Cryogenic process for desulphurization and gasoline removal of a

Details Cryogenic process for desulphurization and gasoline removal of a Cryogenic process for desulphurization and gasoline removal of a

1989-02-21

1990-06-19

Caposselo, Ronald C.

Refrigeration

Processes

Circulating external gas

62 24, F25J 300

Patent

active

049350439

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention concerns a cryogenic process of simultaneous selective desulphuration and gasoline removal of a gaseous mixture consisting mainly of methane and likewise containing H.sub.2 S, hydrocarbons with C.sub.2 and more, and eventually one or more gaseous compounds selected among the inert gases H.sub.2 O, CO.sub.2, COS and mercaptans, said gaseous mixture being under an absolute pressure above 0.5 MPa. The process according to the invention makes it possible directly to separate a gaseous mixture of the above mentioned type in three components, namely: H.sub.2 S is less than 65 Pa and the total partial pressure of sulphur-containing compounds, when the gaseous mixture to be treated contains COS and/or mercaptans in addition to H.sub.2 S, is less than 260 Pa, hydrocarbons of C.sub.3 and more present in the gaseous mixture to be treated, and or less considerable quantity of acid compounds CO.sub.2, COS and mercaptans, when said compounds are present in the gaseous mixture to be treated, said stream of acid gas containing, one the one hand, less than 5% molar of hydrocarbons expressed in methane equivalent in relation to the H.sub.2 S and other acid compounds and more than 80% of the H.sub.2 S contained in the gaseous mixture to be treated, and, on the other hand, having a molar ratio H.sub.2 S:CO.sub.2 higher than the ratio that corresponds in the gaseous mixtures to be treated.


STATEMENT OF RELATED ART

There are known several processes industrially used for the treatment of gaseous mixtures such as defined above, the main examples of them being represented by the different natural gases which include an operation of deacidification, that is, an elimination of the H.sub.2 S and other acid gases, and an operation of gasoline removal, that is, a separation of the heavy hydrocarbons, for example, of C.sub.3 and more, from the gaseous mixture, which make it possible to carry out the separation of said gaseous mixture into the three components mentioned above. Said operations of deacidification and gasoline removal are generally carried out separately and form part of a succession of operations effected on the gaseous mixture to be treated and mainly including an elimination of the acid gases, drying, an adsorption of water on a suitable solid material such as a molecular sieve, a separation by cryogenic distillation between -30.degree. C. and -90.degree. C. associated or not with an extraction by a solvent in order to obtain the fraction of liquid of natural gas, and finally a reheating of the treated gas to room temperature in order, generally, to feed the network of commercial gas.
In such a diagram of treatment of a gaseous mixture of the natural gas type containing the above mentioned constituents, the lowering of the temperature of the gaseous mixture is imposed only by the production of the fraction of natural gas, no other operation being effected at this level of temperature.
In this type of treatment diagram, the performance in series of operations which are based on very different principles and are conducted at different levels of temperature involves serious inconveniences. There is only scant possibility of thermal integration, which makes said diagram of treatment extremely burdensome from the point of view of energy and from the point of view of investments. Besides, at the level of the stage of elimination of the acid gaseous compounds, which generally constitutes the first stage of said diagram of treatment, and usually consists in washing the gaseous mixture to be treated, in counter-current, by means of a solvent of acid gaseous compounds, selective or not of the H.sub.2 S, and regeneratable as an aqueous solution of an alkanolamine or of potassium carbonate, or even an organic solvent, restraints appear in the selection of the solvent from the moment the gaseous mixture to be treated contains quantities, even if quite small, of hydrocarbons having C.sub.3 or more.
In effect, the industrially available organic solvents susceptible of efficiently dissolving

REFERENCES:
patent: 4488890 (1984-12-01), Foerg et al.
patent: 4556404 (1985-12-01), Shenoy et al.
patent: 4563202 (1986-01-01), Yao et al.
patent: 4707171 (1987-11-01), Bauer
patent: 4710211 (1987-12-01), Gazzi et al.
patent: 4713940 (1987-12-01), Ranke et al.
patent: 4740222 (1988-04-01), Mehra et al.

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