Catalyst for the preparation of dimethyl ether, method of producing catalyst and method of producing dimethyl ether

Abstract: A catalyst suitable for producing dimethyl ether comprises alumina particles having an average size of 200 µm or less and a methanol synthesis catalyst layer formed around each of the alumina particles. The methanol synthesis catalyst has a weight ratio of 0.05 to 5 to a weight of the alumina particles. The catalyst is produced by forming a layer comprising a methanol synthesis catalyst around each of alumina particles. The dimethyl ether is produced by the method of foming a slurry by introducing the catalyst into a solvent and introducing a mixed gas comprising carbon monoxide and hydrogen into the slurry.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for dimethyl ether, a method for producing the catalyst, and a method for producing dimethyl ether by using the catalyst. 2. Description of the Related Arts There are several known methods for manufacturing dimethyl ether starting from a mixed gas of carbon monoxide, carbon dioxide, and hydrogen under the presence of a catalyst suspended in a solvent. For example, JP-A-2-9833 (the term "JP-A-" referred to herein signifies "Unexamined Japanese patent publication"), JP-A -3-181435, JP-A-3-52835, JP-A-4-264046 (corresponding to EP-A-0483609, WO 93 / 10069 (corresponding to EP-A-0591538), disclose methods for manufacturing dimethyl ether or a mixture of dimethyl ether and methanol through the contact of a synthesis gas with a mixture of a methanol synthesis catalyst and a methanol dehydration catalyst suspended in an inert liquid. The method disclosed in JP-A-2-9833 is a method of direct synthesis of dimethyl ether from a synthesis gas, which method comprises the step of contacting a synthesis gas consisting of hydrogen, carbon monoxide and carbon dioxide with a solid catalyst, or reacting the synthesis gas react under the presence of the solid catalyst to conduct catalytic synthesis of dimethyl ether from the synthesis gas, wherein the synthesis gas undergoes catalytic action under the presence of the solid catalyst system, and wherein the solid catalyst is a single catalyst or a mixture of plurality of catalysts which are suspended in a liquid medium in a three-phase (slurry phase) reactor system, and wherein the three-phase reactor system comprises at least a single three-phase reactor. The method disclosed in JP-A-3-181435 is a method for manufacturing dimethyl ether from a mixed gas of carbon monoxide and hydrogen, or a mixed gas of carbon monoxide and hydrogen and further containing carbon dioxide and/or water vapor, wherein a catalyst is used in a slurry form by suspending thereof in a solvent. The method disclosed in JP-A-3-52835 is a method of dimethyl ether synthesis characterized in that a synthesis gas is reacted under the presence of a solid methanol synthesis catalyst to produce methanol, and that the produced methanol is reacted under the presence of a solid dehydration catalyst to produce dimethyl ether. According to the method, dimethyl ether is synthesized from a synthesis gas consisting of hydrogen, carbon monoxide, and carbon dioxide. That is, the synthesis gas is contacted with a solid catalyst system comprising a methanol-synthesizing ingredient and a dehydrating (ether-forming) ingredient, wherein the solid catalyst system is a single catalyst or a mixture of plurality of catalysts in a three-phase (liquid phase) reactor system, and wherein the reactor system is controlled to keep the minimum effective methanol rate to at least a level of 1.0 g-mole of methanol per 1 kg of catalyst per hour. The method disclosed in WO 93 / 10069 (EP-A- 0591 538) is a method for manufacturing dimethyl ether from a mixed gas containing carbon monoxide and either or both of water and water vapor, or from a mixed gas containing carbon monoxide and either or both of water and water vapor and further containing carbon dioxide, wherein a catalyst is used in a form of solvent slurry, which catalyst is prepared by pulverizing a mixed catalyst containing at least zinc oxide and, copper oxide or chromium oxide, and aluminum oxide, by adhering these ingredients together under pressure, and by pulverizing them again to suspend in the solvent. On the other hand, dimethyl ether is synthesized generally in a fixed bed system. There is a known catalyst for fixed bed system, which catalyst is prepared by depositing a methanol synthesis catalyst onto a support of metallic oxide such as alumina, then by calcining them together. (JP-A-2-280386) The methods for manufacturing dimethyl ether disclosed in JP-A-2-9833, JP-A- 3-52835, JP-A-4-264046 (EP-A-0483 609), and JP-A-3-181435, however, raise problems such that the two kinds of or three kinds of catalysts suspended in a solvent separate from each other in the reactor owing to the difference in specific gravity among the methanol synthesis catalyst, the methanol dehydration catalyst, and the water gas shift catalyst, which induces a distribution in catalyst concentration or deposition of one of these catalysts, thus significantly degrading the use efficiency of the catalysts. The catalyst disclosed in WO 93 / 10069 (EP-A-0 591 538) is prepared by integrating the above-described three kinds of catalysts by means of a mechanical method. That type of catalysts also raises a problem that, during a period of use in a slurry state, the catalyst particles separate from each other to induce a distribution in catalyst concentration and catalyst deposition. SUMMARY OF THE INVENTION It is an object of the present invention to provide a catalyst suitable for producing dimethyl ether at a high yield and a method for producing the catalyst, and to provide a method for producing dimethyl ether at a high space time yield. To attain the object, the present invention provides a catalyst suitable for producing dimethyl ether, the catalyst comprising: alumina particles having an average size of 200 µm or less; a layer comprising a methanol synthesis catalyst which comprises copper oxide, zinc oxide and alumina, the layer being formed around each of the alumina particles; and the methanol synthesis catalyst having a weight ratio of 0.05 to 5 to a weight of the alumina particles. In the catalyst, the average size of the alumina particles is preferably 1 to 100 µm. The average size of 1 to 50 µm is more preferable. It is desirable that a weight ratio of the copper oxide : the zinc oxide : the alumina is 1 : 0.05 to 20 : up to 2. The catalyst suitable for producing dimethyl ether is produced by the following method comprising the steps of: forming a layer comprising a methanol synthesis catalyst around each of alumina particles; and washing the alumina particles, around which the layer was formed, with an acid aqueous solution. The forming of the layer comprises forming a slurry by introducing the alumina particles into an aqueous solution containing a metallic salt of active element of the methanol synthesis catalyst; heating the slurry; and neutralizing the heated slurry with a base solution, thereby the active element of the methanol synthesis catalyst being deposited around each of the alumina particles. The deposition of the active element of the methanol synthesis catalyst is carried out at a temperature of 50 to 90 °C. Dimethyl ether is produced by using the catalyst. A method for producing dimethyl ether comprising the steps of : providing the catalyst suitable for producing dimethyl ether, the catalyst; forming a slurry by introducing the catalyst into a solvent; and introducing a mixed gas comprising carbon monoxide and hydrogen into the slurry. DESCRIPTION OF THE EMBODIMENT The catalyst according to the present invention comprises alumina particles and a methanol synthesis catalyst layer formed around each of the alumina particles. Alumina functions as a methanol-dehydration catalyst, and alumina in use as an ordinary catalyst may be applied without further processing. A preferable size of alumina particles is fine one, preferably 200 µm or less of average particle size, more preferably in an approximate range of from 1 to 100 µm, and most preferably in an approximate range of from 1 to 50 µm. To prepare the preferred average particle size, alumina may be pulverized at need. Methanol synthesis catalyst may be copper oxide - zinc oxide - alumina system. A preferable mixing ratio of individual ingredients of copper oxide, zinc oxide, and alumina is: in an approximate range of from 0.05 to 20 wt.parts of zinc oxide to 1 wt.parts of copper oxide, more preferably in an approximate range of from 0.1 to 5 wt.parts; in an approximate range of up to 2 wt.parts of alumina, more preferably in an approximate range of up to 1 wt.parts. The ratio of the methanol synthesis catalyst layer formed around alumina particle is in a range of from 0.05 to 5 by wt.parts to 1 wt.parts of alumina, preferably in a range of from 0.1 to 3 wt.parts, and more preferably in a range of from 0.5 to 2 wt.parts. The catalyst achieves 30 % or higher CO conversion, or normally in an approximate range of from 35 to 60 %, and particularly in an approximate range of from 45 to 55 %, and achieves 20 % or higher dimethyl ether yield, or normally in an approximate range of from 25 to 45 %, and particularly in an approximate range of from 35 to 45 %. A preferred particle size of the catalyst is small as far as possible within a range that no agglomeration problem occurs. A preferable average particle size of the catalyst is 200 µm or less, more preferably in an approximate range of from 1 to 100 µm, and most preferably in an approximate range of from 1 to 50 µm. The method for manufacturing the catalyst according to the present invention is characterized in the steps of: forming a methanol synthesis catalyst around each of alumina particles; and washing the catalyst layer with an acid aqueous solution. For manufacturing the catalyst, powdered alumina is charged into an aqueous solution containing a metallic salt of active ingredient of methanol synthesis catalyst, an aqueous solution of copper salt, zinc salt, and aluminum salt, to prepare a slurry. Copper salt, zinc salt, and aluminum salt may be either inorganic salt or organic salt if only the salt is a water soluble salt. Nevertheless, a salt that likely generates hydroxide in water is not suitable one. As for the salt of copper and of zinc, nitrate, carbonate, organic acid salt are applicable. For the salt of halide and of aluminum, nitrate, carbonate, and organic salt are applicable. A preferable concentration of each ingredient is in an approximate range of from 0.1 to 3 mole/liter. Thus prepared alumina slurry is then heated, and a base solution is added dropwise to the heated slurry to neutralize to deposit the active ingredient of methanol synthesis catalyst around each of alumina particles. The alumina particle may be coated by copper salt, zinc salt, and aluminum salt separately at need. The temperature of slurry during the period of deposition is in a range of from 50 to 90 °C, more preferably in a range of from 60 to 85 °C. Any kind of base is applicable if only it can neutralize the acid in the slurry. The neutralization is to deposit copper, zinc, and aluminum, and a preferable pH value is in an approximate range of from 6 to 12, more preferably in an approximate range of from 7 to 10. After neutralized, the slurry is allowed to stand for an appropriate time or is subjected to mild agitation for aging to sufficiently develop the deposits. The alumina particles on each of which the deposit is formed are separated from liquid. Thus separated solid alumina particles are washed with warm water. Normally, succeeding drying and calcining treatment provides a catalyst configured by alumina coated by a methanol synthesis catalyst. With the catalyst according to the present invention, however, methanol which is generated on the methanol synthesis catalyst migrates onto the alumina which is a methanol-dehydration catalyst, where the methanol undergoes dehydration and condensation by the action of acid active centers on the alumina to yield dimethyl ether, which mechanism is described later. In the deposit-forming operation described above, alumina contacts with base solution, and the acid active centers on alumina are vanished. To recover the acid active centers on alumina, the method for manufacturing catalyst according to the present invention washes the alumina particles with an acid aqueous solution after forming the above-described deposit. For washing, the alumina particles may be suspended in an acid aqueous solution. Applicable acid for washing is either inorganic acid or organic acid. A preferable acid includes nitric acid, hydrochloric acid, and acetic acid, and more preferably nitric acid and hydrochloric acid. The concentration of acid for acid washing is in an approximate range of from 0.1 to 5 mole/liter, more preferably in an approximate range of from 0.5 to 2 mole/liter. The temperature for washing may be room temperature, and a warm temperature may also be applicable. The period for washing may be in an approximate range of from 10 to 30 min. Next step is washing the alumina particles and deposits thoroughly with ion-exchanged water or the like to remove acid and base ions, followed by drying and calcining. The calcining may be carried out in air. The calcining temperature may be a temperature level that the metal hydroxide in the catalyst ingredients for methanol- synthesis is converted to metal oxide. For instance, a preferable calcining condition is preferably carried out at a temperature range of from 250 to 400 °C for a period of from 1 to 10 hours. The above-described catalyst is used in a state of slurry of a solvent. The amount of catalyst in the solvent depends on the kind of the solvent, the reaction conditions, and other variables. Normally, the amount of catalyst is in a range of from 1 to 50 wt.% to the amount of the solvent. The kind of solvent used for synthesizing dimethyl ether according to the present invention is arbitrarily selected if only the solvent is in liquid phase under the reaction condition. Examples of the solvent are hydrocarbons of aliphatic, aromatic, and alicyclic groups, alcohol, ether, ester, ketone, halide, or their mixture. Alternatively, gas oil after removing sulfur ingredients, vacuum gas oil, high boiling point distillates of coal tar after treated by hydrogenation are also applicable as the solvent. By passing a mixed gas of carbon monoxide and hydrogen through thus prepared slurry of catalyst with solvent, dimethyl ether is obtained at a high yield. Applicable range of molar mixing ratio of hydrogen to carbon monoxide (H 2 / CO) is wide, for instance, in a range of from 20 to 0.1 as (H 2 / CO), and more preferably from 10 to 0.2. According to the reaction system, the mixed gas does not directly contact with the catalyst, which direct contact occurs in a gas-solid catalytic reaction system, but the carbon monoxide and hydrogen contact with catalyst only after dissolved into a solvent. Consequently, selection of an adequate kind of solvent taking into account of the solubility of carbon monoxide and hydrogen to the solvent establishes a constant composition of carbon monoxide and hydrogen in the solvent independent of the gas composition, and sustains the supply of the mixed gas at an established composition to the catalyst surface. In the case of a mixed gas with significantly low ratio of (H 2 / CO), for example, 0.1 or less, or in the case of sole carbon monoxide without containing hydrogen, it is necessary to separately supply steam to convert a part of the carbon monoxide into hydrogen and carbon dioxide within the reactor. Since solvent exists between the raw material gases and the catalyst, the gas composition does not necessarily agree with the composition on the catalyst surface. Therefore, it is acceptable that the mixed gas of carbon monoxide and hydrogen, or sole carbon monoxide gas includes relatively high concentration of carbon dioxide (in a range of from 20 to 50 %). The manufacturing method according to the present invention significantly reduces the effect of ingredients that may act as catalyst-poison on the catalyst compared with the gas-solid contact catalyst system. Examples of the catalyst-poisoning ingredients which may exist in the raw material gas are sulfur compounds such as hydrogen sulfide, cyan compounds such as hydrogen cyanide, and chlorine compounds such as hydrogen chloride. Even when the catalyst decreased its activity resulted from poisoning, the productivity of total reactor system is maintained at a constant level by withdrawing the slurry from the reactor and by charging fresh slurry containing catalyst of high activity to the reactor. The reaction heat is recovered in a form of medium pressure steam using a cooling coil installed inside of the reactor while passing hot water through the cooling coil. The cooling system controls the reaction temperature at arbitrary level. A preferable reaction temperature is in a range of from 150 to 400 °C, and particularly preferable in a range of from 200 to 350 °C. The reaction temperature below 150 °C and above 400 °C degrades the conversion of carbon monoxide. A preferable reaction pressure is in a range of from 10 to 300 kg/cm 2 , and particularly preferable in a range of from 15 to 150 kg/cm 2 . The reaction pressure below 10 kg/cm 2 results in a low conversion of carbon monoxide, and that above 300 kg/cm 2 requires special design of reactor and is uneconomical because of the need of large amount of energy for pressurizing the system. A preferable space velocity (charge rate of mixed gas per 1 g of catalyst under standard condition) is in a range of from 100 to 50000 ml/g.h, and particularly preferable from 500 to 30000 ml/g·h. The space velocity above 50000 ml/g·h degrades the conversion of carbon monoxide, and that below 100 ml/g.h is uneconomical because of the need of an excessively large reactor. The catalyst for manufacturing dimethyl ether according to the present invention comprises alumina particles with a methanol synthesis catalyst layer formed around each of the alumina particles. The method for manufacturing the catalyst is characterized in the steps of: forming a catalyst active ingredients for synthesizing methanol around each of alumina particles; and washing the catalyst active ingredients with an acid aqueous solution. Since every catalyst ingredient has a size of molecular level and since each of the ingredients chemically adsorbs by each other, they do not separate during reaction period. In addition, very small distance of adjacent active ingredients allows the reaction cycle described below to proceed promptly, thus improves the yield of dimethyl ether. That is, the sequent order of the reaction begins with the yielding of methanol from carbon monoxide and hydrogen on the methanol synthesis catalyst, then the produced methanol migrates onto the alumina inside of the catalyst, where the methanol undergoes dehydration and condensation on the acid active centers on alumina, thus yielding dimethyl ether and water. Furthermore, the water migrates onto the methanol synthesis catalyst, where the water react with carbon monoxide to yield carbon dioxide and hydrogen. The reaction follows the reaction formulae given below. CO + 2H 2 → CH 3 OH 2CH 3 OH → CH 3 OCH 3 + H 2 O CO+H 2 O → CO 3 +H 2 The method for manufacturing dimethyl ether according to the present invention significantly increases the yield of dimethyl ether by using the catalyst which comprises alumina particles and methanol synthesis catalyst layer formed around each of the alumina particles in a state of slurry with a solvent. The method is free from problems such as plugging of catalyst and mechanical strength of catalyst, is designed to readily absorb the reaction heat through a cooling pipe or the like, and is designed to conduct withdrawing and filling of catalyst easily. Example I. Preparation of catalyst Examples 1, 5 through 8 Each of 185 g of copper nitrate (Cu(NO 3 ) 2 ·3H 2 O), 117 g of zinc nitrate (Zn(NO 3 ) 2 ·6H 2 O), and 52 g of aluminum nitrate (Al(NO 3 ) 3 · 9H 2 O) were dissolved into about 1 liter of ion-exchanged water. To the solution, 100 g of fine powder of γ-alumina (N612, Nikki Kagaku Co.) having approximate particle size of 20 µm or less was added. The prepared slurry was heated to around 80 °C and held at the temperature. Separately, about 1.4 kg of sodium carbonate (Na 2 CO 3 ) was dissolved into about 1 liter of ion-exchanged water, which solution was then heated to about 80 °C. The solution was added dropwise to the slurry until the slurry reached to pH 8.0. After completed the dropwise addition, the slurry was allowed to stand for about 1 hour for aging. Then, the slurry was filtered, and the cake was rinsed by ion-exchanged water at about 80 °C until sodium ion and nitric acid ion are not detected anymore. After the rinse, the resulted alumina particles were suspended in about 1 liter of aqueous solution of 1 mole/liter nitric acid, and were washed at room temperature for 20 min. The suspension was filtered to recover the alumina particles. The alumina particles were further rinsed with ion-exchanged water until no acid was detected anymore. The alumina particles were then dried at 120 °C for 24 hours followed by calcining thereof in air at 350 °C for 5 hours. The calcined alumina particles were classified to recover 120 µm or finer ones as the target catalyst. Analysis of thus obtained catalyst gave the composition as CuO:ZnO:Al 2 O 3 = 31:16:53 (by weight). Example 2 Each of 37.1 g of copper nitrate (Cu(NO 3 ) 2 ·3H 2 O), 23.4 g of zinc nitrate (Zn(NO 3 ) 2 ·6H 2 O), and 10.3 g of aluminum nitrate (Al(NO 3 ) 3 · 9H 2 O) were dissolved into about 1 liter of ion-exchanged water. To the solution, 100 g of fine powder of γ-alumina (N612, Nikki Kagaku Co.) having approximate particle size of 20 µm or less was added. The prepared slurry was heated to around 80 °C and held at the temperature. Separately, about 0.3 kg of sodium carbonate (Na 2 CO 3 ) was dissolved into about 1 liter of ion-exchanged water, which solution was then heated to about 80 °C. The solution was added dropwise to the slurry until the slurry reached to pH 8.0. After completed the dropwise addition, the slurry was allowed to stand for about 1 hour for aging. Then, the slurry was filtered, and the cake was rinsed by ion-exchanged water at about 80 °C until sodium ion and nitric acid ion were not detected anymore. After the rinse, the resulted alumina particles were suspended in about 1 liter of aqueous solution of 1 mole/liter nitric acid, and were washed following the procedure applied in Example 1. The alumina particles were then dried at 120 °C for 24 hours. followed by calcining thereof in air at 350 °C for 5 hours. The calcined alumina particles were classified to recover 120 µm or finer ones as the target catalyst. Analysis of thus obtained catalyst gave the composition as CuO:ZnO:Al 2 O 3 = 20:11:69 (by weight). Example 3 Each of 92.6 g of copper nitrate (Cu(NO 3 ) 2 ·3H 2 O), 58.5 g of zinc nitrate (Zn(NO 3 ) 2 ·6H 2 O), and 25.5 g of aluminum nitrate (Al(NO 3 ) 3 · 9H 2 O) were dissolved into about 1 liter of ion-exchanged water. To the solution, 100 g of fine powder of γ-alumina (N612, Nikki Kagaku Co.) having approximate particle size of 20 µm or less was added. The prepared slurry was heated to around 80 °C and held at the temperature. Separately, about 0.7 kg of sodium carbonate (Na 2 CO 3 ) was dissolved into about 1 liter of ion-exchanged water, which solution was then heated to about 80 °C. The solution was added dropwise to the slurry until the slurry reached to pH 8.0. After completed the dropwise addition, the slurry was allowed to stand for about 1 hour for aging. Then, the slurry was filtered, and the cake was rinsed by ion-exchanged water at about 80 °C until sodium ion and nitric acid ion were not detected anymore. After the rinse, the resulted alumina particles were suspended in about 1 liter of aqueous solution of 1 mole/liter nitric acid, and were washed following the procedure applied in Example 1. The alumina particles were then dried at 120 °C for 24 hours. followed by calcining thereof in air at 350 °C for 5 hours. The calcined alumina particles were classified to recover 120 µm or finer ones as the target catalyst. Analysis of thus obtained catalyst gave the composition as CuO:ZnO:Al 2 O 3 = 31:16:53 (by weight). Example 4 Each of 185 g of copper nitrate (Cu(NO 3 ) 2 ·3H 2 O), 117 g of zinc nitrate (Zn(NO 3 ) 2 ·6H 2 O), and 52 g of aluminum nitrate (Al(NO 3 ) 3 · 9H 2 O) were dissolved into about 1 liter of ion-exchanged water. To the solution, 50 g of fine powder of γ-alumina (N612, Nikki Kagaku Co.) having approximate particle size of 20 µm or less was added. The prepared slurry was heated to around 80 °C and held at the temperature. Separately, about 1.4 kg of sodium carbonate (Na 2 CO 3 ) was dissolved into about 1 liter of ion-exchanged water, which solution was then heated to about 80 °C. The solution was added dropwise to the slurry until the slurry reached to pH 8.0. After completed the dropwise addition, the slurry was allowed to stand for about 1 hr for aging. Then, the slurry was filtered, and the cake was rinsed by ion-exchanged water at about 80 °C until sodium ion and nitric acid ion were not detected anymore. After the rinse, the resulted alumina particles were washed by about 1 liter of aqueous solution of 1 mole/liter nitric acid following the procedure applied in Example 1. The alumina particles were then dried at 120 °C for 24 hours followed by calcining thereof in air at 350 °C for 5 hours. The calcined alumina particles were classified to recover 120 µm or finer ones as the target catalyst. Analysis of thus obtained catalyst gave the composition as CuO:ZnO:Al 2 O 3 = 41:21:38 (by weight). Example 9 A catalyst was prepared following the procedure applied in Example 1 except that the temperature of slurry was set to 40 °C. Example 10 A catalyst was prepared following the procedure applied in Example 1 except that the temperature of slurry was set to 50 °C. Example 11 A catalyst was prepared following the procedure applied in Example 1 except that the temperature of slurry was set to 60°C. Example 12 A catalyst was prepared following the procedure applied in Example 1 except that the temperature of slurry was set to 70 °C. Example 13 A catalyst was prepared following the procedure applied in Example 1 except that the temperature of slurry was set to 90 °C. Example 14 A catalyst was prepared following the procedure applied in Example 1 except that the temperature of slurry was set to 95 °C. Comparative Example 1 A catalyst was prepared following the procedure applied in Example 1 except that the temperature of slurry was set to 20 °C. Comparative Example 2 A catalyst was prepared following the procedure applied in Example 1 except that the case was rinsed only with ion-exchanged water and not rinsed with aqueous solution of nitric acid. Comparative Example 3 Each of 185 g of copper nitrate (Cu(NO 3 ) 2 ·3H 2 O), 117 g of zinc nitrate (Zn(NO 3 ) 2 ·6H 2 O), and 52 g of aluminum nitrate (Al(NO 3 ) 3 · 9H 2 O) were dissolved into about 1 liter of ion-exchanged water. Separately, about 1.4 kg of sodium carbonate (Na 2 CO 3 ) was dissolved into about 1 liter of ion-exchanged water. Both of these solutions were added dropwise to about 3 liters of ion-exchanged water in a stainless steel vessel controlled at about 80 °C, for a period of about 2 hours while maintaining the pH value of the mixture to 8.0 ± 0.5. After completed the dropwise addition, the mixture was allowed to stand for about 1 hour for aging. When, during the processing period, pH value came outside of a range of 8.0 ± 0.5, an aqueous solution of about 1 mole/liter nitric acid or of about 1 mole/liter sodium carbonate was added dropwise to the mixture to sustain the pH value in a range of 8.0 ± 0.5. Then, the generated precipitate was filtered, and the cake was rinsed by ion-exchanged water until nitric acid ion is not detected in the filtrate anymore. The cake was then dried at 120 °C for 24 hours. followed by calcining thereof in air at 350 °C for 5 hours. A 50 g portion of the calcined cake was powdered in a ball mill along with 50 g of γ-alumina (N612, Nikki Kagaku Co.) for about 3 hours. The powder mixture was calcined in air at 450 °C for 3 hours. The calcined mixture was further powdered to about 120 µm or finer size as the target catalyst. Analysis of thus obtained catalyst gave the composition as CuO:ZnO:Al 2 O 3 = 31:16:53 (by weight). II. Method for activating catalyst and reaction method A 24 g of n-hexadecane (31.1 ml) was charged to a bubble-tower reactor having 2 cm of inside diameter and 2 m of height, and 3.6 g of each of the above-described catalyst powders was added to make the contents of the reactor in a suspended state. In Examples 5 through 8, the catalyst of Example 1 was used. A mixed gas of hydrogen, carbon monoxide, and nitrogen (at a molar ratio H 2 :CO:N 2 of 1:1:9) was introduced to pass through the bubble-tower at a flow rate of about 300 ml/min. While flowing the mixed gas through the bubble-tower, the temperature in the bubble-tower was gradually raised from room temperature to 220 °C within a period of several hours. At the same time, the concentration of nitrogen in the mixed gas was gradually reduced to a final level of zero. Then, the reaction system was held at 220 °C for about 3 hours. to activate the catalyst. The reaction was conducted at a specified temperature and pressure while introducing the mixed gas of hydrogen, carbon monoxide, and carbon dioxide at a molar ratio of H 2 /CO/CO 2 = 47.5/47.5/5.0 and at a flow rate of 336 ml/min. (converted at a condition of normal temperature and pressure). The obtained reaction products and non-reacted substances were analyzed by gas chromatography. III. Reaction conditions and experimental results The reaction conditions and experimental results are shown in Tables 1 through 5. Example 1 Example 2 Example 3 Example 4 Condition Temparature (°C) 280 280 280 280 Pressure (kg/cm 2 -G) 30 30 30 30 Reaction Result CO conversion (%) 47.7 37.8 40.5 48.3 Yield (C-mol%) Dimethyl ether 36.5 25.3 28.4 35.7 Methanol 2.0 0.7 1.1 2.4 Hydrocarbons 0.3 0.2 0.3 0.1 CO 2 8.9 11.6 10.7 10.1 Dimethyl ether space time yield (g/kg-cat·h) 998 692 777 976 Example 5 Example 6 Example 7 Example 8 Condition Temparature (°C) 250 300 280 280 Pressure (kg/cm 2 -G) 30 30 20 50 Reaction Result CO conversion (%) 40.3 45.1 38.4 55.9 Yield (C-mol%) Dimethyl ether 24.2 33.8 26.5 43.6 Methanol 3.8 1.7 1.5 2.2 Hydrocarbons 0.1 2.8 0.4 0.8 CO 2 12.2 6.8 10.0 9.3 Dimethyl ether space time yield (g/kg-cat·h) 662 924 725 1192 Example 9 Example 10 Example 11 Example 12 Condition Temparature (°C) 280 280 280 280 Pressure (kg/cm 2 -G) 30 30 30 30 Reaction Result CO conversion (%) 38.8 40.2 46.9 47.8 Yield (C-mol%) Dimethyl ether 28.5 31.1 36.1 35.9 Methanol 3.1 2.4 1.8 2.2 Hydrocarbons 0.1 0.1 0.2 0.2 CO 2 7.1 6.6 8.8 9.5 Dimethyl ether space time yield (g/kg-cat·h) 779 850 987 982 Example 13 Example 14 Comparative Example 1 Comparative Example 2 Condition Temparature (°C) 280 280 280 280 Pressure (kg/cm 2 -G) 30 30 30 30 Reaction Result CO conversion (%) 41.9 40.0 30.1 18.4 Yield (C-mol%) Dimethyl ether 32.1 29.3 17.5 6.5 Methanol 1.7 2.0 5.7 6.5 Hydrocarbons 0.1 0.2 0.1 0.1 CO 2 8.0 8.5 6.8 1.3 Dimethyl ether space time yield (g/kg-cat·h) 878 801 478 178 Reaction result in Example 1 after 100 hours, of continuous reaction Reaction result in Example 3 after 100 hours, of continuous reaction Condition Temparature (C) 280 280 Pressure (kg/cm 2 -G) 30 30 Reaction Result CO conversion (%) 41.9 27.3 Yield (C-mol%) Dimethyl ether 36.3 13.8 Methanol 1.8 9.8 Hydrocarbons 0.2 0.5 CO 2 8.8 3.2 Dimethyl ether space time yield (g/kg-cat·h) 992 377 The catalyst for manufacturing dimethyl ether according to the present invention provides effects of preventing separation of individual catalyst ingredients from each other during reaction, of assuring smooth progress of reaction cycle, and of achieving high dimethyl ether yield owing to the configuration thereof comprising alumina particles and methanol synthesis catalyst layer formed around each of the alumina particles. The method for manufacturing dimethyl ether according to the present invention uses a slurry of solvent with a catalyst comprising alumina particles and methanol synthesis catalyst layer formed around each of the alumina particles, so the method provides effects of achieving high space time yield of dimethyl ether, of being free from problems of plugging of catalyst and of mechanical strength of catalyst, of easiness for removing reaction heat and for controlling reaction heat, of assuring wide application range of the ratio of carbon monoxide to hydrogen, of progress of reaction under the presence of high concentration of carbon dioxide, and of less influence of impurities and catalyst poisons.

Claims: A catalyst suitable for producing dimethyl ether, obtainable by the method comprising the steps of: forming a layer comprising a methanol synthesis catalyst which comprises copper oxide, zinc oxide and alumina, around alumina particles having an average size of 200 µm or less, wherein the ratio of the methanol synthesis catalyst layer formed around alumina particle is in a range of from 0.05 to 5 by wt.parts to 1 wt.parts of alumina, wherein the steps of forming the layer comprise: a) forming a slurry by introducing the alumina particles into an aqueous solution containing a metallic salt of the active element(s) of the methanol synthesis catalyst; b) heating the slurry at a temperature of 50 to 90°C, c) neutralising the heated slurry with a base solution, whereby the active element of the methanol synthesis catalyst is deposited on the alumina particles, d) allowing the slurry to stand for an appropriate time or subjecting the slurry to mild agitation for aging to sufficiently develop the deposits. e) washing the alumina particles around which the layer was formed with an acidic aqeous solution. The catalyst of claim 1 wherein the average size of the alumina particles is 1 to 100 µm. The catalyst of claim 2 wherein the average size of the alumina particles is 1 to 50 µ m. The catalyst of claims 1 to 3 wherein the methanol synthesis catalyst has a weight ratio of the copper oxide : the zinc oxide : the alumina being 1: (0.05 to 20) : up to 2). The catalyst of claims 1 to 4 wherein the acid aqueous solution is an aqueous solution of an inorganic acid. The catalyst of claim 5 wherein the inorganic acid is nitric acid or hydrochloric acid. The catalyst of claim 1 to 4 wherein the acid aqueous solution is an aqueous solution of an organic acid. The catalyst of claim 7 wherein the organic acid is acetic acid. The catalyst of claims 1 to 8 wherein the slurry in step b) is heated at a temperarure in the range of 60 to 85°C. The catalyst of claims 1 to 9 , wherein the methanol synthesis layer formed around alumina particle is in a range of from 0.1 to 3 wt.parts, and most preferably in a range of from 0.5 to 2 wt.parts. A method for producing a catalyst following the steps as defined in claims 1 to 10. A method for producing dimethyl ether comprising the steps of: providing a catalyst according to any of claims 1 to 10; forming a slurry by introducing the catalyst into a solvent; and introducing a mixed gas comprising carbon monoxide and hydrogen into the slurry. The method of claim 12 wherein the mixed gas further comprises carbon dioxide. The method of claim 13 wherein the mixed gas further comprises water vapour.

Inventors: FUJIMOTO KAORU, MIZUGUCHI MASATSUGU GROUP CO C, OGAWA TAKASHI, OHNO YOTARO, ONO MASAMI, SHIKADA TSUTOMU, FUJIMOTO, KAORU, MIZUGUCHI, MASATSUGU, GROUP CO. CONSULTING DEPT., OGAWA, TAKASHI, OHNO, YOTARO, ONO, MASAMI, SHIKADA, TSUTOMU, Ogawa, Takashi, Intellectual Property Dept., Ohno, Yotaro, Intellectual Property Dept., Ono, Masami, Intellectual Property Dept., Shikada, Tsutomu, Intellectual Property Dept.
Applicants: JFE HOLDINGS INC, JFE HOLDINGS, INC.
Application year: 1997
Main classification: C07C43
IPC codes: B01J23, B01J21, B01J37, G06Q20