甲烷的二氧化碳重整动力学研究

The kinetics of CO2 reforming of methane has been studied at 976-1033K on a commercial NiO/CaO/Al2O3 catalyst in a packed-bed continuous reactor. The reaction was carried out at atmospheric pressure and CO2/CH4 ratio > 2. The Hougen-Watson rate models were fitted to experimental data assuming the dissociative adsorption of methane as the rate-determining step. The reaction rate showed an effective reaction order of about unity for CH4. The apparent activity energy was found to be 104kJ·mol-1. Therefore the kinetic reaction parameters were determined and a possible reaction mechanism was proposed.     

液态二氧化碳置换整形甲烷水合物过程特性

通过可视化水合物反应装置和影像设备,研究了注入液态CO2分解CH4水合物同时原位生成气体水合物并保持整块水合物结构稳定的完整过程,验证了水合物分解和生成同时进行的第二类原位置换过程的可行性. 通过控制压力实现在CO2?CH4混合水合物四相区(水合物?水?液相?气相)的CH4置换过程,得到富CH4气体产物. 通过分析气相色谱和测定产气量得到CH4产气特性和CO2对CH4水合物的置换率. 结果表明,低压有利于获得较优的置换效果,4.5 MPa下的置换过程较5 MPa时产气量提高14.6%,甲烷水合物置换率提高13.7%.     

生物质粗燃气自热重整调变的热力学分析

运用吉布斯自由能最小化方法对生物质粗燃气自热重整过程进行了热力学分析,研究了重整反应过程中的温度,O2/CH4摩尔比及焦油摩尔分数等因素对平衡产物组成的影响规律。研究结果表明:低温有利于CO歧化与加氢反应,而高温促进了CH4和CO2的转化,提高合成气H2+CO摩尔分数,降低H2/CO摩尔比。O2/CH4摩尔比的增加有利于生物质燃气从部分氧化反应向完全氧化反应转变,促进了CH4的重整反应而抑制了CO2的转化;O2/CH4摩尔比的增加降低了合成气H2+CO摩尔分数,降低了H2/CO摩尔比,在重整后的生物质粗燃气中,n(H2)/n(CO)≈1。积碳量随温度升高和O2/CH4摩尔比的增加逐渐减少,随着焦油(C10H8)物质的量的增加而增加。焦油物质的量增加提高了合成气中H2与CO摩尔分数,是重整反应的重要原料。优化的生物质燃气自热重整反应条件为温度1 023 K,O2/CH4摩尔比0.7,焦油摩尔分数<1%。     

O2/CO2气氛中水蒸气预混CH4燃烧特性与烟气余热梯级利用方案

对O2/CO2气氛中甲烷预混水蒸气燃烧特性及主要污染物生成进行了数值模拟研究,在加湿燃烧的基础上提出一种全新的清洁燃烧方式,即在保证甲烷流量一定时,通过改变入口处水蒸气的质量分数,研究水蒸气预混比Rf(0, 0.1, 0.2, 0.3, 0.4和0.5)对燃烧流场、燃烧组分和污染物浓度的影响。结果表明,随Rf增大,燃烧反应速率上升、燃烧效率提高且污染物排放量降低。模拟所得甲烷预混水蒸气的最优气氛为81%CH4/19%H2O,提出了一种高效节能的O2/CO2气氛下水蒸气预混CH4燃烧与烟气余热梯级利用方案。     

Na2CO3-K2CO3熔盐法同时制取合成气和金属锌

针对传统的甲烷转化制合成气及金属锌制备技术的缺陷,提出了一种新型的熔融盐反应体系,在熔融盐反应器中以熔融盐(质量比为1:1的Na2CO3/K2CO3)为反应介质对CH4与ZnO反应同时生成金属锌和合成气作了实验研究,利用气相色谱对气体组分进行了分析. 结果表明,反应尾气组分主要是H2, CO和CH4,未检测到CO2,其中合成气的量及H2/CO比例随反应温度的升高而增加,在1198 K左右获得了H2/CO比为2的合成气. 合成气和金属锌分别从气相和熔融盐中获得. 用XRD, SEM及EDS对金属锌产品和熔融盐进行了表征,发现反应后的熔融盐含有少量Na2O和NaOH,来自于CH4与熔融盐之间的微弱反应,由此推断熔融盐还具有消碳功能.     

不同工艺条件下耐硫甲烷化催化剂的反应活性研究

考察了钼基耐硫甲烷化催化剂在不同反应温度下的催化活性,结果表明反应温度在560℃附近时甲烷化活性最高。在此温度下研究了空速、原料气中H2S、H2O、CO2、CH4、H2/CO等浓度对反应活性的影响,结果表明,原料气中H2S含量的增加有利于提高催化剂的甲烷化反应活性;H2O的加入促进了水煤气变换反应的进行但抑制了甲烷化反应,因此CO转化率虽没有下降但甲烷化效率却有所降低;添加CH4对甲烷化反应没有明显影响,而添加CO2则明显抑制了甲烷的生成。结合催化剂表征结果进一步对各因素的影响机理进行了分析,这为耐硫甲烷化工艺条件优化及催化剂设计提供了重要依据。     

耐硫甲烷化催化剂的研究

煤制天然气采用耐硫甲烷化催化剂,减小了反应设备体积,对节省投资和降低能耗有积极意义。采用等体积浸渍法制备系列Mo-Ni/γ-Al2O3耐硫甲烷化催化剂,并对催化剂活性及耐硫性进行评价,考察浸渍液中不同Co和W元素添加量对催化剂活性的影响。结果表明,耐硫甲烷化催化剂活性中心MoS2和WS2的生成有利于提高CO转化率和CH4选择性,促进合成气生成CH4,Co的添加不利于提高催化剂的CO转化率和CH4选择性,而W元素的添加有利于提高催化剂的CO转化率和CH4选择性。在反应温度550℃、压力2 MPa和空速1 800 h-1条件下,n（H2）∶n（CO）=1∶1时,CO转化率为64.24%,CH4选择性为52.00%。n（H2）∶n（CO）=3∶1时,CO转化率为77.90%,CH4选择性为68.41%。     

甲烷空气催化部分氧化制含氮合成气的研究

采用常规的浸渍法制备了镍基催化剂和经过镧改性的镍基催化剂,研究了甲烷催化部分氧化制备含氮合成气的催化功能,结果说明,镍含量在8％时催化活性达到最好,同时加入镧进行改性后催化剂的活性和选择性有所提高;该催化剂对甲烷空气催化部分氧化制合成气在常压下具有较高的转化率,随压力升高,转化率明显下降,并且积极严重,通过向体系加入H2O和CO2可以提高加压条件下甲烷的转化率并抑制催化剂积碳,还可以获得H2／CO接近2的合成气,满足合成液体燃料的要求。     

NiO/MgO整体式催化剂上甲烷部分氧化制备合成气

甲烷部分氧化制备合成气反应过程具有反应速率快、能耗低和H₂与CO物质的量比适用于合成甲醇及F-T合成等优点,是一种有希望替代传统水蒸汽重整的方法。研究在NiO/MgO蜂窝陶瓷整体式催化剂上的甲烷部分氧化过程,主要考察涂层载体、活性组分Ni含量、涂层载体前驱体、焙烧温度和还原温度对催化剂反应性能的影响。采用XRD、H₂-TPR和N2吸附等表征前驱体及其负载活性组分NiO后的晶相、还原特性和吸附性能。结果表明,采用浸渍法制备催化剂时,Mg(NO₃)₂为涂层载体MgO前驱体,在NiO负载质量分数20%、焙烧温度（500~600） ℃和还原温度750 ℃条件下制备的催化剂NiO/MgO-N性能较好,活性较稳定;以NiO/MgO-N为催化剂,在反应温度800 ℃、n(O₂)∶n(CH₄)＝0.5和空速9 723 h^-1条件下,CH₄转化率94.4%,H₂选择性99.9%,CO选择性92.9%。     

水合物法分离低浓度煤层气中的甲烷

向模拟煤层气(13.11vol% CH4+86.89vol% N2)中添加5.8mol%四氢呋喃(THF)?0.03mol%十二烷基硫酸钠(SDS)促进剂溶液分离提纯煤层气,考察了压力、温度、反应时间对气体消耗量、反应速率、分解气中甲烷浓度、甲烷回收率和甲烷分离因子的影响,采用色谱分析法分别测定了CH4在剩余气相和分解气相中的浓度。结果表明,压力增加,CH4回收率增大,CH4分离因子增大,CH4分离效果越好;温度是影响甲烷分离因子的关键因素,温度降低,氮气和甲烷竞争进入水合物晶体中,导致水合物相中甲烷浓度降低;温度升高有利于提高水合物对甲烷的选择性。甲烷回收效率最高可达98.65%,分离因子最大为14.83。随反应时间增加,分解气中CH4浓度升高。     

沉淀剂对SrCO3/La2O2CO3上低温甲烷氧化偶联反应的影响

利用共沉淀法制备了系列SrCO3/La2O2CO3催化剂,制备中沉淀剂的选择影响催化剂的物理化学性质,并最终决定其在低温甲烷氧化偶联(OCM)中的催化性能,其中以摩尔比2：1的NaOH/Na2CO3 为复合沉淀剂效果最好,对应的催化剂中检测到两种La2O2CO3的组分,分别为四方晶相的(I-)和六方晶相的(II-)La2O2CO3。这两种晶相的共存为OCM的低温反应提供所需要的活性位。助剂SrCO3 抑制了甲烷的过度氧化,提高了C2的选择性。所得到的最佳的催化剂能在100 oC炉温下维持OCM反应至少24 h,使CH4.转化率达到25.6%,C2选择性达到43.4%。伴随OCM的甲烷氧化生成COx的副反应产生的热点效应为OCM温和反应提供了热源。     

Permeation properties of CO2and CH4in asymmetric polyethersulfone/polyesterurethane and polyethersulfone/polyetherurethane blend membranes

The transport performances of carbon dioxide and methane were studied in polyethersulfone,polyethersulfone/polyeterurethane (PES-ETPU) and polyethersulfone/polyestherurethane (PES-ESPU) blend membranes separately with different compositions.The variations in the structural characteristics of PES membrane after incorporation of ESPU and ETPU were investigated by different techniques.Additionally,the effect of pressure and composition on the permeance of CO2,CH4and ideal selectivity of CO2/CH4were checked on the membranes. The results revealed that the morphology of the blend membranes was affected by two opposite factors:thermo-dynamic enhancement and kinetic hindrance.The membranes with denser sponge layers were formed at lower ratio of PU/PES,while more porous structure with enlarged macrovoids membranes were observed at higher PU content.The results indicated that adding PU to PES membrane,caused permeance improvement of the gases with nearly no change and/or reduction in ideal selectivity of CO2/CH4.Moreover,PES-ETPU membranes showed higher permeability and less CO2/CH4selectivity in comparison with PES-ESPU samples. For PES-ESPU membrane containing 1.5% ESPU,CO2permeance at 10 bar was improved up to 20% with almost no change in CO2/CH4selectivity with respect to PES.Finally,response surface methodology was used to evaluate the effects of the operating parameters on the permeance and ideal selectivity.     

以类水滑石为前体的Ni催化剂及其催化甲烷水蒸气重整制氢:催化活性和动力学(英文)

Ni/Mg–Al catalysts derived from hydrotalcite-type precursors were prepared by a co-precipitation technique and applied to steam reforming of methane. By comparison with Ni/γ-Al2O3 and Ni/α-Al2O3 catalysts prepared by in-cipient wetness impregnation, the Ni/Mg–Al catalyst presented much higher activity as a result of higher specific surface area and better Ni dispersion. The Ni/Mg–Al catalyst with a Ni/Mg/Al molar ratio of 0.5:2.5:1 exhibited the highest activity for steam methane reforming and was selected for kinetic investigation. With external and inter-nal diffusion limitations eliminated, kinetic experiments were carried out at atmospheric pressure and over a temperature range of 823–973 K. The results demonstrated that the overal conversion of CH4 and the conversion of CH4 to CO2 were strongly influenced by reaction temperature, residence time of reactants as wel as molar ratio of steam to methane. A classical Langmuir–Hinshelwood kinetic model proposed by Xu and Froment (1989) fitted the experimental data with excellent agreement. The estimated adsorption parameters were consistent thermodynamical y.     

合成气甲烷化制替代天然气热力学分析

根据热力学分析建立了等温条件和绝热条件下的合成气甲烷化的热力学模型,选取CO甲烷化反应、水汽变换反应、CO歧化反应为独立反应,CO、CH4和H2O为关键组分.基于此热力学模型可以得到等温条件下的输出气体组成、CO转化率与CH4选择性和绝热条件下的输出气体温度、组成、CO转化率与CH4选择性.并在绝热条件下讨论了输入温度...     

Adsorption separation of CO2, CH4 and N2 on β-zeolite with different SiO2/Al2O3 ratios

采用体积法在273 K和303 K温度下对CO2、CH4和N2在不同硅/铝比的β沸石上的吸附分离性能进行了研究。实验结果表明,Langmuir-Freundlich模型能够较好地拟合吸附实验数据;同一样品上,CO2的吸附量要大于CH4和N2的吸附量;随着硅铝比的减小CO2的吸附量增加,而硅/铝比对CH4和N2的吸附量的影响较小。通过结合Virial方程计算CO2、CH4和N2在不同硅/铝比β沸石上的亨利定律常数和吸附选择性,发现所研究样品对CO2/CH4和CO2/N2均具有很高的吸附选择性,随着样品硅/铝比的减小,CO2/CH4和CO2/N2的吸附选择性显著增加,说明较低硅/铝比β沸石有利于分离CO2。用Clausius-Clapeyron方程求得CO2、CH4和N2在不同硅/铝比的β沸石上的吸附热与吸附量无关,表明β沸石是一种表面势场均匀的吸附剂。     

CO2吸附强化CH4/H2O重整制氢催化剂研究进展

CO_2吸附强化CH_4/H_2O重整制氢是提供低成本高纯氢气和实现CO_2减排的方法之一。其中,催化剂和吸附剂是该工艺的重要组成部分,其活性与选择性制约了反应速率和产率,寿命长短关系到生产成本。综述了CO_2吸附强化CH_4/H_2O重整制氢催化剂和吸附剂的研究现状及存在的问题,机械混合的催化剂与吸附剂在反应过程中存在吸附产物包覆催化活性位点的问题,导致催化剂活性迅速下降。针对该问题,进一步探讨了不同结构双功能复合催化剂的结构特性、研究现状及其在循环-再生过程中存在的问题,核壳型双功能催化剂具有吸附组分与催化剂组分相对独立、催化组分分散分布和比表面积大等优点,在吸附强化制氢中有进一步研究的潜力。利用双功能催化剂的结构特点,实现反复循环再生过程中催化与脱碳反应的匹配,是推动CO_2吸附强化CH_4/H_2O重整制氢技术工业化发展的关键。     

甲烷二氧化碳催化重整催化剂研究进展

甲烷二氧化碳催化重整反应由于对于环境保护与综合利用资源具有重大意义,近年来得到了研究者的广泛重视。本文参阅众多文献,概述了二氧化碳、甲烷催化重整反应的研究动态。着重介绍了催化剂活性组分的选取,载体影响和助剂作用等方面的最新进展。     

甲烷水蒸汽催化转化的动力学模型

在常压下使用内循环式无梯度反应器研究了Z102镍催化剂上甲烷水蒸汽催化转化反应的动力学。实验条件如下:反应温度500—700℃,H_2O/CH_4=2.5—4.5（克分子比）,甲烷空速为2000—10000ml/h·g-cat。根据实验结果的分析,作者认为在反应过程中一氧化碳和二氧化碳是同时生成的,即甲烷水蒸汽催化转化反应可用平行反应模型来表示。所得到的一氧化碳及二氧化碳的生成速度方程分别为: rco=k,p_(CH_4)~(0.8)及 rco_2=k_2p_(CH_4)~(0.8) p_(H_2O)~(1.5)反应速度常数k_1及k_2与温度的关系均符合阿累尼乌斯方程。一些研究者认为在通常的操作条件下,甲烷水蒸汽催化转化反应过程中,水煤气变换反应很快就达到平衡,我们的实验数据计算证明这个见解是不妥的。     

Kinetic contribution of CO2/O2 additive in methane conversion activated by non-equilibrium plasmas

A temperature-controlled and pressure-controlled coaxial dielectric barrier discharge(DBD) reactor was developed to decouple the thermal and kinetic effects of radio frequency(RF) discharge on methane conversion,and further to compare the kinetic behaviors of the mechanistically similar reactions of methane conversion with O_2 and CO_2 additives. A kinetic mechanism for RF plasma assisted methane conversion was assembled. The formation of products in the RF plasma reactor was measured with Gas Chromatography(GC–TCD) and the data were used to validate the kinetic model. The experimental and computational results showed the different kinetic roles of carbon dioxide and oxygen additives in methane conversion, due to the different dissociation and ionization energy of the two additive gases, as well as the thus produced electron energy distribution function(EEDF). Fuel oxidation by plasma generated O, O(~1 D), O_2(a~1Δg), O_2(b~1Σ_g~+) and O+in partial oxidation of methane was observed essential for methane consumption, which resulted in an increase in methane conversion rate,compared to pure methane pyrolysis and dry reforming of methane with CO_2 additive. It was also found that dry reforming of methane with CO_2 was by far the easier to produce the syngas as well as C_2 hydrocarbon species,due to the weak oxidation ability of CO_2 and also the significant deposition of the electron energy on CH_4 dissociation in a dry reforming discharge mixture. This kinetic study produced comparative data to demonstrate the contribution of CO_2/O_2 additive in non-equilibrium plasma assisted methane conversion.     

Methane Steam Reforming Kinetics on a Ni/Mg/K/Al2O3 Catalyst

The kinetics of methane steam reforming were studied on a Ni/Mg/K/Al₂O₃ catalyst that was developed for conditioning of biomass-derived syngas. Reactions were conducted in a packed-bed reactor while the concentrations of reactants (methane and steam) and products (hydrogen, carbon monoxide, and carbon dioxide) were varied at atmospheric pressure, with the effects of temperature (525–700 °C) and residence time also being investigated. A power law rate model was developed using nonlinear regression to provide a predictive capability for the rate of methane conversion over this catalyst, to be used for reactor design and technoeconomic analysis of process designs. In order to provide some mechanistic insight, and to compare this catalyst to other non-promoted Ni/Al₂O₃ catalysts reported in the literature, a reaction mechanism consisting of five elementary steps, using a Langmuir–Hinshelwood type approach, was also considered. These five steps included: (i) CH₄ adsorption, (ii) H₂O adsorption, (iii) surface reaction of adsorbed CH₄ and H₂O to form CO and H₂, (iv) CO desorption, and (v) H₂ desorption. Nonlinear regression was then used to fit each of the rate laws to the experimental data. From these results, the model that assumed CH₄ adsorption to be the rate determining step provided the best fit of the experimental data. This finding is consistent with literature studies on non-promoted Ni/Al₂O₃ catalysts, in which methane adsorption has been proposed to be the rate determining step during catalytic methane steam reforming. Both the power rate laws and the rate law assuming CH₄ adsorption to be the rate determining step can be used as predictive tools for determining methane conversion for a given set of process conditions. Additionally, a rate expression that assumed the rate was only a function of methane partial pressure was considered, namely, $rate = k*P_{{CH_{4} }}$ rate = k ? P CH 4 , where $k = k_{0} *e^{{^{{ - {\text{Ea}}/{\text{RT}}}} }}$ k = k 0 ? e ? Ea / RT , with P_CH4 in units of Torr. This first-order-methane rate expression fit the data well, yielding an apparent activation energy over this catalyst of E_a = 93 kJ/mol and the pre-exponential rate constant of k₀ = 7.67 × 10⁵ mol/(g-cat s Torr CH₄).