RU2592627C1 - Gas chemical membrane reactor - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to membrane technologies and concerns devices engaged into release of oxygen from gas mixture on ceramic membranes with mixed ion-electron conductivity. Gas chemical membrane reactor includes a module of oxygen permeable membranes (2) assembled from tubes made from oxides with mixed oxygen electronic conductivity with general formula Sr_1-xA_xB_1-y-zB^/ _yM_zO_3-δ, where A=Ca, Ba, Ln; x=0-1; B=Co; B^/=Fe; y=0-1; M are metals of d and p units of periodic table, preferably: Nb, Ta, Mo, W; z=0-0.3; and δ is number, which provides charge neutrality, edges of membranes are connected to source of alternating current passed through membranes and heating them.

EFFECT: reduced energy consumption, reduction of start-up time of device and inertia at regulation of temperature mode of synthesis, increase of efficiency and stability of operation of gas and chemical membrane reactor.

1 cl, 7 dwg

Description

The invention relates to the field of membrane technology and relates to devices that produce oxygen from a mixture of gases on ceramic membranes with mixed ion-electron conductivity.

The inventive gas chemical reactor can be used as an oxygen separator (SC), the separated pure oxygen can be used for various applications in medicine, metallurgy, transport and gas chemistry, including the oxidative conversion of hydrocarbon feedstocks.

The main element of the claimed device are oxygen-permeable membranes, which have a high mixed ion-electron conductivity.

High electronic conductivity ensures the occurrence of redox processes on the surface with the formation of molecular oxygen and oxide of ions. High ionic (oxygen) conductivity provides the transport of oxide of ions through the crystal lattice of the oxide, which ensures absolute selectivity of the process.

If on different sides of a gas-tight membrane made of oxides with mixed oxygen electrode conductivity, various partial oxygen pressures (pO ₂ ) are created, then the following processes will occur under the influence of the difference of chemical potentials:

(1) on the surface of larger pO ₂ , dissociative adsorption of molecular oxygen and the restoration of oxygen atoms due to electrons of the transition metals that make up the membrane material, with the formation of oxygen ions;

(2) under the influence of the gradient of the chemical potential, the oxide ions diffuse onto the surface of a smaller pO ₂ ;

(3) oxide of ions is oxidized on the surface of lower pO ₂ with electron transfer to transition metal ions in the membrane material and associative desorption of molecular oxygen.

Thus, a mixed conductivity oxide-based membrane provides oxide oxide and electron flows, which leads to the release of oxygen from an oxygen-containing gas with 100% selectivity. This unique property of materials with mixed oxygen electron conductivity allows them to be used in devices for producing pure oxygen for various applications in medicine, metallurgy, and transport. In addition, the released pure oxygen can be used as a reagent in the oxidative conversion of hydrocarbons, for example, in the partial oxidation of methane to synthesis gas, dimerization of methane to form ethane, etc.

Oxygen-permeable membranes are of two types: planar and tubular. Planar ones provide a more uniform distribution of reagents, while tubular ones provide increased thermal and mechanical strength, ease of sealing and scaling.

Known technical solutions that describe planar (1. US 8486184 B2, publ. July 16, 2013) and tubular (2. US 5599383 A, publ. Feb 4, 1997) ceramic membranes from various materials with mixed oxygen electronic conductivity that separate oxygen from oxygen-containing gas.

Known technical solutions (3. USA 5,306,411, publ. 03/26/1994 and 4. 5,591,315. Publ. 01/07/1997), which describe ceramic membranes from various materials that separate oxygen from an oxygen-containing gas, and the resulting pure oxygen reacts with a gas containing methane, resulting in the formation of synthesis gas (CO + 2H2).

A common disadvantage of devices with flat oxygen-permeable membranes is the high requirements for the absence of significant temperature gradients along the membranes, which leads to a low start-up speed, design complexity, membrane destruction during thermal cycling, and sudden changes in temperature that occur in chemical processes.

, где Α, Α′, Α′′ являются элементами групп 1, 2 и 3 и лантаноидами (предпочтительно кальцием, стронцием, барием и магнием), a Β, Β′, Β′′ являются переходными металлами (предпочтительно кобальтом, железом и медью) d-блока Периодической системы элементов. При этом 0<x<1, 0≤x′≤1, 0≤x′′≤1, 0<y≤1, 0≤y′≤1, 0≤y′′≤1, 1.1>x+x′+x′′>0.9, 1.1>y+y′+y′′>0.9, a z является числом, которое обеспечивает нейтральность заряда. Реактор может быть использован для получения синтез-газа, для этого реактор нагревают до температуры от 300 до 1200°C. Кислородсодержащий газ проходит внутри трубок, а метансодержащий газ проходит снаружи трубок. Кислород проникает через стенки трубки, обладающей смешанной ионно-электронной проводимостью, и вступает в реакцию с метансодержащим газом в регулируемых условиях. При этом образуется синтез-газ, содержащий водород и оксид углерода. На внешней поверхности трубок может применяться катализатор, ускоряющий образование синтез-газа.The closest technical solution selected for the prototype is a membrane reactor (5. USA 5,599,383, published 04.02.1997), including oxygen-permeable membranes in the form of tubes assembled into a module, each of which contains a porous material that supports the walls of the tube, and a gas-tight layer through which oxygen is separated. The chemical composition of the material from which tubular membranes can be made is described by the formula: $$A{}_{x}A{}_{x\text{'}\text{'}}^{\text{'}\text{'}}{A}_{x\text{'}\text{'}\text{'}\text{'}}^{\text{'}\text{'}\text{'}\text{'}}B{}_{y}B{}_{y\text{'}\text{'}}^{\text{'}\text{'}}{B}_{y\text{'}\text{'}\text{'}\text{'}}^{\text{'}\text{'}\text{'}\text{'}}$$

, where Α, Α ′, Α ″ are elements of groups 1, 2 and 3 and lanthanides (preferably calcium, strontium, barium and magnesium), a a, Β ′, Β ″ are transition metals (preferably cobalt, iron and copper ) d-block of the Periodic system of elements. Moreover, 0 <x <1, 0≤x′≤1, 0≤x′′≤≤1, 0 <y≤1, 0≤y′≤1, 0≤y′′′≤1, 1.1> x + x ′ + x ′ ′> 0.9, 1.1> y + y ′ + y ′ ′> 0.9, az is the number that ensures charge neutrality. The reactor can be used to produce synthesis gas, for this the reactor is heated to a temperature of 300 to 1200 ° C. Oxygen-containing gas passes inside the tubes, and methane-containing gas passes outside the tubes. Oxygen penetrates through the walls of the tube, which has mixed ion-electron conductivity, and reacts with a methane-containing gas under controlled conditions. This produces a synthesis gas containing hydrogen and carbon monoxide. A catalyst accelerating the production of synthesis gas may be used on the outer surface of the tubes.

It is known that the rates of oxygen flows through membranes with mixed oxygen electronic conductivity (SKEP membranes) that are acceptable for practical use can be achieved, as a rule, at temperatures above 600 ° C. In the known patents, the membranes are heated to the required temperature, and the temperature is maintained during the reaction due to external heating and / or due to the heat generated during exothermic chemical reactions.

The disadvantage of external heating used in [1-5] is the high energy consumption (since there is not only heating of the reactor, but also gaseous reagents flowing through the reactor) and the inertia of heating, which makes it difficult to quickly adjust the temperature in the reaction zone (since the reaction zone requires a certain time to warm up the source of external heating, gaseous reagents entering the reactor, and then the membrane itself), which leads to its unstable operation.

The problem solved by the claimed technical solution is to increase the efficiency, productivity and stability of the gas-chemical membrane reactor.

, где А=Са, Ва, Ln; x=0-1; В=Со; В^/=Fe; y=0-1; М - металлы d и p блоков Периодической таблицы элементов, предпочтительно: Nb, Та, Mo, W; z=0-0.3; a δ является числом, которое обеспечивает нейтральность заряда, края мембран подсоединены к источнику переменного тока, пропускаемого непосредственно через мембраны и нагревающего их.The problem is solved due to the fact that in the inventive gas-chemical membrane reactor, comprising a module of oxygen-permeable membranes assembled from tubes, oxygen-permeable membranes are made of oxides with mixed oxygen electron conductivity with the general formula $${\text{Sr}}_{\text{1-x}}{\text{A}}_{\text{x}}{\text{B}}_{\text{1-yz}}{B}_y^{/}{M}_z{O}_{3-\delta }$$

where A = Ca, Ba, Ln; x is 0-1; B = Co; B ^/ = Fe; y = 0-1; M - metals d and p blocks of the Periodic table of the elements, preferably: Nb, Ta, Mo, W; z is 0-0.3; a δ is a number that ensures charge neutrality, the edges of the membranes are connected to an alternating current source, which is passed directly through the membranes and heats them.

Oxygen permeable membranes in the form of tubes with a diameter of 1-5 mm are preferably used.

The salient features of the claimed technical solution are:

, где А=Са, Ва, Ln - лантоиды; x=0-1; В=Со; В^/=Fe; y=0-1; М - металлы d и p блоков Периодической таблицы элементов, предпочтительно: Nb, Та, Mo, W; z=0-0.3; a δ является числом, которое обеспечивает нейтральность заряда, выполняющие одновременно роли селективной по кислороду мембраны и нагревателя, обеспечивающего необходимую температуру мембраны для получения кислородных потоков, приемлемых для практического использования;- reactor membranes are made of oxides with mixed oxygen electronic conductivity with the general formula: $${\text{Sr}}_{\text{1-x}}{\text{A}}_{\text{x}}{\text{B}}_{\text{1-yz}}{B}_y^{/}{M}_z{O}_{3-\delta }$$

where A = Ca, Ba, Ln are lantoids; x is 0-1; B = Co; B ^/ = Fe; y = 0-1; M - metals d and p blocks of the Periodic table of the elements, preferably: Nb, Ta, Mo, W; z is 0-0.3; a δ is a number that ensures charge neutrality, performing simultaneously the roles of an oxygen selective membrane and a heater, providing the necessary temperature of the membrane to obtain oxygen flows that are acceptable for practical use;

- reactor membranes are connected to an alternating current source, passed directly through the membrane and heating them.

The problem is solved thanks to a combination of essential distinguishing features.

In FIG. 1 is a schematic representation of a gas chemical membrane reactor.

The inventive gas chemical reactor contains:

, где А=Са, Ва, Ln - лантаноиды; x=0-1; В=Со; B^/=Fe; y=0-1; М - металлы d и p блоков Периодической таблицы элементов, предпочтительно: Nb, Та, Mo, W; z=0-0.3; a δ является числом, которое обеспечивает нейтральность заряда;1) a housing (1) with nozzles for supplying (1c) and exhaust gases (1g), in which tubular oxygen-permeable membranes (2) based on perovskites with the general formula $${\text{Sr}}_{\text{1-x}}{\text{A}}_{\text{x}}{\text{B}}_{\text{1-yz}}{B}_y^{/}{M}_z{O}_{3-\delta }$$

where A = Ca, Ba, Ln are lanthanides; x is 0-1; B = Co; B ^/ = Fe; y is 0-1; M - metals d and p blocks of the Periodic table of the elements, preferably: Nb, Ta, Mo, W; z is 0-0.3; a δ is a number that ensures charge neutrality;

2) each membrane contains nozzles for supplying (1a) and venting gases (1b), by means of a conductive coating (3) and connected to an alternating electric current source (4), the membrane material allows electric current to pass directly through oxygen-permeable membranes (2);

3) using a temperature meter (5) and a current regulator (6), controlled heating of the membranes (2) is carried out, which provides the necessary temperature regime in the process of oxygen separation from air;

4) the regulation of oxygen flows is carried out by changing the speed of the air flow over oxygen-permeable membranes using the air flow regulator (7).

The inventive gas-chemical membrane reactor operates as follows.

Oxygen-permeable membranes (2) made in the form of tubes with a diameter of preferably 1-3 mm are fixed in the housing (1) with gas inlet and outlet pipes (1c, 1g). An oxygen-containing gas with a variable composition and with a variable flow rate is supplied to the outer side of the membranes through the pipe (1c). Next, a controlled heating of the membranes to operating temperature is carried out using a current controller (6) and a temperature meter (5). The selection of oxygen from the outlet (16) is carried out either by a compressor or a carrier gas passed through the inlet (1a) and the outlet (1b) with an adjustable flow rate. Oxygen membranes can be assembled into modules to provide the required performance of a gas chemical reactor.

The resulting pure oxygen can be used for the oxidative conversion of hydrocarbons, for example, partial oxidation of methane to form synthesis gas (CO + 2H2), dimerization of methane to form ethane, etc. For this, the corresponding catalyst is loaded into the gas-chemical membrane reactor and methane-containing gas is supplied from the oxygen evolution side.

It is known that the most promising materials for the manufacture of oxygen-permeable membranes for the evolution of oxygen from mixtures containing it are complex oxide compounds with a perovskite structure based on cobaltites and strontium ferrites [9. Teraoka Υ., Zhang N.-M., Yamazoe N. Oxygen-sorptive properties of defect perovskite-type La1-xSrxCo1-yFeyO3-δ, Chemistry Letters. 1985. V. 14. P. 1367-1370; Teraoka Y., Zhang H., Furukawa S., Yamazo N. Oxygen permeation through perovskite-type oxides, Chemistry Letters. 1985. V. 14. P. 1743-1746]. It is also known that the material composition Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-δ (BSCF) has the highest oxygen fluxes [10. Shao ZP, Yang WS, Cong Y., Dong H., Tong JH, Xiong GX Investigation of the permeation behavior and stability of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ oxygen membrane, Journal of Membrane Science. 2000. V. 172. P. 177-188]. The disadvantage of this compound is the presence of a polymorphic transition "cubic - hexagonal perovskite" at temperatures below 900 ° C, which leads to a significant drop in oxygen flows [11. Švarcová S., Wiik K., Tolchard J., Bouwmeester HJM, Grande T. Structural instability of cubic perovskite BaxSr1-xCo1-yFeyO3-δ, Solid State Ionics. 2008. V. 178. P. 1787-17918, Arnold M, Gesing TM, Martynczuk J., Feldhoff A. Correlation of the formation and the decomposition process of the BSCF perovskite at intermediate temperatures // Chem. Mater. 2008. V. 20. P. 5851-5858]. In addition, BSCF is unstable in an atmosphere containing carbon dioxide [12. Shao ZP, Yang WS, Cong Y., Dong H., Tong JH, Xiong GX Investigation of the permeation behavior and stability of a Ba0.5Sr0.5Co0.8Fe0.2O3-δ oxygen membrane, Journal of Membrane Science. 2000. V. 172. P. 177-188].

In the inventive membrane reactor, oxygen-permeable membranes are made of SCEP perovskites with the General formula:

, где А=Са, Ва, Ln - лантаноиды; x=0-1; В=Со; B^/=Fe; y=0-1; М - металлы d и p блоков Периодической таблицы элементов, предпочтительно: Nb, Та, Mo, W; z=0-0.3; a δ является числом, которое обеспечивает нейтральность заряда. $${\text{Sr}}_{\text{1-x}}{\text{A}}_{\text{x}}{\text{B}}_{\text{1-yz}}{B}_y^{/}{M}_z{O}_{3-\delta }$$

where A = Ca, Ba, Ln are lanthanides; x is 0-1; B = Co; B ^/ = Fe; y = 0-1; M - metals d and p blocks of the Periodic table of the elements, preferably: Nb, Ta, Mo, W; z is 0-0.3; a δ is the number that ensures charge neutrality.

In membrane materials due to dopants, preferably M = Nb, Ta, Mo, W, there are no phase and polymorphic transitions and the interaction with carbon dioxide is suppressed, which stabilizes oxygen flows. This is confirmed by the comparison of oxygen flows through disk membranes of the claimed composition Ba _0.5 Sr _0.5 Co _0.78 W _0.02 Fe _0.2 O _3-δ and the known in the literature Ba _0.5 Sr _0.5 Co _0.8 Fe _0.2 O _3-δ as a function of time; (a) a flow stability test, (b) in the presence of carbon dioxide, shown in FIG. 2. According to FIG. 2, membranes of the above composition, in which cobalt ions are partially replaced by highly charged tungsten cations, demonstrate stable oxygen flows in long-term tests, including in the presence of carbon dioxide.

Membranes made in the form of microtubular oxygen-permeable membranes have a porous part (0.5-1 mm), which plays the role of a strong carrier, and a thin gas-tight part (0.01-0.03 mm), which provides selective oxygen separation and high oxygen flows. The structure of microtubular membranes made from SCEC perovskites of the composition Ba _0.5 Sr _0.5 Co _0.78 W _0.02 Fe _0.2 O _3-δ is shown in FIG. 3. It provides their mechanical strength and resistance to temperature gradients, which leads to high startup speed, simplicity of design, stability of membranes during thermal cycling and sudden changes in temperature.

The inventive compositions have electrical conductivity, which ensures the passage of current through the membrane, which leads to their heating. In FIG. 4. The data on the electrical conductivity of the SCEC membranes of the composition Ba _0.5 Sr _0.5 Co _0.8-x Mo _x Fe _0.2 O _3-δ with different molybdenum contents, x = 0.06, 0.08, and 0.01, are presented.

Heating the EPDM membranes with alternating electric current ensures uniform and efficient heating of the entire membrane, which leads to higher performance of oxygen-permeable membranes. In FIG. Figure 5 shows the data on the comparison of oxygen flows through a microtubular membrane with the composition Ba _0.5 Sr _0.5 Co _0.78 W _0.02 Fe _0.2 O _3-δ when heated by passing alternating current directly through the membrane and with an external heater.

Heating the EPDM membranes with alternating electric current removes the polarization of the electrodes and prevents the destruction of the membrane material under the influence of electric current. In FIG. Figure 6 shows the data of x-ray phase analysis of the membrane material before (1) and after (2) continuous operation when heated by passing alternating current directly through the membrane for 7 days, which confirm the stability of the material under the influence of alternating current.

Heating the EPDM membranes with alternating electric current provides higher energy efficiency of the oxygen separation process in the membrane reactor. FIG. 7 shows a comparison of energy consumption for obtaining 1 m ^{3 of} pure (100%) oxygen using microtubular membranes of the composition Ba _0.5 Sr _0.5 Co _0.78 W _0.02 Fe _0.2 O _3-δ , heated by passing alternating current directly through the membrane and the external heating source is an electric resistance furnace . From FIG. 7 shows that the most effective heating by the current manifests itself at low temperatures. Energy costs when using an external heating source can be reduced by improving the thermal insulation of the furnace and recovering the heat of the exhaust gases. However, the energy efficiency of heating the membranes by passing current will remain higher, because in this case, heating of the entire volume of air passing over the membrane is not required; it is enough to warm a thin diffusion layer located directly above the membrane. The presence of high temperature gradients between the membrane preheated to temperatures of 600-1000 ° C and the membrane module housing reduces the requirements for structural materials, for example, replacing chrome steels resistant to high temperatures with cheaper and environmentally friendly ones.

Achievable technical result obtained using this technical solution consists in reducing energy consumption, reducing the startup time of the device and inertia when controlling the temperature of synthesis, increasing the productivity and stability of the gas chemical membrane reactor.

Compared with the prototype of the inventive gas-chemical membrane reactor has the following advantages:

- simplification of the design of the reactor;

- membranes at the same time play the role of selective oxygen separators and heating elements, providing the necessary temperature of the membrane to obtain oxygen flows that are acceptable for practical use;

- efficiency in starting up and maintaining stable operation of the reactor in operating mode;

 - membrane stability during thermal cycling and sudden changes in temperature and energy efficiency;

- performance.

Claims (2)

1. Gas-chemical membrane reactor, comprising a module of oxygen-permeable membranes, assembled from tubes, characterized in that the oxygen-permeable membranes are made of oxides with mixed oxygen electron conductivity with the general formula Sr _1-x A _x B. _1-yz B ^/ _y M _z O _3-δ , where A = Ca, Ba, Ln; x is 0-1; B = Co; B ^/ = Fe; y is 0-1; M - metals d and p blocks of the Periodic table of the elements, preferably: Nb, Ta, Mo, W; z is 0-0.3; and δ is a number that ensures charge neutrality, the membranes are connected to an alternating current source and are heated by alternating current passing through them. 2. Gas chemical membrane reactor according to claim 1, characterized in that it is made of tubes with a diameter of 1-3 mm

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