Separate Issue

Tom Shelley reports on an innovation that enables the low cost processing of biogas to produce motor fuels



Taking oil and gas out of the ground is an expensive but necessary business. It requires huge amounts of infrastructure set-up in harsh and often inhospitable environments.
To make matters more difficult, gas extracted from underground wells has to be processed near the well head before it can be pumped ashore. The reason is the gas contains methane, carbon dioxide, a small amount of water vapour and hydrogen sulphide as well as some other contaminants which cause havoc in values and pipe work.
As well as reducing calorific value, carbon dioxide is an acidic gas which causes corrosion. Additionally, it liquefies under pressure and can even solidify above 5000bar. A chemical process is normally used to remove it, but various researchers round the world are engaged in developing membrane separation technologies that will potentially do the job cheaper.
One such effort is a Malaysian research team that has developed a new membrane filter that, it hopes, will enable lower cost well head processing of natural gas on a large scale. A demonstration plant has already been mooted by one of the world’s biggest gas producers, Saudi Aramco.
When we encountered Professor Ahmad Fauzi Ismail at the British Invention Show, he revealed that the membrane separation technology developed by his team in the Membrane Research Unit at the Universiti Teknologi Malaysia was, “very near to commercialisation.”
But the technology may also enable the small scale and low cost separation of methane from other gas mixtures containing carbon dioxide. As a result, it may facilitate the processing of locally produced biogas to a point where the resulting fuel could be used in an engine.
There are large numbers of both biodigesters and compressed methane powered motor vehicles in South Asia, with the largest number of biogas digesters in Nepal, about 140,000. The largest number of methane powered vehicles is in Pakistan, more than 1.2 million.
Different problems are associated with producing biogas in village biodigesters. Although the resultant raw gas will burn and can be used for cooking, it is not pure enough to be used in engines.
Being able to process biogas locally therefore opens up a possible way in which villages in many countries could become energy independent, without requiring the invention of any radically new technologies. It may also encourage the composting of organic waste in such a way as to reduce the release of methane; a global warming gas more than 20 times as potent as CO2.
As well as inventing a new membrane to perform the separation, the team has also invented a continuous asymmetric membrane casting system that can produce this and other membranes as flat sheets.
The system uses a conveyor to produce a continuous membrane that ranges in thickness between 50 to 500mm at various casting rates. The prototype machine, a fully working model of which we were shown, can produce wet and dry/wet phase inversion membranes at various casting shear rates.
The membrane can then be wound around a perforated central tube so that the permeate passes through the membrane into an envelope and spirals inward for collection. An inverter and an Oriental motor control the speed. A patent has been applied for and the development won a double gold award at the show.


Pointers
* A new membrane technology has been developed to permit the low cost separation of methane from carbon dioxide
* A new continuous casting machine has been developed to produce this and other flat membranes that can then be wound into spiral separators
* The Hybrid Mixed Matrix Composite (H2MC) includes the development of a new host polymer with a new type of silane coupling agent to modify a zeolite surface

Author
Tom Shelley

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