Decarbonisation Technology – August 2021

A novel approach of CO 2 removal from natural gas A new process combining membranes followed by liquefaction provides a significant advantage in CO 2 removal from natural gas Mahin Rameshni and Stephen Santo Rameshni & Associates Technology & Engineering Priyanka Tiwari, Sachin Joshi, Kaaeid Lokhandwala and Daaniya Rahman Membrane Technology & Research

I n recent years, there have been many developments in LNG, shale gas and others where it is required to remove CO 2 from natural gas. The recovered CO 2 is compressed and reinjected to reduce CO 2 emissions. Producing high-purity dry CO 2 is always a challenge with the conventional process. Dry high-purity CO 2 is usually required to either reinject or for other usages. The conventional method has been to design an amine unit configuration with a selective solvent for CO 2 removal. The capital and the operating costs are relatively high because it requires considerable solvent circulation and extensive equipment. Also, for offshore processing of natural gas with high CO 2 , conventional processes such as amine are complex, bulky and energy- intensive. Two-stage membrane system technology is well known to recover natural gas processing offshore, but it requires recycle compression. The size of recycle compression is in excess due to the residual CO 2 . A new process combining membranes followed by liquefaction provides a significant advantage in CO 2 removal from natural gas while recovering high-purity dry CO 2 as a by-product. Membrane Technology & Research (MTR) patented such a process with a combination of membrane and CO 2 liquefaction to separate the CO 2 from natural gas. MTR and Rameshni & Associates Technology & Engineering (RATE) are working together, where MTR designs the membrane systems and RATE designs the CO 2 liquefaction system downstream of the membranes. The advantage of using the liquefaction system downstream is to reduce the

Selective layer

Microporous support layer

Figure 1 Cross-section of MTR’s multi-layer composite membrane

overall recycling of CO 2 to feed the membranes. The advantage of using membranes is to maximise hydrocarbon recovery in the first stage and avoid losing ethane and heavy hydrocarbons to liquefaction. This has the significant benefit of not forming ethane and CO 2 azeotrope, which is difficult to break in standalone liquefaction systems. The combination of membranes and liquefaction system can produce up to 99%+ pure dry CO 2 . This joint article discusses the advantage of this scheme vs the conventional method. In addition, special compact equipment with higher operating efficiency, used in CO 2 liquefaction to reduce plot space, is highlighted along with costs. CO 2 recovery by membrane separation Key to the CO 2 recovery process is a size-selective composite membrane that is more permeable to CO 2 than the hydrocarbons present in natural gas (C 1 and C 2 +). MTR can achieve efficient separation