US2947685A - Catalytic hydrogenation of sulfurbearing hydrocarbon oils - Google Patents

Description

CATALYTIC HYDROGENATION F SULFUR- BEARING HY DROCARBON OILS Jacob Koome and Gerardus J. F. Stijntjes, Amsterdam,

Netherlands, assignors to Shell Oil Company, a corporation of Delaware N0 Drawing. Filed Feb. 11, 1958, Ser. No. 714,497

Claims. (Cl. 208-416) This invention relates to the catalytic hydrogenation of sulfur-bearing hydrocarbon oils boiling at least 90% by volume above 300 C. or above 450 C.

Various high boiling hydrocarbon oils have been hydrogenated under conditions of temperature, pressure and contact time, depending upon the particular catalyst and particular oil feed, to efiect a substantial conversion of the oil to lower boiling products. When carried out with this result such operation is referred to as destructive hydrogenation or hydrocracking. While hydrocracking is a desirable process in some cases, there are cases where hydrocracking is undesired and is avoided, e.g. in the hydrogenation of lubricating oil, transformer oil, etc.

Hydrogenation under conditions where not more than about of the feed oil is converted to lower boiling products is often called non-destructive hydrogenation. There is usually at least a small amount of lower boiling material unavoidably produced, e.g. 2-5 due to a lowering of the boiling point upon extracting a sulfur atom from the sulfur compounds which are normally present in the feed but hydrocracking is suppressed. The process of the present invention is a process of this latter or nondestructive type.

The non-destructive hydrogenation of hydrocarbon oils may be efiected in several ways. In one type of operation, for instance, sulfur-bearing oils are hydrogenated with a catalyst containing a metal or metal oxide which is capable of taking up sulfur from the oil and reacting therewith. In this type of process, which may be called regenerative, the process is stopped as soon as the metal has been substantially converted to the sulfide (which is manifested by the appearance of hydrogen sulfide in the reactor efliuent), the catalyst is re-oxidized or roasted to convert the metal sulfide back to the active oxide or metallic form and a new process period is then started. The process periods between successive oxidations or roastings of the catalyst are normally quite short. Since it is necessary to free the catalyst of oil preceding each oxidau'on or roasting step, it is only practical to operate this type of process when treating low boiling easily volatilized feeds or to ensure that the feed oil, if heavy, is completely vaporized by the use of a large amount of gas.

The more preferred type of hydrogenation process is one in which the oil and hydrogen gas are passed substantially continuously in contact with a fixed bed of a suitable metal sulfide catalyst. The process of the present invention is of this type, referred to as non-regenerative. Thus any regeneration that may be required is only required after a relatively long period of continuous use usually measured in Weeks or months.

When hydrogenating sulfur-bearing oils by this latter or non-regenerative kind of process it is found that as the molecular weight (and hence boiling point) of the feed oil is increased the rate of hydrogenation declines. Thus, when the feed oil is one which boils at least 90% by volume above 300 C., and especially one which boils at least 90% by volume above 450 0,, it is generally oil.

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not possible to elfect the desired hydrogenation at space rates that are economically attractive. In Drennan pat ent, US. 2,365,751, this problem is touched upon (note page 2, column 2, lines 7-15) and it is proposed either to lengthen the reactor or to employ two or more reactors connected in series. This solution amounts to a reduction in the space velocity.

The extent of this difficulty may be seen from the following comparative tests. A West Texas crude petroleum was fractionated to separate four fractions of increasing boiling point as follows:

TABLE 1 Fraction 1 2 3 4 Boiling range, O

TABLE II Fraction 1 2 3 4 Time in Hours 1 300 s.c.fJb 1. 5 400 s.e.f./b 4

1 Taken from a plot of H2 uptake vs. time. 2 During this time fraction No. 1 took up ca 650 s.c.lJb.

The drastic reduction in hydrogenation rate with increasing molecular weight is clearly evident.

When the above fractions were blended in their original ratio and the mixture was hydrogenated under the same conditions it was found that the rate of hydrogen uptake was somewhat slower than the rate calculated from the rates of the individual fractions. Thus, whereas one would have expected 400 s.c.f./ b. of hydrogen to be taken up by the blend in about 6 hours, a time of about 8 /2 hours was actually required. This would indicate that the best results would be obtained by hydrogenating the individual fractions separately.

In the process according to the invention the hydrogenation of heavy oils is effected in a particular Way, referred to herein as the trickle technique. This technique is substantially as described in Hoog patent, US. 2,608,- 521. It is found using the trickle technique under the conditions later set forth that the hydrogenation of heavy oils is materially improved if the heavy oil is hydrogenated in the presence of a suitable lower boiling auxiliary A possible explanation for this unexpected result may be seen from the results of the following tests.

A hydrocarbon oil containing both light and heavy components (boiling range ca 221 C. to above 477 C.) was fractionated into five narrow fractions and these fractions carefully analyzed in detail. A portion of this oil was hydrogenated using the trickle technique in a 2" diameter reactor under the following conditions.

TABLE III Catalyst. 6-14 mesh The product from this hydrogenation was then fractionated as before and the fractions carefully analyzed. From comparison of the analyses of the corresponding unhydrogenated and hydrogenated fractions it was possible to calculate the disposition of the consumed hydrogen. Such calculation indicated that the lightest 20%w of the oil had taken up only about 90 s.c.f./b. whereas the heaviest 20% of the oil had taken up about 640 s.c.f./b. This unexpected result was confirmed in another case with a different oil. This oil was hydrogenated using the trickle technique to a total hydrogen uptake of about 220 s.c.f./b. The higher and lower boiling halves of this oil were carefully analyzed and compared to the corresponding parts of the untreated oil. It was found that the lower boiling half had consumed approximately 70 s.c.f./b. whereas the higher boiling half had consumed approximately 346 s.c.f./b.

As will be demonstrated by examples, the process of the invention allows heavy oils to be hydrogenated more effectively.

The process of the invention is effective for the hydrogenation of various hydrocarbon oils which boil essentially above 300 C., i.e. at least 90% by volume boils above 300 C. It is particularly useful for the hydrogenation of hydrocarbon oils boiling essentially above 450 C., i.e. at least 90% by volume boils above 450 C. Thus it is possible to eifectively hydrogenate the residues remaining after the vacuum or steam distillation of crude oil. These latter oils, if residues, are preferably first subjected to a deasphalting treatment, e.g. with propane and/or butane in the known manner. Another type of material which may be hydrogenated by the process of this invention is a hydrocarbon distillate over 90% of which boils above 300 C. and no more than 20% of which boils above 500 C., e.g. lubricating oil distillates. In the case of these higher boiling oils it is customary to effect the actual distillation under vacuum or with steam to prevent excessive cracking and then to calculate the corresponding boiling points at atmospheric pressure. These higher boiling oils from natural sources normally contain from appreciable to considerable amounts of sulfur compounds and other impurities.

These oils are hydrogenated in the presence of an auxiliary oil having a boiling range entirely or substantially entirely below that of the heavy oil to be treated. The boiling range of the auxiliary oil may adjoin that of the heavy oil without a gap. A slight overlap of the boiling ranges is also possible, e.g. 90% by volume or more boiling below the initial boiling point of the heavy oil. A complete separation of the hydrogenated heavy oil fraction from the auxiliary oil in the treated mixture by fractional distillation is of course impossible in these cases. On the other hand, the separation of the two oils by distillation is greatly facilitated by the use of an auxiliary oil having a final boiling point several degrees, e.g. at least 25 0, below the initial boiling point of the heavy oil thereby form a distinct gap. In any case the auxiliary oil isobtained as a separate fraction and then added to the oil fraction to be hydrogenated. Examples of auxiliary oils having a boiling range entirely or substantially below that of the heavy hydrocarbon oil to be hydrogenated are kerosene, gas oil, and flashed distillate. The auxiliary oil may be produced by the distillation of crude petroleum oils or from similar boiling range materials obtained from oils subjected to thermal or catalytic treatment. The cycle stocks obtained in the catalytic cracking of heavy oil fractions are quite suitable when in the desired boiling range.

The auxiliary oil is preferably a substantially saturated oil, i.e. one which contains little or no olefins or diolefins, and is-preferably a relatively heavy oil, although lighter than the oil to be hydrogenated. The reason for this is that oils boiling below about 200 C. at atmospheric pressure vaporize excessively in the hydrogenation operation thereby increasing the extent of vaporization of the heavy oil and diluting the hydrogen.

While the lower boiling auxiliary oil is essential its amount is not very critical. Thus, for an example, a straight run heavy Kuwait gas oil was hydrogenated using a kerosene (IBP=250 C.) as the auxiliary oil in amounts corresponding to 10, 20 and 30% in the blends. A substantial improvement Was obtained when the auxiliary oil constituted only 10% of the mixture (i.e. 1:9 ratio) but there was little further improvement in the blends containing 20 and 30% of the auxiliary oil. It is within invention to use still higher concentrations of the auxiliary oil up to and including at least 1.25 parts by weight per part of the heavy oil.

The present process is carried out using a catalyst comprising at least one element of group VIII, preferably Ni and/or Co, and one element of group VI of the periodic table of the elements, preferably Mo and/or W, and, if desired, a support, preferably alumina. A particularly suitable catalyst is one containing 5 to 15% of cobalt in an atomic ratio between 1:10 and 9:10 supported on an activated alumina support which may include a small amount (110%) of silica and a trace (0.1-1%) of fluorine.

The metals may be present initially in their metallic form or in the form compounds with oxygen or sulfur. During use they are however present in the form of sulfides. Thus the catalyst may be presulfided or it may become sulfided during the process itself. A preferred pretreatment is to pass hydrogen and a liquid oil containing a large amount of sulfur, i.e. at least 1% S, over the catalyst starting at a low temperature below about C. and then gradually increase the temperature to the desired operating temperature over a period of at least several hours.

As mentioned above, the hydrogenation is effected according to the invention in a particular way called the trickle technique. The mixture of the heavy oil and the auxiliary oil is passed continuously in the liquid phase with gas consisting predominently of hydrogen downwardly through a foraminous bed of the catalyst. The liquid flows down in the form of a thin film on the surface of the catalyst particles. Thus the oil rate should not be sufficiently high to flood the bed.

It is preferred that the oil to be hydrogenated and the auxiliary oil be well mixed and contacted with the gas before contacting the catalyst since this ensures that the oil contacting the catalyst contains dissolved hydrogen. Y

The amount of gas consisting mainly of hydrogen supplied with the oil should be such. that after cooling the reaction product and removing hydrogen sulfide from the uncondensed gas thequantity of the latter gas is at least 50 liters (measured H 8 free at 0 C. and 1 atm.) per kilogram of the heavy oil plus auxiliary oil fed to the reaction zone. This is equivalent to about 240 s.c.f./b. On the other hand, the amount of exit gas is preferably not too large since large amounts of gas insuflicient to effect complete vaporization of all of ,the oil tends to cause vaporization of a large part of the feed .oil leaving a thick tarry material, which does not trickle properly. The quantity of uncondensed gas freed ofhydrogen sulfide leaving the reaction space preferably lies between 50 and 600 liters per kilogram of the oil mixture supplied. This off gas is in part recycled to the reactor preferably after treating it to remove hydrogen sulfide. Sufficient fresh hydrogen is supplied to maintain the hydrogen content in the gas fed to the reactor above about 50%. The hydrogenation is effected at temperatures between 325 and 500 C., more preferably between 325 and 400 C. The operating pressure is in the range of from 10 to 100 atm. and is preferably in the range of from 25 to75 atm. These conditions are correlated such that the oil remains largely in the liquid phase.

After the described hydrogenation treatment the auxiliary oil may be separated from the hydrogenated heavy oil by distillation with or without the use of vacuum or steam. If, as in the preferred case there is a gap, e.g. 25 C. or more, between the boiling ranges of the two oils, this separation may be made quite cleanly. Otherwise there will be some smearing. Such smearing is generally undesired but is not objectionable in some cases, e.g. in the hydrogenation of catalytic cracking feed stock.

When hydrogenating heavy oils according to the process of this invention it is found that the oils are much more deeply hydrogenated at a given thruput rate than if the heavy oil were treated alone using the trickle technique; For example, if a heavy oil is hydrogenated alone using a space velocity of 0.5 kg/L/hr. the extent of hydrogenation as indicated by the percent desulfurization may be in a typical case about 55 to 60% Whereas if a suitable auxiliary oil is added to the heavy oil and the mixture is passed through the reactor at a space velocity of l kg./l./hr. so that the heavy oil is being treated at the same rate as'in the case where it was not mixed with the auxiliary oil, the extent of hydrogenation as indicated by the percent desulfurization is substantially greater, e.g. 70-75%. At the same time a major proportion of the sulfur in the auxiliary oil is removed.

Example I From a Venezuelan crude petroleum a number of distillate fractions and a residue were separated in a conventional manner by distillation at atmospheric pressure and subsequent distillation under vacuum. The residue remaining was deasphalted with butane. The resulting deasphalted heavy oil boiled above 450 C., (90% by volume above 492 C.) and had a sulfur content of 2.73% by weight. This heavy hydrocarbon oil fraction was hydrogenated using the trickle technique and within the conditions specified above. The catalyst was a cobalt-molybdenum-alumina catalyst containing about 3.1% Co and 7.1% M Three carefully controlled test runs (C, D and E) were carried out under the conditions and with the results shown in Table IV. Test runs C and D were performed on the heavy oil as such, the conditions differing only as regards the space velocity. Test run E was according to the invention. To the heavy deasphalted residue there was added a flashed distillate (90% by volume distilled up to 490 C.) in a weight ratio of about 1.25:1. For comparison purposes two test runs A and B were carried out with the flashed distillate in the absence of the heavy oil.

All runs carefully controlled to these values, slight variations were unavoidable.

The hydrogenated mixture of flashed distillate and deasphalted residue obtained in experiment E was separated 6. by distillation into two fractions in the same ratio by weight as in the starting mixture. The flashed distillate was found to have been 93% desulfurizedby hydrogenation, i.e. to the same degree as that attained in the hydrogenation of the flashed distillate separately at the same space velocity (1.0). However, the deasphalted residual oil was found to have been 74% desulfurized instead of 49% which occurred at the same space velocity when there was no previous dilution of this oil with the auxiliary oil. This shows a much greater extent of hydrogenation. Comparison with the results in columns B, D, and E shows that in the case of the combined Example I] The heavy oil fraction treated was a paraffinic lubrieating oil obtained from a Venezuelan crude oil. This fraction had a sulfur content of about 2.11% by weight, an initial boiling point of about 350 C. and 80% by volume distilled over a temperature of about 484 C. (The distillation was carried out under a pressure of 10 mm. Hg and the boiling temperatures measured were then converted to the corresponding value at atmospheric pressure.) This heavy hydrocarbon fraction was then hydrogenated using the trickle technique and Within the conditions specified above. The catalyst was the same cobalt-molybdenum-alumina catalyst as described in Example I.. Three I'llllS (F,.G and H) were carried out under the conditions and with the results shown in Table V. Experiments F and G were made with the heavy fraction as such, the conditions difiering only as regards the space velocity. Run H was according to the present invention. To the heavy fraction there was added a kerosene boiling from 187 to 261 C. (A.S.T.M.) in a ratio of 1:1 by weight. The kerosene contained 0.34% by weight sulfur. For comparison purposes two runs (I and J) were carried out with kerosene in the absence of the heavy oil; the results are also shown in Table II.

The mixture of lubricating oil and kerosene obtained in experiment H was separated by distillation into a kerosene fraction and a lubricating oil fraction.

TABLE V Run F G H I J Lubri- Feed Lubricating eating Kerosene Oil oil Kerosene Sulfur content, percent by weight 2.11 Pressure, kg./sq. cm. 50 50 Temperature, 0... 385 Quantity of HZS-irce gas leaving the reaction space in liters (standard conditions) per kg. of oil 250 250 250 Space velocity, kg./l./hr. 1.0 0.5 1.0 1.0 0.5 S in total quantity of reac 11 product, percent 0.86 0.58 0.14 0.001 0.001 S in lubricating oil, percent..- 0.86 0.58 0.311 S in kerosene, percent 0.007 0.001 0. 001 Total desulfurization, percent. 59.3 72. 5 88.5 I 99 99 Desulfurization of the lubricating oil, percent 59.3 72.5 85.3 Desulfurization of the kerosene,-

percent 97 99 99. 6

The kerosene was found to have been 97% desul furized, i.e. tdsubstantially the same degree as that att ained in the hydrogenation of the kerosene separately at the same space velocity (1.0). However, the lubricating oil was found to have been 85.3% desulfurized instead of 59.3% which occur-red at the same space velocity (1.0) when the oil was not previously diluted with kerosene.

The above data clearly show that when operating according to the invention at a space velocity of 1.0 kg./l/hr. the hydrogenation of the lubricating oil is considerably improved as indicated by the greater percent desulfurization (85.3 instead of 72.5). At the same time the desulfurization of the auxiliary oil (kerosene) is only slightly lower than in the case of the separate treatment of this material at a space velocity of 0.5 kg./1/hr. (97% instead of 99.5%).

We hereby claim as our invention:

1. An improved process for the continuous nondestructive hydrogenation of sulfur-bearing lubricating oil boiling at least 90% by volume above 300 C. but not more than about 2 by volume above 500 0, without conversion of more than about 10% by volume of said lubricating oil to lower boiling products, which comprises the steps of (1) admixing the lubricating oil to be hydrogenated with an auxiliary oil at least 90% by volume of which boils below the initial boiling point of the lubricating oil, the amount of the auxiliary oil being from about 0.10 to about 1.25 parts by weight per part of the lubricating oil, (2) mixing the admixture of lubricating oil and auxiliary oil with a hydrogen-containing gas, (3) passing the mixture of lubricating oil, auxiliary oil and hydrogen-containing gas downwardly through a foraminous bed of a hydrogenation catalyst in a reaction zone, the catalyst comprising as active hydrogenation promoters sulfides of a metal of group VI and metal of group VIII, at a rate insufficient to flood the catalyst so that the oil flows as a film over the catalyst particles, while maintaining the temperature in the reaction zone above about 325 C. but below about 400 C. and the pressure above about 10 atm. but below about 100 atm., said temperature and pressure being correlated to maintain the oil largely in the liquid phase, and the amount of hydrogen-containing gas being such that the eflluent gas from the reaction zone contains between 50 and 600 liters (measured as H 8 free gas at 0 C. and 1 atm.) per kilogram of lubricating oil charged.

2. An improved process for the continuous nondestructive hydrogenation of sulfur-bearing lubricating oil boiling at least 90% by volume above 300 C. but not more than about 20% by volume above 500 C., without conversion of more than about 10% by volume of said lubricating oil to lower boiling products, which comprises the steps of (l) admixing the lubricating oil to be hydrogenated with a kerosene, auxiliary oil boiling essentially above 200 C. and having a final boiling point substantially below the initial boiling point of the lubricating oil, the amount of the auxiliary oil being from about 0.10 to about 1.25 parts by weight per part of the lubricating oil, (2) mixing the mixture of lubricating oil and auxiliary oil with a hydrogen-containing gas, (3) passing the mixture of lubricating oil, auxiliary oil and hydrogen-containing gas downwardly through a foraminous bed of a hydrogenation catalyst in a reaction zone, the catalyst comprising as active hydrogenation promoters sulfides of a metal of group VI and metal of group VIII, at a rate insufficient to flood the catalyst so that the oil flows as a film over the catalyst particles, while maintaining the temperature in the reaction zone above about 325 C. but below about 400 C. and the pressure above about 10 atm. but below about 100 atm., said temperature and pressure being correlated to maintain the oil largely in the liquid phase, and the amount of hydrogen-containing gas being such that the eflluent gas from the reaction zone contains between 50 and 600 liters (measured as H S free gas at 0 C. and 1 atm.) per kilogram of lubricating oil charged.

3. Process according to claim 1 in which the final boiling point of the auxiliary oil is at least 25 C. below the initial boiling point of the lubricating oil.

4. An improved process for the continuous nonde-. structive hydrogenation of sulfur-bearing lubricating oil boiling at least by volume above 300 C. but not more than about 20% by volume above 500 C., without conversion of more than about 10% by volume of said lubricating oil to lower boiling products, which comprises the steps of (l) admixing the lubricating oil to.

be hydrogenated with an auxiliary oil at least 90% by volume of which boils below the initial boiling point of the lubricating oil, the amount of the auxiliary oil being from about 0.10 to about 1.25 parts by weight per part of the lubricating oil, (2) mixing the admixture of lubricating oil and auxiliary oil with a hydrogen-containing gas, (3) passing the mixture of lubricating oil, auxiliary oil and hydrogen-containing gas downwardly through a forarninous bed of a hydrogenation catalyst in a reaction zone, the catalyst comprising as active hydrogenation promoters sulfides of a metal of group VI and metal of group VIII, at a rate insufficient to flood the catalyst so that the oil flows as a film over the catalyst particles, while maintaining the temperature in the reaction zone above about 325 C. but below about 400 C. and the pressure above about 10 atm. but below about atm., said temperature and pressure being" correlated to maintain the oil largely in the liquid phase, and the amount of hydrogen-containin gas being such that the efiluent gas from the reaction zone contains between 50 and 600 liters (measured as H S free gas at 0 C. and 1 atm.) per kilogram of lubricating oil charged, and (4) separating the reacted mixture by distillation into two fractions having boiling ranges substantially similar to those of the original lubricating and auxiliary oils.

5. An improved process for the continuous nondestructive hydrogenation of sulfur-bearing lubricating oil boiling at least 90% by volume above 300 C. but not more than about 20% by volume above 500 C., without conversion of more than about 10% by volume of said lubricating oil to lower boiling products, which comprises the steps of (1) admixing the lubricating oil to be hydrogenated with an auxiliary oil at least 90% by volume of which boils below the initial boiling point of the lubricating oil, the amount of the auxiliary oil being from about 0.10 to about 1.25 parts by weight per part of the lubricating oil, (2) mixing the admixture of lubricating oil and auxiliary oil with a hydrogen-containing gas, (33) passing the mixture of lubricating oil, auxiliary oil and hydrogen-containing gas downwardly through a foraminous bed of a hydrogenation catalyst in a reaction zone, the catalyst comprising as active hydrogenation promoters sulfides of a metal of group VI and metal of group VIII, at a rate insufiicient to flood the catalyst so that the oil flows as a film over the catalyst particles, while maintaining the temperature in the reaction zone above about 325 C. but below about 400 C. and the pressure above about 10 atm. but below T about 100 atm., said temperature and pressure being cor- References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. AN IMPROVED PROCESS FOR THE CONTINUOUS NONDESTRUCTIVE HYDROGENATION OF SULFUR-BEARING LUBRICATING OIL BOILING AT LEAST 90% BY VOLUME ABOVE 300* C. BUT NOT MORE THAN ABOUT 20% BY VOLUME ABOUVE 500* C., WITHOUT CONVERSION OF MORE THAN ABOUT 10% BY VOLUME OF SAID LUBRICATING OIL TO LOWER BOILING PRODUCTS, WHICH COMPRISES THE STEPS OF (1) ADMIXING THE LUBRICATING OIL TO BE HYDROGENATED WITH AN AUXILIARY OIL AT LEAST 90% BY VOLUME OF WHICH BOILS BELOW THE INITIAL BOILING POINT OF THE LUBRICATING OIL, THE AMOUNT OF THE AUCILIARY OIL BEING FROM ABOUT 0.10 TO ABOUT 1.25 PARTS BY WEIGHT PER PART OF THE LUBRICATING OIL, (2) MIXING THE ADMIXTURE OF LUBRICATING OIL AND AUXILIARY OIL WITH A HYDROGEN-CONTAINING GAS, (3) PASSING THE MIXTURE OF LUBRICATING OIL, AUXILIARY OIL AND HYDROGEN-CONTAINING GAS DOWNWARDKY THROUGH A FORAMINOUS BED OF A HYDROGENATION CATALYST IN A REACTION ZONE, THE CATALYST COMPRISING AS ACTIVE HYDROGENATION PROMOTERS SULFIDES OF A METAL OF GROUP VI AND METAL OF GROUP VIII, AT A RATE INSUFFICIENT TO FLOOD THE CATALYST SO THAT THE OIL FLOWS AS A FILM OVER THE CATALYST PARTICLES, WHILE MAINTAINING THE TEMPERATURE IN THE REACTION ZONE ABOVE ABOUT 325* C. BUT BELOW ABOUT 400* C. AND THE PRESSURE ABOVE ABOUT 10 ATM. BUT BELOW ABOUT 100 ATM., SAID TEMPERATURE AND PRESSURE BEING CORRELATED TO MAINTAIN THE OIL LARGELY IN THE LIQUID PHASE, AND THE AMOUNT OF HYDROGEN-CONTAINING GAS BEING SUCH THAT THE EFFLUENT GAS FROM THE REACTION ZONE CONTAINS BETWEEN 50 AND 600 LITERS (MEASURED AS H2S FREE GAS AT O* C. AND 1 ATM.) PER KILOGRAM OF LUBRICATING OIL CHARGED.