Oxygen
Oxygen is a catalyst poison for some catalysts. Some typical requirements limit the oxygen content in the syngas to ca. 5 ppmv. In high-temperature gasification processes, whether of coal or oil, the oxygen is completely consumed in the reaction and no oxygen is contained in the synthesis gas. One should, however, be aware of the danger of introducing small quantities of oxygen into the gas in the subsequent processing. Typically, if using a water wash for solids removal, it is possible to introduce oxygen via the water. It is therefore advisable in critical circumstances to eliminate such sources of accidental contamination by, for example, using only deaerated water for scrubbing. Atmospheric gasification processes also have a risk of introducing oxygen from unintended sources.
Any oxygen in gas subjected to CO shift will react with the hydrogen present (BASF undated). It is worth mentioning that oxygen is often measured together with argon, and occasionally an analysis result showing oxygen in syngas can cause some considerable concern before this “misleading message” is understood.