Gas separation: apparatus – Apparatus for selective diffusion of gases – Plural layers
Reexamination Certificate
2000-12-29
2002-10-22
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Apparatus for selective diffusion of gases
Plural layers
C096S004000, C096S013000
Reexamination Certificate
active
06468331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid state facilitated transport separation membrane for the separation of alkenes prepared by using a polymer electrolyte, wherein the membrane has high permeance and selectivity of alkene-series hydrocarbons even under dry conditions. More specifically, the present invention relates to a solid state facilitated transport separation membrane prepared by coating a polymer electrolyte layer consisting of a metal salt and a polymer onto a porous supported membrane, wherein the separation membrane is characterized in that its permeance and selectivity to alkenes is high and in that the complex formed by a polymer ligand in the polymer electrolyte maintains its activity as a carrier for alkene-series hydrocarbons for a long time, even under dry conditions.
2. Description of the Prior Art
Alkene-series hydrocarbons, such as ethylene and propylene, are important raw materials that form the basis of the current petrochemical industry. They are primarily produced by high temperature thermal decomposition of naphtha that is obtained from a purification process of petroleum. However, since alkane-series hydrocarbons such as ethane and propane are also produced by this process of thermal decomposition, use of alkene-series hydrocarbons as raw materials should be preceded by the separation process of mixtures having alkene-series hydrocarbons. Currently, a sub-zero distillation process is generally used in the separation of these mixtures. For example, a column having at least 100 trays of theoretical number at a low temperature of −25° C. and at a high pressure of about 23 atm is required in the sub-zero distillation process to separate the mixture of ethylene/ethane. In the separation of propylene/propane, similar operation conditions are also required. Therefore, there has been a continued need for the development of a new separation process that can replace the prior distillation process, which requires investment of large-scale equipment and high-energy costs.
A separation process that could be considered as a replacement for distillation processes is one that uses a separation membrane. The separation membrane process has progressed remarkably over the past few decades in the field of separating nitrogen/oxygen, nitrogen/carbon dioxide and nitrogen/methane, and the like. In the separation of mixtures, such as alkenes/alkanes, however, a satisfactory separation performance cannot be accomplished by using general polymer separation membranes because they are similar in both molecular size and in such physical properties as the degree of condensation.
The process utilizing the separation membrane that uses the concept of facilitated transport could be considered as an alternative process. Facilitated transport refers to a transport phenomenon in which the general mass transport according to Fick's law and the mass transport mediated by a carrier occur simultaneously. A supported liquid membrane is one membrane prepared by using such a concept. This membrane facilitates said mass transport by filling a porous membrane with a solution containing a carrier. Supported liquid membranes of this type have succeeded to a certain extent but have drawbacks in that solvent is gradually lost and permeance is gradually reduced over time. By using a membrane of this type, for example, Steigelmann and Hughes prepared a supported liquid membrane wherein the selectivity of ethylene/ethane is about 400 to 700 and the permeance of ethylene is 60 GPU [1 GPU=1×10
−6
cm
3
(STP)/cm
2
sec cmHg] (see, U.S. Pat. Nos. 3,758,603 and 3,758,605). These values show considerably good results, but there remains the problem that such a state cannot be maintained for an extended period of time due to the aforementioned solvent loss.
To solve this problem of the supported liquid membrane, a method which enables facilitated transport by substituting a suitable ion in an ion exchange resin was proposed by Kimura, et al. (see U.S. Pat. No. 4,318,714). However, this ion exchange resin membrane also has a drawback in that the facilitated transport phenomenon is exhibited only under humid conditions, which is similar to the supported liquid membrane. This membrane, which must always be maintained in humid conditions, is inconvenient and inefficient in the actual separation process. Also, a carrier loss into the aqueous phase can still occur, as with the supported liquid membrane.
Another method proposed by Ho is a process for producing a complex by using water-soluble glassy polymers, such as polyvinylalcohol (see U.S. Pat. Nos. 5,015,268 and 5,062,866). However, this method also had a drawback in that satisfactory results can be obtained only where feed gas is saturated with water vapor by passing it through water, or where the membrane is swelled by using ethylene glycol or water.
Kraus, et al. also have developed a facilitated transport separation membrane by using a similar method (see U.S. Pat. No. 4,614,524). According to this patent, an Ag ion is substituted for an ion exchange membrane, such as Nafion, and said membrane is then plasticized, for example, with glycerol. However, this membrane could not be utilized because the selectivity of ethylene/ethane is as low as about 10 when dry feed was used. And when a plasticizer was not used, the selectivity could not be seen.
Thus, the development of a solid state facilitated transport separation membrane in which selectivity and permeance are high and stable even under dry operating conditions is sincerely required in the separation of alkene/alkane hydrocarbons.
Considering that the usual polymer separation membrane cannot separate alkene/alkane mixtures having similar molecular size or physical properties, as described above, use of a facilitated transport separation membrane capable of selectively separating only alkene hydrocarbons is needed. The conventional facilitated transport separation membranes, however, have a disadvantage in that the mobility of a carrier should be increased by using the following method: filling a solution containing a carrier into a porous membrane, adding a plasticizer or saturating feed gases with water vapor, etc. Such a conventional facilitated transport separation membrane cannot be utilized due to the problem of declining stability of the membrane, since the materials added are gradually lost with time. There is also the problem of having to remove water that is contained in the feed before the preparation of the product.
SUMMARY OF THE INVENTION
Therefore, the purpose of the present invention is to prepare a facilitated transport separation membrane by introducing, for example, the polymer electrolytes used in polymer batteries into the facilitated transport separation membrane, wherein the problem of stability, such as with carrier loss, is solved and unsaturated hydrocarbons such as alkene can be separated even under dry conditions.
That is, an object of the present invention is to prepare a solid state facilitated transport separation membrane for use in the separation of alkene-series hydrocarbons from alkenes/alkanes mixtures, wherein the separation membrane has high permeance and selectivity for alkene-series hydrocarbons under dry operating conditions.
DETAILED DESCRIPTION OF THE INVENTION
This object of the present invention is accomplished through the use of a solid state facilitated transport composite separation membrane; said membrane consisting of a porous supported membrane and a polymer electrolyte layer consisting of a metal salt and a polymer, wherein the composite separation membrane has an ideal selectivity expressed by [permeance of pure alkenes/permeance of pure alkanes] of at least 100.
The present invention is described in greater detail below.
The solid state facilitated transport separation membrane according to the present invention is composed of a polymer electrolyte having a selective permeance for alkene-series hydrocarbons and a porous supported membrane supporting
Hong Seong-Uk
Kang Yong-Soo
Won Jong-Ok
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