The Carbo-X process separates carbon dioxide from methane or other gases such as hydrogen or air. It is a modified pressure swing adsorption (PSA) process that uses a natural zeolite as the adsorbent. It differs from normal PSA processes in that an air rinse is used for regeneration instead of pressure reduction. The process is covered by U.S. Patent No. 5,938,819, and Chinese Patent No. 98808487.2.
The most distinctive feature of the Carbo-X process is its ability to achieve a high separation factor at very low operating pressures. This enables significant savings in both capital and operating costs over other processes. At only 15 psig, for example, the process can remove nearly all of the CO2 from a 50-50 mixture of methane and CO2, producing an enriched methane containing less than one percent CO2. If a higher purity product is desired, the operating pressure can be increased. For example, an operating pressure of 75 psia will produce a gas containing only about 0.3% carbon dioxide.
The process is designed to be economical for relatively small gas flows, from 0.5 million to several million cubic feet per day. Applications for the process are in landfill gas, coalbed methane, and small natural gas fields containing too much carbon dioxide to put into a pipeline.
GST has performed extensive bench scale tests in the laboratory, but has not yet built a commercial sized plant. The technology is however fairly simple and not a radical departure from traditional PSA processes, so little difficulty is anticipated in scaling up.
More details on the process, including a process cycle, plant layout sketch, estimated capital and operating costs for a typical landfill gas and an example of low quality natural gas, are covered in the slide show below.