CATALYST FOR SELECTIVE HYDROGENATION OF ALKYNES IN THE PRESENCE OF DIENES

Abstract: Catalyst for the hydrogenation of alkynes having a gamma alumina support carrying copper metal and optional­ ly an activator metal. The support has a surface area of 68 to 350 m²/g, 50 to 90 per cent of the pores have an average diameter of 4 to 12 nm, 0.5 to 25 per cent of the pores have an average diameter of 100 to 1000 nm. The catalyst is advantageously employed for the remov­ al of alkynes (such as 1-butyn-3-ene) from a diene (such as 1,3-butadiene) with relatively little degradation of the diene.

Description: CATALYST FOR SELECTIVE HYDROGENATION OF ALKYNES IN THE PRESENCE OF DIENES This invention relates to catalysts useful for the hydrogenation of alkynes e.g. to remove such alkynes from a hydrocarbon stream, and to methods for preparing such catalysts. Copper metal, activated with one or more of the metals silver, platinum, palladium, manganese, cobalt, nickel, chromium and/or molybdenum on an alumina support, is well known as a catalyst for hydrogenation of alkynes. Frevel et al. have issued several patents in which improved results are obtained (improved selectivity of hydrogenation of carbon-carbon triple bonds in the presence of diene bonds) by increasing the sodium content of the activated catalyst, U.S. Patent 4,101,451, and/or high sodium oxide alumina, U.S. Patent 3,912,789. However, these catalysts still hydrogenate some considerable amount of the diene components of such streams. As the diene content of these streams becomes more valuable it would be advantageous to reduce the hydrogenation of these dienes (particularly 1,3-butadiene) without also reducing the hydrogenation of the alkynes. It has now been found that by employing a gamma alumina containing not more than 35 percent by weight of alpha alumina, having a surface area of between 68 and 350 square meters per gram, 90 to 50 percent (preferably 90 to 55, more preferably 90 to 60 percent) of the pores having a pore diameter between 4 nm and 12 nm and not more than 25 percent of the pores nor less than 0.5 percent (preferably not less than 1 percent, more preferably not less than 2 percent) having a pore diameter between 100 nm to 1,000 nm, produces a catalyst support which when coated with copper and optionally an activator metal, permits reaching lower alkyne levels with less alkene loss than prior art catalysts, and additionally can be effectively regenerated to 90 plus percent activity over several cycles. The gamma alumina preferably has one or more of the followingharacteristics less than 0.15 weight percent silica as SiO2; less than 0.15 weight percent, more preferably less than 0.10 weight percent sodium as Na20; less than 0.06 weight percent iron as Fe203; and less than 0.01 weight percent sulfur. Preferably the catalyst includes at least one activator metal such as silver, platinum, palladium, manganese, cobalt, nickel, chromium or molybdenum. The activator metal may be present at up to 15% by weight of the copper. The copper preferably is present at a level of 3 to 13% of the weight of the support, particularly if there is an activator metal present also at the level of up to 15% by weight of the copper. The invention includes processes for the hydrogenation of alkynes, e.g. the selective hydrogenation of alkynes in a hydrocarbon stream containing a diene such as 1,3-butadiene, comprising contacting the alkynes with such a catalyst under appropriate reaction conditions. It has also been found that during use the gamma alumina described above undergoes a phase change, probably due to thermal treatment during operation and regeneration. Thus, a gamma alumina within the scope above defined will undergo a gradual change, as for example, during a nine month, thirteen cycle (with regeneration) run, to analyze about 35 percent alpha alumina with an attendant reduction in surface area from about 165 square meters per gram to about 68 square meters per gram. There is also a change in the pore volume distribution associated with the reduction in surface area and presence of the alpha alumina. However, the pore sizes remain within the aforedefined range. Thus, while it is preferred to start with a relative high purity gamma alumina having the above described properties and physical characteristics, it is to be understood that a carrier or support may be a combined unitary alumina consisting of a high purity alumina as above defined but having up to fifty percent alpha alumina in admixture with gamma alumina. Such a support can be readily obtained by thermal treatment of gamma alumina of the requisite purity in the presence of cuprous oxide. The phase change apparently occurs during the oxidation and/or reduction during regeneration. Presumably the cuprous oxide acts as a seed to effectuate the phase change from gamma to alpha state. However, no specific theory based on scientific data of how such a change occurs can yet be set forth. While the aforestated procedure appears to effect the change, other methods may be available from those skilled in the art of alumina production The catalyst carrier or support which appears to be greatly preferred for obtaining the aforesaid results is a special grade of gamma alumina (y-A12O3) prepared by decomposing trialkyl alumina to alpha aluminum monohydrate then calcining the alpha aluminum monohydrate to gamma alumina. This process produces a grade of gamma alumina normally not obtainable from naturally occuring aluminum containing ores and which has, when pressed or extruded into pellets, a higher purity than naturally occurring alumina, and a pore size and pore size distribution sufficiently different from that obtainable using naturally occurring aluminas and converting them to gamma alumina. Throughout this specification, by the term "gamma alumina" is meant a true gamma alumina. Such a true gamma alumina will match the published X-ray diffraction pattern (it 29-63) of the Joint Committee on Powder Diffraction Standards (a non-profit scientific body based in Philidelphia, PA, USA). The most ready sources of catalyst support size pellets are The Harshaw Chemicals Co. sold as 3438T; Norton Company as SA6173 and Calcicat Division, Mallinckrodt Chemical Works as CALCICAT Type A and AA. Although Conoco Chemicals Division, Conoco, Inc., manufactures a powder, CATAPAL type SB which has been found suitable and is believed to be the precursor powder for the three pellet producers, pellets produced by Conoco are not readily available except through the three pelletizers. The alkynes present in a typical feed stream will usually be a mixture of C2 to C6 alkynes, and more commonly C3-C4 alkynes. A typical feed stream will have l-butyne-3-ene (vinyl acetylene) as the major alkyne component, along with lesser quantities of 1-butyne (ethyl acetylene) and l-propyne (methyl acetylene). While the catalysts of the invention may be used to hydrogenate virtually any alkyne feed stream, a liquid stream is preferred. A particular advantage of these catalysts is their selectivity for carbon-carbon triple bonds to the relative exclusion of carbon-carbon double bonds. Thus, these catalysts have extreme economic importance for the removal of alkynes from alkenes. A typical situation in which these catalysts may be used is the removal of mixed alkynes from a mixture of 1,3-butadiene and l-butene. These catalysts will cause very little hydrogenation of 1,3-butadiene into the much less valuable l-butene. In fact, if l-butyne-3-ene is the major alkyne contaminant, it is possible to actually increase the level of 1,3-butadiene by the hydrogenation of the alkyne contaminant. The drawings, Figures 1-9 and 16-20, illustrate the results of the several experiments employing different supports as carriers for the catalytically active components, with respect to the alkynes in the product stream and the loss of 1,3-butadiene from the feed stream as a result of the process. Figures 10, 11, 14 and 15 illustrate the pore size distribution of the several supports of the examples, and Figures 12 and 13 illustrate the results obtained when the heretofore conventional support, y-AlOOH, REYNOLDS RA-1 is employed. Figure 21 illustrates the effect of water vapor on copper crystallite size and, in conjuction with Example 8, the results of such growth on catalyst activity. Example 1 In accordance with the present invention 300 grams of y-Al2O3 obtained from Conoco Chemicals Division, Conoco, Inc., as 1/8 inch (3.2 mm) diameter by 1/4 inch (6.3 mm) long pellets identified as CATAPAL SB had the following properties: x-ray diffraction pattern matches Joint Committee on Powder Diffraction standards it29-63; % Na2O 0.004 Sulfur 0.01 % SiO2 0.008 %Fe2O3 0.005 Surface area (m2/g) 241 Pore volume (cc/g) 0.57 Bulk density (g/cc) 0.79 75% of its pores were less than 7.5 nm 82% of its pores were less than 10 nm 18% of the pores were between 10.2 nm and 839 nm The unburdened support was impregnated with a solution consisting of: : Cu(NO3)2.2¸H2O 113 g Ni(N03)262O 4.0 g H2O -40 g HN03 59 g Mn(NO3)2 50% active 3.1 g AgNO3 0.2 g Cr(NO3)3 9H2O 1.7 g Co(NO3)2.6H2O 1.7 g Solubilization of the numerous metal salts was obtained by gentle heating. The resulting solution was poured over 300 grams of the support in a beaker while stirring to obtain even distribution. When all of the solution had been sorbed, the support was dried over night at 1100C, then calcined at 4000C for about 6 hours. The catalyst was loaded to a depth of about 12 inches (305 mm) at the middle of a laboratory 1 inch (25.4 mm) diameter by 36 inch (914 mm) long reactor. The remaining space of the reactor, above and below the catalyst, was filled with raschig rings. The catalyst was reduced over night with hydrogen at between 3000C to 3500C. In the morning the temperature recording from several thermocouples in the bed showed an exotherm had passed up the column during the night signifying reduction of the metal oxides to their metal state. The reactor was cooled to ambient temperature and hydrogen and a liquid hydrocarbon stream having about 61% by weight 1,3-butadiene and 8716 ppm mixed alkynes was fed to the reactor. The reactor conditions were: Feed 300 cc/hour Recycle 600 cc/hour H2 Flow 2.8 liters/hr at atm STP H2:C= ratio 4:1 Inlet temperature of liquid 600C T at thermocouple &num;1 ca. 700C &num;2 ca. 670C &num;3 ca. 660C &num;4 ca. 620C &num;5 ca. 580C Regeneration was accomplished by purging the reactor with N2 at about 12 liters/min., followed by introduction of air first at 18.15 liters/min. then 13.3 liters/min. Finally the air was shut off and H2 was admitted at 4.1 liters/min. The GHSV (gas hourly space velocity values) were: N2 1650 hr-1 N2 + air (max.) 3460 hr l; and, N2 + H2 2215 hr-1 respectively. The results of two runs with regeneration are illustrated in Figure 1 which shows that the product had an average of less than 80 ppm alkynes having hydrogenated over 8630 ppm of the alkynes in the feed with less than 1% total butadiene loss based on the butadiene present in the feed. Example 2 To 400 grams of a catalyst support obtained from Calsicat Division, Mallinckrodt Chemical Works, identified as CALSICAT Type A having the following physical properties as 1/8 inch (3.2 mm) pellets: x-ray diffraction pattern matches Joint Committee on Powder Diffraction Standards &num;29-63; %Na2O 0.005 % sio2 0.01 %Fe2O3 ( < 0.1) % Sulfur 0.01 Surface area (m2/g) 200 Pore volume (cc/g) 0.50 Bulk density (g/cc) 0.8 was added the following liquid mixture: grams Cu(NO3)2.2¸H2O 140 Ni(N03) 6H20 4.75 Mn(NO3)2 50% solution 4 Co(NO3)2.6H2O 2 Cr(NO3)3.9H2O 2 HN03 (conc.) 7.1 AgNO3 0.25 H2O -50 with stirring and heating, 50-600C, until the liquid was sorbed. Thereafter the wetted support was dried in an oven at 1100C for 2 hours, then placed in a furnace at 4000C at about noon and left overnight. The next morning the catalyst was removed from the furnace, cooled and packed in a reactor of like size and in the same manner as described in Example 1. The 72-day results of 5 cycles with regeneration as previously described are illustrated in Figures 2-6. The average l-alkyne content of the outlet product was less than 100 ppm (from 8000-10,000 ppm in feed) and a loss of butadiene of less than 1 percent of that in the feed. Example 3 In a similar manner as Example 2, 300 grams of a 1/8 inch (3.2 mm) pellet CALSICAT Type AA catalyst support was impregnated with a proportionate volume of the catalyst formulation, dried, packed in a similar reactor, reduced with H2, and operated without regeneration for 57 days. The results of a two-month cycle, illustrated in Figure 7, show an average of < 50 ppm alkyne coming through during the first 35 days and < 150 ppm alkyne coming through the next 22 days. The loss of butadiene during the entire 57 days was about 1 percent. Example 4 Likewise, a catalyst prepared on HARSHAW Al-3438T support was prepared and tested in a similar manner to the foregoing Examples. The results of six (6) days operation showed 200 ppm alkyne (avg.) remaining in the treated liquids and a loss of about 2 percent butadiene. Example 5 A NORTON SA6173 support was employed to prepare a catalyst and operated for a first cycle of 18 days in a test as afore described. Regeneration occurred on the 18th day. The processed liquids had an average of 200 ppm alkyne and about a 1 percent loss in butadiene content on the initial run. The butadiene losses increased from 2 to 4 percent on the regenerated catalyst over a 15-day second cycle. The graphic daily results are shown in Figures 8 and 9. In order to identify each support, the physical properties of each are set forth in Table I. Table I Surface Pore Bulk Area Volume Density %Na2O SiO2 % % Fe2O3 m /g cc/g g/cc Sulfur(ê) CALSICAT Type A 0.005 0.01 ( < 0.01) 200 0.50 0.80 (0.01) HARSHAW Al-3438T (0.005) (0.01) < 0.01 175 0.50 0.78 (0.01) CATAPAL Type SB 0.004 0.008 0.005 241 0.57 0.79 0.01 CALSICAT Type AA 0.07 0.12 < 0.06 215 0.70 0.63 - NORTON SA-6173 0.015 0.09 0.06 240 0.56 0.69 - REYNOLDS RA-1(Ú) 0.35 66ppm 190ppm 213 0.18 0.88 - (Ú) Conventional &gamma;.AlOOH support. ( ) No value listed indicates the level present was below detection limits. Note: values in parentheses are assumed values. The pore distribution of each support is shown in the drawings, Figures 10 and 11. In Figures 10 and 11, "A" refers to 10 10 meters, and p refers to pm. Comparative Example 1 For purposes of comparison, a catalyst having the exact composition as that applied in Example 1 was applied to a conventional gamma alumina (REYNOLDS RA-l a y-AlOOH) having a normal sodium content and pore size distribution. The results of 2 cycles, with regeneration after the 35th day of the first cycle, shows results illustrated in Figures 12 and 13; to wit: 100-200 ppm of mixed alkynes during the first cycle rising to 200-400 during the second cycle, with loss of 1,3-butadiene in the 1 to 4 percent range in both cycles. Example 6 A catalyst prepared from a high purity Norton SA-6173 1/16 inch (1.59 mm) extrudates upon which copper and promoter metals were impregnated, was calcined at 4000C for 8 hours. The proportions employed to prepare this catalyst were: grams Norton SA-6173 1/16 inch 4800 Cu(NO3)2 2lWH2o 1680 Ni(NO3)6N2O 57 Mn(N03)2 50% solution 48 Co(NO3)2 6H2O 24 Cr(NO3)3 9H2O 24 HNO, (conc.) 85 AgNO3 3 H2O 600 The calcined catalyst was loaded into a reactor, heated to 2500C in the presence of nitrogen then reduced with up to 5 volume percent H2 in nitrogen for about 12 hours. The reactor was cooled and liquid hydrocarbon was introduced into the reactor and catalyst bed. The reactor temperature was maintained between about 50 C and 700C. Hydrogen to alkyne molar ratio was maintained at about 3 to 4 throughout thirteen cycles Regeneration of the catalyst was carried out about every 14 to 21 days by heating to about 2500 to 3000C in the presence of nitrogen, then in the presence of air until an exotherm had passed through the bed, and then maintained on air for 2-4 hours, until no other exotherm wave was observed. The air was stopped and hydrogen of up to 5 volume percent in nitrogen passed through the bed until an exotherm moved through the bed. When no additional exotherm was observed within 2 to 4 hours on hydrogen, the bed was cooled and placed on line with hydrocarbon feed. The catalyst carrier had the initial pore volume distribution shown in Fig. 14 and a BET nitrogen surface area of 165 m2/g. Following the twelfth cycle before regeneration the carrier had a pore volume distribution as shown in Fig. 15. The BET nitrogen surface area was 68 m2/g. The initial data of operation for the 13th cycle for 3 days was comparable to the initial 3 days operation of the first and subsequent cycles. Example 7 In evaluating the performance of the catalyst and its support in respect to materials of construction, it was found that the materials of construction for the reactor are critical if long, fourteen day, on stream cycles are desired Thus when one employs a stainless steel containing nickel, the efficiencies of the catalysts of the present invention are somewhat reduced due to the necessity to regenerate the catalyst more often. This phenomenom is overcome when carbon steel is employed as the material of construction for the reactor. The effects of the presence of nickel even though only small amounts are possible at the internal surface of the reactor (wall effect) are clearly seen in Figures 16, 17, and 18, the 9th, 12th, and 13th cycles, in a 304 stainless steel reactor. The use of a carbon steel reactor illustrates the improved efficiency, i.e. longer run time between regeneration before the alkynes are no longer effectually hydrogenated and is shown by comparing results of the three just mentioned runs, Figures 16, 17, and 18, with the results of the carbon steel reactor shown in Figures 19 and 20. Example 8 Another point which long run data establishes is that steam regeneration markedly reduces the life of a catalyst by a loss of surface copper and an increase in copper crystallite size following regeneration and/or oxidation of the catalyst. Results are illustrated in the Table II. Samples were prepared in the sequence shown in Figure 21. Table II COMPARISON OF STEAM AND N2 DILUENTS DURING REGENERATION Cu /&gamma;-Al2O3 Cu /&gamma;-Al2O3 R x-ray FINAL ESCA X-RAYÚ R ESCA OXIDATION SMALL LARGE LARGE TO SMALL SAMPLE DILUENT % Cu++ SURFACE SPECIES BULK SPECIES CRYSTAL RATIO 1 --- Ox. 100 1.58 --- --2 Steam Red. 5 0.50 0.86 1.7 3 N2 Red. 5 0.83 1.16 1.4 4 Steam Ox. 73 0.97 0.25 0.3 5 N2 Ox. 29 0.89 0.75 0.8 6 Steam Red. 1 0.27 0.69 2.6 7 N2 Red. 19 0.60 0.78 1.3 8 N2 Red. 7 0.54 1.13 2.1 Ú Total area for ESCA scan of the Cu 2p3/2 peak to total area per ESCA scan of the aluminum 2s peak was taken as amount of small copper particles present in the catalyst. The ratio of the height of the copper 0.209 nm peak by x-ray diffraction to the &gamma;-Al2O3 0.140 nm peak of x-ray diffraction was calculated as a measure of the large copper crystallites present. Ratio of x-ray ratio to ESCA ratio was calculated as ratio of large to small copper crystallites.

Claims: CLAIMS 1. A catalyst for the hydrogenation of alkynes, comprising a support having thereon finely divided copper metal, characterised in that the support is a gamma alumina having a surface area of 68 to 350 m2/g, 50 to 90 percent of the pores having an average diameter of 4 to 12 nm, 0.5 to 25 percent of the pores having an average diameter of 100 to 1000 nm. 2. A catalyst as claimed in Claim 1 wherein from 1 to 25 percent of the pores have an average diameter of from 100 to 1000 nm. 3. A catalyst as claimed in Claim 2 wherein from 2 to 25 percent of the pores have an average diameter of from 100 to 1000 microns. 4. A catalyst as claimed in any preceding claim wherein from 55 to 90 percent of the pores have an average diameter of from 4 to 12 nm. 5. A catalyst as claimed in Claim 4 wherein from 60 to 90 percent of the pores have an average diameter of from 4 to 12 nm. 6. A catalyst as claimed in any preceding claim wherein said support contains less than 0.1 percent sodium as Na2O and less than 0.15 percent silicon as SiO2. 7. A catalyst as claimed in any preceding claim wherein said support contains less than 0.01 percent sulfur, and less than 0.06 percent iron as Fe203. 8. A catalyst as claimed in any preceding claim wherein the copper metal is present at 3 to 13 percent of the weight of the support. 9. A catalyst as claimed in any preceding claim wherein the support has been prepared by decomposing a trialkyl alumina to alpha aluminium monohydrate and calcining the alpha aluminium monohydrate to gamma alumina. 10. A catalyst as claimed in any preceding claim wherein the support also has thereon an activator metal comprising silver, platinum, palladium, manganese, cobalt, nickel, chromium, or molybdenum. 11. A cataylst as claimed in Claim 10 wherein the activator metal is present at less than 15 percent of the weight of the copper metal. 12. A process for the hydrogenation of an alkyne comprising reacting the alkyne with hydrogen in the presence of a catalyst characterised in that the catalyst is a catalyst as claimed in any one of Claims 1 to 11. 13. A process for the removal of alkynes from a hydrocarbon stream containing at least one diene which comprises contacting the hydrocarbon stream with a catalyst under selective hydrogenation conditions characterised in that the catalyst is as claimed in any one of Claims 1 to 11. 14. A process for the removal of alkynes from a hydrocarbon stream containing 1,3-butadiene comprising contacting the stream with a catalyst comprising of copper metal and one or more of the activator metals silver, platinum, palladium, manganese, cobalt, nickel, chromium and molybdenum dispersed on an alumina support characterised in that the catalyst is as claimed in Claim 10 or Claim 11.

Inventors: COUVILLION, MARK CAMPBELL
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1983
Main classification: B01J35
IPC codes: B01J23, C10G45, B01J35, C07C7, C07B61, C07C11, C07C1, B01J21, C07C5, C07C67