Synthesis and characterization of zeolite membranes for binary gas separation
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Date
2007
Authors
Tan, Sek Choong
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Abstract
Three types of MFI zeolite membranes (ZSM-5 and Silicalite-1) with minimum
defect were synthesized using different synthesis approach. These membranes were
Silicalite-1 (Si/Al = ∞), Na-ZSM-5 (Si/Al = 25) and B-ZSM-5 (Si/B = 100). Silicalite-1
zeolite membrane was synthesized using secondary growth method whereas Na-ZSM-
5 and B-ZSM-5 membranes were synthesized using in-situ crystallization method. All
the membranes were supported over surface modified α-alumina coated with
mesoporous silica layer.
To evaluate the membrane microstructure, zeolite membranes were
characterized by XRD for their crystalline phase and crystal orientation, SEM for visual
observation of the membrane surface morphology and to obtain the thickness of the
zeolite thin film. TGA was conducted to assess the thermal stability of the membrane
as well as to confirm the removal of the structure directing agent (SDA) from the zeolite
structure. Zeolite colloidal seeds used for the synthesis of Silicalite-1 zeolite membrane
were characterized by TEM for its seed size and structure morphology.
Binary gas mixtures containing CO2/N2, CO2/CH4 and H2/CO2 were used to
evaluate the membrane separation performance. The separation of CO2/N2 and
CO2/CH4 took place due to the preferential adsorption of CO2 on MFI zeolite pores.
This competitive adsorption effect was not present for the separation of H2/CO2 system.
The highest separation selectivity for CO2/N2 and CO2/CH4 binary mixture was obtained
over B-ZSM-5 membrane at low temperature and high pressure. The highest
separation selectivity for H2/CO2 binary gas mixture was obtained at high temperature
and high pressure. The selectivity obtained was 9.27, 8.17 and 1.39 with the
permeation flux of 13.14, 14.52 and 6.98 cm3/min for the separation of CO2/N2,
CO2/CH4 and H2/CO2 respectively.
Centre composite design (CCD) was used to evaluate the contribution of the
operating parameters to the two responses (selectivity and permeation flux) for the
separation of CO2/N2, CO2/CH4 and H2/CO2 using B-ZSM-5 membrane. A response
surface methodology (RSM) was used to obtain the optimum values of the operating
parameters. The optimum conditions for the separation of CO2/N2 system were:
temperature = 25 oC, retentate total pressure = 5 bar, CO2 content in feed = 44.03%
and sweep gas flowrate = 300 cm3/min with selectivity = 8.89 and CO2 permeation flux
of 13.50 cm3/min. The optimum conditions for separation of CO2/CH4 were:
temperature = 25 oC, retentate total pressure = 4.74 bar, CO2 content in feed = 45.73%
and sweep gas flowrate = 300cm3/min with selectivity = 8.05 and CO2 permeation flux
of 14.36cm3/min. For the separation of H2/CO2, the optimum conditions obtained were:
temperature = 150 oC, retentate total pressure = 4.09 bar, CO2 content in feed =
16.52% and sweep gas flowrate = 213.34cm3/min with selectivity = 1.65 and H2
permeation flux of 9.19 cm3/min.
Description
Master
Keywords
Biological science , Zeolite membranes , Binary gas