Carbon membranes

Topic

Carbon membranes on the inner surface of an Al2O3 ceramic support tube.
Carbon layer on an Al2O3 substrate.
Turbostratic lamellar structure of deposited carbon layers.

Carbon has a layer structure that makes it highly promising as a membrane material for gas separation. Carbon membranes are superior to polymer membranes in terms of thermal stability and chemical resistance. Membrane-based gas separation depends strongly on material structure, pore size, membrane thickness, and gas species. Differentiation is made between two types of carbon membranes: molecular sieve carbon membranes (MSCMs) and adsorption-selective carbon membranes (ASCMs).

In a molecular sieve carbon membrane, gas molecules smaller than the pore size of the membrane can permeate the membrane. Larger molecules are completely retained. Molecular sieve carbon membranes exhibit very high selectivities and can be used, e.g., for selective separation of hydrogen from natural gas.

Adsorption-selective carbon membranes have pore sizes enabling permeation of hydrocarbons. The molecular components possess different adsorption properties and diffusion rates, resulting in adsorption of the component with the highest strength of adsorption on the pore surfaces. A concentration gradient with respect to the permeate causes this component to diffuse along the pore walls to the permeate side, where it is desorbed. Compared with MSCMs, ASCMs usually exhibit lower selectivities, but the permeance can also be higher. ASCMs are used, for example, in biogas treatment for CO2 and CH4 separation.

 

Services offered

 

  • Production of samples of asymmetric carbon membranes on tubes with lengths of up to 1.2 m
  • Development of carbon membranes for customer-specific tasks in gas separation, pervaporation, vapor permeation, and liquid filtration
  • Membrane preparation on in-house or customer-supplied ceramic substrates
  • Scale-up of membrane preparation to industrial scale including sample production