News Column

Patent Issued for Gas Separation Composite Membrane

May 28, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Asano, Shushi (Kurashiki, JP); Nobuto, Yoshiki (Kurashiki, JP); Fujiwara, Naoki (Kurashiki, JP); Duan, Shuhong (Kizugawa, JP); Kazama, Shingo (Kizugawa, JP), filed on February 15, 2011, was published online on May 13, 2014.

The assignee for this patent, patent number 8721774, is Research Institute of Innovative Technology for the Earth (Kizugawa-shi, JP).

Reporters obtained the following quote from the background information supplied by the inventors: "Separation technologies using separation membranes have recently been making remarkable progress. Such separation technologies include various examples, such as separation between liquid and solid, e.g., obtaining drinking water by separating impurities, and separation of gases, e.g., oxygen-enrichment by separating nitrogen from air. Particularly, in gas separation technologies, the establishment of technologies to separate carbon dioxide selectively from a mixed gas is desired earnestly from the viewpoint of efficient recovery of fossil resources or prevention of global warming and promoted actively.

"However, since conventional polymer membranes can exhibit only insufficient carbon dioxide selectivity (the membrane permeability of carbon dioxide/the membrane permeability of other gases), carbon dioxide of a desired concentration has not been recovered successfully therewith. In order to obtain a separation membrane superior in carbon dioxide selectivity, the use of a material with high affinity to carbon dioxide has been proposed; for example, there has been proposed a separation membrane in which a microporous support has been impregnated with a polyamidoamine dendrimer that in the form of a liquid material at room temperature (non-patent documents 1 and 2). Although this impregnated membrane exhibits high carbon dioxide selectivity with a value of 1,000 or more under such a condition that no pressure difference is applied to the membrane, it is insufficient for practical use because of its low membrane flux due to no pressure difference. On the other hand, it has not been used practically also under the application of pressure because the polyamidoamine dendrimer flows out from the support with time under the application of pressure to become impossible to maintain its selectivity.

"As a method for solving this problem, there has been proposed a composite membrane in which a layer of a hydrophilic macromolecular material crosslinked with a crosslinking agent as a matrix impregnated with a specific amine compound has been formed on the surface of a porous support membrane (patent document 1). This composite membrane is considered to be a separation membrane that not only is high in carbon dioxide selectivity but also can withstand a certain pressure difference. Where water vapor is contained in the mixed gas to be subjected to separation, however, there are required properties contrary to each other, i.e., a moderate hydrophilicity with which affinity is exhibited between the mixed gas and a membrane surface and water resistance with which the separation membrane exhibits no structural change under a water vapor atmosphere. The aforementioned composite membrane is difficult to be used for practical use because if a mixed gas is supplied under a water vapor atmosphere, then the contained amine compound flows out from the composite membrane with time and the composite membrane cannot maintain its carbon dioxide selectivity. Since the number of examples of inclusion of water vapor in a mixed gas is expected to increase greatly due to the establishment of coal gasification power plants, there has been desired earnestly the development of a separation membrane that has moderate hydrophilicity and water resistance and can be used practically even for a mixed gas containing water vapor."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Problem to be Solved by the Invention

"The present invention was devised in order to solve the above-described problems and aims to provide a gas separation composite membrane capable of separating a specific type of gas even if a mixed gas containing water vapor is applied.

"Means for Solving the Problems

"As a result of earnest investigations for solving the above-described problems, the present inventors accomplished the present invention by finding that there can be obtained a gas separation composite membrane capable of exhibiting high carbon dioxide selectivity even for a mixed gas containing water vapor and capable of being used practically, when a gas separation composite membrane comprises a vinyl alcohol-based copolymer modified in a specific amount with carboxyl groups, a polyamidoamine dendrimer, and a crosslinking agent having an azetidinium group, and a mass ratio (A)/(C) of the polyamidoamine dendrimer (A) to the crosslinking agent (C) having an azetidinium group and a mass ratio (B)/(C) of the vinyl alcohol-based polymer (B) to the crosslinking agent (C) having an azetidinium group fall within specific ranges.

"That is, the aforementioned problems can be solved by providing a gas separation composite membrane comprising a polyamidoamine dendrimer (A) having a group represented by formula (1):

"##STR00001## wherein A.sup.1 represents a divalent organic residue having 1 to 3 carbon atoms and n represents an integer of 0 or 1, or a group represented by formula (2):

"##STR00002## wherein A.sup.2 represents a divalent organic residue having 1 to 3 carbon atoms and n represents an integer of 0 or 1, a vinyl alcohol-based polymer (B) containing 0.5 to 5 mold of carboxyl groups, and a crosslinking agent (C) having an azetidinium group, wherein the mass ratio (A)/(C) of the polyamidoamine dendrimer (A) to the crosslinking agent (C) having an azetidinium group is 20/80 to 65/35, and the mass ratio (B)/(C) of the vinyl alcohol-based polymer (B) to the crosslinking agent (C) having an azetidinium group is 20/80 to 80/20.

"Preferably, the composite membrane exhibits a weight retention of the composite membrane of 60% by mass or more and a weight retention of nitrogen element of 60% by mass or more when the composite membrane has been immersed in distilled water of 30.degree. C. for 3 hours.

"An aforementioned problem can be solved also by providing a gas separation composite membrane comprising a polyamidoamine dendrimer (A) having a group represented by formula (1):

"##STR00003## wherein A.sup.1 represents a divalent organic residue having 1 to 3 carbon atoms and n represents an integer of 0 or 1, or a group represented by formula (2):

"##STR00004## wherein A.sup.2 represents a divalent organic residue having 1 to 3 carbon atoms and n represents an integer of 0 or 1, a vinyl alcohol-based polymer (B) containing 0.5 to 5 mol % of carboxyl groups, a crosslinking agent (C) having an azetidinium group, and a polyfunctional crosslinking agent (D), wherein the mass ratio (A)/(C) of the polyamidoamine dendrimer (A) to the crosslinking agent (C) having an azetidinium group is 20/80 to 65/35, the mass ratio (B)/(C) of the vinyl alcohol-based polymer (B) to the crosslinking agent (C) having an azetidinium group is 20/80 to 80/20, and the mass ratio (B)/(D) of the vinyl alcohol-based polymer (B) to the polyfunctional crosslinking agent (D) is 60/40 to 90/10.

"Preferably, the composite membrane exhibits a weight retention of the composite membrane of 60% by mass or more and a weight retention of nitrogen element of 60% by mass or more when the composite membrane has been immersed in distilled water of 30.degree. C. for 3 hours.

"Effect of the Invention

"The gas separation composite membrane of the present invention can separate a specific type of gas even from a mixed gas containing water vapor."

For more information, see this patent: Asano, Shushi; Nobuto, Yoshiki; Fujiwara, Naoki; Duan, Shuhong; Kazama, Shingo. Gas Separation Composite Membrane. U.S. Patent Number 8721774, filed February 15, 2011, and published online on May 13, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=104&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=5157&f=G&l=50&co1=AND&d=PTXT&s1=20140513.PD.&OS=ISD/20140513&RS=ISD/20140513

Keywords for this news article include: Nitrogen, Chemicals, Chemistry, Carbon Dioxide, Inorganic Carbon Compounds, Research Institute of Innovative Technology for the Earth.

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Source: Journal of Engineering


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