Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

The present invention relates to methods and devices for thermochemical reactions. In particular, the present invention relates to a method and an apparatus for increasing the reaction rate of a thermochemical reaction.

As used herein, the thermochemical reaction includes an exothermic chemical reaction and an endothermic chemical reaction.

Thermochemical reactions, including exothermic and endothermic chemistries, are well known. Examples of thermochemical reactions include, but are not limited to, hydrogen and hydrocarbon conversion reactions including, but not limited to, steam reforming, water gas conversion reactions and combustion. However, it is not limited to these. These reactions are usually carried out in the presence of a catalyst at temperatures up to about 1000 ° C. The reaction rate of the product is limited because the reaction rate inherent in thermochemical reactions is much faster than the thermal transfer rate between the reaction vessel and the thermal sink or the environment. The limited reaction rate will typically be characterized as a residence time of seconds to minutes in a conventional thermochemical reaction vessel.

For example, the water gas conversion reaction is routinely carried out in a fixed bed reactor. The water gas conversion reaction, in which carbon monoxide and water are converted to carbon dioxide and hydrogen, suffers multiple-second residence times (movement disorders) when performed in a fixed bed reactor. The theoretical reaction rate suggests a possible residence time on the order of milliseconds. There are two factors that delay the reaction rate compared to conventional reactors. The first factor is the diffusion limitation of the reactants diffusing into and out of the catalyst carrying the porous pellets, and the second factor is the thermal transfer parameters (conductivity, length) of the catalyst carrier and the reactor. Thermal transfer limitation, which is a combination of overall geometric shapes (shapes and dimensions). Since the water gas conversion reaction is important for multi-reactor fuel processing systems that support the energy products distributed during fuel cell use, a smaller and faster water gas conversion reactor is needed.

As another example, a conventional methane steam reforming reactor that produces syngas with an effective coefficient of 0.01 to 0.05 and an average residence time of a few seconds is Adris, A., Pruden, B., Lim, C., Reported by J. Grace, 1996. It is reportedly intended to essentially improve the performance of steam methane reforming reactors (Canadian Journal of Chemical Engineering, 74, 177-186). In a typical industrial operating process, the ratio of methane to steam is operated at 3: 1 to prevent coke formation.

<p><nplcit num="1"><text>Canadian Journal of Chemical Engineering, 74, 177-186</text></nplcit></p>

<p> Efforts to improve the thermal transfer between the reaction vessel and the thermal sink are seen by recent improvements in the formation reaction rate. Therefore, in the field of thermochemical reactions, there is a need for methods and devices that increase the thermal transfer rate between the reaction vessel and the thermal sink to approach the theoretical intrinsic reaction rate of reaction and formation.</p>

<p> The present invention is a method and apparatus for increasing the reaction rate per reaction chamber volume of a reaction chamber having inlets and outlets for thermochemical reactions. Here, the ratio of the increased reaction rate per reaction chamber volume to the reaction rate per reaction chamber volume for conventional thermochemical reactions is at least 2. For example, in conventional steam reforming, the residence time is on the order of seconds, whereas in the present invention, the residence time is on the order of milliseconds, which is a factor of 2 or less. The method and apparatus of the present invention (a) The reaction chamber contains a porous insert through which the reactant flow is substantially completely passed, and the reaction chamber volume with the porous insert has an average porosity of less than 1 and a travel distance of 3 mm or less. And have. (b) The reaction chamber has a length of 6 inches (15.24 cm) or less parallel to the bulk reactant flow and a height of 2 inches (5.08 cm) or less, thus penetrating the porous insert. Transfer heat of reaction at an increased thermal transfer rate. (c) The heat transfer chamber is in thermal contact with the reaction chamber, which transfers heat across the wall between the heat transfer chamber and the reaction chamber at an increased heat transfer rate. Thus, the thermal reaction rate per thermochemical reaction chamber volume is increased so that the ratio of the increased reaction rate per reaction chamber volume to the reaction rate per conventional thermochemical reaction reaction chamber volume is at least 2.</p><p> These features have been found to be associated with a reaction rate that transfers heat at a rate sufficient to avoid substantial impairment of movement. These features are effective for both catalytic thermochemical and non-catalytic thermochemical reactions. For catalytic chemistry, the addition of a catalyst on a porous insert allows the reactant to pass through the catalytic site, rather than limiting the movement of the reactant with respect to diffusion as in conventional systems. Therefore, according to the present invention, for a catalytic chemical reaction, both movement disorders are substantially reduced, and a theoretical reaction rate or a reaction rate close to a theoretical value can be achieved. In particular, the water gas conversion reactor produced by the present invention is 1/10 to 1/100 the size of a conventional processing apparatus for obtaining the same amount of production.</p><p> The gist of the present invention is specifically pointed out and directly described by the claims of the present specification. However, the configuration and method of operation as well as the advantages and objectives will be best understood by reference to the following description with reference to the accompanying drawings. In the drawings, similar elements are designated by the same reference numerals.</p>

<figref num="1">FIG. 1a is a cross-sectional view of a laminated reaction chamber having a heat exchange chamber. FIG. 1b is an isometric view of a nested reaction chamber with a heat exchange chamber.</figref><figref num="2">FIG. 2a is a graph of the selectivity and residence time for water gas conversion when in contact with the powder catalyst porous insert for a long time. FIG. 2b is a graph of selectivity and residence time for water gas conversion when contacted with a powder contact porous insert for a short time.</figref><figref num="3">FIG. 3 is a graph of selectivity and temperature at various residence times for water gas conversion in coated metal foam porous inserts.</figref><figref num="4">FIG. 4 is a graph of methane conversion and temperature at various residence times when the ratio of steam to methane is 2.5: 1.</figref><figref num="5">FIG. 5a is a graph of conversion rate, selectivity and residence time for n-butane steam reforming in a porous insert of an interface layer and a porous sublayer having a catalytic material. FIG. 5b is a graph of conversion and selectivity and time for n-butane steam reforming in regenerated porous inserts.</figref>

With reference to FIGS. 1a and 1b, a thermochemical reaction vessel 100 having two chambers 102 and 104 and a wall 106 between the chambers is shown. Both of the two chambers 102 and 104 can be reaction chambers. The bulk flow of reactants in the reaction chamber 102 is approximately orthogonal to cross section 108. Container 100 may be a stacked chamber as shown in FIG. 1a or a nested chamber as shown in FIG. 1b. The reaction in the reaction chamber may be an endothermic reaction or an exothermic reaction.

In a thermochemical reaction, the formation rate (reaction rate) is limited by either the heat transfer rate to the reaction site (endothermic reaction) or the heat transfer rate from the reaction site (exothermic reaction). To increase the thermal transfer rate or reaction rate, the reaction chamber has a porous insert (not shown) within the reaction chamber. The reaction chamber volume with the porous insert has an average porosity of less than 1 and a heat transfer distance of 3 mm or less, thus penetrating the porous insert and reacting at an increased thermal transfer rate. Transfer heat.

Porous inserts are powders, porous monoliths (eg, metal or ceramic foams, honeycombs, tube banks, laminated microchannel assemblies, and combinations thereof, but not limited to), fibers (eg, steel wool). ), Or a combination thereof. In the case of catalytic reactions, the porous inserts are preferably removable from the reaction chamber in terms of the cost of replacing the consumed catalyst. The porous insert may be arranged to have a single or multiple passage for the flow of reactants through the reaction chamber volume. The porous insert may be placed on the inner surface of the reaction chamber or may be in contact with a raised shape formed on the inner surface of the reaction chamber.

For catalytic thermochemical reactions, the preferred porous insert is a porous carrier carrying a catalytic material on it. More preferably, the porous insert is a porous insert having a solution deposited interfacial layer between the porous carrier and the catalytic material. A more preferred porous insert has a buffer layer between the porous carrier and the interface layer.

In addition, the reaction chamber has a length of 6 inches (15.24 cm) or less parallel to the bulk reaction stream and a height of 2 inches (5.08 cm) or less. The limited length and height shorten the distance of the protrusions and allow rapid thermal transfer. In addition, the short length reduces the overall pressure drop through the reaction chamber.

The thermal transfer chamber is in thermal contact with the reaction chamber. The heat transfer chamber transfers heat at an increased heat transfer rate across the wall 106 between the heat transfer chamber and the reaction chamber. In this way, the reaction rate per chamber volume for thermochemical reaction can be increased.

The interface layer is an interface layer made of a metal oxide produced by a solution deposition method. The interface layer made of metal oxide by the solution deposition method is γAl.₂O₃, SiO₂, ZrO₂, TiO₂, Magnesium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, nickel oxide, cobalt oxide, copper oxide, zinc oxide, molybdenum oxide, tin oxide, calcium oxide, aluminum oxide, lanthanum oxide series, zeolites and combinations thereof. However, but is not limited to these. Typically, the porous carrier has a coefficient of thermal expansion that is different from the coefficient of thermal expansion of the interface layer. Therefore, for high temperature catalysts (T&gt; 150 ° C), the buffer layer needs to transition between two different coefficients of thermal expansion.

The buffer layer is Al₂O₃, TiO₂And a metal oxide that is a combination of these. In particular, Al₂O₃Is α-Al₂O₃, Γ-Al₂O₃And a combination of these. TiO₂Is not as good as alumina for oxygen diffusion, so α-Al₂O₃The structure is preferred. Therefore, it is expected that resistance to high temperature oxidation can be improved by alumina coated foam. When the porous substrate 100 is a metal foam, a preferred embodiment has a buffer layer formed from two sub-layers. The first sublayer is α-Al, which passivates the metal foam.₂O₃The second sublayer is TiO bound to the interface layer.₂Is.

The deposition of the buffer layer 102 may be performed by vapor deposition including, but not limited to, chemical vapor deposition, physical vapor deposition or a combination thereof. Since the vapor deposition is carried out at a high temperature, a polycrystalline phase is formed that exhibits good adhesion of the metal oxide to the surface of the metal foam.

Alternatively, the buffer layer 102 can also be obtained by solution coating. The solution coating comprises a metal surface functionalization step by forming a hydroxide and a surface hydrolysis step of the alkoxide to obtain a polycrystalline phase. This solution coating is preferred as it is a lower cost buffer layer 102 deposition method.

Polycrystalline metal oxides do not easily come off in flakes under the thermal cycle. The open cells of the metal foam<u style="single">Approximately 8ppcm (20ppi) ~ Approximately 390ppcm (1000ppi)</u>Is in the range of, preferably<u style="single">About 3.1ppcm (80ppi)</u>Is.

The catalytic material (if used) deposits on the interface layer. Catalytic substances include, but are not limited to, noble metals, transition metals and combinations thereof, and are not limited to magnesium oxide, titanium oxide, vanadium oxide, chromium oxide, magnesium oxide, iron oxide, nickel oxide, cobalt oxide and copper oxide. , Zinc oxide, zirconium oxide, molybdenum oxide, tin oxide, calcium oxide, aluminum oxide, silicon oxide, lanthanum oxide series, zeolites and combinations thereof. You may.

Preferred catalyst production methods include a step of selecting a porous carrier, a step of depositing a buffer layer on the porous carrier, a step of forming an interface layer on the buffer layer by a solution deposition method, and a catalyst on the interface layer. Includes a step of depositing metal. When the metal foam is used as a porous carrier, the metal foam is etched before depositing the buffer layer. Etching is done with an acid such as HCl. Optionally, the catalyst layer may be deposited on the interface layer.

<p> Experiments were performed to show a chemical thermal reaction according to the present invention using a water gas conversion reaction.</p><p> Pre-reduced and stabilized 5 wt% Ru / ZrO obtained from Degussa Corporation for the first porous insert₂Made with a catalytic material consisting of a catalyst (1/8 inch (0.32 cm) extruded material). The catalyst material was crushed and sieved into 65-100 meshes.</p><p> The second porous insert was machined to fit a 0.5-2.5 cm long, 7 mm ID quartz tube.<u style="single">3.1 Pore / cm (ppcm) (80 Pore / inch (ppi))</u>Made of Ni metal foam. The metal foam was continuously washed with acetone, chloroform and water in an ultrasonic cleaner at 10 minute intervals. In addition, it was etched in 1M HCl at 60 ° C. for 30 minutes. The etched metal foam was saturated with zirconium n-propoxide / 1-propanol solution (Aldrich), hydrolyzed in the environment for 72 hours with steam and fired at 450 ° C. for 4 hours to form an interface layer. ZrO₂-Dilute coated metal foam RuCl₃Aqueous solution (RuCl₃Saturated with hydrate, Aldrich). The saturation process was repeated several times until the desired Ru loading was obtained. Finally, the Ru catalyst-supported coated metal foam was dried under vacuum overnight at 100 ° C. and calcined at 350 ° C. for 1 hour. 10% H catalyst before testing₂The / He mixture was activated at 350 ° C for at least 1 hour.</p><p> Both porous inserts were tested using a catalytic plug flow reactor (PFR) system. The PFR is formed in a single zone furnace as a heat transfer chamber. The reactor system included a steam generator located just in front of the reactor inlet, a PFR housed in the reactor, and a capacitor located at the reactor outlet. The porous insert was filled into a narrow centered quartz tube with an ID of 7 mm.</p><p> The feed water was supplied to the steam generator using a Cole Parmer syringe pump. Carbon monoxide and nitrogen (diluent) were supplied to the system using a Matheson mass flow controller. The mixed feed stream was circulated to the steam generator in a downward flow mode before entering the PFR. The produced gas was flowed through a capacitor and sent to online gas chromatography to analyze the produced stream.</p><p> Two thermocouples were placed inside the catalytic PFR system. One thermocouple was placed above the porous insert. The other thermocouple was placed adjacent to the porous insert on the outside of the quartz tube and the furnace temperature was measured. A pressure gauge was placed at the reactor inlet to measure the pressure difference across the porous insert.</p><p> Microsensor Technology Inc., (MTI) M200 gas chromatography was used to analyze the resulting gas immediately after discharge from the reactor. Parallel 10-m molecular sieve columns (carrier gas: argon, 100 ° C, 34.1 psig) and 8-m Pollaplot U columns (carrier gas: helium, 65 ° C,<u style="single">2905kPa (gauge) (26.9psig)</u>) Was used for gas chromatographic analysis of hydrogen, nitrogen, oxygen, methane, carbon monoxide, air, carbon dioxide, ethane and ethylene for 75 seconds. The M200 used a vacuum pump to aspirate a small amount of sample from the generated stream with a purge time of 40 seconds and an injection time of 100 ms. Water was removed from the gas stream before it was placed in the M200.</p><p> Carbon monoxide conversion was calculated based on the number of moles of the substance in the inlet gas stream and the outlet gas stream, as shown in the following formula (1). The selectivity for carbon dioxide (and hydrogen) or methane was calculated by the following equations (2) and (3), respectively.</p><p><maths num="1"><img file="JP5111419B2_D0001.tif" /></maths></p><p> Using the first porous insert, the catalyst fine powder (65-100 mesh) and the intrinsic reaction rate were approximately measured. The contact time was changed from 10 milliseconds to 1 second. Figures 2a and 2b show performance for long and short contact times. At 300 ° C, with a vapor to carbon ratio of 3: 1, a contact time of 25 ms on a Ru-based catalyst would convert more than 98% of carbon monoxide to carbon dioxide and hydrogen. It was enough. Desired product (CO) in 50 ms₂And H₂), With a selectivity of 100%, a CO conversion rate of 99.8% was measured. The equilibrium conversion rate of CO was 99.93% when the ratio of steam to carbon was 3: 1 at 300 ° C.</p><p> Test results at longer contact times (&gt; 100 ms) showed methane formation with an equilibrium selectivity of 22.8%. The equilibrium selectivity line for carbon dioxide and hydrogen is shown in Figure 2a. As the contact time increases, so does the formation of methane. All equilibrium calculations were performed using the software package FACT®.</p><p> The results of the second porous insert (coated metal foam) are shown in FIG. At 300 ° C, the CO conversion rate was less than 10%. However, at 500 ° C and a vapor to carbon ratio of 3: 1, the measured carbon monoxide conversion reached 94% with a contact time of 50 ms. Under these conditions, the equilibrium conversion was 94.53%. The conversion rate of carbon monoxide in a short contact time of about 10 milliseconds exceeded 90%, and the selectivity for carbon dioxide and hydrogen was observed to be 100%. Equilibrium CO₂The selectivity was 93.52% at 500 ° C.</p><p> At contact times of 10 ms, 50 ms and 100 ms, methane was below the detection limit of GC (gas chromatography) and the measured selectivity was near 100%. These observations indicate that the desired non-equilibrium chemical was utilized in the coated metal foam. Unwanted series and slow parallel reaction pathways such as methane formation were effectively eliminated.</p><p> The second porous insert of the coated metal foam had a higher activity temperature than the first porous insert of the catalyst powder. This is due to the following two reasons. First, the catalyst washcoat has a slightly different composition and structure than the catalyst powder. Independent catalytic tests on powders made from the same washcoat have demonstrated that higher activity temperatures are required. Another difference between the two porous inserts was the reduced weight (about 10%) of the active catalyst on the coated metal foam.</p>

<p> Experiments were performed to demonstrate hydrocarbon steam reforming according to the present invention.</p><p> Using the first porous insert (powder) as in Example 1, 5% Rh / γ-Al₂O₃Achieved methane steam reforming on the catalyst at 850 ° C for 25 milliseconds at 100% conversion (Fig. 4). Using a second porous insert (coated metal foam), as in Example 1,<u style="single">3.1ppcm (80ppi)</u>5% Rh / γ-Al on stainless steel metal foam₂O₃At the catalyst / interface layer, the operating temperature was lowered by 100 ° C to achieve the same performance as at 750 ° C.</p><p> No coke formation was observed during the millisecond residence time seen at low vapor to methane ratios (2.5: 1).</p><p> The results for other hydrocarbons are shown in Table E2-1. Here, "time" is the residence time.</p><p><tables num="1"><img file="JP5111419B2_D0002.tif" /></tables></p><p> Further data for the n-butane steam reforming experiment is shown in Figure 5a.<u style="single">3.1ppcm (80ppi)</u>The stainless steel porous insert had an alumina interface layer and a rhodium catalyst (Rh 15.6 wt% on 17.1 wt% alumina, the rest stainless steel foam, no buffer layer). The conditions were a vapor to carbon ratio of 3.58: 1, 650 ° C, and a residence time of 95 ms (milliseconds). The pressure drop increased from very small to over 7 psig, causing cracking and spalling of the interfacial and catalytic layers. The catalyst was regenerated in air to remove the deposited carbon. Figure 5b shows relatively inferior performance. The pressure drop is after only 5 hours of operation time in 2 days<u style="single">756kPa (gauge) (7psig)</u>Increased until it exceeded.</p><p> [Conclusion] Having described preferred embodiments of the invention, it will be apparent to those skilled in the art that many changes and modifications can be made without departing from the broad scope of the invention. Therefore, the claims are intended to cover all changes and modifications to the extent that they are within the true scope of the invention.</p><p> Embodiments of the present invention are as follows. [1] A method for carrying out a hydrocarbon steam reforming reaction, which comprises a step of passing steam and hydrocarbons into a reaction chamber. The reaction chamber has a reaction chamber volume defined by a length of 6 inches (15 cm) or less and a height of 2 inches (5 cm) or less parallel to the bulk reactant flow. The reaction chamber contains a porous insert on which the catalytic material is placed. Heat is transferred from the thermal transfer chamber, which is in thermal contact with the reaction chamber volume, to the porous insert, and the heat is transferred across the wall between the thermal transfer chamber and the reaction chamber with a thermal transfer distance of 3 mm or less. Move with Vapors and hydrocarbons come into contact with catalysts with a contact time of 100 ms or less A method characterized by that. [2] A method of obtaining a high reaction rate per reaction chamber volume of a reaction chamber having inlets and outlets for thermochemical reactions. (a) Porous insertion within a reaction chamber volume having a length of 6 inches (15 cm) or less and a height of 2 inches (5 cm) or less parallel to the bulk reactant flow so as to have a thermal transfer distance of 3 mm or less. The process of placing things (b) A step of providing a heat transfer chamber in a state of thermal contact with the volume of the reaction chamber and transferring heat across the wall between the heat transfer chamber and the reaction chamber. The method comprising, wherein the porous insert is in contact with a raised shape on the inner surface of the reaction chamber. [3] The method according to [2], wherein the porous insert is a porous monolith, a fiber, or a combination thereof. [4] The method according to [3], wherein the catalyst is on the porous insert. [5] The method according to [4], wherein the porous insert contains a porous monolith, and has an interface layer by a solution deposition method on the porous monolith and a catalytic metal on the interface layer. [6] The method according to [5], wherein the porous insert has a buffer layer between the porous monolith and an interface layer by the solution deposition method. [7] The method according to [6], wherein the buffer layer is made of a metal oxide. [8] The method according to [5], wherein the porous monolith is a metal foam, ceramic foam, honeycomb, tube bank or laminated microchannel assembly. [9] The method according to [2], wherein the porous insert is a powder. [10] The method according to any one of [2] to [9], wherein the thermochemical reaction is a hydrocarbon steam reforming thermochemical reaction. [11] The method according to [10], wherein the hydrocarbon steam reforming thermochemical reaction is carried out with a contact time of 100 milliseconds or less. [12] The method according to [5], wherein the buffer layer is a polycrystalline metal oxide formed by vapor deposition. [13] The method according to any one of [2] to [12], wherein the thermochemical reaction is an aqueous gas conversion thermochemical reaction. [14] A vessel that increases the reaction rate per reaction chamber volume of a reaction chamber with inlets and outlets for thermochemical reactions. (a) A reaction chamber volume with a length of 6 inches (15 cm) or less and a height of 2 inches (5 cm) or less parallel to the bulk reactant flow. (b) With the porous insert placed in the reaction chamber volume so that the reactant flow passes through the porous insert during operation and has a thermal transfer distance of 3 mm or less. (c) A thermal transfer chamber that is in thermal contact with the reaction chamber volume, The vessel comprises, wherein heat is transferred across the wall between the thermal transfer chamber and the reaction chamber, and the porous insert comes into contact with a raised shape on the inner surface of the reaction chamber. .. [15] The container according to [14], wherein the porous insert is a powder. [16] The container according to [14] or [15], wherein the catalyst is above the porous insert. [17] The container according to [15], wherein the porous insert has an interface layer by a solution deposition method between a porous carrier and a catalyst substance. [18] The container according to [17], wherein the porous insert is a porous monolith that is a ceramic foam, honeycomb, tube bank or laminated microchannel assembly. [19] The container according to any one of [14] to [18], wherein the porous insert is a porous monolith having a buffer layer deposited between a porous carrier and an interface layer by a solution deposition method. .. [20] The container according to [19], wherein the buffer layer is made of a metal oxide. [21] The container according to any one of [14] to [20], wherein the porous insert comprises a powder, a porous monolith, a fiber or a combination thereof. [22] The method according to [17], wherein the porous carrier is a metal foam. [23] The method according to [17], wherein the porous carrier is a porous ceramic. [24] The method according to [17], wherein the interface layer is made of a metal oxide by a solution deposition method. [25] The metal oxide obtained by the solution deposition method is γAl.₂O₃, SiO₂, ZrO₂, TiO₂And the container according to [24] selected from the group consisting of combinations thereof. [26] The container according to any one of [14] to [25], wherein the porous insert is removable from the reaction chamber. [27] The container according to [14], wherein the porous insert is a porous monolith having a buffer layer which is a vapor-deposited metal oxide. [28] The deposited metal oxide is Al.₂O₃, TiO₂And the container according to [27] selected from the group consisting of combinations thereof. [29] The Al₂O₃Is αAl₂O₃, ΓAl₂O₃And the container according to [28] selected from the group consisting of combinations thereof. [30] The container according to [27], wherein the buffer layer includes a plurality of sublayers.</p>