DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention provides a selective hydrogenation catalyst, which can comprise:

[0028] an inorganic oxide support selected from alumina, titania, and a chemical composite of alumina and titania;

[0029] a major active component Pd of a content of about 0.002-1.0% based on the total weight of the catalyst; and

[0030] one or more promoters selected from Group IB metals and the mole ratio of palladium to the Group IB metal is in range between about 1 and about 20;

[0031] wherein the major component palladium and the promoter are uniformly dispersed together in the catalyst body within a thickness between the support surface and the depth of more than about 300 μm.

[0032] The catalyst support of the present invention can comprise a chemical composite of alumina-titania. The weight percent of alumina can be about 1-99%, preferably about 10-90%, more preferably about 20-80%, and most preferably about 40-60%. The support can have the following physical properties: bulk density about 0.7-0.9 g/ml, pore volume about 0.3-0.6 ml/g, specific surface area about 10-60 m ² /g, mean pore diameter about 40-100 nm. The pore distribution can exhibit a doublet at about 50 nm and about 1000 nm.

[0033] The content of the major active component, palladium, can be about 0.002- 1.0% based on the total weight of the catalyst, preferably about 0.005-0.5%, and most preferably about 0.01-0.05%.

[0034] The promoters of the present invention can be one or more selected from Group IB metals, such as Cu, Ag, and Au. The mole ratio between palladium and the Group IB metals can be about 1-20, preferably about 1-10, and most preferably about 1.5-5.0.

[0035] The major component palladium and the promoter can be uniformly dispersed in the catalyst body within a thickness between the support surface and the depth of more than about 300 μm, preferably about 500-1000 μm. Generally speaking, when the radius of the φ=3 support particle R is about 1.5 mm, the region where the active component is uniformly distributed is the within the portion formed between the two spherical surfaces with radiuses of r=1.5 mm and r<l .2 mm, i.e., the portion of the hollow sphere from r=R to r<0.8R. This region is at least deeper than that of the comparative reference (such as CN 95197324.9), which is formed between the two spherical surfaces with radiuses of r-R and r>0.8R. When the active component is distributed in the catalyst body within the thickness between the support surface and the depth of r=500 μm, even to r-1000 μm, its distribution region is the portion of the hollow sphere from r=R to r--0.67 R, even from r=R to r=0.3R. The catalyst of the present invention can exist as oxides in the catalyst body within a thickness between the support surface and the depth of more than about 300 μm. In the hydrogen atmosphere under reaction conditions, the major active component palladium and the promoter are reduced to fine alloy particles with diameters of about 2-10 nm.

[0036] The catalyst of the present invention can also comprise alkali metals and/or alkali earth metals. The content of such alkali metals and/or alkali earth metals can be about 0.05-20% of the total weight of the catalyst. Said alkali metal can be one or more selected from the group consisting of Li, Na, K, Rb, and Cs, preferably Li, Na, K. The alkali earth metal can be one or more selected from the group consisting of Be, Mg, Ca, Sr, and Ba, preferably Mg, Ca, and Ba.

[0037] The preparation process of the present invention can comprise three steps: preparing the support, impregnating the active component, and decomposing the catalyst.

[0038] 1. Preparing the Support

[0039] The support of the present invention can be prepared by the conventional process. For example, aluminite (the major component is alumina) can be dissolved in a NaOH solution. The solution can be neutralized with a diluted solution of nitric acid to yield a Al(OH) ₃ precipitate, which is then washed with deionized water for several times to wash away Na ⁺ and NO ₃ ⁻ . The precipitate can be dried, formed, and calcined at a high temperature to yield the alumina support.

[0040] The chemical composite support of alumina and titania of the present invention can be prepared by the various processes. For example, MAlO ₂ and soluble titanium salt can be dissolved in water at about 20-80° C. The mixture can be neutralized with an MOH solution to neutrality to form a co-precipitate of aluminum-titanium hydroxide, which is stirred for about 10-30 h to form uniform crystal particles. The resultant can be filtered and washed away the M ⁺ and acid radical negative ions with deionized water. The derived aluminium-titanium hydroxide can be dried at about 100-150° C. After pulverizing, the solid sample can be formed by kneading and then calcined at about 800-1100° C to obtain the chemical composite support of alumina-titania, wherein the M is Na, K, or Li.

[0041] In a preferred embodiment of the present invention, the support of the present invention can be prepared by the following process: NaAlO ₂ and TiCl ₄ solutions can be mixed at about 20-80° C. (the equivalent ratio of Al to Ti can be about (10-0.5): 1). The mixture can be neutralized with a NaOH solution to form a co-precipitate of aluminum-titanium hydroxide, which is stirred for about 10-30 h to form uniform crystal particles. The resultant is filtered and washed away the Na ⁺ and Cl ⁻ ions with deionized water and then the resultant mixed hydroxide can be dried at about 100-150° C. The dry sample can be pulverized into fine powders of about 120-180 mesh and after kneading. The fine powders can be extruded into long strips of about φ3 to about φ6 mm, such as using a twin screw extruder.

[0042] After being dried at about 100-150° C., the strips can be calcined in a muffle furnace at about 500-1100° C., such as in an air atmosphere at about 800-1000° C. for about 0.5-10 h, or for about 1-3 h to yield a mixed alumina-titania support. In one embodiment, the support can have a bulk density of about 0.7-0.9 g/ml, a pore volume of about 0.3-0.6 ml/g, a specific surface area of about 10-50 m ² /g (BET nitrogen method) or about 20-60 m ² /g (mercury intrusion method). The pore diameter can exhibit a two peaks distribution at about about 50 nm and 1000 nm. The most probable pore diameter can be about 200-1000 nm. The mean pore diameter (4V/A ⁺ ) can be about 40-100 nm.

[0043] 2. Impregnating the Active Component The chemical composite support of alumina-titania can be impregnated with a mixed solution of water-soluble inorganic salts of palladium and a Group IB metal to allow the active component and the promoter to be absorbed into the pores of the support together and uniformly distributed. The inorganic salts of palladium and the Group IB metal can be dissolved in deionized water to form an impregnation solution, the total amount of which can equal the pore volume. The pH value of the impregnation solution can be adjusted to be about 1-4 to control the dispersion depth of the active component and the promoter. The impregnated support can be dried at about 80-150° C. The distribution of the active component of the catalyst is determined with SEM and the particle size is determined with

[0044] TEM.

[0045] 3. Decomposing the Catalyst

[0046] The supported catalyst can be decomposed in an air atmosphere at about 300-800° C., preferably about 400-500° C., for about 2-10 h. The active components of the catalyst can exist as oxides in the catalyst body within the thickness between the support surface and the depth of more than about 300 μm. In the hydrogen atmosphere under reaction conditions, the active components of the catalyst can be reduced to alloy.

[0047] When the catalyst of the present invention is applied to the selective hydrogenation of mixed components containing alkynes and dienes to convert them into mono-olefins by means of the conventional method, not only the activity, but also the selectivity is high, and the performance of the catalyst is basically not affected by the variation in CO concentration. The catalyst of the present invention is particularly suitable for the “fore-hydrogenation alkyne removal” technology of C ₂ , C ₃ , or a mixed C ₂ and C ₃ feed containing any amount of hydrogen and CO. The catalyst of the present invention is suitable for the reactors of the isothermal bed, adiabatic bed, etc.

[0048] The preparation process of the present invention can ensure a uniform dispersion of the major active component Pd and the Group IB metal promoter of the catalyst in the catalyst body within the thickness between the support surface and the depth of more than about 300 μm. Metal Pd and Group IB or other metals can form stable and uniform alloy particles, such as by reducing the composite oxide, which is formed at a high temperature and in oxygen atmosphere, in hydrogen atmosphere. Because of the surface tension caused by the formation of the alloy, the atoms of the Group IB metal concentrate on the surface of the alloy. The activity and selectivity of the catalyst for hydrogenation can be enhanced via a synergetic effect of palladium and the Group IB metal.

[0049] Since the active component of the catalyst of the present invention can be dispersed in the catalyst body to a sufficient depth, generally from the support surface to more than about 300 μm, the active component can have a higher dispersion, which can decrease the yield of the green oil formed from oligomers decreases. Thus, the catalyst can have a longer lifetime. According to the present invention, a higher activity of the catalyst is ensured at various concentrations of hydrogen and CO. The use of a chemical composite support of alumina-titania provided by the present invention can overcome the shortcomings of the high yield of the green oil and the low selectivity for hydrogenation when the conventional alumina support of the prior art is used in the hydrogenation (due to the large number of small and micro pores and the higher surface acidity). Thereby, the catalyst of the present invention can have a high activity and selectivity for hydrogenation, a long operation period, and resistance to sulfur and arsenic poisoning.

[0050] During the course of the application, various publications mentioned above have been referred to, the disclosures of which are all incorporated herein for reference.

EXAMPLES

Comparative Example 1

[0051] A commercial dry gel of pseudo-boehmite aluminum hydroxide was formed into small spheres with diameters of 2-4 mm. The spheres were calcined in a muffle furnace to 1400° C. at a rate of 200° C./h and maintained at this temperature for 4 h to yield the required support having a pore volume of 0.37 ml/g, a bulk density of 1.0 g/ml, a specific surface area of 4.6 m ² /g (BET nitrogen method) or 12.5 m ² /g (mercury intrusion method), a most probable pore diameter of 270 nm, and a mean pore diameter of 274 nm. 0.85 ml of palladium nitrate solution containing 4.7 mg Pd/ml, and 6.5 ml of water were added into a beaker and thoroughly mixed to prepare the impregnation solution. 20 g of the support was put into a 100 ml beaker, into which the prepared impregnation solution was added to impregnate the support. The resultant was dried at 120° C. for 8 h and decomposed in an air atmosphere at 450° C. to yield catalyst 1-1. The SEM measurement shows that 90% palladium is distributed within a shell of about 300 μm in thickness.

Comparative Example 2

[0052] In this Comparative Example, 3 ml of silver nitrate solution containing 5 mg Ag/ml, and then 4.4 ml of water were added into a beaker and thoroughly mixed to prepare the silver impregnation solution. 20 g of the support as in Comparative Example 1 was put into a 100 ml beaker, into which the prepared silver impregnation solution was added to impregnate the support. The impregnated support was dried at 120° C. for 8 h. 0.6 ml of palladium chloride solution containing 10.3 mg Pd/ml, and then 6.8 ml of water were added in a beaker, and thoroughly mixed to prepare the palladium impregnation solution. The support which had been impregnated with silver nitrate solution was added into the palladium impregnation solution to fully be impregnated. Then the wet catalyst was dried at 120° C. for 8 h and decomposed in an air atmosphere at 450° C to yield catalyst 1-2. The SEM measurement shows that 90% palladium is distributed within a shell of about 300 μm in thickness and that silver is uniformly distributed.

Example 1

[0053] According to Example 1, about 0.6 ml of cupric nitrate containing about 10 mg Cu/ml, about 0.85 ml of palladium nitrate containing about 4.7 mg Pd/ml and about 6.8 ml of water were added into a beaker and thoroughly mixed. The pH value of the solution was adjusted to pH =1.2 with, such as nitric acid and ammonia, to prepare the impregnation solution. About 20 g of the support as in Comparative Example 1 was put into a 100 ml beaker, into which the prepared impregnation solution was added to impregnate the support. The impregnated support was dried at about 120° C. for about 8 h and decomposed in an air atmosphere at about 450° C. to yield catalyst 2-1. The SEM measurement shows that about 90% palladium and silver were distributed in the catalyst body within the thickness between the support surface and the depth of about 500-1000 μm.

Example 2

[0054] About 1.0 ml of silver nitrate containing about 10 mg Ag/ml, about 0.85 ml of palladium nitrate containing about 4.7 mg Pd/ml and about 5.5 ml of water were added into a beaker and thoroughly mixed. The pH value of the solution was adjusted to pH=1.2 with, such as nitric acid and ammonia, to prepare the impregnation solution. About 20 g of the support as in Comparative Example 1 was put into a 100 ml beaker, into which the prepared impregnation solution was added to impregnate the support. The impregnated support was dried at about 120° C. for about 8 h and decomposed in an air atmosphere at about 450° C. to yield catalyst 2-2. The SEM measurement shows that 90% palladium and silver were distributed in the catalyst body within the thickness between the support surface and the depth of about 500-1000 μm.

Example 3

[0055] About 3.9 ml of auric chloride containing about 4.8 mg Au/ml, about 0.85 ml of palladium nitrate containing about 4.7 mg Pd/ml and about 2.5 ml of water were added into a beaker and thoroughly mixed. The pH value of the solution was adjusted to pH =1.2 with, such as nitric acid and ammonia, to prepare the impregnation solution. About 20 g of the support as in Comparative Example 1 was put into a 100 ml beaker, into which the prepared impregnation solution was added to impregnate the support. The impregnated support was dried at about 120° C. for about 8 h and decomposed in an air atmosphere at about 450° C. to yield catalyst 2-3. The SEM measurement shows that 90% palladium and silver were distributed in the catalyst body within the thickness between the support surface and the depth of about 500-1000 μm.

Example 4

[0056] About 1.2 ml of silver nitrate containing about 5 mg Ag/ml, about 1.2ml of palladium nitrate containing about 4.7 mg Pd/ml and about 5.0 ml of water were added into a beaker and thoroughly mixed. The pH value of the solution was adjusted to pH=1.2 with, such as nitric acid and ammonia, to prepare the impregnation solution. About 20 g of the support as in Comparative Example 1 was put into a 100 ml beaker, into which the prepared impregnation solution was added to impregnate the support. The impregnated support was dried at about 120° C. for about 8 h and decomposed in an air atmosphere at about 450° C. to yield catalyst 2-4. The SEM measurement shows that 90% palladium and silver were distributed in the catalyst body within the thickness between the support surface and the depth of about 500-1000 μm.

Example 5

[0057] About 6 ml of silver nitrate containing about 5 mg Ag/ml, about 1.2 ml of palladium nitrate containing about 4.7 mg Pd/ml were added into a beaker and thoroughly mixed. The pH value of the solution was adjusted to pH=1.2 with, such as nitric acid and ammonia, to prepare the impregnation solution. About 20 g of the support as in Comparative Example 1 was put into a 100 ml beaker, into which the prepared impregnation solution was added to impregnate the support. The impregnated support was dried at about 120° C. for about 8 h and decomposed in an air atmosphere at about 450° C. to yield catalyst 2-5. The SEM measurement shows that 90% palladium and silver were distributed in the catalyst body within the thickness between the support surface and the depth of about 500-1000 μm.

Example 6

[0058] TiCl ₄ solution was neutralized with NaOH solution of the same equivalence as that of TiCl ₄ at 40° C. to conduct co-precipitation, and then stirred for about 24 h to turn the resultant titanium hydroxide into uniform crystal particles. The suspension was filtered and washed away the Na+and Cl- ions with deionized distilled water and then the resultant hydroxide was dried at about 120° C. The dry sample was pulverized into fine powders of about 120-180 mesh. After kneading, it was extruded into long strips of about (p3 mm using such as a twin screw extruder. The strips were dried at about 120° C. and calcined in a muffle furnace at about 1 100° C. for about 4 h to yield the required TiO ₂ support having a bulk density of about 1.25 g/ml, a pore volume of about 0.17 ml/g, a specific surface area of about 4.9 m ² /g (BET nitrogen method) or about 17.5 m ² /g (mercury intrusion method), a most probable pore diameter of about 98 nm, and a mean pore diameter of about 51 nm.

[0059] About 1.0 ml of silver nitrate containing about 10 mg Ag/ml, about 0.85 ml of palladium nitrate containing about 4.7 mg Pd/ml and about 2.0 ml of water were added into a beaker and thoroughly mixed, then pH value of the solution was adjusted to pH 1.2 with, such as nitric acid and ammonia, to prepare the impregnation solution. About 20 g of the support was put into a 100 ml beaker, into which the impregnation solution was added to impregnate the support. The impregnated support was dried at about 120° C. for about 8 h and decomposed in an air atmosphere at about 450° C. to yield catalyst 2-6. The SEM measurement shows that 90% palladium and silver were distributed in the catalyst body within the thickness between the support surface and the depth of about 500-1000 μm.

Example 7

[0060] NaAlO ₂ solution and TiCl ₄ solution were mixed at about 40° C, then the mixture was neutralized with NaOH solution to form a co-precipitate of aluminum-titanium hydroxide, which was stirred for about 24 h to form uniform crystal particles. The resultant was filtered and washed away the Na ⁺ and Cl ⁻ ions with deionized distilled water and then the resultant mixed hydroxide was dried at about 120° C. The dry sample was pulverized into fine powders of about 120-180 mesh. After kneading, it was extruded into long strips of about (p3 mm, such as using a twin screw extruder. After being dried at about 120° C., the strips were calcined in a muffle furnace at about 900° C. for about 2 h to yield an alumina-titania mixed support (Al ₂ O ₃ /TiO ₂ =:1) having a bulk density of about 0.8 g/ml, a pore volume of about 0.4 ml/g, a specific surface area of about 22.1 m ² /g (BET nitrogen method) or about 36.6 m ² /g (mercury intrusion method). The support exhibited a two peaks distribution at about 50 nm and about 1000 nm and the mean pore diameter was about 58 nm.

[0061] About 1.0 ml of silver nitrate containing about 10 mg Ag/ml, about 0.85 ml of palladium nitrate containing about 4.7 mg Pd/ml and about 6.1 ml of water were added into a beaker and thoroughly mixed. The pH value of the solution was adjusted to pH=1.2 with, such as nitric acid and ammonia, to prepare the impregnation solution. About 20 g of the support was put into a 100 ml beaker, into which the impregnation solution was added to impregnate the support. The impregnated support was dried at about 120° C. for about 8 h and decomposed in an air atmosphere at about 450° C. to yield catalyst 2-7. The SEM measurement shows that 90% palladium and silver were distributed in the catalyst body within the thickness between the support surface and the depth of about 500-1000 μm.

Example 8

[0062] About 0.8 ml of each catalyst prepared in the above examples was loaded into an isothermal reactor with a loading diameter of about 5mm and a loading height of about 40mm. The composition of the feed is shown in Table 1. Selective hydrogenation was conducted under a reaction pressure of about 1.6 MPa and a space velocity of about 10000 h- ¹ . Table 2 presents the temperature, selectivity for acetylene hydrogenation and conversion of propyne and propadiene (MAPD) corresponding to an exit acetylene concentration less than about 1 ppm.

[0063] The selectivity for acetylene hydrogenation (abbreviated as selec.) and the conversion of MAPD (abbreviated as conv.) are important indices reflecting the activity and selectivity of the catalyst, and the formula for their calculation are as follows: 1 $\mathrm{Selec}.=\frac{\begin{array}{c}{C}_2H_4\mathrm{conc}.\left(\mathrm{mol}\%\right)\mathrm{after}\mathrm{reaction}-\\ C_2H_4\mathrm{conc}.\left(\mathrm{mol}\%\right)\mathrm{before}\mathrm{reaction}\end{array}}{\begin{array}{c}{C}_2H_2\mathrm{conc}.\left(\mathrm{mol}\%\right)\mathrm{before}\mathrm{reaction}-\\ C_2H_2\mathrm{conc}.\left(\mathrm{mol}\%\right)\mathrm{after}\mathrm{reaction}\end{array}}\times 100\%$ $\mathrm{Conv}.=\frac{\begin{array}{c}\mathrm{MADP}\mathrm{conc}.\left(\mathrm{mol}\%\right)\mathrm{before}\mathrm{reaction}-\\ \mathrm{MADP}\mathrm{conc}.\left(\mathrm{mol}\%\right)\mathrm{after}\mathrm{reaction}\end{array}}{\mathrm{MADP}\mathrm{conc}.\left(\mathrm{mol}\%\right)\mathrm{before}\mathrm{reaction}}\times 100\%$ 1

[0064] 2

[0065] Table 2 shows that the catalysts of the present invention all have higher selectivity for acetylene hydrogenation into ethylene and higher MAPD conversion at various concentrations of hydrogen and CO. At higher hydrogen content, the catalyst containing only active component palladium has very low selectivity for acetylene hydrogenation into ethylene (only 1.5%) and very low MAPD conversion, while under the identical reaction conditions, the selectivity of the Pd/Ag catalyst of the present invention is about 64.2% and the selectivity of the Pd/Au catalyst of the present invention is about 21.4%. Under the identical reaction conditions, the selectivity of the catalyst wherein palladium is distributed in shell and silver is distributed in bulk is about 12.2%, while the selectivity of the catalysts of the present invention is about 49.5% and about 49.3%, respectively.

Example 9

[0066] The activity for the selective hydrogenation of alkynes and dienes over catalyst 2-2 was examined using a series of two adiabatic reactors with a cooler in between. Each reactor was made from stainless steel of about 25 mm i.d., the 10 upper part of which was the preheating section and the lower part was the catalyst bed. The catalyst loading of each reactor was about 200 ml. The height of the catalyst bed was about 400 mm. The conversion of acetylene in the first reactor was controlled to be about 90%. The results are shown in Table 3. 3

Example 10

[0067] Catalyst 1-4 and 2-2 were loaded in two parallel reactors and the relation of their activity and selectivity with time on stream (TOS) was determined under the identical reaction conditions, such as shown in FIG. 1 . Each reactor was made from stainless steel of about 25 mm i.d., the upper part of which was the preheating section and the lower part was the catalyst bed. Heating wire was wrapped around the outer wall to heat the reactor or maintain its temperature. The loading of each reactor was about 200 ml. The height of the catalyst bed was about 400 mm.

[0068] Catalyst 1-4 was a commercial Pd/Ag/Al ₂ O ₃ catalyst containing about 0.024 wt % Pd and about 0.068 wt % Ag with the other being alumina. The catalyst was prepared completely according to the process, such as disclosed in U.S. Pat. No. 4,404,124. Pd was distributed in the shell of about 300 μm in thickness and Ag in the bulk. The catalyst was provided by Nissan Girdler Catalyst Co. Ltd. and had a tradename of G-83C.

[0069] The catalysts had not been reduced and the reactant feed was directly introduced to effect the reaction. During the about 0-250 h of TOS, the space velocity was about 8000 h ⁻¹ . During about 250-560 h of TOS, the space velocity was about 12000 h ⁻¹ . At the inlet, the concentration of acetylene was about 0.6-0.7 mol %. The concentration of hydrogen was about 10-20 mol %. The concentration of CO was about 600-1000 ppm. The reaction temperature was about 60-120° C. The reaction pressure was about 3.6 MPa.

[0070] After near 600 h of TOS, the weight of Catalyst 1-4 increased by about 19.1 g, and that of Catalyst 2-2 increased by about 16.7 g, showing that the yield of the green oil on the catalyst of the present invention was lower. FIG. 1 shows that the conversions of acetylene and MAPD on the catalyst of the present invention maintained basically constant during the about 600 h of TOS and the selectivity for the acetylene hydrogenation into ethylene was always higher than that of Catalyst 1-3, while the conversions of acetylene and MAPD on the comparative catalyst started to drop at about 380 h. This demonstrates that the uniform distribution of the active components palladium and silver increases the selectivity of the catalyst and the suitably deep distribution of the active components increases the activity of the catalyst, decreases the yield of the green oil, and improve the stability of the catalyst.

Example 11

[0071] The support derived in Comparative Example 1 was impregnated using the same method as in Comparative Example 2 to yield Catalyst 1-3 with the exception that the support was impregnated after the pH value of the impregnation solution had been adjusted to be about 5. The distribution of the metals in the catalyst was determined with SEM and the result showed that about 90% Pd and Ag were distributed in the shell of about 300 ,m in thickness.

[0072] About 0.8 ml of the catalyst was loaded into an isothermal reactor to form a bed of about 5 mm in diameter and about 40 mm in length. The composition of the feed as shown in Table 4. The pressure of the feed stream was about 1.6 MPa and the space velocity was about 10000 h ⁻¹ . The results of the selective hydrogenation were shown in Table 5. 4

[0073] 5

Example 12

[0074] About 0.8 ml of Catalyst 2-2 was loaded into an isothermal reactor to form a bed of about 5 mm in diameter and about 40 mm in height. The composition of the feed is shown in Table 6. The pressure of the feed stream was about 1.6 MPa and the space velocity was about 10000 h ⁻¹ . The results of the selective hydrogenation are shown in Table 7. 6

[0075] 7

[0076] It can be seen from the above results that the catalyst of the present invention can attain higher acetylene conversion, higher selectivity for acetylene hydrogenation into ethylene, and higher MAPD conversion at low temperatures compared to the catalyst wherein the active components are distributed within the shell of thickness between the support surface and the depth of less than about 300 μm, therefore it has higher activity.