US2194185A - Method of purifying wax - Google Patents

Description

March 19, 1940.v F. w. PAIZ QGETT 2,194,185

I union 0F PURIFYING WAX I Filed larch 13, 1936 v sou/rlo/v 2/ T 24 T 7 FROPA IVE MIL E 7' SLURRY /0 O Arm/PW:

Patented Mar. 19, 1940 UNI/TED stares mop orrunn'mo wax Frederick w. m and! Park, I. all nor I'hilalelphia,

to Sun Oil Companyporatlon or New Jena Pa.,aoog- Application mm 13, m0. Serial no. can:

-, 4 Gains.

This invention relates to a method of washing wax crystals to remove oil and otherimpurities therefrom when wax bearing oils are dewaxed in accordance with any of the well-known de- 5 waxing processes, the crude wax thus'obtalned contains a relatively large percentage of oil, generally 50% or higher. In order to produce a commercial grade oi! wax, it is necessary that a large percentage of this ofl be removed from the wax. 10 Various methods'ior removing this oil have heretorore been practiced, the most common of which is the process known as sweating, All of the known processes for removing oil from wax are objectionable in that they require relatively large ll amounts of equipment and space, and the sweating process in particular requires a great deal of time, generally several days to a week.

It is therefore an object of this invention to provide an improved method of separating oil from wax which is simple in operating and re-' 7 quires simple and inexpensive equipment. Otherand further objects will be apparent as this, description progresses.

m the drawing, attached hereto and forming U a part of this specification:

Fig.1 is a diagrammatic representation of a form of apparatus adapted for use in practicin my process. Fig. 2 is a diagrammatic representation'oi a 8.0 modified form of apparatus 101' practicing my process.

1 The crude wax which may be obtainedirom any of the known dewaxing processes, and which contains approximately 50% of oil, is first mixed 5 with a light liquefied normally gaseous hydrocarbon, preferably propane or some other liquefled normally gaseous hydrocarbon-such as propylene, butane, isd-butane, butylene, ethane and ethylene, or mixture of the same; or other sol- 40 vent known to have selective wax solvent properties at low temperature, whose density is not substantially greater than .6 at F.,- and preiferably is not substantially greater than that of propane. The amount of propane which is" added to I the crude waxneed not be more than an amount sufilcient to make a slurry which may be readily handled. If'the crude wax was obtained by a propane dewaxing operation in which the separation of waxfrom oil was accomplished by set- 50 tling or centrlfugation; so that the crude wax was obtained in the form of a slurry, this slurry itself may beused. The slurry of crude wax in propane is introduced through line ,I to the upper portion or tank 2 which is filled withliqnefied u propane at a temperature sufilciently low so that.

(ol. m-a) the waxes will be precipitated in the format their crystals. The exact temperature of the bath of propane will or course varywith the nature of the waxes-being treated and those which it is desired to recover. The temperature of the bath may be as low as 45 F. when it is desired to recover all the waxes and may be as high as +50 I". when only the high melting point wax is to be recovered.

Chilled propane is admitted through line 3 to 10 the lower portion of tank 2 and rises through tank 2 and'goes out through line 4. The wax crystals introduced with this slurry through line I settle through the bath of cold propane in tank 2 and collect at the bottom, from whence they are discharged through line 5 in the form of a slurry. The bath 01' cold propane in tank 2 will dissolve most of the oil contained in the wax crystals, and will carry thisoil out through line I in the i'orm oi a propane-oil solution. .Due to the large body, of liquefied propane-maintained in tank 2, practically all of the oil will be dissolved or leeched from the wax crystals, so that the wax crystals which fall tothe bottom of tank 2 will be relatively pure and will then contain only minor proportions of oil. The pressure on the bath of cold propane in tank 2 is preferably maintained .above the vapor pressure of the propane at the 'itemperature in tank 2 by regulating valve 8 in line I, so that there will be no bubbling'oi the liquid in. tank 2 to hinder the settling of wax. The wax slurry discharged through line 5 may be subjected to filtration to remove most of the propane and any'oil in solution with the propane,

andthen distilled to remove any remaining propane from the purified wax. As shown in the drawing, the slurry from line 5 is discharged on to a, belt l0, whichmay be a filter cloth which passes between rollers II and i2 to squeezeout the oil and propane which falls into tank IS; the 40 wax, which remains on belt I 0,.is discharged as the-belt passes over roller l4 and falls into wax tank l5, as described in my copending applications, Serial No. 68,613 filed March 13, 1936.

As an alternative procedure the slurry obtained from, line 5 may be introduced into a second tower similar to tower 2, the slurry inthis case taking 7 the place of the'blend above described, which is introduced through line, linto tower 2. In'my copending application, Serial No. 68,610, filed so March 13, 1936, I have described a process in which thecr'ude wax, .while in the filter media, is washed bysolvent at gradually increasing temperature. However, itis possible'to' treat the wax in' accordance withthe' present invention in a u manner similar to that described in my aforementioned application. v

When it is desired to so treat the wax, the temperature of the blend introduced into the second tower may be increased slightly, either by heat exchange or mixing additional warmer propane with the slurry, and the temperature of the propane forming the body of liquid contained in the second tower is increased slightly over that of the propane in the first tower, preferably 5-20 F.

The apparatus shown in Fig. 2 is a diagrammatic representation of a form of apparatus adapted for carrying out this alternative procedure. The chilled slurry of wax crystals in a solvent is introduced into the upper portion of a bath of chilled solvent in tower l8, through valved line i9, while chilled solvent is introduced into the lower portion of tower it through valved line 20. The chilled solvent in tower it rises slowly and dissolves any oil contained in the wax slurry introduced through line I 8. The solution of solvent and oil is removed from tower i6 through valved line 2i. The wax crystals fall through the bath of chilled solvent and are removed from the bottom of tower I! through valved line 22 in the form of a wax slurry. The

temperature of the bath of chilled solvent in tower I6 is preferably maintained sufiiciently low so that substantially all of the wax is precipitated as wax crystals. The wax slurry removed through valved line 22 is introduced into the upper portion of a bath of chilled solvent maintained in tower l'l, while additional solvent is introduced to the lower portion of tower I! through valved line 23. The temperature of the solvent introduced through valved line 23 and of the bath of solvent in tower I! is somewhat higher than that in tower i6, preferably 5-20" 1''. higher.

At this increased temperature the lower melting point waxes will be taken into solution by the chilled solvent and will be removed from tower I! through valved line 24. The higher melting point waxes which are not dissolved by the solvent fall to the bottom of tower l1 and are removed through valved line 25 and introduced into the upper portion of a bath of chilled solvent maintained in tower I8. Additional solvent is introduced to the lower portion of tower i8 through valved line 28. The temperatureof the solvent thus introduced and of the bath of the solvent in tower i8 is somewhat higher than the temperature maintained in tower I'I. At this temperature the medium melting point waxes contained in the slurry introduced through valved line 25 will be dissolved by a bath of chilled solvent and will be removed through valved line 2'! in solution with the solvent. The higher melting point waxes which are not dissolved by the solvent settle to the bottom of tower l8 and are removed therefrom through valved line 28. The solution of solvent with oil or wax dissolved therein, which are withdrawn from the top of each tower. are collected separately and the solvent may be separated from the material dissolved therein in any desired manner as by distillation. There are thus obtained as many fractions of wax of diflerent melting points as there are settling towers- It is, of course, to be understood that any desired number of settling towers may be connected in series.

I am aware that it has heretofore been proposed to wash crude wax crystals by permitting them to settle through a bath of cold naphtha.

aromas However, this prior process has not been adopted since the difference in density between the wax crystals and naphtha was not sufliclent and the viscosity oi naphtha was too great to permit the rapid settling of wax which is necessary, if the process is to be a continuous and economic one. In fact, when it is attempted to use naphtha as the solvent it is frequently almost impossible to obtain any noticeable settling. Satisfactory operation of my process demands that the rate of upward flow of fresh solvent must be great enough to overcome the tendency of the oil to difluse downwardly and that the rate of settling of the wax crystals must be greater than the rate of upward flow of the solvent, so that downward settling will take place. These conditions are not economically possible with naphtha but are attainable with propane since the settling rate of wax through propane is more than ten times as fast as through naphtha.

A working equation (Stokess) for finding the velocity at which the wax crystals would settle in a solvent is as follows:

(d1 a)r i) where v=velocity of fall of particle.

K=a constant. d1=density of falling particle. dz=density of medium.

r=radius of falling particle. n=viscosity of medium.

60 A. P. r. naphtha at 0 1".

For propane at 0 1".

From the above calculations it is apparent that by using chilled propane as the solvent bath the settling rate will be sufllciently high so that relatively large quantities of crude wax may be continuously purified by this method.

What I claim and desire to protect by Letters Patent is as follows:

1. The method of iractionating a crude wax into a plurality of waxes of varying melting points which comprises forming a slurry of said crude wax in a diluent having selective wax solvent properties at low temperatures and having a density not substantially greater than .6 at 0 F., chilling said slurry to a temperature at which substantially all of the wax will be precipitated in the form of wax crystals, introducing said chilled slurry into the upper portion of the first of a series of settling zones, maintaining a body of chilled diluent having the properties specified in each of said settling zones, introducing said chilled diluent into the lower portion of each of said settling zones, withdrawing a wax slurry from the bottom of each of said settling zones, introducing the slurry thus withdrawn into the upper portion of the next succeeding settling zone, maintaining the body of diluent in each of said settling zones at a temperature higher than that of the preceding zone to cause said diluent in each successive settling zone to dissolve successive fractions of wax of increasingly higher melting point from wax slurry introduced theredissolved matter therein from the top of each of said settling zones.

2. The method of fractionating a crude wax into a plurality of waxes of varying melting points which comprises forming a slurry of said crude wax in a diluent having selective wax solvent properties at low temperatures and having a density not substantially greater than .6 at 0 F., chilling said slurry to a temperature at which substantially all of the wax will be precipitated in the form of wax crystals, introducing said chilled slurry into the upper portion of the first of a series of settling zones, maintaining a body of chilled diluent havmg the properties specified in each of said settling zones, introducing said chilled diluent into the lower portion of each of said settling zones, withdrawing a wax slurry from the bottom of each of said settling zones, introducing the slurry thus withdrawn into the upper portion of the next succeeding settling zone, maintaining the body of diluent in each of said settling zones at a temperature higher than that of the preceding zone to cause said diluent in each successive settling zone to dissolve successive fractions of wax of increasingly higher melting point from wax slurry introduced thereinto, withdrawing a solution of diluent with dissolved matter therein from the top of each of said settling zones, and maintaining the pressure in each of said settling zones above the vapor pressure of the diluent at the temperature maintained therein.

3. The method of separating oil from wax and fractionating the wax into a plurality of waxes of varyingmelting points which comprises adding to the oil-wax mixture a diluent having selectivewax solvent properties at low temperature and having a density not substantially, greater than .6 at 0 F., chilling to obtain crystallization of the wax, introducing the chilled mixture into the upper portion of the first of a series of settling zones, maintaining in each of said settling zones a body of chilled diluent having the characteris- .thus withdrawn from each tics specified, introducing said chilled diluent into the lower portion of each of said settling zones, withdrawing a wax slurry from the bottom of each of said settling zones, introducing the slurry thus withdrawn from each zone except the'last into the upper portion of the next succeeding settling zone, diluent in each zone a temperature higher than zone to cause said diluent in successive settling zones to dissolve successive fractions of wax of increasingly higher melting point, and withdrawing a solution therein from the top of' each of said settling zones. t

4. The method of separating oil from following the first zone at that of the preceding wax and maintaining the body of of diluent with dissolved matter f'ractionating the waxinto a plurality of waxes of varying melting points which comprises adding to the oil-wax mixture a diluent having selec-- tive wax solvent properties at low temperature and having a density not substantially greater than .6 at 0 FL, chilling to obtain crystallization of the wax, introducing the chilled the upper portion of the first of a series of settling the lower portion of each of said settling zones, 2. body of chilled diluent having the characteristics specified, introducing said chilled diluent into the lower portion of each of said settling zones, withdrawing a wax slurry from the bottom of each of said settling zones, introducing the slurry 1 zone except the last into theupper portion of the next succeeding settling zone, maintaining the body of diluent in each zone following the first zone at a temperature higher than that of the preceding zone to cause said diluent in successive settling zones to dissolve successive fractions of wax of increasingly higher melting point, withdrawin a solution of diluent with dissolved matter therein from the top of each of said, settling zones, and maintaining the pressure in each of said settling zones above the vapor pressure of the diluent at the temperature maintained therein.

FREDERICK W. PADGEI'I.

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