A Calcium-Nickel Phosphate Dehydrogenation Catalyst E. C. BRITTON, A. J. DIETZLER, AND C. R. NODDINGS The Dow Chemical Co., Organic Research Laboratory, Midland, Mich.
A
the carbon deposited during NEW and selective This research was undertaken to provide an effective the process period and for catalyst has been catalyst for the dehydrogenation of n-butenes to 1,3subsequent oxidation of the developed for the dehydrobutadiene, using superheated steam as heating medium genation of n-butenes to and diluent. catalyst. A calcium-nickel phosphate catalyst, promoted with 1,3-butadiene (1) Ultimate yields of 1,3-butadiene of 93 chromium oxide, has given excellent results. Ultimate 93 SCOPE OF THE CATALYST to 97% have been obtained to 97% yields of 1,3-butadiene have been obtained in labin plant Calcium-nickel phosphate in laboratory units a t noratory units at conversion levels of 20 to 45%. operations, ultimate yields of 1,3-butadiene of 86 to 88% is effective for the dehydrobutene conversions of 20 to have been obtained at 35% n-butene conversion. genation of olefins with four 45y0, In plant operations Industrial use of this catalyst should result in improved carbon atoms in the chain. ultimate 86 to 88% yields of 1,3-butadiene have been yields of 1,3-butadiene from n-butenes. In commercial Thus, n-butenes and methyltrials the new catalyst has significantly increased plant butenes are dehydrogenated obtained a t a 35% %-butene capacity for this important synthetic rubber intermediate. in good yields with high conversion level (6). EthylIt is of particular interest where efficient utilization of nselectivity to 1,3-butadiene benzene has been selectively and isoprene, respectively. dehydrogenated to styrene buteneiis necessary. Olefins with a carbon chain over this catalyst. greater than four are not The selectivity of the selectively dehydrogenated to diolefins. catalyst did not change in 3l/* months of continuous operation Propane, propylene, butane, isabutane, and isobutylene pas3 in the laboratory unit, and remained constant a t all conversion over the catalyst in the presence of steam with essentially no conlevels except when operated at temperatures where thermal crackversion. ing affected selectivity. Of particular importance is the high nEthylbenzene is dehydrogenated selectively to styrene, and isobutene utilization a t high conversions which are realized with propylbenzene to a-methylstyrene. this catalyst. The catalyst of this discussion is a calcium-nickel phosphate CATALYST PREPARATION stabilized with chromium oxide. The composition of the calciumnickel phosphate corresponds approximately to the formula The following is a typical preparation of calcium-nickel phosCad%(PO&. phate: Prior to this paper the production of 1,3-butadiene by the deNine and one-half kilograms of a dilute aqueous ammonia hydrogenation of n-butenes in the presence of steam over 1707 solution, containing 372 grams (21.9 moles, 1.56 moles excess) of catalyst was described by Xearby (3). Ultimate yields of 1,3ammonia, were added with stirring to 90.7 kg. of a dilute aqueous butadiene of 70 to 85% were obtained a t n-butene conversion levsolution of o-phosphoric acid. This solution contained 665 els of 40 to 20%. The ultimate yield was shown to vary grams (6.78 moles) of phosphoric acid. To the resultant ammonium phos hate solution was added in 2 hours with stirring a t with the conversion level. Grosse, Morrell, and Mavity ( 2 )have 25" to 30' Cf 37.6 kg. of an aqueous solution containing 986 described the dehydrogenation of n-butenes at reduced pressures grams (8.88 moles) of calcium chloride and 245 grams (1.02 over alumina-chromia catalysts. The once-through yields varied moles) of nickel chloride, NiC12.6HtO. Durin this treatment a flocculent precipitate of calcium-nickel pfosphate formed. from 11to 30% and ultimate yields up to 79% resulted. After addin the ingredients, stirring was continued for 0.5 hour, The preparation, physical properties, use, performance in labThe pH of t k s slurry was 8.0. The mixture was allowed to stand oratory units, and peculiarities of calcium-nickel phosphate defor 6 hours during which time the calcium-nickel phosphate hydrogenation catalyst are discussed. settled to about 40% of the original volume. The supernatant liquor was removed by decantation and the residue washed by decantation until the final washings were substantially free of DEFINITlON OF TERMS chlorides and soluble nickel salts. The slurry of calcium-nickel By conversion is meant the moles of n-butenes disappearing per hosphate was then filtered. The filter cake was dried for 12 {ours at 60" C. and finally for 24 hours a t 130' C. The product pass through the catalyst per 100 moles n-butenes passed through was a hard yellow gel. the catalyst. Selectivity or ultimate yield is the term given to the moles of The following is a typical chemical analysis of this product: 1,3-butadiene produced per 100 moles of n-butene disappearing. Material Weight % ' Space velocity is the volumes of gas passed through the cataPO4 55.77 lyst bed per volume of catalyst per hour, corrected to 0' C. and Ca 31.31 Ni 5.22 760 mm. of mercury pressure, assuming a perfect gas. Hl0 6.24 The steam ratio is the molar ratio of steam to n-butenes passed The calcium to nickel atomic ratio was 8.79 to 1. The calcium over the catalyst. plus nickel to phosphate ratio was 1.47 to 1. The process period is that portion of a cycle during which nThe calcium-nickel phosphate gel was ground to pass a 28butenes and steam are passed through the catalyst and 1,3-butamesh screen, and then mixed with 2% of the graphite and chrodiene is produced. mium sesquioxide stabilizer (when used) and compressed into 3/,$ The regeneration period is that portion of a cycle during which X s/16 inch cylindrical pellets. air and steam are passed through the catalyst for the removal of
-
2871
INDUSTRIAL AND ENGINEERING CHEMISTRY
2872
The graphite was removed from the catalyst pellets by passing a mixture of steam and air over the catalyst a t 350' to 650' C. The pellets then had an apparent bulk density of about 1.
Vol. 43, No. 12
0.25-inch Berl saddles and served as the preheating section. The gas flow was downward. CATALYST USE FOR 1,3-BUTADIEKE PRODUCTION
NATURE OF THE CATALYST
The calcium-nickel phosphate catalyst, after precipitation and drying, was shown to be amorphous by x-ray and electron diffraction studies. After roasting or use it was found to be a singlephase solid solution containing p-calcium phosphate in which Borne of the calcium ions had been replaced with nickel ions, Figure 1shows a comparison of the x-ray diffraction patterns of pcalcium phosphate and p-calcium-nickel phosphate. The p-calcium phosphate phase is shown in pattern 8 , and the p-calciumnickel phosphate phase in pattern B.
A
B
Figure 1. Comparison of S - N a y 1)iifraction Patterns of p-Calcium Phuspha Le a ~ i d3-Calc~ium-Sicl.c.I Phospha I e .I.
?-Cnlrium plroigliote
I#.
j-(:ulcium-nirhel pho.pliatr
These patterns were made by the equatorial shutter method with both patterns on the same film, using filtered CuK, radiation. The camera radius n-as 71.8 mm. Since the ionic radius of nickel (0.78 A , ) is less than that of calcium (1.06 A), the lattice of the calcium-nickel phosphate is contracted. This is shown by the lower value of the interplanar spacings represented by the lines on the pattern. The ionic structure of the calcium-nickel phosphate catalyst was further proved by magnetic susceptibility measurements. These studies showed that the nickel is present in the catalyst as nickel ions and that these are dispersed throughout the mass. In all samples of catalyst examined, both unused and used, the effective magnetic moment of the nickel m-orked out to be 3.5 Bohr magnetrons (6). This is practically within the range 2.9 to 3.4 generally reported for the magnetically dilute nickel ion. Calcium-nickel phosphate after roasting has a low surface area as determined by nitrogen adsorption. The surface areas of both freshly prepared and used catalysts vary betveen 2.71 and 7.33 square meters per gram (4). The bulk density of the pelleted catalyst is about 1 gram per ml. The absolute density of the unused calcium-nickel phosphate is 2.475 to 2.500. LABORATORY APPARATUS
FURNACE ARRANGEMENT. The catalyst tube, which was a 1inch iron pipe size X 46 inch Type 446 stainless steel tube, was placed in a vertical position inside a 37/16 X 40 inch aluminum bronze block enclosed by electrical heating elements. This unit was placed vertically in a 103/s X 45.5 inch transite flue pipe. The space between the heating elements and the transite case was filled with Filter-Cel. A close temperature control of +2O C. over the central 90% of the aluminum bronze block x a s realized by using three independently controlled heating coils-two 6-inch coils at the ends of the block and a 28-inch coil at the center of the block. One-quarter inch porcelain CATALYST TUBEARRAKGEMEKT. Bed saddles were placed in the bottom of the catalyst tube extending to a point 4 inches above the bottom of the aluminum bronze block. Then 150 ml. of catalyst were placed in the reaction tube. The depth of the catalyst bed u-as 11 inches for a 150 ml. catalyst charge. The upper 25 inches of the catalyst tube were filled with
ACTIVATION.The chromium-oxide stabilized calcium-nickel phosphate catalyst as formed contains graphite. This graphite must' be removed before the catalyst can be used effectively. The catalyst is first heated t o 200" to 300" C. in the presence of carbon dioxide or nitrogen. Steam is not to be used during the initial warmup or the pellet strength will be decreased. The temperature of the catalyst is then raised in the presence of steam to 600' C. at the rate of 25' to 50" C. per hour with 5 niininium steam space velocity of 800. While heating from 300 t o 600" C., the catalyst changes from an amorphous to a crystalline state. If steam is not used during this transition the catalyst pellets will shatter. When the catalyst temperature reaches 600" C., air along with t,hesteam is passed over the catalyst at a space velocit'y of about 5. Thc air space velocity is kept between 5 and 25 until the initial rapid burning of the graphite has subsided, and the air space velocity is adjusted so t,hat the catalyst bed temperature does not exceed 650" C. Khen the initial rapid burning has ceased (in about 1 hour in the laboratory unit), the air space velocity should be increased to 100 to 150 and kept there until all of the graphite is burned out. This may require about 6 hours and must be checked by the carbon dioxide content of the effluent gas. In a plant unit the initial combustion front passed through the catalyst bed in about 14 hours and the graphite Tvas all removed in about 30 hours. OPERATION.This catalyst is operated c~-clically,0.5 to 1 hour on a process using n-butenes and steam, and 0.5 t o 1 hour on regeneration using air and steam. For successful operation an initial break-in time of about 10 days is required before all operating conditions can be stabilized. PROCESS PERIOD.The following conditions of operation are recommended for the 10-day break-in stage: A &earn ratio of a t least 21. A n-butene space velocity (neglecting the presence of steam) such that the n-butene linear velocity at conditions of operating temperature and pressure, assuming a perfect' gas, is greater than 0.2 feet per second through an empty space equivalent in size and shape of the bed. Space velocities between 85 and 400 have been used but a n-butene space velocity of 90 to 150 is recommended with the length of the process period being 0.5 to 1 hour. The catalyst temperature is started low, about 525" C., and raised 10" C. per cycle until a conversion level of not over 30% is reached. The following conditions of operation are used after the break-in stage: A minimum steam ratio of 18 is used. Any n-butene space velocity in the 85 to 400 range may be used but this should be held constant from cycle to cycle. For efficient catalyst use, a low space velocity through a deep catalyst. bed-e.g., 90 to 150 space velocity in a 6-foot deep bed-is desirable with the length of the process period being the same as for the regeneration period. The catalyst temperature depends on the n-butene space velocity used and the conversion level desired, and must be increased to maintain constant conversion as the catalyst ages. The conversion should be held at 30 to 40% in a 6-foot deep catalyst bed with a n-butene space velocity of about 100. REGENERATIOX PERIOD.The length of this period is equal t o that of the process period. The temperature of the air-steam mixture should be the same as that of the n-butene-steam mixture fed during the process period. The maximum catalyst temperature during regeneration should be kept below 675" C. The steam and air flow rates may be varied to keep below this temperature. A minimum steam space velocity of 600 is required; an air space velocity of about 150 is suitable. Good mixing and distribution of the steam and air are essential. Complete carbon removal is required w-it'hin the first three quarters of the regeneration period. The last quarter of this period is an oxidation period wherein no carbon is being burned. EFFECT OF ADDING CHROM1UR.I OXIDE TO CALCIUM-NICKEL PHOSPHATE
Calcium-nickel phosphate alone is an active and selective catalyst for the dehydrogenation of n-butene8 to 1,3-butadiene. The addition of chromium oxide to calcium-nickel phosphate has the effects of stabilizing the catalyst, of increasing the catalytic activ-
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1951
The selectivities remained unchanged during these life studies.
TABLEI. COMPARISOKOF ACTIVITYOF CALCIUM-NICKEL This fact has been confirmed in plant usage ( 5 ) . PHOSPHATE WITH CALCIUM-NICKEL PHOSPHATE STABILIZED WITH The actual life of the catalyst is a t present unknown. A plant CHROMIUM OXIDE run of 6l/~months has been completed. Data on this will be
39.0 38.6 38.4 32.8 32.4 32.0 32 .O
1 2 3 18 19 20 21 22 42 49 256
42.4 43.0 43.4 44.4 44.2 43.0 43.4 42.8 42.2
29.4
ity over that of the calcium-nickel phosphate component alone, and of prolonging the effective life of the catalyst. In Table I is shown a comparison between the calcium-nickel phosphate alone and the same calcium-nickel phosphate containing 1% of chromium oxide. The experiments described in Table I were run under the following conditions: n-butene space velocity, 300; steam ratio, 20; cycle time, 1 hour; and temperature, 650" C. The conditions of the experiment, especially with respect to temperature, are severe for a new catalyst but show very definitely the stabili5ing effect of added chromium oxide.
published (6). The conversions and selectivities were calculated by a carbon balance method from an analysis of the total effluent gas after condensation of the steam, and corrected for the carbon deposited on the catalyst. This correction is equivalent to about 0.05 moles of n-butene per 100 moles of hydrocarbon feed a t a conversion level of 29% with a cycle length of 1hour. A correction of 0.4 was found when the catalyst was operated a t a conversion level of 40% using 2-hour cycles ( 5 ) . The catalyst bed in this case was 1 inch in diameter and 30 inches deep. The n-butene space velocity wab 100. Table I11 shows the composition of a typical product gas and the analysis of the n-butene feed.
Table I1 gives the average results of two laboratory life studies on calcium-nickel phosphate chromium-o+de catalysts. Life study A was made on one of the first plant lots of catalyst while life study B was made on more recent plant production.
TABLE 11. LIFE STUDYDATAON CALCIUM-NICKEL PHOSPHATE CHROMIUM-OXIDE CATALYSTS
Cyole KO.
0-2400 0-2037
Temperature, c. 600-630 590-630
Converaion 26.4 30.0
Selectivity 92.9 93.7
Both tests were run under substantially identical conditions. n-Butene space velocity was from 188 t o 197. The steam ratio was 21.4. The cycle time was 1 hour-i.e., 28 minutes on process, a 2-minute purge, 28 minutes regeneration, and a 2-minute purge. Regeneration air space velocity was 85 and 150 ml. of catalyst in an 11-inch deep bed was used. Temperature on life study A was adjusted to maintain about a 25% conversion, while the temperature on life study B was adjusted to maintain a 30% conversion. The catalyst used in life study B was of higher activity than was that used in life study A. A temperature rise of 30" C., from 600" to 630" C., was required to maintain about a 26% conversion for 2400 cycles in life study A; a temperature rise of 40' C., from 590' to 630' C., was required to maintain a conversion of 30% for 2000 cycles in life study B.
TABLE 111. Material Carbon dioxidq Carbon monoxide Hydrogen Methane Ethane and ethylene Propane and propylene 1 3-Butadiene Ikobutylene n-Butenes Butanes Pentane and pentenes
PRODUCT AND
FEED ANALYSIS
-Mole o/o in Feed
1.1 4.9 70.5 22.3 0.8
In order to obtain high selectivities with calcium-nickel phosphate catalyst it is essential that the dehydrogenation be run in the presence of steam. In Table IV is shown the effect of variation of the molar steam to n-butene ratio on the conversion and selectivity of n-butenes to 1,3-butadiene over a stabilized calciumnickel phosphate catalyst.
TABLE IV. EFFECTOF VARIATION OF STEAM RATIOON CONVERSION AND SELECTIV~TY
CATALYST LIFE STUDY
Life Study No. A B
EFFECT OF VARIATION OF STEAM TO n-BUTENE RATIO
Mole % in Product 0.7 0.3 17.6 0.8 0.5 0.2 16.5 2 9 41.3 18.2 0 9
Run No. A B
C
Molar Ratio, Steam to n-Butene 21.4 15.1 21.4
Conversion 30.5 33.0 25.0
Selectivity 92.0 78.0 54 .O
Other conditions of operation for the above experiment are aa follows: tem erature, 630" C.; n-butene space velocity, 193; cycle time, 1 four; catalyst age a t the start of Run No. A , 1400 hours on stream; Run No. A , average of 323 cycles; Run No. B, average of 328 cycles immediately following Run No. A; Run No. C , average of 341 cycles immediately following Run No. B; Run Nos. A , B , and C were parts of one continuous experiment, When the steam ratio was decreased to 15.1 in the laboratory unit the conversion increased to 33% and the selectivity dropped a t once to 78%. On returning to the 21.4 steam ratio the selectivity returned to the original value, but the eonversion was lowered to 25% and remained a t this level until completion of the experiment. Other experiments have shown that a steam ratio of 18 to 19 may be used successfully after the first week of operation. Increasing steam ratios above 21.4 in the laboratory isothermal unit caused a gradual decrease in conversion with no change in selectivity. EFFECT OF n-BUTENE SPACE VELOCITY ON CONVERSION AND SELECTIVITY TO 1,5-BUTADIENE
Decreasing the n-butene space velocity a t a given temperature level results in increased conversion. This effect is illustrated in
TABLE v. EFFECTO F n-BUTENE SPACE l T E L 0 C I T Y O N CONVERSION AND SELECTIVITY Temperature,
c.
600 600 620 620 630 630
n-Bbtene Space Velocity 100 193 100 193 100 193
Conversion 31.0 25.4 37.6 27.0 38.0 30.2
Selectivity 95 0 92.0 57.0 93.0 96.6 92.0
Catalyst Age, Cycles 200 200 700 700 1200 1400
INDUSTRIAL AND ENGINEERING CHEMISTRY
2814
Table F'. As stated previously it is recommended that calciumnickel phosphate catalyst be operated a t a low n-butene space velocity and in a deep catalyst bed because these conditions permit operation a t high conversion levels a t relatively low temperatures. In this way, thermal cracking effects are minimized and high production with efficient n-butene utilization is realized. The large surges of cracked products a t the beginning of the process period, which have made 6-foot bed operation difficult with other n-butene dehydrogenation catalysts, are not in evidence with calcium-nickel phosphate catalyst (5). The data in Table V were obtained at a steam ratio of 21.4 on the same lot of plant catalyst in laboratory equipment as deecribed above.
TABLE VII. EFFECT OF KA2 REACTION TUBEON SELECTIVITY OF
CALCIUM-NICKEL PHOSPH.4TE CHROYIUY-OXIDE CATALYST DEHYDROGENATION O F n-BUTESES TO I,%BUTADIENE
FOR
Cycle No.
TABLE
VI. EFFECTO F CYCLE TIMEO N COKVERSIOX
Cyole Length, Hours 1
2
Conversion
Selectivity
41.2 38.8
97.4 97.3
Temperature, O
123 381 603 817 1146 1271 1588 1902 1972 2228 2399
EFFECT OF LENGTH O F CYCLE ON CONVERSION
Increasing cycle time from 1 to 2 hours causes a decrease in 11-butene conversion of from 2 to 3% as shown in Table VI,
Vol. 43, No. 12
c.
Conversion
Seleotivity
30.9 25.2 30.3 27.1 30.5 30.6 28.2 25.6 26.7 31.6 29.4
82.3 90.1 88.3 86.4 80.9 76.8 79.8 79.5 83.0 72.3 70.7
610 610 620 620 620 620 620 620 630 630 630
EFFECT OF IMPURITIES IN FEED
The following impurities in the feed under the conditions of the test have not effected catalyst, activity: Acetone to 0.5% of the hydrocarbon feed; organic chlorides as methyl chloride to 15 p.p.m.; ammonia to 100 p.p.m.; carbon dioxide in the quantities found in the steam and formed by the reaction; and butanes and isobutylene. OTHER LMATERIALS CATALYTICALLY DEHYDROGEVATED
Ethylbenzene was selectively dehydrogenated t o styrene over calcium-nickel phosphate catalyst as shown in Table VIII. Table V I shows that no change in selectivity was apparent. At a 25% conversion level samples taken a t various times through a 2-hour cycie gave the following results: Sampling Time, Minutes after Start of Cycle
Conversion
2 17 32 47
28.4 25.7 24.8 23.1
T A B L E YIII. DEHYDROGENATIOS O F ETHYLBEXZEXE TO STYRENE OVER CALCIUM-NICKEL PHOSPHATE C.4TALYST
Ethylbenzene Space Velocity
-
Steam Ratio
Temperature,
c.
Conversion
Selectivity
A 25.1% conversion was obtained for the total 60-minute process period of the 2-hour cycle. EFFECT O F MATERIAL OF CONSTRUCTION ON SELECTIVITY
Nickel containing stainless steels in contact with the catalyst in the catalyst case will cause erratic action of the catalyst with a decrease in catalyst selectivity. This effect is shown in Table VII. The experiment described in Table VI1 was run at a n-butene space velocity of 170, a steam ratio of 21.4, and with a cycle length of 1 hour. The decline in selectivity was quite rapid from 92% at the start of the run to about 70% a t the end of 2399 cycles. In a Type 446 stainless steel tube as shown in life test A , Table 11, this same catalyst showed no loss of selectivity in 2400 hours of operation. Life tests in Type 446 stainlees steel, fused silica tubes, Walsh XX brick, and in bricked catalyst cases covered with a finish coat of Smoothset have shown no adverse effect of these materials on catalyst activity. CATALYST POISONS
Nickel-containing steels in contact with the catalyst or any contamination of the catalyst with nickel compounds will result in lowered selectivity. Colitamination of the catalyst with a number of metallic oxides, especially the oxides of the alkali and alkaline earth metals, Causes lowered selectivity. Iron oxide coatings on the pellets, such as have been encountered in the laboratory units where this work was done and in commercial units, have not affected catalyst activity. Carbon deposits on the catalyst cause lowered conversion, and if allowed to accumulate on the catalyst through successive cycles n,ill cause lorn-ered selectivities.
The experiments described in Table VI11 were made by running 1 hour on process and 0.5 hour on regeneration. The effects of temperature, ethylbenzene space velocity, and steam ratio are shown. Isopropylbensene, when passed over the catalyst at a space velocity of 54.5 and a steam ratio of 18.4 at 575' C., showed a conversion of 34.8% with a selectivity of 88.9% to a-methylstyrene. ACKNOWLEDGMENT
This paper is based principally on work done by the Organic Research Laboratory, the Chemical Engineering Laboratory, the Spectroscopy Laboratory, and the Main Laboratory of the Dow Chemical Co. The assistance of various members of t h e e groups is greatly appreciated. We are indebted to Polynier Corp., Ltd., Sarnia, Ontario, for its cooperation in further laboratory studies and development of the plant use of this catalyst. LITERATURE CITED
(1) Britton, E. C., and Dietaler, -4.J., U. S.P a t e n t s 2,442,319 and (2) (3) (4) (5) (6)
2,442,320 (May 25, 1948), 2,456,367 and 2,456,368 (Dec. 14, 1948); Heath, S. B., U.S. Patent 2,542,813 (Feb. 20, 1951). Grosse, A. V., Morrell, J. C., and RIavity, J. M., IND.ENG. CHEM.,32, 309-11 (1940). Kearby, K. K., Ibid., 42, 295-300 (1950). Kummer, J. T., Mellon Institute, private communication. Polymer Corp., Ltd., Sarnia, Ontario, Can., private oommunication. Selwood, P. W., Northwestern Cniversity, private communication.
RECEIVED May 4, 1951.
