US2907708A - Urea-dewaxing of hydrocarbon oils - Google Patents

Description

A. HOPPE ETAL UREA-DEWAXING OF HYDROCARBON OILS oct. 6, 1959 2 Sheets-Sheet 'l Filed May 23. 1956 invult* int Oct. 6, 1959 A. Hoppla` E rAL uREA-DEwAxING oF HYDROCARBON oILs md May 2s. 195e 2 Sheets-Sheet 2 fi Patented Get. 6, i959 United tapes patent @hire UREA-DEWAXlNG E HYDRCARBON OILS Alfred Hoppe and Hermann Franz, Frankfurt am Main, Germany, assignors to Edeleann Gesellschaft rn.b.H., Frankfurt am Main, Germany Application May 23, 1956, Serial No. 586,750

Claims priority, application Germany May 28, `1955 8 Claims.` (Cl. 20S- 25) The present invention relates to the dewaxing of hydrocarbon oils and to apparatus systems suitable therefor. More particularly, it relates to an improved process for the removal of parafnic components from paraffinrich oils so that the pourpoint thereof is increased.

Straight-chain organic compounds form crystalline complexes or adducts with urea per se or urea solutions. Branched compounds and cycloaliphatics such as naphthenes combine in a similar manner with thiourea to form adducts. These reactions are useful in the petroleum industry for the removal of paraiiin waxes, the

adducts being subsequently decomposed for re-use of the adduct forming material after separation from the wax.

For the formation of the urea complex compounds, it is merely necessary to bring the solid urea into contact with straight-chain hydrocarbons. it is advantageous in order to accelerate the formation of adduct to use a solvent for the urea, such as water or a low-molecular weight alcohol. There may also be added an organic liquid which has a good dissolving power for the oil but not for the adduct, so as to dilute the oil and reduce the viscosity thereof. s

So that the formation of the adduct does not proceed too smoothly, it is absolutely necessary for the mixture of oil, urea solution and oil solvent to be intensively stirred and mixed. ln order to obtain oils having a low pourpoint, the time of contact between the urea solution and oil solution must also be sutiiciently long.V For the dewaxing of viscous and paraffin-rich oils which are diluted so that they may be handled more easily, very large units with corresponding stirring devices are therefore required. The stirring capacities and stirring energy required, however, add considerably to the overall cost of dewaxing.

It is accordingly an object of the present invention t0 reduce the size of equipment required for contact of a paratn-containing oil with a dewaxing agent.

It is a further object of the present invention to provide a process for dewaxing oils wherein the energy requirements are kept to a low value.

In accordance with the present invention, it is proposed that the formation of the adduct be carried out in two stages, namely a iirst stage in which the mixture of oil, oil solvent and dewaxing agent is stirred intensively but only -for a short period of time, and a second stage in which the mixture remains for a longer period of time with slight mixing. In this way, it is possible to make the agitators smaller and considerably to reduce the consumption of power. s

If oils which are rich in paraiiin are employed there is obtained in connection with the formation of the adduct a thick paste inwhich the percentage of solids is very high as compared with the percentage of liquid and which can be stirred only wtih diihculty even though it already contains an oil solvent. The mixing and pumping of the mixture can be facilitated by dilution with additional oil solvent. Since large quantities of solvent are involved, however, considerable heat would be neces- Sary to separate the solvent from the ratinatege., the

2 solution of oil in solvent. Accordingly, whatever energy saving was realized by further dilution of the oil would be lost by the additional heat required to distill oif the solvent.

In accordance with a modiiication of the present invention, however, the advantages of additional dilution are realized without increasing the heat requirements for fractionating the raiiinate. To this end, a portion of the oil solution which discharges from the separator upon the removal of the solid adduct is returned to the mixer while only the remainder is passed to the evaporator. The total heat consumption in the evaporator station is thereby not increased while the additional power required for the mixing and the transportation of the more strongly diluted mixture is minor compared to the power necessary to move the pulpy less dilute mixture.

`The return of the oil solution to the .mixture can be eiected continuously and the increased degree of dilution in the mixture maintained both in the mixing stage and in the rest stage. However, it is also possible to dilute the mixture strongly only in the mixing stage and to separate the excess diluent after leaving the mixing stage and before entering the rest stage, return it again to the mixing stage and thereupon conduct the mixture through the rest stage in the ratio of solid to raiiinate solution which corresponds to the quantities of oil used. Since the solid separates almost spontaneously from the ranate solution, it is suiiicient to allow the mixture leaving the mixing stage to settle out for a short time in a settling basin; the solid adduct is then charged with the corresponding quantity of ranate solution through the Zone of rest, while the suiiciently claried remaining raiinate solution is returned to the mixer. In this way the mixture is maintained in stronger dilution only in the mixer and the corresponding mixer circuit. For this purpose, it is necessary to introduce the desired additional quantity of diluent into the mixer only a single time, namely upon starting-up operations. The stirring and rest capacities can therefore be kept smaller, and the paraiiin waxes removed as well as the rafnate will have a homogeneous composition.

in the separation of the solids from the liquid phase two possibilities are available in practice. lf the liquid phase consisting of oil and solvent is of lower specific gravity than the solid, the latter will settle out in the settling basin and pass at the bottom from said basin into the rest zone while the supernatant raffinate phase is drawn oir" at the top and returned to the mixer. If on the other hand the liquid phase is heavier, the solid which now separates on the top is conducted by means of an overiiow into the rest zone and the raffinate solution is withdrawn from the bottom of the settling basin and conducted to the mixer.

In another embodiment of the invention, it may prove advantageous to subdivide the intensive mixing stage into a plurality of agitating stages. The adduct mixture leaving the irst agitating stage lproceeds through further agitation stages before it enters the rest stage, these further agitation stages` cach consisting of a mixing apparatus having an intensive agitator followed by a settling basin.

In this way, Athere is obtained an adduct which is of a sandy grit-like form, rapidly settles out and can be ltered considerably more rapidly and scrubbed considerably more intensively and gives better yields of dewaxed `oil. The reason for the better adduct formation is the intensive mixing carried out in each agitation stage, which ensures the required ne distribution and intimate mixing of the oil and urea solution. Whereas hydrocarbons of low molecular weight require considerable time to form adducts and would otherwise be comi bined only during the rest stage, if at all, by subdivision 3 of the mixing stage it is ensured that these lower hydrocarbons will be removed during mixing.

This presents still another .advantage since the adduct formation is accompanied by 'the liberation of heat,'i.e., is exothermic, and this heat cannot be as readily removed in the yrest stage as in the mixers which are already provided with cooling means.

With a multi-mixing stage operation it is also beneicial to recycle a portion of the lraffinate to reduce the solids:liquid `ratio and thereby reduce the power consumption during transport from the mixer Vto the rest stage. While the re-cycledrainate for each stage could come from the final rest stage, this is uneconomical since the oil in this raffinate has already been dewaxed and brought to the `desired pourpoint. Accordingly, it is preferable to employ the raffinate from each settling basin to be re-cycled to its own mixer.

The invention will now be described with reference t-o the accompanying drawing, wherein:

Fig. 1 is a schematic ow sheet of a dewaxing system with a single mixing stage and a single rest stage; and

. Fig. 2 is a schematic ow sheet of a dewaxing system with three mixing stages and one rest stage.

Referring now more particularly to Fig. l, a mixture of 100 parts oil containing about 150 grams of paraflins per liter, 0 parts of urea solution saturated at 70 C. andvlOO parts of methylene chloride is allowed to flow into a mixer l11 from lines 12, 13 and 14v and is stirred therein. The -mixture passes via lines 15 and 17 and pump 16 into the settling tan-k 18 and then passes to inclined screw conveyor 19 which constitutes the rest stage. Initially, the material passing to conveyor 19 is almost exclusively adduct. The supernatant raffinate solution in ythe settling and clarification tank 18 is conducted, also by itself, via the regulating valve 20 and conduit 21 back rinto the mixer 11 until the desired dilution, i.e., -iiuidity, has been obtained there. After this point has been reached, sufficient raiinate solution is allowed to enter the screw conveyor 19 from the clarification tank 18 to correspond to the oil introduced, i.e., the vdifference between lthe oil constituting the original batch Vand the adduct. In this way continuous operation is instituted, there being received at the end ofthe conveyor 19 the quantities of adduct and rafnate solution which are obtained from the oil introduced into the mixer 11. Thecapacity of the conveyor 19 is greater than that `of the mixer 11 so that lthe dwelling Vtime is greater inthe conveyor than in the mixer.

From the'c'onveyor 19 the mixture of adduct and rafnate solution passes vto a separator 22. Here lthe solid adduct is removed andtranspor'ted by means of a device 23 to the adduct decomposer (not shown) where the Vadduct Vforming agent is regenerated. The raffinate solution obtained in the separator 22 is conducted by pump 25 and pipelines 24 and 27 to be processed for the recovery of the solvent.

If the mixture is to lbe diluted both -in 'the mixing stage and in the rest "stage, -parts of the raffinate solution are 'continuously returned into the -rnixer 11 from the 'separator 22 by means'of pump 25" and line 26; this raffinate solution then passes 'both through mixer 11 and through the tank 18 to returnV to theseparator 22.

A 'In `the operation "schematically illustrated inFig. 2, the mixing stage is subdivided into three agitation stages. A mixture consisting, for instance, of 100 "parts 'of oil containing 120 grams of Iparaffins per liter,` 100 parts of a urea solution saturated 'at 70 C. and 100 parts of methylene 'chloride is allowed to flow into the mixer `11 from-lines z12, 13-andl14 and there agitated vigorously. The mixture -Vof'a'dduct and 'rafnate solution passes via. line 15,1purnp 16 and line :117 into the settling tank 18.' Through branch -28 afpart of the mixture which has previously passed through the turbomixer 29 is returned again to -mixer 11, whereby av closed circuit is formed which affords better mixing. The ranate Separated from the adduct mixture in the settling tank 18 is returned via line 21 to theV mixer 11, the quantity being controlled by valve 20. The mixture leaving the settling tank drops into the second mixer 11a and is thoroughly agitated therein as well as by passage through the mixing circuit comprising line 15a, pump 16a, line 17a, turbomixer 29a and line 28a. The portionrwithdrawn from the mixer circuit passes into the settling tank 18a from whence the separated raflinate is fed Via valve 20w and line 21a back to the mixer 11a.

Another thorough mixing is carried out in the third `agitating stage, which consists of a mixer 11b and a mixing circuit including conduit 15b, pump 16b, line 17b, turbomixer 29b and line 28b and the settling tank 18b with the raffinate return line 2lb and valve 20b. From the settling tank 18b, the adduct mixture passes into the screw conveyor 19, is separated in the separating device 22 from liquid components and discharged via line 23 for further working. The filtrate obtained is removed via line 24 and pump 25 and conducted via line 27'to the evaporator station (not shown) for separation of diluent from the dewaxed oil.

ln the event Athat in the first agitator stage in order to reduce thesolid-liquid ratio, there is used a raffinate 'solution which has already passed through the rest stage, a corresponding portion of this rainate solution is conducted viaconduit 26 into the mixer 11. Of course,'it is also possible to force the washrltrate obtained upon the washing ofthe adduct in the separator 22via line y24', pump 25 and line 26 to the mixer 11; the wash ltrate can then, in Whole or in part, replace the oil solvent.

'This Vprocess need not necessarily be carried out in three mixing stages as described here, but the number of stages can be varied as required. The number of circulation systems belonging to one mixing apparatus can also be increased as desired.

As has lbeen pointed out, adduct crystals easily deposit on variousV places of the apparatus and may form crusts or reduce the cross-section, for instance at the walls of the'vessels, at the agitators or the worms. The deposits are avoided if the surfaces of these substances are maintained smooth, and accordingly these surfaces are either highly polished or provided with a suitable protective coating, for instance, of enamel or plastics.

The nature of the dewaxing agent will of course depend upon the chemical constitution of the materials which it is desired to remove from the oil. Similarly, the diluent will have to dissolve the oil but should not dissolve the adduct. By way of example, with an essentially aromatic oil containing a straight-chain parainic wax an aqueous solution of urea is suitable as the dewaxing kagent lin conjunction With the use of methylene Vchloride as the diluent. The suitability of other materials can readily Vbe determined by reference to solubility tables. v

VVarious changes and modifications can 'be Vmade without departing from the spirit and scope of the present invention and it is intended 'that such obvious changes and modifications be embraced by the annexed claims.

. What is claimed is:

1. The method of dewaxing an oil which comprises vigorouslyagitating for a `short period of time in .a mixing stage, a mixture of a wax-containing oil, a solvent for said oil and an adduct form-ing agentselected from the group consisting of urea and thiourea Vto thereby form an insoluble adduct of said wax and said adduct formingagent, permitting said mixture to settle at least partially into a rafnate phase and an adduct phase, withdrawing aportion of said raffinate and recycling same to Isaid mixing stage to thereby vincrease the fluidity of 'the mixture therein, conveying the balance of 'said' 'ra'inate together with adduct "from said adduct phase to a rest stage, mixing slightly in saidrest stage over :a longer-'period of ytime than-in said mixing stage, and separating said Vadduct from said raffinate.

2. The method defined in claim 1, wherein said wax comprises essentially straight-chain paraffins and the adduct forming agent comprises a solution of urea.

3. The method defined in claim 1, wherein said wax comprises essentially branched paraiins and the adduct forming agent comprises a solution of thiourea.

4. The method defined in claim 1, wherein said oil solvent is methylene chloride.

5. The method of dewaxing van oil which comprises continuously introducing into a mixing stage, oil, a solvent for said oil and urea, vigorously agitating the contents of said mixing stage to thereby form yan insoluble adduct of said urea yand said wax and a rainate of said oil and solvent, continuously withdrawing the contents of said mixing stage after la short dwelling time and permitting at least partial settling, initially passing substantially all of the `adduct formed into a rest stage, continuously withdrawing the contents of said rest stage after -a comparatively longer dwelling time, initially recycling substantially all of said raffinate to said mixing stage to increase vthe fluidity, continuing lsaid recycling until the fluidity of the contents Withdrawn from said mixing stage reaches a predetermined value, and thereafter continuously adding a portion of said rainate to the adduct passing through said rest stage while continuously recycling another portion of ysaid raiiinate to said mixing stage.

6. The method defined in claim 5, wherein said mixing stage is subdivided into a plurality of agitating stages, the mixture of rainate and adduct following each -agitation being permitted to settle land `at least a portion of the settled raflinate being recycled to the respective agitating stage while the balance ofthe mixture is passed on to the next agitating stage.

7. The method of dewaxing an oil which comprises vigorously agitating in a iirst mixer stage a. mixture of wax containing oil, an oil solvent land urea for a short period of time to form an adduct of urea and wax, permitting `said agitated mixture to settle to provide adduct and rainate, continuously recycling a portion of said rainate Ato `said irst mixer stage while passing another portion of said rainate together with said adduct to a second mixer stage wherein Ithe raffinate and adduct are `slightly agitated over an extended period of time, and thereafter separating the adduct from lsaid raffinate.

8. The method of claim 7, wherein said first mixer stage comprises a plurality of successive agitation stages and a settling stage following each agitation stage, and a portion of the raflinate in each settling stage is continuously recycled to the preceding agitation stage.

References Cited in the le of this patent UNITED STATES PATENTS 1,717,780 Imhoff June 18, 1929 2,044,724 Govers June 16, 1936 2,089,215 Lomax Aug. 10, 1937 2,604,430 Skelton et al. July 22, 1952 2,642,422 Gorin June 16, 1953 2,642,424 Gorin et al. June 16, 1953 2,653,123 Kirsch et al Sept. 22, 1953 2,743,213 Backlund Apr. 24, 1956 2,744,887 Dutcher et al. May 8, 1956 2,814,611 Desty et al Nov. 26, 1957

Claims (1)

1. THE METHOD OF DEWAXING AN OIL WHICH COMPRISES VIGOROUSLY AGITATING FOR A SHORT PERIOD OF TIME IN A MIXING STAGE, A MIXTURE OF A WAX-CONTAINING OIL, A SOLVENT FOR SAID OIL AND AN ADDUCT FORMING AGENT SELECTED FROM THE GROUP CONSISTING OF UREA AND TSHIOUREA TO THEREBY FORM AN INSOLUBLE ADDUCT OF SAID WAX AND SAID ADDUCT FORMING AGENT, PERMITTING SAID MIXTURE TO SETTLE ATA LEAST PARTIALLY INTO A RAFFINATE PHASE AND AN ADDUCT PHASE, WITHDRAWING A PORTION OF SAID RAFFINATE AND RECYCLING SAME TO SAID MIXING STAGE TO THEREBY INCREASE THE FLUIDITY OF THE MIXTURE THEREIN, CONVEYING THE BALANCE OF SAID RAFFINATAE TOGETHER WITH ADDUCT FROM SAID ADDUCT PHASE TO A REST STAGE, MIXING SLIGHTLY IN SAID REST STAGE OVER A LONGER PERIOD OF TIME THAN IN SAID MIXING STAGE, AND SEPARATING SAID ADDUCT FROM SAID RAFFINATAE.

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