PROCESS FOR THE PRODUCTION OF HYDROCARBONS

Abstract: A process for production of hydrocarbons having two or more carbon atoms, such as ethane and ethylene, from methane is disclosed, comprising contacting methane with a catalyst containing at least one rare earth in the presence of oxygen. The present process permits production of the desired hydrocarbons with high efficiency at relatively low temperatures.

Description: PROCESS FOR THE PRODUCTION OF HYDROCARBONS BACKGROUND OF THE INVENTION The present invention relates to a process for the production of hydrocarbons. More particularly, it is concerned with a process for producing industrially useful hydrocarbons having two or more carbon atoms, such as ethane and ethylene, from methane with high efficiency by the use of specific catalysts. Methane contained in natural gas, for example, has been used to produce industrially useful hydrocarbons such as ethane, ethylene and acetylene. Various methods of production of such useful hydrocarbons are known. In any of the known methods, the hydrocarbons are produced by the oxidative dehydrogenation reaction at temperatures as high as more than 1,000 degree centigrade (OC). In industrial application, therefore, the methods have disadvantages in that expensive heat-resistant equipment and a large amount of energy are needed and in that the operation is difficult. In recent years, several methods to produce hydrocarbons having two or more carbon atoms from methane at lower temperature have been proposed. These methods, however, are unsuitable for practical use because the conversion of methane and selectivities for ethane and ethylene, for example, are low. SUMMARY OF THE INVENTION As a result of extensive investigations to produce useful hydrocarbons such as ethane and ethylene from methane with high efficiency at relatively low temperatures, it has been found that the object can be attained by using specific catalysts containing rare earth metals. The present invention relates to a process for producing hydrocarbons having two or more carbon atoms from methane which comprises contacting methane with a catalyst containing at least one rare earth metal. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the effect of reaction temperature on selectivity and conversion when samarium oxide was used as a catalyst; and Fig. 2 is a graph showing the effect of reaction temperature on selectivity and conversion when dysprosium oxide was used as a catalyst. DETAILED DESCRIPTION OF THE INVENTION As the methane that is used as a feedstock in the present invention, as well as high purity methane gas, natural gas composed of various kinds of gas can be used. In use the methane feedstock may be diluted with inert gas such as helium, nitrogen and argon, or steam. In the process of the present invention, it is necessary for the reaction to be carried out in the presence of oxygen. The concentration of oxygen in the reaction system can be determined taking into consideration a degree of reaction and an explosion limit. As the oxygen to be supplied to the reaction system, as well as pure oxygen, mixed gas containing oxygen and other gas not exerting adverse influences on the reaction (e.g., air) can be used. The catalysts of the present invention contain at least one rare earth metal. The rare earth metal includes scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), itterbium (Yb) and lutetium (Lu). Of these metals, Sc, Y, La, Nb, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu are particularly suitable. Examples of the catalyst of the present invention are one metal selected from the above metals, a mixture of two or more metals selected from the above metals, the oxide of one metal selected from the above metals, and a mixture of the oxides of two or more metals selected from the above metals. In particular, metal oxides are suitable for use in the present invention. Representative examples of such metal oxides are scandium oxide (Sc203), ittrium oxide (Y203), lanthanum oxide (La203), samarium oxide (Sm203), europium oxide (Eu203), gadolinium oxide (Gd203), disprosium oxide (Dy203), holmium oxide (Ho203), erbium oxide (Er203), thulium oxide (Tm203), itterbium oxide (Yb203), and lutetium oxide (Lu203). In the process of the present invention, the metal or metal oxide as the catalyst can be used as such. In practical use, however, since the surface area of the catalyst is desirable to be large, it is suitable for the catalyst to be used in a powdery or granular form. The metal or metal oxide may be deposited on an inorganic oxide carrier. Inorganic oxide carriers which can be used for this purpose include silica, alumina, magnesia, titania, and zirconia. Deposition of the metal or metal oxide on such inorganic carrier can be carried out by known techniques such as impregnation and kneading. To the catalyst of the present invention can be added the oxides of alkali metals and/or alkaline earth metals. Representative examples of such oxides are calcium oxide (CaO), magnesium oxide (MgO), sodium oxide (Na2O), and potassium oxide (K20). Addition of such oxides retards complete oxidation and increases the selectivity of methane to hydrocarbons having two or more carbon atoms. In accordance with the process of the present invention, the methane feedstock is contacted with the above-prepared catalyst in the presence of oxygen. The reaction is continuously carried out by passing methane and oxygen, if necessary, in combination with inert gas as a dilutent through a tube-shaped flow reactor packed with the catalyst. Thus, in the process of the present invention, the desired hydrocarbons are produced with high efficiency. In connection with reaction conditions, the pressure is atmospheric pressure to 50 kilograms per square centimeter by gauge (kg/cm2G) and preferably atmospheric pressure to 10 kg/cm2G, and the temperature is about 500 to 1,0000C and preferably about 650 to 7500C. In the process of the present invention, various hydrocarbons having two or more carbon atoms are produced, and in particular, ethane and ethylene are obtained in a selectivity as high as about 90%. As described above, the process of the present invention permits to continuously and efficiently produce hydrocarbons having two or more carbon atoms, particularly ethylene and ethane useful as starting materials for prcduction of various chemical products from methane in a very high selectivity under relatively low temperature conditions. Accordingly the process of the present invention is very useful from an industrial standpoint. The present invention is described below in greater detail with reference to the following examples. EXAMPLE 1 A quartz glass reactor was charged with 0.5 gram (g) of samarium oxide (Sm203), and 4.5 milliliters per minute (ml/min) of methane, 0.1 ml/min of oxygen and 20.4 ml/min of helium were passed through the reactor while heating in an electric furnace. The heating temperature was adjusted to 5000C, 5500C, 6000C, 6500C or 7000C. Reaction products obtained at each heating temperature were analysized by gas chromatography. This gas chromatographic analysis showed that the reaction products were ethylene, ethane, carbon dioxide and water. The results are shown in Fig. 1. The selectivity in Fig. 1 is calculated based on a carbon atom. EXAMPLE 2 The procedure of Example 1 was repeated wherein 0.5 g of dysprosium oxide was used as the catalyst. The results are shown in Fig. 2. EXAMPLES 3 TO 13 A predetermined amount of a catalyst as shown in Table 1 was placed in a quartz glass reactor, and 4.5 ml/min of methane, 0.1 ml/min of oxygen and 20.4 ml/min of helium were passed through the reactor while heating at 7000C in an electric furnace. Selectivities and rates of formation of reaction products, ethylene, ethane, carbon dioxide and water are shown in Table 1. Table 1 Run Catalyst Selectivity (%)*Ú Rate of Formation ( mol/mê min)*ê No. Type Amount Ethane Ethylene CO2 Ethane Ethylene CO2 Water (g) Example 3 Sc2O3 0.5 57 18 25 - - - " 4 Y2O3 " 54 23 23 0.8 0.3 0.7 2.4 " 5 La2O3 " 57 29 14 0.45 0.2 0.2 1.1 " 6 Nd2O3 " 61 26 13 0.55 0.2 0.2 1.4 " 7 Eu2O3 " 55 29 16 0.4 0.25 0.25 1.3 " 8 Gd2O3 " 58 26 16 1.4 0.65 0.8 3.7 " 9 Ho2O3 " 72 16 12 2.1 0.4 0.7 4.5 " 10 Er2O3 " 72 11 17 1.2 0.2 0.6 2.7 " 11 Tm2O3 " 74 15 11 0.9 0.2 0.3 1.8 " 12 Yb2O3 " 70 16 14 1.0 0.2 0.4 2.3 " 13 Lu2O3 " 50 30 20 0.4 0.2 0.3 1.3 Note: *1 Calculated based on a carbon atom. *2 Amount ( mol) formed per square meter of the catalyst surface area and per minute. EXAMPLES 14 TO 17 A quartz glass reactor was charged with 1.0 g of samarium oxide (Sm2O3), and a mixed gas of methane, oxygen and helium was passed through the reactor at a rate of 25 ml/min in such a manner that the methane partial pressure and oxygen partial pressure were maintained at predetermined values, and the total pressure was 100 kilo Pascal (KPa), while heating at 7000C in an electric furnace. Reaction products obtained were analyzed by gas chromatography. The results are shown in Table 2. EXAMPLE 18 The procedure of Example 14 was repeated wherein the heating temperature was changed to 7200C. The results are shown in Table 2. EXAMPLES 19 TO 21 A quartz glass reactor was charged with 2.22 g of lithium-containing samarium oxide (Li/Sm203)(lithium content: 7 percent by weight (wt%)), and a mixed gas of methane, oxygen and helium was passed through the reactor at a rate of 25 ml/min in such a manner that the methane partial pressure and oxygen partial pressure were maintained at predetermined values and the total pressure was 100 KPa, while heating at 7000C in an electric furnace. Reaction products obtained were analyzed by gas chromatography. The results are shown in Table 3. EXAMPLE 22 The procedure of Example 19 was repeated wherein the heating temperature was changed to 7200C. The results are shown in Table 3. Table 2 Methane Oxygen Run Partial Partial No. Pressure Pressure Methane Oxygen Ethylene CO + CO2 Ethylene Ethane (KPa) (KPa) + Ethane Example 14 17.5 3.39 15.7 89.6 48.9 27.4 23.7 51.1 " 15 17.9 4.20 18.4 90.7 51.4 27.1 21.5 48.6 " 16 19.2 7.94 27.4 92.6 62.7 22.8 14.5 37.3 " 17 8.9 4.20 31.0 90.5 63.9 21.7 14.4 36.1 " 18 8.7 5.00 36.4 92.5 67.7 20.6 11.7 32.3 Note: *1 Calculated based on a carbon atom. Table 3 Methane Oxygen Run Partial Partial Conversion (%) Selectivity (%)*Ú No. Pressure pressure Methane Oxygen CO + CO2 Ethylene Ethane Ethylene (KPa) (KPa) + Ethane Example 19 19.3 5.23 18.6 71.7 41.1 34.7 24.2 58.9 " 20 17.9 8.10 25.3 67.3 50.7 31.3 18.0 49.3 " 21 8.2 4.77 30.4 64.9 53.2 28.9 17.9 46.8 " 22 8.3 5.09 35.1 75.1 57.0 28.0 15.0 43.0

Claims: WHAT IS CLAIMED IS: 1. A process for producing hydrocarbons having two or more carbon atoms from methane which comprises contacting the methane with a catalyst containing at least one rare earth metal in the presence of oxygen. 2. The process as claimed in Claim 1, wherein the hydrocarbons having two or more carbon atoms are ethylene, ethane or a mixture thereof. 3. The process as claimed in Claim 1, wherein the rare earth metal is scandium, ittrium, lanthanum, neodynium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium. 4. The process as claimed in Claim 1, wherein the catalyst is the oxide of a rare earth metal.

Inventors: MORIKAWA, AKIRA, OTSUKA, KIYOSHI
Applicants: IDEMITSU KOSAN COMPANY LIMITED
Application year: 1986
Main classification: C07C2
IPC codes: C07C1, C07C2, C07C11, B01J23, C07B61, C07C67, C07C9