I
SIGMUND J. LUKASIEWICZ and GEORGE C. JOHNSON Research Department, Socony Mobil Oil Co., Inc., Paulsboro,
N. J.
Desulfurization of Petroleum Coke Sodium carbonate is added in the calcining step, and later sodium sulfide is leached from the coke with water to yield low-sulfur coke
I
ALTHOUGH
coke made from many petroleum sources contains less than 2% (weight) sulfur, that made from some petroleums contains u p to 7% (weight) sulfur. Two trends in many refineries are toward the use of higher sulfur content petroleums and toward the use of increased proportions of high sulfur content residua as charge to coking units. These trends, in turn, lead to a higher sulfur content in the petroleum coke. One route for reducing the sulfur content of the coke is to reduce the sulfur content of the charge to the coker, either by stock selection or by a desulfurization step. Another route is to process the coke itself. This work concerned the latter alternative. The choice is justified in part because many of the advantages of a coker to the refinery as a whole depend upon using the coker on any and all residua to produce naphtha and gas oil for further processing. Addition of a coker to a refinery increases the production of gasoline and reduces the production of residual fuel oil. Too, the coker makes a low metal content gas oil for use as a charge stock to catalytic cracking. Partial desulfurization of high sulfur content petroleum coke has been achieved in the present work by calcining with sodium carbonate and with related compounds. I n several cases the product coke meets the present specification of 2% maximum sulfur for electrode coke. The process consists of four steps: pulverizing the coke to pass a 60-mesh screen; adding an alkaline reagent-for example, 10% (weight) sodium carbonate; calcining-for example, 1 hour at 1400' F.; cooling, leaching with water, and drying. In an alternate process ( 5 ) , a high sulfur content residual oil is mixed with the alkaline reagent; coked at 900" to 1000' F . ; calcined; cooled, leached, and
H
C F%
I
A 9670 silica glass reactor was used in runs up to 1500° F.; above that temperature a quartz reactor was used A. 8. C. D. E.
Furnace Thermowell Ice bath Liquid receiver Mercury-filled manometer controller
dried. An earlier reported attempt to desulfurize petroleum coke with sodium carbonate gave only slight desulfurization (7). Related treatments have been used with selected coals ( 2 , 3 , 6 ) .
Experimental
Materials. The salts used in this study, with the exception of sodium
F. G.
H. 1.
Magnetic valve W a t e r displacement graduated gas holder Vent Outlet to water reservoir
sesquicarbonate (trona), were reagent grade. Trona was used in two grades: a laboratory preparation and a technical grade product. The high sulfur cokes were prepared in the laboratory from Santa Maria Valley, West Cat Canyon, and Kuwait residua. These coke samples are similar to the coke made in delayed coking operation. Properties of the petroleum
In recent months I/EC has published these ariicles on the desulfurization of petroleum coke, petroleum fractions, and coal chars: Mason, R. B., September 1959, Pt. I, p. 1027. Kirsch, F. W., Shalit, H., Heinemann, H., November 1959, p. 1379. Batchelor, J. D., Gorin, E., Zielke, C. W., February 1960, pp. 161 , 164. Sef, F., July 1960, p. 599.
VOL. 52,
NO. 8
AUGUST 1960
675
Properties o f Charge Stocks
Table 1. S
Source
C
H
Coking Temp.,
Wt. 7 0 N
0
Na
Ash Sp.Gr.
1.53
...
2.4
900
1.08 0.12 0.85 ... ...... ............ ......... ............
1000 916 1036
...
cokes and residual oils are listed in Table I. Equipment. The desulfurizing runs were made at atmospheric pressure in the set-up shown. A 96y0 silica glass reactor was used in the runs up to 1500 F. A quartz reactor, heated by a multiple unit horizontal furnace, was used in runs above 1500 F. Procedure. Weighed amounts of coke and reagent were mixed together and charged to the reactor. The reactor and the transfer lines were flushed with nitrogen. The furnace, heated to the desired temperature, was brought up around the reactor, and timing was begun. From 10 to 15 minutes was required for the furnace and reactor temperatures to equalize. The life of the 96oj’, silica glass reactor was short because of the reactivity of alkali salts with silica. The reactor was replaced after each three runs at 1400’ F. At the end of the run the reactor was cooled and weighed. The coke was poured out, weighed, and transferred to the thimble of a Soxhlet extractor. I t was then extracted with water, dried, weighed, and analyzed for sulfur. The extract water was also analyzed for sulfur. This water was usually green in color, alkaline, and deposited a fine black precipitate on standing; the supernatant liquid meanwhile became colorless.
61
I
I
i 0
u
z
4
d 3
I
2 3
1
m 3
I
2 800
1000 1200 1400 TEMPERATURE,
Maximum desulfurization tained at 1400’ F.
I
I
1600
1800
was
ob-
OF.
M a r i a Valley coke; 60-100 mesh; 20% (weight) sodium carbonate; 1 -hour re-
Santa
action time
676
INDUSTRIAL
OF.
...
Westcatcanyoncoke 7.01 82.80 3.86 2.64 Santa Maria Valley coke 5.64 86.05 2.70 2.93 Batch A Batch B 5.57 Kuwait coke 7.29 Santa Maria Valley 72% residuum 6.41 81.61 10.14 0.85
0.66
...
0.13
1.024
...
Gas was collected over water by an automatically controlled system. The gas composition was determined by mass spectrometry. The minor amount of liquid collected during the desulfurization run was largely water. It was weighed and was not further examined.
Results
petroleum coke (Tables 11, Runs 28 and 29). Hutchings (4) and Boram and Machu (7) also found sodium hydroxide to be effective. Sodium chloride and calcium oxide were relatively ineffective (Table 11, Runs 30 and 31). Repeated treatment of the coke with sodium carbonate resulted in further desulfurization (Table 11, Runs 14, 15, and 32). The stoichiometric amount of sodium carbonate required for conversion of the sulfur in the coke to sodium sulfide is 23.2 grams per 100 grams for the West Cat Canyon coke and 18.4 grams per 100 grams for the Santa Maria Valley coke. Despite this, there was little advantage in using 20 grams of sodium carbonate per 100 grams of coke rather than 10 grams per 100 grams (Table 11, Runs 2, 8, 33, and 34). Poorer results were obtained with only 5 grams per 100 grams (Table 11, Runs 8, 34, and 35). Material Balance. A representative material balance for recoking at 1400 F. was averaged from Runs 2 and 10 to 15 of Table 11.
Process Variables. TEMPERATURE. The optimum temperature for the desulfurization of petroleum coke was In about 1400 F. Results for a coke made Material Grams from Santa Maria Valley residuum are Coke (5.64Y0 S) 100.0 shown. Further details are given in N~zCOB 20.3 __ Table I1 (Runs 1 to 5). Similar results Total 120.3 were obtained with coke made from a West Cat Canyon residuum (Table 11, out Runs 6 to 8). The effects of other procMaterial Grams ess variables were studied at the optimum temperature of 1400’ F. Run 2 of Leached and dried coke (2.86% S) 91.0 Solids from leaching (11.0 grams total) Table I was taken as the base case. Na2Sa 5.3 CRUDE SOURCE. The three crude Other solids 5.7 sources tested-Kuwait and West Cat Liquid (mainly water) 2.5 Canyon as well as Santa Maria ValleyGases (15.8grams total) co 8.1 were all satisfactory (Table 11, Runs 2, coz 3.8 8, 9 ) . HzS 1.0 PHYSICAL STATE. A mesh size of GO or H, and hydrocarbons 2.9 __ less for the coke was preferable (Table Total 120.3 11, Runs 2 and 10 to 12). The sodium a Calculated from the sulfur content of the carbonate could either be mixed with the leach mater. coke or impregnated onto the coke from water solution with no significant difference in desulfurization (Table I, Runs The “other solids” leached from the coke 2 and 13). were rich in sodium. The leached and REACTION TIME. A 1-hour reaction dried coke itself contained only O.26Y0 time gave better desulfurization than (weight) sodium. 0.5-hour reaction time, but 4 hours gave Coking of Residuum with Sodium about the same desulfurization (Table 11, Carbonate. In addition to the desulRuns 2,14, and 15). Heating at 1400° F. furization of coke with sodium carbonate, for 1 hour was about as effective as runs were made with sodium carbonate heating at 1200’ F. for 4 hours (Table 11, added directly to the liquid residuum Runs 2 and 16). prior to coking. The equipment was ALKALINE REAGENT.Other members similar to that shown. A stirrer was of the sodium carbonate family were added to the reactor to maintain intisuitable. Among these were sodium mate mixing of the residuum and sodium sesquicarbonate (trona), sodium bicarcarbonate. The head of the reactor was bonate, sodium carbonate monohydrate, at a lower temperature than the reactor; and sodium carbonate decahydrate this led to more refluxing with consequent (Table 11, Runs 17 to 25). Only slight greater coke yield than when the head desulfurization occurred in the absence was at the same temperature as the reacof added materials (Table 11, Runs 26 tor. and 27). The results (Table 111) show that the Potassium carbonate and sodium hyproduct coke was desulfurized to about droxide were effective in desulfurizing
AND ENGINEERING CHEMISTRY
PETROLEUM C O K E Table II. Optimum temperature of 1400'
Original Coking Temp., Run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Coke Charged
OF.
Santa Maria Valley
1000 1000 1000
West Cat Canyon Kuwait Santa Maria Valley
West Cat Canyon Santa Maria Valley
Product of Runs 14,15 Santa Maria Valley West Cat Canyon
Mixed. commercial.
1000 1000 900 900 900 1036 1000 1000 1000 1000 1000 1000 1000 1000 916 916 916 916 1000 916 1000 916 916 900 1000 1000 1000 1000 14100 916 900 900
F.,
Desulfurizaiion of Petroleum Coke
a t which other process variables were studied, was determined from results of Runs 1-8
Mesh Size of Coke 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 20-60 100-200 < 100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 60-100 65100 60-100 60-100 60-100
Material Added
Amount Added, Wt. %
Na&Oa" NazCOa" Na2C0aa Na2COaa NazCOaa Na2COab Na2COab Na2COab Na2COla Na2COP NazCOP Na2COsa Na2COab NazCOaa Na2COP NazCOsa Tronaa, 0
20 20 20 20 20 20 20 20 23.4 20 20 20 20 20 20 20 28.4 Tronaa, 20, Trona". 0 20 Trona". * 20 Trona". f 20 NaRCOaa 20 NaHCOt" 31.7 NaZCOs HzO" 2 3 . 4 NazCOa 10H20a 54.0
--
None None KzCOa' NaOHb NaCP CaOa NatCOaa NazCOa" Na2COab NadXhb
Impregnated. Laboratory preparation. Average of 1402O and 1418' F.
0
0 20 20 20 20 20 10 10 5
Recoking Temp., Time, O F . Hr. 1215 1405 1527 1600 1763 925 1204 1417 1410 1408 1408 1407 1410 1402 1418 1227 1410 1403 1405 1404 1406 1408 1400 1400 1402 1404 1390 1408 1413 141 1 1413 1407 1400 1405 1405
1.0 1.0 1.0
1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.5 4.0 4.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1.0 1.0 1.0 1.0
Commercial purified needles.
8
Sulfur, Wt. % In charge In product Removal
Coke Yield Wt. %
4.03 2.88 3.54 3.45 3.88 6.97 4.45 3.15 2.63 3.32 2.70 2.32 2.85 3.09 2.88 2.77 1.85 2.56 1.99 2.59 2.30 3.51 2.75 2.79 2.35 4.83 6.37 1.86 1.17 5.06 4.67 1.83 2.92 3.23 5.57
94 91 95 96 98 96 88 85 91 95 90 89 90 91 95 92 91 92 90 91 89 92 91 89 90 92 88 92 90 92 95 97 89 85 86
5.64 5.64 5.64 5.64 5.64 7.01 7.01 7.01 7.29 5.64 5.64 5.64 5.64 5.64 5.64 5.64 5.64 5.57 5.57 5.57 5.57 5.64 5.57 5.64 5.57 5.57 7.01 5.64 5.64 5.64 5.64 2.98 5.57 7.01 7.01
'
60-100 mesh: oommercial.
29 49 37 39 31 1 37 55 64 41 52 59 50 45 49 51 67 54 64 54 59 38 51 51
58 13 9 67 79 10 17 39 48 54 21 f
Below 200 mesh; I
0
the same extent when sodium carbonate was reacted with residuum as when reacted with coke; a n optimum temperature of about 1400' F. existed as before; a large volume of hydrogen sulfide was evolved without reacting with sodium carbonate. I n Run 41 the sodium carbonate was added during the coking
operation at 880' F. to secure dispersion of the sodium carbonate without substantial desulfurization (compare with Run 36). The coke-sodium carbonate mixture was then heated to 1400O F. to effect desulfurization. This procedure eliminated the crushing step before recoking.
Acknowledgment
The authors express appreciation to
J. J. Dickert and D. S. Henderson for their consultation and for obtaining portions of the data. Literature Cited
~
Table 111.
~~
Adding Sodium Carbonate to Residuum before Coking Was as Effective as Addition after the Coking Step"
Temp.,
Run
NaZCOa, Grams/100 Grams Residuum
36 37 38 39 40 41b
20.6 20.0 20.2 20.7 5.3 3.6
916 1200 1404 1488 1401 880 1405
O
F.
Coke Yield, Wt: 70 of Residuum Charged
Product Coke, Wt. %
22.4 16.6 13.9 12.4 10.1
5.16 3.27 2.63 2.96 3.15
... 19.7
S in
3.43
Santa Maria Valley residuum amounting to 72 wt. % ' of crude; 6.41 wt. 70sulfur; all runs for 1.0 hour. Santa Maria Valley crude; 4.65 wt. % sulfur.
(1) Boram, M., Machu, W., Petroleum (London) 22, 359 (1959). (2) Chowdhury, J. K., Datta, P. B., Ghosh, S. R., J. Sci. Ind. Research (India) IIB,
146 (1952).
(3) Ghosh, J. K., Brewer, R. E., TND. ENG. CHEM.42, 1550 (1950). (4) Hutchings, L. E. ( t o Pure Oil Co.), U . S. Patent 2,878,169 (March 17, 1959). (5) Johnson, G. C., Lukasiewicz, S. J. (to Socony Mobil Oil Co.), U. S. Patent 2,921,017 (Jan. 12, 1960). (6) Lowry, H. H., ed., "Chemistry of Coal Utilization," Vol. I, p. 448, Wiley,
New York, 1945.
(7) Sabott, F. K., Quart. Colo. School Mines 47, NO. 3, 1-22 (1952).
RECEIVED for review January 4, 1960 ACCEPTED April 29, 1960 VOL. 52,
NO. 8
AUGUST 1960
677
