Silicone (PDMS) has a very high permeability to CO2 compared to methane. This difference in permeability facilitates the transfer of CO2 preferentially over methane, thus enabling the removal of CO2 from a natural gas stream. Similarly other contaminants such as hydrogen sulfide (H2S), heavy hydrocarbons (C3+), siloxanes, and other VOC can be readily removed from methane. The separation factor for CO2/CH4 is approximately 3 for a 50/50 gas mix, indicating that the ratio of the mass fraction of CO2 to CH4 in the feed/retentate is three times smaller than the ratio in the permeate.
How to remove CO2 (and other contaminants) from methane?
Natural Gas upgrading is simple and straightforward as shown in the figure below. A pressurized feed gas is supplied to one side of the membrane though the feed port, and depending on the feed pressure, a vacuum supply to the opposite side of the membrane may be necessary at the permeate ports. The contaminants with higher permeability compared to natural gas will permeate the membrane much faster than the methane, thereby stripping the feed from these contaminants. A higher purity natural gas will exit at the permeate port. The permeate can be vented or flared as necessary.
Our silicone hollow fiber membrane packaging provides many advantages over the spiral wound format, especially in low feed pressure applications (< 100 psi), including up to ten times higher membrane area density per volume, no porous substrate to impede gas transfer or limit compatibility, and substantially lower cost per unit area.
Currently, PermSelect® membrane modules can be used for slip-stream testing in low feed pressure applications (<45 psi) such as landfill biogas and limited onsite fuel gas conditioning. While we currently provide modules for preliminary laboratory testing, we are actively seeking strategic partners with well established presence in this field to collaborate on scaling-up and developing optimized products incorporating our membrane technology. If your organization is interested in providing methane separating solutions using our patented technology, Contact us or call us at +1 (734) 769-1066 x21 to discuss opportunities.
WARNING. Our standard PermSelect® membrane modules have not been optimized for pilot scale, or production upgrading of methane, and may not endure to the user's satisfaction. Please contact us to discuss your application.
Low Pressure Methane Upgrading using a PermSelect Membrane Module.
Silicone has been used effectively for the upgrading of natural gas commercially and by many researchers. The following list of publications describes using PDMS for purifying methane:
LOW PRESSURE SEPARATION TECHNIQUE OF BIOGAS INTO CH4 AND CO2 EMPLOYING PDMS MEMBRANE International Journal of Advanced Engineering Technology Vol.III/ Issue I/January-March, 2012/311-315 Swanand Kalambe et al.
Abstract Continuous research has been going on to find out easy and cheap technique for separation of biogas employing membrane technology. Work has been carried out to find the best suited membrane for gas separation with low operational pressure and cost. Membrane gas separation technique is very advantageous as it doesn’t require huge infrastructure for plant set up due to low pressure requirement for the process and availability of membrane at a reasonable cost. This technique has generated immense commercial interest. This paper deals with an advanced separation technique employing poly dimethylsiloxane (PDMS) hollow fiber membrane module. The results clearly show that, PDMS double membrane module in series gave the upgraded methane with 93 % purity and carbon dioxide with 96% purity.
Evaluation of two gas membrane modules for fermentative hydrogen separation International Journal of Hydrogen Energy Volume 38, Issue 32, 25 October 2013, Pages 14042–14052 J.E. Ramírez-Morales et al.
Abstract The ability of (dimethyl siloxane) (PDMS) and SAPO 34 membrane modules to separate a H2/CO2 gas mixture was investigated in a continuous permeation system in order to decide if they were suitable to be coupled to a biological hydrogen production process. Permeation studies were carried out at relatively low feed pressures ranging from 110 to 180 kPa. The separation ability of SAPO 34 membrane module appeared to be overestimated since the effect concentration polarization phenomena was not taken into consideration in the permeation parameter estimation. On the other hand, the PDMS membrane was the most suitable to separate the binary gas mixture. This membrane reached a maximum CO2/H2 separation selectivity of 6.1 at 120 kPa of feed pressure. The pressure dependence of CO2 and H2 permeability was not considerable and only an apparent slight decrease was observed for CO2 and H2. The mean values of permeability coefficients for CO2 and H2 were 3285 ± 160 and 569 ± 65 Barrer, respectively. The operational feed pressure found to be more adequate to operate initially the PDMS membrane module coupled to the fermentation system was 180 kPa, at 296 K. In these conditions it was possible to achieve an acceptable CO2/H2 separation selectivity of 5.8 and a sufficient recovery of the CO2 in the permeate stream.