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1.
Multiwalled carbon nanotubes (MWNTs) were synthesized on Al2O3 supported Ni catalysts from C2H2 and C2H4 feedstocks in a fluidized bed. The influence of the ratio of superficial gas velocity to the minimum fluidization velocity (U/Umf), feedstock type, the ratio of carbon in the total quantity of gas fed to the reactor, reaction temperature, the ratio of hydrogen to carbon in the feed gas, and nickel loading were all investigated. Significantly, the pressure drop across the fluidized‐bed increased as the reaction time increased for all experiments, due to the deposition of MWNTs on the catalyst particles. This resulted in substantial changes to the depth and structure of the fluidized bed as the reaction proceeded, significantly altering the bed hydrodynamics. TEM images of the bed materials showed that MWNTs, metal catalysts, and alumina supports were predominant in the product mixture, with some coiled carbon nanotubes as a by‐product. © 2009 American Institute of Chemical Engineers AIChE J, 2009 相似文献
2.
To reveal the effect mechanism of CO atmosphere on coal pyrolysis, a study on raw and demineralized lignite was carried out in a horizontal tube furnace under N2 and CO/N2 atmosphere. CO had a negligible effect on the char yield at low temperatures, whereas it enhances the char yield at temperatures higher than 550 °C. The release of tar was higher in the presence of CO above 450 °C because of more free radicals, which reduced low‐temperature crosslinking, and higher selectivity of hydroxyl groups to phenols in the CO‐containing atmosphere. The yields of CO2 and H2 increased, water and CO yields decreased under CO/N2 atmosphere. Light hydrocarbon gases were not affected by changing the reaction atmosphere. The difference between product yields from raw and demineralized coal confirmed that the catalysis of inherent minerals had a great catalytic effect on the water‐gas shift reaction and Boudouard reaction. 相似文献
3.
In this study, for the first time, a particle size effect on crystal structure of Y2O3 particles was exploited to synthesize phase-pure monoclinic Y2O3 particles. In the synthesis process, a precursor aerosol consisting of H2 fuel gas and precursor droplets passed through an impactor before it entered a flame to form yttria particles. A round-jet impactor was used to remove the large precursor droplets, so that the product Y2O3 particles were all smaller than a critical size of approximately 1.5 µm. Due to the particle size effect on crystal structure, the Y2O3 particles thus obtained were essentially phase-pure with the monoclinic structure. The result shows that, by using an impactor to alter the particle size distribution, it is possible to control the crystal structure of Y2O3 particles while maintaining relatively high synthesis yield. 相似文献
4.
Karen Engelen MichelH. Lefebvre Annick Hubin 《Propellants, Explosives, Pyrotechnics》2002,27(5):290-299
In general gas generators are defined as devices which produce force or power in the form of gas. In the present work we will focus on cold gas generators actuated by pyrotechnics. These gas generators are often applied for pressurizing or inflating systems in which high temperatures are not acceptable. Typical applications are: airbags, seat‐belt tensioners, fire extinguishers. Depending on the application, gas‐generating materials have to fulfil a series of requirements, such as good performance reproducibility, easy and reliable ignition, low explosion temperature, high yield of gas, low yield of condensed products, specific gas composition, and adequate burning rate and vivacity. In previous work a whole range of possibly suitable single compounds, such as sodium azide, double base propellant, azodicarbonamide, guanidine derivatives and azole derivatives were studied. These compounds – whether or not stoichiometrically mixed with an oxidizer (e.g. KNO3, KClO4 or NH4NO3) – were theoretically and experimentally examined in order to evaluate their combustion properties. The objective of this work is to experimentally investigate the influence of the particle size of an oxidizer on the combustion behavior of a gas‐generating pyrotechnic mixture. As an example a series of nitroguanidine (NQ) / potassium nitrate (KNO3)‐mixtures with well‐defined KNO3‐particle size fractions are selected. Raman spectroscopy is used to examine the constituent distribution within the bulk and thus the mixing efficiency. Closed vessel tests are used to experimentally compare ignition delay, burning rate, dynamic vivacity, and yield of gas. The composition of the combustion gases is examined through gas analysis. The experiments show that a decrease of the particle size of the KNO3‐particles has a positive influence on the mixing efficiency and on the investigated combustion properties of a NQ/KNO3‐composition. The combustion process of this mixture becomes better controllable when a small KNO3‐particle size fraction is selected, but its combustion behavior is comparable to that of a NQ/KNO3‐mixture containing a broad KNO3‐particle size distribution. 相似文献
5.
1‐Hexene metathesis was performed over standard and potassium‐doped WO3/SiO2 catalysts. The samples were tested at various reaction temperatures, molar feed compositions, and space times. Under the applied reaction conditions, doping with potassium reduced the isomerization and cracking activity of the catalyst by at least half and improved the yield of detergent‐range alkenes twofold. However, increasing the potassium loading to a higher amount resulted in a significant reduction in the metathesis activity as both Brønsted and Lewis acid sites were affected. Optimum operating conditions for the yield of detergent‐range alkenes were identified using response surface methodology. 相似文献
6.
The gas‐liquid mass transfer coefficients (MTCs) of a trickle bed reactor used for the study of benzene hydrogenation were investigated. The Ni/Al2O3 catalyst bed was diluted with a coarse‐grained inert carborundum (SiC) particle catalyst. Gas‐liquid mass transfer coefficients were estimated by using a heterogeneous model for reactor simulation, incorporating reaction kinetics, vapor‐liquid equilibrium, and catalyst particle internal mass transfer apart from gas‐liquid interface mass transfer. The effects of liquid axial dispersion and the catalyst wetting efficiency are shown to be negligible. Partial external mass transfer coefficients are correlated with gas superficial velocity, and comparison between them and those obtained from experiments conducted on a bed diluted with fine particles is also presented. On both sides of the gas‐liquid interface the hydrogen mass transfer coefficient is higher than the corresponding benzene one and both increase significantly with gas velocity. The gas‐side mass transfer limitations appear to be higher in the case of dilution with fine particles. On the liquid side, the mass transfer resistances are higher in the case of dilution with coarse inerts for gas velocities up to 3 · 10–2 cm/sec, while for higher gas velocities this was inversed and higher mass transfer limitations were obtained for the beds diluted with fine inerts. 相似文献
7.
Experimental study of the effect of zeolite 4A treated with magnesium hydroxide on the characteristics and gas‐permeation properties of polysulfone‐based mixed‐matrix membranes
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Nowadays, new methods for gas‐separation processes are being quickly developed. The separation of CH4/CO2 and CH4/H2 is usually the subject of most related research studies, especially in the membrane gas‐separation process, because of their important role in industry. In this study, we attempted to improve the separation properties of a polysulfone/zeolite 4A mixed‐matrix membrane by modifying the zeolite particle surface. The method included a simple ion‐exchange reaction of magnesium chloride with ammonium hydroxide that yielded the formation and precipitation of magnesium hydroxide whiskers on the surface of the zeolites. The whiskers could omit most of the nonselective voids by interlocking the polymer chains through them and, consequently, improve the permeability, selectivity, and elastic modulus of the membranes. X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and dynamic mechanical analysis proved all the changes recorded after the particle and membrane treatments. SEM images showed the petal‐like morphology of the whiskers that formed on the surface of the particles after the reaction against the smooth surface of the untreated zeolite. At a 30 wt % loading of particles in the polymeric matrix, the selectivities for H2/CH4 and CO2/CH4 increased by 69 and 56%, respectively; in contrast, the H2 and CO2 permeabilities decreased by 2.5 and 10%, respectively. The modulus of elasticity for the treated membrane also increased by 14 and 30% compared to those of the pure and untreated membranes, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44329. 相似文献
8.
Martin Schiemann Peter Fischer Viktor Scherer Günter Schmid Dan Taroata 《化学工程与技术》2014,37(9):1600-1605
Combustion examinations on the single‐grain level were carried out in order to get further fundamental insight into the ignition and combustion of lithium particles. Combustion of solid lithium particles in a defined size fraction was analyzed in a laminar‐flow reactor. The exhaust gases of a methane‐air flame provided the reactants O2, CO2, N2, and H2O for the lithium conversion. Two different atmospheres at various temperatures were investigated. A high‐speed camera system measured size and radiation intensity of burning particles. The results indicate that two different combustion phenomena occurred in lithium combustion. The first was identified as a homogeneously enveloping flame around the lithium particle and the second as a reaction zone next to the particle surface. 相似文献
9.
D. J. Ashen G. C. Bromberger T. J. Lewis 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1968,18(12):348-352
Reaction products from SiCl4/H2 and SiHCl3/H2 mixtures have been examined over the temperature range 800–1200°K, and the conditions under which equilibrium is reached have been established. The results point to a ΔH° for SiCl4 of between ?162 and ?163 kcal/mole. The reaction rates expressed in mole/1/sec were: d[SiHCl3]/dt = 7.8 × 1010 [SiCl4] [H2]1/2 exp ?55,000/RT and d[SiH2Cl3]/dt = 2.0 × 1010 [SiHCl3] exp ?51,000/RT and kinetic mechanisms have been suggested. 相似文献
10.
The growth of carbon nanofibers from Fe-Cu catalyzed decomposition of CO/C2H4/H2 mixtures at temperatures over the range 500-650 °C has been investigated. Based on analysis of the gas phase and solid products it is apparent that co-adsorption of CO and C2H4 induces major perturbations in the surfaces of the bimetallic catalyst particles. These features are reflected in an increase in the yield of solid carbon and subtle changes in the structural characteristics of the carbon nanofibers. Optimum performance with respect to the yield of carbon nanofibers is found for iron-rich particles treated in CO/C2H4/H2 (1:3:1) at 600 °C. Deactivation of the catalyst is observed to occur with high Cu concentrations and at reaction temperatures in excess of 600 °C. It is suggested that under these conditions the surface of the particles in contact with the reactant gas mixture become enriched in Cu, which does not possess the ability to dissociatively chemisorb either CO or C2H4. 相似文献
11.
采用浸渍法分别以MCM-41,Al2O3和SiO2 为载体制备了不同镍负载量的甲烷化催化剂,并在连续流动固定床反应装置上对其甲烷化催化活性进行了评价。研究结果表明,与Ni/Al2O3和Ni/SiO2相比,相同镍负载量的Ni/MCM-41催化剂具有更好的催化活性。同时研究了Ni含量对于Ni/MCM-41催化剂催化活性的影响,发现随着Ni含量的增加,CO转化率和CH4收率逐渐升高,并且在Ni含量大于10%(质量分数)以后趋于稳定。在n(H2):n(CO)=3:1、反应压力1.5 MPa、反应温度350℃及质量空速12000 ml·h-1·g-1的反应条件下,10%Ni/MCM-41催化剂CH4选择性达到94.9%,CO转化率接近100%。在100 h催化活性稳定性试验中,10%Ni/MCM-41催化活性无明显下降,表现出良好的催化活性稳定性。采用X射线衍射(XRD)、氮气物理吸附(BET)、热重分析(TG)及氢气程序升温还原(H2-TPR)等技术手段对催化剂进行了表征,结果表明Ni颗粒大小是影响Ni/MCM-41催化剂催化活性的主要因素。 相似文献
12.
《Fuel Processing Technology》2002,79(2):141-155
The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H2, CO, CO2, H2S and hydrocarbons such as CH4, C2H4, C2H6, C3H6, C3H8, C4H8 and C4H6 with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm3. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H2S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended. 相似文献
13.
Hydrogen production via gasification of meat and bone meal in two-stage fixed bed reactor system 总被引:1,自引:0,他引:1
Gasification of meat and bone meal followed by thermal cracking of tar was carried out at atmospheric pressure using a two-stage fixed bed reaction system in series. The first stage was used for the gasification and the second stage was used for thermal cracking of tar. In this work, the effects of temperature (650-850 °C) of both stages, equivalence ratio (actual O2 supply/stoichiometric O2 required for complete combustion) (0.15-0.3) and the second stage packed bed height (40-100 mm) on the product (char, tar and gas) yield and gas (H2, CO, CO2, CH4, C2H4, C2H6, C3H6, C3H8) composition were studied. It was observed that the two-stage process increased hydrogen production from 7.3 to 22.3 vol.% (N2 free basis) and gas yield from 30.8 to 54.6 wt.% compared to single stage. Temperature and equivalence ratio had significant effects on the hydrogen production and product distribution. It was observed that higher gasification (850 °C) and cracking (850 °C) reaction temperatures were favorable for higher gas yield of 52.2 wt.% at packed bed height of 60 mm and equivalence ratio of 0.2. The residence time of tar and product gases was varied by varying the packed bed height of second stage. The tar yield decreased from 18.6 wt.% to 14.2 wt.% and that of gas increased from 50.6 wt.% to 54.6 wt.% by changing the packed bed height of second stage from 40 to 100 mm while the gross heating value (GHV) of the product gas remained almost constant (16.2-16.5 MJ/m3). 相似文献
14.
Mustafa Karaman N. Aslı Sezgi H. Önder Özbelge 《American Institute of Chemical Engineers》2009,55(11):2914-2919
β‐rhombohedral boron carbide (B4C) was deposited on a tungsten substrate from a BCl3? H2? CH4 gas mixture in a dual impinging‐jet chemical vapor deposition reactor. On‐line FTIR analysis of the product stream proved the formation of BHCl2 and HCl as by products, in a competing parallel reaction. A maximum of 13% chemical yield of boron carbide was observed, and the yield was found to have increasing trend with an increase in temperature. XRD analysis proved the existence of rhombohedral B4C phase at 1300°C without any other B4C phases or impurities. At this temperature, the formation of 5‐fold icosahedral boron carbide crystals up to 30 micron sizes was observed. Such highly symmetric crystalline regions were observed to have a very high hardness value of 4750 kg/mm2 as revealed from the microhardness analysis. The change in product morphology at low substrate temperatures resulted in a decrease in the hardness values. © 2009 American Institute of Chemical Engineers AIChE J, 2009 相似文献
15.
Australian coal loaded with a mixed catalyst of K2SO4+Ni(NO3)2 has been gasified with steam in a fluidized bed reactor of 0.1 m inside diameter at atmospheric pressure. The effects of
gas velocity (2-5 Ug/Umf), reaction temperature (750-900 °C), air/coal ratio (1.6-3.2), and steam/coal ratio (0.63-1.26) on gas compositions, gas
yield and gas calorific value of the product gas and carbon conversion have been determined. The product gas quality and carbon
conversion can be greatly improved by applying the catalyst; they can also be enhanced by increasing gas velocity and temperature.
Up to 31% of the catalytic increment in gas calorific value could be obtained at higher temperatures. In the experimental
runs with variation of steam/coal ratio, the catalytic increments were 16-38% in gas calorific value, 14-57% in carbon conversion,
5-46% in gas yield, and 7-44% in cold gas efficiency. With increasing fluidization gas velocity and reaction temperature,
the unburned carbon fraction of cyclone fine for catalytic gasification decreased 4-18% and 13-16%, respectively, compared
to that for non-catalytic gasification.
Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his
retirement from Korea University. 相似文献
16.
Catalytic steam reforming of bio‐oil is an economically‐feasible route which produces renewable hydrogen. The Ni/MgO‐La2O3‐Al2O3 catalyst was prepared with Ni as active agent, Al2O3 as support, and MgO and La2O3 as promoters. The experiments were conducted in fixed bed and fluidized bed reactors, respectively. Temperature, steam‐to‐carbon mole ratio (S/C), and liquid hourly space velocity (LHSV) were investigated with hydrogen yield as index. For the fluidized bed reactor, maximum hydrogen yield was obtained under temperatures 700–800 °C, S/C 15–20, LHSV 0.5–1.0 h–1, and the maximum H2 yield was 75.88 %. The carbon deposition content obtained from the fluidized bed was lower than that from the fixed bed. The maximum H2 yield obtained in the fluidized bed was 7 % higher than that of the fixed bed. The carbon deposition contents obtained from the fluidized bed was lower than that of the fixed bed at the same reaction temperature. 相似文献
17.
Woon-Jae Lee Sang-Done Kim Byung-Ho Song 《Korean Journal of Chemical Engineering》2002,19(6):1091-1096
To produce low calorific value gas, Australian coal has been gasified with air and steam in a fluidized bed reactor (0.1 m-I.Dx1.6
m-high) at atmospheric pressure. The effects of fluidizing gas velocity (2–5 Uf/Umf), reaction temperature (750–900 °C), air/coal ratio (1.6-3.2), and steam/coal ratio (0.63–1.26) on gas composition, gas yield,
gas calorific value of the product gas and carbon conversion have been determined. The calorific value and yield of the product
gas, cold gas efficiency, and carbon conversion increase with increasing fluidization gas velocity and reaction temperature.
With increasing air/coal ratio, carbon conversion, cold gas efficiency and yield of the product gas increase, but the calorific
value of the product gas decreases. When steam/coal ratio is increased, cold gas efficiency, yield and calorific value of
the product gas increase, but carbon conversion is little changed. Unburned carbon fraction of cyclone fine decreases with
increasing fluidization gas velocity, reaction temperature and air/coal ratio, but is nearly constant with increasing steam/coal
ratio. Overall carbon conversion decreases with increasing fluidization velocity and air/ coal ratio, but increases with increasing
reaction temperature. The particle entrainment rate increases with increasing fluidization velocity, but decreases with increasing
reaction temperature.
This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University. 相似文献
18.
Fast pyrolysis experiments of larch sawdust were conducted in a conical spouted‐bed reactor to study the influences of reaction temperature, inlet gas velocity, feeding rate, and particle size on the product yield and pyrolysis oil quality. For the first time, the optimal conditions were determined for various pyrolysis operations of such reactor to increase the yield and quality of pyrolysis oil. The results demonstrate that the biomass particle size, reaction temperature, biomass feeding rate, and inlet gas velocity all affected the quality and yield of the pyrolysis oil, in this order. 相似文献
19.
Synthesis of ultrafine WC‐Co composite powders under hydrogen atmosphere with in situ carbon via a one‐step reduction‐carbonization process
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Qiumin Yang Jiangao Yang Hailin Yang Hao Chen Wei Su Jianming Ruan 《International Journal of Applied Ceramic Technology》2017,14(2):220-227
An inexpensive and facile direct method to synthesis ultrafine WC‐Co composite powders was proposed employing soluble starch as an in situ carbon source in a H2 atmosphere via a one‐step reduction‐carbonization process. Influences of processing factors, such as temperature, H2 flow rate, and reaction time have been investigated. The results revealed that the system of synthesis process was dynamic in nature where temperature, H2 flow rate, and reaction time had a suitable value to achieve the desired product phase. Mainly due to the gas reaction and homogeneous in situ carbon, the synthesizing temperature and reaction time were greatly lower than the conventional method. Lowering the reaction temperature and increasing the reaction rate would lead to finer WC‐Co composite powders. Ultrafine WC‐Co composite powders with almost no unwanted phases were obtained under the H2 flow rate of 0.75 m3/h at 950°C for 0.5 hour and the average particle size was 155 nm with good dispersion. Furthermore, the mechanism for the phase transformation was discussed in this study as well. 相似文献
20.
The influence of sulfonation reaction time, temperature and the parent polystyrene (PS) particle size on the degree of sulfonation (DS), ion exchange capacity (IEC), morphology and glass transition temperature (Tg) of sulfonated polystyrene (SPS) particles was investigated. A longer reaction time (ca 2 h) at 40 °C and a smaller particle size resulted in SPS particles with a high DS. It was found that a larger PS particle size did not readily yield SPS particles with a high DS even with a longer reaction time. Contrary to the popular belief in the literature that a higher DS ensures a high IEC, we observed that the proportionality of IEC to DS is primarily controlled by the SPS particle size. Larger IEC values were obtained for larger particles rather than smaller ones despite their similar DS, owing to the presence of strong interactions between ? SO3H groups within the particles in the latter case which restricts the availability of free H+ for ion exchange. The SPS particles displayed a core‐shell morphology in which the outer shell appeared because of sulfonation on the PS. The DS value and the SPS particle size significantly influenced the shell thickness and thereby the morphology of the SPS particles. Copyright © 2012 Society of Chemical Industry 相似文献