Gas separation: processes – Solid sorption – Including reduction of pressure
Reexamination Certificate
1999-09-01
2001-03-13
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Including reduction of pressure
C095S102000, C095S103000, C095S105000, C095S144000, C095S902000
Reexamination Certificate
active
06200366
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the separation of hydrocarbon gases, and more particularly to the separation of gaseous alkenes from alkanes by adsorption. Specifically, the invention relates to the separation of ethene from ethane by pressure swing adsorption (PSA) using a modified type A zeolite adsorbent.
BACKGROUND OF THE INVENTION
It is known to separate alkenes (e.g. propene) from alkanes (e.g. propane) by distillation. The propene-propane mixture is fed into a C
3
-splitter, which typically is a 2-column distillation system. The second column is substantially equal in size to the first column. The first column separates a substantial portion of the propane to produce a chemical or refinery grade propene of at least 90 volume percent purity, typically about 96 volume percent. The second column improves the purity level to 99+ volume percent to obtain polymer grade propene. The separation of propene from propane by distillation is both difficult and costly because the process requires two large columns and is very energy intensive.
It is also known to separate alkenes from alkanes by adsorption. U.S. Pat. No. 4,917,711 describes the adsorption of an alkene from a mixture containing the alkene and an alkane using an adsorbent comprising a copper compound and a high surface area support such as silica gel or zeolite molecular sieves, such as 4A zeolite, 5A zeolite, type X zeolite or type Y zeolite.
East German Patent No. 150885 describes the separation of alkenes from alkanes using 4A zeolite which has some of its exchangeable cations replaced by calcium or magnesium ions.
U.S. Pat. No. 5,365,011 describes the separation of alkenes having 2 to 6 carbon atoms from alkanes having 2 to 6 carbon atoms by pressure swing adsorption at temperatures in the range of about 50 to about 200° C. using 4A zeolite. The 4A zeolite may have up to 25% of its exchangeable sodium ions replaced by other ions, including potassium ions, calcium ions, strontium ions, etc., provided that the presence of the other ions does not cause the 4A character of the adsorbent to change.
Breck et al, “The Properties of a New Synthetic Zeolite, Type A”, Journal of the American Chemical Society, Vol. 78, Number 23, 1956, pp. 5963-5977, describes the adsorption of various hydrocarbons using partially potassium-exchanged type 4A zeolite.
Because of the importance of adsorption as a method of separating alkenes from alkanes, adsorbents having enhanced alkene—alkane separation ability are continuously sought. This invention provides new adsorbents which can efficiently and effectively separate selected alkenes, particularly ethene from selected alkanes, particularly ethane.
SUMMARY OF THE INVENTION
According to a broad embodiment, the invention is a method of separating an alkene selected from ethene, propene, normal butenes or mixtures of these from a gas mixture comprising said alkene and an alkane selected from ethane, propane, normal or branched chain butanes and mixtures of these by a pressure swing adsorption process comprising the steps:
(a) passing the gas mixture through at least one adsorption zone containing type A zeolite having, as its exchangeable cations, about 50 to about 77% sodium ions, about 23 to about 40% potassium ions and about 0 to about 10% other ions selected from Group IA ions other than sodium and potassium, Group IB, Group IIA ions, Group IIIA ions, Group IIIB ions, lanthanide series ions and mixtures of these, thereby adsorbing at least part of said alkene from said gas mixture and producing an alkene-depleted gas; and
(b) regenerating the zeolite, thereby producing an alkene-enriched gas.
In a preferred aspect of the broad embodiment, the adsorption step, i.e., step (a), is carried out at a temperature of at least 50° C. In a more preferred aspect, step (a) is carried out at a temperature in the range of about 50 to about 200° C., and in a most preferred aspect of this embodiment, step (a) is carried out at a temperature in the range of about 70 to about 160° C.
In another preferred aspect of the broad embodiment, step (a) is carried out at a pressure in the range of about 1 to about 120 bara, and step (b) is carried out at a pressure in the range of about 0.15 to about 5 bara. In a more preferred aspect, step (a) is carried out at a pressure in the range of about 1 to about 25 bara and step (b) is carried out at a pressure in the range of about 0.2 to about 2 bara.
The method of the invention is particularly useful for the separation of the alkenes from alkanes when the alkene and the alkane being separated contain the same number of carbon atoms.
The method of the invention is especially useful for separating ethene from gas mixtures containing alkanes, especially gas mixtures containing ethane, and it can be effectively used to separate ethene from a gas mixture when the gas mixture contains only ethene and ethane.
In another preferred aspect of the broad embodiment, step (a) comprises passing the gas mixture through type A zeolite whose exchangeable cations comprise more than 25% potassium ions.
In another preferred aspect of the broad embodiment, step (a) comprises passing the gas mixture through type A zeolite having as its exchangeable cations, about 55 to about 73% sodium ions, about 27 to about 40% potassium ions and about 0 to about 5% ions selected from said residual ions, and in a most preferred aspect of this preferred embodiment, step (a) comprises passing the gas mixture through type A zeolite whose exchangeable cations consist substantially of sodium and potassium ions. More preferably the exchangeable cations of said type A zeolite comprise at least about 30% potassium ions, and most preferably they comprise about 30 to about 35% potassium ions.
In another embodiment of the invention, the adsorbent is at least partly regenerated by depressurizing and preferably evacuating the adsorption zone. In this embodiment, or in an independent embodiment, the adsorbent can be at least partly regenerated by purging the adsorption zone with alkene-depleted gas.
In another embodiment, the adsorption zone is purged with alkene-enriched gas prior to step (b).
In another embodiment, step (b) is at least partly carried out by purging the adsorption zone with alkene-depleted gas. Yet another embodiment comprises purging the adsorption zone with alkene-enriched gas prior to step (b).
Another embodiment comprises at least partly repressurizing the adsorption zone with alkene-depleted gas after step (b).
REFERENCES:
patent: 2963519 (1960-12-01), Kasperik et al.
patent: 3723561 (1973-03-01), Priegnitz
patent: 3785122 (1974-01-01), Yatsurugi et al.
patent: 3982912 (1976-09-01), Yatsurugi et al.
patent: 4137054 (1979-01-01), Miyake et al.
patent: 4453952 (1984-06-01), Izumi et al.
patent: 4461631 (1984-07-01), Itabashi et al.
patent: 4498910 (1985-02-01), Benkmann
patent: 4554141 (1985-11-01), Scull et al.
patent: 4917711 (1990-04-01), Xie et al.
patent: 5206004 (1993-04-01), Park
patent: 5245099 (1993-09-01), Mitariten
patent: 5365011 (1994-11-01), Ramachandran et al.
patent: 5507857 (1996-04-01), Kumar et al.
patent: 5744687 (1998-04-01), Ramachandran et al.
patent: 150 885 (1981-09-01), None
Zeolite Molecular Sieves: Structure, Chemistry, and Use, Donald W. Breck, Krieger Publishing Company, Malabar, Florida (1984), pp. 608-650.
Y. T. Yeh and R. T. Yang, “Diffusion in Zeolites Containing Mixed Cations”, AIChE Journal, Oct. 1989, vol. 35, No. 10, pp. 1659-1666.
“Modification of the sorption properties of Linde sieve A by cation exchange and pre-sorption of ammonia”, T. Berry, Chemistry Dept., Imperial College of Science and Technology, London, S.W.7, Oct, 1996, pp. 111, 112, 114, and 143.
Journal of the American Chemical Society, vol. 78, No. 23, Dec. 8, 1956, by D. W. Breck, W. G. Eversole, R. M. Milton, T. B. Reed and T. L. Thomas-Crystalline Zeolites. I. The Properties of a New Synthetic Zeolite, Type A, pp. 5963-5977.
Bulow Martin
Fitch Frank R.
Guo Chang Jie
Malik Virginia A.
Shen Dongmin
Neida Philip H. Von
Pace Salvatore P.
Spitzer Robert H.
The BOC Group Inc.
LandOfFree
Separation of alkenes and alkanes does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Separation of alkenes and alkanes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Separation of alkenes and alkanes will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2543613