US2223939A - Method of dewaxing mineral oils - Google Patents

Description

Dec. 3,.1940. Q 1.. D. JONES 2323,9353.

METHOD OF DEWAXING MINERAL OILS Filed Sept. 10, 1937 IL. L OIL somzm c- C c H D *f H C- I L 1 L IN N L -L g L E R 12 R C R H 1 E- L L E C C WAX WASHING I fi H TANK. 1L L L A P a C C l L E E 1; 5 N T R T R 1 1 1 F 1: 8 R- g 53. E E

T PURIPIiD WAY INVENTOR.

LEO D. JONES ATTORNEY.

Patented Dec. 3, 1940 UNITED STATES PATENT OFFICE 2,223,929 METHOD or DEWAXING MINERAL OILS Leo D. Jones, Philadelphia, Pa., assignor to The Sharples Corporation, Philadelphia, Pa a corporation of Delaware Application September 10, 1937, Serial No. 163,180

5 Claims.

This application is a continuation in part of my co -pending application for Method of dewaxing mineral oils, Serial N 0. 35,476, filed August 9, 1935. I

The present invention pertains to the art of separating wax from wax containing oils, such as petroleum residues and distillates and mixtures thereof and products obtained therefrom by various refining processes such as acid treating, sol vent extraction, etc. In the performance of processes of this character, it has been customary to add a diluent to the stock to be dewaxed at a temperature suificiently high to form a solution of both the oil and the wax in the diluent and thereafter to chill the solution to a temperature sulficiently low to precipitate the major portion of the wax in aform in which it may be removed by mechanical means, such as centrifuges or filter presses.

In connection with the chilling step of an operation of this character, it is important that the operation be carried on in such'a manner as to avoid accumulation of wax on the chilling surfaces, as such accumulation would necessarily entail partial insulation of the material subjected to the chilling operation from the refrigerant and consequent inefficiency in heat transfer of the chilling surfaces. It has accordingly been customary, in connection with this type of chilling operation, to provide scraping machinery operating on the chilling surfaces for maintaining them vrelatively free of wax. In operations in which large bulks of material are treated, chilling machines are used which must necessarily be of large capacity and the provision of machines presenting the necessary chilling surfaces and the incidental scraping machinery accordingly, entails a considerable expense. It is naturally desirable that such expense be reduced.

It has been proposed heretofore to chill the stock without first diluting it and to chill the diluent to the dewaxing temperature separately fromthis stock in simpler apparatus, thus reducing the amount of chilling equipment which must be provided with the relatively expensive scraping machinery. Such proposals are based upon a supposition that a reduction in the bulk of the wax-containing material under treatment would reduce the amount of chilling equipment which must be provided with scraping machinery and would accordingly involve a simplification of the chilling problem. While this proposal would appear to be fundamentally sound, it cannot be adopted in practical operation for the reason that the separately chilled stock solidifies at a relatively high temperature and thus renders further chilling impracticable.

A proposal has also been made heretofore that the stock be diluted to a limited extent with a portion of the diluent which is used in the ulti- 5 mate dewaxing step and chilled in the presence of this diluent to the dewaxing temperature prior to the addition of the remainder of the diluent to be used in the dewaxing operation. The pro- .w;

remainder of the diluent is added after the stock has been chilled to a temperature at which sub- 20 stantially all of the Wax has been precipitated and the step of separation of Wax from the oil solution is to take place, it is, of course, desirable to dilute the stool; initially with the smallest amount of diluent which can be employed con- 25' sistently with precipitation of the wax in the desired form and efiicient performance of the chilling operation. When only a relatively small proportion of the diluent is added prior to chilling to a wax-precipitating temperature, however, 30

the. subsequent step of precipitation of the wax content of the stock by chilling results in the formation of a mass which is not sufiiciently fluid to be continuously passed through the chilling apparatus or efiiciently removed from that ap- 3 5 paratus. If the stock is diluted with a relatively small proportion of diluent, and is thereafter chilled to a temperature at which a large proportion of the Wax is precipitated from the solution, the substantially non-fluid mass so obtained can 40 not be thereafter diluted with further diluent efficiently at the temperature to which it has been chilled except by resort to mechanical manipulation of an inconvenient and expensive character, e. g., mechanical comminution of the viscous 45 mass resulting from the chilling operation.

Experiments in the practice of operations of this character have indicated that it is not only necessary to maintain the wax-containing mass in a liquid state during the chilling and dewaxing operation, but that it is also necessary to avoid precipitation from this mass of any substantial proportion of the parafiinic oil, especially in those cases where dewaxing solvents are used which give pour tests on dewaxed oil relatively 55 close to the temperature at which the precipitated wax is separated. In cases of such operation in which the chilling operation has been conducted in such a manner as to entail incidental precipitation of oil, it has been found that the wax precipitate obtained as the result of such a chilling operation has been, at least in part, in such finely divided form as to render eificient centrifugation impossible. The finely divided state of the precipitate is not avoided, in cases in which paraffinic oil is allowed to precipitate during the chilling, even in cases in which such stock is redissolved by diluent added at a later stage of the operation. This fact adds another factor of difficulty to the solution of the problem of avoidance of the use of expensive chilling machinery by chilling of any portion of the diluent separately from the stock.

The present invention has an object the avoidance of all of the difficulties discussed above in connection with efforts to separately chill the stock and a portion of the diluent.

A further object of the invention has been to aiford a procedure in which a portion of the diluent is chilled separately from the stock and in. which the amount of diluent added to the stock prior to chilling the stock to. Wax-precipitating temperatures may be much smaller than the proportion of such initially added diluent which may be employed in prior art processes consistently with the avoidance of the above described difficulties.

In accordance with the invention, the stock is first mixed with a solvent at a temperature sufficiently high to effect complete solution of both oil and wax in the solvent. The solution is then chilled to a temperature sufiiciently low to effect precipitation of the major proportion, or at least a substantial part, of the wax in the stock and the mixture so produced is then diluted with further solvent and is thereafter further chilled to efiect further substantially complete precipitation of the wax. In connection with an operation of this charactena mixture of solvents may be used of which one component is amuch better solvent for both paraffinic oil and wax than the other. In cases in which such a mixture is used, the practice of the invention is simplified and the proportion of. solvent which may be separately chilled from the oil is increased by reason of the fact that the good solvent may comprise a larger proportion of the solvent mixture with which the oil is diluted prior to the chilling step than of the solvent mixture with which the oil-wax mixture is further diluted after the chilling step.

In. the practice of the invention, the stock is initially diluted with a proportion of solvent which is sufficient only to keep the stock fluid and avoid precipitation of parafiinic oil during the precipitation of the majority, or at least a substantial part, of the wax. Further diluent is added before the stock has been chilled to its ultimate dewaxing temperature, such further diluent being added after the stock has been chilled to a temperature below 40 F. (e. g., between 20 and 40 F.) ,the temperature at which such further diluent is added depending upon the temperature at which paraflinic oil begins to be precipitated or the initially diluted mixture becomes substantially non-fluid. The quantity of diluent added at this intermediate stage of the chilling operation is sufficient to keep the mixture fluid and avoid precipitation of any substantial quantity of paraffinic oil during the ensuing part of the chilling step which effects precipitation of the remainder of the wax in the stock and reduces the temperature of the mixture to the point at which the ultimate step of wax removal (as by centrifuging, cold settling or filter pressing) is to take place. By operating in this manner, the proportion of diluent initially added to the stock may be much smaller than that necessary in prior art processes in which the separately chilled diluent is not added until the stock has been chilled to the ultimate dewaxing temperature. The proportion of diluent which may be separately and relatively economically chilled is therefore much greater in operations in accordance with the present invention than in prior art operations.

One preferred solvent mixture comprises ethylene dichloride and benzol and experiments have demonstrated that, with most oils, a mixture containing approximately 35% benzol and 65% ethylene dichloride constitutes an effective solvent mixture for dewaxing purposes. When it is desired to dilute the oil with this mixture of solvents in these proportions, the oil may be first diluted with a mixture of these same solvents comprising a larger proportion of benzol than that desired in the ultimate mixture and a smaller proportion of ethylene dichloride, for exam ple, 45% benzol and 55% ethylene dichloride, and a further solvent mixture comprising a smaller proportion of benzol and a larger proportion of ethylene dichloride may be added to the partially diluted stock subsequent to the chilling operation or between a succession of chilling operations. By using in the first place a mixture containing a large proportion of the better oil solvent, the precipitation of oil and the solidification of the stock during the chilling operation may be avoided with a minimum amount of initially added diluent, thereby enabling the operator to chill a maximum proportion of the diluent separately in simple and inexpensive heat exchangers.

In accordance with a-further modification of the invention, wax may be initially removed from a portion of the oil under tretament by full dilution of the oil in accordance with prior art practice, this wax being thereafter purified by a washing operation performed with the aid of the same diluent or diluent mixture used in the removal of the wax from the oil, and diluent obtained from the wax-washing operation may be used in connection with continued performance of the process by decreasing the quantity of diluent with which the oil is initially diluted in such continued practice and adding diluent obtained as a separate eflluent from the wax-washing operation to dilute the partially chilled oil further between successive chilling operations. This method of operation is especially advantageous because of the fact that it avoids the necessity of distilling the diluent-containing effluent from the waxwashing operation to recover the diluent which it contains.

The invention may be practiced in connection with the use of any diluent or mixture of diluents suitable or heretofore used in the practice of a sequence of steps involving dilution of petroleum stock with solvent, chilling of the diluted stock and subsequent removal of precipitated wax from the diluted stock by apparatus and methods which may be employed to attain that end. Thus, the invention has important advantages in connection with dilution of the stock with chlorinated hydrocarbon solvents and mixtures including such solvents, such as ethylene dichloride, propylene dichloride, butylene dichloride, trichlorethylene, dichlorethylene, tetrachlorethane, trichlorethane, carbontetrachloride, chlorbenzene, dichlorbenzene, etc., i. e., with any of the chlorine derivatives of the various saturated and unsaturated lower aliphatic and aromatic hydrocarbons which are useful in such a process. It is also useful in connection with dilution of stock with hydrocarbon solvents such as naphtha, benzoil, toluol and other normally liquid petroluem hydrocarbons and mixtures of such hydrocarbons with other diluents. Thus, the invention may be practiced by initially diluting the stock with naphtha, chilling the stock to a temperature at which a substantial proportion of its wax content is precipitated (e. g., below 40 F.), separately chilling an addtiional quantity of naphtha or other diluent, adding the separately chilled diluent to the stock containing the precipitated wax before that stock has been chilled to a temperature at which it solidifies or at which parafiinic oil is precipitated therefrom (e. g., between -20 and 40 F.) and thereafter chilling the stock to which the diluent has been added in this stepwise manner to its ultimate dewaxing temperature and separating precipitated wax from the stock by centrifugation or equivalent means.

The manner in which the invention is performed is illustrated in the accompanying flow sheet, in which Figure 1 illustrates a method of practice of the invention, and

Figure 2 illustrates an alternative method by which the invention may be practiced.

Stock from an oil container A is first mixed with solvent from container B. This mixing operation takes place at a temperature sufficiently high to effect solution of all of the oil and wax constituents of the stock in the solvent (e. g., in the case of dilution with naphtha, usually about 120 F.). The solution is then passed through a chilling apparatus C which chills the diluted stock to a temperature below 40 F. and causes precipitation of a substantial proportion of the wax in the stock. Solvent from container D is separately chilled in a chiller E and this solvent is then mixed with chilled stock from chiller C, the temperature of the separately chilled diluent from chiller E being substantially the same as or colder than that of the stock from chiller C. The mixture is then passed through chiller F to lower its temperature to the point at which the dewaxing opertaion is to take place, and the mixture is separated into a wax phase and a Wax-free oil phase by suitable means such as a centrifuge G which passes the oil and wax separately to containers H and I.

It is not necessary that separate chillers C and F be employed, for it is entirely feasible to introduce the separately chilled diluent from chiller E at an intermediate point of a single chiller employed for chilling the stock solution, the diluent from chiller E being introduced at an intermediate point of such stock chiller at which the stock has already been chilled to a temperature below 40 F.

In connection with the embodiment of Figure 1, the oil obtained from the centrifuges is distilled in order that the solvent which it contains may be recovered and reused in the dilution of further oil to be dewaxed. Figure 2 represents a form of the invention in which wax is washed by diluent of the same characteristics as that employed in the removal of wax from the oil. According to the flow sheet of this figure, oil from container K is first diluted with solvent from container Land is thereafter passed through chilling apparatus comprising two or more chillers M and 0, arranged in series, to a continuous centrifugal separator in which it is resolved into oil and crude wax, which are separately discharged to containers T and S. Crude wax obtained from this operation is then passed through a wax washing tank P in which it is washed with chilled solvent and from which it is passed to the wax purifying centrifuge R. From this centrifuge purified wax and diluent containing a small proportion of oil are continuously discharged, the wax passing to container U. When the process has been operated in this manner for a sufficient length of time to obtain a steady supply of oil-diluent mixture from the wax purifying centrifuge R, the amount of diluent added to the oil before passage through the first chiller M may be substantially reduced and the mixture of oil and diluent issuing from the centrifuge R may thereafter be passed into confluence with the mixture of oil andwax passing from this chiller M and mixed therewith. The mixture so obtained may then be further chilled to the desired dewaxing temperature and separated. It will be seen that the practice of the invention in this manner not only involves initial chilling of the oil in limited dilution to a temperature below 40 F., and consequent economy in the use of chilling equipment, butthat it also avoids the necessity of effecting a further distillation opera-,

tion with respect to the mixture of oil and diluent discharged from the centrifuge R.

In the practice of a process of this character, for example, oil may be initially dissolved in a mixture of ethylene dichloride and benzol comprising 65 parts of ethylene dichloride to 35 parts of benzol in the ratio of 3.6 parts of diluent to one part of oil. This solution may then be passed through the chillers M and O to effect precipitation of wax and through the centrifuge Q to effect separation of wax from the oil and separate discharge of wax and oil eflluents to containers S and T. The wax is then passed to the wax washing tank P, where it may be mixed with chilled ethylene dichloride and benzol in the ratio of 65 parts ethylene dichloride to 35 parts benzol. The mixture obtained from the wax-washing tank P may then be passed through the centrifuge R, which resolves the mixture into separately and continuously discharged wax and oil solution. After this operation has been carried on for a suflrlcient length of time to effect a steady discharge of oil solution from the centrifuge R, the ratio of diluent from the receptacle K to oil from the receptacle L may be reduced to 1.6 parts of diluent to one part of oil and the remaining two parts of diluent returned to the dewaxing operation in the form of oil efiluent from centrifuge R, by passage of such eflluent into confluence with the oil-solvent mixture passing from the chiller M to the chiller 0.

Modifications will be obvious to those skilled in the art and I do not therefore wish to be limited except by the scope of the sub-joined claims.

I claim:

1. The process of dewaxing petroleum stock comprising diluting the stock with a quantity and type of normally liquid solvent insufficient to prevent precipitation of parafiinic oil from said stock and retain said stock fluid at the final dewaxing temperature, chilling the diluted stock by contact with a heat exchange surface to a temperature below 40 F. and sufficiently low to effect precipitation of a substantial proportion of the wax content of the stock but not so low as to render the stock non-fluid or precipitate a substantial quantity of parafiinic oil from the solution, thereafter mixing a sufiicient further quantity of separately chilled solvent with the stock to maintain the stock fluid and avoid precipitation of paraflinic oil during the continued chilling of the stock to a temperature sufficiently low to cause precipitation of the remainder of its wax content, thereafter chilling the mixture of the stock with the initially added solvent and the separately added solvent to a temperature sufficiently low to complete the precipitation of the wax contained therein and thereafter removing precipitated wax from the diluted and chilled stock.

2. A process as defined in claim 1 in which the initially added solvent is different from the subsequently added solvent and is a better solvent for parafiinic oil than the subsequently added solvent.

3. A process as defined in claim 1 in which the initially added solvent is a mixture of ethylene dichloride and benzol and the solvent added after chilling to a temperature below 40 F. is a mixwax from the oil, washing wax separated from the portion of the stock so treated by mixing said wax with a diluent that is a solvent for oil and centrifuging the mixture so obtained to effect removal of oil solution so obtained from the wax, diluting further stock to be dewaxed with a diluent, which is a solvent for the oil, the quantity of said last-mentioned diluent with which said further stock is so diluted being insufiicient to prevent precipitation of parafiinic oil from said a stock and retain said stock fluid at the final dewaxing temperature, thereafter chilling said further stock which has been so diluted to a temperature below 40 F., thereafter mixing the oil and diluent removed from the wax in the wax purifying stage of the initial operation with the subsequently processed diluted and chilled stock in sufficient quantity to maintain the stock fluid and avoid precipitation of paraffinic oil during the continued chilling of the stock to a temperature suiiiciently low to cause precipitation of the remainder of its wax content, thereafter chilling said further stock with the diluent initially added thereto. and the solution of oil in diluent subsequently added thereto to a temperature sufficiently low: to complete the precipitation of the wax contained therein, and thereafter removing precipitated wax from the diluted and chilled stock.

5. A process of dewaxing petroleum stock which comprises diluting a portion of the oil to be dewaxed with a diluent that is a solvent for the stock, chilling the dilutedstock to a temperature below 40 F. to effect precipitation of wax therefrom, thereafter mechanically separating wax from the oil, washing wax separated from the portion of the stock so treated by mixing said wax with a diluent that is a solvent for oil and separating oil solution so obtained from the wax, diluting further stock to be dewaxed with a diluent, which is a solvent for the oil, the quantity of said last-mentioned diluent with which said further stock is so diluted being insufiicient to prevent precipitation of parafiinic oil from said stock and retain said stock fluid at the final dewaxing temperature, thereafter chilling said further stock which has been diluted to a temperature below 40 F., thereafter mixing the oil and diluent removed from the wax in the wax purifying stage of the initial operation with the subsequently processed diluted and chilled stock in sufiicient quantity to maintain the stock fluid and avoid precipitation of parafiinic oil during the continued chilling of the stock to a temperature sufficiently low to cause precipitation of the remainder of its wax content, thereafter chilling said further stock with the diluent initially added thereto and the solution of oil in diluent subsequently added thereto to a temperature sufficiently low to complete the precipitation of the wax contained therein, and thereafter removing precipitated wax from the diluted and chilled stock.

LEO D. JONES.

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