Our objective was to design a process to co-produce hydrogen and dimethyl ether (DME) from solar thermochemical syngas. This process uses syngas made via a process designed by researchers at Pacific Northwest National Laboratories (PNNL) which uses a parabolic solar dish to provide clean solar energy for the reaction which reforms natural gas to make syngas. This inital process is on a microscale and uses micro-reactors and heat exchanges on the nacelle of the solar dish to achieve an impressive solar-to-chemical energy efficiency of over 70%. DME is an alternative diesel fuel with can be used without emitting particulates like the fuel which is currently used in diesel engines, and is desired to be made from this syngas as it is also easier to transport and store. Methanol and hydrogen are side products in the reaction used to make the DME which are also purified for sale to help with the economic feasibility of the process.
To maximize the amount of DME that is produced we take advantage of the Reverse Water-Gas Shift Reaction to change the ratio of carbon monoxide to hydrogen in the syngas as this ratio greatly effects the productivity of DME production. Furthermore, we reduce carbon emissions throughout the process by using selective gas membranes to efficiently separate components without constant utility use and by using the excess heat produced from reactions to heat other parts of the process. We also took several green chemistry aspects into account, for example not using a solvent to separate any of our components to reduce the amount of waste and toxicity, and reducing our number of distillation columns as much as possible as distillation is a very energy-intensive process. Using the green chemistry metric E-factor, which is the ratio of waste to product produced, we are within the range of acceptable E-factors for the manufacturing of bulk chemicals.
|Slides describing our project and breaking down our design and results