This invention relates to the removal of impurities from natural gas. In one of its aspects this invention relates to the removal of hydrogen sulfide as an impurity from a stream of gas. In another of its aspects this invention relates to adsorption using molecular sieves. In still another aspect of this invention it relates to the conversion of hydrogen sulfide to carbonyl sulfide (COS) in the presence of a molecular sieve catalyst.
Perhaps the best known and most frequently used means for removing hydrogen sulfide contaminant from a gas stream, particularly a natural gas stream, is the use of an amine contactor for the absorption of the H.sub.2 S. This system is not, however, economically attractive for the selective absorption of H.sub.2 S when the ratio of carbon dioxide to hydrogen sulfide is high. In such a system it is necessary to remove the majority of the CO.sub.2 to insure adequate removal of the H.sub.2 S. In a standard amine absorbant system the majority of the energy used to run an amine contactor, an amine regeneration system, and a waste gas incinerator is used to remove CO.sub.2.
As another type of economically attractive system for the removal of H.sub.2 S contaminant, molecular sieves can be used to remove H.sub.2 S by a combination of adsorption and chemical conversion of H.sub.2 S to carbonyl sulfide (COS). In such a system, the regeneration of the molecular sieve bed causes the concentration of the H.sub.2 S in the regeneration gas stream to be much higher than in the original gas stream. The removal of H.sub.2 S and water from the molecular sieve bed regeneration gas which normally is accomplished using an amine contactor followed by a glycol contactor has been shown not to be economically attractive if, as stated above, the ratio of CO.sub.2 to H.sub.2 S is high.
In solving the problem of providing an adsorption and regeneration system for removal of hydrogen sulfide contaminant from gases, particularly natural gas, it has now been found that an integrated system using molecular sieve beds can be used to eliminate the need for an amine absorption system and the glycol dehydration system that is normally used in conjunction with the amine system.
It is therefore an object of this invention to provide a process for the removal of hydrogen sulfide contaminant from a gas stream using contact with molecular sieves both to treat an inlet gas stream to remove sufficient hydrogen sulfide and water to produce a salable effluent and to treat the effluent from the regeneration of the molecular sieves so that a salable product is produced from this stream. It is also an object of this invention to provide a method for producing natural gas of reduced hydrogen sulfide content and a water dew point of less than -70.degree. C.
These and other objects, aspects, and the various advantages of this invention will become apparent upon study of the specification, the drawing, and the appended claims.