Hydrogenation of Bituminous Coal in Experimental Flow Plant Process Variable Study M. A. ELLIOTT, H. J. KANDINER, R. H. KALLENBERGER, R. W. HITESHUE, AND H. H. STORCH Bureau of Mines, Bruceton, P a .
e
*
I
A n experimental flow plant in which cod-oil pastes are treated with hydrogen gas a t elevated temperatures and high pressures is described. Recent runs on the preparation of heavy fuel oils (similar to Bunker C) by the hydrogenation of Bruceton (Pittsburgh bed) and Rock Springs No, 9 bituminous coals are reported. A consistent set of curves is presented showing the interrelationship of the salient process variables. The effect of temperature in the reactors was investigated over the range 420" to 480' C. and contact times were varied from 1minute to 80 minutes. Stannous sulfide-iodoform and molybdenum trioxide oatalysts were tested separately and the concentration of coal in the feed paste was varied from 20 to 50% b y weight. A s secondary variables, the following product parameters were evaluated : residual oxygen, asphalt, sulfur, and nondistillable soluble oil content; viscosity; soluble oil yield; hydrogen absorption; and hydrocarbon
gas formati0.n. Eight graphical correlations are presented showing the dependence of these variables on temperature, contact time, paste composition, catalyst, and coal over the ranges investigated. A tentative correlation is presented showing the variation of soluble oil yield, hydrogen absorption, and hydrocarbon gas formation with product viscosity. It was found that higher temperatures, longer contact times, and more active catalysts simultaneously reduce product viscosity and boiling point and increase the removal of oxygen, sulfur, and asphaltic materials from the feed stock as well as increase hydrogen absorption and light hydrocarbon formation. The dependence of soluble oil yield on the primary variables is rather more complex, and it appears that optimum yields of soluble oil are obtained a t a given temperature a t low contact times together with high product viscosity and low hydrogen absorption and hydrocarbon gas formation.
A
The reactor system consists of two converters which normally have a 3-inch internal diameter and a free inside length of 87 inches. In these tests, the converters were fitted with removable liners fabricated of 2-inch extra-heavy pipe, in order to reduce the available system reaction volume t o about 40% of that of the empty converters. This permitted the attainment of higher space velocities with existing paste preparation and pumping facilities. Figure 2 shows construction details of the liner. T h e converters were heated in radiant electric furnaces which covered the entire length, excluding the end closures. Details of the closures, heaters, and other features of the converters have been published ( 1 , 6 ) . The remaining plant equipment may be regarded as merely auxiliary to the reaction system, to provide facilities for feed preparation and product treatment. Make-up hydrogen is obtained from high-pressure storage tanks. After reduction in pressure to nearly atmospheric, it is mixed with recycled gas containing about 99% hydrogen, 1% methane and a trace of ethane, from the end of the system, and delivered to a 500-cubic foot gas holder. For compression a 5-stage compressor is used with a stand-by 4-stage unit available. In the first series of tests, operation 180, the paste preheater was not used and hydrogen was delivered directly to the first converter bottom after passing through the high pressure flowmeter. T h e paste preheater was installed after these tests were completed and was in service during the second series of tests, operation 182. In these latter tests, most of the inlet hydrogen was sent (unmetered) through the paste preheater, thus entering the converter together with the aste through a common line. In order to maintain a gas inlet gne clear for emergencies some of the inlet hydrogen bypasses the preheater and goes directly to the first converter bottom. This stream is metered (its rate is held constant a t about 10% of the total hydrogen circulation rate), and it is not intentionally used for temperature control in the converters. Mine-run cod is crushed, dried, and ground in a ball mill to 90% through 200 mesh. It is mixed with centrifuged heavy oil, so-called pasting oil, from a previous operating period. Catal sts when used are added a t this time. T h e coal-oil paste, usual& containing 35 t o 50% coal, is made up in batches sufficient for about 8 hours' operation. Mixed paste is stored in an agitated and steam-jacketed feed weighing tank provided with a continuously operated circulating pump. A portion of the circulating
BOUT 10 yeam ago, the Bureau of Mines started research and development work (5)on the hydrogenation and liquefaction of coal a t high pressures, using a continuous smallscale plant with a design capacity of approximately 100 pounds of coal per 24 hours. The plant was initially used, a t 3500 pounds per square inch pressure, t o investigate the amenability of various typical American coals and lignites t o hydrogenation. During the recent war, a research program was begun for the production of fuel oil from coal a t the comparatively low pressure of 1000 pounds per square inch, in an attempt to alleviate the fuel-oil shortage and relieve somewhat its transportation problem. A suitable process was developed, operating a t about 420' C., which produced a Bunker C-type fuel oil from coal (4). Because of the difficulties experienced in operation at low hydrogen pressures, particularly the marked tendency of the feed to coke under these conditions, this research was extended at the conclusion of the war to a higher pressure range-3500 to 4500 pounds per square inch. In these later investigations, some of the primary process variables have been explored. This report covers a recent series of tests on the conversion of Bruceton coal (from the Bureau of Mines experimental mine a t Bruceton, Pa.) and Rock Springs coal (D. 0. Clarke Mine, No. 9, Superior, Wyo.) into fuel oils meeting the requirements of the Bunker C or A.S.T.M. 6-grade. While one aim of this series of tests was t o make fuel oil of this grade, a sufficiently wide range of primary variables was investigated so that a comprehensive process variable study could be made. EXPERIMENTAL PLANT EQUIPMENT AND OPERATION
GENERALDESCRIPTION AND PROCESS FLOW.The arrangement of the hydrogenation plant has been modified considerably since its description in the first Bureau of Mines paper (6) on assaying coals. A typical flow sheet for the tests discussed here is shown schematically in Figure 1.
83
INDUSTRIAL AND ENGINEERING CHEMISTRY
84
paste is drawn by the high-pressure paste pump and introduced, through a paste preheater, into the bottom of the first converter. T h e total product from the first converter, a mixture of excess hydrogen, partly reacted paste, product oils, and hydrocarbon vapors, leaves by a n internal standpipe set for a liquid level of 76 inches. It then enters the second converter and leaves, again by standpipe, t o enter the heavy-oil reflux trap or hot catchpot. This latter unit is a vessel of the same size and type as the empty converters; internal reflux cooling is provided a t the top and heat supplied externally at the bottqm. The hot catchpot is a crude high-pressure separator and gives two fractions, so-called heavy oil and a n overhead vapor. The heavy oil contains high-boiling benzene-soluble oils, mineral matter, unreacted coal, and benzene-insoluble organic material. The overhead product contains excess hydrogen, volatile hydrocarbon vapors water vapor, ammonia, hydrogen sulfide, carbon dioxide, and possibly carbon monoxide. The heavy oil is drained intermittently by manual throttling. It is centrifuged t o remove a portion of the mineral matter, insolubles, and unreacted coal and then used for recycle as pasting oil for a subsequent batch. Oil produced in excess of pasting-oil recycle requirements is the product of the process. Depending on the potential end use of the oil, this centrifugation can be applied only to the oil required for recycle, and in this event the product of the process would be excess uncentrifuged heavy oil.
c cot0
The overhead vapor from the heavy-oil trap goes to the lightoil trap, after external cooling and water injection. The latter serves t o dissolve ammonium or other salts t h a t might otherwise deposit and plug this line. Two liquid phases are removed from the light-oil trap-an aqueous layer containing water solubles and a light-oil layer containing comparatively low-boiling liquid hydrocarbons, t a r acids, and t a r bases. The gas leaving the light-oil trap passes through a spray knock-out trap and then into the water and kerosene scrubbing system, where it is reconditioned for recycle. The tail gas from the scrubbing system is returned t o the gas holder, after reduction in pressure to atmospheric, Traps and scrubbers all operate a t system pressure. PLANT OPERATION AND CONTROL
Weighing tanks are used for metering liquids into and out of the system. Piping t o the weighing tanks includes short, flexible hose sections; the paste-circulating line has an internal copper tubing steam heater. Weighings are considered reliable within about 0.1 t o 0.2 pound in 200 t o 300 pounds, and the scales are periodically recalibrated and adjusted. Gas volumes leaving the highpressure system are measured a t approximately atmospheric pressure and room temperature by bellows-type integrating dry test meters. A high-pressure flowmeter also was used to measure continuously the rate of flow of compressed feed gas t o the fist converters-i.e., the preheater by-pass stream in operation 182, and the total gas stream in operation 180. Pressures are measured by indicating and recording Bourdon-tube instruments on each high-pressure vessel in the system, as well as a t certain
Vol. 42, No. 1
points in the lines. Temperatures are controlled by potentiometer-type electrical temperature controller recorders actuated by thermocouples on the external surfaces of all heated vessels. For operational control, temperatures are measured a t various points in the converters, traps, and lines. Upon withdrawal of liquid products from the heavy-oil trap, light-oil trap, water scrubber, and kerosene scrubber, dissolved gases are flashed during the let-down to atmospheric pressure. These gases are metered, sampled, and discarded. Specificgravity meters are used to obtain a continuous record of the density of the various flashed gases as well as the recycle gas. In putting the plant on stream, the dry system is first purged with nitrogen, then with hydrogen, and then pressure-tested. Next, system pressure is set at the desired value by the backpressure regulator, hydrogen circulation established at about 300 cubic feet a n hour, and power applied to all heating units, When the converters reach approximate operating temperatures, water injection, water scrubber, and kerosene scrubber pumps are started and set at specified rates. "Pre-run" oil is then pumped through the system t o fill it t o operating liquid level and to get the traps and paste pump operating. Following several hours of pre-run oil pumping, the first batch of paste is introduced. Hydrogen circulation rate is then adjusted to its specified value, and gas-density instruments and other accessories are put on stream. After this starting-ur? arocedure. which generally requires 8 t o 16hours, a test period at any particular set of steady operating conditions is run for 1 t o 12 batches or some 8 to 100 hours. When a test period is completed, operating conditions are changed to new values, and, after a brief transition, the next test is started. I n this manner, a program for determining the effect of changing operating conditions may be conducted in a continuous manner. Paste batches are successively fed into the system. The different products collected or sampled are designated as being derived from a specific batch. A time lag of 1 t o 2 hours from the start of pumping a particular batch is allowed at each collecting or sampling point t o ensure that the effluent stream at that point is adequately representative of material being fed into the plant during the batch (3). Heavy oil is discharged manually at intervals of 5 to 15 minutes, depending on paste p u m p ing rate; a liquid-level indicator of the differential pressure type shown in Figure 3 is used to permit holding a liquid seal on the discharge line from this trap, thus avoiding dilution of the heavy-oil-flashed gas with system hydrogen. The heavy oil is collected in 5-gallon open-top steel buckets from the low-pressure slurry receiver, composited for a n entire paste batch, and pumped a t 90" t o 120' C. to a supercentrifuge operated at 15,000 t o 19,000 r.p.m. Residue is removed from the centrifuge after each batch. Light oil and water are drained from the low-pressure-light-oil trap into glass decanter bottles; after settling, the water layer is drained, weighed, occasionally sampled, and discarded while the cumulated light-oil product of a single paste batch is blended, sampled, and delivered t o storage. Ultimate analyses for carbon, hydrogen, nitrogen, oxygen (by difference), sulfur, ash, and water are made on coal (1 sample per 3000 pounds composite); heavy oil and pasting oil (1 sample per composite of a n entire test period-sometimes 1 sample per batch); and light oil (1 sample per test period). Decanter water scrubber water, and scrubber kerosene are occasionally sampled and analyzed. Samples of recycle gas and the various flashed gases, cumulated over a 1- or 2-batch period, are analyzed on a mass spectrometer. In addition t o these ultimate chemical analyses, the following tests also are made: Test Organic insolublesb Distillation T a r acid and t a r base Saturates, aromatics, and naphthenes Density Viscosity [Saybolt Furol a t 180' F. (82' C . ) ] Asphaltc
-
Material" HO P O HO: PO, LO LO LO HO L 0 , P O HO: P O KO, PO
-
.. 7 HO heavy oil, P O = pasting oil-i.e., centrifuged heavy oil, LO light oil. b A modified A.S.T.M. D 163-42 procedure is used with chloroform as a solvent. The results obtained are closely comparable with the benzene method previously reported (8). C Defined a8 chloroform-soluble, petroleum-ether-insoluble material.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1950
The analytical procedures used are based on the A.S.T.M. standards, modified somewhat where necessary t o accommodate the authors’ requirements. CALCULATIONS
The plant data and analytical reports are processed t o give: Material balance Gas stream densities a t atmospheric pressure Hydrogen absorption Hydrocarbon-gas loss Organic insoluble ield Inorganic insolubc yield Ash yield Soluble oil yield Oil distilling t o 300” (and 355”) C. yield Asphalt yield Water yield Hydrogen sulfide yield Ammonia yield Carbon and hydrogen balance Hydrogen absorption, gas loss, and the various yields are reported as pounds per 100 pounds of moisture- and ash-free coal (M.A.F. coal) fed into the system. In addition t o these calculations, it has been found useful to compute the “quantity remaining’] on certain parameters of composition based on total paste feed. Thus, “fraction nondistillable oil remaining’’ is defined as:
Figure 2.
Converter Liner
Soluble oil in the heavy oil, undistilled t o 355” C. (Soluble oil in pasting oil, undistilled to 355” C.) 4(M.A.F. coal)
Moisture- and ash-free coal is here regarded as potential oil distilling above 355 c. In calculating material balance, total weight output is compared with weight input. Output is regarded as the heavy oil, light oil, decanter water, and flashed gases; input is hydrogen make-up, coal-oil feed paste, and injected solvent water. The water and kerosene flows, into and out of their respective scrubbers, are omitted from the material balance; for these units, the liquid input is assumed to be sensibly equal to the liquid output. Gas densities are calculated from mass spectrometer analyses rather than by integration and averaging of the recording charts of the plant gas density metcrs. Hydrogen absorption is the net hydrogen reacting chemically with the feed paste, and is calculated as the difference between the make-up hydrogen fed into the system and that leaving the system in the several flash gases as free hydrogen. T h e “gas loss” is the quantity of hydrocarbons leaving the system in the flash gases. It is calculated as the differencebetween the total weight of the out gases and the weight of free hydrogen they contain. While this calculation is referred t o as a loss, it should not be considered waste because, in a large plant, such hydrocarbons can be recovered and utilized. T h e yield of organic insolubles is calculated from the weight difference between organic insolubles in the product heavy oil and organic insolubles in the feed pasting oil. The remaining
85
yields, except for water, hydrogen sulfide, and ammonia, are similarly computed. The water yield is calculated from an oxygen balance over the feed paste and product heavy and light oils; the unaccounted-for oxygen is assumed t o be converted to water. The ammonia and hydrogen sulfide yields are obtained from nitrogen and sulfur balances. If the material balance, analyses, and calculations were perfect, the numerical sum of yields of organic insolubles, soluble oil, hydrocarbon-gas loss, water, hydrogen sulfide, and ammonia should equal 100 plus the hydrogen absorption. Since all these yield values are based on the moisture- and ash-free coal, which is only about one third of the total feed t o the plant, such a comparison is about three times as sensitive t o any errors as a n over-all material balance. Thus, a plant material balance within 95 t o l05%, which was regarded as acceptable, might result in the yield summation differing from 100 hydrogen absorption by *15%. The largest source of uncertainty in the plant-material balance lies in the solvent and decanter water streams. The gain in water through the plant between these two streams should be equal t o water formed by reaction plus moisture introduced with the paste. Actually, however, the flow rate of these two streams is so large that slight errors in metering make large variations in the measured difference between them This discrepancy is then further magnified when tlie yield comparison based on moisture- and ash-free coal is made. If the plant material balance is recalculated omitting these water streams and a calculated water gain (from reaction)is introduced, an adjusted material balance can be arrived a t which is acceptably consistent with the yield summation. The data reported in this paper have not been modified in any way. It would be quite acceptable to adjust all of the yields so that the sum of product yields exactly equaled 100 plus hydrogen absorption. This procedure might smooth out some of the experimental dispersion, as well as provide a set of yield figures having greater apparent consistency.
+
Heavy-oil trap
tubing
I
O
c
x
6 slots I”
2
*
I
manometer
Inlet line Liquid outlet-
Figure 3,
Heavy-Oil Trap Liquid Level Indicator Not to saale
.
86
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE
Operation 180
Operation 182
Test No. 1 2 3 4 5 6 7 8 9 10 11 1 2 3 4
5 6 7 8 9 10 11 12 14 15 16 17 18 19
20
Total Batches per Test 11 6 5 6 6 1 5 1 4 4 2 1
2 6 6 7h 8 5i 7 6 15 i 5 3 2 3 2
11 10 8 1
Total Hours per Test 92 51 41 50 50 8 39 8 31 32 10 8.5 15.5 37 40 48 56 22 43 41 79 32 16 30 39 21 150 87 63 6.5
I.
SUMfilARY OF OPERATIONAL
Coal Used Brucetond
Rock Springsg
None Rock Springs None Bruceton Rock Springs
Paste Compositiona, % Coal 35 35 35 35 35 35 35 50 45 35 35 45 45 45 40 40 40 40 40 40 40 20 40 0 40 0 40 40
40 40
i
T
~
Vol. 42, No. 1
~
Reaction Temp.. C.b 420 420 423 440 440 455 460 4:O
Volume a t Reaction Temp., Cu. Ft.b 0.183 0.183 0.183 0.151 0.166 0.166 0.120 0.103
Estimated Contact Time, Hr.h 1.05 0.63 0.54 0.35 0.56 0.47 0.27 0.25
44.5
o:iio
O:S7
440 445 440 442 440 458
o:ii2 0.208 0.224 0.216 0.239
0 : 68
0.201
0.37
460 480 470 438 440 440 440 440 440 440 46 0 455
0.081 0.096 0.096 0.157 0.094 0.148 0.193 0.184 0.216 0.239 0.155 0.128
f
0.50 0.42 0.41
0.91
0:i5 0.18 0.14 0.30 0.18 0.55 1.25 1.15 1.15 1.32 0.48 0.25
~ Catalystc A A A A A A A A A A A A A
-4
A A A A A A A A A None None None
B
C C C
5 Percentage based on coal as received. b Estimated from t e m p e r a h e gradient in converters; reaction volume and contact time in tests 8 to 11 (operation 180) are corrected for coke formation (see text). 0 Catalysts: A = 0.1% 0.1% SnS, 0.05% CHIS (based on coal); B = 1% h'fooa h'f0Oa not on fuller's earth (based on coal); C = 1% of impregnated fuller's earth containing 7.5% MoOa (based on,coal); with A catalyst, 0.5% NHiCl was also added in all tests employlng employing Rock Springs coal d U. U. 8.Bureau of Mines Experimental Mine, Bruceton, Allegheny County, Pa. 8 At temperature for for only 0.02 t o 0.03 cu. ft. volume, steep linear gradlent gradient for balance of converter. .ature a t exit of h o . 2 converter after a steep gradient. f Barely attained reaction temperature I Rock Springs, D. 0. Clarke Mine No. 9, Clearyater County, Superior, Wyo. h Batch 5-3 omitted in nurnbering (Dlant (plant difficulties). i Batch 7-2 omitted in numberini numbering (blant (plant difficulties). i Batch 10-4, 10-5, omitted in numbering (plant difficulties).
I n addition t o the calculations of yield values, effective contact time at reaction temperature for each test period is estimated using the following procedure. Temperatures inside the converters are measured by a set of 9 thermocouples, located as follows: Distance from Bottom Head, Inches First converter Second converter 0.5 .. 12 .. 20 30: 0 30 54 54 77 77
I n a number of tests, 6 points were used in the second converter a t locations corresponding t o those in the first converter. The average temperature at each thermocouple point is calculated for an entire test and a temperature profile plot constructed. This plot has temperatures as ordinates and linear distance to each thermocouple point from the first converter bottom as abscissas. By visual integration, the average temperature of the hot zone can be determined as well as the approximate length of the converter system a t that temperature. The paste rate is known, and the paste density a t reaction conditions is estimated to be 55 pounds per cubic foot by extrapolation from laboratory tests a t atmospheric pressure. Using these data and 2.63 square inches as the free cross section of the converter liner (allowing for standpipe and thermowell), an estimate can he made of the residence time in the hot zone. For those periods during which the entire length of the hot zone is a t reasonably constant temperature and in which the gradient in the preheating zone is comparatively steep, it is possible by this method to obtain a fairly reliable estimate for contact time. An attempt was made t o allow for the reaction occurring during heating to reaction temperature. However, it was found that the reproducibility and accuracy of the data were not high enough to justify
this correction, which was estimated to range from about 0.01 t o 0.04 hour. KOallowance was made for the volume of gas bubbles, as it was found in some experiments, in which air was bubbled through water, that the total time of contact of the liquid was not significantly affected over the range of flows by the gas rate. This indicates that the effective total bubble volume was comparatively small compared with the total vessel volume available to the liquid, and did not change materially with gas rate. T E S T CONDITIONS AND EXPERIMEa-TAL RESULTS
In the first series, operation 180, 11 tests were run on Bruceton coal, as follows: three a t 420' C., three a t 440" C., and five a t 460" C. At each temperature various paste pumping and hydrogen circulation rates were employed. The contact times ranged from about 1 t o 70 minutes, with paste compositions ranging from 35 to 50% coal. I n the second series, operation 182 containing 19 tests, 16 were performed on Rock Springs coal, 1with Bruceton coal, and 2 with no coal. Twelve tests were conducted a t 440" C., 5 at 460" C., and 1 each a t 470' and 480" C. Paste compositions varied between 20 and 45% coal, with most of the tests a t or near the latter value. Estimated contact time in the hot zone varied from about 10 to 80 minutes. Catalysts were used in 28 of the 30 tests; 2 tests were run on an especially clean plant without any added catalyst and with a minimum of residual trace catalysts in the equipment. The catalysts employed were: A. 0.1% stannous sulfide, 0.05% iodoform B. 1%molybdenum trioxide, not supported on fuller's earth C. 1% of a n impregnated fuller's earth, containing 7.5% molybdenum trioxide Percentages are based on gross coal, as used. When employing catalyst A on Rock Springs coal, 0.5% ammonium chloride ~vsts
~
87
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1950
approximate correction was made to the reactor volume otherwise available, in order t o correct for the effect of the coke. About 43% of the free volume was occupied by coke which was regarded merely as a n inert packing. It was thus assumed t h a t its only effect was t o reduce the volume available and hence reduce contact time a t any paste rate. Because of this correction, contact times in tests 8 t o 11, inclusive, of operation 180 are somewhat more uncertain than those for other test periods. I n test 11, operation 180, reaction temperature was barely attained by the time the paste left the hot zone of the second converter. The contact time at reaction temperature, equivalent to the reaction that took place here during preheating, was estimated to be about 1 minute. While the results of this test were not employed in the correlations discussed below, it will be seen that they are quite consistent with those of most of the other tests. The viscosity of the heavy oil obtained in this test, reported at 5200 S.S.F.(Saybolt seconds, Furol) at 180' F. (82 C.), was estimated by determining the viscosity of several blends of this heavy oil with varying quantities of light oil and extrapolating the results t o zero light oil.
added t o neutralize alkalinity of ash. I n the Bruceton coal tests with catalyst A , this addition was not made. How much of the improved liquefaction behavior of the Rock Springs coal when compared with Bruceton coal is due t o this concomitant addition of ammonium chloride is not altogether clear. From earlier semiquantitative work, the indications are that addition of ammonium chloride t o a stannous sulfide catalyst already promoted with iodoform does not have too significant a n effect. More recent small-scale investigations indicate that increased concentrations of halogen-containing compounds tend t o reduce the formation of asphalts when tin catalysts are employed. On the experimental plant scale, the data are insufficient t o demonstrate the presence or absence of this trend. The coals used had the following average analysis, in per cent by weight, dry basis: Rock Springs No. 9, High-Volatile C Bituminous, Catalyst
Bruceton, High-Volatile A Bituminous, Catalyst
5.4 74.1 14.1 1.5 0.9 4.0 2.4
5.3 77.5 7.8 1.5 1.6 6.3 2.1
Hydrogen Carbon Oxygen (by difference) Nitrogen Sulfur Ash Water (as received)
O
CORRELATION OF PROCESS VARIABLES
Summarized test conditions and yield data for operations 180 and 182 are given in Tables I and 11. The values are weighted test averages, with certain batches omitted where necessary because of missing or discordant data. I n Table 11, all values except viscosities and material balance are percentages of moisture- and ash-free coal charged during the pertinent operating period. Contact time, as reported in Table I, for the last 4 tests of operation 180 has been corrected for the reduction in available reactor volume caused by coking of the converters in the early part of test 8, where operation at 460" C. with a 50% coal paste feed was attempted. Temporary breakdown of the paste pump resulted in partial coking of the hot converter system under these conditions. At the end of the operation, the converters were dismantled and the liners removed and cut up into 1-foot lengths. From the weight of coke in each section and its density, an
I n this experimental plant, the authors are concerned primarily with what occurs in the reaction zone of the converters. Their separation of products and the performance of their recycle-gas reconditioning units cannot be used t o characterize the results likely t o be obtained in larger, more efficient industrial-scale fractionators and scrubbers. However, relationships among operating variables in the converters themselves are more amenable t o such characterization. T o make process correlations at converter outlet conditions, it is necessary either to obtain material from this point or t o simulate such material by a weighted blend of the products obtained farther downstream. The authors are interested in the liquid products obtainable by cooling the converter effluent t o room temperature and letting it down in pressure t o atmospheric. A total blend of the plant heavy and light oils obtained during a given operating period apparently closely simulates this material. All of the correla-
TABLE 11. TESTAVERAGE YIELDS~ Soluble Oil DistillDistillable to able to
~
Batches Test InPeriod cluded
Gas Loss
Hydrogen Absorbed
Insolubles Gross
Or:
ganic
Total 300' C.
OPERATION
1 2 3 4 5 6 7 8 9 10 11
111 6 5 6 6 1 5 1 4 4 2
11.4 8.6 7.0 11.2 13.9 20.1 16.1 14.7 12.9 19.5 4.1
6.2 4.9 3.9 4.1 6.3 5.0 5.1 4.6 4.0 8.6 2.9
14.4 16.8 18.4 12.7 13.5 12.9 13.3 14.1 16.4 11.2 54.8
7.7 9.2 11.4 5.6 8.1 7.8 6.0 7.3 6.6 8.9 47.9
80.4 84.9 81.9 83.5 78.5 76.3 76.4 86.4 79.4 70.7 44.5
15.7 19.3 21.6 16.4 26.7 39.8 27.2 22.3 16.5 36.8 -0.6
As-
355' C. 39.6 33.2 34.5 27.2 43.4 53.1 36.5 38.0 30.3 46.7 -0.4
AMaterial Balance,
%
phalt
HzO
HzS
NHz
33.8 15.7 4.3 3.5 4.6 4.0 6 5 6.0 16.2 6.4 13.0
5.7 2.7 3.1 3.8 5.5 8.3 6.8 6.4 5.4 7.6 5.1
1.0 1.1 1.7 1.1 1.1 1.3 1.1 1.1 1.0 1.4 0.5
1.1 0.7 0.7 0.8 1.1 0.6 1.0 0.6 0.7 1.2 0.01
96.7 105.8 96.6 98.5 96.8 97.6 98.0 100.6 100.0 86.6 99.2
0.9 0.7 0.6 0.8 0.9 0.8 0.7 0.7 0.9 0.6 0.8 0.6 0.1 0.8
1.1 0.7 0.7 1.0 1.6 1.3 0.7 0.5 1.4 0.8 1.6 0.5 0.1 0.7 0.1 0.5 0.3 0.8 0.7
96.1 96.3 96.9 94.5 95.0 94.5 96.9 94.5 96.9 97.0 97.3 94.7 95.0 95.3 98.6 99.8 101.0 100.2
Viscosity S S F. a t 180° F.'(82' C.) Heavy Pastoil ing oil H.O.L.D.
180
OPERATION 182 1 -1.0 94.8 35.7 56.5 -1.3 13.1 ,. 2.3 48.6 8.9 11.4 2 2 6:5 35.1 9.2 5.9 85.9 13:s 14.2 25.1 9.8 6.9 82.8 37.8 3 6 8.5 6.1 8.4 52.7 4 5.2 2.2 76.0 5.7 13.2 9.8 5.6 44.7 6 4.5 65.4 58.9 14.3 52.6 13.1 6 -4.1 1.8 5 9.1 3.4 70.0 54.8 6 11.8 2.6 13.2 7.6 8.0 7 9.8 5.5 72.0 36.7 7 4.9 6.4 5 18.4 13.8 26:6 20.4 12.5 16.6 10.6 7.1 76.1 25.3 8 3.7 5 6.1 3.7 59.7 39.8 14.0 27.8 7.2 9.2 -1.6 9 8.3 6 25.0 10.6 12.4 9.2 70.2 33.5 10.6 13.6 7.0 10 13 4.4 71.9 39.0 4.3 18.0 5.8 15.7 11 3 11.5 8.2 22.6 12.3 16.2 24.6 11.3 12 2 11.3 74.6 7.7 4.0 0.5 14b 2 -1.3 -1.0 0.8 -1.3 2.6 -2.5 0.1 7.9 3 34.6 39.0 23.6 15.0 2.4 14.4 15 10.0 9.6 36.5 2.5 -2.3. 1.2 0.1 2 1.4 -1.6 -3.2 1.6 -0.8 166 14.4 26.5 77.4 16.9 18.5 14.6 6.8 11 10.3 8.7 17 33.4 21.5 16.2 11.8 17.5 8.9 7.2 79.5 10.4 18 9 35.5 22.4 14.6 10.9 20.0 11.0 77.9 19 7.0 8 13.4 12.3 20.2 11.4 13.5 5.0 19.5 72.8 25.9 1 19.4 20 a Values are per cent of M.A.F. coal charged, except for material balance and viscosity data. b Reported a8 per cent of total oil feed (no coal used).
i.2 0.6 0.9 0.9
...
30 215 198 164 26 16 18 25 56 28 5200
26 130 157 264 39 28 19 20 46 30 46
98 (S.S.U.) 12 21 22 27
85 13 16 19 22 78 76 25 27 83 65 65 91 40 133 50 22 16 23
77
134 54
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88
43 156 40 ) ; : 2 ( 41 18 15 67
20 210 190 151 26 15 18 23 52 27 4600 11.2 12 21 13.6 13.1 25 134 48 11.4 68 43 156
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.... 41 18 15 57
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Figure 4. Viscosity of Heavy-Oil Letdown as Function of Contact Time and Temperature for Bruceton and Rock Springs Coals SnS and MOO, catalysts
$ions presented in this paper are based on this primary product, designated as H.O.L.D. (This abbreviation, which stands for heavy-oil-letdown, is to be clearly distinguished from the German notation where the term referred to the material removed from the hot catchpot. The authors' term "heavy oil" is equivalent t o the German "H.O.L.D.," while the authors' "H.O.L.D." has the significance defined above.) The blending operation may not actually have been performed in every case, for considerations dictated by plant operation or other requirements, but the equivalent effect that would have resulted from such blending is readily calculated. To study the reactions occurring, changes in a number of variables related t o the composition of the reactants at various points in the plant are used. By operating at different paste rates and lengths (hence volumes) of the hot zone, varying contact times are obtained and the properties of the final product studied as a function of contact time. It is convenient t o visualize a preliminary stage in which the coal first becomes a high-molecular weight complex liquid or semiliquid, which is then converted by hydrogenolysis into simpler materials. Thus, one can anticipate smooth changes, for isothermal reactions, in the properties of the converter burden with contact time after the initial formation of this preliminary liquid phase. REDUCTION O F VISCOSITY
A convenient meamre of the extent of molecular weight reduction is obtained by studying the change in viscosity of the heavyoil letdown with contact time a t constant temperature. Figure 4 shows the interrelationship of viscosity of heavy-oil letdown, type of coal, operating temperature, catalyst, and contact time. The points fall along fairly well defined straight-line isotherms in the range studied. Heavy-oil letdown viscosities for Bruceton coal apparently are considerably higher than for Rock Springs coal. Heavy-oil letdown viscosity of test 11, operation 180, estimated as 4600 S.S.F. at 180" F. (82" C.), obtained in something like 0.02-hour contact time, has not been plotted in this figure.
IC
Figure 5.
Effect of Paste Composition at
440" C. Using Rock Springs Coal
All of the viscosity data for the products from Rock Springs coal at 440' C. with stannous sulfide catalyst, regardless of paste composition, fall along a fairly smooth straight line whose slope changes abruptly a t about 0.5-hour contact time. No attempt has been made t o segregate the high-temperature points for Rock Springs coal with this catalyst; they lie along a single line (with the exception of one point-test 6) although they cover a range in temperatures from 460" to 480" C. The comparison between the stannous sulfide and molybdenum trioxide catalysts is also particularly evident here. At 460" C. the data for Rock Springs coal using molybdenum trioxide as catalyst (tests 19 and 20) are very close t o the 440" C. stannous sulfide catalyst line. Similarly, using this coal at 440" C., the molybdenum trioxide catalyst is seen t o be considerably inferior to the stannous sulfide catalyst for viscosity-breaking reactions, as about three times the contact time is required with the former catalyst t o reach a viscosity of about 18 S.S.F.than with the latter. By comparison of the data for Rock Springs coal without catalyst with that for the same coal using molybdenum trioxide, it is seen that this catalyst has a distinct effect, but not as large aa t h a t of stannous sulfide. Bruceton coal shows trends qualitatively similar t o Rock Springs coal. The low-range S.S.F. values were obtained by measuring viacosity with the Universal tip and converting back t o S.S.F. using an extrapolated conversion plot of S.S.F. versus S.S.U. (Saybolt seconds, Universal). Generally the viscosity of the heavy-oil letdown was determined on actually reblended heavy and light oils. I n those tests where the blend was not made in the plant, the blended viscosity was estimated from the heavyoil letdown viscosities by a modified A.S.T.M. D 341-43 procedure. Viscosities were measured a t 180" F. (82" C.) rather than the 120" F. (49" C.) standard temperature used in the limit a t 120" F. Bunker C viscosity specification. The 300 S.S.F. (49" C.) is equivalent t o about 40 S.S.F.at 180' F. (82" C.) on oils having viscosity-temperature characteristics similar to the authors' products. Oil meeting the Bunker C viscosity requirement can he made from Rock Springs coal a t 440" C., using a 0.3-hour contact time with stannous sulfide catalyst. Similar oils can be obtained from Bruceton coal a t this tem-
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Figure 7. +355” C. Oil as Function of Contact Time and Temperature for Rock Springs and Bruceton Coal SnS and MOOScatalysts
perature in 0.5-hour contact time using this catalyst. All of the product oils meet the flash-point requirement of the specification. ELIMINATION OF OXYGEN
Elimination of oxygen from the coal is a necessary step in converting oxygen-containing coal into comparatively oxygen-free liquid fuel. Study of the variation in oxygen content of the converter burden with contact time provides another means of correlating extent of reaction with operational parameters. It was possible t o differentiate approximately between the removal of oxygen from the vehicle and that removed from the coal alone. Using the two tests without coal at 440’ C. as a basis, an estimate was obtained of the oxygen unremoved from the pasting oil on passage through the converter system. This was applied t o the other tests at 440’ C. with coal to obtain an estimate of how much of the oxygen remaining in the heavy oil in these tests came from the coal itself. The term “net oxygen remaining, per cent of initial in coal,” used as the ordinate in Figure 5, was defined as: (Oxygen in heavy oil) -(oxygen unremoved from vehicle) (Oxygen in coal feed)
x
one fourth of the oxygen remaining in the heavy oil is in the form of distillable material, which could be efficiently separated in a larger plant; hence, the values shown in Figure 5 are somewhat high if they are interpreted to mean oxygen only in an entirely or comparatively unattached form. ASPHALT
In Figure 6, “asphalt remaining,” defined as: Asphalt in heavy oil (Asphalt in pasting oil) (M.A.F. coal)
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All points shown on Figure 5 are for 440” C. and were based on operation 182 alone. Although the data are somewhat scattered, they may be grouped in terms of feed-paste composition and catalyst. It will be seen that molybdenum trioxide is inferior to stannous sulfide in ability t o promote elimination of oxygen from the coal complex. T h e curve for 40% paste and stannous sulfide catalyst shows a break point at 0.5-hour contact time in much the same manner as does the corresponding viscosity isotherm. This may indicate t h a t viscosity-reduction and oxygen-elimination reactions are closely related in the over-all process of coal liquefaction. There are several modes of eliminating oxygen-namely, formation of water, oxides of carbon, t a r acids, or simple oxygenated organic compounds. The evaluation of catalysts and process variables must consider these competing processes before the breakdown of coal can be fully interpreted. Further work on these problems is planned. About
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Figure 8.
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Space Time Yield of Soluble Oil us. Time of Contact in Operation 182
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to stannous sulfide in the reduction of high-boiling coal fragments into distillable material. In general, increasing reaction temperature, longer contact times, and more effective catalysts tend t o reduce the production of higher boiling fractions of the soluble oil. Increasing coal concentration in the paste, with the exception of the 20% paste point, appears in effect t o increase the load on the converters and hence produce higher boiling product oils, other factors remaining reasonably comparable. Because of experimental dispersion, the apparent curvatures indicated in this and some of the other correlations are somewhat doubtful. It would be necessary t o cover a still larger range of contact times as well as to reduce the uncertainty of each plotted point before the exact nature of the isothermal functional dependence of the reduction in nondistillable soluble oil with contact timr was definitely established.
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Figure 9. Effect of Temperature and Contact Time on Hydrogen Absorption Rock Springs coal, 40% paste, and SnS catalyst except where noted
is plotted against contact time for several combinations of coal, reaction temperature, paste composition, and catalyst. (All of the moisture- and ash-free coal is regarded here as potential asphalt.) The uppermost curve is for operation 180, using Bruceton coal and stannous sulfide catalyst The other curves are drawn through points for tests in operation 182. The second curve is for Rock Springs coal at 460" C., 4Oy0paste with molybdenum trioxide catalyst. The third curve is for the same coal a t 440" C., with the stannous sulfide catalyst and 40 to 45% coal in the paste. The lowest curve is a t 460' C. for Rock Springs coal with stannous sulfide, in a 40% paste. The temperature effect for Rock Springs coal is quite consistent, as can be seen from the location of the 470" and 480" C. points. Here the molybdenum trioxide catalyst, even a t 460" C., is seen to be inferior t o the stannous sulfide catalyst at 440" C. It appears that no catalyst a t all was somewhat better than molybdenum trioxide on Rock Springs coal a t 440' C. The point for 20% paste is out of line on this correlation; however, by applying a correction for fraction of coal liquefied and also netting out the change in vehicle and thus basing the ordinate on residual asphalt in the liquefied portion of the coal, the results for the 20,40, and 45% pastes can be correlated in curves similar t o those shown in Figure 5 . The parameter used for the liquefied portion of the coal was (Asphalt in H.O. - asphalt unremoved from vehicle) (M.A.F. coal) (100 - % insoluble yield)
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Figure 10. Effect of Temperature and Contact Time on Gas Loss Rock Springs coal, 4070 paste, and SnS catalyst except where noted
NONDISTILLABLE SOLUBLE OIL
The distillation characteristics of the soluble fraction of the heavy oil afford another criterion for relating reduction in molecular ITeight t o contact time and temperature. It is convenient t o study the nondistillable fraction rather than the distillable material. Figure 7 is a plot showing the reduction in nondistillable soluble oil as a function of contact time, temperature, and paste composition. The uppermost curve is for operation 180, Bruceton coal, with stannous sulfide catalyst a t 420 ' C. The three 'I marked points are for the same feed a t 440' C. with the same catalyst. The second cuive is for treatment of Rock Springs coal a t 460" C. with molybdenum trioxide catalyst. The next two curves segregate, in terms of paste composition (45% coal, 40y0 coal), the runs with this coal a t 440" C. and stannous sulfide catalyst. The final solid curve is for a comparable feed a t 460" C., and the trend with increasing temperature is continued as high as 480" C. The Rock Springs 2070 paste test is badly out of line in this plot. However, this is improved by a correction similar t o the one used in Figure 5, for the effect of vehicle. It will be seen that molybdenum trioxide catalyst is very inferior
+"
TOT4L SOLUBLE OIL
Figure 8 presents data on soluble oil yield as a function of contact time for several isothermal series of tests at particular coal-paste composition-catalyst conditions. Contact time enters into the parameter plotted as an ordinate as well as along the abscissas. Because of the marked dependence of coalhydrogenation reactions on contact time, data plotted in this manner should cluster as shown, especially a t low values of contact time. The isotherms do not extend over sufficiently Ride contact-time ranges t o differentiate clearly between definite variation in space-time yield and experimental dispersion, particularly a t low contact time. At longer contact times, where the effects of other variables become more important, the data fall along a fan-shaped family of curves. The indicated trend with paste composition a t 440" C. for Rock Springs coal appears reasonable. It will be seen that Rock Springs coal again gives results practically identical, in a 40y0 coal paste with molybdenum trioxide catalyst a t 460' C., t o those obtained a t 440 C. with the stannous sulfide catalyst. O
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Figure 11. Sulfur Removal as Function of Contact Time, Temperature, and Paste Composition for Rock Springs Coal SnS and Moo8 catalysts HYDROGEN ABSORPTION AND GAS LOSS
II
Variation of hydrogen absorption with contact time and temperature is indicated in Figure 9. All of the points shown are for a 40% paste using Rock Springs coal and stannous sulfide catalyst except as otherwise indicated. These curves should be regarded as indicative of trends to be expected with changing temperatures and contact time rather than precise quantitative relationships. This figure is based on rather fragmentary data, and insufficient material is available a t present to check the validity of the linear isothermal relationship shown between hydrogen absorption and contact time a t otherwise fixed conditions. The hydrogen-absorption data reported in the text and in Figure 9 are higher than the correct values by some 1 t o 3 percentage units. This condition resulted from small, unlocatable, and hence uncontxollable leaks in the high-pressure system, estimated t o be of the order of 0.1 pound of hydrogen per hour. Figure 10 is a tentative correlation for gas loss with temperature and contact time subject to the same qualifications as listed above for hydrogen absorption. Figure 11 is a plot showing the dependence of sulfur removal on contact time, temperature, paste composition, and catalyst for Rock Springs coal. Molybdenum trioxide is not as effective as stannous sulfide and does not seem to be more effective than no catalyst a t all. The secondary variables depend on imposed operating conditions in an interrelated manner. Figure 12 shows the approximate dependence of hydrogen absorption, hydrocarbon-gas loss, and soluble oil yields on heavy-oil letdown viscosity for Bruceton coal. Although considerable dispersion is present, there is no consistent secondary trend with temperature or paste composition. Data for Hock Springs coal scatter around the indicated bands for Bruceton coal. These bands have been drawn 11 percentage unit wide for hydrogen absorption and *2 percentage units wide for hydrocarbon-gas loss and soluble oil yield. Since more than half of the points lie within these bands, the half-band width is somewhat larger than the probable error of the correlation in each instance. The hydrogen absorption point, which is plotted just off scale, is for test 17, operation 182, while all of the other points are for operation 180. It appears likely t o assume that the hydrogen leakage in the earlier operation, 180, generally was not as great as in the later one. The Oil yield (44’5%) Obtained in test “9 ‘peration 180, has not been included on Figure 12 because only one com-
91
Figure 12. Dependence of Heavy-Oil Letdown Viscosity of Hydrogen Absorption, Hydrocarbon Gas Loss, and Soluble Oil Yield for Bruceton Coal
paratively short test was made under these relatively difficult operating conditions. It appears reasonable t o expect the soluble oil yield to be small at extremely short contact times because insufficient time is allowed for completion of the primary liquefaction process. Consequently, a maximum soluble oil yield should be obtained a t some optimum contact time and this appears t o be indicated by the limited data available. Although it was not the intent of this series of testa t o make elaborate studies on the nature of the organic compounds produced in the product oils, data on t a r acids were obtained from both coals. It was found t h a t some 7 to 8% of the moistureand ash-free coal (either Rock Springs or Bruceton) was converted to crude t a r acids. From characterization studies on Brucetoncoal heavy oils, it is estimated that about 50 to 55% of these crude tar acids boil in the xylenol and lighter range. More detailed data on t a r acids and on the changes in tar-acid yield with operating conditions are desirable and will be obtained. ACKNOWLEDGMENT
The authors wish to express their thanks t o all of the maintenance and operating personnel of the Coal Hydrogenation Section whose efforts in assembling the plant and getting the data made this study possible. Particular mention should be made of: J. Hammond, J. Nana, R. Ramsden, and C. Zimmerman of the maintenance group; W. Wilson, A. Pipelin, J. D’Amico, and S. Weinstein (deceased), shift supervisors for the operations group; and E. McCullough, W. Wolfe, W. Tomlinson, and J. Hoffman, shift foremen for operations. Plant-control analyses were made by J. Lederer and his group. The ultimate analyses were done by H. Cooper and R. Raymond and their associates. R. Friedel and his staff performed the many mass spectrometer determinations. Marie Lytle performed most of the calculations. E. L. Clark and M. Orchin assisted materially in planning the experimental program. LITERATURE CITED
(1) Clark, E. L., Golden, P. L., Whitehouse, A. M., and Storch, H. H., IND. ENG.CHEM.,39, 1555 (1947). (2) Fein, M . L., Eisner, A., Cooper, H. M., and Fisher, C. H., IND. ENQ.CHEM.,ANAL.ED.,11, 432 (1939). (3) Kandiner, H. J., Chem. Eng. Progress, 44,383 (1948). (4) Storch, H. H., Hirst, L. L., Boyer, R. L., Field, J. H., and Kaplan, E. H., U. S. Bureau of Mines, “Confidential Report No. 1 on Heavy Fuel Oil,” Oct. 16, 1943. ( 5 ) Storch, H. H., Hirst, L. L., Fisher, C. H., and Sprunk, G. C., U . S . Bur. Mines, Tech. Paper 622 (1941). RECEIVED September 15, 1948. Presented before the Division of Industrial and Engineering Chemistry at the 113th Meeting of the AMERICAN CHEMICAL S O ~ I E ~ YChicago, , 111.
