(504e) Membrane Distillation with Carbon-Based Membranes

Membrane distillation (MD) is an emerging technology for water
desalination, industrial wastewater and radioactive waste treatment, removal of
volatile organic compounds, concentration of agro-based and organic solutions, and
other separation applications. In spite of having high potentials, MD is still
an emerging separation technology mainly due to the short comings of available
membrane materials and limitations of existing MD systems. Available membranes
are relatively expensive and cannot be used at high temperatures. Carbon-based
membranes (CBMs) can be alternative types of membrane materials for the MD
process. Surface chemistry of CBMs can be tailored for different MD separation
or simultaneous MD separation/catalytic applications even at high temperatures
under harsh chemical conditions.

Different types of carbon membranes are developed by using
different support materials including porous graphite sheet, carbon nanofiber
mat, porous alumina disc, and quartz fiber tissue, and coated with chemical vapor
deposition of pyrolytic carbon and/or deposition of amorphous carbon by
pyrolysis of sucrose. CBM were heat treated in hydrogen or grafted with methyl
groups by sonication in acetone to enhance their hydrophobicity. These membranes
(e.g., Figure 1) had different porosities ranging from 100 nm to 1000 nm,
demonstrated high degree of hydrophobicity, and maintained their properties at
temperatures up to 400 °C under harsh conditions. Membranes were characterized
by water contact angle measurement, nitrogen permeability, SEM, and XPS.

The CBMs were tested in a sweeping gas MD system for water
desalination at a temperature range of 50-150 °C. Developed CBMs can be
potentially used for water desalination and other separation applications at
elevated temperatures where the existing polymer-based membranes cannot be
properly used due to structural changes and thermal decomposition effects.

Figure 1: An example
of developed CBM: Pyrolytic carbon-coated tissue quartz membrane.