Method for preparing ethane and ethylene from methane

Abstract: A method for preparing ethane and ethylene by reacting methane or a methane-containing natural gas in the presence of oxygen or an oxygen-containing gas, i.e., by partially oxidizing, at a temperature of 500 through 1000°C using shellfishes or shells as a catalyst is disclosed. The oxidation coupling reaction of methane is controlled so as to remarkably increase the conversion ratio of methane and the selectivity of C₂⁺ compounds. The waste matter abundantly released from food industries as well as easily accessible natural resources is used as a raw material of a catalyst for the reaction. The present method is extremely useful from the viewpoint of the recycling of waste as well.

Description: Field of the Invention: This invention relates to a method for preparing ethane and ethylene by reacting methane or a methane-containing natural gas in the presence of oxygen or an oxygen-containing gas. Description of the Prior Art: Methane is one of the resources which are abundant in the world as a main component of natural gases. However, since methane has low reactivity, the greater part of methane is exhausted as a fuel, and the utilized methods as a raw material for chemical industries are available on a limited basis. In 1982, however, Keller and Bhasin reported that ethane and ethylene are produced by partial oxidation of methane using various metal oxides as a catalyst in the presence of oxygen (Journal of Catalysis published in U.S.A. Vol. 73, pp. 9-19, 1982). Since then, many reports have been made on the useful catalysts for this reaction, which is called oxidative coupling of methane. In case of classifying these catalysts, alkali metals and alkaline-earth metals, and for example, rare-earth metals such as lanthanide or their combinations are used as these catalysts in the majority of these catalysts. In particular, there are many reports on the catalysts which mainly consist of alkaline-earth metal. For instance, it is disclosed in Japanese Pat. Laid-open No. 62-267243 that ethane and ethylene are produced using a catalyst of an alkaline-earth metal compound such as calcium oxide. In most of the above cases, however, the conversion ratio of methane and the selectivity of C₂⁺ hydrocarbons in the product are still low and the abilities are not so high as a practical catalyst. Therefore, it is desired to develop catalysts with higher activity and higher selectively. SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a method for preparing ethane and ethylene using accessible catalysts for further developing the activity and selectivity. Another object of the present invention is to increase remarkably the conversion ratio of methane and the selectivity to C₂⁺ hydrocarbons in the oxidative coupling of methane by reacting methane or a methane-containing natural gas in the presence of oxygen or an oxygen-containing gas, i.e., by partial oxidation, using shellfishes or shells as a catalyst at a temperature of 500 to 1000°C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have variously examined the catalysts for the oxidative coupling of methane and found that hydrocarbons with two or more carbon atoms such as ethane, ethylene can be prepared at a high activity and a high selectivity by using shellfishes or shells as a catalyst. On the basis of these findings, the present invention has, accordingly, been completed. The present invention relates to a method for preparing ethane and ethylene by partial oxidation of methane or a methane-containing natural gas with oxygen or an oxygen-containing gas in the presence of shellfishes or shells at a temperature of 500 to 1000°C. In the present invention, shellfishes or shells are used as a catalyst. The main component of shells is calcium carbonate and contains inorganic salts such as strontium, sodium, magnesium, sulfur or the like, and 1% of a conchiolin, a kind of a protein. The outermost portion of the shells is covered with thin shell epidermis, the intermediate portion has prismatic layers and the innermost portion has mother-of-pearl layer. Furthermore, shells have a lot of fine capillaries which are opened perpendicular to the shell surfaces through the three layers. The catalysts to be used in the present invention are usually prepared as follows. Namely, they are prepared by putting shellfishes or shells in an alumina-made crucible and by calcining at 500 to 1300°C, preferably 600 to 1100°C and more preferably 700 to 1000°C. It is also possible to prepare the catalysts by calcining at 500 to 1300°C likewise after pulverization. When the temperature for calcination is set at not more than 500°C, the selectivity to C₂⁺ hydrocarbons decreases. On the other hand, when the temperature for calcination is set at not less than 1300°C, the activity decreases likewise. Therefore, it is necessary to set the calcination temperature in a range from 500 to 1300°C. The catalysts prepared from shellfishes or shells have a fine pore structure which contributes to the manifestation of the high efficiency. It is considered that this fine pore structure is formed on calcination at which conchiolin in shells, three-layer-structure of shell epidermis, prismatic layer and mother-of-pearl layer, and numberless fine capillaries are referred complicatedly to one another. Therefore, the calcination temperature is extremely important to the formation of the fine pore structure of the catalysts. The catalysts thus obtained are crushed into powder having a size of not less than 100 mesh, which can also be used. However, depending on the necessity, the catalysts are molded by a compacting molding machine and then, the catalysts are further crushed into granules with a size of preferably 16 to 32 mesh, which can also be used. Furthermore, these catalysts can also be used with silica sand, alumina, magnesia, calcia, and other diluents. In addition, one or more kinds of elements selected from the group consisting of alkali metals, metals of Group IIa, metals of Group IIIa, metals of Group IVa, metals of Group Va and metals of Group VIIIa of the periodic table can be used by adding to shellfishes or shells. The salts, oxides and hydroxides of these elements can be used by adding to shellfishes or shells. In case of conducting the oxidative coupling of methane by utilizing the above catalysts, methane and oxygen are used by mixing methane with oxygen at the molar ratio of CH₄/O₂ of 1 to 100, preferably 2 to 70 and more preferably 3 to 50. It is of course justified to allow the catalysts to coexist with an inert gas such as helium, argon and nitrogen as a diluent. These mixed gases are supplied to a reaction tube packed with the catalysts and the reaction is conducted at a temperature of normally 500 to 1000°C, more preferably 600 to 900°C or most preferably 700 to 850°C. The reaction is normally conducted under atmospheric pressure, but it may, if necessary, be conducted under reduced or compressed pressure as well. Methane separated from natural gases is usually used in the reaction described above, but methane produced from coal and other materials may be utilized. Furthermore, methane-containing natural gases themselves can also be used as a raw material. Oxygen separated from air by low temperature processing and oxygen concentrated by means of gas separation membranes can be used. Furthermore, oxygen in the air can also be used as it is. In the case of executing the present invention, the catalysts can be used in any modes of fixed bed, moving bed and fluidized bed reactors. On the basis of the following examples, further detailed description will be given. However, it is to be understood that other forms might be adopted. In addition, shells may be used instead of shellfishes, and the shellfishes including the contents may be used as they are. Results in Examples 1 to 7 are given in Tables 1 and 2 respectively and those in Comparative Examples 1-2 and examples 8-9 are given in Table 3. Example 1 (1) Preparation of Catalysts Shells of corbiculas were put in an alumina-made crucible, dried at 120°C and calcined at 900°C for 10 hours. (2) Reaction Test After 1g of the above catalyst was packed in an alumina-made reaction tube, mixed gas of methane and oxygen in the molar ratio of 9 : 1 was passed through the reaction tube at a flow rate of 100ml/min at temperatures of 750°C and 800°C under atmospheric pressure to react the mixed gas. The reaction products prepared by the procedure described above were introduced into a gas chromatograph column using a sampling loop attached to the outlet of the reaction tube and then analyzed. The analytical results thus obtained are given in Table 1. In Table 1, methane and oxygen conversion ratios of methane and oxygen represent the proportion of the reacted methane and oxygen and C₂⁺ selectivity represents the composition ratio of the hydrocarbons of two or more carbon atoms in the reaction products. Example 2 Following the procedure described in Example 1 except the use of clams instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 1. Example 3 Following the procedure described in Example 1 except the use of trough-shells instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 1. Example 4 Following the procedure described in Example 1 except the use of sea mussels instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 1. Catalyst Temp. (°C) Conversion Ratio (%) Selectivity (%) C₂⁺ CH₄ O₂ Example 1 corbicula 750 14.8 94.8 85.2 800 14.7 94.4 84.8 Example 2 clam 750 17.7 97.8 79.2 800 17.4 98.3 79.1 Example 3 trough-shell 750 15.1 90.3 77.4 800 15.9 97.0 78.5 Example 4 sea mussel 750 16.2 97.8 77.5 800 16.6 98.1 78.5 Reaction condition: CH₄ : O₂ = 9 : 1 (mole ratio), total gas supply: 100ml/min and catalyst amount : 1g Example 5 Following the procedure described in Example 1 except the use of scallops instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 2. Example 6 Following the procedure described in Example 1 except the use of periwinkles instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 2. Example 7 Following the procedure described in Example 1 except the use of ark shells instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 2. Catalyst Temp. (°C) Conversion Ratio (%) Selectivity (%) C₂⁺ CH₄ O₂ Example 5 scallop 750 17.8 96.2 81.1 800 17.5 98.2 80.4 Example 6 periwinkle 750 16.8 83.7 79.8 800 17.6 96.7 82.4 Example 7 ark shell 750 16.7 97.8 78.3 800 16.5 98.3 77.2 Reaction condition: CH₄ : O₂ = 9 : 1 (mole ratio), total gas supply: 100ml/min and catalyst amount : 1g Comparative Example 1 Following the procedure described in Example 1 except the use of calcium oxide instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 3. Comparative Example 2 Following the procedure described in Example 1 except the use of calcium carbonate instead of corbiculas, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 3. Example 8 Following the procedure described in Example 1 by use of corbiculas and except heating them at 1300°C, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 3. Example 9 Following the procedure described in Example 1 by use of corbiculas and except heating them at 1700°C, the catalyst was prepared and then the reaction was conducted. The results thus obtained are shown in Table 3. Catalyst Temp. (°C) Conversion Ratio (%) Selectivity (%) C₂⁺ CH₄ O₂ Comparative example 1 Calcium oxide 750 9.9 95.2 40.1 800 11.9 98.0 55.1 Comparative example 2 Calcium carbonate 750 9.0 97.5 48.1 800 10.7 98.9 60.8 example 8 Corbicula (calcining at 1300°C) 750 8.5 64.6 60.5 800 12.4 94.4 64.8 example 9 Corbicula (calcining at 1700°C) 750 1.6 16.9 30.8 800 6.1 85.2 39.7 Reaction condition: CH₄ : O₂ = 9 : 1 (mole ratio), total gas supply: 100ml/min and catalyst amount : 1g

Claims: A method for preparing ethane and ethylene from methane comprising the step of partial oxidation of methane or a methane-containing natural gas with oxygen or an oxygen-containing gas using shellfishes or shells as a catalyst at a temperature of 500 through 1000°C. A method for preparing ethane and ethylene from methane according to claim 1, wherein said shellfishes or shells are corbiculas. A method for preparing ethane and ethylene from methane according to claim 1, wherein said shellfishes or shells are clams. A method for preparing ethane and ethylene from methane according to claim 1, wherein said shellfishes or shells are scallops.

Inventors: CHAKI KAZUTOSHI, OKADO HIDEO, TSUZUKI NAOHIDE, WAKATSUKI TOSHIYA, YAMAMURA MASAMI, CHAKI, KAZUTOSHI, OKADO, HIDEO, TSUZUKI, NAOHIDE, WAKATSUKI, TOSHIYA, YAMAMURA, MASAMI
Applicants: COSMO SOGO KENKYUSHO KK, JAPAN NATIONAL OIL, SEKIYUSHIGEN KAIHATSU KABUSHIK, COSMO RESEARCH INSTITUTE, JAPAN NATIONAL OIL CORPORATION, SEKIYUSHIGEN KAIHATSU KABUSHIKI KAISHA
Application year: 1993
Main classification: C07C9
IPC codes: C07C9, B01J23, C07C2, B01J27, C07B61, C07C11