Abstract

All fossil fuels contain some level of sulfur, and processing of these resources typically produces H₂S. The resulting “sour” fuels are treated, usually with a solvent acid gas removal (AGR) step, to produce “sweet” gas or crude along with an acid gas (CO₂ and H₂S) waste stream.  The H₂S in this stream is subsequently converted into elemental sulfur and recovered in this benign form in a Claus plant, while the CO₂ is generally vented to the atmosphere. Installation of a downstream CO₂ capture process is technically feasible, but capital and energy intensive because the CO₂ is diluted in nitrogen after the Claus process.  CO₂ emissions from these sulfur recovery systems are significant, estimated at 100 million tonne CO₂/year worldwide.

This presentation will describe a new membrane-based design for low-cost CO₂ capture from sulfur processing systems developed by MTR and Saudi Aramco. In this Membrane Acid Gas Enrichment (MAGE) process, a special type of membrane selectively separates CO₂ from H₂S by treating the AGR outlet acid gas before sending it to the Claus unit, and importantly, before the gas is diluted with nitrogen. The membrane permeate, containing most of the acid gas CO₂, can be sent to an existing amine column or a liquefier for purification and CO₂ capture. Greater than 90% CO₂ capture can be achieved at much lower cost than typical downstream tail gas treatment options.  For example, our estimates show a capture cost of ~35 USD/tonne CO₂ compared to typical tail gas capture costs of 60 – 100 USD/tonne CO₂.  The membrane retentate, enriched in H₂S, is routed to the Claus unit. Because most of the diluent CO₂ has been removed, the Claus plant now operates more efficiently, with improved sulfur conversion and lower SO₂ emissions, as well as the potential to process more gas or to be downsized for capital savings.

Design studies show that a membrane CO₂/H₂S selectivity of at least 10 and preferably higher is required to make the process attractive.  Results from a year-long field test using commercial-sized membrane modules treating real gas containing up to 40 wt% H₂S demonstrate that selectivities of 15 to 30 can be achieved. Based on this success, a large demonstration plant is currently being built in California with startup expected in early 2026.  Future plans on process optimization and technology deployment will be reviewed.

Biography

Tim Merkel received his B.S. in Chemical Engineering from Polytechnic University, Brooklyn, NY, and his M.S. and Ph.D. in Chemical Engineering from North Carolina State University, Raleigh, NC, completing a dissertation on transport in nanocomposite membranes under the guidance of Professor Benny Freeman. 

Dr. Merkel joined Membrane Technology and Research, Inc. (MTR) full-time as a Senior Research Scientist in 2003, became Director of MTR’s Research and Development Group in 2009, and Vice-President of Technology in 2013.  In his current role, Dr. Merkel leads a team of researchers developing new membrane materials and processes for use in industrial gas and liquid separations.  Some of his group’s recent work includes an industry-leading program on development of a membrane solution for carbon capture from power and industrial exhaust gases.  

Dr. Merkel has published over 50 peer-reviewed articles on various aspects of membrane materials and process development, and he has given numerous invited presentations at academic and industrial meetings. He is inventor/co-inventor on 30 patents in the field of membrane gas separations.  He has previously served on the Board of Directors of the North American Membrane Society and has been an instructor in the membrane gas separation workshop at the Society’s annual meeting for more than a decade.