KR101763609B1 - Palladium deposited separation membrane having PBI based membrane support and method for preparing the same - Google Patents

Abstract

There is provided a palladium plating separator in which palladium is electroless plated with a polybenzimidazole based polymer membrane as a support and a method for producing the same. Accordingly, it is possible to provide a separation membrane excellent in hydrogen selectivity, hydrogen / carbon dioxide, or hydrogen / nitrogen selectivity. In addition, the defects can be reduced in the palladium-plated film, and the palladium particles can be uniformly distributed without agglomerate, and thus the hydrogen permeation performance can be improved.

Description

[0001] The present invention relates to a palladium-plated separator using a polybenzimidazole-based polymer membrane as a support and a method for preparing the same.

TECHNICAL FIELD The present invention relates to a palladium-plated separator having a polybenzimidazole-based polymer membrane as a support and a method for producing the same.

Hydrogen has recently gained attention as an alternative energy source to mitigate and solve environmental problems caused by fossil fuels. Technologies employed for hydrogen separation include solvent adsorption, pressure swing adsorption, cryogenic recovery, membrane separation, and the like.

In contrast to other approaches, membrane separation technology has great economic potential because it reduces operating costs, minimizes unit operations, and reduces energy consumption. In addition, as demand for high purity hydrogen increases, effective hydrogen separator development has attracted considerable interest in academia and industry.

Since the palladium membrane has a higher hydrogen solubility in a bulk state over a wide temperature range, it is likely to be used as a hydrogen separation membrane because of its excellent ability to transport hydrogen through the metal.

To date, various studies have been made to solve problems such as durability, hydrogen embrittlement, contamination by hydrocarbons or sulfides, and high cost of palladium, and accordingly, the industrial application of the palladium film is gradually increasing have.

However, it is still a challenge to produce palladium-based membranes with higher permeability and hydrogen selectivity with a thin, defect-free palladium layer with long-term thermal and chemical stability.

On the other hand, various methods for producing a palladium film are known.

The most common methods are electroless plating (ELP), chemical vapor deposition (CVD), physical vapor deposition (PVD), and electrodeposition (EPD).

Among these, electroless plating is most often used for palladium film production. The electroless plating method has the advantage that it is easily coated even in the case of materials having any form, is inexpensive, and uses a very simple device. However, electroless plating is disadvantageous in that it requires a series of pretreatment steps such as activation or sensitization before the final plating of the desired metal is performed, which is complex and time consuming.

In order to increase the adhesion between the metal layer and the substrate and to improve the thermal durability of the palladium composite membrane, a palladium composite membrane was prepared by electroless plating through osmosis in Varma's group 1, 2). In addition, a palladium composite membrane was also prepared by using a suction-assisted electoless deposition which is carried out in a plating process by evacuation from the backside of the porous support (Non-Patent Documents 3 and 4) .

By such a suction or osmotic gradient, good adhesion can be obtained between the palladium layer and the support and the durability of the film can be improved.

K.L. Yeung, A. Varma, Novel preparation technique for thin metal-ceramic composite membranes, AIChE J. 41 (1995) 2131. R.S. Souleimanova, A.S. Mukasyan, A. Varma, Effects of osmosis on microstructure of Pd-composite membranes synthesized by electroless plating technique, J. Membr. Sci. 166 (2000) 249. H. Chen, C. Chu, and T. Huang, Comprehensive characterization and permeation analysis of thin Pd / Al2O3 composite membranes prepared by suction-assisted electroless deposition, Sep. Sci. Technol. 39 (2004) 1461. D.A.P. Tanaka, M.A.L. Tanco, T. Nagase, J. Okazaki, Y. Wahui, F. Mizukami, T.M. Suzuki, Fabrication of hydrogen-permeable composite membranes packed with palladium nanoparticles, Adv. Mater. 18 (2006) 630. L.M. Robeson, The upper bound revisited, J. Membr. Sci. 320 (2008) 390-400.

In an exemplary embodiment of the present invention, in one aspect, there is provided a novel palladium plating membrane capable of improving hydrogen permeability or selectivity. In addition, another aspect of the present invention is to provide a novel palladium plating film excellent in hydrogen / carbon dioxide or hydrogen / nitrogen selectivity.

Further, according to the exemplary embodiments of the present invention, in another aspect, it is possible to reduce defects in the palladium plating film and to make the palladium particles uniformly distributed without agglomerate, And a method for producing a palladium-plated film.

Exemplary embodiments of the present invention provide a palladium-plated separator membrane in which a polybenzimidazole-based polymer membrane is used as a support and palladium is electroless plated on the support.

In one exemplary embodiment of the present invention, there is provided a process for producing a palladium-plated separator, which comprises using a polybenzimidazole-based polymer separation membrane as a support and electroless plating palladium on the support.

According to exemplary embodiments of the present invention, in one aspect, a novel palladium plating film having excellent hydrogen permeability or selectivity can be provided. Further, in another aspect, a novel palladium plating film excellent in hydrogen / carbon dioxide or hydrogen / nitrogen selectivity can be provided. In another aspect, it is possible to reduce the defects in the palladium-plated film and uniformly distribute the palladium particles without agglomerate, thereby making it possible to improve the hydrogen permeability and the like.

1 is a schematic view showing a vacuum electroless plating method used in an embodiment of the present invention.
2 is a schematic diagram showing a high temperature gas permeation setup used in one embodiment of the present invention.
3 shows an SEM image of the palladium film produced in one embodiment of the present invention. 3A shows electroless plating using a conventional electroless plating method for 1 hour (CELP [Fig. 3A], and Fig. 3B shows electroless plating using vacuum electroless plating for 1 hour. Vacuum electroless plating (VELP) [Fig. 3b].
4 is an SEM image showing the effect of the hydrazine amount on the microstructure of a palladium-plated film in one embodiment of the present invention.
Figure 5 is a graphical representation of H ₂ O ₂ SEM image of PBI-HFA membrane after activation according to presence or absence of surface treatment.
5A is a graphical representation of the H ₂ O ₂ The PBI-HFA film not subjected to the surface treatment is activated, and FIG. 5B shows the PBI-HFA film subjected to the surface treatment by activation treatment.
6 shows the surface treatment effect of the PBI-HFA film in one embodiment of the present invention.
FIG. 7 is a graph showing changes in hydrogen permeation (FIG. 7A) and general electroless plating (CELP), vacuum electroless plating (VELP) through a palladium coating film prepared by a general electroless plating (CELP) ) And a change in hydrogen permeation (FIG. 7B) through a palladium coating film prepared by a vacuum electroless plating (H-VELP) method on a PBI-HFA film treated with H ₂ O ₂ . And: (kg _f / cm ² unit), Y-axis and the X axis represents the hydrogen permeable Figure 7a the pressure difference in FIG. 7b: is (in cc / min).
FIG. 8a is a schematic view of an embodiment of the present invention in which a vacuum electroless plating (H-VELP) process is performed on a general electroless plating (CELP), a vacuum electroless plating (VELP) and a H ₂ O ₂ treated PBI- FIG. 2 is a graph showing the change in carbon dioxide permeation through the coated palladium coating film. FIG. FIG. 8B is a graph showing the H ₂ / CO ₂ selectivity coefficient obtained from the gas permeation experiment as a function of the pressure difference in the embodiment of the present invention.
FIG. 9 is a graph showing the H ₂ / CO ₂ selectivity coefficient obtained as a function of hydrogen permeation (unit: barrer) obtained from a gas permeation experiment of a palladium membrane produced by the H-VELP method according to an embodiment of the present invention. For reference, the upper limit of 2008 lines (upper bound) means the upper limit of the line time revealed the coefficient H ₂ / CO ₂ in the selection of the polymeric membrane by Robeson is presented as a function of the hydrogen permeable (non-patent document 5).

Hereinafter, exemplary embodiments of the present invention will be described in detail.

In the present specification, the general electroless plating means that Pd is formed by the reaction of only 2Pd ^{2 +} + N ₂ H ₄ + 4OH ^- -> 2Pd ⁰ + N ₂ + 4H ₂ O without using external pressure difference such as osmotic pressure or vacuum ≪ / RTI >

In the present specification, vacuum electroless plating means that by using a vacuum, the N ₂ gas generated in the above reaction can be efficiently removed from the PBI-HFA surface, thereby promoting the progress of the above reaction.

In one exemplary embodiment of the present invention, a palladium-plated polybenzimidazole-based separation membrane is provided by using a polybenzimidazole-based polymer separation membrane as a support and electroless-plating palladium on the support. Thus, the palladium-plated polybenzimidazole-based polymer membranes have gas-tight gas selectivity, hydrogen selectivity, H ₂ / CO ₂ and H ₂ / N ₂ gas selectivity. In addition, when palladium is electrolessly plated using a porous substrate as in the conventional techniques, the thickness of the palladium film is several tens of micrometers. In contrast, according to embodiments of the present invention, the polybenzimidazole- When palladium is electroless-plated, sufficient hydrogen selectivity, H ₂ / CO ₂ and H ₂ / N ₂ gas selectivity can be obtained even if the thickness of the palladium film is 1 μm or less.

In one embodiment, the polybenzimidazole-based polymer is not particularly limited, but hexafluoroisopropylidene may be bonded to the repeating unit of polybenzimidazole.

Specifically, the polybenzimidazole-based polymer may have the following formula (1).

[Chemical Formula 1]

이고, R은 수소, 메틸기, 네오펜틸기 및 벤질기 중에서 선택된 어느 하나일 수 있다.Here, Ar

And R may be any one selected from the group consisting of hydrogen, a methyl group, a neopentyl group and a benzyl group.

Also, in one embodiment, the surface of the polybenzimidazole-based polymer membrane is preferably surface-treated with hydrogen peroxide (H ₂ O ₂ ).

Since the surface of the polybenzimidazole-based polymer membrane is hydrophobic (for example, a contact angle of 85 ^{° C} ), it is possible to reduce the contact angle (water contact angle) before the surface treatment by surface treatment. Thereby reducing the grain size of the palladium-plated layer and decreasing pinholes (see Examples described later).

In one embodiment, the water droplet contact angle of the surface of the polybenzimidazole-based polymer membrane may be 20 to 85 ^{° C} , and preferably 70 ^{° C} or less.

In one embodiment, the hydrogen peroxide surface treatment preferably has a hydrogen peroxide concentration of 0.1 to 30 wt% and a hydrogen peroxide surface treatment time of 1 second to 2 hours, more preferably a hydrogen peroxide concentration of 10 wt% .

Also, in one embodiment, the palladium electroless plating is preferably performed by vacuum electroless plating.

When vacuum electroless plating (VELP) is used, a uniform microstructure can be obtained in which the palladium particles are packed without agglomerated Pd particles. In addition, since the palladium layer having such a microstructure can be more strongly anchored and bonded to the polybenzimidazole-based polymer as the support, there is no phenomenon such as delamination in general electroless plating (see Examples to be described later).

Further, in one embodiment, it is more preferable that the palladium electroless plating is surface-treated with hydrogen peroxide and then subjected to vacuum electroless plating (H-VELP). As a result, a palladium layer having a finer microstructure without pinholes can be obtained (see Examples described later).

For reference, the palladium plated film produced in one embodiment has a palladium plating layer thickness of about 250 nm and an effective permeable area of 8.3 cm ² .

In one embodiment, at least one of sensitization and activation may be performed on the polybenzimidazole-based polymer membrane prior to electroless plating after surface treatment of the polymer membrane. When performing the above sensing and activation, activation may be performed after the sensing, but is not limited thereto.

Sensitization is a process of sensitizing the polymer separator, including the above-mentioned method, thereby improving the plating efficiency and improving the selectivity.

The sensitization, for example, be carried out using SnCl ₂ solution and, for example, for the solution, for example, that the polymer membrane comprises a SnCl ₂ solution and an acid solution to the polymer membrane include SnCl ₂ and HCl For example. The pH of the solution used for the sensitization may be 4 to 5, and the immersion time may be 1 to 20 minutes, for example, 3 to 6 minutes.

The polymer separator may be immersed in the HCl solution for 1 to 30 seconds and then washed.

Activation is to activate the palladium plating by forming palladium nuclei on the surface of the polymer membrane. The plating efficiency can be improved by this, and the process speed can be improved and the selectivity can be improved.

The activation, for example, can be carried out using PdCl ₂ solution, for example a solution of the polymer membrane comprises a PdCl ₂ solution and an acid, for example be done by immersion in a solution containing PdCl ₂ and HCl . The pH of the solution used for the activation may be 4 to 5, and the immersion time may be 1 to 20 minutes, for example, 3 to 6 minutes.

Said sensitization and activation may be repeated one or more times, more than two times, for example two to three times, preferably two times. The selectivity can be improved by repeating the above patterning and activation, and hydrogen / carbon dioxide selectivity, hydrogen / nitrogen selectivity, particularly hydrogen / carbon dioxide selectivity at a middle temperature (100 ° C to 200 ° C) The selectivity can be improved.

The palladium-plated separator according to the exemplary embodiments of the present invention may be usefully used as a gas separation membrane, particularly as a hydrogen separation membrane capable of selectively separating hydrogen.

Hereinafter, specific embodiments according to embodiments of the present invention will be described in more detail. It should be understood, however, that the invention is not limited to the embodiments described below, but that various embodiments of the invention may be practiced within the scope of the appended claims, It will be understood that the invention is intended to facilitate the practice of the invention to those skilled in the art.

[Example: Preparation and characterization of palladium-plated film]

(1) Membrane Preparation

First, PBI-HFA membranes were prepared as follows.

4,4'- (hexafluoro-isopropylidene) bis (benzoic acid) [4,4 '- (hexafluoro-isopropylidene) bis (benzoic acid)] (HFA, 21.96 g) and 3,3'-diaminobenzidine (3,3'-diaminobenzidine) (DAB, 12 g) was dried under vacuum at 60 ° C for 3-4 days.

The dried HFA and DAB mixture was stirred in a round bottom flask at 100 < 0 > C under inert atmosphere in a round bottom flask using a mechanical stirrer, followed by addition of polyphosporic acid (600 g).

The resulting mixture was initially heated with stirring at 12O < 0 > C for 12 hours, and the temperature was slowly increased to 220 < 0 > C with continuous stirring for 5 hours to obtain a very high viscosity yellowish brown polymer mixture. After pouring the reaction mixture into water, a fibrous polymer was obtained. The precipitated polymer was washed with distilled water at < RTI ID = 0.0 > 60 C < / RTI > The polymer purification process was repeated several times. In order to remove residual phosphoric acid, further potassium hydroxide (1 M) washes were performed at 60 ° C for 2 hours, and filtering was performed with several successive washes with distilled water. The washed polymer was dried in vacuum 5 minutes preheated to 100 占 폚 to obtain a PBI-HFA membrane.

Prior to palladium plating, the surface of the PBI-HFA membrane support was sensitized and activated by continuous dipping in an activating solution (SnCl ₂ and PdCl ₂ ).

Each dipping was continued for 5 minutes and washed in deionized water.

Subsequently, the support was dried at 80 DEG C for 2 hours. The purpose of surface activation is to grow the palladium nuclei seeded on the surface. This initiates the autocatalytic process of the metastable palladium salt complex reduction on the PBI-HFA membrane surface. The sensitizing and activating composition is as shown in Table 1.

Sensitization solution Activation solution SnCl ₂ 1 g / l PdCl ₂ 0.1 g / l 10M HCl 1 ml / l 10M HCl 1 ml / l

For surface treatment, the surface of the PBI-HFA membrane was immersed in a 10 wt% H ₂ O ₂ solution for 1 minute before the activation process.

The electroless plating was carried out by immersing the PBI-HFA membrane support activated at 60 DEG C in a palladium plating bath. The palladium electrolytic bath used tetraamminepalladium (II) nitrate solution, ethylenediaminetetraacetic acid disodium salt (EDTA disodium salt) as the stabilizing agent and hydrazine as the reducing agent.

For reference, a typical plating bath composition is also shown in Table 2.

Electroless plating bath compositions _{(NH 3) 4 Pd (NO} 3) 2 10 g / l Na ₂ EDTA (0.1M) 70 g / l NH ₄ OH (25-30%) 200 ml / l H ₂ NNH ₂ (1M) 12.5 ml / l pH ~ 10.4 Temperature 60 ^o C

1 is a schematic view showing a vacuum electroless plating method used in an embodiment of the present invention.

As shown in Fig. 1, a vacuum was applied to both sides of the PBI-HFA film during palladium plating in a Pd bath for palladium plating. The bass is placed in a double boiler and heated by a heating source. Subsequently, the as-deposited Pd composite membrane was completely washed in deionized water maintained at 60 ° C., and was weighed overnight at 80 ° C. to measure its weight. Nitrogen permeation experiments were performed at room temperature and pressure differences of up to 4 bar to measure the gas tightness of the prepared membrane.

2 is a schematic diagram showing a high temperature gas permeation setup used in one embodiment of the present invention.

Referring to FIG. 2, permeation experiments were performed using a high temperature gas permeation cell (temperature control chamber) as shown in FIG. Specifically, a single gas controlled by a needle valve was injected into the polymer membrane, and the permeated gas flux was determined using a bubble flow meter (or flow indicator, FI). The pressure of the feed gas was regulated by a back-pressure regulator (P). The flux of pure gas was measured in the order of H ₂ , N ₂ , CO ₂ , and CO (99.9% purity) at various temperatures from 35 to 200 ° C. In all permeation tests, an operating pressure of 4 to 8 bar was adjusted using a pressure regulator (P).

As described above, a palladium-plated film was successfully prepared through an electroless plating method on a PBI-HFA support. Further, at 1 hour after the palladium plating, at the pressure differences of up to 35 DEG C and 4 bar, no nitrogen flow through the palladium plating film was detected. This means that the produced palladium-plated film is defect-free.

The thickness of the palladium-plated layer was about 250 nm as measured from the weight gain. The effective permeating area of the prepared membrane was 8.3 cm < ^{2 &} gt ;.

(2) Confirmation method of membrane microstructure

On the other hand, the surface morphology and cross-sectional structure of the palladium-plated films were examined through SEM (SEM; XL30 ESEM, Philips, Netherlands).

(3) Vacuum Electroless  Study on the vacuum effect of palladium plated films prepared by plating

The electroless plating of palladium is carried out with an autocatalytic reaction mechanism. This is initiated by the Pd nuclei seeded on the activated surface of the PBI substrate. This reaction involves an electron transfer reaction through the interface and an oxidation-reduction reaction. For reference, an autocatalytic reaction can be expressed as:

[Reaction Scheme 1]

2Pd ^{2 +} + N ₂ H ₄ + 4OH ^- -> 2Pd ⁰ + N ₂ + 4H ₂ O

That is, the palladium metal is plated on the nucleus and is grown. The deposition rate increases with the number of palladium sites (Pd sites) and exhibits autocatalytic behavior. During the plating, nitrogen gas was generated as bubbles.

3 shows an SEM image of the palladium film produced in one embodiment of the present invention.

FIG. 3A shows electroless plating (ELP) using electroless plating for 1 hour (FIG. 3A), and FIG. 3B shows electroless plating using vacuum electroless plating for 1 hour Vacuum electroless plating (VELP) [Fig. 3b].

Figure 3 shows that the microstructure of each membrane is different. That is, in Figure 3a, the film has noticeable defects and has a rough surface morphology. The defects are HFA-PBI membrane ^{(23 × 10 -6 K - 1} ) - is due to the thermal expansion coefficient difference between the palladium layer ^{(1 11.8 × 10 -6 K)} . The compressive residual stress is generated in the palladium layer due to the temperature difference between the plating and drying temperature and the room temperature. This compressive residual stress causes buckling and delamination of the palladium layer. The thickness of the palladium layer was about 232.5 nm and the deposition rate was 2.37 nm / min.

On the other hand, in the case of the palladium film prepared by using the vacuum electroless plating (VELP), a uniform microstructure was shown, and no delamination or buckling as shown in FIG. 3A was seen. (See FIG. 3B).

Uniform palladium particles having an average size of 0.2 占 퐉 were tightly packed to form a dense palladium film. Furthermore, the thickness of the palladium layer was 261 nm, and the vacuum electroless plating (VELP) deposition rate was 5.67 nm / min, 2.4 times faster than conventional electroless plating (ELP). Nevertheless, the palladium layer has some small pinholes visible and needs to be improved in some way. Accordingly, in one embodiment of the present invention, surface treatment with H ₂ O ₂ has been further improved to reduce the pinholes.

Table 3 150 ℃ and ^{_{8 kg f / cm 2 H 2}} , N 2, CO 2 and (ideal selectivity) and single gas permeation characteristics (single-gas permeability) select at least palladium plated PBI-HFA film for CO in .

P (H ₂₎ P (N ₂ ) P (CO ₂ ) P (CO) α (H ₂ / N ₂₎ α (H ₂ / CO ₂₎ α (H ₂ / CO) alpha (CO ₂ / N ₂ ) Example 1
(CELP) 238 7.35 44 0 32.4 5.4 ∞ 6 Example 2
(VELP) 223 6.43 39.7 0 34.7 5.6 ∞ 6.2 Example 3
(H-VELP) 247 0 34.8 0 ∞ 7.1 ∞ ∞

As shown in Table 3, the gas selectivities of palladium membranes prepared using vacuum electroless plating (VELP) under the same conditions were significantly higher when compared to palladium membranes prepared using conventional electroless plating (CELP) . And all the palladium membranes were not permeable to carbon monoxide. In addition, palladium membranes prepared by vacuum electroless plating (H-VELP) after surface treatment with H ₂ O ₂ did not transmit nitrogen as well as carbon monoxide.

The difference in hydrogen permeability is related to the microstructure of the palladium-plated membrane depending on the manufacturing method.

The vacuum is effective in causing the nitrogen gas produced during the plating process, which nitrogen gas causes a defect in the palladium film, to be removed from the surface of the film, thereby reducing the defects of the palladium film. Moreover, the vacuum can increase the deposition rate of the palladium and improve the adhesion between the palladium layer and the PBI.

In connection with this, since the electroless plating process is limited by mass transfer, it can provide additional driving force to improve mass transfer when vacuum is applied. In addition, the adhesion between the palladium layer and the PBI-HFA depends on mechanical bonding and anchoring effect. When the vacuum is applied, the dense palladium layer can be more strongly anchored to the PBI-HFA.

4 is an SEM image showing the effect of the hydrazine amount on the microstructure of a palladium-plated film in an embodiment of the present invention. For reference, hydrazine acts as a reducing agent in electroless palladium plating.

As the amount of hydrazine decreases, the tendency to grow in the form of nanowires decreases. In addition, it can be seen that the palladium electroless plating film has a more dense structure without pinholes as the amount of the reducing agent (hydrazine) decreases. It is believed that as the amount of hydrazine decreases, the plating rate decreases, resulting in a more dense microstructure.

(4) PBI - HFA  Examination of effect of surface treatment of membrane

The contact angle of the PBI-HFA surface without any treatment is 85 ^° C. When the surface was treated with 10 wt% H ₂ O ₂ , the PBI-HFA surface contact angle was reduced to 70 ^° and the hydrophilicity could be increased. In the H ₂ O ₂ solution, the PBI-HFA surface is attacked by hydroxyl radicals, becoming unstable, activated, and polarized. Therefore, the mutual interaction strength between the water molecule and the H ₂ O ₂ treated surface becomes much stronger than before treatment.

Figure 5, on the other hand, shows that in embodiments of the present invention, H ₂ O ₂ SEM image of PBI-HFA membrane after activation according to presence or absence of surface treatment. 5A is a graphical representation of the H ₂ O ₂ The PBI-HFA film not subjected to the surface treatment is activated, and FIG. 5B shows the PBI-HFA film subjected to the surface treatment by activation treatment.

Before electroless plating, the seeded PBI-HFA surface consisted of a small palladium nuclei. These nuclei are H ₂ O ₂ When the surface treatment was carried out, it was more uniformly distributed on the surface of PBI.

6 is an SEM image showing the surface treatment effect of the PBI-HFA film in one embodiment of the present invention.

6A shows the microstructure of a palladium-plated film made by vacuum electroless plating (VELP) on a PBI-HFA film. 3b. As mentioned above, the palladium layer has some small pinholes.

In a non-limiting embodiment of the present invention, an H ₂ O ₂ surface treatment is performed instead of an O ₂ plasma in order to perform a continuous plating process and reduce the manufacturing cost of a palladium plated film.

FIG. 6b shows that the palladium-plated film microstructure was prepared by vacuum electroless plating (VELP) on a PBI-HFA film treated with 10 wt% H ₂ O ₂ for 1 minute. The average particle size of the palladium-plated film was about 0.19 탆, and the palladium-plated film showed a finer microstructure as compared with the case where the surface treatment of H ₂ O ₂ was not performed. In addition, the corresponding palladium-plated PBI-HFA film (FIG. 6B) showed higher luster and excellent adhesion. In addition, the N ₂ leakage test also showed that the palladium-plated film was dense and free of pin-holes.

(5) Examination of hydrogen permeation performance through palladium plating membrane

The permeation of hydrogen through the dense palladium plating membrane of this embodiment follows a mechanism different from the conventional diffusion mechanism. This permeation mechanism is known as a solution-diffusion mechanism and involves the following steps.

(i) adsorption of gaseous hydrogen molecules on the high hydrogen pressure side of the high-hydrogen side membrane surface;

(ii) dissociation to atomic hydrogen;

(iii) dissolution of atomic hydrogen in the bulk metal;

(iv) diffusion of atomic hydrogen through the bulk metal;

(v) reforming and releasing hydrogen molecules from the low hydrogen pressure membrane surface.

These steps can be rate-limiting elements during hydrogen transfer through the membrane, respectively, but bulk atom diffusion is a rate-limiting factor for relatively thick palladium membranes (> 25 mm). On the other hand, in the case of thinner films and lower temperatures, the surface steps have a significant effect. When the surface reaction or mass transport is a rate-controlling step, the hydrogen permeation flux through the palladium-plated membrane is expressed by the following Henry's law .

=

(P_h-P_l)

=

(P _h -P _l )

및

는 각각 수소 투과 플럭스(hydrogen permeation flux) 및 수소 투과성(hydrogen permeance)을 나타낸다.

및

은 각각 고 수소압 및 저 수소압을 나타낸다. 표면으로의 또는 표면으로부터의 물질 전달 또는 해리 흡착(dissociative adsorption) 또는 결합 탈착(associative desorption)이 속도 결정 요소가 되는 경우에, 해당 과정들은 수소 분자의 농도에 비례하기 때문에 압력 지수(pressure exponent)의 예상 값은 1이다. (here,

And

Respectively denote hydrogen permeation flux and hydrogen permeance.

And

Denote the high hydrogen pressure and the low hydrogen pressure, respectively. In the case of mass transfer or dissociative adsorption or associative desorption to the surface or from the surface being the rate determining element, the processes are proportional to the concentration of hydrogen molecules, so that the pressure exponent The expected value is 1.

On the other hand, the hydrogen permeation flux is measured as a function of the pressure difference from room temperature to 200 DEG C using a single hydrogen gas. The hydrogen permeation flux was obtained from a bubble flow meter.

FIG. 7 is a graph showing changes in hydrogen permeation (FIG. 7A) and general electroless plating (CELP), vacuum electroless plating (VELP) through a palladium coating film prepared by a general electroless plating (CELP) ) And a change in hydrogen permeation (FIG. 7B) through a palladium coating film prepared by a vacuum electroless plating (H-VELP) method on a PBI-HFA film treated with H ₂ O ₂ . And: (kg _f / cm ² unit), Y-axis and the X axis represents the hydrogen permeable Figure 7a the pressure difference in FIG. 7b: is (in cc / min).

FIG. 7A is a graph showing the hydrogen permeation change as a function of the pressure difference through a palladium coating film produced by a general electroless plating (CELP) method of an embodiment of the present invention. FIG.

Referring to Figure 7a, as expected, a high hydrogen permeation flux was obtained at higher pressures. The hydrogen permeation flux showed a linear relationship with the hydrogen pressure difference. This indicates that the step of determining the rate of hydrogen permeation in the palladium plated film is the process of bonding hydrogen atoms on the surface or the process of hydrogen molecule diffusion from the surface to the surface.

Figure 7b illustrates a palladium membrane fabricated with vacuum electroless plating (H-VELP) on a conventional electroless plating (CELP), vacuum electroless plating (VELP) and a PBI- HFA membrane treated with H ₂ O ₂ Is a graph showing the hydrogen permeation change as a function of the pressure difference. The H-VELP palladium membrane showed higher hydrogen permeability than the other two cases. The difference in hydrogen permeability is related to the microstructure of the palladium membranes fabricated by different methods. The lattice defects, grain boundaries and microvoids act as hydrogen traps, Slowing permeation and increasing activation energy for diffusion. Some small pinholes shown in Figure 6a may act as hydrogen traps. Thus, in some embodiments of the present invention, hydrogen permeation of the palladium-plated separator improves by reducing hydrogen traps.

(6) Selectivity Coefficient Review

The selectivity coefficient, α, is a commonly used index to indicate membrane separation performance. The selectivity factor is defined as the ratio of the permeation fluxes of the pure gas through the membrane. Therefore, the selectivity of hydrogen (H ₂ ) to carbon dioxide (CO ₂ ) is as follows.

_{α (H 2 / CO 2)} = J H2 / J CO2

The selectivity factor represents the ideal separation performance derived from a single gas permeation and is the ratio of the permeability of the gas converted to Barrer units.

FIG. 8a is a schematic view of an embodiment of the present invention in which a vacuum electroless plating (H-VELP) process is performed on a general electroless plating (CELP), a vacuum electroless plating (VELP) and a H ₂ O ₂ treated PBI- FIG. 2 is a graph showing the change in carbon dioxide permeation through a palladium coating film as a function of pressure difference. FIG. 8B is a graph showing the selectivity coefficient obtained from the gas permeability test as a function of the pressure difference in an embodiment of the present invention.

The permeability of the H-VELP palladium membrane was clearly lower than that of the other two membranes. As a result, the best H ₂ / CO ₂ gas separation performance was shown (FIG. 8B).

9 is a graph showing the H ₂ / CO ₂ selectivity coefficient obtained as a function of hydrogen permeability (unit: barrer) obtained from a gas permeation experiment of a palladium membrane produced by the H-VELP method conducted in the embodiment of the present invention 9 is a palladium-plated film of Examples, and black is a pre-palladium-plated film).

There is no previous report on the H ₂ / CO ₂ gas separation performance for palladium plated membranes. In this example, the palladium plated membrane showed gas separation performance over the upper limit of Robeson at most temperatures. In addition, since the palladium-plated film produced by the H-VELP method does not permeate nitrogen, the H ₂ / N ₂ gas separation characteristics needless to say exceed the upper limit of Robeson.

(7) activartion iteration

4,4'- (hexafluoro-isopropylidene) bis (benzoic acid) [4,4 '- (hexafluoro-isopropylidene) bis (benzoic acid)] (HFA, 21.96 g) and 3,3'-diaminobenzidine (3,3'-diaminobenzidine) (DAB, 12 g) was dried under vacuum at 60 ° C for 3-4 days.

The dried HFA and DAB mixture was stirred in a round bottom flask under an inert atmosphere at 100 < 0 > C for 40 minutes using a mechanical stirrer, followed by addition of polyphosporic acid (600 g).

The resulting mixture was initially heated with stirring for 12 hours at 150 占 폚, and the temperature was slowly increased to 220 占 폚 while continuously stirring for 5 hours to obtain a very high viscosity yellowish brown polymer mixture. After pouring the reaction mixture into water, a fibrous polymer was obtained. The precipitated polymer was washed with distilled water at < RTI ID = 0.0 > 60 C < / RTI > The polymer purification process was repeated several times. In order to remove residual phosphoric acid, further potassium hydroxide (1 M) washes were performed at 60 ° C for 2 hours, and filtering was performed with several successive washes with distilled water. The washed polymer was dried in a vacuum oven preheated to 100 DEG C to obtain a polybenzimidazole-based polymer membrane (PBI-HFA membrane).

The obtained PBI-HFA membrane was surface-treated by immersing the surface of the PBI-HFA membrane in a 10 wt% H ₂ O ₂ solution for 1 minute.

The surface treatment film on SnCl ₂ 1g / l and 10M HCl 1ml / l solution is drawn closed by dipping for 5 minutes. Washed for 5 minutes in distilled water, and then immersed in 0.1 g / l PdCl ₂ and 1 ml / l solution of 10 M HCl for 5 minutes to activate. The sensitization and activation were repeated two times (Example 4) or three times (Example 5).

The palladium electrolytic bath for the palladium plating of the above Table 1 was heated and maintained at 60 DEG C, and then the activated PBI-HFA membrane was immersed. Immediately after adding hydrazine 12.5 ml / l, palladium plating was carried out on both sides of the PBI- Vacuum was applied and the plate was plated at a vacuum degree of -0.45. Vacuum was applied to both sides of the PBI-HFA film during the palladium plating. The bass is placed in a double boiler and heated by a heating source. Subsequently, the as-deposited Pd composite membrane was thoroughly washed with deionized water maintained at 60 ° C and dried overnight at 80 ° C to prepare palladium-plated separators of Examples 4 and 5.

(8) Examination of gas permeability and selectivity

The palladium-plated separator prepared in (7) above was tested for gas permeability in the same manner as in the above (1) and (3), and the single gas permeability and selectivity were measured and the results are shown in Table 4 below.

- Gas permeation experiment: The permeation experiment was carried out using a high temperature gas permeation cell (temperature control chamber) as shown in FIG. Specifically, the gas permeability was measured after 1 hour of palladium plating at 35 ° C to 200 ° C and pressure differences of 4 to 8 bar. A single gas controlled by a needle valve was injected into the separator and the permeated gas flux was measured using a bubble flow meter (or flow indicator, FI). The pressure of the feed gas was regulated by a back-pressure gauge (P). The flux of pure gas was measured in the order of H ₂ , N ₂ , CO ₂ , and CO (99.9% purity) at various temperatures from 35 to 200 ° C. In all permeation tests, an operating pressure of 4 to 8 bar was adjusted using a pressure regulator (P). The thickness of the palladium-plated layer was about 250 nm as measured from the weight gain. The effective permeating area of the prepared membrane was 8.3 cm 2.

Gas permeability: The gas permeability was calculated from the gas permeation test results and the single gas permeability of hydrogen, nitrogen and carbon dioxide for the palladium-plated separator measured at 150 ° C and 8 kgf / Respectively.

Wherein a unit of gas permeability of Barrer (1 Barrer = 1 × 10 -10 cm 3 (STP) cm cm -2 s -1 cmHg - 1) , and, Q is the volumetric flow rate of gas (volumetric flow rate, cm ³ ( A is the effective area of the film (㎠), T is the operating temperature (K), and ΔP is the pressure difference across the membrane (cmHg).

- Selectivity: Hydrogen / nitrogen, hydrogen / carbon dioxide, hydrogen / carbon monoxide, carbon dioxide / nitrogen selectivity were calculated from the above gas permeability by the following formulas and shown in Table 4 below.

? (A / B) = (gas permeability of A) / (gas permeability of B)

P (H ₂₎ P (N ₂ ) P (CO ₂ ) P (CO) α (H ₂ / N ₂₎ α (H ₂ / CO ₂₎ α (H ₂ / CO) alpha (CO ₂ / N ₂ ) Example 4
(2 activations) 200.93 7.47 8.9 - 26.9 22.58 - 1.19 Example 5
(3 activations) 216.65 12.71 34.2 - 17.05 6.33 - 2.69

From the results in Table 4, it can be seen that when the activation is repeated two or more times, the hydrogen selectivity is remarkably increased as compared with the case where the activation is performed once. In particular, the hydrogen / carbon dioxide selectivity is very remarkable when the activation is carried out twice.

Claims (19)

Using a polybenzimidazole-based polymer membrane as a support,
The surface of the polybenzimidazole-based polymer membrane was surface-treated with hydrogen peroxide (H ₂ O ₂ )
And electroless-plating palladium on the surface-treated support,
Wherein the polybenzimidazole-based polymer has a structure represented by the following formula (1): < EMI ID =
[Chemical Formula 1]

Here, Ar

, And R is any one selected from the group consisting of hydrogen, a methyl group, a neopentyl group and a benzyl group.
delete delete delete The method according to claim 1,
Wherein the hydrogen peroxide concentration is 0.1 to 30 wt%, and the hydrogen peroxide surface treatment time is 1 second to 2 hours.
The method according to claim 1,
Wherein the palladium electroless plating is a vacuum electroless plating.
delete The method according to claim 1,
And performing at least one of sensitization and activation of the support before the electroless plating after the surface treatment.
9. The method of claim 8,
The sensitization method is a palladium-coated membrane, comprising immersing the support into the solution containing the acid and SnCl _2.
9. The method of claim 8,
The activation method for producing a palladium-coated membrane, comprising immersing the support in a solution containing PdCl ₂ and an acid.
9. The method of claim 8,
Wherein the activation is performed two or more times.
Using a polybenzimidazole-based polymer membrane as a support,
The support has a palladium plating layer on which palladium is electroless plated,
The palladium plating layer is a palladium plating separator having a microstructure of palladium particles packed therein,
The polybenzimidazole-based polymer has a structure represented by the following Formula 1:
[Chemical Formula 1]

(Wherein Ar is

And R is any one selected from a hydrogen, a methyl group, a neopentyl group and a benzyl group)
Wherein the surface of the polybenzimidazole-based polymer membrane is surface-treated with hydrogen peroxide (H ₂ O ₂ ) and then plated.
delete delete 13. The method of claim 12,
Wherein the polybenzimidazole-based polymer membrane has a water contact angle of 20 to 70 ^° .
delete 13. The method of claim 12,
Wherein the polybenzimidazole-based polymer membrane is treated with at least one of sensitization and activation before plating after surface treatment.
18. The method of claim 17,
Wherein the polybenzimidazole-based polymer membrane has palladium nuclei (seeds) formed on its surface.
The method according to any one of claims 12, 15, 17, and 18,
A palladium-plated separator characterized in that the polybenzimidazole-based polymer membrane and the palladium plating layer are anchored.

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