Introduction
The Hysep® 108 module is the smallest module currently offered in the Hysep® product line and consists of a single-membrane unit with a total area of 0.04 m2. It is especially suited for a first assessment of performance of TNO’s thin film palladium membranes under the specific conditions (compositions, pressures, temperatures) of interest to your application.
Applications
The hydrogen separation module can be used to extract hydrogen from any reformed fuel. This can be an effective means to deliver high quality hydrogen for industrial process gas, for hydrogen fuelling stations or for PEM fuel cells.
Benefits
Quality
- High hydrogen selectivity, high hydrogen recovery possible
Reliability
- No moving parts and therefore reliable (passive operation)
Cost efficient
- Lower Capital Costs. Thin film palladium composite membranes are relatively low cost and allow high hydrogen separation rate per unit membrane area
- Lower operating cost; dramatic reduction in energy use
Flexibility
- Expansion of capacity is straightforward; more membrane modules are added.
- Additional future capacity can easily and cheaply be “designed in” during the fi rst phase of a project
- Small size
Principle of operation
The hydrogen separation module, type 108, consists of a 316L stainless steel construction, incorporating tubular palladium composite membranes that act as the catalytic/diffusion element.
In order to effectively utilize the membranes the hydrogen is brought into contact with the outer surface of the palladium coated ceramic support tube. The thin palladium film acts as a selective barrier, passing only atomic hydrogen through the tube wall, while excluding other gasses. Molecular hydrogen is adsorbed onto the surface where it is dissociated to become atomic hydrogen. The hydrogen diffuses through the layer in a direction determined by the pressure gradient. The hydrogen atom recombines on the low pressure side of the membrane with another hydrogen atom and is desorbed as a hydrogen molecule.
In addition to the separation of hydrogen, the palladium membranes can drive reactions beyond traditional equilibrium levels because the palladium acts as a catalyst. As an example, the membranes can further drive water gas shift reactions for reformats. This membrane configuration may be operated to maximize hydrogen recovery to extremely high levels (>95%).
The Hysep® Technology
TNO has developed the Hysep® technology to enable low cost and reliable hydrogen separation based on thin-film palladium membrane technology.
The supported palladium membrane layer in the Hysep® module has a thickness as low as 3-9 µm, a substantial improvement over current commercially available palladium membranes which are based on self-supporting metals foils with a thicknesses of 20-100 µm.
To create these membranes TNO has developed the technology to apply a very thin layer of palladium on a ceramic support tube. The assembly combines the excellent hydrogen selectivity of the palladium layer with the robustness of a ceramic support tube. Focus of all aspects of membrane development is on a low-cost final product.
Using thin layers reduces the amount of palladium on a membrane to a minimum. But because these membranes perform better, at the same time less membrane area will be required which will reduce the amount of palladium even further. Cost is crucial in the selection of the support system and manufacturing steps as well.
Although the support tube is a high-tech product requiring unique expertise to manufacture, it is based on low-cost ceramic tubes. In producing membranes based on these tubes only production methods are used which enable scale-up to cost-effective high-volume industrial fabrication.
Key characteristics of the membranes are the hydrogen flux, selectivity and lifetime. These will depend on the specific process, most importantly on the pressure at which the hydrogen containing mixture is available, gas composition and presence of contaminants. Lifetimes of several thousands of hours have been shown under different conditions and purities which can be reached range from 99.5% to 99.995% depending on the initial composition.
The thin palladium layer, combined with the ceramic support tubes on which the Hysep® technology is based, creates a cost-effective and reliable solution to deliver high quality hydrogen.