RU2542251C1 - Catalytic reactor for vapour conversion of hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: reactor contains input branch pipe, evaporator of liquid initial reaction mixture, device, creating vortex gas flow, porous distribution membrane, monolithic multi-channel unit, additional porous membrane and output branch pipe. Multi-channel unit is made of material with high heat conductivity, is disc-shaped and has channels, directed perpendicular to disc plane, length of which is considerably smaller than disc diameter.

EFFECT: uniform distribution of input flow by channels, reduction of gradient of temperatures along flow direction, reduction of hydrodynamic resistance in case of immobile layer of catalyst and possibility of fast replacement of catalyst.

13 cl, 3 dwg

Description

The invention relates to the field of heterogeneous catalysis and is aimed at creating catalytic multichannel reactors for conducting heterogeneous reactions accompanied by an endothermic thermal effect, for example, steam conversion of hydrocarbons to produce a hydrogen-containing gas.

The main requirements for a reactor for conducting heterogeneous catalytic reactions accompanied by an endothermic thermal effect are:

1) the high mass transfer rate of the reactants with the catalyst and the absence of diffusion restrictions;

2) high rate of heat transfer to create isothermal conditions for the process.

A microchannel reactor can satisfy these conditions. Typically, catalytic microchannel reactors are, as a rule, a layered structure consisting of a set of metal microchannel (MK) plates with submillimeter-sized channels on the surface of which a catalyst is deposited. Due to the small size of the channels, high surface / volume ratios and very high mass and heat transfer rates are realized — 1-2 orders of magnitude higher than in systems with a massive catalyst layer, which significantly reduces the temperature gradient along the reaction zone [K. Schubert, J. Brandner, M. Fichtner, G. Linder, U. Schygulla, A. Wenka, Microscale Thermophys. Eng. 5 (2001) 17]. In addition, due to the small size of the channels, a laminar flow of the gas stream is achieved with a uniform distribution in speed or in contact time of the reactants with the catalyst [W. Ehrfeld, V. Hessel, H. L ∗ we. Microreactors - new technology for modern chemistry. Weinheim: Willey-VCH; 2000], while unwanted radical processes are quenched, which increases the yield of useful reaction products [K.F. Jensen Microreaction engineering - is small better? Chem. Eng. Sci. 56 (2001) 293].

An example of the use of a microchannel reactor is the most studied catalytic process of steam conversion of methanol into a hydrogen-containing gas, which can be characterized by two endothermic reactions - steam conversion of methanol (I) and reverse water-gas shift reaction (II).

$${\text{CH}}_{\text{3}}\text{OH}+{\text{H}}_{\text{2}}\text{O}={\text{<figure-callout id="2" label="CO" filenames="00000005.png" state="{{state}}">CO</figure-callout>}}_{\text{2}}+{\text{<figure-callout id="2" label="3H" filenames="00000005.png" state="{{state}}">3H</figure-callout>}}_{\text{2}}\text{,}{\mathrm{<figure-callout\; id="0"\; label="\Delta \; r\; H"\; filenames="00000003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}}_r{H}^{}{}^0{}_{298}=49,5\mathrm{to}D\mathrm{well}/m\mathrm{about}lb.\left(I\right)$$

$${\text{H}}_{\text{2}}+{\text{<figure-callout id="2" label="CO" filenames="00000005.png" state="{{state}}">CO</figure-callout>}}_{\text{2}}=CO+H_{2}O\text{,}{\Delta }_r{H}^0{}_{298}=41,2\mathrm{to}D\mathrm{well}/m\mathrm{about}lb.\left(II\right)$$

This process proceeds on the catalyst under fairly mild conditions at a temperature of 240-300 ° C and atmospheric pressure with high efficiency. In addition, methanol is quite common and can be obtained from renewable energy sources [S.P. Asprey, B.W. Wojciechowski, B.A. Peppley, Applied Catalysis. A, General 179 (1999) p. 51. J.C. Amphlett, R.F. Mann, B.A. Peppley, International Journal of Hydrogen Energy 21 (8) (1996) p. 673. B.A. Peppley, J.C. Amphlett, L.M. Kearns, R.F. Mann, Applied Catalysis. A, General 179 (1999) p. 21. B.A. Peppley, J.C. Amphlett, L.M. Kearns, R.F. Mann, Applied Catalysis. A, General 179 (1999) p. 31. R.O. Idem, N.N. Bakhshi, Chemical Engineering Science 51 (14) (1996) p. 3697.].

To date, there are a large number of different designs of microchannel reactors for carrying out the catalytic process of steam conversion of hydrocarbons, the main difference of which is the method of fixing the catalyst in microchannels. The most widely used are microreactors with a fixed catalyst bed. This is due to the relative ease of loading and replacing the catalyst in the reactor. However, one of the undesirable features of such reactors is the high hydrodynamic resistance of the fixed catalyst bed to the flow of reagents.

Studying the methanol steam reforming process on a catalyst of the composition Cu-Ce-Al-O [L.L. Makarshin, D.V. Andreev, A.G. Gribovskiy, V.N. Parmon. Influence of the microchannel plates design on the efficiency of the methanol steam reforming in microreactors. International Journal of Hydrogen Energy, 2007, Vol 32/16, pp. 3864-3869.] Showed that in a reactor with a fixed catalyst bed, the endothermic process leads to the appearance of a large temperature gradient along the moving reagent stream, which reduces the efficiency of the reactor and increases the concentration an undesirable by-product of the reaction is carbon monoxide. Obviously, a decrease in the temperature gradient can be achieved by reducing the reaction volume of the reactor and increasing the thermal conductivity of the walls of the channels in which the catalyst is located. Such conditions correspond to a microchannel reactor in which the catalyst is fixed in microchannel plates made of metal [Cao C, Xia G, Holladay J, Jones E, Wang Y. Kinetic studies of methanol steam reforming over Pd / ZnO catalyst using a microchannel reactor. Appl Catal A 2004; 262 (1): 19-29 .; Karim A, Bravo J, Gorm D, Conant T, Datye A. Comparison of wall-coated and packed-bed reactors for steam reforming of methanol. Catal Today 2005; 110 (1-2): 86-91].

One way to reduce the temperature gradient in a microchannel reactor is to use instead of microchannel plates a monolithic multichannel block made of metal with high thermal conductivity, in which channels of a millimeter or submillimeter diameter containing a catalyst are located.

The closest prototype of the invention is a microchannel reactor for screening catalysts described in [MJM Mies, EV Rebrov, MHJM de Croon, JC Schouten. Design of a molybdenum high throughput microreactor for high temperature screening of catalytic coatings. Chemical Engineering Journal 101 (2004) 225-235]. This reactor consists of eight sections (eight microchannel plates each) made of molybdenum, formed in two sets so that they form 32 flat channels with the following dimensions: width 10.18 mm, height 0.13 mm and length 40 mm (see Fig. 9 in the cited paper). Various catalysts are deposited on the microchannel plates, the reactor is heated by a built-in electric heater, temperature control along the length of the channels and in the radial direction is carried out by thermocouples. In order to ensure uniform flow of the gas mixture into each channel, a gas flow distributor is installed in front of each microchannel unit entrance, which consists of a metal grid of eight sections, rotated 90 ^° relative to the plane of the channels (see Fig. 2 in the cited paper). Fig. 3, 4 show the results of modeling the heterogeneity of the inlet gas flow depending on the geometric parameters a (distance between two walls of adjacent microchannels) and b (distance between the wall of the upper channel and the wall of the flow distributor). It can be seen that in a narrow range of b / a ratios, a minimum of flow heterogeneity is observed (less than 1%), and when deviating from the optimum and with an increase in the input gas flow rate, the inhomogeneity increases sharply. The consequence of this is a large variation in the contact time in different channels of the reactor, varying degrees of catalyst use, an increase in the nonisothermality of the reactor in the case of strongly endo - or exothermic reactions.

A catalytic reactor is proposed for the steam conversion of hydrocarbons into a hydrogen-containing gas, which contains a massive matrix made of a material with high thermal conductivity of arbitrary cross section (circle, square, etc.) with a length significantly smaller than its cross section. Channels with a supported catalyst are located along the matrix.

At the inlet of the reactor, a device is installed for distributing the inlet gas stream, which ensures uniform (over the entire area of the microchannel matrix) introduction of the initial reaction mixture into the reactor channels. The device includes an input for a liquid initial reaction mixture, an evaporator, consisting of a round metal plate with radially located channels, at the end of which there are openings, a unit for creating a vortex flow of a gaseous initial reaction mixture - a ring that contains two or more tangential channels, ( the number of which is equal to the number of radial channels and openings of the evaporator block), which create a circulation of the initial reaction mixture, a porous membrane for the distribution of the gas stream, which also serves as a reactor lid for holding catalyst particles within the channels.

The technical result is a decrease in the temperature gradient along the direction of the reaction stream, a uniform distribution of the input stream over the channels, a decrease in hydrodynamic resistance in the case of a fixed catalyst bed, and the possibility of a quick change of the catalyst.

The results of mathematical modeling on the distribution of the input gas stream of reagents through the channels of a monolithic multichannel unit without using (a) and using (b) a membrane are shown in Fig. 1.

It is seen that the near-wall heterogeneity of the flow resulting from the vortex movement of the reagents at the entrance to the multichannel unit is significantly reduced when using a porous distribution membrane. The flow non-uniformity decreases from 86% to 0.47% when the input flow is up to 1800 cm ³ / min, while for the prototype, when the input flow rate is 1000 cm ³ / min, the flow non-uniformity reaches 10% (see Fig. 4 in the cited work).

The General scheme of the microreactor for the steam conversion of hydrocarbons is illustrated in Figure 2. The microreactor is heated to operating temperature. At the input 1 serves a liquid initial reaction mixture consisting of water and hydrocarbon in the corresponding stoichiometric ratio. The flow of the initial reaction mixture enters the Central part of the evaporator 2, is distributed through the channels of the evaporator 8, the gaseous initial reaction mixture through the holes 9 enters the device, creating a vortex flow of the stream 3 through the channels 10. Next, the flow passes through the distribution membrane 4. After the membrane 4, the original the reaction mixture with a uniform flow distribution enters the monolithic multichannel unit 5, in the channels 11 of which there is a catalyst. As a result of the catalytic process of steam conversion of hydrocarbons, the resulting hydrogen-containing gas passes through the membrane 6 and enters the outlet through the pipe 7.

A detailed description of the components of a multi-channel hydrocarbon steam reforming reactor.

The hydrocarbon steam reforming reactor consists of an inlet pipe 1. an evaporator of a liquid initial reaction mixture 2, a device creating a vortex gas stream 3, a porous distribution membrane 4, a multi-channel block 5, an additional porous membrane 6 and an outlet pipe 7 (Figure 3).

The number of channels 8 in the evaporator 2 can be from two or more, the channel arrangement is radial, the channel width is at least 0.1 mm, length is 1-50 mm.

The size and number of tangential channels 10 in the device for creating a vortex flow 3 corresponds to the size and number of channels of the evaporator.

The pore size in the porous membrane 4 is 50-1000 microns, the membrane thickness is 5-1000 microns.

The monolithic multi-channel block 5 is made of a material with high thermal conductivity - silicon, copper, copper-containing alloy, etc.

The diameter of the channels 11 in the multi-channel block is 0.25-5 mm.

The catalyst can be mounted on the walls of the channels in the form of a thin layer with a thickness of 0.1-100 micrometers.

The catalyst can be placed in the channels in the form of a granular fraction of the initial powder with a size of 10 to 50% of the diameter of the channels.

An additional membrane 6 serves as a cover for a monolithic multichannel block and, in the case of a fixed catalyst layer, holds it in the channels.

All parts of the microchannel reactor are interconnected into a single unit and enclosed in a housing.

Thus, the proposed design of a multichannel reactor for the steam conversion of hydrocarbons into a hydrogen-containing gas solves the problem of ensuring a uniform feed of the initial reaction mixture through all channels of the reactor by means of a device creating vortex motion of a gas stream and a porous distribution membrane at the inlet, and also solves the problem of providing isothermal conditions for the process of steam reforming of hydrocarbons through the use of a monolithic multichannel block made and h material with high thermal conductivity. In addition, a removable multi-channel unit allows quick catalyst replacement.

Claims (13)

1. A catalytic reactor for steam conversion of hydrocarbons, consisting of an inlet pipe, an evaporator of the liquid source reaction mixture, a device that creates a vortex gas stream, a porous distribution membrane, a multi-channel block, an additional porous membrane and an output pipe, characterized in that the monolithic multi-channel block has a disk a shape made of a material with high thermal conductivity, with channels directed perpendicular to the plane of the disk and having a length significantly less than the diameter d ska. 2. The catalytic reactor according to claim 1, characterized in that the monolithic microchannel disk-shaped block is made of a material with high thermal conductivity, such as silicon, copper, copper-containing alloys, etc. 3. The catalytic reactor according to claim 1, characterized in that the diameter of the channels in the multi-channel block is 0.25-5 mm 4. The catalytic reactor according to claim 1, characterized in that the catalyst can be fixed in the form of a thin layer on the walls of the channel of the multichannel block, the thickness of which can vary from 0.1-100 micrometers. 5. The catalytic reactor according to claim 1, characterized in that the granular fraction of the catalyst with a size of from 10 to 50% of the diameter of the channels can be filled into the channels, forming a fixed catalyst layer. 6. The catalytic reactor according to claim 1, characterized in that the reactor is integrated with an evaporator to evaporate the liquid initial reaction mixture, which consists of radial channels located in the reactor vessel. 7. The catalytic reactor according to claim 6, characterized in that the number of radial channels in the evaporator is at least two. 8. The catalytic reactor according to claim 6, characterized in that the channel cross section in the evaporator is at least 0.1 mm, the length is 1-50 mm. 9. The catalytic reactor according to claim 1, characterized in that the reactor is equipped with a device for creating a vortex flow of the gas source of the reaction mixture through tangential channels. 10. The catalytic reactor according to claim 1, characterized in that the reactor is equipped with a porous distribution membrane. 11. The catalytic reactor according to claim 10, characterized in that the pore size in the distribution membrane is 50-1000 microns, the membrane thickness is 5-1000 microns. 12. The catalytic reactor according to claim 1, characterized in that the reactor, when a fixed catalyst bed is used, is provided with an additional membrane serving to hold the catalyst in the channels of the multi-channel block. 13. The catalytic reactor according to p. 12, characterized in that the pore size in the additional membrane is 50-1000 microns, the membrane thickness is 5-1000 microns.

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