US2161569A - Dewaxing hydrocarbon oil - Google Patents

Description

June 6, 1939. H. H. GROSS 2,161,569

DEWAXING HYDROCARBON OIL .Filed Feb. 19, 195s FIGLI.

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` PRIMARY i HILLER FILTER A L I a l SOLVENT MIXER PRIMAgY om o s [l0 APOUR 9 1--1 'f Smm? CHILLER FILTER I J' soLvl-:N-r

SECONDA RY WA X C AKE WAX HOWARD HLGRoss ATTORNEYS Patented June 6, ,'19-39 UNITED STATES PATENT oFFicE DEWAXIN G HYDROCARBQN OIL Howard H. Gross, Beacon, N. Y., assignor to The Texas Company, New York, N. Y., a corporation -of Delaware Application February 19, issa'seriai No. 191,350

s claims.

This invention relates to a method of dewaxing hydrocarbon oil, and particularly to a method of separating wax from wax-bearing. mineral lubricating oil. y

The invention broadly contemplates dewaxing wax-bearing hydrocarbon oil with a selective solvent under conditions of concentration, composition of solvent, and temperature of dewaxing,

such thatthe solid hydrocarbons can be removed from a cold mixture of solvent andV oil by filtration at relatively rapid rates to produce a relatively high yield of dewaxed oil.

The invention has reference to the dewaxlng of mineral lubricating oil stocks to produce therefrom products of low pour test as, for example, having a pour test of around F. and below. It

has particular reference to the dewa'xing `ofI certain types of lubricating oil stock, as Will be more fully explained. v

In more detail, the invention comprises mixing the wax-bearing oil with a relatively small proportion of selective dewaxing solvent liquid. For

example, the oil is mixed with about one to two parts by Volume of the solvent, depending upon the character of the oil. This mixture is then chilled to about the dewaxing temperature and to a temperatureI just above that at which liquid hydrocarbons begin to separate from the mixture. To this chilled mixture, a further quantity of solventl in a prechilled condition is addedso that, ata temperature' of 0d F., the solvent contained in the entire mixture has substantially complete selective action as between liquid an solid hydrocarbons.

At about this temperature, there occurs formation of a liquid phase comprising liquid hydrocarbons substantially free'from solid hydrocarv bons, and asolid phasecomprising solid hydrocarbons. v

The mixture ofdiluted charge and prechilled solvent is chilled-'to a slightly lower temperature 'to cause separationrofva third phase consisting of a mixture comprising petroleum hydrocarbons relatively lean in solvent and composed of oil associated with wax. It is desirable that this third phase be present'in the form of small discrete particles of solid or semi-solid character which impart freefflltering characteristics to the chilled waxy mass. This iinal chilling is usually to a temperature of about 6 to 8 F. lower than the temperature at which incipient oil separation ocurs.

It has been discovered that, in the case of certain'types of wax-bearing oil, by having a. small amount of this third phase materialpresent during dewaxin'g, the rate at which the precipitated solid lhydrocarbons can be .removed from the Ychilled mixture by filtration is'very substantially increased. For example, thefilter rate may be increased by 10 to -30% from that normally obtaining in the conventional dewaxing procedure.

This improvementl in filtration rate obtains where the precipitated solid hydrocarbons contain a small amount of this third phase, which is relatively lean in solvent and comprises hydrocarbon particles having a discrete or individually distinct crystalline character at the dewaxing temperature. These particles act as a filter-aid and appear to be a mixture of oil and wax. The resulting precipitated waxy mass is of a much more free-filtering character than when these particles are absent.

, The selective solvent used in practicing the invention advantageously comprises a mixture of an oil solvent such as benzol and `toluol and a wax lanti-solvent, such as acetone and methyl ethyl the mixture chilled to a temperature of from `1 to 10 F. below the temperature at which incipient oil separation occurs, a small amount of va third phase is formed comprising hydrocarbons and solvent containing not less 4than about 40% of petroleum hydrocarbons and amounting to around 1% to10% by volume of the undiluted wax-bearing oil. Lubricating oil stocks `of the type in question comprise distillate lubricating oil fractions of medium and heavy viscosity, for example, ranging from around 40 to 50 seconds to 100 01"-120 seconds Saybolt Universal at 210 F.

Examples of such distillates are those derived ,from Pennsylvania, `Kettleman Hills, Mid-Continent and Rodessa crud'es. The process is particularly applicable to the dewa'xing of lubricating oil stocks .whichhave been previouslyrened by solvent extraction to remove the low viscosityindex constituents. v

It is applicableA also to residual fractions provided the desired type of third phase is present, as maybe the case with lighter residual fractions which contain av relatively large proportion of neutral oils. y, l

The third phase material previously mentioned Vis distinct from the main body of wax-free oil dissolved in solvent',` and it is' distinct from thev main body' of solidified wax. On the otherhand,

it is to be contrasted with the type oi third phase also relatively lean in solvent, and whichmay be obtained under somewhat similar conditions from certain types of oil, particularly certain'y heavy residiual lubricating oil fractions. o

4The third phase which may be formed in the case of the latter type of oil is of a sticky character. It does not comprise particles of distinguishable crystalline character. For this reason its presence actually impedes ltration.

Moreover, the type of third phase having the desired iilter-aid characteristics is to be contrasted with the type of third phase which is relatively lean in solvent liquid and which occurs under certain other conditions of solvent vcomposition and dosage for a particular stock. A third phase rich in solvent does 4not give the desired improvement in iilter rate.

The conditions which give rise to a third phase lean insolvent and one rich in solvent may be explained by reference to the curve shown in Figurel 1 of the drawing andshowing the miscibility temperatures for a distillate lubricating oil fraction with diiertent amounts of solvent.

The distillate is one of about 100 Saybolt Universal seconds viscosity at 210. F. such as derived from arnixed-base crude previously dewaxed to a pour test of around 0 to 5 F. 'I'he solvent consists of a mixture of equal parts by volumeof methyl ethyl ketone and commercial -benzol known as 90% benzol.

The values represented by this curve are ob tainedby dissolving samples of oil in different quantities of the solvent mixture and gradually cooling the resulting solutions until the appear- `ance of a cloud occurs. The temperature at which thiscloud appears is the point, at which there is incipient separation of oil from the so- It is possible between a condition of incipient oil separation and incipient wax separation; -The separation of wax is characterized by a translucent h aze consisting of a ne, iiocky, non-striating precipitate of crystalline wax which 'redissolves only after considerable warming above the precipitation temperature.

.Oil separaticnfon the other hand, isevidenced by a sharp turbidity or cloud which forms stria'- tions on being agitated.H This cloud dissolves more rapidly on reheating than does the wax cloud. The area above the curve is-the sone of com'- plete miscibility between the oil and solvent mixlliquid phases, disregarding the presence of any substantial amountoi wax, whichlatter constitute another and Solid Phase. A

As indicated by the curvefthe `cloud point is relatively low with low .dilution ratios, and rapidly rises to a maximum with a dilution ration! about two parts otsolvent-to one-part of oil. Thereafter, itdecreases with increasing dilution ratios. A

Thus, in Condition I whereinne part' of oil is dissolved in one part of solvent, separation into phases does not-occur until cooling to a temperature of around' -5 F. At a temperature of around 15? F. the main body of oil and solvent will have a' composition corresponding to the point A, while 'the small amount of separated phase will have a composition corresponding to the point C; that is, it will consist of a mixture of about ve parts of sol-vent to oe part Vof oil, and is therefore rich Ain solvent. y

would oil separation occurs. Thereafter,` an additional' Under Condition II however, where one part of oil is dissolved in four parts of solvent to begin with, separation into liquid phases begins at` a temperature of around -7 or 8 F. At a temperature of around -15 F., the composition of the main'body of oil and solvent will correspond to point C, while the separated phase will have a composition indicated by point A, In other words, the separated phase is now lean insolvent.

Thus, the type of third phase formedl under Condition II, which is relatively lean in solvent, imparts the desired free-filtering characteristics to the lter cake on dewaxing, in accordance with the method of this invention.

While a substantial increase in ltration rate is realized by dewaxing in the presence of thisY third phase, nevertheless the maximum yield of dewaxed o il is not realized ina single stage filtering operation. This is due in part at least to the intentional removal of part of the oil with the waxin the form oi the third phase.

It is, therefore, necessary to treat the resulting filter cake with further solvent in order to recover the oil associated with thewax.

I have found'that this reduction in yield of dewaxed oil can be oiset, in substantial measure, v byy modifying the procedure with respect to chilling. Instead of mixing all the solvent with the quantity of the solvent prechilled to about (-5" F. is added to bring the dilution ratio up to the desired amount so that at around 0. lF. the solvent will have substantially complete selective action as between wax and oil.

This mixture is then chilled to a slightly lower temperature, for example, around, 15 F., to cause formation of the third phase in a relatively small amount. Thereafter. the chilled mixture is filtered in the presence of this third phase.

Chilling the wax-bearing oil in the presence -of a small proportion of the selective solvent results vin substantially higher yields of dewaxed oil although this 'is' frequently' accompanied bya reduction in ltration rates, unless provision is made for increasing the ltration rate by dewaxing in the presence of a lter-aid comprising the third phase material described above.

Accordingly, the invention involves chilling wax-bearing oil in the presence of a relatively small proportion of selective dewaxing solvent to enhance the yield of dewaxed oil, and separatin'g the wax from the chilled mixture 'of oil and solventvin the presence of the above described filter-aid material to thereby enhance the rate of iiltration. l o

In order to further illustratethe invention, reference will now be made to Figure 2 of the accompanying drawing. A.

A wax distillate of ,about 'I0 seconds viscosity at 210 F. Saybolt Universal, derived from Mid- Continent crude, and previously rened by solvent extraction, is conducted to a mixer l. It is there mixed with 'a selective solvent comprising a mixposition Which has been chilled to about -5 F. in a chiller I. This solvent 'is added to bring the dilution ratio up to about four parts of solvent to one part of oil.

'I'his mixture is then passed through. a chiller 5 wherein it is chilled to a temperature of around 15 F., which is about 6 to 8 below the tem- "perature at which oil begins to separate from the solution. The chilled mixture is then. charged to a continuous rotary filter 6. The resulting filtrate is drawn off to a stripper 1 wherein the solvent is recovered for re-use,.and a dewaxed oil having a pour test of around to 5 F. is produced.

'Ihe primary wax cake containing some oil is then conducted to a mixer 8 wherein it is commingled with fresh solvent from the chlller 4. The solvent used may be in the proportion of one-half to three parts of solvent to one part of wax cake.

From the mixer 8, the mixture is conducted to a chiller I where it may be conducted directly to a secondary filter I0 wherein the wax'is removed as a wax cake, and the oil associated with the Wax is removed along with the solvent as a filtrate. 35 The wax cake is drawn off to a stripper Il to remove therefrom any remaining solvent and leave awax substantially free from oil. The secondary filtrate is drawn oil.' as indicated and is returned, all or in part, to the mixer l for recycling to the primary filtering operation. If desired. it may be mixed with the charge as it enters the primary illter 6. i

A portion of this secondary filtrate may be re-4 turned to the cake discharge side of the primary filtert wherein it is used as a sluicing agent to facilitate removal of the primary cake from the primary lter. In this case, it is forced through .jets against the filter surface carrying the i'llter cake, and this jetting action acts to dislodge the cake. i

When operating in the above manner, the secondary -filtrate produced fromth'e lter l0 comprises around I to 8% of oil.

' Obviously, many modications and variations 55 of the invention, as hereinbefore set forth, may be made without departing from' th'e yspirit and scope thereof, and therefore only-such limitations -shou1d be imposed as are indicated in the append- 'waxing temperature. chilling the mixture-to a ytemperature of.at" least as low as about 0 F.'.1ust

iabove that 'at which liquid hydrocarbons would begin .to separate from the mixtum-addins PIQ- I0 chilled solvent `at susbtan same temper- -ature to the chilled that at a tem 1 perature of around Q' l". the solvent contained in the entire mixture has susbtantially complete selective4 action as between liquid and solid hydrocarbons, forming a precipitate of solid hydrocarbons, chilling this mixture to a slightly lower temperature to cause separation of a small amount of a third phase consisting of a mixture of petroleum hydrocarbons relatively lean in solvent and having a crystalline character, and separating the solid hydrocarbons from the chilled mixture in the presence of said small amount of third phase material.

2. The method according to claim 1 in which the wax-bearing oil is initially mixed .with about one to two parts by volume of selective dewaxing solvent.

3. The method according to claim 1 in which the mixture of diluted charge and prechilled solvent liquid is chilled to a temperature ofl around 6 to 8 F. below the mixing temperature to cause separation of a small amount of a third phase consisting of a mixture of petroleum hydrocarbons relatively lean in solvent and having a crystalline character prior to filtering.

4. In the dewaxing of wax-bearing hydrocarbon oil to produce oil of around 0 F. pour, the

`method comprising'mixing the oil with a small proportion of selective dewaxing solvent having the essential selective action of a mixture of methyl ethyl ketone and benzol containing around 40 to 60% 'of ketone sufficient to render the mixture relatively fluid at the dewaxing temperature, chilling the mixture to a temperature of at least as low as about 0 F. just above that at which" liquid hydrocarbons -would begin to separate phase comprising liquid'.hydrocarbons substantially free from solid hydrocarbons, and a solid phase comprising solid hydrocarbons, chilling this mixture to a slightly lower temperature such consisting of a mixture of petroleum hydrocarbons relatively lean in solvent andhaving a crystalline character, and separating the solid hydrocarbons from the chilled mixture in the presence of said third phase.

5. In the dewaxing of wax-bearinghydrocarbon oil to produce oil of around 0 F. pour, the method comprising mixing the oil with about one to two parts by-volume of selective solvent com- '.prising a mixture of methyl ethyl yketone and benzol containing around 40 to 60% of ketone, chilling the mixture to a temperature of around 0` F., mixing therewith a further quantity of solvent prechilled to about 0 F. and such that at this temperature lthe solvent mixture has suhstantially complete selective action as between liquid andsolid hydrocarbons, forming a liquid phase comprising liquid hydrocarbons and a.solid phaseV `comprising solid hydrocarbons, chilling 'l this mixture to a slightly lower temperature such that a small amount of a third phase is formed consisting ot-a mixture of petroleum hydrocarbonsrelatively lean in solvent and having a crysthat a small amount of a third phase is formed/'45 talune character, and filtering thesolid'hydr'o carbons from the chilled mixture in the presence

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