Upgrading of Bio-Hydrogen applying Membrane Gas Permeation – A Simulative and Experimental Assessment

Hydrogen is often referred as one of the most promising energy carriers of the future. In fact, hydrogen has one of the highest known fuel mass specific energy densities and it can be converted to electrical power with relatively high efficiencies. The transition to a hydrogen-supported economy relies on the sufficient and economic provision of high-quality hydrogen gas. Nevertheless, only the sustainable production of hydrogen from renewable sources results in a climate-neutral energy system. Nowadays, the main production pathways for hydrogen are natural gas steam reforming and water electrolysis.
One promising alternative production possibility for renewable hydrogen is the biotechnological process of dark fermentation. In this particular case the fermentation of a wide variety of biomass residues results in the production of a gas mainly containing hydrogen and carbon dioxide. In order to obtain a valuable energy carrier from this gas a substantial removal of carbon dioxide has to be performed. Conventional gas upgrading methods to meet this tasks are amine absorption and pressure swing adsorption. One very promising method for cost- and energy-efficient gas separation in this regard is membrane gas permeation.
The current work focusses on the development and optimisation of a gas processing chain for the upgrading of gas produced by biomass dark fermentation which mainly relies on membrane gas permeation. After a comprehensive literature research on possible membrane materials the most promising materials are selected for further analysis. This analysis comprises the performance assessment for a wide variety of operational parameters performed on a single-stage lab-scale membrane module test bench utilising pure gases as well as different gas mixtures. With the fundamental membrane material properties evaluated an extensive process simulation investigation is performed in order to define the most economic and most effective process layout. This step takes advantage of a very well-developed in-house code for the numerical modelling of multicomponent-multistage gas permeation systems. This tool will be used for the optimisation of the separation chain regarding the following aspects: 1) number and topology of permeator stages including gas recompression, recycling and sweep gas streams, 2) optimisation of membrane area distribution amongst different permeator stages, 3) optimisation of operational parameters like pressure and stage cut for the different permeator stages. Additionally, the possibilities for a final hydrogen purification step will be analysed in order to reach gas grades suitable for e.g. high-pressure storage in vehicle tanks or utilisation in fuel cells.
The work performed leads to the design and construction of a small-scale pilot plant with a simplified one-stage layout. The operation of this pilot plant at an existing hydrogen dark fermenter will proof the real-life feasibility of the membrane-based hydrogen upgrading concept. Data collected during simulation and experimental runs will be used to give a first rough estimate on the economic potential of the analysed concept.