US2321460A - Process for decolorizing mineral oil - Google Patents

Description

June 8, 1943- w. B. cHENAuL'r ETAL 2,321,460

PROCESS FOR DECOLORIZING' MINERL OIL Filed Nov. 6, 1941 Patented June 8, 17943 rnoonss Fon DECoLoRIzING MINERAL oIL William B. Chenault, Wellsville, N. Y., and Albert E. Miller, Westfield, N. J., assignors to Sinclair Reining Company, New York, N. Y., a corporation of Maine Application November 6, 1941, Serial No. 418,002 In Canada November 27, 1940 6 Claims.

This invention relates to the refining of mineral cils, and more particularly, to the decolorizing of mineral oils. The invention provides an eiiicient and relatively inexpensive process for the continuous decolorization of mineral oils and the continuous recovery, reactivation and cyclic reuse of the materials used in, and in connection with, the decolorization of such oils.

Numerous processes have been proposed heretofore and are now in commercial use in which mineral oils are subjected. to the action of decolorizing earths, that is, earths which have the property of removing objectionable coloring matter from such cils. In general these processes employ elevated temperatures in order to obtain eflicient contact between oil and decolorizing earth, and many of these processes elect such contact in the presence of oxidizing atmospheres, such as air. Such processes employing elevated tempera-tures, `generally in the neighborhood of about 500-650 F., whether conducted in an oxidizing atmosphere either intentionally or due to the presence of adventitious air or air liberated from the grains of earth by the elevated temperatures, promote oxidation of the treated oil and of the coloring matter removed from the oil by the decolorizing earth. Oxidation of the treated oil is an obvious objection to these processes. Moreover, modication of the coloring matter removed from the oil and adsorbed by the decolorizing earth which occurs at the elevated temperatures employed in such processes, and which is promoted by oxidation, prevents or renders impracticable reactivation of the spent earth with solvents. In the few instances where reactivation of the spent decolorizing earthfrom such processes may be accomplished with solvents, .large and complex mixtures of expensive solvents are required and even then the reactivated earth is not restored to its original high decolcrizing efliciency. Reactivation of spent decolorizing earth is necessary if such decolorizing processes are to be commercially feasible. Regeneration of spent earth by burning such earth to restore its decolorizing efiiciency is accompanied by destruction of the grains of earth with the production of an excessive quantity of earth too iine for efficient oil-earth separation. Moreover, when such earths regenerated by burning are cooled, air is adsorbed by the grains of earth and this air is subsequently liberated in situ in the oil by the elevated temperature employed in the decolorizing operations.

We have devised a novel process whereby mineral oils may be decolorized with decolorizing earths at moderately elevated temperatures with efficient and effective solvent reactivation of the decolorizing earth and with eiiicient and effective re-use of the decolorizing earth and the materials used in its reactivation. Our process is adapted to be carried out continuously and in a closed system wherein a non-oxidizing atmosphere is maintained so that external disturbing inuences are eliminated. Y

In its broadest aspect our processinvolves admixing the oil to be decolorized with reactivated decolorizing earth wet with naphtha from the iinal washing 'stage of the reactivating treatment hereinafter described, with or without additional naphtha, and heating the mixture in a contact heater to an elevated temperature less than the critical temperature, approximating 450 F. with most oils, at which coloring matter adsorbed from the oil by the earth becomes modied to an objectionable extent precluding reactivation of the earth to a high decolorizing eiciency by eXtraction with the usual color-solvents. This mixture is maintained at an elevated temperature for a period of time adequate to effect the desired degree of decolorization andthe spent earth is thereafter filtered, in a primary deoiling lter, from the decolorized oil with or without intervening stripping `o1 the naphtha present in the mixture subjected to the heating operation first mentioned.

'Ihe primary de-oiling ltration is carried out at an elevated temperature which varies with the viscosity of the oil to be decolorized and with the proportion of naphtha present in the liquid component of the mixture supplied to the filtering operation. The temperature and naphtha content, if any, of` this liquid component are correlated to maintain the viscosity of the liquid component at a value permitting filtration at a high lter rate while avoiding substantial vaporization. Correlation of the temperature maintained in the primary de-oiling lter and of the naphtha content of the mixture supplied thereto so that the liquid component of the mixture will have a kinematic viscosity of 4-6 centistokes at the temperature prevailing in the ltering operation will permit filtration at the desired high lter rates. g

The spent earth separated from the decolorized oil, or from the decolorized oil-naphtha blend, by this initial filtering operation is then reactivated by subjecting it in succession to an initial washing with naphtha, or equivalent oil-solvent, to remove oil retained by the earth, thereafter to an extraction treatment wherein the substantially oil-free spent earth in the form of a slurry is extracted with a suitable color-solvent for adsorbed coloring matter, such as acetone or methyl ethyl ketone, and thereafter to a final washing treatment in which the reactivated earth is Washed with an additional quantity of naphtha to displace at least the major portion of the color-solvent retained by' the earth. The thus reactivated earth wet with naphtha and in some instances containing a minor but significant proportion of residual color-solvent not removed in the nal naphtha washing treatment, is then slurried with such additional naphtha as may be necessary to form a pumpable mixture and returned to the contact heater first mentioned where it is used in decolorizing additional oil. If desired, the oil-naphtha mixture resulting from the naphtha washing treatment comprising the initial stage of the reactivation, may be returned to the contact heater for recovery of its oil component and further use of its naphtha component.

We have found that when the maximum temperature attained in the decolorizing operation proper, i. e., in the contact heater, is limited to a value less than about 200 F., adequate decolorization may be obtained if the contact treatment is effected when the oil is diluted with a relatively large amount of naphtha Varying from 25% to about 150% naphtha by volume on the oil depending on the viscosity of the oil being treated, and that at this relatively low temperature modification of the adsorbed coloring matter occurs, if at all, to an extent so negligible that the spent earth may be repeatedly reactivated by the above described procedure to a decolorizing efhciency not significantly different from vthat of the original decolorizing earth. In this relatively low temperature and high naphtha dilution form of operation, the color-solvent may quite readily be removed almost completely from the reactivated earth in the final naphtha wash- 'ing stage of the reactivating operation. Accordingly', in this type of operation the trace of residual color-solvent remaining in the earth returned to the contact treatment is insignificant in that it does not appear to involve a significant loss of color-solvent and has no noticeable adverse effect on the decolorizing operation, a circumstance perhaps due in part to the low temperature, to the relatively high ratio of decolorizing earth to oil, and to the relatively large volumes of naphtha employed as a consequence of the relatively high earth to oil ratio. That modification of our invention involving the use of very low temperatures and extreme dilution is described in detail in our application, Serial No. 295,706, filed September 20, 1939.

One objection to this very low temperature embodiment of our invention lies in the fact that the activity of the decolorizing eartlis is greatly reduced at temperatures lower than 200 F. and this circumstance not only increases the amount of decolorizing earth required to treat a given amount of oil, but it also involves an increase in the size and cost of the equipment employed to carry out the decolorizing and reactivating operations together with a corresponding increase in the materials used in the reactivating treatment.

The activity of most decolorizing earths increases rapidly with increase in temperature and we have found that if the earth-'oil mixture is heated in the contact heater to a temperature of 250-400 F. the desired degree of decolorization can be effected in the absence of excessive naphtha dilution in a time no longer than that required to heat the oil to this temperature even though the amount of earth incorporated in the oil is less than of that required to obtain the desired degree of decolorization with similar oils when the vmaximum temperature is maintained at a value less than 200 F. We have also found that modification of the coloring matter adsorbed by the earth, which accompanies an increase in the temperature up to a critical value approximating 450 F. with most oils, is not of a character that precludes reactivation of the earth to a decolorizing efficiency at least closely approaching that of the original earth by the procedure herein described. However, when using these higher temperatures and the lesser proportion of decolorizing earth thereby made permissible, there is some modification of the adsorbed coloring matter and a somewhat more rigorous extraction with the color-solvent is required. Moreover, it appears to be more dicult to remove color-solvent retained by the earth Without excessive naphtha washing. In any event, we have found that in such higher temperature operations the residual color-solvent may reach a value as high as 3% by weight on the reactivated earth unless excessive naphtha washing is employed.

With the lesser amount of naphtha required as a diluent and lesser proportion of decolorizing earth permissible when using higher temperatures, the minor but nevertheless significant amount of residual color-solvent retained by the earth in the absence of excessive naphtha washing in the final stage of the reactivating treatment may thus become an undesirable factor of significant proportions in that it tends both to involve a significant loss of the relatively costly color-solvent and, by its presence during the decolorizing operation, to impair the decolorizing efficiency of the earth by opposing its decolorizing action. However, in that form of our process wherein relatively higher temperatures are utilized to obtain high decolorizing activity and to permit the use of smaller proportions of decolorizing earth, and wherein excessive naphtha washing is not resorted to in the final stage of the reactivating treatment, both of the abovementioned undesirable effects are avoided by stripping the residual color-solvent from the mixture as discharged from the contact-heater prior to separation of the earth from the oil. Such stripping advantageously may be effected by the contained heat of the mixture, that is by flash distillation, and it may be effected in one or more stages. By such procedure the oil remains in contact with the decolorizing earth at an elevated temperature after separation of residual color-solvent and during the period immediately preceding separation of the earth from the decolorized oil. Accordingly, the presence of a relatively small proportion of residual color-solvent in the earth while heating the earth-oil mixture to the temperature attained in the contact heater is not particularly objectionable.

If desired, the naphtha content in the mixture undergoing heating in the decolorizing operation proper, as well as any residual color-solvent, both may be flash stripped prior to separation of the earth from the oil. By so doing the oil is obtained directly from the initial filtering operation in finished form. This procedure is particularly desirable when treating unstable oils. When the earth is separated from the oil before complete stripping of the naphtha it is necessary thereafter to distil off residual naphtha to obtain the decolorized oil in finished form and such distillation, effected in the absence of earth, causes a significant color reversion with unstable oils necessitating a final brightening treatment wherein the oil is again treated with fresh decolorizing earth.

When it is desired to strip completely both residual color-solvent and naphtha from the oil prior to separation of the earth therefrom, it is advantageous to employ a two-stage stripping operation wherein residual color-solvent is stripped in the first stage together with such proportion of the naphtha as it may be necessary to remove in order to insure complete stripping of the-residual color-solvent. The remainder of the naphtha may then be stripped in the second stage with the aid of reduced pressure and steam. Steam should not be used to assist the stripping operation when employing only one stage or in l the first stage of a two-stage stripping operation,

in order to provide for recovery of the residual color-solvent uncontaminated by moisture.

A desirable embodiment of that form of the process of our invention wherein residual colorsolvent and naphtha both are stripped from the oil by an eicient two-stage stripping system prior to separation of the earth from the decolorized oil so that the decolorized oil is directly obtained in finished form is described in our application Serial No. 313,878, filed January 15, 1940.

When treating either an oil that is relatively stable or an oil containing coloring matter of a character that is modied to an undesirable extent by moderately elevated temperature, it usuall;7 is undesirable to attempt to strip completely both residual color-solvent and naphtha from the decolorized oil prior to the separation of the earth therefrom. In order to effect such complete stripping by the contained heat of the mixture discharged from the contact heater it usually is necessary either to heat to a temperature upwards of 400 F. or to resort to an excessively reduced pressure in the stripping operation. This relatively high temperature s higher than is required to eiiect adequate decolorization if the heat requirements of the stripping operation are ignored. Yet a temperature exceeding 400 F. modifies the character of the adsorbed coloring matter contained in certain oils to an extent precluding solvent reactivation of the decolorizing earth to a decolorizing eiciency even closely approaching that of the original earth.

Moreover, even with an oil which does not contain coloring matter of a character susceptible to such extreme modification, an appreciable modification of the adsorbed coloring matter nevertheless occurs at a temperature as high as 400 F. Accordingly, the use of a temperature higher than that required to secure adequate decolorization, solely for the purpose of supplying the heat requirements of the stripping operation, involves an unnecessary reduction in the average decolorn izing eiciency of the reactivated earth with a corresponding increase in the amount of earth required, a sacrifice which is not necessary when the oil being treated is sufiiciently stable to resist signiiicant color reversion when completing the stripping operation after separation of the decolorizing earth from the oil.

Even in the unusual case where the oil is not suiciently stable to resist significant color reversion when stripping after separation of the earth, and when the coloring matter contained in the oil is of a character which undergoes a substantial undesirable modiiication at the lowest contact heater temperature which will permit com'- plete stripping of the naphtha prior to separation of the earth, that form of our process which avoids the higher temperatures incident to complete flash stripping of the naphtha prior to separation of the earth from the oil but in which intervening stripping of residual color-solvent is nevertheless obtained, may be employed satisfactorily. In such a case one may merely employ a slight excess of the decolorizing earth so as to decolorize the oil to an extent greater than that desired in the iinished oil and thus allow forvthe color reversion which occurs'in the final stripping operation.

In that form of our process in which the maximum temperature attained in the contact heater is maintained at a value high enough to obtain rapid decolorizing action Without resorting to excessive naphtha dilution, and high enough to effect complete stripping of the residualr colorsolvent contained in the mixture subjected to heating in the decolorizing operation proper, but not high enough to permit complete stripping of the naphtha by the contained heat of the oil prior to separation of the spent earth from the oil, it may be necessary to cool the bottoms fraction from the stripping operation to avoid difn ficulties incident to substantial vaporization, in the primary deoiling filter, of the naphtha component of the mixture supplied thereto. When naphtha is present in the mixture supplied to the primary deoiling filter, the filter temperature should be maintained at F.-180 F. preferably about 175 F. At these temperatures the naphtha content of the bottomsV fraction discharged from the stripping operation may not be high enough to produce a viscosity suitable to permit the desired filter rates. In such cases additional naphtha may be introduced to theV bottoms fraction prior to its introduction into the primary deoiling filter. Such additional naphtha may be supplied at a relatively low temperature and may be used to provide all or a part of the cooling where both coolingfand further naphtha dilution are necessary. Naphtha for such dilution may be obtained from an extraneous source or from'other parts of the combined oil-decolorizing and earth-reactivating system. However, the naphtha used for this purpose should not contain color-solvent. Therefore, the mixture of color-solvent and naphtha flash stripped from the hot mixture discharged from the contact heater is not suitable for this v purpose.

The oil-solvents useful in our process include any of the various solvents generally used for this purpose. It is only necessary that the oilsolvent shall be capable of dissolving oil, sufiiciently volatile to be completely separable from the oil by distillation at relatively low temperatures, partially separable by distillation from the color-solvent, and that it have in itself substantiallyno solvent capacity for coloring matter adsorbed from the oil in the earth. We have found that naphtha having an initial boiling point of 250"` F. and an end point of 350 F., is particularly adapted for use in our process.

Moreover, naphthas known as 2,00/300 or 30G/400 F., the proportion of :.-naphtha'will in most instances be substantially less than that required in the very low temperature decolorizing operations previously mentioned. Thus in the treatment of Pennsylvania neutrals using that form of operation in which the reactivated earth is slurried with only enough naphtha to render it pumpable before admixing it with additional oil preparatory to reintroducing it into the contact heater, the percentage of naphtha to oil may be as low as 5% by volume on the oil-naphtha blend. On the other hand, when decolorizing viscous raflinates or cylinder stocks and employing that form of operation in which naphtha washings from the deoiling operation are introduced into the contact heater for recovery of the oil removed from the spent earth, the proportion of naphtha in the oil-naphtha blend supplied to the contact heater may vary from about 40% to 60%, or even higher,

A wide variety of finely-divided decolorizing earths may be used in carrying out the process of our invention. For example, finely-divided fullers earth, activated bauxites, such as Porocel and acid-treated bentonites, such as Filtrol, or Tonsil, may be used. We have found, however, that the snthetic adsorbent decolorizing earth known as Magnesol may be used with particular advantage. Magnesol is a synthetic hydrated magnesium silicate normally obtained by rst preparing a hydrated calcium silicate and then reacting the calcium silicate with magnesium chloride. If Magnesol is used, from 2% to about 16% of the decolorizing earth on a dry basis by weight of oil treated may be used with advantage. We have found 8% to 12% of Magnesol to be particularly advantageous in decolorizing viscous raiiinates when employing a contact heater temperature approximating 350-400 F. These percentages will be somewhat increased when using reactivated clay, the increase depending upon the decolorizing efciency of the reactivated clay. At temperatures approximating 250-350 F. this type of clay has a decolorizing activity exceeding by more than 50% that exerted at temperatures of l50-l90 F., and the activity is further increased with still higher temperatures. When employing a clay such as Magnesol in the treatment of a Pennsylvania neutral, adequate decolorization can be obtained in a time no longer than that usually required to heat the oil to a temperature approximating 250 F. The corresponding temperature would approximate 350 F. in the case of a viscous raffinate or cylinder stock.

We have investigated numerous color-solvents for removing from the decolorizing earth coloring matter adsorbed from the oil, and have found that the lower alcohols and ketones may in our process be used for this purpose with advantage. Thus, methyl, ethyl and isopropyl alcohols and such ketones as acetone, methyl ethyl ketone, methyl propyl ketone and methyl isopropyl ketone may be used advantageously. These solvents either alone or in combination, and preferably in further admixture with naphtha or equivalent oil-solvent, have been found to be particularly efficient in the process of our invention. A mixture of one part of methyl ethyl ketone and two parts naphtha by volume has been used with particular effectiveness. The abovementioned color-Solvents effect removal of coloring matter from spent decolorizing earth at temperatures ranging from atmospheric temperature to about 150 F., or somewhat higher. However, we have found especially eicient results to be obtainable with an extraction temperature of about F. i

Other advantages of the process of our invention will be apparent from thefollowing more detailed description of one specific embodiment of our process with reference to the accompanying schematic drawing which represents diagrammatically one arrangement of apparatus adapted to carry out the process of our invention. In this further description of our process we will describe, for the purpose of illustration, an embodiment of our invention in which Magnesol is used as the decolorizing earth, in which naphtha is used as the oil-solvent, in which a solvent blend comprising one-third methyl ethyl ketone and two-thirds naphtha is used as the color-solvent, in which only a single stage stripping operation is interposed between the contact heater and the primary deoiling filter, and in which the oil-earth solvent mixture in the contact heater is heated to a temperature permitting complete stripping of the color-solvent but in which no attempt is made to completely strip the naphtha component by the contained heat of the mixture discharged from the contact heater.

Referring to the drawing, oil to be decolorized, preferably preheated to a temperature of approximately F. or somewhat higher, is introduced through line I into contact heater feed tank 2 of the enclosed type. The oil is mixed in this tank with reactivated decolorizing earth wet with naphtha and containing a minor amount of color-solvent from sources hereinafter more fully discussed. Continuous mixing and contact are provided by conventional mechanical means, assisted, if desired, by recirculation from the bottom to the top of the tank by means of a circulating pump. The earth-oil-naphtha mixture, in the form of a slurry, is delivered through line 3 into contact heater or heaters 4. In the contact heater, which may comprise a direct fired pipe still, or pipe stills, the temperature of the mixture is raised to an outlet temperature approximating 250-400 F. depending upon the nature of the oil being treated and the temperature required to effect substantially complete vaporization of the color-solvent present, as above described. Under these conditions approximately the desired degree of decolorization is completed by the time the mixture reaches the outlet of heater 4. When more than one heater is employed the heaters may be arranged either in series or in parallel. The hot mixture is then delivered through line 5 into flash tower 6.

The color-solvent contained in the earth supplied to heater feed tank 2 is taken ofi as an overheadvapor fraction from ash tower 6 together with such proportion of naphtha as may be necessary to insure complete stripping of the colorsolvent. This vapor fraction is condensed in cooler 1 and the resultant condensate may be conveyed to the color-solvent recovery unit l0.

The bottom fraction from tower 6 consists of the decolorized oil and the earth contained in the mixture discharged from the contact heater 4, together with such naphtha as is not removed in the overhead from tower 6. This mixture is still at an elevated temperature and further decolorization occurs in the bottom of flash tower 6 where'there is no opposing action by the colorsolvent present in the contact heater 4.

The bottoms fraction from flash tower 6 is conveyed alternatively through line 8, cooler 9 and line I2, or through line 8, by-pass Il and line l2, to primary deoiling filter I3. While passing from flash tower 6 to primary deoiling filter I3 the temperature of the bottoms fraction is reduced to a Value approximating l50180 F.,

preferably about 175 F., if its temperature exceeds this value as discharged from the flash tower. Prior to introduction into the primary deoiling filter I3 which is preferably a continuous rotary vacuum filter, additional naphtha may be added to the mixture through line I9 in a quantity sufhcient to bring the viscosity of the liquid component of the mixture entering the filter to a Value not higher than 40 seconds Saybolt Universal at the temperature maintained in the filter I3 if the naphtha content of the bottoms fraction discharged from fiash tower 6 is less than this value. It will be appreciated that these low viscosities cannot be accurately determined directly and can be ascertained only by actually determining the kinematic viscosities in centistokes and then converting to Saybolt Universal viscosities. At a temperature approximating 175 F. a suitable viscosity is obtained with a blend of which the liquid component comprises approximately 70% oil and 30% naphtha when the oil is a neutral, or 50% oil and 50% naphtha when the oil is a viscous raffinate` By maintaining a temperature approximating l50180 F. in the filter I3, substantial vaporization of the naphtha present may be avoided. Moreover, significant color reversion of the decolorized oil through oxidation by adventitious air is avoided at this temperature.

When the naphtha 'content ofthe bottoms as discharged from fiash tower 6 is high enough to produce the desired viscosity at the temperature prevailing inv filter I3, no additional naphtha need be supplied at I9, andthe requisite cooling, if cooling is required, may be effected in cooler 9. On the other hand, when the amount lof naphtha required to be supplied through I9 is substantial, and when cooling also is required, all of the requisite cooling of the vbottoms from flashtower may be effected in this manner. In either the latter case or when no cooling is required, the cooler may be by-passed as'indicated at II.

In filter I3 the spent decolorizing earth is separated from the naphtha solution of decolorized oil which then passes through line I4 to a stripping still'conventionally illustrated at I5. The filter cake formed in filter I3 may be washed in a section of the filter with naphtha supplied through line 20. The initial washings, containing a relatively large proportion of decolorized oil, may be discharged through line I4 to stripping still I5. Subsequent washings may be returned via lines 28 and 29 to the contact heater feed' tank 2.

In still I5 the principalA filtrate from Afilter I3 should be stripped under a sufficiently reduced pressure or with a sufficient amount of steam to avoid color reversion when the oil being decolorized is relatively stable, such as an oil which has been stabilized by solvent extraction. The naphtha stripped in I5 passes through condenser Il to naphtha storage tank I8 for re-use in the system. The bottoms fraction discharged from I5 through line I6 normally represents the finished decolorized oil; If cloudy, it may be passed through a conventional blotter-paper filter press before passing to finished oil being processed is one of those oils which would be subject toV some color reversion during the step of distilling off the naphtha in I5, the oilV may initially be decolorized to a point slightly beyond the color desired in the finished product in order to allow for the slight color reversion storage. If the oil encountered in the stripping operation. This may be done, for example, by slightly increasing the ratio of decolorizing earth to oil vin the mixture supplied to contact heater 4.

The spent earth separated in the primary deoiling filter i3 passes vla conveyor 2| to deoiling slurry tank 22 where it is reduced to the form of a pumpable slurry with additional naphtha supplied through line 25. This slurry may contain about 20-25.% by weight of spent earth on a dry basis and about %"/5% by weight of naphtha. This slurry is supplied through line 23 to secondary deoiling filter 24 which, like filter I3, also is preferably a continuous rotary vacuum filter. The filter cake which forms in secondary deoiling filter 24 may be subjected to additional washing with naphtha supplied at 30 to remove more completely any oil retained by the spent decolorizing earth. The primary filtrate from filter 24 may be returned to the contact heater feed tank 2 via lines 26, (i9, 48 and 29 for recovery of its oil component and further use of its naphtha content. The secondary filtrate or final washings from filter 24 advantageously are conveyed through line 25 to deoiling slurry tank 22 to, provide the naphtha employed therein.

The washed filter cake obtained from the secondary `deoiling filter 24, comprising approximately equal parts by weight of naptha and spent earth, is removed continuously from the filter and carried by conveyor 21 to spent-earth slurry mix tank SI. Here the earth again is mixedwith a sufficient quantity of naphtha to produce a pumpable slurry containing about 25- 30% by weight of earth, This naphtha may be supplied through line 32. The slurry thus obtained is pumped through line 33 into spent-earth extractor 34 which is )provided` with conventional mixing means whereby the spent earth is extracted by highlyrefcient admixture withv the color-solvent, which, under the conditions just described, may comprise a blend of methyl ethyl ketone and naphtha. The color-solvent blend supplied through line 35 is preferably preheated to a temperature of about--150o F. before introduction into extractor 34. `A temperature of about 100 -l 50 F., and preferably about 130- l50 F., is maintained in extractor 34 in order to enhance the solubility of the coloring matter in the color-solvent, The resulting slurry comprising about l5 20%v by weight of solvent-extracted earth together with naphtha, color-solvent and the coloring matter dissolved therein, then Apasses through line 3S into reactivated earth filter unit 3i. This filter unit may comprise one or more continuous rotary vacuum type filters maintained at an operating temperature of about 100 F. to about F., higher temperatures promoting higher filtering rates with the actual temperature depending to an important extent upon the boiling point of the color-solvent and the vacuum maintained on the filter unit. The major portion of the color-solvent is washed from theV filter cake which forms in 37 by means of naphtha supplied through line 33. Y

The first filtrate from reactivating filter 31, containing a relatively high concentration of color-solvent, passes via line39 to color-solvent recovery unit I 0 in which coloring matter, removed from the treated oil by the earth and dissolved out of the earth by the color-solvent, is removed and discarded. The recovered blend of color-solvent and an appropriate quantityA of naphtha to make up the desired color-solvent blend is discharged from the solvent recoveryunit through line 35, while naphtha in excess of that desired in the color solvent blend is discharged from the color-solvent recovery unit through line 40 and may be either returned to naphtha storage tank I8 or directly supplied to other points in the system where naphtha is required. The iinal washings from lter 31 may be conveyed through line 32 to slurry tank 3l with or Without additional naphtha for use in producing the slurry supplied to extractor 34.

Thewashed filter cake obtained from reactivated earth lter 31, normally comprising reactivated earth of high eiciency containing about an equal amount of naphtha and 0.5% to 1.5% of color-solvent, passes Via conveyor 42 to the reactivated earth slurry mix tank 43 wherein it is worked up into a thick pumpable slurry with additional naphtha supplied from tank I8 via lines 41 and 44. Naphtha for this purpose may be supplied to slurry mix tank 43 as a blend consisting predominantly of naphtha derived from filter I3 via lines 28 and 45 or from lter 24 via lines 2S, 46 and 44. The slurry thus obtained, containing about 28-30% by weight of earth on a dry basis and the balance essentially of naphtha, is then delivered through lines 29 into contact heater feed tank 2 as the source of the decolorizing earth, and at least in part the source of the naphtha to be admixed with the oil to be decolorized to form the earth-oil-naphtha mixture that supplies the contact heater. When additional naphtha is desired in the mixture supplied to contact heater 4 it may be directly introduced into line 29 from naphtha storage tank I8 via lines 41 and 48, or supplied to line 29 as a blend consisting predominantly of naphtha from lter I3 via line 28 or from lter 24 via lines 26, 49 and 48.

Where it is not desired to de-oil the spent earth to a very low oil content prior to extraction of the color solvent, adequate deoiling may be obtained in the primary filter unit I3. Under these circumstances the washed clay cake may be conveyed directly from lter I3 to slurry mix tank 3l via conveyors 2|, 50 and 21. In this simplified arrangement, which may be desirable in small installations, the slurry tank 22 and secondary deoiling filter 24 need not be provided.

It will be appreciated by those skilled in the art that the foregoing description is concerned only with the more essential details of our process and that in practice a system such as that schematically illustrated in the drawing normally will be provided with the usual filtrate receivers, pumps, and the like, which have not been specically illustrated nor described. Similarly, it will be obvious that such elements as the conveyors 2|, 23, 21, 42 and 50, slurry tanks 22, 3I and 43, and lters I3, 24 and 31, should be of the enclosed type to avoid loss of solvents through evaporation. will also appreciate that Where adventitious air and volatile solvents ordinarily might be present simultaneously in zones of elevated temperature, as in the vacuum filters I3, 24 and 31, an atmosphere of inert or non-oxidizing gas, such as flue gas, should be provided. This inert gas may be utilized to blow the filter cake lfrom the filter units.

We claim:

1. In a process for decolorizing mineral oils the improvement which comprises heating the oil to be decolorized, in admixture with a reactivated decolorizing earth wet with naphtha and containinga relatively small amount of a color-` solvent more volatile .than the naphtha andV capable of extracting from the earth coloring matter adsorbed from the oil by the earth, to a temperature upwards of about 200 F. and less than about 450 F. but high enough at least to vaporize said color-solvent substantially completely and to effect approximately the desired degree of oil decolorization in the time required to attain said temperature, discharging the heated mixture into a stripping zone and therein in the absence of moisture stripping at least the color-solvent substantially completely and a part of the naphtha from the mixture by the contained heat of the mixture, filtering the spent earth from a mixture comprising the bottoms fraction discharged from said stripping zone prior to further contact with the color-solvent, reactivating the spent earth by subjecting it `firstly to washing with naphtha to remove oil Those skilled in the art retained by the spent earth, secondly to an extraction treatment in which the spent de-oiled earth in the form of a slurry is extracted withy a color-solvent capable of extracting from the earth coloring matter adsorbed from the oil by the earth, and thirdly to a further washing with naphtha wherein the major portion of the retained color-solvent is displaced from the reactivated earth, and returning the 'reactivated earth wet with naphtha and containing a minor proportion of the color-solvent to the heating operation rst mentioned.

2. The method of decolorizing oil which comprises subjecting the oil in the presence of naphtha to the action of a decolorizing earth at an elevated temperature and for a period of time adequate to effect substantial decolorization of the oil, separating the earth from the decolorized oil, reactivating the separated earth by subjecting it in the form of a slurry to the action of a color solvent capable of extracting from the earth the coloring matter removed from the` oil by said earth, washing the reactivated earth withn naphtha to remove color solvent and coloring matter contained therein, and returning the washed reactivated earth wet with naphtha to the oil-decolorizing operation.

3. The method of decolorizing oil which comprises subjecting the oil in the presence of naphtha to the action of a decolorizing earth at a temperature in the range substantially above atmospheric and up to about 450 F. such as to eiect the desired degree of decolorization during the time the mixture remains at said elevated temperature, separating the earth from the decolorized oil, reactivating the separated earth by subjecting it in the form of a slurry to the action of a color solvent capable of extracting from the earth the coloring matter removed froml the oil by said earth, Washing the reactivated earth with naphtha to remove color solvent and' coloring matter contained therein, and returning the washed earth wet with naphtha to the.

oil-decolorizing operation.

4. A continuous process for decolorizing oil by contact with a decolorizing earth and reactivating the earth for re-use, which comprises heating a mixture of the oil and decolorizing earth in the presence of naphtha to an elevated temperature at which coloring matter contained in the oil is extracted by the earth, separating the earth from the decolorized oil, reactivating Athe separted earth by successive Washings, rst with naphtha, then with a color solvent capable of extracting from the earth the coloring matter absorbed from the oil and then with naphthaL the earth being contacted with the color solvent in the form of a slurry during the second mentioned Washing, and returning reactivated earth wet with naphtha from the last mentioned washing treatment to the heating treatment rst mentioned.

5. The method of decolorizing oil which comprises heating a mixture of the oil and reactivated decolorizing earth in the presence of naphtha and residual color solvent to an elevated temperature for a period of time adequate to effect substantial decolorization, passing the heated mixture to an evaporating zone and there evaporating residual color solvent from the earth-oil mixture While said mixture remains at an active decolorizing temperature, subsequently separating the earth from the decolorized oil, reactivating the separated earth by subjecting it in the form of a slurry to the action of a color solvent capable of extracting from the earth the coloring matter removed from the oil by said earth, washing the reactivated earth with naphtha to remove a substantial part of the color solvent retained by the earth, and returning the reactivated earth wet with naphtha and containing residual color solvent from the last mentioned Washing treatment to the heating treatment lrst mentioned.

6. The method of decolorizing oil which cornprises heating a mixture of the oil and a decolorizing earth in the presence of naphtha to an elevated temperature substantially above atmospheric temperature at which coloring matter contained in the oil is extracted by the earth, stripping naphtha from the heated mixture of earth and oil, subsequently separating the earth from the decolorized oil, reactivating the separated earth by subjecting it in the form of a slurry to the action of a color solvent capable of extracting from the earth the coloring matter removed from the oil by said earth, Washing the reactivated earth with naphtha to remove a substantial part of the color solvent retained by the earth, and returning the washed reactivated earth Wet with naphtha to the heating operation Iirst mentioned.

ALBERT E. MILLER. WILLIAM B. CHENAULT.

Images