In a plant in Houston Texas, coffee is decaffeinated by supercritical carbon dioxide using a semi-continuous process in a plant shown schematically in the figure above. A large vessel has two smaller vessels above and below it connected to it by large-bore valves. Large-bore valves are also in place to fill the upper small vessel and empty the lower small vessels. The green coffee beans are extracted, i.e. before roasting, with pure carbon dioxide. These are mostly located in the central vessel and carbon dioxide passes up through it. Periodically, decaffeinated coffee beans are taken out via the smaller lower vessel and new coffee beans are put into the system via the upper small vessel by operating the valves and filling and emptying the small vessels with carbon dioxide. Caffeine is removed from the carbon dioxide after extraction by scrubbing with water. Carbon dioxide from all vessels is recycled to the maximum extent.
Coffee is not a very valuable commodity and the only way the process can be made viable is by economies of scale. The plant is therefore very large and the large vessel is more than 60 m3 in volume. The production volume is estimated to be around 25,000 tonnes per year. A picture of the large vessel being manoeuvred into position is shown below.