1. Field of the Invention
The present invention is generally related to a carbon molecular sieve membrane, and more particularly to a method for fabricating carbon molecular sieve membrane.
2. Description of the Prior Art
A carbon molecular sieve membrane is not only with molecular sieve character, but also can provide better gas separation performance than general polymer films. To one skilled in that art, it is known that the manufacturing cost of a carbon molecular sieve membrane is too high, and the produced carbon molecular sieve membrane is usually with defects. Therefore, it is a hard choice to one skilled in that art to entering the study of carbon molecular sieve membrane.
In order to obtain high performance carbon molecular sieve membrane, the resistance in the selective layer should be decreased. A carbon molecular sieve membrane is brittle, so that most researchers try to produce carbon molecular sieve “composite” membrane to avoid the mentioned brittleness problem. The mentioned composite membrane is usually obtained by coating polymer onto a heat-resistant substrate with high mechanical property, processing cross-linking or thermal treatment, and carbonizing.
If the carbon molecular sieve membrane obtained from performing one time of the manufacturing in
In view of the above matters, developing a novel method for fabricating carbon molecular sieve membrane, wherein the carbon molecular sieve membrane is with high separation performance and defects free, having the advantage of simply operating and low cost is still an important task for the industry.
In light of the above background, in order to fulfill the requirements of the industry, the present invention provides a novel method for fabricating carbon molecular sieve membrane having the advantage of simply operating and lower cost than the cost of the manufacturing in the prior art. And, the carbon molecular sieve membrane obtained from the method of this invention can provide great gas separation performance and permeability. So that the mentioned method of this invention can efficiently improve the industrial competitive ability.
One object of the present invention is to provide a method for fabricating carbon molecular sieve membrane to produce carbon molecular sieve membrane by forming pristine membrane with polymerization deposition, and modulating the fine structure of the pristine membrane through carbonizing process to producing carbon molecular sieve membrane.
Another object of the present invention is to provide a method for fabricating carbon molecular sieve membrane to produce carbon molecular sieve membrane without surface defects by performing one time of polymerization deposition-carbonization manufacturing, so that the thickness of the produced carbon molecular sieve membrane can be reduced and the permeability of the produced carbon molecular sieve membrane can be efficiently improved.
Still another object of the present invention is to provide a method for fabricating carbon molecular sieve membrane to produce carbon molecular sieve membrane without defects by performing one time of polymerization deposition-carbonization manufacturing, so that the mentioned method is more saving time and energy, and more simply operating than the manufacturing in the prior art.
Accordingly, the present invention discloses a method for fabricating carbon molecular sieve membrane. The mentioned method for fabricating carbon molecular sieve membrane comprises performing plasma enhanced chemical vapor deposition (PECVD) process to uniformly coat reacting monomer onto the surface of a substrate, and performing carbonizing process. Through the mentioned PECVD process, a pristine membrane is formed on the substrate. The mentioned carbonizing process can transfer the substrate with the pristine membrane into carbon molecular sieve membrane, and can further modulate the fine structure in the membrane for improving the separation performance of the carbon molecular sieve membrane. According to this invention, carbon molecular sieve membrane, with high separation performance and high permeability and without defects, can be obtained by one time deposition-carbonization process. Comparing with the multiple polymer coating-carbonizing process in the prior art, the method of this invention can reduce the manufacturing time, save the energy and cost of the manufacturing, and produce less environmental waste. Preferably, the method of this invention is more simply operating than the manufacturing process in the prior art. More preferably, the carbon molecular sieve membrane fabricated by this invention can provide really good gas permeability and gas selectivity. Therefore, the method of this invention can help to increase industrial competitive ability.
The present disclosure can be described by the embodiments given below. It is understood, however, that the embodiments below are not necessarily limitations to the present disclosure, but are used to a typical implementation of the invention.
What probed into the invention is a method for fabricating carbon molecular sieve membrane. Detailed descriptions of the structure and elements will be provided in the following in order to make the invention thoroughly understood. Obviously, the application of the invention is not confined to specific details familiar to those who are skilled in the art. On the other hand, the common structures and elements that are known to everyone are not described in details to avoid unnecessary limits of the invention. Some preferred embodiments of the present invention will now be described in greater details in the following. However, it should be recognized that the present invention can be practiced in a wide range of other embodiments besides those explicitly described, that is, this invention can also be applied extensively to other embodiments, and the scope of the present invention is expressly not limited except as specified in the accompanying claims.
One preferred embodiment according to this specification discloses a method for fabricating carbon molecular sieve membrane. The mentioned method comprises performing a chemical vapor deposition (CVD) process to coat reacting monomer onto the surface of a substrate to form a pristine membrane, and performing a carbonizing process. In one preferred example of this embodiment, through the test result of gas separation, one deposition-carbonization process can provide the carbon molecular sieve membrane with very thin selective layer and without structure defects.
In one preferred example of this embodiment, the reacting monomer can be coated onto the surface of the substrate through Plasma-enhanced chemical vapor deposition (PECVD) process. In one preferred example, the power of the PECVD process is about 10-100 W. According to this embodiment, through the PECVD process, the reacting monomer can form a polymer pristine membrane on the surface of the substrate. Preferably, there exists excellent cross-linking property inside the pristine membrane, and there is great connection between the pristine membrane and the surface of the substrate.
Subsequently, the substrate with the pristine membrane is passed through a carbonizing process, as shown in the step 240, to produce the carbon molecular sieve membrane of this embodiment. In one preferred example of this embodiment, the temperature range of the mentioned carbonizing process is about 450-900° C. Preferably, in one preferred example, the temperature range of the mentioned carbonizing process is about 500-700° C. In one preferred example of this embodiment, the thickness of the mentioned carbon molecular sieve membrane is about 0.1-1.0 μm. In another preferred example of this embodiment, the thickness of the mentioned carbon molecular sieve membrane is about 0.2-0.6 μm. In still another preferred example of this embodiment, the thickness of the mentioned carbon molecular sieve membrane is about 200 nm. In one preferred example of this embodiment, the CO2/N2 gas selectivity of the mentioned carbon molecular sieve membrane is about 2.0-20. In one preferred example of this embodiment, the O2/N2 gas selectivity of the mentioned carbon molecular sieve membrane is about 5.0-15.
According to this embodiment, after the carbonizing process, the obtained carbon molecular sieve membrane is defect free, and can provide excellent gas permeability and selectivity, so that the mentioned carbon molecular sieve membrane can present excellent gas separating performance. Preferably, the mentioned carbon molecular sieve membrane does not have to perform multiple repeating times of coating-carbonizing process to erase the defects in the carbon molecular sieve membrane. In other words, comparing with the manufacturing process of carbon molecular sieve membrane in the prior art, the method for fabricating carbon molecular sieve membrane of this embodiment can save time and energy of the manufacturing process, and efficiently decrease the thickness of the carbon molecular sieve membrane.
The preferred examples of the structure and fabricating method for fabricating carbon molecular sieve membrane according to the invention are described in the following. However, the scope of the invention should be based on the claims, but is not restricted by the following examples.
Equipments:
1. Three-zone horizontal vacuum furnace: Thermal Fisher Scientific
2. plasma-enhanced chemical vapor deposition: assembled by Inventors
3. scanning electron microscope (SEM): Hitachi Co., Model S-3000N and FE-SEM Model S-4800
4. ATR-FTIR: Perkine Elmer, Miracle-Dou
5. X-ray Photoelectron Spectroscope (XPS): Thermo Fisher Scientific K-Alpha
6. Raman spectrum Analyzer: Coherent Innova 70
7. Gas Permeability Analyzer: Yanoco GTR-10
8. Gas Chromatography: Shimadzu Co., GC-14A
9. positron annihilation lifetime spectroscopy (PALS): assembled by Inventors
10. variable mono-energy slow positron beam (VMSPB): assembled by Inventors
Method for Fabricating Carbon Molecular Sieve Membrane:
A Example of the method for fabricating carbon molecular sieve membrane according to the invention are described in the following. However, the scope of the invention should be based on the claims, but is not restricted by the following examples.
After cleaning the surface of a ceramic substrate with air gun, the ceramic substrate is put into the center of a plasma reactor. When the plasma reactor is vacuumed to 0.045 torr with rotary pump, a cylinder with furfuryl alcohol (FA) monomer is opened, wherein the cylinder is put at 50° C. for at least one day. The pressure of entire system is controlled at about 0.2 torr. After opening the cylinder for 30 minutes, the ceramic substrate is performed a deposition process for 1 hour under the plasma power as 10 w to form a plasma deposition pristine membrane on the ceramic substrate.
The ceramic substrate with pristine membrane is subsequently passed through a carbonizing process in the three-zone horizontal vacuum furnace to produce the carbon molecular sieve membrane. The mentioned three-zone horizontal vacuum furnace has three heating zone. Those two side heating zones are used to keep the temperature of the central heating zone in consistency. The mentioned ceramic substrate with pristine membrane is put on a quartz boat, and the quartz boat is pushed to the central heating area by a quartz rod. After vacuumed to 10−2 torr for at least 8 hours, the temperature raising step of the carbonizing process is begun. When the carbonizing process is finished, the temperature is lowered by fixed speed cooling or natural cooling, and then the carbon molecular sieve membrane is obtained.
Polyfurfuryl alcohol (PFA) is directly coated onto a substrate by one time spin-coating to obtain the pristine membrane as the control group. We found that it is not easy to obtain a pristine membrane without defects through spin-coating process.
Table 1 shows the gas separation comparison between the membrane from one time spin-coating/carbonizing process, as shown in
Referred to Table 1, CPFA500 (1 layer) is the membrane obtained from one time spin-coating/carbonizing process in the prior art with PFA. CPFA (2 layers) is the membrane CPFA500 (1 layer) passed through another time spin-coating/carbonizing process in the prior art with PFA. FA-cp500 is the carbon molecular sieve membrane obtained from one time of plasma depositing/carbonizing process of this invention with FA as monomer, carbonizing temperature about 500° C. PFA (1 layer) is the carbon molecular sieve membrane obtained from one time spin-coating/carbonizing process with PFA as monomer. PFA (2 layers) is the carbon molecular sieve membrane obtained from two times of spin-coating/carbonizing process with PFA as monomer. FA-pristine is the pristine membrane obtained from one time plasma depositing procedure with FA as monomer. As shown in Table 1, the PFA membrane without carbonizing process is almost with no gas selectivity. And, the gas selectivity of the FAcp500 membrane obtained from the method of this invention is as good as the gas selectivity of the membrane passed through two times of spin-coating/carbonizing process.
After performing plasma depositing process with FA monomer, a continue plasma depositing layer with thickness about 1 μm is formed and entirely covered on the surface of a porous ceramic substrate, as shown in
The plasma depositing pristine membrane is individually passed through carbonizing process at 300° C., 500° C., and 700° C., and presented as cp300, cp500, and cp700. Referred to
The tendency of the thickness decreased also can be found in the spectrum of variable mono-energy slow positron beam (VMSPB) with depth profile measured by Doppler broadening energy spectroscopy, as shown in
Besides, from the surface image as shown in
The difference between the FA-pristine membrane before and after the carbonizing process can be observed by the ATR-FTIR spectrum in
Moreover, we also use X-ray Photoelectron Spectroscopy (XPS) for indentifying the surface element, and the result is shown as
From the Raman spectrums as shown in
The mentioned results can be connected with
In Table 2, FA-cp300, FA-cp500, FA-cp700 individually represent those carbon molecular sieve membranes consisted of FA monomer obtained from one time plasma depositing/carbonizing process of this invention, and the carbonizing temperature of FA-cp300, FA-cp500, FA-cp700 is respectively 300° C., 500° C., 700° C. The data of the membrane PFA-600 is extracted from the literature of Chengwen Song, Tonghua Wang, Xiuyue Wang, Jieshan Qiu, Yiming Cao, Preparation and gas separation properties of poly(furfuryl alcohol)-based C/CMS composite membranes, Separation and Purification Technology 58 (2008) 412-418. The data of the membrane VDP-600 is extracted from the literature of Huanting Wang, Lixiong Zhang, George R. Gavalas, Preparation of supported carbon membranes from furfuryl alcohol by vapor deposition polymerization, Journal of Membrane Science 177 (2000) 25-31. The data of the membrane cPFA500 is extracted from the literature of Clare J. Anderson, Steven J. Pas, Gaurav Arora, Sandra E. Kentish, Anita J. Hill, Stanley I. Sandler, GeoffW. Stevens, Effect of pyrolysis temperature and operating temperature on the performance of nanoporous carbon membranes, Journal of Membrane Science 322 (2008) 19-27.
Comparing the gas separation performance the carbon molecular sieve membrane consisted of FA monomer obtained from the method of this invention and the data of the carbon molecular sieve membrane made of PFA in literature, we find that the gas separation performances of the carbon molecular sieve membranes of this invention are better than that of the carbon molecular sieve membranes in literature, as shown in the above Table 2. The possible reasons are as the following. (1) During the manufacturing process in the prior art, the PFA solution is easily permeated into the pores of the substrate, and the resistance of the produced membrane will be increased. (2) Because the defects free carbon molecular sieve membrane of this invention is fabricated by one time plasma depositing/carbonizing process, not by multiple times coating/carbonizing process in the prior art, the resistance of the carbon molecular sieve membrane of this invention is lower than that of the composite membrane in the prior art. (3) In the fabricating method of this invention, during the plasma depositing process, the monomer will be cross-linked directly after the coating process. If necessary, more than one times of coating and cross-linking procedure can be performed. And the carbonizing process is finally performed. Oppositely, in the prior art, the manufacturing process is to repeat the PFA coating/carbonizing process for several times, and it can not be ensured that whether the carbonized composite membrane formed in the last procedure is better in the performance.
According to the above examples, it can be found that the fabricating method combining plasma depositing process with carbonizing process of this invention can provide defects free carbon molecular sieve membrane through one time depositing/carbonizing process. Therefore, comparing with the method in the prior art employing multiple times coating/carbonizing process to reduce defects, this invention provides a method for fabricating carbon molecular sieve membrane with more industrial competitive ability.
Because oxygen contained material will be released to form pores during the carbonizing process, the mentioned examples use FA as the monomer for plasma depositing onto a porous ceramic substrate to produce plasma deposited pristine membrane. And then, through carbonizing process, the chemical characteristics of the mentioned pristine membrane will be changed and the thickness of the membrane will be decreased, so that the gas separation performance will be increased.
From the SEM images and the spectra of variable monoenergy slow positron beam (VMSPB) measured by Doppler broadening energy spectroscopy in the above examples, it can be found that when the carbonizing temperature is higher, the thickness of the produced membrane will be decreased. The membrane surface is still defects free, and the gas resistance of the membrane can be decreased, so that the permeance can be improved.
From the XPS spectra and the Raman spectra in the above examples, it can be found that when the carbonizing temperature is higher than 500° C., the structure of the membrane is going to be inorganized and form graphite structure. The defects shown as the D band is also possible to increase the gas permeance. When the carbonizing temperature is 700° C., the thickness of the membrane is the thinnest one among those samples. But, from the S parameter of the selective layer, it can be seen that the pore size of membranes decreased, resulting in the gas permeance and the selectivity of the membrane are decreased at the same time.
The carbon molecular sieve membrane without defects obtained from one time of the process combining plasma depositing and carbonizing in the examples can provide excellent gas permeability and selectivity. The carbon dioxide permeance of the carbon molecular sieve membrane is 772.1 GPU, and the oxygen permeance of the carbon molecular sieve membrane is 150.6. The selectivity of carbon dioxide/nitrogen of the carbon molecular sieve membrane is 14.3, and the selectivity of oxygen/nitrogen of the carbon molecular sieve membrane is 2.8.
In summary, this invention has reported a method for fabricating carbon molecular sieve membrane. The method for fabricating carbon molecular sieve membrane comprises performing chemical vapor deposition (CVD) with reacting monomer to form a pristine membrane on a substrate, and then performing carbonizing. According to this invention, the mentioned chemical vapor deposition can be plasma enhanced chemical vapor deposition. As the disclosure of this specification, through combining the technology of chemical vapor deposition and carbonization, one time depositing/carbonizing process can produce a carbon molecular sieve membrane without defects and the thickness of the carbon molecular sieve membrane is ultra-thin. During the CVD process, the monomer is uniformly coated on the surface of the substrate and forming a pristine membrane. And, the surface of the mentioned pristine membrane does not have defects. Through the carbonizing process, the chemical characteristics of the pristine membrane will be changed, and the thickness of the pristine membrane will be decreased, so that the gas separating performance of the mentioned carbon molecular sieve membrane will be improved. The mentioned method for fabricating carbon molecular sieve membrane can provide the carbon molecular sieve membrane without defects through one time depositing/carbonizing process, and the carbon molecular sieve membrane can provide excellent gas permeability and separating performance. Comparing with the manufacturing method in the prior art to reduce the defects by operating multiple times of coating/carbonizing process, this invention provide a method to produce defects free carbon molecular sieve membrane, and the mentioned method can save more time and energy in the manufacturing process for forming the carbon molecular sieve membrane. Preferably, the carbon molecular sieve membrane of this invention is with the advantages of thin thickness, high gas permeance, and high gas selectivity. More preferably, in one preferred example of this invention, we also can perform multiple times of CVD to form pristine membranes on the substrate, and then perform a carbonizing process to form the carbon molecular sieve membrane, so that a membrane with more improved separating performance can be produced therefrom. More preferably, in another preferred example of this invention, the same or different monomer(s) can be employed in the multiple times CVD to form pristine membranes on the substrate, and then perform a carbonizing process to form the carbon molecular sieve membrane, so that a membrane with more improved characteristics can be obtained, wherein the mentioned carbon molecular sieve membrane, with the used monomer(s), can provide better separating performance, or can be applied in more kinds of gas separation. Therefore, this invention discloses a more simply operating, more economic manufacturing, more fast membrane forming, and more environmental friendly method for fabricating carbon molecular sieve membrane.
Obviously many modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the present invention can be practiced otherwise than as specifically described herein. Although specific embodiments have been illustrated and described herein, it is obvious to those skilled in the art that many modifications of the present invention may be made without departing from what is intended to be limited solely by the appended claims.