Natural gas treatment with membrane systems

Evolution of Natural Gas Treatment with Membrane Systems... 

This chapter will describe some of the market forces driving m brane growth in natural gas treatment, explore some of the competing technologies to CA membranes, examine membrane compaction and the implication to long-term performance, report both recent laboratory and field studies with CA membranes and comment on some of the technical challenges and trends existing today in natural gas treatment with membrane systems that would benefit from future research and development activities. 

For new system builds the same strategy can be done with spiral wound modules designed for natural gas treatment. Grace has constructed a 30-cm (12-inch) diameter module versus the standard 20-cm (8-inch) diameter module. Since membrane area is a squared function of diameter, the ratio of 144 to 64 means a 225% increase in membrane area per module. Although the larger diameter modules and pressure housings each cost more there is potential for reduction in total system cost. 

New installations in natural gas treatment are increasingly favourable to membrane systems as they expand in scale and treat streams higher in CO2 content. In systems with large volumes of CO2 a membrane system can be employed to make the bulk cut and then an amine system can provide the finishing treatment. This is especially applicable in fields employing CO2 injection for enhanced oil recovery. 

Air Liquide and ConocoPhilUps report that a membrane system in Indonesia installed in 1998 processed 310 MMSCFD (9300000mVday) of natural gas, reducing CO2 from 30% to 15% [15], The polyimide hollow fibres are protected from heavy hydrocarbons through pre-treatment of the inlet gas with a thermal swing adsorption unit utilizing silica gel. 

The Institute of Environmental and Energy Technology (TNO) in Netherlands have developed macroporous polypropylene membrane contactors and used it with alkali aminoacid salt as absorbant. No wetting or degradation of polypropylene membrane surface was observed and hence stable membrane performance was reported. The Kvaerner Process is used for Teflon membranes with aqueous amine solutions of MEA, DEA, MDEA and DIP A. The membrane system was used to recover acid gases from natural gas for offshore platform applications. No performance data are available for the flue gas treatment. 

Membranes with extremely small pores ( < 2.5 nm diameter) can be made by pyrolysis of polymeric precursors or by modification methods listed above. Molecular sieve carbon or silica membranes with pore diameters of 1 nm have been made by controlled pyrolysis of certain thermoset polymers (e.g. Koresh, Jacob and Soffer 1983) or silicone rubbers (Lee and Khang 1986), respectively. There is, however, very little information in the published literature. Molecular sieve dimensions can also be obtained by modifying the pore system of an already formed membrane structure. It has been claimed that zeolitic membranes can be prepared by reaction of alumina membranes with silica and alkali followed by hydrothermal treatment (Suzuki 1987). Very small pores are also obtained by hydrolysis of organometallic silicium compounds in alumina membranes followed by heat treatment (Uhlhom, Keizer and Burggraaf 1989). Finally, oxides or metals can be precipitated or adsorbed from solutions or by gas phase deposition within the pores of an already formed membrane to modify the chemical nature of the membrane or to decrease the effective pore size. In the last case a high concentration of the precipitated material in the pore system is necessary. The above-mentioned methods have been reported very recently (1987-1989) and the results are not yet substantiated very well. 

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