BUTYLENE FROM ETHYLENE Cobalt-Carbon Catalyst HARRY .4. CHENEY, S. €I. XlcALLISTER, E. B. FOUNTAIN, JOHN ANDERSON', AND W. H. PETERSON Shell Derelopmsnt Company, Bmeryville, Calif.
A
process has been developed for polymerizing ethylene
to hu tylene over cobalt-charcoal catalyst at temperatures
below 150" C. and at pressures of 1 to 100 atmospheres. The polymer consists of olefins having even numbers of carbon atoms and is predominantly straight chain. tinder suitable operating conditions polymerization per
I
N RECENT years interest in the supply and availability of normal butylenes has been stimulated by their widespread and expanding use as raw materials in the manufacture of aviation gasoline, synthetic rubber, and chemicals such as methyl ethyl ketone. One promising source of butylene is through the dimerization of ethylene which is potentially available in waste refinery gases or from t,he cracking of propane. The literature on ethylene polymerization, both thermal and c:italyt,ic, is quite extensive, I n most of the experimental work the chief products have been light liquid hydrocarbons, oils, and c v ~ nwasy solids. Thermal polymerization, which is evidently a chain reathion ( 4 , 167, begins a t 350" tJo400' C. (7, dS),but at best, but,ylene is obtainable in yields of only about 30% on the reacted ethylene ( f 1 ). Higher temperatures lead to still poorer yields (3, 17, 18,2.9). Catalyst,s such as nickel, cobalt, or iron on kieselguhr ( I f ), Raney nickel (I), molybdenum trioxide on silica gel ( 8 O ) , phosphoric anhydride on kieselguhr (IO), aluminum chloridp (bo), and aluminum chloride plus nickel (8) polymerize ethylene to liquids and oils. Dimerization has been achieved with some succes over nickel on kieselguhr and cobalt on kieselguhr a t about 300" C. ( I f , 18, 14, 16). I n 1932 Schuster (9, 1 9 ) discwvered the highly selective cobalt-charcoal dimerization catalyst while studying the kinetics of ethylene hydrogenation on artive carbon surfaces. Anderson, Peterson, and McAllister (21, working in these laboratories, devised a continuous process based on a catalyst of this type. This paper covers the practical devdopment of this process to the stage where study in a semiscale p1:tnt would be feasible. Table I shows that virtually complete ethylene dirncrization is to be espected at equilibrium under all ordinary conditions. €Towever, further polyrnerizat,ion to hexylene and octylene is also highly favored on the basis of free energy chimge, and unless :t catalyst, of unique selectivity is used, the major products arc> hydrocarbons of high molecular weight. Figure 1 is a schematic flow diagram of the dimerization apparatus and details of the catalyst tube are shown in Figure 2 . Et,hyIene from the feed cylinder passed through a pressure re1
pass averages approximately SO%, with the product containing about 75% butylenes, 15% hexylenes, and 10% higher boiling olefins. Catalyst lives in excess of 16s kg. of polymer per liter of catalyst are indicated, and average polymer production rates of 300 grams per liter of catalyst per hour are possible.
ducing valve which served to maintain the desired pressure on the reaction system. Reaction products left through a flowcontrol valve at the lower end of the catalyst tube and pawed into cold traps; uncondensables were memured with a wet-test meter. Temperatures were read on an indicating potentiometcr by means of five iron-const,antan thermocouples spaced equally through the catalyst bed. Temperatures were controlled by a Celectray controller actuating t'he electrical heating c-ircuit. This controller was either switched to the hottest point in fhe tube t80control the maximum temperature or switched to all (,he (equal resistance) thermocouples connected in parallel to control the average temperature. The catalyst bed was heated by passing a low voltage, high amperage electrical current longit udinally through the tube wall. During polymerization cycles escws heat was removed by circulating water through t,ho reactor jacket, and during activation and regeneration cycles, air was passed upward through the jacket. I n initiating a dimerization cycle t,he system was brought to pressure with nitrogen. The use of ethylene for this purpose was not feasible when operating a t elevated pressures because excessive catalyst bed temperatures developed through the heat of adsorption of ethylene on the catalyst combined wit,h t,he initial heat of polymerization. Cold-t.rap samples were analyzcd by low temperature distillation. Butylene and ethylene in the uncondensable gas were determined by absorpt,ion in 87v0 sulfuric acid; this conwntra-
, ....... ..-... Ethylene Eqiiilihri!irn Partial Conversion Pressiire. to 1-Butene", htm. Xlole Yo
-
'Teinp.. C. 2.5
Preshiire, Atrn. 5.3
AVO
Cal./G.-Mole of Biit lene Forinex(@) -15,6OQ
Eqiiilihriiiiii ConHtant (Kp), Atin-i
3 X 10'1
1 . 4 X 10-5 10-6 10-2 10-3
23 1 3 X 101' 2 X -115,600 -9,500 5; 1 . 4 x 10' 6 x 227 1 -8,500 227 1 . 4 x 104 8 x 227 0.01 --o.joo 1 . 4 x 10' E X a Conversion t o one of the %butenes or to a inirture of would be practically the same.
Present address, Shell Chemical Corporation, Houston, Tex.
2580
99.99908 99.9998 98.90
90.2
10-4 9 2 the normal isomers
December 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion of acid does not appreciably absorb ethylehe but does absorb normal butylenes quantitatively. Ethylene was then determined by absorption in acid mercuric sulfate solution (prepared by adding 40 grams of mercuric sulfate t o 200 grams of 25% sulfuric acid). Because the reactor usually contained both a liquid and a vapor phase the rate of flow and the composition of the product fluctuated somewhat and representative instantaneous product samples could not be obtained. Product samples were therefore accumulated over rather long periods, usually 4 hours, yielding cumultttive production data which were plotted against cumulative feed t o give curves whose point slopes were instantaneous conversions. Ethylene (Ohio Chemical Company, Medical Grade) ordinarily analyzed over 99.5'% pure as received. For some experiments the feed was fractionated twice before use in a continuous rectification system a t -60" C. under 80 pounds pressure t o remove light ends and heavy ends. Purified material ordinarily contained less than 0.001 mole % oxygen and less than 0.02% of material boiling higher than ethylene. Nitrogen (Air Reduction Sales Company) and hydrogen (Stuart Oxygen Company) were passed a t 300' C. through a 2.5 x 100 crn. tube packed with reduced copper prepared by reducing copper oxide wire a t 250' t o 300" C. After purification, both gases contained less than 0.001 mole yooxygen. CATALYST
Study of the factors involved in preparing an active dimerization catalyst was the subject of an extensive investigation. After a survey of a wide variety of supports the catalyst selected for process development was prepared from coconut charcoal (Columbia, 4s) and cobalt nitrate and contained approximately 17 weight '% cobalt. This catalyst was prepared as follows: One part by weight of cobalt nitrate hexahydrate (Harshaw Chemical Company) was dissolved in 1 part by weight of water at or near room temperature. The solution was poured over 1 part by weight of 4-14 mesh charcoal. The mixture was heated with agitation to 300" C. in about 3 hours to drive off water and to decompose the nitrate. After cooling, the catalyst (not yet active for dimerization) was stored in glass bottles until needed. I n this state it was fully stable in air.
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Spontaneous oxidation of the carbon during the nitrate decomposition step proved t o be a serious problem. This difficulty was overcome by using reduced pressure ( 6 ) and by introducing additional water during the heating cycle (6). Chief factors which determine the ultimate activity of the dimerization catalyst are the type of charcoal and its pretreatment, the cobalt concentration, and the salt from which the cobalt is derived. Carbon is evidently an essential catalyst ingredient and not merely a support; virtually no activity was exhibited by analogous cobalt combinations with alumina, kieselguhr, porcelain chips, or silica gel. Appreciable activity was obtained with catalyst prepared from all the various charcoals tested, although some of the carbons required pretreatment with carbon dioxide, nitrogen, or steam-air mixtures a t 850' to 1OOO" C. Even the best carbons could be improved by carbon dioxide treatment a t 900"C. The activating effect is evidently due to charring of residual gums and t o enlargement of the pores through oxidation. Catalyst activity was found to increase nearly linearly with cobalt concentration up t o about 20 parts of cobalt per 100 parts of carbon. Attempts t o prepare higher concentrations in a single step resulted in disintegration of the support during the drying and decomposition steps. One catalyst having a cobalt to carbon ratio of 40:100 was prepared in two steps with complete decomposition of the nitrate after each step. The resulting catalyst was only 25% more active than the normal 20:100 catalyst. Possibly the additional cobalt decreased the porosity or the effective surface area. Other salts of cobalt failed to give cat,alysts whose activities even approached those prepared from the nitrate. The acetate and the formate yielded catalysts, respectively, only about 1 and 3% as active as did the nitrate. Even when mixed with the nitrate, the acetate failed to supply cobalt in a more active form. Cobaltous chloride when mixed with the nitrate poisoned the catalyst. Iron-charcoal catalysts prepared in analogy t o the cobaltcharcoal combination showed no appreciable polymerization activity. Nickel-charcoal catalysts were, however, somewhat active, particularly at temperatures above 200' C. which is above the useful temperature range of cobalt-charcoal. Nickelcharcoal catalyst is probably not truly analogous t o cobalt-
c
Shell Development Laboratories, Emeryville, Calif. N o w office building (left)and furnace shed Lforeground); workmen are standing a t base of oil cracking pilot plant; farther right is
acrolein pilot plant
INDUSTRIAL AND ENGINEERING CHEMISTRY
2582
charcoal; unlike the latter, it requires reduction with hydrogen before any activity appears and is active on supports other than carbon. Activation of the cobalt-charcoal catalyst was accomplished by passing hydrogen over it for 3 to 6 hours at 300" C. Alternatively t>hecatalyst could be activated by sweeping with an inert gas a t 300' to 500' C. or even by evacuation in this temperature range. I n the absence of hydrogen, however, a different catalyst modification resulted, characterized by higher activity but lower dimerization selectivity.
"T
PRESSURE REDUCING VALVE
MICRO ROTAMETER ETHYLENE
CATALYST
Vol. 42, No. 12
EFFECTS OF OPERATING VARIABLES
Temperature. Exploratory data on the effect of tcnipcmturc on conversion are shown in Figure 3. Increasing the tcmperature to about 100' C. accelerated the reaction rate. Further increases. however, had little effect on initial conversion, although they did cause a more rapid decline in catalyst activity during the cycle. Temperatures as high as 150" C. were observed to cause no permanent injury t o the catalyst, whereas at 200' C. n permanent loss in activity ensued H hirh could not be recovered by regenerat ion. Owing to the high exotherniic heat of reaction [over 26,000 calories per mole of butylene formed ( S S ) ] , temperatures in the catalyst bed were never uniform with an active catalyst. Typical temperature profiles are shown irl Table 11. At the start of each cycle the point of maximum temperature was always near the inlet end of the reactor. As the run progressed this point moved through the bed nearing the outlet b y the end of the cycle. Heat output from the catalyst decreased with decreasing conversion during each cycle necessitating progrcwively higher cooling\\ ater tempeiatures to maintain the proper maximum temperatule.
CYLINDER P
2
I
T
,
TYPE 416 STEEL
----/:HEX
V:-INCH
PIPE THREAD
ELECTRODE STEAMHEATED MICRO NEEDLE VALVE
-HEX
CAP, STEEL
Figure 1. Dimerization Apparatus
During use, catalyst activity gradually declined, and eventually regeneration became necessary. This was accomplished by sweeping with hydrogen under the conditions used for hydrogen activation. Gases other than hydrogen failed to effect regeneration. Regeneration products comprised methane, ethane, ethylene, and saturated liquid hydrocarbons having an average molecular weight of about 140. Catalyst activity was apparently restored by hydrogenation, hydrogenolysis, and desorption of high-boiling olefins which gradually formed on the catalyst surface during use. Small amounts of water formed during the first few regeneration c>cles evidently through reduction of cobalt oxides. As mentioned above, freshly prepared catalyst can be stored satisfactorily in the air after the decomposition of the nitrate is compieted. Alternately, if desired, the catalyst may be stored in air after merely drying to remove excess water. Both methods were employed in the laboratory for storage periods as long as a year with no evidence of deleterious effects. However, evposure to air after activation or regeneration was found to cause complete loss of polymerization activity, most of which could be regained by further sweeping with hydrogen or nitrogen. Regenerated catalyst can be stored for prolonged periods of time in a nitrogen atmosphere without loss in activity; in one case a catalyst was regenerated and then stored for 100 days under nitrogen with no decrease in activity evident in the ensuing c j cle. I n the active state the cobalt-charcoal catalyst is somewhat pyrophoric. This is particularly true of hydrogen-treated catalysts which under certain conditions can be made to glow in air. Used catalysts show only slight reactivity toward air prior to regeneration.
REACTOR TUBE I-INCH PIPE SIZE 18-8 STAINLESS STEEL 3 9 INCHES LONG
I'/2-INCH STEEL PIPE 33 I/~-INCHESLONG THERMOCOUPLE WELL
20 GA. STEEL 405/s-INCHES LONG
Figure 2. Detail of Catalyst Tube for Ethylene Dimerization
Pressure and Dilution. Data on the cffect of ethylene partial pressure are summarized in Figures 4 and 5. With pure ethylene feed, the polymer production rate increased continuously as the pressure was raised t o 140 atmospheres (2000 pounds per square inch gage) a t 90' C. A! an operating temperature of 40' C. the polymer production rate reached a mavimum at 50 atmospheres. Reducing the ethylene partial pressure by dilution with ethane (the chief contaminant anticipated in a practical refinery feed stock) had the same effect as reducing the total pressure in the absence of a diluent. Polymer production rntes incrcased nearly linear]) with prcwure u p to 55 atmos-
December 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
2583
TABLE 11. TEMPERATURES I N CATALYST BEDSDURINO POI~YME~IZATION (Maximum controlled at 100' C . ) Temperatures, e C. H~~~~ (3001Diiitance from Inlet End of C a t a l y s t from ing Bed, % of Total Length Start water 10 30 50 70 90 84 79 60 100 95 58 3 5 75 98 100 95 92 86 15 8 0 76 94 98 100 98 90 30 57 0 79 96 98 100 100 92 36 62 100 83 57 46 2.5 48 57 91 ,100 89 61 19.0 98 100 93 35 0 63 73 93 54.0 78 79 91 93 95 100 60 100 94 86 86 84 0.5 60 93 99 91 90 83 2.0 6.5 68 90 100 100 100 96 99 100 69 88 96 96 8.0 11.0 71 90 98 99 100 96 66.5 86 92 94 98 99 100
~-
Description of Cycle Fresh catalyst, hydrogen act]vated Fresh catalyst, hydrogen sctivated Catalyst re enerated witb hydrogen
REACTION TEMPERATURE (AVERAGE THROUGH BE0)PC.
pheres, indicating close to first-order dependence on ethylene concentration rather than the second-order dependence which might be expected. Others have observed this same relationship a t low pressures both with cobalt-charcoal catalyst (19) and with nickel-kieselguhr catalyst (16). Critical pressures of ethylene and of butylene are lower than the normal operating pressure of 800 pounds per square inch gage. Since the critical temperature of ethylene is 9.5" C . and that of the butylenes is well over the usual operating temperature of 100' C., the feed enters the top of the reactor normally as a vapor, and the butylene product, leaves the bottom as a liquid. At moderate conversion levels all the unconverted ethylene leaves in liquid solution, but a t lower conversions two phases will exist throughout the tube. A single fluid phase is attainable at low pressures of the order of 1 atmosphere and a t high prcssures ahove the critical pressure of any mixture in the reactor (estimated to be about 1400 pounds per square inch). However, no particular advantrtge is seen for either of thesc conditions (Figure 4). Liquid phase operation can he achieved either by operating at low temperatures and high pressures, so that the feed is liquid, or by employing a solvent. I n either case the normal direction of flow must be reversed-feed entering the bottom and products leaving from the top-in order to keep the catalyst tube liquidfull. Liquid phase operation has the advantage of better heat transfer leading to easier catalyst temperature control but hns other disadvantageous effects. Operating a t 0" C. under 800 pounds presshre with liquid ethylene feed resulted in very low polymer production rates, as might be expected at such a low temperature. Reaction products were employed as the solvent in one experiment at 100" C. under 800 pounds pressure. Polymer production rates were practically identical with the usual vapor phase operation, but yields of butylenes on converted ethylene were only approximately 8070 as high, more ethylene going to hexylene and higher polymers. This is evidently the natural result ot increasing the average butylene concentration in the system. (Normally the butylene concentration at the tube entrance would be quite low.) Liquid phase operation with pentane as a solvent was found to have considerable promise. The feed cylinder and the reactor were both maintained a t 100" C. and 800 pounds per square inch gage, and feed was displaced from the feed cylinder with ethylene. The feed contained 16 weight yo ethylene. During the first 15 hours of this experiment the polymer production was the same as in vapor phase operation. After thig it declined, and when the catalyst was regenerated its activity was decidedly lower than in the first cycle. The pentane solvent was a cut from straight u n gasoline and contained about 0.001% sulfur or 5 mg. per IO& grams of ethylene; this amounk. of sulfur could account for the loss in catalyst activity. Fortunately, in an industrial application the solvent would be recycled so that poisoning would not progress as it did in this
Figure 3. Effect of Temperature on Conversion Pressure, 800 Ib./sq. inch gage; feed rate, 240 grams/liter-hour; cycle length, 6 7 hdurn; fresh catalyst activated with hydrogen
experiment. If, as seems prohable, sulfur poisoning was responsible, the results indicate that the solvent liquid phase process is equivalent to the vapor phase process a t the same pressure as regards reactor capacity and product quality. Introduction of a solvent does, of' course, complicate the problem of product recovery.
Space Velocity. As space velocity was increased polymer production rates increased markedly until the conversion had fallen to about 50%. With further increases in space velocity the production rate remained fairly constant as the conversion fell. Figure 6 shows the general relationship. Data on product butylene composition as related to space velocity are given in Table HI. Analysis was by analytical fractional distillation: 1-butene boils at -6.3" C., trans-2butene at 0.9" C., and cis-Zbutene a t 3.7" C. Under conditions of long contact time the butylene product was almost entirely 2butene, whereas with shorter contact times, I-butene predominated. Evidently 1-butene is the primary product of dimerization, and 2-butene is formed by the isomerization of 1-butene. Cobalt-charcoal catalyst has been demonstrated to be active tor this isomei ization reaction (IC%. 400,
PRESSURE, ATMOSPHERES
Figure 4.
Effect of Pressure in DimeriAation of Ethylene
Temperatures, averages through bed; cycle length, 6 hours; fresh catalyst activated with hydrogen
2584
INDUSTRIAL AND ENGINEERING CHEMISTRY
.
ETHYLENE PARTIAL PRESSURE, ATMOSPHERES
Figure 5.
Polymer Production Rate as a Function of Ethylene Partial Pressure
Feed rate adjusted to give approximately constant contact time of 0.6 hour; temperature, 90" C., average through bed; fresh catalyat activated with hydrogen
EFFECTS OF FEhO IMPURITIES
Virtually all the impurities which might be expected in ethylene from petroleum refinery sources were tested with regard to their effects on the catalyst. Generalized results of these tests are summarized in Table IV, which shows that catalyst activity is not decreased by carbon dioxide, hydrogen, water, nitrogen, paraffins, olefins, or aromatics. However, carbon monoxide, oxygen, carbonyl sulfide, hydrogen sulfide, and acetylene are catalyst poisons and must be largely eliminated if long dimerization cycles are desired. Temporary introduction of these poisons (except for the sulfur compounds) should not have serious consequences, for the catalyst regains full activit,y when regenerated in the normal manner. Hydrogen in the feed reacts with olefins in the presence of the cobalt-charcoal catalyst. I n one test in which 0.5 mole 7'0 hydrogen was added to the ethylene feed, roughly 90% of the hydrogen appeared as butane in the product. I n another run made with 4 mole % hydrogen, less than one fortieth of this hydrogen could be found in the product.
TOTAL FEED, KG. PER LITER OF CATALYST
FEED RATE GRAMS PER LITER
Figure 6.
Vol. 42, No. 12
- HOUR
Influence of Feed Rate on Conversion and Prodiiction Rate
Pressure, 750 lb./sq. inch Rage; temperature S5-4Qo C., average through bed; freah catalyst activated with hydrogen
The deleterious effect of hydrwen sulfide is illustrated in Figure 7 . Catalyst poisoning, rather than inhibition, was evidently involved, for no increase in polymer production rate resulted from changing t o pure feed. Regeneration failed to remove sulfur from the catalyst and restored only a small fraction of the original activity. Analyses of the catalyst accounted for practically all the sulfur introduced in the feeds. No hydrogen sulfide rould be detected in the products.
TABLE111. BUTYLENE COMPOSITION AS FUNCTION OF SPACE VELOCITY (Polymerization pressure: 750 lb./sq. inch gage: temperature, 35-40' C . , average through bed) Av. conversion Compoaition of Butylene, Feed Rate, Run Wt. % G./LiterDuration, to Polymer, Hour Hours wt. % 1-butene 2-butene 72 12 74 9 91 104 12 69 6 94 228 6 58 60 40 360 3 37 70 30 376 4 35 60 40 480 a 28 54 46 484 3 28 52 48
TOTAL FEED, K G PER LITER OF CATALYST
Figure 7 . Hydrogen Sulfide Poisoning of Cobalt-Charcoal Catalyst
Figure 8. Carbonyl Sulfide Poisoning of Cobalt-Charcoal Catalyst
Pressure, 800 Ib./sq. inch gage; temperature, 100' C., max. i n bed; feed rate, loo0 grama/liter-hour; fresh catalyst activated with nitrogen
Pressure, 808 lb./sq. inch gage; temperature 100' C., max. in bed; fresh cdtalyat activated with feed rate, loo0 grams/liter-hour; nitrogen
I N D U STRJAL A N D EN G INEER IN G CHEMISTRY
December 1950
TABLE IV. EFFECT OF VARIOUS FEED IMPURITIES ON COBALTCHARCOAL CATALYST
Substance Carbon monoxide
Poisoning Effect Severe, partially temporary Carbon dioxide Nil Carbonyl sulfide Severe H drogen Nil dter Nil Hydrogen sulfide Moderate Nitrogen Nil Ammonia Severe Ox gen Severe Etiane Nil Acetylene Severe Propane Nil Very slight Propylene +Butane Nil Diethyl ether" Severe Nil n-Pentane Nil Isopentane Nil, slight proBenzene motion Nil. slight proXylene motion Not anticipsted in refinery ethylene.
Recovery on Regeneration Complete
Fai;'
*
... ...
Slight Co&&eta Complete
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Complete co&iete Pariii1
...
... ...
A
and reduce dimerization selectivity. Poisoning ensues. Removal of oxygen by the catalyst is not quantitative; in one run with 23 p.p.m. (molar) of oxygen in the feed the product analyzed 6 p.p.m. Figure 10 shows results of tests with feeds containing acetylene. Appreciable poisoning resulted with m little &s 0.005 mole Yo acetylene in the feed, and no improvement in conversion resulted on switching t o pure ethylene after partial poisoning with acetylene. CATALYST LlFE
...
Carbonyl sulfide poisoning is shown in Figure 8. Again no inhibitory effect was evident. Although good response t o regeneration was observed, the catalyst still retained almost all the sulfur introduced, and some cumulative effect is t o be expected. Diethyl ether was a serious catalyst poison, and its effects could not be removed entirely by regeneration. Some evidence indicates t h a t other oxygen-containing organic compounds behave similarly. Such substances would ordinarily be absent from petroleum refinery ethylene, but in the laboratory study using ethylene derived from ethyl alcohol, careful rectification waa necessary to avoid these materials. Results of experiments with 0.1, 0.01, and 0.001 mole yocarbon monoxide added t o the feed are shown in Figure 9. The deleterious effect of concentrations of 0.01% and higher is obvious. At least in part, carbon monoxide inhibits rather than poisons the catalyst; in the experiment with O . O l ~ ocarbon monoxide in the feed a marked increase in the polymer production rate occurred after changing to pure ethylene feed. Oxygen affects the catalyst in a complex manner and is apparently related to a delicate adjustment of the degree of oxidation of the active components of the catalyst. When oxygon is introduced in the feed, the first effect is to increase catalyst activity
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2585
I
For the purpose of evaluating the cobalt-charcoal catalyst, a prolonged catalystrlife test was made using carefully purified ethylene. Polymerization cycles were carried out at 800 pounds per square inch gage with a maximum catalyst bed temperature of 100' C. Feed rates of lo00 grams per liter of catalyst per hour were used in the first portion of each cycle. When conversion to polymer fell to 30%, feed rates were dropped to 500 grams per liter-hour. Each polymerization cycle was terminated, and the catalyst was regenerated when the conversion again declined to 3oyO. Regenerations comprised sweeping with hydrogen for 3 hours at 300" C. In this one run a total of seventeen dimerization cycles were completed with a total operating time of 669 hours, excluding regeneration. Polymer production totaled 165 kg. per liter of catalyst, and there was no indication of any permanent loss of catalyst activity in normal operation. Available data indicate approximately the following average operating characteristics for the process under the above conditions (exclusive of regeneration cycles): Cycle length hours Average feed rate, g./liter-hour Average conversion to pol$mer, wt. % Yield of butylene in polymer, wt. yo Polymer production rate, g./liter-hour Butylene production rate, g./liter-hour
40 635
49 77 310 240
COMPOSlTION OF PRODUCT
Under ordinary conditions polymer produced from ethylene over cobalt-charcoal catalyst analyzes 75 to 80% butylene. The remainder contains approximately 60% hexylene, 20% octylene, 10% decylene, 5% dodecylene, 2% tetradecylene, and 3% higher boiling material. Small amounts of waxes having molecular weights of at least 1400 are also produced. A typical distillation curve of the higher boiling fractions of the product is shown in Figure 11. The butylene fraction from- ethylene dimerization provides an
,HOURS Effect of C a r b o n Monoxide on CobaltCharcoal C a t a l y s t
F i g u r e 10. Acetylene Poisoning of Cobalt-Charcoal Catalyst
Pressure 8M lb./sq. inch gage- temperature 100' C., max. in bed; rate, 1000 grams/lit&-houri fresh catalyst activated with nitrogen
Pressure 800 lb./sq. inch gage; tern rature, 100' C., max. in bed; feed rat;, 1000 gramdliter-hour; E s b catalysts activated with nitrogen
TOTAL OPERATING TIME
Figure 9.
feeh
TOTAL FEED, KO. PER LITER OF CATALYST
180 GI0
.
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160 -
3
0.140
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IDISTILLATION. rI %
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- 240
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200
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consumed. That this result was due to purely physical suppression of butylene desorption from the catalyst appears unlikely, for when propylene was added to the feed 30% of the polymer product was a.mylenes. The catalyst is quite specific for ethylene-pure propylene, for example, dimerizes at only about one fortieth the rate for ethylene, despite the fairly rapid copolymerization of ethylene with propylene. Any satisfact,ory explanation of the kinetics of the dimerization reaction must account for the facts t,hat straightchain olefins predominate and that 1-butene appears to be the primary butylene product. The ability of the catalyst to shift the double bond and to catalyze hydrogenation of olefins is probably significant to the kinetics of the dimerization
~r
TABLEV.
(1941). PROBABLE COMPOSITION OF HEXYLENE FRACTION (2) Anderson, J., Peterson, IT. H., and McAllister, S. If. (to Shell FROM ETAYLENE POLYMER Development Company), U. S. Patent 2,380,358 (July 10,
Component cis-2-Hexene cis-3-Hexene trans-2-Hexene trans-3-Hexene 1-Hexene trans-3- Methyl-2-pentene 2-Ethyl-1-butene cis-3-Methyl-2-pentene 3-Methyl-I-pentene
1
1
Weight %
38 38 10
9’
3 2
0.2
The butylenes are exclusively normal isomers; careful analyses have failed to detect any isobutylene. Both 1-butene and 2butene are present, their relative proportions being dependent on catalyst activity and operating conditions as mentioned above. Hydrogenation of the hexylene fraction yielded a mixture comprising 86% n-hexane, 14Yo %methyIpentane, and no other isomers detectable in the infrared spectrum. Thus the hexylene components are constructed wholly of C, units, and no isomerization of the carbon skeleton takes place during polymerization. Comparison of the infrared spectra of distillation cuts of the hexylene fraction with the known spectra of various hexylene isomers indicated the probable composition shown in Table TT. All possible isomers having the required carbon skeleton were detected, but the normal hexenes and tvans-3-methyl-2-pentene predominate. Hydrogenation of the octylene fraction yielded a product whose infrared spectrum indicated 84Yo n-octane, 8% 3-methylheptane, and 8% 3-ethylhexane. Almost certainly the higher boiling olefins form chiefly through stepwise addition of ethylene The catalyst does show slight activity for the dimerization of n-butylene, but in ethylene polymerization hesylene production is always much higher than octylene production even a t high conversions to butylene. Adding 50% 2-butene .bo the ethylene feed, however, increased by 50Yo the amount of hexylene formed per unit weight of ethylene
1945). (3) Burk, R. E., Baldwin, B. G., and Whitacre, C. H., IND.ENG. CHEM.,29, 326-30 (1937). (4) Bumham, H. D., and Pease, It. N., J . A m . Chem. Soc., 62, 453 (1940). (5) Cheney, H. A. (to Shell Development Co.), U. S. Patent 2,407,813 (Sept. 17, 1946). (6) Zbid., 2,407,814 (Sept. 17, 1946). (7) Day, D. T., J . Am. Chem. Soc., 8 , 153-67 (1886). (8) Hessels, W. J., Krevelen, D. W. van, and Waterman, H. I., Rec. Trau. Chim., 59, 697-702 (1940). (9) I. G. Farbenindustrie, German Patent 559,736 (1933). (10) Ipatieff, V. N., and Pines, H., IND.ENG.CHEM.,27, 1364 (1935). (11) Konaka, Y., J . Sac. Chem. I n d . , Japan, 39, 4473 (1936); 40, 236B (1937); 41, 22-~3B (1938); 43, 330-1B, 363B (1940). (12) Morikawa, K., Ibid., 41, 350-1B (1938). (13) Peterson, W.H., and Anderson, J. (to Shell Development C o . ) , U. S.Patent 2,375,687 (May 8 , 1943). (14) Pshezhetskii, S. Ya., J . Phys. Chenh. (U.S.S.R.), 14, 1376-7 (1940). (15) Psherhetskii, S. Ya., and Gladyshev, A . T., J . Phys. Chem. (U.S.S.R.), 15, 333-45 (1941); U.O.P. Survey of Foreign Petroleum Literature, Translation 344 (1942). (16) Rice, 0. K., and Sickman, D. V., J . Am. Chem. Sac., 57, 1384--5 (1935). (17) Sohneider, V., and Frolich, P. K., IND.ENG.CHEM.,23, 140510 (1931). (18) Schultre, M., and Schultze, G. R., 001 Kohle Erdoel u. Teer, 15, 193-8, 215-20, 233-41 ; Kautschuk, 15, 182-5, 195-201 (1939). (19) Schuster, C., Z. Electrochem., 38, 614-18 (1932). (20) Sinnatt, F. S.,“Report Fuel Research Board with Report Director of Fuel Research,” pp. 146-8, London, His Majesty’s Stationery Office, 1936. (21) Storch, H. H., J . A m . Chem. Sac., 57, 2598-601 (1935). (22) Thacker, C. M., Folkins, H. O., and Miller, E. L., IND.ENG. CHEM.,33, 584-90 (1941). (23) Wheeler, R. V., and Wood, W. L., J . Chem. Sac., 1930, pp. 1819-28. RECEIVED April 11, 1950. Presented as a part of the Symposium on Pilot Plants before the Division of Industrial and Engineering Chemistry a t the 117th Meeting of the AMERICAN CHEMICAL SOCIETY,Houston, Tex.
