Abstract:
A process of a catalytic combustion is disclosed. The process can be started at a cold temperature and raise to a desired high temperature in a very short time by employing a noble metal catalyst dispersed on a supporting material. Moreover, a method for dispersing a noble metal catalyst used in the catalytic combustion is also disclosed for increasing a specific surface area of the catalyst so as to facilitate the catalytic combustion. Furthermore, a substance including a boron nitride supported noble metal catalyst, a substrate for suspending the catalyst, and a supporting material for dispersing the substrate with said catalyst is also disclosed so that a total surface area of the catalyst can be increased, thereby the catalytic combustion can be initiated in a very short time.

Description:
FIELD OF THE INVENTION  
         [0001]    This is a continuation-in-part application of U.S. patent application Ser. No. 10/287,991 filed on Nov. 4, 2002. This invention relates to a method and a substance for a catalytic combustion, and more particularly to a method and a substance for rapidly catalyzing a combustion reaction.  
         BACKGROUND OF THE INVENTION  
         [0002]    Vapor phase combustion is notorious for generating nitrogen oxides, NO X , which always causes a noxious pollution hazard. Furthermore, during the vapor phase combustion, it losses a large function of the thermal energy thereof through the chimney effect. On the other hand, a catalytic oxidation is a much cleaner type of combustion without yielding nitrogen oxides. However, the catalytic oxidation generally requires a long induction time to initiate the reaction until its exothermic reaction heat can provide enough activation energy to sustain its continuous auto-oxidation. Thus, it always needs to preheat the fuel to a high temperature for shortening the induction period thereof. As a result, the catalytic oxidation reaction is difficult to be used as a heating method for supplying heat to an industrial reactor or facilities. This is because the conventional oxidation catalyst is not reactive enough and is unable to heat up the fuel from the ambient temperature to the desired high temperature in a very short period of time, for example, 10 to 30 minutes.  
           [0003]    Consequently, it will need a reactive oxidation catalyst capable of heating up from room temperature to the desired high temperature in a very short time, for example, 10 to 30 minutes, so that the catalytic oxidation reaction can be used for supplying heating to an industrial reactor or facilities. That means the catalyst must be able to cold start a reactor to its desired reaction temperature in a short period of time without external heating source or facility.  
           [0004]    Because the defects in the prior art and the demands for a future application of the catalytic combustion, the present invention discloses a method and a substance for rapidly catalyzing the combustion in a short time. Therefore, the combustion can be completed in a rapid and clean way.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present invention to provide a method and substance for a catalytic combustion which can rapidly reach to a high temperature sufficient to initiate another reaction also in a very short time.  
           [0006]    In accordance with an aspect of the present invention, a process of a catalytic combustion is provided. The process includes steps of providing a fuel at a first temperature, e.g., room temperature, and contacting the fuel with a noble metal catalyst dispersed on a supporting material so as to raise the fuel to a second temperature, for example, a temperature ranged from 500 to 1000° C., sufficient to initiate the combustion, wherein a raising time from the first temperature to the second temperature is within 15 minutes.  
           [0007]    In this process, the fuel can be a methanol or an n-hexane, the noble metal catalyst is a boron nitride supported noble metal catalyst, wherein the noble metal is selected from a group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), Ruthenium (Ru) and a mixture thereof, the catalyst is dispersed on the supporting material through a substrate, e.g. a paste, which is a hydrophobic paste with a thermal conductive property and the supporting material is a porous element having a relatively higher specific surface area for facilitating the combustion, for example, y-alumina, titania, zirconia, or commercial oxidation catalysts, silica, DASH220 or N200.  
           [0008]    In accordance with another aspect of the present invention, a method for dispersing a noble metal catalyst used in a catalytic combustion is further provided. The method includes steps of providing the noble metal catalyst, mixing the catalyst into a substrate, and dispersing the substrate with the catalyst on a supporting material, thereby a specific surface area of the catalyst being increased so as to facilitate the catalytic combustion.  
           [0009]    In accordance with further another aspect of the present invention, a substance for a catalytic combustion is disclosed. The substance includes a boron nitride supported noble metal catalyst for catalyzing the combustion, a substrate for suspending the catalyst, and a supporting material for dispersing the substrate with the catalyst for increasing a total surface area of the catalyst, thereby the catalytic combustion is initiated within a short time, e.g. 15-30 minutes.  
           [0010]    In accordance with additional aspect of the present invention, a catalyst for catalytic combustion is disclosed. The catalyst includes a boron nitride support and a noble metal, wherein the noble metal is dispersed on a surface of the boron nitride support. A specific surface area of the catalyst ranges from 1 to 200 m 2 /g, and a loading of the noble metal ranges from 0.1 to 5.0 wt %.  
           [0011]    The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1A is a schematic view showing a reactor system for the catalytic combustion according to the present invention;  
         [0013]    [0013]FIG. 1B is a sectional drawing showing a catalytic bed of the reactor in FIG. 1A according to the present invention;  
         [0014]    [0014]FIG. 2 is a temperature profile showing a catalytic combustion of methanol using various oxidation catalysts and oxygen/methanol ratios with WHSV=3.2 to start from room temperature, wherein T 1  represents the temperature at the peak and T 2  represents the temperature at the steady;  
         [0015]    [0015]FIG. 3 is a temperature profile showing a catalytic combustion of n-hexane with Pt/BN-N-220 and an O 2 /n-Hexane=10.45 according to the present invention;  
         [0016]    [0016]FIG. 4 is a schematic view showing a double jacket stainless steel reactor for the catalytic combustion of methanol fuel to initiate a steam reforming reaction of methanol according to the present invention; and  
         [0017]    [0017]FIG. 5 is a temperature profile of a 10 hours duration test showing a catalytic combustion with a catalyst of PtBN/N220, MeOH=0.4 mL/min, Air=2 L/min, WHSV=3.2, 0 2 /C=1.65 to start from room temperature after 10 hours on stream operation, wherein T 1  represents the temperature at the peak and T 2  represents the temperature at the steady. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    The invention is described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed.  
         [0019]    The purpose of rapidly inducing a catalytic combustion according to the present invention is achieved by a supported noble metal catalyst, preferably a boron nitride (BN) supported noble metal catalyst.  
         [0020]    The advantages of using BN as a catalyst support for oxidation reaction are described below.  
         [0021]    (a) The physical or chemical properties of the interface support (BN) are stable at high temperature because of its high thermal stability.  
         [0022]    (b) No hot spot will develop by exothermic oxidation reaction because of high thermal conductivity of support (BN). Thus, the clusters of noble metal, which is supported on support (BN), won&#39;t be sintered during reaction. The catalyst activity can be maintained for a longer time.  
         [0023]    (c) The catalyst is not damaged by acidic or basic agents because of chemical inertness of the BN.  
         [0024]    (d) Moisture cannot condense inside the pores of this interface support (BN) because of its hydrophobicity. Therefore, the surface of catalyst won&#39;t be covered by moisture to hinder further catalytic reaction, and the oxidation activity is enhanced.  
         [0025]    A BN supported noble metal catalyst is used to completely oxidize organic compounds to water and carbon dioxide. BN is a white flake-type powder compound in appearance which can be purchased on the commercial market. The noble metal is selected from a group consisting of platinum (Pt), palladium (Pd), rhodium (Rh), Ruthenium (Ru) and a mixture thereof, preferably Pt. The noble metal is dispersed on the surface of BN, and the loading is from 0.1 to 5.0 wt %. The specific surface area of BN supported noble metal catalyst is from 1 to 200 m 2 /g, preferably from 30 to 80 m 2 /g.  
         [0026]    The noble metal is dispersed on the surface of BN by the so called “incipient wetness technique”. For better soaking on the hydrophobic BN support, an organic solvent of alcohols, preferably methanol is chosen as the diluting solvent. The quantity of methanol required to completely fill the pore volume of support (BN) is predetermined. A noble metal complex compound of Pt, Pd, Rh or Ru, preferably in hexachloride or its amine salt, e.g., H 2 PtCl 6  H 2 0, is dissolved in methanol resulting in a Pt-methanol solution.  
         [0027]    For use in the catalytic combustion, this BN dispersed noble metal catalyst described above is uniquely designed and fabricated by the use of an active metal on a hydrophobic paste and thereafter this pasted noble metal catalyst is further dispersed on a stable high surface area supporting material, wherein the paste functions as an interface substrate for facilitating the further dispersion of the catalyst onto the supporting material. Thus, through the high surface area supporting material, it will be easier for the catalyst to contact with the fuel so as to increase the reaction rate. Hence, a porous supporting material, such as a γ-alumina, might be a great solution which has a high surface area and also in a stable state. Additionally, the hydrophobic substrate is chosen to reduce the chemisorption of water molecule and to prevent the water from competing an active catalyst site and blocking the chemisorption of the fuel molecule on the active metal. Moreover, this substrate compound is an excellent thermal conductive material and is capable of dispersing the exothermal heat from the active metal site. Therefore, this design makes a rapid oxidation possible.  
       EXAMPLE 1  
     Preparation of Supported Pt/BN Catalyst  
       [0028]    One gram (1 g) of H 2 PtCl 6 *6H 2 O [Hexachloroplatinic acid hexahydrate] was dissolved in a small quantity of methanol to form a total volume of 12 cc. This solution is then added drop wise onto 10 g of h-boron nitride. The incipient dry mass was then heated at 70° C. to dry under an infrared lamp (250W). It was then transferred into a steel reactor tube and heated at 300° C. with an air flow of 15 cc/min for 2 hr. The BET surface area of the catalyst was 49 M 2 /g.  
       EXAMPLE 2  
     Preparation of the Supported Pt/BN Catalyst on the Supporting Material  
       [0029]    Five gram (5 g) of a stable porous supporting material in sizes of 8-16 mesh, such as γ-alumina or an industrial oxidation catalyst itself was added with small volume of methanol equivalent to pore volume of the support. Then, one gram (1 g) of the above catalyst, Pt/BN, was suspended in 3 cc of methanol, and the paste was then dispersed onto the supporting material under mild stirring with a glass rod. The mixture is first dried at 70° C. under an infrared lamp and then further heated to 300° C. under an air stream of 15 cc/min for two hours (2hr). The BET surface area of this supported catalyst, Pt/BN/g-Al 2 O 3 , was 170 M 2 /g.  
         [0030]    The same procedure was used to prepare a host of supported Pt/BN with two commercial oxidation catalyst, N220 and DASH-220. The surface properties are shown in Table 1.  
                                                                                         TABLE 1                           Surface properties of supported Pt/BN catalysts                Before oxidation reaction   30 Hr after oxidation reaction                BET area   Pore vol.   Pore size   BET area   Pore vol.   Pore size       Catalyst   M 2 /g   cc/g   Å   M 2 /g   cc/g   Å                    Pt/BN   39.4   0.16   165.3   37.9   0.18   191.8       Pt/BN/γ-Alumina a     169.4   0.45   107.3   144.4   0.42   116.2       Pt/BN/DASH220 b     135.5   0.38   112.1   85.5   0.34   160.7       Pt/BN/N220 c     126.5   0.34   117.4   100   0.36   142.1                                          
 
       EXAMPLE 3  
     Cold Started Catalytic Combustion of Methanol with Pt/BN/Support  
       [0031]    In this series of tests, 6 g of supported Pt/BN catalyst shown in Example 2 (1 g of Pt/BN on 5 g of support) were filled in a stainless steel tubular reactor of 10 mmID×250 mmL placed in an insulated oven without any external heating facility, as shown in FIG. 1. An appropriate amount of liquid methanol corresponding to the required WHSV of methanol was injected through a metering pump and air was fed upstream of methanol at room temperature. The reaction temperature surged up rapidly from room temperature to a peak temperature, T 1 , over 800° C. within 3 to 6 min and then maintained at a steady temperature, T 2  of 450° C. to 1000° C. depending upon the nature of support and the value of WHSV. Three catalysts were made using γ-alumina and two commercial Pt/alumuna oxidation catalysts, N220 and Dash-220 of Suid Chemie Catalysts Japan, Inc and N.E. Chemtac Corp. of Japan, respectively, as the support for Pt/BN and were tested for their temperature rise in the catalytic combustion of methanol. The results of these catalytic combustion reactions are shown in FIG. 2, Table 2 and Table 3 for T 1  and T 2 .  
                                                       TABLE 2                           Catalytic combustion of methanol with WHSV = 2.4 #                          Time to       Catalysts at O 2 /CH 3 OH═   T 1  (° C.)   T 2  (° C.)   T 1  (min)                    Pt/BN/g-Alumina   1.65   800   443   6       Pt/BN/g-Alumina   1.80   811   485   6       Pt/BN/DASH220   1.65   &gt;1000   886   5       Pt/BN/DASH220   1.80   &gt;1000   945   3       Pt/BN/N220   1.65   &gt;1000   &gt;1000   4       Pt/BN/N220   1.80   &gt;1000   &gt;1000   3                          
 
         [0032]    [0032]                                                       TABLE 3                           Catalytic combustion of methanol with WHSV = 3.2 #                          Time to       Catalysts at O 2 /CH 3 OH═   T 1  (° C.)   T 2  (° C.)   T 1  (min)                    Pt/BN/g-Aluinina   1.65   947   500   6       Pt/BN/g-Alumina   1.80   875   550   6       Pt/BN/DASH220   1.65   &gt;1000   &gt;1000   4       Pt/BN/DASH220   1.80   &gt;1000   &gt;1000   3       Pt/BN/N220   1.65   &gt;1000   &gt;1000   6       Pt/BN/N220   1.80   &gt;1000   &gt;1000   5                            
       EXAMPLE 4  
     Catalytic Combustion of n-hexane with Pt/BN-N-220  
       [0033]    With an O 2 /n-Hexane=10.45 (10% exceed the theoretical oxygen demand from air), n-hexane 9.96 glhr was fed at room temperature onto 6 g of Pt/BN-N-220 catalyst which was made as shown in Example 2 with a space velocity of WHSV=1.66. The reaction temperature rose to 850° C. in 6 min and 999 in 10 min and maintained at a steady temperature of 980-970° C. The temperature profile of catalyst zone is shown in FIG. 3.  
       EXAMPLE 5  
     Catalytic Combustion of Fuel to Start up a Steam Reforming Reaction  
       [0034]    In a double jacket stainless steel reactor, as shown in FIG. 4, the reactor is composed of an inner tube 41 of 13 mmOD×300 mInL containing 12 g of Pt/BN-γ-Al 2 0 3  and a jacket 42 of 25 mmID×32 mmL containing 160 g of CuOZnO catalyst (G-66B of Suid Chemie Catalyst Japan, Inc). The reactor was wrapped with mineral wool for insulation (not shown). Both the inner reactor and the jacket reactor were independently connected with delivery pumps (not shown) for feeding combustion fuel and raw material to reformer, respectively. Methanol fuel, 7.5 mmo1/min or WHSV=2.4, was firstly injected into the combustion catalyst zone through an inlet 43 for oxidation and then, within 12 minutes, the bed temperature, Tox, rose to 560° C. while the temperature in the steam reforming zone 44, TSR, shoot up to 360° C. simultaneously. The steam reforming reaction of methanol was set on with the injection of raw material mixture, 7.5 mmo1/min of methanol and 9 mmo1/min of water, hydrogen and carbon dioxide mixture evolved from the side tube 45. After maintaining steady for another 60 min, the methanol fuel for catalytic combustion was changed to the same aqueous methanol mixture, MeOH: 6.7 mmol/min and H 2 O: 8 mmo1/rnin and immediately Tox and TSR dropped to 460° C. and 3 10° C., respectively. The reaction is allowed to continue for another 40 minutes smoothly before shut down.  
       EXAMPLE 6  
     Ten Hours Life Test of Catalytic Combustion with Pt/BN/N220  
       [0035]    In this experiment, a catalytic combustion with a catalyst of PtBN/N220, MeOH=0.4 mL/min, Air=2 L/min, WHSV=3.2, O 2 /C=1.65 is started from room temperature and is undergone a 10-hours on-streaming operation. The result is shown in FIG. 5, wherein T 1  represents the temperature at the peak and T 2  represents the temperature at the steady.  
         [0036]    In view of afore said, the catalytic combustion according to the present invention can easily achieve a desired high temperature within a very short time and maintain at a steady temperature for a long time. Furthermore, the fuel does not need to be preheated for shortening the initiating time, namely, the fuel can start at room temperature. Moreover, as shown in EXAMPLE 3, the desired reaction temperature or the steady temperature, T 2 , can be controlled by choosing proper catalyst, space time, WHSV, and oxygen/methanol ratio. Therefore, through these features described above, the present invention can be easily employed for supplying the heat to an industrial reactor or facilities.  
         [0037]    While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention need not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustration should not be taken as limiting the scope of the present invention which is defined by the appended claims.