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1.
Oxidative coupling of methane in a dual-bed reactor comprising of particle/cordierite monolithic catalysts
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A dual-bed reactor was constructed comprising of a 5%Na2WO4-2%Mn/SiO2 particle catalyst and a 4%Ce-5%Na2WO4-2%Mn/SiO2/cordierite monolithic catalyst. The reaction performance of the oxidative coupling of methane (OCM) over the dual-bed reactor system was evaluated. The effects of the bed height and operation mode, as well as the reaction parameters such as reaction temperature, CH4/O2 ratio and flowrate of feed gas, on the catalytic performance were investigated. The results indicated that the suggested dual-bed reactor exhibited a good performance for the OCM reaction when the feed gases firstly passed through the particle catalyst bed and then to the monolithic catalyst bed. A CH4 conversion of 38.2% and a C2H4 selectivity of 43.3% could be obtained using the dual-bed reactor with a particle catalyst bed height of 10 mm and a monolithic catalyst bed height of 50 mm. Both the CH4 conversion and C2H4 selectivity have increased by 2.5% and 12.8%, respectively, as compared with the 5%Na2WO4-2%Mn/SiO2 particle catalyst in a conventional single-bed reactor and by 12.9% and 23.0%, respectively, as compared with the 4%Ce-5%Na2WO4-2%Mn/SiO2/cordierite monolithic catalyst in a single-bed reactor. The catalytic performance of the OCM in the dual-bed reactor system has been improved remarkably. 相似文献
2.
甲烷 (页岩气、天然气、可燃冰和煤层气的主要成分) 是地球上储量巨大的优质能源和高品味的碳氢资源, 我国也拥有储量居全球前列的页岩气、可燃冰和煤层气. 虽然甲烷经由合成气可以间接转化为乙烯等产品, 但工艺流程长以及合成气造气高温、高能耗和高物耗也是不争的事实, 这在一定程度上降低了间接合成路线的竞争优势. 特别是, 甲烷的间接转化需要将本应部分保留于产品的 C-H 键全部打断生成合成气, 然后再在催化剂作用下重组得到烃类产品, 故而并不完美.因此, 甲烷的直接转化一直是科学家孜孜以求的理想路径, 甲烷氧化偶联制乙烯 (OCM 反应) 也再一次引起关注.目前, Mn2O3-Na2WO4/SiO2是最富有应用前景的催化剂, 但其适宜反应温度仍高达 800 ℃ 以上, 极大地制约了其工业化应用. 为提高其低温催化性能, 本文采用金属氧化物 MOx(TiO2, MgO, Ga2O3或 ZrO2) 对 Mn2O3-Na2WO4/SiO2催化剂进行了掺杂改性, 利用扫描电子显微镜、N2吸附-脱附等温曲线、X 射线衍射、拉曼光谱、电感耦合等离子体原子发射光谱等手段对改性后的催化剂进行了系统表征. 结果表明, TiO2掺杂的 Mn2O3-Na2WO4/SiO2催化剂在 700 ℃(催化剂床层温度)下, CH4转化率可达 23%, 同时 C2-C3烃类选择性约为 73%, 且能够稳定运行 300 h 无失活迹象; MnTiO3的形成对提高OCM 反应的低温活性和选择性至关重要, 本质在于低温 (≤ 700 ℃) 化学循环"MnTiO3?Mn2O3"的形成替代了未改性催化剂的高温 (> 800 ℃) 化学循环"MnWO4?Mn2O3". 对于 MgO 改性的 Mn2O3-Na2WO4/SiO2催化剂, 其催化性能与未改性催化剂相当, 反应过程中 Mn2O3与 MgO 生成了新物相 Mg2MnO4; 虽然也形成了新的 MnWO4?Mg2MnO4氧化还原循环, 但是该循环与 MnWO4?Mn2O3循环类似, 需在高温下才可高效进行. 对于 Ga2O3或 ZrO2改性的催化剂, 其催化性能低于未改性催化剂, 原因在于反应过程中 Ga2O3或 ZrO2的引入促进了 MnWO4物相的生成并对其有稳定作用, 反应后的催化剂无论是体相还是表面都只能检测到 MnWO4, 推测认为α-方石英、Na2WO4和 Mn2O3的缺失是导致 Ga2O3或 ZrO2改性催化剂性能下降的主要原因. 相似文献
3.
甲烷氧化偶联W-Mn催化剂的制备及表征 总被引:12,自引:10,他引:12
本文详细报道了制备因素对Na-W-Mn—O/SiO_2催化剂反应性能的影响,并用O_2-TPD,XRD,FT-IR,LRS等方法对催化剂进行了表征。结果表明,该催化剂的最佳组成是Mn 0.32wt%—Na_2WO_4 4wt%/SiO_2,由混浆法制备的催化剂具有较好的稳定性,连续反应30 h后,其甲烷转化活性和C_2烃收率均保持不变。催化剂的结构研究表明,Na_2WO_4与SiO_2发生了相互作用,形成有Si参与的表面钨氧物种,该催化剂具有较好的催化活性与表面钨氧物种的形成相关联,Mn的加入,可能大大提高了该催化剂中表面晶格氧的浓度,从而加快了CH_4的活化速度。 相似文献
4.
S.Jao S.Sadjadi H.R.Godini U.Simon S.Arndt O.Grke A.Berthold H.Arellano-Garcia H.Schubert R.Schomcker G.Wozny 《天然气化学杂志》2012,(5):534-543
Performance of the oxidative coupling of methane in fluidized-bed reactor was experimentally investigated using Mn-Na2WO4/SiO2,La2O3/CaO and La2O3-SrO/CaO catalysts.These catalysts were found to be stable,especially Mn-Na2WO4/SiO2 catalyst.The effect of sodium content of this catalyst was analyzed and the challenge of catalyst agglomeration was addressed using proper catalyst composition of 2%Mn2.2%Na2WO4/SiO2.For other two catalysts,the effect of Lanthanum-Strontium content was analyzed and 10%La2O 3-20%SrO/CaO catalyst was found to provide higher ethylene yield than La2O3/CaO catalyst.Furthermore,the effect of operating parameters such as temperature and methane to oxygen ratio were also reviewed.The highest ethylene and ethane (C2) yield was achieved with the lowest methane to oxygen ratio around 2.40.5% selectivity to ethylene and ethane and 41% methane conversion were achieved over La2O3-SrO/CaO catalyst while over Mn-Na2WO4 /SiO2 catalyst,40% and 48% were recorded,respectively.Moreover,the consecutive effects of nitrogen dilution,ethylene to ethane production ratio and other performance indicators on the down-stream process units were qualitatively discussed and Mn-Na2WO4/SiO2 catalyst showed a better performance in the reactor and process scale analysis. 相似文献
5.
N. A. S. Amin Sriraj Ammasi 《天然气化学杂志》2006,15(3):191-202
A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650-800℃), methane to oxygen ratio (4 10), and SiO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH:j techniques. The rise in oxygen concentration is not beneficial for the C5 selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO CO2) products is more dominant than the oligomerization reaction. The dual-bed catalytie system is highly potential for directly converting methane to liquid fuels. 相似文献
6.
7.
Scale up and stability test for oxidative coupling of methane over Na2WO4-Mn/SiO2 catalyst in a 200 ml fixed-bed reactor
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The study of scale up for the oxidative coupling of methane (OCM) has been carried out in a 200 ml stainless steel fixed-bed reactor over a 5wt% Na2WO4-1.9wt% Mn/SiO2 (W-Mn/SiO2) catalyst. The effects of reaction conditions were investigated in detail. The results showed that, with increasing reaction temperature, the gas-phase reaction was enhanced and a significant amount of methane was converted into COx; with the CH4/O2 molar ratio of 5, the highest C2 (ethylene and ethane) yield of 25% was achieved; the presence of steam (as diluent) had a positive effect on the C2 selectivity and yield. Under lower methane gaseous hourly space velocity (GHSV), higher selectivity and yield of C2 were obtained as the result of the decrease of released heat energy. In 100 h reaction time, the C2 selectivity of 66%-61% and C2 yield of 24.2%-25.4% were achieved by a single pass without any significant loss in catalytic performance. 相似文献
8.
Na-Mn-W/SiO2 catalysts were studied for the oxidative coupling of methane (OCM) in a micro fixed bed reactor made of stainless steel reactor at elevated pressures. The effect of operating conditions, such as GHSV, pressure, temperature and CH4/O2 ratio on the catalytic performance of OCM was investigated. The C2+ selectivity of 80.3% was obtained at a CH4 conversion of 16.1% at 750℃,1.5× 105h-1 GHSV, and 0.6 MPa. Also, there is a small output of C3 and C4 hydrocarbons in the tail gas. The results show that unfavorable effects due to elevated pressure can be overcome by increasing GHSV, and the OCM reaction is strongly dependent on the operating conditions at elevated pressures,particularly GHSV and the CH4/O2 ratio. 相似文献
9.
Sonia Jam Masume Ghalbi Ahangary Ahmad Tavasoli Kambiz Sadaghiani Ali Nakhaei Pour 《Reaction Kinetics and Catalysis Letters》2006,89(1):71-79
Summary An integrated process for producing liquid fuels from synthesis gas via a two-stage Fischer-Tropsch (FT) reaction is disclosed. An iron catalyst was used in the first bed of a fixed-bed reactor
followed by a ruthenium promoted cobalt catalyst in the second bed. The activity and selectivity of the dual-bed system were
assessed and compared with those using catalysts in a single bed system, separately. The methane selectivity in the dual-bed
reactor was about 11% less compared to that of the single-bed system. The C5+ selectivity for the dual-bed reactor was 19.7% higher than that of the single-bed system. 相似文献
10.
《Journal of Energy Chemistry》2015,(4)
In this work,the influence of CO2 on the structural variation and catalytic performance of Na2WO4/Mn/Si O2 for oxidative coupling of methane to ethylene was investigated. The catalyst was prepared by impregnation method and characterized by XRD,Raman and XPS techniques. Appropriate amount of CO2 in the reactant gases enhanced the formation of surface tetrahedral Na2WO4 species and promoted the migration of O in MOx,Na,W from the catalyst bulk to surface,which were favorable for oxidative coupling of methane. When the molar ratio of CH4/O2/CO2 was 3/1/2,enriched surface tetrahedral Na2WO4 species and high surface concentration of O in MOx,Na,W were detected,and then high CH4 conversion of 33.1% and high C2H4 selectivity of 56.2% were obtained. With further increase of CO2 in the reagent gases,the content of active surface tetrahedral Na2WO4 species and surface concentration of O in MOx,Na,W decreased,while that of inactive species(Mn WO4 and Mn2O3) increased dramatically,leading to low CH4 conversion and low C2H4 selectivity. It could be speculated that Na2WO4 crystal was transformed into Mn WO4 crystal with excessive CO2 added under the reaction conditions. Pretreatment of Na2WO4/Mn/Si O2 catalyst by moderate amount of CO2 before OCM also promoted the formation of Na2WO4 species. 相似文献
11.
Reaction chemistry of the OCM reaction on W-Mn/SiO2 catalyst has been reviewed in this account.Initial activity and selectivity,stability in a long-term reaction,reaction at elevated pressures and a modelling test in a stainless-steel fluidized-bed reactor show that W-Mn/SiO2 has promising performance for the development of an OCM process that directly produces ethylene from natural gas.A study on surface catalytic reaction kinetics and used cataly st structure characterization revealed a possible reason why C2 and COx selectivity changed during the long-term reaction.Further improvement of the catalyst composition and preparation metbod should be a future direction of study on OCM reaction over W-Mn/SiO2 catalyst. 相似文献
12.
Li-Mn/WO_(3)/TiO_(2)催化剂具有良好的低温OCM催化性能,采用浸渍法制备Li-Mn/WO_(3)/TiO_(2)催化剂,并详细考察WO_(3)对催化剂物理化学性质及催化性能的影响.利用X射线衍射(XRD)、CO_(2)程序升温脱附(CO_(2)-TPD)、O_(2)程序升温脱附(O_(2)-TPD)、H_(2)程序升温还原(H_(2)-TPR)、拉曼光谱(Raman)和X射线光电子能谱(XPS)等表征技术对催化剂进行了研究,发现WO_(3)的添加提高了C_(2)选择性,并有效抑制了深度氧化.XRD与CO_(2)-TPD结果表明,WO_(3)的添加不仅有利于金红石型TiO_(2)的形成而且能够中和催化剂表面的强碱位,从而抑制了深度氧化反应.O_(2)-TPD和H_(2)-TPR结果表明,WO_(3)的添加降低了晶格氧(O^(2-))移动性,进而提高了反应的C_(2)选择性.此外,WO_(3)的添加促使了低温氧化偶联活性物种MnTiO_(3)的形成并提高了活性物种的分散性,因此提高了催化剂甲烷氧化偶联的反应活性和选择性.所有Li-Mn/x%WO_(3)/TiO_(2)催化剂中,Li-Mn/5%WO_(3)/TiO_(2)催化剂显示出最佳的OCM反应性能.在750℃,CH_(4)∶O_(2)∶N_(2)=10∶4∶5,GHSV=2280 mL·g^(-1)·h^(-1)条件下,最高的C_(2)产物收率可达16.3%. 相似文献
13.
整体式催化剂催化重整净化生物质粗燃气性能研究 总被引:6,自引:0,他引:6
采用分步浸渍法制备了以Ni为活性组分的整体式催化剂,以萘为生物质焦油的模型化合物,考察了整体式催化剂催化重整生物质粗燃气的性能,通过元素分析、热重分析等方法对催化剂的表面积炭进行了研究。结果表明,在整体式催化剂作用下,108h的连续反应中,CH4的平均转化率达到92%,最高达到93.8%。合成气H2/CO的摩尔比保持0.95左右,最高达到1.15,适合液体燃料合成。CO2 的平均转化率为80%,最高达到88%。实验中添加萘模拟生物质焦油的成分,经检测焦油全部转化为H2、CO及微量轻质组分。反应连续进行108h,未发现反应器压降变化和CH4与焦油转化率的下降,表明整体式催化剂具有较好的活性和抗积炭性能。 相似文献
14.
采用浸渍法、粉末涂覆法、沉积沉淀浸渍法、溶胶高温分解法、原位溶液燃烧法和微乳液法制备了 CuO-CeO2/Al2O3/FeCrAl 整体催化剂, 并运用扫描电镜、X 射线衍射、程序升温还原、超声波振动和热振荡等手段研究了制备方法对活性组分的负载及其分布、催化剂结构、粘附稳定性和催化 CO 优先氧化反应性能的影响. 结果表明, 溶胶高温分解法、原位溶液燃烧法和微乳液法制备的整体催化剂表现出较好的催化 CO 优先氧化反应性能和较高的粘附稳定性. 相似文献
15.
甲烷氧化偶联Mn_2O_3-Na_2WO_4/SiO_2催化剂——Ⅱ.表面氧种和结构 总被引:1,自引:0,他引:1
本文用XPS详细考察了Mn_2O_3-Na_2WO_4/SiO-2催化剂的表面氧种,提出了该催化剂表面活性相在SiO_2表面分散的一种可能的表面结构模型。 实验部分详见另文,这里需要指出。所有催化剂样品在XPS分析前,均经在能谱仪预处理室(~10~(-3)Pa)和超高真空测试室(基础真空6.7×10~(-8)Pa)递次的450C和700C原位加热处理,以使在大气中吸附的水分和气体脱附。各元素的特征谱峰由联机计算机以多道模式同时录取(通能50eV),并累加1 h以获取高信噪比数据。Ols峰的解迭用联机计算机以高斯函数拟合,为考察该解迭结果的可靠性,曾对1.9wt%Mn_2O_3-5wt%Na_2WO_4/SiO_2催化利的 相似文献
16.
Ce-promoted Mn/Na2WO4/SiO2 catalyst for oxidative coupling of methane at atmospheric pressure
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A series of Ce-promoted Mn-Na2WO4/SiO2 catalysts were prepared by incipient wetness impregnation method, and their catalytic performance for oxidative coupling of methane (OCM) was investigated at atmospheric pressure in a micro-quartz-tube reactor. The catalysts were characterized by X-ray diffraction (XRD), temperature program reduction (TPR) and BET surface area. Ce promoter increased surface area and Na2WO4 species dispersion, which enriched the amount of the surface species. In addition, Ce promoter in... 相似文献
17.
高效甲醇水蒸气重整制氢的SBA-15改性的Cu/ZnO/Al2O3催化剂 总被引:1,自引:0,他引:1
以介孔SBA-15为结构助剂, 制备出用于甲醇水蒸气重整制氢的新型高效氧化硅掺杂的Cu/ZnO/Al2O3催化剂, 并与传统Cu/ZnO/Al2O3催化剂在相同条件下的催化性能进行了比较. 结果表明, 添加适量介孔SBA-15可显著提高催化剂的催化活性和选择性, 在大幅度提高甲醇转化率的同时有效降低了重整产气中CO的含量. 原位XRD分析证实适量介孔SBA-15的添加对传统Cu/ZnO/Al2O3催化剂的微结构性质可产生重要的调控作用, 从而大大改善其催化活性和制氢选择性. 相似文献
18.
采用常规浸渍法制备了一系列Na(wt%)含量不同的Na-W-Mn/SiO_2催化剂,在流动态微型固定床常压反应装置上评价了这些催化剂的甲烷氧化偶联(OCM)制乙烯催化反应性能,并进行了XPS、XRD表征。实验结果表明,Na含量为0.39wt%-2.34Wt%的Na-W-Mn/SiO_2催化剂具有好的甲烷氧化偶联制乙烯性能,此时Mn以对反应有利的晶相存在,同时由于Na的表面富集,引起W、Mn向催化剂表面发生迁移。由此可见,在Na-W-Mn/SiO_2催化剂中,Na是甲烷转化和乙烯生成不可缺少的活性组分之一。 相似文献
19.
Oxidative coupling of methane over (Na2WO4+Mn or Ce)/SiO2 catalysts: In situ measurement of electrical conductivity
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Zeinab Gholipour Azim Malekzadeh Reza Hatami Yadollah Mortazavi Abasali Khodadadi 《天然气化学杂志》2010,19(1):35-42
The effects of manganese oxide or ceria promoters on the performance of Na2WO4/SiO2 catalysts for oxidative coupling of methane (OCM) are reported. The OCM reaction was performed in a continuous-flow microreactor at 800 ℃, atmospheric pressure and under GHSV = 13200 ml gC-1at h-1. Catalysts were characterized by in situ conductivity measurement, FT-IR spectroscopy, XRD, SEM and temperature programmed reduction analysis. Manganese oxide promoted Na2WO4/SiO2 is considered as one of the active and selective ca... 相似文献
20.
CONVERSION OF METHANE AND CARBON DIOXIDE TO AROMATICS OVER CHROMIUM-BASED CATALYSTS:SELECTIVITY AND YIELD OF MAIN PRODUCTS
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在840℃,0.5MPa,CH4/CO2摩尔比为1.4,接触时间(W/F)为0.79h·g·L-l的条件下,甲烷和二氧化碳在7.5wt%Cr/5.0wt%Na/SiO2催化剂上共活化得到了4.8%的C2选择性,48.7%的芳烃选择性及1.9%的芳烃收率。在钠修饰的铬基催化剂上,成功地一步实现了CH4和CO2转化为乙烯及中间物乙烯聚合为芳烃的过程 相似文献