JPH0363431B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a catalyst for selective hydrogenation of acetylene compounds. In the petrochemical industry, large amounts of ethylene or propylene are produced by thermal decomposition of naphtha, natural gas, etc., but each olefin fraction obtained contains small amounts of acetylene compounds such as acetylene and methylacetylene. There is. In chemical reactions using these olefins as raw materials, contamination with acetylene compounds is often avoided.
It is usually purified by selectively hydrogenating an acetylene compound using a catalyst in which palladium is supported on a refractory support such as alumina, silica, or diatomaceous earth. However, in the purification of such olefins, since the reaction is carried out in the olefin atmosphere in the presence of more than an equivalent amount of hydrogen relative to the acetylene compound, the excess hydrogen is added to the olefins, producing low-value paraffins. Undesirable side reactions are induced. In order to suppress the by-product of paraffin, it is required to make the supply ratio of hydrogen to the acetylene compound as close to equimolar as possible, but as the amount of excess hydrogen is reduced, the removal rate of the acetylene compound decreases. In order to solve this dilemma, there is a long-awaited development of highly active and highly selective catalysts that can selectively hydrogenate and remove acetylene compounds while reducing the amount of excess hydrogen. A proposal has been made. For example, palladium catalysts using alumina as a carrier with pore diameters controlled within a predetermined range, and catalysts containing a second component such as silver, copper, gold, iron, or chromium in addition to palladium are known. However, even in methods using these catalysts, acetylenes polymerize alone or copolymerize with olefins during hydrogenation, resulting in the production of so-called polymerized oils, resulting in loss of olefin yield and the production of these polymerized oils. However, there remains the problem that these substances accumulate on the catalyst, leading to loss of activity. In view of the above, the present inventors have conducted intensive studies to obtain a catalyst that has an excellent selective hydrogenation effect on acetylene and produces less polymerized oil, and as a result has arrived at the present invention. That is, the present invention is a catalyst in which palladium is supported on alumina, and the specific surface area S (m ² /g), radius
The total volume V (ml/g) of pores with a diameter of 37.5 Å to 75000 Å is within the following range, and the pore distribution has distinct peaks at a radius of 37.5 Å to 100 Å and a radius of 100 Å to 1000 Å, respectively. This relates to a catalyst for selective hydrogenation where 120<S<350 0.6<V<1.5. The catalyst of the present invention has a specific surface area S (m ² /g) and a total volume V (ml/g) of pores with a radius of 37.5 Å to 75000 Å such that 120<S<350 0.6<V<1.5, preferably 130<S<300 The range is 0.6<V<1.2, more preferably 150<S<300, 0.6<V<1.2. Further, the catalyst of the present invention is characterized by exhibiting a pore distribution having distinct peaks at radii of 37.5 Å to 100 Å and 100 Å to 1000 Å, and each pore volume is 0.1 ml/g or more, preferably 0.2 to 0.8 ml/
It is preferable that it is g. The carrier preferably has an alumina component of 80% by weight or more, and of course a carrier containing 100% alumina can also be used. In addition to alumina, other components that can make up the carrier include silica, titania, zirconia,
Examples include refractory oxides such as magnesia. Catalyst used in the present invention (hereinafter referred to as the present catalyst)
One of its features is its large specific surface area, which is 37.5 Å~
It has a large number of pores at both micro and meso positions of 100 Å and 100 Å to 1000 Å. Generally, when hydrogenating and removing acetylene compounds in olefins, a catalyst with a large specific surface area of the carrier has high activity but poor selectivity, and a catalyst with a small specific surface area of the carrier has high selectivity but tends to have low activity. . On the other hand, this catalyst has a specific surface area larger than 120 m ² /g, and at the same time retains a large amount of pore volume, and has relatively micro pores with a radius of 37.5 Å to 100 Å and meso pores with a radius of 100 Å to 1000 Å. Pores are distributed on both sides. Surprisingly, such a catalyst simultaneously achieves extremely high activity and high selectivity, and at the same time reduces the by-product of polymerized oil. The reason for this is not always clear, but
It is thought that the large specific surface area improves palladium dispersion and imparts activity, and at the same time, the special pore structure improves selectivity. The physical properties of such a catalyst can usually be imparted to the catalyst by using an alumina support having a special pore distribution and capacity defined in the present invention. To produce the alumina support used as a support for this catalyst, activated alumina such as γ-alumina and η-alumina, or alumina hydrate such as boehmite, pseudoboehmite, gypsite, etc., or rehydratable transition alumina is used. It can be manufactured by mixing carbon black with alumina raw materials such as, adding water and a forming aid if necessary, kneading and forming, and then firing in an oxygen-containing air stream to burn off the carbon black. can. The carbon black to be mixed with the alumina raw material has a particle size ranging from 150 to 3000 Å. Carbon black generally has individual particles aggregated to form a large chain-like higher-order structure (hereinafter referred to as "structure"), and the position and width of the pore distribution of the resulting alumina support depend on the particle diameter of carbon black and the size of the structure. It is greatly influenced by. The size of the structure is expressed by the oil absorption capacity of carbon black (for example, DBP absorption capacity: capacity of dibutyl phthalate absorbed by 100 g of carbon black, unit: ml/100 g).
And in normal carbon black, its DBP
Absorption amount is about 60-300ml/100g, special type
There are also over 300ml/100g. There are no particular restrictions on the type of carbon black that can be used, and commercially available carbon blacks such as channel blacks such as Mitsubishi Carbon Black #100 and #600 (manufactured by Mitsubishi Chemical Industries, Ltd.), Diablack A, and Diablack H ( Mitsubishi Chemical Industries, Ltd.
), Asahi Thermal FT, etc.
(manufactured by Asahi Carbon Co., Ltd.), Denka Acetylene (manufactured by Denki Kagaku Kogyo Co., Ltd.), and Ketsutien Black EC (manufactured by Akzochemy Co., Ltd.). During molding, the alumina raw material and carbon black should be mixed as uniformly as possible to obtain better physical properties. The amount of carbon black added to the alumina raw material is 5 to 120
% by weight, preferably 10 to 100% by weight. When using additives that disappear upon firing, the upper limit of the amount of additives is approximately 10% by weight to avoid impairing the strength and other physical properties of the resulting molded product. Compared to the usual case, when producing the porous activated alumina molded article of the present invention, the amount of carbon black added is extremely large. Moreover, it is quite surprising that the addition of such a large amount imparts mesopores in a controlled location and amount, yet does not impair the required physical properties. The raw material alumina and carbon black that have been uniformly mixed in this way are further mixed and kneaded by adding water and other forming aids if necessary.
formed into the desired shape. Well-known molding methods include tableting, extrusion, and extrusion.
There are methods such as the Marmo method, rolling granulation method, and briquetting method, among which extrusion molding method is easy and versatile. The molding method will be described by taking as an example a case where pseudoboehmite (an X-ray analysis thereof shows a broad boehmite structure - hydrated alumina) is used as a raw material. For example, 30 to 100 parts of pseudoboehmite
After adding 50% of carbon black and mixing uniformly with a mixer, transfer to a kneader, add water and auxiliary agents, and knead. Preferred auxiliaries include inorganic acids,
Examples include organic acids or basic nitrogen compounds such as ammonia, hydrazine, aliphatic amines, aromatic amines, and heterocyclic amines, and organic substances such as polyvinyl alcohol. The kneaded material thus obtained is then extruded using an extruder through a die hole of a desired size. The molded product can also be aged in a closed container if desired. The alumina molded bodies formed by various methods as described above are then dried and fired, and finally have properties as a carrier. However, oxidative calcination must be accomplished with great care. This is because carbon black is flammable and the amount added is relatively large, so if the removal of combustion heat is insufficient, the desired temperature cannot be controlled and there is a great possibility that the temperature will become high. A rapid temperature rise is not desirable even if the temperature is below the upper limit temperature. The firing temperature required to burn off the carbon black as described above is about 500°C or higher, and the final firing temperature to obtain the alumina used in the present invention is 600 to 800°C. Further, the firing time is not particularly limited, but is usually about 1 hour to 1 day. Thus, an alumina support is obtained which has excellent mechanical strength, abrasion resistance and physical properties such as large surface area, large pore volume, and characteristic pore distribution. It is preferable that at least a portion, preferably substantially all, of the alumina support is in the γ form. There are no particular restrictions on the size of the carrier, but hydrogenation of acetylene compounds in olefins usually
Since the process is carried out in a fixed bed, the size of the mesh is preferably about 4 to 25 meshes. In addition, the shape of the carrier is cylindrical,
It may be in any shape, such as spherical, tablet-shaped, or crushed products thereof. The amount of palladium supported on the above-mentioned carrier is
Usually 0.01 to 1% by weight based on the carrier, preferably
It is 0.02 to 0.4% by weight, and in many cases it is supported intensively on the surface layer of the carrier. As raw materials for palladium used in producing this catalyst, common palladium compounds such as palladium chloride, palladium nitrate, potassium chloropalladate, sodium chloropalladate, palladium oxide, and palladium ammine complex salts are used. . Supporting of palladium can be carried out by dissolving the palladium compound in a solvent such as water, supporting the palladium compound by a known supporting method such as a dipping method, a spraying method, or a precipitation method, followed by reduction. The catalyst supporting the palladium compound can be used in the reaction as is after drying, or if there are residual substances harmful to the reaction, such as chlorine radicals or nitrate radicals, it can be subjected to heat treatment, reduction treatment, or washing with water. It is used after applying. However, in order to guarantee the stability of the reaction immediately after the reaction starts, it is preferable to perform a reduction treatment before use. The reduction treatment is carried out at a temperature of room temperature to 300° C. in an atmosphere of a reducing gas such as hydrogen gas. This catalyst is used for the reaction of hydrogenating acetylene compounds up to the olefin stage, particularly for the selective hydrogenation of acetylene compounds in olefins such as ethylene and propylene obtained by thermal decomposition of hydrocarbons such as naphtha and natural gas. It is effective for When the reaction is carried out by the so-called post-hydrogenation method, the amount of hydrogen gas required for the reaction is 1 to 5 times the mole of the acetylene compound in the raw material gas, and if the amount of hydrogen gas is increased more than this, the amount of paraffin by-product will increase. Not only does this increase the reaction temperature, but also the large reaction heat makes it difficult to control the reaction temperature. The reaction temperature is variable depending on the required removal rate of the acetylene compound and the molar ratio of hydrogen gas to the acetylene compound, but it is preferably as low as possible, and is usually selected within the range of room temperature to 200°C. The reaction pressure is selected within the range of normal pressure to about 30 atmospheres. Since the above reaction has an extremely high reaction rate, the space velocity can be increased. Normally, the gas space velocity is within the range of 1000 to 10000 Hr ^-1 in terms of standard conditions. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it departs from the gist thereof. In addition, in the following examples, reaction tests of the prepared catalysts were conducted in the following manner. 15 ml of the prepared catalyst was packed into a SUS316 reactor with an inner diameter of 20 mm, heated to 60°C, and hydrogen gas was passed through it for 1 hour to reduce the catalyst.
%, nitrogen 18.5%, acetylene 0.5%, hydrogen 1.0%,
Gas with a composition of 0.001% carbon monoxide (unit: volume %) at 60℃, 25Kg/cm ² G and 75Nl/Hr/hour
(GHSV5000Hr ^-1 ) to remove hydrogenation of acetylene in ethylene. The reactor outlet gas was analyzed by gas chromatography, and the acetylene removal rate and selectivity were calculated according to the following formula. Acetylene removal rate (%) = △ [C ₂ ] / [C ₂ ] in × 100 Selectivity (%) = △ [C ₂ ] / [H ₂ ] in − [H ₂ ] out × 100 However, [ ] in … ...Reactor inlet concentration [ ] out ... Reactor outlet concentration [C ₂ ] ... Acetylene concentration [H ₂ ] ... Hydrogen concentration △ [C ₂ ] = [C ₂ ] in - [C ₂ ] out Also, reactor A dry ice/ethanol bath trap was attached to the outlet to collect the polymerized oil, and the polymerized oil adhering to the catalyst extracted after the completion of the reaction was measured, and the polymerization rate was calculated using the following formula. Polymerization rate (%) = Weight of collected polymerized oil (g) + Weight of polymerized oil attached to catalyst (g) / Weight of supplied acetylene (g) x 100 The pore distribution and amount in the example are Measured using a mercury intrusion porosimeter. The machine used is Carlo Erba Porosimeter Series 2000 with a maximum pressure of 2000 kg/
cm ^2G . Therefore, the measurement range of the pore is 37.5 Å radius.
~75000Å. The specific surface area was calculated using the BET method using the nitrogen adsorption method. The machine used is a soap tomato made by Carlo Erba.
It is 1800. Further, Table 1 shows the physical properties of carbon black used in the following examples.

[Table] Example 1 Boehmite powder Pural SB manufactured by Condea (Al ₂ O ₃
75%) 225g and carbon black
After dry mixing 67.5g of A (30% by weight based on boehmite) in a mixer for 60 minutes, transfer it to a batch kneader (inner capacity 2) and add a 4.3% nitric acid aqueous solution.
Add 220g while kneading for about 5 minutes, and then
Kneading continued for 25 minutes. Next, 128 g of 2.1% ammonia water was added, kneaded for 25 minutes, and then extruded to a diameter of 3.5 mm using a screw extruder. After drying the molded product at 120°C for 3 hours, the temperature was gradually increased in an electric furnace under drying air flow, and it was fired at 600°C for 3 hours, then at 700°C.
An alumina molded body was obtained by firing at a temperature of 3 hours. The diameter of the extruded product after firing was approximately 3 mm, and the specific surface area was 202 m ² /g. The pore volume and pore distribution of this alumina carrier were as follows. Pore volume with a radius of 37.5 Å to 100 Å 0.612 ml/g Pore volume with a radius of 100 Å to 1000 Å 0.344 ml/g Total pore volume (37.5 Å to 75000 Å) 0.966 ml/g Modest pore radius (distribution shows maximum radius)
60 Å and 240 Å The pore distribution curves of this alumina support are shown in FIG. Next, 200 g of this alumina carrier was immersed in 600 ml of an aqueous solution containing 0.17 g of palladium chloride and 0.2 ml of hydrochloric acid for 1 hour, drained, and dried at 120°C for 24 hours to reduce the amount of palladium chloride to 0.05 in terms of palladium.
A catalyst (catalyst-A) supported on weight% alumina was obtained. The specific surface area and pore distribution curves were almost identical to those of the alumina support. i.e. specific surface area
197 m ² /g, radius 37.5 Å to 100 Å, pore volume 0.502
ml/g, pore volume with radius 100Å to 1000Å 0.326ml/
g, total pore volume 0.828ml/g, mode pore radius 60Å
and 240 Å. When the reaction test was conducted using Catalyst A, the results shown in Table 2 were obtained. Example 2 An alumina carrier was produced in the same manner as in Example 1 except that 78.75 g of carbon black B (35% by weight based on boehmite) was used, and the specific surface area was 221 m ² /
g of alumina carrier was obtained. The pore volume and pore distribution of the obtained alumina carrier were as follows. Pore volume with a radius of 37.5 Å to 100 Å 0.405 ml/g Pore volume with a radius of 100 Å to 1000 Å 0.402 ml/g Total pore volume (37.5 Å to 75000 Å) 0.811 ml/g Modest pore radius (distribution shows maximum radius)
55 Å and 400 Å The pore distribution curves of this alumina support are shown in FIG. Next, palladium chloride was supported on this alumina carrier in the same manner as in Example 1, and the loading rate in terms of palladium was
A 0.05% by weight catalyst (catalyst-B) was obtained. The pore distribution curve was almost the same as that of the alumina support. When the reaction test was conducted using Catalyst B, the results shown in Table 2 were obtained. Comparative Example 1 An alumina carrier was produced in the same manner as in Example 1 except that carbon black was not added, and an alumina carrier with a specific surface area of 184 m ² /g was obtained. The pore volume and pore distribution of the obtained alumina carrier were as follows. Pore volume from radius 37.5Å to 100Å 0.618ml/g Pore volume from radius 100Å to 1000Å 0.061ml/g Total pore volume (37.5Å to 75000Å) 0.679ml/g Modest pore radius (distribution is maximum) The pore distribution curve of this alumina support is shown in Figure 3. Next, palladium chloride was supported on this alumina carrier in the same manner as in Example 1, and the loading rate in terms of palladium was
A 0.05% by weight catalyst (catalyst-X) was obtained. The pore distribution curve was almost the same as that of the alumina support. When the reaction test was conducted using Catalyst-X, the results shown in Table 2 were obtained.

【table】 [Brief explanation of drawings]

Figures 1, 2 and 3 are pore distribution diagrams of the alumina supports produced in Example 1, Example 2 and Comparative Example 1, respectively, with curves 1, 3 and 5.
is a curve showing the state of pore distribution, and curves 2 and 4
and 6 are integrated curves of pore volume.

Claims (1)

[Claims] 1. A catalyst in which palladium is supported on alumina, with a specific surface area S (m ² /g) and a radius of 37.5 Å to 75000 Å.
The total volume V (ml/g) of the pores is within the following range, and the radius is 37.5 Å to 100 Å and the radius is 100 Å to
A selective hydrogenation catalyst characterized by exhibiting a pore distribution with distinct peaks at 1000 Å. 120<S<350 0.6<V<1.5 2 Palladium content is 0.01 to 1 to the carrier
% by weight of the catalyst according to claim 1. 3 Pore capacity with radius 37.5 Å to 100 Å and radius 100
The catalyst according to claim 1 or 2, each having a pore volume of 0.1 ml/g or more between Å and 1000 Å.