaviour is found for the blocked-off simulations due to the stairstep representation,which is avoided by using interpolation stencils as in the smooth IBM.With higher mesh refinement in the blocked-off IBM this effect can be reduced,but this also increases the computational effort.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-Project-ID 422037413-TRR 287Gefördert durch die Deutsche Forschungsgemeinschaft(DFG)-Projektnummer 422037413-TRR 287.
文摘The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell(SUC)and body-centred cubic(BCC)configuration of particles in packed beds.The experimental setup is built in such a way that suitable and simplified boundary conditions are imposed for the corresponding numerical framework,so the simulations can be done under very similar conditions as the experiments.Accordingly,a porous plate is used for the co-flow to achieve the uniform velocity and the fully developed flow is ensured for the jet flow.The SUC and BCC particle beds consist of 3D-printed spheres,and the non-isotropy near the walls is mostly eliminated by placing half-spheres at the channel walls.The flow velocities are analysed directly at the exit of the particle bed for both beds over 36 pores for the SUC configuration and 60 pores for the BCC configuration,for particle Reynolds numbers of 200,300,and 400.Stereo particle image velocimetry is experimentally arranged in such a way that the velocities over the entire region at the exit of the packed bed are obtained instantaneously.The numerical method consists of a state-of-the-art immersed boundary method with adaptive mesh refinement.The paper presents the pore jet structure and velocity field exiting from each pore for the SUC and BCC packed particle beds.The numerical and experimental studies show a good agreement for the SUC configuration for all flow velocities.For the BCC configuration,some differences can be observed in the pore jet flow structure between the simulations and the experiments,but the general flow velocity distribution shows a good overall agreement.The axial velocity is generally higher for the pores located near the centre of the packed bed than for the pores near the wall.In addition,the axial velocities are observed to increase near the peripheral pores of the packed bed.This behaviour is predominant for the BCC configuration as compared to the SUC configuration.The velocities near the peripheral pores can become even higher than those at the central pores for the BCC configuration.It is shown that both the experiments as well as the simulations can be used to study the complex fluid structures inside a packed bed reactor.
基金supported by the project of the National Science and Technology Development Agency (NSTDA),Thailand
文摘Recently, Fischer-Tropsch synthesis (FTS) has become an interesting technology because of its potential role in producing biofuels via Biomass- to-Liquids (BTL) processes. In Fischer-Tropsch (FT) section, biomass-derived syngas, mainly composed of a mixture of carbon monoxide (CO) and hydrogen (H2), is converted into various forms of hydrocarbon products over a catalyst at specified temperature and pressure. Fixed-bed reactors are typically used for these processes as conventional FT reactors. The fixed-bed or packed-bed type reactor has its drawbacks, which are heat transfer limitation, i.e. a hot spot problem involved highly exothermic characteristics of FT reaction, and mass transfer limitation due to the condensation of liquid hydrocarbon products occurred on catalyst surface. This work is initiated to develop a new chemical reactor design in which a better distribution of gaseous reactants and hydrocarbon products could be achieved, and led to higher throughput and conversion. The main goal of the research is the enhancement of a fixed-bed reactor, focusing on the application of KenicsTM static mixer insertion in the tubular packed-bed reactor. Two FTS experiments were carried out using two reactors i.e., with and without static mixer insertion within catalytic beds. The modeled syngas used was a mixed gas composed of H2/CO in 2 : 1 molar ratio that was fed at the rate of 30 mL(STP)·min^- 1 (GHSV ≈ 136 mL·gcat^-1 ·h^-1) into the fixed Ru supported aluminum catalyst bed of weight 13.3 g. The reaction was carried out at 180 ℃ and atmospheric pressure continuously for 36 h for both experiments. Both transient and steady-state conversions (in terms of time on stream) were reported. The results revealed that the steady-state CO conversion for the case using the static mixer was approximately 3.5 times higher than that of the case without static mixer. In both cases, the values of chain growth probability of hydrocarbon products (α) for Fischer-Tropsch synthesis were 0.92 and 0.89 for the case with and without static mixer, respectively.
基金funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No.813393partially funded by the Portuguese FCT-Funda??o para a Ciência e a Tecnologia,under projects UIDB/50010/2020,UIDP/50010/2020 and PTDC/FIS-PLA/1616/2021。
文摘This paper brings the comparison of performances of CO_(2)conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field,organised in an open access online database.This tool is open to all users to carry out their own analyses,but also to contributors who wish to add their data to the database in order to improve the relevance of the comparisons made,and ultimately to improve the efficiency of CO_(2)conversion by plasma-catalysis.The creation of this database and database user interface is motivated by the fact that plasma-catalysis is a fast-growing field for all CO_(2)conversion processes,be it methanation,dry reforming of methane,methanolisation,or others.As a result of this rapid increase,there is a need for a set of standard procedures to rigorously compare performances of different systems.However,this is currently not possible because the fundamental mechanisms of plasma-catalysis are still too poorly understood to define these standard procedures.Fortunately however,the accumulated data within the CO_(2)plasma-catalysis community has become large enough to warrant so-called“big data”studies more familiar in the fields of medicine and the social sciences.To enable comparisons between multiple data sets and make future research more effective,this work proposes the first database on CO_(2)conversion performances by plasma-catalysis open to the whole community.This database has been initiated in the framework of a H_(2)0_(2)0 European project and is called the“PIONEER Data Base”.The database gathers a large amount of CO_(2)conversion performance data such as conversion rate,energy efficiency,and selectivity for numerous plasma sources coupled with or without a catalyst.Each data set is associated with metadata describing the gas mixture,the plasma source,the nature of the catalyst,and the form of coupling with the plasma.Beyond the database itself,a data extraction tool with direct visualisation features or advanced filtering functionalities has been developed and is available online to the public.The simple and fast visualisation of the state of the art puts new results into context,identifies literal gaps in data,and consequently points towards promising research routes.More advanced data extraction illustrates the impact that the database can have in the understanding of plasma-catalyst coupling.Lessons learned from the review of a large amount of literature during the setup of the database lead to best practice advice to increase comparability between future CO_(2)plasma-catalytic studies.Finally,the community is strongly encouraged to contribute to the database not only to increase the visibility of their data but also the relevance of the comparisons allowed by this tool.
基金supported by the National Natural Science Foundation of China under(Grant No.51276181 and 51106158)the National Basic Research Program of China under(Grant No.2011CB710705)
文摘Fixed-bed reactors randomly packed with catalysts have many disadvantages that may adversely affect the desired chemical reaction.The increasingly used monolithic reactor,in contrast,has many operational advantages;however,for a kinetically-controlled reaction,it does not contain sufficient catalyst to sustain the reaction.To address the problems associated with both randomly packed-bed reactor and the monolithic reactor,a structured packed-bed reactor was proposed and mathematical models were built for randomly packed-bed reactor and structured packed-bed reactor.Their respective performances were compared when applied to the exothermic reaction of the isopropanol-acetone-hydrogen chemical heat pump system.The results showed that the structured packed-bed reactor performed better in terms of pressure drop and heat transfer capacity,and had a lower radial temperature gradient,indicating that this reactor had a higher effective heat conductivity.Isopropanol on the catalyst particle surfaces was more concentrated near the tube wall because a wall effect existed in the boundary layer around the particle-wall contact points.
文摘The performance of heat transfer is a key issue for reactor design in petrochemical industry. Since the heat transfer in reactors is a complicated process and depends on multiple parameters, the evaluation of the heat transfer performance is usually challenging, and few previous studies gave an overall view of heat exchange performance of different types of reactors. In this review, heat transfer coefficients of two types of petrochemical reactors, including the packed bed and the fluidized bed, were systematically analyzed and compared based on a number of reported correlations. The relationship between heat transfer coefficients and fluid flow velocity in different reactors has been well established, which clearly demonstrates the varying range of their heat transfer coefficients. Heat transfer coefficients of gas-phase packed bed can exceed 200 W/m^2·K, rather than the suggested values(17—89 W/m^2·K) mentioned in the literature. The fluidized bed shows better performance for both two-phase and three-phase beds as compared to the packed bed. Systems with liquid phase also show better heat transfer performance than other phases because of the larger heat capacity of liquid. Thus the industrial three-phase fluidized beds have the best heat transfer performance with an overall heat transfer coefficient of greater than 1 000 W/m^2·K. The heat transfer results provided by this review can afford not only new insights into the heat transfer in typical reactors, but also the basis and guidelines for reactor design and selection.
基金Australian Research Council,Grant/Award Numbers:DP190100120,FT200100015National Key Research and Development Program,Grant/Award Number:2021YFA1600800Shenzhen Science and Technology Program,Grant/Award Numbers:RCJC20200714114434086,JCYJ20190808142001745,JCYJ20200812160737002,20180921273B。
文摘One of the most unique properties of two-dimensional carbides and nitrides of transition metals(MXenes)is their excellent water dispersibility and yet possessing superior electrical conductivity but their industrial-scale application is limited by their costly chemical synthesis methods.In this work,the niche feature of MXenes was capitalized in the packed-bed electrochemical reactor to produce MXenes at an unprecedented reaction rate and yield with minimal chemical waste.A simple NH4F solution was employed as the green electrolyte,which could be used repeatedly without any loss in its efficacy.Surprisingly,both fluoride and ammonium were found to play critical roles in the electrochemical etching,functionalization,and expansion of the layered parent materials(MAXs)through which the liberation of ammonia gas was observed.The electrochemically produced MXenes with excellent conductivity,applied as supercapacitor electrodes,could deliver an ultrahigh volumetric capacity(1408 F cm^(−3))and a volumetric energy density(75.8 Wh L^(−1)).This revolutionary green,energy-efficient,and scalable electrochemical route will not only pave the way for industrial-scale production of MXenes but also open up a myriad of versatile electrochemical modifications for improved functional MXenes.