Integrated microchemical systems for processing methanol reformer effluents for portable fuel cell applications

Micro fuel cells that run on hydrogen produced by micro steam reformers is an exciting and conceivable alternative to rechargeable batteries used today to run portable electrical/electronic devices. Fuel cell based alternatives could significantly reduce weight, volume and recharge frequency of these portable devices.; The effluent stream from steam-reformers, however, contains carbon monoxide (CO) that can poison fuel cell catalyst at even low concentrations. The treatment of micro-reformer effluent to make it suitable for running portable micro fuel cells was studied using experimentation, i.e. fabrication, characterization, and simulation. Restated, the goal of this thesis is to study design and fabrication issues related to hydrogen purification or conversely CO removal from the microreformer effluent using a membrane microreactor. The membrane microreactor refers to a single device that combines metal-based membrane for hydrogen separation and water gas shift (WGS) reaction for conversion of unwanted CO to useful hydrogen. The study of these two aspects formed the thrust of this work.; The constraints for the system are portability, compact size, energy efficiency along with ability to withstand high temperature and pressure. Effective portability and compact size require miniaturization of reaction, separation, vaporization, heat transfer and mixing. A low-cost prototype design for studying WGS reaction is proposed. This proposed reactor fabrication method is template-free and therefore more easily modifiable, and also significantly cheaper than previously available microreactor prototyping methods. The separator/reactor system need other peripheral units for its operation. For this, an improved fluidic inter-connector, two micro-mixer designs for improved mixing and pulsation-free micro-vaporizer design have also been proposed. Furthermore, a flow-sheet that improves energy efficiency is studied.; Design of effective and robust permeation system requires thorough knowledge of its functioning. Fabrication aspects of the following membrane systems were examined: (a) MEMs-based free-standing ultra-thin (1mum) membrane and (b) electrolessly plated Pd/Ag on tantalum foil and porous PTFE. Finally the causes of deactivation and means of activation of commercially procured Pd and Pd/Ag were investigated using XPS and permeation study. Significantly, this type of membrane was found to deactivate when subjected to high temperature due to Zn aggregation from the bulk to the surface.