|
Simulation of bubble column reactors using CFD coupled with a population balance model
Tiefeng WANG
Front Chem Sci Eng. 2011, 5 (2): 162-172.
https://doi.org/10.1007/s11705-009-0267-5
Bubble columns are widely used in chemical and biochemical processes due to their excellent mass and heat transfer characteristics and simple construction. However, their fundamental hydrodynamic behaviors, which are essential for reactor scale-up and design, are still not fully understood. To develop design tools for engineering purposes, much research has been carried out in the area of computational fluid dynamics (CFD) modeling and simulation of gas-liquid flows. Due to the importance of the bubble behavior, the bubble size distribution must be considered in the CFD models. The population balance model (PBM) is an effective approach to predict the bubble size distribution, and great efforts have been made in recent years to couple the PBM into CFD simulations. This article gives a selective review of the modeling and simulation of bubble column reactors using CFD coupled with PBM. Bubble breakup and coalescence models due to different mechanisms are discussed. It is shown that the CFD-PBM coupled model with proper bubble breakup and coalescence models and interphase force formulations has the ability of predicting the complex hydrodynamics in different flow regimes and, thus, provides a unified description of both the homogeneous and heterogeneous regimes. Further study is needed to improve the models of bubble coalescence and breakup, turbulence modification in high gas holdup, and interphase forces of bubble swarms.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
Carbon dioxide sequestration in petrochemical industries with the aim of reduction in greenhouse gas emissions
Maryam Takht Ravanchi, Saeed Sahebdelfar, Farnaz Tahriri Zangeneh
Front Chem Sci Eng. 2011, 5 (2): 173-178.
https://doi.org/10.1007/s11705-010-0562-1
The mitigation of greenhouse gas emissions to acceptable levels is arguably the greatest environmental challenge these days. Vast utilization of fossil fuels and forest destruction are main causes of CO2 increase in the atmosphere. Carbon dioxide sequestration that consists of separation, transportation and utilization or storage of CO2, is one way for reduction of its emission, in which the most costly section is separation. Different methods can be used for carbon dioxide separation such as absorption, membrane separation, adsorption and cryogenic distillation. Economic, technical and environmental issues should be considered in selection of the technology for particular application. Carbon dioxide concentration, temperature, pressure and flow rate are influential operating parameters in the selection of the appropriate separation method. Nowadays, absorption is the worldwide industrial separation method. New researches are focused on developing new stable solvents and efficient column configuration with suitable internals to minimize pressure drop. Membrane separation and adsorption (PSA type) are other long-term alternatives that can increase separation efficiency and decrease separation cost. The level of energy consumption in various separation methods are in the order: chemical absorption>physical absorption>membrane separation. Because of high investment costs, current separation technologies are suitable for large concentrated sources. In the present paper, different processes for carbon dioxide separation are investigated and compared. Available technologies and commercial plants for CO2 sequestration are provided.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
Recent advances in the catalytic pyrolysis of biomass
Changwei HU, Yu YANG, Jia LUO, Pan PAN, Dongmei TONG, Guiying LI
Front Chem Sci Eng. 2011, 5 (2): 188-193.
https://doi.org/10.1007/s11705-010-1015-6
Biomass is considered as a renewable and alternative resource for the production of fuels and chemicals, since it is the only carbon and hydrogen containing resource that we can find in the world except for fossil resources, capable of being converted to hydrocarbons. The pyrolytic liquefaction of biomass is a promising way to convert biomass to useful products. This paper briefly surveys the present status of the direct catalytic pyrolysis for the liquefaction of biomass. The direct use of catalysts could decrease the pyrolysis temperature, increase the conversion of biomass and the yield of bio-oil, and change the distribution of the pyrolytic liquid products then improve the quality of the bio-oil obtained. The fact that biomass is in solid state present great challenges for its conversion and for the effective use of catalysts due to the bad heat transfer characteristics and bad mass transfer properties. These barriers appeal for the development of a new catalyst and new catalytic process as well as the integration of both. Process design and process intensification are of significant importance in the catalytic conversion of biomass.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
Investigation of bubble diameter and flow regime between water and dilute aqueous ethanol solutions in an airlift reactor
Baharak SAJJADI, Mostafa Keshavarz MORAVEJI, Reza DAVARNEJAD
Front Chem Sci Eng. 2011, 5 (2): 194-202.
https://doi.org/10.1007/s11705-010-1019-2
In this study, the effect of ethanol addition into pure water and its concentration on bubble diameter, gas hold-up and flow regimes were investigated in an airlift reactor. Air and water with ethanol (concentration ranging from 0%–1%, v/v) were as dispersed and continuous phases, respectively. Superficial gas velocity was considered as an effective parameter. Bubble size distribution was measured by photography and picture analysis at various concentrations of ethanol and various velocities of gas. Alcohol concentration enhancement caused bubble diameter to decrease. Furthermore, the bubbles diameter in pure water was nearly 4 times higher than that of ethanol with concentration of 1% (v/v) and also was 3.4 times higher than that of ethanol with concentration of 0.25% (v/v) at the highest aeration gas velocity inlet. For ethanol solutions in lower superficial gas velocity, a homogenous flow regime was observed. This trend continued to inlet gas velocity of about 0.4 cm/s. The transition flow regime occurred after this datum although in pure water, a homogenous flow regime was observed up to a superficial gas velocity of 0.7 cm/s. The gas hold-up in dilute ethanol solutions were more than (around 2 times) that of pure water and increased with increasing concentration of ethanol in those solutions.
References |
Related Articles |
Metrics
|
|
Hydrogen production from methanol through dielectric barrier discharge
Baowei WANG, Xu ZHANG, Haiying BAI, Yijun Lü, Shuanghui HU
Front Chem Sci Eng. 2011, 5 (2): 209-214.
https://doi.org/10.1007/s11705-010-1018-3
The hydrogen fuel cell is a promising option as a future energy resource and the production of hydrogen is mainly depended on fossil fuels now. In this paper, methanol reforming to produce H2 through dielectric-barrier discharge (DBD) plasma reaction was studied. Effects of the power supply parameters, reactor parameters and process conditions on conversion of methanol and distribution of products were investigated. The best reaction conditions were following: input power (45 W), material of inner electrode (stainless steel), discharge gap (3.40 mm), length of reaction zone (90.00 mm), dielectric thickness (1.25 mm), and methanol content (37.65%). The highest conversion of methanol and the yield of H2 were 82.38% and 27.43%, respectively.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
Capture of carbon dioxide over porous solid adsorbents lithium silicate, lithium aluminate and magnesium aluminate at pre-combustion temperatures
P. V. Korake, A. G. Gaikwad
Front Chem Sci Eng. 2011, 5 (2): 215-226.
https://doi.org/10.1007/s11705-010-1012-9
The capturing process for carbon dioxide over porous solid adsorbents such as lithium silicate, lithium aluminate, and magnesium aluminate at pre- combustion temperatures was studied. Lithium silicate was prepared by the sol gel and solid fusion methods. The lithium silicate adsorbent was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and surface area. The capturing of carbon dioxide over lithium silicate, lithium aluminate, and magnesium aluminate was explored at different experimental conditions such as exposure time, temperature variation, and exposure carbon dioxide pressure. The capturing process for carbon dioxide was investigated over these adsorbents with variation of their metal mole ratios. The effect of the addition of (promoter) sodium, potassium, and cesium in the lithium silicate adsorbent was explored to investigate the variation of the capture of carbon dioxide over these adsorbents.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
Design, synthesis and HIV-RT inhibitory activity of novel thiazolidin-4-one derivatives
Hua CHEN, Zaihong GUO, Qingmei YIN, Xiaoxu DUAN, Yunjing GU, Xiaoliu LI
Front Chem Sci Eng. 2011, 5 (2): 231-237.
https://doi.org/10.1007/s11705-010-1022-7
A series of 2-aryl-3-(4,5,6-trimethylpyrimidin-2-yl) thiazolidin-4-ones (1a–1c) and their derivatives bearing a lipophilic substituent, like acetoxy group (3a–3c), propionyloxy group (4a–4c), methyl (5d and 5e) at C-5 on thiazolidin-4-one ring were designed, synthesized and evaluated for their HIV-RT inhibitory activity. Using self-catalyzed Pummerer reaction, compounds 3a–3c and 4a–4c were obtained in good yield (63.1%–75.2%). Preliminary anti-HIV-RT test of these derivatives indicated that compounds 1a–1c, 4b (propionyloxy group at C-5) showed moderate HIV-RT inhibitory activity and compounds 5d and 5e with methyl at C-5 showed a weak HIV-RT inhibitory activity. Structure activity relationship analysis suggested that the substituted groups on C-5 would be unfavorable to anti-HIV-RT activity and that the steric effect might play a critical role in the anti-HIV RT activity.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
Anti-hyperglycemic effect of the polysaccharide fraction isolated from mactra veneriformis
Lingchong WANG, Hao WU, Nian CHANG, Kun ZHANG
Front Chem Sci Eng. 2011, 5 (2): 238-244.
https://doi.org/10.1007/s11705-010-0002-2
Total macromolecule extract was obtained from the soft body of Mactra veneriformis by the coupling techniques of decoction and alcohol precipitation. The extract was deproteinized with an ion exchange column, and resulted in the purifying of the crude polysaccharide fraction. It was found by chemical analysis that the crude polysaccharide part is composed of abundant polysaccharides (>95%) and few proteins (<1%). Furthermore, only one type of monosaccharide, glucose, was detected from its hydrolytes by thin-layer chromatography, indicating that the polysaccharides might be analogs of glucosan. The anti-hyperglycemia effects of the crude polysaccharide part were preliminarily investigated using several pharmacological methods in normal and diabetic mice. Animal experimental results showed that the crude polysaccharide fraction exhibited proper glycemia inhibition activity, and 300 mg/kg-weight dose has the optimal effect among all the studied doses. It is concluded that the crude polysaccharide fraction can be explored as a novel health product that possesses potential as an anti-hyperglycemic agent.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
A study on rapid acid chrome black (MB 7) spectrophotometric determination of ClO2 and catalytic degradation of 2,6-dinitro-p-cresol (DNPC) by ClO2
Jing DONG, Huilong WANG
Front Chem Sci Eng. 2011, 5 (2): 245-251.
https://doi.org/10.1007/s11705-010-1003-x
Experiments were conducted to investigate the degradation of 2,6-dinitro-p-cresol (DNPC) in the chlorine dioxide (ClO2) catalytic oxidation process. Pure aluminum oxide was used as the catalyst in this process. The degradation of DNPC by ClO2 using aluminum oxide as catalyst was systematically studied by varying the experimental parameters, such as pH values, catalyst dosage, the initial concentration of DNPC and ClO2, reaction time, etc. Under optimal condition (DNPC concentration 39 mg·L-1, ClO2 concentration 0.234 g·L-1, reaction time 15 min, catalyst dosage 4.7 g·L-1 and pH 4.32), almost complete degradation of DNPC can be achieved. The kinetic studies revealed that the ClO2 catalytic oxidation degradation of DNPC followed pseudo-first-order kinetics with respect to both ClO2 and DNPC concentration. The repetitive use of the catalyst was investigated along sequential feed-batch trials. The catalyst performed efficiently after five runs. In addition, a simple and convenient method for the determination of ClO2 in water was developed by using acid chrome black 7 (MB 7) spectrophotometry in this paper.
Figures and Tables |
References |
Related Articles |
Metrics
|
|
Atomistic simulations for adsorption and separation of flue gas in MFI zeolite and MFI/MCM-41 micro/mesoporous composite
Shengchi ZHUO, Yongmin HUANG, Jun HU, Honglai LIU
Front Chem Sci Eng. 2011, 5 (2): 264-273.
https://doi.org/10.1007/s11705-010-1007-6
Adsorption of pure CO2 and N2 and separation of CO2/N2 mixture in MFI zeolite and MFI/MCM-41 micro/mesoporous composite have been studied by using atomistic simulations. Fully atomistic models of MFI and MFI/MCM-41 are constructed and characterized. A bimodal pore size distribution is observed in MFI/MCM-41 from simulated small- and broad-angle X-ray diffraction patterns. The density of MFI/MCM-41 is lower than MFI, while its free volume and specific surface area are greater than MFI due to the presence of mesopores. CO2 is preferentially adsorbed than N2, and thus, the loading and isosteric heat of CO2 are greater than N2 in both MFI and MFI/MCM-41. CO2 isotherm in MFI/MCM-41 is similar to that in MFI at low pressures, but resembles that in MCM-41 at high pressures. N2 shows similar amount of loading in MFI, MCM-41 and MFI/MCM-41. The selectivity of CO2 over N2 in the three adsorbents decreases in the order of MFI>MFI/MCM-41>MCM-41. With increasing pressure, the selectivity increases in MFI and MFI/MCM-41, but decreases in MCM-41. The self-diffusivity of CO2 and N2 in MFI decreases as loading increases, while in MFI/MCM-41, it first increases and then drops.
Figures and Tables |
References |
Related Articles |
Metrics
|
16 articles
|