Performance characteristics of fluidized bed syngas methanation over Ni-Mg/Al2O3 catalyst

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.     

二氧化碳甲烷化催化剂的研究进展

CO₂催化加氢甲烷化反应是温室气体CO₂资源化利用的有效途径之一。本文回顾了CO₂催化加氢甲烷化催化剂的研究现状, 其中Ni基催化剂是研究最为广泛的CO₂甲烷化催化剂。重点介绍了Al₂O₃、SiO₂和La₂O₃载体及CeO₂和La₂O₃助剂等对Ni基催化剂CO₂甲烷化性能的影响, 阐述了载体的结构、电子性能、化学性能和助剂等对Ni基催化剂CO₂甲烷化性能的影响。结合几种非Ni基CO₂甲烷化催化剂的对比研究发现, 具有有序介孔结构的Co基催化剂也表现出了优越的CO₂甲烷化性能。由此表明, 催化剂新颖的结构也是影响CO₂甲烷化性能的重要因素, 通过催化剂结构、组成等的调变, 能实现CO₂低温高效甲烷化, 为CO₂甲烷化工业化进程奠定基础。     

CO2甲烷化研究进展

CO_2是造成温室效应的主要气体,作为碳基能源使用的末端形态,CO_2也是种重要的基础碳源。因此,将CO_2转化为能源产品可以快速实现碳的循环,对环境与能源领域意义重大。介绍了CO_2的排放、回收以及资源化利用现状,从催化剂体系、反应机理、合成工艺以及工业化现状等方面系统地介绍了CO_2甲烷化的发展。针对H2供给对CO_2甲烷化应用的限制,分析了电解水制氢再与CO_2进行甲烷化反应的电制气(Pt G)技术的发展现状、工艺路线及其经济性,讨论了该技术在我国应用的可行性。提出随着CO_2捕集与新能源相关技术的发展,Pt G技术会更加成熟,将有望成为未来CO_2资源化利用的重要形式。     

Liquid phase methanol reforming with water over silica supported Pt–Ru catalysts

The mechanism of the liquid phase methanol reforming reaction over silica supported Pt–Ru catalyst was investigated by kinetic studies, employing a pyrex glass reactor with reflux condensers connected to a closed gas circulation system under ambient pressure. The rate of H₂ formation over Pt–Ru/SiO₂ catalysts was more than 20 times faster than that over Pt/SiO₂ catalysts with high selectivity for CO₂ (72.3%), indicating a marked addition effect of Ru. In the case of HCHO–H₂O reaction over Pt–Ru/SiO₂, the H₂ formation rate was five times larger than that in the CH₃OH–H₂O reaction but selectivity to CO₂ was only 4%. On the contrary, in the HCOOCH₃–H₂O and HCOOH–H₂O reactions, both high activity and selectivity were observed over Pt–Ru/SiO₂. These results clearly indicate that the CO₂ formation does not proceed via HCHO decomposition and following water gas shift reaction. We propose the following pathway for liquid phase methanol reforming reaction over Pt–Ru/SiO₂; a partly dehydrogenated methanol (CH₂OH^*) is the initial reaction intermediate, from which H₂ and CO₂ are formed through HCOOCH₃ and HCOOH as the successive reaction intermediates.     

新型VESTA甲烷化工艺路线探究

分析了现有煤制合成天然气技术主要存在的问题,介绍了新型无循环、适应宽氢碳比的VESTA甲烷化技术。VESTA甲烷化技术的显著特征是利用合成气中的CO₂和外加水蒸汽来控制甲烷化反应温升,不需要操作条件苛刻的循环气压缩机;在甲烷化反应之前对原料气只脱硫、不脱碳,甲烷化反应之后再集中脱碳;经中试试验得出原料气中的H₂/CO比不影响最终的SNG产品指标;甲烷化后的粗SNG产品气中的CO₂体积分数高达71%,因而可在脱碳前低成本联产中压液体CO₂产品。这部分液体CO₂产品除了可用泵增压输送到粉煤气化单元用作输送气体外,还可以直接作为副产品为企业增加收益,并间接降低了碳排放。新型VESTA甲烷化技术与现有带循环压缩机的甲烷化技术相比,不但更容易操控,而且还提高了操作的稳定性和安全性,同时又能极大地降低净化装置、甲烷化装置及SNG干燥装置的投资和能耗。因此,采用VESTA甲烷化技术,能有效地提高煤制合成天然气的市场竞争力。     

Comparison of the dynamics of the high-temperature water-gas shift reaction on oxide catalysts

The dynamics of the high-temperature water-gas shift reaction on iron oxide and Co-Mo-oxide catalysts was studied with transient response experiments performed at 563–673 K at atmospheric pressure in a gradientless spinning basket reactor. At the reaction start-up the step response of CO₂ on the iron oxide catalyst was always faster than the response of H₂, whereas the response of H₂ on the Co-Mo catalyst was faster than the response of CO₂. Water pretreatment retarded the response of H₂ on the iron oxide catalyst, whereas a similar pretreatment accelerated the response of H₂ on the Co-Mo catalyst. Based on the results of the transient response experiments reaction mechanisms were proposed for the water-gas shift reaction on both catalysts. The rate determining steps on the iron oxide catalyst were assumed to be the CO₂ desorption and surface hydroxyl decomposition steps. The rate determining steps on the Co-Mo catalyst were assumed to be the surface reaction and CO₂ desorption steps. The transient responses were modelled with non-steady-state rate equations based on the mechanisms, and the kinetic constants were determined by regression analysis. The kinetic models were able to describe the transient behaviours of the oxide catalysts.     

宽温型镍基甲烷化催化剂制备及催化性能

利用挤条成型及等体积浸渍法制备了负载型镍基甲烷化催化剂。通过H₂-TPR等表征方法对催化剂进行表征,研究了MgO对镍基催化剂中NiO与载体Al₂O₃相互作用力的影响。催化剂活性评价表明,助剂MgO在甲烷化反应中对CH₄选择性具有明显的促进作用。考察了催化剂的高温稳定性,并对镍基催化剂的低温失活现象进行了研究。     

一种低能耗捕集CO2煤基甲醇和电力联产过程设计

传统的煤制甲醇过程所需合成气的氢碳比为2.1左右,而煤气化粗合成气氢碳比仅为0.7左右,因此需要将部分合成气进行变换来调节氢碳比。然而,变换气与未变换气混合后使得CO₂浓度降低,从而导致CO₂捕集能耗增加。提出了一种低能耗捕集CO₂煤基甲醇和电力联产过程。新联产过程中部分粗合成气首先经过变换,将CO转变为H₂和CO₂,CO₂浓度提高,在此时进行CO₂捕集可实现捕集能耗的降低。经CO₂捕集后,得到富H₂气体,富H₂气体分流后与另一部分煤气化粗合成气混合调节甲醇合成的氢碳比。对新的过程进行了建模、模拟与分析。结果表明相比传统的带CO₂捕集的煤制甲醇和IGCC发电过程,新的联产过程的能量节约率可达到16.5%,CO₂捕集能耗下降30.3%。     

Ni-CeO2-K/γ-Al2O3催化剂上沼气联合重整制合成气

采用超声波辅助等体积浸渍法制备Ni-CeO₂-K/γ-Al₂O₃催化剂用于沼气联合重整反应,采用 BET、XRD、TG/DTG等技术对催化剂性质进行了表征,在微型固定床反应装置中研究了反应温度、体积空速、原料气组成等对沼气联合重整反应特性的影响,并对催化剂的稳定性进行了研究。结果表明,助剂CeO₂的加入,提高了催化剂中Ni的分散度,降低了催化剂还原温度。升高反应温度和减小体积空速,能够提高沼气中CH₄和CO₂的转化率;原料气中加入水蒸气,能够明显提高H₂/CO体积比;加入的O₂容易与H₂、CO发生反应,CH₄转化率稍有提高。在常压、反应温度850℃、体积空速为100000h^-1、摩尔比CH₄∶CO₂∶H₂O∶O₂∶Ar=1∶0.5∶0.5∶0.1∶0.01的优化条件下,沼气中CH₄转化率超过95%,CO₂转化率超过75%,生成合成气H₂/CO体积比约为1.6,反应48h后,催化剂未见积炭,保持稳定的活性。与沼气干重整相比,沼气联合重整不利于沼气中CO₂的转化。     

CATALYTIC PRODUCTION OF ELEMENTAL SULFUR FROM THE THERMAL DECOMPOSITION OF H2S IN THE PRESENCE OF CO2

The feasibility of using a cobalt-molybdenum (Co-Mo) sulfide catalyst that was prepared from a commercial Co-Mo oxide catalyst for the production of elemental sulfur from hydrogen sulfide (H₂S) and carbon dioxide (CO₂) in a packed bed catalytic reactor was studied. It was demonstrated that the desired sulfide catalyst could be prepared by first reducing, then sulphiding the corresponding oxide. The results showed that the prepared catalyst was capable of producing elemental sulfur from the thermal decomposition of H₂S in the presence of CO₂ over a temperature range of 465-700°C and at atmospheric pressure. A specific rate coefficient was calculated as well as the Arrhenius parameters for the non-equilibrated reaction. The H₂S decomposition reaction was found to be a second order reaction and have an activation energy of 114.4kJ/mol(27.3kcal/mol).     

煤基合成气甲烷化用镍基催化剂失活热力学和抗失活预测

利用热力学数据对煤基合成气甲烷化用镍基催化剂硫中毒以及积炭热力学进行了详细的计算。计算发现,活性金属Ni、Mo在甲烷化反应条件下与H₂S、COS发生反应是自发进行的过程。10^-10数量级分压的H₂S含量、10^-14数量级分压的COS含量即可使镍金属活性组分生成硫化镍而使催化剂失活;当Mo作为助剂添加到Ni基催化剂时,硫含量不能超过10^-6数量级。不同温度区间发生的积炭反应类型不同,当温度为633.15～898.15K时,积炭反应主要以CO歧化反应、CO还原反应为主;898.15～983.15K时以CH₄裂解反应为主。另外,在0.1MPa下,添加摩尔分数为11.11%及以上含量水蒸气可以避免积炭。     

ALTERNATIVE GENERATION OF H2, CO AND H2, CO2 MIXTURES FROM STEAM-CARBON DIOXIDE REFORMING OF METHANE AND THE WATER GAS SHIFT WITH PERMEABLE (MEMBRANE) REACTORS

A new process is proposed which converts CO₂ and CH₄ containing gas streams to synthesis gas, a mixture of CO and H₂ via the catalytic reaction scheme of steam-carbon dioxide reforming of methane or the respective one of only carbon dioxide reforming of methane, in permeable (membrane) reactors. The membrane reformer (permreactor) can be made by reactive or inert materials such as metal alloys, microporous ceramics, glasses and composites which all are hydrogen permselective. The rejected CO reacts with steam and converted catalytically to CO₂ and H₂ via the water gas shift in a consecutive permreactor made by similar to the reformer materials and alternatively by high glass transition temperature polymers. Both permreactors can recover H₂ in permeate by using metal membranes, and H₂ rich mixtures by using ceramic, glass and composite type permselective membranes. H₂ and CO₂ can be recovered simultaneously in water gas shift step after steam condensation by using organic polymer membranes. Product yields are increased through permreactor equilibrium shift and reaction separation process integration.

CO and H₂ can be combined in first step to be used for chemical synthesis or as fuel in power generation cycles. Mixtures of CO₂ and H₂ in second step can be used for synthesis as well (e.g., alternative methanol synthesis) and as direct feed in molten carbonate fuel cells. Pure H₂ from the above processes can be used also for synthesis or as fuel in power systems and fuel cells. The overall process can be considered environmentally benign because it offers an in-situ abatement of the greenhouse CO₂ and CH₄ gases and related hydrocarbon-CO₂ feedstocks (e.g., coal, landfill, natural, flue gases), through chemical reactions, to the upgraded calorific value synthesis gas and H₂, H₂ mixture products.     

MnOx对Pt/CeZrO2催化剂在水汽和CO2环境下CO氧化的影响

以CeZrO₂固溶体为载体,发现MnO_x的添加能促进Pt/CeZrO₂催化剂的CO氧化性能,并研究了MnO_x含量对催化剂CO氧化活性及抗H₂O和CO₂性能的影响。结果表明,随着MnO_x含量增加,催化剂活性呈现先升高后降低的趋势,在MnO_x含量为0.5%（质量分数）时活性最佳。MnO_x的添加降低了Pt颗粒尺寸并影响催化剂还原性能从而促进反应活性。水汽和CO₂对Pt/CeZrO₂催化剂的CO氧化活性有抑制作用,而MnO_x的加入能显著提高催化剂的抗水汽和CO₂的能力。反应动力学结果表明,在Pt/CeZrO₂催化剂上,反应气中引入H₂O和CO₂后,CO的反应级数有明显升高,说明H₂O和CO₂在催化剂表面与CO竞争吸附,导致CO反应活性下降;而在Pt/MnO_x/CeZrO₂催化剂上,CO的反应级数略有升高,说明MnO_x的添加能有效抑制H₂O和CO₂与CO的竞争吸附,从而改善了催化剂的抗H₂O和CO₂性能。     

Development of novel Ru catalyst of preferential CO oxidation for residential polymer electrolyte fuel cell systems

CO preferential oxidation on a novel Ru catalyst greatly improved in activity and selectivity over a wide temperature range by the pre-treatment of H₂ reduction was characterized. The high performance was obtained by increasing the population of surface Ru(0) which improved O₂ activation at low temperatures. Methanation of CO on the catalyst can also contribute to the final CO clean-up from ca. 100 to <1 ppm at low temperatures where the influence of CO₂ methanation can be ignored.     

甲醇合成催化剂的工艺参数优化及反应机理探讨

对自主研制的甲醇合成催化剂进行工艺参数优化,同时根据实验结果对合成气条件下甲醇合成的反应机理进行探讨。实验采用16通道反应器,考察反应温度和接触时间对合成甲醇反应速率的影响,确定适宜的催化剂工艺条件。结果表明,在较长接触时间下,随着温度的升高,CO转化率、H_2转化率和甲醇相对含量先升高后降低,CO_2转化率降低。在较低温度下,CO_2转化率随接触时间延长基本不变,表明甲醇中碳元素主要来自于CO,而CO_2浓度处于水汽变换反应与加氢形成甲醇反应之间的平衡状态。     

Kinetics of the water–gas shift reaction over nanostructured copper–ceria catalysts

Water–gas shift reaction was studied over two nanostructured Cu_xCe_1−xO_2−y catalysts: a Cu_0.1Ce_0.9O_2−y catalyst prepared by a sol–gel method and a Cu_0.2Ce_0.8O_2−y catalyst prepared by co-precipitation method. A commercial low temperature water–gas shift CuO–ZnO–Al₂O₃ catalyst was used as reference. The kinetics was studied in a plug flow micro reactor at an atmospheric pressure in the temperature interval between 298 and 673 K at two different space velocities: 5.000 and 30.000 h⁻¹, respectively. Experimentally estimated activation energy, E_af, of the forward water–gas shift reaction at CO/H₂O = 1/3 was 51 kJ/mol over the Cu_0.1Ce_0.9O_2−y, 34 kJ/mol over the Cu_0.2Ce_0.8O_2−y and 47 kJ/mol over the CuO–ZnO–Al₂O₃ catalyst. A simple rate expression approximating the water–gas shift process as a single reversible surface reaction was used to fit the experimental data in order to evaluate the rate constants of the forward and backward reactions and of the activation energy for the backward reaction.     

REACTOR-MEMBRANE PERMEATOR CASCADE FOR ENHANCED PRODUCTION AND RECOVERY OF H2 AND CO2 FROM THE CATALYTIC METHANE-STEAM REFORMING REACTION

The catalytic reforming of methane by steam is an important industrial process that produces H₂, CO and CO₂, thus chemically transforming natural gas, coal gas and light hydrocarbon feedstocks to synthesis gas or hydrogen fuel. Methane-steam reforming may consist of a number of reactions depending on the reforming catalyst, operating conditions and feedstock composition, The typical industrially desirable reactions are the reverse of methanation (CH₄ + H₂O = CO + 3H₂) and the water-gas shift (CO + H₂O = CO₂ + H₂). Both reactions are equilibrium limited and the composition of the mixture that exits the reformer is in accordance with the one calculated thermodynarmically. Removal of reaction products at the reactor exit by means of selective membrane permeation can offer improved CH₄ conversions and CO₂ and H₂ yields, assuming the subsequent utilization of the reject streams by a second methane-steam reformer. We numerically investigated the feasibility of a system of two tubular methane-steam reformers, in series with an intermediate permselective polyimide membrane permeator, as means of improving the overall CH₄ conversion and the H₂, CO₂ yields over conventional methane-steam reforming equilibrium reaction-separation schemes that are currently in industrial practice. The unique feature of the permselective polyimide separator is the simultaneous removal of H₂ and CO₂ versus CH₄ and CO from the reformed streams. The utilized 6FDA-3,3', 5,5'-TMB aromatic polyimide was reportedly characterized [10] and found to exhibit superior permselective properties compared with other polyimides of the same or different dianhydride sequence. Conversion and yield of the designed reactor-membrane permeator reforming system can be maximized by optimizing the permselective properties of the membrane material and the design variables of the reactors and the permeator. Product recovery and purity in the permeate stream need to be compromised to overall enhance methane conversion and product yield. The operating variables that were varied to investigate their effect on the magnitude of conversion and yield included the inlet pressure of the first reformer, the temperature of both reformers, and the permeator dimensionless Pe' number (variation of the first two variables results to a drastic change in the composition of the reformed stream that enters into the permeator). The numerical results show that the new reformer-membrane permeator cascade process can be more effective (it can offer increased CH₄ conversions and H₂, CO₂ yields) than conventional equilibrium methane-steam reforming reaction-separation processes currently in practice.     

Control of the product ratio of CO2/(CO+CO2) and inhibition of catalyst deactivation for steam reforming of gasoline to produce hydrogen

Factors controlling the product ratio of CO₂/(CO+CO₂) and methods for inhibiting deactivation of catalyst for steam reforming of gasoline were studied. Syngas (H₂+CO) as major product was produced on Ni-Mo/Al₂O₃ and the major product on Ni-Re/Al₂O₃ was H₂ and CO₂ at the same reaction conditions. Hydrogen with a high CO₂/(CO+CO₂) ratio of about 92% was produced by coupling reaction of steam reforming and water gas shift on Ni-Re/Al₂O₃ catalyst at 805 K. The multifunctional activity of the bimetallic catalyst of Ni-Re/Al₂O₃ and the suitable reaction temperature were of crucial significance for the coupling reaction. Although no deactivation could be observed on both Ni-Mo/Al₂O₃ and Ni-Re/Al₂O₃ catalysts for steam reforming of sulfur-free fuels in about 200 h of time on stream, the activity and sulfur-tolerance of Ni-Re/Al₂O₃ was much better than the values of Ni-Mo/Al₂O₃ for steam reforming of sulfur-containing fuels because of the unique role of rhenium in the Ni-Re catalyst. The unique role of rhenium in Ni-Re catalyst was mainly because of alloying of rhenium with nickel to form bimetallic Ni-Re sites and interaction of rhenium with sulfur to form S-Re binds. The sulfur-tolerance of Ni-Re/Al₂O₃ for steam reforming of sulfur-containing gasoline was improved further by addition of a small amount of ZSM-5. The activity and sulfur-tolerance of Ni-Mo/Al₂O₃ was also enhanced by the addition of ZSM-5.     

制备方法对钼基耐硫甲烷化催化剂性能的影响

合成气甲烷化是煤制天然气工艺的主要过程之一。与传统的镍基催化剂相比,钼基催化剂用于耐硫甲烷化可以省去精脱硫过程和水汽变换过程,具有一定的技术和成本优势。但是钼基催化剂活性相对较低,尤其是低温活性和高温稳定性有待提高。对比研究不同方法制备的MoO₃/ZrO₂催化剂在固定床反应器上的耐硫甲烷化性能,发现采用溶液燃烧法制备的催化剂在相同条件下具有较高的耐硫甲烷化活性,当空速为5000 h^-1、反应压力为3MPa、反应温度为300℃和400℃时其CO转化率可分别达到26%和79%。催化剂的N₂物理吸附、透射电镜、X射线衍射和Raman光谱等表征结果表明,溶液燃烧法制备的催化剂具有较小的ZrO₂晶粒尺寸和较大的比表面积,活性组分Mo物种在ZrO₂载体上的分散性更好。而采用共沉淀法和浸渍法制得的MoO₃/ZrO₂催化剂存在不同程度的Mo物种团聚现象,导致其耐硫甲烷化活性较低。     

Study of the reverse water gas shift (RWGS) reaction over Pt in a solid oxide fuel cell (SOFC) operating under open and closed-circuit conditions

The (electro-)kinetics of the reverse water gas shift (RWGS) reaction was studied in a solid oxide fuel cell (SOFC) of the type Pt/YSZ/Pt. The effect of imposed potentials, cell temperature (650–800 °C), H₂ (1–10 kPa) and CO₂ (1–10 kPa) partial pressures on the kinetics and mechanism of the catalytic and electrocatalytic RWGS reaction, were systematically examined. The apparent catalytic activation energy was found equal to 15.6 kcal/mol, while H₂ and CO₂ apparent reaction orders were equal to 0.5 and 0.7, respectively. At both open and closed circuit operation, the associative formate decomposition reaction mechanism was considered to describe kinetics. Under closed circuit operation, rate enhancement factor, |Λ|, values up to 10 were achieved. Finally, current density–voltage and current density–power density characteristics of the cell were recorded at various temperatures and gas mixtures of CO₂ and H₂. It was found that electrical power output of the cell was optimized by increasing temperature and decreasing CO₂/H₂ feed ratio. Maximum power density obtained was 9 mW/cm² (at 520 mV cell voltage and a current density of 17.3 mA/cm², at 800 °C and P_CO2/P_H2=0.16).