Fouty Nicholas J, Carrasco Juan C, Lima Fernando V
Department of Chemical and Biomedical Engineering, West Virginia University, Morgantown, WV 26506, USA.
Membranes (Basel). 2017 Aug 29;7(3):48. doi: 10.3390/membranes7030048.
Due to the recent increase of natural gas production in the U.S., utilizing natural gas for higher-value chemicals has become imperative. Direct methane aromatization (DMA) is a promising process used to convert methane to benzene, but it is limited by low conversion of methane and rapid catalyst deactivation by coking. Past work has shown that membrane separation of the hydrogen produced in the DMA reactions can dramatically increase the methane conversion by shifting the equilibrium toward the products, but it also increases coke production. Oxygen introduction into the system has been shown to inhibit this coke production while not inhibiting the benzene production. This paper introduces a novel mathematical model and design to employ both methods in a multifunctional membrane reactor to push the DMA process into further viability. Multifunctional membrane reactors, in this case, are reactors where two different separations occur using two differently selective membranes, on which no systems studies have been found. The proposed multifunctional membrane design incorporates a hydrogen-selective membrane on the outer wall of the reaction zone, and an inner tube filled with airflow surrounded by an oxygen-selective membrane in the middle of the reactor. The design is shown to increase conversion via hydrogen removal by around 100%, and decrease coke production via oxygen addition by 10% when compared to a tubular reactor without any membranes. Optimization studies are performed to determine the best reactor design based on methane conversion, along with coke and benzene production. The obtained optimal design considers a small reactor (length = 25 cm, diameter of reaction tube = 0.7 cm) to subvert coke production and consumption of the product benzene as well as a high permeance (0.01 mol/s·m²·atm) through the hydrogen-permeable membrane. This modeling and design approach sets the stage for guiding further development of multifunctional membrane reactor models and designs for natural gas utilization and other chemical reaction systems.
由于美国近期天然气产量增加，将天然气用于生产高附加值化学品变得势在必行。直接甲烷芳构化（DMA）是一种将甲烷转化为苯的很有前景的工艺，但它受到甲烷转化率低和结焦导致催化剂快速失活的限制。过去的研究表明，通过膜分离DMA反应中产生的氢气，可以通过使平衡向产物方向移动来显著提高甲烷转化率，但这也会增加焦炭的生成。已证明向系统中引入氧气可抑制这种焦炭生成，同时不抑制苯的生成。本文介绍了一种新颖的数学模型和设计，将这两种方法应用于多功能膜反应器中，以推动DMA工艺进一步可行。在这种情况下，多功能膜反应器是指使用两种具有不同选择性的膜进行两种不同分离的反应器，目前尚未发现有相关系统研究。所提出的多功能膜设计在反应区外壁采用氢选择性膜，在反应器中间有一个内管，内管中填充有气流，周围是氧选择性膜。结果表明，与没有任何膜的管式反应器相比，该设计通过氢气去除使转化率提高了约100%，通过添加氧气使焦炭生成减少了10%。进行了优化研究，以根据甲烷转化率以及焦炭和苯的生成情况确定最佳反应器设计。获得的最佳设计考虑采用小型反应器（长度 = 25 cm，反应管直径 = 0.7 cm），以避免焦炭生成和产物苯的消耗，以及通过氢渗透膜具有高渗透率（0.01 mol/s·m²·atm）。这种建模和设计方法为指导多功能膜反应器模型的进一步开发以及天然气利用和其他化学反应系统的设计奠定了基础。
