共查询到20条相似文献,搜索用时 437 毫秒
1.
Oxygen permeation fluxes through dense disk-shaped Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCFO) membranes were investigated as a function of temperature (973–1123 K), pressure (2–10 atm), and membrane thickness (1–2 mm) under an air/helium gradient. A high oxygen permeation flux of 2.01 ml/cm 2 min was achieved at 1123 K and 10 atm under an air/He oxygen partial pressure gradient. Based on the dependence of the oxygen permeation flux on the oxygen partial pressure difference across the membrane and the membrane thickness, it is assumed that bulk diffusion of oxygen ions was the rate-controlling step in the oxygen transport across the BSCFO membrane disk under an air/He gradient. The partial oxidation of methane (POM) to syngas using LiLaNiO x/γ-Al 2O 3 as catalyst in a BSCFO membrane reactor was successfully performed at high pressure (5 atm). Ninety-two percent methane conversion, 90% CO selectivity, and 15.5 ml/cm 2 min oxygen permeation flux were achieved in steady state at a temperature of 1123 K and a pressure of 5 atm. A syngas production rate of 79 ml/cm 2 min was obtained. Characterization of the membrane surface by SEM and XRD after reaction showed that the surface exposed to the air side preserved the Perovskite structure while the surface exposed to the reaction side was eroded. 相似文献
2.
La 2NiO 4 tubular membranes of relative density over 92% were used to separate oxygen from air and facilitate the partial oxidation of methane to H 2 and CO at 900 °C. When methane was fed into a tube of inner surface area 5.11 cm 2 at a rate of 10.5 ml/min, methane throughput conversion was 89%, CO selectivity 96%, H 2/CO ratio 1.5, and the equivalent oxygen flux was 6.8 ml/min. The surface of the La 2NiO 4 membrane exposed to CH 4 decomposed into La 2O 3 and Ni, while the surface in contact with air remained almost unchanged. It is suggested that the conversion of methane in the membrane reactor involves the reforming of methane by the H 2O and CO 2 catalyzed by nickel. 相似文献
3.
A perovskite material of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCF), with both electronic and ionic conductivity, was synthesized by a combined citrate–EDTA complexing method. The dense membrane tube made of BSCF was fabricated using the plastic extrusion method. The partial oxidation of methane (POM) to syngas was performed in the tubular BSCF membrane reactor packed with a LiLaNiO/γ–Al 2O 3 catalyst. The reaction performance of the membrane reactor was investigated as functions of temperature, air flow rate in the shell side and methane concentration in the tube side. The mechanism of POM in the membrane reactor was discussed in detail. It was found that in the tubular membrane reactor, combustion reaction of methane with permeated oxygen took place in the reaction zone close to the surface of the membrane, then followed by steam and CO 2 reforming of methane in the middle zone of the tube side. The membrane tube can be operated steadily for 500 h in pure methane with 94% methane conversion and higher than 95% CO selectivity, and higher than 8.0 ml/cm 2 min oxygen permeation flux. 相似文献
4.
The performance characteristics of isothermal fluidized bed syngas methanation for substitute natural gas are investigated over a self-made Ni–Mg/Al2O3 catalyst. Via atmospheric methanation in a laboratory fluidized bed reactor it was clarified that the CO conversion varied in 5% when changing the space velocity in 40–120 L·g?1·h?1 but the conversion increased obviously by raising the superficial gas velocity from 4 to 12.4 cm·s?1. The temperature at 823 K is suitable for syngas methanation while obvious deposition of uneasy-oxidizing Cγoccurs on the catalyst at temperatures around 873 K. From a kinetic aspect, the lowest reaction temperature is suggested to be 750 K when the space velocity is 60 L·g?1·h?1. Raising the H2/CO ratio of the syngas increased proportionally the CO conversion and CH4 selectivity, showing that at enough high H2/CO ratios the active sites on the catalyst are sufficient for CO adsorption and in turn the reaction with H2 for forming CH4. Introducing CO2 into the syngas feed suppresses the water gas shift and Boudouard reactions and thus increased H2 consumption. The ratio of CO2/CO in syngas should be better below 0.52 because varying the ratio from 0.52 to 0.92 resulted in negligible increases in the H2 conversion and CH4 selectivity but decreased the CH4 yield. Introducing steam into the feed gas affected little the CO conversion but decreased the selectivity to CH4. The tested Ni–Mg/Al2O3 catalyst manifested good stability in structure and activity even in syngas containing water vapor. 相似文献
5.
Short contact time catalytic partial oxidation (SCT-CPO) of natural gas is a promising technology for syngas production, representing an appealing alternative to existing processes. The high conversion and selectivity observed since the earlier works in this field can make this process attractive. Moreover, the SCT-CPO reactors can be autothermally operated and the possibility to use air as oxidant appears a feasible route to reduce syngas production costs: these two issues make possible the use of a SCT-CPO reactor as the reformer of a fuel processor for H 2 production for fuel cells. The present work refers to an experimental study of syngas production from CH4 and O2 via a SCT-CPO reactor made of a fixed bed of Rh/-Al2O3 spheres. The main obtained results are: (i) an increase in GHSV produces an enhancement of transport rates and this in turn determines an improvement in CH4 conversion, despite the reduction in residence time; (ii) the catalyst pellets get hotter than the gas phase thus favouring the H2 and CO production; syngas formation is in fact both thermodynamically and kinetically promoted at high temperatures; (iii) a similar improvement of conversion was obtained with a reduction of the catalyst particle size, thanks once again to an increase in the heat transport and a higher geometrical surface area of the catalyst itself. By a slight increase of the O2 fed to the reactor, H2 and CO yields can be maximised and a complete CH4 conversion achieved. 相似文献
6.
Fuel cells are recognized as the most promising new power generation technology, but hydrogen supply is still a problem. In our previous work, we have developed a LiLaNiO/γ-Al 2O 3 catalyst, which is excellent not only for partial oxidation of hydrocarbons, but also for steam reforming and autothermal reforming. However, the reaction needs pure oxygen or air as oxidant. We have developed a dense oxygen permeable membrane Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3 which has an oxygen permeation flux around 11.5 ml/cm 2 min at reaction conditions. Therefore, this work is to combine the oxygen permeable membrane with the catalyst LiLaNiO/γ-Al 2O 3 in a membrane reactor for hydrogen production by mixed reforming of heptane. Under optimized reaction conditions, a heptane conversion of 100%, a CO selectivity of 91–93% and a H 2 selectivity of 95–97% have been achieved. 相似文献
7.
A series of calcium-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method, and the effect of calcium on the catalytic performances of the catalysts for the partial oxidation of methane to syngas (CO and H 2) was investigated at 750 °C. Also, the catalysts were characterized by XRD, TEM, TPR and ( in situ) Raman. At 6 wt.% of cobalt loading, the unmodified alumina-supported cobalt catalyst showed a very low activity and a rapid deactivation, while the calcium-modified catalyst presented a good performance for this process with the CH 4 conversion of 88%, CO selectivity of 94% and undetectable carbon deposition during a long-time running. Characterization results showed that the calcium modification can effectively increase the dispersion and reducibility of Co 3O 4, decrease the Co metal particle size, and suppress the reoxidation of cobalt as well as the phase transformation to form CoAl 2O 4 spinel phases under the reaction conditions. These could be related to the excellent catalytic performances of Co/Ca/Al 2O 3 catalysts. 相似文献
8.
提出一种铁基氧载体(Fe 3O 4/FeO)化学链CO 2重整CH 4方法制备合成气。为评价该系统的性能,采用Aspen Plus软件对其进行过程模拟和热力学分析。以CH 4转化率、CO 2转化率、能源利用效率和产气氢碳比(H 2/CO)为评价指标,得到系统的优化运行条件,并研究各操作参数(包括各反应器的温度和压力、氧载体甲烷比和CO 2甲烷比)对系统性能的影响。结果表明:当系统处于优化工况时,得到CH 4转化率为97.91%、CO 2转化率为32.76%、能源利用效率为93.77%及产气氢碳比为0.93。该系统能有效利用CO 2和CH 4这两种温室气体获得较低氢碳比的合成气,利于二甲醚的高效合成。 相似文献
9.
提出了一种化学链甲烷干重整联合制氢工艺。该工艺由还原反应器、干重整反应器、蒸汽反应器和空气反应器组成,在实现制氢的同时获得可变H 2/CO比的合成气。借助ASPEN plus软件和小型流化床实验台,在等温条件下,温度900℃,采用Fe 2O 3/Al 2O 3载氧体,对该工艺进行热力学分析和实验验证。结果显示,当铁氧化物被还原至FeO/Fe时,干重整反应器内甲烷转化率可以达到98%,CO产率可以达到94%。干重整反应器中同时发生甲烷干重整和部分氧化反应,载氧体内部晶格氧可以有效降低积炭并提高合成气H 2/CO比。积炭发生于晶格氧消耗殆尽时。积炭进入蒸汽反应器,发生气化反应,降低氢气纯度。 相似文献
10.
The effect of the addition of a second fuel such as CO, C 3H 8 or H 2 on the catalytic combustion of methane was investigated over ceramic monoliths coated with LaMnO 3/La-γAl 2O 3 catalyst. Results of autothermal ignition of different binary fuel mixtures characterised by the same overall heating value show that the presence of a more reactive compound reduces the minimum pre-heating temperature necessary to burn methane. The effect is more pronounced for the addition of CO and very similar for C 3H 8 and H 2. Order of reactivity of the different fuels established in isothermal activity measurements was: CO>H 2≥C 3H 8>CH 4. Under autothermal conditions, nearly complete methane conversion is obtained with catalyst temperatures around 800 °C mainly through heterogeneous reactions, with about 60–70 ppm of unburned CH 4 when pure methane or CO/CH 4 mixtures are used. For H 2/CH 4 and C 3H 8/CH 4 mixtures, emissions of unburned methane are lower, probably due to the proceeding of CH 4 homogeneous oxidation promoted by H and OH radicals generated by propane and hydrogen pyrolysis at such relatively high temperatures. Finally, a steady state multiplicity is found by decreasing the pre-heating temperature from the ignited state. This occurrence can be successfully employed to pilot the catalytic ignition of methane at temperatures close to compressor discharge or easily achieved in regenerative burners. 相似文献
11.
An electrochemical membrane reactor, RhIYSZIAg, has been tested for the partial oxidation of CH 4 to CO/H 2 under oxygen pumping through YSZ. An ionically transported oxygen species over the Rh anode was highly active for the partial oxidation. The reaction mode of the CH 4 oxidation strongly depends on the surface state of Rh particles; a highly oxidized Rh surface accelerates complete oxidation of CH 4 to CO 2/H 2O, while a reduced Rh surface catalyzes the partial oxidation to CO/H 2. Oxygen concentration over the Rh predominantly determines the selectivity; a high oxygen concentration leads to the complete oxidation, while an adsorbed oxygen species gives the partial oxidation. 相似文献
12.
The influence of the addition of 1–10 vol.% of hydrogen or carbon dioxide to the feed during the partial oxidation of methane was studied over a NiO/γ-Al 2O 3 catalyst. The addition of H 2 decreases the conversion and syngas selectivity. This decrease of performance seems to be related to a higher reduction of the catalyst due to the H 2 co-feeding. The addition of CO 2 also appears unfavorable to the production of hydrogen but increases the CO yield. A combination of the dry reforming and the reverse water gas shift reactions is suggested to explain the observed modifications in the product yields. 相似文献
13.
Micro-channel plates with dimension of 1 mm × 0.3 mm × 48 mm were prepared by chemical etching of stainless steel plates followed by wash coating of CeO 2 and Al 2O 3 on the channels. After coating the support on the plate, Pt, Co, and Cu were added to the plate by incipient wetness method. Reaction experiments of a single reactor showed that the micro-channel reactor coated with CuO/CeO 2 catalyst was highly selective for CO oxidation while the one coated with Pt-Co/Al 2O 3 catalyst was highly active for CO oxidation. The 7-layered reactors coated with two different catalysts were prepared by laser welding and the performances of each reactor were tested in large scale of PROX conditions. The multi-layered reactor coated with Pt-Co/Al 2O 3 catalyst was highly active for PROX and the outlet concentration of CO gradually increased with the O 2/CO ratio due to the oxidation of H 2 which maintained the reactor temperature. The multi-layered reactor coated with CuO/CeO 2 showed lower catalytic activity than that coated with Pt catalyst, but its selectivity was not changed with the increase of O 2/CO ratios due to the high selectivity. In order to combine advantages (high activity and high selectivity) of the two individual catalysts (Pt-Co/Al 2O 3, CuO/CeO 2), a serial reactor was prepared by connecting the two multi-layered micro-channel reactors with different catalysts. The prepared serial reactor exhibited excellent performance for PROX. 相似文献
14.
Conversion of NO x with reducing agents H 2, CO and CH 4, with and without O 2, H 2O, and CO 2 were studied with catalysts based on MOR zeolite loaded with palladium and cerium. The catalysts reached high NO x to N 2 conversion with H 2 and CO (>90% conversion and N 2 selectivity) range under lean conditions. The formation of N 2O is absent in the presence of both H 2 and CO together with oxygen in the feed, which will be the case in lean engine exhaust. PdMOR shows synergic co-operation between H 2 and CO at 450–500 K. The positive effect of cerium is significant in the case of H 2 and CH 4 reducing agent but is less obvious with H 2/CO mixture and under lean conditions. Cerium lowers the reducibility of Pd species in the zeolite micropores. The catalysts showed excellent stability at temperatures up to 673 K in a feed with 2500 ppm CH 4, 500 ppm NO, 5% O 2, 10% H 2O (0–1% H 2), N 2 balance but deactivation is noticed at higher temperatures. Combining results of the present study with those of previous studies it shows that the PdMOR-based catalysts are good catalysts for NO x reduction with H 2, CO, hydrocarbons, alcohols and aldehydes under lean conditions at temperatures up to 673 K. 相似文献
15.
This paper presents an investigation into the complex interactions between catalytic combustion and CH 4 steam reforming in a co-flow heat exchanger where the surface combustion drives the endothermic steam reforming on opposite sides of separating plates in alternating channel flows. To this end, a simplified transient model was established to assess the stability of a system combining H 2 or CH 4 combustion over a supported Pd catalyst and CH 4 steam reforming over a supported Rh catalyst. The model uses previously reported detailed surface chemistry mechanisms, and results compared favorably with experiments using a flat-plate reactor with simultaneous H 2 combustion over a γ-Al 2O 3-supported Pd catalyst and CH 4 steam reforming over a γ-Al 2O 3-supported Rh catalyst. Results indicate that stable reactor operation is achievable at relatively low inlet temperatures (400 °C) with H 2 combustion. Model results for a reactor with CH 4 combustion indicated that stable reactor operation with reforming fuel conversion to H 2 requires higher inlet temperatures. The results indicate that slow transient decay of conversion, on the order of minutes, can arise due to loss of combustion activity from high-temperature reduction of the Pd catalyst near the reactor entrance. However, model results also show that under preferred conditions, the endothermic reforming can be sustained with adequate conversion to maintain combustion catalyst temperatures within the range where activity is high. A parametric study of combustion inlet stoichiometry, temperature, and velocity reveals that higher combustion fuel/air ratios are preferred with lower inlet temperatures (≤500 °C) while lower fuel/air ratios are necessary at higher inlet temperatures (600 °C). 相似文献
16.
The kinetics of CO and H 2 oxidation over a CuO-CeO 2 catalyst were simultaneously investigated under reaction conditions of preferential CO oxidation (PROX) in hydrogen-rich mixtures with CO 2 and H 2O. An integral packed-bed tubular reactor was used to produce kinetic data for power-law kinetics for both CO and H 2 oxidations. The experimental results showed that the CO oxidation rate was essentially independent of H 2 and O 2 concentrations, while the H 2 oxidation rate was practically independent of CO and O 2 concentrations. In the CO oxidation, the reaction orders were 0.91, −0.37 and −0.62 with respect to the partial pressure of CO, CO 2 and H 2O, respectively. In the H 2 oxidation, the orders were 1.0, −0.48 and −0.69 with respect to the partial pressure of H 2, CO 2 and H 2O, respectively. The activation energies of the CO oxidation and the H 2 oxidation were 94.4 and 142 kJ/mol, respectively. The rate expressions of both oxidations were able to predict the performance of the PROX reactor with accuracy. The independence between the CO and the H 2 oxidation suggested different sites for CO and H 2 adsorption on the CuO-CeO 2 catalyst. Based on the results, we proposed a new reaction model for the preferential CO oxidation. The model assumes that CO adsorbs selectively on the Cu + sites; H 2 dissociates and adsorbs on the Cu 0 sites; the adsorbed species migrates to the interface between the copper components and the ceria support, and reacts there with the oxygen supplied by the ceria support; and the oxygen deficiency on the support is replenished by the oxygen in the reaction mixture. 相似文献
17.
During the reactions related to oxidative steam reforming and combustion of methane over -alumina-supported Ni catalysts, the temperature profiles of the catalyst bed were studied using an infrared (IR) thermograph. IR thermographical images revealed an interesting result: that the temperature at the catalyst bed inlet is much higher under CH 4/H 2O/O 2/Ar = 20/10/20/50 than under CH 4/H 2O/O 2/Ar = 10/0/20/70; the former temperature is comparable to that over noble metal catalysts such as Pt and Pd. Based on the temperature-programmed reduction and oxidation measurements over fresh and used catalysts, the metallic Ni is recognized at the catalyst bed inlet under CH 4/H 2O/O 2/Ar = 20/10/20/50, although it is mainly oxidized to NiAl 2O 4 under CH 4/H 2O/O 2/Ar = 10/0/20/70. This result indicates that the addition of reforming gas (CH 4/H 2O = 10/10) to the combustion gas (CH 4/O 2 = 10/20) can stabilize Ni species in the metallic state even under the presence of oxygen in the gas phase. This would account for its extremely high combustion activity. 相似文献
18.
The oxidation of CH 4 over Pt–NiO/δ-Al 2O 3 has been studied in a fluidised bed reactor as part of a major project on an autothermal (combined oxidation–steam reforming) system for CH 4 conversion. The kinetic data were collected between 773 and 893 K and 101 kPa total pressure using CH 4 and O 2 compositions of 10–35% and 8–30%, respectively. Rate–temperature data were also obtained over alumina-supported monometallic catalysts, Pt and NiO. The bimetallic Pt–NiO system has a lower activation energy (80.8 kJ mol −1) than either Pt (86.45 kJ mol −1) and NiO (103.73 kJ mol −1). The superior performance of the bimetallic catalyst was attributed to chemical synergy. The reaction rate over the Pt–NiO catalyst increased monotonically with CH 4 partial pressure but was inhibited by O 2. At low partial pressures (<30 kPa), H 2O has a detrimental effect on CH 4 conversion, whilst above 30 kPa, the rate increased dramatically with water content. 相似文献
19.
A dense membrane tube made of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCF) was prepared by plastic extrusion from BSCF oxide synthesized by the complexing EDTA-citrate method. The membrane tube was used in a catalytic membrane reactor for oxidative coupling of methane (OCM) to C 2 without an additional catalyst. At high methane concentration (93%), about 62% C 2 selectivity was obtained, which is higher than that achieved in a conventional reactor using the BSCF as a catalyst. The dependence of the OCM reaction on temperature and methane concentration indicates that the C 2 selectivity in the BSCF membrane reactor is limited by high ion recombination rates. If an active OCM catalyst (La-Sr/CaO) was packed in the membrane tube, C 2 selectivity and CH 4 conversion increased compared to the blank run. The highest C 2 yield in the BSCF membrane reactor in presence of the La-Sr/CaO catalyst was about 15%, similar to that in a packed-bed reactor with the same catalyst under the same conditions. However, the ratio of C 2H 4/C 2H 6 in the membrane reactor was much higher than that in the packed-bed reactor, which is an advantage of the membrane reactor. 相似文献
20.
La 1- x A' x Fe 0.8Co 0.2O 3-δ (A'= Ca, Sr, Ba) perovskite powders were synthesized to attain the desired properties of high O 2 flux and stability under reducing conditions. Steady-state oxygen permeation rates for La 1- x A' x Fe 0.8-Co 0.2O 3-δ perovskite membranes in nonreacting experiments with air on one side and helium on the other side of the membrane were in the order A' x = Ba 0.8 > Ba 0.6 > Ca 0.6 > Sr 0.6. Partial oxidation of methane to syngas (CO + H 2) was performed in a dense La 0.2Ba 0.8Fe 0.8Co 0.2O 3-δ membrane reactor at 850°C in which oxygen was separated from air and simultaneously fed into the methane stream. The reducing atmosphere affected the membrane reaction-side surface while barium enrichment occurred on the air-side surface. Oxygen continuously transported from the air side appeared to stabilize the membrane interior, and the reactor was operated for up to 850 h. 相似文献
|