Simulation of a membrane separation process for the purification of hydrogen produced by fermentation based on small scale pilot plant results

  • Posted on: 11 June 2018
  • By: mmiltner
TitleSimulation of a membrane separation process for the purification of hydrogen produced by fermentation based on small scale pilot plant results
Publication TypeConference Paper
Year of Publication2013
AuthorsLassmann T, Friedl A, Harasek M, Miltner M
Conference Name7th International Conference on Environmental Engineering and Management ICEEM2017, Vienna, Austria

Concerning a world running short in fossil energy sources, alternatives have to be found. In this regard hydrogen is often mentioned as the most promising energy carrier of the future. Today, a lot of research is done on developing and improving the technologies for utilization, storage and distribution. However, it must be recalled that common methods in hydrogen production still are either based on fossil fuels or water electrolysis. These techniques do not fulfill nowadays requirements in a modern provision of energy: sustainability and efficiency.

With biomass gasification as additional hydrogen production method, sustainability can be achieved. This thermo-chemical conversion of biomass turns out to be one first step into a sustainable hydrogen economy. Another step towards sustainability and energy efficiency could be the hydrogen production based on biotechnological pathways, such as dark fermentation. With this technique biomass residues as well as second generation biomasses can be utilized to produce a hydrogen-rich gas. Depending on the micro-organisms used, the chosen feed stock and reactor design, a gas mainly containing hydrogen and carbon dioxide will be obtained. At the moment research focuses especially on the optimization of the yield accompanied by an increase in quality of the product gas. Simultaneously to hydrogen carbon dioxide is also generated during fermentation and has to be subsequently separated to obtain pure hydrogen as a final product. Well established upgrading methods from fossil resources-based hydrogen production, such as amine absorption or pressure swing absorption can also be utilized when hydrogen is produced by dark fermentation. Even though these methods are suitable from a technological point of view, some of them might not be the most energy efficient method because gas capacity, composition and conditions differ considerably from the parameters obtained after methane reforming. This makes membrane technology, more precisely gas permeation (GP), very interesting for the upgrading of fermentative produced hydrogen.

GP has the advantage of being a simple, flexible and even mobile method, which doesn’t require a lot of space. It is often characterized by a low energy requirement and also low investment costs. The selectivity of the membrane defines the separation grade and the recovery of a component in the gas. The effective transport speed is a function of the membrane material, the type of gas and the driving force which depends on the process parameters on both sides of the membrane. The goal of this project is to develop an innovative small scale process to upgrade hydrogen rich gas using membrane technology. Special attention should be paid in a flexible and cost-effective separation process setup.

Based on membrane data from literature mass and energy balances for different separation sequences are calculated applying the process simulation tool ASPEN PLUS. The obtained results are then used to select commercially available membranes or respective membrane materials for screening in the laboratory. Detailed lab results on the separation performance together with extended process simulation finally lead to the design and parameters of the separation process to be used to set-up a small scale pilot plant.

The separation behavior of the pilot plant is tested connected to a real hydrogen fermentation reactor to obtain detailed information on process data and gas qualities. By changing the conditions in the membrane separation unit it is possible to define the boundaries to guarantee a stable product gas flow rate and a stable gas quality. The obtained results are then used to further develop the gas permeation model in ASPEN PLUS. This simulation model is then used to find the right separation sequence to reach a requested hydrogen quality and overall hydrogen recovery as well as to estimate investment and operational costs for the gas-upgrading process.

At the end of the project the simulation model of the hydrogen purification process should reflect the results in hydrogen quality and recovery obtained from the pilot plant. Furthermore, the behavior of the membranes due to changing process conditions has to be ensured. The process should enable a simple and stable operation under changing gas flow rates and gas compositions.

The results from simulation will show which process setup can be applied for a robust, effective and economic separation of hydrogen and carbon dioxide during fermentative hydrogen production.