Large ceramic membrane filter
for water treatment systems
NGK has long been involved in businesses that are aimed to protect global environment. In the water and sewage fields, we do plant engineering for water and sludge treatment. To prevent air pollution, we manufacture honeycomb ceramics that are indispensable for purifying exhaust gas emitted from vehicles. With these as the core business, NGK has established a firm position in each field.
Positioning porous ceramics as the key material and pore-size control and surface modification as the key technologies, NGK has developed and started mass-producing diesel particulate filters (DPFs) for diesel powered vehicles. Currently, research on the application of these key materials and technologies to gas separation and purification system is under way, starting with hydrogen gas.
Porous ceramics has a number of continuous or randomly distributed pores in its interior with each pore diameter different depending on its usage. Exploiting this feature, porous ceramics can separate solid, liquid and gas. In addition, by utilizing large surface area of pores, they are capable of absorption and carrying catalysts. By forming another membrane with different function on the surface, porous ceramics can be used as a substrate as well.
Frame format of DPF
Exterior of DPF
Particulate matter (PM) contained in black smoke that is exhausted from diesel-powered vehicles is becoming one of the largest problems of air pollution. Against this background, diesel particulate filters (DPFs) are gaining growing attention as the measure to reduce PM. DPFs comprise porous ceramic honeycomb substrates with channels plugged at alternate ends, thereby acting as filters for PM with the pore size of a few to ten micrometers.
Gas separation membrane using zeolite
(12 mm in diameter, 160 mm in length)
In the petrochemistry arena, the main existing methods to extract specific gas are the distillation process, which consumes a lot of energy, and the absorption process, which requires complex devices. In view of saving energy, more attention is given to the membrane separation process as a simple and efficient alternative to the conservative separation processes.
Zeolite has a mesh-like crystalline structure with micropores of less than 1 nm (one nanometer is equal to one billionth of a meter) arrayed regularly. It features a molecular sieving effect capable of separating specific gas, which has a slightly different molecular size. By forming a film on a porous ceramic substrate using this zeolite, we are developing gas separation membranes.
For example, by exploiting MF1-type Zeolite, we have succeeded in developing a gas separation membrane, which extracts paraxylene (raw materials for PET bottles) from xylene isomers produced in petroleum refinery process.
In addition, NGK has successfully isolated carbon dioxide from a mixture of methane and carbon dioxide by forming DDR-type Zeolite on a porous ceramic substrate for the first time in the world. It is expected to find applications in refining natural gas and in refining methane contained in biogas generated from raw garbage by fermentation.
Hydrogen separation membrane
(30 mm in diameter, 300 mm in length)
Hydrogen has recently gotten increasing attention as the clean energy of choice. Although using absorbents is one of the existing methods used to recover hydrogen, it has disadvantages in that the experimental equipment is large. NGK is developing a gas separation membrane, which efficiently recovers hydrogen, by forming a film on a porous ceramic substrate using palladium alloy known for its feature of selective permeation of hydrogen. The key here is to simultaneously achieve cost effectiveness and high hydrogen selectivity, by making expensive palladium membranes thinner. We are considering of applying this membrane technology to the hydrogen station business as a membrane reactor by combining it with compact hydrogen recovery equipment or catalyst.
