US2296458A - Separation of different melting point materials - Google Patents

Description

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" 55 Lwmm I fig k 1i bw- 60 Sept. 22, 1942. A SCHUTTE 2,296,458

SEPARATION OF DIFFERENT MELTING POINT MATERIALS Filed Sept. 20, 1941 v Fatented Sept, 22, E942 SEPARA'EEGN @IF IDHIFFERENT MIEL'KHNG IPUIIN'JT MATERIALS August llilenry Schutte, Hastings on Hudson, N. Y. Application September 20, 1 .941, Serial No. 411,64?

-7 Claims.

This invention relates to a method for the partial separation of various melting point materials from mixtures thereof and more particularly to the concentration of higher melting point materials from lower melting point materials in a mixture thereof. It is, in a sense, a fractional solidification and separation by the aid of an emulsion whereby separation is facilitated. It is a continuation-in-part of my co-pending application, S. N. 274,412 filed May 18, 1939, and entitled Separation of different melting point ma-= terials.

The principal object of my invention is to provide an improved method of separation of mixtures of materials which have separate melting points and of which at least one will solidify when cooled. Such separation of many materials is normally very dificult because of the tendency of the initially solidifying material to obstruct the flow of the liquid medium or the tendency of the liquid component to adhere to the solid matter. Filter rates, or settling rates are frequently very low, and therefore a liquidsolid separation is often impracticable.

I have discovered that I can obtain a highly effective separation of mixtures of materials having difierent melting points by forming an emulsiOn of said mixture with a non-solvent material and thereafter cooling said emulsion to such a point that one of the materials to be separated becomes filterable or separable by liquid solid separation from the other. In this case the nonsolvent surrounds the crystals or solid particles and the liquid particles and produces a free settling, free draining and free filtering system. I then separate the liquids from the solids and thereafter separate out the non-solvent material.

I believe that my invention is of rather gen eral application inasmuch as I have found it en tirely successful on materials of different char-= acteristics. As an example of the materials on which I have had considerable success, I have separated wax from lubricating oils to materially improve the cold test thereof; and I have also been able to separate crude scale wax or finished high melting point wax from slack wax while producing a relatively low melting point foots oil.

In my prior copending application, I have noted that I can separate certain mixtures of animal and vegetable oils, the constituents of which have various melting points, and particularly mixtures of fatty acids such as a mixture of stearic and oleic acids and a mixture of linoleic and oleic acids with water as the non-solvent. A

M resent invention relates more particularly tillate, aromatic hydrocarbon, or the like as the non-solvent.

In accordance with a preferred form of embodiment of my invention, as shown on the attached drawing, which represents a general or typical fiow sheet, it will be noted that I conveniently provide a plurality of tanks it and ii, in one of which I provide a suitable source of non-solvent liquid and in the other of which I provide the mixture of materials having difierent melting points. These tanks may be steam-jack-= eted if high melting point materials are treated, and in such case the steam enters .at l2 and the condensate is removed at i Predetermined quantities of the non-solvent liquid and multiple melting point mixture are then intimately mixed as by proportioning pump it, the streams being consolidated in the manifold it and introduced into mixer i TI. This mixer is of any suitable type of emulsifier or homogenizer, but I find that in many cases a rotary pump is adequate it provided with a by-pass l8 and a relief valve it. It will be appreciated that by adjusting the capacity of the mixer ll it willbe possible to recycle the material through the mixer as many times as may be desirable so that the resulting material discharged through line Eli is suitably emulsified. I may find it desirable to add a gas through line 2i to the mixture in manifold iii to aerate or otherwiseexpand the emulsion, and in some cases, I can use the gas to the exclusion oi a liquid non-solvent material. I prefer to directly cool the emulsion as by the direct introduction of a coolant at 22 into the by-pass line iii, where this is possible, otherwise indirect cooling may be applied satisfactorily. Both direct and indirect cooling may be used, if desired.

Having established a suitable emulsion with a large interfacial area between the crystallized material and the non-solvent, I am able to obtain a very high rate of separation in the liquidsolid separator 23. Although this is indicated as of the centrifugal type, it may be either a centrifugal filter, having a foramlnous filter basket, or it may be of a clarifler type, having a solid bowl. It is, of course, in the contemplation of my invention, that the separator, the primary function of which is to separate liquids from solids, may be of any desired type, including pressure or vacuum filters of the continuous or other type, and having filter discs or a drum as may be desired. In some cases gravity settling may be practicable.

In the preferred form of embodiment of my invention and for some types of mixtures to be separated, I find a centrifugal basket filter having a perforated, rotating basket lined on the interior with a foraminous filter medium to be most effective. This is rotated at such a speed that a high separating force is obtained, which may be in the range of: 500 to 1,000 times gravity or more.

The cake formed is normally a fine-grained, free-filtering, porous type; and, inasmuch as the filtering force is gravitational by nature, the entire cake is submitted to the filtering force without an external crushing action. It is, of course, possible and usually desirable to wash such cake with a wash liquid from line 26; such wash liquid will readily permeate the cake, and uniform drying and washing of the cake are thus possible.

The wash liquid may be either a diluent for the liquid material of the emulsion, or a liquid which is inert and non-reactive therewith. In the method of dewaxing an oil as disclosed in my patent, No. 2,168,140, issued August 1, 1939 on application S. N. 192,534, filed February 25, 1938, the temperature of the materialis such that naphtha or other oil solvent is desirable. However, it may be preferable to use an inert and non-solvent wash liquid as set forth in my patent, No.

2,168,306, issued August 1, 1939 on application S. N. 232,263, filed September 29, 1938, and in such case the wash liquid does not dilute the liq- Mid part of the emulsion and yet serves as a suitable displacing medium which is especially eflective where the solid part of the emulsion is porous as in the instant case.

With the proper temperature control the liquid that is removed from the filter cake is withdrawn through the line 25 either into the wash tank 21 or into the filtrate tank 28, each of which is suitably heated to assure continuity of flow. If the quality of the material in the wash tank 21 is found to have substantial value, it can be conveniently recycled through the linev 29 back through the multiple melting point mixture tank H. The tanks 21 and 28 have discharge lines ill and 3| and a steam condensate drain indicated at 32. The filter cake, which is the high melting point material, may be removed from the separator and placed in the tank 34 and heated so that the higher melting material may be withdrawn as a liquid at 35.

My process is pplicable to the concentration and dehydration of aqueous solutions of the lower fatty acids. The concentration of aqueous acetic acid comprises an important application of my invention. By means of my process a high strength acetic acid solution or substantially wator-free acetic acid can be obtained.

The desired separation can be accomplished by suitably forming an emulsion of the aqueous acetic acid preferably with the aid of an acetic acidcontacted liquid hydrocarbon as the non-solvent fluid. The liquid hydrocarbon non-solvent may comprise a petroleum distillate such as a light or heavy gas oil, an aromatic hydrocarbon such as benzol, or the like. A mixture of a gas oil and benzol may be used as the non=solvent. Such a non-solvent should have a sumcient viscosity so that the resulting emulsion is at least temporarily stable and can be fed to a centrifugal device or the like to effect the desired separation; otherwise, if the non-solvent is not sufiiciently viscous, the emulsion will break, and no separation can be eflected. Upon separation, a free-filtering, porous cake is obtained. Recycling of the filtrate may be found desirable in order to obtain the desired purity and the maximum yield of acetic acid concentrate according to my process.

It is well known that the freezing point curve for acetic acid-water solutions has a eutectic or minimum piont, at which the composition of the solution is about acetic acid and 40% water by weight. Accordingly, it will be appreciated that the composition of the filter cake, whether composed principally of ice crystals or solidified acetic acid, will depend on which side of the eutectic point the composition of the starting mixture I falls. If a dilute aqueous solution is being concentrated, glacial acetic acid, for example, may be added to the solution when its composition approaches the eutectic so that the resulting solution can be further concentrated for the ultimate production of glacial acetic acid.

Separation and concentration of aqueous solutions of other lower fatty acids including formic, propionic, and butyric acids and the like can also be accomplished in accordance with my invention. In each case it is necessary only to select a suitable non-solvent, inert emulsifying fluid, whether liquid, gas, or both. My process may also be applied to the concentration of an aqueous solution containing more than one of the lower fatty acids.

This process is far quicker and more economical than the usual methods of crystallization since it makes possible a better separation with truly continuous operation and accurate tem-' perature control.

While I have shown and described a preferred form of embodiment of my invention, I am aware that modifications may be made thereto; and I, therefore, desire a broad interpretation of my invention within the scope and spirit of the disclosure herein and of the claims appended hereinafter.

I claim:

1. The method of concentrating an aqueous solution of at least one of the lower fatty acids, which comprises forming an emulsion of such a solution while in liquid condition with a nonsolvent, non-reactive hydrocarbon fluid, cooling said emulsion to a temperature such that at least the highest melting point material partially solidifies, and thereafter effecting a liquid-solid separation of the chilled emulsion whereby a fraction is obtained containing at least one of said fatty acids in greater concentration than in the initial solution.

2. The method of concentrating an aqueous solution. of at least one of the lower fatty acids, which comprises forming an emulsion of such a solution while in liquid condition with a nonsolvent, non-reactive hydrocarbon liquid, cooling said emulsion to a temperature such that at least the highest melting point material partially solidifies, and thereafter effecting a liquid-solid separation of the chilled emulsion whereby a fraction is obtained containing at least one of said fatty acids-in greater concentration than in the initial solution.

, 3. The method of concentrating an aqueous solution of at least one of the lower fatty acids, which comprises forming an emulsion of such a solution while in liquid condition with a nonf solvent, non-reactive hydrocarbon liquid and an inert, non-solvent gas, cooling said emulsion to a temperature such that at least the highest melting point material partially solidifies, and thereafter effecting a liquid-solid separation of the chilled emulsion whereby a fraction is obtained containing at least one of said fatty acids in greater concentration than in the initial solution.

4. The method of concentrating an aqueous solution of acetic acid, which comprises forming an emulsion of the aqueous acetic acid while in liquid condition with a hydrocarbon liquid, cooling said emulsion to a temperature such that at least the highest melting point material partially solidifies, and thereafter effecting a liquid-solid separation of the chilled emulsion whereby a fraction is obtained containing the acetic acid in greater concentration than in the initial solution.

5. The method of concentrating an aqueous solution of acetic acid, which comprises forming h melting point material partially solidifies, andthereafter efiecting a liquid-solid separation of the chilled emulsion whereby a fraction is ob tained containing the acetic acid in greater concentration than in the initial solution.

7. The method of concentrating an aqueous solution of acetic acid, the proportion of acetic acid in which is lower than that in the eutectic, which comprises forming an emulsion of the aqueous acetic acid while in liquid condition with a hydrocarbon liquid and an inert, non-solvent gas, cooling said emulsion to .a temperature such that at least a portion of the water partially solidifies, thereafter effecting a liquid-solid separation of the chilled emulsion whereby a fraction is obtained containing the acetic acid in greater concentration than in the initial solution and having a composition approaching that of the eutectic, adding to said fraction acetic acid of greater concentration than that of the eutectic, and thereafter further concentrating the acetic acid fraction to a composition greater than that of the eutectic.

AUGUST HENRY SCHUTTE.

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