US2122019A - Separation of wax from oils - Google Patents

Description

June '28, 1938. c; E. ADAMS ET AL 2,122,019

' .SEPARATlON 0F .WAX FROM OILS Filed Dec. 1, 1934 2 Sheets-Sheet 1 l INVENT Rs Chester'figfidams Fredl/llficfzememczn 50M I ATTORNEY June 28,1938. c.- E. ADAMS ET AL SEPARATION OF WAX FROM OIL5 Filed Dec. 1 1934 2 Sheets-Sheet 2 m Rg fieknwwa N na MN NNSm RDRQQQQQK INVENTCIRS v Cheatenifidams I F e W. 5072a n ATTORNEY 7 Patented June 28, 1938 luted oil-wax mixtures so thatthe optimum wax {UNITE-D "STATES SEPARATION OF WAX FROM OILS Chester E. Adams, Hammond, Ind., and Fred W.

Scheineinan, Chicago, 111., assignors to Stand-' v v i1 5 Chicago, Ill.,'a corporation ard Oil Company,

of Indiana ApplicationDecember 1, 1934, Serial No. 755,602 8 Claims. (o1. 196-18) This invention relates to the separation of wax from oils and it pertains'more particularly to an improved system for the use of normally g'aseous diluent refrigerants, such as liquid propane. This application is a continuation in part of applicants copending application No. 599,730, filed .March 18, 1932. The object of our invention is to provide a commercial'large-scale dewaxing plant for petroleum refineries in which inflammable volatile diluents or refrigerants may be used with safety. In other words, ourob-ject is to provide a closed system and means for regulating the pressure in all parts of the system so that leakage of propane will be prevented. We want to avoid the necessity for opening filters and this means, in turn, that we must provide a system whereby the filter leaves will not become clogged with amorphous or finely divided wax. Our object is to provide a special design for filters that will fit into a specially designed filter system to accomplish the continuous dewaxing of oil in a closed system which willnot have to be frequently interrupted for repair or cleaning.

A further object of our invention is to provide an improved system and method of-chilling dicrystal formation may be obtained. In other words,. we wantv to determine the sequence of steps, the relative volumes of diluent refrigerant and waxy oil in the several steps, the optimum manner and rate of cooling, and the method of handling the crystals which will prevent them arrange heat exchangers and chillers so that it will be possibleto abstract all of the heat from wax-bearing oil without the use of the conventional wax chillers whereinscrapers are necessary for removing wax from cold walls. We also want to obtain the'maximum benefit from the low temperatures of dewaxed oil and diluent'so that the expense of refrigeration may be reduced to a minimum.

Affurther object is to provide improved means for eliminating water from all parts of the system.

I A further object is to provide an improved "method andmeans for chilling the oil-wax mixture to obtain readily filterable wax crystals, for

use of scrapers is avoided.

effectively utilizing available refrigeration and used propane in this chilling'step, and for providing improved-methods and means of handling the slurry during and subsequent to the chilling step; r v

A further object is to provide an improved method and means for operating a wax filtration system whereby maximum flexibility of operation may be obtained by the use of a minimum number of pumps, conduits and connections. A furl0 ther object is-to provide improved means. for

characterized as follows: In the first place, we

employ a dewaxing system which is tied together by a gas line, all parts of said system being operatively connected with said line. Vaporized propane fromall parts of the system are sucked from this line by suitable pumps, compressed, condensed and returned to storage for re-use. This tying. together of the whole system by suction gas lines insures safety, and at the same time it' enables the temperature of each respective ele'-' .ment of the combination to be separately controlled in a very simple and expeditious manner.

'In other words, the tying together of thewhole dewaxing system with a suction gas line makes it possibleto employ volatile and expensive refrigerants and diluents which were heretofore too dangerous for commercial use and makes it possible to improve the operation of filters, chillers, etc. so that the operation is uninterrupted over a long period of time. 7 I

Another feature of our invention is the combination with our suction gas line of an improved, closed vertical filter in which reverse flow and pressure regulation co-act to remove the filter cake and clean the filter cloth. Another feature of our invention is the combination of wash propane and used wash propane tankswith the chillers and filters so thatpractically all of the oil can be removed from the wax without the remelting or redissolving the same in oil or diluent. Another feature is our improved heat exchange system whereby cold oil-diluent mixtures are used to coolthe waxy oil without the formation of wax crystals on the sides of containers so that the PATENT," OFFICE:

Another feature of our invention is the use of liquid traps for removing water from the system and for preventing liquids from entering the compressors. A further feature is the provision of safety means to adequately relieve the system of propane gas in case of failure of condenser, Water 01 COIHDIESSOIS.

Another feature of our invention is the improved system of chillers, filter supply tanks and connections from said chillers and supply tanks to the other elements of the system.

Another feature of our invention is the use of two banks of filters with separate charging means therefor and with means for obtaining maximum flexibility of operation with a minimum number of connecting lines. ture is the use of the Wax discharge means as a means for introducing wax slurry into the filter.

A most important feature of our invention is the method of operating the chilling and the filtering system.

The invention will be more clearly understood from the following description taken in connection with the accompanying drawings which form a part of the specification and in which similar parts are designated by like reference characters throughout the several views. In these drawings:

Figure 1 is a diagrammatic plan of our entire system.

Figure 2 is a modification of the system illustrated in Figure 1 showing additional liquid trapout systems and improved chilling and filtering units. I

Our invention will be described as used for the separation of wax'from a treated distillate lubricating oil from Mid-Continent crude petroleum, the particular distillate having a viscosity of about 100 seconds Saybolt at 210 F. and an A. P. I, gravity of 21.3. It should be understood, however, that the invention is equally applicable to any wax-bearing oils.

In the description of our preferred embodiment we will disclose the use of commercial propane as a combined diluent and refrigerant. It should be understood that other normally gaseous hydrocarbons, such as butane, isobutane, butylene, ethane, ethylene, propane, propylene, etc. may be used either separately or in admixture with each other. The waxy oil may be diluted all through the system with a smallamount of filter naphtha or other light oil which may be useful as a viscosity breaker. Instead of using normally gaseous hydrocarbons we may use normally gaseous ethers such as methyl ether or we may use chlorinated or fluorinated hydrocarbons such as methyl chloride or dichlor-difluor-methane or oxygenated compounds such as ethylene oxide; the last named substances are useful in the de- Waxing process because they have a tendency to throw wax out of solution. We may use normally liquid antisolvents for wax, such as acetone, acid esters, etc; or mixtures of liquid antisolvents with miscibility agents such as benzene or mixtures of benzene with naphtha. If liquids of this type are mixed with the oil they may be considered in the following description as a part of the oil. In our preferred embodiment we effect practically complete dewaxing of the oil by the use of commercial propane.

The propane enters the system through line I and is introduced by pipes H into storage tanks l2 which are designed to hold the propane at temperatures as high as 95 F. at which temperature the propane may exert a pressure of 165 pounds gauge (above atmospheric). The liquid Another feapropane may be selectively removed from one of these storage chambers through line l4, passed through heat exchanger l5, and thence into wash tank I6. The propane is usually at a temperature of 95 F. in line H! and it is cooled in exchanger E5 to a temperature of about 20 F. The propane in Wash tank I6 is cooled to a temperature of -40 F. by the evaporation of a part of the propane, vapors being removed from the tank through conduit I1 and line E8 to compressor I9 which is designed to maintain atmospheric pressure in line is. The gases may then be passed through pipe 20 to compressor 2| which boosts them to a pressure of about 200 pounds, or compressor I9 may be designed to boost them to this pressure, in which case compressor 2! is cut out by pipe 22. We prefer to use compressor H! as a holding compressor and compressor 2! as a chilling compressor, as will be hereinafter described. In any case, the highly compressed vapors are passed through line 23 and condensers 24 back .to storage tanks I2. The cold propane from Wash tank I6 is pumped through pipe 25 by pump 26 to the filter system.

The wax-bearing oil is pumped from storage tank 21 by pump 28 through one branch of pipe 29 into one of the gauging tanks 30, one of these tanks being filled While the other is being emptied. The oil from the gauging tanks is transferred by pump 3! to mixer 32 where it is mixed with propane, forced by pump 33 through pipe 34, and the mixture of waxy oil and propane is cooled in exchanger 35 to a temperature of about 90 F. to 100 F., this temperature being preferably selected so that the wax will be completely dissolved in the diluted oil. The mixture of wax and diluent is then selectively introduced through one of the pipes 36 into one of the chill chambers A, B, C, or D. When one of these chambers is about one-third to three-fourths full the flow thereto is cut off and the propane-oil mixture is introduced into the following chamber. While this mixture is being charged into the tank the vapor outlets 3! and 38 are preferably closed so that no appreciable cooling by evaporation of diluent takes place, and the tanks are warmed up prior to being filled so that shook chilling will be avoided.

The cooling of the oil to effect precipitation of wax in filterable form is not as simple a matter as it might appear. In the first place, oil and 'wax should be in complete solution in the propane beforethe chilling is initiated and since a chiller which has just been emptied is very cold, it is necessary to warm up this chiller before adding a new batch of propane-oil-wax solution. The bulk of wax precipitates as the solution is cooled from 100 F. toabout 30 or 0 F. and cooling throughout this range is effected by the withdrawal of propane vapors by means of chilling compressor 2!. At this. time cold used wash propane is introduced into the chiller through line 39 to make up propane lost through vaporization and to supply additionalrefrigeration. The cooled slurry should have about two volumes of propane per volume of oil when the temperature reaches 40 F. After the introduction of the cold used propane the evaporative refrigeration is continued, the propane vapors being discharged through line 40 into compressor 2| and thence to the condensers 24 and back to storage chambers 12. When the temperature has been reduced to about 40". F. the vapor outlet conduit 31 is closed. and outlet 33 is opened to vent the chill chamber to the suction gas line and the holding compressor.

At about -40 F. the wax slurry is withdrawn through one of the pipes 4|, pump 42, line 43, "and one of the feed pipes 44 to filter L, M or N. The filters which are diagrammatically shown in the drawings arevertical cylinders'containing a :ilplurality of stationaryv filter .leaves, .but it..:.should .be understood that we may employ continuous filters or filters of any other type which are known to the art. The transfer pump 42 should be of a type which will not unduly macerate or break up the wax crystals and, in fact, it maybe ferred by pump 52 into pipes 39. in-the used wash tank 5| is maintained. at 40 F. by the vaporization of a partthereof, the vapors being removed through pipe 53.. to I desirable to employ fluid pressure to charge the filters or to maintain the chillers and filter supplies ata sufficiently elevated position so that the 'liquid head will afford the necessary filter pressure. Filtrate is withdrawn from. the filters by meansof one of the pipes 45, each of which is connected with header 45. The clear filtrate is then conveyed by gravity through pipes 41 to filtrate receiver 48. When a suflicient cake is deposited on the filter elements the oil mixture .is introduced into the next filter. or bank of filters and the cake in the first filter is washed with propane from wash tank l6, line 25, pump 26 and one of the feed pipes 49. When the filters are being washed with propane the so-called wash pro pane filtrate passes by gravity through pipes to used Wash tank 5| from which it is trans- The propane line l8.

y We connect the filters to line l8 by valved pipes, '54. These valves are closed during actual filter operation, but for purposes of cooling the filter or removing the filter cake,. the valves may be opened.

Wax is removed from the base of the filter in the manner hereinafter described through one of pipes 55,. thence through pipe 56 to wax pumping drum 5'I. The wax lines are preferably large conduits provided-with screw conveyors although in some instances the'wax slurry may be pumped by ordinary methods. Wax from drum 51 is forced by pump 58 into high pressure heater 59 which is maintained under a pressure of about 200 pounds gauge. temperature in the heater of about 235 F.

Liquid wax, together with some propane, is with-- drawn from the base of the heater through pipe BI and passes through regulating valve 62 into atmospheric flash drum 53. Valve 62 is auto-. matically controlled to maintain a constant liquid level in heater 59. The propane vaporized in wax heater 59 is withdrawn through pipe 23-which leads directly to condensers 24. Propane from atmospheric flash drum 63 is withdrawn to line l8.

The wax from the based the flash chamber is withdrawn in amounts controlled by liquid level operated valve 64 and'i'ntroduced into wax stripper 65 in which, steam or other suitable stripping gas may be injected; The stearnfrom the top of the stripper. is condensed by thejwater injet condenser 66, the liberated propane being vented to propane line I8.

Finally the wax which has been freed from oil and propane is forced by pump 61 through cooler 68 into storage tank 69.

Returning to the filtrate in tanks? 48, this filtrate is withdrawn through one of pipes 10 and 2 "pump 10a to heat exchanger [5 wherein it cools the incoming propane which is to be used in.

washing the filters. The filtrate then passes pounds is maintained in the heater.

"steam or other suitable gas. drawn throughexchanger H. and thence to jet condenser .80,-the liberated propane being returned to line. I 8.

Steam coil 60 maintains a throughheat exchanger H and heat exchanger 12 to the top plate of the oil heater 13. Heat'may -be supplied thereto by steamcoil 14 so that a temperature ofabout 235, F. at a pressure of 2.00

Oil is .with- 5.5 drawnfrom the base of the heater by pipe 15 through a regulating. valve 16 to lowpressure .fiash drum TI; Regulating valve 16 is automatically controlled to maintain a constant. liquid level in heater [3. Propane vapors are removed l from the flash drum to line l8. The oil from the base of the flash drum is passed in amounts regulated by liquid level control valve 18 into steam stripping chamber 19 where it is stripped with The oil from the base of the. stripper'lais'with drawn through heat exchanger 12 and to oill'20 I storage tank. 8 I.

. compressor I!) to about. 200 pounds. -It' will be understood that suitable valves or pressure regu-mll) lating means will be installed betweenfthevarious :tanks, filters,, chillers, etc. and gas line 18. The chill chambers, filtrate receivers and wax pumping drum will tend to have a temperature, substantia'lly equal to the dewaxing temperature, 3

while the unused wash propane andused wash .apropane will havev a temperature slightly lower than the dewaxing temperature on account of the vapor pressure of pure propane being higher than that of a mixture.

Temperatures may be con-(x40 trolled, however, by'regulating the valves leading I to line l8.

If the pressure in the system exceeds about 200 pounds-itwill be released through pressure release valves on the stills or on the lines connectedIAEi thereto, which valves are preferably connected to vent or fuel line 82. Pressure release valves on the diluent storage tank are preferably set to open at about 165 pounds pressure and these valves are likewise connected to the vent or fuel line. 1 have diagrammatically illustrated a pressure release valve 83 in line 82, but it should be understood that similar valves will be used wherever "safety requires them. Pressure in the storage tanks I2 is usually about 150 pounds to 165 pounds gauge and use mayjbemade of this-pressure to blow the filter cake from the filter leaves (-as will be hereinafter described), the propane gasbei ng conducted through line 84 to the re spective filtrate dischargepipes 45, suitable by-f passes and valves being provided so that propane can be used to discharge the filter cake without interfering with the normal filtrate discharge.

If'desired, propane from line' 23 may be lily- 3365 passed into line 84 by line 85. When gasis used to blow back. thefilter cake there will vbe a condensation of propane in the filter cloth due to its .cold temperature, andthere will be an almost "instantaneous boiling or revaporizatio-n of this-70 propane due to the low pressure on the other side of the filter cakeand, as a result, the filter cake'is quickly and thoroughly removed from the filter cloth' and the cloth iswashed by the reversed fiow of propane. The same end may be accomplished? 75 The steam is with- :15

wash propane liquid.

The filters may be either of the vertical cylindrical batch type diagrammatically illustrated in the drawings or they may be of the continuous pressure rotary type. In either case they will be designed to Withstand considerable pressure, they will be heavily insulated and they will be provided with means for steaming or washing out the propane therefrom prior to opening for repair or replacement so that there will be no hazard from escaping propane gas.

Filtration is continued until a cake about to 1" is built up on the leaf, at which time the flow of the wax slurry is stopped by closing outlet valves in line 45, and the wash propane from tank I6 is introduced at the top of the filter through line 49a. The flow of this liquid propane is continued until all of the unfiltered oil in the filter is forced back (through by-pass 42a) to the chillers by displacement. The flow of the wash propane is then changed so as to enter the filter at the bottom and to pass through the wax cake and the filter leaves and out through line 45. The

flow of this propane is continued until practically all of the oil is washed out of the wax cake. The first wash propane may contain large amounts of oil and it may therefore be discharged with the filtrate into filtrate receivers 48 through pipes 41. Later amounts of wash propane are removed from the filter leaves through pipe 50 to used wash propane tank 5|. Propane from the lattertank, as stated above, is used for diluting incoming waxy oil in chillers A, B, C, etc.

Finally the fioW of wash propane from tank I6 is stopped and the remaining propane liquid .is pumped from the bottom of the filter back-to wash tank I6. During this operation. a small pressure is maintained inside the filter (outside of the leaves) by means of vapors admitted through lines 84 and 54. To remove the filter cake we may employ a reverse flow of wash propane or we may employ gas from'line 84. In either case, liquid propane will be formed in the filter medium and it will be violently expanded by opening the valve in pipe 54, this expansion causing the immediate and thorough removal of the cake from the leaf. The filter cake is directed by the hopper bottom 88 into an enlarged con duit 56 wherein a screw conveys it to wax sump 5'1. If desired, a spray of liquid propane may be used to assist in washing the outside of the leaves.

Precoats or filter aids may be employed to increase filter rates and prevent clogging. Some oils are readily dewaxed with the ordinary filter elements, but other oils show a cloud at low temperatures after dewaxing. It is highly desirable that lubricating oil should be zero-bright. Therefore, in some cases we make a slurry of infusorial earth or other filter-aid in propane or light oil, and apply a precoat to the filter by spraying or by passing some of the liquid through the filter. Other fibrous or crystalline filter aids may be used, either as a precoat or admixed with the wax slurry. I

In'the chilling step we may simultaneously remove propane vapors and add propane liquid to the chillers, we may cool by evaporating propane and subsequently adding more cold propane, or we may add all of the propane before we start to chill by evaporation. Our preferred method of cooling and of operating the filter system will now be described in connection with Figure 2.

In the modification shown in Figure 2, the ,propane which is withdrawn from storage isfirst "by the reverse flow of a slight amountof used .passed through line I06 to water trapout tank ID! from which the water is withdrawn through .1 line I08 in amounts regulated by liquid level controlled valve I09. Propane from trap IN is withdrawn through line H0 to Wash tank I6 and 5 through line! I I topump 33, line 3d and mixer 32 .ashereinabove described. Any Water or other immiscible liquid impurity is thus separated from the propane before itis discharged into the plant.

The next distinguishing feature of Figure 2 is -10 the arrangement and operation of the chilling system. The warm propane-oil-wax mixture from cooler 35 and .line 36 is introduced through lines H2 to one of a plurality of chillers A, B. In actual commercial use we have found that lc three of such chillers give excellent results, -although it should be understood that any .number may be used. The upper-parts of these chillers are connected through gas line II 3 so that if chiller A has just been emptied and chiller B hasjust been filled, the vapor line I I3 between these chillers may be opened and propane may be boiled out of chiller B and condensed in chiller. A thereby warming the latter chiller sufficiently to prevent shock chilling when the propane-oil wax solution is introduced into it. When equilibrium has been established between the two chillers, this vapor line isv closed, and propane vapors are removed from the filled chiller through .lines 31 and 00. When the temperature in this chillerf for instance chiller B, reaches about 0 to 30 F.,

. additional propane-oil-wax solution is introduced into it through line I I2.

From the above descriptionit will be seen that the slurry is first chill-ed by evaporative cooling,. preferably at a rate of about to 4 F. per minute, it is then chilled and diluted by means of used wash propane and it is finally chilled by evaporative cooling and dropped into the filter supply tank. Before transferring the slurry frome chiller B to filter supply tank I I8, we preferably I connect the vapor spaces of these two tanks through line H9 so that they will be in equilibrium both as to temperature and pressure when I the slurry is transferred and so that there willh5 be no shock chilling.- Lines I20 are also connectedto the top of the filter supply tanks and areconnected to each other through line I2I so that this system may be used to equalize the pressure on filter supply tanks as well as to re-mo turn cold slurry from the filter system back to the filter supply tanks.

The multiplicity of pipes and valves need not be described in detail, but it a will be apparent that each chiller may be connected to chilling compressor 2! through lines 31 and .40, they may be connected to holding compressor I9 through line 38, they may be connected to each other through line H3, or they may be connected to the upper part of filter supply tanks through lines I IS. The warm propane solution may be introduced'into each chiller K through line 30 and cold used propane may be .introduced thereto through line 39.

any chiller maybe selectively introduced into any Slurry from fi ter supply tankand slurry romt fi te sy 15 tem may be returned to any desired filter supply tank.

Referring now to the filter system, we have again diagrammaticallyv shown the use of vertical batch filters L, M, LL and'MM. It will be observed that thefirst two of these filters are connected in parallel to operate as one bank while of the filters, When continuous filters are-used,

it will be understood that line I24 will lead to the wax slurry reservoir in the filter chamber. For charging wax slurry to the other bankof filters, the slurry is passed through line I25, pump I26 and line I 21 to line 56A, which likewise serves as a wax discharge pipe;

.When a filter cake has been built up on the filter elements and it is desired to wash the oil \out of said cake, fresh cold propane from wash tank I6 is introduced through line 25, line I28, pump I23 and line I24 to filters L and M or through line I29, pump I26 and line I2'I to filters LL and MM. T I v When it is desired to'withdraw wax slurry from the base of the filters, this material may be withdrawn through line 56, line I30, pump I23,

line I24v and line I3I .through which it may be returned to the filter supply tanks I I8. Likewise, slurry from the base of filters LL or M may be withdrawn through line 56A, line I36A, pump I26,

line I21 and line I3IA which joins with line I3I and returns to the filter supply tanksj If it is desired to empty wash propane out of the filters, the wash propane is withdrawn through line 56, line I30, pump I23, line I24 and line I32 to line I 25 which leads. to wash tank I6. Similarly,wash

propane from filters LL and MM may be passed through line 56A, line I36A, pump I26, line I2I and line I32A, which leads into line I32 for returning the wash propane to wash tank I6.

If it is desired to introduce wax slurry or wash propane into the filters at the top instead of at 5 the bottom, this may be" accomplished by opening the valve in line I33v so that pump I23 may force the liquids through line I24 and then through line I33 which acts as a manifold to which filters'L and M in the first bank arecon nected. Similarly, pump I26 can .force liquids through line I27 and line I33A into the upper parts of filters LL and MM. Manifold I33'is connected by line I34 with'low pressure gas line I8 and this low pressure gas line is likewise connected to manifold I33A through line I34A. Thus, positive connection may be made between the low pressure gas line and the shell of any filter through lines 54, I33 and I34 or lines 54A, I33A and I34A. I I

Manifold I33 is also connected to high pressure 'or blowing gas line 84 through line-I35 and manifold I33A is connected thereto through line I35A.

For removing wax cake from the filter leavesit is desirable to blow back with propane gas.

The filter leaves are connected to the low pressure gas line I8 through lines I36 and I3I which lead to manifold 46 and lines I36 and I3'IA which I38 and I39'to manifold 46 and through lines I38 and I39A to manifold 46A.

It is sometimes desirable to recirculate slurry from the filters back to the filter supply tank and for this purpose we employ line I40 which is connected to manifold I33 through line MI and to manifold I33A through line I4IA. When the filter operation is just beginning and the cake is being formed on the leaves, it may be desirable to have valve I42 open, but as soon as the cake is built up and a clear filtrate is being obtained. valve 42 may be closed so that the pump which is. forcing the slurry into thefilter may build up apressure of about 50 pounds per square inch on the-filtering surface. If the pressure exceeds this value, valve I42 maybe slightly opened.-

The filter leaves in filters L and M are connected through lines 45 and 46 to filtrateline 41 and filtrate collector 48; similarly, filtrate from filters LL and MM pass through lines 45A, 46A and 41. Cloudy filtrate from manifold 46 may be passed through lines I43 and I44 to line I3I through which it maybe returned to the filter supply tank. Likewise, cloudy filtrate from manifold 46A may be passed through line i43A to I44 and thence back to the filter supply tank. Alternatively, the cloudy filtrate may be passed from manifold 46 through line 50 or from manifold 46A through line 56A back to the used wash tank 5|.

The operation of our filter system may be described as follows: The filters are first cooled, preferably by passing cold oil through them or evaporating propane in them. Chilled wax slurry is then-forced throughv line H6 by pump I23 through lines I24, 56 and into filters L and M.

The slurry is allowed to fill the filters and to overflow through lines 54 into manifold I33,

Y filtratemay be cloudy and it may therefore be discharged from manifold 46 through lines I43 and I44 back to the filter supply tank. As soon as the sight glasses on the filtrate lines indicate that it is clear, the valve .in line I43is closed and the valve to line 41 is opened allowing the filtrate to be passed to they filtrate collectors 48. At this time the valves in line 54 are'closed so that the pressure is gradually; built up in the filters'to about 50 pounds per square inch. In about 20 minutes a cake of about to 1" thick is built upon the leaves.

preferably by Propane gas from lines 84, I35 and I33, the .valves in lines 54 being opened for this purpose. The displaced wax slurry is withdrawn through line 56 and may either be forced back to the filter supply tank through line I30, pump I 23, line I24 and line -I3I or may be forced directly back to the filter supply tank through lines 56, line I24 and line I3I bythe propane pressure. The pressure of the propane gas maintains the wax cake on the filter leaves and although a "small amount of the propane is condensed by the cold wax cake 'we have found that in a short The first wash liquid may contain a large amount of oil and practically no wax so that it may be passed through manifold46 and line 41 to the cry. The wax cake which is discharged from the filtrate collector. The bulk of the wash propane is, however, passed through manifold 46 and line to the used wash propane tank, from which tank it is withdrawn at intervals to supply the chillers as hereinabove described. When the oil has been washed out of the wax cake, the valves in lines 54, which were closed during the washing step, are now opened again and propane gas is employed to displace the propane from the filters back to the fresh cold propane tank I6. This, again, may be accomplished by direct gas pressure or it may be accomplished by means of pump I23 and lines I24 and I32.

Instead of employing propane gas to displace the wax slurry, we may introduce liquid propane through line I33 from the top of the filters while We are displacing wax slurry from the base thereof through lines I24 and I3I back to the filter supply tank. Instead of introducing wash propane at the top and displacing the slurry from the bottom of the filters, we may merely substitute the wash propane for the wax slurry which is being introduced at the base of the filter and We may return the wax slurry to the filter supply tank through the recirculating line I40. Other modifications in operating procedure will be apparent from the detailed arrangement of valves, lines and pumps shown in Figure 2.

When all of the wash liquid has been displaced from the filter in the presence of sufficient propane gas pressure to hold the cake on the leaves, propane gas from lines 84, I36, I31, 46 and 45 is intermittently blown back from the filtrate side to cause a distending of the filter element and the removal of the wax cake therefrom. We may employ liquid propane for removing the wax from the cakes, but this is undesirable because it necessitates an undue amount of propane recovfilter elements is conveyed by screw conveyors in line 56 to wax sump 51, as hereinabove described. This bank of filters is now ready to repeat the filtering operation. The other bank of filters operates in the same manner andfurther description is deemed unnecessary.

We have already described the trap for removing water from propane entering the system,

but since steam is usedto strip propane gas in.

the low pressure oil and wax stills, it is necessary to use special precautions tov keep additional water from entering the system. The propane gas from the steam stripping stills is introduced through line I46 into jet condenser 66 and water is introduced through line It? at the upper part thereof. The water and condensed steam are Withdrawn from the base of this jet condenser through line I48 and We preferably employ a liquid level controller I49 which may be a simple fioat which mechanically or electrically operates the discharge valve in line I48. Propane gas from the upper part of the jet condenser is withdrawn by compressor I50 and forced through line I 5| to vent 82, high pressure gas line 23 or low pressure gas line I8.

Another feature of our system is the use of a liquid trap I52 in line I8 on the suction side of holding compressor IS. A constant liquid level may be maintained in this trap by a suitable float control which operates valve I53 in liquid discharge pipe I56. This liquid will usually consist of propane and it may be returned to one of the diluent storage tanks or to the chiller, filter supply tanks or other cold propane tanks.

The supply of propane gas for blowing the presses is preferably obtained from the upper part of the propane storage tanks because'the gas therein contains a larger amount of ethane or a larger amount of air or inert gas and therefore is less condensible. The pressure in line 84 may be regulated on the filter side of a pressure reducing valve, as illustrated in Figure l. The filtration pressure has been described as 50 pounds per square inch, but we may employ pressures as high as or pounds per square inch.

The filters are provided with connections through which they may be washed out at intervals with a warm wax solvent, but since the drawings are already quite complicated, the additional wax solvent washing line will not be illustrated. Likewise, the filters are preferably provided with steam connections so that they may be steamed out prior to being opened. Other modifications in operating procedure will be apparent from the detailed arrangement of valves, lines and pumps shown in Figure 2. I

It is desirable in any dewaxing process that rapid and efficient separation of oil from wax be obtained and this in turn necessitates a careful regulation of wax crystallizing and filtering operations. The wax should be completely dissolved in propane before chilling is commenced and at no time subsequent to this complete solution step should the mixture be shock chilled, i. e., come in contact with any liquid or equipment at a much lower temperature or be suddenly released from a high pressure into a zone of substantially lower pressure.

We have found that the chilling should be effected in three steps: First, the vapor space of a chiller containing warm solution should be connected to the vapor space of a cold chiller which has just been emptied so that the solution is chilled by evaporative cooling as the pressures are equalized. Cooling may then be continued by operating the variable compressor 2| until a temperature of 30 F. to 0 is reached. Next, the, 7 cold wash propane (propane which may contain some wax or oil) is added at a temperature which distilled and recondensed. The final chilling to about /l0 F. is effectedby evaporative cooling by means of variable compressor 2I. While we prefer to use this method of cooling, it should be understood that the cooling may be effected ,by

conventional heat exchangers or any other means without losing other advantages of our invention hereinabove and hereinafter pointed out.

We have found that it is very desirable to filter the crystallized wax as soon as possible after it has been chilled to filtering temperature. If the chilled slurry is held for too long a time in filter supply tanks H8, we have found that filtrationis more difiicult and that yields are decreased. The filter supply tank should be well insulated so that none of the solidified wax will be redissolved and all valves leading to and from the supply tank should be extremely tight so that there will not be any leakage through filter valves which would cause shock chilling and which would thereby impair filter rates. We have found that a reciprocating block valve pump is quite satisfactory for transferring slurry from the filter supply tank to the filters, but even better results may be obtained by employing fluid pressure, such as compressed nitrogen, ethane or other gas, for forcing the slurry into the filters. Where continuous filters are employed'and a relatively low pressure differential is sufficient, we mount the chillers and filter supply tanks at a higher level than the filters so that the liquid head, due to difference in elevation, will be suflicient to force the diluted oil through the filter element.

Some light ,distillates may tend to give a flocculent wax cake which is difficult to filter, giving poor filter rates and low oil yields. To such distillates we may add a small amount of a heavier lubricating oil stock, a small amount of asphaltic material or a wax crystallization regulator of the type prepared by condensing chlorinated wax and naphthalene with aluminum chloride. Amounts of the latter material as low as .3% have been found to increase dewaxed oil yields on S. A. E.

i 20 Mid-Continent distillate from 70% to 84% and i introducing kerosene for washing out thefilters I before opening them. and/ or for introducing steam to blow out all traces of propane. From a safety standpoint, it is highly necessary that precautions be taken to prevent the formation of explosive oil-propane mixtures. I

While we have described in detail preferred embodiments of our invention, it should be understood that we do not limit ourselves to the details hereinabove set forth except as defined by the following claims, which should be construed as broadly as the prior art will permit.

We claim: 1. In a propane dewaxing system wherein a waxy oil is dissolved in propane at elevated temperatures and pressures, cooled to solidify the wax in readily separable form, mechanically separated into wax and diluted oil and finally freed from the propane diluent, a filter vessel containing a filter element, a conduit for withdrawing wax slurry from said filter vessel, positive means for moving wax through said conduit and means for forcing a wax slurry into said vessel through the same conduit through which wax is removed therefrom.

2. In a propane dewaxing system wherein a waxy oil is dissolved in propane at elevated temperatures and pressures, cooled to solidify the wax in readily separable form, mechanically separated into wax and diluted oil and finally freed from the propane diluent, a closed pressure chilling tank, a filter supply tank connected with said chilling tank, a closed filter vessel, a filter element in said vessel, a fresh cold propane tank, a filtrate collector means including a pump and inlet connections therefor separately connected to said cold propane tank and said filter supply" tank, respectively for selectively introducing into said filter a slurry from said supply tank or fresh cold propane from said fresh cold propane tank,

means for returning slurry from said filter vessel to said filter supply tank and means for selec- 7 tively transferring liquid from said filter element to said filtrate collector or said filter supply tank. 3. The apparatus of claim 2 which includes a used wash propanetank, means for transferring liquid from said filter element to said tank, and means for transferring liquid from said tank to said closed pressure chilling tank.

4. The apparatus of claim 2 wherein the filter element is also selectively connected to a blow back line leading from a source of propane gas;

5. In a propane dewaxing system wherein a waxy oil is dissolved in propane at elevated temperatures and pressures, cooled to solidify the wax in readily separable form, mechanically separated into wax and diluted oil and finally freed from .the propane diluent, the step of periodically washing the separation means with kerosene for removing propane and improving separation rates.

6. In apparatus of the class described, a propane. storage tank, a chiller, a filter, a filtrate collector, a low pressure gas line, means for mixing propane from said storage tank with waxy oil, and for introducing said mixture into said chiller, means for venting said chiller to saidlow pressure gas line'to provide evaporative cooling in the chiller, means for introducing slurry from the chiller to said filter, means for transferring filtrate from the-filter to the filtrate collector, a

connection from said filtrate collector to said 1 low pressure gas line, a propane recovery system and meansfor passing filtrate from said collector to said recovery system, means for stripping propane from oil with steam in said recovery system, means for condensing steam from saidstripping step, separating propane therefrom and returning the propane to said low pressure gas line, a compressor and condenser connected between said low pressure gas line and said propane storage tank, a liquid trap interposed immediately in front of said compressor for trapping out and removing any condensate which may collect in that part of the propane gas line connected to the inlet side of the compressor, an inlet to said trap connected with said low pressure gas line, a connection from the upper part of said trap to the inlet of said compressor, and means for withdrawing liquid from the lower part of said trap.

'7. A propane dewaxing system which comprises a propane storage tank, a chiller, a filter supply tank, a cold propane storage tank, a used propane storage tank, a filter, a filtrate receiver, means.

for mixing propane from said storage tank with waxy oil and for introducing said mixture into said chiller, means for transferring cold slurry to said filter supply tank, a pump with its inlet selectively connected to said chiller, filter supply tank, cold propane tank and filter shell, and with its outlet connected to said filter shell, means for'

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