Gas separation: apparatus – Apparatus for selective diffusion of gases – Immobilized liquid membrane
Reexamination Certificate
2002-02-01
2003-11-11
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Apparatus for selective diffusion of gases
Immobilized liquid membrane
C095S045000, C095S050000, C096S014000
Reexamination Certificate
active
06645276
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a facilitated transport membrane with improved permeance and selectivity to alkene-based unsaturated hydrocarbons, which includes a solid state polymer electrolyte and additionally a non-volatile surfactant that remarkably enhances the long-term operation stability. More particularly, the present invention relates to a facilitated transport membrane prepared by coating a solid state polymer electrolyte layer, comprising a surfactant, a salt of a transition metal and a non-volatile polymer, on a porous supporting membrane excellent in permeability and mechanical strength, thereby the facilitated transport membrane having high permeability and selectivity to alkenes and long-term operation stability and comprising the complex of a metal and a polymer ligand in the solid state polymer electrolyte has a long-lasting activity as a carrier of alkene even under a long-term dry operating condition.
2. Background of the Related Art
Hydrocarbon mixtures of alkenes such as ethylene and propylene and alkanes such as ethane and propane are primarily produced during a naphtha cracking process. Alkenes such as ethylene and propylene are an important raw material in the petrochemical industry. For that reason, the alkene/alkane separation technology is of great importance in the related industry. Distillation is chiefly used as a separation method for alkene/alkane mixtures such as ethylene/ethane or propylene/propane. However, the separation of those mixtures requires large-scale facilities and high energy expenses, because the alkene in the alkene/alkane mixture is similar to the alkane in molecular size and such physical properties as relative volatility.
For example, the distillation method needs a 120 to 160-stage distillation column at a temperature of −30° C. and a high pressure of about 20 atmospheres for separation of an ethylene/ethane mixture, or a 180 to 200-stage distillation column with a reflux ratio of greater than 10 at −30° C. and several atmospheres. There is thus a need for a novel separation method as a substitute for the conventional distillation method that requires large-scale facilities and high energy expenses.
A substitute for the conventional distillation method is a membrane-based separation method, which has amazingly progressed for the past several decades in the field of gaseous mixture separation, such as N
2
/O
2
, N
2
/CO
2
, or N
2
/CH
4
separation.
Such a classical separation membrane for gaseous mixtures is not suitable to acquire a satisfactory separation performance for an alkene/alkane mixture because the alkene of the mixture is very similar in molecular size and physical property to the alkane. In this regard, a facilitated transport membrane based on a different concept from the classical separation membrane for gaseous mixtures is suggested as a separation membrane having a high separation performance for alkene/alkane mixtures.
The membrane-based separation performance is achieved depending on the difference in permeability among the constituent substances of the mixture. The materials of the membrane mostly have a limitation on their application because of a counter-correlation between permeability and selectivity. The use of the facilitated transport concept increases both permeability and selectivity and thereby extends the application range of the membrane. With a carrier contained in the membrane that reacts reversibly with a specific constituent substance of the mixture, the reversible reaction gives an additional transport of the specific substance and facilitates the substance transport. Accordingly, the total substance transport is the sum of the substance transport caused by the Fick law and the carrier-mediated transport, which is called “facilitated transport”.
A supported liquid membrane is an example of the membrane based on the principle of the facilitated transport. The supported liquid membrane is prepared by coating a porous thin film with a solution of a carrier in a solvent such as water and operated in the liquid state. Such a supported liquid membrane is somewhat satisfactory in separation performance.
U.S. Pat. Nos. 3,758,603 and 3,758,605 (by Steigelmann and Hughes), for example, disclose a supported liquid membrane containing silver salts having a selectivity to ethylene/ethane of about 400 to 700 and a permeability to ethylene of 60 GPU [1 GPU=1×10
−6
cm
3
(STP)/cm
2
cmHgsec], the separation performance of the membrane is considerably satisfactory. However, the supported liquid membrane has the facilitated transport ability only in a wet condition, causing a loss of the solvent and a reduced separation performance with an elapse of time and not maintaining the initial separation performance for a long time.
To solve this problem, Kimura et al. suggests a facilitated transport membrane using silver salts and an ion exchange membrane (U.S. Pat. No. 4,318,714). However, the membrane has the facilitated transport ability only in a wet condition as in the case of the supported liquid membrane.
In addition, U.S. Pat. Nos. 5,015,268 and 5,062,866 (by Ho) disclose a method for forming a complex of silver salts with a water soluble polymer, such as polyvinylalcohol. However, the separation performance is satisfactory only upon passing a feed gas saturated with water or swelling the membrane with ethylene glycol or water. In all the above-stated methods, the separation membranes are required to contain water or a similar solvent and maintain a wet condition. A loss of the solvent over time is thus unavoidable when these membranes are used in separating a dry mixture of hydrocarbon gases that does not contain a solvent such as water. So, there is a need for a method for periodically feeding a solvent to maintain the separation membrane in a wet condition. But, such a method is inapplicable to the actual separation.
Krause et al. suggests another facilitated transport membrane as disclosed in U.S. Pat. No. 4,614,524, in which an ion exchange membrane such as Nafion is ion-exchanged to a silver ion and plasticized with glycerol. The membrane exhibits a low selectivity to ethylene/ethane of only about 10 when using a dry feed mixture or even no selectivity without a plasticizer, and causes a loss of the plasticizer with an elapse of time.
In a supported liquid membrane, a volatile plasticizer, or saturating a feed gas with vapor of the volatile plasticizer is required to maintain the activity of the carrier. Such a supported liquid membrane is also impractical because it causes a loss of the plasticizer with an elapse of time to deteriorate the membrane stability and requires removal of the plasticizer such as water periodically in order to maintain the activity of the carrier from the separated product.
Accordingly, as a substitute for the conventional distillation method that requires high facility and energy expenses in separation of alkene/alkane mixtures, there is a need for a separation membrane excellent in selectivity and permeability and destitute of a volatile component to have a long-term lasting activity even when a dry feed mixture is used.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a stabilized solid polymer electrolyte facilitated transport membrane that substantially obviates one or more problems due to limitations and disadvantages of the related art. An object of the present invention is to provide a facilitated transport membrane suitable for separation of alkenes from alkanes in an alkene/alkane mixture and excellent in permeability and selectivity to alkenes and long-term operation stability in a dry operating condition, thereby maintaining the activity of the carrier without the supply of a liquid solvent.
To achieve the object of the present invention, there is provided a facilitated transport membrane suitable for separation of alkene-based hydrocarbons that includes: a polymer electrolyte layer comprising a salt of a transition metal selectively and
Jung Bum Suk
Kang Yong Soo
Oh Seong Geun
Park Hye Hun
Won Jong Ok
Korea Institute of Science and Technology
Rosenberg , Klein & Lee
Spitzer Robert H.
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