US3539504A - Furfural extraction of middle distillates - Google Patents

Description

United States Patent 3,539,504 FURFURAL EXTRACTION 0F MIDDLE DISTILLATES Billy H. Cummins, Nederland, Tex., assignor to Texaco Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 12, 1968, Ser. No. 783,422 Int. Cl. Cg 21/16 US. Cl. 208327 11 Claims ABSTRACT OF THE DISCLOSURE A process for preparing middle distillate fuels with improved burning qualities and color utilizing a furfural solvent extraction process wherein the solvent during the process contains color impurities by contacting a middle distillate charge stock with a furfural solvent at an upper raflinate temperature above about 150 F. separating a primary raffinate phase from a primary extract phase, reducing the temperature of the primary raffinate phase to Within the temperature range of from about 60 F. to about 130 F. and maintaining the temperature of the secondary extract and secondary raflinate phases during separation of the phases within such temperature range.

This invention relates to a solvent extraction process for producing middle distillate fuels with improved burning qualities and color and more particularly to a process utilizing a furfural solvent which contains color impurities.

Generally speaking, solvent extraction operations are well known in the art. Ordinarily, in one form of operation, a liquid-liquid extraction is accomplished by feeding a material to be extracted, that is, a charge stock in which there are present at least two different chemical entities which have different solubilities or preferences in the presence of each other or a solvent, into a solvent extraction zone in which the charge stock is contacted with a solvent, usually in countercurrent flow. At one end of the zone, there is removed a rafiinate portion which represents that chemical entity which is not as soluble in the solvent and at the other end an extract phase which contains said other entity.

Prior art solvent extraction processes in general require temperatures of operation usually in the range of from 200 F. to 250 F. In certain solvent extraction process a temperature differential between the bottom and top portion of the extraction zone is utilized, that is a bottom extract temperature of from about 150 to 160 F. and an upper rafi'inate temperature of from ZOO-250 F.

A problem associated with the manufacture of middle distillate fuels and particularly kerosene is the requirement that such fuels have good color and burning qualities. In order to improve the good burning characteristics of, for example, a kerosene fuel, it is necessary to utilize various refining processes such as extraction, distillation and adsorption techniques to remove aromatics and olefins. A particular problem that is encountered during processes to improve burning characteristics of a kerosene type is that color bodies can be imparted to the kerosene which can completely alter the color characteristics of the fuel. It therefore is important in the refining of kerosene fuels to produce not only kerosene having good burning characteristics but also acceptable color.

During the solvent extraction processes utilizing furfural as a solvent a problem is encountered during the extrac tion process of color rejection to the raflinate phase. It has been found that during the furfural solvent extraction of a middle distillate fuel utilizing furfural as a solvent a color develops in the furfural phases, possibly due to the polymerization or oxidation of the furfural (e.g., a

3,539,504 Patented Nov. 10, 1970 color impurity), which is imparted to the raflinate (fuel) phase and subsequently to the fuel phase.

It is therefore an object of this invention to prepare a middle distillate fuel having good burning characteristics and good color utilizing a furfural extraction process wherein the furfural solvent contains color impurities.

It has now been found that a middle distillate fuel can be produced having good burning characteristics and color utilizing a furfural solvent extraction process wherein the furfural solvent during the extraction process contains color impurities by contacting a middle distillate charge stock with furfural solvent in an amount sufficient to form a primary extract and a primary raflinate phase wherein the raflinate outlet temperature is maintained above about 150 F., separating a primary raffinate phase from the primary extract phase, reducing the temperature of the primary rafiinate phase to below about 135 F. and maintaining the temperature of the secondary extract and secondary rafiinate phase, during separation of the phases below about 135 F., generally Within a temperature range of from about 60 F. to about 130 F. In carrying out the process of this invention a middle distillate charge stock (hereinafter referred to as charge stock) is charged into a separator together with furfural solvent, the amount of furfural solvent being sufficient to form a primary extract and a primary raffinate phase and a raffinate outlet temperature is maintained above about 150 F. The primary raflinate phase is then separated from the primary extract phase and the temperature of the primary rafiinate phase is reduced to below about 135 P. such that a secondary extract and secondary ratlinate phase are formed. A temperature below about 135 F. generally Within the range of from about 60 F. to about 130 F. is then maintained during separation and recovery of at least about a major amount of the secondary raflinate phase from the secondary extract phase. A middle distillate fuel is then recovered from the secondary rafiinate phase. The criterion of this invention is that the temperature be maintained below about 135 F. preferably Within the range of from about 60 F. to about 130 F. By the use of the term maintaining a temperature is meant that this temperature has to be maintained only during that time when color can be imparted to or remains in the secondary rafiinate phase. Thus a temperature within the above range is maintained during separation of the two phases and such temperature is generally an average temperature during such separation of the secondary extract and raffinate phases. It has been found that if separation of the two phases takes place below about 135 F. or Within this temperature range a middle distillate fuel is obtained which has improved color whereas the middle distillate fuel recovered from the primary rafiinate phase is considerably darker than the middle distillate charge stock. The preferred temperature range is from about F. to about 130 F. and still more preferably within the range of from about F. to about F.

A particularly preferred embodiment of this invention comprises the process of charging a middle distillate charge stock together with furfural solvent in countercurrent flow to a separator at a top rafiinate temperature above F. such as a top raflinate temperature in the range of from about F. to about 240 F. to form a primary extract and rafiinate phase and separating the primary raffinate phase from the primary extract phase. The primary rafiinate phase is then reduced in temperature to Within the range of from about 60 F. to about 130 F. wherein a secondary raflinate and secondary extract is formed. The secondary rafiinate is separated from the secondary extract and a middle distillate fuel is obtained which has improved color and burning characteristics as compared to the feed obtained from the original primary raflinate utilizing higher extraction temperatures.

The middle distillate charge stock, in general, can be naphthas, kerosenes, gas oils, catalytic cycle gas oils, and similar boiling virgin distillates.

The ratio of solvent to charge stock in liquid-liquid extractions, must be suflicient to exceed the solvent solubility under the extraction conditions in said charge stock in order to form two distinct liquid phases, viz, a primary raffinate phase containing little or no solvent and an immiscible primary extract phase comprising the solvent and extracted hydrocarbons. Generally, from about 0.5 to about volumes of solvent per volume of middle distillate charging stock is utilized. Ordinarily from about 1 to about 5 volumes of solvent per volume of charge stock is utilized, especially in the treatment of kerosene boiling range stocks (about 500 F. end-point). Sufiicient pressure is maintained within the extraction zone to prevent substantial volatilization of the charge stock or solvent under the liquid-liquid extraction conditions. Usually pressures within the range of about 0 to about 100 p.s.i. are suflicient, it being appreciated that the particular pressure which is required in a given case can readily be determined by experiment.

Any means of separating extracted materials from the extract phase and of recovering solvent therefrom may be employed. Thus under certain conditions, it may be desirable to distill extracted materials from the extract phase or to wash them out of the extract layer with a paraffin hydrocarbon having a different boiling point. Also, the solvent may in some instances be recovered from the extract phase by crystallization or by washing with a solvent which is highly selective therefore, such as ethers, etc.

The raflinate phase (or in extractive distillation, the distillate) can be treated by conventional methods to effect further refining thereof such as distillation. Thus, the rafiinate or distillate can be washed with water, aqueous alkalies, etc., treated with adsorbent solids such as activated carbon, activated clays, etc., redistilled, or a combination of the above processes. In addition the furfural from the secondary rafiinate and the primary and secondary extract phases can be recycled to the extraction zone for use as a solvent. In addition in the case of the preferred process, the secondary extract can be recycled to the primary extraction zone at a point preferably below the introduction of the furfural and above the introduction of the charge stock.

In carrying out the process of this invention, furfural solvent is introduced into an extraction zone in countercurrent flow with the charge stock. By the use of the term furfural solvent is meant that furfural is used as the primary solvent. Thus auxiliary solvents and anti-solvents can be utilized in combination with furfural. In general, it is preferred to use a major amount of furfural in the furfural solvent system more preferably 80 percent by weight furfural and still more preferably 90 percent by weight furfural. In a preferred embodiment of this invention the furfural solvent system is substantially furfural that is over 90 percent by weight furfural. It may be desirable to employ diluents or auxiliary solvents (including anti-solvents) in specific cases in order to modify selectivity of the furfural solvent, to lower the melting point of the furfural solvent to permit its use at low temperatures, or for other reasons. The amount of auxiliary solvent can be selected with reference to specific cases; generally up to about weight percent or more, based on the furfural solvent, can be employed. The auxiliary solvent should be miscible to the desired extent with the furfural solvent, and should preferably be a neutral compound. As examples of auxiliary solvents which can be employed are water, the sulfolanes, for example, 2,4-dimethylsulfolane, 2,3-dimethylsulfolane and the like; various nitriles such as acetonitrile, bis-Z-cyanoethyl ether and the like; various ethers such as diethyl ether, methyl-tertbutyl ethers; glycols or their ethers, tetrahydrofuran and the like; halogenated hydrocarbon solvents such as chloroform, carbon tetrachloride, ethylene dichloride, trichloroethane, tetrachloroethane and the like; esters of carbonic acid, monocarboxylic acids, and dicarboxylic acids, for instance, diethyl carbonate, bis-Z-hydroxyethyl carbonate, bis-Z-chloroethyl carbonate, bis-2-methoxyethyl carbonate, ethylene carbonate, n-butyl formate, methyl furoate, dimethyl oxalate, diethyl succinate, dimethyl phthalate, dimethylisophthalate, and the like; neutral organic nitrogen compounds such as N,N-dialkyl formamides (particularly dimethyl formamide), nitro aromatics such as nitrobenzene and the like; kctones, for example, methyl ethyl ketone, methyl isobutyl ketone and the like, crotonaldehyde and the like; butylrolactone, butylrolactam, etc.

Anti-solvents or diluents may also be employed in the practice of the present invention. Thus, diluents such as saturated hydrocarbons, perfluorocarbons, perfluoroamines, perfiuoroethers, etc., may be added to the charge stock or introduced directly into the extraction zone.

In the extraction, a small proportion of a suitable surface-active agent may be added to increase the efiiciency of extraction equipment. Thus, long chain esters of perfluoroalkyl alcohols or perfluoroalkyl acids, perfluoroalkyl amides and amines, etc., may be employed, in suitable concentrations between about 0.0001 and about 1 weight percent, based on the weight of the solvent (note G. B. Blake et al.-paper presented before the Division of Petroleum Chemistry of the American Chemical Society, September 1954 p. 313 if).

The present invention can be carried out in batch, con tinuous or semi-continuous operating cycles, and in one or more actual or theoretical stages, employing contacting and separation equipment such as has heretofore been employed in the selective solvent refining of petroleum stocks. In addition a multi-stage mode of operation that is a repeating of the process several times can be utilized in carrying out the process of this invention. Various types of liquid-liquid extraction operations and suitable extraction equipment are described, for example, in Chemical Engineers Handbook (McGraw-Hill Pub lishing Co., Inc., N.Y., 1950), pp. 716 ff. and 474 if. It should be understood that the specific equipment employed forms no part of the present invention and that any equipment adaptable for the purposes of contacting the furfural solvent with the charge stock and thereafter separating an extract phase from the refined charging stock can be employed for the purposes of this invention.

The process of this invention can be better appreciated by the following non-limiting examples.

EXAMPLE 1 A middle distillate charge stock having an ASTM boiling range of 316 to 502 F. and a Saybolt color of +11 is charged to an extractor at the rate of 5,030 milliliters per hour. The middle distillate charge stock is contacted countercurrently with a furfural at a rate of 7500 milliliters per hour. The temperatures of the extractor are F. bottom and 180 F. top temperature. The rafiinate phase is separated from the extract phase and a sample withdrawn and stripped of any dissolved solvent. The middle distillate after water washing of the furfural solsvent form the middle distillate has a Saybolt color of EXAMPLE 2 The solvent-contained raffinate phase from Example 1 is cooled to 81 F. and charged into a liquid-liquid separator. A secondary raftinate is formed and removed from the extract phase. After water Washing the furfural solvent from the middle distillate fuel, the middle distillate fuel has a Saybolt color of +9.

Examples 1 and 2 clearly demonstrate that a middle distillate fuel can be obtained which has good color by maintaining the average temperature at the time of separation of the secondary raflinate and secondary extract phase within the temperature range of from about 60 F. to about 130 F. Thus, the oil obtained after contacting the middle distillate charge stock with furfural at a temperature of 180 F. had a Saybolt color of 5, whereas the charge stock had a Saybolt color of +11. Of particular importance is the color of middle distillate fuel that is obtained when the primary rafiinate is cooled to 81 F. More particularly, the recovered fuel obtained utilizing the process of this invention has a Saybolt color of +9. The data set forth in the preceding example clearly demonstrates the outstanding performance of the process of this invention for producing middle distillate fuels having improved color and burning qualities utilizing a furfural solvent extraction process.

While this invention has been described with respect to various specific examples and embodiments it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

I claim:

1. A solvent extraction process which comprises contacting a middle distillate charge stock with a furfural solvent in an amount sufficient to form a primary extract phase and a primary ratfinate phase, maintaining a raifinate outlet temperature above about 150 F., separating the primary raflinate phase from the primary extract phase, reducing the temperature of the primary rafiinate phase to below about 135 F. to form a secondary extract and secondary raffinate phase, separating the secondary rafiinate phase from the secondary extract phase while maintaining the temperature of the secondary extract phase and the secondary rafiinate phase during separation below about 135 F. and recovering a middle distillate fuel from the secondary raflinate phase, provided that the furfural solvent during the formation of the primary ratiinate phase and the primary extract phase contains color impurities which would produce a middle distillate fuel from the primary raflinate phase which is darker in color than the charge stock.

2. A process of claim 1 wherein the furfural solvent comprises about 90% furfural.

3. A process of claim 2 wherein the furfural solvent comprises substantially furfural.

4. A process of claim 1 wherein the primary rafiinate is reduced in temperature to within the range of from about F. to about 130 F.

5. A process of claim 3 wherein the primary raffinate is reduced in temperature to within the range of from about 80 F. to about 130 F.

6. A process of claim 1 wherein the primary raffinate is reduced in temperature to within the range of from about F. to about F.

7. A process of claim 3 wherein the primary raffinate is reduced in temperature to within the range of from about 90 F. to about 110 F.

8. A process of claim 1 wherein the middle distillate fuel is kerosene.

9. A process of claim 3 wherein the middle distillate fuel is kerosene.

10. A process of claim 5 wherein the middle distillate fuel is kerosene.

11. A process of claim 7 wherein the middle distillate fuel is kerosene.

References Cited UNITED STATES PATENTS 2,121,323 6/1938 Manley et al 208-327 3,205,167 9/ 1965 Demeester 208-327 3,247,101 4/1966 Woodle 208327 3,291,727 12/1966 Woodle et a1 208327 HERBERT LEVINE, Primary Examiner US. Cl. X.R.