US2917446A - Method of regenerating urea which - Google Patents

Description

United States Patent" G F NIETHOD F REGENERATING UREA WHICH HAS PREVIOUSLY BEEN USED FOR DEWAX- ING LUBRICATING OILS Juan Rodriguez Jurado, Madrid, Spain, assignor to Empresa Nacional Calvo Sotelo de Combustibles Liqurdos y Lubricantes, S.A., Madrid, Spain, a corporation of Spain No Drawing. Application May 24, 1956 Serial No. 586,928

Claims priority, application Spain June 1, 1955 3 Claims. (Cl. 20825) This invention relates to the freeing of mineral lubricating oils from paratfin and it has particular relation to a process of this type in which freeing from parafiin or dewaxing is carried out with the use of urea.

It has been known that urea is capable of incorporating and fixing in its crystal lattice molecules of organic compounds, in which the number of carbon atoms exceeds a minimum (in general 5) and in which the links between the atoms are linear and not branched or cyclic. In carrying out such incorporation, it is in general not essentialat least as far as the quality is concerned whether the urea is brought in contact in solid or dissolved condition with the substance to be incorporated. In the last mentioned case, even if a liquid system (which may be homogeneous or polyphase) is used as the starting material, under analogous working conditions, crystals of the compounds are formed.

The area of the thermal stability of such compounds is variable in dependence on the molecular weight of the compound to be incorporated in urea and on the chemical group to which said compound belongs, but is in general adequate as if the formation took place at ordinary room temperature or at a temperature which differs only slightly from the same. Normally, ordinary atmospheric pressure is used. If the crystal structure is destroyed (for example, by dissolution in water), the beforernentioned compounds formed by incorporation are decomposed. In this manner, the urea, as well as the incorporated substances, can be recovered and the urea can be used repeatedly.

Different terms have been hitherto used for denoting the above mentioned compounds formed by incorporation. The term adduct, which is frequently used, is not always adequate, but it has been in use for a long time for the products obtainable by the Diels-Alder condensation. There are fundamental differences in several respects between the latter and the urea products here in question. For denoting these urea compounds, in the present application the term .incorporation compounds will be used insofar as the compounds are obtained from urea and normal aliphatic compounds and the term included compound will be used for the organic compounds which have been incorporated by reaction with urea in its lattice.

The incorporation of organic linear compounds in the urea crystal is not completely selective and compounds having slightly branched molecules can also form anal ogous compounds with urea. However, the incorporation in urea is capable of extracting from a complex mixture the aliphatic compounds of normal structure with increased purity already in a first step and the purity can be further increased if, after decomposition, the first extract is subjected to further treatments with urea.

ptilization of the above described characteristic of 2,917,446 Iatented Dec. 15, 1959 ICC bring about formation of the solid, crystalline incorporation compounds.

(2) Purification of the crystalline product obtained in step (1) in order to remove therefrom components which did not react with urea.

(3) Decomposition of the incorporation compounds into urea which can be' repeatedly, used and included compounds which represent an extract consisting exclusively or primarily of normalaliphatic compounds.

It has now been found that the formation of the above described incorporation compounds can be used for separation of paraffin. from lubricating oils by proceeding in the manner hereinafter described; The novel process of this invention is particularly suitable for the production of lubricating oils having a very low solidifying point. Such lubricating oils are required forvarious purposes, for example, for refrigerating machines.

According to the processes known from the prior art, in the above mentioned step (3), decomposition of the incorporation compounds was carried out either in an aqueous medium or in a molten medium at elevated temperatures, at which urea is not stable. In the first'mentioned case, hydrolysis of the urea with the formation of NH and CO takes place. It has been found that in the separation of paraffin from oils, the decomposition of incorporation compounds by means of water, dissolution of the urea and formation of an upper layer of molten parafiin does not yield satisfactory results because in this manner a milky mass results, which is a stable emulsion at alkaline'as Well as acid pH and cannot be used for recovering the urea in pure form by recrystallization. Even to obtain this unsatisfactory result, protracted heating to at least 7080 C. is necessary, whereby the losses of urea and the splitting off of ammonia represent a serious drawback.

If the above mentioned step (3) is carried out in the absence of water, but at a temperature sufficiently high for causing decomposition of the crystal structure by melting and thus liberating the included compounds, the results are likewise unsatisfactory and render it necessary to restrict such action to a minimum because urea is decomposed at 132 C. by melting to a varying extent.

According to the present invention, the above outlined disadvantages can be eliminated in a satisfactory manner by proceeding as follows:

As soon as the crystalline mass is Washed in order to remove the adhering compounds which do not react with urea but cover the crystals, the crystalline mass is treated with commercial xylene at -l00 C., i.e., at a temperature at which practically no decomposition of the urea occurs. In this treatment, the Xylene extracts the hydrocarbons included in the urea crystals and the urea is recovered in a condition in which it can be repeatedly used after drying and recovery of the adhering xylene. The solution of the paraflin in xylene is subjected to fractionation by distillation. In contrast to parafiin, urea is not dissolved in xylene. This procedure yields excellent results.

It has been further found that after a number of repeated uses (at least seven), the urea regenerated in the manner described in the preceding paragraph gradually loses its activity. In, such a case, the crystal structure 3 must be destroyed by melting in order to thoroughly regenerate it by recrystallization. In carrying out this step (which is necessary after each 7-10 repetitions of the dewaxing process only), according to the present invention, the paraffin-containing starting oil is used as the medium in which the urea is heated in order to cause the melting. About two to four parts by weight of the paraffin-containing oil are used for one part by weight of the urea.

The paraffin-containing oil is thereby heated to 130- 135 C. and the urea of weakened activity is added thereto under stirring. Stirring is continued until the urea is molten and settles as a lower layer as its specific gravity in molten condition is considerably higher, than that of the oil. During melting, the parafiin retained in the urea crystals is taken up by the hot oil. This is no disadvantage because the over-all yield of the process is only slightly changed thereby. The simple character of the procedure and the absence of the necessity of using a new product in the regeneration represent considerable advantages.

After the molten urea is settled in the oil, the latter is separated and its dewaxing is continued in the above described manner. The molten urea is dissolved .in water at 40-60" C. The resulting solution is not clear because it contains some oil adhering to the urea, and this oil is emulsified in the solution. However, it has been found that it is sufficient to adjust the pH of the slightly alkaline solution to 4-6 in order to cause breaking of the emulsion. The small amount of the upper hydrocarbonlayer is removed by decanting or filtration, whereupon the transparent urea solution is subjected to crystallization by cooling to ordinary room temperature. The crystals are separated and dried, whereby urea crystals having their original activity are obtained. The mother liquors obtained in crystallization are utilized in later steps.

In the above described process, in which the urea is subjected to alternate extraction and melting, the decomposition of urea, as well as the difficulties occurring in the decomposition of the paraffin, urea incorporation compounds are reduced to a minimum.

The following example describes by way of example an embodiment of and a best mode of carrying out the invention.

Example The starting material used was a lubricating oil which was obtained by vacuum distillation of mineral oil and had a viscosity of 13.6 cst. at 50 C. and a solidifying point of +19 C.

200 parts by weight of this oil were treated by the addition of 100 parts by weight of urea which had been moistened by 5 parts by weight of methanol. The mixture of oil and urea was subjected to stirring for 1 hour at ordinary room temperature, e.g., 25 C. The mixture was then subjected to filtration in order to separate the solid crystalline material from the oil. The crystals obtained by filtration were washed by iso-octane and the washing liquid was added to the filtered oil. The latter was subjected to distillation in order to recover methanol and iso-octane and residual amounts of methanol and iso-octane were removed from the oil by steam. The solidifying point of the oil thus obtained is stated in the table further below.

After being freed from oil by washing, the crystalline material consisting of the incorporation compounds was dried at 35 C. and then treated at 90 C. with 200 parts by weight of xylene for about 30 minutes. The mixture of xylene and solid material was then filtered, the solid residue washed with xylene once at ordinary room temperature and the xylene used for washing added to the filtrate. The xylene in which the paraffin extracted from the incorporation compound was dissolved, was subjected to distillation in order to recover the xylene and 4 the rest of the xylene was driven out from the paraflin by treatment with steam. The urea obtained from the incorporation compound by the extraction with xylene was dried at about C. and used again in the manner described above in this example for the treatment of a new batch of paraffin-containing oil. This treatment of parafiin-containing oil with urea was repeated seven times with the same urea. Small losses of urea (which amount, in an average, to about 1%) were supplemented by the addition of fresh urea in each treatment.

The results of this procedure are shown in the follow ing table:

Parts by Weight Pour Point Number of the Batch Amount of of the 'Parafiln Oil Freed Urea Oil, O Obtained from Recovered Paraifln After seven batches (whereby the mixture of the oil thus obtained had a pour point of --18 C.), the urea was subjected to re-crystallization after previous melting in paraffin-containing oil and dissolution in water inthe above described manner. The recrystallized urea was used in a further series of batches, whereby substantially the same results were obtained. The examination of the oil treated with urea, with regard to the pour point of the oil, indicates when a regeneration of the urea in the above described manner becomes necessary.

The process of the present invention can be used for dewaxing of oils, particularly lubricating oils, by itself, as well as an additional treatment for oils, e.g., lubricating oils which have been already subjected to dewaxing according to other methods and the pour point of which has to be further lowered. In using as starting material, an oil which has been subjected to dewaxing by means of solventsand had a pour point of 18 C., according to the present process, the pour point could be lowered to 45 C. Such very deep pour points can be obtained by treatment with urea only, if the amount of urea is correspondingly increased.

In the treatment of oils of relatively low viscosity, the oils can be treated with urea according to the present invention without the application of diluting agents. However, lubricating oils or other paraffin-containing oils of higher viscosity are preferably diluted in the first step by means of a low boiling branched aliphatic hydrocarbon such as iso-octane. The latter has no adverse effect on the formation of the incorporation compounds and the dilution and lower viscosity resulting therefrom have a favorable effect on the action of urea on the hydrocarbon mixture. Instead of iso-octane, other liquid hydrocarbons having a branched chain structure and low molecular weight can be used.

The abbreviation cst. is used herein to denote centistoke. The parts are by weight if not otherwise stated. What is claimed is:

1. A process for regenerating urea used for freeing oil from parafiin by the formation of urea-paraffin incor-. poration compounds, comprising melting said used urea by heating it in said oil, mechanically separating the molten urea from said oil, dissolving the separated urea in water, adjusting the pH to 4-6 in order to separate emulsified oil from the aqueous solution, and subjecting the resulting solution to recrystalization.

2. A process as claimed in claim 1, in which for 1 part adjustment of the pH to 4-6 in order to break the emul- 10 sion and subjecting the resulting clear solution to crystallization.

References Cited in the file of this patent UNITED STATES PATENTS Strzyzewski et a1. Sept.'29, 1942 Michelitsch Nov. 24, 1953 Wiles et a1. Dec. 22, 1953 Weitkamp et a1. Dec. 6, 1955 Rumberger et al Feb. 11, 1958 FOREIGN PATENTS Great Britain May 7, 1952

Claims (1)

1. A PROCESS FOR REGENERATING UREA USED FOR FREEING OIL FROM PARAFFIN BY THE FORMATION OF UREA-PARRAFIN INCORPORATION COMPOUNDS, COMPRISING MELTING SAID USED UREA BY HEATING IT IN SAID OIL, MECHANICALLY SEPARATING THE MOLTEN UREA FROM SAID OIL, DISSOLVING THE SEPARATED UREA IN WATER, ADJUSTING THE PH TO 4-6 IN ORDER TO SEPARATE EMULSIFIED OIL FROM THE AQUEOUS SOLUTION, AND SUBJECTING THE RESULTING SOLUTION TO RECRYSTALIZATION.