Enhancing CO2 Hydrogenation to Methanol by Super-Hydrophobic Zeolite Membrane Reactor

甲醇既是合成大宗化工产品的重要原料，又是长期储能的有前途的能源载体。通过二氧化碳与氢气反应生产甲醇使得温室气体转化为有用的化学产品或燃料成为可能。然而，该反应具有低的甲醇产率，受到热力学平衡约束和副反应的限制。在开发亲水性（吸水性）膜方面已经取得了进展，该膜对于水渗透的选择性超过甲醇。它们在膜反应器中用于CO2加氢制甲醇，通过提高CO2转化率提高了甲醇产率。然而，这些亲水性沸石膜反应器显示出50%的最大甲醇产率，这是由于反应选择性或转化率的提高受到限制。该项目的重点是研究一种新的疏水（防水）膜反应器，用于将CO2转化为甲醇，同时从化学反应器中去除甲醇而不是水。这种新型膜反应器设计用于直接从反应器中生产高纯度甲醇，显著提高了CO2转化率和甲醇选择性。该项目将导致更好地理解疏水沸石膜的蒸汽/气体分离特性，以及如何操作新的膜反应器以实现最大化的CO2转化。膜反应器将能够有效地合成甲醇，甲醇是一种重要的化学原料和有前途的能源载体，对化学生产和能源储存至关重要。该项目将为各类研究生提供宝贵的培训经验，产生重要的科学发现，通过出版物和会议介绍加以传播，并缩小公众在化学工程方面的知识差距，膜科学和可持续性通过一个新的互联网-通过二氧化碳加氢生产甲醇将使温室气体转化为有用的化学品或可储存的燃料成为可能。然而，采用目前的反应器和催化剂设计，该反应具有低的甲醇产率和选择性，其受到热力学平衡约束和不希望的副反应的组合的限制。本计画主要研究一种疏水性沸石膜反应器，用于二氧化碳加氢制甲醇，并可在反应区中原位脱除甲醇。这种新型膜反应器有望直接从反应器中生产高纯度甲醇，并显著提高CO2转化率和甲醇选择性。本项目的目标是了解超疏水沸石膜的含甲醇蒸气/气体分离性能，并优化新型沸石膜反应器的设计及其操作条件，以最大限度地提高甲醇选择性和CO2加氢反应的产率。该项目针对（1）在氧化锆载体上的超疏水、高结晶度、无铝MFI型沸石膜的合成和表征，（2）在与膜反应器应用相关的条件下，超疏水膜对甲醇、水蒸气、CO2、CO和H2的蒸气/气体混合物的渗透和分离性能的实验和建模研究，（3）CO2加氢制甲醇疏水沸石膜反应器的模型分析;（4）CO2和H2高产率、高选择性合成甲醇的甲醇选择性沸石膜反应器的实验验证和优化。这些拟议的研究活动将提高对新型超疏水性、醇选择性沸石膜和膜反应器的设计、合成和操作的理解，以提高对受平衡转化率和副反应限制的低产物产率的化学反应的转化率和选择性。该项目将推进影响化学加工能源和环境可持续性的新技术，为研究生提供宝贵的培训经验，并提高公众对化学工程，膜科学和可持续性的认识。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Methanol is both an important feedstock for the synthesis of commodity chemical products and is a promising energy carrier for long-term energy storage. Production of methanol by reacting carbon dioxide with hydrogen makes possible conversion of a greenhouse gas to a useful chemical product or fuel. However, this reaction has a low methanol yield limited by thermodynamic equilibrium constraints and side reactions. Progress has been made in developing hydrophilic (water attracting) membranes selective for water permeation over methanol. Their use in membrane reactors for CO2 hydrogenation to methanol has improved methanol yield through increasing CO2 conversion. However, these hydrophilic zeolite membrane reactors show a maximum methanol yield of 50% due to the limit in the improvement of either reaction selectivity or conversion. This project is focused on studying a new hydrophobic (water repellent) membrane reactor for conversion of CO2 to methanol, with simultaneous removal of methanol instead of water from the chemical reactor. This new membrane reactor is designed to produce high purity methanol directly from the reactor with significantly improved CO2 conversion and methanol selectivity. The project will lead to an improved understanding of vapor/gas separation properties for hydrophobic zeolite membranes and how to operate the new membrane reactor for maximized CO2 conversion. The membrane reactor will enable efficient synthesis of methanol, an important chemical feedstock and promising energy carrier critical to chemical production and energy storage. The project will provide valuable training experiences for a diverse group of graduate students, produce important scientific findings to be disseminated through publications and conference presentations, and narrow the public’s knowledge gaps about chemical engineering, membrane science and sustainability through a new internet-based outreach activity.Production of methanol by CO2 hydrogenation would make possible the conversion of a greenhouse gas to a useful chemical or storable fuel. However, this reaction, with current reactor and catalyst designs, has a low methanol yield and selectivity that are limited by a combination of thermodynamic equilibrium constraints and undesired side reactions. This project is focused on studying a hydrophobic zeolite membrane reactor for CO2 hydrogenation to methanol with in-situ removal of methanol from the reaction zone. Such a new membrane reactor is expected to produce high purity methanol directly from the reactor with significantly improved CO2 conversion and methanol selectivity. The objectives of this project are to understand methanol-containing vapor/gas separation properties of the super-hydrophobic zeolite membranes and to optimize design of the new zeolite membrane reactor and its operation conditions that maximize methanol selectivity and yield of CO2 hydrogenation reactions. This project is directed towards (1) synthesis and characterization of super-hydrophobic, high crystallinity, aluminum-free MFI-type zeolite membranes on zirconia supports, (2) an experimental and modeling study of permeation and separation properties of vapor/gas mixtures of methanol, water vapor, CO2, CO and H2 for the super-hydrophobic membranes at conditions relevant to membrane reactor applications, (3) modeling analysis of a hydrophobic zeolite membrane reactor for CO2 hydrogenation to methanol, and (4) experimental verification and optimization of the methanol-selective zeolite membrane reactor for high-yield and high selectivity synthesis of methanol from CO2 and H2. These proposed research activities will improve the understanding of design, synthesis, and operation of the new super-hydrophobic, alcohol-selective zeolite membranes and membrane reactor to enhance both the conversion and selectivity for chemical reactions of low product yield limited by the equilibrium conversion and side reactions. The project will advance new technologies that impact chemical processing energy and environmental sustainability, will provide a valuable training experience for graduate students, and improve public’s knowledge about chemical engineering, membrane science and sustainability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.