CN1141172C - Oxygen permeating film material with high oxygen permeating amount, high stability and high mechanical performance - Google Patents

Abstract

A mixed conductor oxygen-permeable membrane material has a perovskite and perovskite-like structure, and its molecular formula is A _a B _b C _c D _d O ₃ O _3-δ , wherein A is selected from Ba, Sr, Ca, Cd, Pb , one of Ce, Sn, Sm, Pr; B, C selected from one or more of Ca, Ce, Pb, Cr, Cu, Fe, Mn, Ni, Mg, Co; D selected from Zr, One of Ti, Ce, Zn, Sn, Bi, V, Pb; 0<δ<1, 0.7<a/(b+c+d)<1.3. Using this material, a set of membrane reactor with excellent sealing effect was designed and used in the process of partial oxidation of methane to synthesis gas. This membrane reaction process directly uses air as the oxygen source, which simplifies the operation process and reduces the operating cost. cost, increased methane conversion and CO selectivity.

Description

Oxygen permeable membrane material with high oxygen permeability, high stability and high mechanical properties

The invention provides an oxygen-permeable membrane material with high oxygen permeability, high stability and high mechanical performance, and uses this material to design a set of oxygen-permeable membrane reactor with excellent sealing performance for partial oxidation of low-carbon alkane. The reactor can be used to stably carry out the process of producing syngas by partial oxidation of methane for a long time.

Composite oxides with both oxygen ion conductance and electron conductance are a kind of mixed conduction type materials. Such materials can be used as electrode materials for solid oxide fuel cells and oxygen sensors, and can also be used as membrane materials for selectively separating oxygen from oxygen mixtures. Such membranes are called mixed conductivity oxygen-permeable membranes. Applying it to a membrane reactor to dynamically provide oxygen for high-temperature oxidation reactions, such as partial oxidation of methane to synthesis gas (POM) and oxidative coupling (OCM) reactions, can simplify the operation process and reduce operating costs.

Today, when oil resources are decreasing and proven reserves of natural gas are increasing, the effective utilization of natural gas is particularly important in the development of new energy sources. The catalytic conversion of natural gas mainly composed of methane can be divided into direct conversion and indirect conversion. Direct conversion such as oxidative coupling of methane to ethylene, selective oxidation to formaldehyde and methanol, methane cracking to hydrogen and methane oxygen-free aromatization to benzene and hydrogen. However, due to the fact that the intermediate products are more active than the reactants, the direct conversion of oxygen will be further deeply oxidized and the selectivity of the target product will be reduced. So far, no economically significant industrial scale application has been achieved. For the direct conversion without oxygen, the carbon deposition and deactivation of the catalyst is a huge obstacle for industrial practical application. Therefore, the indirect conversion of natural gas is particularly important. At present, it has been industrialized to use steam reforming of methane to produce synthesis gas, which is then further converted into various liquid fuels and organic chemical raw materials such as gasoline, diesel, ethylene glycol and olefins by Fischer-Tropsch reaction. However, this process has complex equipment, large investment, high temperature, high pressure, high corrosion and other reasons, so it cannot be compared with the petroleum processing process. The partial oxidation of methane to synthesis gas, which is currently under development, is a good direction for the indirect conversion of methane. However, the increase in process costs due to the need for pure oxygen in the reaction process or the separation of products brought about by using air as a raw material makes it lose the same direction. Competitive advantage in the petroleum refining process. However, the application of membrane reactors prepared with oxygen-permeable membrane materials has brought hope to the indirect conversion of methane. Compared with the fixed bed reactor, the mixed conductor membrane reactor has the following advantages: (1) Omits the special equipment for oxygen production and reduces capital investment. (2) Although the POM reaction is a weakly exothermic process, the reaction, especially at high space velocities, is prone to runaway temperatures. With a membrane reactor, since the supply of oxygen is the control step of the reaction, the generation of runaway temperature can be avoided. (3) Cheap air can be directly used as the oxygen source, and at the same time, the pollution of nitrogen to the product can be eliminated, so that the operation cost can be significantly reduced and the operation process can be simplified. (4) Nitrogen does not exist in the reaction process, which avoids the possibility of forming environmental pollutants _NOx in a high-temperature environment. These advantages of the mixed conduction type oxygen permeable membrane reactor make it occupy a clear advantage in the competition with the petroleum refining process.

For the mixed conductor oxygen permeable membrane reactor to be used for POM reaction, in addition to requiring a large oxygen permeability, it is also required to have a high pressure and temperature range (750-900 ° C, 30-10 ^-18 atm) in operation. Thermochemical stability and high mechanical strength. However, currently materials with high oxygen permeability, for example, SrCo _0.8 Fe _0.2 O _3-δ cannot exist stably under POM reaction conditions; while Sr-La-Ga-Fe-O which can exist stably under POM reaction conditions Oxygen film materials have not achieved satisfactory oxygen permeability even when operated at very high temperature (950°C). Moreover, it is difficult to design a membrane reactor with good sealing performance under high temperature conditions. Therefore, the development of an oxygen-permeable membrane material with high oxygen permeability, high structural stability and high mechanical strength is the basic premise of using a mixed conductor membrane for POM reaction. At the same time, it is necessary to design a membrane reactor with excellent sealing performance and The development of a highly active and stable POM catalyst is also the key to the problem.

The purpose of the present invention will start from these three aspects exactly, develop a kind of new oxygen-permeable membrane material, and apply it to the POM reaction process of mixed conductor membrane reactor.

The invention provides a mixed-conductor oxygen-permeable film material with high oxygen permeability, high structural stability and high mechanical strength used in the partial oxidation reaction of methane, which is characterized in that its structure is perovskite structure or perovskite-like Ore structure, its molecular formula can be expressed as A _a B _b C _c D _d O _3-δ ; wherein A is selected from one of Ba, Sr, Ca, Cd, Pb, Ce, Sn, La, Sm, Pr; B and C are respectively selected from one or more of Ca, Ce, Pb, Cr, Cu, Fe, Mn, Ni, Mg, Co; D is selected from Zr, Ti, Ce, Zn, Sn, Bi, V, A kind of Pb; 0<δ<1, a, b, c, d are respectively greater than 0 and less than or equal to 1, and 0.7<a/(b+c+d)<1.3.

Among the above-mentioned oxygen-permeable membrane materials, the preferred composition of the mixed conductor dense oxygen-permeable membrane is: Ba(Co _1-xy Fe _{x Zry} ) _z O _3-δ , where 0<x<1, 0<y< 1, 0.9<z<1.1, 0<δ<1.

In the above-mentioned mixed conductor oxygen-permeable membrane material, it is characterized in that z=1.

In addition, the present invention provides a synthesis method of a mixed conductor oxygen-permeable membrane material, which is characterized in that: EDTA and citric acid are used as co-complexing agents, and soluble metal salts including nitrates, chlorides or acetates are used as starting materials. The starting material is polyethylene glycol, glycerol or lactic acid as a dispersant, and the pH value of the solution is adjusted to be neutral. The system is stirred at a constant temperature of 50-90°C to evaporate the viscous colloid of water, 140-200 °C to solidify to obtain gel powder, and finally bake at a temperature of 700-1000 °C for 1-10 hours to obtain a powder.

In addition, the present invention also provides a mixed-conductor oxygen-permeable membrane reactor, including a reactor outer tube, an inner tube, a gas channel, a mixed-conductor oxygen-permeable membrane and a catalyst layer, characterized in that the mixed-conductor oxygen-permeable membrane is made of the above-mentioned A membrane or a membrane tube made of the oxygen-permeable membrane material of the present invention.

In the above-mentioned mixed conductor oxygen-permeable membrane reactor, it is characterized in that the diaphragm and the membrane tube reactor adopt sealing agents such as gold, silver, inorganic ceramic glue and glass ring.

The synthesis method of the oxygen-permeable membrane material powder in the present invention adopts the joint complexation method, uses EDTA and citric acid as a co-complexing agent, and uses soluble metal salts including nitrate, chloride, acetate, etc. as starting materials, Polyethylene glycol, glycerol, lactic acid, etc. are used as dispersants to inhibit the agglomeration of ions, the pH of the solution is adjusted to a neutral value with nitric acid and ammonia water, and the system is stirred and evaporated to remove water at a constant temperature of 50-90°C to obtain Viscous colloid, solidified at 140-200°C to obtain gel powder, and finally roasted at 700-1000°C for 1-10 hours to obtain powder.

The preparation of the dense mixed conductor film in the present invention is completed through powder screening, dry pressing molding, high temperature sintering and other processes. The density of the membranes was obtained by the usual mercury porosimetry, and those membranes with densities greater than 95% were used in the experimental procedure.

The oxygen permeability (Air/He) measurement of the present invention is carried out in the high-temperature osmotic cell, adopts high-temperature ceramic glue to seal, and the air of 150ml/min passes through the high oxygen pressure side of membrane, and 99.995% high-purity He passes through the low oxygen of membrane. Pressure side. The exhaust gas is sampled through the six-way valve and analyzed online by HP5890.

The present invention designs a membrane-type mixed conductor membrane reactor, as shown in FIG. 1 . Air enters the reactor outer tube 3 through 1, and then exits the reactor through 2; the oxygen in the air enters the reactor inner tube catalyst layer 5 through the mixed conductor oxygen permeable membrane 4; the mixed gas of methane and helium enters the reactor through 6 The inner tube 7 reacts with the oxygen permeated through the mixed conductor oxygen-permeable membrane 4 near the catalyst 5, and the synthesis gas produced by the reaction passes through 8 out of the reactor; 9 is a gold sealant; the spring 10 acts to increase the pressure when sealing Function: the quartz tube 11 can make the mixed conductor oxygen-permeable membrane 4 and the gold sealant 9 be stressed evenly when sealed. In addition, a temperature-measuring thermocouple 12 and a temperature-controlling thermocouple 13 are set for control. In the above reactor, the mixed-conductor oxygen-permeable membrane is a diaphragm or membrane tube made by using the above-mentioned mixed-conductor oxygen-permeable membrane material of the present invention according to conventional techniques. In addition, sealants such as gold, silver or phase-free ceramic glue are used for sealing.

The present invention has developed a mixed conductor oxygen permeable membrane material with high oxygen permeability, high structural stability and high mechanical strength; successfully designed a set of mixed conductor oxygen permeable membrane reactor with excellent sealing performance for partial oxidation of methane; using this mixed conductor The oxygen-permeable membrane reactor has carried out the reaction of partial oxidation of methane to synthesis gas, which directly uses cheap air as the oxygen source to reduce the operating cost, and the conversion rate of methane and the selectivity of carbon monoxide in the reaction are very high. Describe the present invention in detail below by example and accompanying drawing.

A brief description of the attached drawings.

Fig. 1 is a schematic diagram of the structure of the membrane reactor of the present invention.

Fig. 2 is the XRD spectrum of the BaCo _0.4 Fe _0.6-x Zr _x O _3-δ (x=0-0.4) series mixed conductor oxygen-permeable membrane material.

Fig. 3 is a graph showing the variation of the oxygen permeability of the mixed conductor oxygen permeable membrane with temperature for the BaCo _0.4 Fe _0.6-x Zr _x O _3-δ (x=0-0.4) series.

Fig. 4 is the multi-round O ₂ -TPD spectra of the oxygen permeable membrane material BaCo _0.4 Fe _0.4 Zr _0.2 .

Fig. 5 is the multi-round H ₂ -TPD spectra of the oxygen permeable membrane material BaCo _0.4 Fe _0.4 Zr _0.2 .

Fig. 6 is a graph showing the influence of reaction temperature on reaction performance and oxygen permeability.

Fig. 7 is a graph showing the influence of CH ₄ flow rate on the reaction performance and oxygen permeability.

Fig. 8 is a graph showing the stability results of the BaCo _0.4 Fe _0.4 Zr _0.2 O _3-δ membrane reactor.

Example 1

BaCo _0.4 Fe _0.6-x Zr _x O _3-δ (0≤x≤0.4) series mixed conductor oxygen-permeable membrane materials were synthesized by the combined complexation method of citric acid and EDTA acid. Weigh 80 grams of EDTA acid and 100 grams of citric acid, dissolve them in 300ml of concentrated ammonia water under heating; add 0.2mol Ba(NO ₃ ) ₂ , 0.08mol Co(NO ₃ ) ₂ , (0.12-0.2x)mol Fe(NO ₃ ) ₃ and 0.2x mol Zr(NO ₃ ) ₄ solution; heated to 80°C, then stirred at constant temperature, with the evaporation of water, a transparent hot-soluble colloid was finally obtained, and the colloid was treated at 200°C for several hours, and finally in Calcined at 950°C for 5 hours to obtain powder. The measurement by XRD powder diffraction method shows that a pure-phase cubic perovskite structure composite oxide is formed, as shown in FIG. 2 .

Example 2

BaCo _0.4 Fe _0.6-x Zr _x O _3-δ (0≤x≤0.4) series mixed conductor oxygen permeable membrane oxygen permeability measurement, the diaphragm is polished on both sides with SiC sandpaper, the final thickness of the diaphragm is 1.00mm, using Inorganic ceramic glue for sealing. Synthetic air is passed through the outer tube of the permeation cell at a flow rate of 150ml/min, and the inner tube is purged with high-purity helium (99.995%) at a flow rate of 30ml/min. It can be clearly seen from Figure 3 that the oxygen permeability of all components varies with temperature. Increase with increasing, among them, 0≤x≤0.2 has a higher oxygen permeability, which is close to the 1.00ml/ ^mincm2 proposed by Professor Steele.

Example 3

Determination of structural stability of BaCo _0.4 Fe _0.4 Zr _0.2 O _3-δ oxygen permeable membrane material. The structural stability of membrane materials in inert atmosphere and reducing atmosphere was measured by multiple O ₂ -TPD and H ₂ -TPR. These two experiments were carried out on a self-made multifunctional TP device, and the detailed process can be found in references. Figure 4 and Figure 5 show the multiple rounds of O ₂ -TPD and H ₂ -TPR spectra of the material, respectively. The results show that the BaCo _0.4 Fe _0.4 Zr _0.2 O _3-δ oxygen permeable membrane material exhibits excellent structural reversible stability no matter in the inert atmosphere or in the reducing atmosphere.

Example 4

We investigated the effect of reaction temperature on the reaction performance of BaCo _0.4 Fe _0.4 Zr _0.2 O _3-δ oxygen-permeable membrane material for partial oxidation of methane to synthesis gas. Add 300 mg of Ni-based catalyst between 20 and 40 mesh. The flow rate of the mixed gas of 50% methane and 50% He is 18ml/min, and the flow rate of air is 150ml/min. The results are shown in Figure 6. As the reaction temperature increases, the conversion rate of methane increases, and the selectivity of carbon monoxide increases first, and then decreases slowly; the oxygen permeability of the membrane increases rapidly with the increase of temperature, which is One of the reasons for the increased conversion of methane. The optimum reaction temperature is 850°C

Example 5

We investigated the influence of methane flow rate on the reaction performance when BaCo _0.4 Fe _0.4 Zr _0.2 O _3-δ oxygen permeable membrane material was used in the reaction of partial oxidation of methane to synthesis gas. Catalyst and outer tube air flow rate are the same as embodiment 4, but this experiment is to fix reaction temperature, constantly change the flow rate of methane and helium gas mixture to investigate the change of reaction performance and the change of diaphragm oxygen permeability. As shown in Figure 7, with the increase of methane flow rate, the conversion rate of methane does not change much, the selectivity of carbon monoxide increases rapidly, on the contrary, the selectivity of carbon dioxide gradually decreases; but when it increases to a certain extent, the selectivity of methane The conversion rate decreased rapidly with the increase of the flow rate, and the selectivity of carbon monoxide and carbon dioxide did not change greatly. This shows that the oxygen permeability of the oxygen-permeable membrane also increases when the methane flow rate first increases, but its speed is far less than that of the methane flow rate, and it does not increase to a certain extent. This turns oxygen from a small excess (carbon dioxide production) to a deficit (reduced methane conversion). This coincides with the variation of membrane oxygen permeability with methane flow rate.

Example 6

We investigated the change of BaCo _0.4 Fe _0.4 Zr _0.2 O _3-δ oxygen permeable membrane material in the reaction of partial oxidation of methane to synthesis gas within 1000 hours. Reaction conditions are similar to the conditions of previous several examples, add the Ni base catalyst between 300mg20 to 40 orders, the flow rate of the mixed gas of 50% methane and 50% He is 18ml/min, and the air flow rate is 150ml/min, reaction The temperature is 850°C. The change of the conversion rate of methane, the selectivity of carbon monoxide, the selectivity of carbon dioxide and the oxygen permeability of the membrane with time are shown in Fig. 8 . It can be clearly seen that during the 2000 hours of operation, the methane conversion rate, carbon monoxide selectivity, carbon dioxide selectivity, and oxygen permeability of the membrane have not changed significantly, and the methane conversion rate is always greater than 96%. The carbon monoxide selectivity The performance is always greater than 99%, and the oxygen permeability is always around 5.6. This shows that the oxygen-permeable membrane material we developed has very high structural stability during the partial oxidation of methane to synthesis gas.

Comparative example 1

U.S. Patent, U.S.Patent, 3,330697 (1967), and document "Preparation of perovskite-type oxide with large surface area by citrate process", Hua-MinZHANG, Chem.Lett, PP665-668, 1987. In this patent and document A series of low-alkali metal content and Pb-containing perovskite composite oxide powders were synthesized at low temperature by using citric acid complexation method. Advantages of Synthesizing High Specific Surface Area Composite Oxide Powders. However, the formation of colloids is very sensitive to the pH value, and if the pH value is not well controlled, precipitation is easy to occur during the gelation process.

Comparative example 2

US Patent, US. Patent, 5,240,480 (1993). This patent provides a novel composite solid conductor membrane with a multilayer structure for selectively separating oxygen from oxygen-containing gases. Its material composition is A _x A′ _x′ A″ _x″ By _y B′B″ _y″ O _3-δ , where A, A′, A″ select the first, second, third main group elements and lanthanides Elements, B, B', B" are selected from transition elements in the periodic table, and 0≤x≤1, 0≤x'≤1, 0≤x"≤1, 0≤y≤1, 0≤y' ≤1, 0≤y"≤1, x+x'+x"=1, y+y'+y"=1, where A, A', A" mainly come from Ca, Sr, Ba, Mg. A good composition is La _x A _1-x Co _y Fe _1-y O _3-δ , wherein x is between 0 and 1, y is between 0 and 1, and A is mainly selected from Ba, Sr, and Ca.

Comparative example 3

H.Kruidhof in the title "Influence of order-disorder transitions on oxygen permeability through selected nonstoichiometric perovskite-type oxides", Solid State Ionics, 63-65 (1993) 816-822, the composition is La _0.6 Sr _0.4 CoO _3-δ The oxygen permeability stability of the mixed conductor oxygen permeable membrane at 750 ℃ was studied. One end of the membrane was passed with air, and the other end was passed with helium. It was found that the oxygen permeability decreased from the initial value of more than 10 ^-9 mol/cm ² s to 10 ^-1 1 mol/cm ² s in 350 hours, and the oxygen permeability decreased by nearly two orders of magnitude.

Comparative example 4

The world patent WO 94/24065 uses Sr _α (Fe _1-x Co _α+β )O _δ as the oxygen permeable membrane material, where 0.01<x<1, 1<α<4, 0<β<20, δ makes the composite oxidation To keep charge balance, two kinds of reactors were designed, and the partial oxidation reaction of methane was carried out. Its design also adopts cross flow, but the design of the two reactors is complicated, difficult to press, not conducive to manufacture, and the oxygen permeability can only reach 0.4ml(STM)/cm ² ·min during the reaction, which is far lower than our reaction. 5.6ml(STM)/cm ² ·min, which is not conducive to large-scale production.

Comparative Example 5

European patent EP 0 399833 A1 describes an electrochemical reactor using a solid membrane comprising (1) multi-layered electron-conducting species; (2) oxygen ion-conducting species, or (3) perovskite-type mixed metal oxides. Oxygen from the oxygen-containing gas passes through the membrane into another gas that requires oxygen. In the reactor, the two gases flow in parallel on both sides of the membrane. An external power supply is required when using this membrane reactor for reaction.

Comparative example 6

The document "Dense perovskite membrane reactor for partial oxidation of methaneto syngas, Chung-Y Tsai, et al. AIChE Journal, 43, pp2741, 1997" uses La _0.2 Ba _0.8 Co _0.2 Fe _0.8 O _3-δ as the mixed conductor oxygen permeable membrane material Make the diaphragm, design two kinds of catalyst contact modes as shown in Figure 9, wherein (A) is to put the catalyst in the quartz tube in the middle in the reactor, and the distance between the bottom of the catalyst and the oxygen permeable membrane is 8mm. (B) In the reactor, the catalyst particles are directly placed on the surface of the oxygen-permeable membrane, and a part of the middle quartz tube is inserted into the catalyst. The reaction gas is a mixed gas of methane and helium containing 4.6% methane, and the catalyst is 5% Rh/Al ₂ O ₃ or 5% Ni/Al ₂ O ₃ . In the reactor (A) using 5% Rh/Al ₂ O ₃ and 5% Ni/Al ₂ O ₃ as catalysts respectively, the conversion rate of methane is stable at 15% and does not change with time. In (B) reactor, 5% Ni/Al ₂ O ₃ is used as catalyst, and the methane flow rate is kept constant, and the methane conversion rate and the oxygen permeability increase with the reaction time, and the methane conversion rate is from the initial 17 to 500h. % rises to 80% to reach the highest, and the oxygen permeability increases from the initial 0.5ml (STM)/cm ² ·min to 4.4ml (STM)/cm ² ·min at 700h, and then the methane conversion rate and oxygen permeability are both slow reduce. The reaction was carried out for a total of 850 hours, and finally the methane conversion rate reached 78%, and the oxygen permeability was 4.2ml (STM)/cm ² ·min.

Comparative Example 7

Document "Failure mechanism of ceramic membrane reactors in partial oxidation of methane to synthesis gas" S.Pei, et al.Catal.Lett., 30(1995) 201 in SrCo _0.8 Fe _0.2 O _3-δ mixed conductor oxygen permeable membrane reactor The failure mechanism of the membrane tube in the case of the partial oxidation of methane to synthesis gas was studied, and it was found that there were two types of cracks in the membrane tube during operation: the first type appeared shortly after the start of the reaction, and appeared in the hot zone of the tube The second type occurs after a long time of reaction, and large cracks parallel to the tube axis appear in the membrane tube. It is pointed out that the first type of defects is caused by the surface tension induced by the presence of oxygen concentration gradient on both sides. The second type of cracks is caused by the decomposition of the constituent materials in the film in the presence of reducing atmosphere H ₂ and CO, resulting in a large expansion coefficient.

Claims (4)

1. A mixed conductor oxygen-permeable film material, characterized in that the structure is a perovskite structure or a perovskite-like structure, consisting of: Ba(Co _1-xy Fe _{x Zry} ) _z O _3-δ , wherein 0<x<1,0<y<1,0.9<z<1.1,0<δ<1. 2. The mixed conductor oxygen-permeable membrane material according to claim 1, characterized in that: z=1. 3. A synthetic method of the mixed conductor oxygen-permeable membrane material as claimed in claim 1, characterized in that: utilize EDTA and citric acid as co-complexing agent, and include nitrate, chloride or acetate etc. with soluble metal salt As the starting material, use polyethylene glycol, glycerol or lactic acid as the dispersant, adjust the pH value of the solution to be neutral, and evaporate the viscous colloid of the system under constant temperature conditions of 50-90 ° C to remove water, 140- Solidify at 200°C to obtain a gel powder, and finally bake at a temperature of 700-1000°C for 1-10 hours to obtain a powder. 4. The use of the mixed conductor oxygen-permeable membrane material according to claim 1 as a mixed conductor oxygen-permeable membrane reactor.

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