KR100296941B1 - Silver supported catalyst for the production of ethylene oxide - Google Patents

Abstract

PURPOSE: The present invention relates to silver supported catalyst that is used for the manufacture of ethylene oxide by gas-phase partial oxidation reaction between ethylene and oxygen/oxygen-containing gas. CONSTITUTION: In the forming of a carrier for the production of catalyst, 5-40wt.% of Nb2O5 is added to the carrier. The carrier material is selected from alpha-alumina, silica, silicon carbide, and zirconia. The carrier of the present invention shows superior activity, selectivity and its catalytic activity last long.

Description

[Name of invention]

Silver supported catalyst for ethylene oxide production

Detailed description of the invention

The present invention relates to a silver supported catalyst used for preparing ethylene oxide by gas phase contact partial oxidation of ethylene and oxygen or an oxygen-containing gas. More specifically, the specific surface area is 2 by mixing niobium oxide with alpha alumina. Ethylene oxide is prepared by preparing a carrier by molding into a porous material of ㎡ / g or less or by doping niobium hydroxide on a carrier which has already been molded, and then partially oxidation of ethylene using a catalyst prepared by supporting silver on the carrier. It relates to a silver supported catalyst which has a very good activity and selectivity used to prepare the catalyst as compared to the existing catalyst.

In the reaction for producing ethylene oxide by direct oxidation of ethylene, silver is known as the only catalyst showing excellent performance. Under good reaction conditions, a good catalyst at low ethylene conversion may have a selectivity of over 80%. Selectivity refers to the mole percent of ethylene that reacts to ethylene oxide, with the main byproduct being carbon dioxide. Commercially, ethylene oxide is produced at temperatures between 20 and 300 ° C and pressures between 150 and 300 psig. In general, selectivity decreases with increasing ethylene conversion and selectivity in commercial processes ranges from 65 to 80% depending on operating conditions. Although partial oxidation of ethylene to ethylene oxide occurs only in the presence of a silver catalyst, the physical shape of the catalyst and the presence of trace impurities in the catalyst have a significant effect on selectivity and activity. In the early days of the study of silver catalysts, silver (Ag) was used in bulk as thin films, powders, foils or alloys. The use of this type of silver has the advantage of suppressing side reactions by enabling the rapid removal of the heat generated in the exothermic reaction, but this bulk catalyst is not economical because of its low inertness, which requires a large amount of metal on a commercial scale. . Therefore, in order to use expensive silver more efficiently by increasing the dispersion degree of silver, the catalyst which supported silver on the porous inorganic carrier has been used. As the carrier, many having a suitable mechanical strength of 40 to 60% porosity and 0.1 to 1 m 2 / g specific surface area were used. In catalysis, the carrier is considered to be inert and does not affect the catalytic performance, and inertness of the carrier has been emphasized in most patents and literature.

The inertness of the carrier has been controversial in that small amounts of impurities contained in the carrier may affect the catalyst performance. In fact, among the various metals supported on the carrier together with silver as a co-catalyst in the preparation of the ethylene oxidation catalyst, it is often present in the carrier. Representative examples are alkali or alkaline earth metal based promoters. Although the role of the promoter in the catalyst has not been clearly identified, it appears to prevent the aggregation of small, evenly dispersed particles, to inhibit side reactions or to affect the activity. However, most of these cocatalyst components originally present in the carrier are chemically bound to the bulk inside the carrier rather than to the surface of the carrier which is easily accessible to the reactants. As a technique for supporting silver on a carrier, there are spray supporting method, impregnation method, precipitation method, evaporation drying method, etc .. After supporting, silver is calcined under oxidation or reduction conditions to activate the silver catalyst. In most catalyst production techniques to date, it is known that a carrier does not participate in catalysis at all and only changes in the type and amount of a component supported on the surface of the inert carrier change the performance of the catalyst.

Silver supported catalysts are industrially used to produce ethylene oxide by vapor phase contact between ethylene and oxygen or an oxygen-containing gas, and it is known that only a catalyst supporting silver on a porous inorganic carrier is used for this reaction. Silver is widely known as the main catalyst used to oxidize ethylene to ethylene oxide. There are many proposals to add a small amount of reaction accelerators recently, such as alkali metals, alkaline earth metals, iron, copper, manganese, cadmium, zirconium, aluminum, etc., alone or in combination of two or more as co-catalyst components. lost. Among them, there is a method of using an alkali metal as an accelerator. These catalysts have improved activity or selectivity compared to catalysts carrying only silver, but are not sufficient. In addition, catalysts containing alkali metals usually have a lower activity degradation rate than catalysts containing only silver, which shortens the lifetime of the catalyst, and increases the reaction temperature due to the addition of alkali metals. It may be necessary. Since the alkali metal is supported on the catalyst, a complicated process is required, and there are many improvements, such as reproducibility when producing on an industrial scale. Also containing toxic substances, their surface area-to-weight ratio decreases with time at the temperatures normally used in oxidation processes, resulting in reduced catalytic activity. Therefore, the reaction temperature must not be increased in order to overcome the deactivation of the catalyst and to keep the productivity of the plant constant. This is a major drawback that increases production costs and shortens catalyst life. In addition, the selectivity of the supported silver catalyst is easily influenced by the method of supporting the silver on the porous inorganic carrier and the type of the cocatalyst contained in the catalyst, so that the method of supporting the silver on the porous inorganic carrier is inappropriate or the component of the promoter and its Inadequate amounts result in a lower selectivity of the catalyst, producing more carbon dioxide, and a little less ethylene oxide, the desired product.Therefore, high selectivity, high activity and durability of catalyst life as a catalyst for producing ethylene oxide with high efficiency. There have been many attempts so far and many methods have been proposed. That is, the main contents were the combination of additives such as silver and alkali metals as the main active ingredient or an accelerator, and the optimization of the mixing ratio thereof, and the improvement of the porous inorganic carrier supporting them. In particular, the improvement of the carrier was to improve the dispersion of silver by increasing the surface area to enable use at low temperatures, and to exhibit long life and high selectivity. However, by simply increasing the surface area, the desired effect cannot be obtained due to the effect of diffusion of reaction and product, side reactions on the surface of the carrier, and the like. In general, alkali metals such as sodium (Na), lithium (Li), rubidium (Rb), potassium (K), cesium (Cs) and magnesium (Mg), calcium (Ca) and strontium (Sr), alkaline earth metals such as barium (Ba) and copper (Cu), gold (Au), zinc (Zn), cadmium (Cd), niobium (Nb), tantalum (Ta), molybdenum (Mo), One or more metals such as tungsten (W), chromium (Cr), vanadium (V), mercury (Hg), thallium (TI) and tin (Sn) are selected and added as an accelerator or activator. In general, alkali metals are known as effective accelerators, and cesium, sodium, potassium, rubidium, calcium and barium are known as the most effective accelerators in recent years. Recently, a technique for obtaining a synergistic effect by mixing these alkali metals has been emphasized. Generally, the amount of alkali metal added is smaller as the atomic weight is higher. Usually, 0.05 to 1 mol of sodium, 0.02 to 0.2 mol of potassium, 0.001 to 0.008 mol of rubidium, and 0.0005 to 0.005 mol of cesium are added to 1 mol of silver. do. Addition amount of copper, gold, magnesium, zinc, cadmium, mercury, etc. is 0.001-1 mol per 1 mol of silver, calcium, barium 0.001-0.1 mol, tantalum, molybdenum, tungsten, chromium, vanadium, etc. It is most effective to add 0.00001 to 0.005 moles and add 0.0001 to 0.0002 moles. The above-mentioned metals may be added together with the reaction conditions, catalyst production method, specific surface area of the carrier, pore structure and surface chemical properties, silver loading amount, other anions, cations, and compounds present in addition to the alkali metals, for example, alkali metals. It may be changed depending on the ions and the compound remaining without being removed in the supported solution. These reaction promoters or activators can be used in the form of soluble compounds in water or low-boiling organic solvents and supported on the carrier according to the present invention before or after supporting the silver. The type of anion moiety associated with these reaction promoter or activator metals is not known to have a significant effect on the performance of the catalyst. Anions such as or similar silver compounds may be used. For example, hydroxides, carbonates, bicarbonates, nitrates, nitrites, formates, acetates, oxalates, citrates, lactates, and the like, and examples of using halides, sulfates, and the like.

Silver supported catalysts are determined for their performance by activity and selectivity. Selectivity is the mole percent ethylene reacts to form ethylene oxide. Selectivity is particularly economically important when the price of the raw material is high and the raw material is scarce. Activity is expressed as the concentration of ethylene oxide at the reactor outlet under certain constant conditions (e.g. temperature, pressure, gas amount and catalytic amount), the higher the concentration of ethylene oxide, the higher the activity. In other words, the lower the temperature required to achieve a constant concentration of ethylene oxide, the higher the activity. When the activity is lowered, the reaction is maintained at a higher temperature to maintain a constant yield, thereby maintaining the same activity. Therefore, the selectivity is further lowered and the life of the catalyst is shortened. Therefore, silver supported catalysts have poor activity and selectivity over time and should be replaced with new catalysts after several years. Replacing largely inactive catalysts in larger units is time-consuming and requires intensive work, resulting in lower production and higher costs.

The present inventors have made careful examinations on the fact that the trace components contained in the carrier have any effect on the catalytic action and that niobium has a very good effect on the reaction activity and selectivity in the silver supported catalyst. As a result, the catalyst was prepared by adding a specific substance to a conventional carrier to test the performance and found that the activity and selectivity of the catalyst were improved, thereby completing the present invention.

The silver supported catalyst for producing ethylene oxide according to the present invention is a catalyst which is used to prepare ethylene oxide by gas phase catalytic oxidation of ethylene with molecular oxygen, and niobium oxide is added to a carrier which is already formed or niobium hydroxide in forming a carrier. It characterized in that the carrier is treated by doping (doping).

According to the present invention, the amount of niobium oxide mixed with alumina when forming a carrier has a significant effect on the performance of the catalyst. The amount of niobium oxide mixed with the carrier is preferably 5 to 40% by weight based on the total weight of the carrier. 30 weight% is more preferable. In the present invention, niobium oxide may be added during molding of the carrier, and niobium hydroxide may also be doped to an already molded carrier. When niobium hydroxide is used, niobium is added to the total weight of the carrier. Use an amount that will contain 100-500 ppm. A similar effect is obtained when zinc oxide, lanthanum oxide and magnesium oxide are added instead of niobium oxide, but the effect is lower than when niobium oxide is added, and the performance of the catalyst is deteriorated when titanium oxide or manganese oxide is used. . As the carrier material, alpha alumina, silica, silicon carbide, zirconia or the like is used, and alumina or alumina containing a small amount of silica is preferable.

The silver supported catalyst for producing ethylene oxide according to the present invention contains an appropriate amount of alkali metal, alkaline earth metal and chlorine as the main catalyst silver and cocatalyst, and is prepared by simultaneously or separately supporting silver and the cocatalyst, the main catalyst of the carrier. .

The silver supported catalyst prepared using the carrier prepared by the method of the present invention increases the activity and selectivity of the catalyst. This can lower the reaction temperature in the case of the catalyst produced by the present invention which shows the same or slightly higher conversion. Such low reaction temperatures can inhibit the induction of side reactions and lower the formation of byproducts such as carbon dioxide, formaldehyde and acetaldehyde.

The catalyst according to the present invention can be used at a temperature of 140 ~ 300 ℃ and suitable to use at 160 ~ 250 ℃, can be used in the reaction pressure 0 ~ 40kg / ㎠G range and used in the 0 ~ 30 kg / ㎠G range It is suitable to use the gas flow in the range of 1000 ~ 10000cc / hr and it is suitable to use in the range of 3000 ~ 7000cc / hr. In preparing ethylene oxide by molecular oxygen and gas phase contact partial oxidation using the catalyst of the present invention, the source gas composition is usually 1-40 mol% of ethylene, 3-20 mol% of oxygen, and the rest is carbon dioxide and methane. And lower hydrocarbons such as ethane and ethane, and inert gases such as nitrogen and argon. In addition, 0.1 to 20 ppm of chlorine compounds such as ethylene dichloride and vinyl chloride can be added to the raw material gas as a combustion inhibitor to obtain good results.

As described above, the silver supported catalyst for producing ethylene oxide according to the present invention has very high activity and selectivity, and has a long service life.

In the following Examples, the present invention is described for easy understanding, and the present invention is not limited.

Example 1

(Production of carrier)

In preparing an alumina carrier required for preparing a silver supported catalyst, first, 100 g of alpha alumina, a pore control agent, and a molding agent are mixed with 11 g and 1 g, respectively. 1 to 2 g of a clay adhesive, which can increase the mechanical strength of the carrier, are added thereto, and a lubricating dough such as petrolatum and water is sufficiently added to form a thick dough to be molded into a desired shape. The dough was molded into a ring shape using a molding machine, dried in air at room temperature, and then fired in an electric furnace. The surface area of the carrier thus prepared was 1 m 2 / g or less.

(Production of Catalyst)

The catalyst was prepared using the alumina carrier prepared above, and the catalyst used in the catalyst performance test was prepared as follows. First, add 0.072 g of cesium nitrate, 0.02 g of ammonium chloride, and 0.096 g of niobium oxalate in 33 ml of distilled water, and dissolve while stirring. To this solution, add 7.2 g of silver oxalate, a mixed solution of 15 ml of ethylenediamine and 5 ml of ethanolamine, and dissolve the silver oxalate while stirring well. At this time, the exothermic reaction occurs and the temperature rises sharply, so it is necessary to cool the water filled with ice. After 25 g of ring-shaped alumina was added thereto and left for 30 minutes, the alumina loaded with silver was filtered, dried at 110 ° C. for 2 hours, and then calcined at 270 ° C. for 4 hours to use as a catalyst.

(Production of ethylene oxide)

3 g of the catalyst and 5 g of quartz yarn were mixed and filled into a quartz reactor having an inner diameter of 16 mm, and a reaction temperature was supplied at a rate of 4800 cc / hr by supplying a reaction mixture gas containing 8.0 mol% of oxygen, 24 mol% of ethylene, and the remainder of nitrogen at 4800 cc / hr The conversion rate of ethylene was 9% and the selectivity of ethylene oxide 69.0% was obtained at 240 degreeC.

Example 2

A carrier was prepared in the same manner as in Example 1 except that 30 g of niobium oxide was added instead of 100 g of alpha alumina, and the amount of alumina was 70 g. Preparation and Reaction of Catalyst The reaction was carried out in the same manner as in Example 1, whereupon the reaction temperature of 230 ° C. yielded an ethylene conversion of 10% and an ethylene oxide selectivity of 62.5%.

Example 3

A carrier was prepared in the same manner as in Example 1 except that 20 g of niobium oxide was added instead of 100 g of alpha alumina, and the amount of alumina was 80 g. Preparation and Reaction of Catalyst The reaction was carried out in the same manner as in Example 1, and the reaction temperature was 232 占 폚 to obtain an ethylene conversion of 9.7% and an ethylene oxide selectivity of 64.4%.

Example 4

A carrier was prepared in the same manner as in Example 1 except that instead of 100 g of alpha alumina, 10 g of niobium oxide was added, and the amount of alumina was 90 g. Preparation and Reaction of Catalyst The reaction was carried out in the same manner as in Example 1, and the reaction temperature was 233 ° C. to obtain an ethylene conversion of 9.8% and an selectivity of ethylene oxide of 63.8%.

Example 5

The carrier prepared in the same manner as in Example 1 was used as a carrier after doping niobium with respect to the total weight of the carrier using an aqueous solution of niobium hydroxide. Preparation and Reaction of Catalyst The reaction was carried out in the same manner as in Example 1, and the reaction temperature was 231 占 폚 to obtain 9.63% ethylene conversion and 64.2% selectivity for ethylene oxide.

Example 6

The carrier was used as a carrier after 700 ppm doping of niobium with respect to the total weight of the carrier using an aqueous solution of niobium hydroxide. Preparation and Reaction of Catalyst The reaction was carried out in the same manner as in Example 1, and the reaction temperature was 232 占 폚 to obtain 9.7% ethylene conversion and 64.5% selectivity for ethylene oxide.

Example 7

The carrier was used as a carrier after 1500 ppm doping of niobium with respect to the total weight of the carrier using an aqueous solution of niobium hydroxide. Preparation and Reaction of Catalyst The reaction was carried out in the same manner as in Example 1, and the reaction temperature was 232 占 폚, whereby 9.8% of ethylene conversion and 64.0% of ethylene oxide were obtained.

Claims (2)

A silver supported catalyst for producing ethylene oxide using a carrier prepared by adding 5 to 40% by weight of niobium oxide based on the total weight of the carrier when forming the carrier. 2. The silver supported catalyst for producing ethylene oxide according to claim 1, wherein alpha alumina, silica, silicon carbide, and zirconia are used as the carrier material.