FUELGASGENERATOR A Development Using Electrical Energy as a Source of Heat
-
HARRY A. CURTIS', RALPH B . STITZER, AND WILBUR J. DARBY Tennessee Valley Authority, Wilson Dam. Ala. patents ( 3 ) . Presumably H E idea of using *I0"DIA. GRAPHITE ELECTROE B no commercial plant folelectrically produced lowing the Detroit Edison heat for the carbond e v e l o p m e n t has been ization of coal is not new. COIL FLED c m s built. Scores of patents have Considering the relative been issued covering proccosts of electrical energy esses and equipment for and the energy available carbonizing coal electriin coal gas, it might a t cally. Many of the early first be thought that it patents in this field have would not be feasible to expired, many are still in use electrical energy for force, and new ones a p coal carbonization. The pear frequently. There is present paper and the always opportunity for inearlier results presented vention in any field, but by Walker indicate that, it is amusing t o note under certain special conthat certain present day ditions, such a process is inventors "discover" the practical. old idea of carbonizing coal electrically and claim Experimental Work that their particular schemes will revolutionize T h e T V A w o r k on the gas industry. carbonizing coal electriA detailed review of the cally was begun on a patent situation is not laboratory scale in Knoxnecessary, but a few of ville, Tenn., in October, the ideas covered will be 1934. The project was t r a n s f e r r e d t o Wilson mentioned. Both continuous and batchwise Dam, Ala., in March, 1935, processes h a v e been where a semiworks-scale plant, having a retort 1 patented. Externally and square foot in area and 16 internally heated retorts using metallic resistors feet long, was built. F I G U R1.~ FINALRETORT DEVELOPSD have been proposed. The This semiworks-scale idea of usine the carunit was operated interbonaceous material within the-retort as a resistor is involved mittently from June to December, 1935, making forty-six in many patents. The use of coke or charcoal, or a metallic runs in all. Direct current was used because it happened to conductor, to establish the initial current is covered in several be available where the plant was set up, but it was realieed claims. Inventors have long appreciated the advantages of that a full-scale plant would probably have to use alternating heat recovery and have patented many ways of accomplishing current. The difficulties encountered were mostly mechanical. this. The importance of removing a portion of the volatile The results obtained were considered sufficiently promising to warrant the construction of a somewhat larger unit. matter of the coal to increase its conductivity has long been recognized. This larger unit was put into operation in May, 1936, Many arrangements of electrodes have been proposed. and tests of various sorts were made in it for several months. I n the retorts proposed by White in 1909, Berglof in 1914, The mechanical difficulties were solved; but with this retort, Fueler in 1918 (4), and several others, the electrodes are in in which alternating current was used, the current sooner or the retort walls and the current passes transversely through later in every run established paths around the retort wall the column of coke or partially carbonized material. I n from one electrode to the other instead of passing through the retorts of Hoopes in 1921, Duchesne in 1924 (I), and the partially coked charge between electrodes. The refracothers, ring electrodes a t different elevations are used. In tory wall separating electrodes would then begin t o melt the McKee (1918) and Stevens (1933) retorts (8) the elecalong the paths of the current and a hot spot would eventually trodes are a t the top and bottom of the carbonaceous charge. appear on the retort shell. The electrode section was rebuilt Several years ago the Detroit Edison Company undertook again and again in trying various schemes to prevent the the development of a practical retort based on Stevens' current from following the retort wall. Runs lasting up to 92 hours could be made, but the difficulty was not overcome. 1 Present addresa. University of Missouri, Columbia. Mo.
T
757
758
INDUSTRIAL AND ENGINEERING CHEMISTRY
Finally, a t the end of 1936 it was decided t o try an entirely different arrangement of electrodes. Another retort was designed and built early in 1937 and put into operation in April. It proved to be a practical unit, but the lower end of the carbon electrode forming the retort wall would overheat, which suggested that a longer section of carbon wall electrode would be desirable. Some difficulty was also encountered in controlling temperature a t the top of the retort. The retort shown in Figure 1 was then built. Inasmuch as this retort represents the final development, its construction and method of operation will be described briefly. The retort is a steel shell 4 feet in diameter and 24 feet long, lined with refractory with a layer of insulation between the shell and the refractory. The inner lining is composed of carbon brick and tile extending to within 4 feet of the bottom. The carbon lining acts as one terminal of the electric circuit, electrical connection to the lining being made through two 16 X 16 inch carbon blocks set into the lining near the top of the retort. The other electrode consists of a 10-inchdiameter cylinder of graphite passing through a packed and insulated gland in the top of the retort. Coal, or a mixture of coal and coke, is fed into the retort continuously through a gastight feeder, and coke is removed continuously through a water seal a t the foot of the retort. The rate of fuel flow through the retort is controlled by the coke discharge mechanism, and the feeder a t the top of the retort is started and stopped by an automatic derice which keeps the fuel level in the retort between fixed limits. The electric current probably does not pass directly from the central electrode radially to the carbon electrode forming the retort wall, but travels for some distance down a core of coke which forms in the center of the downward-moving column of carbonizing charge in the retort and eventually reaches the carbon retort wall several feet below the central electrode. Gas is removed from the retort by offtake pipes connected to both the top and bottom. This arrangement was finally adopted after trials during which gas was discharged exclusively from each end of the retort. The effect was tried of returning gas to the base of the retort and removing all of the products from the top. This was abandoned because it was found that the hydrocarbons were cracked on passing through the high-temperature zone, and the calorific value of the gas was thereby reduced. With gas outlets a t both ends of the retort, a large proportion of the rich gases are removed below their cracking temperatures. By regulating the proportions of gas removed a t the top and bottom offtakes, it is possible not only to control the temperatures within the retort, but to fix the calorific value of the gas by controlling the amount of steam passing up through the charge. Under good operating conditions, about, 300 pounds of water are evaporated from the water seal per ton of coal charged. When all of the steam from quenching the coke passes up through the charge and out through the top offtake, it is difficult to maintain temperatures high enough for carbonization; as a result power consumption is high, gas yield low and of poor quality, and coke high in volatile content. The carbonizing capacity is determined by the maximum power that can be applied, which in turn is governed by the maximum voltage the assembly will permit. For the retort shown in Figure 1, the limit is about 2400 pounds of coal per hour at 165 volts and 600 kilovolt-amperes, With higher voltages, difficulty is encountered a t the insulating ring supporting the gland around the central electrode. Deposits of carbon on the insulating ring cause failure of insulation between the central electrode and the steel top of the retort. Use of an offtake at the bottom in addition t o the one at the top diminishes carbon deposits in the top of the
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chamber, and very little trouble arises from electrical leakage in that area. Also, the dust and lampblack carried by the gas is materially reduced. Electric power is received a t 12,000volts and stepped down by a single-phase, 850-kilovolt-ampere transformer to a secondary voltage, which may be regulated between 75 and 600 volts by primary taps on the transformer, a steptype voltage regulator, and secondary switches. This voltage range is much greater than is actually needed.
FIGURE 2. EXPERIMENTAL PLANT
The gas is exhausted, cooled, and washed by simple e q u i p ment common in one form or another t o all gas plants. As far as possible, atmospheric pressure is carried a t the gas offtakes of the retort. Figure 2 is a photograph of the experimental plant. Coal is handled by a track hopper and skip hoist to a bunker over the retort. Provision has been made to mix coke with the coal as required for starting the retort when temperatures are low and fuel bed resistance is high. In the experimental plant, coke is handled from the retort discharge by hand, but mechanical coke-handling equipment could, of course, be installed. The operating personnel necessary for the single retort could easily handle two or perhaps three additional units. At present four men per shift are employed; one man is fully occupied moving coke, and another is engaged in taking an elaborate series of operating data. The other two men attend to the fuel, operate the condensing and gas-handling equipment, and meet emergency requirements of the plant. I n a commercial plant the rate of coal carbonization should be from 1000 to 1500 pounds per man-hour, including all requirements t o place gas in the holder. The capacity of the present retort is 400 pounds of coal charged per square foot of retort section per hour. Coal is
JUNE, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
in the carbonizing zone 2 hours from the time i t leaves the feed pipes a t the top of the Carbonizing chamber. The results obtained with the experimental plant may be summarized as follows: Capacity, lb. coal carbonized/hr. Gas yield, cu. ft./ton coal B. t. u./cu. f t . gas produced Power consuniption kw.-hr./ton coal Gas, B. t. u . i B . t. u.' electricity used T a r yield, gal./ton coal Coke, Ib./ton coal
2400 16,333 461 433 5.09 12 1200
COALA N D COKEANALYSES (DRYBASIS) Coal Charged Coke Discharged 36.9 11.5 Volatile matter, % 61.2 85.4 Fixed carbon, 70 1.9 3.1 Ash, %
759
obtained in the small plant actually built and operated, and certain stated assumptions as to cost of coal, power, labor, etc., the cost of producing gas in a four-retort and a sevenretort plant has been estimated. In so far as possible, the bases for the assumptions are stated in the discussion which follows the cost estimate, so that the estimate may be adjusted readily to situations other than those postulated. As will be indicated later, it is difficult to set up costs for this process which will be comparable to those for other processes, for the reason that the cost of gas in any one plant is so dependent on local conditions. For instance, in one large gas plant the cost of gas in the holder would be increased nearly fourfold if the coke produced had to be sold a t the price paid for coal.
GAS ANALYSIS
coz, ro
Illuminants, yo
% cos 70
0 2 1
1.4
2.8
0.6 14.3
HZ! 70 C H I , 70 h-2,
470
sp. gr.
64.8 15.3 0.8 0.3336
The coke produced is porous and suffers considerable degradation in handling, but kindles readily and is a satisfactory fuel for use in certain types of domestic and industrial heating equipment. The proportion of volatile matter can be regulated over a considerable range by the rate of throughput. No attempt has been made to recover ammonia in the experimental plant. The use of a water seal a t the foot of the retort makes the recovery of ammonia difficult because of the large amount of water vapor in the gas due to quenching the coke and disposing of the steam in the condensing system. It might be feasible to recover ammonia by cooling the scrubber water and returning it to the coke-quenching compartment, and thus build up the ammonia content t o a value which would justify recovery. The plant can be started and shut down quickly. A cold retort can be raised to full production in about 3 hours. Starting up after a short shutdown can be accomplished in less than one hour. The zone of maximum temperature is in the center of the charge and surrounded by coal in varying degrees of carbonization. As a result, the surface temperature of the retort shell is about 136" F. and the loss due to radiation is only 12 kilowatts for the retort. The temperature of the gas leaving the unit is held a t about 260" F., and that of the coke 2 feet above the water seal a t 1000" F. Utility of the Process The foregoing pages describe the development of a technically successful process through various stages up to that of a small plant having a capacity of about 470,000 cubic feet of gas per day. Obviously the development is only of academic interest unless the process can. under some set of conditions, be used to advantage in comparison with one of the standard gas-making processes. Inasmuch as the process uses energy in an expensive form (electrical) to generate heat which could readily be obtained by burning gas, the process must show some unusual advantages if it is to find application. I n this respect, however, the process is no different than many others in which electrically generated heat is actually used. The most likely application of the process would appear to be in the utilization of off-peak power to produce gas for city use. The short time required to start or stop gas production and the easy adjustment to a change in power input make the process well suited to off-peak power use. The final criterion which the process must face, however, is the cost of producing gas. I n order to arrive a t a reasonable estimate as to what this cost might be, a full-scale plant was laid out as shown in Figures 3 and 4. From the results
Plant Postulated for Cost Estimating Figures 3 and 4 show a four-retort plant. Coal is dumped from hopper bottom cars into a receiving track hopper, A , from which pan feeder B drops it into roll crusher C, discharging into elevator D , in turn discharging into either of two concrete silos, EF (Figure 3). Silo E is used for coal, silo F for coke storage. Each silo is equipped with a star feeder, GG, for filling skip hoist H by means of which the charge material (coal, coke, or a mixture of the two) is raised to receiving hopper 1over the row of retorts, 1, 2 , 3 , and 4. The receiving hopper discharges onto a horizontal flight conveyor, J, by means of a pan feeder. This conveyor fills the hopper above each retort. The operator needs only to fill the skip and start it up the incline. Filling of the hopper over each retort follows without further attention. A separate small bin, L (Figure 3), over each retort provides a coke reserve to break high internal electrical resistance in the retorts when required. This bin is filled by the same charge which handles equipment. Selective openings in the pan conveyor covered by slide gates make it possible t o fill the coke as well as coal hoppers. Coal is used ab soon after delivery as possible to obtain the best operating results. Coal will be stored only in caSe of emergency or n-hen surplus coal is received. The stored coal will be discharged on the ground from the coal silo a t M and carried to storage by dragline scraper N . The same scraper system will reclaim coal from the storage pile as required. From the hoppers over the retort, coal is fed into the carbonizing chamber by a motor-driven gastight feeder, 0, controlled by a level indicator which cuts off the feeder as the retort becomes full. Coke is discharged from the retort by a revolving water seal pan, P , shown a t the lower extremity. The coke drops on belt conveyor Q directly from the seal pan and is carried to the storage bin from which it is reclaimed by dragline scraper R and dropped into elevator D to be lifted into coke silo F. Star feeders GG which supply the skip car are interconnected by means of a variable-speed drive for charging the mixture as required by variations in the quality of the coal. The rate of charge movement through the retort is controlled entirely by the rate of rotation of the water-sealed coke discharge, P, which is varied by a variable-speed mechanism in the motor drive link. Automatic feeder 0 keeps the fuel level a t the top of the retort. Gas is taken from the retort by offtakes SS a t both top and bottom which are connected to hydraulic mains TT. Proportioning the amount of gas between the two offtakes is accomplished by regulation of the seals on the offtakes in the hydraulic mains. From the hydraulic mains the gas passes through a centrifugal tar extractor, U , which also acts as a primary cooler and contact washer. The fan in this unit has a capacity which is four times the rate of production and
INDUSTRIAL AND ENGINEERING CHEMISTRY
760
VOL. 32, NO. 6
TRACK HOPPER
MACHINE SHOP
W
N
;e
FIG.3
FIG. 4
FRONT ELEVATION
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A TRACK HOPPER B PAN FEEDER C ROLL CRUSHER D ELEVATOR E - C O A L SILO F - C O K E SILO GG STAR FEEDER H SKIP HOIST I RECEIVING HOPPER 1-2-3-4- RETORTS
-
-
SIDE ELEVATION
- FLIGHT CONVEYOR - FEED BIN OVER RETORT M - COAL DISCHARGE ON SILO N - DRAGLINE SCRAPER FOR COAL 0 - FEEDER TO RETORT
- TAR EXTRACTORS
J L
U V
P
SCRUBBERS XX PURIFIERS Y METER 2 HOLDER
- SEAL
PAN ON RETORT
'0 - BELT CONVEYOR FOR DISCHARGED COKE
-
R DRAGLINE SCRAPER FOR COKE S S GAS OFFTAKES T T -HYDRAULIC MAINS
-
- EXHAUSTER
WW
-
-
ELECTRIC HEATING EQUIPMENT a - TRANFORMERS b - VOLTAGE REGULATORS c . d CARBON TERMINALS f CONTROL BOARD
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-
JUNE, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY ~~
The following comments are submitted in explanation of Tables 11 and 111.
~~
TABLE I. COSTSOF PROPOSED PLANT -72-Ton
Land Railroad connection Fuel-handling equipment Building Retorts a n d steel structures Electric svstem Condensiig and purifying equi ment Boiler Kouse, repair shop, etc. Laboratory, office, etc. Gas holder Wiring, light and power" Service a n d grading Overheadb
PlantCost/ton Total of daily cost capacity $ 2,500 S 35 2,440 34 22,671 315 6,030 84 40.287 560 421568 592 26,346 10,455 3,825 93,725 3,124 6,000 40,296
366 145 53 1300 44 84 560
-144-Ton Total cost $ 2,500 2,440 23,572 7,030 69.398 74:494 40,066 10,455 3,825 170,420 4,184 10,000 64,850
_ _ _ - - - -
PlantCost/ton of dai!y capacity $ 17 17 163 49 482 516 278 73 27 1180 29 70 455
Total investment 300,267 4172 483,234 3356 a Exclusive of t h e retorts. b Overhead on construction in t h e above tabulation of investment is taken a t 15.5 per cent of cost, based on t h e following allowances (in per cent): Engineering supervision during construction Administration during construction Interest on investment during construction Organization of construction Legal expenses, insurance, and taxes during construction
761
5.0 2.0 6.0 0.5 2.0
15.5
recirculates the gas through the washer separator chamber four times before it enters exhauster V to be forced (Figure 3) through secondary scrubbers WW and purifiers XX to meter Y and storage holder Z. Each retort is provided with a separate 750-kilovolt-ampere single-phase power transformer, a, and voltage regulator, b. The transformer is directly connected to retort electrodes cd by copper bus bars e. Facilities for transferring transformer connections are provided on the high-tension side by disconnect and remote-control oil switches. Transformer tapchanging switch shaft extensions place this manual control on the switching panel,f, in the control room, safeguarded by a signal light and interlocking latch. Each control panel is equipped with a voltmeter, ammeter, and wattmeter, recording and indicating pyrometer, ground detector, and revolution counters on the feeder and revolving discharge. There are also remote control switches for the feeder and discharge motors as well as the primary oil switch on the transformer. A small boiler plant is used only for auxiliary steam, cleaning drain lines, and heating if weather requires. The usual drips, drains, tar separators, and storage tanks common to gas plants have been provided for in the estimate, a t costs which are well established.
Cost of Proposed Plant A detailed estimate of the cost of plants to carbonize 72 and 144 tons of coal per 16-hour day was made and is summarized in Table I. The retorts should be in groups of three to balance on three-phase electric power. For this reason a four-retort and a seven-retort plant have been considered, allowing in each case one spare retort for emergency use. The i'z-ton plant would be adequate for the average city of 55,000 inhabitants, with 8000 customers taking 55 per cent of the gas output and the balance going to house heating and industrial uses.
Cost of Operation The capacity of the plants is based on 16 hours of operation per day, so scheduled that the power demand will not increase the demand of the electric power system. It has also been assumed that contingencies arising would prevent the plant from operating more than 70 per cent of the total annual available 16 hours per day, a total of 4088 out of 8760 hours per year. The data in Table I1 are used as the basis of the operating costs given in Table 111.
1. The data as to retort capacity, yields, and power consum tion are based on the results obtained with the semiworks-scaE plant. 2. Inasmuch as there are 168 hours in a week, four men per job, working 40 hours per week, will not furnish quite continuow service. In view of the fact that the plant is assumed to be in actual operation only 78.4 hours per week, presumably it would not be difficult to work out a satisfactory schedule for each job. 3. The cost of coal is assumed t o be $3.50 per ton and the value of coke $6.00. The spread between cost of coal and value of coke is determined almost wholly by local conditions. The spread assumed here is less than actually prevails in cities where manufactured gas is used. 4. Tar is credited at a fuel oil price, which is presumably the lowest rice it would command in any town. a. &-peak power is taken arbitrarily a t 4 mills per kilowatt-hour. This is more than a public utility supplying both electric energy and gas to a city would need to charge its gas plant for off-peak power. In the Tennessee Valley, cities buying TVA primary power could use the off-peak power at about 2 mills per kilowatt-hour and still allow the city's electrical department a profit on energy sold the gas department. 6. Depreciation is taken a t 2.5 per cent on a straight sinkingfund basis. With interest at 3 per cent this would retire the investment in about 26.5 years. State regulatory commissions frequently allow only 2 per cent depreciation, which will retire an investment in about 31 years at 3 per cent interest. One large gas company is known to be using 3.5 cents per thousand cubic feet of gas as a depreciation charge. If this charge be applied to the total manufactured gas made in the United States in 1937 and the annual 'charge compared with the total plant investment in 1937, the depreciation rate is seen to be only 0.54 per cent, requiring about 64 years at 3 per cent interest t o retire the investment. Another large gas company is known
COSTS TABLE11. BASISOF OPERATIKG 4 Retorts 1.5 16 72 70 4,088 18,396 1,200 12 16,333 453" 300,468
Capacity coal carbonized, tons/retort/hr. Off-peak hr./day Coal carbonized, tons/day Av. annual production factor, % Total annual operating hr. (0.7 X 16 X 365) Coal carbonized tons/year Coke yield/ton koa1 carbonized Ib. T a r yield/ton coal carbonized, kal. Gas yield/ton coal Carbonized cu. ft. Power/ton coal carbonized, k&.-hr. Annual make, 1000 cu. ft. Laborb Foreman a t $2000/year Retort operators a t $1320 Fuel men a t 51080 Maintenance foreman a t $2000 Repairmen a t $1800 Laborers a t $960 T o t a l operating crew
4
7 Retorts 1.5 16 144 70 4,088 36,792 1,200 12 16,333 453' 600,936 4 8 6 1 2 3
4
4 1 2 2
-
-
17
24
Includes 20 kw.-hr. per ton coal carbonized for fuel handling and gas scrubbing and pumping. b On a 40-hour week basis. Allowance of 3.85 per cent added for 2 weeks annual vacations with pay. a
--
BASIS) TABLE 111. OPERATINQ ESTIMATE (ANNUAL Carbonizing Capacity:7 - 7 2 Tons/Day-144 Tons/DayPer 1000 Per 1000 Expense cu. ft. Expense cu. f t .
Coal carbonized a t $3.50/ton $ 64,386 Power, 453 kw.-hr./ton coal a t 33,333 0.46 4,599 Graphite electrode, 25b/ton coal 18,571 Operating labor 9,857 Maintenance labor and material 5,600 SupGvision 2,750 Purification 6,000 Taxes 7,500 Depreciation
$0.2143
$128,772
0.1109 0.0153 0.0618 0.0328 0.0186 0.0091 0.0200 0.0250
66,666 9,198 25,114 15,038 5,600 3,000 9,700 12,000
0.1109 0.0153 0.0419 0.0250 0,0093 0.0050 0.0161 0.0199
152,596
0.5078
275,088
0.4577
66,228
0.2204
132,456
0.2204
75,331
0.2507
120,558
0.2006
Total generation Credits Coke 0.6 ton/ton coal a t $6 Tar.. i 2 eal./ton coal a t 56 Total K e t generating expense
$0.2143
0.0367 0,0367 22,074 11.037 154,530 0.2571 0.2571 77,265
INDUSTRIAL AND ENGINEERING CHEMISTRY
762
to be using a 3.5 per cent retirement rate, which at 3 per cent interest requires a useful life of 21 years. To chemical engineers who often use from 5 to 20 per cent depreciation rates and thus retire investments in 16 to 4.5 years, a depreciation rate retiring an investment in 26.5 years may appear unreasonable. It can only be ointed out that the parts of a gas plant not renewed frequentg under routine maintenance do indeed have a long life. Gasholders with over 50 years of service are to be found in many places, and the same is true of other types of simple equipment used in gas plants. The general opinion evidently prevails in the gas industry that an average life of 20 to 30 years may be assumed for gas plant equipment. In the present estimate an average life of 26.5 years has been assumed and a liberal allowance made for current maintenance. 7. The allowance for taxes is another item difficult to determine in this type of estimate. If the statistics for the manufactured gas industry for 1937 be used, the tax item is 1.96 per cent of the- lant investment. In one large city plant the property tax is Enown to be approximately 1.3 per cent on full plant value, to which must be added the taxes based on employment pay rolls, etc. In estimating the cost of gas in the holder, it is
VOL. 32, NO. 6
common practice to include only property taxes and taxes based directly on pay roll; items such as interest on depreciated investment, licenses, income taxes, etc., are included with the other numerous ones which must be added to the holder cost of gas in order to arrive a t a permissible domestic rate for gas. Since the purpose of the present estimate is only to arrive a t a gas-inthe-holder cost which may be compared with corresponding costs by other processes, a tax of 2 per cent of total investment has been used to correspond with the 1.96 per cent shown in the statistics of the gas industry. As stated above, this does not include taxes based on income or any of the other necessary expenses incurred in supplying gas to the ultimate consumer.
Literature Cited (1) Hoopes, W., U. S. Patents 1,366,457-8 (Jan. 25, 1921) ; Duchesne, M. H., French Patent 682,347 (Oct. 13, 1924). (2) MoKee, B. F., U. S. Patents 1,282,445 (Oct. 22, 1918); Stevens, Harold, Ibid., 1,938,121-4 (Dec. 5 , 1933). (3) Walker, H. S., Gaa Age-Record, 70, 27-30 (1932). (4) White, C. E., U. S. Pat,ents 935,344 (Sept. 28, 1909); Berglof, A., Ibid., 1,085,096 (Jan. 20, 1914); Fueler, H. F., Ibid., 1,286,577 (Dec. 3, 1918).
Destructive Hydrogenation of
High=Molecular= Weight Polymers Isobutene Polymer, Butadiene Polymer, and Natural Rubber VLADIMIR N. LPATIEFF AND RAYMOND E. SCHAAD Universal Oil Products Company, Riverside, Ill.
Destructive hydrogenation of rubberlike isobutene polymers produced only paraffinic hydrocarbons and thus showed that the original rubberlike polymers probably had long aliphatic carbon chains. Destructive hydrogenation of butadiene thermal rubber and of natural rubber gave only naphthenic hydrocarbons. Hydrogenation of isoprene yielded isopentane as well as cyclic hydropolymers.
ESTRUCTIVE hydrogenation under pressure in the
D
presence of nickel oxide and molybdenum oxide has been used (2) to show the presence of naphthenic hydrocarbons in high-boiling olefin polymer. It was of interest t o apply this tool to other hydrocarbons having large molecules, especially rubber and synthetic rubberlike polymers. The destructive hydrogenation of isobutene polymer yielded paraffinic hydrocarbons only, including isobutane in the gases. Butadiene polymer, on the other hand, gave only naphthenic products, chiefly ethylcyclohexane and a dicyclic hydrocarbon. Similarly, natural rubber yielded naphthenes only, with p-methylisopropylcyclohexane as the major constituent of the lower boiling portion of the product. Isoprene,
under the conditions used for the destructive hydrogenation of the rubber, yielded isopentane and an unsaturated naphthene (i. e., a hydropolymer of isoprene) which was converted into p-methylisopropylcyclohexane by further hydrogenation. Discussion of the relation of these results to the structures of the polymeric substances hydrogenated is re8erved for a future publication of further work now in progress undertaken to aid in the proper interpretation of the above indicated experiments.
Apparatus and Procedure The destructive hydrogenations were carried out in electrically heated, rotating autoclaves (450- and 3515-cc. capacity) of the Ipatieff type made of stainless steel (17-19 per cent chromium and 7.0-9.5 per cent nickel). Equal weights of the rubberlike polymer or rubber (cut into small pieces) and solvent, and black nickel oxide (Baker's) equivalent t o 10 per cent of the weight of the polymer were placed in the autoclave in the order named. The autoclave was closed, the air was swept from it by hydrogen, and it was charged with hydrogen t o an initial pressure of 100 kg. per sq. em. at 25" C. and then heated a t 250" for 4 to 12 hours (an additional 1.5 to 2.0 hours usually being required to reach the desired operating temperature). After the heating, the autoclave was permitted to cool, the gases were released through a trap cooled by solid carbon dioxide and acetone, and the noncondenaable gases were collected in a gas holder over salt water. The head was then removed from the autoclave, and the liquid product and solvent were taken from the bomb by means of a pipet and filtered to remove the catalyst. The solvent was removed and the product was separated by fractional distillation.
