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。     

不同CO2捕集技术的CO2耦合绿氢制甲醇工艺研究

大量的化石燃料燃烧导致温室气体排放增加,全球气候变暖。世界各国以全球协约的方式减排CO₂,我国也由此提出“碳达峰·碳中和”目标。CO₂捕集以及转化制液体燃料和化学品是双碳目标下行之有效的碳减排措施之一,不仅可以实现CO₂的资源化利用,同时也缓解了国家能源安全问题。本文以燃煤电厂烟气CO₂捕集和CO₂合成甲醇为研究对象,分析了基于四种不同CO₂捕集技术的CO₂耦合绿氢制甲醇工艺。对四种不同CO₂捕集技术的CO₂制甲醇工艺进行了严格的稳态建模和模拟,分析和比较了不同CO₂捕集技术情景下的CO₂制甲醇工艺的技术和经济性能。结果表明,MEA、PCS、DMC和GMS情景的单位甲醇能耗分别是7.81、5.48、5.91和4.66 GJ/ t CH₃OH,GMS情景的单位能耗最低,其次是PCS情景,但随着更高效相变吸收剂的开发,PCS情景的单位甲醇产品的能耗将降低至2.29~2.58 GJ/t CH₃OH。四种情景的总生产成本分别是4314、4204、4279和4367 CNY/ t CH₃OH,PCS情景的成本最低,更具有经济优势。综合分析表明PCS情景的性能表现最好,为可用于燃煤电厂最佳的碳捕集技术,为CO₂高效合成燃料化学品提供方向,缓解化石燃料短缺和环境污染问题。     

不同CO2捕集技术的CO2耦合绿氢制甲醇工艺研究

大量的化石燃料燃烧导致温室气体排放增加,全球气候变暖。世界各国以全球协约的方式减排CO₂,我国也由此提出“碳达峰·碳中和”目标。CO₂捕集以及转化制液体燃料和化学品是双碳目标下行之有效的碳减排措施之一,不仅可以实现CO₂的资源化利用,同时也缓解了国家能源安全问题。本文以燃煤电厂烟气CO₂捕集和CO₂合成甲醇为研究对象,分析了基于四种不同CO₂捕集技术的CO₂耦合绿氢制甲醇工艺。对四种不同CO₂捕集技术的CO₂制甲醇工艺进行了严格的稳态建模和模拟,分析和比较了不同CO₂捕集技术情景下的CO₂制甲醇工艺的技术和经济性能。结果表明,MEA、PCS、DMC和GMS情景的单位甲醇能耗分别是7.81、5.48、5.91和4.66 GJ/ t CH₃OH,GMS情景的单位能耗最低,其次是PCS情景,但随着更高效相变吸收剂的开发,PCS情景的单位甲醇产品的能耗将降低至2.29~2.58 GJ/t CH₃OH。四种情景的总生产成本分别是4314、4204、4279和4367 CNY/ t CH₃OH,PCS情景的成本最低,更具有经济优势。综合分析表明PCS情景的性能表现最好,为可用于燃煤电厂最佳的碳捕集技术,为CO₂高效合成燃料化学品提供方向,缓解化石燃料短缺和环境污染问题。     

Selective formation of CH3OH in the photocatalytic reduction of CO2 with H2O on titanium oxides highly dispersed within zeolites and mesoporous molecular sieves

Highly dispersed titanium oxide catalysts have been prepared within zeolite cavities as well as in the zeolite framework and utilized as photocatalysts for the reduction of CO₂ with H₂O to produce CH₄ and CH₃OH at 328 K. In situ photoluminescence, ESR, diffuse reflectance absorption and XAFS investigations indicate that the titanium oxide species are highly dispersed within the zeolite cavities and framework and exist in tetrahedral coordination. The charge transfer excited state of the highly dispersed titanium oxide species play a significant role in the reduction of CO₂ with H₂O with a high selectivity for the formation of CH₃OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH₄, being similar to reactions on the powdered TiO₂ catalysts. Ti-mesoporous molecular sieves exhibit high photocatalytic reactivity for the formation of CH₃OH, its reactivity being much higher than the powdered TiO₂ catalysts. The addition of Pt onto the highly dispersed titanium oxide catalysts promotes the charge separation which leads to an increase in the formation of CH₄ in place of CH₃OH formation.     

锆基双金属氧化物催化剂硫中毒的研究

在工业二氧化碳加氢制甲醇过程中,硫化氢气体的引入将对该过程中使用的催化剂活性及稳定性带来负面的影响。基于此,采用微反应合成法成功制备了InZrO_x和ZnZrO_x锆基催化剂,并研究了在二氧化碳加氢反应中,硫化氢气体对锆基催化剂的结构性质及其催化性能的影响规律。结果表明,在T=573 K、p=3.0 MPa和GHSV=18 000 mL/(g_cat·h)条件下,仅通入二氧化碳/氢气反应气时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择性分别为7.2%、9.3%和93%、92%。在二氧化碳/氢气原料气中通入体积分数为5×10^-3硫化氢气体时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择性都降为0,这主要是因为硫化氢气体占据了氧空位,导致锆基双金属氧化物催化剂硫中毒失活。当停止通硫化氢气体时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择...     

Si掺杂对Cu/ZrO2催化CO2加氢制甲醇性能的影响

为了提高Cu/ZrO₂催化剂在二氧化碳加氢制甲醇中的催化活性,制备了一系列不同Si/Zr的Si-ZrO₂载体并负载5%（质量分数）Cu得到了Cu/Si-ZrO₂催化剂。对所制备的催化剂进行了X射线衍射（XRD）、N₂物理吸脱附（BET）、X射线光电子能谱（XPS）、氢气程序升温还原（H₂-TPR）、二氧化碳程序升温脱附（CO₂-TPD）及高分辨透射电子显微镜 （HRTEM） 的表征。结果表明,Si的掺杂使得Cu/ZrO₂体系获得了稳定的晶相,大的比表面积和更多的碱性位点,尤其是中强碱性位点,同时产生了更多的氧空位,促进了CO₂的吸附和转化,因此得到了更高活性的催化剂。当Si与Zr的摩尔比为0.2时,在质量空速为6000 ml·g^-1·h^-1,温度为220℃、压力为3.0 MPa,V（H₂）∶V（CO₂）=3∶1（体积比）条件下,催化剂的CO₂转化率为4.6%,CH₃OH选择性为85%。     

Si掺杂对Cu/ZrO2催化CO2加氢制甲醇性能的影响

为了提高Cu/ZrO₂催化剂在二氧化碳加氢制甲醇中的催化活性,制备了一系列不同Si/Zr的Si-ZrO₂载体并负载5%（质量分数）Cu得到了Cu/Si-ZrO₂催化剂。对所制备的催化剂进行了X射线衍射（XRD）、N₂物理吸脱附（BET）、X射线光电子能谱（XPS）、氢气程序升温还原（H₂-TPR）、二氧化碳程序升温脱附（CO₂-TPD）及高分辨透射电子显微镜 （HRTEM） 的表征。结果表明,Si的掺杂使得Cu/ZrO₂体系获得了稳定的晶相,大的比表面积和更多的碱性位点,尤其是中强碱性位点,同时产生了更多的氧空位,促进了CO₂的吸附和转化,因此得到了更高活性的催化剂。当Si与Zr的摩尔比为0.2时,在质量空速为6000 ml·g^-1·h^-1,温度为220℃、压力为3.0 MPa,V（H₂）∶V（CO₂）=3∶1（体积比）条件下,催化剂的CO₂转化率为4.6%,CH₃OH选择性为85%。     

PERMEATION THROUGH KAPTON® POLYIMIDE AT ELEVATED TEMPERATURES

The permeabilities of CH₄, CO₂, CH₃OH, H₂O, O₂, and CO through films of Kapton® polyimide were measured at temperatures of 50, 100, 150, 200, and 250°C and pressures below 1 atm. Apparent activation energies for the permeation of the pure components ranged from 31.6kJ mol^-1 for CH₄ to nearly 0 for H₂O under the conditions studied. The ideal permselectivity for methanol relative to methane decreased from over 100 to under 10 as the temperature was increased from 50 to 250°C.     

醇羟基反应活性与DBU/C3-醇/CO2离子化合物稳定性

利用红外光谱、核磁共振和热重分析表征了1,8-二氮杂环[5,4,0]十一烯-7(DBU)和CO₂分别与C₃-醇,即正丙醇、异丙醇、1,2-丙二醇、1,3-丙二醇和甘油,反应生成的离子化合物的组成和结构,研究了伯羟基和仲羟基与DBU和CO₂反应的活性,以及空间位阻对羟基反应活性和生成的离子化合物的热稳定性的影响。结果表明,DBU+C₃-醇+CO₂体系中伯羟基比仲羟基具有更高的反应活性,反应产物更稳定。由于空间位阻和电子效应等影响,二元醇中第2个羟基的反应活性远低于第1个羟基。在DBU+甘油+CO₂体系中由于空间位阻和电子效应的影响,当DBU和甘油的摩尔比为3:1时,其中1位羟基的转化率可达100%,3位羟基的转化率约为34%,而2位的仲羟基反应很少。     

New high permeable polysulfone/ionic liquid membrane for gas separation

In this study, the effects of 1-Ethyl-3-methylimidazolium tetrafluoroborate ionic liquid on CO₂/CH₄ separation performance of symmetric polysulfone membranes are investigated. Pure polysulfone membrane and ionic liquid-containing membranes are characterized. Field emission scanning electron microscopy (FE-SEM) is used to analyze surface morphology and thickness of the fabricated membranes. Energy dispersive spectroscopy (EDS) and elemental mapping, Fourier transform infrared (FTIR), thermal gravimetric (TGA), X-ray diffraction (XRD) and Tensile strength analyses are also conducted to characterize the prepared membranes. CO₂/CH₄ separation performance of the membranes are measured twice at 0.3 MPa and room temperature (25 °C). Permeability measurements confirm that increasing ionic liquid content in polymer-ionic liquid membranes leads to a growth in CO₂ permeation and CO₂/CH₄ selectivity due to high affinity of the ionic liquid to carbon dioxide. CO₂ permeation significantly increases from 4.3 Barrer (1 Barrer=10^-10 cm³(STP)·cm·cm^-2·s^-1·cmHg^-1, 1cmHg=1.333kPa) for the pure polymer membrane to 601.9 Barrer for the 30 wt% ionic liquid membrane. Also, selectivity of this membrane is improved from 8.2 to 25.8. mixed gas tests are implemented to investigate gases interaction. The results showed, the disruptive effect of CH₄ molecules for CO₂ permeation lead to selectivity decrement compare to pure gas test. The fabricated membranes with high ionic liquid content in this study are promising materials for industrial CO₂/CH₄ separation membranes.     

Reduction of carbon dioxide with water under concentrated sunlight using photocatalyst combined with Fe-based catalyst

The reduction of CO₂ with water into valuable organic compounds under concentrated sunlight was investigated for the first time over a hybrid catalyst, in which a Pt-loaded K₂Ti₆O₁₃ photocatalyst was combined with a Fe-based catalyst supported on a dealuminated Y-type zeolite (Fe-Cu-K/DAY). In this reaction system, the Pt/K₂Ti₆O₁₃ catalyst decomposes water to produce H₂ and the Fe-Cu-K/DAY catalyst reduces CO₂ with the resulting H₂ into organic compounds. When only the Pt/K₂Ti₆O₁₃ photocatalyst was used, organic compounds such as CH₄, HCOOH, and HCHO were formed together with H₂, indicating that CO₂ can also be directly reduced over Pt/K₂Ti₆O₁₃. On the contrary, when the hybrid catalyst was used, CH₃OH and C₂H₅OH were produced in addition to the above products, depending on the reaction temperature and catalyst composition. The reaction temperature significantly increased by concentrating the solar irradiation, reaching 600 K and increasing the product yields. It is suggested that such a high reaction temperature facilitates both the photoreduction and hydrogenation of CO₂ over Pt/K₂Ti₆O₁₃ and Fe-Cu-K/DAY, respectively.     

Characterization of self-standing Ti-containing porous silica thin films and their reactivity for the photocatalytic reduction of CO2 with H2O

Self-standing porous silica thin films with different pore structures were synthesized by a solvent evaporation method and used as photocatalysts for the photocatalytic reduction of CO₂ with H₂O at 323 K. UV irradiation of these Ti-containing porous silica thin films in the presence of CO₂ and H₂O led to the formation of CH₄ and CH₃OH as well as CO and O₂ as minor products. Such thin films having hexagonal pore structure exhibited higher photocatalytic reactivity than the Ti-MCM-41 powder catalyst even with the same pore structure. From FTIR investigations, it was found that these Ti-containing porous silica thin films had different concentrations of surface OH groups and showed different adsorption properties for the H₂O molecules toward the catalyst surface. Furthermore, the concentration of the surface OH groups was found to play a role in the selectivity for the formation of CH₃OH.     

Production of hydrogen via partial oxidation of methanol over Au/TiO2 catalysts

Selective production of hydrogen by partial oxidation of methanol (CH₃OH + (1/2)O₂ → 2H₂ + CO₂) over Au/TiO₂ catalysts, prepared by a deposition–precipitation method, was studied. The catalysts were characterized by XRD, TEM, and XPS analyses. TEM observations show that the Au/TiO₂ catalysts exhibit hemispherical gold particles, which are strongly attached to the metal oxide support at their flat planes. The size of the gold particles decreases from 3.5 to 1.9 nm during preparation of the catalysts with the rise in pH from 6 to 9 and increases from 2.9 to 4.3 nm with the rise in calcination temperature up to 673 K. XPS analyses demonstrate that in uncalcined catalysts gold existed in three different states: i.e., metallic gold (Au⁰), non-metallic gold (Au^δ+) and Au₂O₃, and in catalysts calcined at 573 K only in metallic state. The catalytic activity is strongly dependent on the gold particle size. The catalyst precipitated at pH 8 and uncalcined catalysts show the highest activity for hydrogen generation. The partial pressure of oxygen plays an important role in determining the product distribution. There is no carbon monoxide detected when the O₂/CH₃OH molar ratio in the feed is 0.3. Both hydrogen selectivity and methanol conversion increase with increasing the reaction temperature. The reaction pathway is suggested to consist of consecutive methanol combustion, partial oxidation and steam reforming.     

SCR of NOx with CH3OH on H-mordenite: mechanism and reaction intermediates

The selective reduction of NO_x over H-mordenite (H-m) was studied using CH₃OH as reducing agent. Results are compared with those obtained with other conventional reducing agents (ethylene and methane), with gas-phase reactions, and with other metal-exchanged mordenites (Cu-mordenite (Cu-m) and Co-mordenite (Co-m)). H-m was found to be an effective catalyst for the SCR of NO_x with CH₃OH. When different reducing agents were compared over H-m, CH₃OH > C₂H₄ > CH₄ was the order according to the maximum NO conversion obtained using 1% of oxygen in the feed. Instead, if selectivity is considered, the order results CH₄ > CH₃OH > C₂H₄. In reaction experiments, two distinct zones defined by two maxima with NO to N₂ conversion are obtained at two different temperatures. A correlation exists between the said zones and the CO : CO₂ ratio. At low temperatures, CO prevails whereas at high temperatures CO₂ prevails. These results indicate that there exist different reaction intermediates. Evidence from reaction experiments, FTIR results, and transient experiments suggest that the reaction mechanism involves formaldehyde and dimethyl ether (DME) as intermediates in the 200–500°C temperature range. The surface interaction between CH₃OH (or its decomposition products) and NO is negligible if compared with NO₂, indicating that the oxidation of NO to NO₂ on acid sites is a fundamental path in this system. Different from other non-oxygenated reductants (methane and ethylene), a gas-phase NO_x initiation effect on hydrocarbon combustion was not observed.     

Intensification of low-grade methane enrichment in nitrogen mixture by CH4/CO2 displacement

To solve the problem of CO₂ uncompleted desorption in the process of CO₂ displacement enhancing the adsorption separation of CH₄/N₂, a small amount of product gas CH₄ was used as purge gas to improve the CO₂ desorption. CH₄/CO₂ mixture gas obtained from desorption step was recycled as the displacement gas to enhance the enrichment of low-grade methane in nitrogen mixture. In this work, the research conducted the experiments for CH₄/N₂ separation using CH₄/CO₂ displacement intensification adsorption and the laboratory-made coconut shell activated carbon as sorbent. The mathematical models were built in gPROMS and the accuracy of models was verified by comparison of simulations and CH₄/N₂/CO₂ breakthrough experiments. The performance of enrichment of low-grade methane with displacement intensification using different displacer was compared. The result showed that the process with CH₄/CO₂ displacement had higher purity product than CO₂ displacement. The CH₄/ CO₂ mixed gas replacement enhanced vacuum pressure swing adsorption cycle experiment was carried out, which can jointly enrich 14% CH₄/ N₂ and 53% CH₄/CO₂ to 98.8%, and at the same time obtain a recovery rate of 77.8%.     

TiO2基催化剂还原CO2研究进展

能源危机和环境污染是当今世界发展面临的两大挑战,如何有效缓解煤、石油等不可再生化石资源过度消耗所引发的能源危机,以及由此造成CO₂过量排放引起的温室效应问题,是当前人类发展亟待解决的重大科学问题之一。基于此,本文综述了近年来以TiO₂为光催化剂,以绿色、清洁的太阳光能催化还原CO₂成低价态含碳燃料(如CH₄、CH₃OH、HCHO、HCOOH、C₂H₅OH等)研究进展。在TiO₂光还原CO₂机理基础上,对元素掺杂、半导体复合与染料敏化、高活性晶面调控、低维纳米结构设计、助催化剂、Z型结构设计和单原子催化等方法来提高光还原CO₂反应效率和选择性进行分析,并指出目前研究存在的关键问题和未来CO₂光还原的发展方向。     

CH4/CO2混合气置换强化含氮低品质甲烷的浓缩

针对CO₂置换吸附分离CH₄/N₂过程中CO₂再生困难的问题,采用少量产品气CH₄真空吹扫以提高CO₂的解吸效果,并以解吸得到的CH₄/CO₂混合气为置换步骤的置换气,通过置换来强化含氮低品质甲烷的浓缩过程。以自制椰壳活性炭为吸附剂,对CH₄/CO₂混合气置换强化吸附回收含氮低品质甲烷工艺过程进行了实验与模拟研究。在gPROMS软件中建立并求解固定床吸附分离模型方程,预测了CH₄、N₂ 和CO₂在自制椰壳活性炭上的竞争吸附穿透曲线,通过预测结果和实验的对比,验证了数学模型方程的准确性。对比了不同置换气强化吸附分离低品质甲烷的效果,结果表明CH₄/CO₂混合气置换强化相对于CO₂置换强化可获得更高纯度产品。进行了CH₄/CO₂混合气置换强化真空变压吸附循环实验,可以将14%的CH₄/N₂和53%的CH₄/CO₂联合富集到98.8%,同时获得77.8%的回收率。     

Photocatalytic reduction of CO2 with H2O on Ti-MCM-41 and Ti-MCM-48 mesoporous zeolite catalysts

Titanium oxide species included within the framework of mesoporous zeolites (Ti-MCM-41 and Ti-MCM-48) prepared by a hydrothermal synthesis exhibited high and unique photocatalytic reactivity for the reduction of CO₂ with H₂O at 328 K to produce CH₄ and CH₃OH in the gas phase. In situ photoluminescence, diffuse reflectance absorption, ESR and XAFS investigations indicated that the titanium oxide species are highly dispersed within the zeolite framework and exist in tetrahedral coordination. The charge transfer excited state of the highly dispersed titanium oxide species played a significant role in the reduction of CO₂ with H₂O exhibiting a high selectivity for the formation of CH₃OH.     

Photocatalytic conversion of CH4 and CO2 to oxygenated compounds over Cu/CdS–TiO2/SiO2 catalyst

Coupled semiconductor (CS) Cu/CdS–TiO₂/SiO₂ photocatalyst was prepared using a mutli-step impregnation method. Its optical property was characterized by UV–vis spectra. BET, XRD, Raman and IR were used to study the structure of the photocatalyst. Fine CdS was found dispersed over the surface of anatase TiO₂/SiO₂ substrate. Chemisorption and IR analysis showed methane absorbed in the molecular state interacted weakly with the surface of catalyst, and the interaction of CO₂ with CS produced various forms of absorbed CO₂ species that were primarily present in the form of formate, bidentate and linear absorption species. Photocatalytic direct conversion of CH₄ and CO₂ was performed under the operation conditions: 373 K, 1:1 of CO₂/CH₄, 1 atm, space velocity of 200 h⁻¹ and UV intensity of 20.0 mW/cm². The conversion was 1.47% for CH₄ and 0.74% for CO₂ with a selectivity of acetone up to 92.3%. The reaction mechanisms were proposed based on the experimental observations.     

DBU/甘油/CO2反应过程及动力学

1,8-二氮朵双环[5.4.0]十一碳-7-烯（DBU）-甘油溶液作为一种新型溶剂,具有低热容、高沸点等优点,目前被广泛研究应用于化学合成和产物分离等。本文考察了不同摩尔比的DBU-甘油溶液吸收CO₂效果,测定了不同摩尔比的DBU-甘油溶液吸收CO₂反应过程中体系的黏度变化,研究了DBU-甘油溶液吸收CO₂反应的动力学。结果表明,在反应温度25℃、CO₂气体流速为238mL/min的条件下,DBU与甘油摩尔比为0.49~1的溶液对CO₂的吸收量可在120min的反应时间内达到10.88g/100g溶液;DBU与甘油摩尔比为0.49∶1和1.12∶1的溶液在吸收CO₂后体系的黏度显著增大,而DBU与甘油摩尔比为0.11∶1和3.43∶1的溶液在吸收CO₂后体系的黏度变化较小。25℃、常压下,在消除扩散影响,甘油大大过量时,DBU/甘油/CO₂反应的速率方程为r=0.22C_DBUP_CO2^0.5,反应的活化能为40.44kJ/mol。