HYDROTREATING T O PRODUCE HIGH VISCOSITY INDEX LUBRICATIhlG OILS H A R O L D B E U T H E R , R . E. DONALDSON, A N b A.
M . H E N K E
Gulf ReJearch @ Development Co., Pithburgh, Pa.
A process for converting untreated petroleum fractions to unusually stable, high viscosity index oils combines hydrogenation with controlled hydrocracking to give high selectivities to motor oil fractions. Yields are 10 to 50% greater than by solvent extraction. High yields of oils having viscosity indexes of 120 t6 125 can b e obtained from most crudes. Data are shown for Pennsylvania, Kuwait, West Texas, and Ordovician. These new oils have very excellent colors and low carbon residue and sulfur contents regardless of their crude source. They show good stability a t high temperatures (725” to 750” F.), good inhibitor response, and oxidation stability; turbine oils showed twice the oxidation stability at one half the inhibitor dosage as a highly solvent-treated oil.
the past decade considerable interest has developed in the catalytic finishing of lubricating oils, using hydrogen. Several articles (7, 6-9, 77, 72) have described such processing, and a n u m b e r of commercial plants (73) have been put into operation. These operations are generally carried out a t moderate pressures and replace the conventional acid and/or clay treating processes normally employed as the final processing steps to produce finished lubricating oil base stocks. These processes are intended to improve color, color stability, and oxidation stability, a n d to reduce neutralization number a n d the level of trace contaminants-Le., sulfur, oxygen, a n d nitrogen. Such “hydrofinishing” operations d o not, however, saturate aromatics or hydrocrack. As a result, viscosity index improvement is small o r negligible and results only from molecular rearrangement due to desulfurization arid denitrogenation. By the use of higher severities (4, 5) and specific catalysts (2, 3 ) it is possible to saturate most o r all of the aromatics and to hydrocrack the condensed structures to high viscosity index lubricating oil constituents. This type of operation, hydrotreating, is a combination of hydrogenation, hydrocracking, and isomerization which is controlled to allow a n efficient conversion of raw petroleum distillates o r deasphalted residua to lubricating oils of exceptional quality without prior solvent extraction o r acid treating. As far back as the early 1930’s hydrogenation of lubricating oil stocks was reported (74), but only recently has the concept of producing multigrade lubricating oils been proposed. Improved catalysts have allowed processing a t high efficiencies with a long catalyst life a n d easy catalyst regeneration. From crudes having lubricating oil fractions in the viscosity index range of 7.5 to 100, one can readily produce 10W/20 and 20\.1;/ 30 base oils Lvhich require n o viscosity index improver, a n d 10\1.’/30 oils Lvhich rrquire but a modest amount. From almost a n y oil fraction regardless of sulfur content or viscosity index a good quality, stable oil in the 95 to 110 VI range can be produced by hydrotreating. T h e process for producing such oils is drscribrd in this report, a n d d a t a are given for typical hydrotreating operations carried out on charge stocks from several crudr sources. IJRING
Process Flow and Operation
A simplified process flow diagram for the hydrotreating of lubricating oils is given in Figure 1. T h e hydrotreater charge stock consists of a mixture of distillate oil and deasphalted 174
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P R O D U C T RESEARCH A N D DEVELOPMENT,
residue, in proportion varying with the product distribution and quality required. For producing a 105 VI oil from Kuwait crude, the ratio of distillate to deasphalted oil is about the same as from the crude. If a 125 V I oil is required, however, the charge stock must be largely o r solely a deasphalted oil. Inspection data on charge stocks to hvdrotreating. a deasphalted residue and a distillate oil from Ordovician crude are shown in Table I. T h e charge stock is hydrotreated over a catalyst having aromatic saturation. ring scission. and isomerization activity. A particularly effective catalyst is one comprising a mixture of nickel sulfide and tungsten sulfide with a nickel-tungsten ratio of 1 to 4 (4) Such a catalyst is prepared by treating a mixture of ammonium thiotungstate a n d nickel nitrate with sulfuric acid. This product is then dried and roasted a t 750’ F. in the presence of hydrogen and hydrogen sulfide. More recently supported catalysts have been developed which are lower in cost And completely regenerable. Saturation o r hydrogenation activity is required of the catalyst to eliminate essentially all impurities, such as sulfur. oxygen, and nitrogen, a n d to saturate aromatics. Ring-scission activity is required to produce high viscosity index oils having, in general, a noncondensed naphthenic ring structure. T h e reactor conditions must be severe enough (generally 1000 to 3000 p.s.i.g. and 650’ to 7750 F ) to saturate the high-boiling aromatics. The
Vd
‘ o u ~ ~ u ~ ~ D uDISTILLATE c E D OIL
BASOLINE
ASPHALT
I.
DEASPHALTER
2.
HYDROTREATER
8.
ATMOSPHERIC S T I L L
I
T
EAVY BLENDINQ OIL
1
SLACK WAX
Figure 1 .
Hydrotreating process flow diagram
,
Table I.
Hydrotreater Charge Stock Hydrotreuter~C_h_g_e_Stocks _ Dmsbhalted Dzstillate iesiduurn oil
Yield, c;C of crude Inspections Gravity, ' API Viscosity, SUV, sec. 210" F. Viscosity index Carbon residue, Conradson, 7c Flash point, F. Fire point, O F. Pour point, F. Iodine No., mod. Hanus
Table II.
Table 111.
9.8
23.2 149.4 95 1.6 590 680 +go 13.0
25.2 55.1 95 0.20 .540 615 +loo 12.4
Base Oils from Hydrotreatment of Ordovician Deasphalted Residuum 70W i 20 20TY/30
Rase oil Yield. vol. Yc of charge Composition. yc Liqht blending oil Heavy blending oil Inspections Viscosity, SUV, sec. 0" F. (extrapolated) 100" F. 210' F. Viscosity index Iodine No., mod. Hanus Color. ;\STM CTnion Carbon residue, Conradson, Total nitroqen. p.p.m, Pasic nitrogen. p.p.m. Sulfur.
4.9
70
yc
19.8
37.0
62.0 38.0
22.1 77.9 27,500 425 65.0 120 1.5 1.75 0.04
10,000 208 49.2 122 1.8 1. o
50
b.0 n
1
40
51 9 122
x
---I
I (VISCOSITY
INDEX]
1O\V ,'20
Yield, vol. S;iC of base oil Gravity. .%PI Viscosity, SUV, sec. 0" F. (extrapolated) 2 1 0 " F. Viscosity index
22 9 33 8
80 4 34 9
10.000 48 1 115
10,000 50 1 122
77 1 33 6
19 6 34 1
I10
20\V 30
0.40.60.8
Yield, vol. 7;of base oil Gravity, h P I Viscosity, SUV, sec. o o F. 210' F. Viscosity index
33,700
65 0 115
27,000 65 0 119
2 0 and 20\V:30 can also be changed by varying the viscosity of the charge >tuck to the hydrotreater. C:harge stocks coriaisting of blends of Ordovician dea.qj)halred residuum \ \ i t h from 0 to 507' of a n Ordovician heavy vacuum gas oil \\ere hydrotrcated (Figure 3). 'rhe viacosii) a i 2 1 0 c F, for these charge stocks varied from 1.58 SYS ( n o gas oil) to 104 S C S (5OC& gas o i l ) . -4s the viscosity of the charge stock \\as decreascd a t constant operating conditions. the yield a n d viscosity index of the total base oil increased only 4ighrly lvhile 176
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L-d
PRODUCT RESEARCH A N D
DEVELOPMENT
1.0 1.2
1.4 1.6 1.8
VOL. RATIO IOW/20:20W/30 Figure 4.
Distribution of base oils
0
V a r i e d severities of treating deasphalted residuum V a r i e d amounts of heavy vocuum gas oil in deasphaltedr residuum a t fixed severity
0
rhe ratio of l O T \ - 20 to 20\\' '30 base oil increased rapidly. These t\\o methodv for changing base oil distribution are sho\vn comparatively i n Figure 4. Changing the viscosity of the charge stock at fixed hydrotreating severity affords a n appreciable change in the volume ratio of the 1OTV 20 arid 2OTV 30 basr oils with substantially n o change in the yield of total base oil and compdratively litrle change i n the viscosity index. Increacirig processing temperature \vith a fixrd charge gives a greater increase i n the viscosity index: but the yield of
Mildly Hydrotreated Oils from Various Crude Sources Ptbst Texas Kuzoait ________-_ Hjdrotreated Hjdrotreated Charge base oil Charge base oil
Table V. Crude S o u r c e Fraction
Yield. 101. cG Hydrotreated charge Crude Inspections Grai-ity. .\PI Viscosity. SUV. sec. 210' F. \'iscosity index Iodine S o . , mod. Hanus Pour point. F. Sulfur. 'IC Carbon residue, Conradson, yc Color. ASTM Union O
Ordo~ician Hydrotreated Charge base oil
~-
100 9.9
46.0 4.6
100 12.2
54.5 6.6
100 3.6
65,6 2 4
22 0
32 . 0
20.0
30.5
24.0
30 4
65.9 108 2.8
161 96 13.2 80 0 19 1 86 8-
77 3 109 3 4 -5
