CN100563801C - A kind of preparation method of multi-channel hydrogen permeable palladium composite membrane - Google Patents

Abstract

The invention relates to a chemical plating preparation method of a multi-channel palladium composite membrane, which is a high-efficiency hydrogen permeable membrane for hydrogen separation and purification. Firstly, wrapping the outer side of a carrier by using a plastic or rubber material, then placing a plating solution in a channel of the carrier, adding a reducing agent into the plating solution, and stirring the plating solution by using a gas bubbling method. The method is simple to operate, effectively realizes uniform growth of the film layer, and ensures the compactness and the adhesive force of the palladium film. The coating can be carried out at room temperature, and the emission of toxic gas is reduced.

Description

A kind of preparation method of multi-channel hydrogen permeable palladium composite membrane

Technical field:

The invention relates to a method for preparing a multi-channel palladium composite membrane. The prepared palladium membrane can provide a larger membrane area and is especially suitable for a hydrogen membrane separator.

Background technique:

Palladium and palladium alloy membranes have excellent hydrogen permeability and can be used for the separation and purification of hydrogen. For example, the process of producing high-purity hydrogen by palladium-silver alloy membrane filtration has a history of decades. Research and development in recent years has mainly focused on palladium composite membranes, that is, ultrathin palladium membranes deposited on porous materials to replace traditional self-supporting palladium membranes. In this way, on the one hand, the thickness of the membrane can be greatly reduced, saving precious metal palladium; on the other hand, the permeability of hydrogen gas has been greatly improved [Huang Yan, Li Xue, Fan Yiqun, Xu Nanping. Research progress of hydrogen permeable palladium composite membrane: principle, preparation and Characterization. Advances in Chemistry, 2006, 18(2-3): 230-238]. There are many carrier materials for palladium membranes, but they are mainly porous ceramic tubes and porous stainless steel tubes, among which the former is the most widely used, which is mainly due to its excellent chemical stability and mature preparation process. At present, the main use of porous ceramic tubes is filter elements, which have two types of single-channel and multi-channel. Among them, the porous ceramic filter elements used in large-scale commercial filters are mainly multi-channel, which is obviously due to the filter element per unit volume. High filter surface. The palladium film ceramic carriers involved in the existing literature and patent reports are almost all single-channel type, and the palladium film is either plated on the outside or inside of the ceramic tube. Since the membrane area of each single-channel palladium composite membrane is limited, although the membrane area can be increased simply by increasing the number of membrane tubes, this increases the space occupied by the membrane tubes, increases equipment investment and increases installation costs. and monitoring difficulties. Based on the above reasons, the new palladium membrane with multi-channel porous ceramics as the carrier will have a better application prospect, and its working method is generally shown in Figure 1. The high-pressure mixed gas is introduced from one end of the channel, the hydrogen gas escapes through the palladium membrane along the channel wall of the carrier to obtain pure hydrogen, and the residual gas is discharged from the other end of the channel.

Since the unit volume of the multi-channel palladium membrane can provide a larger membrane area, the hydrogen separator can be made smaller while ensuring the hydrogen flux, and is especially suitable for portable or on-site hydrogen production devices. In addition, the multi-channel type palladium membrane is an inner membrane type, and its ultra-thin metal layer is not easily damaged during mounting operations. However, the channel of the multichannel ceramic carrier has a huge aspect ratio (that is, the ratio of the length of the channel to the diameter of the channel), which brings great difficulties to the preparation of the palladium membrane. Therefore, the preparation of the multichannel palladium membrane is whether it can be obtained. key to successful application.

There are many preparation techniques for supported palladium films in the literature, such as electroless plating, electroplating, PVD, CVD, high velocity oxygen flame (HVOF) thermal spraying, magnetron sputtering, plasma spraying, and photocatalytic methods. etc. Among them, electroless plating has been recognized as the most successful process. The principle is to first deposit a layer of metal particles on the surface of porous ceramics as a catalyst (i.e., surface activation), and after immersing in the plating solution, under the action of a reducing agent, these catalysts can catalyze the reduction of palladium ions in the plating solution and make the generated metal palladium Covering the surface of these catalyst particles, the generated metal palladium layer can still continue to catalyze the above reaction, thereby causing the growth and thickening of the palladium layer until the reaction stops. Therefore, electroless plating is also called self-catalytic plating. Electroless plating generally includes four steps of carrier pretreatment, surface activation, electroless plating, and post-treatment. There are many surface activation methods, but most of them are to deposit metal palladium particles on the surface of the carrier, and the more commonly used method is the SnCl ₂ /PdCl ₂ method. Most of the literature adopts higher electroless plating temperature, on the one hand, it will lead to the rapid decomposition of ammonia water in the plating solution, on the other hand, it will cause the discharge of ammonia gas and toxic hydrazine vapor, causing environmental pollution; this patent is aimed at multi-channel palladium membrane The key issues in the preparation of electroless plating and an effective preparation process are proposed.

The porous ceramic carrier is a multi-channel type, and its channels are thin and long, making it difficult to coat. The main problems are: the mass transfer of palladium ions and reducing agents can easily lead to the thick orifice of the palladium membrane and the thin middle, and the local reaction is too fast, resulting in the precipitation of palladium; a large number of nitrogen bubbles generated during the reaction process adhere to the palladium layer surface, which hinders the uniform growth of the palladium layer; after the porous carrier contacts the plating solution, the plating solution will enter the hole wall, and if the gas generated in the plating solution cannot be discharged in time, it will bring the palladium film on the surface of the channel. The pressure will damage the adhesion of the palladium membrane in light cases, and cause blistering or even rupture of the palladium film in severe cases.

Invention content:

The purpose of the present invention is to overcome the problems of high temperature, toxic hydrazine vapor discharge, and difficult coating in the prior art, and propose a bubbling method in which the carrier is wrapped outside and the plating solution is placed inside the carrier channel. A method for preparing a multi-channel palladium composite membrane.

The technical scheme of the present invention is: during the electroless plating process, the removal of the nitrogen generated by the reaction can be realized by vigorously stirring the plating solution, and the methods include mechanical stirring, pump circulation of the plating solution, and rotation of the carrier. However, the conventional stirring method cannot stir the plating solution in the elongated channel, which is obviously not as good as the stirring effect caused by the reciprocating movement of the carrier in the plating solution in the axial direction, because this can cause the plating solution to quickly wash the carrier channel , not only ensures the uniformity of the concentration of the plating solution, but also helps the nitrogen bubbles generated by the reaction to leave the metal surface quickly. During electroless plating, the carrier is wrapped outside, and the plating solution is placed inside the channel of the carrier, so that the plating solution forms a good contact with the channel of the carrier, and the plating solution exerts a certain pressure on the channel wall of the carrier.

In the present invention, the reducing agent hydrazine is not mixed with the palladium complex ion plating solution in advance, but slowly added to the plating solution with a pump. In the initial stage of the reaction, the concentration of palladium complex ions in the plating solution is high, and the addition of reducing agent needs to be controlled to prevent the reaction speed from being too fast to generate palladium precipitation. As the reaction progresses, the concentration of palladium complex ions decreases, and the addition of the reducing agent can be appropriately accelerated to maintain a faster reaction rate. At the end of the reaction, palladium complex ions are exhausted, and excess reducing agent can be added to ensure the conversion rate of palladium. Experiments have found that this method can achieve almost 100% palladium conversion rate, avoiding the waste of precious metal palladium, and the total amount of palladium in the film layer can be estimated according to the feeding amount of the plating solution, so that the film thickness can be further estimated.

Concrete technical scheme of the present invention is:

A method for preparing a multi-channel hydrogen-permeable palladium composite membrane. The specific steps include four steps of carrier pretreatment, surface activation, electroless plating, and post-treatment. It is characterized in that after the inner surface of the multi-channel carrier is activated, the outer surface of the carrier is first Wrapping with plastic or rubber material to prevent the leakage of the plating solution, and then placing the plating solution in the channel of the carrier; then adding the reducing agent to the plating solution; stirring the plating solution by bubbling the gas through the channel.

Wherein the multi-channel carrier is a multi-channel ceramic carrier; the number and shape of the channels of the multi-channel carrier are not limited, and the ratio of the length to the diameter of the carrier is between 1-60, preferably 1-30.

The gas is nitrogen, compressed air, oxygen or argon, etc., and the stirring of the plating solution is realized by bubbling through the channels.

In the present invention, the reducing agent is not added to the plating solution before the electroless plating starts, but is added to the plating solution with a pump after the plating solution is added in the carrier channel. The adding speed of reducing agent is controlled at 0.05-5ml/min. In the commercial preparation process, in order to save time, the addition rate of the reducing agent may not be as constant as that in the laboratory. In the initial stage of the reaction, the concentration of palladium complex ions in the plating solution is high, so it is necessary to control the amount of the reducing agent added to prevent the reaction speed. Palladium precipitates too quickly. As the reaction progresses, the concentration of palladium complex ions decreases, and the addition of the reducing agent can be appropriately accelerated to maintain a faster reaction rate. At the end of the reaction, palladium complex ions are exhausted, and excess reducing agent can be added to ensure the conversion rate of palladium.

The palladium plating solution of the present invention is: based on the total volume of the plating solution, the addition of Pd ²⁺ is the palladium salt of 0.006-0.06mol/L, the ethylenediaminetetraacetic acid salt of 30-100g/L, 100-500ml/L ammonia water; the reducing agent is N ₂ H ₄ with a concentration of 0.2-2M; the above-mentioned palladium salt is palladium chloride, palladium acetate, palladium nitrate or palladium sulfate; the ethylenediaminetetraethylene The acid salt is disodium edetate, dipotassium edetate or diammonium edetate.

Electroless coating can also be repeated many times, generally divided into 2-10 times. Before updating the plating solution, turn the carrier upside down to ensure uniform coating. The temperature of electroless plating is 10-50°C

The pretreatment, surface activation and posttreatment procedures of the present invention are operated according to the prior art, and the present invention, like other electroless plating processes, has no special requirements for the pretreatment and surface activation of the carrier. The most commonly used surface activation method is the SnCl ₂ /PdCl ₂ method; or a Pd(OH) ₂ colloid activation method invented by our research group [Huang Yan, Fan Jingjing, Hu Xiaojuan, patent application number 200710022996.6].

The concrete steps of the preparation method of the multi-channel type palladium composite membrane provided by the present invention are described below:

A. The selected channel porous ceramic carrier adopts conventional methods to activate the inner surface of the carrier channel;

B. As shown in Figure 2, wrap the outside of the activated carrier 1 with plastic or rubber material, connect a section of silicon rubber tube 2, 3 at both ends, seal the lower end of the tube 3 and connect it to the pipeline 4, the latter gas source 7 Connect and control the flow of nitrogen gas to 20-200ml/min through the needle valve 5. The plating solution 6 (with different lengths and different amounts of plating solution) is injected from the mouth of the silicone rubber tube 2, so that the carrier channel is completely filled with the plating solution 6. Due to the bubbling effect of the bottom gas 7, the plating solution 6 is well stirred. A reducing agent 8 is added to the plating solution 6 through a pump 9;

C. After the primary coating is finished, the carrier 1 is turned upside down, and the plating solution 6 is renewed to carry out the electroless plating reaction. In the future, the carrier 1 will be turned upside down once before the plating solution 6 is updated each time to ensure uniform coating; it can also be completed in one coating;

D. After fully rinsing the prepared palladium membrane with deionized water, soak it in ethanol for 20-100 min, and finally dry it overnight at 100-200°C.

The technical ideas proposed by the present invention are not limited to the preparation of metal palladium films, but can also be used in the preparation of other metal films or alloy films, such as Ag, Pt, Cu, Ni films, Ni-P, Ni-B alloy films, etc. The invention can not only prepare dense composite membranes, but also obtain porous composite membranes, which can be used as catalysts.

What needs to be emphasized here is that the multi-channel ceramic carrier involved in this patent does not include the short and thick carrier with a small aspect ratio. Although it is relatively easier to prepare short, thick and multi-channel palladium membranes by using the present invention, each membrane module can provide limited membrane area and relatively large mass transfer resistance, making it difficult to have commercial practical value.

Beneficial effect:

The electroless plating method provided by the invention solves the difficult problem of preparing multi-channel palladium composite membranes. The electroless plating reaction can be carried out at room temperature, which not only makes the operation more convenient, but also reduces the emission of toxic gases. The invention also effectively realizes the uniform growth of the film layer and ensures the compactness and adhesion of the palladium film. The conversion rate of palladium in the plating solution is close to 100%.

Description of drawings:

Figure 1 is a working principle diagram of a hydrogen separator based on a multi-channel palladium composite membrane, where A is feed gas, B is hydrogen, and C is tail gas.

Fig. 2 is the used electroless plating device figure of the present invention, and wherein 1 is a multichannel ceramic carrier, 2, 3, 4 are silicon rubber tubes, 5 is a needle valve, 6 is a plating solution, 7 is a gas, and 8 is a reducing agent, 9 is a peristaltic pump.

Fig. 3 is a photo showing the multi-channel palladium composite membrane prepared by the present invention, wherein D is a channel, E is a palladium film layer, and F is a carrier layer.

Fig. 4 is a metallographic micrograph showing the section of the multi-channel palladium composite membrane prepared by the present invention.

Fig. 5 is a surface electron micrograph showing the multi-channel palladium composite membrane prepared by the present invention.

Detailed ways:

The number and shape of multi-channel porous ceramic channels applicable to the present invention are not limited. Typical porous ceramic tubes on the market have 7, 19, 34 channels, etc., and the channel shapes are circular, hexagonal, etc.

Embodiment one:

(1). The selected porous ceramic carrier has an average pore diameter of 0.2 μm, 19 channels, an outer diameter of 30 mm, and a length of 5 cm. The channels are circular and the channel diameter is 4 mm.

(2). Wash the multi-channel ceramic carrier with a commercially available detergent solution, and then rinse with water.

(3). Use the conventional SnCl ₂ /PdCl ₂ method to activate the inner surface of the channel, wherein the sensitization solution contains SnCl ₂ ·2H ₂ O 5g/L, concentrated hydrochloric acid 1ml/L; the activation solution contains PdCl ₂ 0.2g/L L, concentrated hydrochloric acid 1ml/L. Wrap the outer surface of the carrier with polytetrafluoroethylene tape, first dip in the sensitizing solution and rinse with water, then dip in the activation solution and rinse with water. Sensitization——After 5 times of activation treatment, disassemble the PTFE tape and soak it in water for 1 hour.

(4). As shown in Figure 2, the electroless plating reaction temperature is 20°C. Wrap the outside of the activated carrier 1 with polytetrafluoroethylene tape again, and connect a section of silicon rubber tube 2 and 3 to each end, and the lower end of the tube 3 is sealed and connected to the pipeline 4, which is connected to the nitrogen cylinder and passed through a needle Valve 5 controls the nitrogen flow rate to be 60ml/min. 65ml of the plating solution 6 is injected through the mouth of the silicone rubber tube 2, so that the carrier channel is completely filled with the plating solution 6. The composition of plating solution 6 is: PdCl ₂ 5g/L, concentrated ammonia water 250ml/L, Na ₂ EDTA 70g/L. Due to the bubbling effect of the nitrogen gas 7 at the bottom, the plating solution 6 is well stirred. The reducing agent 8 is 0.2 mol/L N ₂ H ₄ solution, the adding speed of the reducing agent is 0.08ml/min, and it is added into the plating solution 6 through the peristaltic pump 9 until the palladium ions in the plating solution are completely converted.

(5). The carrier 1 is turned upside down, and the plating solution 6 is renewed to carry out the electroless plating reaction. Afterwards, the carrier 1 is inverted once before the plating solution 6 is updated each time, so as to ensure uniform coating.

(6). When the theoretically calculated palladium film thickness is 6 μm, stop the electroless plating. The prepared palladium membrane was fully rinsed with deionized water, soaked in absolute ethanol for half an hour, and finally dried overnight at 120°C. The airtightness of the palladium membrane is measured by nitrogen gas, and the nitrogen flux is close to 0 under the pressure of 1 bar.

Embodiment two:

The operation method is the same as in Example 1, but the length of the porous ceramic carrier selected is 11 cm, and the composition of the plating solution is: Pd(C ₂ H ₃ O ₂ ) ₂ 3g/L, concentrated ammonia water 150ml/L, K ₂ EDTA 50g/L. The total amount of plating solution used is 530ml, and the thickness of the palladium film produced is about 5 μm.

Embodiment three:

Same as Example 1, but the length of the porous ceramic carrier selected is 50cm, _the electroless plating reaction temperature is 35°C, the reducing agent is 0.2mol/L _N2H4 solution, the gas flow rate is 70ml/min, and the reducing agent addition rate is 0.1 ml/min, the bubbling gas at the bottom is argon, the total usage of the plating solution is 3000ml, and the thickness of the prepared palladium film is about 6.2 μm.

Embodiment four:

Same as Example 1, but the selected porous ceramic carrier has a length of 20 cm, 37 channels, a channel diameter of 40 mm, and a single hole diameter of 3.6 mm; the reducing agent is 0.5 mol/L N ₂ H ₄ , and the addition rate is 0.12 ml/min; In the later stage of a coating, the adding rate of the reducing agent is 0.5ml/min. The total amount of plating solution used is 1850ml, and the thickness of the palladium film produced is about 5.5 μm.

Embodiment five:

Same as Example 1, but the selected porous ceramic carrier has a length of 20 cm, 7 channels, a channel diameter of 30 mm, and a single hole diameter of 6 mm. The total amount of plating solution used is 630ml, and the thickness of the palladium film produced is about 6um.

The above embodiments are only used to illustrate the present invention, and any equivalent changes made without departing from the spirit of the present invention belong to the scope of the claims of the present invention.

Claims (9)

1. A method for preparing a multi-channel hydrogen-permeable palladium composite membrane, comprising four steps of carrier pretreatment, surface activation, electroless plating, and post-treatment, characterized in that in the electroless plating step, the inner surface of the multi-channel carrier is activated Finally, wrap the outer side of the carrier with plastic or rubber material to prevent the leakage of the plating solution, then place the plating solution in the channel of the carrier; then add the reducing agent to the plating solution with a pump, the adding speed of reducing agent The control is at 0.01-5ml/min; the plating solution is stirred by gas bubbling through the channel, and the flow rate of the bubbling gas is 20-200ml/min. 2. The preparation method according to claim 1, characterized in that the multi-channel carrier is a multi-channel ceramic carrier. 3. The preparation method according to claim 1, characterized in that the number and shape of the channels of the multi-channel carrier are not limited, and the ratio of the length to the diameter of the carrier is 1-60. 4. The preparation method according to claim 1, characterized in that the ratio of the length to the diameter of the multi-channel carrier is 1-30. 5. The preparation method according to claim 1, characterized in that said gas is nitrogen, air, oxygen or argon. 6. The preparation method according to claim 1, characterized in that the palladium plating solution is: based on the total volume of the plating solution, a palladium salt with a Pd ²⁺ of 0.006-0.06mol/L, 30-100g/L EDTA, 100-500ml/L ammonia water; the reducing agent is N ₂ H ₄ , the concentration is 0.2-2M. 7. The preparation method according to claim 1, characterized in that the palladium salt is palladium chloride, palladium acetate, palladium nitrate or palladium sulfate; the ethylenediaminetetraacetic acid salt is ethylenediaminetetraacetic acid Disodium, Dipotassium EDTA, or Diammonium EDTA. 8. The preparation method according to claim 1, characterized in that the electroless plating is divided into 2-10 times, and the carrier is turned upside down before updating the plating solution to ensure uniform coating. 9. The preparation method according to claim 1, characterized in that the temperature of electroless plating is 10-50°C.

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