Gas separation: processes – Liquid contacting – And degasification of a liquid
Reexamination Certificate
1999-12-20
2001-09-18
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
And degasification of a liquid
C095S174000, C095S183000, C095S235000, C095S236000, C423S228000
Reexamination Certificate
active
06290754
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a regenerative process for the deacidification of a gas containing CO
2
and liquid hydrocarbons, using an absorbent liquid based on activated methyldiethanolamine.
BACKGROUND OF THE INVENTION
WO-A-8911327 describes a regenerative process for the deacidification of a gas containing CO
2
and possibly other acid gas compounds such as H
2
S, using an absorbent liquid based on activated methyldiethanolamine (MDEA), that is to say an absorbent liquid consisting of an aqueous solution of MDEA and an activator of the absorption of CO
2
by MDEA. This process of deacidification, that is to say of removing CO
2
and other possible acid gas compounds contained in the gas, includes an absorption step, in which the gas to be deacidified is brought into contact with the absorbent liquid, in an absorption zone, in order to produce a treated gas with reduced CO
2
content and an absorbent liquid loaded with CO
2
, and a regeneration step, in which the absorbent liquid loaded with CO
2
is subjected to a regeneration treatment, in particular by pressure reduction, in order to release the CO
2
, and to produce, on the one hand, at least one acid gas fraction rich in CO
2
and, on the other hand, at least one regenerated absorbent liquid, that is to say with reduced CO
2
content, which is recycled into the absorption zone.
The activator combined with MDEA in the absorbent liquid may be selected from:
i) polyalkylenepolyamines, in particular diethylenetriamine, triethylenetetraamine, tetraethylenepentaamine and dipropylenetriamine,
ii) alkylenediamines and cycloalkylenediamines, in particular hexamethylenediamine, aminoethylethanolmine, dimethylaminopropylamine and 1,2-diaminocyclohexane,
iii) aminoalkyl derivatives of heterocycles such as piperazine, piperidine, furan, tetrahydrofuran, thiophene and tetrahydrothiophene, in particular aminoethylpiperazine, aminopropylpiperazine, aminoethylpiperidine, aminopropylpiperidine and furfurylamine,
iv) alkoxyalkylamines, in particular methoxypropylamine and ethoxypropylaminee, and
v) alkylmonoalkanolamines, in particular ethylmonoethanolamine and butylmonoethanolamine.
As is apparent emerges from the information provided by the examples in WO '327, the aforementioned activators, employed in the treatment of removing the CO
2
contained in a gas such as methane using an absorbent liquid based on activated MDEA, have substantially equivalent effectiveness with regard to accelerating the absorption of CO
2
by MDEA.
The gases containing CO
2
, and in particular the natural gases containing CO
2
, which are subjected industrially to the deacidification treatment using an absorbent liquid based on activated MDEA, may contain liquid hydrocarbons in varying overall concentration. It is in practice considered that a gas to be treated containing CO
2
is substantially free of hydrocarbons if the overall level of these products which it contains is less than a threshold representing 14 liters of liquid hydrocarbon per million standard cubic meters of gas.
The applicants observed that the presence of liquid hydrocarbons, in an overall amount greater than the abovementioned threshold, in a gas to be deacidified containing CO
2
would greatly impair the action of the aforementioned activators on the absorption of the CO
2
by MDEA, and have found that the activators consisting of lower aminoalkylethanolamines such as aminoethylethanolamine would lead, when the gas containing CO
2
to be deacidified contains liquid hydrocarbons, to absorption of CO
2
by MDEA greater by about 15% to 20% than the absorption obtained under comparable conditions in the presence of the other activators proposed in the cited document WO '327.
SUMMARY OF THE INVENTION
The invention therefore relates to a regenerative process for the deacidification of a gas containing CO
2
and liquid hydrocarbons, of the type including an absorption step, in which the gas to be treated is brought into contact, in an absorption zone, with an absorbent liquid based on methyldiethanolamine (MDEA) and an accelerator of the absorption of CO
2
by the amine, in order to produce a treated gas with reduced CO
2
content and an absorbent liquid loaded with CO
2
, and a regeneration step, in which the loaded absorbent liquid is subjected to a regeneration treatment in order to release the CO
2
which it has bound, and to produce, on the one hand, at least one acid gas fraction rich in CO
2
and, on the other hand, at least one regenerated absorbent liquid which is recycled into the absorption zone, the process being characterized in that the overall liquid hydrocarbon content in the gas to be deacidified containing CO
2
is greater than 14 liters of liquid hydrocarbons per million standard cubic meters of gas, and in that the activator combined with methyldiethanolamine in the absorbent liquid brought into contact with the gas containing CO
2
and liquid hydrocarbons consists of at least one compound of formula H
2
N—C
n
H
2n
—NH—CH
2
—CH
2
OH in which n represents an integer ranging from 1 to 4.
In particular, the activator combined with MDEA is selected from the compounds of formula H
2
N— (CH
2
)
p
—NH—CH
2
—CH
2
OH, in which p is an integer equal to 2, 3 or 4, the said activator consisting quite especially of the aminoethylethanolamine compound of formula H
2
N—CH
2
—CH
2
—NH—CH
2
—CH
2
OH.
The absorbent liquid is advantageously in the form of an aqueous solution of MDEA and the activator. If appropriate, the aqueous solution may furthermore contain a minor amount of one or more organic solvents of CO
2
which are soluble in water, in particular sulpholane, methanol or N-methylpyrrolidone.
The concentration of MDEA in the absorbent liquid may be between 1N and 6N, and is preferably from 2.5N to 5N.
The amount of activator which is combined with the MDEA in the absorbent liquid can vary quite widely. The said amount is advantageously such that the ratio of the number of moles of activator to the total number of moles of activator and MDEA is between 0.01 and 0.5, and preferably ranges from 0.05 to 0.25.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, the gas to be treated contains CO
2
and liquid hydrocarbons, and it may further contain one or more acid gas compounds other than CO
2
, such as for example H
2
S. A gas of this type is in particular a natural gas, and the overall level of CO
2
and other possible acid gas compounds such as H
2
S which it contains may range from a few tenths per cent to a few tens per cent by volume.
The overall liquid hydrocarbon content in the gas to be treated is greater than 14 liters of liquid hydrocarbons per million standard cubic meters (m
3
STP) of gas, it being possible, in particular, for the content to be up to 10 m
3
or more per million m
3
(STP) of gas. The volume of gas expressed in “standard cubic meters” represents the volume of gas calculated in cubic meters under standard temperature and pressure conditions, that is to say 0° C. and 1 atmosphere.
The term liquid hydrocarbons is intended according to the invention to mean all the hydrocarbons present in the gas, which are liquid under the working conditions in which the absorbent liquid is brought into contact with the gas to be treated. The liquid hydrocarbons may, in particular, be paraffin hydrocarbons, aromatic hydrocarbons or naphthenic hydrocarbons, such as those which are usually present in the natural gases extracted from deposits.
As indicated above, the implementation of the process according to the invention includes an absorption step, in which the gas to be treated and the absorbent liquid are brought into contact, preferably in counter-current, in an absorption zone in order to produce a treated gas containing a reduced level of CO
2
and other possible acid gas compounds, the level corresponding generally to that of the specifications in force for the gas which is treated, and an absorbent liquid loaded with CO
2
and other possible acid gas compounds, and a regeneration step, in which the loaded absorbent liquid is su
Capdeville Serge
Lacamoire Herve
Peytavy Jean-Louis
Elf Exploration Production
Schnader Harrison Segal & Lewis LLP
Smith Duane S.
LandOfFree
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